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

Abstract

Abstract. The southern tip of South America, commonly referred to as Patagonia, is a key area to understand Southern Hemisphere Westerlies (SHW) dynamics and orographic isotope effects in precipitation. However, only few studies have addressed these topics. We evaluated the stable isotope (δ2H, δ18O) compositions of precipitation, lentic waters, and lotic waters in that area to characterize and understand isotope fractionation processes associated with orographic rainout, moisture recycling and moisture sources. Observational data were interpreted with the help of backward trajectory modelling of moisture sources 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 δ18O and δ2H, respectively, occurs due to orographic rainout corresponding to a drying ratio of 0.45.

Revisiting extreme precipitation amounts over southern South America and implications for the Patagonian Icefields

“…To provide a first assessment of the magnitude of precipitation, mean precipitation is estimated along the western slopes of the 10 Andes (45°-52°S and 73°-76°W) using a simple DR-scaling. The DR in Patagonia, defined as the fraction of the WVF removed by orographic precipitation, is known to be the highest (~0.45-0.5) worldwide (Mayr et al, 2018;Smith & Evans, 2007). The ratio is a characteristic measure for mountain ranges and is independent of the incoming WVF.…”

“…The ratio is a characteristic measure for mountain ranges and is independent of the incoming WVF. As the WVF and the DR (here we use 0.45) are known from ERA-Interim data and isotope observations (Langhamer et al, 2018;Mayr et al, 2018;Smith & Evans, 2007), one can estimate the mean homogeneous (uniform) precipitation amount. To add altitude-dependent 15 precipitation variability, the amount was redistributed mass-consistently by optimizing (Newton-Raphson algorithm) the vertical precipitation gradient.…”

“…The ensembles members account for the initial condition uncertainty in the wind direction and moisture content by randomly perturbing (5%), (5%), and " (10%) around its mean value. In the first experiment, it was tested whether a composite of 'realistic' atmospheric ambient conditions (derived from the reanalysis data), the observed drying ratio of 0.45 (Mayr et al, 2018) and WVF provides the basis to sustain the precipitation estimates of previous studies. The second experiment deliver an 20 'extreme' scenario by fixing the drying ratio at a higher value of 0.6 and setting the uplift sensitivity factor ( " = 0.004) and moist stability frequency ( $ = 0.007) to their 98th percentile values.…”

Long-Term Isotope Records of Precipitation in Zagreb, Croatia

“…Precipitation presents an input to groundwater, and therefore knowledge on the isotope composition of precipitation is a prerequisite for groundwater studies. Temporal and spatial patterns of isotopes in precipitation (expressed as δ 2 H and δ 18 O values and the tritium activity concentration, A) have been observed since the 1950s and have contributed to hydrological and hydrogeological research [13][14][15][16], climate and paleoclimate studies [4,15,[17][18][19][20][21][22], and ecological research [23][24][25]; further, precipitation isotope mapping has been widely implemented during recent decades [25,26].…”

“…Map of stations with isotope-in-precipitation data in Croatia (locations 1-12) and in Slovenia (locations[13][14][15]. Details on stations are in…”