2009 Portland GSA Annual Meeting (18-21 October 2009)

Paper No. 7
Presentation Time: 9:30 AM


UPCHURCH Jr, Garland R., Biology, Texas State University, 601 University Drive, San Marcos, TX 78666, KIEHL, Jeffrey, Climate Change Research Section, National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305, SHIELDS, Christine, Global Climate Dynamics, National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80305 and SCOTESE, Christopher R., Geology, U. Texas at Arlington, PALEOMAP Project, 700 Tanglewood Lane, Arlington, TX 76012, gu01@txstate.edu

Earth’s future climate is expected to warm considerably due to increased atmospheric carbon dioxide. Paleoclimate records indicate that pre-Quaternary time periods provide the best possible view of Earth under warm greenhouse conditions. Thus, past warm greenhouse climates provide an important tool to evaluate fully coupled climate models that are currently used to study future climate change. In this study, we use the Community Climate System Model (CCSM3) to investigate the climate of the latest Cretaceous (Maastrichtian). CCSM3 is a fully coupled three-dimensional global model that includes atmospheric, oceanic, sea-ice and terrestrial processes. The CCSM3 simulations employ the paleogeographic and global vegetation reconstructions used in earlier simulations of the late Maastrichtian with the GENESIS Earth System Model (Upchurch, Otto-Bliesner, and Scotese, 1999). CCSM3 simulations include two levels of atmospheric carbon dioxide (2XPAL and 6XPAL), elevated levels of atmospheric methane, changes to low level liquid cloud properties based on the hypothesis of Kump and Pollard (2008), and different paleoelevations for the interior of Siberia. A coupled simulation of multi-century length is carried out to study steady state conditions for the oceans. For terrestrial regions, model mean annual temperatures and seasonality are compared with data from angiosperm leaf physiognomy, plant life form distribution, and other climatic indicators to determine how well the model represents high latitude warmth on a zonal and regional basis. Model precipitation is compared with a database of climatically restricted sediments and angiosperm leaf physiognomy for specific sites. For oceanic regions, the CCSM3 simulations are compared to marine proxies of surface and benthic temperatures to study how well the model captures global Cretaceous ocean circulation patterns. Our results underscore the need for accurate boundary conditions in model simulations and provide a series of baseline simulations for the study of climatic change at the Cretaceous-Paleogene boundary.