Ocean Bi-Polar Seesaw and Climate: Southern Versus Northern Meltwater Impacts

Abstract

Model simulations targeting the ocean circulation response to changes in surface salinity in the high latitudes of both Northern and Southern Hemispheres demonstrate that meltwater impacts in one hemisphere may lead to a strengthening of the thermohaline conveyor driven by the source in the opposite hemisphere. This, in turn, leads to significant changes in poleward heat transport. Further, meltwater events caused largely by sea ice melting can lead to deep-sea warming and thermal expansion of abyssal water, that in turn can cause a substantial sea level change even without a major ice sheet melting. Experiments with a glacial ocean circulation regime prone to northern and southern meltwater events imply that glacial cycles may have been influenced by both northern and southern deepwater sources. Importantly, the experiments suggest that the southern source can be a more powerful modulator of the meridional deep-ocean conveyor that the northern source, which challenges our current vision of the North Atlantic Deep Water as an ultimate driver of deep-ocean circulation. Our experiments show that the southern impact can overpower northern ones. Even in the experiment in which the amplitude of the perturbation in the North Atlantic was as high as -3 psu, and the amplitude in the Southern Ocean was only-1 psu, the deep-water regime was qualitatively the same as in the pure Southern Ocean scenario, with somewhat less deep-ocean warming, yet still global and substantial.