The oceans play important roles in the formation of the earth's climate, and in climatic variations and change. One of these important roles is meridional heat transport due to oceanic general circulation, especially three-dimensional thermohaline circulation through the entire water column. The oceans transport a huge amount of heat-as much as that of the atmosphere. Accordingly, the north-south gradient of surface air temperature is greatly mitigated. Corresponding to global warming due to increases of greenhouse gasses, the oceanic heat content hasincreased sharply. Global warming might cause a weakening of the strength of thermohaline circulation.
