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Keywords:

  • bipolar climate see-saw;
  • Heinrich events;
  • Dansgaard–Oeschger cycles;
  • hemispheric heat piracy;
  • deep-water circulation;
  • ocean circulation modelling

Abstract

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-equatorial sea-surface perturbations. Based on the results of recent modelling of generic Heinrich and Dansgaard–Oeschger scenarios, we discuss the possibility 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 Atlantic counter heat piracy. Ocean circulation has an enhanced sensitivity to the northern deep-water source as the North Atlantic Deep Water (NADW) cannot enter the Southern Ocean at depths shallower than the bottom of the Drake Passage. Any shoaling of the NADW can, therefore, increase the northward incursion of Antarctic Bottom Water (AABW), and trigger an interhemispheric climate oscillation. As hundreds of years are required to warm the respective high latitudes, the observed climate lead and lags between the two hemispheres can be explained entirely by the variability of the meridional overturning and by the corresponding change in the oceanic heat transport. Accordingly, it is entirely feasible for the global climate to work like a pendulum, which theoretically could be controlled by pushing at either of the deep-water sources. Our model scenarios suggest that it is entirely feasible for the bipolar climate see-saw to be controlled solely by variations in NADW formation. Copyright © 2001 John Wiley & Sons, Ltd.