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7 Ocean Currents
7.3.3 General Pattern of Wind-Driven Ocean Circulation
The two major circulation ellipses (gyres) lie between the lines of 60° latitude.
The flow of currents is not uniform and varies substantially in different parts of
the gyres. The strongest currents are the Gulf Stream in the north-western
Atlantic, and the Kuroshio Current in the north-western Pacific. Both flow
northward as narrow streams along the western edges of the Atlantic and Pacific Oceans, respectively. The typical width of these currents is 50-75 km
and typical speed is 1-3 m/s. There are a few factors which contribute to an
intensification of current flow along the western edge of ocean basins. Rotation of the Earth from West to East results in sea water 'lagging' behind the
rotating solid ocean bottom. This pushes water against the western side of a
basin. Additionally, an equatorial drift induced by the Trade Winds piles large
quantities of water against the eastern margins of the continents. The resulting
mound of water produces a steep, poleward pressure gradient causing strong
currents away from the equator.
The western arms of these gyres contrast with the eastern arms, namely the
Canary Current in the Atlantic Ocean, and the California Current in the
Pacific Ocean. Both these relatively sluggish currents (their speed is less than
0.3 m/s) are several thousand kilometres wide. In the Northern Hemisphere,
the southern section of the gyre is known as the North Equatorial Current
and its northern section is the North Atlantic Current (in the Atlantic
Ocean) and the North Pacific Current (in the Pacific Ocean). The pattern
of the northern sections of the circulation gyres are complicated due to the
interaction with currents flowing out of the polar seas. In the North Atlantic,
these currents are the Labrador Current and East Greenland Current,
west and east of Greenland, respectively. In the Pacific Ocean, the northern
section of gyre is joined by the Oyasho Current in the Bering Sea.
Similar gyres in the Southern Hemisphere are the Brazil Current, at the
western edges of the South Atlantic basin, and the Benguela Current, at the
eastern edge of the basin, with the South Equatorial Current at the low
latitudes. The Brazil Current is weaker than the Gulf Stream because part
of the South Equatorial Current is deflected by the South American continent
into the Northern Hemisphere.
The South Pacific Gyre includes the South Equatorial Current, East
Australian Current and Peru Current. The Indian Ocean Gyre is less stable than the persistent gyres of the North Atlantic and North Pacific; it varies
seasonally in response to the reversal of the monsoon winds. The southern
section of the gyres in the Southern Hemisphere forms the Antarctic Circumpolar Current circulating around the Antarctic Continent.
On both sides ofthe Equator, the Trade Winds generate the North Equatorial Current and South Equatorial Current which are deflected poleward
by land masses. Due to complexities of the wind between the Trade Wind belts,
there is another surface, eastward-flowing current known as the Equatorial
Countercurrent and a subsurface eastward-flowing current, the Equatorial
7 Ocean Currents
7.3.3 General Pattern of Wind-Driven Ocean Circulation
The two major circulation ellipses (gyres) lie between the lines of 60° latitude.
The flow of currents is not uniform and varies substantially in different parts of
the gyres. The strongest currents are the Gulf Stream in the north-western
Atlantic, and the Kuroshio Current in the north-western Pacific. Both flow
northward as narrow streams along the western edges of the Atlantic and Pacific Oceans, respectively. The typical width of these currents is 50-75 km
and typical speed is 1-3 m/s. There are a few factors which contribute to an
intensification of current flow along the western edge of ocean basins. Rotation of the Earth from West to East results in sea water 'lagging' behind the
rotating solid ocean bottom. This pushes water against the western side of a
basin. Additionally, an equatorial drift induced by the Trade Winds piles large
quantities of water against the eastern margins of the continents. The resulting
mound of water produces a steep, poleward pressure gradient causing strong
currents away from the equator.
The western arms of these gyres contrast with the eastern arms, namely the
Canary Current in the Atlantic Ocean, and the California Current in the
Pacific Ocean. Both these relatively sluggish currents (their speed is less than
0.3 m/s) are several thousand kilometres wide. In the Northern Hemisphere,
the southern section of the gyre is known as the North Equatorial Current
and its northern section is the North Atlantic Current (in the Atlantic
Ocean) and the North Pacific Current (in the Pacific Ocean). The pattern
of the northern sections of the circulation gyres are complicated due to the
interaction with currents flowing out of the polar seas. In the North Atlantic,
these currents are the Labrador Current and East Greenland Current,
west and east of Greenland, respectively. In the Pacific Ocean, the northern
section of gyre is joined by the Oyasho Current in the Bering Sea.
Similar gyres in the Southern Hemisphere are the Brazil Current, at the
western edges of the South Atlantic basin, and the Benguela Current, at the
eastern edge of the basin, with the South Equatorial Current at the low
latitudes. The Brazil Current is weaker than the Gulf Stream because part
of the South Equatorial Current is deflected by the South American continent
into the Northern Hemisphere.
The South Pacific Gyre includes the South Equatorial Current, East
Australian Current and Peru Current. The Indian Ocean Gyre is less stable than the persistent gyres of the North Atlantic and North Pacific; it varies
seasonally in response to the reversal of the monsoon winds. The southern
section of the gyres in the Southern Hemisphere forms the Antarctic Circumpolar Current circulating around the Antarctic Continent.
On both sides ofthe Equator, the Trade Winds generate the North Equatorial Current and South Equatorial Current which are deflected poleward
by land masses. Due to complexities of the wind between the Trade Wind belts,
there is another surface, eastward-flowing current known as the Equatorial
Countercurrent and a subsurface eastward-flowing current, the Equatorial