Atmospheric controls on hydrogen and oxygen isotope composition of meteoric and surface waters in Patagonia

Abstract

The southern tip of South America, commonly referred to as Patagonia, is a key area to understand SouthernHemisphere Westerlies (SHW) dynamics and orographic isotope effects in precipitation. However, only few studies haveaddressed these topics. We evaluated the stable isotope (2H, 18O) compositions of precipitation, lentic waters, and lotic waters in that area to characterize and understand isotope fractionation processes associated with orographic rainout, moisture 20 recycling and moisture sources. Observational data were interpreted with the help of backward trajectory modelling of moisturesources using reanalysis climate data. While the Pacific serves as the exclusive moisture source for sites upwind of the Andes and on the immediate downwind area of the Andes, recycled moisture from the continent seems to be the main humidity source at the Patagonian Atlantic coast. In contrast, the Pampean Atlantic coast north of Patagonia obtains moisture from the Atlantic Ocean. In the core zone of the SHW at a latitude of 50° S, a depletion in the heavy isotopes of 10 ? and 85 ?, for 18O and 25 2H, respectively, occurs due to orographic rainout corresponding to a drying ratio of 0.45.