Session: Glacial Climates (LGM, Last deglaciation, Ice sheet uncertainties, Glacial-interglacial cycles)
Author: Lauren J. Gregoire / firstname.lastname@example.org / University of Leeds
Co-author: Ruza Ivanovic, University of Leeds;
Amanda C. Maycock, University of Leeds;
Paul J. Valdes, University of Bristol;
Ice sheet topography is an important control on glacial climate. The presence of the large North American Laurentide Ice Sheet (LIS) at the Last Glacial Maximum (LGM; 21 ka) produces a stronger and more zonal jet stream, modifies surface climate and storminess over the North Atlantic and affects North Atlantic gyre circulation and the Meridional Overturning Circulation. By the start of the Holocene, 9.0 ka, the size of the LIS was much reduced, yet, it has been suggested that the demise of the LIS played a role in the 8.2 ka abrupt cooling event through its topographical influence on atmospheric circulation.
Here, for the first time, we evaluate how the demise of the LIS 9.5-7 ka directly influences atmospheric circulation through changing topography, and the wider implications for climate. We ran a series of 500 year-long equilibrium experiments using the HadCM3 ocean-atmosphere-vegetation General Circulation Model with LIS topographies and ice masks taken from a transient simulation of the ice sheet, using snapshots at 9.5, 9.0, 8.5 and 8.0 ka.
We find that the lowering of the LIS produces a dipole pattern of surface ocean and air temperature anomalies over the North Atlantic. Between 9.5 and 8.0 ka, we model a progressive 2 °C cooling south of Iceland and 1 °C warming between 40-50° N, matching sedimentary records. This is associated with a weakening of the Subtropical and Subpolar Gyres caused by a decreasing wind stress curl over the gyres as the ice sheet lowers. However, topographical changes between 8.5 ka and 8.0 ka induce minor climatic change relative to the ~160 year-long cooling pattern of the 8.2 kyr event.