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THE CIRCULATION OF THE PACIFIC AND INDIAN OCEAN

The Circulation of the Pacific Ocean

The pattern of circulation in the Pacific is similar to that of the Atlantic except in modifications which can be expected from the greater size and the more open nature of the Pacific.

The North Equatorial Current flows westwards with a compensating Equatorial Counter Current running in the opposite direction. Due to the greater expanse of the Pacific and the absence of an obstructing land-mass the volume of water is very much greater than that of the Atlantic Equatorial Current. The North-East Trade Winds blow the North Equatorial Current off the coasts of the Philippines and Taiwan into the East China Sea as the Kuroshio or Kuro Siwo or Japan Current.

Its warm waters are carried polewards as the North Pacific Drift, keeping the ports of the Alaskan coast ice-free in winter. The cold Bering Current or Alaskan Current creeps southwards from the narrow Bering Strait and is joined by the Okhotsk Current to meet the warm Japan Current as the Oyashio, off Hokkaido. The cold water eventually sinks beneath the warmer waters of the North Pacific Drift. Part of it drifts eastwards as the cool Californian Current along the coasts of the western U.S.A. and coalesces with the North Equatorial Current to complete the clockwise circulation.

The current system of the South Pacific is the same as that of the South Atlantic. The South Equatorial Current driven by the South East Trade winds, flows southwards along the coast of Queensland as the East Australian Current, bringing warm equatorial waters into temperate waters. The current turns eastwards towards New Zealand under the full force of the Westerlies in the Tasman Sea and merges with part of the cold West Wind Drift as the South Pacific Current. Obstructed by the tip of southern Chile, the current turns northwards along the western coast of South America as the cold Humboldt or Peruvian Current. The cold water chills any wind that blows on shore so that the Chilean and Peruvian coasts are practically rainless. The region is rich in microscopic marine plants and animals that attract huge shoals of fish. Consequently, millions of sea birds gather here to feed on the fish. Their droppings completely whiten the coastal cliffs and islands, forming thick deposits of guano, a valuable source of fertilizer. The Peruvian Current eventually links up with the South Equatorial Current and completes the cycle of currents in the South Pacific.

 

The Indian Ocean Circulation

The currents of the South Indian Ocean form a circuit. The Equatorial Current, turning southwards past Malagasy as the Agulhas or Mozambique Current merges with the West Wind Drift, flowing eastward and turns equatorwards as the West Australian Current.

In the North Indian Ocean, there is a complete reversal of the direction of currents between summer and winter, due to the changes of monsoon winds. In summer from June to October, when the dominant wind is the South-West Monsoon, the currents are blown from a south-westerly direction as the South-West Monsoon Drift. This is reversed in winter, beginning from December, when the NorthEast Monsoon blows the currents from the north-east as the North-East Monsoon Drift. The currents of the North Indian Ocean demonstrate most convincingly the dominant effects of winds on the circulation of ocean currents.

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