Abstract
Warming across the globe is expected to alter the strength and amount of regional precipitation, but there is uncertainty associated with the magnitude of these expected changes, and also how these changes in temperature and the hydrologic cycle will affect humans. For example, the climate in central-south Chile is projected to become significantly warmer and drier over the next several decades in response to anthropogenically driven warming, but these anthropogenic changes are superimposed on natural climate variability. The stable isotope composition of meteoric water provides significant information regarding the moisture source, pathways, and rain-out history of an air mass, but precipitation samples suitable for stable isotope measurements require long-term placement of field equipment making them difficult to obtain. The International Atomic Energy Agency (IAEA) Global Network of Isotopes in Precipitation (GNIP) stations generate isotopic and ancillary data of precipitation from many locations around the world, but remote areas of developing countries like Chile typically have sparse networks of meteorological stations, which inhibit our ability to accurately model regional precipitation. Central-south Chile, in particular, has a sparse network of GNIP stations and, as a result, the isotopic composition of meteoric water is underrepresented in the global database complicating efforts to constrain modern day hydroclimate variability as well as paleohydrologic reconstruction for southern South America. In this study, we measured the stable isotope compositions of hydrogen (δ2H) and oxygen (δ18O) in surface lacustrine waters of central-south Chile to determine what physical and/or climatic features are the dominant controls on lacustrine δ18O and δ2H composition, assess whether or not the isotopic composition of the lakes record time-averaged isotope composition of meteoric water, and determine whether an isoscape map based on lake surface waters could predict the H and O isotope compositions of precipitation at the few GNIP stations in the region.
Highlights
Warming across the globe is expected to alter the strength and amount of regional precipitation, but there is uncertainty associated with the magnitude of these expected changes, and how these changes in temperature and the hydrologic cycle will affect humans
The present-day hydroclimate on the western side of southern South America is dominated by the Southern Westerly Winds (SWW)[1]
Global isoscapes[6,7] that interpolate precipitation isotope values between Global Network of Isotopes in Precipitation (GNIP) stations have been developed to give a spatial representation of isotopes in regions that lack an abundance of GNIP stations. While this development has been extremely powerful for studies involving precipitation isotopes, uncertainty of predicted isotope values increases in regions with sparse GNIP station coverage
Summary
Warming across the globe is expected to alter the strength and amount of regional precipitation, but there is uncertainty associated with the magnitude of these expected changes, and how these changes in temperature and the hydrologic cycle will affect humans. We measured the stable isotope compositions of hydrogen (δ2H) and oxygen (δ18O) in surface lacustrine waters of central-south Chile to determine what physical and/or climatic features are the dominant controls on lacustrine δ18O and δ2H composition, assess whether or not the isotopic composition of the lakes record time-averaged isotope composition of meteoric water, and determine whether an isoscape map based on lake surface waters could predict the H and O isotope compositions of precipitation at the few GNIP stations in the region. The stable isotope composition of H and O in water is a function of the cumulative isotope effects associated with conditions during evaporation over the open ocean and the rain-out history between initial formation of the water vapor and its ultimate deposition to the system of interest (e.g., lake water[3]) This relationship is expressed in the Global Meteoric Water Line (GMWL), which reflects the coupled, spatiotemporal variations in H and O isotope ratios of precipitation. While many lacustrine systems fed by meteoric water are subject to isotopic enrichment through evaporation, which skews the isotopic signal away from the original meteoric source w ater[5], others can record meteoric water signals with high fidelity
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