A Holocene history of the Indian monsoon from Qilu Lake, southwestern China

Understanding the magnitude, nature, and forcing mechanisms of past abrupt changes in Indian Summer Monsoon (ISM) strength is central to characterizing future manifestations in the face of global climate change, particularly at centennial time scales. Here we summarize a 6200 year record of oxygen isotopes from Lake Qilu in Yunnan Province, China. The lake is sensitive to changes in precipitation-evaporation balance and precipitates calcite, potentially providing insight into past hydroclimate through oxygen isotope analysis. Beginning at 5200 cal years BP, oxygen isotopes shift to higher values, indicative of a period of aridity and lower lake levels which persist until 3600 cal years BP. Thereafter, lake levels are extraordinarily stable until 1500 cal years BP. At 1500 cal years BP, measurable anthropogenic impacts occur, resulting in the delivery of red, iron-rich catchment soil to the lake and higher oxygen isotope values. These changes are likely the result of land clearance for the expansion of agricultural activities. The Ojlu record is remarkably consistent with the record from Xingyun Lake, 10 km to the north, strongly suggesting that regional climate drivers are responsible for the changes after 5200 cal years BP and then the stability from 3600 to 1500 cal years BP. Comparison of both these records with Dongge Cave illustrate the importance of evaporative enrichment in driving higher oxygen isotope values from 5200 to 3600 cal years BP. (C) 2019 Elsevier Ltd. All rights reserved.