The Elusive Origin of Continental Moisture in Asia

Abstract:

Central Asia holds the distinction of being located further from an oceanic source than any continental environment world-wide. As such, the small amount of precipitation that does fall in this region must travel a long, often complex path from its original oceanic source. This journey likely involves multiple episodes of moisture recycling where surface water evaporates and falls again as precipitation further downwind. A thorough understanding of modern atmospheric circulation in the region and the ultimate source of meteoric water is fundamental to water resource management and our understanding of atmospheric circulation under a changing climate.

Within the isotope community, it has been argued that the initial oceanic source of moisture throughout the Tarim Basin and the northern Tibetan Plateau is Atlantic or Mediterranean water, transported across Central Asia via westerlies. This interpretation is based on seasonal patterns of stable isotope variations in meteoric water (δ¹⁸O and δD) correlated with temperature (Araguas-Araguas et al., 1998 and others) and modeling of atmospheric circulation using re-analysis data.

Here, we revisit stable isotope and climate modeling data in addition to spatio-temporal climate patterns to present an alternative interpretation of moisture source for precipitation across the northern Tibetan Plateau and Tarim Basin. Specifically, we argue that the Pamir and Tian Shan mountains are the threshold between westerly-derived and southerly (monsoon) derived precipitation, pushing the boundary much further north than previous interpretations. This alternative interpretation is based on seasonal patterns of precipitation, modeling of atmospheric circulation, and modern water isoscapes throughout Asia.