Comparison of precipitation isotope variability across the tropical Pacific in observations and SWING2 model simulations

Abstract

AbstractProbing the dynamics of the Earth's hydrologic cycle benefits from the use of isotope‐equipped global climate models. However, isotope model simulations are not often compared together, along with existing observations, to assess the distribution of simulated stable isotope variability. Here we evaluate the spatial and temporal patterns of tropical Pacific precipitation isotope variability in global climate models from the second Stable Water Isotope Intercomparison Group experiment and in observations. The tropical Pacific is home to many isotope‐based proxies of paleoclimatic change, and as such is an important target for such model‐data comparisons. We find spatial and temporal examples of precipitation‐isotope mismatches, highlighting that factors beyond the amount effect influence precipitation isotope variability across the tropical Pacific. The models that best capture mean annual precipitation in the tropical Pacific are not necessarily the models that best simulate the mean annual stable isotopic composition of precipitation. Nudging with reanalysis winds has a small effect on precipitation δ18O values. Model performance and the strength of the relationship between precipitation and precipitation δ18O values varies between the western, central, and eastern equatorial Pacific. In the majority of the simulations, western equatorial Pacific δ18O values are correlated with large‐scale, but not local precipitation, whereas in the central and eastern equatorial Pacific, δ18O values are correlated most strongly with regional precipitation. This comparison provides a cautionary note on using results from a single model to assist in interpretation of paleoclimate proxy records.