The thermohaline circulation in relation to the general circulation in the oceans

Abstract

To arrive at an estimate of the role of the thermohaline circulation in the oceans, the magnitude and the implications of the various thermohaline effects are discussed numerically. From a consideration of the heat balance of the surface layer in lower latitudes it follows that the average ascending motion through the thermocline is limited to between 1 and 5 × 10−5 cm/sec. The discussion of the thermocline suggests a resultant downward heat flow in spite of the ascending motion, which is balanced by horizontal advection. A method for the calculation of the vertical exchange coefficient is given and shows that it has a pronounced minimum in the discontinuity layer. The discussion of the sinking processes of the Bottom Water and the Intermediate Waters indicates the existence of two nearly independent circulation systems in meridional direction. The deep meridional spreading of the different water masses cannot be explained satisfactorily by a two-layer model, but a four-layer model would be required. A model of a pure thermohaline circulation in an ocean covering the entire earth including frictional terms shows that a circumpolar current would exist in each hemisphere, carrying 134 × 106 m3/sec, but that the strength of the meridional circulation across 45° latitude would be only 10 × 106 m3/sec. This indicates that also in the actual ocean the thermohaline circulation can only be weak and its strength must be less than that of the wind driven circulation. In a detailed study of the deep circulation its influence, however, cannot be completely disregarded. A four-layer model of the wind driven and thermohaline circulation in a meridional plane is constructed, its implications are discussed and the results are found in agreement with the circulation pattern resulting from water mass analysis.