Holocene paleoceanography and glacial history of the West Spitsbergen area, Euro-Arctic margin
Introduction
The West Spitsbergen continental margin is a climatically sensitive area. The main reason for this is the present oceanographic regime characterized by north-flowing warm Atlantic Water in the West Spitsbergen Current along the continental margin with sharp gradients to cool, partly sea-ice covered Polar Water (Fig. 1). Small geographical displacements in the ocean fronts in this area may impose large climatic changes affecting the society, life habitats and earth processes in the area. Climate models predict that the global warming will have its largest impact in the high northern latitudes (e.g. Hadley Centre (2004)). However, the instrumental record of climate variability is too short and spatially incomplete to reveal the full range of seasonal to millennial-scale climate variability, or to provide empirical examples of how the climate system responds to large changes in climate forcing. Longer time series may be provided with well dated and high resolution proxy records.
We have investigated two proxy records from the West Spitsbergen area, one from the open ocean upper continental margin and one from a silled fjord setting, Van Mijenfjord. The core from the continental margin is located under the axis of Arctic Water. This core should reflect changes and variability in heat flux to the high northern latitudes, representing the northern limb of the North Atlantic conveyor circulation. The fjord record on the other hand represents more of a continental climate signal, linked to processes such as iceberg rafting from tidewater glaciers and exchange between fjord water and open oceanic water. Our knowledge of the Holocene climatic record of the Svalbard area is sparse due to lack of high resolution and well-dated proxy records. The purpose of the present paper is to (1) present well-dated paleoclimate data for the West Spitsbergen area during the Holocene and (2) investigate century to decadal scale climate changes and variability.
Section snippets
Physical setting
Spitsbergen is the largest island of the Svalbard archipelago, situated between 76° and 80°N, and bordered by the Arctic Ocean to the north, the Barents Sea to the south and east, and the Norwegian–Greenland Sea to the west (Fig. 1). The archipelago is dominated by Phanerozoic sedimentary rocks (Steel and Worsley, 1984).
The continental margin west of Spitsbergen is characterized by a relatively narrow shelf with a typical glacial morphology represented by shallow banks between glacial troughs,
Material and methods
We investigated two sediment cores, core MD99-2304 is located on the upper West Spitsbergen continental margin 77° 37. 26′N and 09° 56. 90′E, at 1315 m water depth, and core MD99-2305 located in Van Mijenfjord 77° 46.87′N and 15° 17.81′E at 110 m water depth. The sampling sites were determined by several high resolution seismic surveys during the 1990s using 3.5 kHz penetration echo sounder and Sparker. Both cores were sampled during the IMAGES-1999 cruise with “R/V Marion Dufresne” using a
Chronology
The chronology of MD99-2305 is based on 21 AMS radiocarbon dates performed on mollusc bivalves (Table 1). Most of these bivalves were identified to species level. All the dates were corrected for a reservoir effect of 464 years (including a ΔR value of 64 +/− 35 years) (Mangerud and Gulliksen, 1975) and show increasing ages versus depth in core (Fig. 2). An age model was produced by converting the dates to calendar years following the calibration model of Stuiver et al. (1998) (Fig. 4F).
The SiZer analysis
The results of the SiZer analysis for core MD99-2305 are shown in Fig. 3. In the top panels of Fig. 3 A–C, a family of smoothes (h) is given. The curves plotted have smooth ranges as given in the figure. The thick solid line corresponds to a choice of h one typically would use if only one scale was to be used. This “optimal” h is a data driven bandwidth and a best choice of the bandwidth from a purely mathematical point of view (Ruppert et al., 1995). In the lower panels of Fig. 3A–C, SiZer
The proxy indicators
Planktonic foraminifera are reliable tracers of surface and sub-surface ocean temperatures (e.g. Bé and Tolderlund, 1971) and quantitative reconstructions of SST based on various statistical approaches have been applied over the last three decades. In the present study the planktonic foraminiferal fauna was counted in the 100 μm fraction, were as the modern data set of Pflaumann et al., 1996, Pflaumann et al., 2003 used for the SST-1 reconstruction (Fig. 5E) represents the 150 μm fraction. This
Holocene glacial history of Spitsbergen
The content of grains >1 mm in the MD99-2305 (Fig. 4) may reflect both rafting from icebergs and sea-ice. In addition, coarser grains may be induced by storm-induced sediment suspensions in shallow water (Rumohr et al., 2001). However, lack of turbidites or other bottom current structures in the sediments, indicate that this latter process is of less importance in van Mijenfjord. To our knowledge, no systematic studies have been undertaken with respect to the content of debris in sea-ice in the
Correlations
We compare the proxy records from the Svalbard margin and Van Mijenfjord with a high resolution marine SST proxy record from the Western Barents Sea, ca 75°N (Sarnthein et al., 2003) (Fig. 6). Both SST-records are reconstructed by applying the modern analogue technique to planktonic foraminiferal faunal data, and they are interpreted to reflect latitudinal temperature gradients of Atlantic Water in the Spitsbergen Current during the Holocene. These SST-records are compared to the Van Mijenfjord
Conclusions
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Sea surface temperatures, significantly warmer than at present, were recorded on the continental margin off West Spitsbergen from ca 11,200–8800 cal. years BP.
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As the Van Mijenfjord was deglaciated after the Younger Dryas, ca 11,200 cal. years BP, water warmer than present almost immediately invaded the fjord bottom.
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The presence of IRD throughout the entire Holocene indicates that central Spitsbergen was never completely deglaciated during this interglacial period. After the glaciation during the
Acknowledgements
Funding was provided by the VISTA programme, the Research Council of Norway to the Strategic University Programme SPONCOM, and by the Roald Amundsen Centre, University of Tromsø. Technical assistance was provided by the crews onboard R/V Jan Mayen and R/V Marion Dufresne, Jan P. Holm (computer drawings), Edel Ellingsen, Trine Dahl, Odd Aasheim (laboratory work), Elsebeth Thomsen Hanken (macrofossil identification). Carin Andersson Dahl and Kari-Lise Rørvik helped with the C2-SST
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