What has driven the long-term drying of the Southwest: precipitation or evaporation? A paleohydrologic study at multiple lake basins in California
Tuesday, April 21, 2015
John Arthur Mering1, Juan Manuel Lora1, Victoria A Petryshyn1, Aiden Jonsson1, John Wilson1, Andrew Kowler2, Audrey Brown1, Lilian Chou1, David M Miller3, Daniel E Ibarra4, Camille M Risi5, Jonathan Mitchell1 and Aradhna K. Tripati1, (1)University of California Los Angeles, Los Angeles, CA, United States, (2)University of Arizona, Tucson, AZ, United States, (3)USGS California Water Science Center Menlo Park, Menlo Park, CA, United States, (4)Stanford University, Stanford, CA, United States, (5)LMD, Paris, France
Abstract:
Anthropogenic global warming is expected to intensify droughts across the Southwestern United States. In California this is problematic, where water resources are already overdrawn. Data on past variability in temperature and moisture can be used to study regional climate sensitivity and assess water budget calculations. Specifically, lacustrine deposits are physically and chemically sensitive to changes in the balance between precipitation and evaporation. Here, we evaluate past hydrographic conditions in five regions: Mono Lake, Owens Lake, paleo-Lake Surprise, the Los Angeles Basin, and the Mojave Basin (paleolake Manix), by using carbonate clumped isotope thermometry and oxygen isotopes. These systems were extensive during, and in some cases after, the Last Glacial Maximum (LGM), but began to retreat before 12 ka BP. We reconstruct lake surface temperature, air temperature, and the oxygen isotope composition of paleolake water to evaluate the amplitude of changes in summer temperatures and examine whether changes in evaporation or precipitation, or both, have driven the long-term drying out of the Southwest. Clumped isotope analyses were carried out on multiple phases of ancient lacustrine material, including endogenic calcite, and aragonitic bivalve shells (genus Anodonta). We compare our results to CMIP output from climate models, as well as high-resolution oxygen isotope-enabled models for precipitation. Ultimately, we provide guidelines for integrating stable isotope based proxies with climate models, and identify strategies for incorporating both sources of data into water policy decision-making in California.
