Climatic and environmental impacts on source-to-sink processes in SW Taiwan since the last deglaciation

Abstract

In recent decades, many scientific studies have been conducted to constrain present and past source-to-sink processes and their controlling factors. The role of typhoon and monsoon summer rainfall on chemical weathering and soils erosion in east Asia is still not well established. Clay minerals and major elements, combined with Nd and Sr isotopic compositions were analyzed on sediments from Core MD18-3569 located close to the Penghu Canyon on the Taiwan margin (northeastern South China Sea) in order to establish climatic and environmental controls on source-to-sink processes and weathering history of small river basins of southwest Taiwan since the last glacial period. The 87Sr/86Sr ratios and ɛNd values of the detrital and clay fractions combined with the high content of illite and chlorite suggest that the mountainous rivers of southwest Taiwan are the main sources of sediments to the Taiwan margin since the last deglaciation. Such results permit to evaluate past intensity of chemical weathering in the rivers of southwest Taiwan from major elements composition and clay mineral assemblages. The long-term changes of chemical weathering intensity in Taiwan are driven by the variations of east Asian summer monsoon rainfall. During the deglaciation, the progressive strengthening of rainfall enhanced the chemical weathering intensity which peaked in the early Holocene. The Holocene is characterized by a decrease of the chemical weathering degree of sediments derived from Taiwan. This coincides with the weakening of summer monsoon rainfall, an increase in typhoon activity, and changes in vegetation cover in southwest Taiwan. These processes caused soil destabilization and erosion, regressive pedogenesis, and weaker chemical weathering intensity. This was due to the shorter residence time of sediments in the soils of southwest Taiwan. Our multi-proxy study highlights the strong link between summer monsoon and typhoon rainfalls, environmental changes, and chemical weathering history in Taiwan.