A modelling insight into the Icelandic Last Glacial Maximum ice sheet

A three-dimensional thermomechanical model is used to investigate the Last Glacial Maximum (LGM) Icelandic ice sheet and the climate responsible for it at ∼21kaBP. A series of sensitivity experiments reveal that Iceland is susceptible to the onset large-scale glaciation with only a 3 °C cooling perturbation relative to recent (1961–1990) climate. A 5 °C cooling perturbation is enough to force an ice sheet to beyond the present day coastline in virtually all sectors. A suite of 15 experiments driven by a GRIP δO18 time-series for 15,000 years from a climatic optimum at 36 ka to 21 ka BP scaled with 5.0–15.0 °C maximum cooling perturbation are initiated in order to identify a best-fit LGM ice sheet configuration compatible with the available empirical evidence. The optimum LGM model isolated requires an annual cooling of 10.0–12.5 °C relative to the recent climatology with over 50% precipitation suppression across the north and yields an extensive offshore ice sheet with an area of 3.29×105km2 and a volume of 3.09×105km3. Over-extension of ice extent across the northern shelf is addressed by the introduction of strong aridity across this region but otherwise the ice-sheet is well pinned to the continental shelf-break in remaining sectors which tends to decouple it from further climatic forcing. The optimum LGM ice-sheet has a substantial proportion of its base grounded below sea-level and is dominated by basal sliding which activates extensive zones of fast flow. This results in a highly dynamic, low aspect ice sheet with a mean ice thickness of 940 m and a plateau elevation of ∼2000m breached by numerous nunataks and ice-free zones providing potential, but spatially limited and frigid, ecological refugia through the vicissitudes of the LGM.