Savanna/rainforest dynamics and hydroclimate changes in northern boundary of tropical Asia over the past 150 kyrs

How tropical hydroclimate and ecosystems in Asia have varied on orbital timescales has been an important topic for decades. The northern boundary of tropical Asia under strong influence of monsoon system has been highly sensitive to global climate changes on orbital timescales. Among the available proxy data, limited terrestrial evidence of glacial-interglacial variation of vegetation impedes the understanding of tropical climate dynamics. Here, we report a lacustrine record covering the last 150 kyrs from a tropical maar paleolake located between the Asian landmass and the South China Sea. Our pollen and & delta;13C results consistently show strong glacial-interglacial variability of vegetation changes between savanna dominated by C4 herbs and rainforest characterized by C3 trees over the past 150 kyrs. The glacial/stadials with C4 herb dominance during MIS6, 4 and 2 corresponded to drier conditions with rainfall amounts <650 mm/yr, which has been considered as the climatic threshold for the growth of savanna biome. The vegetation variations in relation to large-amplitude variations of regional hydroclimate were tightly coupled with the internal glacial forcings (e.g., global ice volume) in addition to external insolation, and coincided with changes in sea level/continental shelf exposure and sea surface temperature in the northern South China Sea. These significant correlations suggest a more important role of glacial forcings than insolation in controlling tropical hydroclimate and vegetation changes, which is transmitted and amplified by tropical warm pool environments (i.e., spatial extent of shelf exposure and water temperature).