Early Local Last Glacial Maximum in the Tropical Andes

Abstract

The local last glacial maximum in the tropical Andes was earlier and less extensive than previously thought, based on 106 cosmogenic ages (from beryllium-10 dating) from moraines in Peru and Bolivia. Glaciers reached their greatest extent in the last glacial cycle ∼34,000 years before the present and were retreating by ∼21,000 years before the present, implying that tropical controls on ice volumes were asynchronous with those in the Northern Hemisphere. Our estimates of snowline depression reflect about half the temperature change indicated by previous widely cited figures, which helps resolve the discrepancy between estimates of terrestrial and marine temperature depression during the last glacial cycle.

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

“…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 last deglaciation of Peru and Bolivia

“…. TCN-based chronologies of moraines in Peru and Bolivia substantiated the previously hypothesized local maximum extent as occurring early during the last glacial cycle, with a more diminutive extension during the global LGM (Smith et al, 2005). However, methodological differences in the application of TCN techniques (sampling, production rate choice, age calculation, and interpretation) have resulted in different interpretations of glaciation timing and paleoclimate forcing Glasser et al, 2009;Smith and Rodbell, 2010).…”

“…Basal sediments from moraine-dammed lakes and peatlands in the Palcoco and Milluni valleys have radiocarbon ages that range from 12.8 to 10.9 ka (10.9 ± 0.1 to 9.6 ± 0.1 14 Cka) (Seltzer, 1992). Smith et al (2005) reported TCN ages of late glacial moraines that date from 19.4 to 10.3 ka.…”

“…In the same Zongo valley, TCN ages on older Late Glacial moraines range from 21.9 to 14.2 ka. A younger group of Late Glacial moraines dates from 18.1 to 14.1 ka (Smith et al, 2005). Basal sediments from moraine-dammed lakes and peatlands in the Palcoco and Milluni valleys have radiocarbon ages that range from 12.8 to 10.9 ka (10.9 ± 0.1 to 9.6 ± 0.1 14 Cka) (Seltzer, 1992).…”

“…Wright suggested the lake dates may be too old given carbonate bedrock and hard water effects. Smith et al (2005) published 146 TCN dates sampled from boulders and bedrock exposures in four of the valleys east of Lake Junin, draining the Cordillera Oriental. These ages cluster into four groupings (A to D), with the oldest (C and D) having ages considerably older (>65 ka to >200 ka) than the last glacial cycle.…”