Ocean waters are constantly on the move. Currents flow in complex patterns affected by wind, the water's salinity and heat content, bottom topography, and the earth's rotation.
Warm surface currents invariably flow from the tropics to the higher latitudes, driven mainly by atmospheric winds, as well as the earth's rotation. Deep water forms when sea water entering polar regions cools or freezes, becoming saltier and denser. Colder or saltier water tends to sink.
A global "conveyor belt" is set in motion when deep water forms in the North Atlantic, sinks, moves south, and circulates around Antarctica, and then moves northward to the Indian, Pacific, and Atlantic basins. It can take a thousand years for water from the North Atlantic to find its way into the North Pacific.
These maps wonderfully help illustrate the patterns and inter-relationships of ocean currents across the globe.