Equilibrium line altitudes along the Andes during the Last millennium: Paleoclimatic implications

Abstract

Deciphering the climate changes that influenced the glacial fluctuations of the last millennium requires documenting the spatial and temporal patterns of these glacial events. Here, we estimate the change in equilibrium line altitudes (ELAs) between the most prominent glacial advance of the last millennium and the present for four alpine glaciers located in different climatic regimes along the Andes. For each glacier, we reconstruct scenarios of climatic conditions (temperature and precipitation anomalies) that accommodate the observed ELA changes. We focus on the following glaciers: an alpine glacier in the Cordillera Vilcanota (13°S), Tapado glacier (30°S), Cipreses glacier (34°S), and Tranquilo glacier (47°S). Our results show that the range of possible temperature and precipitation anomalies that accommodate the observed ELA changes overlap significantly at three of the four sites (i.e. Vilcanota, Cipreses, and Tranquilo). Only Tapado glacier exhibits a set of climate anomalies that differs from the other three sites. Assuming no change in precipitation, the estimated ELA changes require a cooling of at least 0.7°C in the Cordillera Vilcanota, 1.0°C at Tapado glacier, 0.6°C at Cipreses glacier, and 0.7°C at Tranquilo glacier. Conversely, assuming no change in temperature, the estimated ELA changes are explained by increases in precipitation exceeding 0.52 m yr−1 (64% of the annual precipitation) in the Cordillera Vilcanota, 0.31 m yr−1 (89%) at Tapado glacier, 0.22 m yr−1 (27%) at Cipreses glacier, and 0.3 m yr−1 (27%) at Tranquilo glacier. By mapping the ELA changes and modeling the potential climate forcing across diverse climate settings, we aim to contribute toward documenting the spatial variability of climate conditions during the last millennium, a key step to decipher the mechanisms underlying the glacial fluctuation that occurred during this period.

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

“…We also use this scaling for the new results presented here (sites 4, 6, and the new 36 Cl samples from site 7). Sagredo et al (2016) also presented their ages for site 9 using this scaling. Therefore, only the published 36 Cl ages from sites 1 and 7 needed to be rescaled.…”

“…Calculated exposure ages increased due to rescaling by 45-51% at site 8 and by 25-51% at site 10 ( Table 2). Cl, we employ the newer time-varying Lifton-Sato-Dunai (LSD) scheme (Lifton et al, 2014), which for this region gives both 36 Cl and 10 Be ages within ~1-2% of the time-varying Lal-Stone scheme, i.e., within analytical error of the scheme used above for 10 Be (e.g., Sagredo et al, 2016). We also use this scaling for the new results presented here (sites 4, 6, and the new 36 Cl samples from site 7).…”

“…The inner moraine is interpreted as being deposited between 500-1000 yr BP. The more distal moraines, on the other hand, were probably deposited during the mid-Holocene (Sagredo et al, 2016). (Zech et al, 2007) Zech et al (2007 dated many locations along a deglaciated valley in the Cordón de Doña Rosa (30.7ºS).…”

“…Small lateral moraines are apparent in satellite imagery between these late glacial moraines and the extant large rock glacier, and are locally overridden by talus and small rock glaciers. (Sagredo et al, 2016) Cerro Tapado (30.14°S; 69.93°W; 5536 m asl), receives most of its precipitation from winter cut-offs of cold air-masses from the Pacific (Vuille and Ammann, 1997;Ginot et al, 2002;Marengo et al, 2004). The southeast slope of Cerro Tapado hosts a ~1.5 km-long glacier (Schotterer et al, 2003), which has an estimated ELA of 5300 m (Kull et al, 2002) and terminates near 4700 m. With a surface area of ~1.2 km 2 , this is the northernmost significant glacier in the western cordillera south of the Arid Diagonal, and its mass balance is strongly influenced by sublimation (Ginot et al, 2006).…”

“…Sagredo et al (2016) interpret several moraine stages. Innermost is a moraine complex among debris-covered ice about 200 m below and 500 m downvalley from the current terminus.…”