Talk by Torge Martin, GEOMAR Helmholtz, Centre for Ocean Research

Southern Ocean Forcing of Centennial Climate Variability

A reduced Atlantic Meridional Overturning Circulation (AMOC) causes the North Atlantic to cool and the South Atlantic to warm due to decreased heat transport. This bipolar seesaw concept—particular when extended by a heat reservoir in the South—has been instrumental in explaining opposing temperature trends in Greenlandic and Antarctic ice cores. While often the North Atlantic is viewed as most influential on the AMOC, variations in overturning can be forced by processes in the South as well. Multi-millennial control simulations with the Kiel Climate Model (KCM), a combination of the ECHAM5 atmosphere (T31 grid) and NEMO-LIM2 ocean model (2˚ grid, 0.5˚ in tropics), exhibit self-sustained oscillations of open ocean deep convection in the Southern Ocean on a (multi-)centennial timescale. The enhanced formation of Antarctic Bottom Water during periods of open ocean deep convection impinges on the AMOC by altering the meridional density gradient in the Atlantic similar to the bipolar seesaw. More on the mechanism behind the deep convection flip-flop and its link to the North Atlantic in this seminar.