Paleoenvironmental changes on the central Tibetan Plateau over the last two millennia inferred from sedimentological proxies and brGDGTs in Bamu Co

Abstract

Understanding multi-centennial climate variations and their impact on lake catchment productivity over the last 2000 years (the Common Era), is crucial for assessing the role of natural climatic factors in driving productivity changes, and for predicting productivity changes under recent global warming scenarios. However, the climate patterns on the Tibetan Plateau (TP), including temperature and hydrological variations, during the Common Era, and their possible links with productivity, are poorly understood. We present a quantitative reconstruction of mean annual air temperature (MAAT), together with grain size and other sedimentary records, from a non-glacial lake sediment archive on the central TP, with the objective of tracking changes in climate and lake catchment productivity over the past two millennia. Our results reveal an overall cooling trend in temperature reconstructed from branched glycerol dialkyl glycerol tetraethers (brGDGTs), with multi-centennial-scale fluctuations superimposed. These fluctuations include relatively warm periods during 200 BCE–400 CE and the Medieval Climate Anomaly (1050–1400 CE), and cold periods centered on ∼500–1000 CE and the Little Ice Age (∼1500–1900 CE). A rapid warming trend since 1900 CE corresponds to the Current Warm Period. The variations in sedimentary grain size reflect lake level changes associated with changes in the summer monsoon. Paleoproductivity inferred from total organic carbon (TOC) shows a similar pattern to the paleoclimate records, suggesting that millennial-scale productivity was influenced by both temperature and the catchment hydrology. In recent decades, human activities exerted a more substantial influence on lake productivity. Additionally, we suggest that the use of brGDGTs for temperature reconstruction necessitates the investigation of the temperature relationship of various fractions of brGDGTs, specifically tetramethyl-brGDGTs; and that careful selection of the temperature calibration equation is needed to minimize inaccuracies in paleotemperature reconstruction.