Past environmental and climatic changes in the Arctic – evidence from marine sediment cores covering the past 17,000 years

 

Dorthe Klitgaard Kristensen¹, Marta Slubowska-Woldengen², Tine L. Rasmussen³, Nalan Koз¹

 

 

The arctic regions are currently in focus in climate debates and for scientific research. The reason is the warming over the past couple of decades that has been more pronounced in the Arctic than elsewhere on the globe (ACIA, 2004; IPCC, 2007). The warming in the Arctic and the associated sea ice retreat have been attributed to increased temperatures and flow strength of the incoming Atlantic water (e.g., Zhang et al., 1998; Schauer et al., 2004). The West Spitsbergen Current (WSC), the poleward continuation of the Gulfstream, has been considered as the major pathway both for heat and water volume transport to the Arctic Ocean (Aagaard and Greisman, 1975; Gammelsrшd and Rudels, 1983; Aagaard et al., 1987; Schauer et al., 2004). It flows along the western Svalbard shelf and continental slope, and as the Svalbard Branch (SB) along the northern margin. Therefore, Svalbard’s western margin is especially sensitive to changes in the intensity of the flow of Atlantic Water through time. The amounts of observational data, however, are scarce and only cover a short time period. The data cannot reveal the full potential range of natural variations the Arctic has experienced in the past, and hence may experience in the future. Hence, assessing past Arctic long-term climate changes must be obtained using proxy records.

We have investigated several marine sediment cores from three locations on the shelf of Svalbard in order to reconstruct the changes in flow and character of the Atlantic Water through the last 17,000 calendar year BP. These locations on the shelf are presently experiencing subsurface inflow of Atlantic water but are also close to the cold, icy polar water transported from the Arctic Ocean around the southern tip of Spitsbergen and northwards along the western coast in the so-called East Spitsbergen Current. In all cores, the content of benthic foraminifera species together with planktonic and benthic foraminifera abundances, stable oxygen isotopes and lithology have been studied. The chronology in all cores is based on numerous AMS radiocarbon dates.

Comparison of the faunal changes from the three Svalbard shelf areas reveals similar general long-term faunal development through the last 17000 calendar year BP. This similarity in the fauna between the sites implies a common cause related to variability in the inflow of Atlantic water to the shelf. In more detail, we find no clear indications of Atlantic Water being present in the shelf areas around the western and northern part of Svalbard in the bottom waters prior to 15.000 calendar years BP. Here, the shelf area was characterized by glaciomarine conditions with lowered salinity and high content of Ice Rafted Debris (IRD). During the Boelling-Alleroed period (from 14.500-12.600 calendar years BP) a strong inflow of subsurface warm Atlantic Water occurred probably associated with seasonally sea ice covered surface waters This period also exhibits low benthic and planktonic foraminiferal productivity. The warm period was interrupted by the Younger Dryas cold interval (12.600-11.500 calendar years) that in the northern and western part on the shelf bear evidence of a proximal location of the Polar Front to the core sites while the bottom waters were cold and salinity was lowered at the southern site. During the Early Holocene (10.800-6800 calendar years BP), the flow of Atlantic Water to the Svalbard shelf was strong resulting in a prominent increase in salinity. A distinct cooling and freshening of the bottom water masses occurred during the Mid- and Late Holocene (6800 calendar years BP to present time), and was accompanied by glacier re-advances inferred from the IRD content in the sediment cores leading to the present-day conditions. The paleoceanographic changes described above at the Svalbard shelf since the initiation of the last deglaciation will be discussed in the light of the variations found in cores in the Nordic Seas region.

 

 

References

Aagaard, K., and Greisman, P., 1975, Towards new mass and heat budgets in the Arctic Ocean: Journal of Geophysical Research, v. 80, p. 3821-3827.

Aagaard, K., Foldvik, A., and Hillman, S.R., 1987, The West Spitsbergen Current: Disposition and water mass transformation: Journal of Geophysical Research, v. 92, p. 3778-3784.

IPCC, 2007: see http://www.ipcc.ch/

Schauer, U., Fahrbach, E., Шsterhus, S., and Rohardt, G., 2004, Arctic warming through the Fram Strait: Oceanic heat transport from 3 years of measurements: Journal of Geophysical Research,  v. 109, doi:10.1029/2003JC001823.

Zhang, J., D.A. Rothrock, M. Steele. 1998, Warming of the Arctic Ocean by a strengthened Atlantic inflow: Model results: Geophysical Research Letters, v. 25(10), p. 1745-1748.