Wind and Ocean Circulation. Density of air is controlled by temperature, pressure and moisture content. Warm air is less dense than cold air and moist air is less dense than dry air.
Pressure gradients develop in the ocean because the sea surface is warped into broad mounds and depressions with a relief of about one meter.
With time, wind-driven surface water motion extends downward into the water column, but speed decreases and direction changes because of Coriolis deflection.
The biology of these rings has been the subject of a concerted research effort. This work examined how the communities of plankton (both phytoplankton and zooplankton) changed as the ring aged. The physical characteristics of the ring also changed -- the water in the core slowly mixed with the surrounding circulating ring, modifying to become warmer or colder depending on the type of ring.
In general, the rings are about 100-300 km in diameter, and they extend to considerable depths. They should be visualized as concentric cylinders, rather than simply surface features. Rings are examples of mesoscale phenomena in the oceans,
The major thermohaline currents appear to flow mainly equatorward, but this is because they originate in the polar regions and their outward flow is confined between the continents.
Most seas are indentations into continents, partially isolated from the ocean and strongly influenced by continental climate and river drainage.