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Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73°S: Distribution, ecology and fossilization potential
Marine Micropaleontology, 16 ( 1990 ) 241-283
241
Elsevier Science Publishers B.V., Amsterdam
Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73°S: Distribution, ecology and fossilization potential A. Mackensen, H. Grobe, G. Kuhn and D.K. Fiitterer Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, D-2850 Bremerhaven (F.R.G.) (Received July 20, 1989; revised and accepted February 12, 1990)
ABSTRACT Mackensen, A., Grobe, H., Kuhn, G. and FiJtterer, D.K., 1990. Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73 °S: Distribution, ecology and fossilization potential. Mar. Micropaleontol., 16: 241-283. Surface sediment samples taken with a vented box corer from the eastern Wcddell Sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content. The live fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Based on the dead assemblages, potential fossil assemblages were calculated to facilitate the analogy with late Neogene core material. Five distinct live assemblages inhabit the continental margin today. Six dead assemblages and five potential fossil assemblages, respectively, correspond to these biocoenoses. A predominantly calcareous live fauna dominated by Trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope. Below this, on the upper slope down to 2000 m water depth, the predominantly calcareous Bulimina aculeata assemblage coincides with the core of warm ( > 0 ° C) Weddell Deep Water and with fine and more organic-rich sediments. These calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment, which depends largely on the grain size distribution of the sediment and the fluxes of organic matter. Therefore, a still calcareous T. angulosadominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope, whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by Martinottiella nodulosa, the characteristic arenaceous fossil remnant of the former predominantly calcareous live B. aculeata fauna. On a continental terrace between 2500 and 3500 m water depth Cribrostomoides subglobosus dominates the live fauna, but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by Oridorsalis umbonatus and Epistominella exigua comprises the dead assemblage and the potential fossil assemblage, respectively. On the lower continental slope, between the carbonate lysocline (3500 m ) and the carbonate compensation depth (4000 m), tests of Nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna, which is ~ssociated with the lower part of the Antarctic Bottom Water (AABW). This corroborates earlier investigations suggesting a relationship between the carbonate-corrosiveness of water masses and the distribution ofN. urnbonifer. This is important for inferring paleo-routes and estimates of paleo-production rates of AABW during the Neogene.
Introduction Since the discovery that during peak cold climatic periods (glacial stages 6 and 2) atmospheric CO2 concentration was about 30% below interglacial values (Barnola et al., 1987 ), one of the most challenging tasks in paleocean0377-8398/90/$03.50
ographic research has been to understand the global carbon cycle. Atmospheric CO 2 changes during the ice ages should be forced by a redistribution of carbon within the ocean, which is the world's largest CO2 reservoir (Broecker and Peng, 1986 ). Bottom water circulation and biological productivity are two of the mecha-
© 1990 - - Elsevier Science Publishers B.V.
242
nisms responsible for the partitioning and the redistribution of carbon within the ocean. Thus it is important to reconstruct the changes in bottom water circulation patterns and paleoproductivity. Benthic foraminifera are abundant and ubiquitous faunal constituents of deep-sea sediments and record information concerning both paleoproductivity and bottom water circulation. Specific high productivity faunas are associated with upwelling zones and reflect high fluxes of particulate organic matter (Lutze and Coulbourn, 1984; Corliss and Chen, 1988). Other assemblages are associated with specific bottom water mass characteristics and substrate conditions (Douglas and Woodruff, 1981; Mackensen et al., 1985 ) and can be used to infer bottom water routes and distribution (Corliss, 1983; Mackensen and Hald, 1988 ). The Antarctic Ocean plays a key role in controlling both global paleoproductivity and bottom water circulation in the following way. Increased surface productivity in the Antarctic Ocean during glacials, (Keir, 1988), or by contrast, reduced productivity there (Mackensen et al., 1989; Grobe et al., 1990 ) and high productive zones at low latitudes, as calculated by Mix ( 1989 ), might cause an enhanced CO2 storage in the deep ocean (Sarnthein and Winn, 1990) and explain the fall of atmospheric CO2. In addition, the Antarctic Ocean is one of the earth's two principal sources of oceanic bottom waters (Foster and Middleton, 1980; Foldvik et al., 1985 ) and changes in bottom water production cause changes in ocean circulation patterns. Thus it is important to monitor benthic foraminiferal assemblage changes in late Quaternary cores from the Southern Ocean. This in turn calls for an inventory of the relationship between Recent benthic foraminifera and the specific environments of the Southern Ocean, as an analogy and basis for paleontological interpretations of high-latitude fossil assemblages. We document here the distribution patterns, the community structure, and the fossil-
A. M A C K E N S E N ET AL.
ization potential of benthic foraminifera from the eastern Weddell Sea in relation to Recent environmental conditions. Previous work
Previous reports from the era of the national expeditions into the Antarctic Ocean include Wiesner ( 1931 ), Earland ( 1933, 1934, 1936), Heron-Allen and Earland (1932) and Uchio (1960). More recent studies of benthic foraminiferal distribution patterns and their physical and chemical environment include McKnight ( 1962 ), Echols ( 1971 ), Herb ( 1971 ), Anderson (1975), Osterman and Kellogg (1979), Corliss ( 1979, 1983), Milam and Anderson ( 1981 ), Lindenberg and Auras ( 1984 ) and Mead and Kennett ( 1987 ). None of these studies give quantitative data on the live distribution of benthic foraminifera. The only available study on benthic foraminiferal distribution patterns in the Weddell Sea is based on 58 piston and trigger core tops, and differentiates between six distinct benthic foraminiferal assemblages (Anderson, 1975). Water masses, depth and the multibathyal carbonate compensation depth (CCD) are believed to be the major factors controlling the distribution of these assemblages. Some new data reflecting the influence of high surface productivity at the eastern Weddell Sea continental margin on the distribution and preservation of live calcareous faunas are given in Mackensen and Douglas ( 1989 ). Materials and methods
During cruise ANT-IV/3 (1985/1986) of the RV "POLARSTERN", undisturbed surface sediment samples (412 cm z, 1-2 cm thick) were taken from sediments collected with a large vented box corer (0.25 m 2) at 37 stations on four profiles perpendicular to the Antarctic continental margin (Figs. 1,2, Table I). Immediately after sampling, all samples were preserved in Rose Bengal stained alcohol
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
I
X,
243
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:~iii:ii~i~i!i~i!~i~!!!~iii!i~!!!~!ii~iiii~i~i~i~i~i~iiiiiiii~ii~:i!iiiiiii:~i~i~i~ii!i~i!!~i!i~!~!~i~ii!~!~!~i~!ii~!~i~i:~i~i~i:;)?i:~;i:~i~!i i!ii!!!ii!i!i!i!i!ii:)i:i:i:i:iii:iii:iii!ilili!i!i!:i!ii!!!i::" ~i~i~:~:?~:?~:~:~:~!~:~:~:~i~i~i~i~i~i~i~i~i~i~i~:~:~:~:?~:!~:~:~:!~:~:~:~:~i~iii~i~:~i~!~i!i~i~!~i~:~ :~:~:~:?~:!:!:~:~:!:~:~:~!)~:~!~!~i~i~i~i~:~:~:~:!~:~?~:!:~:!~:!~:~!~!~:~:~:~i~i~i~:??~:~:~:~:?~:!~i:!:~:~i~!!:~i~i~i~i~i~i~i~i~i~i!i~:~:~i~!~:~i~!~i~i~i)~ 73 °
200
W
15 °
10 °
5°
Fig. 1. Samplelocationsand bathymetryof the eastern WeddellSea continentalmargin. Bathymetriccontours (givenin 1000 m intervals), groundingline and ice shelfedgeare from GeneralBathymetricChart of the Oceans (GEBCO), 1983, sheet 5.18. (Lutze, 1964; Mackensen et al., 1985 ). For determination of carbonate and organic carbon contents 5-10 sub-samples taken randomly from the box corer sediment surface were lumped and kept frozen until final treatment on shore. At most stations water temperature and salinity were simultaneously measured with a CTD-probe (Table I). Prior to sampling, the four investigated profiles were surveyed by SEABEAM and 3.5 kHz bottom profiling systems to select optimum sample localities (Kuhn and Wissmann, 1987 ). At two stations sub-cores were taken from
the box corer with a 100 cm 2 plastic tube to quantify the infaunal component of the live benthic foraminiferal assemblages (Mackensen, 1978b, Mackensen and Douglas, 1989). Between 28 and 46% of the total live fauna was found below the topmost 1.5 centimeter of the sediment. In the area under investigation, most of the specimens found below 1.5 cm belonged to species which are also found within the uppermost sediment layer. However, some species prefer to live several centimeters within the sediment, and even though they are rare and do not significantly alter the total faunal composition as calculated from the top 1-1.5 cm,
244
A. MACKENSEN ET AL.
5ow 0
E
1
tt3.
2
"0 (1)
3
0 1425 o 1426 0 1427 o 1428 1393001395 139100 1394-3 -01394-1-138~o 1389 u 1388 o1390 01588
10 ° 1385 o
o 1406 o 1407 o 1408 14--09_
1384 0 1.31~-
o1367
1381
o1410 14120 0 1411
'1380
1481
~370
o1224 o o1379
o1369
O1378 o1377
4
20 °
o 1372 1373 o o 1374 o 1375
1380 -- 0
15 °
0 1386
5
1482
1368 o-14830
0
o1405
Stations
Fig. 2. Sample locations projected on a profile plane parallel to the continental margin according to depth and longitude.
these deeply infaunal species are underrepresented in the live data set. The sampling design of this study also has to be kept in mind if standing stock calculations are performed. The grain size distribution of the surface sediments was determined by wet sieving of 5 cm 3 sediment to separate the sand-size fraction and by hydraulic separation in settling tubes (Atterberg method) for quantification of the clay and silt fractions. The organic carbon and carbonate contents were determined with a Coulomat 702, measuring the CO2 generated by combustion of the bulk sediment for total carbon and by treatment with H3PO4 for analysis of CaCO3. The grain size distribution of gravel ( > 2 ram), sand ( 125-2000 #m) and mud ( <63 gm) as well as carbonate and organic carbon contents were calculated as weight percent of the bulk dry sediment (Figs. 3-6 ). The foraminifera samples were washed through a 63 #m screen. Then the coarse residue was dry sieved and the fraction > 125/tin was investigated for its benthic foraminiferal content. Samples containing high amounts of
terrigenous material were floated twice in C2C14 to concentrate the foraminiferal tests. Stained (live) and unstained (dead) foraminiferal tests were counted separately from different splits obtained by a micro splitter. Between 104 and 533 dead specimens from each sample and between 25 and 3077 live specimens were counted, respectively (Table I ). In addition, the residual sediment of sampies concentrated by the floating method was inspected and residues which contained high numbers of thick-walled arenaceous species were counted in order to correct the original faunal counts. It is well known that the Rose Bengal staining method has its limitations (Murray, 1973; Douglas et al., 1980; Bernhard, 1988). To minimize misinterpretations, in particular agglutinated species were individually wetted with water and if the identification of dense protoplasm was still doubtful the tests were crushed. All species that comprised less than 1% of the total fauna in all samples or which oc-
245
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
TABLE I Grain-size distribution, water depth, positions, carbonate and organic carbon contents of surface sediment samples with in situ temperatures and salinities of water masses, as measured according to CTD-depth. Faunal counts and standing stock data are given for comparison. Sample
Polite
Sand
Gravel
Depth
Latitude
(%)
(%)
(%)
(rn)
{° S)
(° W)
71o20 . 72°20 ' 70029 . 71°15 ' 70021 ' 70019 ' 70°28 ' 71o14 ' 72°12 ' 70019 , 71014 ` 70o26 ` 70o16 , 72°15 ' 70°16 ' 72013 ' 70°17 ' 70013 ' 71011 ' 70°06 ' 72°I0 ' 70°06 ' 71°09' 70012 ` 71003 ` 70006 ' 70°00 ' 72003 , 69°14 ' 68°44 ' 70050 ' 69°02 ' 70°37 ' 69°37 ' 71054 ` 69°44 ' 68o32 ' 69026 ' 69°16 . 71045 ' 71043 . 66020 , 70041 ' 70o30 '
13°25 ' 16°31 ' 09°36 ' 13°34 ' 06°46 ' 06°50 ' 09°37 ' 13o36 ' 16°43 ' 06°54 ' 13°37 ' 09°35 ' 06°54 ' 16°53 ' 06~49 ' 16~56 ' 09o42 ' 06059 , 13°33 ' 06o47 , 17008 ' 06°30 . 13°34 ' 09047 ' 13014 ' 06o41 ' 09058 ' 17°27 ' 05069 ' 05050 ' 13°57 ' 05o53 ` 13°58 ' 06°24 ' 18o16 ' 10°15' 05°46 . 10o30 ' 10044 ' 18059 , 19015 ' 05037 . 18°48 ' 14050 ,
1406-1 45.1 54.4 0.5 1367-1 47.1 49.8 3.1 1385-1 29.2 56.7 14.0 1407-1 100.0 1425-1 12.4 83.1 4.5 1426-1 36.6 47.2 16.2 1384-1 10.0 85.9 4.1 1408-2 ° 1372-2 12.9 73.9 13.3 1427-1 7.1 77,5 15.4 1409-2 * 1383-1 4.9 94.7 O.4 1426-1 35.4 63.8 0.8 1373-2 10.4 46.5 43.1 1393-2 1374-2 40.5 59.5 0.0 1382-1 61.1 36.6 2.3 1395-1 57.7 41.2 1.1 1410-1 9.1 90.8 0.1 1394-3 94.6 5.4 0,0 1375-2 91.3 6.6 0.1 1391-I 55.5 36.0 6.5 1411-1 50.8 48.1 1.2 1381-1 94.5 5.4 0.1 1412-1 81.9 17.2 0.9 1394-1 94.7 4.8 0.4 1380-1 96.7 2.9 0.4 1370-1 79.2 13.5 7.3 1389-1 95.1 4.2 0.8 1387-1 93.2 6.2 0.6 1481-2 85.4 11.5 3.1 1388-1 92.2 6.5 1.4 1224-3 90.0 9.6 0.4 1390-1 93.1 3.9 3.0 1369-1 87.6 3.1 9.3 1379-1 81.3 12,5 6.2 1588-3 77.8 18.8 3.5 1378-1 88.1 6.1 5.8 1377-1 89.3 5.6 5.2 1368-1 85.8 9.0 5.2 1483-2 79.9 9.6 10.5 1386-1 73.6 9.0 17.4 1405-1 57.7 42.0 0.3 1482-2 43.9 53.4 2.7 • denotes no recovery, hydrographicdata only "
237 310 340 431 458 612 714 794 802 803 975 1068 1165 1237 1388 1468 1492 1499 1521 1759 1772 1797 1622 1866 1901 1948 2072 2289 2292 2435 2499 2531 2765 2784 3181 3210 3471 3735 3812 4017 4133 4405 4528 4541
Longitude Carbonate
turfed at only two stations, have been omitted in the statistical data treatment. Orthogonal rotated (Varimax) Q-mode Principal Component Analysis was then used to reduce the 99 "live" and 85 "dead" variables (species) of the resultant two revised data matrices (Tables II, III ) to five and six variables [Principal Components (PC's)], respectively (Mackensen, 1985). The proposed solutions explain 71.8% and 82.3% of the total variance of the revised data sets, respectively. To develop a reliable paleoecological interpretation of fossil assemblages of cores from the investigated area (Mackensen et al., 1989; Grobe et al., 1990) by tracing back the fossil assemblage via the dead assemblage to the live
(°/o)
C org. (%)
0.49 0.62 5.79 9.51 0.87
0.56 0.45 0.44 0.56 0.18
0.14
0.30
0.73 0.25
0.40 0.20
0.18 0.16 0.11
0.15 0.21 0.20
0.26 0.15 0.14 0.19
0.22 0.28 0.18 0.18
0.17 0.35 0.27 0.12 0.25 0.32 0.29 0.66 1.82 5.21 1.39 4.6 6.7 3.18 3.7 7.36 12.82 2.35 1.57 0.23 0.08 0.13 0.08 0.05
0.56 0.26 0.26 0.40 0.41 0.43 0.40 0.42 0.36 0.32 0.41 0.38 0.34 0.39 0.38 0.36 0.23 0.35 0.34 0.36 0.38 0.35 0.10 0.05
CTD Temperat. depth(m) {in silo °C)
Salinity Counts Counts St. stock ~,) dead live (ind./lO crn2 /
220
-1.75
34.360
335 425
-1.82 -1.80
34.427 34.419
675 750 827
-0.97 -0.01 -0,57
34.515 34.604 34.550
975 1027
0.31 0.22
34,649 34.652
1217 1330 1455 1534
0.32 0.40 0.32 0.23
34.685 34.762 34.6}'3
925
0.27
34.642
1765 880 1024 1034 819 1880 751
0.20 0.32 0.33 0.47 0.52 -0.01 0.42
34.680 34.665 34.652 34.668 34.667 34.676 34.661
626 614 2482 612
0.61 0.60 -0.13 0.59
34.696 34.699
596
0.50
34.684
656
0.60
34.688
518
0.60
34.694
4000 4125
-0.31 -0.30
34.654
969 4530
0.37 -0.31
34.684
34.695
310 473
3077 522
74.7 12.7
2658
64.5
417 399
611
14.8
229 257
122 773
23.7 18.8
208 152 235
1058 612 351
25.7 237.7 34.1
352 106 106 244 424 224 186 521 209 186 230 226 237 237 152 384 104 204 221 284 178 275 283 157
305 60 120 144 337 169 85 390 194 162 649 521 196 121 84 108 238 203 274 56 111 26 152 207 108
59.2 124.3 93.2 14.0 33.7 65.6 132.0 37.9 75.3 62.9 64.9 101.2 76,1 47.0 32.6 41.9 46.2 19,7 53.2 21.7 43.1 19,4 29.5 20.1 21.0
145 528 533
114 470 507
44.3 11.4 12.3
fauna and its present environment, the dead assemblages were reduced by all arenaceous species except Karreriella and Eggerella spp., Martinottiella nodulosa and Miliarnmina arenacea. These agglutinated species are ineluded into the potential fossil assemblage, as defined here, because they are known to be resistant against early diagenetic processes (Douglas and Woodruff, 1981 p. 1249; Schr6der, 1986; Mackensen and Douglas, 1989) and are frequently found in Pleistocene cores from the area under study (Grobe 1986; Melles, 1987; Mackensen et al., 1989). The composition and distribution of this potential fossil benthic foraminiferal assemblage, as calculated by deleting non-resistant arenaceous
246
A. MACKENSEN
5°W
10 °
ET
AL
20 °
15 °
0
E v
i--
2
- -36°-°°s O4
"O
50 '3
5
686 o4
3
013
12 o o10
o13 o19
4
17
O3
6 Oo 6
-
~9~-~0
o9 -T--
--
--
--
Fig. 3. Distribution of the sand-size fraction of the bulk dry sediment in the investigated area plotted on the profile shown in Fig. 2.
0
5°W
10 °
i
o 07
E
lo°
15 °
o,, oo
20 ° 0 47 013
1
V
(.-
2 "D
3 4
5 Fig. 4. Distribution of the mud content of the bulk dry sediment in the investigated area plotted on the profile shown in Fig. 2.
BENTHIC FORAMINIFERAL
247
A S S E M B L A G E S F R O M E A S T E R N W E D D E L L SEA
5ow
10 °
15 °
20 °
0 00.9
00.3
E
1
00.2 O. o 0.1 40__00.3
v
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0.2
00"7
~
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0.2 o 0.1
°0"1 o 0.3 o 0.2
,
2
00.7 i ~t::ili~
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$,I
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4
:'.':&"::":~::'!~- "4-::: •
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~
01
o
5
>30
00. I Carbonate
>10
in %
Fig. 5. Distribution of the carbonate content of the bulk dry sediment in the investi ~ated area plotted on the profile shown in Fig. 2.
5°W
10 °
15 °
20 °
0 ..........
E
1
.......................... 0:3:: :':~:::'l~ii i ; i o 0.3 • o l 00.2 002. . . .
: i i
0i6 iii ;I
........... ........
:: ~
i 00.2
~-
v
tO_ (1,1 "0
2
(9
3
t'l:i
4 0
5
0 U-I
Organic carbon in %
Fig. 6. Distribution of the organic carbon content of the bulk dry sediment in the investigated area plotted on the profile shown in Fig. 2.
TABLE II Percentages of species of live benthic ~ r a m i n i ~ r a . X denotes occurrence of less than 0.5%, ~
n
~
.~cmm Adercottyma
,
1
1
1
1
1
4 8 2
4 0 5
3 8 6
3 6 8
3 3 5 3 3 2 3 3 4 3 3 3 3 3 7 7 8 7 6 2 9 8 8 8 8 7 8 9 7 8 8 9 9 4 0 8 1 7 9 0 0 4 1
glomerata
Ammobaculiles
3
1
6
-
•
-
3
.
.
-
.
.
agglutinans
AR~rlodiscus
Spp.
A ~ g i n u l i n a
en$/s
A~rginulina
foliacea
A ~ i n u l i n a
fol~cea
A$ttOtlOf~
3 cutvata
1
-
.
4
5
9
5
5
-
2
2
.
Cib~ides
grc~sepunctatus
.
Cibicides
Iobatulus
.
.
.
.
.
8p.
-
I
-
.
.
.
.
.
.
~p,
-
Cyc/att~r~na
ofbicularis
Cyc,~mm/na
j~.s///a
.
sp.
. x
.
.
.
. 3
-
1
-
-
1
-
.
. 5
2
1
1
1
420
.
. !
Ep~tontwella
vitrea?
-
x
.
Gtobocassi#ulina
crassa
G/oboca£~idulina
subglobosa
Glomo~ifa
.
.
.
bradyi
Haptophfagnloides
sp. 1
H ~ O l q P h f ~ S
sphaetiloculus
Htppoctepkla
-
x
-
x
.
-
x
-
Hofmosina
Kate#ella
1
x
x
-
.
1 2 .
.
.
pauperata
.
.
.
2 2
-
2
2
x
.
. .
t~#/(~a
-
arenacea
x
.
.
1
2
2
1
.
Milioline~a
spp.
Milio#nella
subrotunda
.
.
.
.
Non~nel!a Non/o/~/a
bra#yi /t/dea
Nutta#ides
umb~ifer
Oridorsalis
sidebottomi
Oddolsalis
utr~onatus
x
.
Paraftssuhna Patellkna
. .
.
1
.
1
1
. .
Portatrocham/~t~l
x
-
1
.
2
1
-
2
2
4
x
-
bulloides stmplex
.
.
-
-
4 x
2 1
112
1
3
1
1 2
-
.
4
-
pygmaea
1 111
5
1
1
.
.
.
.
x
~
3
-
.
. .
. .
1
x x
1 5
. .
x
.
-
2
3
12
3
4
5
3
5
5
1
5
4
-
3
5
3
213
Reophax
d~tans
.
-
x
1
R
f~ifom~s
6
4
1 lx
6
3
3
-
8
2
ovicula
1
1
1
2
2
1 2
1
Robeninok~
•
11
Saccorhiza
ratnosa
1 2 1 3
Subfeopha~ adunca Textularia wtesneri Thurammina paplllata
I
-
-
x
1
3
1
.
1
2
2
1
. 121
frigida
. 2
2
Triloculina
tricannata
x 2 l x 1
Trochammina
3
5
.
.
.
.
nitlda sp. 39+52
11
Trochammina
Spp
21 2
11 4 x 2
5
4
3
-
.
.
.
.
1
-
4
5
5
x
1
2
1
-
2
1
2 .
.
.
1
.
1
.
x 1
1
1
-
5
.
1
.
-
I
x
. 1
t
5
7 19
-
.
.
.
4
2
414
2
7
4
1
2
1
7
4
-
x 211
1 7 2
1 1
1
1
2
.
-
x
1
1
2
1
8
2
-
2
.
-
7
.
x
3
.
.
.
x
-
x
.
.
2 .
x
4
722
6
x
6
.
-
.
.
-
1
-
1 x
.
x
x
t
1
~
2
.
x
-
x
1
x
x
x
7
2
2
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x
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-
x
.
x
1
33
1
2
1
1 2
1. 2 9
x 2 -
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5 4
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x -
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x
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1
x
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2
.
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4
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~ 3
- 1614
1
. sp~.
Saccandna
Trifarina
11120
- - sp.
Rotaliammina
1 411 1
sp. indivLsa/algaelormis
1 4
-
Re~hax spiculiler Rhabdamn~rka cf lineans
Rhizammina
x
1
1
I
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x
-
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1
x
dentalin#otm~s
x
3 .
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x
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1
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sp.
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1
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61412
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x
-
1 .
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Recutvoktes
1
x
1
chapmani
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1
-
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.
1 lx
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1
2
.
.
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.
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1
.
2
.
.
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4 .
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2
. .
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PsammoslN~e~a
.
.
x
1
~ .
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1
x
.
1
.
. .
6
spp.
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all others
1
. 15 x
x .
. .
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-
x
1
x
1
.
.
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2
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.
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.
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. x
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.
72430131715
1
affinis
Mlliafnm~na
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x
.
.
e/ot~ataVcylindrica
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.
1 2
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x
2
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.
1
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3
1
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1
1
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1
.
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.
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.
.
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. .
1
.
.
.
-
.
.
.
.
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-
1
3
.
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normandcarpenten
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.
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.
.
-
1 .
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2
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1
1
41521201228
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91311
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.
x
sp.
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.
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.
1
2
1
3
1
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1
.
x
2
.
11023
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x
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4 3 3 3 3 4 3 4 3 3 4 3 4 1 9 8 7 7 2 8 2 7 8 2 6 0 3 0 5 2 4 3 8 3 7 2 4 5 7 6
x
-
4
.
.
-
1
3 9 4
3
1
glabra
.
.
1
3 7 5
1
.
x
1
3 9 1
4
.
x
1
4 1 1
1
.
4
1
2
.
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3 8 1
-
2
1
1
4 1 2
2
.
x
1
4
.
. -
1
-
3
ex~gua
Fissu#na
.
5
.
.
.
1
1
.
1
. 8
.
1
.
.
.
4
.
.
2
.
4
x
.
.
6 .
1
1
1
.
E p c s t ~
Epon/des
.
.
1 7
5
. .
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Eponide6
-
.
4 -
- 14 6
2
.
.
1
x
.
x
.
-
.
Eggeretlabradyi
.
.
.
352215
4
-
.
1
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3
1
1
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.
x
x
6
1
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3
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1
1
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.
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1
5
. .
.
.
jeffteysi
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.
.
-
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.
.
oo~ulenlus
812
.
teretls berlhetoti
Clbicide~
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2
.
-
.
1
.
7
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C d b t o s t o ~
-
. .
6
.
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1
-
.
cL wuellelstorh
-
. .
5
1
1
.
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2 .
1
2
cochk~a
Cibicidoides
5
1
-
Bu#mina~'uleata Cass~dulina
1
1
antarcticus
Buliminella
1
3 2
1
-
1
3
X
t
x
2
223
7
5
:(
-
4
!
x
2
3
2
x
1
I
2 2
6
3
6
3
2
X
x
I
1
2
I
2
2
2
4
6 3
5
5
3
-
2
-
1
1
1
249
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
TABLE III Percentages of species of dead benthic foraminifera. X denotes occurrence of less than 0.5%. S ~ N o n 4 8 2
Specle8 Adercoftyma
g/omerata
~ 4 0 5
2
1
Arnmobaculitesagglutit)an.s
.
A/r~od/6cus
x
sop.
A ~ l n u l i n a
ens~ foliacwa
.
A ~ i n u t i n a
fot/aceacutvata
1
pseudoeptral~,
8
.
1
.
.
-
3
Ammomarginulina Ammoscalal~
. 1 1 1 1 1 1 1 1 3 3 3 3 5 3 3 2 8 6 7 7 8 7 6 2 6 8 7 8 8 9 9 4
1 .
-
.
.
. 2
2
.
2
1
.
.
.
1 3 8 3
2
1
-
2
1
.
1
-
-
.
.
2
1
-
.
2
.
3
.
.
3
.
.
-
. 1
4 .
1
1
.
-
-
.
2
.
-
1 3 9 0
.
.
1 4 8 1
1 3 8 7
1 .
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 3 3 4 3 4 3 3 3 4 3 3 3 3 4 3 4 8 7 8 1 8 1 9 7 9 1 9 8 7 7 2 8 2 9 0 0 2 1 1 1 5 4 3 0 5 2 4 3 8 3 7 1
1
-
1
-
x
.
.
.
-
.
1
2
-
-
-10 .
x
2
.
.
9
.
.
4
-
1
2
1
1
3
1
x
.
.
4
1
2
3
3
1
1
1
3
-
x
1
1
-
x
x
1
x
1
-
1
1
.
.
.
1
1
1
1
2
6
3
6
-
-
2
x
.
.
.
2
.
2
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
echoJsi
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Bultmlna
aculeata
Cassk~ulina
.
crassa
CtOic~dee
.
rossensB
.
.
.
.
.
.
.
.
.
.
.
.
~otpu/entus
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. -
.
.
. -
.
.
. .
~op.
x crasslmergo jelfreysi
C r i b r o s t ~
sp.
1
Ct'bmetomo/d~s~bg/o~sc~ Cyc~n'mw'na orb/cu/ar/s Cyc~mminapusilla Cyclammnina Eggerella
bradyi
Eggerella
sp.
-
-
-
-
1
.
2
-
-
1
1
-
-
111526 . . . 2
.
9 .
.
.
.
.
.
1
x
1
vitrea?
.
.
-
x
earlazldi
x
.
Epistorninella
ex~gua
Fissutinaspp.
x
.
5
3
8 -
bk)ta
.
.
Cdob~assidulina
subglobosa
x
x
G ~ p ~ a ~ GytoldttwolbJcularis
2 .
sp.ldein
311 .
.
.
-
6
-
2 .
. 1
2
.
1
. .
.
. 4
1
-
1
-
2
3
3
2
.
-
-
-
-
1
-
-
2
-
x
1
2 4
L anticu#na
spp.
Mattinottiella Me/onis
.
x
nodulosa
.
-
zaan#ami
Miliammina
aranacea
.
.
.
1
1
.
.
.
.
.
.
.
Nutta/#do6
umbonifer
.
x
1
1
x
-
-
.
.
-
-
1
sp.
x
1
-
2417
-
314
1 2
1 x
1 .
x .
.
.
.
3
2
x
.
.
.
.
.
x
3 .
-
.
. .
. .
. -
.
.
.
.
.
2 . 2
6
-
x
x
-
-
1
4
-
Reophax
sp~culifer
-
2
.
.
-
5
-
1
2
1
3
5 .
x
4
.
Trocharnmk~sp.39+52
3
Ttochammina
1
a//others
globulosa
Spp.
.
.
.
.
-
.
.
1
.
.
.
.
.
.
.
1 .
-
1
.
.
.
.
.
.
.
.
.
.
.
.
.
-
-
1
x
.
1
2
4
-
2
1
1
-
2
.
3
2
5
2
1
4
3
3
5
4
6
4
x
x
2
4
2
-
9
-
1
-
x
x
2 x
-
x
-
-
-
x
.
. .
.
.
.
.
. x
. .
.
.
1
-
2
3
1
3
1
-
2
-
x
-
x
.
.
.
. . . . . .
.
.
.
-
.
. x
.
.
.
.
.
.
.
.
.
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A. MACKENSENET AL.
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in situ bottom water temperature in °C
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Fig. 7. Distribution of in situ bottom water temperatures as measured simultaneously with sampling. Area of measured temperatures > 0 ° C is shaded. Suggested water mass distribution is indicated without defining oceanographic boundaries. Water masses according to Foldvik et al., (1985). (ESW=Eastern Shelf Water, M W D W = M o d i f i e d Weddell Deep Water; WD W= Weddell Deep Water, AAB W= Antarctic Bottom Water; WSB W= Weddell Sea Bottom Water).
species from the dead assemblage, does not consider ongoing calcite dissolution with continuous burial below accumulating sediments. Consequently, the potential fossil assemblage is an ideal fossil assemblage which would be saved in the geological record, if calcite dissolution, biological destruction and physical disaggregation ceased below the top 1-2 cm sediment. Finally, the 39 species of the resultant "fossil" data matrix were reduced to five Principal Components, which explained 79.9% of the total variance. The hydrographic and surface sediment data, as well as the results of the statistical treatment of the benthic foraminiferal raw data, are plotted on a projection plane, which is imagined to be erected more or less parallel to the continental margin (Figs. 8-11 ). On this theoretical plane the stations are projected according to water depth and longitude (Fig. 2 ). The observer is placed as though he is somewhere on
the Weddell abyssal plain, looking towards the southeast on to the eastern continental margin. Environmental setting
Topography, hydrography and sea ice The Weddell Sea as the southernmost part of the South Atlantic Ocean is bounded on its eastern and southeastern margin by the East Antarctic craton (Fig. 1 ). The eastern continental margin between 5 and 20 °W can be divided morphologically into a continental shelf with the shelf break occurring between 500 and 600 m water depth; an upper continental slope between 500 and 1800 m; an approx. 200 km wide, gently dipping flat terrace between 1800 and 3000 m; and finally, a lower slope down to the abyssal floor in about 5000 m water depth. The width between the grounding line of the continental ice sheet and the continental shelf
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
break off East Antarctica varies from a few tens of kilometers to about 150 kin. In the investigated area the continental margin is deeply cut by at least one major canyon system, i.e. the Wegener Canyon off Kapp Norvegia (Fiitterer et al., in press ). Numerous 3.5 kHz bottom profiling tracks between the canyons and the general morphology show no signs of major slumping and sliding events. Thick undisturbed Quaternary sedimentary sequences, merely effected by turbidites and hiatuses, have accumulated, especially on the terrace. Today, the hydrographic regime on the continental shelf and the shelf break is controlled by the Antarctic Coastal Current (ACC) flowing along the shelf break and transporting very cold Eastern Shelf Water (ESW) of low salinity towards the southwest. The deep part of the ACC is formed by the Modified Weddell Deep Water (MWDW: - 1 . 6 < 0 < 0 , 34.4
2 51
dell Sea are permanently covered with sea ice, whereas the eastern parts are more or less icefree from November until February, with minimum coverage during February. A huge, yearround open water area, the Weddell Polynya, was present during austral winters 1973 through 1977 off the eastern continental margin between 30°W and 15°E (Zwally et al., 1983), thus covering the area investigated in this study. It is speculated that this polynya may have been a persistent phenomenon in geological times and may have strongly influenced the regional surface productivity; this in turn may be documented in the sedimentological record (FiJtterer et al., 1988 ).
Sediments The surface sediments on the eastern continental margin in general consist of silty and clayey muds with varying amounts of coarse sand and gravelly dropstones. Above about 1600 m water depth the sand size fraction exceeds 40%, and below about 1400 m the mud content ( < 6 3 / t m ) exceeds 50%, of the bulk dry sediment (Figs. 3,4). Only at the southern continental rise, off the mouth of the Wegener Canyon, does the sand content increase and consequently the mud content is diminished. The high sand content on the shelf and the upper slope is caused by winnowing of the fine fraction from a gravelly diamicton by the ACC (Grobe, 1986). The carbonate content of the surface sediments is arranged in four depth zones (Fig. 5 ). On the shelf carbonate contents of up to 9.5% of the bulk dry sediment are accounted for by bryozoans, bivalves, gastropods, brachiopods, rugose corals, red algae, and benthic foraminifera. At the shelf break and on the upper slope down to over 2000 m, the carbonate content never exceeds 1%. This depth range corresponds to the range where the core of the WDW and the M W D W reside. On the slope terrace between 2500 and 3500 m, carbonate contents from 3 through 13% are found. Here the car-
252
A. MACKENSEN ET AL.
bonate includes almost exclusively foraminifera, Below 4000 m virtually no carbonate was found in the surface sediments. The organic carbon contents of the surface sediments in general are low ( < 0.9%), but lowest between approximately 500 and 1800 m and at abyssal depths (Fig. 6 ). Benthic foraminiferal assemblages
Haplophragmoides bradyi ( Robertson ) = Trochammina hradyi Robertson 1891. Plate VIII, 3, 6. Haploph ragmoides canariensis ( d'Orbigny ) = Nonion ina canariensis d'Orbigny 1839. Plate VIII, 7-9. Hyperammina laevigata Wright=Hyperammina elongata Brady var. laevigata Wright 1891. Plate II, 12. Jaculella obtusa Brady 1881. Plate II, 11. Laticarinina pauperata ( Parker and Jones) = Pulvinulina repanda Fichtel and Moll, var. menardii d'Orbigny, subv. pauperata Parker and Jones 1865. Plate VII, 3. Miliammina arenacea ( Chapman ) = Miliolina oblonga (Montagu) vat. arenacea Chapman 1916. Plate II, 4, 5.
t a x o n o m i c notes
Alphabetical listing of dominant and characteristic species from the eastern continental margin with original designation, references to plates and figures in this paper, and some remarks. AdercoOTma glomerata
( B r a d y ) = L i t u o l a glomerata Brady 1878. Plate Ill, 7, 8. .4mmobaculites agglutinans ( d ' O r b i g n y ) = S p i r o l i n a agglutinans d'Orbigny 1946. Plate V, 8.
Ammomarginulina foliacea ( Brady ) = Haplophragmium foliaceum Brady 1881. Plate V, 5, 6. .4rnrnomarginulina recurva Earland =Ammornarginulina foliacea (Brady) vat. recurva Earland 1934. Plate V, 1,2.
Ammomarginulina ensis Wiesner 1931. Plate V, 3. Bulirnina aculeata d'Orbigny 1826. Plate II, 1-3. Since our B. aculeata has long spines and no intergradations to B. marginata are found in the lower bathyal depth range it may well be, following the speculation of Van Morkhoven et al. ( 1986 ), that B. aculeata is the deepwater ecophenotype of B. marginata. ('ribrostomoides jeffreysii (Williamson) = Nonionina jef[i'eysii Williamson 1858. Plate IV, 1. Cribrostomoides subglobosus (G.O. Sars ) = Lituola subglobosa G.O. Sars 1872. Plate IV, 7-9. Cribrostomoides wiesneri (Parr) = Labrospira wiesneri Parr 1950. Plate IV, 2, 3.
Cribrostomoides weddellensis ( Earland ) = Haplophragmoides weddellensis Earland 1946. Plate IV, 4, 5. ~),clammina pusilla Brady 1884. Plate VIII, 1,2. (),clammina trullissata (Brady) = Trochammina trullissara Brady 1879, Plate VIII, 4, 5. Eggerella bradyi (Cushman) = Verneuilina bradyi Cushman 1911. Plate III, 9, 10.
Ehrenbergina glabra Heron-Allen and Earland=Ehrenbergina hystrix var. glabra Heron-Allen and Earland 1922. Plate I, 5, 6.
Epistominella exigua (Brady) = Pulvinulina exlgua Brady 1884. Plate VII, 1, 2.
Martinottiella nodulosa (Cushman) = CYavulina nodulosa Cushman 1922. Plate II, 8, 9, Nonionella iridea Heron-Allen and Earland 1932. Plate l, 7-9.
Nonionella
bradii (Chapman) = Nonionina scapha (Fichtel and Moll) vat. bradii Chapman t 916. Plate 1, 4. Nuttallides urnboni[er (Cushman) = Pulvinulinella umbonifera Cushman 1933. Plate VII, 7-9. This species is also identified as Epistominella, ?Epistominella or Osangularia and typifies the complex and often confusing nomenclatural problems associated with many deep-sea species. Oridorsalis umbonatus
( Reuss )=Gotalina
umbonata
Reuss 1851. Plate VII, 4-6. We understand this species in a broad sense and include torms with a more acute periphery like O tener (Brady) as figured in Lohmann (1978, pl. 5, 5-7) and in Lagoe (1977: Eponides tener pl. 5, 3, 7, 14).
Pullenia bulloides (d'Orbigny)=Nonionina
bulloides
d'Orbigny 1839. Plate IV, 6. Psammosphaerafusca Schulze 1875. Plate II, 7. Pseudobolivina antarctica Wiesner 1931. Plate V. 7. Reophax bilocularis Flint 1899. Plate VI, 10-12. In this study we followed the classification ofSchr6der ( 1986 ) who recognized single chambers, which often are described as Reophax d(fflugifi~rmis Brady (1879), but are fragments of the originally two-chambered R. bilocularis Flint. Reophax dentaliniformis Brady 1881. Plate VI, 3. Reophax difflug(formis Brady 1879. Plate VI, 9. Reophax fusiformis (Williamson ) = Proteonina fus~formis Williamson 1858. Plate VI, 6. Reophaxpilulifer Brady 1884. Plate VI, 1, 2, 4. Reophax spiculifer Brady 1884. Plate VI, 7, 8. Rhabdammina linearis Brady 1879. Plate II. 10. Subreophax adunca (Brady)=Reophax adunca 1882. Plate VI. 5. 7Er,tularia wiesneri Earland 1933. Plate V, 4, 9. Trochammina nana (Brady) = Lituola nana Brady 1884. Plate III, 4-6. 7)'ifarina angulosa (Williamson ) = Uvigerina angulosa Williamson 1858. Plate I, 1-3. We use a broad species concept and include Angulogerina carinata Cushman
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
1927 and Angulogerina earlandi Parr 1950. Triloculinafrigida Lagoe 1977. Plate II, 6. Trochamtnina sp. 39 + 52. Plate III, 1-3. "The genus Trochammina poses many problems in classification." (SchrSder, 1986). We fully agree with this statement and we refer to her discussion of the Trochamminidae (ibid.: 22). In this paper we have therefore preliminary grouped different forms in an open classification.
253
Distribution patterns On the eastern Weddell Sea continental margin the live, dead, and potential fossil assemblages in general are bathymetrically arranged, although some faunal boundaries may
PLATE I (see p. 254 ) (Scale = 100 ~m) 1-3. Trifarina angulosa (Williamson ); Sample PS 1425-1. 4. Nonioaella bradii (Chapman); Sample PS 1384- l 5,6. Ehrenbergina glabra Heron-Allen and Earland; Sample PS 1425-1. 7-9. Nonwnella iridea Heron-Allen and Eadand; Sample PS 1425-1.
PLATE II (see p. 255) (Scale = 100 ~m ) 1-3. Bulimina aculeata d'Orhigny; Sample PS1391-1. 4,5. Miliammina arenacea (Chapman). Sample PS 1425-1. 6. Triloculinafrigida Lagoe. Sample PS1388-1.
(Scale = l mm)
7. Psammosphaerafusca Schulze. Sample PS 1224-3. 8,9. Martinottiella nodulosa (Cushman). Sample PS 1224-3. l O. Rhabdammina linearis Brady. Sample PSI 395-1. 1I. Jaculella obtusa Brady. Sample PS1395-1. 12. Hyperammina laevigata Wright. Sample PS 1395-1. PLATE Ill (see p.256) (Scale= l'00 ~m) 1. Trochammina sp. 39. Sample PS1368-1. 2, 3. Trochammina sp. 52. Sample PS1368-1. 4-6. Trochammina nana (Brady). Sample PS1427-1. 7, 8. Adercotryma glomerata (Brady). Sample PS 1388-1. 9, 10. Eg~erella bradyi (Cushman). Sample PS 1388- I. PLATE IV (see p. 257) (Scale= 100 lan)
1. Cribrostomoides jeffreysii ( Williamson ). Sample PS 1425-1. 2, 3. Cribrostomoides wiesneri (Parr). Sample PS 1368-1. 4, 5. Crib~ostomoides weddellensis (Eadand). Sample P S 1368-1. 6. Pulleni~ bulloides (d'Orbigny). Sample PSI 368-1. 7-9. Crib~ostomoides subglobosus (G.O. Sars). Sample PSI 368-1. 9. Enlarged view of the same specimen as in 7. The aperture of this live captured specimen is closed by agglutinated grains leaving only a small reduced opening. This may represent a resting stage of the animal between the extremely seasonal times of food supply in the eastern Weddell Sea. PLATE V(see p. 258) ( Scale = 100 ~m ) 1,2 Ammomarginulina recurva Eadand. Sample PS 1388-1. 3. Ammomarginulina ensis Wiesner. Sample PS 1368- I. 4, 9. Textularia wiesneri Earland. Sample PSI 384-1. 5, 6. A mn~omarginulina foliacea "(Brady). Sample PS1390-1. 7. Pseudo~olivina antarctica Wiesner. Sample PS 1384- I. (Scale= 1 ~nm) 8. Ammob~culites agglutinans (d'Orbigny). Sample PS 1224-3.
~i Ii ¸
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
PLATE II (for explanation see p. 253)
255
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BENTHIC FORAMINIFERALASSEMBLAGESFROM EASTERNWEDDELLSEA PLATE IV (for explanation see p. 253 )
257
BENTHICFORAMINIFERALASSEMBLAGESFROMEASTERNWEDDELLSEA
cross perpendicularly the isobaths (Figs. 811 ). In addition, lower principal component loadings of many live assemblages (PC'2) in the southwest indicate a major change in benthic assemblage composition close to the southern boundary of the area investigated in this study (Figs. 8-11 ). As also indicated in Figs. 8-11, in many cases the composition of the dead assemblages substantia~y differs from the corresponding biocoenoses, whereas the calculated potential assemblage either resemble the original live or the dead assemblages (Table IV, Fig. 12). Discussion
Although there are different trends and correlations detectable by comparing plots of dominant PC-loadings (assemblage distribution) with plotted environmental parameters, multivariate quantitative techniques (canonical correlation nor simple pair-wise correlation) have not revealed significant correla-
259
tions, except self-evident ones like, for example, a negative correlation between sand and mud content. This may be due in part to the limited environmental data set, but more likely reflects the fact that many independent patterns of benthic foraminiferal species variation cannot be explained through simple correlation with single or combined environmental parameters. Hence the discussion of the observed distinctive distribution patterns of species assemblages and their environmental preferences needs to be a qualitative one, whereas the discussion of the transition from live via dead to fossil assemblages includes quantitative aspects.
Continental shelf, shelf break and uppermost slope Live assemblages and their environmental preferences Down to about 1500 m water depth two live
PLATE VI (see p. 260) (Scale = 100 #m )
1, 2, 4. Reophax pilulifer Brady. Sample PSI 395-1. 3. Reopkitlx dentaliniformis Brady. Sample PSI 388-1. 5. Subreophax adunca (Brady). Sample PS 1364-1. 6. Reoptuzx fusiformis ( WiUiamson ). Sample PS 1388-1. 7, 8. Reophax spiculifer Brady. Sample PS 1391- I. 9. Reophax difflugiformis Brady. Sample PS 1368-1. 1O- 12. Reophax bilocularis Hint. Sample PS 1368-1. PLATE VII (see p. 261 ) (Scale= 100/an)
1, 2. Epistominella exigua (Brady). Sample PS 1387-1. 3. Laticarininapauperata (Parker and Jones), Sample PS1388-1. 4-6. Oridorsalis umbonatus (Reuss). Sample 1388-1. 7-9. Nuttallides umbonifer (Cushman). Sample 1368- I. PLATE VIII (see p. 262) (Scale = i100/zm ) 1, 2. Cydammina pusilla Brady. Sample PS 1368-1. 3, 6. Ha~lophragmoides bradyi ( Robertson ). Sample PS 139 l- 1. 4, 5. Cydammina trullissata (Brady). Sample PS1224-3. 7-9. Ha[?lophragmoides canariensis ( d'Orbigny ). Sample PS 1427-1. 9. Enlarged view of same specimen as in 7 and 8. The aperture of this live captured specimen is closed by agglutinated grains leaving only a small reduced opening. This may represent a resting stage of the animal between the extremely seasonal!times of food supply in the eastern Weddell Sea.
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BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
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264
A. M A C K E N S E N
ET AL
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BENTHIC
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265
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A MACKENSENET AL.
266
TABLE IV Species composition of live, dead and potential fossil assemblages with reference to figures 8-1 l, Principal Component No., dominant species, significant associated species and explained variance in percent of total variance. LIVE ASSEMBLAGES associated spp. var.(%)DpEcAD ASSEMBLAGES PC
dominant spp.
dominant spp.
o POTENTIAL FOSSIL ASSEMBLAGES associated spp. var.('/.) PC dominant spp. assoc ated spp. var.('/0)
Continental Shelf~ Shelf Break and Uppermost Slope (Fig. 8) 5
N. irldea
2
T. angulosa
G. crassa R. b/Iocularis R. dentaliniformis T. angulosa 7-. nana 7-. nana G crassa C. jeffreysii R. dentaliniformis
7.1
2
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T. nitida C. jeffreysii
20.7
18.0
5
7". angulosa R. linearis
P. fusca B. aculeata nana S. ramosa ,G crassa
5.4
2
T. angulosa
E. vitrea? G. crassa
20.7
17.5
1
C. subglobosus Troch. sp.39+52
R. linearis R. bilocularis C. pusilla
23.6
3
B. aculeata
136
5
M. nodulosa
M. arenacea T. angulosa F. earlandi E. vitrea ? G. crassa F. earlandi B. aculeata
1
O. umbonatus L. pauperata E. bradyi
20.0
4
N. umbonifer E. exigua
15.4
Upper Slope (Fig. 9) 3
B. aculeata C, subglobosus
Troch. sp.39+52 R. dentaliniformis
Continental Terrace and Abyssal Plain (FI 9. io) 3 1 C. subglobosus O. umbonatus 19.9 R bilocularis R. dentaliniformis
B. aculeata Troch. sp.39+52 R. fusiformis E, bradyi
O. urnbonatus C. subglobosus L. pauperata
R. tinearis E. bradyi
16.0
C. pusilla P. fusca C. subglobosus Troch. sp.39+52
R. linearis R. bilocularis O. umbonatus
8.0
N. umbonifer E. exigua
O. umbonatus R. linearis C. subglobosus G. crassa T. angulosa
8.6
10.2
Lower Slope (Fig. 11) 4
R. plluflfer R a/gaeformis A. ensis
FL fusiformis A. foliacea E. exigua C. subglobosus Pelosinella sp. G. crassa R. bilocularis A. recurva O. umbonatus
9.3
6
assemblages dominate the benthic foraminiferal fauna (Table IV, Fig. 8 ). Trifarina angulosa, the dominant species of PC 2, clearly outnumbers all other species in most of the samples in this depth range, except on the eastern shelf off Atka Bay and in a few samples on the continental slope, where a fauna characterized by Nonionella iridea (sensu lato) with Globocassidulina crassa as a second important constituent, is present. The shelf and the upper continental slope dominated by T. angulosa is covered by a sandy
and gravelly lag sediment. The lower boundary of the distribution of PC2 ( T. angulosa) and PC 5 (N. iridea) coincides with the boundary above which the sand content of the surface sediments exceeds 50% (Fig. 3 ). At some stations very high gravel contents of up to 43% are found between 340 and 1240 m water depth (Table I ). Three different bottom water masses reside on the shelf and the uppermost slope, and characterize the distribution area of T. angulosa (Fig. 7). This excludes a preference of a
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267
specific water mass by the T. angulosa Assemblage and it definitely shows an independence from bottom water temperature and salinity since the temperature ranges from - 1 . 8 to 0.4°C and in salinity from 34.43 to 34.72%0. This is in contrast to the results of Williamson et al. (1984) who calculated a strong correlation between a salinity of 35%o and the distribution pattern of Trifarina angulosa at the shelf break off Nova Scotia. On the other hand, our findings are in agreement with earlier investigations from the Norwegian continental margin and Iceland-Faeroe Ridge which show a strong relationship of Trifarina angulosa to sandy substrates and relatively high bottom current velocities, independent of conservative water mass characteristics such as temperature and salinity (Mackensen et al., 1985; Mackensen, 1987a). Trifarina angulosa (partly documented as T.
earlandi, Angulogerina angulosa, A. carinata, Uvigerina bassensis) seems to be present all
o
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Fig. 11. Distribution of lower slope benthic foraminiferal assemblages. Contours are 100× Varimax Component Loadings. Top row: distribution of the live Reophax pilulifer assemblage. Middle row: distribution of the corresponding dead Nuttallides umbonifer assemblage. Bottom row: distribution of the potential fossil Nuttallides umbonifer assemblage.
around Antarctica on the shelf, the shelf break and the upper continental slope: It is found in surface sediments from the eastern Weddell Sea (Anderson, 1975; this study), the Cosmonout Sea (Uchio, 1960), the Kerguelen Plateau (Lindenberg and Auras, 1985; Mackensen, in press), the Adelie-George V continental slope (Milam and Anderson, 1981 ), the Ross Sea (Osterman and Kellogg, 1979), off King George Island (Li and Zhang, 1986) and the southern and eastern Falkland Plateau area (Herb, 1971; Mead and Kennett, 1987). The organic carbon and the carbonate content is relatively high on the shelf and extremely low on the upper slope (Figs. 5, 6 ). At station 1425 on the eastern shelf, a dominance ofNonionella iridea (Fig. 8 ) coincides with the highest measured organic carbon content in the investigated area (Fig. 6 ). To speculate on relations between high organic carbon contents, high productivity, and the distribution of the N. iridea Assemblage, clearly requires more stations on the continental slope. However, N.
268
A. MACKENSEN ET AL
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BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
iridea encapsulating itself with sediment and living within the upper 3 cm (Gooday, 1986; Mackensen, 1988), may depend on high organic carbon fluxes to thrive within the sediment.
Dead assemblages and early diagenesis The composition of the dead benthic foraminiferal assemblages on the shelf and the uppermost slope is different from their corresponding biocoenoses. West of ca. 7°W the thanatocoenosis is dominated by tests of the arenaceous Trochammina nana (PC 2), whereas the eastern part is characterized by empty tests of T. angulosa (Fig. 8, Table IV). On the shelf, the shift in species composition from mainly calcareous live to mainly arenaceous dead assemblages is caused by calcite dissolution in the uppermost sediment. The infaunal N. iridea is dissolved after reproduction or death within the uppermost centimeters of the sediment, enhanced by relatively high organic carbon contents. This is also documented in the Bransfield Strait, an area with high particulate organic carbon contents in the sediments. There, live N. iridea are found down to 3 cm within the sediments, but only a few empty tests occur within the top 2 cm; below 2 cm no dead specimens are found at all (Mackensen, 1988). In deeper waters on the continental slope, where the M W D W and WDW reside, calcite dissolution changes the benthic faunal composition already at the sediment-water interface. Below 1000 m water depth the number of empty T. angulosa tests drastically decreases in spite of the still high percentage of live specimens (Fig. 12).
Potentialfossil assemblage In contrast to the live and the dead faunas, which are characterized by different assemblages, the potential fossil assemblage on the continental shelf and the uppermost slope is clearly dominated by T. angulosa (Fig. 8 ). This implies that fossil Neogene benthic foramini-
269
feral assemblages that are dominated by T. angulosa indicate deeper shelf, shelf break and upper continental slope conditions, with strong to moderate bottom currents. However, it also implies that various live assemblages that are adapted to different environmental niches are not recorded in the fossil assemblage. On the other hand, the absence of fossil T. angulosa in Neogene core material does not necessarily exclude a former live assemblage characterized by T. angulosa; on the contrary, coarse and sandy sediments with no foraminifera other than a few resistant and corroded specimens, from an estimated paleodepth between 500 and 2000 m, may well have been deposited under strong current conditions on the shelf break and uppermost continental slope.
Upper slope Live assemblage and its environmental preferences Between 1400 and 2000 m water depth the northeastern part of the investigated area is inhabited by the Bulimina aculeata Assemblage (PC 3 ). Towards the southwest, into the more central part of the Weddell Sea, the distribution area becomes narrower and the number of live B. aculeata decreases (Table IV, Fig. 9 ). At this water depth, below 1400 m, the winnowing force of the ACC is reduced, indicated by higher mud contents of the surface sediment (Fig. 4). With increasing content of the fine fraction, slightly higher organic carbon contents are evident (Fig. 6), also indicating low bottom current activity. The carbonate content down to 2000 m depth is still negligible (Fig. 5 ). As indicated by temperature measurements, this belt with an extremely low carbonate content of the surface sediments coincides with that area on the upper slope where warm WDW resides (Fig. 7 ). The distribution of the B. aculeata Assemblage on the eastern Weddell Sea continental slope suggests that B. aculeata prefers water
270
temperatures > 0 ° C, a fine substrate and consequently low bottom current activities which do not hamper sufficient particulate organic matter fluxes. High productivity zones, often associated with water mass boundaries, seem to be favoured by this biocoenoses. B. aculeata itself is a cosmopolitan species, for which Van Morkhoven et al. (1986) and other have provided extensive references. Our data on living organisms corroborate conclusions based on late Neogene material from the Mediterranean, where B. aculeata has been correlated with high organic carbon (Olausson, 1960) and high m u d content (Van der Zwaan, 1982 ). Close to the Polar Front in the southwestern Atlantic, Mead and Kennett (1987 ) found a Bulimina aculeata assemblage associated with the core of the Lower Circumpolar Deep Water (LCDW) between water depths of 1500 and 2600 m. The WDW which resides on the eastern Weddell Sea continental margin can oceanographically be subdivided from the CDW (Hellmer et al., 1985 ). Also in the Cosmonaut Sea on the Gunnerus Ridge a benthic foraminiferal assemblage, dominated by B. aculeata, is found to be associated with the CDW and its high temperature (Uchio, 1960). North of this area on the Crozet Plateau, Corliss (1983:110) reported a B. aculeata-dominated assemblage overlain by warm Antarctic Intermediate Water. West of Heard Island on the Kerguelen Plateau, B. aculeata is consistently found together with Angulogerina earlandi (here T. angulosa), but it dominates the fauna at around 2000 m depth (Lindenberg and Auras, 1984).
Dead assemblage and early diagenesis The dead assemblage on the upper slope is almost exclusively composed of agglutinated species and is dominated by Cribrostomoides subglobosus (PC 1 ) (Fig. 9). Trochammina sp. 3 9 + 5 2 are the next important constituents (Tables II, IV). This change in species composition from a calcareous B. aculeata Assemblage to an arenaceous C subglobosus Assem-
A. MACKENSEN ET AL.
blage is described in detail by Mackensen and Douglas (1989). Investigation of separately stained sediment slices have revealed live B. aculeata concentrated in the uppermost centimeter of the sediment, whereas only a few, probably bioturbated, specimens occur between 1 and 2 cm sub-bottom depth. On the other hand, almost no empty tests were found in the surface sample and definitely no tests below the top centimeter of the sediment. Calculation of the degree of calcite saturation shows that WDW is not undersaturated above 3000 m water depth (M.M. Rutgers van der Loeff, pers. commun. ). Consequently, destruction and dissolution of dead B. aculeata takes place within the uppermost sediment, where, because of the decay of organic material, the interstitial water is undersaturated relative to calcite. Therefore it is likely that B. aculeata lives in the top few millimeters of the sediment and is similar to Uvigerina peregrina. Our conclusion is in agreement with Corliss and Chen (1988) who suggested, based on shape analysis of Norwegian Sea faunal counts from Mackensen et al. ( 1985 ), that B. marginata, the shallow water relative of B. aculeata, belongs to a morphotype associated with an infaunal microhabitat.
Potential jbssil assemblages Below the bioturbated zone, the tiny agglutinated Trochammina spp. and Reophax bilocularis, which characterize the upper slope dead and live assemblages, are disintegrated, and below 25 cm sub-bottom depth, the more resistant C. subglobosus and Cyclammina spp. also disappear (Mackensen and Douglas, 1989). This explains the composition of the potential fossil assemblages calculated for the upper slope: The potential fossil assemblage is dominated by B. aculeata if the live assemblage has been dominated by B. aculeata. After subsequent destruction of the agglutinated species, a few empty B. aculeata tests of the dead assemblage became the only remnant of the for-
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
merly highly diverse biocoenosis. In the more southern parts of the area investigated, where the dominance ofB. aculeata in the live assemblage is less strong, Martinottiella nodulosa and Miliammina arenacea dominate the fossil assemblage (Fig. 9 ). The latter species are highly resistant and do not disintegrate in dilute hydrochloric acid. They are found to be the only remnants of the B. aculeata Assemblage below 25 cm sub-bottom depths (Mackensen and Douglas, 1989 ). Throughout this discussion it is important to keep in mind that in many samples from the upper slope the potential fossil assemblage accounts for only a small percentage of the original live fauna. In conclusion, it is very reasonable to interpret a low diversity Neogene benthic foraminiferal assemblage dominated by B. aculeata or M. noduiosa and M. arenacea, buried in a silty clay or clayey silt, as an indicator of upper continental slope conditions (lower bathyal) with high supply of organic matter, may be close to a water mass boundary or an oceanic front.
Continental terrace and abyssal plain Live assemblage and its environmental preferences On the fiat continental terrace between 2000 and 3000 m water depth, and especially in the southern part of the investigated area, below 4500 m, the live benthic foraminiferal fauna is dominated by Cribrostomoides subglobosus (PC 1 ) (Fig. 10). Calcareous components include Oridorsalis umbonatus as accessory species (Table IV). The surface sediments on the continental terrace consist of mud with varying sand content and dropstones (Fig. 3). In the southern part off the mouth of the Wegener Canyon, sand contents of over 50% of the bulk dry sediment are found (Fig. 3 ). The upper boundary of the C. subglobosus Assemblage coincides with the upper boundary of the AABW (Fig. 7 ). In addition, the distribution of the highest levels of carbonate content, disregarding the
2 71
continental shelf, roughly coincides with the distribution of the C. subglobosus Assemblage on the continental terrace. We suggest that the C. subglobosus Assemblage prefers environmental conditions related to plains at the foot of continental slopes, independent of water depth and conservative water mass characteristics. Consequently, in the investigated area the unique situation of a continental slope divided by a terrace results in a bipartite distribution of the C. subglobosus Assemblage (Fig. 10). This relationship between C. subglobosus and a continental rise morphology has previously been reported from the Norwegian Sea continental margin (Mackensen, 1985; Mackensen et al., 1985) and the Iceland-Faeroe Ridge (Mackensen, 1987a). There, a combination of hemipelagic sedimentation with according particulate organic matter fluxes and the availability of coarse grain sizes for test construction is inferred as the critical environmental limit for the distribution ofa C. subglobosus-dominated assemblage. In the Norwegian Sea as well as in the Weddell Sea, ice rafted material is the source of coarse material within pelagic sedimentation realms. Few investigations, other than those of the senior author, have dealt with distribution patterns of agglutinated species as part of the benthic foraminiferal deep-sea fauna, and to our knowledge, none of them have treated live faunas of higher latitudes quantitatively. Herb (1971) reported abundant C. subglobosus in the Drake Passage between 3800 and 4200 m water depth, as did Lindenberg and Auras (1984) from the continental slope off Prydz Bay in 1590 and 2688 m. Unfortunately, both paper do not differentiate between live and dead specimens, in spite of Rose Bengal treatment of most of the samples.
Dead assemblages and early diagenesis The dead assemblage on the continental terrace is dominated by O. umbonatus (PC 3),
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whereas the continental rise and the foot of the lower slope is dominated by Cyclammina pusilla (PC 4) (Fig. 10). In both of these assemblages empty C. subglobosum tests are characteristic of the associated components (Table IV). The shift from a mainly agglutinated live fauna on the terrace to a mainly calcareous death assemblage may simply reflect, that (i) the physical a n d / o r bacterial destruction of empty C. subglabasum tests takes place rather quickly on and in the uppermost sediment and (ii) no carbonate dissolution hinders the accumulation of dead O. umbanatus. At the Norwegian continental margin an identical situation has been reported: the live fauna is dominated by C. subglabasum but the corresponding dead assemblage is dominated by calcareous species (Mackensen et al., 1985; Mackensen, 1987a). However, on the Weddell abyssal plain below 4000 m, calcite dissolution diminishes the number of calcareous tests faster than C. subglobosum is destroyed and C. subglobosum is destroyed faster than the more resistant arenaceous species. Given low sedimentation rates, C. pusilla accumulates over several generations and becomes the dominant constituent of the dead assemblage (Fig. 12 ).
Potential fossil assemblage The composition of the calculated potential fossil assemblage (PC 1 ) on the continental terrace is the preliminary terminal state of what begun at the transition from live to dead. All C. subglobosus test have been destroyed and broken down into their mineral components. There is thus an enrichment of O. umbonatus and other calcareous, and especially resistant agglutinated species, indicated by Laticarinina pauperata and Eggerella bradyi, respectively. The latter two species occur only as accessory constituents in the live assemblage (Table IV). On the continental terrace, there is evidence, that a further transition from the Holocene O. umbonatus potential fossil assemblage
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to a Pleistocene E. exigua real fossil assemblage takes place. This can be explained either by diagenetic processes deeper within the sediment or, more likely, by averaging out and dilution of the record of the special circumstances of the last 1000 years over a longer interglacial sequence. In a virtually complete record of 1 million years from station 1388 (Figs. 1, 2 ), which was dated by means of stable oxygen isotope stratigraphy and paleomagnetism (Mackensen et al., 1989), the interglacials are clearly dominated by E. exigua (Mackensen, unpublished data). The Holocene epoch, the last deglaciation period, only represents a short phase of a glacial-interglacial cycle with special environmental conditions. Therefore it is likely that averaging out with further future interglacial assemblages may result in an E. exigua-dominated fossil assemblage, and the short phase of climatic improvement, characterized by the O. umbonatus dead assemblage is no longer documented in the sediments. We have also calculated a potential assemblage including C. pusilla, because Cyclammina sp. is reported to be abundant at early Miocene sites on King George Island (Birkenmajer et al., 1983; Gazdzicki and Wrona, 1986) and in some Arctic cores (Scott et al., 1988). However, composition and distribution of the fossil assemblage on the continental terrace shows no significant change. This solution accounts for only a minor part of the total variance and adds an additional C. cyclammina PC similar in distribution and composition to the dead assemblage (PC 4) that occurs at abyssal depths (Fig. 10). In conclusion, a Neogene calcareous fossil assemblage dominated by O. umbonatus may be the remnant of a former arenaceous C. subglobosum assemblage and, at least around Antarctica, may indicate depositon on the continental rise or on very gently dipping parts of the lower continental slope. In addition, a Pleistocene E. exigua-dominated assemblage may also include a former O. umbonatus-dom-
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
inated dead assemblage and a C. subglobosum dominated live assemblage, respectively (cf. discussion below).
Lower slope Live assemblage and its environmental preferences On the lower continental slope between the continental terrace and the Weddell abyssal plain, i.e. between approximately 3000 and 4000 m water depth, Reophax pilulifer (PC 4 ) dominates a predominantly arenaceous live assemblage (Fig. 11, Table IV). The sand content of the surface sediments in this depth interval is somewhat higher than on the terrace, but lower than on the continental rise below 4000 m (Fig. 4). The carbonate and organic carbon contents vary in about the same range as on the continental terrace (Figs. 5, 6). The lower slope is overlain by the AABW. The upper boundary of the colder WSBW, which resides on the Weddell abyssal plain, seems to coincide with the lower boundary of the live PC 4.
Dead assemblages and early diagenesis The dead assemblage on the lower continental slope is dominated by Nuttallides umbonifer with Epistominella exigua as the second important constituent (Figs. 11, 12, Table IV). Essentially, the same mechanism of physical and bacteriological/chemical destruction of agglutinated tests and subsequent accumulation of calcareous tests in an environment above the CCD, as discussed for the continental terrace, causes the shift from a predominantly areanaceous live fauna to a calcareous dead assemblage. Both N. umbonifer and E. exigua are cosmopolitan deep water species which were used to infer bottom water characteristics and routes in late Neogene time (Streeter, 1973; Schnitker, 1974). Today a benthic foraminiferal assemblage dominated by N. umbonifer characterizes the AABW in the Atlantic Ocean
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(Lohmann, 1978). In the Indian Ocean, AABW is found associated with N. umbonifer and Cibicidoides wuellerstorfi (Corliss, 1979, 1983 ), but in the Pacific with N. umboniferand E. exigua (Douglas and Woodruff, 1981 ). In the Pacific Ocean "In the zone between the lysocline ( 3500 m ) and the CCD, E. umbonifera becomes the dominate species" (ibid.: 1280). From the southwestern Weddell Sea continental slope, abundant N. umbonifer have been reported between 3100 and 3800 m water depth (Anderson, 1975 ). In summary, N. umbonifer today is a characteristic constituent of dead benthic foraminiferal assemblages on most of the world ocean floors over which AABW flows, that is essentially between the depth of the carbonate lysocline and the CCD. This agrees with our measurements, which indicate a drastic decrease in carbonate percentage [carbonate lysocline in the sense of Broecker and Takahashi (1978) and Berger (1979) ] below 3500 m (Fig. 5). Calculation of saturation profiles with respect to calcite as a function of temperature, salinity and pressure based on published data ofpH, SCO2 and carbonate alkalinity in the area under investigation, reveals a calcite undersaturation of AABW below ca. 4000 m water depth (Schliiter and M.M. Rutgers van der Loeff, pers. commun. ). Corliss and Honjo ( 1981 ), in a comparison of seven deep-sea benthic foraminiferal species (which excluded E. exigua) with respect to their resistance to carbonate dissolution, documented that dissolution probably has no major role in preferentially concentrating N. umbonifer. This is because N. umbonifer is as susceptible to carbonate dissolution as are other c o m m o n deep-sea species. This is consistent with Bremer and L o h m a n n (1982) who suggested that N. umbonifer in the Atlantic Ocean shows a negative correlation with the degree of carbonate saturation of deep water masses. Our data based on live specimens corroborate Bremer and L o h m a n n (1982), who suggested that the relationship between car-
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bonate saturation and faunal distribution resuits from the ecological influence on the live organisms, rather than from selective dissolution. On the eastern Weddell Sea continental margin, the upper boundary of the AABW does not coincide with the lysocline. Consequently, N. umbonifer in the area under study is associated with the lower AABW between the carbonate lysocline and the CCD and it is missing above the lysocline. In contrast, live N. umbonifer have been reported from the central Weddell Sea from below the CCD (Mackensen, 1987b). Also Anderson (1975, p. 78) reported a few specimens from the western Weddell Sea abyssal depth (4500 m ) , which we consider to be alive. This indicates that N. umbonifer prefers an environment that is corrosive to carbonate, but it also implicates that N. umbonifer is able to tolerate strongly undersaturated water masses, in which the empty tests rapidly dissolve after death of the animals. From the Antarctic continental slope overlain by AABW, one sample with abundant E. exigua was reported by Uchio (1960). On the other hand E. exigua is reported to be associated with North Atlantic Deep water i n t h e Atlantic (Schnitker, 1974; Lohmann, 1978), Indian Bottom Water in the Indian Ocean (Corliss, 1979 ) and Pacific Deep Water in the Pacific Ocean (Douglas and Woodruff, 1981 ). In the Norwegian Sea E. exigua and C. wuellerstorfi dominate the live fauna between 2000 and 3000 m water depth (Norwegian Sea Bottom Water). A correlation between relatively coarse and organic-rich sediments and this assemblage was documented and a preference of high food supply and a tolerance of low interstitial water oxygen content was proposed (Mackensen et al., 1985 ). Recently it was documented, that both E. exigua and C. wuellerstorfi are epibenthic species (Gooday, 1988; Lutze and Thiel, 1989), which tend to live elevated above the actual sediment-water interface and therefore should not care too much about pore water chemistry.
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Potential fossil assemblage The potential fossil assemblage on the lower continental slope and rise is clearly dominated by N. umbonifer, with E.exigua as an associated constituent. The calculation of the potential fossil assemblage indicates no difference in resistivity against dissolution or destruction between N. umbonifer and E. exigua, as one might expect considering the relatively thickwalled and compactly constructed test of N. umbonifer as compared with the very thin, hyaline and small tests of E. exigua. This is important to know when interpreting down-core changes in benthic foraminiferal composition from an E. exigua-dominated assemblage to a N. umbonifer-dominated fauna; i.e. on the Maud Rise and southern Kerguelen Plateau, where an early Oligocene through early late Miocene N. umbonifer-dominated fauna precedes a middle late Miocene through late early Pliocene E. exigua fauna (Barker, Kennett et al., 1988; Schlich, Wise et al., 1989; Mackensen, in press). Such a faunal shift can be explained by a primary response of the benthic fauna to a change in bottom water carbonate saturation, rather than to a change in preservation. This is because of changes in within-sediment conditions produced by increasing surface productivity and resultant high organic matter fluxes, which in turn produce highly aggressive pore waters relative to carbonate. In summary, our data suggest that a late Paleogene/Neogene N. umbonifer dominated fauna with E. exigua as a minor associated constituent, indicates a paleoenvironment characterized by a water mass similar to AABW within the zone between the carbonate lysocline and the CCD, whereas an E. exigua (0. umbonatus) dominated fauna around Antarctica may also indicate AABW or similar water mass conditions, but above the carbonate lysocline.
Conclusions Today five distinct benthic foraminiferal
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
communities (stained tests) inhabit the continental margin of the eastern Weddell Sea, recognized on the basis of multivariate statistical analyses. Six dead assemblages (empty, unstained tests) and five potential fossil assemblages (empty tests, non-resistant agglutinated species excluded) correspond to the biocoenoses. The benthic foraminiferal assemblages in general are bathymetrically arranged, although towards the southwest a major faunal change perpendicularly crossing the isobaths is indicated. On the outer continental shelf, shelf break and upper slope, the live assemblages are predominantly calcareous, whereas deeper than 2000 m water depth they are strongly dominated by arenaceous species. Each of these live assemblages undergoes its specific early diagenetic transition via a dead assemblage to the fossil assemblage. The changes in species composition and distribution patterns depend largely on the corrosiveness of the pore water and bottom water masses to carbonate and also the resistance of the agglutinated tests to disintegration. The corrosiveness of the pore water, in turn, depends largely on the fluxes of organic matter. Consequently calcareous benthic foraminiferal biocoenoses which are adapted to high organic matter supply become badly preserved in the sediment and the geological record. Deeply infaunal species like Nonionella iridea rapidly dissolve after the death of the animals, because on the shelf and the upper slope the pore water is carbonate-undersaturated below the upper few centimeters of sediment. In contrast, tests of species like Trifarina angulosa, which live on the sediment surface, or (if infaunal), within the top few millimeters of sediment, can comprise a significant portion of the dead assemblage. This is because T. angulosa is associated with a sandy substrate and strong bottom currents and consequently a well oxygenated, non-corrosive interstitial water. Agglutinated tests of species like Trochammina nana may dominate the dead assem-
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blage, but they become disintegrated within the upper sediment during early diagenesis as a result of the predatory actions of macro-benthos, among others, and they are thus not recorded in the fossil assemblage. In summary, above 2000 m water depth, only calcareous tests of epifaunal or shallow infaunal species are preserved within the sediment. They document the former diverse live assemblages and their corresponding habitats as follows: ( 1 ) A fossil Neogene fauna characterized by T. angulosa indicates outer shelf, shelf break and upper continental slope conditions with strong bottom current activity. (2) Fossil assemblages characterized by Bulimina aculeata a n d / o r Martinottiella nodulosa indicate lower continental slope conditions with a calm hemipelagic environment, in which fine sedimentation and high particulate organic matter fluxes proceed unhampered. Between 2000 and 3500 m water depth where the AABW, which resides on the lower continental slope and rise, is carbonate supersaturated and the fluxes of organic matter are low, a predominantly arenaceous fauna, dominated by Cribrostomoides subglobosus, turns to a calcareous fossil assemblage. Simultaneous with the disintegration of the agglutinated tests, there is preservation and subsequent accumulation of the calcareous species Oridorsalis umbonatus and Epistominella exigua. Below the carbonate lysocline around 3500 m water depth, but above the CCD, after the disintegration of a predominantly arenaceous live fauna, a dead and a potential fossil assemblage remain, which are both dominated by the calcareous species Nuttalides umbonifer. In the eastern Weddell Sea, this benthic foraminiferal assemblage is associated with the deeper part of the AABW, and clearly corroborates earlier investigations suggesting a primary relationship between the carbonate-corrosiveness of water masses and N. umbonifer. We have thus been able to relate distinct paleoenvironments to distinct (potential) fossil assemblages. The application of our results to
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faunal assemblages from Neogene core material from the Weddell Sea and from the southern Kerguelen Plateau, where T. angulosa assemblages are overlain by B. aculeata assemblages and where N. umbonifer faunas precede E. exigua-dominated faunas, will provide a check for their utility and feasibility in high-latitude paleoceanographic reconstructions.
Appendix
TABLE I. 1. Varimax Principal Component Loadings of live assemblages Sample PS1482 PS1370 PS1387 PS1481 PS1405 PS1224 PS1388 PS1380 PS1390 PS1389 PS1386 PS1412 PS1367 PS1384 PS1383 PS1410 PS1373 PS1427 PS1374 PS1428 PS138S PS1406 PS1425 PS13943 PS13941 PS1391 PS1395 PS1381 PS1411 PS1375 PS1379 PS1376 PS1377 PS1369 PS1372 PS1588 PS1368
PC 1
PC 2
PC 3
PC 4
PC 5
0.840 0.835 0.782 0.777 0.771 0.743 0 732 0.714 0.587 0.582 0.544 0.541 -0,044 0.005 -0,127 0.057 -0.078 -0.073 0.175 0.080 -0 0 5 7 0014 -0.033 0.154 0,328 0.345 -0,137 0.451 0045 0.495 0159 0.154 0.398 0.142 0.188 0.392 0.266
-0.036 0.089 0.015 -0 054 -0.039 0.059 0.015 -0.065 0033 -0080 0 039 -0089 0.919 0.871 0.869 0.818 0.815 0734 0.705 0.692 0.666 0.586 0.513 0.100 -0.028 0.078 0.424 0.010 0.096 -0.085 -0 0 2 8 0.025 0 000 0.004 0368 -0.044 0 101
0.191 0.273 0 110 0150 0.201 0.016 0.043 0.532 0.004 0.278 0.071 0.328 -0.008 -0004 0.363 0.150 0.107 0.064 0.607 0.130 0.630 -0.053 0.035 0.934 0.891 0.873 0.842 0.801 0.763 0.669 0.086 -0.003 0.047 -0029 -0142 -0049 0.064
-0009 0.016 0.162 0179 0182 0230 0 431 -0.026 0144 0.439 0.363 0.023 -0.029 0.003 -0001 -0 0 2 0 0.062 0.070 -0 0 2 3 -0.029 0184 -0.154 -0.061 0.020 0.078 -0.003 0019 0.031 0.101 0.034 0.851 0.840 0752 0 625 0 015 0248 0.479
0.000 0113 0062 0.058 0.023 ~0.109 -0 0 1 6 0036 ~0 0 5 0 0.067 ~0.052 0.699 0.021 0.010 0.089 0.485 0.043 0.638 0077 0 677 0003 0.087 0.820 0.020 0.025 0.025 0.017 -0.024 0 488 0,120 0 013 -0.043 0.026 -0.006 0207 -0.015 0009
Comm. 0.743 0.793 0.654 0.665 0.67( 0.621 0.72~ 0.79~ 0.36£ 0.62{ 0.43; 0.89; 0.84E 0.75£ 0.911 0.93( 0.68; 0.96( 0.903 0.961 0.87E 0.37E 0.94~ 0.907 0.90£ 0.68E O.90E 0,847 0 . 8 4 -~ 0.715 0.75£ 0.732 0727 0.412 0.234 0.22C 0.315
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TABLE 1.2 Varimax Principal Component Loadings of dead assemblages Sample PS1380 PS13943 PS1361 PS1375 PS1391 PS1411 PS1370 PS1412 PS1389 PS1382 PS1481 PS1395 PS1383 PS1372 PS1373 PS1374 PS1410 PS1427 PS1367 PS1384 PS1406 PS1390 PS1379 PS1388 PS1387 PS1224 PS1369 PS1368 PS1405 PS1462 PS1386 PS1428 PS1426 PS1378 PS1588 PS1377
PC 1 0 .9 2 4 0.907 0.900 0.895 0.868 0.863 0.831 0 .6 2 2 0 .6 4 5 0 .6 1 6 0 .5 3 6 0 .5 3 0 0 .0 4 3 -0.015 0,037 0.150 0.092 -0.024 -0.053 -0.033 -0.097 0.143 0 .0 7 5 0.383 0 .4 0 8 -0.078 -0.026 0.051 0,414 0.377 0 .4 7 2 0 .1 0 6 -0.140 -0,045 -0.078 0.000
PC 2 -0.071 0.002 -0.048 -0.038 0.029 0.143 -0.054 -0.066 -0.030 0.148 -0.060 0.337 0.984 0,946 0.940 0.901 0.887 0.685 0.884 0.865 0.649 -0.059 -0,040 -0,074 -0.092 -0.038 -0.066 -0.047 -0.050 0,122 0.068 0.194 0.288 -0.058 -0.048 -0042
PC 3 0.208 0,096 0.225 0.087 0.223 -0.047 0.319 0.245 0.622 -0.070 0.730 -0.184 -0,057 -0.032 -0.065 -0.113 -0.100 -0002 -0.010 -0.017 0.029 0.924 0.892 0.843 0.831 0.828 0.613 0.004 0.052 0.074 0.225 -0 101 0.089 0.366 0.145 0,330
PC 4 0.127 0.050 0.270 0.119 0.279 -0.044 0.313 0.273 0.148 0.028 0.256 -0.060 0.012 0.004 -0.017 -0.028 0.008 0.015 0.014 0.021 0.007 0.020 -0.024 0.142 0.115 -0.086 0.131 0.865 0.801 0.669 0.667 0.085 -0.003 0,126 -0.015 0,259
PC 6 0.022 0.056 0.021 0.018 -0.028 0.015 0.03 3 0,048 0.046 -0.358 0.014 -0.396 0.045 -0.100 -0.075 0.06 0 0.16 6 -0.366 -0.196 -0.136 -0.273 -0.006 0.018 0.03 4 0.023 0.02 2 -0.021 -0.002 -0.113 -0.074 0.113 -0.866 -0.753 0.013 0.037 0.030
PC 6 -0.046 -0.028 -0.083 0.004 -0.083 0.071 -0.104 -0.127 0.084 0.106 0.017 0.159 0.018 -0.034 0.021 0.071 0.066 -0.060 -0.089 -0.061 -0.153 0.155 0.334 0.037 0.110 0.263 0.585 0.226 0.057 0.154 -0.093 0.065 -0.186 0.870 0.870 0.857
TABLE 1.3 Varimax Principal Component Loadings of fossil assemblages Sample PS1390 PS1388 PS1379 PS1389 PS1481 PS1387 PS1224 PS1369 PS1370 PS1426 PS1427 PS1383 PS1372 PS1367 PS1373 PS1382 PS1384 PS1428 PS1406 PS1410 PS1396 PS1411 PS1374 PS13943
PC 1 0.967 0.924 0.922 0.919 0.917 0.906 0.884 0.696 0.632 -0.036 -0.025 -0.074 -0.063 -0.106 -0.017 0 .0 3 3 -0.101 -0,038 -0.104 -0.018 -0.088 -0.070 -0.062 -0.020
PC 2 -0,052 -0.101 -0.072 -0,061 -0.024 -0.100 -0.083 -0.048 0.002 0.972 0,934 0,920 0,660 0.824 0.820 0.810 0.731 0.649 0.630 0524 0.035 -0.068 0.305 0.103
PC 3 0.049 0.030 0.031 0.012 0.027 0.003 0.035 0.074 0.044 -0.132 -0.238 -0,021 -0,160 -0.030 -0.438 -0.342 0.144 -0.686 0.118 -0604 -0.846 -0.745 -0.731 -0.719
PC 4 0.102 0.042 0.276 0.067 0.104 0.171 0.201 0.575 0.089 -0.032 -0.012 -0.063 -0.057 -0.086 -0.009 0,026 -0,092 -0.011 -0.089 -0.027 -0.066 -0.039 -0.058 -0.096
PC 5 -0.095 0.049 0.081 -0.131 -0,238 0.070 0.107 0.025 -0.708 0.030 0.072 0.002 0.083 -0.015 0,112 0.094 -0,062 0.008 -0.080 0.19 3 -0.067 -0.563 0,169 -0.278
Comm. 0.960 0.869 0.939 0.870 0.910 0.665 0.841 0.823 0.911 0.966 0.935 0.856 0.779 0.699 0.877 0.784 0.578 0.893 0.436 0.678 0.732 0.682 0.660 0.61
Comm. 0.921 0.838 0.943 0.825 0.890 0.775 0.905 0.833 0.836 0.546 0.890 0,617 0.976 0.907 0.896 0.855 0.834 0.914 0.832 0.776 0.529 0.902 0.915 0.886 0.891 0.770 0.739 0.804 0.834 0.639 0.744 0.820 0.713 0.912 0.768 0.913
278 PS1380 P81391 PS1375 PS1482 PS1588 PS1368 PS1377 PS1378 PS1386 PS1412 PS1381 PS1405
A. M A C K E N S E N
0 110 -0.016 -0.084 0.083 0.082 0 056 0.302 0346 0024 0.001 0.021 0,295
0191 0.438 0.057 0.027 -0.066 0.043 -0047 0070 -0.122 0.021 -0.096 -0,058
0666 -0 631 -0555 0.006 0.041 0.044 0047 0.056 0.008 0.002 -0.353 0.05t
0.045 .0 001 -0 0 4 8 0.963 0.950 0.941 0.923 0.906 0.627 0.023 0034 0,433
-0.552 -0.336 0 617 0.118 0.088 -0.255 0.034 0,025 -0.187 -0.922 -0878 0,100
0.79g 0.703 0.701 094g 0.923 0.956 0.949 0.949 0.444 0.851 0.906 0.290
TABLE II. 1 Varimax Principal Component Scores of live assemblages Species
Adercotryma glomerata Ammobaculitesagglutinans Ammodiscus spp. Ammomarginulina ensis Ammomarginulina foliacea Ammomarginulina foliacea curvata Astrononion antarcticus Bulimina aculeata Buliminella cochlea Cassidulina teretis Cibicides bertheloti Cibicides corpulentus Cibicides grossepunctatus Cibicides Iobatulus Cibicidoides cf wuellerstorh Cribrostemoides crassimargo Cribrostomoides jeffreysi Cribrostomoidessp. 1 Cribrostomoides subglobosus Crithionina spp. Cyclammina orbiculans Cyclammina pusilla Eggerella bradyi Eggerellasp. Ehrenbergina glabra Epistominella exigua Epistominella vitrea? Eponides tumidulus Eponidesweddellensls Fissurina spp. Fursenkoina earlandi Globocassidulina crassa Globocassidulinasubglobosa Glomospiracharoides Gyroidina sp. iHaplophragmoides bradyi Haplophragmoidessp. l Haplophragmoides sphaeeloculus Hippocrepina flexibilis Hormosina normani/carpenteri Hormosina robusta Hyperammina laevigata Kareriella novangliae Lagenaspp. Laticarinina pauperata Marsipella elongata/cylindrica Martinottiella nodulosa Melonis affinis Miliammina arenacea Miliolinella spp. Miliolinella subrotunda Nonionella bradyi Nonionella iridea Nuttallides umbonifer Oridorsalis sidebottomi
PC 1
PC 2
PC 3
PC 4
PC 5
0.958 0305 -0.248 0134 0.054 0.229 -0344 -2.127 -0.402 0.472 -0 644 0.406 -0 195 0.350 -0326 0 118 0 028 0,416 7.525 0.245 0.371 0.163 1 252 -0.448 0010 0730 0.266
0.511 -0.410 0 114 0376 0390 0.277 -0.063 0,330 0.289 0.071 0 289 0.292 0.275 0.069 0 350 0.203 1.368 -0 1 7 9 0 210 0.315 -0448 0 290 0 096 0 209 0.715 0397 0.119
-0.861 0.635 0.232 -0.422 -0.099 0.097 0.258 8 660 -0.202 -0.002 0.289 0175 -0.224 -0.302 0.221 -0.324 -0,320 -0.162 2.172 0.088 0.052 0.300 0.640 0.215 0.672 0.652 .0.352
0.498 0.459 - 0.495 2.321 1.572 1.047 -0.484 -0.117 0.455 -0.439 0.911 0.428 0.043 0.485 -0.243 0.384 -0.555 -0.448 - 1.407 -0.269 -0.405 0.172 0.600 -0 2 1 9 0878 1.467 0.489
0 279
0 304
~0 1 4 6
0 440
0.389 -0 0 2 3 -0. 1 8 0 0 250 0.023 0.404 0067 -0265 -0.402 -0. 0 7 8 -0.047 -0276 0 436 0 387 0 389 -0 1 9 7 0.194 0 265 0 305 0 257 -0.472 0.305 0 453 -0.291 0 265 0.043 0 334
-0281 0.196 0.226 1. 3 8 0 0168 0.430 0 293 0 493 0 290 0 339 0 428 0 345 0 144 -0283 -0376 0 195 0 217 0250 0385 0177 0 198 .0170 0 241 0029 -0 3 2 3 -0.316 0 106
0.227 0 243 -0.261 0.266 0.463 0 126 0.320 0.145 -0.208 0.235 0.085 -0.247 -0.519 0. 1 9 0 -0.127 -0 1 1 9 -0,404 0.131 -0,200 0.343 0.080 0.318 -0.205 -0.293 -0.436 -0.431 -0 1 4 7
-0467 -0.463 0.584 - 1.193 -0.429 -0.490 0047 -0.263 -0457 -0 116 0404 ~0.340 0 441 0 451 0346 -0432 -0.362 -052t 0.141 -0.555 -0.426 -0.007 0.333 -0 5 7 3 -0 2 8 9 0839 -0.472
-0.080 -0.01 0.24 0.12£ 0.26 -009, 0.205 0 614 -0114 -0.09~ 0.061 0.11(] 0.020 0061 0.068 0.256 0734 0177 0161 0150 0.058 0123 0144 0 141 0244 0517 0203 -0.094 -0.011 0.223 -0.51( 1 ,06z 0 62£ 007~ 0.017 007 c ~0.06! 003: 0.2( 0.077 0.34(] 0.126 0.081 0.121 0154 0.009 0003 0.398 0.244 0.134 0.057 -0.267 9118 0.053 0.273
ET AL
279
BENTHIC FORAMINIFERALASSEMBLAGESFROM EASTERNWEDDELLSEA Oridorsalis umbonatus Parafissurina spp. Patellina eorrugata Pelosinella sp. Portatrochammina spp Psammosphaerafusca Pseudobofivinaantarctica Pseudobulimina chapmani Pullenia bulloides Pullenia simplex Pullenia subcarinata Pyrgo murrhina Pyrgo williamsoni Quinqueloculinapygmaea Quinqueloculinasp. Recurvoides contortus Reophax bilocularis Reophax dentaliniformis Rsophaxdistans Reophax fusiformis Reophaxovicu/a Reophax pi/ulifer Reophax spiculifer Rhabdarnmina cf. linearis Rhabdammina/1-1yperammina spp. Rhezarkinasp. Rhizammina indivisa/algaeformis Robertinoides sp. Rotaliamminaochracea Saccaminasphaerica Saccorhizaramosa Subreophaxadunca Textularia wiesneri Thurammina papillata Trifarina angulosa Triloculina frigida Triloculina tricarinata Tritaxis squamata Trochammina globulosa Trochamminanana Trochammina nitida Trochammina sp.39+52 Trochamminaspp. all others
1.915 -0.356 -0.369 -0.311 -0.411 0.398 -0.386 -0.401 -0.378 -0.336 0.238 -0.061 -0.404 -0.156 0.199 -0.341 -0.161 3.109 2.487 -0.338 1.255 -0.026 - 0.61 1 -0.424 -0.541 -0.490 -0.359 -0.597 -0.254 -0.381 -0.244 0.520 -0.601 -0.446 -0.354 -0.341 -0.438 -0.405 0.307 0.378 -0.503 1.557 -0.099 0.302
0050 -0.195 -0.156 -0.647 -0.248 -0.146 -0.134 -0.246 -0.128 -0.312 0.168 -0 249 -0 221 0296 0.113 -0.424 -0.422 -0.454 1.205 -0.226 -0.317 0.081 0,721 -0.515 -0.377 -0.070 -0.361 -0.380 -0.382 -0.214 -0.290 -0.040 0.682 -0.323 8.931 -0.217 -0.267 -0.364 0.537 1.448 0.265 -0.963 -0.220 0.849
-0.786 -0.169 -0.253 0.720 0.162 -0.231 -0.211 -0.201 0.038 -0.054 -0.398 -0.318 -0.242 -0360 -0.205 0.755 0.160 1.707 -1,468 -0.234 0.728 0,461 0,174 0.793 0.268 -0.017 -0.208 0.252 -0.164 -0.229 -0.178 -0.373 0.304 -0.191 0.311 -0.013 -0.203 -0.186 0.162 -0.514 -0.030 1.598 -0.020 0074
1.019 -0.277 -0.479 1.399 -0.388 0.507 -0.473 -0.454 -0.359 -0.475 -0.220 -0.503 -0.457 -0.484 0.221 -0.223 -0.190 1.129 0.685 -0.467 1.649 0.047 7.107 0.000 -0.352 0.116 -0.355 2.824 -0.330 -0.467 0.006 0.801 -0.228 -0.244 -0.281 -0.276 -0.178 -0.176 -0. 133 -0.813 -0.365 -0.279 0.137 1.566
-0.245 -0.155 -0.075 0.389 0.459 -0.051 -0.105; -0.13; -0.17--. 0.03, -0.28C -0.19; 0.16~ -0.53,E -0.20,E 0.40,' -0.052 1.292 -1.446 -0.020 -0.082 -0.280 -0.096 0.266 0.090 -0.352 -0.057 0.065 -0.024 -0.068 -0.142 -0.199 -0.685 0.048 1.380 -0.211 -0.137 -0.072 -0.395 -1.313 -0.021 0.799 -0.013 -0.606
PC 4
PC 5
TABLE II.2 Varimax Principal Component Scores of dead assemblages Sample
Adercotryma glomerata Ammobaculltesagglutinans Ammodiscusspp. Arrimomarginulina ensis Ammomarginulina foliacea Ammomarginulina foliacea curvata Ammoscalaria pseudospiralis Astrononion antarcticus Astrononionecholsi Astrorhiza sp. Bufimina aculeata Cassidulinacrassarossensis Cibicides bertheloti Cibicides corpulentus Cibicidesgrossepunctatus Cibicides Iobatulus Cibicidoides cf. wuellerstorfi Cibicidoides spp. Cfibrostomoides crassimargo Cribrostomoides jeffreysi Cribrostomoidessp. I Cribrostomoides subglobosus Cyclammina orbicularis
PC 1 -0.434 0.592 -0.257 -0.369 0.058 -0.317 0.729 -0.303 -0.311 -0.277 0834 -0.734 -0.395 -0.249 -0.326 -0.469 -0.269 -0.360 -0.167 0.022 -0.233 6.279 0.283
PC 2
PC 3
0.760 -0.342 -0.178 -0.293 -0.246 -0.324 -0.203 -0.220 -0.148 -0.327 -0.357 0.826 -0.219 -0.298 -0.340 0.172 -0.329 -0.288 -0.289 1.174 -0.214 -0.307 -0.333
0.044 -0.521 -0.290 0.140 0.282 -0.140 -0.340 -0.317 -0306 -0.362 -0~880 0.330 0.226 -0.255 -0.120 0.029 -0.361 -0.004 -0.087 -0.339 -0.407 3.000 -0.308
0.774 -0.556 -0.180 0.520 -0.445 0.253 -0.515 -0.174 -0.165 -0.042 -0.806 0.100 -0.288 -0.206 -0.222 -0.159 -0.147 -0.276 -0.195 -0.195 -0.127 2.783 -0.314
0.419 0.283 0.320 0.279 0.306 0307 -0.347 0.196 0.254 0.320 -1.624 -1.158 0.028 0.307 0.103 -0.049 0.345 0.271 0.371 0.263 0.437 0.350 0.289
PC 6 -0.240 -0.027 -0.240 0.381 -0.21( -0.00; -0.11 -0.369 -0.384 -0.308 0.394 -1.161 -0.093 -0.360 -0.422 -0.568 -0.195 0.221 -0.409 -0.225 -0.243 -1.433 -0.257
280
A. MACKENSEN ET AL
Cyclammina pusilla Cyclammnina trullissata Eggerella bradyi Eggerellasp. Ehrenbergina glabra Epistominefla exigua Epistominella vitrea? Fissurina spp. Fursenkoina earlandi Globocassidulinabiora Globocassidufinasubglobosa Glomospiracharoides Gyroidina orbicularis Gyroidina sp.klein Haplophragmoidesbradyt Haplophragmoides sphaeriloculus Hormosina normani/carpenteri Hormosinarobusta Kareriella novangliae/bradyJ Lagenaspp. Laticarinina pauperata Lenticulina spp. Martinottiella nodulosa Meloniszaandami Miliammina arenacea Nonionella bradyi Nonionella iridea Nuttallides umbonffer Oridorsalis umbonatus Parafissurina spp. Pelosinella bJcaudata Pelosinella sp Psammosphaeratusca Pseudobolivma antarctica Pullenia bullo/des Pullenia simplex Pullenia ";rTata Pyrgo ~ Recurvt Reophax Reophax con, ,,'o,,rlls Reqohaxnodutosus Reophaxowcula Reophax pitulifer Reophax splculifer Rhabdammlna lineans Rhabdammina/Hyperamminaspp Rhizammina indivisa/algaeformis Rotaliamminaochracea Subreophaxadunca Saccaminasphaerica Saccorhizaramosa Textularia wiesneri Trifarina angulosa Triloculina sp./frigida Tritaxis squamata Trochamminaglobulosa Trochamminanana Trochammina nitida Trochammina sp,39+52 Trochamminaspp. allothers
1 .137 -0.348 -0.246 -0.271 0 450 -0 3 6 5 0 620 -0 452 0 159 0 286 -0 242 0047 -0.276 0 459 0 228 0.226 -0.278 0.259 0 245 0 239 -0 6 4 5 -0 279 0 060 -0 2 7 1 0237 0 353 0 217 0.333 0984 0 288 0 237 0336 0079 0270 0 196 0.260 0 320 -0 3 0 2 0 457 0 204 1 390 0 167 0 224 0 156 0 079 0 041 1 818 0.027 0.310 -0.277 -0.274 0.173 0.325 0.744 -0.244 -0 226 0.535 0.484 0.007 5,302 0,068 -0.043
-0.279 0361 -0 2 4 2 0 249 0.256 0.202 0.807 0.063 0.349 0.336 O. 1 4 2 0.219 0.321 0.251 0 318 0282 0.338 0 327 -0329 0299 -0 197 0 329 0 314 0 332 0,183 0.065 0.072 0.258 0.109 0.328 -0.294 0.345 0 403 0321 0 287 0 271 0 292 0 318 0 324 0333 0.558 0 270 0 300 0 289 0 208 0.330 0530 O. 1 9 8 -0.334 0,009 -0.259 0.456 0.550 1.908 0.322 -0.297 0.889 8.207 1.580 0.351 0.256 0,297
-0427 -0.367 1 377 0.328 0.062 0928 0.144 0.402 0 384 0 340 0 753 -0 289 0 049 0 934 0.159 0 282 0.316 -0 296 0 250 0.135 2230 0 275 0.443 0 239 0 695 -0 2 5 2 0 199 0.876 7 153 0 214 0 000 0352 -0.390 0 340 -0 3 9 1 0 310 0 368 0 203 0 439 0280 0 155 0 170 0 166 0 376 0 170 0 452 1 813 0498 -0.195 -0 3 0 4 0.433 0,427 0.761 0623 -0 171 -0.320 -0.791 -0291 0558 0 904 0 362 0.710
5996 0.838 -0.519 0.181 0.051 -0.429 0.026 0.199 0,285 0.187 -0.492 0.459 -0.225 0 404 0 100 0.140 0 097 -0 169 0 227 0274 -0 639 0 213 0.008 -0 2 1 4 -0.632 -0.131 0 177 0.597 -1129 0 215 0 160 -0409 4.577 0187 0 248 0 189 0 097 0 223 .0.220 0 084 1 784 0 128 0073 0 158 0 011 0.141 1212 0339 0086 -0166 -0.354 -0.051 0.719 0.071 -0.298 0.463 -0.212 0.047 0.364 -2.244 -0.158
0567 0 191 0 302 0.299 0.482 0289 0.885 0,352 0.509 0.189 -0.255 0.532 0328 0.243 0370 0.392 0299 0341 0.332 0.327 0 162 0327 0384 0.324 1.139 0 187 0345 0.202 0149 0317 0 278 0072 1 677 0518 0369 0.353 0 286 0 319 -0.147 0339 0154 0307 0354 0.356 -0 5 0 0 0028 3 694 -0 066 0173 0.399 0044 -1 4 2 5 0.329 -6.959 0.248 0.381 0638 1 602 0709 0518 0302
0.256
0.260
T A B L E 11.3 Varimax Principal C o m p o n e n t Scores o f fossil assemblages Species Astrononion antarcticus Astrononion echolsi Bulimina aculeata Cassidulina crassa rossensis
PC 1 0.384 -0.386 -0.386 -0.407
PC 2 -0.171 -0.062 -1 0 9 1 1. 6 2 5
PC 3 0.380 0.441 -4.538 1.168
PC 4 -0.343 -0.348 -0.222 -0. 4 0 6
PC 5 0.200 I 0.160 I -1.009 O. 6 7 2
0.235 0.280 -0 083 0.350 -0.683 3 26~ 0.84E 0.07 0 15 0 35C 0 17~ 0.31C 0 481 0.28? 0 36C 0.581 029g 0 169 0.277 0176 -0 837 0.258 0 248 0.355 0220 0 456 0 424 7221 1854 0 298 0.630 0 034 0 954 0291 0 038 0 275 0 465 0 304 0 131 0299 0335 0 228 0 360 0 030 0 140 0 223 1 670 0 171 0379 -0357 0 355 0 765 0.340 1 072 0296 0 325 0434 0544 0.213 0.835 0 163 0 291
281
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
Cibicides bertheloti Cibicides corpulentus Cibicidesgrossepunctatus Cibicides Iobatulus Cibicidoides cf. wue/lerstorfi Cibicidoidesspp. Eggerella bradyi Eggere/lasp. Ehrenbergina glabra Epistominella exigua Epistominelia sp.A Fissurina spp. Fursenkoina earlandi Globocassidulina biota G/obocassidulinasubglobosa Gyroidina orbicularis Gyroidina sp.klein Kareriella novangliae/bradyi Laoenaspp. Laticarmina pauperata Lenticulina spp. Martinotie/la nodulosa Meloniszaa~dami Mi/iammina arenacea Nonione//a I)radyi Nonionella iridea Nuttalides umbonifer Oridorsalis umbonatus Parafissurina spp. Pu/lenia bulloides Pullenia simplex Pullenia subcarinata Pyrgo murrhina Trifarina earlandi Tri/oculina sp./fr~qida
-0.046 -0.261 -0.267 -0.291 -0. 4 7 2 -0.185 1.034 -0.394 -0.460 0.281 -0.358 0.152 -0.199 -0.389 0.435 -0.064 0.441 -0.256 -0.235 1.266 -0,341 0.228 -0.296 -0.407 -0.403 -0.303 -0.913 5.562 -0.292 -0.389 -0.316 0.141 -0.267 0.063 -0.236
-0.131 -0.330 -(5.318 0.377 -0.380 -0.335. -0.526 -0.235 0.547 -0.365 1.820 0.450 0.105 -0.328 -0.114 -0.387 -0.358 -0.369 -0.359 -0.385 -0.375 -0.080 -0.378 -0.545 -0.001 -0.107 -0.123 0.034 -0.371 -0.428 -0.307 -0.394 -0.372 5.187 -0.419
0.155 0.325 0.343 0.642 0.345 0.281 -0.433 0.420 0.768 0.007 1.397 0.397 -1.607 0.348 -0.948 0.281 0.255 0.323 0.167 0.136 0.306 0.101 0.312 -1.860 0.558 0.079 0.219 0.222 0.324 -0.276 0.178 0.165 0.302 -1.858 0.173
-0.225 -0.387 -0.378 -0.360 -0.017 -0.019 -0.324 -0.345 -0.232 2.509 -0.338 0.040 -0.247 -0.346 0.073 -0.441 0.092 -0.359 -0.052 -0.617 -0.264 0.327 -0.367 -0.321 -0.357 -0.403 5.283 0.437 -0.350 -0.248 -0.332 0.394 -0.277 0.141 -0.371
Acknowledgements We acknowledge the assistance of R.V. Polarstern's crew and master during cruise ANTIV/3. We thank M.M. Rutgers van der Loeff and H.W. Hubberten for discussion. We are grateful to M.J. Hambrey who thoroughly improved the English text, and to M. Heyn who carefully performed the photographic work and assisted in the preparation of the plates. Part of the work of A.M. was sponsored by the D.A.A.D. (Deutscher Akademischer Austauschdienst) as part of the NATO Science Fellowship Programme. This is A.W.I. publication No. 267. References Anderson, J.B., 1975. Ecology and distribution of foraminifera in the Weddell Sea of Antarctica. Micropaleontology, 21 ( 1): 69-96. Barker, P.F., Kennett, J.P. et al., 1988. Proc. Ocean Drilling Program, Initial Rep., 113: 213-214.
0.187 0.23¢ 0.221 O.04E O. 113 0.35,4 0.44; -0.03~= -0.387 0.39E -0.41 .¢, -0.027 1.40E 0.21 ,= 0.31=~ 0.31 ,~ 0.30E 0.23C 0.081 0.64E 0.271 - 5 . 5 9 ,= 0.25.d 0.07"/ O. 06-. -0,66E 0.31E -0.003 O. 23,E -O.05E 0.22E 0.40¢~ 0.30,q 0.493 0.33;
Barnola, J.M., Raynaud, D., Korotkevich, Y.S. and Lorius, C., 1987. Vostok ice core provides 160,000-year record of atmospheric CO2. Nature, 329:408-414. Berger, W.H., 1979. Preservation of foraminifera. In: J.H. Lipps, W.H. Berger, K.A. Buzas, R.G. Douglas and C.A. Ross (Editors), Foraminiferal Ecology and Paleoecology. SEPM Short Course No. 6, Houston, Texas, pp. 105-155. Bernhard, J.M., 1988. Postmortem vital staining in benthic foraminifera: duration and importance in population and distributional studies. J. Foraminiferal Res., 18(2): 143-146. Birkenmajer, K., Gazdzicki, A. and Wrona, R., 1983. Cretaceous and Tertiary fossils in glacio-marine strata at Cape Melville, Antarctica. Nature, 303: 56-59. Bremer, M.L. and Lohmann, G.P., 1982. Evidence for primary control of the distribution of certain Atlantic Ocean benthonic foraminifera by degree of carbonate saturation. Deep-Sea Res., 29: 987-998. Broecker, W.S. and Takahashi, T., 1978. The relationship between lysocline depth and in situ carbonate ion concentration. Deep-Sea Res., 25: 65-95. Broecker, W.S. and Peng, T.-H., 1986. Global carbon cycle: 1985. Radiocarbon, 28: 309-327. Carmack, E.C., 1974. A quantitative characterization of water masses in the Weddell Sea during summer. DeepSea Res., 21: 431-443.
282 Carmack, E.C. and Foster, T.D., 1975. On the flow of water out of the Weddell Sea. Deep-Sea Res., 22:711724. Corliss, B.H., 1979. Recent deep-sea benthonic foraminiferal distributions in the southeast Indian Ocean: inferred bottom-water routes and ecological implications. Mar. Geol., 31:115-138. Corliss, B.H., 1983. Distribution of Holocene deep-sea benthonic foraminifera in the southwest Indian Ocean. Deep-Sea Res., 30(2A): 95-117. Corliss, B.H. and Honjo, S., 1981. Dissolution of deepsea benthonic foraminifera. Mieropaleontology, 27: 356-387. Corliss, B.H. and Chen, C., 1988. Morphotype patterns of Norwegian Sea deep-sea benthic foraminifera and ecological implications. Geology, 16:716-7 t 9. Douglas, R.G., Liestman, J., Walch, C., Blake, G. and Cotton, M.L., 1980. The transition from live to sediment assemblage in benthic foraminifera from the southern California borderland. In: M. Field, A, Bouma, I. Colburn, R. Douglas and I. Ingle (Editors), Quaternary depositional environments of the Pacific coast. Pac. Coat Paleogeogr., Symp., Vol. 4, Pac. Sect., SEPM, pp. 257-280. Douglas, R.G. and Woodruff, F., 1981. Deep-sea benthic foraminifera. The Oceanic Lithosphere. In: C. Emiliani (Editor), The Sea, vol. 7. Wiley-Interscience, New York, N.Y., pp. 1233-1327. Earland, A., 1933, Foraminifera, Pt. 2. South Georgia. Discovery Repts., 7: 27-138. Earland, A., 1934. Foraminifera, Pt. 3. The Falklands sector of the Antarctic (excluding South Georgia). Discovery Repts., 10: 1-208. Earland, A., 1936. Foraminifera, Pt. 4. Additional records from the Weddell Sea sector from material obtained by the S.Y. Scotia. Discovery Rep., 13: 1-76. Echols, R.J., 1971. Distribution of foraminifera in sediments of the Scotia Sea area, Antarctic waters. In: J.L. Reid (Editor), Antarctic Oceanology. Antarct. Res. Ser., 15: 93-168. Foldvik, A,, Gammelsr~d, T. and T~rresen, T., 1985. Circulation and water masses on the southern Weddell Sea shelf. In: S.S. Jacobs (Editor), Oceanology of the Antarctic continental shelf. Antarct. Res. Ser., 43: 5-20. Foster, T.D. and Carmack E.C., 1977. Antarctic bottom water formation in the Weddeil Sea. Polar Oceans. In: M.J. Dunbar (Editor), Proc. Polar Oceans Conf., Montreal, pp. 167-176. Foster, T.D. and Middleton, J.H., 1980. Bottom water formation in the western Weddell Sea, Deep-Sea Res., 27A: 367-381. Ffitterer, D.K., Grobe, H. and Griinig, S., 1988. Quaternary sediment patterns in the Weddell Sea: relations and environmental conditions. Paleoceanography, 3: 551-561. Fiitterer, D.K., Kuhn, G. and Schenke, H.W. (in press). Wegener Canyon bathymetry and results from rock
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dredging near ODP Sites 691-693, Weddell Sea, Antarctica. In: P.F. Barker and J.P. Kennett (Editors), Proc. O.D.P. Sci. Results, 113: College Station, TX. Gazdzicki, A. and Wrona, R., 1986. Polish paleontological investigations in West Antarctica in 1986. Przegl. Geol., 11: 609-617. Gooday, A.J., 1986. Meiofaunal foraminiferans from the bathyal Porcupine seabight (northeast Atlantic): size structure, standing stock, species diversity and vertical distribution in the sediment. Deep-Sea Res., 33(1 ): 1345-1373. Gooday, A.J., 1988. A response by benthic Foraminifera to the depositon of phytodetritus in the deep sea. Nature, 332: 70-73. Gordon, A.L., 1982. The U.S.-U.S.S.R. Weddell Polynya expedition. Antarct. J. U.S., 17: 96-98. Grobe, H., 1986. Sp~itpleistoz~ine Sedimentationsprozesse am antarktisehen Kontinentalhang vor Kapp Norvegia, 6stliche Weddell Sea. Ber. Polarforsch., 27: 1-127. Grobe, H., 1987. Fazielle Gliederung glazialmariner Sedimente in der Antarktis. Facies, 17: 99-108. Grobe, H., Mackensen, A., Hubberten, H.-W., Spiess, V. and Fiitterer, D.K., 1990. Stable isotope record and late Quaternary sedimentation rates at the Antarctic continental margin. In: U. Bleil and J. Thiede (Editors), Geologic History of the Polar Oceans: Arctic versus Antarctic. NATO AS1 Series C. Kluwer, Dordrecht, The Netherlands, pp. 539-571. Hellmer, H., Bersch, M., Augstein, E. and Grabermann, 1., 1985. The southern ocean: a survey of oceanographic and marine meteorological research work. Bet. Polarforsch., 26:1-115. Heron-Allen, E. and Earland, A., 1932. Foraminifera. Pt. t. The ice-free area of the Falkland Islands and adjacent seas. Discovery Rep., 4:291-460. Herb, R., 1971, Distribution of Recent benthonic foraminifera in the Drake Passage. In: Llano and I.E. Wallen (Editors), Biology of the Antarctic Seas IV, A. Antarct. Res. Ser., 17:251-300. Keir, R.S., 1988. On the late Pleistocene ocean geochemistry and circulation. Paleoceanography, 3: 413-445. Kuhn, G. and Wissmann, G., 1987. Continuous 3.5 kHz sub-bottom echo sounding. In: D.K. Fiitterer (EditorL Die Expedition ANTARKTIS-IV mit FS "Polarstern" 1985/86, Bericht von den Fahrtabschnitten ANT-IV/3-4. Ber. Polarforsch., 33: 77-79. Lagoe, M.B., 1977. Recent benthic foraminifera from the central Arctic Ocean, J. Foraminiferal Res., 7:106-130. Li, Yuan-fang and Zhang, Qing-song, 1986. Recent foraminifers from Great Wall Bay, King George Island, Antarctica. Acta Mieropaleontol. Sin., 3 (4): 345-349. Lindenberg, H.G. and Auras, A., 1984. Distribution of arenaceous foraminifera in depth profiles of the Southern Ocean (Kerguelen Plateau area). Palaeogeogr., Paleoclimatol., Palaeoecol., 48:61-106.
BENTHICFORAMINIFERALASSEMBLAGESFROMEASTERNWEDDELLSEA Lohmann, G.P., 1978. Abyssal benthonic foraminifera as hydrographic indicators in the western South Atlantic Ocean. J. Foraminiferal Res., 8: 6-34. Lutze, G.F., 1964. Zum Fiirben rezenter Foraminiferen. Meyniana, 14: 43-47. Lutze, G.F. and Coulbourn, W.T., 1984. Recent benthic foraminifera from the continental margin of northwest Africa: community structure and distribution. Mar. Micropaleontol., 8:361-401. Lutze, G.F. and Thiel, H., 1987. Cibicidoides wuellerstorfl and Planulina ariminensis, elevated epibenthic Foraminifera. In: A.V. Altenbach, G.F. Lutze and P. Weinholz (Editors), Beobachtungen an Benthos-Foraminiferen. Ber. Sonderforschungsbereich 313, Univ. Kiel, 6:17-30. Mackensen, A., 1985. Verbreitung und Umwelt benthischer Foraminiferen in der norwegischen See. Diss., Kiel Univ., pp. 1-126. Mackensen, A., 1987a. Benthische Foraminiferen-Artengruppen auf dem Island-SchottlandoRiicken. Pal[iontol. Z., 61: 149-179. Mackensen, A., 1987b. Benthic foraminifera in the eastern Weddell Sea. In: D. Fiitterer (Hrsg.): Die Expedition Antarktis IV mit FS "Polarstern" 1985/86. Ber. Polarforsch., 33: 89-94. Mackensen, A., 1988. Verbreitung benthischer Foraminiferen. In: D. Fiitterer (Hrsg.): Die Expedition Antarktis VI mit FS "Polarstern" 1987 / 1988. Ber. Polarforseh., 58: 55-56. Mackensen, A., in press. Neogene benthic foraminifers from the southern Indian Ocean (Kerguelen Plateau): Biostratigraphy and Paleoecology. In: R. Schlich and S.W. Wise, Jr., et al., (Editors). Proc. ODP, Sci. Resuits, 120: College Station, TX. Mackensen, A. and Hald, M., 1988. Cassidulina teretis TAPPAN and C. laevigata D'ORBIGNY:their living and Late Quarternary distribution in northern seas. J. Foraminiferal Res., 18:16-24. Mackensen, A. and Douglas, R.G., 1989. Down-core distribution of live and dead deep-water benthic foraminifera in box cores from the Weddell Sea and the California Borderland. Deep-Sea Res., 36 (6): 879-900. Mackensen, A., Sejrup, H.P. and Jansen, E., 1985. The distribution of living and dead benthic foraminifera on the continental slope and rise off southwest Norway. Mar. Micropaleontol., 9:275-306. Mackensen, A., Grobe, H., Hubberten, H.W., SpieB, V. and Fiitterer, D.K., 1989. Stable isotope stratigraphy from the Antarctic continental margin during the last one million years. Mar. Geol., 87:315-321. McKnight, W.M., Jr., 1962. The distribution of foraminifera off parts of the Antarctic coast. Bull. Am. Paleontol., 44(201 ): 65-158. Mead', G.A. and Kennett, J.P., 1987. The distribution of recent benthic foraminifera in the Polar Front region, southwest Atlantic. Mar. Micropaleontol., 11: 343-360. MeUes, M., 1987. Sedimentation in der Filchner-Depression, siid6stlicher WeddeUmeer-Schelf, Antarktis. Unpublished. Thesis, Geol.-Paliiontol. Inst., Univ. G6ttingen, pp. 1-180.
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Milam, R.W. and Anderson, J.B., 1981. Distribution and ecolog of recent benthonic foraminifera of the AdelieGeorge V continental shelf and slope, Antarctica. Mar. Micropaleontol., 6: 297-325. Mix, A.C., 1989. Pleistocene paleoproductivity: evidence from organic carbon and foraminiferal species. In: W.H. Berger, V.S. Smetacek and G. Wefer (Editors), Productivity of the Oceans: Present and Past. Wiley, New York, pp. 313-340. Murray, J.W., 1973. Distribution and ecology of living benthic foraminiferids. Heinemann, 274 pp. Olausson, E., 1960. Description of sediment cores from the Mediterranean and the Red Sea. Rep. Swed. DeepSea Exped. 1947-1948,, 8(3): 287-334. Osterman, L.E. and Kellogg, T.B., 1979. Recent benthic foraminiferal distributions from the Ross Sea, Antarctica: relation to ecologic and oceanographic conditions. J. Foraminiferal Res., 9 ( 3 ): 250-269. Sarnthein, M. and Winn, K., 1990. Reconstruction of low and middle latitude export productivity, 30,000 years BP to present: implications for global carbon reservoirs. In: M. Schlesinger (Editor), Climate-Ocean Interaction. Proc. NATO ARW Series, 319-342. Schlich, R., Wise, S.W. et al., 1989. Proc. ODP, Init. Repts., 120: College Station, TX. Schnitker, D., 1974. West Atlantic abyssa91 circulation during the past 120,000 years. Nature. 248: 385-387. Schr6der, C.J., 1986. Deep-water arenaceous foraminifera in the northwest Atlantic Ocean. Can. Tech. Rep. Hydrogr. Ocean. Sci., 71: l - 19 I. Scott, D.B., Mudie, P.J., Baki, V., MacKinnon, K.D. and Cole, F.E., 1989. Biostratigraphy and late Cenozoic paleoceanography of the Arctic Ocean: Foraminiferal, lithostratigraphic, and isotopic evidence. Geol. Soc. Am. Bull, 101: 260-277. Streeter, S.S., 1973. Bottom water and benthonic foraminifera in the North Atlantic, Glacial-Interglacial contrasts. Quat. Res., 3: 131-141. Uchio, T., 1960. Biological Results of the Japanese Antarctic Research Expedition, Benthonic foraminifera of the Antarctic Ocean. Seto Marine Biol. Lab. Spec. Publ., 12: 1-21. Van der Zwaan, G.J., 1983. Quantitative analyses and the reconstruction of benthic foraminiferal communities. Utrecht Macropaleontol. Bull., 30: 49-69. Van Morkhoven, F.P.C.M., Berggren, W.A. and Edwards, A.S., 1986. Cenozoic cosmopolitan deep-water benthic foraminifera. Bull. Centres Rech. Explor.-Prod. ElfAqitaine, Mem. 1 l: 421 pp. Wiesner, H., 1931. Die Foraminiferen der deutschen SiJdpolar-Expedition. In: E.v. Drygalski (Editor), Deutsche Siidpolar-Expedition, 1901-1903, 20: 49169. Williamson, M.A., Keen, C.E. and Mudie, P.J., 1984. Foraminiferal distribution on the continental margin offNova Scotia. Mar. Micropaleontol., 9:219-239. Zwally, H.J., Comisco, J.C., Parkison, C.L., Campbell, W.J., Carsey, F.D. and Gloersen, P., 1983. Antarctic sea ice, 1973-1976: satellite passive microwave observations. NASA, Sp.-459, Washington, D.C., 1-206.
241
Elsevier Science Publishers B.V., Amsterdam
Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73°S: Distribution, ecology and fossilization potential A. Mackensen, H. Grobe, G. Kuhn and D.K. Fiitterer Alfred Wegener Institute for Polar and Marine Research, Columbusstrasse, D-2850 Bremerhaven (F.R.G.) (Received July 20, 1989; revised and accepted February 12, 1990)
ABSTRACT Mackensen, A., Grobe, H., Kuhn, G. and FiJtterer, D.K., 1990. Benthic foraminiferal assemblages from the eastern Weddell Sea between 68 and 73 °S: Distribution, ecology and fossilization potential. Mar. Micropaleontol., 16: 241-283. Surface sediment samples taken with a vented box corer from the eastern Wcddell Sea on four profiles perpendicular to the continental margin have been investigated for their benthic foraminiferal content. The live fauna was differentiated from empty tests comprising the foraminiferal death assemblage. Based on the dead assemblages, potential fossil assemblages were calculated to facilitate the analogy with late Neogene core material. Five distinct live assemblages inhabit the continental margin today. Six dead assemblages and five potential fossil assemblages, respectively, correspond to these biocoenoses. A predominantly calcareous live fauna dominated by Trifarina angulosa is correlated with strong bottom currents and sandy sediments at the shelf break and on the uppermost continental slope. Below this, on the upper slope down to 2000 m water depth, the predominantly calcareous Bulimina aculeata assemblage coincides with the core of warm ( > 0 ° C) Weddell Deep Water and with fine and more organic-rich sediments. These calcareous live assemblages completely change composition during early diagenesis because of calcite dissolution within the uppermost sediment, which depends largely on the grain size distribution of the sediment and the fluxes of organic matter. Therefore, a still calcareous T. angulosadominated fossil assemblage indicates the sandy substrates on the shelf break and the upper slope, whereas the deeper slope with hemipelagic calm sedimentation and with high fluxes of organic matter is indicated by Martinottiella nodulosa, the characteristic arenaceous fossil remnant of the former predominantly calcareous live B. aculeata fauna. On a continental terrace between 2500 and 3500 m water depth Cribrostomoides subglobosus dominates the live fauna, but because of rapid disintegration of the empty tests of this agglutinated species a predominantly calcareous fauna characterized by Oridorsalis umbonatus and Epistominella exigua comprises the dead assemblage and the potential fossil assemblage, respectively. On the lower continental slope, between the carbonate lysocline (3500 m ) and the carbonate compensation depth (4000 m), tests of Nuttallides umbonifer are the characteristic dead and potential fossil remnants of a former predominantly arenaceous live fauna, which is ~ssociated with the lower part of the Antarctic Bottom Water (AABW). This corroborates earlier investigations suggesting a relationship between the carbonate-corrosiveness of water masses and the distribution ofN. urnbonifer. This is important for inferring paleo-routes and estimates of paleo-production rates of AABW during the Neogene.
Introduction Since the discovery that during peak cold climatic periods (glacial stages 6 and 2) atmospheric CO2 concentration was about 30% below interglacial values (Barnola et al., 1987 ), one of the most challenging tasks in paleocean0377-8398/90/$03.50
ographic research has been to understand the global carbon cycle. Atmospheric CO 2 changes during the ice ages should be forced by a redistribution of carbon within the ocean, which is the world's largest CO2 reservoir (Broecker and Peng, 1986 ). Bottom water circulation and biological productivity are two of the mecha-
© 1990 - - Elsevier Science Publishers B.V.
242
nisms responsible for the partitioning and the redistribution of carbon within the ocean. Thus it is important to reconstruct the changes in bottom water circulation patterns and paleoproductivity. Benthic foraminifera are abundant and ubiquitous faunal constituents of deep-sea sediments and record information concerning both paleoproductivity and bottom water circulation. Specific high productivity faunas are associated with upwelling zones and reflect high fluxes of particulate organic matter (Lutze and Coulbourn, 1984; Corliss and Chen, 1988). Other assemblages are associated with specific bottom water mass characteristics and substrate conditions (Douglas and Woodruff, 1981; Mackensen et al., 1985 ) and can be used to infer bottom water routes and distribution (Corliss, 1983; Mackensen and Hald, 1988 ). The Antarctic Ocean plays a key role in controlling both global paleoproductivity and bottom water circulation in the following way. Increased surface productivity in the Antarctic Ocean during glacials, (Keir, 1988), or by contrast, reduced productivity there (Mackensen et al., 1989; Grobe et al., 1990 ) and high productive zones at low latitudes, as calculated by Mix ( 1989 ), might cause an enhanced CO2 storage in the deep ocean (Sarnthein and Winn, 1990) and explain the fall of atmospheric CO2. In addition, the Antarctic Ocean is one of the earth's two principal sources of oceanic bottom waters (Foster and Middleton, 1980; Foldvik et al., 1985 ) and changes in bottom water production cause changes in ocean circulation patterns. Thus it is important to monitor benthic foraminiferal assemblage changes in late Quaternary cores from the Southern Ocean. This in turn calls for an inventory of the relationship between Recent benthic foraminifera and the specific environments of the Southern Ocean, as an analogy and basis for paleontological interpretations of high-latitude fossil assemblages. We document here the distribution patterns, the community structure, and the fossil-
A. M A C K E N S E N ET AL.
ization potential of benthic foraminifera from the eastern Weddell Sea in relation to Recent environmental conditions. Previous work
Previous reports from the era of the national expeditions into the Antarctic Ocean include Wiesner ( 1931 ), Earland ( 1933, 1934, 1936), Heron-Allen and Earland (1932) and Uchio (1960). More recent studies of benthic foraminiferal distribution patterns and their physical and chemical environment include McKnight ( 1962 ), Echols ( 1971 ), Herb ( 1971 ), Anderson (1975), Osterman and Kellogg (1979), Corliss ( 1979, 1983), Milam and Anderson ( 1981 ), Lindenberg and Auras ( 1984 ) and Mead and Kennett ( 1987 ). None of these studies give quantitative data on the live distribution of benthic foraminifera. The only available study on benthic foraminiferal distribution patterns in the Weddell Sea is based on 58 piston and trigger core tops, and differentiates between six distinct benthic foraminiferal assemblages (Anderson, 1975). Water masses, depth and the multibathyal carbonate compensation depth (CCD) are believed to be the major factors controlling the distribution of these assemblages. Some new data reflecting the influence of high surface productivity at the eastern Weddell Sea continental margin on the distribution and preservation of live calcareous faunas are given in Mackensen and Douglas ( 1989 ). Materials and methods
During cruise ANT-IV/3 (1985/1986) of the RV "POLARSTERN", undisturbed surface sediment samples (412 cm z, 1-2 cm thick) were taken from sediments collected with a large vented box corer (0.25 m 2) at 37 stations on four profiles perpendicular to the Antarctic continental margin (Figs. 1,2, Table I). Immediately after sampling, all samples were preserved in Rose Bengal stained alcohol
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the box corer with a 100 cm 2 plastic tube to quantify the infaunal component of the live benthic foraminiferal assemblages (Mackensen, 1978b, Mackensen and Douglas, 1989). Between 28 and 46% of the total live fauna was found below the topmost 1.5 centimeter of the sediment. In the area under investigation, most of the specimens found below 1.5 cm belonged to species which are also found within the uppermost sediment layer. However, some species prefer to live several centimeters within the sediment, and even though they are rare and do not significantly alter the total faunal composition as calculated from the top 1-1.5 cm,
244
A. MACKENSEN ET AL.
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these deeply infaunal species are underrepresented in the live data set. The sampling design of this study also has to be kept in mind if standing stock calculations are performed. The grain size distribution of the surface sediments was determined by wet sieving of 5 cm 3 sediment to separate the sand-size fraction and by hydraulic separation in settling tubes (Atterberg method) for quantification of the clay and silt fractions. The organic carbon and carbonate contents were determined with a Coulomat 702, measuring the CO2 generated by combustion of the bulk sediment for total carbon and by treatment with H3PO4 for analysis of CaCO3. The grain size distribution of gravel ( > 2 ram), sand ( 125-2000 #m) and mud ( <63 gm) as well as carbonate and organic carbon contents were calculated as weight percent of the bulk dry sediment (Figs. 3-6 ). The foraminifera samples were washed through a 63 #m screen. Then the coarse residue was dry sieved and the fraction > 125/tin was investigated for its benthic foraminiferal content. Samples containing high amounts of
terrigenous material were floated twice in C2C14 to concentrate the foraminiferal tests. Stained (live) and unstained (dead) foraminiferal tests were counted separately from different splits obtained by a micro splitter. Between 104 and 533 dead specimens from each sample and between 25 and 3077 live specimens were counted, respectively (Table I ). In addition, the residual sediment of sampies concentrated by the floating method was inspected and residues which contained high numbers of thick-walled arenaceous species were counted in order to correct the original faunal counts. It is well known that the Rose Bengal staining method has its limitations (Murray, 1973; Douglas et al., 1980; Bernhard, 1988). To minimize misinterpretations, in particular agglutinated species were individually wetted with water and if the identification of dense protoplasm was still doubtful the tests were crushed. All species that comprised less than 1% of the total fauna in all samples or which oc-
245
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
TABLE I Grain-size distribution, water depth, positions, carbonate and organic carbon contents of surface sediment samples with in situ temperatures and salinities of water masses, as measured according to CTD-depth. Faunal counts and standing stock data are given for comparison. Sample
Polite
Sand
Gravel
Depth
Latitude
(%)
(%)
(%)
(rn)
{° S)
(° W)
71o20 . 72°20 ' 70029 . 71°15 ' 70021 ' 70019 ' 70°28 ' 71o14 ' 72°12 ' 70019 , 71014 ` 70o26 ` 70o16 , 72°15 ' 70°16 ' 72013 ' 70°17 ' 70013 ' 71011 ' 70°06 ' 72°I0 ' 70°06 ' 71°09' 70012 ` 71003 ` 70006 ' 70°00 ' 72003 , 69°14 ' 68°44 ' 70050 ' 69°02 ' 70°37 ' 69°37 ' 71054 ` 69°44 ' 68o32 ' 69026 ' 69°16 . 71045 ' 71043 . 66020 , 70041 ' 70o30 '
13°25 ' 16°31 ' 09°36 ' 13°34 ' 06°46 ' 06°50 ' 09°37 ' 13o36 ' 16°43 ' 06°54 ' 13°37 ' 09°35 ' 06°54 ' 16°53 ' 06~49 ' 16~56 ' 09o42 ' 06059 , 13°33 ' 06o47 , 17008 ' 06°30 . 13°34 ' 09047 ' 13014 ' 06o41 ' 09058 ' 17°27 ' 05069 ' 05050 ' 13°57 ' 05o53 ` 13°58 ' 06°24 ' 18o16 ' 10°15' 05°46 . 10o30 ' 10044 ' 18059 , 19015 ' 05037 . 18°48 ' 14050 ,
1406-1 45.1 54.4 0.5 1367-1 47.1 49.8 3.1 1385-1 29.2 56.7 14.0 1407-1 100.0 1425-1 12.4 83.1 4.5 1426-1 36.6 47.2 16.2 1384-1 10.0 85.9 4.1 1408-2 ° 1372-2 12.9 73.9 13.3 1427-1 7.1 77,5 15.4 1409-2 * 1383-1 4.9 94.7 O.4 1426-1 35.4 63.8 0.8 1373-2 10.4 46.5 43.1 1393-2 1374-2 40.5 59.5 0.0 1382-1 61.1 36.6 2.3 1395-1 57.7 41.2 1.1 1410-1 9.1 90.8 0.1 1394-3 94.6 5.4 0,0 1375-2 91.3 6.6 0.1 1391-I 55.5 36.0 6.5 1411-1 50.8 48.1 1.2 1381-1 94.5 5.4 0.1 1412-1 81.9 17.2 0.9 1394-1 94.7 4.8 0.4 1380-1 96.7 2.9 0.4 1370-1 79.2 13.5 7.3 1389-1 95.1 4.2 0.8 1387-1 93.2 6.2 0.6 1481-2 85.4 11.5 3.1 1388-1 92.2 6.5 1.4 1224-3 90.0 9.6 0.4 1390-1 93.1 3.9 3.0 1369-1 87.6 3.1 9.3 1379-1 81.3 12,5 6.2 1588-3 77.8 18.8 3.5 1378-1 88.1 6.1 5.8 1377-1 89.3 5.6 5.2 1368-1 85.8 9.0 5.2 1483-2 79.9 9.6 10.5 1386-1 73.6 9.0 17.4 1405-1 57.7 42.0 0.3 1482-2 43.9 53.4 2.7 • denotes no recovery, hydrographicdata only "
237 310 340 431 458 612 714 794 802 803 975 1068 1165 1237 1388 1468 1492 1499 1521 1759 1772 1797 1622 1866 1901 1948 2072 2289 2292 2435 2499 2531 2765 2784 3181 3210 3471 3735 3812 4017 4133 4405 4528 4541
Longitude Carbonate
turfed at only two stations, have been omitted in the statistical data treatment. Orthogonal rotated (Varimax) Q-mode Principal Component Analysis was then used to reduce the 99 "live" and 85 "dead" variables (species) of the resultant two revised data matrices (Tables II, III ) to five and six variables [Principal Components (PC's)], respectively (Mackensen, 1985). The proposed solutions explain 71.8% and 82.3% of the total variance of the revised data sets, respectively. To develop a reliable paleoecological interpretation of fossil assemblages of cores from the investigated area (Mackensen et al., 1989; Grobe et al., 1990) by tracing back the fossil assemblage via the dead assemblage to the live
(°/o)
C org. (%)
0.49 0.62 5.79 9.51 0.87
0.56 0.45 0.44 0.56 0.18
0.14
0.30
0.73 0.25
0.40 0.20
0.18 0.16 0.11
0.15 0.21 0.20
0.26 0.15 0.14 0.19
0.22 0.28 0.18 0.18
0.17 0.35 0.27 0.12 0.25 0.32 0.29 0.66 1.82 5.21 1.39 4.6 6.7 3.18 3.7 7.36 12.82 2.35 1.57 0.23 0.08 0.13 0.08 0.05
0.56 0.26 0.26 0.40 0.41 0.43 0.40 0.42 0.36 0.32 0.41 0.38 0.34 0.39 0.38 0.36 0.23 0.35 0.34 0.36 0.38 0.35 0.10 0.05
CTD Temperat. depth(m) {in silo °C)
Salinity Counts Counts St. stock ~,) dead live (ind./lO crn2 /
220
-1.75
34.360
335 425
-1.82 -1.80
34.427 34.419
675 750 827
-0.97 -0.01 -0,57
34.515 34.604 34.550
975 1027
0.31 0.22
34,649 34.652
1217 1330 1455 1534
0.32 0.40 0.32 0.23
34.685 34.762 34.6}'3
925
0.27
34.642
1765 880 1024 1034 819 1880 751
0.20 0.32 0.33 0.47 0.52 -0.01 0.42
34.680 34.665 34.652 34.668 34.667 34.676 34.661
626 614 2482 612
0.61 0.60 -0.13 0.59
34.696 34.699
596
0.50
34.684
656
0.60
34.688
518
0.60
34.694
4000 4125
-0.31 -0.30
34.654
969 4530
0.37 -0.31
34.684
34.695
310 473
3077 522
74.7 12.7
2658
64.5
417 399
611
14.8
229 257
122 773
23.7 18.8
208 152 235
1058 612 351
25.7 237.7 34.1
352 106 106 244 424 224 186 521 209 186 230 226 237 237 152 384 104 204 221 284 178 275 283 157
305 60 120 144 337 169 85 390 194 162 649 521 196 121 84 108 238 203 274 56 111 26 152 207 108
59.2 124.3 93.2 14.0 33.7 65.6 132.0 37.9 75.3 62.9 64.9 101.2 76,1 47.0 32.6 41.9 46.2 19,7 53.2 21.7 43.1 19,4 29.5 20.1 21.0
145 528 533
114 470 507
44.3 11.4 12.3
fauna and its present environment, the dead assemblages were reduced by all arenaceous species except Karreriella and Eggerella spp., Martinottiella nodulosa and Miliarnmina arenacea. These agglutinated species are ineluded into the potential fossil assemblage, as defined here, because they are known to be resistant against early diagenetic processes (Douglas and Woodruff, 1981 p. 1249; Schr6der, 1986; Mackensen and Douglas, 1989) and are frequently found in Pleistocene cores from the area under study (Grobe 1986; Melles, 1987; Mackensen et al., 1989). The composition and distribution of this potential fossil benthic foraminiferal assemblage, as calculated by deleting non-resistant arenaceous
246
A. MACKENSEN
5°W
10 °
ET
AL
20 °
15 °
0
E v
i--
2
- -36°-°°s O4
"O
50 '3
5
686 o4
3
013
12 o o10
o13 o19
4
17
O3
6 Oo 6
-
~9~-~0
o9 -T--
--
--
--
Fig. 3. Distribution of the sand-size fraction of the bulk dry sediment in the investigated area plotted on the profile shown in Fig. 2.
0
5°W
10 °
i
o 07
E
lo°
15 °
o,, oo
20 ° 0 47 013
1
V
(.-
2 "D
3 4
5 Fig. 4. Distribution of the mud content of the bulk dry sediment in the investigated area plotted on the profile shown in Fig. 2.
BENTHIC FORAMINIFERAL
247
A S S E M B L A G E S F R O M E A S T E R N W E D D E L L SEA
5ow
10 °
15 °
20 °
0 00.9
00.3
E
1
00.2 O. o 0.1 40__00.3
v
..C (D_ (9 "13
~
0.2
00"7
~
0.2 o 0.~ o 0.3
0.2 o 0.1
°0"1 o 0.3 o 0.2
,
2
00.7 i ~t::ili~
:~:~iz~!~:~i:~:~: !z!:~i:~if:i~iii~ :i:::%i:;:i:iiiiii:iiiiiiiiiii :i ii: : i:::iiiiiiii:iii:
$,I
(D ¢0
3 :::::::?~:~
4
:'.':&"::":~::'!~- "4-::: •
~llllll,lll~ll~lllll~ll~lllll~llll~ IIlll~l~llC C D 00.1
IIiiliiiiiillllllllllllllll
~
01
o
5
>30
00. I Carbonate
>10
in %
Fig. 5. Distribution of the carbonate content of the bulk dry sediment in the investi ~ated area plotted on the profile shown in Fig. 2.
5°W
10 °
15 °
20 °
0 ..........
E
1
.......................... 0:3:: :':~:::'l~ii i ; i o 0.3 • o l 00.2 002. . . .
: i i
0i6 iii ;I
........... ........
:: ~
i 00.2
~-
v
tO_ (1,1 "0
2
(9
3
t'l:i
4 0
5
0 U-I
Organic carbon in %
Fig. 6. Distribution of the organic carbon content of the bulk dry sediment in the investigated area plotted on the profile shown in Fig. 2.
TABLE II Percentages of species of live benthic ~ r a m i n i ~ r a . X denotes occurrence of less than 0.5%, ~
n
~
.~cmm Adercottyma
,
1
1
1
1
1
4 8 2
4 0 5
3 8 6
3 6 8
3 3 5 3 3 2 3 3 4 3 3 3 3 3 7 7 8 7 6 2 9 8 8 8 8 7 8 9 7 8 8 9 9 4 0 8 1 7 9 0 0 4 1
glomerata
Ammobaculiles
3
1
6
-
•
-
3
.
.
-
.
.
agglutinans
AR~rlodiscus
Spp.
A ~ g i n u l i n a
en$/s
A~rginulina
foliacea
A ~ i n u l i n a
fol~cea
A$ttOtlOf~
3 cutvata
1
-
.
4
5
9
5
5
-
2
2
.
Cib~ides
grc~sepunctatus
.
Cibicides
Iobatulus
.
.
.
.
.
8p.
-
I
-
.
.
.
.
.
.
~p,
-
Cyc/att~r~na
ofbicularis
Cyc,~mm/na
j~.s///a
.
sp.
. x
.
.
.
. 3
-
1
-
-
1
-
.
. 5
2
1
1
1
420
.
. !
Ep~tontwella
vitrea?
-
x
.
Gtobocassi#ulina
crassa
G/oboca£~idulina
subglobosa
Glomo~ifa
.
.
.
bradyi
Haptophfagnloides
sp. 1
H ~ O l q P h f ~ S
sphaetiloculus
Htppoctepkla
-
x
-
x
.
-
x
-
Hofmosina
Kate#ella
1
x
x
-
.
1 2 .
.
.
pauperata
.
.
.
2 2
-
2
2
x
.
. .
t~#/(~a
-
arenacea
x
.
.
1
2
2
1
.
Milioline~a
spp.
Milio#nella
subrotunda
.
.
.
.
Non~nel!a Non/o/~/a
bra#yi /t/dea
Nutta#ides
umb~ifer
Oridorsalis
sidebottomi
Oddolsalis
utr~onatus
x
.
Paraftssuhna Patellkna
. .
.
1
.
1
1
. .
Portatrocham/~t~l
x
-
1
.
2
1
-
2
2
4
x
-
bulloides stmplex
.
.
-
-
4 x
2 1
112
1
3
1
1 2
-
.
4
-
pygmaea
1 111
5
1
1
.
.
.
.
x
~
3
-
.
. .
. .
1
x x
1 5
. .
x
.
-
2
3
12
3
4
5
3
5
5
1
5
4
-
3
5
3
213
Reophax
d~tans
.
-
x
1
R
f~ifom~s
6
4
1 lx
6
3
3
-
8
2
ovicula
1
1
1
2
2
1 2
1
Robeninok~
•
11
Saccorhiza
ratnosa
1 2 1 3
Subfeopha~ adunca Textularia wtesneri Thurammina paplllata
I
-
-
x
1
3
1
.
1
2
2
1
. 121
frigida
. 2
2
Triloculina
tricannata
x 2 l x 1
Trochammina
3
5
.
.
.
.
nitlda sp. 39+52
11
Trochammina
Spp
21 2
11 4 x 2
5
4
3
-
.
.
.
.
1
-
4
5
5
x
1
2
1
-
2
1
2 .
.
.
1
.
1
.
x 1
1
1
-
5
.
1
.
-
I
x
. 1
t
5
7 19
-
.
.
.
4
2
414
2
7
4
1
2
1
7
4
-
x 211
1 7 2
1 1
1
1
2
.
-
x
1
1
2
1
8
2
-
2
.
-
7
.
x
3
.
.
.
x
-
x
.
.
2 .
x
4
722
6
x
6
.
-
.
.
-
1
-
1 x
.
x
x
t
1
~
2
.
x
-
x
1
x
x
x
7
2
2
. I
2
1
x
-
-
x
.
x
1
33
1
2
1
1 2
1. 2 9
x 2 -
122
5 4
. .
I
1
-
x
x -
1
x
1
.
-
1
x
x
1
I
3
-
2
1 4
x
-
-
x
-
x
.
2
-
x
-
3
-
-
-
3
-
x .
1
.
x
2
-
3
3
11
3
4
2
1
.
.
.
2
1
2
6
3
5
5
3
x
1
2
4
1
1
1
1
2
2 x
1 ×
2 2
3 1
3 2
6 1
1 1
1 .
2 -
2 4
x
1
1
1
-
.
I x
1
1
x
1
-
x
1
.
1
6
-
x
x
4
-
x
-
x
2 2
2
1
1
I
x
1
2
!
-
-
x
.
1
!
3
-
1 -
-
i
25
. -
x 5
. 3
1
2
3
x
x
-
x
-
1
x
1
2
7
I
1
~
4
-
-
x
-
-
-
1
.
1
1
x 1
. x
. 1
1 2 -
2
-
.
2
1
1
21
.
.
.
x l 1
1 -
x 1
2 x
x
1
x
6
5
1
1
I
x
3
1
2
2
1
3
x
~
-
1
-
1
x
x
3
2
X .
x
x -
-
2
1 1
-
.
.
1 1
.
2
1
x
-
2
x
2
-
x
1
x x
x l
x ! 4 x
2
1
1 9
5
4 x 5 !
1 x 2 1 4 3 5 1 5 2 0 2 9 2 8 4 1 2 9 2 9 •
3
3
1
1
1
3
1
2
1
1
4
2!3
7
21212515 -
x
x
2
!
I
1×
1 1 2
5
x
1
! 1 1 ~
.
-
x x ×
2
x
- 2 3 !
1× .
1
x
2
x
2
1
x
.
1
1
-
1
x
1
.
3
2
- -
.
3
-
1
.
!
x
x
1
1 2
.
-
1
-
219 .
2
.
.
.
x
2
2
.
.
3
1
1
-
-
2
-
.
2
.
5
1
.
5
4
.
112
-
1
.
4 .
2
1
.
1
1
7
1 3
1
x
x
2
5
2
2
- . 4 5 5 2 8 1 2 1 7 4 7 5
3
3
2 3
2
.
4
.
2
.
2 2 .
•
.
.
. .
1
!
.
12
.
x
1 1
. -
-
.
. 6
2
.
3
1
2
. x
I
116
4
4 2 2 3
! .
1
-
.
.
1
1
I
1
1
1
2
. 1
.
x
x
5
.
9
4
x
-
x
nana
Trocharmnlna Trochammina
1
x
2 x
2
.
1
-
3 1 x l
1
*
-
.
x 2 1
1
1 .
.
.
.
1
1
2
.
.
-
2
x
Tritaxis squamata globulo,sa
.
-
.
.
I
. .
3
4
2
2
2
.
-
1
-
.
x
1
6
x
.
-
.
.
.
.
I
.
x
1
.
.
1
1
2
.
-
.
1
1
1
x
Trochammina
.
1
1
x
1
1
14
1
1
x
-
2
2
-
1
.
. - 15
-
3
-
-
2 1
x
4
-
.
.
. .
.
1
.
.
.
angulosa
Tri~culina
.
I
1
×
1
1
-
1 .
.
1
1
.
x
. .
.
x
3
2
.
1
×
2
2
.
.
.
1
.
1
1 .
x
-
1
1
x
-
.
x
.
1
.
-
.
13
.
-
2
2
.
.
.
1
.
7
.
2
2
.
15
2 2 4
2
.
2
.
3
1
.
-
-
5
-
. .
1
1
7
-
1
.
3
x .
9
3
.
2
.
x
-
6
142 .
x
.
1 -
2
ochraoea
2
7
x
.
2
5
.
1
.
.
. .
x
x
.
.
1
6
-
1 6 - 5 1 0 1
sphaerica
x
x
2 -
5
1
.
1
-
.
. .
.
5 .
x . .
x x
. 1
.
.
1
.
I
. . .
.
. .
3
.
-
-
4
.
1
2
.
-
1
~ 3
- 1614
1
. sp~.
Saccandna
Trifarina
11120
- - sp.
Rotaliammina
1 411 1
sp. indivLsa/algaelormis
1 4
-
Re~hax spiculiler Rhabdamn~rka cf lineans
Rhizammina
x
1
1
I
.
.
4
x
-
.
.
1
x
dentalin#otm~s
x
3 .
.
Reophax
Reophaxp~ulifer
x
.
. .
1
2
.
.
2
.
. .
. -
I
-
x
.
.
.
. 2
.
.
.
.
x
1
.
1 .
1
x
1 . .
4
x
.
-
-
. . .
4
1 .
.
6
.
.
1
3
1
4
2
1
1
.
1
515 .
.
.
1
.
1
4
.
1
.
1
.
.
.
2
.
.
.
.
.
2
.
.
.
5
.
2
.
1
4
x
.
1
.
. -
.
.
6
8
.
.
t
.
.
-
.
. 1
-
.
.
1
. .
.
x. .
.
1
.
. 8
1 .
5
1 .
.
8
•
.
.
3
. x
. .
.
.
.
311
.
x
1
.
2
x
1
.
.
.
. -
.
1
.
.
.
-
-
.
.
. .
-
.
.
2 1
1
. .
1 .
.
.
. .
5
1
1
1
. .
.
-
1
. .
x
I
.
.
x
x
3
x
2
x
I
-
-
2
x
.
x
4
.
21
-
-
I
.
1
. 2
1
1
-
.
-
1
2
-
5
1
.
.
2
.
2
Reqo~axb//oc#/ans
Rhezarklna
1
. . 5
.
.
2 .
.
sp.
Rh~bdarnfry~aVHyperammina
•
-
3
.
x
. 1
1
.
.
.
2
-
x .
Quklqueloculit~l
contottus
. 1
.
3 1
.
8 .
x
-
! .
1
812
x
-
x
•
-
.
2
1
2
. 1
4
1 .
x
4
. .
Quit)qeelocufina
Reo~hax
2
.
1
. .
. .
-
x
1
-
3
.
-
5
-
1
x .
1
1
-
x
4
.
8
1
1
1
.
1
.
. -
1
-
. .
.
. .
x
.
-
3
-
.
4
.
1
1
x
1
-
. x
-
2 2
-
x
1 .
-
. -
.
x
1 3.
1 .
.
. x
1
1
. .
.
.
1
x
x
x
1
1
x
1
3
1
-
2
. .
1
~
1
.
-
x
x
.
.
4
x
w~liarr~oni
~
. -
.
1
.
.
1
x
3
6291924
-
3 .
1
1
.
.
1
.
3
.
61412
.
-
.
-
. .
5
x
-
1 .
Pul/et~ia subcatinata P)~go nlurfhina
Recutvoktes
1
x
1
chapmani
Pu#enia
1
-
. .
8
.
1 lx
antarctica
Pseudobulimina Pulk~ia
1
2
.
.
8
.
s~o. fusca
PseudobolNina
1
.
2
.
.
.
.
2
4 .
.
.
s~o.
2
. .
oottugata
PsammoslN~e~a
.
.
x
1
~ .
.
. 1
1
x
.
1
.
. .
6
spp.
Pek~sine//a
all others
1
. 15 x
x .
. .
7
-
x
1
x
1
.
.
I
2
.
.
4
1
x
.
.
.
.
. -
1 1 1
.
-
x
-
.
1
.
.
.
. -
.
.
. 3
.
1
.
.
. 1
x
2 .
.
x
. .
.
x
.
x
.
2
-
.
.
1
. .
.
.
-
.
.
×
.
.
1
.
-
. x
.
.
-
. -
.
72430131715
1
affinis
Mlliafnm~na
Pyrgo
x
.
.
e/ot~ataVcylindrica
MattillN~tNWl~ Melon~
.
1 2
.
x
2
x
.
1
.
.
3
1
2
3
.
1
1
.
. .
1
.
.
.
-
.
-
spp.
Mal~oel/a
.
.
3
. .
1
.
.
.
-
.
.
.
.
I x
-
1
3
.
2
.
.
-
novang#ae
Laticarinina
.
.
x
normandcarpenten
Hofrlr~ina robu$ta Hyperammma laewgata
.
.
1
1
flexbi/Ls
.
.
.
-
-
.
. .
.
.
.
.
-
1 .
-
.
-
2 .
.
1
1 .
x
.
2 -
.
1
. -
.
1
.
.
.
1
1
-
4
.
.
.
1
.
-
1
1
1
.
2
7
. 4
1
1
41521201228
.
.
91311
-
.
.
1
.
x
sp.
H~ok~ohra~oides
L~tla
.
charoides
Gyroidina
.
1
2
1
3
1
.
.
1
.
x
2
.
11023
.
.
.
.
.
.
.
. .
-
. 7
-
-
x
.
.
.
eaflandi
.
.
. .
Fursenkoina
]
2
8
.
1
2
.
.
.
2
1
9
4
1
x
1
-
x
.
.
-
1
3
8
2
5
2
-
.
.
I
.
3
7
x
2
1
.
2
-
3
3
wedde/,~nsJs
4
-
-
.
.
.
.
. 3
.
2
turtY.dulos
2
-
. 213
.
x
-
.
spp,
-
4 3 3 3 3 4 3 4 3 3 4 3 4 1 9 8 7 7 2 8 2 7 8 2 6 0 3 0 5 2 4 3 8 3 7 2 4 5 7 6
x
-
4
.
.
-
1
3 9 4
3
1
glabra
.
.
1
3 7 5
1
.
x
1
3 9 1
4
.
x
1
4 1 1
1
.
4
1
2
.
-
3 8 1
-
2
1
1
4 1 2
2
.
x
1
4
.
. -
1
-
3
ex~gua
Fissu#na
.
5
.
.
.
1
1
.
1
. 8
.
1
.
.
.
4
.
.
2
.
4
x
.
.
6 .
1
1
1
.
E p c s t ~
Epon/des
.
.
1 7
5
. .
Ehfetlbergina
Eponide6
-
.
4 -
- 14 6
2
.
.
1
x
.
x
.
-
.
Eggeretlabradyi
.
.
.
352215
4
-
.
1
.
3
1
1
-
.
x
x
6
1
116
.
.
3
.
.
.
.
x
.
.
.
.
1
1
.
. .
1
1
.
.
.
.
.
.
.
.
1
5
. .
.
.
jeffteysi
Eggemfla
.
.
-
CrbroMo~subgtobosus CrithtonkN!
.
.
oo~ulenlus
812
.
teretls berlhetoti
Clbicide~
CrlbtoBlon1~
2
.
-
.
1
.
7
CibicJd~s
C d b t o s t o ~
-
. .
6
.
CrS~Je~afgo
1
-
.
cL wuellelstorh
-
. .
5
1
1
.
Crbrostot~
2 .
1
2
cochk~a
Cibicidoides
5
1
-
Bu#mina~'uleata Cass~dulina
1
1
antarcticus
Buliminella
1
3 2
1
-
1
3
X
t
x
2
223
7
5
:(
-
4
!
x
2
3
2
x
1
I
2 2
6
3
6
3
2
X
x
I
1
2
I
2
2
2
4
6 3
5
5
3
-
2
-
1
1
1
249
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
TABLE III Percentages of species of dead benthic foraminifera. X denotes occurrence of less than 0.5%. S ~ N o n 4 8 2
Specle8 Adercoftyma
g/omerata
~ 4 0 5
2
1
Arnmobaculitesagglutit)an.s
.
A/r~od/6cus
x
sop.
A ~ l n u l i n a
ens~ foliacwa
.
A ~ i n u t i n a
fot/aceacutvata
1
pseudoeptral~,
8
.
1
.
.
-
3
Ammomarginulina Ammoscalal~
. 1 1 1 1 1 1 1 1 3 3 3 3 5 3 3 2 8 6 7 7 8 7 6 2 6 8 7 8 8 9 9 4
1 .
-
.
.
. 2
2
.
2
1
.
.
.
1 3 8 3
2
1
-
2
1
.
1
-
-
.
.
2
1
-
.
2
.
3
.
.
3
.
.
-
. 1
4 .
1
1
.
-
-
.
2
.
-
1 3 9 0
.
.
1 4 8 1
1 3 8 7
1 .
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 3 3 3 4 3 4 3 3 3 4 3 3 3 3 4 3 4 8 7 8 1 8 1 9 7 9 1 9 8 7 7 2 8 2 9 0 0 2 1 1 1 5 4 3 0 5 2 4 3 8 3 7 1
1
-
1
-
x
.
.
.
-
.
1
2
-
-
-10 .
x
2
.
.
9
.
.
4
-
1
2
1
1
3
1
x
.
.
4
1
2
3
3
1
1
1
3
-
x
1
1
-
x
x
1
x
1
-
1
1
.
.
.
1
1
1
1
2
6
3
6
-
-
2
x
.
.
.
2
.
2
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
echoJsi
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
Bultmlna
aculeata
Cassk~ulina
.
crassa
CtOic~dee
.
rossensB
.
.
.
.
.
.
.
.
.
.
.
.
~otpu/entus
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. -
.
.
. -
.
.
. .
~op.
x crasslmergo jelfreysi
C r i b r o s t ~
sp.
1
Ct'bmetomo/d~s~bg/o~sc~ Cyc~n'mw'na orb/cu/ar/s Cyc~mminapusilla Cyclammnina Eggerella
bradyi
Eggerella
sp.
-
-
-
-
1
.
2
-
-
1
1
-
-
111526 . . . 2
.
9 .
.
.
.
.
.
1
x
1
vitrea?
.
.
-
x
earlazldi
x
.
Epistorninella
ex~gua
Fissutinaspp.
x
.
5
3
8 -
bk)ta
.
.
Cdob~assidulina
subglobosa
x
x
G ~ p ~ a ~ GytoldttwolbJcularis
2 .
sp.ldein
311 .
.
.
-
6
-
2 .
. 1
2
.
1
. .
.
. 4
1
-
1
-
2
3
3
2
.
-
-
-
-
1
-
-
2
-
x
1
2 4
L anticu#na
spp.
Mattinottiella Me/onis
.
x
nodulosa
.
-
zaan#ami
Miliammina
aranacea
.
.
.
1
1
.
.
.
.
.
.
.
Nutta/#do6
umbonifer
.
x
1
1
x
-
-
.
.
-
-
1
sp.
x
1
-
2417
-
314
1 2
1 x
1 .
x .
.
.
.
3
2
x
.
.
.
.
.
x
3 .
-
.
. .
. .
. -
.
.
.
.
.
2 . 2
6
-
x
x
-
-
1
4
-
Reophax
sp~culifer
-
2
.
.
-
5
-
1
2
1
3
5 .
x
4
.
Trocharnmk~sp.39+52
3
Ttochammina
1
a//others
globulosa
Spp.
.
.
.
.
-
.
.
1
.
.
.
.
.
.
.
1 .
-
1
.
.
.
.
.
.
.
.
.
.
.
.
.
-
-
1
x
.
1
2
4
-
2
1
1
-
2
.
3
2
5
2
1
4
3
3
5
4
6
4
x
x
2
4
2
-
9
-
1
-
x
x
2 x
-
x
-
-
-
x
.
. .
.
.
.
.
. x
. .
.
.
1
-
2
3
1
3
1
-
2
-
x
-
x
.
.
.
. . . . . .
.
.
.
-
.
. x
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
1 .
.
.
.
.
2
.
.
.
1
2
4
x
3
1
3
2
2
3
-
2
4
1
x
2
.
1 x
6 -
6 -
4 *
510 1 -
4 x
217 -
9 2
8 -
5 -
1 -
3 x
3 -
4 1
6 -
-
-
x
1
-
1
x
1
x
1
x
-
-
x
.
-
-
1
-
1
x
1
1
2
2
2
1
4
x
1
-
3
2
1
x
1
-
1
1
-
-
-
1
1
2
-
1
-
2
-
1
2
5
I
x
1
-
x
1
-
1
1
1
-
1
x
x
2
I
5
5
1
-
x 14 30
3
110
x
2
1 1
.
1
-
-
2
3 -
3 1
. .
2 -
3 1
3 .
x
-
-
. -
1 .
. -
1
2
4
.
.
5 x
. .
.
.
.
.
.
1 .
.
.
.
.
1 .
.
.
-
2 .
.
1
-
x
1
-
-
-
x
-
1
-
x
2
-
1
.
.
-
7
2
1
-
3
1
-
1
1
-
x
1
-
-
x
1
2
2
2
1
x
x
1
1
1
-
4
1
1
-
-
x
2
8
4 3 .
1
3
.
.
.
. 1
. -
1
-
x
.
.
.
. .
2 .
.
x x
-
.
4 .
. x
-
.
.
.
x 1
. .
1
1
x
x
1
1
. . -
1
.
4
-
2
1
x
1
1
-
-
2
4
3
4101222
-
2
-
1
-
-
*
x
-
x
-
-
1
1
1
1
.
3
4
.
-
.
-
. .
1
5
.
.
x .
-
3
. .
1
.
4
.
3
.
. 1
. .
.
x
.
.
1
2
1
5
2
1
- 10
7
.
6 2
4 1
-
232 - 20
8 1
93231 - 714
- 2 1
.
2
1
3
4
-
4
-
1
1
-
-
1
-
-
-
x
-
-
-
-
-
-
x
-
-
-
x
x . . .
1
2
-
x
-
-
-
2
-
-
-
-
-
1
-
22419 -
-
.
. . .
2
.
6
2
.
.
2
.
91527122925
3 1
1 .
.
9
.
.
.
. -
. 2
.
.
x .
.
72211 . . .
.
.
-
5
-
4
1
5
7
-
x
1
-
4
x
2
.
1
1
2
1
2
x
1
2
1 .
. .
x
.
.
1
2
.
3
4
2 .
.
x 2
3
. -
1
1 .
x
x
9401313 . .
1
.
x 1
.
x x
.
.
.
.
339263124 5 8 7
x
. x
2
. x
. -
. 3
.
3
.
2
41220 . . . .
.
.
.
.
.
x
x
x
.
x
3
x
.
.
.
-
x
.
-
.
.
5
.
.
-
x
. x
.
1
1 .
.
2
x
2
.
4 .
.
2
.
.
. .
.
.
x
x
.
2
. .
1 1
.
-
. 1
. -
. .
4 -
-
-
3 . .
.
.
1
.
.
.
1 .
.
.
.
1
.
I
.
.
x
.
1 -
.
.
.
.
-
.
4
2
1
4 3
.
1
5
x
.
.
.
x
.
I
x
. . .
x
.
2 x
.
. .
.
-
.
-
1 4 .
x
1 1
.
.
.
.
5 .
.
.
.
3
x
1 3 1
.
.
1
1
2 1 4 1
.
.
1
1 1 . . .
.
.
.
1
1
5 x
.
.
.
.
.
-
.
x x
.
.
.
.
.
.
.
.
1
x
-
. -
.
.
.
. x
.
*
4 .
.
.
.
-
-
-
. .
2
.
1
.
x
.
. .
1
x
-
.
.
x
. .
-
1
.
.
. .
.
-
.
. . 6
1 .
.
. .
1
-
.
-
.
. .
.
. .
2
-
.
1
. .
. .
-
4
.
2
. .
.
. .
2
.
.
. .
. .
8
1
-
.
. -
. .
-
.
x
x
.
1
.
1
. x
. .
x
.
.
.
-
.
. -
. x
.
.
.
1 1
.
x
. -
.
-
.
.
1
1
.
.
1
.
.
.
1
. 1
.
-
.
-
. -
.
1 .
-
.
1
.
.
.
.
1
.
1
.
.
2 .
.
x
-
. .
.
4 .
3
.
.
Trochammlna
Trochamminanana Trochammina nitida
.
1
1
.
.
3 .
.
.
x
-
2
.
x 1
6
-
.
.
2
1
.
.
.
3
.
.
.
.
3
.
3
x
.
.
x
1
.
.
1
3
.
.
1
ovicula
1
.
-
p#ulifer
.
.
5
Reophax
x .
.
-
Reophax
4
.
2
.
x
Tritaxts 8quamata
.
x
.
-
Trifatinaangulosa Triloculina spJ~/g/da
.
4
1
1
.
.
.
-
6
.
.
1
.
.
x
.
.
1
4
.
.
.
1
.
.
.
.
.
.
x
1
.
.
.
.
.
nodulosus
.
.
.
.
.
.
Reophax
-
.
.
. .
.
.
.
.
.
. .
.
x 1
3
.
.
.
.
x
.
.
.
.
1 1
.
.
.
. .
.
2
1
.
.
7 -
ramoea
. .
.
3
Textulariawiesneri
.
.
. .
.
-
Saccorhiza
.
.
.
.
.
.
.
.
2
x
. x
.
-
.
. -
.
-
.
.
x
.
x
x
.
.
-
.
x
-
.
.
.
.
1
.
.
x
x
-
x .
.
-
-
1
-
.
.
x
x
x
.
x
.
.
-
-
1
-
-
.
.
1
1
-
-
.
.
-
. 1
1
x
1 .
.
-
. 1
adunca
-
.
.
1
1
sphaerica
-
.
.
3
Saccamlna
-
.
4
Subreophax
-
.
.
-
5
.
.
.
-
.
1
-
1
.
1
.
-
x
.
1 I
.
-
-
.
1
4 1
2
-
1
.
-
.
-
x 1
.
1
.
x
1 3
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250
A. MACKENSENET AL.
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Fig. 7. Distribution of in situ bottom water temperatures as measured simultaneously with sampling. Area of measured temperatures > 0 ° C is shaded. Suggested water mass distribution is indicated without defining oceanographic boundaries. Water masses according to Foldvik et al., (1985). (ESW=Eastern Shelf Water, M W D W = M o d i f i e d Weddell Deep Water; WD W= Weddell Deep Water, AAB W= Antarctic Bottom Water; WSB W= Weddell Sea Bottom Water).
species from the dead assemblage, does not consider ongoing calcite dissolution with continuous burial below accumulating sediments. Consequently, the potential fossil assemblage is an ideal fossil assemblage which would be saved in the geological record, if calcite dissolution, biological destruction and physical disaggregation ceased below the top 1-2 cm sediment. Finally, the 39 species of the resultant "fossil" data matrix were reduced to five Principal Components, which explained 79.9% of the total variance. The hydrographic and surface sediment data, as well as the results of the statistical treatment of the benthic foraminiferal raw data, are plotted on a projection plane, which is imagined to be erected more or less parallel to the continental margin (Figs. 8-11 ). On this theoretical plane the stations are projected according to water depth and longitude (Fig. 2 ). The observer is placed as though he is somewhere on
the Weddell abyssal plain, looking towards the southeast on to the eastern continental margin. Environmental setting
Topography, hydrography and sea ice The Weddell Sea as the southernmost part of the South Atlantic Ocean is bounded on its eastern and southeastern margin by the East Antarctic craton (Fig. 1 ). The eastern continental margin between 5 and 20 °W can be divided morphologically into a continental shelf with the shelf break occurring between 500 and 600 m water depth; an upper continental slope between 500 and 1800 m; an approx. 200 km wide, gently dipping flat terrace between 1800 and 3000 m; and finally, a lower slope down to the abyssal floor in about 5000 m water depth. The width between the grounding line of the continental ice sheet and the continental shelf
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
break off East Antarctica varies from a few tens of kilometers to about 150 kin. In the investigated area the continental margin is deeply cut by at least one major canyon system, i.e. the Wegener Canyon off Kapp Norvegia (Fiitterer et al., in press ). Numerous 3.5 kHz bottom profiling tracks between the canyons and the general morphology show no signs of major slumping and sliding events. Thick undisturbed Quaternary sedimentary sequences, merely effected by turbidites and hiatuses, have accumulated, especially on the terrace. Today, the hydrographic regime on the continental shelf and the shelf break is controlled by the Antarctic Coastal Current (ACC) flowing along the shelf break and transporting very cold Eastern Shelf Water (ESW) of low salinity towards the southwest. The deep part of the ACC is formed by the Modified Weddell Deep Water (MWDW: - 1 . 6 < 0 < 0 , 34.4
2 51
dell Sea are permanently covered with sea ice, whereas the eastern parts are more or less icefree from November until February, with minimum coverage during February. A huge, yearround open water area, the Weddell Polynya, was present during austral winters 1973 through 1977 off the eastern continental margin between 30°W and 15°E (Zwally et al., 1983), thus covering the area investigated in this study. It is speculated that this polynya may have been a persistent phenomenon in geological times and may have strongly influenced the regional surface productivity; this in turn may be documented in the sedimentological record (FiJtterer et al., 1988 ).
Sediments The surface sediments on the eastern continental margin in general consist of silty and clayey muds with varying amounts of coarse sand and gravelly dropstones. Above about 1600 m water depth the sand size fraction exceeds 40%, and below about 1400 m the mud content ( < 6 3 / t m ) exceeds 50%, of the bulk dry sediment (Figs. 3,4). Only at the southern continental rise, off the mouth of the Wegener Canyon, does the sand content increase and consequently the mud content is diminished. The high sand content on the shelf and the upper slope is caused by winnowing of the fine fraction from a gravelly diamicton by the ACC (Grobe, 1986). The carbonate content of the surface sediments is arranged in four depth zones (Fig. 5 ). On the shelf carbonate contents of up to 9.5% of the bulk dry sediment are accounted for by bryozoans, bivalves, gastropods, brachiopods, rugose corals, red algae, and benthic foraminifera. At the shelf break and on the upper slope down to over 2000 m, the carbonate content never exceeds 1%. This depth range corresponds to the range where the core of the WDW and the M W D W reside. On the slope terrace between 2500 and 3500 m, carbonate contents from 3 through 13% are found. Here the car-
252
A. MACKENSEN ET AL.
bonate includes almost exclusively foraminifera, Below 4000 m virtually no carbonate was found in the surface sediments. The organic carbon contents of the surface sediments in general are low ( < 0.9%), but lowest between approximately 500 and 1800 m and at abyssal depths (Fig. 6 ). Benthic foraminiferal assemblages
Haplophragmoides bradyi ( Robertson ) = Trochammina hradyi Robertson 1891. Plate VIII, 3, 6. Haploph ragmoides canariensis ( d'Orbigny ) = Nonion ina canariensis d'Orbigny 1839. Plate VIII, 7-9. Hyperammina laevigata Wright=Hyperammina elongata Brady var. laevigata Wright 1891. Plate II, 12. Jaculella obtusa Brady 1881. Plate II, 11. Laticarinina pauperata ( Parker and Jones) = Pulvinulina repanda Fichtel and Moll, var. menardii d'Orbigny, subv. pauperata Parker and Jones 1865. Plate VII, 3. Miliammina arenacea ( Chapman ) = Miliolina oblonga (Montagu) vat. arenacea Chapman 1916. Plate II, 4, 5.
t a x o n o m i c notes
Alphabetical listing of dominant and characteristic species from the eastern continental margin with original designation, references to plates and figures in this paper, and some remarks. AdercoOTma glomerata
( B r a d y ) = L i t u o l a glomerata Brady 1878. Plate Ill, 7, 8. .4mmobaculites agglutinans ( d ' O r b i g n y ) = S p i r o l i n a agglutinans d'Orbigny 1946. Plate V, 8.
Ammomarginulina foliacea ( Brady ) = Haplophragmium foliaceum Brady 1881. Plate V, 5, 6. .4rnrnomarginulina recurva Earland =Ammornarginulina foliacea (Brady) vat. recurva Earland 1934. Plate V, 1,2.
Ammomarginulina ensis Wiesner 1931. Plate V, 3. Bulirnina aculeata d'Orbigny 1826. Plate II, 1-3. Since our B. aculeata has long spines and no intergradations to B. marginata are found in the lower bathyal depth range it may well be, following the speculation of Van Morkhoven et al. ( 1986 ), that B. aculeata is the deepwater ecophenotype of B. marginata. ('ribrostomoides jeffreysii (Williamson) = Nonionina jef[i'eysii Williamson 1858. Plate IV, 1. Cribrostomoides subglobosus (G.O. Sars ) = Lituola subglobosa G.O. Sars 1872. Plate IV, 7-9. Cribrostomoides wiesneri (Parr) = Labrospira wiesneri Parr 1950. Plate IV, 2, 3.
Cribrostomoides weddellensis ( Earland ) = Haplophragmoides weddellensis Earland 1946. Plate IV, 4, 5. ~),clammina pusilla Brady 1884. Plate VIII, 1,2. (),clammina trullissata (Brady) = Trochammina trullissara Brady 1879, Plate VIII, 4, 5. Eggerella bradyi (Cushman) = Verneuilina bradyi Cushman 1911. Plate III, 9, 10.
Ehrenbergina glabra Heron-Allen and Earland=Ehrenbergina hystrix var. glabra Heron-Allen and Earland 1922. Plate I, 5, 6.
Epistominella exigua (Brady) = Pulvinulina exlgua Brady 1884. Plate VII, 1, 2.
Martinottiella nodulosa (Cushman) = CYavulina nodulosa Cushman 1922. Plate II, 8, 9, Nonionella iridea Heron-Allen and Earland 1932. Plate l, 7-9.
Nonionella
bradii (Chapman) = Nonionina scapha (Fichtel and Moll) vat. bradii Chapman t 916. Plate 1, 4. Nuttallides urnboni[er (Cushman) = Pulvinulinella umbonifera Cushman 1933. Plate VII, 7-9. This species is also identified as Epistominella, ?Epistominella or Osangularia and typifies the complex and often confusing nomenclatural problems associated with many deep-sea species. Oridorsalis umbonatus
( Reuss )=Gotalina
umbonata
Reuss 1851. Plate VII, 4-6. We understand this species in a broad sense and include torms with a more acute periphery like O tener (Brady) as figured in Lohmann (1978, pl. 5, 5-7) and in Lagoe (1977: Eponides tener pl. 5, 3, 7, 14).
Pullenia bulloides (d'Orbigny)=Nonionina
bulloides
d'Orbigny 1839. Plate IV, 6. Psammosphaerafusca Schulze 1875. Plate II, 7. Pseudobolivina antarctica Wiesner 1931. Plate V. 7. Reophax bilocularis Flint 1899. Plate VI, 10-12. In this study we followed the classification ofSchr6der ( 1986 ) who recognized single chambers, which often are described as Reophax d(fflugifi~rmis Brady (1879), but are fragments of the originally two-chambered R. bilocularis Flint. Reophax dentaliniformis Brady 1881. Plate VI, 3. Reophax difflug(formis Brady 1879. Plate VI, 9. Reophax fusiformis (Williamson ) = Proteonina fus~formis Williamson 1858. Plate VI, 6. Reophaxpilulifer Brady 1884. Plate VI, 1, 2, 4. Reophax spiculifer Brady 1884. Plate VI, 7, 8. Rhabdammina linearis Brady 1879. Plate II. 10. Subreophax adunca (Brady)=Reophax adunca 1882. Plate VI. 5. 7Er,tularia wiesneri Earland 1933. Plate V, 4, 9. Trochammina nana (Brady) = Lituola nana Brady 1884. Plate III, 4-6. 7)'ifarina angulosa (Williamson ) = Uvigerina angulosa Williamson 1858. Plate I, 1-3. We use a broad species concept and include Angulogerina carinata Cushman
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
1927 and Angulogerina earlandi Parr 1950. Triloculinafrigida Lagoe 1977. Plate II, 6. Trochamtnina sp. 39 + 52. Plate III, 1-3. "The genus Trochammina poses many problems in classification." (SchrSder, 1986). We fully agree with this statement and we refer to her discussion of the Trochamminidae (ibid.: 22). In this paper we have therefore preliminary grouped different forms in an open classification.
253
Distribution patterns On the eastern Weddell Sea continental margin the live, dead, and potential fossil assemblages in general are bathymetrically arranged, although some faunal boundaries may
PLATE I (see p. 254 ) (Scale = 100 ~m) 1-3. Trifarina angulosa (Williamson ); Sample PS 1425-1. 4. Nonioaella bradii (Chapman); Sample PS 1384- l 5,6. Ehrenbergina glabra Heron-Allen and Earland; Sample PS 1425-1. 7-9. Nonwnella iridea Heron-Allen and Eadand; Sample PS 1425-1.
PLATE II (see p. 255) (Scale = 100 ~m ) 1-3. Bulimina aculeata d'Orhigny; Sample PS1391-1. 4,5. Miliammina arenacea (Chapman). Sample PS 1425-1. 6. Triloculinafrigida Lagoe. Sample PS1388-1.
(Scale = l mm)
7. Psammosphaerafusca Schulze. Sample PS 1224-3. 8,9. Martinottiella nodulosa (Cushman). Sample PS 1224-3. l O. Rhabdammina linearis Brady. Sample PSI 395-1. 1I. Jaculella obtusa Brady. Sample PS1395-1. 12. Hyperammina laevigata Wright. Sample PS 1395-1. PLATE Ill (see p.256) (Scale= l'00 ~m) 1. Trochammina sp. 39. Sample PS1368-1. 2, 3. Trochammina sp. 52. Sample PS1368-1. 4-6. Trochammina nana (Brady). Sample PS1427-1. 7, 8. Adercotryma glomerata (Brady). Sample PS 1388-1. 9, 10. Eg~erella bradyi (Cushman). Sample PS 1388- I. PLATE IV (see p. 257) (Scale= 100 lan)
1. Cribrostomoides jeffreysii ( Williamson ). Sample PS 1425-1. 2, 3. Cribrostomoides wiesneri (Parr). Sample PS 1368-1. 4, 5. Crib~ostomoides weddellensis (Eadand). Sample P S 1368-1. 6. Pulleni~ bulloides (d'Orbigny). Sample PSI 368-1. 7-9. Crib~ostomoides subglobosus (G.O. Sars). Sample PSI 368-1. 9. Enlarged view of the same specimen as in 7. The aperture of this live captured specimen is closed by agglutinated grains leaving only a small reduced opening. This may represent a resting stage of the animal between the extremely seasonal times of food supply in the eastern Weddell Sea. PLATE V(see p. 258) ( Scale = 100 ~m ) 1,2 Ammomarginulina recurva Eadand. Sample PS 1388-1. 3. Ammomarginulina ensis Wiesner. Sample PS 1368- I. 4, 9. Textularia wiesneri Earland. Sample PSI 384-1. 5, 6. A mn~omarginulina foliacea "(Brady). Sample PS1390-1. 7. Pseudo~olivina antarctica Wiesner. Sample PS 1384- I. (Scale= 1 ~nm) 8. Ammob~culites agglutinans (d'Orbigny). Sample PS 1224-3.
~i Ii ¸
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
PLATE II (for explanation see p. 253)
255
~ iii~ii~ ~
i
•
BENTHIC FORAMINIFERALASSEMBLAGESFROM EASTERNWEDDELLSEA PLATE IV (for explanation see p. 253 )
257
BENTHICFORAMINIFERALASSEMBLAGESFROMEASTERNWEDDELLSEA
cross perpendicularly the isobaths (Figs. 811 ). In addition, lower principal component loadings of many live assemblages (PC'2) in the southwest indicate a major change in benthic assemblage composition close to the southern boundary of the area investigated in this study (Figs. 8-11 ). As also indicated in Figs. 8-11, in many cases the composition of the dead assemblages substantia~y differs from the corresponding biocoenoses, whereas the calculated potential assemblage either resemble the original live or the dead assemblages (Table IV, Fig. 12). Discussion
Although there are different trends and correlations detectable by comparing plots of dominant PC-loadings (assemblage distribution) with plotted environmental parameters, multivariate quantitative techniques (canonical correlation nor simple pair-wise correlation) have not revealed significant correla-
259
tions, except self-evident ones like, for example, a negative correlation between sand and mud content. This may be due in part to the limited environmental data set, but more likely reflects the fact that many independent patterns of benthic foraminiferal species variation cannot be explained through simple correlation with single or combined environmental parameters. Hence the discussion of the observed distinctive distribution patterns of species assemblages and their environmental preferences needs to be a qualitative one, whereas the discussion of the transition from live via dead to fossil assemblages includes quantitative aspects.
Continental shelf, shelf break and uppermost slope Live assemblages and their environmental preferences Down to about 1500 m water depth two live
PLATE VI (see p. 260) (Scale = 100 #m )
1, 2, 4. Reophax pilulifer Brady. Sample PSI 395-1. 3. Reopkitlx dentaliniformis Brady. Sample PSI 388-1. 5. Subreophax adunca (Brady). Sample PS 1364-1. 6. Reoptuzx fusiformis ( WiUiamson ). Sample PS 1388-1. 7, 8. Reophax spiculifer Brady. Sample PS 1391- I. 9. Reophax difflugiformis Brady. Sample PS 1368-1. 1O- 12. Reophax bilocularis Hint. Sample PS 1368-1. PLATE VII (see p. 261 ) (Scale= 100/an)
1, 2. Epistominella exigua (Brady). Sample PS 1387-1. 3. Laticarininapauperata (Parker and Jones), Sample PS1388-1. 4-6. Oridorsalis umbonatus (Reuss). Sample 1388-1. 7-9. Nuttallides umbonifer (Cushman). Sample 1368- I. PLATE VIII (see p. 262) (Scale = i100/zm ) 1, 2. Cydammina pusilla Brady. Sample PS 1368-1. 3, 6. Ha~lophragmoides bradyi ( Robertson ). Sample PS 139 l- 1. 4, 5. Cydammina trullissata (Brady). Sample PS1224-3. 7-9. Ha[?lophragmoides canariensis ( d'Orbigny ). Sample PS 1427-1. 9. Enlarged view of same specimen as in 7 and 8. The aperture of this live captured specimen is closed by agglutinated grains leaving only a small reduced opening. This may represent a resting stage of the animal between the extremely seasonal!times of food supply in the eastern Weddell Sea.
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BENTHIC FORAMINIFERALASSEMBLAGESFROM EASTERNWEDDELLSEA P L A T E VII (for e x p l a n a t i o n see p. 2 5 9 )
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BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
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264
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BENTHIC
FORAMINIFERAL
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265
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A MACKENSENET AL.
266
TABLE IV Species composition of live, dead and potential fossil assemblages with reference to figures 8-1 l, Principal Component No., dominant species, significant associated species and explained variance in percent of total variance. LIVE ASSEMBLAGES associated spp. var.(%)DpEcAD ASSEMBLAGES PC
dominant spp.
dominant spp.
o POTENTIAL FOSSIL ASSEMBLAGES associated spp. var.('/.) PC dominant spp. assoc ated spp. var.('/0)
Continental Shelf~ Shelf Break and Uppermost Slope (Fig. 8) 5
N. irldea
2
T. angulosa
G. crassa R. b/Iocularis R. dentaliniformis T. angulosa 7-. nana 7-. nana G crassa C. jeffreysii R. dentaliniformis
7.1
2
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T. nitida C. jeffreysii
20.7
18.0
5
7". angulosa R. linearis
P. fusca B. aculeata nana S. ramosa ,G crassa
5.4
2
T. angulosa
E. vitrea? G. crassa
20.7
17.5
1
C. subglobosus Troch. sp.39+52
R. linearis R. bilocularis C. pusilla
23.6
3
B. aculeata
136
5
M. nodulosa
M. arenacea T. angulosa F. earlandi E. vitrea ? G. crassa F. earlandi B. aculeata
1
O. umbonatus L. pauperata E. bradyi
20.0
4
N. umbonifer E. exigua
15.4
Upper Slope (Fig. 9) 3
B. aculeata C, subglobosus
Troch. sp.39+52 R. dentaliniformis
Continental Terrace and Abyssal Plain (FI 9. io) 3 1 C. subglobosus O. umbonatus 19.9 R bilocularis R. dentaliniformis
B. aculeata Troch. sp.39+52 R. fusiformis E, bradyi
O. urnbonatus C. subglobosus L. pauperata
R. tinearis E. bradyi
16.0
C. pusilla P. fusca C. subglobosus Troch. sp.39+52
R. linearis R. bilocularis O. umbonatus
8.0
N. umbonifer E. exigua
O. umbonatus R. linearis C. subglobosus G. crassa T. angulosa
8.6
10.2
Lower Slope (Fig. 11) 4
R. plluflfer R a/gaeformis A. ensis
FL fusiformis A. foliacea E. exigua C. subglobosus Pelosinella sp. G. crassa R. bilocularis A. recurva O. umbonatus
9.3
6
assemblages dominate the benthic foraminiferal fauna (Table IV, Fig. 8 ). Trifarina angulosa, the dominant species of PC 2, clearly outnumbers all other species in most of the samples in this depth range, except on the eastern shelf off Atka Bay and in a few samples on the continental slope, where a fauna characterized by Nonionella iridea (sensu lato) with Globocassidulina crassa as a second important constituent, is present. The shelf and the upper continental slope dominated by T. angulosa is covered by a sandy
and gravelly lag sediment. The lower boundary of the distribution of PC2 ( T. angulosa) and PC 5 (N. iridea) coincides with the boundary above which the sand content of the surface sediments exceeds 50% (Fig. 3 ). At some stations very high gravel contents of up to 43% are found between 340 and 1240 m water depth (Table I ). Three different bottom water masses reside on the shelf and the uppermost slope, and characterize the distribution area of T. angulosa (Fig. 7). This excludes a preference of a
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267
specific water mass by the T. angulosa Assemblage and it definitely shows an independence from bottom water temperature and salinity since the temperature ranges from - 1 . 8 to 0.4°C and in salinity from 34.43 to 34.72%0. This is in contrast to the results of Williamson et al. (1984) who calculated a strong correlation between a salinity of 35%o and the distribution pattern of Trifarina angulosa at the shelf break off Nova Scotia. On the other hand, our findings are in agreement with earlier investigations from the Norwegian continental margin and Iceland-Faeroe Ridge which show a strong relationship of Trifarina angulosa to sandy substrates and relatively high bottom current velocities, independent of conservative water mass characteristics such as temperature and salinity (Mackensen et al., 1985; Mackensen, 1987a). Trifarina angulosa (partly documented as T.
earlandi, Angulogerina angulosa, A. carinata, Uvigerina bassensis) seems to be present all
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Fig. 11. Distribution of lower slope benthic foraminiferal assemblages. Contours are 100× Varimax Component Loadings. Top row: distribution of the live Reophax pilulifer assemblage. Middle row: distribution of the corresponding dead Nuttallides umbonifer assemblage. Bottom row: distribution of the potential fossil Nuttallides umbonifer assemblage.
around Antarctica on the shelf, the shelf break and the upper continental slope: It is found in surface sediments from the eastern Weddell Sea (Anderson, 1975; this study), the Cosmonout Sea (Uchio, 1960), the Kerguelen Plateau (Lindenberg and Auras, 1985; Mackensen, in press), the Adelie-George V continental slope (Milam and Anderson, 1981 ), the Ross Sea (Osterman and Kellogg, 1979), off King George Island (Li and Zhang, 1986) and the southern and eastern Falkland Plateau area (Herb, 1971; Mead and Kennett, 1987). The organic carbon and the carbonate content is relatively high on the shelf and extremely low on the upper slope (Figs. 5, 6 ). At station 1425 on the eastern shelf, a dominance ofNonionella iridea (Fig. 8 ) coincides with the highest measured organic carbon content in the investigated area (Fig. 6 ). To speculate on relations between high organic carbon contents, high productivity, and the distribution of the N. iridea Assemblage, clearly requires more stations on the continental slope. However, N.
268
A. MACKENSEN ET AL
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BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
iridea encapsulating itself with sediment and living within the upper 3 cm (Gooday, 1986; Mackensen, 1988), may depend on high organic carbon fluxes to thrive within the sediment.
Dead assemblages and early diagenesis The composition of the dead benthic foraminiferal assemblages on the shelf and the uppermost slope is different from their corresponding biocoenoses. West of ca. 7°W the thanatocoenosis is dominated by tests of the arenaceous Trochammina nana (PC 2), whereas the eastern part is characterized by empty tests of T. angulosa (Fig. 8, Table IV). On the shelf, the shift in species composition from mainly calcareous live to mainly arenaceous dead assemblages is caused by calcite dissolution in the uppermost sediment. The infaunal N. iridea is dissolved after reproduction or death within the uppermost centimeters of the sediment, enhanced by relatively high organic carbon contents. This is also documented in the Bransfield Strait, an area with high particulate organic carbon contents in the sediments. There, live N. iridea are found down to 3 cm within the sediments, but only a few empty tests occur within the top 2 cm; below 2 cm no dead specimens are found at all (Mackensen, 1988). In deeper waters on the continental slope, where the M W D W and WDW reside, calcite dissolution changes the benthic faunal composition already at the sediment-water interface. Below 1000 m water depth the number of empty T. angulosa tests drastically decreases in spite of the still high percentage of live specimens (Fig. 12).
Potentialfossil assemblage In contrast to the live and the dead faunas, which are characterized by different assemblages, the potential fossil assemblage on the continental shelf and the uppermost slope is clearly dominated by T. angulosa (Fig. 8 ). This implies that fossil Neogene benthic foramini-
269
feral assemblages that are dominated by T. angulosa indicate deeper shelf, shelf break and upper continental slope conditions, with strong to moderate bottom currents. However, it also implies that various live assemblages that are adapted to different environmental niches are not recorded in the fossil assemblage. On the other hand, the absence of fossil T. angulosa in Neogene core material does not necessarily exclude a former live assemblage characterized by T. angulosa; on the contrary, coarse and sandy sediments with no foraminifera other than a few resistant and corroded specimens, from an estimated paleodepth between 500 and 2000 m, may well have been deposited under strong current conditions on the shelf break and uppermost continental slope.
Upper slope Live assemblage and its environmental preferences Between 1400 and 2000 m water depth the northeastern part of the investigated area is inhabited by the Bulimina aculeata Assemblage (PC 3 ). Towards the southwest, into the more central part of the Weddell Sea, the distribution area becomes narrower and the number of live B. aculeata decreases (Table IV, Fig. 9 ). At this water depth, below 1400 m, the winnowing force of the ACC is reduced, indicated by higher mud contents of the surface sediment (Fig. 4). With increasing content of the fine fraction, slightly higher organic carbon contents are evident (Fig. 6), also indicating low bottom current activity. The carbonate content down to 2000 m depth is still negligible (Fig. 5 ). As indicated by temperature measurements, this belt with an extremely low carbonate content of the surface sediments coincides with that area on the upper slope where warm WDW resides (Fig. 7 ). The distribution of the B. aculeata Assemblage on the eastern Weddell Sea continental slope suggests that B. aculeata prefers water
270
temperatures > 0 ° C, a fine substrate and consequently low bottom current activities which do not hamper sufficient particulate organic matter fluxes. High productivity zones, often associated with water mass boundaries, seem to be favoured by this biocoenoses. B. aculeata itself is a cosmopolitan species, for which Van Morkhoven et al. (1986) and other have provided extensive references. Our data on living organisms corroborate conclusions based on late Neogene material from the Mediterranean, where B. aculeata has been correlated with high organic carbon (Olausson, 1960) and high m u d content (Van der Zwaan, 1982 ). Close to the Polar Front in the southwestern Atlantic, Mead and Kennett (1987 ) found a Bulimina aculeata assemblage associated with the core of the Lower Circumpolar Deep Water (LCDW) between water depths of 1500 and 2600 m. The WDW which resides on the eastern Weddell Sea continental margin can oceanographically be subdivided from the CDW (Hellmer et al., 1985 ). Also in the Cosmonaut Sea on the Gunnerus Ridge a benthic foraminiferal assemblage, dominated by B. aculeata, is found to be associated with the CDW and its high temperature (Uchio, 1960). North of this area on the Crozet Plateau, Corliss (1983:110) reported a B. aculeata-dominated assemblage overlain by warm Antarctic Intermediate Water. West of Heard Island on the Kerguelen Plateau, B. aculeata is consistently found together with Angulogerina earlandi (here T. angulosa), but it dominates the fauna at around 2000 m depth (Lindenberg and Auras, 1984).
Dead assemblage and early diagenesis The dead assemblage on the upper slope is almost exclusively composed of agglutinated species and is dominated by Cribrostomoides subglobosus (PC 1 ) (Fig. 9). Trochammina sp. 3 9 + 5 2 are the next important constituents (Tables II, IV). This change in species composition from a calcareous B. aculeata Assemblage to an arenaceous C subglobosus Assem-
A. MACKENSEN ET AL.
blage is described in detail by Mackensen and Douglas (1989). Investigation of separately stained sediment slices have revealed live B. aculeata concentrated in the uppermost centimeter of the sediment, whereas only a few, probably bioturbated, specimens occur between 1 and 2 cm sub-bottom depth. On the other hand, almost no empty tests were found in the surface sample and definitely no tests below the top centimeter of the sediment. Calculation of the degree of calcite saturation shows that WDW is not undersaturated above 3000 m water depth (M.M. Rutgers van der Loeff, pers. commun. ). Consequently, destruction and dissolution of dead B. aculeata takes place within the uppermost sediment, where, because of the decay of organic material, the interstitial water is undersaturated relative to calcite. Therefore it is likely that B. aculeata lives in the top few millimeters of the sediment and is similar to Uvigerina peregrina. Our conclusion is in agreement with Corliss and Chen (1988) who suggested, based on shape analysis of Norwegian Sea faunal counts from Mackensen et al. ( 1985 ), that B. marginata, the shallow water relative of B. aculeata, belongs to a morphotype associated with an infaunal microhabitat.
Potential jbssil assemblages Below the bioturbated zone, the tiny agglutinated Trochammina spp. and Reophax bilocularis, which characterize the upper slope dead and live assemblages, are disintegrated, and below 25 cm sub-bottom depth, the more resistant C. subglobosus and Cyclammina spp. also disappear (Mackensen and Douglas, 1989). This explains the composition of the potential fossil assemblages calculated for the upper slope: The potential fossil assemblage is dominated by B. aculeata if the live assemblage has been dominated by B. aculeata. After subsequent destruction of the agglutinated species, a few empty B. aculeata tests of the dead assemblage became the only remnant of the for-
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
merly highly diverse biocoenosis. In the more southern parts of the area investigated, where the dominance ofB. aculeata in the live assemblage is less strong, Martinottiella nodulosa and Miliammina arenacea dominate the fossil assemblage (Fig. 9 ). The latter species are highly resistant and do not disintegrate in dilute hydrochloric acid. They are found to be the only remnants of the B. aculeata Assemblage below 25 cm sub-bottom depths (Mackensen and Douglas, 1989 ). Throughout this discussion it is important to keep in mind that in many samples from the upper slope the potential fossil assemblage accounts for only a small percentage of the original live fauna. In conclusion, it is very reasonable to interpret a low diversity Neogene benthic foraminiferal assemblage dominated by B. aculeata or M. noduiosa and M. arenacea, buried in a silty clay or clayey silt, as an indicator of upper continental slope conditions (lower bathyal) with high supply of organic matter, may be close to a water mass boundary or an oceanic front.
Continental terrace and abyssal plain Live assemblage and its environmental preferences On the fiat continental terrace between 2000 and 3000 m water depth, and especially in the southern part of the investigated area, below 4500 m, the live benthic foraminiferal fauna is dominated by Cribrostomoides subglobosus (PC 1 ) (Fig. 10). Calcareous components include Oridorsalis umbonatus as accessory species (Table IV). The surface sediments on the continental terrace consist of mud with varying sand content and dropstones (Fig. 3). In the southern part off the mouth of the Wegener Canyon, sand contents of over 50% of the bulk dry sediment are found (Fig. 3 ). The upper boundary of the C. subglobosus Assemblage coincides with the upper boundary of the AABW (Fig. 7 ). In addition, the distribution of the highest levels of carbonate content, disregarding the
2 71
continental shelf, roughly coincides with the distribution of the C. subglobosus Assemblage on the continental terrace. We suggest that the C. subglobosus Assemblage prefers environmental conditions related to plains at the foot of continental slopes, independent of water depth and conservative water mass characteristics. Consequently, in the investigated area the unique situation of a continental slope divided by a terrace results in a bipartite distribution of the C. subglobosus Assemblage (Fig. 10). This relationship between C. subglobosus and a continental rise morphology has previously been reported from the Norwegian Sea continental margin (Mackensen, 1985; Mackensen et al., 1985) and the Iceland-Faeroe Ridge (Mackensen, 1987a). There, a combination of hemipelagic sedimentation with according particulate organic matter fluxes and the availability of coarse grain sizes for test construction is inferred as the critical environmental limit for the distribution ofa C. subglobosus-dominated assemblage. In the Norwegian Sea as well as in the Weddell Sea, ice rafted material is the source of coarse material within pelagic sedimentation realms. Few investigations, other than those of the senior author, have dealt with distribution patterns of agglutinated species as part of the benthic foraminiferal deep-sea fauna, and to our knowledge, none of them have treated live faunas of higher latitudes quantitatively. Herb (1971) reported abundant C. subglobosus in the Drake Passage between 3800 and 4200 m water depth, as did Lindenberg and Auras (1984) from the continental slope off Prydz Bay in 1590 and 2688 m. Unfortunately, both paper do not differentiate between live and dead specimens, in spite of Rose Bengal treatment of most of the samples.
Dead assemblages and early diagenesis The dead assemblage on the continental terrace is dominated by O. umbonatus (PC 3),
272
whereas the continental rise and the foot of the lower slope is dominated by Cyclammina pusilla (PC 4) (Fig. 10). In both of these assemblages empty C. subglobosum tests are characteristic of the associated components (Table IV). The shift from a mainly agglutinated live fauna on the terrace to a mainly calcareous death assemblage may simply reflect, that (i) the physical a n d / o r bacterial destruction of empty C. subglabasum tests takes place rather quickly on and in the uppermost sediment and (ii) no carbonate dissolution hinders the accumulation of dead O. umbanatus. At the Norwegian continental margin an identical situation has been reported: the live fauna is dominated by C. subglabasum but the corresponding dead assemblage is dominated by calcareous species (Mackensen et al., 1985; Mackensen, 1987a). However, on the Weddell abyssal plain below 4000 m, calcite dissolution diminishes the number of calcareous tests faster than C. subglobosum is destroyed and C. subglobosum is destroyed faster than the more resistant arenaceous species. Given low sedimentation rates, C. pusilla accumulates over several generations and becomes the dominant constituent of the dead assemblage (Fig. 12 ).
Potential fossil assemblage The composition of the calculated potential fossil assemblage (PC 1 ) on the continental terrace is the preliminary terminal state of what begun at the transition from live to dead. All C. subglobosus test have been destroyed and broken down into their mineral components. There is thus an enrichment of O. umbonatus and other calcareous, and especially resistant agglutinated species, indicated by Laticarinina pauperata and Eggerella bradyi, respectively. The latter two species occur only as accessory constituents in the live assemblage (Table IV). On the continental terrace, there is evidence, that a further transition from the Holocene O. umbonatus potential fossil assemblage
~. MACKENSEN ET AL.
to a Pleistocene E. exigua real fossil assemblage takes place. This can be explained either by diagenetic processes deeper within the sediment or, more likely, by averaging out and dilution of the record of the special circumstances of the last 1000 years over a longer interglacial sequence. In a virtually complete record of 1 million years from station 1388 (Figs. 1, 2 ), which was dated by means of stable oxygen isotope stratigraphy and paleomagnetism (Mackensen et al., 1989), the interglacials are clearly dominated by E. exigua (Mackensen, unpublished data). The Holocene epoch, the last deglaciation period, only represents a short phase of a glacial-interglacial cycle with special environmental conditions. Therefore it is likely that averaging out with further future interglacial assemblages may result in an E. exigua-dominated fossil assemblage, and the short phase of climatic improvement, characterized by the O. umbonatus dead assemblage is no longer documented in the sediments. We have also calculated a potential assemblage including C. pusilla, because Cyclammina sp. is reported to be abundant at early Miocene sites on King George Island (Birkenmajer et al., 1983; Gazdzicki and Wrona, 1986) and in some Arctic cores (Scott et al., 1988). However, composition and distribution of the fossil assemblage on the continental terrace shows no significant change. This solution accounts for only a minor part of the total variance and adds an additional C. cyclammina PC similar in distribution and composition to the dead assemblage (PC 4) that occurs at abyssal depths (Fig. 10). In conclusion, a Neogene calcareous fossil assemblage dominated by O. umbonatus may be the remnant of a former arenaceous C. subglobosum assemblage and, at least around Antarctica, may indicate depositon on the continental rise or on very gently dipping parts of the lower continental slope. In addition, a Pleistocene E. exigua-dominated assemblage may also include a former O. umbonatus-dom-
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
inated dead assemblage and a C. subglobosum dominated live assemblage, respectively (cf. discussion below).
Lower slope Live assemblage and its environmental preferences On the lower continental slope between the continental terrace and the Weddell abyssal plain, i.e. between approximately 3000 and 4000 m water depth, Reophax pilulifer (PC 4 ) dominates a predominantly arenaceous live assemblage (Fig. 11, Table IV). The sand content of the surface sediments in this depth interval is somewhat higher than on the terrace, but lower than on the continental rise below 4000 m (Fig. 4). The carbonate and organic carbon contents vary in about the same range as on the continental terrace (Figs. 5, 6). The lower slope is overlain by the AABW. The upper boundary of the colder WSBW, which resides on the Weddell abyssal plain, seems to coincide with the lower boundary of the live PC 4.
Dead assemblages and early diagenesis The dead assemblage on the lower continental slope is dominated by Nuttallides umbonifer with Epistominella exigua as the second important constituent (Figs. 11, 12, Table IV). Essentially, the same mechanism of physical and bacteriological/chemical destruction of agglutinated tests and subsequent accumulation of calcareous tests in an environment above the CCD, as discussed for the continental terrace, causes the shift from a predominantly areanaceous live fauna to a calcareous dead assemblage. Both N. umbonifer and E. exigua are cosmopolitan deep water species which were used to infer bottom water characteristics and routes in late Neogene time (Streeter, 1973; Schnitker, 1974). Today a benthic foraminiferal assemblage dominated by N. umbonifer characterizes the AABW in the Atlantic Ocean
273
(Lohmann, 1978). In the Indian Ocean, AABW is found associated with N. umbonifer and Cibicidoides wuellerstorfi (Corliss, 1979, 1983 ), but in the Pacific with N. umboniferand E. exigua (Douglas and Woodruff, 1981 ). In the Pacific Ocean "In the zone between the lysocline ( 3500 m ) and the CCD, E. umbonifera becomes the dominate species" (ibid.: 1280). From the southwestern Weddell Sea continental slope, abundant N. umbonifer have been reported between 3100 and 3800 m water depth (Anderson, 1975 ). In summary, N. umbonifer today is a characteristic constituent of dead benthic foraminiferal assemblages on most of the world ocean floors over which AABW flows, that is essentially between the depth of the carbonate lysocline and the CCD. This agrees with our measurements, which indicate a drastic decrease in carbonate percentage [carbonate lysocline in the sense of Broecker and Takahashi (1978) and Berger (1979) ] below 3500 m (Fig. 5). Calculation of saturation profiles with respect to calcite as a function of temperature, salinity and pressure based on published data ofpH, SCO2 and carbonate alkalinity in the area under investigation, reveals a calcite undersaturation of AABW below ca. 4000 m water depth (Schliiter and M.M. Rutgers van der Loeff, pers. commun. ). Corliss and Honjo ( 1981 ), in a comparison of seven deep-sea benthic foraminiferal species (which excluded E. exigua) with respect to their resistance to carbonate dissolution, documented that dissolution probably has no major role in preferentially concentrating N. umbonifer. This is because N. umbonifer is as susceptible to carbonate dissolution as are other c o m m o n deep-sea species. This is consistent with Bremer and L o h m a n n (1982) who suggested that N. umbonifer in the Atlantic Ocean shows a negative correlation with the degree of carbonate saturation of deep water masses. Our data based on live specimens corroborate Bremer and L o h m a n n (1982), who suggested that the relationship between car-
274
bonate saturation and faunal distribution resuits from the ecological influence on the live organisms, rather than from selective dissolution. On the eastern Weddell Sea continental margin, the upper boundary of the AABW does not coincide with the lysocline. Consequently, N. umbonifer in the area under study is associated with the lower AABW between the carbonate lysocline and the CCD and it is missing above the lysocline. In contrast, live N. umbonifer have been reported from the central Weddell Sea from below the CCD (Mackensen, 1987b). Also Anderson (1975, p. 78) reported a few specimens from the western Weddell Sea abyssal depth (4500 m ) , which we consider to be alive. This indicates that N. umbonifer prefers an environment that is corrosive to carbonate, but it also implicates that N. umbonifer is able to tolerate strongly undersaturated water masses, in which the empty tests rapidly dissolve after death of the animals. From the Antarctic continental slope overlain by AABW, one sample with abundant E. exigua was reported by Uchio (1960). On the other hand E. exigua is reported to be associated with North Atlantic Deep water i n t h e Atlantic (Schnitker, 1974; Lohmann, 1978), Indian Bottom Water in the Indian Ocean (Corliss, 1979 ) and Pacific Deep Water in the Pacific Ocean (Douglas and Woodruff, 1981 ). In the Norwegian Sea E. exigua and C. wuellerstorfi dominate the live fauna between 2000 and 3000 m water depth (Norwegian Sea Bottom Water). A correlation between relatively coarse and organic-rich sediments and this assemblage was documented and a preference of high food supply and a tolerance of low interstitial water oxygen content was proposed (Mackensen et al., 1985 ). Recently it was documented, that both E. exigua and C. wuellerstorfi are epibenthic species (Gooday, 1988; Lutze and Thiel, 1989), which tend to live elevated above the actual sediment-water interface and therefore should not care too much about pore water chemistry.
A, MACKENSEN ET AL.
Potential fossil assemblage The potential fossil assemblage on the lower continental slope and rise is clearly dominated by N. umbonifer, with E.exigua as an associated constituent. The calculation of the potential fossil assemblage indicates no difference in resistivity against dissolution or destruction between N. umbonifer and E. exigua, as one might expect considering the relatively thickwalled and compactly constructed test of N. umbonifer as compared with the very thin, hyaline and small tests of E. exigua. This is important to know when interpreting down-core changes in benthic foraminiferal composition from an E. exigua-dominated assemblage to a N. umbonifer-dominated fauna; i.e. on the Maud Rise and southern Kerguelen Plateau, where an early Oligocene through early late Miocene N. umbonifer-dominated fauna precedes a middle late Miocene through late early Pliocene E. exigua fauna (Barker, Kennett et al., 1988; Schlich, Wise et al., 1989; Mackensen, in press). Such a faunal shift can be explained by a primary response of the benthic fauna to a change in bottom water carbonate saturation, rather than to a change in preservation. This is because of changes in within-sediment conditions produced by increasing surface productivity and resultant high organic matter fluxes, which in turn produce highly aggressive pore waters relative to carbonate. In summary, our data suggest that a late Paleogene/Neogene N. umbonifer dominated fauna with E. exigua as a minor associated constituent, indicates a paleoenvironment characterized by a water mass similar to AABW within the zone between the carbonate lysocline and the CCD, whereas an E. exigua (0. umbonatus) dominated fauna around Antarctica may also indicate AABW or similar water mass conditions, but above the carbonate lysocline.
Conclusions Today five distinct benthic foraminiferal
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
communities (stained tests) inhabit the continental margin of the eastern Weddell Sea, recognized on the basis of multivariate statistical analyses. Six dead assemblages (empty, unstained tests) and five potential fossil assemblages (empty tests, non-resistant agglutinated species excluded) correspond to the biocoenoses. The benthic foraminiferal assemblages in general are bathymetrically arranged, although towards the southwest a major faunal change perpendicularly crossing the isobaths is indicated. On the outer continental shelf, shelf break and upper slope, the live assemblages are predominantly calcareous, whereas deeper than 2000 m water depth they are strongly dominated by arenaceous species. Each of these live assemblages undergoes its specific early diagenetic transition via a dead assemblage to the fossil assemblage. The changes in species composition and distribution patterns depend largely on the corrosiveness of the pore water and bottom water masses to carbonate and also the resistance of the agglutinated tests to disintegration. The corrosiveness of the pore water, in turn, depends largely on the fluxes of organic matter. Consequently calcareous benthic foraminiferal biocoenoses which are adapted to high organic matter supply become badly preserved in the sediment and the geological record. Deeply infaunal species like Nonionella iridea rapidly dissolve after the death of the animals, because on the shelf and the upper slope the pore water is carbonate-undersaturated below the upper few centimeters of sediment. In contrast, tests of species like Trifarina angulosa, which live on the sediment surface, or (if infaunal), within the top few millimeters of sediment, can comprise a significant portion of the dead assemblage. This is because T. angulosa is associated with a sandy substrate and strong bottom currents and consequently a well oxygenated, non-corrosive interstitial water. Agglutinated tests of species like Trochammina nana may dominate the dead assem-
275
blage, but they become disintegrated within the upper sediment during early diagenesis as a result of the predatory actions of macro-benthos, among others, and they are thus not recorded in the fossil assemblage. In summary, above 2000 m water depth, only calcareous tests of epifaunal or shallow infaunal species are preserved within the sediment. They document the former diverse live assemblages and their corresponding habitats as follows: ( 1 ) A fossil Neogene fauna characterized by T. angulosa indicates outer shelf, shelf break and upper continental slope conditions with strong bottom current activity. (2) Fossil assemblages characterized by Bulimina aculeata a n d / o r Martinottiella nodulosa indicate lower continental slope conditions with a calm hemipelagic environment, in which fine sedimentation and high particulate organic matter fluxes proceed unhampered. Between 2000 and 3500 m water depth where the AABW, which resides on the lower continental slope and rise, is carbonate supersaturated and the fluxes of organic matter are low, a predominantly arenaceous fauna, dominated by Cribrostomoides subglobosus, turns to a calcareous fossil assemblage. Simultaneous with the disintegration of the agglutinated tests, there is preservation and subsequent accumulation of the calcareous species Oridorsalis umbonatus and Epistominella exigua. Below the carbonate lysocline around 3500 m water depth, but above the CCD, after the disintegration of a predominantly arenaceous live fauna, a dead and a potential fossil assemblage remain, which are both dominated by the calcareous species Nuttalides umbonifer. In the eastern Weddell Sea, this benthic foraminiferal assemblage is associated with the deeper part of the AABW, and clearly corroborates earlier investigations suggesting a primary relationship between the carbonate-corrosiveness of water masses and N. umbonifer. We have thus been able to relate distinct paleoenvironments to distinct (potential) fossil assemblages. The application of our results to
276
A. MACKENSEN ET AL
faunal assemblages from Neogene core material from the Weddell Sea and from the southern Kerguelen Plateau, where T. angulosa assemblages are overlain by B. aculeata assemblages and where N. umbonifer faunas precede E. exigua-dominated faunas, will provide a check for their utility and feasibility in high-latitude paleoceanographic reconstructions.
Appendix
TABLE I. 1. Varimax Principal Component Loadings of live assemblages Sample PS1482 PS1370 PS1387 PS1481 PS1405 PS1224 PS1388 PS1380 PS1390 PS1389 PS1386 PS1412 PS1367 PS1384 PS1383 PS1410 PS1373 PS1427 PS1374 PS1428 PS138S PS1406 PS1425 PS13943 PS13941 PS1391 PS1395 PS1381 PS1411 PS1375 PS1379 PS1376 PS1377 PS1369 PS1372 PS1588 PS1368
PC 1
PC 2
PC 3
PC 4
PC 5
0.840 0.835 0.782 0.777 0.771 0.743 0 732 0.714 0.587 0.582 0.544 0.541 -0,044 0.005 -0,127 0.057 -0.078 -0.073 0.175 0.080 -0 0 5 7 0014 -0.033 0.154 0,328 0.345 -0,137 0.451 0045 0.495 0159 0.154 0.398 0.142 0.188 0.392 0.266
-0.036 0.089 0.015 -0 054 -0.039 0.059 0.015 -0.065 0033 -0080 0 039 -0089 0.919 0.871 0.869 0.818 0.815 0734 0.705 0.692 0.666 0.586 0.513 0.100 -0.028 0.078 0.424 0.010 0.096 -0.085 -0 0 2 8 0.025 0 000 0.004 0368 -0.044 0 101
0.191 0.273 0 110 0150 0.201 0.016 0.043 0.532 0.004 0.278 0.071 0.328 -0.008 -0004 0.363 0.150 0.107 0.064 0.607 0.130 0.630 -0.053 0.035 0.934 0.891 0.873 0.842 0.801 0.763 0.669 0.086 -0.003 0.047 -0029 -0142 -0049 0.064
-0009 0.016 0.162 0179 0182 0230 0 431 -0.026 0144 0.439 0.363 0.023 -0.029 0.003 -0001 -0 0 2 0 0.062 0.070 -0 0 2 3 -0.029 0184 -0.154 -0.061 0.020 0.078 -0.003 0019 0.031 0.101 0.034 0.851 0.840 0752 0 625 0 015 0248 0.479
0.000 0113 0062 0.058 0.023 ~0.109 -0 0 1 6 0036 ~0 0 5 0 0.067 ~0.052 0.699 0.021 0.010 0.089 0.485 0.043 0.638 0077 0 677 0003 0.087 0.820 0.020 0.025 0.025 0.017 -0.024 0 488 0,120 0 013 -0.043 0.026 -0.006 0207 -0.015 0009
Comm. 0.743 0.793 0.654 0.665 0.67( 0.621 0.72~ 0.79~ 0.36£ 0.62{ 0.43; 0.89; 0.84E 0.75£ 0.911 0.93( 0.68; 0.96( 0.903 0.961 0.87E 0.37E 0.94~ 0.907 0.90£ 0.68E O.90E 0,847 0 . 8 4 -~ 0.715 0.75£ 0.732 0727 0.412 0.234 0.22C 0.315
277
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
TABLE 1.2 Varimax Principal Component Loadings of dead assemblages Sample PS1380 PS13943 PS1361 PS1375 PS1391 PS1411 PS1370 PS1412 PS1389 PS1382 PS1481 PS1395 PS1383 PS1372 PS1373 PS1374 PS1410 PS1427 PS1367 PS1384 PS1406 PS1390 PS1379 PS1388 PS1387 PS1224 PS1369 PS1368 PS1405 PS1462 PS1386 PS1428 PS1426 PS1378 PS1588 PS1377
PC 1 0 .9 2 4 0.907 0.900 0.895 0.868 0.863 0.831 0 .6 2 2 0 .6 4 5 0 .6 1 6 0 .5 3 6 0 .5 3 0 0 .0 4 3 -0.015 0,037 0.150 0.092 -0.024 -0.053 -0.033 -0.097 0.143 0 .0 7 5 0.383 0 .4 0 8 -0.078 -0.026 0.051 0,414 0.377 0 .4 7 2 0 .1 0 6 -0.140 -0,045 -0.078 0.000
PC 2 -0.071 0.002 -0.048 -0.038 0.029 0.143 -0.054 -0.066 -0.030 0.148 -0.060 0.337 0.984 0,946 0.940 0.901 0.887 0.685 0.884 0.865 0.649 -0.059 -0,040 -0,074 -0.092 -0.038 -0.066 -0.047 -0.050 0,122 0.068 0.194 0.288 -0.058 -0.048 -0042
PC 3 0.208 0,096 0.225 0.087 0.223 -0.047 0.319 0.245 0.622 -0.070 0.730 -0.184 -0,057 -0.032 -0.065 -0.113 -0.100 -0002 -0.010 -0.017 0.029 0.924 0.892 0.843 0.831 0.828 0.613 0.004 0.052 0.074 0.225 -0 101 0.089 0.366 0.145 0,330
PC 4 0.127 0.050 0.270 0.119 0.279 -0.044 0.313 0.273 0.148 0.028 0.256 -0.060 0.012 0.004 -0.017 -0.028 0.008 0.015 0.014 0.021 0.007 0.020 -0.024 0.142 0.115 -0.086 0.131 0.865 0.801 0.669 0.667 0.085 -0.003 0,126 -0.015 0,259
PC 6 0.022 0.056 0.021 0.018 -0.028 0.015 0.03 3 0,048 0.046 -0.358 0.014 -0.396 0.045 -0.100 -0.075 0.06 0 0.16 6 -0.366 -0.196 -0.136 -0.273 -0.006 0.018 0.03 4 0.023 0.02 2 -0.021 -0.002 -0.113 -0.074 0.113 -0.866 -0.753 0.013 0.037 0.030
PC 6 -0.046 -0.028 -0.083 0.004 -0.083 0.071 -0.104 -0.127 0.084 0.106 0.017 0.159 0.018 -0.034 0.021 0.071 0.066 -0.060 -0.089 -0.061 -0.153 0.155 0.334 0.037 0.110 0.263 0.585 0.226 0.057 0.154 -0.093 0.065 -0.186 0.870 0.870 0.857
TABLE 1.3 Varimax Principal Component Loadings of fossil assemblages Sample PS1390 PS1388 PS1379 PS1389 PS1481 PS1387 PS1224 PS1369 PS1370 PS1426 PS1427 PS1383 PS1372 PS1367 PS1373 PS1382 PS1384 PS1428 PS1406 PS1410 PS1396 PS1411 PS1374 PS13943
PC 1 0.967 0.924 0.922 0.919 0.917 0.906 0.884 0.696 0.632 -0.036 -0.025 -0.074 -0.063 -0.106 -0.017 0 .0 3 3 -0.101 -0,038 -0.104 -0.018 -0.088 -0.070 -0.062 -0.020
PC 2 -0,052 -0.101 -0.072 -0,061 -0.024 -0.100 -0.083 -0.048 0.002 0.972 0,934 0,920 0,660 0.824 0.820 0.810 0.731 0.649 0.630 0524 0.035 -0.068 0.305 0.103
PC 3 0.049 0.030 0.031 0.012 0.027 0.003 0.035 0.074 0.044 -0.132 -0.238 -0,021 -0,160 -0.030 -0.438 -0.342 0.144 -0.686 0.118 -0604 -0.846 -0.745 -0.731 -0.719
PC 4 0.102 0.042 0.276 0.067 0.104 0.171 0.201 0.575 0.089 -0.032 -0.012 -0.063 -0.057 -0.086 -0.009 0,026 -0,092 -0.011 -0.089 -0.027 -0.066 -0.039 -0.058 -0.096
PC 5 -0.095 0.049 0.081 -0.131 -0,238 0.070 0.107 0.025 -0.708 0.030 0.072 0.002 0.083 -0.015 0,112 0.094 -0,062 0.008 -0.080 0.19 3 -0.067 -0.563 0,169 -0.278
Comm. 0.960 0.869 0.939 0.870 0.910 0.665 0.841 0.823 0.911 0.966 0.935 0.856 0.779 0.699 0.877 0.784 0.578 0.893 0.436 0.678 0.732 0.682 0.660 0.61
Comm. 0.921 0.838 0.943 0.825 0.890 0.775 0.905 0.833 0.836 0.546 0.890 0,617 0.976 0.907 0.896 0.855 0.834 0.914 0.832 0.776 0.529 0.902 0.915 0.886 0.891 0.770 0.739 0.804 0.834 0.639 0.744 0.820 0.713 0.912 0.768 0.913
278 PS1380 P81391 PS1375 PS1482 PS1588 PS1368 PS1377 PS1378 PS1386 PS1412 PS1381 PS1405
A. M A C K E N S E N
0 110 -0.016 -0.084 0.083 0.082 0 056 0.302 0346 0024 0.001 0.021 0,295
0191 0.438 0.057 0.027 -0.066 0.043 -0047 0070 -0.122 0.021 -0.096 -0,058
0666 -0 631 -0555 0.006 0.041 0.044 0047 0.056 0.008 0.002 -0.353 0.05t
0.045 .0 001 -0 0 4 8 0.963 0.950 0.941 0.923 0.906 0.627 0.023 0034 0,433
-0.552 -0.336 0 617 0.118 0.088 -0.255 0.034 0,025 -0.187 -0.922 -0878 0,100
0.79g 0.703 0.701 094g 0.923 0.956 0.949 0.949 0.444 0.851 0.906 0.290
TABLE II. 1 Varimax Principal Component Scores of live assemblages Species
Adercotryma glomerata Ammobaculitesagglutinans Ammodiscus spp. Ammomarginulina ensis Ammomarginulina foliacea Ammomarginulina foliacea curvata Astrononion antarcticus Bulimina aculeata Buliminella cochlea Cassidulina teretis Cibicides bertheloti Cibicides corpulentus Cibicides grossepunctatus Cibicides Iobatulus Cibicidoides cf wuellerstorh Cribrostemoides crassimargo Cribrostomoides jeffreysi Cribrostomoidessp. 1 Cribrostomoides subglobosus Crithionina spp. Cyclammina orbiculans Cyclammina pusilla Eggerella bradyi Eggerellasp. Ehrenbergina glabra Epistominella exigua Epistominella vitrea? Eponides tumidulus Eponidesweddellensls Fissurina spp. Fursenkoina earlandi Globocassidulina crassa Globocassidulinasubglobosa Glomospiracharoides Gyroidina sp. iHaplophragmoides bradyi Haplophragmoidessp. l Haplophragmoides sphaeeloculus Hippocrepina flexibilis Hormosina normani/carpenteri Hormosina robusta Hyperammina laevigata Kareriella novangliae Lagenaspp. Laticarinina pauperata Marsipella elongata/cylindrica Martinottiella nodulosa Melonis affinis Miliammina arenacea Miliolinella spp. Miliolinella subrotunda Nonionella bradyi Nonionella iridea Nuttallides umbonifer Oridorsalis sidebottomi
PC 1
PC 2
PC 3
PC 4
PC 5
0.958 0305 -0.248 0134 0.054 0.229 -0344 -2.127 -0.402 0.472 -0 644 0.406 -0 195 0.350 -0326 0 118 0 028 0,416 7.525 0.245 0.371 0.163 1 252 -0.448 0010 0730 0.266
0.511 -0.410 0 114 0376 0390 0.277 -0.063 0,330 0.289 0.071 0 289 0.292 0.275 0.069 0 350 0.203 1.368 -0 1 7 9 0 210 0.315 -0448 0 290 0 096 0 209 0.715 0397 0.119
-0.861 0.635 0.232 -0.422 -0.099 0.097 0.258 8 660 -0.202 -0.002 0.289 0175 -0.224 -0.302 0.221 -0.324 -0,320 -0.162 2.172 0.088 0.052 0.300 0.640 0.215 0.672 0.652 .0.352
0.498 0.459 - 0.495 2.321 1.572 1.047 -0.484 -0.117 0.455 -0.439 0.911 0.428 0.043 0.485 -0.243 0.384 -0.555 -0.448 - 1.407 -0.269 -0.405 0.172 0.600 -0 2 1 9 0878 1.467 0.489
0 279
0 304
~0 1 4 6
0 440
0.389 -0 0 2 3 -0. 1 8 0 0 250 0.023 0.404 0067 -0265 -0.402 -0. 0 7 8 -0.047 -0276 0 436 0 387 0 389 -0 1 9 7 0.194 0 265 0 305 0 257 -0.472 0.305 0 453 -0.291 0 265 0.043 0 334
-0281 0.196 0.226 1. 3 8 0 0168 0.430 0 293 0 493 0 290 0 339 0 428 0 345 0 144 -0283 -0376 0 195 0 217 0250 0385 0177 0 198 .0170 0 241 0029 -0 3 2 3 -0.316 0 106
0.227 0 243 -0.261 0.266 0.463 0 126 0.320 0.145 -0.208 0.235 0.085 -0.247 -0.519 0. 1 9 0 -0.127 -0 1 1 9 -0,404 0.131 -0,200 0.343 0.080 0.318 -0.205 -0.293 -0.436 -0.431 -0 1 4 7
-0467 -0.463 0.584 - 1.193 -0.429 -0.490 0047 -0.263 -0457 -0 116 0404 ~0.340 0 441 0 451 0346 -0432 -0.362 -052t 0.141 -0.555 -0.426 -0.007 0.333 -0 5 7 3 -0 2 8 9 0839 -0.472
-0.080 -0.01 0.24 0.12£ 0.26 -009, 0.205 0 614 -0114 -0.09~ 0.061 0.11(] 0.020 0061 0.068 0.256 0734 0177 0161 0150 0.058 0123 0144 0 141 0244 0517 0203 -0.094 -0.011 0.223 -0.51( 1 ,06z 0 62£ 007~ 0.017 007 c ~0.06! 003: 0.2( 0.077 0.34(] 0.126 0.081 0.121 0154 0.009 0003 0.398 0.244 0.134 0.057 -0.267 9118 0.053 0.273
ET AL
279
BENTHIC FORAMINIFERALASSEMBLAGESFROM EASTERNWEDDELLSEA Oridorsalis umbonatus Parafissurina spp. Patellina eorrugata Pelosinella sp. Portatrochammina spp Psammosphaerafusca Pseudobofivinaantarctica Pseudobulimina chapmani Pullenia bulloides Pullenia simplex Pullenia subcarinata Pyrgo murrhina Pyrgo williamsoni Quinqueloculinapygmaea Quinqueloculinasp. Recurvoides contortus Reophax bilocularis Reophax dentaliniformis Rsophaxdistans Reophax fusiformis Reophaxovicu/a Reophax pi/ulifer Reophax spiculifer Rhabdarnmina cf. linearis Rhabdammina/1-1yperammina spp. Rhezarkinasp. Rhizammina indivisa/algaeformis Robertinoides sp. Rotaliamminaochracea Saccaminasphaerica Saccorhizaramosa Subreophaxadunca Textularia wiesneri Thurammina papillata Trifarina angulosa Triloculina frigida Triloculina tricarinata Tritaxis squamata Trochammina globulosa Trochamminanana Trochammina nitida Trochammina sp.39+52 Trochamminaspp. all others
1.915 -0.356 -0.369 -0.311 -0.411 0.398 -0.386 -0.401 -0.378 -0.336 0.238 -0.061 -0.404 -0.156 0.199 -0.341 -0.161 3.109 2.487 -0.338 1.255 -0.026 - 0.61 1 -0.424 -0.541 -0.490 -0.359 -0.597 -0.254 -0.381 -0.244 0.520 -0.601 -0.446 -0.354 -0.341 -0.438 -0.405 0.307 0.378 -0.503 1.557 -0.099 0.302
0050 -0.195 -0.156 -0.647 -0.248 -0.146 -0.134 -0.246 -0.128 -0.312 0.168 -0 249 -0 221 0296 0.113 -0.424 -0.422 -0.454 1.205 -0.226 -0.317 0.081 0,721 -0.515 -0.377 -0.070 -0.361 -0.380 -0.382 -0.214 -0.290 -0.040 0.682 -0.323 8.931 -0.217 -0.267 -0.364 0.537 1.448 0.265 -0.963 -0.220 0.849
-0.786 -0.169 -0.253 0.720 0.162 -0.231 -0.211 -0.201 0.038 -0.054 -0.398 -0.318 -0.242 -0360 -0.205 0.755 0.160 1.707 -1,468 -0.234 0.728 0,461 0,174 0.793 0.268 -0.017 -0.208 0.252 -0.164 -0.229 -0.178 -0.373 0.304 -0.191 0.311 -0.013 -0.203 -0.186 0.162 -0.514 -0.030 1.598 -0.020 0074
1.019 -0.277 -0.479 1.399 -0.388 0.507 -0.473 -0.454 -0.359 -0.475 -0.220 -0.503 -0.457 -0.484 0.221 -0.223 -0.190 1.129 0.685 -0.467 1.649 0.047 7.107 0.000 -0.352 0.116 -0.355 2.824 -0.330 -0.467 0.006 0.801 -0.228 -0.244 -0.281 -0.276 -0.178 -0.176 -0. 133 -0.813 -0.365 -0.279 0.137 1.566
-0.245 -0.155 -0.075 0.389 0.459 -0.051 -0.105; -0.13; -0.17--. 0.03, -0.28C -0.19; 0.16~ -0.53,E -0.20,E 0.40,' -0.052 1.292 -1.446 -0.020 -0.082 -0.280 -0.096 0.266 0.090 -0.352 -0.057 0.065 -0.024 -0.068 -0.142 -0.199 -0.685 0.048 1.380 -0.211 -0.137 -0.072 -0.395 -1.313 -0.021 0.799 -0.013 -0.606
PC 4
PC 5
TABLE II.2 Varimax Principal Component Scores of dead assemblages Sample
Adercotryma glomerata Ammobaculltesagglutinans Ammodiscusspp. Arrimomarginulina ensis Ammomarginulina foliacea Ammomarginulina foliacea curvata Ammoscalaria pseudospiralis Astrononion antarcticus Astrononionecholsi Astrorhiza sp. Bufimina aculeata Cassidulinacrassarossensis Cibicides bertheloti Cibicides corpulentus Cibicidesgrossepunctatus Cibicides Iobatulus Cibicidoides cf. wuellerstorfi Cibicidoides spp. Cfibrostomoides crassimargo Cribrostomoides jeffreysi Cribrostomoidessp. I Cribrostomoides subglobosus Cyclammina orbicularis
PC 1 -0.434 0.592 -0.257 -0.369 0.058 -0.317 0.729 -0.303 -0.311 -0.277 0834 -0.734 -0.395 -0.249 -0.326 -0.469 -0.269 -0.360 -0.167 0.022 -0.233 6.279 0.283
PC 2
PC 3
0.760 -0.342 -0.178 -0.293 -0.246 -0.324 -0.203 -0.220 -0.148 -0.327 -0.357 0.826 -0.219 -0.298 -0.340 0.172 -0.329 -0.288 -0.289 1.174 -0.214 -0.307 -0.333
0.044 -0.521 -0.290 0.140 0.282 -0.140 -0.340 -0.317 -0306 -0.362 -0~880 0.330 0.226 -0.255 -0.120 0.029 -0.361 -0.004 -0.087 -0.339 -0.407 3.000 -0.308
0.774 -0.556 -0.180 0.520 -0.445 0.253 -0.515 -0.174 -0.165 -0.042 -0.806 0.100 -0.288 -0.206 -0.222 -0.159 -0.147 -0.276 -0.195 -0.195 -0.127 2.783 -0.314
0.419 0.283 0.320 0.279 0.306 0307 -0.347 0.196 0.254 0.320 -1.624 -1.158 0.028 0.307 0.103 -0.049 0.345 0.271 0.371 0.263 0.437 0.350 0.289
PC 6 -0.240 -0.027 -0.240 0.381 -0.21( -0.00; -0.11 -0.369 -0.384 -0.308 0.394 -1.161 -0.093 -0.360 -0.422 -0.568 -0.195 0.221 -0.409 -0.225 -0.243 -1.433 -0.257
280
A. MACKENSEN ET AL
Cyclammina pusilla Cyclammnina trullissata Eggerella bradyi Eggerellasp. Ehrenbergina glabra Epistominefla exigua Epistominella vitrea? Fissurina spp. Fursenkoina earlandi Globocassidulinabiora Globocassidufinasubglobosa Glomospiracharoides Gyroidina orbicularis Gyroidina sp.klein Haplophragmoidesbradyt Haplophragmoides sphaeriloculus Hormosina normani/carpenteri Hormosinarobusta Kareriella novangliae/bradyJ Lagenaspp. Laticarinina pauperata Lenticulina spp. Martinottiella nodulosa Meloniszaandami Miliammina arenacea Nonionella bradyi Nonionella iridea Nuttallides umbonffer Oridorsalis umbonatus Parafissurina spp. Pelosinella bJcaudata Pelosinella sp Psammosphaeratusca Pseudobolivma antarctica Pullenia bullo/des Pullenia simplex Pullenia ";rTata Pyrgo ~ Recurvt Reophax Reophax con, ,,'o,,rlls Reqohaxnodutosus Reophaxowcula Reophax pitulifer Reophax splculifer Rhabdammlna lineans Rhabdammina/Hyperamminaspp Rhizammina indivisa/algaeformis Rotaliamminaochracea Subreophaxadunca Saccaminasphaerica Saccorhizaramosa Textularia wiesneri Trifarina angulosa Triloculina sp./frigida Tritaxis squamata Trochamminaglobulosa Trochamminanana Trochammina nitida Trochammina sp,39+52 Trochamminaspp. allothers
1 .137 -0.348 -0.246 -0.271 0 450 -0 3 6 5 0 620 -0 452 0 159 0 286 -0 242 0047 -0.276 0 459 0 228 0.226 -0.278 0.259 0 245 0 239 -0 6 4 5 -0 279 0 060 -0 2 7 1 0237 0 353 0 217 0.333 0984 0 288 0 237 0336 0079 0270 0 196 0.260 0 320 -0 3 0 2 0 457 0 204 1 390 0 167 0 224 0 156 0 079 0 041 1 818 0.027 0.310 -0.277 -0.274 0.173 0.325 0.744 -0.244 -0 226 0.535 0.484 0.007 5,302 0,068 -0.043
-0.279 0361 -0 2 4 2 0 249 0.256 0.202 0.807 0.063 0.349 0.336 O. 1 4 2 0.219 0.321 0.251 0 318 0282 0.338 0 327 -0329 0299 -0 197 0 329 0 314 0 332 0,183 0.065 0.072 0.258 0.109 0.328 -0.294 0.345 0 403 0321 0 287 0 271 0 292 0 318 0 324 0333 0.558 0 270 0 300 0 289 0 208 0.330 0530 O. 1 9 8 -0.334 0,009 -0.259 0.456 0.550 1.908 0.322 -0.297 0.889 8.207 1.580 0.351 0.256 0,297
-0427 -0.367 1 377 0.328 0.062 0928 0.144 0.402 0 384 0 340 0 753 -0 289 0 049 0 934 0.159 0 282 0.316 -0 296 0 250 0.135 2230 0 275 0.443 0 239 0 695 -0 2 5 2 0 199 0.876 7 153 0 214 0 000 0352 -0.390 0 340 -0 3 9 1 0 310 0 368 0 203 0 439 0280 0 155 0 170 0 166 0 376 0 170 0 452 1 813 0498 -0.195 -0 3 0 4 0.433 0,427 0.761 0623 -0 171 -0.320 -0.791 -0291 0558 0 904 0 362 0.710
5996 0.838 -0.519 0.181 0.051 -0.429 0.026 0.199 0,285 0.187 -0.492 0.459 -0.225 0 404 0 100 0.140 0 097 -0 169 0 227 0274 -0 639 0 213 0.008 -0 2 1 4 -0.632 -0.131 0 177 0.597 -1129 0 215 0 160 -0409 4.577 0187 0 248 0 189 0 097 0 223 .0.220 0 084 1 784 0 128 0073 0 158 0 011 0.141 1212 0339 0086 -0166 -0.354 -0.051 0.719 0.071 -0.298 0.463 -0.212 0.047 0.364 -2.244 -0.158
0567 0 191 0 302 0.299 0.482 0289 0.885 0,352 0.509 0.189 -0.255 0.532 0328 0.243 0370 0.392 0299 0341 0.332 0.327 0 162 0327 0384 0.324 1.139 0 187 0345 0.202 0149 0317 0 278 0072 1 677 0518 0369 0.353 0 286 0 319 -0.147 0339 0154 0307 0354 0.356 -0 5 0 0 0028 3 694 -0 066 0173 0.399 0044 -1 4 2 5 0.329 -6.959 0.248 0.381 0638 1 602 0709 0518 0302
0.256
0.260
T A B L E 11.3 Varimax Principal C o m p o n e n t Scores o f fossil assemblages Species Astrononion antarcticus Astrononion echolsi Bulimina aculeata Cassidulina crassa rossensis
PC 1 0.384 -0.386 -0.386 -0.407
PC 2 -0.171 -0.062 -1 0 9 1 1. 6 2 5
PC 3 0.380 0.441 -4.538 1.168
PC 4 -0.343 -0.348 -0.222 -0. 4 0 6
PC 5 0.200 I 0.160 I -1.009 O. 6 7 2
0.235 0.280 -0 083 0.350 -0.683 3 26~ 0.84E 0.07 0 15 0 35C 0 17~ 0.31C 0 481 0.28? 0 36C 0.581 029g 0 169 0.277 0176 -0 837 0.258 0 248 0.355 0220 0 456 0 424 7221 1854 0 298 0.630 0 034 0 954 0291 0 038 0 275 0 465 0 304 0 131 0299 0335 0 228 0 360 0 030 0 140 0 223 1 670 0 171 0379 -0357 0 355 0 765 0.340 1 072 0296 0 325 0434 0544 0.213 0.835 0 163 0 291
281
BENTHIC FORAMINIFERAL ASSEMBLAGES FROM EASTERN WEDDELL SEA
Cibicides bertheloti Cibicides corpulentus Cibicidesgrossepunctatus Cibicides Iobatulus Cibicidoides cf. wue/lerstorfi Cibicidoidesspp. Eggerella bradyi Eggere/lasp. Ehrenbergina glabra Epistominella exigua Epistominelia sp.A Fissurina spp. Fursenkoina earlandi Globocassidulina biota G/obocassidulinasubglobosa Gyroidina orbicularis Gyroidina sp.klein Kareriella novangliae/bradyi Laoenaspp. Laticarmina pauperata Lenticulina spp. Martinotie/la nodulosa Meloniszaa~dami Mi/iammina arenacea Nonione//a I)radyi Nonionella iridea Nuttalides umbonifer Oridorsalis umbonatus Parafissurina spp. Pu/lenia bulloides Pullenia simplex Pullenia subcarinata Pyrgo murrhina Trifarina earlandi Tri/oculina sp./fr~qida
-0.046 -0.261 -0.267 -0.291 -0. 4 7 2 -0.185 1.034 -0.394 -0.460 0.281 -0.358 0.152 -0.199 -0.389 0.435 -0.064 0.441 -0.256 -0.235 1.266 -0,341 0.228 -0.296 -0.407 -0.403 -0.303 -0.913 5.562 -0.292 -0.389 -0.316 0.141 -0.267 0.063 -0.236
-0.131 -0.330 -(5.318 0.377 -0.380 -0.335. -0.526 -0.235 0.547 -0.365 1.820 0.450 0.105 -0.328 -0.114 -0.387 -0.358 -0.369 -0.359 -0.385 -0.375 -0.080 -0.378 -0.545 -0.001 -0.107 -0.123 0.034 -0.371 -0.428 -0.307 -0.394 -0.372 5.187 -0.419
0.155 0.325 0.343 0.642 0.345 0.281 -0.433 0.420 0.768 0.007 1.397 0.397 -1.607 0.348 -0.948 0.281 0.255 0.323 0.167 0.136 0.306 0.101 0.312 -1.860 0.558 0.079 0.219 0.222 0.324 -0.276 0.178 0.165 0.302 -1.858 0.173
-0.225 -0.387 -0.378 -0.360 -0.017 -0.019 -0.324 -0.345 -0.232 2.509 -0.338 0.040 -0.247 -0.346 0.073 -0.441 0.092 -0.359 -0.052 -0.617 -0.264 0.327 -0.367 -0.321 -0.357 -0.403 5.283 0.437 -0.350 -0.248 -0.332 0.394 -0.277 0.141 -0.371
Acknowledgements We acknowledge the assistance of R.V. Polarstern's crew and master during cruise ANTIV/3. We thank M.M. Rutgers van der Loeff and H.W. Hubberten for discussion. We are grateful to M.J. Hambrey who thoroughly improved the English text, and to M. Heyn who carefully performed the photographic work and assisted in the preparation of the plates. Part of the work of A.M. was sponsored by the D.A.A.D. (Deutscher Akademischer Austauschdienst) as part of the NATO Science Fellowship Programme. This is A.W.I. publication No. 267. References Anderson, J.B., 1975. Ecology and distribution of foraminifera in the Weddell Sea of Antarctica. Micropaleontology, 21 ( 1): 69-96. Barker, P.F., Kennett, J.P. et al., 1988. Proc. Ocean Drilling Program, Initial Rep., 113: 213-214.
0.187 0.23¢ 0.221 O.04E O. 113 0.35,4 0.44; -0.03~= -0.387 0.39E -0.41 .¢, -0.027 1.40E 0.21 ,= 0.31=~ 0.31 ,~ 0.30E 0.23C 0.081 0.64E 0.271 - 5 . 5 9 ,= 0.25.d 0.07"/ O. 06-. -0,66E 0.31E -0.003 O. 23,E -O.05E 0.22E 0.40¢~ 0.30,q 0.493 0.33;
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