Three-phase structure of the East Asia summer monsoon during Heinrich Stadial 4 recorded in Xianyun Cave, southeastern China

Abstract

The Heinrich Stadial (HS) 4 event was the largest of the six HS events and occurred from 40.0 to 38.2 kyr BP (thousand years before present, where present = 1950 CE) recorded in Greenland ice cores. However, its structure, forcings, and related global hydroclimate variation remain poorly understood. Here, an 8-yr-resolved stalagmite δ18O record from Xianyun Cave, southeastern China, is used to reconstruct the multidecadal-to-millennial-scale changes of the East Asian summer monsoon (EASM) from 41.33 ± 0.09 to 37.04 ± 0.05 kyr BP. The Xianyun record shows a corresponding weak monsoon interval from 40.04 ± 0.07 to 37.76 ± 0.05 kyr BP during HS 4 and is the first direct evidence in the Asian monsoon realm to clearly reveal a three-phase EASM structure. The first phase began with a weakening monsoon from 40.04 ± 0.07 to 39.54 ± 0.06 kyr BP, associated with a southward shift of the Intertropical Convergence Zone (ITCZ). The second phase was a long weak monsoon, spanning 1.06 kyr from 39.54 ± 0.06 to 38.48 ± 0.05 kyr BP and corresponding to an ice-rafted debris event in the North Atlantic Ocean and an intense pluvial phase in Northeast (NE) Brazil, suggesting that the ITCZ lingered at its southernmost position during this interval. Following the end of this phase, EASM was gradually enhanced for 720 yrs through 37.76 ± 0.05 kyr BP. The feature expressed in the Xianyun record agrees with the variations in low-latitude climate signals recorded in the Northern Greenland Eemian Ice Drilling (NEEM) 17O-excess and anti-phase matches with dry-wet transition recorded in NE Brazilian stalagmites. These relations suggest multi-phased responses of tropical atmospheric/oceanic circulations to forcing from northern hemisphere high latitudes. Our findings offer essential evidence for understanding low- and high-latitude climate teleconnections and the relationship between the monsoon and the tropical hydrologic cycle.