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Abstract

Sublimation and melt disturb the environmental information obtained from ice core records in the Andes. In two case studies we demonstrate to what extent these post-depositional processes may remove major parts of the accumulated snow cover. Dark ash layers from the Tungurahua eruption changed the albedo of surface snow on Chimborazo glacier (6268 m, 1 • 30 S, 78 • 36 W, Ecuador) between two ice core drilling campaigns and forced substantial melt. Redistribution and washout of the chemical constituents shifted the concentration profiles obtained in December1999 as compared to an equivalent core drilled in December 2000. The stable isotope records showed that approximately the water equivalent (weq) of an annual layer had melted, and that the percolating melt water penetrated within the firn layer to a depth of at least 16.5 m without refreezing. In the second example, from a site on the dry axis between the tropical and extra-tropical precipitation belts, significant loss of accumulated snow layers occurred by sublimation. A surface experiment at Cerro Tapado glacier (5536 m, 30 • 08 S, 69 • 55 W, Chile) revealed that losses of ≈2 mm weq (≈5 mm snow) per day occurred during the dry period following the 1997/98 El Niño. This loss generally included the entire surface layer enriched in stable isotopes, and thus caused minimal disturbance of the isotopic signature (and hence climatic information) of the net accumulation, yet chemical constituents again experienced considerable changes in concentration. From annual layer counting and direct dating it is obvious that the major part of the accumulated ice on both glaciers is younger than 100 years; however, isotopic and chemical variations at least in the basal ice from Cerro Tapado clearly point to climate conditions different from the recent centuries. This evidence is supported by mass balance considerations derived from a glacier-climate model. The possibility of a third type of disturbance aside from sublimation and melting-in this case a significant hiatus in the environmental chronology-also deserves consideration for other ice core records from this region. Potential disruptions or discontinuities need to be carefully evaluated given the profound changes in climatic and glaciological conditions since the Last Glacial Maximum throughout Holocene times.

Rapid decline of snow and ice in the tropical Andes – Impacts, uncertainties and challenges ahead

“…for heating and cooking, as well as local grassland fires, both anthropogenic or natural (Roman-Cuesta et al, 2014). Deposition of ash from volcanic eruptions is also locally important (Schotterer et al, 2003), even though it is not a result of climate change and the forcing is time-limited, as the volcanic aerosol concentration drops rather quickly once the eruptions ends. Some studies have also used ice cores to analyze historical air pollution levels dating back to pre-Incan times (e.g.…”

Seasonal evolution of penitente glaciochemistry at Tapado Glacier, Northern Chile

“…Most precipitation occurs in winter between May and August, when blocking anticyclones move southwards and Pacific cyclone activity dominates (Vuille and Ammann, 1997). The summer months (November to April) are comparatively dry, but convective summer storms from the east may also produce localized snowfall (Schotterer et al, 2003;MacDonell et al, 2013b).…”

Glacier Image Velocimetry: an open-source toolbox for easy and rapid calculation of high-resolution glacier-velocity fields

“…survey (Saberi et al, 2019). Ice cores have been collected at the summit plateau in 1999-2000, the longest of which extends 54.4 m to the glacier bed (Schotterer et al, 2003;Ginot et al, 2010).The general data sparsity but existence of a single point for benchmarking, combined with its water-supply importance for the surrounding communities (La Frenierre and Mark, 2017), makes it an appropriate target for an initial ice-thickness inversion using GIV.…”

“…Meltwater has been identified near the summit of Chimborazo, where coring attempts in December 2000 were disrupted by a layer of waterlogged ice at a depth of 28 m (Schotterer et al, 2003). However, surface melt was exceptional in the 16 https://doi.org/10.5194/tc-2020-204 Preprint.…”

“…CC BY 4.0 License. years 1999-2000 due to tephra fallout from the nearby eruption of Tungurahua (Schotterer et al, 2003;Ginot et al, 2010).…”