Atlantic Ocean heat piracy and the bipolar climate see-saw during Heinrichand Dansgaard-Oeschger events

The millennial-scale asynchrony of Antarctic and Greenland climate records during the last glacial period implies that the global climate system acts as a bipolar see-saw driven by either high-latitudinal and/or near-equatori al sea-surface perturbations. Based on the results of recent modelling of g eneric Heinrich and Dansgaard-Oeschger scenarios, we discuss the possibilit y that oscillations of the deep-ocean conveyor may have been sufficient to cause this bipolar see-saw. The bipolar climate asynchrony in our scenarios is caused by the toggle between North Atlantic heat piracy and South Atlan tic counter heat piracy. Ocean circulation has an enhanced sensitivity to t he northern deep-water source as the North Atlantic Deep Water (NADW) canno t enter the Southern Ocean at depths shallower than the bottom of the Drake Passage. Any shoaling of the NADW can, therefore, increase the northward i ncursion of Antarctic Bottom Water (AABW), and trigger an interhemispheric climate oscillation. As hundreds of years are required to warm the respecti ve high latitudes, the observed climate lead and lags between the two hemis pheres can be explained entirely by the variability of the meridional overt urning and by the corresponding change in the oceanic heat transport. Accor dingly, it is entirely feasible for the global climate to work like a pendu lum, which theoretically could be controlled by pushing at either of the de ep-water sources. Our model scenarios suggest that it is entirely feasible for the bipolar climate see-saw to be controlled solely by variations in NA DW formation. Copyright (C) 2001 John Wiley & Sons, Ltd.