On the relation between sea-surface heat flow and thermal circulation in the ocean

A theoretical framework for the description of the thermal state and circulation in the ocean is presented. Relations between differential heating, diffusive heat flux and surface drift are derived and discussed in the light of the basic mechanical property of the system, i.e. the tendency for light water to spread on top of heavier water. We find that for low and medium temperatures, the poleward surface drift can be determined directly from a knowledge of the heat flux through the sea surface. Preliminary quantitative estimates indicate that the “Hadley circulation” for the entire ocean involves a volume flux of order 70 ± 30 Sverdrup. For the North Atlantic we find a poleward drift of order 10 Sverdrup which compares well with previous estimates of the southward deep flow. Mean values for the diffusive flux in the ocean are found to be of order 20 W m^-2 at 15°C and 60 W m^-2 at 25°C.