Altitude effect of precipitation isotopes in an arid mountain-basin system: Observation and modelling around the world’s second-largest shifting desert

Abstract

The stable water isotopes of precipitation provide important information about the hydrological circulation. In the arid mountain-basin system in central Asia, the altitude effect of precipitation isotopes has been a controversial topic in recent years, but the sample availability in extreme environments constrains the accurate understanding of the relationship between altitude and stable isotopes in precipitation. Based on the observation of precipitation isotopes around the Tarim Basin covered by the world’s second-largest shifting desert, we examined the relationship between altitude and isotope composition. There is an altitude effect of precipitation isotopes between the basin and the surrounding mountains, with the modelled gradient for annual mean δ18O being approximately 1.96 ‰ per 1000 m, which is weaker than the observed gradient focusing on the oases (2.75 ‰ per 1000 m). The largest modelled difference in δ18O between 1000–2000 m and 2000–3000 m above sea level occurs in August and September. The periods with a larger gradient of altitude effect usually have higher temperature and more precipitation. Across the westerlies-dominated central Asia, the below-cloud evaporation enhances the altitude gradient of precipitation isotopes for most areas. The findings are useful to understand the local and remote drivers of precipitation isotopes and the paleoaltimetry of stable isotopes in climate proxies.