That part of the large-scale ocean circulation driven by the fluxes of heat and freshwater at the ocean surface. The freshwater flux affects salinity, and both temperature and salinity changes cause density changes that drive the thermohaline circulation. The present-day forcing consists of cooling and net precipitation in high latitudes, warming and evaporation in subtropical latitudes; note the opposing effects on density. The present-day thermohaline circulation consists of 1) sinking of strongly cooled, moderately saline water in relatively small regions located in areas of relatively strong winter cooling; 2) deep flow throughout the global ocean basins; and 3) slow upwelling toward the surface. Its transport is small compared to wind-driven transport, but it is believed that the thermohaline circulation is responsible for much of the heat transported by the ocean. See gradient current.