Jumat, 24 Juni 2011

DEFINITION OF OCEAN CURRENTS

Like the atmosphere, the ocean is constantly

in motion. Ocean currents are defined by the movement

paths of water in regular courses, driven by the wind

and thermohaline forces across the ocean basins. Shallow

currents are driven primarily by the wind but are systematically

deflected by the Coriolis force to the right of the atmospheric

wind directions in the Northern Hemisphere, and to

the left of the prevailing winds in the Southern Hemisphere.

Therefore, shallow water currents tend to be oriented about

45° from the predominant wind directions.

Deepwater currents, however, are driven primarily by

thermohaline effects, that is the movement of water driven

by differences in temperature and salinity. The Atlantic and

Pacific Ocean basins both show a general clockwise rotation

in the Northern Hemisphere, and a counterclockwise spin in

the Southern Hemisphere, with the strongest currents in the

midlatitude sectors. The pattern in the Indian Ocean is

broadly similar but seasonally different and more complex

because of the effects of the monsoon. Antarctica is bound

on all sides by deep water and has a major clockwise current

surrounding it known as the Antarctic Circumpolar Current,

lying between 40° and 60° south. This is a strong current,

moving at 1.6–5 feet per second (0.5–1.5 m/s), and has a

couple of major gyres in it at the Ross Ice Shelf and near the

Antarctic Peninsula. The Arctic Ocean has a complex pattern,

because it is sometimes ice covered and is nearly completely

surrounded by land with only one major entry and

escape route east of Greenland, called Fram Strait. Circulation

patterns in the Arctic Ocean are dominated by a slow,

0.4–1.6-inch per second (1–4 cm/s) transpolar drift from

Siberia to the Fram Strait, and by a thermohaline-induced

anticyclonic spin known as the Beaufort Gyre that causes ice

to pile up on the Greenland and Canadian coasts. Together

the two effects in the Arctic Ocean bring numerous icebergs

into North Atlantic shipping lanes and send much of the

cold deep water around Greenland into the North Atlantic

ocean basin.

See also EKMAN SPIRALS; GEOSTROPHIC CURRENTS; THERMOHALINE

CIRCULATION.

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