Deep Ocean Circulation in the North Atlantic and Rapid Climate Change During the Last Ice Age
Rapid climate changes characterized the last ice age and deglaciation, with dramatic warming following the coldest intervals in the northern hemisphere. The repeated pattern of alternating temperature swings revealed in ice cores from Greenland and Antactica suggest a bipolar see-saw of heat redistribution by a dynamical component of the Earth system such as the large scale Atlantic Meridional Overturning Circulation (AMOC). Computer model simulations support this possibility, yet direct evidence for these changes in deep ocean circulation has been difficult to obtain. We have examined multiple geochemical and isotopic tracers of the deep circulation throughout the last ice age from rapidly accumulating sediments in the North Atlantic Ocean. They document the systematic association of variations in AMOC and abrupt climate change through the glaciation and deglaciation. Diminished AMOC accompanied the millennial northern coolings, including the cold, stadial, portions of so-called “Dansgaard-Oeschger (DO) events” as well as the extreme stadial “Heinrich events” associated with catastrophic iceberg discharges. Perhaps most notably, rapid increases in AMOC, in the form of surges in the depth and export of North Atlantic Deep Water from the North Atlantic Basin, accompanied the dramatic northern warmings that punctuated the ice age, underscoring the important potential role of internal Earth systems in climate change.