Reconstructing Paleo ELAs on Glaciated Landscapes

Abstract

The equilibrium-line altitude (ELA) marks the area or zone on a glacier where accumulation is balanced by ablation over a 1-year period. The ELA is sensitive to several meteorological factors, such as variations in winter precipitation, summer temperature, and wind transport of dry snow. When the annual net mass balance is negative, the ELA rises, and when the annual net mass balance is positive, the ELA falls. Fluctuations in the ELA provide an important indicator of glacier response to climate change that allows reconstructions of paleoclimate (accumulation season precipitation, ablation season temperature, and prevailing snow-bearing wind directions). Paleoclimatic reconstructions based on former glacier extent commonly include estimates of ELAs and depression of ELAs from present values. Several methods have been developed to estimate steady-state ELAs of former glaciers as a tool to reconstruct paleoclimates in glaciated regions. A survey of the literature related to ELA depressions during the Last Glacial Maximum, Younger Dryas, and the ‘Little Ice Age’ shows reductions from modern values on the order of 1000±300, 500±200, and 100±50m, respectively.