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

CECILIA LAPRIDA; SAUTER,T.; MASSAFERRO,J; SRUR, A. ; WISSEL, H.; MAUAD M.; MAYR, C.; FORSTERRA,. G. ; MEIER, W; LANGHAMER, L.

Stokholm

Congreso; IPA-IAL 2018 I Joint Meeting UnravelLing the Past and Future of Lakes; 2018

IPA

Very strong and persistent zonal atmospheric flow in the mid-latitudes of the Southern Hemisphere forms the westerly wind belt. This wind belt advects moist air masses from the Pacific Ocean towards the Andes and leads to precipitation on its upstream side due to orographic lifting but aridity on the downwind side due to a foehn effect. Knowledge is scarce about the exact regions of moisture uptakes and their respective movement patterns. Moisture origins have been evaluated by backward trajectories and compared with hydrogen and oxygen stable isotope composition of precipitation of stations from the Global Network for Isotopes in Precipitation. Stations downstream of the Andes show isotopic depletion caused by Rayleigh-type isotope fractionation compared to upstream stations, despite of similar moisture sources. Moisture recycling above the continent plays a major role for a station further east at the Atlantic leading to heavy-isotope-enriched rainfall there. This information is of high significance for the interpretation of oxygen isotope records from Patagonian lake sediments, peats or tree-rings used to reconstruct past atmospheric and hydrological dynamics. Beside a few GNIP stations, the modern database needed for the calibration of isotope proxies from remote Patagonia areas is extremely poor. To overcome this lack of data, lentic and lotic waters from Chile and Argentina were sampled between 2013 and 2018. We show that the water balance has a strong influence on the isotopic composition of lentic waters. Bathymetry, exposition to wind, inflows, outflows, and climatic settings influence their water balances, and in turn have a strong influence on the isotopic composition of lakes. Thus, the choice of sites and of reliable proxies for the oxygen isotopic composition of the lake water is especially important. Methodologically refined proxies, such as oxygen isotope ratios of aquatic cellulose and chironomid head capsules, provided promising results in our calibration studies