BERINGIAN PALEOENVIRONMENTS: A VIEW OF THE LANDSCAPE FOR EARLY MIGRATIONS

From ca. 20ka and 30ka cal.years BP during the last glaciation (LGM), the Bering Land Bridge separated the Bering Sea and North Pacific Ocean from the Arctic Ocean by more than 1000 kilometers of herb-dominated tundra. Four interrelated elements, each of which had to be dealt with by people adapting to late Pleistocene Beringia, shaped the ice-age environment: climatic variations, glacial extent, sea-level fluctuations, biota. Without a doubt there was little to prevent human migrations. Just before the LGM, large contrasts in vegetation existed across eastern and western Beringia. While the climate remained relatively harsh across much of Alaska, western Beringia experienced the temporary return of interglacial vegetation and treeline to near modern conditions. Sea level fluctuated in the range of -60 to -80 m before dropping quickly below -120 m (based on far field sea level records) by ca. 30 ka BP. Glaciation across most of Beringia was restricted to local mountain ranges and dominated by valley and cirque glaciers. The most glaciated parts of Beringia were in regions bordering the Gulf of Alaska. A mosaic of dry habitats characterized by herb and forb-tundra dominated ice -free valleys and lowlands with some evidence for mesic conditions across parts of central Beringia. Schematic paleogeography maps (Manley, 2003) imply the southern shore of the Land Bridge was geomorphically complex, with perhaps hundreds of islands located just offshore of a coast riddled with bays and inlets. Such a coastline may have been a rich marine habitat for walrus and seals, both as haul-out spots and breeding localities despite the persistence of sea ice 9 months of the year. A rapid rise of sea level at the end of the LGM likely caused swift migration of the shoreline as summers warmed into the early Holocene and re-established modern vegetation.