Tors, Eustatic Shorelines, and Mammoths: Evidence Against Ice Sheets on Wrangel Island, East Siberian/Chukchi Seas

Assumed glacial flutings on the Chukchi Rise (Polyak et al., 2001) have reinvigorated hypotheses concerning the past presence of the same type of ice sheet or ice shelf on the Chukchi and/or East Siberian Sea shelf. Fieldwork on wrangle Island has been aimed at determining the glacial and sea level history of this geographically strategic island to address these various hypotheses. Cosmogenic isotope ages (Be and Al) on bedrock are all older that 35 ka , at a minimum, the rates of pervasive pariglacial processes. Tors, commonly forming columns 10 m high, are ubiquitous throughout the mountains of Wrangel Island. Eustatic shorelines (and not glacioisostatic shorelines) across the northern tundra plain marked by remnant marine sediments and ancient barrier beaches up to 40 m above seal level are all older than the range of radiocarbon dating and yield amino acid age estimates (D/L Aspartic as well as aIle/Ile) in excess of 400-500 ka, similar to sediments found in the Alaskan North Slope. Radiocarbon dates on mammoth borres, teeth and tusks and other animals (rhinos, bison) yield ages that range continuously through time from >38 ka to 3700 years ago indicating the local presence of large mammals during the Last Glacial Maximum (LGM) and most of the Holocene. These data preclude the presence of an ice sheet during the LGM and probably over the past half million years. Glacial ice extent on the island during the LGM was limited to a few small north facing cirque glaciers. The flutings on the Chukchi Rise could not have been formed by an ice sheet over or near Wrangel Island in at least the last four or five major glacial/interglacial cycles.