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

Abstract

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.

Coupled atmosphere-ice-ocean dynamics during Heinrich Stadial 2

“…We refer to these periods of extreme conditions as Heinrich Stadials (HSs), and note that they are not defined by the duration of the Greenland Stadial counterpart. Mid-to-low-latitude monsoon proxy records suggest a major weakening of the Asian summer monsoon (ASM) during the HSs 6 , 7 [hereafter Asian Heinrich Period (AHP)] and a strengthening of the South American summer monsoon (SASM) 8 [hereafter South American Heinrich Period (SAHP)]. The weakening and strengthening of the two monsoon systems, respectively, are associated with the southward displacement of the Intertropical Convergence Zone (ITCZ) 6 .…”

“…Mid-to-low-latitude monsoon proxy records suggest a major weakening of the Asian summer monsoon (ASM) during the HSs 6 , 7 [hereafter Asian Heinrich Period (AHP)] and a strengthening of the South American summer monsoon (SASM) 8 [hereafter South American Heinrich Period (SAHP)]. The weakening and strengthening of the two monsoon systems, respectively, are associated with the southward displacement of the Intertropical Convergence Zone (ITCZ) 6 . An abrupt positive (negative) isotope excursion during the AHP (SAHP) is well-expressed in the speleothem oxygen-isotope (δ 18 O) records from the interhemispheric monsoon domains 8 , 9 (Supplementary Fig.…”

“…Moreover, observational data points to an active role of hydroclimatic variations in the tropics and Southern Hemisphere around AHP and SAHP and other millennial-scale events 17 , 20 – 22 . Recent research has highlighted the important role of the decreased Amazon River runoff and associated sea-surface salinity anomalies in resuming AMOC 6 , which in turn initiated the termination of AHP4. The noteworthy point is that the termination of SAHP4 [~38.62 ky BP (thousand years before present, where the present is 1950 CE)] predated the termination of AHP4 (~38.34 ky BP) and the associated Greenland warming transition (~38.34 ky BP) by hundreds of years 6 .…”

“…Recent research has highlighted the important role of the decreased Amazon River runoff and associated sea-surface salinity anomalies in resuming AMOC 6 , which in turn initiated the termination of AHP4. The noteworthy point is that the termination of SAHP4 [~38.62 ky BP (thousand years before present, where the present is 1950 CE)] predated the termination of AHP4 (~38.34 ky BP) and the associated Greenland warming transition (~38.34 ky BP) by hundreds of years 6 . Previous studies 6 , 17 , 20 , 22 point to a south-to-north signal propagation around the terminations of AHP and SAHP and other millennial-scale events suggesting a slow ocean response.…”

“…The noteworthy point is that the termination of SAHP4 [~38.62 ky BP (thousand years before present, where the present is 1950 CE)] predated the termination of AHP4 (~38.34 ky BP) and the associated Greenland warming transition (~38.34 ky BP) by hundreds of years 6 . Previous studies 6 , 17 , 20 , 22 point to a south-to-north signal propagation around the terminations of AHP and SAHP and other millennial-scale events suggesting a slow ocean response. Furthermore, during the early Last Glacial Maximum (LGM) (26 to 22 ky BP), the Greenland ice-core records have large age uncertainty (±500–±800 years) 2 and high-resolution absolutely-dated proxy records from low latitudes are still lacking 18 .…”