Influence of Last Glacial Maximum boundary conditions on the global water isotope distribution in an atmospheric general circulation model 1Department of Geosciences, University of Bremen, Bremen, Germany
20 Mar 2013
2MARUM – Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
3Department of Atmospheric and Oceanic Sciences and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, USA
Received: 24 March 2012 – Published in Clim. Past Discuss.: 18 April 2012 Abstract. To understand the validity of δ18O 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
(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 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
δ18Oprecip distribution among the simulations.
Revised: 15 February 2013 – Accepted: 20 February 2013 – Published: 20 March 2013
Citation: Tharammal, T., Paul, A., Merkel, U., and Noone, D.: Influence of Last Glacial Maximum boundary conditions on the global water isotope distribution in an atmospheric general circulation model, Clim. Past, 9, 789-809, doi:10.5194/cp-9-789-2013, 2013.