Influence of LGM boundary conditions on the global water isotope distribution in an atmospheric general circulation model
1Department of Geosciences, University of Bremen, Bremen, Germany
2European Graduate College "Proxies in Earth History" (EUROPROX), University of Bremen, Bremen, Germany
3MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
4Department of Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, USA
Abstract. A series of experiments was conducted using a water isotope tracers-enabled atmospheric general circulation model (Community Atmosphere Model version 3.0, CAM3.0-Iso), by changing the individual boundary conditions (greenhouse gases, ice sheet albedo and topography, sea-surface temperature) each at a time to Last Glacial Maximum (LGM) values. In addition, a combined simulation with all the boundary conditions being set to LGM values was carried out. A pre-industrial (PI) simulation with boundary conditions taken according to the PMIP2 (Paleoclimate Modelling Intercomparison Project) protocol was performed as the control experiment. The experiments were designed in order to analyze the temporal and spatial variations of the oxygen isotopic composition of precipitation (δ18Oprecip) in response to individual climate factors. The change in topography (due to the change in land-ice cover) played a significant role in reducing the surface temperature and δ18Oprecip over North America. Exposed shelf areas and the ice sheet albedo reduced the Northern Hemisphere surface temperature and δ18Oprecip further. A global mean cooling of 4.1 °C was simulated with combined LGM boundary conditions compared to the control simulation, which was in agreement with previous experiments using the fully coupled Community Climate System Model (CCSM3). Large reductions in δ18Oprecip over the LGM ice sheets were highly correlated with the temperature decrease over them. The SST and ice sheet topography changes were found to be responsible for most of the changes in the climate and hence the δ18Oprecip distribution among the simulations.