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Recent Arctic marine diatom assemblages from bottom sediments in Baffin Bay and Davis Strait
Marine Micropaleontology, 10 (1986): 327--341 Elsevier Science Publishers B.V., Amsterdam --Printed in The Netherlands
327
R E C E N T ARCTIC MARINE DIATOM ASSEMBLAGES FROM BOTTOM SEDIMENTS IN B A F F I N BAY AND DAVIS S T R A I T
KERSTIN M. WILLIAMS Institute o f Arctic and Alpine Research, Campus Box 450, University of Colorado, Boulder, CO 80309 (U.S.A.)
(Revised version accepted October 7, 1985)
Abstract Williams, K.M., 1986. Recent Arctic marine diatom assemblages from bottom sediments in Baffin Bay and Davis Strait, Mar. Micropaleontol., 10: 327--341. This study investigates the present geographical boundaries and environmental limits of the diatom flora in the Baffin Bay and Davis Strait area. Seventy-four sea floor surface samples were examined. The raw data were analyzed with the CABFAC factor analysis program. Five factor assemblages, explaining 87% of the observed variance, emerged from this test. The statistically most important assemblage is the "Baffin Current assemblage", composed of Thalassiosira gravida spores. The second assemblage is the "summer pack ice assemblage", consisting of Actinocyclus curvatulus, with a lesser contribution of Thal~ssiosira trifulta. A third assemblage, dominated by Thalassiosira hyalina, is located along the southwest coast of Greenland, indicating low ice concentration, The fourth assemblage consists of Porosira sp. spores and indicates fast ice conditions. The fifth assemblage is dominated by Thalassionema nitzschioides and Porosira glacialis (vegetative cells), and indicates the coastal environment. Diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses, such as salinity and ice conditions. These findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments.
Introduction T he Baffin Bay and Davis Strait area (Fig. 1) has b e c o m e i m p o r t a n t over t h e last decade f o r oil and mineral exploration. In addition, intensive studies are being c o n d u c t e d on the climatological, oceanographic and geological history o f t h e area (e.g. Andrews, 1985). T h e region is also t he subject o f an active debate o n the causes o f ice-sheet growth and decay. Some paleoenvironmental studies have been d o n e on marine cores f r o m Baffin Bay and Davis Strait and f r o m t he Baffin Island shelf and fjords (i.e. Fillon and Duplessy, 1980; Aksu, 1981, 1985; Osterman, 1982; Fillon, 1985; Mudie and Short, 1985). These studies have c o n c e n t r a t e d mainly on t he cal0377-8398/86/$03.50
careous m i crofauna (Vilks, 1964, 1974, 1980; Osterman, 1982), pollen (Mudie and Short, 1985) and sedimentology (Aksu, 1981; Fillon et al., 1981; Osterman and Andrews, 1983). T he research r e p o r t e d here was u n d e r t a k e n t o determine how marine diatoms, deposited in t he surface sediments, reflect different oceanographic environments in the m o d e r n Baffin Bay--Davis Strait area. This informat i on t h e n can be used t o infer past climatological and oceanographic conditions, as recorded in marine cores. No previous work on di at om t hanat ocoenoses has been r e p o r t e d f r o m Baffin Bay and Davis Strait. However, research has been carried o u t in the N o r t h Pacific where m o d e m di at om floras preserved in t h e sediments have
© 1986 Elsevier Science Publishers B.V.
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329 been analyzed using core tops and grab sampies (e.g. Joust, 1962; Kanaya and Koizumi, 1966; Sancetta, 1979, 1982). Relatively few investigators have reported on the modern flora in the sediments of other oceans, although many papers deal with down-core analyses from Antarctica (e.g. Burckle, 1972), the Atlantic Ocean (Schrader, 1977L and the Indian and Pacific Oceans (Joust, 1962; Sancetta, 1979). This lack of attention to
modern floras is unfortunate, because such studies are important and can yield significant information on past climatological and oceanographic change (Sancetta, 1983). Environment The physical oceanography and ice regime of the study area have been described by Aksu (1981), Osterman (1982), Williams
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330 (1984) and others. Baffin Bay is located between Baffin Island and Greenland (Fig. 1). It extends north into a series of channels which connect the Arctic Ocean with Baffin Bay. Water depths range, shown by contour lines on Fig. 1, from ca. 200 m to 2400 m. Davis Strait is shallow, with a maximum depth of 600--800 m. The circulation in Baffin Bay and Davis Strait is counter-clockwise and is driven by currents entering the area both from the Arctic Ocean (the cold Baffin Current) and the Atlantic (the West Greenland Current, Fig. 2). The most important factors controlling the ice regime in Baffin Bay, besides temperature, are ocean currents and, to a lesser degree, wind direction (Markham, 1981). The cold Baffin Current causes early (late September) ice build-up in the northwest part of Baffin Bay. During the next months ice spreads rapidly, and by December ice covers all of Baffin Bay (Markham, 1981), with the exception of the polynya in Smith Sound. Ice break-up is initiated at the end of April, and by the middle of June the west coast of Greenland is clear of ice. Pack ice can last as long as August in west central Baffin Bay. Two major areas of shore-fast ice can be recognized, one along the east coast of Baffin Island, the other (a relatively smaller one) southeast of Thule, in Melville Bay (Weaver et al., 1978). The depth varies with geographical location. The f a s t ice edge along the Baffin Island follows the 180-m contour, whereas along the Siberian coast it runs along the 25-m contour (Zubov, 1945; in: Weaver et al., 1978).
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Techniques and sample preparation
Sediment samples from the sea bed surface were provided by the Bedford Institute of Oceanography, Halifax, Canada, and Grinlands Fiskeriunders~kelser, Denmark (Fig. 3 and Table I). Initially, 90 samples were processed. After eliminating barren samples and
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331
samples with fewer than 30 specimens per slide, 74 samples were left. It is n o t possible to ascertain whether the samples have been reworked. In general, the preservation of the diatoms seems to be fairly good, with many delicate features preserved in the frustules. The samples were prepared as follows: (1) A b o u t 0.1--0.2 g of the sample was boiled for 2 min in dilute HC1. (2) After all the car-
bonate was dissolved, the material was centrifuged, arid the HC1 carefully decanted. (3) The samples were washed with distilled water and again centrifuged. The last step was repeated until no acid was left in the sample. Next, a few drops o f the centrifuged sample were withdrawn with a disposable pipette. Slides were made from this sample and mounted in Hyrax. Two, sometimes three,
TABLE I Sample locations, Baffin Bay/Davis Strait No. Sample no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
Lat. N
HU77-021-089 59034.6 ' HU77-021-108 60°05 ' HU77-021-117 60°00.10 ' HU77-024-012 6 8 ° 0 7 ' 1 9 '' HU77-024-013 69°58 ' HU77-024-017 73°41'30" HU77-024-021 7 1 ° 1 5 ' 4 0 '' HU77-024-024 7 1 ° 1 3 ' 4 0 '' HU77-024-028 7 3 0 4 1 ' 5 9 '' HU74-026-003 6 6 0 2 0 ' 0 8 '' HU78-026-029 71°42'09" HU78-026-032 7 1 o 3 5 ' 5 0 '' HU78-026-035 7 1 0 1 4 ' 5 9 '' HU78-026-038 7 1 0 3 2 ' 4 7 '' HU78-026-039 7 1 ° 2 3 ' 3 5 '' HU78-026-043 7 1 ° 2 9 ' 2 0 '' HU78-026-044 7 0 ° 5 8 ' 1 3 '' HU77-027-018 6 0 o 3 7 ' 2 0 '' HU77-027-023 6 4 ° 1 8 ' 0 0 '' HU77-027-025 64°02.04 ' HU77-027-029 62°58.03 ' HU77-027-031 61°56.40 ' HU78-029-023 71°02.02 ' HU78-029-024 P 71o13.02 ' HU78-029-024 G 71°13.02 ' HU78-029-037 68°15.05 ' HU79-018-071 6 4 ° 4 5 ' 2 0 '' HU79-019-078 5 7 ° 2 3 ' 1 0 '' HU79-019-081 57°35'34" HU79-019-082 5 7 ° 3 7 ' 5 6 '' HU79-019-083 5 7 ° 2 3 ' 5 5 '' HU79-019-084 4 7 ° 1 3 ' 5 9 '' HU79-019-093 5 6 ° 4 1 ' 2 5 '' HU79-019-094 5 6 ° 0 ' 3 1 '' HU79-019-095 5 6 ° 4 8 ' 0 6 '' HU79-019-100 5 6 ° 2 0 ' 4 1 '' HU79-019-102 5 6 ° 2 3 ' 2 1 ''
Long. W
Depth (m)
No. Sample no.
Lat. N
Long. W
61054.40 , 62°24.08 ' 63°30.07 ' 6 1 ° 2 0 ' 0 9 '' 6 2 ° 4 6 ' 1 0 '' 6 4 ° 3 3 ' 0 7 '' 7 0 ° 2 6 ' 5 9 '' 6 9 o 3 5 ' 5 9 '' 7 0 ° 2 9 ' 2 0 '' 6 1 ° 0 1 ' 0 8 '' 6 9 ° 4 6 ' 0 9 '' 7 0 ° 2 5 ' 4 0 '' 6 9 ° 2 3 ' 5 9 '' 70°44'19" 7 1 0 5 2 ' 5 0 '' 70°26'09" 7 0 ° 3 2 ' 2 9 '' 6 0 ° 2 7 ' 4 0 '' 6 2 ° 5 9 ' 0 0 '' 63°55.09 ' 63°00.08 ' 63°26.09 ' 71°29.08 ' 70°45.06 ' 70°45.06 , 65°12.09 ' 5 7 ° 2 8 ' 4 0 '' 59°43'40" 6 0 ° 1 1 ' 2 4 '' 6 0 ° 1 8 ' 3 5 '' 6 0 ° 4 4 ' 5 0 '' 6 0 ° 4 0 ' 0 9 '' 5 9 ° 4 4 ' 1 6 '' 5 9 ° 4 0 ' 1 1 ''
165 230 221 1682 2090 1500 476 183 1463 278
38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
7 4 ° 1 5 ' 2 9 '' 74°15'59" 7 3 ° 5 5 ' 5 9 '' 73°52'59" 7 3 ° 4 5 ' 0 0 '' 7 3 o 4 6 ' 3 0 '' 7 1 ° 4 1 ' 1 0 '' 71°43'20" 7 1 ° 4 7 ' 5 5 '' 7 0 ° 4 9 ' 4 0 '' 66°31'29" 62°29'53" 6 2 ° 1 0 ' 2 9 '' 7 1 ° 5 8 ' 0 8 '' 7 3 ° 3 4 ' 2 0 '' 73°24'06" 73°54'06" 72°15'00" 7 4 ° 5 8 ' 0 8 '' 7 4 ° 2 3 ' 0 8 '' 74°40'08" 74°45'06" 74°52'08" 7 4 ° 5 7 ' 0 6 '' 7 3 ° 5 0 ' 4 0 '' 63°29 ' 65°55 , 66°41 ' 66°10 ' 66°24 ' 66°32 ' 67°00 ' 67°30 ' 67o45 , 66°41 ' 67°00 ' 67°15 '
81°16'40" 810126'40" 81°16'40" 81011'20" 81°08'59" 8 1 ° 0 9 ' 2 0 '' 72°12'50" 72°14'10" 7 2 ° 2 2 ' 4 0 '' 6 7 ° 5 9 ' 2 0 '' 61°13'20" 6 3 ° 5 5 ' 5 6 '' 6 2 ° 5 6 ' 2 5 '' 60°19'20" 61°08'40" 6 2 ° 0 7 ' 0 8 '' 64°09'00" 62°00'08" 6 4 ° 0 6 ' 0 0 '' 6 4 ° 4 2 ' 0 0 '' 62°00'00" 6 1 ° 3 0 ' 0 0 '' 6 0 ° 3 9 ' 0 0 '' 60°06'00" 6 2 0 2 9 ' 4 0 '' 51°36 , 54006 ' 54°06 ' 55°34 ' 55°23 ' 56°19 ' 56°48 ' 56°15 ' 57°15 ' 55°09 ' 54020 ' 54o13 '
59°13'09" 5 9 ° 1 5 ' 5 3 '' 5 8 ° 5 8 ' 1 3 ''
122 117 -574 375 281 155 197 100 512 603 832 832 457 118 159 150 137 150 192 112 132 165 90 125
HU81-045-016 HU81-045-017 HU81-045-018 HU81-045-019 HU81-045-020 HU81-045-021 HU81-045-022 HU81-045-025 HU81-045-026 HU81-045-029 HU81-045-037 HU81-045-042 HU81-045-047 70-K 074' 70-K 108 70-K 109 70-K 129 7 0 - K 131 70-K 141 70-K 185 70-K 188 70°K 189 7 0 - K 191 70-K 192 7 0 - K 201 7503 75~ 15 7531 7537 7540 7541 7551 7564 7571 76- 5 2 9 1 76- 5 2 9 7 76- 5 3 0 1
Depth (m) 825 760 622 768 260 459 9 146 198 118 133 365 900 430 550 880 700 250 1300 500 680' 850 740 580 200 80 475 224 222 198 580 134 220 101 70 50
332 TABLE II Varimax factor matrix Comm.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
HU77-021-089 HU77-021-108 HU77-021-117 HU77-024-012 HU77-024-013 HU77-024-017 HU77-024-021 HU77-024-024 HU77-024-028 HU77-024-003 HU78-026-029 HU78-026-032 HU78-026-035 HU78-026-038 HU78-026-039 HU78-026-043 HU78-026-044 HU77-027-018 HU77-027-023 HU77-027-025 HU77-027-029 HU77-027-031 HU78-029-023 HU78-029-024 HU78-029-024 HU78-029-037 HU79-018-071 HU79-019-078 HU79-019-081 HU79-019-082 HU79-019-083 HU79-019-084 HU79-019-093 HU79-019-094 HU79-019-095 HU79-019-100 HU79-019-102 HU81-045-016 HU81-045-017 HU81-045-018 HU81-045-019 HU81-045-020 HU81-045-021 HU81-045-022 HU81-045-025 HU81-045-026 HU81-045-029 HU81-045-037 HU81-045-042 HU81-045-047
0.967 0.865 0.946 0.841 0.804 0.794 0.935 0.953 0.907 0.968 0.971 0.972 0 855 0 931 0 951 0.927 0.486 0.645 0.893 0 961 0.921 0.921 0.545 0.561 0.868 0.783 0.817 0.969 0.985 0.887 0.967 0.991 0.988 0.991 0.981 0.977 0.970 0.977 0.986 0.960 0.960 0.939 0.829 0.933 0.900 0.857 0.826 0.790 0.785 0.945
Factor 1
2
3
0.963 0.892 0.944 -0.003 0.080 -0.037 0.342 0.762 0.272 0.926 0.943 0.885 0 299 0.556 0556 -0.118 0.177 0.110 0.740 0.895 0.934 0.783 0.444 0 509 0.715 0.362 0.863 0.973 0.978 0.930 0.971 0.980 0.981 0.984 0.980 0.970 0.960 0,946 0.969 0.942 0.921 0.927 0.812 0.707 0.632 0.736 0.032 0.652 0.344 0.941
0.127 0.100 0.146 0.124 0.163 0.116 0.901 - 0 . 0 0 5 0.885 0.020 0.876 - 0 . 0 0 8 0.482 0.026 0.153 0.080 0.796 0.036 0.282 0.094 0.122 0.120 0.222 0.085 0231 0.037 0.168 0.049 0.360 0.045 0.326 0 348 0.223 - 0 . 0 0 0 0.763 0.008 0.545 0.073 0.347 0.091 0.141 0.095 0.518 0.067 0.573 0.047 0.524 0.039 0.533 0.061 0.724 0.066 0.018 0.056 0.075 0.106 0.068 0.136 0.046 0.097 0.070 0.083 0.113 0.092 0.071 0.120 0.078 0.100 0.076 0.101 0.068 0.137 0.076 0.186 0.221 0.080 0.167 0.092 0.172 0.069 0.164 0.082 0.083 0.067 0.023 0.070 0.206 0.070 0.127 0.046 0.115 0.037 0.803 0.148 0.301 0.384 0.054 0.367 0.137 0.148
4 0.100 0.043 0.064 0.168 0.100 0.159 0.765 0.574 0.444 0.116 0.230 0.359 0.841 0.769 0.714 0.814 0.532 0.225 0.187 0158 0.121 0.170 0.081 0.119 0.262 0.167 0.043 0.073 0.071 0.056 0.059 0.071 0.069 0.074 0.064 0.058 0.068 0.111 0.082 0,095 0.067 0.061 0.041 0.145 0.122 0.470 0.133 0.077 -0.046 0.081
5 -0.063 0.178 0.109 0.008 0.069 O.023 -0.010 -0.114 -0.013 -0.093 -0.007 -0.062 -0.054 -0.012 0 026 0.153 0.349 -0.018 -0.081 -0.080 -0.074 -0.087 0.102 0.107 0.018 0.310 0.259 -0.031 0.020 0.090 0.097 0.069 0.036 0.029 0.021 0.099 0.054 0.122 0.063 0.168 0.271 0.254 0.404 0.603 0.684 0.283 0.375 0.349 0.726 0.111
333 TABLE II (continued)
Comm. 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
70-K-074 70-K-108 70-K-109 70-K-129 70-K-131 70-K-141 70-K-185 70-K-188 70-K-189 70-K-191 70-K-192 70-K-201 75-03 75-15 75-31 75-37 75-40 75-41 75-51 75-64 75-71 76-5291 76-5297 76-5301
0.583 0.907 0.310 0.883 -0.467 0.716 0.911 0.897 0.884 0.731 0.776 0.916 0.919 0.547 0.950 0.974 0.977 0.947 0.982 0.964 0.979 0.695 0.968 0.895
Variance Cum. var.
Factor 1
2
3
4
5
0.033 0.522 0.368 0.323 0.072 -0.053 0.238 0.175 -0.064 0.201 0.547 -0.077 0.175 -0.027 0.641 -0.025 0.419 0.208 0.343 0.293 0.931 0.066 -0.023 0.041
0.744 -0.014 0.789 0.052 0.371 0.041 0.859 0.034 0.657 0.009 0.843 0.024 0.921 0.031 0.925 0.040 0.937 -0.001 0.824 0.033 0.689 0.059 0.952 -0.006 0.173 0.915 -0.021 0.527 0.085 0.668 0.011 0.986 0.046 0.892 0.032 0.947 0.052 0.927 0.016 0.936 0.116 0.305 0.040 0.808 -0.015 0.966 -0.017 0.261
0.167 0.054 -0.154 0.202 -0.148 0.041 0.071 0.068 0.029 0.043 0.001 0.063 0.098 0.016 0.038 0.012 0.049 0.064 0.038 0.045 0.077 -0:023 0.001 0.075
0.003 -0.083 -0.108 -0.003 -0.086 0.033 -0.018 0.070 -0.015 0.095 0.003 -0.003 0.113 0.517 0.290 0.043 -0.010 -0.037 0.027 0.005 0.018 0.190 0.183 0.905
42.489 42.489
20.871 11.461 63.360 74.821
6.697 81.518
5.186 86.704
slides were m a d e f r o m each sample. W h e n possible, 2 0 0 - - 3 0 0 s p e c i m e n s were c o u n t e d per sample. More t h a n o n e slide usually h a d t o be a n a l y z e d t o r e a c h as high a n u m b e r o f d i a t o m frustules as possible. F o r centric d i a t o m s each frustule was c o u n t e d as o n e specimen, a n d m o r e t h a n half o f a frustule was r e q u i r e d b e f o r e it was a c c e p t e d as o n e s p e c i m e n ( t o avoid c o u n t i n g t h e various f r a g m e n t s o f a f m s t u l e as so m a n y specimens). P e n n a t e d i a t o m s also r e q u i r e d m o r e t h a n o n e half o f t h e frustule f o r t h e same reasons.
variables (ice c o n c e n t r a t i o n f o r April, J u n e , A u g u s t a n d O c t o b e r , plus s u m m e r surface salinity and surface t e m p e r a t u r e ; T a b l e III) were p l o t t e d against, a n d regressed against, t h e v a r i m a x factors. D a t a o n areal ice e x e n t are detailed, a c c u r a t e a n d n u m e r o u s , w i t h w e e k l y satellite r e p o r t s covering a p e r i o d f r o m a b o u t 1 9 7 7 t o t h e present. I have averaged t h e ice-coverage f o r each s t a t i o n f o r t h e first w e e k o f each m o n t h f o r t h e years 1 9 7 7 - - 1 9 8 3 . Water t e m p e r a t u r e a n d salinity d a t a (U.S. Navy, 1 9 6 8 ) are n o t as detailed as ice e x t e n t d a t a ; t h e harsh w e a t h e r
Statistical m e t h o d s and data analysis
makes sampling difficult.
D u e t o t h e large n u m b e r o f variables ( 7 4 s t a t i o n s a n d up t o 35 species p e r station), Q - m o d e f a c t o r analysis ( C A B F A C ; I m b r i e a n d K i p p , 1 9 7 1 ) was used t o a n a l y z e t h e d a t a (Table II). I n a d d i t i o n , six e n v i r o n m e n t a l
Results and discussion T h e C A B F A C f a c t o r analysis d i f f e r e n t i a t e d five discrete assemblages ( f a c t o r s ) , each occ u p y i n g a specific area in t h e Baffin B a y
334 TABLE III Average ice concentration for April, June, August and October, and average summer surface salinity (°/oo) and temperature (°C), for all stations Station no. 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
April 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 7/10 9/10 8/10 9/10 9/10 9/10 9/10 9/10 9/10 7/10 9/10 9/10 9/10 9/10 9110 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10
June 8/10 8/10 8/10 9/10 9/10 9/10 9/10 9/10 9/10 8/10 9/10 9/10 9/10 9/10 1 9/10 9/10 1110 7/10 9/10 8/10 6/10 1 1 1 9/10 1/10 8]10 8/10 8/10 8/10 8/10 8/10 8/10 8/10 8/10 8/10 6/10 6/10 8/10 8/10 8/10 8/10 1 9/10 1 9/10 8/10 9/10 8/10
August October 0 0 0 4/10 7/10 5/10 7/10 5/10 2/10 5/10 5/10 5/10 5/10 5/10 7/10 4/10 6/10 0 4/10 3/10 2/10 0 9/10 9/10 9/10 6/10 0 0 0 0 0 0 0 0 0 0 0 5/10 5/10 5/10 5/10 5/10 5/10 8/10 8/10 8/10 7/10 6/10 3/10 0
0 0 0 0 0 0 0 0 1/10 0 0 0 1/10 1/10 1/10 1/10 1/10 0 0 0 0 0 1/10 1/10 1/10 1/10 0 0 0 0 0 0 0 0 0 0 0 5/10 5/10 5/10 5/10 5/10 5/10 1/10 1/10 1/10 0 1/10 0 0
Salinity 31.0 31.0 31.0 30.0 27.0 27.0 30.0 30.0 32.0 31.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 34.0 31.0 31.0 31.0 31.0 30.0 30.0 30.0 30.0 33.0 31.0 31.0 31.0 31.0 31.0 31.0 31.0 31.0 31.0 31.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 31.0 31.0 32.0
Temperature 2.0 2.0 2.0 3.1 0.3 3.1 3.1 3.1 4.4 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 4.0 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 5.8 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 1.7 1.7 1.7 1.7 1.7 1.7 3.1 3.1 3.1 3.1 3.1 3.1 3.1
335 TABLE III (continued) Station no.
April June
August October
Salinity
Temperature
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
9/10 9/10 9/10 9/10 9/10 6/10 9/10 9/10 9/10 9/10 9/10 9/10 0 1/10 3/10 3/10 5/10 8/10 9/10 9/10 9/10 4/10 3/10 3/10
9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 0
5/10 4/10 3/10 3/10 3/10 5/10 4/10 3/10 3/10 3/10 3/10 3/10 1/10
0 0 0 0 0 0 0 0 0 0 0 0 0
0
0
0
0 0 0 0 1/10 1/10 1/10 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 33.0 30.0 33.0 33.0 33.0 33.0 33.0 33.0 33.0 33.0
3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 4.4 5.8 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4
and Davis Strait region (Williams, 1983). The total variance explained by the 5 factors (assemblages) is 87% (Table II). There is thus little information to be gained by including more factors.
Factor Assemblage 1, Baffin Current Assemblage This is the statistically most important assemblage. It is located along the east coast of Baffin Island and continues down to eastern Labrador (Fig. 4). This assemblage explains a variance of 42% of the total variance and is almost totally dominated by spores of Thalassiosira gravida Cleve. The most distinctive property o f the water mass corresponding to the distribution o f the Baffin Current F a c t o r is heavy, prolonged ice cover (October--July). Surface water temperature is very low (--1.5-2.0°C) and is influenced by the seasonal continental run-off from Baffin Island ice caps
and valley glaciers, fjord and sea ice decay, and increased surface-water outflow from the Arctic Ocean through the sounds in the north Canadian archipelago. Since the meltwater c o m p o n e n t o f the Baffin Current is large, the surface water salinity along the shelf zone is low during the summer (28.0--31.0%o). Fresh water run-off produces large quantities o f inorganic nutrients, such as Ca 2÷, Mg2÷, NO~- (Church, 1970). These can be utilized by p h y t o p l a n k t o n and probably play a significant role in the early season blooms: Large numbers of T. gravida spores are present in the sediments of the western part of the Bering Sea, along the shelf region (Sancetta, 1979). There are similarities between the western Bering Sea and the Baffin Island shelf in that both areas experience currents (the Baffin Current and the Kamchatka Current) o f low temperature and salinity sweeping along the shelf from the north. Both areas also show comparatively heavy ice concentrations during the winter.
336
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Fig. 4. T h e t h r e e m o s t i m p o r t a n t f a c t o r s in B a f f i n B a y a n d D a v i s S t r a i t . F a c t o r 1 = T. g r a v i d a ( s p o r e s ) , F a c t o r 2 = A . c u r v a t u l u s / T , trifulta, F a c t o r 3 = T. h y a l i n a .
The region of the Kamchatka Current has one of the highest primary productivities in the world. Productivity measurements for Baffin Bay have just begun, and few values are available. Unfortunately, these productivity measurements were taken "m late August
and early September and would not reflect conditions during spring diatom bloom. It is likely, however, that the western side of the bay has relatively high productivity, at least seasonally, as the Baffin Current sweeps along the fast ice edge and causes upwelling. Similar situations have been described by Alexander (1981) from the Bering Sea at icemelt time.
Factor Assemblage 2, Summer Pack Ice Assemblage The second most important factor assemblage, explaining 16% of the variance, is dominated by Actinocyclus curvatulus Grunow with a secondary contribution of Thalassiosira trifulta Fryxell. This assemblage is located in north central Baffin Bay and extends southwest into northern Davis Strait {Fig. 4). The main trend is along the 3--4~C isotherm and the assemblage might be used as an indicator of the Arctic/Subarctic oceanographic boundary. The A. curvatulus/T, trifulta assemblage is located in the northeast central Baffin Bay, an area characterized by heavy summer pack ice (generally 9/10 persisting 3/4 of the year). The pack ice usually forms in late October and lasts through July (Markham, 1981). Surface salinity in the region of the pack ice assemblage is low during ice melt season {July--August) and can reach such extreme low values as 27.0%0 (U.S. Navy, 1968), although an average of 30.0--31.0%o is probably a more meaningful figure. However, the salinity at 10 m depth has generally increased dramatically (Irwin et al., unpublished data) to 32.08--32.84%0. The highest diatom population densities in the water column sometimes do not occur at the surface. Experiments in Baffin Island {Clark Fjord) in autumn 1982 show diatom maxima directly associated with salinity/density changes of the water column (Williams, unpublished data). For the photic zone, this might mean
337 that nutrients accumulate on the pycnocline, which would increase the diatom populations. Or, it may simply provide a layer of suitable buoyancy for certain species. In addition, diatom population maxima can occur below the photic zone on occasion, although the diatoms are probably not viable at such depths. Thus the unusually low salinity might not have anything directly to do with the assemblage, depending on the depth preference of A. curvatulus and T. trifulta. Sampling of the water column would be necessary to determine this. On the other hand, Alexander (1980) and Shandelmeier and Alexander (1981) describe tremendous diatom blooms from the surface of highly stratified water in the North Pacific. Melting ice produces water of significantly lowered salinity, which increases the stability of the water column and seems to favor the diatom blooms. This has also been reported from Arthur Harbor, Antarctica (Krebs, 1983). In the Okhotsk and Bering Seas, A. curvatulus/A, divisus are considered indicators of the subarctic assemblage by Kanaya and Koizumi (1966), and occupy an area north of the subarctic front. Sancetta (1982) found the highest concentrations of A. curvatulus in the central part of the Okhotsk sea. T. trifulta has been reported by Sancetta (1982) from the same region in the Okhotsk sea as A. curvatulus. Jous~ (1962) reported T. eccentrica from this region. It is quite possible that this is the same as the newly named T. trifulta. Thus the areas favored by the curvatulus/trifulta assemblages are very similar, oceanographicaUy, in the North Pacific and Baffin Bay. The environmental implications of these taxa are of great importance for understanding paleoclimates, since they play a crucial role in the down-core floral assemblages in other places (e~. Sancetta, 1983). The Okhotsk Sea is presently unavailable for study, therefore Baffin Bay would be an ideal place for fieldwork to resolve the
present
338
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coastal planktonic species (Kanaya and Koizumi, 1966; Miller, 1982). In the Baffin Bay and Davis Strait area, the greatest concentrations of this species occur along the continental shelves. This factor never dominates except in one sample, in the West Greenland Current (sample 74). Salinity and temperature, together with ice coverage do not seem to be of importance for T. nitzschioides, as it is a ubiquitous species. P. glacialis as mentioned earlier seems to prefer ice marginal situations. Since there is a great deal of geographical scatter and the variance is low, it is possible that this factor is a statistical artifact. Regzession analysis
Factor 5
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Fig. 5. D i s t r i b u t i o n o f F a c t o r 4 = Porosira sp. (spores) and F a c t o r 5 = T. n i t z s c h i o i d e s / P , glacialis.
Factor Assemblage 5, Marine Littoral Assemblage This final factor accounts for 5% of the variance, and consists primarily of Thalassionema nitzschioides (Grunow) Peragallo with an almost equal contribution of P. glacialis (vegetative cells; Fig. 5). T. nitzschioides has been described as a
In search of a m e t h o d of inferring past climatological and oceanographic conditions from the floral assemblages (factors), I plotted graphs with the species assemblages as independent variables and environmental features as dependent variables. These plots revealed either no, or relatively weak relationships. Multiple-regression analyses, using Imbrie and Kipp's (1971) curvilinear model with species assemblages as independent variables, indicated correlations for the dependent variables as follows (associated R 2 values in parentheses); April ice (0.66), June ice {0.69), August ice (0.48), October ice (0.30), salinity (0.41) and summer water surface temperature (0.37). These correlations cannot be considered particularly strong. Thus, most of the environmental features (August ice, October ice, summer surface salinity and temperature) probably cannot be satisfactorily or accurately estimated with this method from the species assemblages at this time. This suggests further that this approach may not be fruitful in paleoenvironmental reconstruction in all areas. These results agree with those of Hsiao (1985), who found that light was the most important limiting factor in phytoplankton growth, in Frobisher Bay, southern Baffin Island, while temperature and salinity were not necessarily limiting by themselves.
339 There can be at least three reasons for the lack of strong relationships between environmental and species data. The first reason is mentioned above - - the most strongly limiting factor for p h y t o p l a n k t o n growth is availability of light. Temperature and salinity are simply not important to the same extent. Second, as mentioned earlier, the data are unequal in regard to accuracy and coverage (spatial and time); t h e y are fairly good as far as ice concentration is concerned, b u t very imprecise when it comes to salinity and temperature. The latter t w o have been measured at the water surface, in August -- the earliest the entire area is accessible to survey ships. Water-surface measurements are n o t necessarily important when it comes to diatoms which might not live at the surface at all. Diatoms do not usually attain their greatest blooms in August, b u t at ice-break-up, when it is very hard to get ships into the area. Third, according to Imbrie and Kipp (1971), the environmental variables must be mutually independent and n o t auto-correlated. F o r m y study area, however, it would be very difficult to consider this requirement fulfilled. F o r example, ice concentrations for different months are n o t independent, either mutually or with respect to temperature and salinity. Salinity obviously varies with ice decay and freeze-up, and so does temperature. As another example, diatoms release vitamins, organic matter and external metabolites into the water (Eppley, 1977), and these affect the growth rate and sequence of appearance o f the assemblages. This autocorrelation could be quite significant. Thus the principal o f mutual independence is violated.
Chaetoceros spores Chaetoceros has been called an indicator o f high productivity and large temperature fluctuations in the north Pacific (Sancetta, 1982). In Baffin Bay and Davis Strait, this genus is also richly represented, b o t h in the water column (McLaren Atlantic, 1978) and
directly underneath the ice (Hsiao, 1985; Williams, 1983). Chaetoceros spores are not limited to any one area in Baffin Bay and Davis Strait, but are quite frequent everywhere. Compared to the Bering Sea, Baffin Bay and Davis Strait are probably more homogenous as far as ice cover is concerned. Chaetoceros seems to be particularly abundant close to the ice edge during the early ice melt stages. This could account for the fairly even distribution of the genus with respect to area in the b o t t o m sediments. The exception is the area occupied b y Factor 2, the Pack-Ice Factor. I have n o t included Chaetoceros spores in the factor analyses for the following reasons: (1) Chaetoceros spores are often so numerous that they totally dominate other species that have more restricted geographical distributions. (2) They are very fragile and seem to be the first diatoms to be dissolved or broken into small fragments. Therefore, it might be incorrect to assume that t h e y were never present in samples where t h e y are not found. (3) Because they are easily fragmented, they are difficult to c o u n t accurately.
Conclusions
Five modern assemblages of diatoms, which explained 87% of the total variance emerged as significant. Each corresponds to a different marine environment in Baffin Bay and Davis Strait. The statistically most important assemblage is the Baffin Current factor, accounting for 42% of the variance (Fig. 4). This factor is characterized by Thalassiosira gravida spores. The second most important assemblage, with a variance of 16%, is dominated b y Actinocyclus curvatulus and Thalassiosira trifulta (Fig. 4). This is the " S u m m e r Packice Factor". The third assemblage, the "West Greenland Current Factor", explains 11% of the
340
variance and is characterized by T. hyalina (Fig. 4). Assemblage 4, with a variance of 7%, is the "Fast Ice" Factor, dominated by Porosira sp. spores {Fig. 5), and the fifth and final assemblage has a variance of 5% and is dominated by Thalassiosira nitzschioides, with a secondary component of Porosira glacialis, vegetative cells. These results are in agreement with those of others who have demonstrated a close relationship between the diatoms that characterize water masses and their areal distribution in surface sediments (Maynard, 1976; Sancetta, 1981). The regression analyses showed low correlations between diatom assemblages and environmental variables, suggesting that this approach to paleoenvironmental reconstruction is of limited use in this case.
Acknowledgements I would like to thank Dr. John Andrews for his untiring support and advice, and for constructively reviewing the manuscript. Drs. Lisa Osterman and Bill Krebs have patiently endured many long discussions and manuscript reviews, for which I am very grateful. Dr. Constance Sancetta and Dr. Lloyd Burckle of Lamont Doherty Geological Observatory spent many valuable hours discussing diatom taxonomy and ecology with ITle.
References Aksu, A.E., 1981. Late Quaternary stratigraphy, paleoenvironmentology and sedimentation history of Baffin Bay and Davis Strait. Thesis. Dalhousie Univ., Halifax, 771 pp. Aksu, A.E., 1985. Climatic and oceanographic changes over the past 400,000 years: evidence from deep-sea cores from Baffin Bay and Davis Strait. In: J.T. Andrews (Editor), Quaternary Environments: Eastern Canadian Arctic, Baffin Bay and West Greenland. Allen and Unwin, Boston, 774 pp. Alexander, V., 1980. Interrelationships between the
seasonal sea ice and biological regimes. Cold Reg. Sci. Technol., 2: 157--178. Alexander, V., 1981. Ice biota interactions: an overview. In: D.W. Hood (Editor), Oceanography and Resources. Off. Mar. Pollut. Assess. NOAA Dep. Inter. (BLM). Univ. Washington Press, Seattle, 780 pp. Andrews, J.T. (Editor), 1985. Late Quaternary Environments: Eastern Canadian Arctic, Baffin Bay and West Greenland. Allen and Unwin, Boston, 774 pp. Burckle, L.H., 1972. Diatom evidence bearing on the Holocene in the south Atlantic. Quat. Res., 2: 323--326. Church, M.A., 1970. Baffin Island Sandur. A study of Arctic fluvial environments. Thesis. Univ. British Columbia, Vancouver, 536 pp. Eppley, R.W., 1977. The growth and culture of diatoms. In: D. Warner (Editor), The Biology of Diatoms. Blackwell, Oxford, 498 pp. Fillon, R.H., 1985. Northwest Labrador Sea stratigraphy, sand input and paleoceanography during the past 160,000 years. In: J.T. Andrews (Editor), Quaternary Environments: Eastern Canadian Arctic, Baffin Bay and West Greenland. Allen and Unwin, Boston, 774 pp. Fillon, R.H. and Duplessy, J.C., 1980. Labrador Sea bio-, tephro-, oxygen isotopic stratigraphy and late Quaternary paleoceanographic trends. Can. J. Earth Sci., 17: 831--854. FiUon, R.H., Miller, G.H. and Andrews, J.T., 1981. Terrigeneous sand in Labrador Sea hemipelagic sediments and paleoglacial events on Baffin Island over the last 100,000 yrs. Boreas, 10: 107--124. Hasle, G.R., 1976. The biogeography of some marine planktonic diatoms. Deep-Sea Res., 23: 319-338. Hsiao, S.I.C., 1983. A checklist of marine phytoplankton and sea ice microalgae recorded from Arctic Canada. Nova Hedwigia, 37: 225--313. Hsiao, S.I.C., 1985. The growth of Arctic marine phytoplankton in Frobisher Bay. Arctic, 38(1): 31 --38. Imbrie, J. and Kipp, N.G., 1971. A new micropaleontological method for quantitative peleoclimatology: application to a late Pleistocene Carribean core. In: K.K. Turekian (Editor), The Late Cenozoic Glacial Ages. Yale University Press, New Haven, Conn., pp. 71--181. J o u ~ , A.P., 1962. Stratigraphic and paleographic investigations in the northwestern parts of the Pacific Ocean. Akad. Nauk. S.S.S.R., Inst. Oceanogr., Moscow, 258 pp. (in Russian). J o u ~ , A.P., 1977. Atlas of microorganisms in bott o m sediments of the Oceans. Nauka, Moscow, 31 pp. (in Russian).
341 Kanaya, T. and Koizurni, I., 1966. Interpretation of diatom thanatocoenoses from the North Pacific as applied to a study of core V20-130. Tohoku Univ. Sci. Rep., Sendal, 2nd Ser., Geol., 37: 89-130. Krebs, W.N., 1983. Ecology of neritic marine diatoms, Arthur Harbor, Antarctica. Micropaleontology, 29(3): 267--297. Markham, W.E., 1981. Ice Atlas. Canadian Arctic Waterways. Can. Gov. Publ. Cent., Quebec, 198 pp. Maynard, N.G., 1976. Relationship between diatoms in surface sediments of the Atlantic Ocean and the biological and physical oceanography of overlying waters. Paleobiology, 2:99--121. McLaren Atlantic, 1978. Report on biological studies, offshore cruises 77-2 and 77-3, April--June 1977 in the Davis Strait for Imperial Oil Ltd. Arctic Petroleum Operator's Project no. 134. Miller, U., 1982. Diatoms. In: E. Olausson (Editor), The Pleistocene/Holocene boundary in southwestern Sweden. Sver. Geol. Unders. Ser. C, 794, Arsbok, 76(7): 187--210. Mudie, P.J. and Short, S.K., 1985. Marine palynology of Baffin Bay. In: J.T. Andrews (Editor), Late Quaternary Environments: Eastern Canadian Arctic, Baffln Bay and West Greenland. Ailen and Unwin, Boston, 774 pp. Osterman, L.E., 1982. Late Quaternary history of southern Baffin Island, Canada: A study of foraminifera and sediments from Frobisher Bay, Baffin Island, N.W.T. Thesis. Univ. Colorado, Boulder, 380 pp. Osterman, L.E. and Andrews, J.T., 1983. Changes in glacial--marine sedimentation in core H077159, Frobisher Bay, Baffin Island, N.W.T.: A record of proximal, distal, and ice-raftingglacial-marine environments. In: B.F. Molnia (Editor)~ Glacial Marine Sedimentation. Plenum Press, N e w York, N.Y., 844 pp. Sancetta, C., 1979. Oceanography of the North Pacific during the last 18,000 years; evidence from fossil diatoms. Mar. Micropaleontol., 4: 103--123. Sancetta, C., 1981. Oceanographic and ecologic significance of diatoms in surface sediments of the Bering and Okhotsk Seas. Deep-Seas Res., 28A(8): 789--817. Sancetta, C., 1982. Distribution of diatom species in surface sediments of the Bering and Okhotsk Seas. Micropaleontology, 28(3): 221--257. Sancetta, C., 1983. Effect of Pleistocene glaciation upon oceanographic characteristics of the North
Pacific Ocean and Bering Sea. Deep-Sea Res., 38(8A): 851--869. Sancetta, C. and Robinson, S.W., 1983. Diatom evidence on Wisconsin and Holocene events in the Bering Sea. Quat. Res., 20: 232--245. Schandelmeier, L. and Alexander, V., 1981. A n analysis of the influence of ice on spring phytoplankton population structure in the southwest Bering Sea. Limnol. Oceanogr., 26(5): 935--943. Schrader, H.J., 1977. Diatom biostratigraphy Deep Sea Drilling Project Leg 37. In: F. Aumento and W.G. Melson (Editors), Initial Reports of the Deep Sea Drilling Project, 37. U.S. Government Printing Office, Washington, D.C., pp. 967--975. Treshnikov, A.F. and Baranov, G.I., 1977. Water masses of the Arctic Basin. In: M.J. Dunbar (Editor), Polar Oceans. Arctic Institute of North America, Montreal, pp, 17--29. U.S. Navy, 1968. Oceanographic Atlas of the Polar Seas, Part H, Arctic. U.S. Hydrogr. Off., Washington, D.C., Publ., 705, 149 pp. Vilks, G., 1964. Fomminiferal study of East Bay, MacKenzie King Island. District of Franklin: Polar Continental Shelf Project. Can. Geol. Surv., pap., 64-53: 1--26. Vilks, G., 1974. The distribution of planktonic foraminifera in the sediments and water of the Northwest Passage and northern Baffin Bay: A tool for paleo-oceanographic synthesis. Geol. Surv. Can., 74-30(1): 109--121. Vilks, G., 1977. Trends in the marine environment of the Canadian Arctic Archipelago during the Holocene. In: M.J. Dunbar (Editor), Polar Oceans. Arctic Institute of North America, Montreal, pp. 643--653. Vilks, G., 1980. Postglacial basin sedimentation of Labrador shelf. Geol. Surv. Can. Pap., 78(8): 28 pp. Weaver, R.L., Jacobs, D.J. and Crane, R.G., 1978. Ice regime. In: R.G. Barry and J.D. Jacobs (Editors), Energy Budget Studies in Relation to Fast Ice Break-Up Processes in Davis Strait. Inst. Arct. Alp. Res., Occas. Pap., 26: 643--653. Williams, K.M., 1983. Diatom analysis of Clark Fjord stations 3--7. In: C. Schafer and J. Syvitsky (Editors), S.A.F.E. Data Report. BIO/AGC, Halifax, 900 pp. Williams, K.M., 1984. Marine diatom assemblages from Baffin Bay and Davis Strait. Thesis. Univ. Colorado, Boulder, 111 pp. Zubov, N.M., 1945. Lydy Arktiki. Izdat. Glavsevmorputi, Moscow. (Translated as: Arctic Sea Ice. U.S. Navy Oceanographic Office, 1963, 491 pp.).
327
R E C E N T ARCTIC MARINE DIATOM ASSEMBLAGES FROM BOTTOM SEDIMENTS IN B A F F I N BAY AND DAVIS S T R A I T
KERSTIN M. WILLIAMS Institute o f Arctic and Alpine Research, Campus Box 450, University of Colorado, Boulder, CO 80309 (U.S.A.)
(Revised version accepted October 7, 1985)
Abstract Williams, K.M., 1986. Recent Arctic marine diatom assemblages from bottom sediments in Baffin Bay and Davis Strait, Mar. Micropaleontol., 10: 327--341. This study investigates the present geographical boundaries and environmental limits of the diatom flora in the Baffin Bay and Davis Strait area. Seventy-four sea floor surface samples were examined. The raw data were analyzed with the CABFAC factor analysis program. Five factor assemblages, explaining 87% of the observed variance, emerged from this test. The statistically most important assemblage is the "Baffin Current assemblage", composed of Thalassiosira gravida spores. The second assemblage is the "summer pack ice assemblage", consisting of Actinocyclus curvatulus, with a lesser contribution of Thal~ssiosira trifulta. A third assemblage, dominated by Thalassiosira hyalina, is located along the southwest coast of Greenland, indicating low ice concentration, The fourth assemblage consists of Porosira sp. spores and indicates fast ice conditions. The fifth assemblage is dominated by Thalassionema nitzschioides and Porosira glacialis (vegetative cells), and indicates the coastal environment. Diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses, such as salinity and ice conditions. These findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments.
Introduction T he Baffin Bay and Davis Strait area (Fig. 1) has b e c o m e i m p o r t a n t over t h e last decade f o r oil and mineral exploration. In addition, intensive studies are being c o n d u c t e d on the climatological, oceanographic and geological history o f t h e area (e.g. Andrews, 1985). T h e region is also t he subject o f an active debate o n the causes o f ice-sheet growth and decay. Some paleoenvironmental studies have been d o n e on marine cores f r o m Baffin Bay and Davis Strait and f r o m t he Baffin Island shelf and fjords (i.e. Fillon and Duplessy, 1980; Aksu, 1981, 1985; Osterman, 1982; Fillon, 1985; Mudie and Short, 1985). These studies have c o n c e n t r a t e d mainly on t he cal0377-8398/86/$03.50
careous m i crofauna (Vilks, 1964, 1974, 1980; Osterman, 1982), pollen (Mudie and Short, 1985) and sedimentology (Aksu, 1981; Fillon et al., 1981; Osterman and Andrews, 1983). T he research r e p o r t e d here was u n d e r t a k e n t o determine how marine diatoms, deposited in t he surface sediments, reflect different oceanographic environments in the m o d e r n Baffin Bay--Davis Strait area. This informat i on t h e n can be used t o infer past climatological and oceanographic conditions, as recorded in marine cores. No previous work on di at om t hanat ocoenoses has been r e p o r t e d f r o m Baffin Bay and Davis Strait. However, research has been carried o u t in the N o r t h Pacific where m o d e m di at om floras preserved in t h e sediments have
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329 been analyzed using core tops and grab sampies (e.g. Joust, 1962; Kanaya and Koizumi, 1966; Sancetta, 1979, 1982). Relatively few investigators have reported on the modern flora in the sediments of other oceans, although many papers deal with down-core analyses from Antarctica (e.g. Burckle, 1972), the Atlantic Ocean (Schrader, 1977L and the Indian and Pacific Oceans (Joust, 1962; Sancetta, 1979). This lack of attention to
modern floras is unfortunate, because such studies are important and can yield significant information on past climatological and oceanographic change (Sancetta, 1983). Environment The physical oceanography and ice regime of the study area have been described by Aksu (1981), Osterman (1982), Williams
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330 (1984) and others. Baffin Bay is located between Baffin Island and Greenland (Fig. 1). It extends north into a series of channels which connect the Arctic Ocean with Baffin Bay. Water depths range, shown by contour lines on Fig. 1, from ca. 200 m to 2400 m. Davis Strait is shallow, with a maximum depth of 600--800 m. The circulation in Baffin Bay and Davis Strait is counter-clockwise and is driven by currents entering the area both from the Arctic Ocean (the cold Baffin Current) and the Atlantic (the West Greenland Current, Fig. 2). The most important factors controlling the ice regime in Baffin Bay, besides temperature, are ocean currents and, to a lesser degree, wind direction (Markham, 1981). The cold Baffin Current causes early (late September) ice build-up in the northwest part of Baffin Bay. During the next months ice spreads rapidly, and by December ice covers all of Baffin Bay (Markham, 1981), with the exception of the polynya in Smith Sound. Ice break-up is initiated at the end of April, and by the middle of June the west coast of Greenland is clear of ice. Pack ice can last as long as August in west central Baffin Bay. Two major areas of shore-fast ice can be recognized, one along the east coast of Baffin Island, the other (a relatively smaller one) southeast of Thule, in Melville Bay (Weaver et al., 1978). The depth varies with geographical location. The f a s t ice edge along the Baffin Island follows the 180-m contour, whereas along the Siberian coast it runs along the 25-m contour (Zubov, 1945; in: Weaver et al., 1978).
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Sediment samples from the sea bed surface were provided by the Bedford Institute of Oceanography, Halifax, Canada, and Grinlands Fiskeriunders~kelser, Denmark (Fig. 3 and Table I). Initially, 90 samples were processed. After eliminating barren samples and
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331
samples with fewer than 30 specimens per slide, 74 samples were left. It is n o t possible to ascertain whether the samples have been reworked. In general, the preservation of the diatoms seems to be fairly good, with many delicate features preserved in the frustules. The samples were prepared as follows: (1) A b o u t 0.1--0.2 g of the sample was boiled for 2 min in dilute HC1. (2) After all the car-
bonate was dissolved, the material was centrifuged, arid the HC1 carefully decanted. (3) The samples were washed with distilled water and again centrifuged. The last step was repeated until no acid was left in the sample. Next, a few drops o f the centrifuged sample were withdrawn with a disposable pipette. Slides were made from this sample and mounted in Hyrax. Two, sometimes three,
TABLE I Sample locations, Baffin Bay/Davis Strait No. Sample no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
Lat. N
HU77-021-089 59034.6 ' HU77-021-108 60°05 ' HU77-021-117 60°00.10 ' HU77-024-012 6 8 ° 0 7 ' 1 9 '' HU77-024-013 69°58 ' HU77-024-017 73°41'30" HU77-024-021 7 1 ° 1 5 ' 4 0 '' HU77-024-024 7 1 ° 1 3 ' 4 0 '' HU77-024-028 7 3 0 4 1 ' 5 9 '' HU74-026-003 6 6 0 2 0 ' 0 8 '' HU78-026-029 71°42'09" HU78-026-032 7 1 o 3 5 ' 5 0 '' HU78-026-035 7 1 0 1 4 ' 5 9 '' HU78-026-038 7 1 0 3 2 ' 4 7 '' HU78-026-039 7 1 ° 2 3 ' 3 5 '' HU78-026-043 7 1 ° 2 9 ' 2 0 '' HU78-026-044 7 0 ° 5 8 ' 1 3 '' HU77-027-018 6 0 o 3 7 ' 2 0 '' HU77-027-023 6 4 ° 1 8 ' 0 0 '' HU77-027-025 64°02.04 ' HU77-027-029 62°58.03 ' HU77-027-031 61°56.40 ' HU78-029-023 71°02.02 ' HU78-029-024 P 71o13.02 ' HU78-029-024 G 71°13.02 ' HU78-029-037 68°15.05 ' HU79-018-071 6 4 ° 4 5 ' 2 0 '' HU79-019-078 5 7 ° 2 3 ' 1 0 '' HU79-019-081 57°35'34" HU79-019-082 5 7 ° 3 7 ' 5 6 '' HU79-019-083 5 7 ° 2 3 ' 5 5 '' HU79-019-084 4 7 ° 1 3 ' 5 9 '' HU79-019-093 5 6 ° 4 1 ' 2 5 '' HU79-019-094 5 6 ° 0 ' 3 1 '' HU79-019-095 5 6 ° 4 8 ' 0 6 '' HU79-019-100 5 6 ° 2 0 ' 4 1 '' HU79-019-102 5 6 ° 2 3 ' 2 1 ''
Long. W
Depth (m)
No. Sample no.
Lat. N
Long. W
61054.40 , 62°24.08 ' 63°30.07 ' 6 1 ° 2 0 ' 0 9 '' 6 2 ° 4 6 ' 1 0 '' 6 4 ° 3 3 ' 0 7 '' 7 0 ° 2 6 ' 5 9 '' 6 9 o 3 5 ' 5 9 '' 7 0 ° 2 9 ' 2 0 '' 6 1 ° 0 1 ' 0 8 '' 6 9 ° 4 6 ' 0 9 '' 7 0 ° 2 5 ' 4 0 '' 6 9 ° 2 3 ' 5 9 '' 70°44'19" 7 1 0 5 2 ' 5 0 '' 70°26'09" 7 0 ° 3 2 ' 2 9 '' 6 0 ° 2 7 ' 4 0 '' 6 2 ° 5 9 ' 0 0 '' 63°55.09 ' 63°00.08 ' 63°26.09 ' 71°29.08 ' 70°45.06 ' 70°45.06 , 65°12.09 ' 5 7 ° 2 8 ' 4 0 '' 59°43'40" 6 0 ° 1 1 ' 2 4 '' 6 0 ° 1 8 ' 3 5 '' 6 0 ° 4 4 ' 5 0 '' 6 0 ° 4 0 ' 0 9 '' 5 9 ° 4 4 ' 1 6 '' 5 9 ° 4 0 ' 1 1 ''
165 230 221 1682 2090 1500 476 183 1463 278
38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
7 4 ° 1 5 ' 2 9 '' 74°15'59" 7 3 ° 5 5 ' 5 9 '' 73°52'59" 7 3 ° 4 5 ' 0 0 '' 7 3 o 4 6 ' 3 0 '' 7 1 ° 4 1 ' 1 0 '' 71°43'20" 7 1 ° 4 7 ' 5 5 '' 7 0 ° 4 9 ' 4 0 '' 66°31'29" 62°29'53" 6 2 ° 1 0 ' 2 9 '' 7 1 ° 5 8 ' 0 8 '' 7 3 ° 3 4 ' 2 0 '' 73°24'06" 73°54'06" 72°15'00" 7 4 ° 5 8 ' 0 8 '' 7 4 ° 2 3 ' 0 8 '' 74°40'08" 74°45'06" 74°52'08" 7 4 ° 5 7 ' 0 6 '' 7 3 ° 5 0 ' 4 0 '' 63°29 ' 65°55 , 66°41 ' 66°10 ' 66°24 ' 66°32 ' 67°00 ' 67°30 ' 67o45 , 66°41 ' 67°00 ' 67°15 '
81°16'40" 810126'40" 81°16'40" 81011'20" 81°08'59" 8 1 ° 0 9 ' 2 0 '' 72°12'50" 72°14'10" 7 2 ° 2 2 ' 4 0 '' 6 7 ° 5 9 ' 2 0 '' 61°13'20" 6 3 ° 5 5 ' 5 6 '' 6 2 ° 5 6 ' 2 5 '' 60°19'20" 61°08'40" 6 2 ° 0 7 ' 0 8 '' 64°09'00" 62°00'08" 6 4 ° 0 6 ' 0 0 '' 6 4 ° 4 2 ' 0 0 '' 62°00'00" 6 1 ° 3 0 ' 0 0 '' 6 0 ° 3 9 ' 0 0 '' 60°06'00" 6 2 0 2 9 ' 4 0 '' 51°36 , 54006 ' 54°06 ' 55°34 ' 55°23 ' 56°19 ' 56°48 ' 56°15 ' 57°15 ' 55°09 ' 54020 ' 54o13 '
59°13'09" 5 9 ° 1 5 ' 5 3 '' 5 8 ° 5 8 ' 1 3 ''
122 117 -574 375 281 155 197 100 512 603 832 832 457 118 159 150 137 150 192 112 132 165 90 125
HU81-045-016 HU81-045-017 HU81-045-018 HU81-045-019 HU81-045-020 HU81-045-021 HU81-045-022 HU81-045-025 HU81-045-026 HU81-045-029 HU81-045-037 HU81-045-042 HU81-045-047 70-K 074' 70-K 108 70-K 109 70-K 129 7 0 - K 131 70-K 141 70-K 185 70-K 188 70°K 189 7 0 - K 191 70-K 192 7 0 - K 201 7503 75~ 15 7531 7537 7540 7541 7551 7564 7571 76- 5 2 9 1 76- 5 2 9 7 76- 5 3 0 1
Depth (m) 825 760 622 768 260 459 9 146 198 118 133 365 900 430 550 880 700 250 1300 500 680' 850 740 580 200 80 475 224 222 198 580 134 220 101 70 50
332 TABLE II Varimax factor matrix Comm.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
HU77-021-089 HU77-021-108 HU77-021-117 HU77-024-012 HU77-024-013 HU77-024-017 HU77-024-021 HU77-024-024 HU77-024-028 HU77-024-003 HU78-026-029 HU78-026-032 HU78-026-035 HU78-026-038 HU78-026-039 HU78-026-043 HU78-026-044 HU77-027-018 HU77-027-023 HU77-027-025 HU77-027-029 HU77-027-031 HU78-029-023 HU78-029-024 HU78-029-024 HU78-029-037 HU79-018-071 HU79-019-078 HU79-019-081 HU79-019-082 HU79-019-083 HU79-019-084 HU79-019-093 HU79-019-094 HU79-019-095 HU79-019-100 HU79-019-102 HU81-045-016 HU81-045-017 HU81-045-018 HU81-045-019 HU81-045-020 HU81-045-021 HU81-045-022 HU81-045-025 HU81-045-026 HU81-045-029 HU81-045-037 HU81-045-042 HU81-045-047
0.967 0.865 0.946 0.841 0.804 0.794 0.935 0.953 0.907 0.968 0.971 0.972 0 855 0 931 0 951 0.927 0.486 0.645 0.893 0 961 0.921 0.921 0.545 0.561 0.868 0.783 0.817 0.969 0.985 0.887 0.967 0.991 0.988 0.991 0.981 0.977 0.970 0.977 0.986 0.960 0.960 0.939 0.829 0.933 0.900 0.857 0.826 0.790 0.785 0.945
Factor 1
2
3
0.963 0.892 0.944 -0.003 0.080 -0.037 0.342 0.762 0.272 0.926 0.943 0.885 0 299 0.556 0556 -0.118 0.177 0.110 0.740 0.895 0.934 0.783 0.444 0 509 0.715 0.362 0.863 0.973 0.978 0.930 0.971 0.980 0.981 0.984 0.980 0.970 0.960 0,946 0.969 0.942 0.921 0.927 0.812 0.707 0.632 0.736 0.032 0.652 0.344 0.941
0.127 0.100 0.146 0.124 0.163 0.116 0.901 - 0 . 0 0 5 0.885 0.020 0.876 - 0 . 0 0 8 0.482 0.026 0.153 0.080 0.796 0.036 0.282 0.094 0.122 0.120 0.222 0.085 0231 0.037 0.168 0.049 0.360 0.045 0.326 0 348 0.223 - 0 . 0 0 0 0.763 0.008 0.545 0.073 0.347 0.091 0.141 0.095 0.518 0.067 0.573 0.047 0.524 0.039 0.533 0.061 0.724 0.066 0.018 0.056 0.075 0.106 0.068 0.136 0.046 0.097 0.070 0.083 0.113 0.092 0.071 0.120 0.078 0.100 0.076 0.101 0.068 0.137 0.076 0.186 0.221 0.080 0.167 0.092 0.172 0.069 0.164 0.082 0.083 0.067 0.023 0.070 0.206 0.070 0.127 0.046 0.115 0.037 0.803 0.148 0.301 0.384 0.054 0.367 0.137 0.148
4 0.100 0.043 0.064 0.168 0.100 0.159 0.765 0.574 0.444 0.116 0.230 0.359 0.841 0.769 0.714 0.814 0.532 0.225 0.187 0158 0.121 0.170 0.081 0.119 0.262 0.167 0.043 0.073 0.071 0.056 0.059 0.071 0.069 0.074 0.064 0.058 0.068 0.111 0.082 0,095 0.067 0.061 0.041 0.145 0.122 0.470 0.133 0.077 -0.046 0.081
5 -0.063 0.178 0.109 0.008 0.069 O.023 -0.010 -0.114 -0.013 -0.093 -0.007 -0.062 -0.054 -0.012 0 026 0.153 0.349 -0.018 -0.081 -0.080 -0.074 -0.087 0.102 0.107 0.018 0.310 0.259 -0.031 0.020 0.090 0.097 0.069 0.036 0.029 0.021 0.099 0.054 0.122 0.063 0.168 0.271 0.254 0.404 0.603 0.684 0.283 0.375 0.349 0.726 0.111
333 TABLE II (continued)
Comm. 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
70-K-074 70-K-108 70-K-109 70-K-129 70-K-131 70-K-141 70-K-185 70-K-188 70-K-189 70-K-191 70-K-192 70-K-201 75-03 75-15 75-31 75-37 75-40 75-41 75-51 75-64 75-71 76-5291 76-5297 76-5301
0.583 0.907 0.310 0.883 -0.467 0.716 0.911 0.897 0.884 0.731 0.776 0.916 0.919 0.547 0.950 0.974 0.977 0.947 0.982 0.964 0.979 0.695 0.968 0.895
Variance Cum. var.
Factor 1
2
3
4
5
0.033 0.522 0.368 0.323 0.072 -0.053 0.238 0.175 -0.064 0.201 0.547 -0.077 0.175 -0.027 0.641 -0.025 0.419 0.208 0.343 0.293 0.931 0.066 -0.023 0.041
0.744 -0.014 0.789 0.052 0.371 0.041 0.859 0.034 0.657 0.009 0.843 0.024 0.921 0.031 0.925 0.040 0.937 -0.001 0.824 0.033 0.689 0.059 0.952 -0.006 0.173 0.915 -0.021 0.527 0.085 0.668 0.011 0.986 0.046 0.892 0.032 0.947 0.052 0.927 0.016 0.936 0.116 0.305 0.040 0.808 -0.015 0.966 -0.017 0.261
0.167 0.054 -0.154 0.202 -0.148 0.041 0.071 0.068 0.029 0.043 0.001 0.063 0.098 0.016 0.038 0.012 0.049 0.064 0.038 0.045 0.077 -0:023 0.001 0.075
0.003 -0.083 -0.108 -0.003 -0.086 0.033 -0.018 0.070 -0.015 0.095 0.003 -0.003 0.113 0.517 0.290 0.043 -0.010 -0.037 0.027 0.005 0.018 0.190 0.183 0.905
42.489 42.489
20.871 11.461 63.360 74.821
6.697 81.518
5.186 86.704
slides were m a d e f r o m each sample. W h e n possible, 2 0 0 - - 3 0 0 s p e c i m e n s were c o u n t e d per sample. More t h a n o n e slide usually h a d t o be a n a l y z e d t o r e a c h as high a n u m b e r o f d i a t o m frustules as possible. F o r centric d i a t o m s each frustule was c o u n t e d as o n e specimen, a n d m o r e t h a n half o f a frustule was r e q u i r e d b e f o r e it was a c c e p t e d as o n e s p e c i m e n ( t o avoid c o u n t i n g t h e various f r a g m e n t s o f a f m s t u l e as so m a n y specimens). P e n n a t e d i a t o m s also r e q u i r e d m o r e t h a n o n e half o f t h e frustule f o r t h e same reasons.
variables (ice c o n c e n t r a t i o n f o r April, J u n e , A u g u s t a n d O c t o b e r , plus s u m m e r surface salinity and surface t e m p e r a t u r e ; T a b l e III) were p l o t t e d against, a n d regressed against, t h e v a r i m a x factors. D a t a o n areal ice e x e n t are detailed, a c c u r a t e a n d n u m e r o u s , w i t h w e e k l y satellite r e p o r t s covering a p e r i o d f r o m a b o u t 1 9 7 7 t o t h e present. I have averaged t h e ice-coverage f o r each s t a t i o n f o r t h e first w e e k o f each m o n t h f o r t h e years 1 9 7 7 - - 1 9 8 3 . Water t e m p e r a t u r e a n d salinity d a t a (U.S. Navy, 1 9 6 8 ) are n o t as detailed as ice e x t e n t d a t a ; t h e harsh w e a t h e r
Statistical m e t h o d s and data analysis
makes sampling difficult.
D u e t o t h e large n u m b e r o f variables ( 7 4 s t a t i o n s a n d up t o 35 species p e r station), Q - m o d e f a c t o r analysis ( C A B F A C ; I m b r i e a n d K i p p , 1 9 7 1 ) was used t o a n a l y z e t h e d a t a (Table II). I n a d d i t i o n , six e n v i r o n m e n t a l
Results and discussion T h e C A B F A C f a c t o r analysis d i f f e r e n t i a t e d five discrete assemblages ( f a c t o r s ) , each occ u p y i n g a specific area in t h e Baffin B a y
334 TABLE III Average ice concentration for April, June, August and October, and average summer surface salinity (°/oo) and temperature (°C), for all stations Station no. 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
April 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 7/10 9/10 8/10 9/10 9/10 9/10 9/10 9/10 9/10 7/10 9/10 9/10 9/10 9/10 9110 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10
June 8/10 8/10 8/10 9/10 9/10 9/10 9/10 9/10 9/10 8/10 9/10 9/10 9/10 9/10 1 9/10 9/10 1110 7/10 9/10 8/10 6/10 1 1 1 9/10 1/10 8]10 8/10 8/10 8/10 8/10 8/10 8/10 8/10 8/10 8/10 6/10 6/10 8/10 8/10 8/10 8/10 1 9/10 1 9/10 8/10 9/10 8/10
August October 0 0 0 4/10 7/10 5/10 7/10 5/10 2/10 5/10 5/10 5/10 5/10 5/10 7/10 4/10 6/10 0 4/10 3/10 2/10 0 9/10 9/10 9/10 6/10 0 0 0 0 0 0 0 0 0 0 0 5/10 5/10 5/10 5/10 5/10 5/10 8/10 8/10 8/10 7/10 6/10 3/10 0
0 0 0 0 0 0 0 0 1/10 0 0 0 1/10 1/10 1/10 1/10 1/10 0 0 0 0 0 1/10 1/10 1/10 1/10 0 0 0 0 0 0 0 0 0 0 0 5/10 5/10 5/10 5/10 5/10 5/10 1/10 1/10 1/10 0 1/10 0 0
Salinity 31.0 31.0 31.0 30.0 27.0 27.0 30.0 30.0 32.0 31.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 34.0 31.0 31.0 31.0 31.0 30.0 30.0 30.0 30.0 33.0 31.0 31.0 31.0 31.0 31.0 31.0 31.0 31.0 31.0 31.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 30.0 31.0 31.0 32.0
Temperature 2.0 2.0 2.0 3.1 0.3 3.1 3.1 3.1 4.4 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 4.0 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 5.8 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 1.7 1.7 1.7 1.7 1.7 1.7 3.1 3.1 3.1 3.1 3.1 3.1 3.1
335 TABLE III (continued) Station no.
April June
August October
Salinity
Temperature
51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74
9/10 9/10 9/10 9/10 9/10 6/10 9/10 9/10 9/10 9/10 9/10 9/10 0 1/10 3/10 3/10 5/10 8/10 9/10 9/10 9/10 4/10 3/10 3/10
9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 9/10 0
5/10 4/10 3/10 3/10 3/10 5/10 4/10 3/10 3/10 3/10 3/10 3/10 1/10
0 0 0 0 0 0 0 0 0 0 0 0 0
0
0
0
0 0 0 0 1/10 1/10 1/10 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 32.0 33.0 30.0 33.0 33.0 33.0 33.0 33.0 33.0 33.0 33.0
3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 3.1 4.4 5.8 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4 4.4
and Davis Strait region (Williams, 1983). The total variance explained by the 5 factors (assemblages) is 87% (Table II). There is thus little information to be gained by including more factors.
Factor Assemblage 1, Baffin Current Assemblage This is the statistically most important assemblage. It is located along the east coast of Baffin Island and continues down to eastern Labrador (Fig. 4). This assemblage explains a variance of 42% of the total variance and is almost totally dominated by spores of Thalassiosira gravida Cleve. The most distinctive property o f the water mass corresponding to the distribution o f the Baffin Current F a c t o r is heavy, prolonged ice cover (October--July). Surface water temperature is very low (--1.5-2.0°C) and is influenced by the seasonal continental run-off from Baffin Island ice caps
and valley glaciers, fjord and sea ice decay, and increased surface-water outflow from the Arctic Ocean through the sounds in the north Canadian archipelago. Since the meltwater c o m p o n e n t o f the Baffin Current is large, the surface water salinity along the shelf zone is low during the summer (28.0--31.0%o). Fresh water run-off produces large quantities o f inorganic nutrients, such as Ca 2÷, Mg2÷, NO~- (Church, 1970). These can be utilized by p h y t o p l a n k t o n and probably play a significant role in the early season blooms: Large numbers of T. gravida spores are present in the sediments of the western part of the Bering Sea, along the shelf region (Sancetta, 1979). There are similarities between the western Bering Sea and the Baffin Island shelf in that both areas experience currents (the Baffin Current and the Kamchatka Current) o f low temperature and salinity sweeping along the shelf from the north. Both areas also show comparatively heavy ice concentrations during the winter.
336
\
76 e
G~
72' m m
]:::, Z
i.i
6 8 o-
64"
60 °50 ° I
Fig. 4. T h e t h r e e m o s t i m p o r t a n t f a c t o r s in B a f f i n B a y a n d D a v i s S t r a i t . F a c t o r 1 = T. g r a v i d a ( s p o r e s ) , F a c t o r 2 = A . c u r v a t u l u s / T , trifulta, F a c t o r 3 = T. h y a l i n a .
The region of the Kamchatka Current has one of the highest primary productivities in the world. Productivity measurements for Baffin Bay have just begun, and few values are available. Unfortunately, these productivity measurements were taken "m late August
and early September and would not reflect conditions during spring diatom bloom. It is likely, however, that the western side of the bay has relatively high productivity, at least seasonally, as the Baffin Current sweeps along the fast ice edge and causes upwelling. Similar situations have been described by Alexander (1981) from the Bering Sea at icemelt time.
Factor Assemblage 2, Summer Pack Ice Assemblage The second most important factor assemblage, explaining 16% of the variance, is dominated by Actinocyclus curvatulus Grunow with a secondary contribution of Thalassiosira trifulta Fryxell. This assemblage is located in north central Baffin Bay and extends southwest into northern Davis Strait {Fig. 4). The main trend is along the 3--4~C isotherm and the assemblage might be used as an indicator of the Arctic/Subarctic oceanographic boundary. The A. curvatulus/T, trifulta assemblage is located in the northeast central Baffin Bay, an area characterized by heavy summer pack ice (generally 9/10 persisting 3/4 of the year). The pack ice usually forms in late October and lasts through July (Markham, 1981). Surface salinity in the region of the pack ice assemblage is low during ice melt season {July--August) and can reach such extreme low values as 27.0%0 (U.S. Navy, 1968), although an average of 30.0--31.0%o is probably a more meaningful figure. However, the salinity at 10 m depth has generally increased dramatically (Irwin et al., unpublished data) to 32.08--32.84%0. The highest diatom population densities in the water column sometimes do not occur at the surface. Experiments in Baffin Island {Clark Fjord) in autumn 1982 show diatom maxima directly associated with salinity/density changes of the water column (Williams, unpublished data). For the photic zone, this might mean
337 that nutrients accumulate on the pycnocline, which would increase the diatom populations. Or, it may simply provide a layer of suitable buoyancy for certain species. In addition, diatom population maxima can occur below the photic zone on occasion, although the diatoms are probably not viable at such depths. Thus the unusually low salinity might not have anything directly to do with the assemblage, depending on the depth preference of A. curvatulus and T. trifulta. Sampling of the water column would be necessary to determine this. On the other hand, Alexander (1980) and Shandelmeier and Alexander (1981) describe tremendous diatom blooms from the surface of highly stratified water in the North Pacific. Melting ice produces water of significantly lowered salinity, which increases the stability of the water column and seems to favor the diatom blooms. This has also been reported from Arthur Harbor, Antarctica (Krebs, 1983). In the Okhotsk and Bering Seas, A. curvatulus/A, divisus are considered indicators of the subarctic assemblage by Kanaya and Koizumi (1966), and occupy an area north of the subarctic front. Sancetta (1982) found the highest concentrations of A. curvatulus in the central part of the Okhotsk sea. T. trifulta has been reported by Sancetta (1982) from the same region in the Okhotsk sea as A. curvatulus. Jous~ (1962) reported T. eccentrica from this region. It is quite possible that this is the same as the newly named T. trifulta. Thus the areas favored by the curvatulus/trifulta assemblages are very similar, oceanographicaUy, in the North Pacific and Baffin Bay. The environmental implications of these taxa are of great importance for understanding paleoclimates, since they play a crucial role in the down-core floral assemblages in other places (e~. Sancetta, 1983). The Okhotsk Sea is presently unavailable for study, therefore Baffin Bay would be an ideal place for fieldwork to resolve the
present
338
C) ;13
72 °
I'rt I"rl
coastal planktonic species (Kanaya and Koizumi, 1966; Miller, 1982). In the Baffin Bay and Davis Strait area, the greatest concentrations of this species occur along the continental shelves. This factor never dominates except in one sample, in the West Greenland Current (sample 74). Salinity and temperature, together with ice coverage do not seem to be of importance for T. nitzschioides, as it is a ubiquitous species. P. glacialis as mentioned earlier seems to prefer ice marginal situations. Since there is a great deal of geographical scatter and the variance is low, it is possible that this factor is a statistical artifact. Regzession analysis
Factor 5
\ Z
68o-
6 4 o-
Q .
[] 75-~oo °/o []
5 0 - 7 4 °/o
]
25-49
[],
%
o - 2 . °/o 600-
6,0 o
55 ° I
t
Fig. 5. D i s t r i b u t i o n o f F a c t o r 4 = Porosira sp. (spores) and F a c t o r 5 = T. n i t z s c h i o i d e s / P , glacialis.
Factor Assemblage 5, Marine Littoral Assemblage This final factor accounts for 5% of the variance, and consists primarily of Thalassionema nitzschioides (Grunow) Peragallo with an almost equal contribution of P. glacialis (vegetative cells; Fig. 5). T. nitzschioides has been described as a
In search of a m e t h o d of inferring past climatological and oceanographic conditions from the floral assemblages (factors), I plotted graphs with the species assemblages as independent variables and environmental features as dependent variables. These plots revealed either no, or relatively weak relationships. Multiple-regression analyses, using Imbrie and Kipp's (1971) curvilinear model with species assemblages as independent variables, indicated correlations for the dependent variables as follows (associated R 2 values in parentheses); April ice (0.66), June ice {0.69), August ice (0.48), October ice (0.30), salinity (0.41) and summer water surface temperature (0.37). These correlations cannot be considered particularly strong. Thus, most of the environmental features (August ice, October ice, summer surface salinity and temperature) probably cannot be satisfactorily or accurately estimated with this method from the species assemblages at this time. This suggests further that this approach may not be fruitful in paleoenvironmental reconstruction in all areas. These results agree with those of Hsiao (1985), who found that light was the most important limiting factor in phytoplankton growth, in Frobisher Bay, southern Baffin Island, while temperature and salinity were not necessarily limiting by themselves.
339 There can be at least three reasons for the lack of strong relationships between environmental and species data. The first reason is mentioned above - - the most strongly limiting factor for p h y t o p l a n k t o n growth is availability of light. Temperature and salinity are simply not important to the same extent. Second, as mentioned earlier, the data are unequal in regard to accuracy and coverage (spatial and time); t h e y are fairly good as far as ice concentration is concerned, b u t very imprecise when it comes to salinity and temperature. The latter t w o have been measured at the water surface, in August -- the earliest the entire area is accessible to survey ships. Water-surface measurements are n o t necessarily important when it comes to diatoms which might not live at the surface at all. Diatoms do not usually attain their greatest blooms in August, b u t at ice-break-up, when it is very hard to get ships into the area. Third, according to Imbrie and Kipp (1971), the environmental variables must be mutually independent and n o t auto-correlated. F o r m y study area, however, it would be very difficult to consider this requirement fulfilled. F o r example, ice concentrations for different months are n o t independent, either mutually or with respect to temperature and salinity. Salinity obviously varies with ice decay and freeze-up, and so does temperature. As another example, diatoms release vitamins, organic matter and external metabolites into the water (Eppley, 1977), and these affect the growth rate and sequence of appearance o f the assemblages. This autocorrelation could be quite significant. Thus the principal o f mutual independence is violated.
Chaetoceros spores Chaetoceros has been called an indicator o f high productivity and large temperature fluctuations in the north Pacific (Sancetta, 1982). In Baffin Bay and Davis Strait, this genus is also richly represented, b o t h in the water column (McLaren Atlantic, 1978) and
directly underneath the ice (Hsiao, 1985; Williams, 1983). Chaetoceros spores are not limited to any one area in Baffin Bay and Davis Strait, but are quite frequent everywhere. Compared to the Bering Sea, Baffin Bay and Davis Strait are probably more homogenous as far as ice cover is concerned. Chaetoceros seems to be particularly abundant close to the ice edge during the early ice melt stages. This could account for the fairly even distribution of the genus with respect to area in the b o t t o m sediments. The exception is the area occupied b y Factor 2, the Pack-Ice Factor. I have n o t included Chaetoceros spores in the factor analyses for the following reasons: (1) Chaetoceros spores are often so numerous that they totally dominate other species that have more restricted geographical distributions. (2) They are very fragile and seem to be the first diatoms to be dissolved or broken into small fragments. Therefore, it might be incorrect to assume that t h e y were never present in samples where t h e y are not found. (3) Because they are easily fragmented, they are difficult to c o u n t accurately.
Conclusions
Five modern assemblages of diatoms, which explained 87% of the total variance emerged as significant. Each corresponds to a different marine environment in Baffin Bay and Davis Strait. The statistically most important assemblage is the Baffin Current factor, accounting for 42% of the variance (Fig. 4). This factor is characterized by Thalassiosira gravida spores. The second most important assemblage, with a variance of 16%, is dominated b y Actinocyclus curvatulus and Thalassiosira trifulta (Fig. 4). This is the " S u m m e r Packice Factor". The third assemblage, the "West Greenland Current Factor", explains 11% of the
340
variance and is characterized by T. hyalina (Fig. 4). Assemblage 4, with a variance of 7%, is the "Fast Ice" Factor, dominated by Porosira sp. spores {Fig. 5), and the fifth and final assemblage has a variance of 5% and is dominated by Thalassiosira nitzschioides, with a secondary component of Porosira glacialis, vegetative cells. These results are in agreement with those of others who have demonstrated a close relationship between the diatoms that characterize water masses and their areal distribution in surface sediments (Maynard, 1976; Sancetta, 1981). The regression analyses showed low correlations between diatom assemblages and environmental variables, suggesting that this approach to paleoenvironmental reconstruction is of limited use in this case.
Acknowledgements I would like to thank Dr. John Andrews for his untiring support and advice, and for constructively reviewing the manuscript. Drs. Lisa Osterman and Bill Krebs have patiently endured many long discussions and manuscript reviews, for which I am very grateful. Dr. Constance Sancetta and Dr. Lloyd Burckle of Lamont Doherty Geological Observatory spent many valuable hours discussing diatom taxonomy and ecology with ITle.
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