Quantifying glacier sensitivity to Late Glacial and Holocene climate changes in the southern Peruvian Andes

Tropical glaciers are highly sensitive to small-amplitude climate changes, implying that paleoglacier positions are valuable proxies for reconstructing paleoclimate conditions. However, it is still unknown how glaciers in different regions along the Andes responded to changes in specific climate parameters, and in particular, to changes in the dominating influences of temperature and precipitation. To identify the dominant controls on tropical paleoglacier mass balance, a surface energy balance model (SEBM), coupled with an ice dynamics model, was applied to three valleys in the Cordillera Vilcabamba of southern Peru. These valleys contain present-day glaciers and preserve evidence for the areal extents and timing of past glacier fluctuations through precisely dated moraine sequences. To constrain the range of conditions that would have supported these paleoglaciers, climate parameters were adjusted in the SEBM to simulate glacier extents marked by moraine positions. Non-unique climate solutions were developed for Little Ice Age (LIA), Neoglacial, early Holocene, and Late Glacial positions. Glacier sensitivity to specific climate parameters was tested by individually perturbing temperature and precipitation and comparing glacier length responses. Model simulations, when placed in the context of regional climate proxy studies, suggest relatively large temperature depressions (at least 3.7°C for the Late Glacial, 2.8°C for the early Holocene and Neoglacial, and 1.6°C for the LIA) combined with moderately enhanced precipitation (no greater that ~3.4 times modern values) are most likely to have supported paleoglaciers. Modeling results also indicate that tropical glacier sensitivity to changes in precipitation greatly increases at lower temperatures, but that glacier sensitivity to temperature remains high irrespective of precipitation amount. This in turn implies the dominant controls on glacier mass balance have varied from the Late Glacial to the present as temperatures have fluctuated. This pattern further suggests modern glaciers in the Cordillera Vilcabamba are relatively insensitive to precipitation changes, and that future warming will play the dominant role in driving continued retreat of glaciers in this region of the tropics.