Climate on the Blanca Massif, Sangre de Cristo Mountains, Colorado, USA, during the Last Glacial Maximum

Keith A Brugger,Eric M Leonard,Peter Dolan,Kurt A Refsnider

doi:10.3390/quat4030027

Keith A Brugger, Eric M Leonard + Show 2 more

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https://doi.org/10.3390/quat4030027

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Abstract

Temperature-index modeling is used to determine the magnitude of temperature depression on the Blanca Massif, Colorado, required to maintain steady-state mass balances of nine reconstructed glaciers at their extent during the Last Glacial Maximum (LGM). The mean temperature depression thus determined is ~8.6 +0.7/−0.9 °C where the uncertainties account for those inherent in the glacier reconstructions, in model parameters (e.g., melt factors), and possible modest changes in LGM precipitation. Associated equilibrium-line altitudes (ELAs) exhibit a statistically significant directional dependency being lower toward the north and east. Under the assumption that regional temperature change was uniform, required changes in precipitation vary systematically—also exhibiting a directional dependency coinciding with that in ELAs—and indicate increases (over modern) occurred on the eastern side of the massif while decreases occurred on the western side. This disparity represents a strengthening of a precipitation asymmetry, particularly winter precipitation, which exists today. The modern precipitation asymmetry may be a consequence of snow being blown over to the eastern side of the massif (advective transport) by southwesterly flow. Intensification of this flow during the LGM would have enhanced advection, and augmented snow accumulation on glaciers, thus explaining the lower ELAs and increased precipitation on that side of the massif.

Highlights

Estimates of temperature change during the Last Glacial Maximum (LGM) based on mass balances and/or equilibrium-line altitudes (ELAs) of paleoglaciers have contributed to our current understanding of Late Pleistocene climate in the Colorado Rocky Mountains [1,2,3,4,5,6,7,8]
This shortcoming arises from both the lack of precipitation proxies in the region, and the fact that the region commonly lies along a transition from wetter to drier LGM conditions indicated in large-scale paleoclimate modeling (e.g., the Paleoclimate Modelling Intercomparison Project (PMIP) [9])
During the local LGM on the Blanca Massif, ca. ~21 ka, glaciers radiated from its high summits

Summary

Introduction

Estimates of temperature change during the Last Glacial Maximum (LGM) based on mass balances and/or equilibrium-line altitudes (ELAs) of paleoglaciers have contributed to our current understanding of Late Pleistocene climate in the Colorado Rocky Mountains [1,2,3,4,5,6,7,8]. These estimates, generally assume either no significant change in LGM precipitation from modern values or assume arbitrary departures, the latter often to assess the sensitivity of inferred temperature depressions. They carry with them implications for changes in atmospheric circulation and hydroclimate during a time of extreme climate change that are not fully

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