Controls on Variations in the Isotope Composition of Precipitation during Warm Climates

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This award supports research using an isotope-capable general circulation model to quantify geographic, global climatic, and orbital effects on the oxygen isotopic composition of precipitation. The researcher will run a series of sensitivity tests will be performed using the GENESIS general circulation model (GCM) with water isotope tracers included in the hydrologic cycle. The researcher and her colleagues will make comparisons among experiments performed with boundary conditions appropriate for the modern and early Paleogene time period with the aim of examining variability in the isotopic composition of rainfall, continental runoff, and high latitude snowfall over a wide variety of boundary conditions and time scales.Specifically, the researcher will provide estimates of freshwater oxygen isotope based on first principles of climate physics and water isotope fractionation. The research will provide a definition of the nonlinear precipitation oxygen isotope-temperature relationships seen at the warm temperatures typical of many pre-Neogene climates. Quantification of plausible ranges in precipitation oxygen isotopes for boundary conditions appropriate for warmer-than-modern climates will allow greater confidence in estimates of paleotemperature, water vapor transport, and seasonality from marine and continental proxy records that currently rely on assumptions of isotope-temperature relationships, oxygen isotope freshwater values, and freshwater flux estimates. The results of this research are likely to have a broad impact on the wider science community through improvements in the reliability of numerical simulations of water isotopes within a model that can be easily applied to modern climate problems and any geologic time period.