Late Quaternary Permafrost Distributions Downscaled for South America: Examinations of GCM-based Maps with Observations

Abstract

High-resolution maps of potential frozen ground distribution in South America have been produced for the present day (0ka) and the Last Glacial Maximum (21ka). Surface air temperature outputs from global climate models (GCMs) of the recent Paleoclimate Model Intercomparison Project were used for the reconstructions, and then downscaled from regional to local scales, with the help of a 1 arc-minute digital elevation model. Their validity was examined using fieldwork-based evidence and knowledge. The downscaled map for the present day successfully reproduces the presence of permafrost in the Andes, a task at which original coarse-resolution GCM output maps failed. The map also shows close correspondence with instrumental observations. Similarly, the downscaled distribution of 21ka frozen ground shows overall consistency with geomorphological and/or palaeoenvironmental reconstructions. Areal coverage of potential permafrost for all of South America is estimated at 139 000km2 for today and 435 000km2 for 21ka, mostly along the Andean mountain ranges. Regional inspections, however, show divergence from field-observed features, attributed to microclimatic effects and past permafrost conditions. For southern Patagonia, and especially the eastern lowlands, the diagnosed lower limit for permafrost is about 1000m asl, whereas field evidence at lower altitudes indicates the presence of either permafrost or deep seasonal frost.