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Oxygen and carbon isotope composition of Quaternary bivalve shells as a water mass indicator: Last interglacial and Holocene, East Greenland
Oxygen and carbon isotope cornposition ofQuaternary bivalve shells as 2 water mass indicator: Last intergkcial and Holocene, East Greenland
1. hntrnduction The isotopic pakoecoIogica1 sipal of arctic bivalves ha: previously been studied by Andre~,~ ( 1973 j, Hillaire-Marcel f 19&I ), Donnet- and N~lrd ( 19X6) and Israelson and Buchardt { 1991 1. The present paper aims to contribute to tiw intcrprctation of the imtopic composition of biva1x.e sRcII~ in the arctic environment xvith special emphasis on paleosaiinities.
Earlier inixxtigations have sho~~:n that marine intcrg~acial beds of Eemian age with a thermophilous ElOllL~SC fauna mist at several localities along the southern coast of Jameson Land. Interglacial she!ls from two !ocaIIries were analysed in this study. The first locality is a coastal clifi near Lang ~!~dselv ( Fig. 1 1. Petersen ( 1932) found s rich mollusc fauna in these sediments which were later described by Landvik et al. ( 1991) and Vosgerau ( I992 ). The marine sediments consist of
During the earlier part of the last ice qe the coast;!1 areas Of Jameson Lund acre covizred by sea. and from this period fJamcson Land m;trine episode) marine sediments ;~re preser~vd. The Jameson Land marine episode reflects a prolonged period of marine conditions in coastal East Greenland. The marine episode was interrupted several times by glacier- advances from the L-~panding Greenl;~nd ice sheet depositing subglacii~l a:ld glaciom;lrinc sediments on lhu corzst of Jamrsun Lund (Funder et ai.. 1991 ). From the Holocene. marine sediments indicate a reIative sea level up to SO m above the present ( Funder. i?78. 1990). A scctinn located in a n!- Imcsc~~ Land COSiLtt Cliflf On i;iS SCUI!~ coast (Fig. 1 ) has bwn studied. The horizontally laminated sand and silt layers display fluid escape structures and “flames” of silt protruding upu-clrds into overlyin layers. indicating high sedimentation rates. This interpretation is supported by the accelerator mass spectrometry (AMS) datin?s (Gulliksen et ~31,.1991 ). The dates indicate that the IowermOst 3 m of the section was deposited within a time period of less thaw 150 years (between 8480 and 5330 yr EP 1. The sedimet:ts contain abundant bi\.alve fossils zind .%I~u Irr4witicr is especially common.
3. Samgiing alld andytical
techniqws
All cxrjmined shells are well preserved and X-ray difiraction analyses shot+- th;it arqonite \vas rhe
2.17
1.47
K2p LmIie
1.44 -0.19
228 1.91
Kap Lrslre
Kap lrslie
r.Fi
1.08
G.08
1.74
K=apHope Kar, HoPe
1.29
’_I23
Nordvcstfjorden
2.42
:!23 I.65
Scoresby Sund
1.20 2.44
Ryefjord
3.M
MIlne Land
1.81 7.26
I .75 1.25
Mine Lmd Nordvcstfjorden
1.98 1.52
0.21
R&e Q1
1.18
NordvesttJorden
1.63
1.37
KTP Hap
1.39
1.39
Kap Hqx
1.39 1.70
1.39 t.51
Kap mqx Kap Hope
1.95 2.14 7. t 1
1.57 146 I .34
fiP Hope tip Hope Kap Hop_
1.75 7.43
1.45 i .60
Kap Ho~c tip Hope
1.72
7.01
2.02 1.80
1.83 1.42
GP f-folxr GP I-iw NordvestfJorden
2.45
1.53 1.77
1.95 2.51 1.74 2.60 3.40 2.85 2.65
1.50 1.74 0.31, 1.34 0. IO 0.81
NordvestfJwhl Nordvestfjorden Nordvesdjorden NorddvesdJordcn Nordvestljnrdcn Nordwstf@en Nordvestf~orden ~ordvcsttjordcn
The surface layer oi the Greenland Sea is dominatrd by waier mass contributions ii-om two m;ljor sources I Buch. 1983): ( 1) The north flowing Norwegian AtIantic Current, which is an extension c>fthe Yorth Atlantic Currr;nt. and is ~haracterizcd by saliniiies close to 35.WL and tcmpcratiires abov 7 0 C. (2) Inflou; From the Arctic Ocean, which is composed of- cDlder. less sniine water (S atout 34.5%~ and T beluw 0 C ). In the Greenland Sea the two water masses mix and give r-ix to the water masses forming the East Greenland Current. The Eat Greenland Current flows from north to south and the coId l~aters are rcsponsibii: [or the arctic climate along the East Greenland coast. The upper 800--900 m of the East Greenland Current are composed of two water masses. with distinct T and S ProPerties. From tile surface down 10 2: depth of l5@200 m, the water column is occupied by Pointy ~t*oli~r-,characterised by temperatures between - 1.S and 0.0 C and s:tIillitier grading from iibo~~t 31.S’L in the uppermost part of the I:!yer 19 34.5% in the losax part. Underncatti the Polar water a body of .2rc,tila Z~ter-~~cr&~~c~\~ri~i extends down to approsimatcfy 800 m. The Arctic Intcrnxdiate water, which is a colder and less saline variant of Atiar,tic water, is (;harxteriqSd by temperatures between 0.0 and i .5 C and salinities between 34.5 al,> 15.1’L. In Scaresby Sd arld other E;+ct Greer.land fjords. Usc;ing ( 1934) ident;ficd, in addition to the water masses already mentioned. a @HY~ IIYIIC’I /UJW*.6-25 m thick with temperatures above 0 C. formed by the melting ofsnow and ice. In Scoresby Sund. this relativdy warm surfxe layreaches its and highest temperature thickness greatcw (S-8 C) in the innermost part of the fjord system whereas it is insignificant at the mouth of the fjord. The Fjord water layer-, which has salinities: from 0.0 to 31.5%, only exists during the summa when melting of the large glaciers in the western part of’ the fjord system is prcatest. This lxge amount of meltwater gives rise to a surface currt:nt moving out of the fjord. compensated by ;2 bottom current moving into the fjord ( Ussing. 1434).
We have measured
7: S and fi”O, from fcjrrr hydrographic statiotlj in the Scar-csby Sund fjord qstem ( Fig. 2). The stations arc placed at lrarying distances fr-om the open sea. and PS 1936 is located some 100 m from one of the larger glacici- fronts a! the head o:‘Nurd;,estfjord f Fig. 1 ). Fig. 2 shows ihat during the fate summer the surFax waters of Scorcsby Sund have low salinity and I80 depleted \vater down to ;I depth of 200 m. tn September. water temperatures rapidly decrease [ Ryder, 1895) ;rnd only two stations still &ow positive tempcratures in the upper loo-20 m or the ivater column. From the rS’“O, values it is seen that Scoresby Sund is influenced by ‘“0 depleted water down to a depth of 300 m (ii’QV less than KL), and that ve I’v ‘“0 depleted water (ii%,& between --6 and - Igf is only si?nilicant in the upper 5 m of the ?yatcr coiumn, It has pretiously been demonstrated that ii%, prof’rles and ii%,-salinity relations can be used in ‘“0 modclling oU flcshwatt_r input into araic seas ( 7an and Str’ai;;. 1980; Bbdar-d ct ai., 1981: Ferronsky a,ld Brezgunov, 1989: &terlund and Hut. 1984). These models operate lvith three main isolopic components in arctic fjords and coastal waters: marine suridard wager, continental fresh ,>nd sea ice meltwater. Marine standard U~:dxx L. ~vater has salinity about 35’1L and d”0, ~1~12s cIos2 to O’h ( Epstein and Mayedci. 1953 i. Salinity of continental freshwaters is o’~i~l,while #QV vaiucs hai.e large geographic variations. ln Scoresby Sund there arc at least three so~w.xs of continental frcshwatcr with diRerent isotopic compositions. The most important is glaciaf mcitwater from the IllIll1erous ouilct ghciers from the Greenland ice sheet. Three ice samples collected Gletscher. Jensen of Daugaxd 011 top Nor-dvcstfjard ( Fig I 1, show ;L mean isotope value of --3S’:L17This value is considered as being represi-ntati\,e for melting ice and therefore for melt-
x *
Y
c
..I
.i
7
Depth 30 m
;‘
I-
Three important conclusions can be drawn from Fig. 4. Fir-st, the predicted nxygerl isotope composition of equilibritim caMication is close to the isotopic composition of the modern shells. This means that the aragonitic shells of the invesCgated species are a good reoordfr of tllr ~:ilvironmental conditions oi‘ ‘t!:e water in lvhich they live. Secondly. it is seen that the relationship between the isotopic composition of \v;ater and shell and the temperature of the lvvater ~111be expressed by the paleotelnpel-aturc equation of Epstein ct al. ( 1953 ). Ir shouId. ho\vtvcr. be borne in mind that the hvdrogmphic parameters that have been used to calculate the predicted oxygen isotope co131posIrneasurcd in early Scptcmber ( Fig. 21, tit313 v+a~ ~~~+ilethe isotopic compositiorl of the modern shells probably reprewlt the enviromnental conditions in ear!y :‘:!333113el-! June-August ) ~vhen the water temperatul-es v.we hi&r than in Septe::ber ( Kyder. 18%; Pigby. I453 ). Thirdly. it is seen that thaw is a clear dll$-erence between predicted oxygen isotope composition in the Polar water and in the Fjjnrd water layer. In Fig. 4 the approximate boundary betwcw the Polar water (predicted ,‘iIQ > Xw) al?4 the Fjord ivatel lap ( -- 2”~~ ==z prcdictcd ii”OC < 2’,L) is drawn with a dashed line. It is seen that there Es;I strong depth dependent PO, gradient within the Fjord water layer. The large spread in isotopic composition between shells from the same depth can pl-obzbly be expiained by \:ari:ttions in temperature, ii’“O, and changes in tfle po?iition of the Polar water:Fjord water layJIM boulldal’y
fioill
y.Xll-
t0
ye2lr.
In the following the estimated living deplh of the fossil bivalves using the predicted oxygen isotopc composition has been compared to the tsti-
Tenperatwe
mated
living depth
of the fauna
found
in t
(“Cj
lt’
sediments.
A
a
A
A
A
The average oxygen isotope composilinn of the shells is about 3%~ which corresponds to a iiviq depth of about 45 m using the predicted oxygen isotope composition and temperature statifcation of the recent fjo_ d ( Fig. 5 j. T’nis again corresponds to a marine IiiIIi~ about 5U m higher than today. givers the elevation of the anatysed samples 1Table 2). Th c occurrence of rhe bivalve species Pt.t,~jeuittzts.~iulll gi.c~i~nl~ll~f~il.srtrl in tb Holocene sediments from LangeZandsctv is in good agreement with the interpreted living depth of the analysed speci~nens. Pi.op~rr~llrt.ssiri131 ,~~O~~/iiuII~,~~‘i.:fIl? has a preference for the Polar,,Fjord water boundThe oxygen isotope values suggest that most of ary and is accordingly most abundant at water the analy:,ed sheik lived in the Fjord eater layer depths between 20 and 60 m (Ockelmann,195S 1.
1.2
m 0 0
0
a
?? 0
v 130
2.80
L~ngeiandsel
3.45
Lal&ehldselv
130
1.5 1.4
1.92
Lar;gelandwiv
130
2.8
3.47
L.m&elandselv
L30
3.2
3 17
hgetanctwlv
130
3.6
3.37
bngelandselv
130
4.0
3.56
Langetandselv
130
1.4
3.s
hngetandsel
s I30
4.8
7.53
hlgelandseiv
130
5.3
?_.78
Lzge!zndseiv
I30
5.6
1.53
Langetandselv
130
5.6
x3
Langefandselv
130
5.6
3.35
Langeiandselv
i30
4.8
3.03
Langetandseiv
I30
4.8
3.53
Langctandselv
130
4.8
3.i”
Langelandselv
130
4.8
3.w
hgellmdAv
i 30
4.8
3.67
‘Langelandselv
130
48
3.81
hgelandselv
131)
4.8
3.82
Lmgelandselv
130
4.8
3.84
Langeiandselv
130
4.8
3.84
Langcl;?ndselv
130
4.8
4sx-l
hgelandsclv
130
4.8
8. Growth increment
anaIyses
Arctic bivalves oniy !b?-m shell materiai in the summer when the light intensity and food availability are at their maxima. The isotopic composition of a single growth incrcrnent thus represents the environmental conditions of the summer whitout any signal Yrom the winter season~The growth inct’cme~~: oi’ the bivalrcs anrj;ysed in this study can thus not be interpreted ;LS resulting from temperature variation through a ivhnlc >‘e;ir, ;is
Ttidanta
borealrs
I.56
Lqelandsclv
76A
1.0
TlldOflt3
IXlilXdiS
0.98
hgelandsclv
‘VA
1.5
Tndanta
bore&Is
1.34
hgelandselv
77A
2.s
Tndanta
bareah
1.93
Langelvldselv
77A
2.5
~ngelandselv
7iA
2.5
bawl~s
1.79
Tndanta
bore&s
1).04
Langelandselv 7-0’A
I.0
Tndoma
hxeaiis
1.03
Langelandselv 77A
i.0
Hiateiia
arctIca
0.92
h-lgelandsch
T7A
I.0
Ttidama
bar&is
1.13
tangelandselv
77A
2.0
Tridanti
bar&u
0.62
hgelandselv
77A
1.0
Tndonla
borcalts
0.59
Langelandsc!v 77A
1.0
Trkhh
baruhs
0.42
hgelandselv
5.8
Tridonb
borealis
0.81
Langelands&
7x
4.0
Tricioma
DoreaLs
0.19
Langrlandselv
78
4.0
Tridanta
hreahs
1.10
h?gehKke?v
78
4.0
Tridonta
lxwc&s
0.34
hgelandselv
78
4.0
Tridonta
bore&
78
4.0
barails
I .a 0.51
Lanplandselv
Tridonta
bngeludselv
7K
5.1
Tridonta
bar&s
0.67
Langelanklv
78
5.5
Tridonta
hare&s
I.01
‘bngela_ndsctv 48
5.8
0.47
l_mgeiandselv ?7A
1.0
[email protected]
l..kulgelandsclv 77A
Tndanu
75
i.0
i).OO Langelands&
VA
1.0
!)I!?
Langelands&
77A
1.0
0.1 I -0.10
hngelattdselv
PIA
1.0
Langelandselv i7A
I.0
0.90
hgekutdscclv
77A
I.0
0.18 0.40
hngelaridseiv
7-‘7A
I.0
hg&ndsclv
‘77A
?.O
-0.47
hgelandselv
7/A
1.0
(i. 14
bngelandsclv
?7A
1.G
-0.3 1
tangelandselv
77A
1.0
0.36
l_xgelandselv
i”lA
1.0
0.45
Langelandsclv 77A
I .o
-0.38
hgclandselv
1.o
77A
0.73
hgelandsclv
7’7A
l.(?
0.57
Langelandwlv
77A
1.C
1.33
Aucellaelv 73,
21.0
1.21
Auceltaelv 72
Z1.Q
1.09
Aucehelv
72.
21.0
ok0
Aurxllaelv
71
71.0
11.76 Auccllaelv
71
11.8
0.74
7:!
20.0
Aucehelv
At 20 m depth. close to the boundary betucen the Fjord wter layer and the Polar water. the water mass is more stable. The less variable tcmperaturcs and PO, values from year to year are reflected in the much smaller variation in the oxygen isotope composition of the specimen sampled from 20 m below sea surface. The growth increment analyses of the Holocene shell support the conclusion that the Holocene bivalves lived in Polar water (Fig. 7. b). The anaIysed shell has a very steady oxygen isotope composition indicating small variations in summer temperature and rj”*O,, values from year to year. From the interglacial sediment. two shells have been analysed ( Fis. 7. b). Both have relatively low Yxi), va!ues and large variation from year to year in oxygen isotope composition. This indicates a shallow habitat in the inter~Jacial Fjord water ayer. with variable temperatures and i’l”O, values cornpal-able to present conditions.
9+ Carbon isotopes
IO. Discussion
Figs. 6. 7 and Tables 1. 2 and 3 show th:it most of the 313C values Ii,- bc:ween 1 and 2.5%~. There is no significant cM”ererlce between the shells from :he recent Scoresby Sund and the fossil shells from the Holocene and the Eemian. Most. marine carbonates reflect the d”C of total dissolved inorganic carbon (TDC ) of the water in
been shown that tht* oceanogr-aphy o,f the Greenland Sea influenced the climate of the North Atlantic and adjacent land areas during the Holocene ( Kapuz and Schrader. 1990: Funder and Weidick. 1991: Williams. f 993 1. The climate during at approsithe Holocene “climatic optimum” mately 8000-4000 yr B.P. teas warmer than today It has
tsnd\?k. J.!‘.. Lysd. A.. Funder. 5.. Israelson. C., Kelly,. M.. Mzdscn. H.. hatiller. P.. Rfipnvaidsson. F.. R undgrcn. M.. Scjrup. H.P.. Sorby. L. and VOS_~C;~U.H.. 19i)l. Depo,:irional history and Z~~~i~Jl~~l~ implication5 of the Efmian and LVurchsclian wq~1cncc3 in l!xL Au,. =llxlv Langclandscl\ area, southern J;tmeson LanJ. East Greenland. Lundqu:, Rep., 33. 27 52.
Xleidrthl. V.. 1992. Ther;r:nlllmii-iesc~ncc dating of sampics from Janmm Land, East Greenland. Lundqua Rep.. 35: 21 I 215. Mook. W.G. and Vogel. J.C.. 196X. Isotopic equilibrium between shells and their ehvironmenl. Science. 159: 874-875. Ockrimann. Ev’.K.. 1958. Zoology of East Greenland marine lame!lihranchiata. Mcdd. Gronl.. 122 (4). 157 pp. &;er!und. H.G. and Hut. G. 1 19X4. Arctic Ocean water mass balance from isotope data. J. Geophys. Res.. 89: 6373 6.181. Petersen. K.S.. 1982. 4rtack by predatory gastropods rccognia2.l in an interglacial marine molluscan fauna from Jamesan Land. East Greenland. Maiacclopia. 22: X!! -716. Ryder. C.. 1895. Den ostgronlandske Expedition udfort i Aarcne 189l~Y1 under led&e af‘ C. Ryder: Hvdrografiske undcrsogclse. Medd. Gmnl.. i 7: 19 I - 22!. Rtignvaldsson. F. and Sejrup. fi.P., IY92. .4~1im acid ratios in molluscs from raised marine duposits. Jamcson Land. East Greenland. Lundqua Rep.. 35: 215-223. Samtleben. C., 1985. Climatic influence on shell microstructure in Illrr,lrrs t,ll~lis from Spitsbergen. In: 75 Jahreslagunp dcr 17.2 2.3 1985. Kiel (poster). Gcologischen Vereinipung. Shacklrton. N.J.. i273. .4trainment of’ isotopic equilibrium berween ocean water 3% the benthonic foraminifera genus Liri,~u?mi: tsotopic changes m the mem durin_g Ihe last glaCIal. Coltoq. ini. C.N.R.S., 219. Shackleron. N.J.. 1977. Carbon-13 in Ci~~&ri~n: ‘Tropical r;lin:‘orcst histog, and the equatorial Pacific carbonate dissolution cycles. In: N.R. Andcrscn and A. MalahoB ( EJitor3~. The Fate of‘Fossil Fuel CO2 in the Oceans. Mar. 4ci.. f~ Shifano. G. and C‘cnsi. P.. 1983. Oxy_ren lsotopc CotilpositioII and rate of gronth of P~IIL,IIu ~~ocr-z~l~~tr. Alorl:>rl~jrt~rnltrl-hirrrrra and .%I. i,rri&rtc~ Lhclls from the \vestcrn coast of Sicily. Palacugcogr.. Paixoclimatol.. Palaeoecol.. 47: 305 -31 1. Tan. F.C. and Frxx. W.D.. 1976. Oxygen isotope studies on sea icr in the Gulf of St. Lawrence. J. Fish. Res. Board Can.. 3.:: 1397 I 101. ‘Tan. F.C. and Strain. P.M.. 1950. Thtz distribution of hea ice mcltuatrr in the Eastern Canadian Arctic. J. Gcophvs. Res.. x5: I Y35m 193,. Thurson. G.. 1934. Contributions to the animal ecology of the -*-*~‘x2.! )_ Mtzk. Scoi-esby Sound fjord complex 1F:Js! GI~~.r, Granl..
100 (3)
40 pp.
Using. H.. 1934. The hydrography of r‘jord complex. Medd. Gtonl.. It3I) ( 1). Willian3s. K.W.. 13Y3. Ice si3uet and ocean oi‘ the Easy GT-ccnland ice sheet ( 13 ka cvidcncc. P~llcoccanopraphy~ 8: 03 X3. Vns.gcr;lu. H.. 1Y92. En pal :omiljo-tolkning fra
Jameson
I46 pp.
Land.
Bstgrunland.
t:ic Scar-esby
Sound
68 pp. interaflions. to Present):
margin Diattim
af Ecm-aflejringer IJniv. Aarhus.
Thesis.
1. hntrnduction The isotopic pakoecoIogica1 sipal of arctic bivalves ha: previously been studied by Andre~,~ ( 1973 j, Hillaire-Marcel f 19&I ), Donnet- and N~lrd ( 19X6) and Israelson and Buchardt { 1991 1. The present paper aims to contribute to tiw intcrprctation of the imtopic composition of biva1x.e sRcII~ in the arctic environment xvith special emphasis on paleosaiinities.
Earlier inixxtigations have sho~~:n that marine intcrg~acial beds of Eemian age with a thermophilous ElOllL~SC fauna mist at several localities along the southern coast of Jameson Land. Interglacial she!ls from two !ocaIIries were analysed in this study. The first locality is a coastal clifi near Lang ~!~dselv ( Fig. 1 1. Petersen ( 1932) found s rich mollusc fauna in these sediments which were later described by Landvik et al. ( 1991) and Vosgerau ( I992 ). The marine sediments consist of
During the earlier part of the last ice qe the coast;!1 areas Of Jameson Lund acre covizred by sea. and from this period fJamcson Land m;trine episode) marine sediments ;~re preser~vd. The Jameson Land marine episode reflects a prolonged period of marine conditions in coastal East Greenland. The marine episode was interrupted several times by glacier- advances from the L-~panding Greenl;~nd ice sheet depositing subglacii~l a:ld glaciom;lrinc sediments on lhu corzst of Jamrsun Lund (Funder et ai.. 1991 ). From the Holocene. marine sediments indicate a reIative sea level up to SO m above the present ( Funder. i?78. 1990). A scctinn located in a n!- Imcsc~~ Land COSiLtt Cliflf On i;iS SCUI!~ coast (Fig. 1 ) has bwn studied. The horizontally laminated sand and silt layers display fluid escape structures and “flames” of silt protruding upu-clrds into overlyin layers. indicating high sedimentation rates. This interpretation is supported by the accelerator mass spectrometry (AMS) datin?s (Gulliksen et ~31,.1991 ). The dates indicate that the IowermOst 3 m of the section was deposited within a time period of less thaw 150 years (between 8480 and 5330 yr EP 1. The sedimet:ts contain abundant bi\.alve fossils zind .%I~u Irr4witicr is especially common.
3. Samgiing alld andytical
techniqws
All cxrjmined shells are well preserved and X-ray difiraction analyses shot+- th;it arqonite \vas rhe
2.17
1.47
K2p LmIie
1.44 -0.19
228 1.91
Kap Lrslre
Kap lrslie
r.Fi
1.08
G.08
1.74
K=apHope Kar, HoPe
1.29
’_I23
Nordvcstfjorden
2.42
:!23 I.65
Scoresby Sund
1.20 2.44
Ryefjord
3.M
MIlne Land
1.81 7.26
I .75 1.25
Mine Lmd Nordvcstfjorden
1.98 1.52
0.21
R&e Q1
1.18
NordvesttJorden
1.63
1.37
KTP Hap
1.39
1.39
Kap Hqx
1.39 1.70
1.39 t.51
Kap mqx Kap Hope
1.95 2.14 7. t 1
1.57 146 I .34
fiP Hope tip Hope Kap Hop_
1.75 7.43
1.45 i .60
Kap Ho~c tip Hope
1.72
7.01
2.02 1.80
1.83 1.42
GP f-folxr GP I-iw NordvestfJorden
2.45
1.53 1.77
1.95 2.51 1.74 2.60 3.40 2.85 2.65
1.50 1.74 0.31, 1.34 0. IO 0.81
NordvestfJwhl Nordvestfjorden Nordvesdjorden NorddvesdJordcn Nordvestljnrdcn Nordwstf@en Nordvestf~orden ~ordvcsttjordcn
The surface layer oi the Greenland Sea is dominatrd by waier mass contributions ii-om two m;ljor sources I Buch. 1983): ( 1) The north flowing Norwegian AtIantic Current, which is an extension c>fthe Yorth Atlantic Currr;nt. and is ~haracterizcd by saliniiies close to 35.WL and tcmpcratiires abov 7 0 C. (2) Inflou; From the Arctic Ocean, which is composed of- cDlder. less sniine water (S atout 34.5%~ and T beluw 0 C ). In the Greenland Sea the two water masses mix and give r-ix to the water masses forming the East Greenland Current. The Eat Greenland Current flows from north to south and the coId l~aters are rcsponsibii: [or the arctic climate along the East Greenland coast. The upper 800--900 m of the East Greenland Current are composed of two water masses. with distinct T and S ProPerties. From tile surface down 10 2: depth of l5@200 m, the water column is occupied by Pointy ~t*oli~r-,characterised by temperatures between - 1.S and 0.0 C and s:tIillitier grading from iibo~~t 31.S’L in the uppermost part of the I:!yer 19 34.5% in the losax part. Underncatti the Polar water a body of .2rc,tila Z~ter-~~cr&~~c~\~ri~i extends down to approsimatcfy 800 m. The Arctic Intcrnxdiate water, which is a colder and less saline variant of Atiar,tic water, is (;harxteriqSd by temperatures between 0.0 and i .5 C and salinities between 34.5 al,> 15.1’L. In Scaresby Sd arld other E;+ct Greer.land fjords. Usc;ing ( 1934) ident;ficd, in addition to the water masses already mentioned. a @HY~ IIYIIC’I /UJW*.6-25 m thick with temperatures above 0 C. formed by the melting ofsnow and ice. In Scoresby Sund. this relativdy warm surfxe layreaches its and highest temperature thickness greatcw (S-8 C) in the innermost part of the fjord system whereas it is insignificant at the mouth of the fjord. The Fjord water layer-, which has salinities: from 0.0 to 31.5%, only exists during the summa when melting of the large glaciers in the western part of’ the fjord system is prcatest. This lxge amount of meltwater gives rise to a surface currt:nt moving out of the fjord. compensated by ;2 bottom current moving into the fjord ( Ussing. 1434).
We have measured
7: S and fi”O, from fcjrrr hydrographic statiotlj in the Scar-csby Sund fjord qstem ( Fig. 2). The stations arc placed at lrarying distances fr-om the open sea. and PS 1936 is located some 100 m from one of the larger glacici- fronts a! the head o:‘Nurd;,estfjord f Fig. 1 ). Fig. 2 shows ihat during the fate summer the surFax waters of Scorcsby Sund have low salinity and I80 depleted \vater down to ;I depth of 200 m. tn September. water temperatures rapidly decrease [ Ryder, 1895) ;rnd only two stations still &ow positive tempcratures in the upper loo-20 m or the ivater column. From the rS’“O, values it is seen that Scoresby Sund is influenced by ‘“0 depleted water down to a depth of 300 m (ii’QV less than KL), and that ve I’v ‘“0 depleted water (ii%,& between --6 and - Igf is only si?nilicant in the upper 5 m of the ?yatcr coiumn, It has pretiously been demonstrated that ii%, prof’rles and ii%,-salinity relations can be used in ‘“0 modclling oU flcshwatt_r input into araic seas ( 7an and Str’ai;;. 1980; Bbdar-d ct ai., 1981: Ferronsky a,ld Brezgunov, 1989: &terlund and Hut. 1984). These models operate lvith three main isolopic components in arctic fjords and coastal waters: marine suridard wager, continental fresh ,>nd sea ice meltwater. Marine standard U~:dxx L. ~vater has salinity about 35’1L and d”0, ~1~12s cIos2 to O’h ( Epstein and Mayedci. 1953 i. Salinity of continental freshwaters is o’~i~l,while #QV vaiucs hai.e large geographic variations. ln Scoresby Sund there arc at least three so~w.xs of continental frcshwatcr with diRerent isotopic compositions. The most important is glaciaf mcitwater from the IllIll1erous ouilct ghciers from the Greenland ice sheet. Three ice samples collected Gletscher. Jensen of Daugaxd 011 top Nor-dvcstfjard ( Fig I 1, show ;L mean isotope value of --3S’:L17This value is considered as being represi-ntati\,e for melting ice and therefore for melt-
x *
Y
c
..I
.i
7
Depth 30 m
;‘
I-
Three important conclusions can be drawn from Fig. 4. Fir-st, the predicted nxygerl isotope composition of equilibritim caMication is close to the isotopic composition of the modern shells. This means that the aragonitic shells of the invesCgated species are a good reoordfr of tllr ~:ilvironmental conditions oi‘ ‘t!:e water in lvhich they live. Secondly. it is seen that the relationship between the isotopic composition of \v;ater and shell and the temperature of the lvvater ~111be expressed by the paleotelnpel-aturc equation of Epstein ct al. ( 1953 ). Ir shouId. ho\vtvcr. be borne in mind that the hvdrogmphic parameters that have been used to calculate the predicted oxygen isotope co131posIrneasurcd in early Scptcmber ( Fig. 21, tit313 v+a~ ~~~+ilethe isotopic compositiorl of the modern shells probably reprewlt the enviromnental conditions in ear!y :‘:!333113el-! June-August ) ~vhen the water temperatul-es v.we hi&r than in Septe::ber ( Kyder. 18%; Pigby. I453 ). Thirdly. it is seen that thaw is a clear dll$-erence between predicted oxygen isotope composition in the Polar water and in the Fjjnrd water layer. In Fig. 4 the approximate boundary betwcw the Polar water (predicted ,‘iIQ > Xw) al?4 the Fjord ivatel lap ( -- 2”~~ ==z prcdictcd ii”OC < 2’,L) is drawn with a dashed line. It is seen that there Es;I strong depth dependent PO, gradient within the Fjord water layer. The large spread in isotopic composition between shells from the same depth can pl-obzbly be expiained by \:ari:ttions in temperature, ii’“O, and changes in tfle po?iition of the Polar water:Fjord water layJIM boulldal’y
fioill
y.Xll-
t0
ye2lr.
In the following the estimated living deplh of the fossil bivalves using the predicted oxygen isotopc composition has been compared to the tsti-
Tenperatwe
mated
living depth
of the fauna
found
in t
(“Cj
lt’
sediments.
A
a
A
A
A
The average oxygen isotope composilinn of the shells is about 3%~ which corresponds to a iiviq depth of about 45 m using the predicted oxygen isotope composition and temperature statifcation of the recent fjo_ d ( Fig. 5 j. T’nis again corresponds to a marine IiiIIi~ about 5U m higher than today. givers the elevation of the anatysed samples 1Table 2). Th c occurrence of rhe bivalve species Pt.t,~jeuittzts.~iulll gi.c~i~nl~ll~f~il.srtrl in tb Holocene sediments from LangeZandsctv is in good agreement with the interpreted living depth of the analysed speci~nens. Pi.op~rr~llrt.ssiri131 ,~~O~~/iiuII~,~~‘i.:fIl? has a preference for the Polar,,Fjord water boundThe oxygen isotope values suggest that most of ary and is accordingly most abundant at water the analy:,ed sheik lived in the Fjord eater layer depths between 20 and 60 m (Ockelmann,195S 1.
1.2
m 0 0
0
a
?? 0
v 130
2.80
L~ngeiandsel
3.45
Lal&ehldselv
130
1.5 1.4
1.92
Lar;gelandwiv
130
2.8
3.47
L.m&elandselv
L30
3.2
3 17
hgetanctwlv
130
3.6
3.37
bngelandselv
130
4.0
3.56
Langetandselv
130
1.4
3.s
hngetandsel
s I30
4.8
7.53
hlgelandseiv
130
5.3
?_.78
Lzge!zndseiv
I30
5.6
1.53
Langetandselv
130
5.6
x3
Langefandselv
130
5.6
3.35
Langeiandselv
i30
4.8
3.03
Langetandseiv
I30
4.8
3.53
Langctandselv
130
4.8
3.i”
Langelandselv
130
4.8
3.w
hgellmdAv
i 30
4.8
3.67
‘Langelandselv
130
48
3.81
hgelandselv
131)
4.8
3.82
Lmgelandselv
130
4.8
3.84
Langeiandselv
130
4.8
3.84
Langcl;?ndselv
130
4.8
4sx-l
hgelandsclv
130
4.8
8. Growth increment
anaIyses
Arctic bivalves oniy !b?-m shell materiai in the summer when the light intensity and food availability are at their maxima. The isotopic composition of a single growth incrcrnent thus represents the environmental conditions of the summer whitout any signal Yrom the winter season~The growth inct’cme~~: oi’ the bivalrcs anrj;ysed in this study can thus not be interpreted ;LS resulting from temperature variation through a ivhnlc >‘e;ir, ;is
Ttidanta
borealrs
I.56
Lqelandsclv
76A
1.0
TlldOflt3
IXlilXdiS
0.98
hgelandsclv
‘VA
1.5
Tndanta
bore&Is
1.34
hgelandselv
77A
2.s
Tndanta
bareah
1.93
Langelvldselv
77A
2.5
~ngelandselv
7iA
2.5
bawl~s
1.79
Tndanta
bore&s
1).04
Langelandselv 7-0’A
I.0
Tndoma
hxeaiis
1.03
Langelandselv 77A
i.0
Hiateiia
arctIca
0.92
h-lgelandsch
T7A
I.0
Ttidama
bar&is
1.13
tangelandselv
77A
2.0
Tridanti
bar&u
0.62
hgelandselv
77A
1.0
Tndonla
borcalts
0.59
Langelandsc!v 77A
1.0
Trkhh
baruhs
0.42
hgelandselv
5.8
Tridonb
borealis
0.81
Langelands&
7x
4.0
Tricioma
DoreaLs
0.19
Langrlandselv
78
4.0
Tridanta
hreahs
1.10
h?gehKke?v
78
4.0
Tridonta
lxwc&s
0.34
hgelandselv
78
4.0
Tridonta
bore&
78
4.0
barails
I .a 0.51
Lanplandselv
Tridonta
bngeludselv
7K
5.1
Tridonta
bar&s
0.67
Langelanklv
78
5.5
Tridonta
hare&s
I.01
‘bngela_ndsctv 48
5.8
0.47
l_mgeiandselv ?7A
1.0
[email protected]
l..kulgelandsclv 77A
Tndanu
75
i.0
i).OO Langelands&
VA
1.0
!)I!?
Langelands&
77A
1.0
0.1 I -0.10
hngelattdselv
PIA
1.0
Langelandselv i7A
I.0
0.90
hgekutdscclv
77A
I.0
0.18 0.40
hngelaridseiv
7-‘7A
I.0
hg&ndsclv
‘77A
?.O
-0.47
hgelandselv
7/A
1.0
(i. 14
bngelandsclv
?7A
1.G
-0.3 1
tangelandselv
77A
1.0
0.36
l_xgelandselv
i”lA
1.0
0.45
Langelandsclv 77A
I .o
-0.38
hgclandselv
1.o
77A
0.73
hgelandsclv
7’7A
l.(?
0.57
Langelandwlv
77A
1.C
1.33
Aucellaelv 73,
21.0
1.21
Auceltaelv 72
Z1.Q
1.09
Aucehelv
72.
21.0
ok0
Aurxllaelv
71
71.0
11.76 Auccllaelv
71
11.8
0.74
7:!
20.0
Aucehelv
At 20 m depth. close to the boundary betucen the Fjord wter layer and the Polar water. the water mass is more stable. The less variable tcmperaturcs and PO, values from year to year are reflected in the much smaller variation in the oxygen isotope composition of the specimen sampled from 20 m below sea surface. The growth increment analyses of the Holocene shell support the conclusion that the Holocene bivalves lived in Polar water (Fig. 7. b). The anaIysed shell has a very steady oxygen isotope composition indicating small variations in summer temperature and rj”*O,, values from year to year. From the interglacial sediment. two shells have been analysed ( Fis. 7. b). Both have relatively low Yxi), va!ues and large variation from year to year in oxygen isotope composition. This indicates a shallow habitat in the inter~Jacial Fjord water ayer. with variable temperatures and i’l”O, values cornpal-able to present conditions.
9+ Carbon isotopes
IO. Discussion
Figs. 6. 7 and Tables 1. 2 and 3 show th:it most of the 313C values Ii,- bc:ween 1 and 2.5%~. There is no significant cM”ererlce between the shells from :he recent Scoresby Sund and the fossil shells from the Holocene and the Eemian. Most. marine carbonates reflect the d”C of total dissolved inorganic carbon (TDC ) of the water in
been shown that tht* oceanogr-aphy o,f the Greenland Sea influenced the climate of the North Atlantic and adjacent land areas during the Holocene ( Kapuz and Schrader. 1990: Funder and Weidick. 1991: Williams. f 993 1. The climate during at approsithe Holocene “climatic optimum” mately 8000-4000 yr B.P. teas warmer than today It has
tsnd\?k. J.!‘.. Lysd. A.. Funder. 5.. Israelson. C., Kelly,. M.. Mzdscn. H.. hatiller. P.. Rfipnvaidsson. F.. R undgrcn. M.. Scjrup. H.P.. Sorby. L. and VOS_~C;~U.H.. 19i)l. Depo,:irional history and Z~~~i~Jl~~l~ implication5 of the Efmian and LVurchsclian wq~1cncc3 in l!xL Au,. =llxlv Langclandscl\ area, southern J;tmeson LanJ. East Greenland. Lundqu:, Rep., 33. 27 52.
Xleidrthl. V.. 1992. Ther;r:nlllmii-iesc~ncc dating of sampics from Janmm Land, East Greenland. Lundqua Rep.. 35: 21 I 215. Mook. W.G. and Vogel. J.C.. 196X. Isotopic equilibrium between shells and their ehvironmenl. Science. 159: 874-875. Ockrimann. Ev’.K.. 1958. Zoology of East Greenland marine lame!lihranchiata. Mcdd. Gronl.. 122 (4). 157 pp. &;er!und. H.G. and Hut. G. 1 19X4. Arctic Ocean water mass balance from isotope data. J. Geophys. Res.. 89: 6373 6.181. Petersen. K.S.. 1982. 4rtack by predatory gastropods rccognia2.l in an interglacial marine molluscan fauna from Jamesan Land. East Greenland. Maiacclopia. 22: X!! -716. Ryder. C.. 1895. Den ostgronlandske Expedition udfort i Aarcne 189l~Y1 under led&e af‘ C. Ryder: Hvdrografiske undcrsogclse. Medd. Gmnl.. i 7: 19 I - 22!. Rtignvaldsson. F. and Sejrup. fi.P., IY92. .4~1im acid ratios in molluscs from raised marine duposits. Jamcson Land. East Greenland. Lundqua Rep.. 35: 215-223. Samtleben. C., 1985. Climatic influence on shell microstructure in Illrr,lrrs t,ll~lis from Spitsbergen. In: 75 Jahreslagunp dcr 17.2 2.3 1985. Kiel (poster). Gcologischen Vereinipung. Shacklrton. N.J.. i273. .4trainment of’ isotopic equilibrium berween ocean water 3% the benthonic foraminifera genus Liri,~u?mi: tsotopic changes m the mem durin_g Ihe last glaCIal. Coltoq. ini. C.N.R.S., 219. Shackleron. N.J.. 1977. Carbon-13 in Ci~~&ri~n: ‘Tropical r;lin:‘orcst histog, and the equatorial Pacific carbonate dissolution cycles. In: N.R. Andcrscn and A. MalahoB ( EJitor3~. The Fate of‘Fossil Fuel CO2 in the Oceans. Mar. 4ci.. f~ Shifano. G. and C‘cnsi. P.. 1983. Oxy_ren lsotopc CotilpositioII and rate of gronth of P~IIL,IIu ~~ocr-z~l~~tr. Alorl:>rl~jrt~rnltrl-hirrrrra and .%I. i,rri&rtc~ Lhclls from the \vestcrn coast of Sicily. Palacugcogr.. Paixoclimatol.. Palaeoecol.. 47: 305 -31 1. Tan. F.C. and Frxx. W.D.. 1976. Oxygen isotope studies on sea icr in the Gulf of St. Lawrence. J. Fish. Res. Board Can.. 3.:: 1397 I 101. ‘Tan. F.C. and Strain. P.M.. 1950. Thtz distribution of hea ice mcltuatrr in the Eastern Canadian Arctic. J. Gcophvs. Res.. x5: I Y35m 193,. Thurson. G.. 1934. Contributions to the animal ecology of the -*-*~‘x2.! )_ Mtzk. Scoi-esby Sound fjord complex 1F:Js! GI~~.r, Granl..
100 (3)
40 pp.
Using. H.. 1934. The hydrography of r‘jord complex. Medd. Gtonl.. It3I) ( 1). Willian3s. K.W.. 13Y3. Ice si3uet and ocean oi‘ the Easy GT-ccnland ice sheet ( 13 ka cvidcncc. P~llcoccanopraphy~ 8: 03 X3. Vns.gcr;lu. H.. 1Y92. En pal :omiljo-tolkning fra
Jameson
I46 pp.
Land.
Bstgrunland.
t:ic Scar-esby
Sound
68 pp. interaflions. to Present):
margin Diattim
af Ecm-aflejringer IJniv. Aarhus.
Thesis.