Modelling the southern extent of the last Icelandic ice-sheet

A three-dimensional, time-dependent numerical ice-sheet model is used to investigate the southern extent of the last Icelandic ice-sheet since the Last Glacial Maximum (LGM, ca. 20 000 C-14 yr BP). Ice development over southern Iceland is forced using a linear relationship between mass balance and altitude based on observations over Solheimajokull, a southern outlet glacier of the Myrdalsjokull ice-cap. A continentality factor is introduced that raises inland equilibrium-line altitudes (ELAs) and also slackens the mass-balance/altitude gradient driving the model. with this calibration the present-day ice distribution can be reconstructed. Growth from ice-free to total ice cover is assessed and the sensitivity of ice extent to ELA change is shown to be non-linear. The model indicates that an ELA lowering of 500 m, consistent with a ca. 5 degreesC temperature depression for southern Iceland at the LGM, would enable glacier ice to cover the whole land surface within the modelled area and inundate any putative ecological refugia. Modelling with a 300 m ELA depression, consistent with previous reconstructions of Younger Dryas (YD, 10000-11 000 C-14 yr BP) ice extent, indicates that the principal outcrops of the Solheimar ignimbrite were glaciated at this time, suggesting that an origin during this stadial (and a correlation with North Atlantic Ash Zone I Vedde Ash) is problematic. Copyright (C) 2003 John Wiley Sons, Ltd.