Intensified climate drying and cooling during the last glacial culmination (20.8–17.5 cal ka BP) in the south-eastern Asian monsoon domain inferred from a high-resolution pollen record

Abstract

Recent global sea-level data indicate that a final growth of ice volume occurred towards the end of the Last Glacial Maximum (LGM). The LGM culmination, LGM-b, lasted from about 21 to 17 ka and was followed by rapid deglaciation. This finding suggests a millennial-scale state with extreme glacial conditions (at least regionally) that immediately preceded the onset of full deglaciation marked by Heinrich event 1. In order to check how regional climate and vegetation in subtropical East Asia responded to the global-scale LGM culmination and the deglaciation onset, a new high-resolution pollen record from the Lijiafang peatland (LJF: 26°36.849′N, 116°08.463′E, 270 m) in Southeast China was generated. This record demonstrates a massive expansion of herbs during LGM-b. The dominance of herbaceous pollen suggests sparse forest cover in the lowlands of the subtropical East Asian Summer Monsoon (EASM) region and indicates an approximately 3300-year-long interval of the driest climate conditions of the entire last glacial-interglacial cycle. The LJF pollen-based reconstruction is consistent with the other vegetation records from the larger region, suggesting the climate change during LGM-b significantly impacted terrestrial ecosystems. The environmental change in the EASM region is likely linked to the Sea Surface Temperatures (SSTs) decrease that weakened the Walker cell convection over the western Pacific Ocean and reduced convection and moisture content in the Intertropical Convergence Zone. The strengthened decrease in moisture supply during LGM-b seems to have resulted in extreme and widespread megadroughts in the EASM and Australian regions. Our data indicate that the cold SSTs may have also decreased air temperatures in the neighboring parts of the continents. We suggest that the widespread SSTs decline in the western Pacific may have been linked to the cooling of the Southern Ocean and the expansion of Antarctic sea ice during LGM-b.