Quantifying the change in equilibrium-line altitude during the Last Glacial Maximum in the Subtropical Andes using a mass-balance model

Abstract:

Quantifying changes in equilibrium-line altitude (ELA) can be used to better understand past regional climates. We use a glacial mass-balance model in conjunction with global climate model (GCM) output data to calculate the change in ELA between modern and Last Glacial Maximum (LGM; 21 ka) climates in the presently hyper-arid subtropical Andes. The region is currently unglaciated, despite cold enough temperatures, as there is too little moisture to sustain glaciers. Previous studies suggest this area was glaciated during the LGM, however, little is known about the extent of the glaciation or the climate required to sustain it. The mass-balance model used in this study calculates the change in ELA using the positive degree-day (PDD) sum, the sum of daily mean air temperatures that are above zero. The PDD sum is used to calculate ablation, which is then assumed to be proportional to temperature, in order to calculate the change in ELA. Using output from several GCM simulations, we compare the change in ELA between LGM and modern climates across the different models for the subtropical Andes. These simulations suggest that the changes in climate resulted in a lowering of ELAs to the extent that parts of the subtropical Andes were glaciated during the LGM.