The relative role of oceanic heat transport and orography on glacial climate

During the Last Glacial Maximum, the Earth's orography and oceanic heat transport contribute to a cooling in the North Atlantic. By using an atmospheric general circulation model of intermediate complexity, we investigate the sensitivity of the atmospheric temperature and circulation during glacial climate, focussing on the impact of the orography and different oceanic heat transports. The results show a strong dependence of the glacial Northern Hemisphere circulation pattern to the changed orography. The blocking effect of the elevated orography due to the Laurentide Ice Sheet over the North American continent forced a deflection of westerlies, their enhancement and a southward displacement over the Atlantic. Independently, the glacial climate is influenced by the oceanic heat transport. The reduced oceanic heat transport on the glacial climate shows a 20-40% contribution for the total cooling relative to the present-day climate in the North Atlantic and polar regions. Finally, we find that the altered orography in the Northern Hemisphere and different oceanic heat transports result in a changed hydrological cycle, a reduction of the Hadley circulation and a southward shift of the Intertropical Convergence Zone in the boreal winter during glacial times.