Interhemispheric teleconnections as drivers of Southern Hemisphere climate in simulations of spontaneous Dansgaard-Oeschger-type events

Abstract

Dansgaard-Oeschger (DO) events are a dominant mode of millennial-scale climate variability during the last glacial period. While the influences of DO events are most pronounced in the North Atlantic region, their impacts are detectable on the global scale. In Antarctica, their imprint primarily manifests as a muted and anti-phased response, which can be explained by the bipolar seesaw mechanism. However, the ice core record revealed an additional in-phase component, suggesting the presence of atmospheric teleconnections. Here, we study the propagation of DO-type signals from the North Atlantic to the Southern Hemisphere in a set of simulations with the general circulation model HadCM3, including an isotope-enabled run. The simulations show spontaneous DO-type oscillations under glacial boundary conditions, which allows studying the timing and interaction of atmospheric and oceanic processes under a continuously varying background state. Consistent with the ice core record, we find a muted and anti-phased temperature response over Antarctica that lags the North Atlantic by ~300 years, and global sea surface temperature patterns in agreement with the bipolar seesaw mechanism. Additionally, we identify a robust Southern Hemisphere mode in phase with the North Atlantic. This mode is associated with hydroclimate changes in the tropical Pacific, which modulate the Southern Hemisphere atmospheric circulation, and, thereby, impact Antarctic temperatures. Notably, the dominant millennial-scale circulation pattern exhibits zonal asymmetries that do not resemble the leading modes of inter-annual variability. Preliminary analyses indicate a good agreement of the simulated millennial-scale variability in oxygen isotopes with a global compilation of speleothem and ice core records.