Southern Hemisphere Westerly Wind Control over the Ocean's Thermohaline Circulation

Abstract

The effect of the position of the Southern Hemisphere subpolar westerly winds (SWWs) on the thermohaline circulation (THC) of the World Ocean is examined. The latitudes of zero wind stress curl position exert a strong control on the distribution of overturning between basins in the Northern Hemisphere. A southward wind shift results in a stronger Atlantic THC and enhanced stratification in the North Pacific, whereas a northward wind shift leads to a significantly reduced Atlantic THC and the development of vigorous sinking (up to 1500-m depth) in the North Pacific. In other words, the Atlantic dominance of the meridional overturning circulation depends on the position of the zero wind stress curl over the Southern Ocean in the experiments. This position has a direct influence on the surface salinity contrast between the Pacific and the Atlantic, which is then further amplified by changes in the distribution of Northern Hemisphere sinking between these basins. The results show that the northward location of the SWW stress maximum inferred for the last glacial period may have contributed to significantly reduced North Atlantic Deep Water formation during this period, and perhaps an enhanced and deeper North Pacific THC. Also, a more poleward location of the SWW stress maximum in the current warming climate may entail stronger salinity stratification of the North Pacific.