Interpreting Oxygen and Hydrogen Isotope Ratios in Precipitation Using a Coupled GCM

While very important, particularly for paleoclimatology, interpreting the oxygen and hydrogen isotope ratios in precipitation and records of precipitation is not straightforward. The source region and the convoluted hydrometeorological details of the trip to the final destination determine the final isotopic ratios in the precipitation. Without some knowledge of these, little can be gleaned with any certainty from the isotopic ratios in the precipitation and its records. Perhaps the most effective (albeit far from perfect) way to do this interpretation is through the use of General Circulation Models (GCMs), which include the relevant hydrometeorological processes. Further, since the source region is a major influence and is usually the ocean, which is variable on many time scales, coupled ocean-atmosphere GCMs should be used rather than just atmosphere GCMs. For these reasons, oxygen 18 and deuterium were added as tracers in the full water cycle (e.g., changes due to cloud, sea ice, ocean, and land surface processes, with isotopic fractionation at phase changes) of a parallelized coupled GCM of 5 x 4 degree resolution and a multi-decadal present-day control run performed. The results are discussed and paleo runs are outlined.