Penetration of monsoonal water vapour into arid central Asia during the Holocene: An isotopic perspective

Abstract

Monsoonal water vapour transport is an active component of the hydrological cycle, which has a profound influence on regional climate changes. This study explored how far can the East Asian summer monsoon (EASM) transport water vapour to the west during the Holocene using published speleothem oxygen isotope (δ18O) records inferred from modern analogues of precipitation δ18O in the summer monsoon season (May to September) at mid-latitudes. Modern climate analyses suggest that there are two water vapour transport pathways to arid central Asia in the summer monsoon season: westerly transport and monsoonal easterly transport. Westerly transport from the North Atlantic and Arctic Oceans is associated with 18O-depleted water vapour, while monsoonal easterly transport from the tropical Indian Ocean, South China Sea, and East Asia is associated with 18O-enriched water vapour. The mixture of these water vapour dominates precipitation δ18O in arid central Asia from May to September. The difference of δ18O between precipitation in arid central Asia and the southern Urals reflects the penetration of monsoonal water vapour into arid central Asia. Speleothem δ18O records from Kesang Cave in the central Tianshan Mountains and Kinderlinskaya Cave in the southern Urals were therefore selected to indicate monsoonal water vapour transport into arid central Asia during the Holocene. Their differences suggest prominent monsoonal water vapour were transported to arid central Asia during the early Holocene, 8.2 ka BP event and late Holocene when the EASM was very weak. The results indicate that monsoonal water vapour could be transported at least as far west as the central Tianshan Mountains (∼81.75° E) in arid central Asia during the Holocene under weak EASM conditions rather than as previously supposed under strong EASM conditions. Although the amount of monsoonal water vapour is relatively less compared with that of westerly water vapour, it cannot be neglected because this source plays an important role in changes of precipitation and its δ18O in arid central Asia during the summer monsoon season.