NUMERICAL MODELING OF LATE PLEISTOCENE GLACIATIONS OF THE CHAJNANTOR PLATEAU (23°S), NORTHERN CHILEAN ANDES

Glaciers are sensitive indicators of climate change and records of past glaciations serve as important archives of climate variability. In subtropical South America, using these glacial archives as paleoclimate proxies is complicated by their multiple sensitivities to temperature, precipitation, and surface radiation balance, as well as high rates of sublimation. Numerical models can test the influence of climate variability on glacial dynamics and assess the sensitivity of glaciers to these specific elements of climate. The Chilean Altiplano of the arid subtropical Andes (18°S-23°S) is presently deglaciated, however, the presence of glacial features imply prior glaciations. Reconstructions of glacial occupation of the Chajnantor Plateau (23°S) using cosmogenic ¹⁰Be and ³⁶Cl exposure ages imply the most recent extensive glaciation ceased prior to or during the global LGM (21 ka), but regionally, both LGM and late glacial glaciations occurred. Independent proxy evidence suggests that the LGM locally was colder but only slightly wetter than present day, and the later glaciations correspond to a warming but much wetter period ca. 14-17 ka, during which cloud feedbacks on radiation balance must be considered. Here we apply a 2D surface energy mass-balance model coupled with an ice dynamics model to assess the sensitivity of the former Chajnantor Ice Cap to these climate variations. Ice thicknesses based on field observations and cosmogenic nuclide concentration patterns are used to better constrain the model. Under conditions that permit glaciation, the model will be used to examine the glacial thermal regime and the timing and magnitude of meltwater generation to understand the contribution of these processes to the evolution of the Chajnantor Ice Cap. The modeled climate conditions will aid in deciphering the glacial history of the Chajnantor Plateau and contribute to understanding the response of subtropical glaciers to climate change in the arid Andes.