Marine Isotope Stages 1 and 3 in the Western Arctic Ocean

Richard Z. Poore (USGS MS 955, 12201 Sunrise Valley Drive, Reston, VA 20192; ph. 703-648-5270; fax 703-648-6040; Internet: rpoore@usgs.gov); Lisa E. Osterman (USGS MS 955, 12201 Sunrise Valley Drive, Reston, VA 20192; ph. 703-648-6063; Internet: osterman@usgs.gov); William B. Curry (WHOI Clark Lab 122, Woods Hole, MA 02543; ph. 508-457-2000; Internet: curry@cod.whoi.edu); R. L. Phillips (USGS MS 999, 345 Middlefield Road, Menlo Park, CA 94025; ph. 650-329-5378; Internet: lphillips@usgs.gov)

Accelerator mass spectrometry (AMS) radiocarbon dated stable isotope and microfaunal data from box cores raised from the Mendeleev Ridge and slope provide a record of marine isotope stage 1 (MIS 1) and much of MIS 3 in the central western Arctic Ocean. No record of MIS 2 is preserved in the cores. Foraminifers are present throughout the sequence but are only abundant in the upper part of MIS 1 and the middle part of MIS 3. Planktic foraminifer faunas are almost exclusively composed of the polar species Neogloboquadrina pachyderma (left-coiling). Oxygen and carbon isotope ratios from N. pachyderma in surface sediment samples from the central western Arctic are 1.5 per mil and 1.0 per mil respectively. Oxygen isotope ratios from N. pachyderma in the lower part of MIS 1 range between 1.0 and 0.0 per mil indicating significant meltwater input to the western Arctic Ocean occurred from about 12 - 7,000 kyr. Carbon isotope ratios are also low during the lower part of MIS 1. Several meltwater pulses may be present in the lower part of Stage 1 but bioturbation makes confident identification of specific events difficult. Oxygen and carbon isotope ratios similar to modern surface sediment values become established around 7 kyr and continue to the top of the cores. The N. pachyderma oxygen isotope record from MIS 3 shows several excursions towards very low ratios indicating the presence of one or more strong melt water events. The most pronounced excursion is older than about 45 kyr. Thus at least some of the abrupt MIS 3 climate oscillations observed in ice cores and in deep sea cores from lower latitudes had a significant impact on the western Arctic Ocean.

Carbon isotope ratios of N. pachyderma and the abundance of foraminifers show a strong correlation. High carbon isotopic ratios equivalent to surface sediment values of 1.0 per mil are found in the foramifer rich intervals whereas foraminifer-poor intervals yield carbon isotopic ratios of 0.5 per mil or less. By comparison with modern conditions, we infer that the intervals of abundant foraminifers and modern N. pachyderma carbon isotope ratios near 1.0 per mil in the upper part of MIS 1 and the middle part of MIS 3 represent intervals of high productivity and seasonally ice-free waters along the margins of the Arctic Ocean. A combination of isotopic and benthic faunal changes indicates stronger Atlantic influence in the western Arctic during parts of MIS 3. The lower limit of the Atlantic-derived Arctic intermediate water mass extended at least 500 m deeper during part of MIS 3.