A multiproxy approach to reconstruct the environmental changes along the Eurasian continental margin over the last 150 000 years
Introduction
Build-up and decay of circum-Arctic ice-sheets, the extension of sea-ice cover and its influence on Earth's albedo, the Nordic Seas thermohaline system, and the Atlantic water circulation are key points for understanding the global climate system (e.g., NAD Science Committee, 1992; Aagaard and Carmack, 1994). However, a critical constraint for environmental reconstructions in the Arctic region is still the stratigraphic resolution of marine and terrestrial records (e.g., Mangerud et al., 1996; Spielhagen et al., 1997; Velitchko et al., 1997a, Velitchko et al., 1997b; Nørgaard-Pedersen et al., 1998). Therefore, the two major discrepancies concerning the extent and volume of the ice-sheets along the Eurasian continental margin during glacials have not yet been resolved (e.g., Denton and Hughes, 1981; Dunayev and Pavlidis, 1988; Grosswald, 1993; Pavlidis et al., 1997; Velitchko et al., 1997a, Velitchko et al., 1997b) and the recently found dynamic coupling of Atlantic water inflow and the Arctic Ocean hydrography (cf. Carmack et al., 1995) could not be classified in Arctic Ocean records (Nørgaard-Pedersen et al., 1998).
However, both aspects are of primary interest for climatic reconstructions because (1) the freshwater supply from the Eurasian ice-sheets may have triggered changes in thermohaline circulation of the North Atlantic (e.g., Oppo and Lehman, 1995) and (2) the seasonal melting of sea-ice caused by intensive inflow of Atlantic water results in distinct changes of the surface albedo, the energy balance, the moisture supply and thus the ocean-ice–atmosphere interaction (e.g., Hibler, 1989; Carmack et al., 1995).
Recently, a few studies documented the connection between the build-up and decay of the Barents/Kara Sea ice-sheets, the outflow of associated meltwater discharge to the central Arctic Ocean, and the inflow of Atlantic water during the last glacial/interglacial cycle (e.g., Hebbeln and Wefer, 1997; Nørgaard-Pedersen et al., 1998; Knies et al., 1999). Lubinski et al. (1996)and Polyak et al. (1997)showed that the marine-based ice-sheets along the northern Barents Sea margin reached the outer shelf, probably the shelf edge, during the Last Glacial Maximum (LGM). At least, it can be said that based on the amounts of coccoliths and foraminifera during the Late Weichselian the subsurface inflow of Atlantic water and the formation of coastal polynyas, resulting in seasonally open-water conditions had a major influence on the final ice-sheet build-up (cf. Hebbeln et al., 1994; Knies et al., 1999). Major deglaciation of the ice-sheets between 15.4 and 13.3 kyr can be traced in sediments of the central Arctic Ocean and the Fram Strait by δ meltwater spikes (e.g., Jones and Keigwin, 1988; Stein et al., 1994c; Nørgaard-Pedersen et al., 1998). Glaciomarine sedimentation on the northern Eurasian continental margins induced by insolation and a rise in sea-level, and enhanced Atlantic water inflow at ∼13 kyr has been established (Polyak and Solheim, 1994). However, indications of Atlantic water inflow and build-up/decay of the ice-sheets preceding the last glacial/interglacial cycle are still very rare (Lloyd et al., 1996; Hebbeln and Wefer, 1997; Nørgaard-Pedersen et al., 1998; Knies et al., 1999). Knies and Stein (1998)postulated that paleoceanographic proxies traditionally used in the North Atlantic are of limited value for paleoenvironmental reconstructions on the northern Barents Sea margin. That means that no single proxy can be relied on to give the whole story. Therefore, we tried to elucidate the environmental changes along the Eurasian continental margin over the last 150 kyr with a multiproxy approach. In order to examine the Barents/Kara Sea ice-sheet build-up and decay we studied the lithology, the input of ice-rafted debris (IRD), the clay mineralogy, and the bulk accumulation rates in two cores, which are located northeast of Svalbard, and northeast of Severnaya Semlya (Fig. 1). Information regarding the paleoceanography along the Eurasian continental margin were achieved by determining bulk organic carbon analysis, biogenic and detrital carbonate, and several marine and terrigenous-derived biomarkers. We show that the intercorrelation of those proxies, including specific organic compounds, elucidate glacial and interglacial paleoclimatic variations along the Eurasian continental margin over the last 150 kyr.
Section snippets
Oceanographic setting
The present-day current pattern in the eastern Arctic Ocean is dominated by the interaction of Atlantic water inflow from the Norwegian Sea through Fram Strait and over the Barents and Kara seas with its counterpart, the Transpolar Drift (TD) and the East Greenland Current (EGC), with their cold, low-saline polar water outflow (Aagaard and Carmack, 1989, Aagaard and Carmack, 1994; Meincke et al., 1997). The permanent sea-ice cover in the central Arctic Ocean caused by high river runoff and net
Materials and methods
The three sediment cores studied were located along the Eurasian continental margin and were recovered during two expeditions with R/V Polarstern (Fig. 1, Table 1) (Rachor, 1992, Rachor, 1997). All cores were routinely sampled at 5–10 cm intervals; additional samples were taken in intervals of changing lithology and/or color. Lithological characteristics and IRD contents were determined by evaluation of X-radiographs (e.g., Grobe, 1987). All cores consist mainly of bioturbated mud, with
Stratigraphy
The sediment records along the Eurasian continental margin cover marine isotope stage (MIS) 6 to the Holocene (Fig. 2Fig. 3). The age model of PS2138-1 is based on the correlation of the stable oxygen isotope records of the planktonic foraminifer N. pachyderma sin. with the chronostratigraphy of Martinson et al. (1987)(Fig. 2) (cf. Knies et al., 1999). The stratigraphical control is further modified by several radiocarbon (AMS ) datings (Fig. 2). Beyond the range of datings, the final
Sedimentation and mass accumulation rates
The mean LSR and ARbulk values along the Eurasian continental margin vary between 0.4 and 21.2 cm/kyr and 0.4 and 42.8 g cm−2 kyr−1, respectively, and show distinct differences between glacial and interglacial periods (Table 3, Fig. 7). On the western margin, the LSR and ARbulk values are generally somewhat higher during glacials (MIS 6 and MIS 2) than during interglacials (MIS 5 and MIS 1). The LSR during MIS 4 and MIS 3 are comparable to interglacial values. On the eastern margin, variations
Glaciation history and correlation to the terrestrial record
The glaciation curves of the Scandinavian (SIS) and the Svalbard/Barents Sea ice-sheets (SBIS) during the Weichselian as interpreted from the onshore sections correlate well with the IRD input in the deep ocean along the western Norwegian and Svalbard margins (e.g., Hebbeln, 1992; Mangerud and Svendsen, 1992; Baumann et al., 1995; Mangerud et al., 1998for a recent discussion). Maximum IRD input occurred particularly during deglaciation phases of the most extended ice-sheets when a broad ice
Conclusions
Environmental changes over 150 kyr have been studied along the Eurasian continental margin. Seasonally, open-water conditions associated with Atlantic water advection, extended at least to the Franz Victoria Trough, and, combined with moisture bearing storms and low summer insolation, had a major influence on the final ice build-up during glacial MIS 6 and MIS 2 on the western Eurasian margin. Large ice-sheet fluctuations on the western Eurasian margin, contemporaneous with major Laurentide
Acknowledgements
We thank the captain and the crew of the R/V Polarstern for cooperation during the expeditions ARK VIII/1 and ARK XI/I. G. Meyer, G. Traue, L. Schönicke, J. Marie-Nadeau, and D. Grootes are greatly acknowledged for stable isotope analysis and AMS measurements. For technical assistance in the geochemical laboratory, we sincerely thank M. Siebold and K. Fahl. We acknowledge N. Nørgaard-Pedersen for discussion and supply of unpublished DBD-data. For discussions of data and helpful comments of
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