TRANSGRESSIONS - RETHINKING BERINGIAN GLACIATION

The purpose of this investigation is to encourage a fresh look at Pleistocene Beringia. Heretofore, flooding of Bering Strait has been cited as the only barrier to migration, with marine sea transgressions being a ''sea gate'' that closed off migration during glacial interstadials and interglaciations. However, the possibility exists that glacial advances were also barriers, with marine ice transgressions being an ''ice gate'' that closed off migration during glacial stadials and glacial maxima. This possibility proceeds from the Marine Ice Transgression Hypothesis (MITH), which states that marine ice sheets form on the broad Arctic continental shelf of Northern Hemisphere continents when sea ice thickens, grounds and domes in shallow water, and then transgresses landward as continental ice sheets and seaward as floating ice shelves (Hughes, 1987). Landward transgression is onto coastal lowlands. During Pleistocene glaciations, a marine ice sheet extending from Spitsbergen to Greenland may have transgressed the circumpolar continental landmass at its lowest and narrowest gap, central Beringia, and calved into the Pacific Ocean. Four models of Beringian glaciation are presented, based on the distinction between marine glaciation and highland glaciation. Central Beringia was glaciated only in highlands in the traditional model (Hopkins et al., 1982), was also glaciated by a self-sustaining ice shelf floating over the deep ocean basins of the Bering Sea in the model by Grosswald and Vozovik (1984), was glaciated by a marine ice sheet that covered highlands, the continental shelf, and supplied the ice shelf in a model for maximum Pleistocene glaciation, and was glaciated by a marine ice sheet in the Chukchi Sea that merged with highland glaciers, transgressed the continental shelf of the western Bering Sea, and calved into the southern Bering Sea along the edge of the continental shelf in a model for the last glaciation. Field tests are suggested to assess the viability of these four models. The first model is already established for highland glaciation in Alaska, but less established in Siberia. The last model should be the easiest to evaluate for marine glaciation. The last model limits human migration across the Beringian land bridge to brief intervals between stadials and interstadials of the last glaciation cycle, when bath the ice gate and the sea gate were opened to human migration. This model can influence the sea change now underway among Quaternary scientists studying peopling of the Americas, based on the archaeological, linguistic and ethnic diversity among native American populations.