LATE WISCONSIN ENVIRONMENTS OF THE BERING LAND-BRIDGE

Late Wisconsin paleobotanical and fossil insect data from the central and northern sectors of the Bering Land Bridge indicate widespread mes ic shrub-tundra environments even during the last glacial maximum. Veg etation before the last glacial maximum was a birch-heath-graminoid tu ndra with few or no steppe elements. Shrubs were not an important elem ent of the vegetation, but were present in small numbers. During the i nterval 20,000-14,000 yr BP, land-bridge vegetation was dominated by b irch-graminoid tundra with small ponds containing aquatic plants. Heat hs were relatively unimportant. Insects from this interval were indica tive of arctic climate, with drier tundra than during the late glacial . During the late-glacial interval (14,000-11,000 yr BP), land-bridge vegetation was dominated by birch-heath-graminoid tundra with small po nds choked with aquatic plants. The insect record indicates open-groun d habitats dominated by mesic tundra. By 11,000 yr BP, insect data sug gest that summer temperatures on the emergent Bering Shelf were warmer than present-day upland regions in western Alaska; summer temperature s on the Chukchi Shelf were warmer than the present-day North Slope of Alaska. Contrary to previous hypotheses, we found no evidence of step pe-tundra on the land bridge. New accelerator mass spectrometer (AMS) C-14 dates show that much of the land bridge was above sea level and t hus available for human and animal migration until as late as 11,000 y r BP. (C) 1997 Elsevier Science B.V.