Modeling the climate sensitivity of Patagonian glaciers and their responses to climatic change during the global last glacial maximum

Abstract

Investigation of the behavior of the former ice sheet over Patagonia aids better understanding of ice-climate interactions and has important implications for deciphering how modern glaciers will respond to rapid increase in global temperature. Here, we use a 1-km resolution ice sheet model to identify the climate sensitivity of Patagonian glaciers and examine their responses to climatic change during the global Last Glacial Maximum (gLGM). Our results demonstrate that the total glacier area increases by ∼78 × 103 km2 and the equilibrium-line altitude (ELA) lowers by ∼163 m for every 1 °C of cooling under modern precipitation regime. Keeping temperature unchanged, there is an increase of total glacier area by ∼21 × 103 km2 and a ΔELA by ∼64 m for every doubling in precipitation. According to the multimodel ensemble mean of 21 PMIP models, an overall colder and drier climate prevails over Patagonia during the gLGM, with a decrease of annual mean temperature and precipitation by ∼4.7 °C and 12%, respectively. Under the modeled gLGM climate, there is an extensive ice sheet (∼387 × 103 km2) almost completely covering the Patagonian Andes, which results largely from the cooling with positive contribution from sea-level fall. The Patagonian ice sheet is drained by ice streams at the western margins and fast-flowing outlet glaciers to the east, with a north-to-south ice divide mainly extending the southern Patagonian Andes. Additionally, the erosion potential induced by the ice sheet exhibits a very strong localization over the fjords and valleys, resembling the pattern of ice velocity. The modeled ice sheet extent and ice flow pattern during the gLGM match well with the latest empirical reconstructions (though with spatial discrepancies), whereas the total ice volume is underestimated. However, the modeled Patagonian ice sheet exhibits high sensitivity to climatic forcing and the values of ice sheet model parameters used.