Onset and termination of Heinrich Stadial 4 and the underlying climate dynamics

Heinrich Stadial 4 during the last glacial period was marked by severe cooling at northern high latitudes along with the attendant changes in Asian Monsoon (Chinese Stadial 4) and South American Monsoon (South American Stadial 4). Here we present improved constraints on timings of Heinrich/Chinese/South American Stadial 4 onset and termination at sub-centennial precision based on speleothem records. We show that their initial onsets were essentially synchronous (40.20 ± 0.08 thousand years ago) and led the Antarctic warming by ~300 years. The Heinrich/Chinese Stadial 4 termination commenced at 38.34 ± 0.07 thousand years ago following a centennial-scale reduction in the Amazon River runoff and a poleward shift of the Southern Westerly wind belt. These two precursor events may have contributed to a reduced Amazon Plume Region and an enhanced Agulhas salt/heat leakage that led to an abrupt resumption of the Atlantic Meridional Ocean Circulation eventually triggering the Heinrich/Chinese Stadial 4 termination. Severe cooling at high northern latitudes, which marked the onset of Heinrich Stadial 4, was synchronous with changes in tropical monsoon systems and preceded Antarctic warming by around 300 years, according to a compilation of speleothem and ice core records.