Extent and timing of the Last Glacial Maximum (LGM) in Britain and Ireland: a review

The Last Glacial Maximum (LGM) of Marine Isotope Stage (MIS) 2 is defined here as the period either of maximum global ice volume or in which major ice sheets reached their maximum extent. Both definitions lack clarity as there is no reason to suppose that maximum volumes or limits were reached simultaneously at either all ice sheets or around the margins of individual ice sheets. Here we review the traditional terrestrial limits of the BIIS (British-Irish Ice Sheet), examine developments in understanding the offshore record, and attempt a redefinition of the extent and timing of the MIS 2 maximum. As a working chronological model the build-up of the BIIS is assigned to after 35-32 ka, the maximum to the period 27 21 ka and a more limited readvance after 19 ka. As marginal oscillations, driven by ice sheet dynamics, appear to have characterised much of the advance, and especially the retreat of the BIIS, caution should be exercised in assigning climatic significance to the many identified ice limits or still-stands. While much of the terrestrial limit in Britain remains relatively unaltered, significant revision is required offshore around Britain and Ireland, to portray an extensive ice advance to the shelf edge and a period when the BIIS was conjoined with the adjacent Fenno-Scandinavian Ice Sheet. Although there appears to be a broad synchrony between the BIIS and other major ice sheets, local controls have produced some variation in the timing of advance to and retreat from maximum limits for particular ice streams or lobes, but much of the offshore limit remains very poorly age constrained. Consequently, a key objective in future research should be to improve and refine the chronological control for all portions of the maximum margin of the BIIS and its subsequent retreat stages. Copyright (C) 2010 John Wiley & Sons, Ltd.