Abstract
Lacustrine sediment serves as a valuable archive for tracing catchment weathering processes associated with past climatic and/or tectonic changes. High-resolution records of fossil ostracod Mg/Ca, Sr/Ca and 87Sr/86Sr ratios from a lake sediment core from the central Tibetan Plateau reveal a temporal link between lake-water chemistry and catchment weathering and distinct monsoonal oscillations over the early to mid-Pleistocene. Between 2.01 and 0.95 Ma, lake-water chemistry was dominated by a high proportion of carbonate weathering related to variations in the Indian monsoon, resulting in relatively low and constant ostracod 87Sr/86Sr but obvious fluctuations in Mg/ Ca, Sr/Ca and d18O. Across the mid-Pleistocene transition (MPT), a significant increase in 87Sr/86Sr and frequently fluctuating ratios of ostracod Mg/Ca, Sr/Ca and d18O are coincident with increases in both Chinese loess grain size and Arabian Sea lithogenic flux. This correlation indicates an increased glaciation and a strong monsoon seasonal contrast over the plateau. The increase in lake-water 87Sr/86Sr across the MPT highlights a change in catchment weathering patterns, rather than one in climate-enhanced weathering intensity, with an increased weathering of 87Sr-rich minerals potentially induced by marked extensive glaciation and strong seasonality in the central plateau.
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