Holocene paleoceanography of the northern Barents Sea and variationsof the northward heat transport by the Atlantic Ocean

JEAN-CLAUDE DUPLESSY, ELENA IVANOVA, IVAR MURDMAA, MARTINE PATERNE AND LAURENT LABEYRIE

Duplessy, J.-C., Ivanova, E., Murdmaa, I., Paterne, M. & Labeyrie, L. 2001 (March): Holocene paleoceanogra-phy of the northern Barents Sea and variations of the northward heat transport by the Atlantic Ocean. Boreas,Vol. 30, pp. 2–16. Oslo. ISSN 0300-9483.

Foraminiferal assemblages were studied in northern Barents Sea core ASV 880 along with oxygen and carbonisotope measurements in planktonic (N. pachyderma sin.) and benthic (E. clavatum ) species. AMS C-14measurements performed on molluscs Yoldiella spp. show that this core provides a detailed and undisturbedrecord of Holocene climatic changes over the last 10 000 calendar years. Surface and deep waters were verycold (<0°C) at the beginning of the Holocene. C. reniforme dominated the highly diverse benthic foraminif-eral assemblage . From 10 to 7.8 cal. ka BP, a warming trend culminated in a temperature optimum, which de-veloped between 7.8 and 6.8 cal. ka BP. During this optimum, the input of Atlantic water to the Barents Seareached its maximum. The Atlantic water mass invaded the whole Franz Victoria Trough and was presentfrom subsurface to the bottom. No bottom water, which would form through rejection of brine during winter,was present at the core depth (388 m). The water strati� cation was therefore greatly reduced as compared tothe present. An increase in percentage of I. helenae /norcrossi points to long seasonal ice-free conditions. Thetemperature optimum ended rather abruptly, with the return of cold polar waters into the trough within a fewcenturies . This was accompanied by a dramatic reduction of the abundance of C. reniforme. During the upperHolocene, the more opportunisti c species E. clavatum became progressivel y dominant and the water columnwas more strati� ed. Deep water in Franz Victoria Trough contained a signi� cant amount of cold Barents Seabottom water as it does today, while subsurface water warmed progressivel y until about 3.7 cal. ka BP andreached temperatures similar to those of today. These long-term climatic changes were cut by several coldevents of short duration, in particular one in the middle of the temperature optimum and another, which coin-cides most probably with the 8.2 ka BP cold event. Both long- and short-term climatic changes in the BarentsSea are associated with changes in the � ow of Atlantic waters and the oceanic conveyor belt.

Jean-Claude Duplessy (e-mail: Jean-Claude.Duplessy@lsce.cnrs-gif.fr) , Martine Paterne (e-mail: Martine.Paterne@lsce.cnrs-gif.fr) , Laurent Labeyrie (e-mail: Laurent.Labeyrie@lsce.cnrs-gif.fr) , Laboratoire desSciences du Climat et de l’Environnement , Laboratoire mixte CNRS-CEA, Parc du CNRS, 91198 Gif surYvette Cedex, France; Elena Ivanova (e-mail: eivanova@geo.sio.rssi.ru) , Ivar Murdmaa (e-mail: murdma@chip.sio.rssi.ru) , Shirshov Institute of Oceanology, Russian Academy of Sciences, 36 Nakhimonovsky Prospect,117851 Moscow, Russia; received 3rd February 2000, accepted 19th July 2000.

One of the major elements of today’s ocean system is aconveyor-like circulation that delivers an enormousamount of tropical heat to the Northern Atlantic Ocean.During winter, this heat is released to the overlyingeastward moving air masses, thereby greatly ameliorat-ing winter temperatures in northern Europe. During thelast glacial period, numerous abrupt climatic changeshave been found in Greenland ice cores (GRIP projectmembers 1993) and North Atlantic sediment cores(Bond et al. 1993; Labeyrie et al. 1995). These largeshifts in climate have been attributed to changes in thethermohaline circulation in response to massive icebergdischarges from the large Laurentide and European icesheets (Bond et al. 1992; Broecker 1997). However,signi� cant changes in sea surface temperature (SST),which sometimes developed rather abruptly, have alsobeen evidenced in the North Atlantic and in theNorwegian Sea during the last interglaciation. Thesehave been attributed to changes in thermohalinecirculation in response to changes in both high andlow latitude insolation (Cortijo et al. 1994; Fronval &

Jansen 1996; Cortijo et al. 1999). Changes in past oceancirculation and the conveyor belt during the presentinterglaciation, the Holocene, are still poorly documen-ted, although SST variations have been reported in theNorth Atlantic (Duplessy et al. 1992), the Norwegian-Greenland Sea (Koc et al. 1993; Koc & Jansen 1994)and the Arctic Ocean (Lubinski et al. 1996; Hald et al.1999). In this paper, we generate a high-resolutionrecord of ocean circulation and climatic changes in thenorthern Barents Sea. This record is used to reconstructvariations of the North Atlantic water � ux into theBarents Sea during the last 10000 years and relate themto the northernmost extension of the ocean conveyorbelt.

Geographic and oceanographic setting of coreASV 880

Core ASV 880 (79°55’5 N, 47°08’2 E, 388 m) was

raised from the southeastern branch of Franz VictoriaTrough, between the Demed Bank and the foot of FranzJosef Land during cruise-11 of R/V Akademik SergeiVavilov (Fig. 1). The trough opens into the continentalslope of the Arctic Ocean in the north, and is restrictedby the Persei Bank slope in the south.

As shown by seasonal temperature maps (Anony-mous 1998), the major heat transport to the Barents Seaby the Atlantic Ocean is related to the North Capecurrent continuation along the Scandinavian coasts. Itcontrols the Polar Front position and the sea-ice limit.Atlantic water penetrates also from the north into theBarents Sea through three troughs: Franz VictoriaTrough along the coasts of Franz Josef Land, BearIsland Trough in the South-West, and St. Anna Troughin the North-East. The circulation in the Franz VictoriaTrough is governed by topography and is characterizedby an in� ow into the Barents Sea of both cold surfaceArctic water from the north-east and warm intermediateAtlantic water from the north-west. Core ASV 880 istherefore ideally located to monitor past variations ofthe Atlantic water � ow into the Barents Sea.

The present hydrographic conditions show a cold(<¡1°C), low salinity (<34%) sur� cial Arctic watermass occupying the upper 40 m at the location of coreASV 880 (Fig. 2). Below 40 m, this water mixes withthe in� owing warm Atlantic water, which forms a warm(‡0.5 to 1°C), saline (34.8%) intermediate water massbetween 120 and 200 m in depth. In fact, this watermass is not pure Atlantic water, but is derived fromAtlantic water by mixing with both the sur� cial Arcticwater and the Barents Sea bottom water. The bottom ofthe trough is occupied by a colder (<0°C) and higher-salinity (34.9%) bottom water layer, which results fromthe mixing of Barents Sea bottom water formed throughrejection of brine during winter freezing (Midttun 1985)with the Atlantic water.

Lithostratigraphy and dating of core ASV 880

Core ASV 880 was subdivided into four units brie� ydescribed below from the bottom to the top (Fig. 3). Afull description is given elsewhere (Murdmaa &Ivanova 1999).

Unit IV (508–494 cm) is represented by very densedark gray diamicton composed of coarse material, fromsand to boulders in size, mixed with clay and silty clay.A glacial till origin of this unit is suggested based on itslithology, physical properties, almost total absence offossils and very low pore water salinity (Murdmaa et al.1997).

Unit III (494–404 cm) consists of dense homo-geneous dark gray sandy-silty clay with scatteredgravels and pebbles. It is characterized by a bimodalgrain-size distribution with modes at <5 mm and>100 mm. This facies is widespread in the BarentsSea and represents a proximal glaciomarine deposit that

Fig. 1. Map of the Barents Sea and the Norwegian Sea showingthe distribution of water masses, currents and fronts. Below, an ex-panded map for the area between 78–81°N and 30–55°E shows thelocation of Core ASV 880 in the Franz Victoria Trough, northernBarents Sea; water depth lower than 200 m is indicated by strip-ping; arrows show intermediate Atlantic water in� ow.

BOREAS 30 (2001) Holocene paleoceanography , northern Barents Sea 3

was formed during the deglaciation, with extensiveiceberg discharge and � ne-grained suspended material(‘glacier milk’) supply. The age of this unit is unknown.

Unit II (404–310 cm) is composed of soft hom-ogeneous greenish gray silty clay with thin sandyinterbeds. This sequence is common to many coresfrom the Barents Sea and is interpreted as periodicalnepheloid � ow deposits or distal turbidities. Glaciermeltwater sediment load was likely the main � ne-grained material source, but unlike Unit III, icebergrafting of coarse material was negligible. Radiocarbondates in a core with similar lithostratigraphy suggestthat this unit was deposited between 13 and 10 14C kaBP (Lubinski et al. 1996).

Unit I (310–0 cm) represents an almost complete

Holocene section. It is composed of olive-gray to darkolive-gray clay mud. The clay fraction is dominant (70–80% of this fraction is <5 mm, including 50–56%,which is <1 mm). The sand fraction is commonly <2%,increasing up to 10–15% in the lowermost part of theHolocene (Fig. 3). This unit represents a typical marinehemipelagic facies, which is widespread in shelfdepressions of the Barents Sea (Lubinski et al. 1996).

The chronology of this unit is based on six AMS 14Cdates performed on mollusk shells (Fig. 3, Table 1). Acorrection of 410 years was applied to all conventional14C ages to take into account the difference between14C-dated terrestrial plant material and marine shellmaterial (the marine reservoir age). This differenceranges between 159 and 764 14C years in coastal marinemollusks from the Barents and Kara seas (Forman &Polyak 1997). The 410-year correction, which is similarto the present reservoir age in the Norwegian Sea(Bondevik et al. 1999), may be underestimated by a fewcenturies. Reservoir ages of ¶700 years have beenreported from coastal areas in the region (Forman &Polyak 1997), but no data are available for open waters.Corrected 14C ages have then been converted intocalendar ages using the marine calibration of Stuiver &Reimer (1993), which is well-established for theHolocene. Finally, the age of each core level has beencalculated using a 4-order polynomial � t of the calendarages at the six levels in which 14C ages where measuredand assuming a modern age for the surface sediment.The discussion below will therefore refer to calendarages.

The sedimentation rate of core ASV 880 is high.During the lower Holocene it was about 87.5 cm/ka.The sediment is characterized by a high sand content(up to 10% in the fraction 50–100 mm and 1–2% in thefraction >100 mm). The sand material, which was lessabundant than during the Late Glacial, was probablybrought by icebergs and abundant suspended materialsupplied by retreating Franz Josef Land glaciers. Thesedimentation rate and the sand fraction both decreasedprogressively during the middle Holocene and thesedimentation rate was only 22 cm/ka during the last4.5 ka.

Foraminifera

Samples of 2 cm thickness were taken every 5 cm alongthe core. When available, 200 to 300 tests of benthicforaminifera were identi� ed in a split aliquot of thesediment fraction >100 mm (Table 2). All planktonicforaminifera were identi� ed and counted. The sizefraction used makes our results comparable to other

Fig. 2. Temperature and salinity pro� les measured at the locationof core ASV 880 on 8 September 1997 during cruise-11 of the R/VAkademik Sergei Vavilov (courtesy of Yuri A. Ivanov).

Fig. 3. Lithology, grain size, number of planktonic and benthic foraminifera (tests/g dry sediment) variations versus depth in Core ASV880.

4 Jean-Claude Duplessy et al. BOREAS 30 (2001)

BOREAS 30 (2001) Holocene paleoceanography , northern Barents Sea 5

studies (Hald & Aspeli 1997; Hald & Korsun 1997;Hald et al. 1994; Steinsund & Hald 1994).

Planktonic foraminifera in core ASV 880 exhibit avariable preservation state and are almost exclusively ofthe species Neogloboquadrina pachyderma (left coil-ing). Their abundance is low (<16 tests/g) in the olive-gray clay and even lower in the older sediment. Theyalmost completely disappear below 295 cm, except forone isolated peak at 305 cm.

Only rare tests of benthic species were found instratigraphic units III and II, together with reworkedMesozoic and Cenozoic foraminifera. Forty benthictaxa were identi� ed in unit I. The number of species in agiven sample ranges from 6 to 23, and the totalabundance of benthic foraminifera varies between 1and 66 tests/g. When foraminifer shells exhibit noevidence of dissolution, we interpret these variations asbeing mainly due to changes in productivity. However,at some levels, dissolution is strong and results in thealmost total disappearance of foraminifer shells (Table2, Fig. 4). This episodic high dissolution has alreadybeen observed in several cores from the Barents Sea(Steinsund & Hald 1994; Polyak & Solheim 1994;Polyak & Mikhailov 1996).

Unit I can be subdivided into three subunits accord-ing to changes in the abundance of four typical Arcticspecies: Elphidium clavatum, Cassidulina reniforme,Islandiella helenae/norcrossi and Buccella spp.(Ivanova 1999). The lower subunit (305–160 cm) ischaracterized by abundant benthic foraminifera (up to66 tests/g) with the dominance (40 to 73%) of C.reniforme, a common species of distal glaciomarineenvironments (Polyak & Solheim 1994). E. clavatum ispresent throughout this subunit, but its abundance doesnot exceed 25%. I. helenae/norcrossi, which is linked toseasonally ice-free environments and is also common inglaciomarine sediments (Polyak & Solheim 1994;Korsun et al. 1995; Hald & Steinsund 1996), showsrather high percentages, especially in the upper part ofthe subunit (34%). The proportion of C. teretis, which atpresent is con� ned to areas in� uenced by Atlantic-derived water (Polyak & Solheim 1994; Jennings &Weiner 1996), is low (<3%).

The distribution of major species changes dramati-cally at 160 cm, i.e. at about 6.8 ka BP (Fig. 4). The

abundance of both benthic and planktonic foraminiferaincreases. Benthic assemblages between 160 and 90 cmexhibit a diversity higher than that in the lower part ofthe core (11 to 24 species per sample) and a similarpercentages of E. clavatum, C. reniforme and Buccellaspp. The latter is assumed to indicate a higher seasonalproductivity (Polyak & Solheim 1994). The permanentpresence of C. teretis and an increased content ofNonion barleeanum, which also prefers the Atlantic-derived water, characterize this subunit, as well as ahigh abundance of stenohaline Nonion labradoricum,which is likely controlled by food supply (Polyak &Solheim 1994; Polyak & Mikhailov 1996).

In the upper subunit (90–0 cm, 4.1–0 ka BP), thespecies diversity is similar to that of the lower subunit.E. clavatum, a common species of proximal glacio-marine and stress environments becomes dominant. N.labradoricum is common. C. teretis and N. barleeanumare present mainly at the bottom of the subunit.

Stable isotopes

Stable isotope measurements were performed with aFinnigan MAT 251 mass spectrometer with an auto-mated Kiel Device and using NBS 19 and NBS 18 asreference standards to ensure a proper calibration on alarge range of 18O values. Oxygen and carbon isotopeswere measured on the planktonic foraminiferal speciesN. pachyderma (left coiling) and on the benthic speciesE. clavatum, which were both continuously present inthe upper 295 cm of the core. Below this level, benthicforaminifera disappear and N. pachyderma (left coiling)is only abundant enough at 305 and 335 cm to make oneisotope analysis (Fig. 5). At these levels, values arealmost equal to those measured at 295 cm depth and wecould � nd no evidence for light 18O values similar tothose measured by Lubinski et al. (1996) during thedeglaciation in the nearby core JPC 5 raised also fromthe Franz Victoria Trough. In fact, the deepest levelsanalyzed in core ASV 880 are younger than those ofcore JPC 5. We did not � nd enough foraminifera forisotope analysis during the deglaciation, because thesedimentation rate of core ASV 880 is larger than that ofcore JPC 5 and foraminifera are strongly diluted by

Table 1. Radiocarbon dates and calculated calendar ages used to provide an age model for Unit 1 of core ASV 880. The AMS 14C agesobtained from marine carbonate s have been adjusted by a standard correction of 410 years for apparent age of bottom water in the BarentsSea (Forman & Polyak 1997).

Lab code GifA Depth (cm) Age (Years BP) 1 (Years) Cal. BP (Years) Species

99457 25 1550 60 1104 Yoldiella lucida99385 46 2440 60 2082 Yoldiella lenticula99386 166 6560 80 7081 Yoldiella fraterna99458 216 7420 80 7866 Yoldiella lenticula , intermedia, lucida99387 266 8830 90 9282 Yoldiella fraterna99388 305 9150 90 9814 Yoldiella fraterna

6 Jean-Claude Duplessy et al. BOREAS 30 (2001)

clay. The AMS 14C dates obtained on core ASV 880 andthe correlation with the record of core JPC 5 indicatesthat the isotope record of core ASV 880 begins about10 ka ago, i.e. 1400 years after the end of the YoungerDryas (Bjorck et al. 1996).

The most striking result of the foraminiferal 18Ovariations in core ASV 880 is the strong correlationbetween the planktonic and benthic records, althoughsome signi� cant differences could be observed. Bothrecords begin with a decreasing trend, which may becorrelated with the last phase of the deglaciation(Termination IB, (Duplessy et al. 1981b)). This trendis interrupted by a cooling event of short duration (8.25–7.85 ka BP). The deglacial warming ends with 18Ovalues lighter than those of today about 7.5 ka ago.However, the light 18O peak, which developedbetween 7.85 and 6.9 ka BP and marks the Holocenetemperature optimum is cut by a sharp 18O increase ofshort duration at 7.3 ka BP. The warm conditions endwith a sharp 18O increase at 6.9 ka BP. The planktonic

18O record then exhibits a slow decrease until 3.7 ka

BP and minor variations during the upper Holocene.During the same time interval, the benthic 18O recordexhibits an increasing trend until 4.8 ka BP, re� ecting asigni� cant change of the hydrological structure of theBarents Sea after the temperature optimum.

Discussion

Signi� cance of the oxygen isotope records

Foraminifer 18O variations in a deep-sea core re� ectboth temperature and 18O changes in the water inwhich these animals grew their shells. Benthic for-aminifera record hydrological changes at the sediment-water interface. However, most benthic species pre-cipitate their shells in isotopic disequilibrium andexhibit a constant offset from the equilibrium value(Duplessy et al. 1970; Woodruff et al. 1980; Graham etal. 1981; Vincent et al. 1981; Duplessy et al. 1984;Grossman 1984; Grossman 1987). Recently, Poole(1994) showed that E. clavatum exhibits 18O valueswhich are 0.85 § 0.20% lighter than equilibrium. Ourcore top measurement for this species in core ASV 880is in agreement with this calibration. Isotopic disequili-brium is also observed in planktonic foraminifera(Fairbanks et al. 1979; Duplessy et al. 1981a; Bauchet al. 1997). Bauch et al. (1997) and Carstens (1997)demonstrated that the average depth of calci� cation ofN. pachyderma (left coiling) in the Arctic Ocean variesbetween 100 and 200 m and that its 18O values areconsistently lighter than equilibrium values by about1%. This offset is somewhat larger than that determinedin the Southern Ocean (Labeyrie et al. 1986; Charles &Fairbanks 1990) and we still do not know its cause.Therefore, in the Arctic Ocean and in the Barents Sea,this species calci� es in Atlantic waters below the lowsalinity layer associated with summer sea ice melting.

The sea water 18O variations re� ect salinity changesresulting from three causes, namely continental icemelting, changes in the hydrological cycle (Precipita-tion ‡ Runoff ¡ Evaporation), and changes in rate ofadvection and mixing, whose effects are additive. Seawater 18O variations caused by global continental icevolume changes are large during the deglaciation, butthey are still signi� cant during the lower Holocene: thesea level was 33 m below present 10 ka ago and still20 m below present 7.5 ka ago (Bard et al. 1990;Fairbanks 1990). The deglaciation was only completedby 5.5 ka BP (Denton & Hughes 1981).

In order to reconstruct foraminifer 18O variationsowing to local sea water temperature and 18O changes,we subtracted the sea water 18O variations caused byice-sheet melting from the planktonic and benthic 18Orecords of core ASV 880. We used the sea water 18Orecord computed by Labeyrie et al. (1987), aftercorrection of the original 14C time scale into calendarages. The resulting local 18O records for the northern

Fig. 4. Abundance variations of the main species of benthic fora-minifera versus calendar age in core ASV 880.

BOREAS 30 (2001) Holocene paleoceanography , northern Barents Sea 7

Barents Sea (Fig. 6A) show that the isotopically lightpeak, which occurred between 7.85 and 6.9 ka BPreached much lighter values than the present, indicatingeither warmer sea-water temperature or lower 18Ovalues (i.e. salinity) than those of today.

The general features of the 18O distributionmeasured in the upper waters of the present-day ArcticOcean exhibit low values in the northern/westernEurasian Basin increasing progressively toward theBarents Shelf, where they reach their maximum value

Fig. 5. A. Oxygen and B. carbon isotope records versus age of the planktonic species Neogloboquadrin a pachyderma (left coiling) andthe benthic species Elphidium clavatum in core ASV 880.

8 Jean-Claude Duplessy et al. BOREAS 30 (2001)

(Bauch et al. 1995). This trend re� ects the strongcontribution of river-runoff to the surface water of thecentral Eurasian Basin and in the Canadian Basin. Bycontrast, the contribution of the Siberian rivers to thenorthern Barents Sea is negligible. During the Holo-cene, a large freshwater supply to the Nordic Seas hasbeen recorded during the early Preboreal (Hald &Hagen 1998), i.e. a few centuries before the beginningof the isotope record of core ASV 880. No other largefreshwater � uxes have been evidenced in the isotopeand climatic records of high latitude Norwegian Seacores (Hald et al. 1996). These results strongly suggestthat the local 18O records of both the N. pachyderma(left coiling) and E. clavatum corrected for the globalcontinental ice-melting effect re� ect mainly BarentsSea water temperature variations respectively forAtlantic waters at intermediate depth (100–200 m)and for the sediment-water interface. This hypothesis issupported by recent 18O measurements performed onbenthic foraminifera from core ASV 1157 (70°33’ N,52°48’ E, 1669 m). This core has been raised from anarea of winter brine formation and surface watersinking. The water temperature is colder than ¡1°Cbelow 100 m depth during late winter and spring and isnot likely to have experienced any large cooling duringthe Holocene. The benthic 18O record of core ASV1157 re� ects therefore mainly Barents Sea water 18Ochanges. In contrast to the 18O record of core ASV 880,the benthic record of core ASV 1157 exhibits nosigni� cant 18O variations between 8200 and 4400cal. yr BP, indicating that the Barents Sea exhibited nosigni� cant local 18O changes associated with fresh-water discharge during the lower to middle Holocene.As N. pachyderma (left coiling) and E. clavatum exhibitalmost the same departure from isotopic equilibrium, anapproximate temperature scale has been reported in Fig.6A, assuming that the core top re� ects modern condi-tions and that the water temperature decreases by 1°Cwhen the foraminifer 18O value increases by 0.25%(Shackleton 1974).

The long-term Holocene record

The local isotope records exhibit both long-term andhigh-frequency variations. We will discuss � rst the low-frequency variations. After the lower Holocene, bothplanktonic and benthic foraminifera underwent aprogressive warming, which culminates about 7.5 kaago. The optimum conditions � nished abruptly about6.9 ka ago and an 0.5% 18O increase of bothplanktonic and benthic foraminifera indicates a ¹2°Ccooling of subsurface and bottom waters within a fewcenturies. About 6.7 ka ago, the subsurface temperaturewas similar to that prevailing before the thermalmaximum. It returned progressively to slightly warmerconditions with several oscillations. However, duringthe last 6000 years, sea surface conditions have neverbeen as warm as those of the thermal optimum, which

lasted only about one thousand years, from 7.85 to6.9 ka BP.

Conditions at the bottom of the Barents Sea evolveddifferently from those of the subsurface after the strongcooling, which followed the temperature optimum.Whereas subsurface temperature increased between6.7 and 3.7 ka BP, the 18O values of benthicforaminifera show that the bottom of the Barents Seacontinued to cool progressively until ¹4.7 ka BP. Thistrend is best explained by the invasion of very coldbottom waters, the temperature of which was close tofreezing point and which mixed with Atlantic waters.Like the planktonic foraminifera, the 18O value ofbenthic foraminifera underwent several oscillationsduring the upper Holocene, but never reached the lightvalues found during the temperature optimum.

In order to compare the evolution of hydrologicconditions prevailing in the Atlantic waters and at thebottom more accurately, we subtracted the planktonic

18O record from the benthic 18O record. Thisdifference measures approximately the temperaturedifference between subsurface and bottom waters andcharacterizes the strati� cation of the water column (Fig.6B). It shows large variations associated with theclimatic and environmental changes in the Barents Sea.

The Lower Holocene (10 to 7.85 ka BP). – About 10cal. ka ago, bottom waters were very cold (¡1°C) andthe strati� cation was characterized by a temperaturedifference of ¹1.5°C between subsurface and deepwaters. During the following centuries, the strati� cationdecreased because the warming of bottom water wasstronger than that of subsurface waters. This trend isbest explained by decreasing penetration of Barents Seabottom water into the Franz Victoria Trough, whereAtlantic water became dominant from subsurface to thebottom.

The benthic assemblage also re� ects fairly favorableconditions during the lower Holocene. The presence ofplanktonic foraminifera and C. teretis above 305 cmsuggests an early invasion of Atlantic waters into theFranz Victoria Trough, in agreement with previousobservations (Polyak & Solheim 1994). High abun-dance of benthic and planktonic foraminifera indicates ahigh surface water productivity during the ice-freeseason.

The thermal optimum (7.85–6.9 ka BP). – The 18Ovalue of benthic foraminifera is barely higher than thatof the planktonic species N. pachyderma. The strati� ca-tion was therefore minimal during the temperatureoptimum and the Franz Victoria Trough was entirelyoccupied by Atlantic water below subsurface. Theabsence of cold water at the bottom of the troughsuggests that the formation of dense bottom water in theBarents Sea was considerably reduced during this warmepisode.

The presence of Atlantic waters in most of the watercolumn of the Barents Sea during the Holocene thermal

BOREAS 30 (2001) Holocene paleoceanography , northern Barents Sea 9

optimum is supported by the 13C values of E. clavatumand N. pachyderma (left coiling), which are lower thantoday. Foraminifer 13C values are generally high in theArctic Ocean, because the ventilation of the surfacewater is high on the seasonally open shelves, whereaslow 13C values in the southern Eurasian basin arerelated to the intrusion of Atlantic water (Spielhagen &Erlenkeuser 1994).

The Holocene thermal optimum is marked by highsedimentation rates, possibly owing to abundant sus-pended matter supply from melting glaciers of FranzJosef Land and Svalbard under relatively warm climaticconditions. Benthic foraminiferal assemblages differfrom the older ones by an increased percentage of I.helenae/norcrossi and lower values of the opportunisticspecies E. clavatum. This possibly re� ects the longerduration of the ice-free season and the retreat of the sea-ice margin. The decrease in benthic foraminiferalabundance supports the latter suggestion. However,the relative abundance of C. teretis and planktonicforaminifera is not increasing, which indicates that theabundance of these species does not depend solely onAtlantic water in� ow, but also on other factors such asprimary production of surface waters and food avail-ability.

The Upper Holocene (6.9 ka BP–present). – Thestrati� cation was small during the cooling whichfollowed the temperature optimum and the temperaturedecrease affected the whole water column of the FranzVictoria Trough. Consequently, either the � ux ofAtlantic waters was strongly reduced or Atlantic waterswhich penetrated the Barents Sea were much colderthan today. The 13C values of N. pachyderma (leftcoiling) exhibit a large increase associated with the

18O increase and their values are similar to the present( 13C ¹0.4–0.6%). However, these 13C values are stilllower than those of N. pachyderma (left coiling) livingin Arctic water, which are commonly >0.7% (Spiel-hagen & Erlenkeuser 1994). This suggests that theintermediate water in Franz Victoria Trough was, liketoday, an Atlantic-derived water mass, but that theAtlantic water was mixed with a much larger amount ofArctic water than during the temperature optimum.

The strati� cation increased during the interval 6.7 to4.7 ka BP, whereas subsurface waters experienced amoderate warming, at least during summer conditionswhen N. pachyderma grows (Kohfeld et al. 1996), thedeep waters continued to cool. The decoupling betweenthe hydrology of subsurface and deep waters indicatesthat Atlantic water became restricted to intermediatedepth, like today. Simultaneously, the bottom of theBarents Sea was invaded by dense and cold waterformed through rejection of brine during freezing, as isobserved today, particularly on the Novaya ZemlyaShelf and other shallow areas (Midttun 1985). Thebottom water at the location of core ASV 880 became amixture of warm Atlantic water and cold dense brine

water. The 18O variations of benthic foraminiferaduring the upper Holocene re� ect in a complex way themixture composition. Atlantic waters are warm (0.5–1°C) with a 18O value of about 0.27%. Brine watersare cold (¡1.8°C when they form) and their 18O valueis probably lower than that of Atlantic waters, becausethey form in coastal areas by freezing of surface seawater diluted by Arctic water or river discharge. Nomeasurements are presently available in the BarentsSea, but 18O value in the range 0 to ¡0.2% have beenmeasured in the Laptev Sea (Bauch 1995). As the 18Ovalues of benthic foraminifera increase by 0.25% whenthe sea water temperature decreases by 1°C, thepresently available data suggest that the temperatureeffect will be dominant: Increasing 18O values ofbenthic foraminifera will re� ect colder bottom waters,richer in brine. As a matter of fact, benthic andplanktonic 18O variations tend to be parallel duringthe Upper Holocene. This suggests that Atlantic waterswere more abundant in the mixture when the subsurfacetemperature (as indicated by the 18O value of N.pachyderma) was high. During these events, thetemperature difference between intermediate and bot-tom water decreased, as is observed noticeably between3.3 and 4.3 ka BP, and at 2.3 ka BP.

Large faunal changes are associated with the coolingthat marked the end of the temperature optimum. Thepercentages of C. reniforme and I. helenae/norcrossidecreased drastically, whereas those of E. clavatum andBuccella spp. increased. The number of both planktonicand benthic foraminifera � rst decreased, but it increasedrapidly with the warming of the Atlantic waters after6 ka BP. A southward shift of summer sea-ice marginafter the thermal optimum resulted in higher primaryproduction, thus providing suf� cient food for bothplanktonic and benthic foraminifera. This, in turn,created favorable conditions for Buccella spp. and N.labradoricum, which are known to be very sensitive tofood supply (Polyak & Mikhailov 1996).

Comparison with other climatic records

An early Holocene temperature maximum has alreadybeen found in both continental and marine records (seeCrowley & North (1991) for a review). In accordancewith the present study, thermophilus molluscs fromSvalbard (Salvigsen et al. 1992), foraminifera anddiatoms from the Iceland and Norwegian seas (KocKarpuz & Jansen 1992; Veum et al. 1992; Koc et al.1993; Sarnthein et al. 1995; Lubinski et al. 1996), andcontinental records from Scandinavia based on vegeta-tion changes (Selsing & Wishman 1984; Makela &Hyvarynen 2000), glacier � uctuations (Karlen 1988;Nesje et al. 1991) or 18O variations from Agassiz IceCap in Ellesmere Island (Fisher et al. 1995) record atemperature optimum around 7–9 ka BP. This optimumappeared about 4 ka after the June solar insolationmaximum at 80°N. The lag in temperature versus

10 Jean-Claude Duplessy et al. BOREAS 30 (2001)

insolation indicates that, in addition to insolation, localfeedback mechanisms, such as the remnants of thecontinental ice sheet, which melted progressively orsea-ice cover variations played a signi� cant role in theregional climate.

Other trends of the paleoclimatic record of core ASV880 have been found in the Barents Sea, in northernScandinavia and at lower latitudes in the NorwegianSea. A general climatic deterioration with heavy iceconditions during the middle and late Holocene waspostulated earlier to explain the general decrease in thetree-line altitude in northern Sweden, the glacieradvance in the Scandinavian mountains (Karlen &Kuylenstierna 1996) and the increasing abundance of E.clavatum in Barents Sea sediment cores (Polyak &Solheim 1994; Polyak & Mikhailov 1996). Low SSTshave been recorded in two cores from the uppercontinental slope of the northern Norwegian Sea about6.514C ka BP, i.e. ¹7.3 ka ago (Hald & Aspeli 1997).These cores, which have a low sedimentation rateduring the Holocene, did not register the short warmevent that is recorded 6.9 cal. ka ago in core ASV 880.A cooling along the coasts of the Nordic Seas at the endof the temperature maximum was required to initiatecold conditions allowing brine formation in the BarentsSea, as shown by the benthic record of core ASV 880. Areturn to warmer conditions about 4.2 ka ago (3.8 14C kaago) was marked by an increase of Atlantic diatomabundance in a core from the southeastern NorwegianSea (Koc Karpuz & Jansen 1992).

The duration of the Holocene thermal optimum wasmuch shorter in the northern Barents Sea than at lowerlatitudes in the Norwegian Sea. Koc et al. (1993)compared the paleoclimatic records of a set of coresfrom the Norwegian-Greenland Sea and showed that theduration of this optimum decreased both towards thenorth and to the margins of this area. The isotope recordof core ASV 880 con� rms this trend dramatically andexhibits a very short temperature optimum: the warmerconditions were maintained during less than 1000 years,from 7.85 to 6.9 ka BP at ¹80°, whereas they lasted¹2200 years, from 9 to 7.8 ka BP, in core M 23071 at¹67°N and ¹3200 years, from 9 to 5.8 ka BP, in coreHO 79 6/4 at ¹63°N (Koc et al. 1993). Both the carbonand oxygen isotope records of core ASV 880 and thediatom changes in the Norwegian Sea cores (Koc et al.1993) show that this climatic trend is associated withthe progressive northward expansion of Atlantic watersfrom 10 ka to 7.8 ka BP, followed by their southwardretreat after 6.9 ka BP. The sharp cooling whichoccurred at this time indicates that the Nordic Seasresponded very early to the decreasing summer insola-tion, as suggested by Imbrie et al. (1992). The climaticevolution of the Holocene is therefore very similar tothat reconstructed for the last interglaciation, theEemian: an early high latitude warming occurred atthe beginning of the interglaciation and a cooling trend,which begins at the highest latitudes, expanded pro-

gressively toward middle latitudes (Cortijo et al. 1994;Cortijo et al. 1999).

The high-frequency variations

In Fig. 6 it is shown that short-term 18O/temperaturevariations are superimposed on the long-term varia-tions, discussed previously. Two abrupt cold events arenoticeable: The � rst one occurred during the terminalphase of the deglaciation. SST increased from 10 to8.7 ka BP in the Barents Sea, and by 8.7 ka BPsubsurface waters were as warm as they are today.This warming period ended in a sharp cooling, whichlasted a few centuries, from 8.25 to 7.85 ka BP. Thiscold event is contemporaneous with the cold perioddetected both in the Greenland ice (Alley et al. 1997)and the ostracod valves present in sediments from lakeAmmersee (southern Germany) around 8.2 ka BP (vonGrafenstein et al. 1998). The 18O records of benthicand planktonic foraminifera show that the temperaturedecrease affected both Atlantic and bottom waters in theBarents Sea. This climatic event, which is bestexplained by the injection into the Labrador Sea ofLaurentide meltwaters (von Grafenstein et al. 1998;Barber et al. 1999), affected Atlantic surface watersbefore they entered the Arctic Ocean. It was associatedwith an increase in Barents Sea bottom-water formationduring winter freezing. This is compatible with areduction of the thermohaline circulation and thenorthward � ux of Atlantic water, allowing this waterto release its heat content into the middle latitudesbefore it reaches the Arctic Ocean.

The second noticeable abrupt cold event cut theHolocene temperature maximum during about threecenturies and culminated about 7.2 ka ago. It isassociated with a moderate increase of the water columnstrati� cation, suggesting that the bottom waters of FranzVictoria Trough might already have received somecontribution of cold brine water. This cold event, whichwas considered as the end of the climatic optimum byHald & Aspeli (1997) in the southern Barents Sea, isstill poorly documented. It coincides with a signi� cantdecline of alder in the western mountains of Norwayand interpreted as the beginning of glacier growth onthe Jostedalsbreen Plateau, at altitudes above 1500 m(Nesje et al. 1991). It is also contemporaneous with asmall, negative 18O excursion (cooling) in Greenlandice (Johnsen et al. 1992), whose amplitude is about halfthat of the 8.2 ka event. However, at the same time,North Atlantic sediment cores contain a minimum ofice-rafted debris, re� ecting warm climatic conditionsbetween 50°N and 65°N (Duplessy et al. 1992; Bond etal. 1997). The cold event that we detected in BarentsSea core ASV 880 is therefore restricted to the highlatitudes and its origin is unknown.

BOREAS 30 (2001) Holocene paleoceanography , northern Barents Sea 11

Conclusion

Faunal and isotope studies of core ASV 880 show thatthe Barents Sea underwent long-term and short-termclimatic changes during the Holocene. The warmer

temperatures occurred between 7.85 and 6.9 ka BP andthis thermal optimum had a much shorter duration at80°N than at lower latitudes, where its duration mayexceed three millennia. Most local climatic changesappeared linked to changes in the � ux of warm Atlantic

Fig. 6. &A. Local 18O changes in the planktonic species Neogloboquadrin a pachyderma (left coiling) and the benthic species Elphidiumclavatum versus age in core ASV 880. The approximate temperature scale has been established assuming that the core top re� ects modernconditions and that the water temperature decreases by 1°C when the foraminifer 18O value increases by 0.25% (Shackleton 1974). &B.

18O difference between the benthic species Elphidium clavatum and the planktonic species Neogloboquadrin a pachyderma (left coiling).This difference re� ects mainly the temperature difference between the Atlantic water and the bottom water at the location of core ASV880.

12 Jean-Claude Duplessy et al. BOREAS 30 (2001)

Tab

le2.

Num

ber

ofpl

ankt

onic

and

bent

hic

fora

min

ifer

a/g

sedi

men

tan

dpe

rcen

tage

abun

danc

eof

bent

hic

fora

min

ifer

ain

core

ASV

880.

Dep

th(c

m)

Plan

kton

icfo

ram

nife

rape

rgr

amse

dim

ent

Ben

thic

fora

mni

fera

per

gram

sedi

men

t%

E.

clav

atum

% Isla

ndie

llasp

p.%

Buc

cell

asp

p.%

Cas

.re

nifo

rme

%C

as.

tero

tis

%N

.ba

rlee

anum

%N

.la

brad

oric

um%

Oth

ers

06

3146

1310

150

05

115

14

4914

84

31

417

1016

3836

1217

150

03

1615

217

4112

1110

00

422

200

0**

***

***

***

***

***

***

***

*25

02

5711

910

00

112

300

136

915

105

05

2035

314

327

2113

01

1016

401

844

1411

90

09

1445

00

***

***

***

***

***

***

***

***

500

0**

***

***

***

***

***

***

***

*55

04

3815

515

00

918

600

0**

***

***

***

***

***

***

***

*65

16

398

75

30

1027

700

351

610

41

09

1775

17

465

154

40

1314

801

642

217

101

114

1485

110

572

179

00

86

900

632

231

61

317

995

03

381

255

10

624

100

110

355

2313

21

120

105

29

375

2022

31

57

110

210

315

2216

20

1311

115

223

294

2324

11

145

120

117

312

2130

00

95

125

220

404

2018

30

86

130

434

374

2423

12

46

135

857

244

2432

10

77

140

432

224

1629

22

149

145

725

375

1719

24

88

150

517

346

1630

21

66

155

18

2221

1322

04

144

160

07

1717

2426

06

74

165

35

1532

246

10

12

170

316

815

370

00

12

175

06

1319

654

30

50

180

39

934

252

00

11

185

18

1019

564

00

11

190

29

1011

273

01

03

195

518

196

370

00

00

200

332

157

173

00

04

205

212

2515

356

00

01

210

110

723

652

00

012

215

26

1719

538

11

417

220

119

1415

359

11

07

225

413

920

554

11

09

230

111

1611

650

04

211

BOREAS 30 (2001) Holocene paleoceanography , northern Barents Sea 13

waters entering the Barents Sea. The deglacial warmingwas associated with the progressive invasion of warmAtlantic waters into this basin. During the temperatureoptimum, the Atlantic water occupied the whole watercolumn of Franz Victoria Trough. This indicates thatvery little deep water sank along the Barents Sea shelf.The strong cooling, which marked the end of theclimatic optimum, was associated with a reduction inthe � ux of Atlantic water reaching the Arctic. Theslowing thermohaline circulation resulted � rst in atemperature drop of the Atlantic waters penetrating theArctic Ocean. These cold conditions allowed surfacewater freezing during winter, so that the bottom of theBarents Sea was progressively invaded by dense andcold water formed through rejection of brine duringfreezing, as is observed today. The bottom water inFranz Victoria Trough became a mixture of Atlanticwater and dense brine water. The composition of thismixture varied during the upper Holocene, followingthe intensity of the oceanic conveyor belt.

Acknowledgements . – Sediment core ASV-880 was sampled duringa cruise of the R/V Akademik Sergei Vavilov, which was � nancedby the P. P. Shirshov Institute of Oceanology , Russian Academy ofSciences. We acknowledge the � nancial support of RFBR-CNRS(PICS grant 98-05-22029) , CEA, CNRS-INSU and EU-DGXII(ENVC-CT97-0643). We also thank E. Jansen for his comments onthe manuscript and express our gratitude to T. A. Khusid for assis-tance with foraminifera l sampling, M. Belusov for drawing � gures,B. Le Coat, E. Kaltnecker , H. Leclaire, B. Lehman, N. Tisnerat forisotope analyses , V. P. Kazakova and A. N. Rudakova for grain-size analyses , and L. V. Polyak and T. A. Khusid for taxonomichelp. We also extend our thanks to Morten Hald and Mark Maslinfor a careful review of the manuscript and for offering constructivecomments.

ReferencesAlley, R. B., Mayewski, P. A., Sowers, T., Stuiver, M., Taylor, K.

C. & Clark, P. U. 1997: Holocene climatic instability : a promi-nent, widespread event 8200 yr ago. Geology 25, 483–486.

Anonymous 1998: Climatic Atlas of the Barents Sea. NOAA AtlasNESDIS 26, World Data Center-A for Oceanography .

Barber, D. C., Dyke, A., Hilaire-Marcel , C., Jennings , A. E.,Andrews, J. T., Kerwin, M. W., Bilodeau, G., McNeely, R.,Southon, J., Morehead, M. D. & Gagnon, J. M. 1999: Forcing ofthe cold event of 8200 years ago by catastrophi c drainage ofLaurentide lakes. Nature 400, 344–348.

Bard, E., Hamelin, B., Fairbanks, R. G. & Zindler, A. 1990: Cali-bration of the 14C timescale over the past 30000 years usingmass spectrometri c U-Th ages from Barbados corals. Nature345, 405–410.

Bauch, D. 1995: The distribution of 18O in the Arctic Ocean:implications for the freshwater balance in the Halocline and thesources of deep and bottom waters. Berichte zur Polarforschung ,144 pp., AWI Bremerhaven.

Bauch, D., Carstens, J. & Wefer, G. 1997: Oxygen isotopic compo-sition of living Neogloboquadrin a pachyderma (sin.) in the Arc-tic Ocean. Earth and Planetary Science Letters 146, 47–58.

Bauch, D., Schlosser, P. & Fairbanks, R. G. 1995: Freshwater bal-ance and the sources of deep and bottom waters in the ArcticOcean inferred from the distribution of H2

18O. Progress inOceanography 35, 53–80.

Bjorck, S., Kromer, B., Johnsen, S., Bennike, O., Hammarlund, D.,Tab

le2.

Con

tinue

d.

Dep

th(c

m)

Plan

kton

icfo

ram

nife

rape

rgr

amse

dim

ent

Ben

thic

fora

mni

fera

per

gram

sedi

men

t%

E.

clav

atum

% Isla

ndie

llasp

p.%

Buc

cell

asp

p.%

Cas

.re

nifo

rme

%C

as.

tero

tis

%N

.ba

rlee

anum

%N

.la

brad

oric

um%

Oth

ers

235

215

109

769

01

32

240

236

78

771

02

12

245

***

***

***

***

***

***

***

***

250

18

1519

438

01

319

255

441

194

554

00

215

260

121

176

251

11

021

265

00

***

***

***

***

***

***

***

***

270

00

***

***

***

***

***

***

***

***

275

663

81

263

00

025

280

12

1512

79

10

354

285

113

205

750

00

117

290

519

217

645

11

514

295

016

2219

541

00

111

300

***

***

***

***

***

***

***

***

305

434

145

364

10

49

14 Jean-Claude Duplessy et al. BOREAS 30 (2001)

Lemdahl, G., Possnert, G., Rasmussen, T., Wohlfarth, B., Ham-mer, C. & Spurk, M. 1996: Synchronized terrestrial-atmospheri cdeglacia l records around the North Atlantic. Science 274, 1155–1160.

Bond, G., Broecker, W. S., Johnsen, S., McManus, J., Labeyrie, L.,Jouzel, J. & Bonani, G. 1993: Correlations between climaterecords from North Atlantic sediments and Greenland ice. Nat-ure 365, 143–147.

Bond, G., Heinrich, H., Broecker, W. S., Labeyrie, L., MacManus,J., Andrews, J., Huon, S., Jantschik , R., Clasen, S., Simet, C.,Tedesco, K., Klas, M., Bonani, G. & Ivy, S. 1992: Evidence formassive discharges of icebergs into the North Atlantic oceanduring the last glacial period. Nature 360, 245–251.

Bond, G., Showers, W., Cheseby, M., Lotti, R., Almasi, P., deMe-nocal, P., Priore, P., Cullen, H., Hajdas, I. & Bonani, G. 1997:A pervasive millenial-scale cycle in North Atlantic Holoceneand glacial climates. Science 278, 1257–1266.

Bondevik, S., Birks, H. H., Gulliksen, S. & Mangerud, J. 1999:Late Weichselian marine 14C reservoir ages at the western coastof Norway. Quaternary Research 52, 104–114.

Broecker, W. S. 1997: Thermohaline circulation , the Achilles heelof our climate system: will man-made CO2 upset the current bal-ance? Science 278, 1582–1588.

Carstens, J., Hebbeln, D. & Wefer, G. 1997: Distribution of plank-tic foraminifera at the ice margin in the Arctic (Fram Strait).Marine Micropaleontolog y 29, 257–269.

Charles, C. D. & Fairbanks, R. G. 1990: Glacial to interglacialchanges in the isotopic gradients of the Southern Ocean surfacewaters. In Bleil, U. & Thiede, J. (eds.): Geologic History of thePolar Oceans, 519–538. Kluwer Academics Publishers, Dor-drecht.

Cortijo, E., Duplessy, J. C., Labeyrie, L., Leclaire, H., Duprat, J. &van Weering, T. C. E. 1994: Eemian cooling in the NorwegianSea and North Atlantic Ocean preceding continental ice-sheetgrowth. Nature 372, 446–449.

Cortijo, E., Lehman, S., Keigwin, L. D., Chapman, M., Paillard, D.& Labeyrie, L. 1999: Changes in meridional temperature andsalinity gradients in the North Atlantic Ocean (32° to 72°N) dur-ing the last interglacia l period. Paleoceanograph y 14, 23–33.

Crowley, T. & North, G. 1991: Paleoclimatology . 339 pp. Univer-sity Press, New York.

Denton, G. & Hughes, T. 1981: The Last Great Ice Sheets 484 pp.J. Wiley & Sons, New York.

Duplessy, J.-C., Blanc, P. L. & Be, A. W. H. 1981a: Oxygen-18enrichment of planktonic foraminifera due to gametogenic calci-� cation below the euphotic zone. Science 213, 1247–1250.

Duplessy, J. C., Delibrias, G., Turon, J. L., Pujol, C. & Duprat, J.1981b: Deglacial warming of the Norheastern Atlantic Ocean:correlation with paleoclimati c evolution of the European conti-nent. Palaeogeography , Palaeoclimatology , Palaeoecology 35,121–144.

Duplessy, J. C., Labeyrie, L., Arnold, M., Paterne, M., Duprat, J.& van Weering, T. C. E. 1992: Changes in surface salinity ofthe North Atlantic Ocean during the last deglaciation . Nature358, 485–487.

Duplessy, J. C., Lalou, C. & Vinot, A. C. 1970: Differentia l isoto-pic fractionation in benthic foraminifera and paleotemperature sreassessed. Science 168, 250–251.

Duplessy, J.-C., Shackleton, N. J., Matthews, R. K., Prell, W., Rud-diman, W. F., Caralp, M. & Hendy, C. H. 1984: 13C recordbenthic foraminifera in the last interglacia l ocean: implicationsfor the carbon cycle and the global deep water circulation. Qua-ternary Research 21, 225–243.

Fairbanks, R. G. 1990: The age and origin of the ‘Younger Dryasclimate event’ in Greenland ice cores. Paleoceanograph y 5,937–948.

Fairbanks, R. G., Wiebe, P. H. & Be, A. W. H. 1979: Vertical dis-tribution and isotopic composition of living planktonic foramini-fera in the western North Atlantic. Science 207, 61–63.

Fisher, D. A., Koerner, R. M. & Reeh, N. 1995: Holocene climatic

records from Agassiz Ice Cap; Ellesmere Island, NWT, Canada.The Holocene 5, 19–24.

Forman, S. L. & Polyak, L. 1997: Radiocarbon content of pre-bomb marine mollusks and variations in the 14C reservoir agefor coastal areas of the Barents and Kara seas, Russia. Geophysi-cal Research Letters 24, 885–888.

Fronval, T. & Jansen, E. 1996: Rapid changes in ocean circulationand heat � ux in the Nordic seas during the last interglacia l per-iod. Nature 383, 806–810.

Graham, D. W., Corliss, B. H., Bender, M. L. & Keigwin, L. D.1981: Carbon and oxygen isotopic disequilibriu m of recent deepsea benthic foraminifera . Marine Micropaleontolog y 6, 483–497.

GRIP project members. 1993: Climatic instability during the lastinterglacial period revealed in the Greenland summit ice-core.Nature 364, 203–207.

Grossman, E. L. 1984: Stable isotope fractionation in live benthicforaminifera from the southern California borderland . Palaeo-geography , Palaeoclimatology , Palaeoecology 47, 301–327.

Grossman, E. L. 1987: Stable isotope in modern benthic foramini-fera: a study of vital effect. Journal of Foraminiferal Research17, 48–61.

Hald, M. & Aspeli, R. 1997: Rapid climatic shifts of the northernNorwegian Sea during the last deglaciation and the Holocene.Boreas 26, 15–28.

Hald, M., Dokken, T. & Hagen, S. 1996: Paleoceanograph y of theEuropean Arctic margin during the last deglaciation . InAndrews, J. T., Austin, W. E. N., Bergsten, H. & Jennings , A.E. (eds.): Late Quaternary Paleoceanograph y of the NorthAtlantic Margins, 275–287. Geological Society Special Publica-tions 111, Boulder.

Hald, M. & Hagen, S. 1998: Early Preboreal cooling in the Nordicseas region triggered by meltwater. Geology 26, 615–618.

Hald, M., Kolstad, V., Polyak, L., Forman, S. L., Herlihy, F. A.,Ivanov, G. & Nescheretov, A. 1999: Late-glacia l and Holocenepaleoceanograph y and sedimentary environment s in the St.Anna Trough, Eurasian Arctic Ocean margin. Palaeogeography,Palaeoclimatology , Palaeoecology 146, 229–249.

Hald, M. & Korsun, S. 1997: Distribution of modern benthic fora-minifera from fjords of Svalbard, European Arctic. Journal ofForaminiferal Research 27, 101–122.

Hald, M. & Steinsund, P. I. 1996: Benthic foraminifera and carbo-nate dissolution in the surface sediments of the Barrents andKara Seas. In Stein, R., Ivanov, G. I., Levitan, M. A. & Fahl, K.(eds.): Surface Sediments Composition and Sedimentary Proces-sess in the Central Arctic Ocean and Along the Eurasian Conti-nental Margin, 285–307. Berichte zur Polarforschun g 212,Bremerhaven.

Hald, M., Steinsund, P. I., Dokken, T., Korsun, S., Polyak, L., &Aspeli, R. 1994: Recent late Quaternary distribution of Elphi-dium excavatum clavatum in Arctic seas. Cushman FoundationSpecial Publication 32, 141–153.

Imbrie, J., Boyle, E. A., Clemens, S. C., Duffy, A., Howard, W.R., Kukla, G., Kutzbach, J., Martinson, D. G., McIntyre, A.,Mix, A. C., Mol� no, B., Morley, J. J., Peterson, L. C., Pisias, N.G., Prell, W. L., Raymo, M. E., Shackleton, N. J. & Toggweiler,J. R. 1992: On the structure and origin of major glaciationcycles 1. linear responses to Milankovitch forcing. Paleoceano-graphy 7, 701–738.

Ivanova, E. 1999: Foraminiferal assemblages of the Barents andKara seas: response to Holocene environmenta l changes. InYudakhin, F. N. (ed.): Geodynamics and Geoecology , 140—142.Inst. of the Ecological Problems of the North, Ural Departmentof the Russian Academy of Sciences, Arkhangelsk .

Jennings , A. E. & Weiner, N. J. 1996: Environmental change ineastern Greenland during the last 1300 years: evidence from for-aminifera and lithofacies in Nansen Fjord, 68°N. The Holocene6, 179–191.

Johnsen, S. J., Clausen, H. B., Dansgaard, W., Fuhrer, K., Gun-destrup, N., Hammer, C. U., Iversen, P., Jouzel, J., Stauffer, B.

BOREAS 30 (2001) Holocene paleoceanography , northern Barents Sea 15

& Steffensen, J. P. 1992: Irregular glacial interstadial s recordedin a new Greenland ice core. Nature 359, 311–313.

Karlen, W. 1988: Scandinavian glacial and climatic � uctuationsduring the Holocene. Quaternary Science Reviews 7, 199–209.

Karlen, W. & Kuylenstierna , J. 1996: On solar forcing of Holoceneclimate: evidence from Scandinavia . The Holocene 6, 359–365.

Koc Karpuz, N. & Jansen, E. 1992: A high-resolutio n diatomrecord of the last deglaciation from SE Norwegian Sea: docu-mentation of rapid climatic changes. Paleoceanograph y 7, 499–520.

Koc, N. & Jansen, E. 1994: Response of high-latitud e NorthernHemisphere to orbital climate forcing: evidence from the NordicSeas. Geology 22, 523–526.

Koc, N., Jansen, E. & Ha� idason, H. 1993: Paleoceanographi creconstruction s of surface ocean conditions in the Greenland,Iceland and Norwegian seas through the last 14 ka based on dia-toms. Quaternary Science Reviews 12, 115–140.

Kohfeld, K. E., Fairbanks, R. G., Smith, S. L. & Walsh, I. D.1996: Neogloboquadrin a pachyderma (sinistral coiling) aspaleoceanographi c tracers in polar oceans: evidence from north-east water polynia plankton tows, sediment traps, and surfacesediments. Paleoceanograph y 11, 679–699.

Korsun, S., Pogodina, I. A., Forman, S. L. & Lubinski, D. J. 1995:Recent foraminifera in glaciomarine sediments from three Arcticfjords of Novaya Zemlya and Svalbard. Polar Research 14, 15–31.

Labeyrie, L., Vidal, L., Cortijo, E., Paterne, M., Arnold, M.,Duplessy, J. C., Vautravers , M., Labracherie, M., Duprat, J.,Turon, J. L., Grousset, F. & van Weering, T. C. E. 1995: Surfaceand deep hydrology of the northern Atlantic Ocean during thelast 150000 years. Philosophica l Transactions of the RoyalSociety of London 348, 255–264.

Labeyrie, L. D., Duplessy, J. C. & Blanc, P. L. 1987: Variations inmode of formation and temperature of oceanic deep waters overthe past 125000 years. Nature 327, 477–482.

Labeyrie, L. D., Pichon, J. J., Labracherie , M., Ippolito, P., Duprat,J. & Duplessy, J. C. 1986: Melting history of Antarctica duringthe past 60000 years. Nature 322, 701–706.

Lubinski, D. J., Korsun, S., Polyak, L., Forman, S. L., Lehman, S.J., Herlihy, F. A. & Miller, G. H. 1996: The last deglaciation ofthe Franz Victoria Trough, northern Barents Sea. Boreas 25, 89–100.

Makela, E. & Hyvarinen, H. 2000: Holocene vegetation history atVatsari, Inari Lapland, northeaster n Finland, with special refer-ence to Betula. The Holocene 10, 75–85.

Midttun, L. 1985: Formation of dense bottom water in the BarentsSea. Deep Sea Research 32, 1233–1241.

Murdmaa, I. O., Bogdanov, Y. A., Ivanova, E., Pavlova, G. A. &Pimenov, N. V. 1997: Late Quaternary Paleoceanograph y of theBarents Sea. 6th Zonenschain Conference on Plate Tectonics, 73pp.

Murdmaa, I. O. & Ivanova, E. 1999: Postglacial sedimentation his-tory in the shelf depressions of the Barents Sea. Lithology andMineral Resources 6.

Nesje, A., Kvanne, M., Rye N. & Lovlie, R. 1991: Holocene gla-cial and climate history of the Jostedalsbree n region, western

Norway: evidence from lake sediments and terrestria l deposits .Quaternary Science Reviews 10, 87–114.

Polyak, L. & Mikhailov, V. 1996: Post-glacia l environment s of thesoutheaster n Barents Sea: foraminiferal evidence . In Andrews, J.T., Austin, W. E. N., Bergsten, H. & Jennings, A. E. (eds.): LateQuaternary Paleoceanograph y of the North Atlantic Margins,323–337. Geological Society Special Publication, Edinburgh.

Polyak, L. & Solheim, A. 1994: Late- and postglacia l environmentsin the northern Barents Sea, west of Franz Josef Land. PolarResearch 13, 197–207.

Poole, D. 1994: Neogene and Quaternary paleoenvironment s onthe Norwegian Sea shelf. Ph.D. dissertation , University ofTromsø.

Salvigsen, O., Forman, S. & Miller, G. H. 1992: Thermophilusmolluscs on Svalbard during Holocene and their paleoclimati cimplications. Polar Research 11, 1–10.

Sarnthein, M., Jansen, E., Weinelt, M., Arnold, M., Duplessy, J.C., Erlenkeuser , H., Flatøy, A., Johannessen , G., Johannessen ,T., Jung, S., Koc, N., Labeyrie, L., Maslin, M., P� aumann, U. &Schulz, H. 1995: Variations in Atlantic surface ocean paleocea-nography , 50–80°N: a time-slice record of the last 30 000 years.Paleoceanograph y 10, 1063–1094.

Selsing, L. & Wishman, E. 1984: Mean summer temperature andcirculation in southwest Norwegian mountain area during theAtlantic period, based upon changes of the Alpine pine-forestlimit. Annals of Glaciology 5, 127–132.

Shackleton, N. J. 1974: Attainment of isotopic equilibrium betweenocean water and benthonic foraminifera genus Uvigerina: isoto-pic changes in the ocean during the last glacial. In Labeyrie, L.(ed.): Variation du climat au cours du Pleistocene, 203–209.Colloques Internationau x du Centre Nationale de la RechercheScienti� que 219.

Spielhagen, R. F. & Erlenkeuser, H. 1994: Stable oxygen and car-bon isotopes in planktic foraminifers from Arctic ocean surfacesediments: re� ection of the low salinity surface water layer.Marine Geology 119, 227–250.

Steinsund, P. I. & Hald, M. 1994: Recent calcium carbonatedissolution in the Barents Sea, Palaeoceanographi c applications .Marine Geology 117, 303–316.

Stuiver, M. & Reimer, P. J. 1993: Extended 14C data base andrevised CALIB 3.0 14C age calibration program. Radiocarbon35, 215–230.

Veum, T., Jansen E., Arnold, M., Beyer, I. & Duplessy, J. C. 1992:Water mass exchange between the North Atlantic and the Nor-wegian Sea during the past 28 000 years. Nature 356, 783–785.

Vincent, E., Killingley, J. S. & Berger, W. H. 1981: Stable isotopecomposition of benthic foraminifera from the equatorial Paci� c.Nature 289, 639–643.

von Grafenstein, U., Erlenkeuser , H., Muller, J., Jouzel, J. & John-sen, S. 1998: The cold event 8200 years ago documented in oxy-gen isotope records of precipitation in Europe and Greenland.Climate Dynamics 14, 73–81.

Woodruff, F., Savin, S. S. & Douglas, R. G. 1980: Biological frac-tionation of oxygen and carbon isotopes by recent benthic fora-minifera. Marine Micropaleontolog y 5, 3–11.

16 Jean-Claude Duplessy et al. BOREAS 30 (2001)