Responses of sedimentary proxy indicators to lake-level fluctuations on the central Tibetan Plateau since the last deglaciation

Abstract

Lake sediments are valuable archives to investigate past changes in climate and environment on various timescales. Closed-basin lakes can be regarded as precipitation gauges, which are ideal for studying past climate changes. However, the climatic implications of various sedimentary proxy indicators from closed-basin lakes are often confounded by lake-level fluctuations, which are affected by lake watershed processes, besides climate change. Here, we present records of multi-proxy indicators since the last deglaciation at Lake Cuoe, on the central Tibetan Plateau, which was once connected with Selin Co and became separated during the middle Holocene, as evidenced by a series of paleo-shorelines. The sedimentary proxies are categorized into three groups based on their origins, with differences in their environmental significance. The proxy indicators derived from within-lake processes effectively revealed past lake-level fluctuations, including the Ca/(Al, Ti, Fe) ratio, Fe/Mn ratio, carbonate minerals, stable carbon and oxygen isotopes of authigenic carbonate, and the percentage of aquatic inputs (Paq) derived from n-alkanoic acids. These proxy indicators showed obvious changes at ∼7–6 ka, when Lake Cuoe became hydrologically separated from Selin Co. The stable oxygen isotope record of Lake Cuoe, apparently modulated by lake-level changes, differs significantly from that from Selin Co. The proxy indicators reflecting watershed processes, including terrigenous elements, Rb/Sr ratio, grain size, and the chain length proxy based on n-alkanoic acids, directly reflected changes in the regional climate and environment. The proxy indicators derived from both allochthonous and authigenic sources, including total organic carbon (TOC) and total nitrogen (TN), reflected the effects of climate change as well as lake-level fluctuations. Overall, our results suggest that great caution should be applied in interpreting proxy records of climatic and environmental changes from closed-basin lakes on the Tibetan Plateau. They also highlight the potential of using sedimentary proxies to reconstruct continuous records of lake-level fluctuations.