The region of the western Arctic stretching from the Lena River in northeast Russia to the Mackenzie River in Canada is geographically known as Beringia. The lowlands of Beringia remained ice-free during Pleistocene glaciations, while nearly all other high-latitude regions of the Northern Hemisphere were covered by ice sheets. The lowering of sea level during glacial stadials exposed large regions of the Bering and Chukchi sea shelves, repeatedly forming the Bering Land Bridge. The Bering Land Bridge cut off circulation between the waters of the North Pacific and Arctic oceans, greatly increasing the continentality of adjacent land masses and diminishing the inland flow of relatively warm, moist air masses from the North Pacific (Harris SA (2005) Thermal history of the Arctic Ocean environs adjacent to North America during the last 3.5 Ma and a possible mechanism for the cause of cold events (major glaciations and permafrost events). Progress in Physical Geography 29: 1–19).