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 mesic shrub-tundra environments even during the last glacial maximum. Vegetation before the last glacial maximum was a birch-heath-graminoid tundra with few or no steppe elements. Shrubs were not an important element of the vegetation, but were present in small numbers. During the interval 20,000–14,000 yr BP, land-bridge vegetation was dominated by birch-graminoid tundra with small ponds containing aquatic plants. Heaths were relatively unimportant. Insects from this interval were indicative 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 ponds choked with aquatic plants. The insect record indicates open-ground habitats dominated by mesic tundra. By 11,000 yr BP, insect data suggest that summer temperatures on the emergent Bering Shelf were warmer than present-day upland regions in western Alaska; summer temperatures on the Chukchi Shelf were warmer than the present-day North Slope of Alaska. Contrary to previous hypotheses, we found no evidence of steppe-tundra on the land bridge. New accelerator mass spectrometer (AMS) 14C dates show that much of the land bridge was above sea level and thus available for human and animal migration until as late as 11,000 yr BP.