The key role of topography in altering North Atlantic atmospheric circulation during the last glacial period
1Bjerknes Centre for Climate Research, Bergen, Norway
2Geophysical Institute, University of Bergen, Bergen, Norway
3Department of Earth Science, University of Bergen, Bergen, Norway
4UNI Bjerknes Centre, Bergen, Norway
5Laboratoire des Sciences du Climat et de L'Environnement, Gif Sur Yvette, France
*now at: the Joint Research Center, Institute for Environment and Sustainability, Ispra, VA, Italy
Abstract. The Last Glacial Maximum (LGM; 21 000 years before present) was a period of low atmospheric greenhouse gas concentrations, when vast ice sheets covered large parts of North America and Eurasia. Paleoclimate reconstructions and modeling studies suggest that the atmospheric circulation was substantially altered compared to today, both in terms of its mean state and its variability. Here we present a suite of coupled model simulations designed to investigate both the separate and combined influences of the main LGM boundary condition changes (greenhouse gases, ice sheet topography and ice sheet albedo) on the mean state and variability of the atmospheric circulation as represented by sea level pressure (SLP), 200-hPa zonal wind in the North Atlantic sector. We find that ice sheet topography accounts for most of the simulated change during the LGM. Greenhouse gases and ice sheet albedo affect the SLP gradient in the North Atlantic, but the overall placement of high and low pressure centers is controlled by topography. We also show that North Atlantic sea surface temperatures do not substantially influence the pattern of the climatological-mean SLP field, SLP variability or the position of the North Atlantic jet in the LGM.