Gradually increasing precipitation since 20 ka as evidenced by loess dolomite abundance in the Ili Basin, Central Asia

Abstract

The mechanisms and processes of precipitation change during warm climatic periods, such as the Holocene, may provide critical insights into future regional precipitation trends in the arid and semiarid Central Asian core in the context of potential global warming. Previous studies have reconstructed different effective moisture changes during the warm Holocene epoch, i.e., a long-term wetting trend vs. a long-term drying trend. A potential reason for these conflicting results is that the reconstructed effective moisture proxies may involve effects from both temperature and precipitation, which can differ in different contexts. A pure precipitation proxy, which could be used to disentangle the interference of temperature, is important to solving this conflict. Here, we present two precipitation records based on the dolomite abundance in loess sections, which is nearly independent of temperature change, in the Ili Basin. These records span the past 20 ka and are constrained by high-resolution chronologies based on quartz optically stimulated luminescence. Our records indicate gradually increasing precipitation since 20 ka. This precipitation change is then assessed in the context of the Northern Hemisphere high-latitude ice volume, migration of the mid-latitude westerlies, and penetration of the Asian monsoon. We conclude that (1) the precipitation change is generally consistent with the reported effective moisture change since 20 ka in the study area; (2) increasing precipitation from the Last Glacial Maximum to the early Holocene was mainly controlled by the decreasing Northern Hemisphere high-latitude ice volume; and (3) further increases in precipitation during the Holocene were possibly related to the southward migration of the mid-latitude westerlies and penetration of the Asian monsoon. Our precipitation records also reconcile the common disconnection using the driving mechanism of precipitation to interpret the geological effective moisture changes in Central Asia.