What is the thermohaline circulation As opposed to wind-driven
currents and tides (which are due to the gravity of moon and
sun), the thermohaline circulation (Fig. 1) is that part of the
ocean circulation which is driven by density differences. Sea
water density depends on temperature and salinity, hence the
name thermo-haline. The salinity and temperature differences
arise from heating/cooling at the sea surface and from the
surface freshwater fluxes (evaporation and sea ice formation
enhance salinity; precipitation, runoff and ice-melt decrease
salinity). Heat sources at the ocean bottom play a minor role.
Figure 1. Schematic representation of the global thermohaline
circulation. Surface currents are shown in red, deep waters in
light blue and bottom waters in dark blue. The main deep water
formation sites are shown in orange. (After , modified by S.R.)
In contrast to the wind-driven currents, the THC is not confined
to surface waters but can be regarded as a big overturning of
the world ocean, from top to