The Concept of Beringia

When Pleistocene glaciations occurred, many billions of tons of water became frozen into continental-sized ice sheets. Because a large proportion of the world's water became ice, global sea level dropped significantly. During the last glaciation, global sea level dropped by about 120 m (almost 400 ft). The continental shelf regions of the Bering and Chukchi seas between Siberia and Alaska are about 30-110 m (100-360 ft) below modern sea level. When the continental ice sheets grew, the sea level dropped, and the shelf regions between Siberia and Alaska became dry land. The former land bridge region was not a narrow isthmus between the two continents. From north to south, the land bridge extended more than 1000 km (600 miles). The land bridge was narrow near its center, in the Bering Strait region, but it was quite broad at both the north and south ends. In fact, the land bridge was larger than the state of Texas.

The Bering Land Bridge cut off circulation between the North Pacific and Arctic oceans. This, in turn, greatly diminished the landward flow of relatively warm, moist air masses from the North Pacific. This is the principal reason why Pleistocene ice sheets did not form in lowland Beringia: it was too dry. The development of ice sheets requires the accumulation of many years of winter snow, without melting in the intervening summers. If the climate is sufficiently cold to keep the snow from melting in summer, glacial ice can begin to form, but only if there is sufficient moisture to cause big snow depths. Without the moisture, cold, dry landscapes developed in Beringia. The drying effect of the land bridge kept glacial ice out of the Beringian lowlands. There were Pleistocene glaciers in Beringia, but only in the highlands. Because of this, Beringia formed a unique refuge for cold-adapted plants and animals.

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