The relationship between the Northern Hemisphere and Southern Hemisphere deep water circulation systems is explored in experiments with gradual and impulsive freshwater input through the St. Lawrence. With sufficient freshwater volume input (50 Sv years), North Atlantic Deep Water (NADW) cessation occurs, as does substantial cooling in the Northern Hemisphere. The colder temperatures are accompanied by increased mass and sea level pressure in the Northern Hemisphere, with corresponding lower pressure in the Southern Hemisphere. The low-pressure response occurs at high southern latitudes, consistent with the Antarctic Annular Mode, the leading mode of variability in the current climate. Stronger winds, associated with this increased cyclonicity, intensify the Antarctic Circumpolar Current (ACC) with heat flux divergences in the South Atlantic and convergences and warming in the Indian Ocean. Weddell Sea Bottom Water production increases in response to the South Atlantic high-latitude cooling and sea ice growth, hence acting as a seesaw with the decreasing NADW, and even global Antarctic Bottom Water increases, although not as strongly. The initial seesaw response occurs within a few years, although it takes some 100 years to maximize due to the response time of the ACC. The South Atlantic cooling occurs approximately in phase with the North Atlantic, so the seesaw is not in temperature within that ocean basin; however, warming in portions of the southern Indian Ocean occurs out of phase with the Northern Hemisphere cooling. NADW does not resume of its own accord once complete cessation occurs even when freshwater input is stopped, but when increased evaporation is used to force NADW formation temporarily, Weddell Sea Bottom Water decreases accordingly. ¿ 2001 American Geophysical Union