A GCM STUDY OF TROPICAL-SUBTROPICAL UPPER-OCEAN WATER EXCHANGE

Experiments with an oceanic general circulation model indicate that th e tropical and subtropical oceanic circulations are linked in three wa ys. Far from coasts in the oceanic interior, equatorial surface waters flow poleward to the southern part of the subtropical gyre, and then are subducted and returned in the thermocline to the upper part of the core of the Equatorial Undercurrent. There is, in addition, a surface western boundary current that carries waters from the equatorial regi on to the northern part of the subtropical gyre. After subduction, tha t water reaches the equator by means of a subsurface western boundary current and provides a substantial part (2/3 approximately) of the ini tial transport of the Equatorial Undercurrent. The eastward flow in th e Equatorial Undercurrent is part of an intense equatorial cell in whi ch water rises to the surface at the equator, drifts westward and pole ward, then sinks near 30 latitude to flow equatorward where it rejoins the undercurrent.