INITIAL RESULTS OF FORAMINIFERAL STUDIES AND PALEOCEANOGRAPHIC RECONSTRUCTIONS FROM LATE PLEISTOCENE AND HOLOCENE SEDIMENTS OF THE CHUKCHI BORDERLAND, ARCTIC OCEAN

The Chukchi Sea margin is being studied in a Shelf-Basin Interaction (SBI) Program to understand oceanographic variability in the western Arctic Ocean. Several piston and box cores from a shelf-to-basin transect are being investigated for Late Pleistocene to Holocene paleoceanographic reconstructions. Reported here are preliminary results of foraminiferal studies from four sediment cores.

Foraminifera were sampled every cm and counted in size fractions >63µm. Piston core P6 and box cores B4 and B5 were taken on the Chukchi slope (400-600 mwd) and show a limited foraminiferal record. Low abundances characterize Holocene sediments of P6, presumably because of strong dissolution. In contrast, sediments from the penultimate interglacial contain significant numbers of benthic and planktonic foraminifers. Two ¹⁴C ages of ~42 ka and lithostratigraphy allow correlation of this interval to at least Oxygen Isotope Stage 3. Planktonic foraminifers consist mostly of Neogloboquadrina pachyderma (sinistral). Abundances of Cassidulina teretis in the core are associated with the Arctic Intermediate Waters of Atlantic origin (~300-900 mwd). Agglutinated foraminifers, diatoms, radiolarians, and dinocysts comprise the fauna of B4 and B5 and are tentatively constrained to the Holocene. Calcareous foraminifers are rare, indicating the strong influence of dissolution on the slope during the Holocene.

B15, from the Northwind basin (2100 mwd), contains abundant foraminifers and allows the recent environments of the Chukchi Borderland to be characterized. Three ¹⁴C ages and the lithostratigraphy indicate the core spans most of the Holocene and the last deglaciation. Investigation of millennial scale variability is possible for this site due to high sedimentation rates (~1.6cm/ka). Foraminifera are rare in the deglacial sediments but increase in abundance starting at ~11 ka. Two abundance peaks in planktonic and benthic foraminifers occur between 6-7 ka and ~4 ka and are accompanied by peaks in productivity, inferred from d¹³C of the benthic foraminifer Cibicidoides wuellerstorfi, P:B ratio, and species diversity. The combined changes in foraminiferal abundances, compositions, and isotopes provide a first record of biological productivity and, thus, sea-ice coverage over the Chukchi Borderland during the Holocene.