Reconstruction of Erosion-Weathering-Vegetation Interactions during the Holocene in subtropical Taiwan
Monday, June 15, 2015: 5:00 PM
Selvaraj Kandasamy, Xiamen University, Xiamen, China, Chen-Tung A Chen, R.O.C. Naval Academy, Department of Marine Science, Kaohsiung, Taiwan, Jiann-Yuh Lou, National Sun Yat-Sen, Department of Oceanography, Kaohsiung, Taiwan and Yen-hong Shau, National Sun Yat-sen University, 4Department of Marine Biotechnology and Resources, Kaohsiung, Taiwan
Abstract:
Erosion and weathering of continental rocks are crucial in regulating the carbon dioxide (CO2) levels in the atmosphere, and hence Earth's climate. However, there is a lack of reconstruction on how Earth's surface processes have changed over time and their link with monsoon changes during the Holocene, a period in which Earth's critical zone has attained a maximum alteration. Here we investigate lake geochemical and minerological records from Taiwan to rebuild erosion-weathering-vegetation interplay during the Holocene. Our records reveal a distinct early, mid and late Holocene erosion-weathering patterns. Organic-rich sediments deposited during the warm Holocene optimum ~8.6‒4.5 ka B.P. show low ratios of alumina to bases but high ratios of Ti-normalized detrital and diagenetic elements, indicating a reduced erosion in the catchment due to dense vegetation. Conversely, these proxy records support derivation of sediments by the dominance of erosion with high quartz content during the early (~10.3‒8.6 ka BP) and late Holocene (since 4.5 ka BP) intervals due to cooler and drier climate with less intense monsoon. We found a decreased erosion-weathering trend since 8.6 ka BP, consistent to the long-term decrease of atmospheric CO2 and decline in carbonate ion concentration in the deep waters of the Pacific during the Holocene interval, though the mechanistic link between the long-term decrease in weathering and decline in dissolved carbonate ion on millennial timescales is mysterious.
