BEAUFORT SEA

outlying sea of the Arctic Ocean situated north of Canada and Alaska. It extends northeastward from Point Barrow, Alaska, toward Lands End on Prince Patrick Island, and westward from Banks Island to the Chukchi Sea. Its surface area is about 184,000 sq mi (476,000 sq km). The average depth is 3,239 ft (1,004 m) and the greatest depth 15,360 ft. It is named for the British rear admiral Sir Francis Beaufort. The continental shelf is narrow, especially near and east of Point Barrow; it widens somewhat north of the Mackenzie River mouth but nowhere exceeds 90 mi (145 km). The usual depth is less than 210 ft, although the slope descends steeply to 5,000 or 6,500 ft in the sea's upper part. Small gravel islands or shallows are often found. The largest islands are west of the Mackenzie River mouth-Herschel (7 sq mi) and Barter (5 sq mi). Very small islands and banks are found in the Mackenzie River Delta. The continental slope of the sea is cut by numerous submarine valleys. The Beaufort plateau, with depths from 6,500 to 10,000 ft, protrudes far into the sea, west of Banks Island. The geological structure of the bottom is that of a massive platform, and seismic data indicate a similarity between the crust of the Canadian Basin and of the oceans. The coasts along the Beaufort Sea are low-lying and almost entirely covered with tundra. Only west of the Mackenzie River's mouth do spurs of the Brooks Range approach the coastline. Banks and Prince Patrick islands are also fairly low, maximum elevations being from about 900 to 2,450 ft. The Beaufort Sea is under ice almost the year round; only in August and September does the ice break up, and then only near the coasts. Four water masses may be distinguished. The surface water mass is nearly 330 ft thick and ranges in temperature from 29.5 F (-1.4 C) in late summer to 28.8 F (-1.8 C) in winter. The subsurface water mass, formed by the waters of the Pacific Ocean and the Bering Sea flowing through the Bering Strait, is much warmer than the surface water and almost reaches the North Pole. The deep Atlantic water is the warmest of all, its temperature ranging from 32 to 34 F (0 to 1 C). The bottom water has temperatures ranging from 30.6 to 31.3 F (-0.4 to -0.8 C). The direction of the surface and subsurface currents is closely related to the general current system of the Arctic Ocean. A clockwise water gyre flows north of the Beaufort Sea; the majority of the sea's currents are thus westward or southwestward. Only in the vicinity of the mouth of the Mackenzie River is an eastward current recorded. The Mackenzie River deposits about 15 million tons of sedimentary material annually into the sea, including high concentrations of dolomite and calcium carbonate, which are found at great distances from the river delta. Gravel, pebble, and sand deposits, sometimes mixed with mud, are widely distributed on the continental shelf underlying the sea. More than 70 phytoplankton species are found in the Beaufort Sea, but the total biomass is not large. Nearly 80 zooplankton species have been found, and the bottom fauna consists of nearly 700 species of polychaetes, bryozoans, crustaceans, and mollusks. The chief settlement along the Beaufort Sea is Prudhoe Bay, Alaska, which is the centre of petroleum production on the coastal lowland known as the North Slope. The Trans-Alaska Pipeline carries crude oil south from Prudhoe Bay to Valdez, an ice-free port almost 800 miles (1,300 km) away on Alaska's southern coast. Fishing and sea hunting along the Beaufort Sea are for local supply only.