Interpreting hydro-isotope records from Patagonia by means of backward trajectories, surface water surveys and refined isotope proxies

MAYR, CHRISTOPH; LANGHAMER, LUKAS; MASSAFERRO, JULIETA; MAUAD, MELINA

estocolmo

Congreso; IPA IAL 2018; 2018

IPA IAL

Very strong and persistent zonal atmospheric flow in the mid-latitudes of the SouthernHemisphere forms the westerly wind belt. This wind belt advects moist air masses from thePacific Ocean towards the Andes and leads to precipitation on its upstream side due to orographiclifting but aridity on the downwind side due to a foehn effect. Knowledge is scarce about theexact regions of moisture uptakes and their respective movement patterns. Moisture origins havebeen evaluated by backward trajectories and compared with hydrogen and oxygen stable isotopecomposition of precipitation of stations from the Global Network for Isotopes in Precipitation.Stations downstream of the Andes show isotopic depletion caused by Rayleigh-type isotopefractionation compared to upstream stations, despite of similar moisture sources. Moisturerecycling above the continent plays a major role for a station further east at the Atlantic leading toheavy-isotope-enriched rainfall there.This information is of high significance for the interpretation of oxygen isotope records fromPatagonian lake sediments, peats or tree-rings used to reconstruct past atmospheric andhydrological dynamics. Beside a few GNIP stations, the modern database needed for thecalibration of isotope proxies from remote Patagonia areas is extremely poor. To overcome thislack of data, lentic and lotic waters from Chile and Argentina were sampled between 2013 and2018.We show that the water balance has a strong influence on the isotopic composition of lenticwaters. Bathymetry, exposition to wind, inflows, outflows, and climatic settings influence theirwater balances, and in turn have a strong influence on the isotopic composition of lakes. Thus, thechoice of sites and of reliable proxies for the oxygen isotopic composition of the lake water isespecially important. Methodologically refined proxies, such as oxygen isotope ratios of aquaticcellulose and chironomid head capsules, provided promising results in our calibration studies.