Evaluation of LPM permafrost distribution in NE Asia reconstructed and downscaled from GCM simulations

A high-resolution map of potential frozen ground distribution in NE Asia (90-150 degrees E, 25-60 degrees N) at the period of the Last Permafrost Maximum (LPM, c. 21000 years ago) was dually reconstructed by means of a statistical classification using air freezing and thawing indices and a topographical downscaling using a digital relief model (ETOPO1). Background LPM climate data were derived from global climate model simulations of the Paleoclimate Model Intercomparison Project, Phase II (PMIP2). The reconstructed LPM map shows the southward shift of the southern limit of climate-driven permafrost by 400-1500km, with the greatest advance in the western sector (90-110 degrees E), encompassing an area from central Siberia to most of the Altai area. The advance of environmentally conditional permafrost and seasonally frozen ground was greatest in the eastern sector (110-150 degrees E), with an average shift of about 450km. The descent of the lower limit of LPM alpine permafrost was in the range of 400-800m. A comparison of the reconstructed map with published literature shows that this method, simplistically constructed yet effectively recognizing seasonality, continentality and topography, captures local features better than more elaborate methods. The sensitivity examination of a constant atmospheric lapse rate shows that altitudes of 2000-5000ma.s.l. were most sensitive, though with only a limited effect on overall LPM distribution.