Core NWR 5 from Northwind Ridge in the westem Arctic Ocean contains a climatic record that extends back for over 1 •11ion years. Dark brown beds with abundant planktonic fomminifers represent interglacial conditions, whereas glacial and transitional conditions are represented by lithologies barren or nearly barren of planktonic foraminifers. We conclude that seven, and possibly all nine, interglacials of the Brunhes magnetic chronozone (the last 780,000 years) are represented in NWR 5. For about the last 800,000 years, the western Arctic Ocean apparently had a permanent, thick ice cover and was unable to support significant populations of planktonic foraminifers except during major interglacials when seasonally open and highproductivity surface waters occurred at least along the basin margins. Our results support previous interpretations that climate variations in the Arctic are in phase with glacial/interglacial cycles observed in other proxy records of the Brunhes. INTRODUCWION The Arctic Ocean is a key component of the Earth's climate system, but the paleoceanographic and paleoclimate record of the Arctic is still poorly •own and controversial. Documenting the late Neogene histo :ry of the Aretic •e• has -been hampered by a lack of suitable marine records. In This paper is not subject to U.S. copyright. Published in 1993 by the American Geophysical Union. Paper number 93PA00146. general, only short piston and gravity cores are available, and most cores from topographic highs in the central and western Arctic recovered sedimentary sections with extremely slow average accumulation rates (about 1 to 2 mm/1000 yr ). Age and environmental interpretations derived from -these cores are complicated by the low resolution of the records. In 1988, the U.S. Coast Guard Icebreaker Polar Star recovered a series of cores from Northwind Ridge, a prominent bathymetric feature extending from the Chukchi Sea continental slope into the Canada Basin of the western Arctic Ocean (Figure 1). Integrated lithostratigraphic, paleomagnetic, and paleontologic analysis of the relatively expanded Pleistocene section recovered in NWR 5 (average accumulation rate >4 rmm/1000 yr ) reveals a more detailed, albeit still condensed, paleoclimate record for the western Arctic Ocean that provides improved information on the features and timing of Arctic Pleistocene paleoceanographic changes over the last 800,000 years. LITHOSTRATIGRAPHY The section recovered in NWR 5 consists of prom•ent •rk brown foraminifer-rich, muddy beds that altemate with gray, olive gray, or tan strata. The distribution of the sand-size fraction (0.•2-2.00 ram), comp•son with published unit des•ptions of Clark et al. [ 1980], which are bas• on T-3 cores from the central Amemsia Basin, and •scussions and examination of b•VR 5 with D. Clark CLlniversity of Wisconsin, private communications, 1992) were used to identify standard Arctic Iithostratigraphic units M through I in NWR 5. A sum.mary of the units is presented below and in
