Postglacial Development of Modern Arctic Ecosystems

The margins of the ice sheets of the last glaciation began to retreat northward, beginning about 14,000—13,000 years ago. The process of glacial retreat was interrupted in the North Atlantic region by a climatic reversal that began about 12,000 years ago. This cooling event is called the Younger Dryas interval, and it lasted approximately 1000 years. During the Younger Dryas, the ice advanced again in Europe, as far south as southern Scandinavia. Following the Younger Dryas interval, the ice retreated rapidly. However, some Arctic regions remained covered by glacial ice until the middle of the Holocene Epoch (about 5000 years ago), or later. The glacial ice dome that sat over the Labrador-Ungava region of eastern Canada is an example of such late-lying ice.

Some of the populations of tundra flora and fauna that had existed in regions south of the continental ice sheets were able to migrate north as the ice retreated, but in some regions, such as the American mid-west, the tundra biota became trapped between late-lying ice lobes to the north and coniferous forests that were rapidly advancing from the south as climate warmed. In these circumstances, the cold-loving flora and fauna had nowhere to go. Further north in Canada, populations of Arctic tundra flora and fauna spread eastward from their Beringian refuge as the ice retreated from the Northwest Territories. Hudson Bay formed a substantial barrier to such migrations, however, and the modern tundra flora and fauna of the Ungava peninsula have substantially fewer species than that of the Arctic regions west of Hudson Bay.

The Bering Land Bridge was flooded by sea water as global sea levels rose at the end of the last glaciation. By about 12,000 years ago, the land connection between Siberia and Alaska was inundated. This event brought large-scale environmental changes to north eastern Siberia and Alaska. The cold, dry, continental climates that had dominated these regions during the last glaciation gave way to more moist, maritime climates as the ocean waters flooded the ancient land bridge. The steppe-tundra and the Pleistocene megafauna it supported vanished at about the same time as the land bridge was flooded, although some of the large mammals survived for a few more centuries. Modern Arctic tundra became established at this time, with its mesic habitats, moss-dominated ground cover, and dwarf shrubs of willow and birch.

Scott A. Elias

See also Beringia; Environmental Problems; Fossils: Animal Species; Quaternary Paleoclimatology

Further Reading

Cwynar, Les & James Ritchie, "Arctic steppe-tundra: a Yukon perspective." Science, 208 (1980): 1375—1377 Elias, Scott, Ice Age History of Alaskan National Parks, Washington, District of Columbia: Smithsonian Institution Press, 1995

Elias, Scott & Julie Brigham-Grette (editors), "Beringian pale-oenvironments." Quaternary Science Reviews, 20(1—3) (2001): 1—574

Guthrie, R. Dale, Frozen Fauna of the Mammoth Steppe. The Story of Blue Babe, Chicago: University of Chicago Press, 1990

Hopkins, David, John Matthews, Charles Schweger & Steven Young, Paleoecology of Beringia, New York: Academic Press, 1982

Martin, Paul & Richard Klein (editors), Quaternary

Extinctions, Tucson: University of Arizona Press, 1989 White, James, Thomas Ager, D.P. Adam, Estella Leopold, G. Liu, H. Jette & Charles Schweger, "An 18 million year record of vegetation and climate change in northwestern Canada and Alaska: tectonic and global climatic correlates." Palaeogeography, Palaeoclimatology, Palaeoecology, 130 (1997): 293—306 Zimov, S., V. Chuprynin, A. Oreshko, F. Chapin, J. Reynolds & M. Chapin, "Steppe-tundra transition: a herbivore-driven biome shift at the end of the Pleistocene." American Naturalist, 146 (1995): 765—794

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