Atmospheric and Oceanic Pathways Drive Separate Modes of Southern Hemisphere Climate in Simulations of Spontaneous Dansgaard-Oeschger-Type Oscillations

Dansgaard-Oeschger (DO) events are a dominant mode of millennial-scale climate variability during the last glacial period. While the influence of DO events is most pronounced in the North Atlantic region, global-scale impacts have been detected. In Antarctica, they manifest primarily as a muted, more gradual, and phase-shifted temperature signal, in concordance with oceanic propagation processes. However, recent studies found an additional in-phase component in Antarctic oxygen isotope records, implying the presence of atmospheric teleconnections.  

In this work, we study the Southern Hemisphere response to spontaneous DO-type oscillations in simulations under glacial boundary conditions with the general circulation model HadCM3. Compared to Greenland temperatures, the dominant Antarctic temperature mode features a smaller amplitude, and is phase-shifted with a lag of ~275 years with respect to North Atlantic climate. This is consistent with the bipolar seesaw mechanism. Additionally, we identify a robust Southern Hemisphere climate mode that varies synchronously with Greenland temperatures. This is the leading mode of millennial-scale atmospheric circulation variations in the Southern Hemisphere and is associated with a westward-shifted Walker circulation and strengthened Hadley cell. Notably, this mode features zonally heterogeneous anomalies in the Southern Hemisphere jet stream that are different from the pattern of the Southern Annular Mode. Comparison of simulated oxygen isotopes with speleothem and ice core records indicates a good model-proxy agreement for the synchronous mode in the tropics and mid-latitudes, but differences for Antarctica. Further research is needed to understand the dependency of the Southern Hemisphere hydroclimate response to DO events on model formulation, background state, DO amplitudes, and oscillation mechanism.