Currents

The surface circulation of the North Pacific Ocean resembles a huge merry-go-round in which various currents move in a clockwise direction around a cell located slightly offcentre in the northern hemisphere. The main spring of this circular movement is the North Equatorial Current which flows westward with its axis at about latitude 12°N. To the south of this current is the eastward flowing Equatorial Countercurrent, which has its southern limits between latitudes 2°N and 4°N where it is bounded by the South Equatorial Current.

The North Equatorial Current is fed mainly by the California Current and the northern branch of the Equatorial Countercurrent. Further west it is reinforced by the North Pacific Current and further still it divides in two, the southern branch revers ing its direction to become the Equatorial Countercurrent, while the northern branch carries on towards Taiwan and Japan. This is the main source of the Kuro Shio, a flow of warm water similar to the Gulf Stream of the North Atlantic. The main difference is that the direction of the Kuro Shio is seasonal, setting to the NE during the SW monsoon, but reversing its direction in winter, at the height of the NE monsoon.

The main direction of the Kuro Shio is NE along the southern coast of Japan. It subsequently fans out in about latitude 35 eN to form the North Pacific Current. This current, reinforced by the Aleutian Current, flows in a broad band across the North Pacific towards America. East of latitude 160"E this current starts fanning out, part of it turning south, while the main body continues eastwards towards the North American continent where it turns SE.

This southerly drift changes its name to the California Current which flows into the North Equatorial Current thus completing the clockwise circulation round the North Pacific basin.

The surface circulation along the Pacific coast of Central America and Gulf of Panama is more erratic, with great seasonal variations that make predictions impossible. The Equatorial Countercurrent flows into this area and normally is deflected to the north west along the coast of Central America to join the California Current and eventually the North Equatorial Current. In the first months of the year a branch of the Equatorial Countercurrent turns south and flows into the South Pacific. In the Gulf of Panama the movement of water is more complicated, with an inflow of water at both extremes and an outflow in the centre that finally joins the South Equatorial Current.

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