Circulation and water masses in the eastern equatorial Pacific Ocean
Int J Oceanol Limnol 1(2): 117-147
Geostrophic transports are calculated for the different branches of the currents in the eastern equatorial Pacific Ocean, and a coherent picture of the circulation in this part of the Ocean is derived. The wind-driven westward flow of about 75 1012cm3/sec in the North and South Equatorial Currents is opposed by an eastward flow of about 50 1012cm3/ sec in the Countercurrent and the Undercurrent, and the difference is made up by meridional flow in the California and Peru Currents. The water carried east in the Undercurrent is chiefly recirculated into the South Equatorial Current. The formation of the main surface water masses is explained in relation to the climatic conditions in their regions of formation. Subsurface water masses are analyzed by means of the core layer method. The main sub-surface water masses in the area are the subsurface salinity maximum originating from the Subtropical Surface Water; the oxygen minimum layer; the upper salinity minimum, originating from temperate climatic regions; the lower salinity maximum; and the salinity minimum of the Intermediate Water. The origin and the spreading of these water masses within the circulation system of the eastern Pacific Ocean are discussed. The Subtropical Surface Water of the South Pacific Ocean extends as a subsurface salinity maximum north, spreads across the equator and occupies the thermocline below the Tropical Surface Water. Its residence time in this area is calculated as 10 years. The oxygen minimum layer represents subsurface water of a long residence time in the eastern and equatorial portions of the ocean where the circulation of the subtropical anticylcones does not penetrate. The upper salinity minimum is formed by low salinity water, which spreads equatorwards in the eastern boundary currents and slides below the Subtropical Surface Water. The salinity minimum of the Intermediate Water follows an anticyclonic path south of 20[degree]S.; north of this position its spreading seems to take place by lateral mixing.