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Tharammal: Influence of Last Glacial Maximum boundary conditions on the global water isotope distribution in an atmospheric general circulation model

2013 April 18


Fig. 3. Annual mean difference of surface temperature (C) of (a) GHG, (b) albedo, (c) topography, (d) orbital, (e) SST, and (f) LGM combined experiments from the control run. Anomalies in the surface temperature at the margins of the Ross and Weddell seas in the SST and the LGM-combined experiments are stippled because the respective grid cells were erroneously defined as ocean.
Influence of Last Glacial Maximum boundary conditions on the global water isotope distribution in an atmospheric general circulation model

Abstract. To understand the validity of d 18 O proxy records as indicators of past temperature change, a series of experiments was conducted using an atmospheric general circulation model fitted with water isotope tracers (Community Atmosphere Model version 3.0, IsoCAM). A pre-industrial simulation was performed as the control experiment, as well as a simulation with all the boundary conditions set to Last Glacial Maximum (LGM) values. Results from the pre-industrial and LGM simulations were compared to experiments in which the influence of individual boundary conditions (greenhouse gases, ice sheet albedo and topography, sea surface temperature (SST), and orbital parameters) were changed each at a time to assess their individual impact. The experiments were designed in order to analyze the spatial variations of the oxygen isotopic composition of precipitation (d 18 O precip ) 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 d 18 O precip over North America. Exposed shelf areas and the ice sheet albedo reduced the Northern Hemisphere surface temperature and d 18 O precip 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 d 18 O precip over the LGM ice sheets were strongly linked to the temperature decrease over them. The SST and ice sheet topography changes were responsible for most of the changes in the climate and hence the d 18 O precip distribution among the simulations.

Influence of Last Glacial Maximum boundary conditions on the global water isotope distribution in an atmospheric general circulation model
T. Tharammal, A. Paul, U. Merkel, and D. Noone
Clim. Past, 9, 789-809, 2013
http://www.clim-past.net/9/789/2013/
doi:10.5194/cp-9-789-2013
© Author(s) 2013. This work is distributed
under the Creative Commons Attribution 3.0 License.

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