THE ovErturnng Crculaton

The other main component of the ocean circulation is the meridional overturning circulation (MOC), circulation essentially occurring in the meridional plane. There are two rather distinct aspects to this circulation, but they each have a common feature, namely the sinking of dense water at high latitudes and its subsequent rise to the surface elsewhere. Thus, in general the overturning circulation may be regarded as being "buoyancy enabled" in the sense that without buoyancy gradients at the surface there would be no deep overturning circulation. The buoyancy gradients themselves are produced by variations in temperature and salinity, and so the circulation is also sometimes known as the thermohaline circulation. The two different aspects are the processes that keep the water circulating. In one case, it is mixing by small-scale turbulent motions, and in the other case, it is the direct effect of the wind. We'll deal with these in turn, but before that, we discuss the buoyancy force itself.

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