Controls of silicate weathering in Taiwan Island: transport-limited or weather limited?

Abstract:

Taiwan Island has increasingly attracted research attentions over the last decade because of its enormous sediment production within the small mountainous catchments, and fast transfer of terrigenous sediment and organic carbon from highland to ocean, in response to extreme monsoon climate and earthquake events. As one typical and active sediment source-to-sink system in East Asia, Taiwan plays an important role in land-sea interaction, biogeochemical cycle and sedimentation in the river-dominated continental margin.

In this contribution, we examine the sedimentary geochemical compositions of Taiwan river sediments, including the clay-separated and bulk samples collected from modern river systems and from one borehole (JRD-S) in the Zhuoshui River estuary, aiming to investigate what major factors control silicate weathering in Taiwan at present and during the late Quaternary.

The analytical results suggest that the silicate weathering process in the tectonically-active Taiwan Island is greatly limited by strong physical denudation and fast sediment transfer, although the monsoon climate brings huge rainfall for weathering. The silicate weathering regime in Taiwan is different from that in China’s mainland catchments where monsoon climate primarily determines the weathering intensity. During the last glacial period, the detritus could stay a longer time in Taiwan’s river basins because of weak rainfall and earth surface erosion, and the silicate weathering was thus relatively stronger. However, in the Holocene, enhancing East Asian summer monsoon caused abundant rainfall and intense physical erosion, which quickly transported the detritus into the sea and thus, the sediment residence time was general short within the basin. This consequently resulted in weaker silicate weathering in the Holocene. This study reveals a unique silicate weathering pattern in Taiwan during the late Quaternary, which provides deep insights on earth surface process and sedimentary response to tectonic and climatic driving in the East Asian continental margin.