IMPICATIONS FOR HOLOCENE CLIMATE CHANGE FROM NUMERICAL MODELING OF PRESENT-DAY GLACIER SENSITIVITY IN THE CORDILLERA VILCABAMBA, PERU

Present-day tropical glaciers are highly sensitive to small-amplitude climate changes, implying that past glaciers were similarly responsive. This makes paleoglacier positions valuable proxies for reconstructing paleoclimate conditions. An understanding of paleoclimatic controls in the tropics is of particular interest because climate fluctuations in this region may be linked to changes in one or both hemispheres. To better identify the dominant controls on tropical paleoglacier mass balance, we have applied a glacier surface energy-mass balance (EMB) model, coupled with an ice dynamics model, to three valleys in the Cordillera Vilcabamba of southern Peru. These valleys contain present-day glaciers as well as precisely dated moraine sequences that document the areal extents and timings of past glaciations. The initial model calibration involves tuning of the EMB model to achieve mass balance for the Vilcabamba glaciers. The climatology of the region is defined by local meteorological records, including regional station data from the Peruvian National Meteorological Service (SENAMHI). Temperature lapse rates are constrained using radiosonde data in conjunction with SENAMHI station data, while the spatial distribution of precipitation is characterized using Tropical Rainfall Measuring Mission (TRMM) climatological estimates available through NASA. Due to the lack of direct mass balance measurements on Vilcabamba glaciers, we use the Zongo Glacier in the Cordillera Real of Bolivia as a tuning target for energy fluxes generated by the EMB model. EMB outputs are used in the ice dynamics model to produce glaciers that match stable ice extents identified from time series of recent Landsat images and air photos. We then use the tuned EMB model to determine perturbations to present-day climate that would have supported past ice extents at each of the dated moraine positions in the three valleys, with a focus on the prominent ‘Little Ice Age’ moraines. Initial model runs suggest glaciers are highly sensitive to temperature, and we further explore the importance of changes in solar radiation, longwave radiation, and humidity on glacier mass balance.