| Summary: | Results obtained from analyses of three sediment cores collected from the Chukchi Shelf at 55m, 80m, and 107m water depths show changes in the composition and quantity of sedimentary organic matter delivered to the core locations from the Late-glacial up to near modern times. Two of the cores (80m, and 107m) show an abrupt and substantial increase in the total organic content and a shift in stable carbon and nitrogen isotopic composition of the organic matter at 8000-9000 years BP. We interpret this shift to be indicative of increased marine primary productivity that subsequently led to the onset of denitrification, as observed today in modern Chukchi Shelf sediments. The shift coincides with the probable re-advance of sea ice coverage at 8500 14C yrs BP, as well as a shift in the Trans Polar Drift. Together, these occurrences suggest a major reorganization of Arctic paleoceanography at 8-9ka that has more or less persisted through the Holocene. A small increase in productivity is also observed at ~11ka in the 80m core that could coincide with the first onset of Bering Strait through-flow following the LGM. Additional studies are underway to help constrain sea ice conditions at various times during the Holocene in the Bering and Chukchi Seas in order to elucidate the relationship between former ice coverage regimes and primary production.
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