Intensified monsoon and spatiotemporal changes in precipitation patterns in the NW Himalaya during the early-mid Holocene

摘要

We have undertaken a high resolution palaeoclimate reconstruction on radiocarbon dated palaeolake sediments from the Spiti valley, NW Himalaya. This site lies in the climatically sensitive winter westerlies and Indian Summer Monsoon (ISM) transitional regime and provides an opportunity to reconstruct the precipitation seasonality, and extreme precipitation events that are characterised by intensified erosion. The lake sediments reveal distinct lithofacies that provide evidence of changes in depositional environment and climate during early to mid Holocene (8.7-6.1 cal ka BP). We have identified three stages during the period of lake's existence: the Stage I (8.7-7.6 cal ka BP) is marked by lake establishment; Stage Ⅱ (～ 7.6-6.8 cal ka BP) by sustained cooler periods and weakened summer monsoon, and Stage Ⅲ (～6.8-6.1 cal ka BP) by a shift from colder to warmer climate with stronger ISM. We have identified several short term cooler periods at ca. 8.7,8.5,8.3 and 7.2-6.9 cal ka BP. Based on an overview of regional climate records we show that there is an abrupt switch in precipitation seasonality ca. 6.8 cal ka BP that is followed by the onset of the intensified monsoon in the NW Himalaya.