Glacier fluctuations in the southern Peruvian Andes during the late‐glacial period, constrained with cosmogenic ³He

Abstract

The occurrence of pronounced climate reversals during the last glacial termination has long been recognised in palaeoclimate records from both hemispheres and from high to low latitudes. Accurate constraint of both the timing and magnitude of events, such as the Younger Dryas and Antarctic Cold Reversal, is vital in order to test different hypotheses for the causes and propagation of abrupt climate change. However, in contrast to higher-latitude regions, well-dated records from the Tropics are rare and the structure of late-glacial tropical climate remains uncertain. As a step toward addressing this problem, we present an in situ cosmogenic 3 He surface exposure chronology from Nevado Coropuna, southern Peru, documenting a significant fluctuation of the ice margin during the late-glacial period. Ten tightly clustered ages from a pair of moraines located halfway between the modern glacier and the Last Glacial Maximum terminus range from 11.9 to 13.9 ka and give an arithmetic mean age of 12.8 AE 0.7 ka (1s). These data constitute direct evidence for a readvance, or prolonged stillstand, of glaciers in the arid Andes of southwestern Peru.

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

“…The glacial ages and paleoclimatic proxies seem consistent with evidence showing a link between tropical glaciers and the Northern Hemisphere cooling episodes, through the tropical circulation southward shift [20][21][22][23][24]. [37,38]; This work; Hualca Hualca [7], Sajama [121] Tunupa [8] and Uturuncu [9]. Gray areas: chronology of lake transgressions on the Bolivian Altiplano [10].…”

“…It is possible that NC9 and NC10 are dating 1-2 older advances and NCNE01 a younger advance, which reached the same place and added a new moraine to pre-existing moraines. The younger moraines aggregation on older moraines, could also be the cause of the dispersed ages in many Andean glacial sites, such as Cajamarca [45], Cordillera Blanca [29], Jeulla Raju [105], Huayhuash [106], Junín [28], Quelccaya ice cap [6,107], Carabaya [46], Huayna Potosí, Río Suturi and Huamaní Loma [39]; Coropuna [37,38]; (this work); Hualca Hualca [7], Cerro Tunupa [8], and Uturuncu volcano [9].…”

“…The available glacial ages (Figures 13 and 14) from the Arid Tropical Andes [7][8][9]121]; (this work) are consistent with the southward increase in aridity and ELA. [37,38]; This work; Hualca Hualca [7], Sajama [121] Tunupa [8] and Uturuncu [9]. Gray areas: chronology of lake transgressions on the Bolivian Altiplano [10].…”

“…GLACIAL AGES. Coropuna 3 He ages, according to models Lm and Li [37,38] and 36 Cl ages from Hualca Hualca [7] and Coropuna (this work). (B).…”

“…Bromley et al [37,38] used the CRONUS online calculator [31] to estimate the 3 He ages from 30 moraine boulder surfaces, in the Huayllaura valley (southwestward), the Chico valley (westward) and the Santiago and Mapa Mayo valleys, westward of the study area of this work (Figure 1), naming the last one as Ullullo valley. Bromley et al [37] defined a lower moraine group (~5000-4900 m), extending to the lower area of the glacial valleys, as CI and a higher moraine group (~5500 m), deposited in the middle part of the Santiago valley, as CII.…”