Late Pleistocene climate conditions in the north Chilean Andes drawn from a climate–glacier model

Abstract

A climate–glacier model was used to reconstruct Late-glacial climate conditions from two case-study glaciers at 18° and 22° S in the arid (sub)tropical western Andes of northern Chile. The model uses (i) the geometry of the Late-glacial maximum glaciation, (ii) modern diurnal and annual cycles, amplitudes and lapse rates of the climate, (iii) empirical–statistical sublimation, melt and accumulation models developed for this area, and (iv) dynamic ice flow through two known cross-sections for steady-state conditions. The model is validated with modern conditions and compares favorably with the glaciological features of today. The mass-balance model calculates the modern equilibrium-line altitude at 18° S as high as 5850 m (field data 5800 m), whereas no glaciers exist in the fully arid southern area at 22° S despite altitudes above 6000 m and continuous permafrost. For Late-glacial times, the model results suggest a substantial increase in tropical summer precipitation (ΔP = +840 (− 50/+ 10) mm a−1 for the northern test area; +1000 (− 10/+ 30) mm a−1 for the southern test area) and a moderate temperature depression (ΔT = −4.4 (− 0.1/+ 0.2) °C at 18° S; −3.2 (±0.1) °C at 22° S). Extratropical frontal winter precipitation (June–September) was <15% of the total annual precipitation. A scenario with higher winter precipitation from the westerlies circulation belt does not yield a numerical solution which matches the observed geometry of the glaciers. Therefore, we conclude that an equatorward displacement of the westerlies must be discarded as a possible explanation for the late Pleistocene glaciation in the Andes of northern Chile.

Across the Arid Diagonal: deglaciation of the western Andean Cordillera in southwest Bolivia and northern Chile

“…The prominent moraines of the glacier modeled by Kull and Grosjean (2000) have not, however, been previously dated. Here, we present 8 new cosmogenic 36 Cl exposure ages.…”

“…Much of the drift surrounding this valley, on the other hand, is thin and exhibits patterning (as described above in Section 3.4) and poor development of lateral moraines, all of which may indicate thin, cold-based ice. Glacial-climate modeling by Kull and Grosjean (2000) based on the prominent moraines indicated that an extra 1 m of precipitation could be necessary to generate this glacier in conjunction with a 3.5ºC temperature depression as was characteristic of the Late Glacial. The model indicated, based on modern precipitation patterns, that most of this moisture must have come from the east during the austral summer.…”

“…The modern mean annual temperatures at the previously glaciated elevations of the study area (>4000 m) range from 4 to -4 ºC (Grenon, 2007;Kull and Grosjean, 2000). Upper elevations of the Puna Plateau and surrounding area receive between 200 and 350 mm/yr of water-equivalent precipitation (Grosjean et al, 2001), with high interannual variability (e.g., Garreaud and Aceituno, 2001;Houston, 2006).…”

“…While moisture is regarded as the limiting factor for glaciation (e.g., Kull and Grosjean, 2000;Sagredo et al, 2014), and so glacial stages have been assumed to coincide with documented wet periods, it was likely also 6-8ºC colder in this area during LGM, and shortwave radiation has changed significantly over the last glacial cycle as well (Kull and Grosjean, 1998). Moreover, the dating of these moraines, recently enabled by advances in cosmogenic dating, indicate a history for glaciation that may be more locally variable and complex than the three-regional-stages model proposed by Jenny et al (1996).…”

Effects of postdepositional processes on snow composition of a subtropical glacier (Cerro Tapado, Chilean Andes)

“…This effect is compensated for in the model by using a mean correction term of AT = -2øC fbr the calculation of temperatures over snow/ice surf;aces compared to gravel surfiaces [Sicart et al, 1998;Kull, 1999;Kull and Grosjean, 2000]. In addition, long-term means of lapse rates fi'om test sites with homogeneous surf;aces were used [l/uille, 1996;Kull, 1999].…”