Vegetation evolution-based hydrological climate history since LGM in southern South China Sea

Abstract The reconstruction of vegetation evolution and climate changes at low latitudes since the Last Glacial Maximum (LGM) remains incomplete. In this study, we reconstructed the palynological history of vegetation changes since the LGM using a sediment core collected from the slope in the southern South China Sea (SCS). The chronology of the core was based on eight AMS14C dates, and 85 stratigraphic samples were palynologically analyzed. Our results denote that the vegetation reconstructed during the LGM in the southern SCS was characterized by a relatively high percentage of herb pollen and a modest decrease in the number of fern spores, suggesting a temperature decline and humidity change in this region. Further, the preservation of a rich diversity of pollen from the tropical lowland rainforest indicated that the rainforests might have covered large areas of the exposed Sunda Shelf during the LGM. The dynamic concentration of the Pinus pollen in the core, which is a proxy for the East Asian winter monsoon (EAWM), satisfactorily matched the changes in the Atlantic meridional overturning circulation and Australian-Indonesian summer monsoon, especially during the Heinrich Stadial 1. This suggests that the climate at the high latitudes of the Northern Hemisphere can drive the Intertropical Convergence Zone (ITCZ) southwards based on the enhanced EAWM. The southward-shifting ITCZ may change the hydrological climate of the equator and the Southern Hemisphere. The pteridophyte spores, which are good regional precipitation indicators, were positively correlated with the warm pool convection and inversely related with the EAWM, possibly indicating the considerable impact of the high-latitude climate in the Northern Hemisphere on precipitation in the tropical regions. Our results indicate that during the last deglaciation, the tropical hydrological changes were relatively moderate when compared with the drastic change observed at high latitudes and were attributed to the regulation of the El Nino-Southern Oscillation-like state. Our sequence of pollen and spores from the southern SCS can be used to observe the detailed dynamics of climatic evolution in tropical regions. The results of this study are essential to understand the complicated climate processes and the relation between high and low latitudes.