Late Pleistocene snowline fluctuations at Nevado Coropuna (15°S), southern Peruvian Andes

Abstract

Deposits preserved on peaks in the southern Peruvian Andes are evidence for past glacial fluctuations and, therefore, serve as a record of both the timing and magnitude of past climate change. Moraines corresponding to the last major expansion of ice on Nevado Coropuna date to 20-25 ka, during the last glacial maximum. We reconstructed the snowline at Coropuna for this period using a combined geomorphic-numeric approach to provide a first-order estimate of the magnitude of late-Pleistocene climate change. Our reconstructions show that snowline was approximately 550-770 m lower during the last glacial maximum than during the late Holocene maximum, which ended in the 19 th century, and $750 m lower than today. While these values are similar to data from nearby Nevado Solimana, reconstructions from the neighbouring peak of Nevado Firura reveal a smaller snowline depression, suggesting the glacial response to climate forcing in the tropics is strongly influenced by non-climatic factors. These data constitute some of the first directly dated palaeo-snowline data from the arid tropics and suggest that the magnitude of the last glaciation in at least parts of the tropical Andes was similar to late-Pleistocene events at higher latitudes.

Prospecting Glacial Ages and Paleoclimatic Reconstructions Northeastward of Nevado Coropuna (16° S, 73° W, 6377 m), Arid Tropical Andes

“…From a geomorphological (non-chronological) point of view, the paleoELA for their CI phase calculated by Bromley et al [47] is equivalent to the paleoELA 1 of this work. In both cases they are paleoELAs from glaciers at their maximum extension, although Bromley et al [47] focused only on the glaciers that originated from the very Coropuna and Cuncaicha summits (source areas >5250 m; Figure 7) and we have analyzed ice flows from lower sites (<5250 m).…”

“…They deduced that the pre-CI moraines were older than the CI moraines, but they did not verify that hypothesis by absolute dating. In a later work, Bromley et al [47] reconstructed the current ELAs and the paleoELAs around the Coropuna. On the northern slope they estimated an ELA of 5915 ± 44 m. Different paleoELAs were presented for the CI phase, depending on the calculation method or the THAR ratio used: Bromley et al [47] used the paleoELA depression (~750 m) and the air temperature lapse ratio (ATLR) 7-6 • C/km, supposing that the past precipitation had been similar to the present one, to argue that the paleotemperature of the CI phase was~5.2-4.5 • C colder than nowadays.…”

“…The application of the same method for current ELAs and paleoELAs is almost a novelty in the Tropical Andes because, with few exceptions [77,82], previous works in Coropuna [47] and other mountains [83] used different procedures for the present and the past. In this work, in addition to the ELAs, the paleoELAs corresponding to two consecutive stages of a hypothetical maximum glacial extension were reconstructed.…”

“…In both cases they are paleoELAs from glaciers at their maximum extension, although Bromley et al [47] focused only on the glaciers that originated from the very Coropuna and Cuncaicha summits (source areas >5250 m; Figure 7) and we have analyzed ice flows from lower sites (<5250 m). Maybe that is why our paleoELA 1 (5078 m) is lower than the paleoELA CI (5167 ± 59 m) from Bromley et al [47].…”

“…Therefore, where precipitation is Moreover, the paleoclimatic reconstructions over the last glacial maximum in the Arid Tropical Andes are not homogenous either. The Coropuna ELA depression shows a~5 • C cooling regarding the current climate [37,47], if no changes in paleoprecipitation (∆ = 0%) are taken into account. Conversely, another work on Tunupa (~20 • S, Figure 1) during the Tauca highstand (~17-15 ka), found somewhat higher cooling (~6.5 • C) and higher precipitation (between ×1.6 and ×3.0) than in the present [8].…”