The Beaufort Sea is a regional sea of the Arctic Ocean situated off the north coast of Canada and Alaska with its northern boundary defined by a line extending from Pt Barrow to Cape Lands End on Prince Patrick Island. It is about 590,000 km2 (227,800 sq mi) in area and connects freely with the Chukchi Sea to the west and the Arctic Ocean to the north. Banks Island and Victoria Island of the Canadian Archipelago form the eastern boundary. The continental shelf (<200 m), which comprises about 30% of the region, is narrow off Alaska (40-100 km), widens in the Canadian sector (150 km), and is cut by four major valleys: Barrow Canyon at the western edge, Mackenzie Canyon, Amundsen Gulf, and the entrance to McClure Strait at the northeastern edge. Shelf sediments exhibit frequent gouges in shallow water (10-50 m) where ice keels have scoured the bottom, and submerged pingo-like features (mounds) on the eastern Canadian Beaufort shelf. At the shelf edge, the ocean bottom drops steeply to 3700 m (12,140 ft) in the Canada Basin.

The Mackenzie River (with an annual discharge of 330 km3 fresh water and 130 million tons of sediments) forms the largest North American Arctic delta, second only to the Lena Delta, and is a dominant influence on the regional oceanography and sediment composition. Coastlines are retreating rapidly in many locations along the Alaskan and Canadian shorelines (up to 20 m per year) due to rising sea level during the Holocene (~65 m during the past 9000 years), low coastal relief, poorly bonded ice-rich soils, and storm surges that may exceed 2 m.

Climate is described as harsh; only from June to September do mean temperatures exceed freezing, with July means from 6.2°C to 13.8°C and January means from -24.0°C to -29.9°C. Annual precipitation ranges from 130 to 260 mm, about half of which falls as snow. The dominant wind direction varies seasonally, ranging from northeast to southeast, and there are typically four to six storms per year (winds exceeding 37 km h-1).

Ice in the interior ocean circulates in the large clockwise Beaufort Gyre centered in the vicinity of 80° N 150° W, but the size and center of the gyre vary on the decadal scale with atmospheric pressure fields. Over the shelves, ice cover is seasonal, breakup occurs in early June, and freezeup occurs in mid-October. Landfast ice, which grows to about 2 m by the end of winter, forms inshore of the 20 m isobath. The discontinuity between the landfast ice and offshore ice, which drifts to the west, forms a flaw lead system where open water may be observed intermittently throughout winter. At the entrance to Amundsen Gulf, the Bathurst Polynya provides an important location for marine life and may encompass over 150,000 km2 (57,900 sq mi) of open water during winter.

Western bowhead whales (about 8200) and Beaufort Sea beluga whales (20,000 or more) are seasonal migrants from the Bering and Chukchi seas to Beaufort Sea summer open water. The resident polar bear population is estimated at 3000 and their major prey, ringed

Beaufort Sea and surrounding islands and territories.

seals, at about 650,000. Bearded seals are less numerous (about 40,000), occurring solitarily within about the 100 m isobath where they feed on benthos. Walruses are seen only rarely in the Canadian Beaufort and more frequently to the west of Herschel Island. Fish include marine species such as sculpins, cod, flounders, smelt, herring and eelpouts, and anadromous fish such as broad whitefish, ciscoes, Arctic char and grayling. The coastal corridor, which is freshened by inflow from the Mackenzie River and numerous smaller rivers, is an important habitat for anadromous fish. Flaw leads and the Bathurst Polynya provide important staging and feeding areas for hundreds of thousands of migratory birds, including king eiders, common eiders, oldsquaw, glaucous gull, and loons.

Major coastal communities include Barrow (population 4580 in 2000) in Alaska, and Tuktoyaktuk (population 940 in 1996), Paulatuk (population 300 in 1996), Sachs Harbour (population 135 in 1996), and Holman (population 400 in 1996) in the Inuvialuit Settlement Region of the Northwest Territories of Canada.

Paleo-Eskimo occupation likely occurred in waves starting in about 4500-4000 years before present (BP) with migration from the Bering Strait region.

Pre-Dorset people (3700-2800 BP), who inhabited the low Arctic lowlands, were followed by the Dorset people (2800-000 BP) whose sudden disappearance coincided with the onset of warming. The Thule people, who developed from the Birnirk culture of north Alaska (1500-1000 BP), followed the bowhead whales, probably displacing the Dorset people to produce a uniform Inuit population from Bering Strait to Greenland. A cooling trend that ultimately became the "Little Ice Age" (350-150 BP) led to a fragmenting that produced locally the Mackenzie Inuit, predecessors to the modern Inuvialuit. Presently within the Beaufort Sea margin, native groups include the Inupiat in Alaska and the Inuvialuit and Gwich'in in the Canadian Beaufort region.

European exploration began when Alexander Mackenzie established the location of the Mackenzie Delta in 1789. Subsequent mapping of the shoreline was conducted predominantly by John Franklin and John Richardson during 1825-1827 and by Robert M'Clure (1850-1854) and Richard Collinson (1850-1855) who were searching for the lost Franklin expedition. Peter Dease and Thomas Simpson completed the westernmost mapping of the Beaufort coast in 1836-1839. In the 1870s, the Pacific whaling fleet began sailing east of Pt Barrow, and with steam power the hunt was extended to the farthest reaches of the Beaufort Sea by the late 1880s. 1899 was the last good year for the whaling fishery.

Coastal communities of the Beaufort Sea rely predominantly upon subsistence hunting and fishing. Important marine mammals include the bowhead whale, of which about 70 are harvested annually, almost all in Alaska. Beluga harvest during the 1990s averaged 111 per year by Inuvialuit and about 60 by Inupiaq in Alaska. Ringed seal and, to a lesser extent, bearded seal are important local sources of food and pelts. The predominant food fish varies with location but includes broad whitefish, Arctic char and, where available, Pacific herring and cisco. Of the mineral natural resources, oil and gas have had and will continue to have the greatest economic importance. Offshore oil was discovered at Prudhoe Bay in 1968 with original reserves estimated at 1.1x109 m3 (35 billion cu ft) and a further 0.3x109 m3 in the adjacent Kuuparuk River field. At 0.18x106 m3/day, Prudhoe accounts for 20% of US domestic oil production. Exploration since the 1970s has discovered 0.16x109m3 of oil and 255x109 m3 of gas in the Mackenzie Delta and nearshore, the largest oil discovery being at Amauligak. Shipping is limited primarily to supply of small communities and to servicing oil industry when active. The lack of natural deep-draft harbors together with ice cover during eight months of the year severely limits the potential for destination shipping.

Robie W. Macdonald

See also Arctic Ocean; Barrow; Beaufort Gyre; Chukchi Sea; Inuvialuit Settlement Region; Mackenzie River; Oil Exploration; Prudhoe Bay

Further Reading

Ayles, B. & N. Snow (editors), Special Issue of the journal

Arctic, Beaufort Sea 2000, 2002 Bockstoce, J.R., Whales, Ice and Men: The History of Whaling in the Western Arctic, Seattle: University of Washington Press, 1986

Burns, B.M., The Climate of the Mackenzie Valley-Beaufort Sea, Volume II, Toronto: Atmospheric Environment Service, Climate Studies No. 24, 1974 McGhee, R., Ancient People of the Arctic, Vancouver: UBC Press in association with Canadian Museum of Civilization, 1996

Pilot of Arctic Canada, Volume 1 (2nd edition), Ottawa: Canadian Hydrographic Service, Department of Energy Mines and Resources, 1970 Stegerwald, M.B. & D.E. McAllister, List of the Canadian marine fish species in the National Museum of Natural Sciences, National Museums of Canada, Syllogeus 41, 1982 Stirling, I. & N.A. 0ritsland, "Relationships between estimates of ringed seal and polar bear populations in the Canadian Arctic." In Canadian Journal of Fisheries and Aquatic Science, 52 (1995): 2594-2612

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