Deglaciation to Holocene Sea-ice History Over Navarin and Pervenets Canyons of the Northern Bering Sea Using Diatoms and Alkenones

The presence or absence of sea-ice over the Bering Sea influences the productivity of its waters as well as the regional climate of Beringia. Not only is the extent and distribution of sea-ice an important climate system feedback because of changes in albedo, it also has the potential to impact oceanographic and atmospheric circulation patterns by altering ocean stratification and impeding gas exchange between the atmosphere and ocean (Smith, et al, 2003). Understanding the history of regional climate change and atmosphere-ice-ocean systems across the western Arctic and North Pacific requires high resolution reconstructions of sea ice extent throughout the Bering Sea. The variability in the position of the ice edge since the last glacial maximum (LGM) has not been mapped or analyzed in detail in the Bering Sea. While it has been hypothesized that sea ice persisted in the eastern Bering Sea for at least 9 months per year during the LGM (Sancetta, 1983), sea-ice today covers only the Bering continental shelf areas 2 to 5 months per year (de Vernal and Hillaire-Marcel, 2000). What is not known are conditions during deglaciation and the Holocene when sea ice margin productivity in the Bering could have influenced the quality of nutrient rich waters flowing to the Arctic with submergence of the Bering Strait. This study presents preliminary results from a 1441 cm-long core extracted between Navarin and Pervenets Canyons. Future work will expand the spatial coverage to include several sites across the Bering Sea and will result in a compilation of maps showing the changing extent and duration of sea ice since the LGM. Down-core changes (at 500 year intervals) in diatom assemblages are documented since the LGM in order to detect the presence or absence of sea ice. Diatom species such as Fragilariopsis grunowii, F. cylindrus,and Thalassiosira gravida are used as indicators of sea ice. These data are compared with the U^K₃₇ index derived from alkenones and a δ ¹⁸O record from foraminifera in order to document changes in SST, nutrient cycling and productivity since the LGM.