Influence of sublimation on stable isotope records recovered from high‐altitude glaciers in the tropical Andes

Abstract

Abstract. Sublimation dominates the ablation process on cold, high-altitude glaciers in the tropical Andes. Transport of water vapor through the firn and exchange with ambient moisture alter the stable isotope composition of the surface layers. A sublimation experiment carried out during an ice core drilling campaign on Cerro Tapado (5536 m above sea level, 30ø08'S, 69ø55'W) revealed a strong enrichment in the 2H and •80 content in the surface layer. Concerning the deuterium excess, a decrease occurred at daytime, while during the night, the values remained comparatively constant. At daytime the sublimation is enhanced due to the higher moisture deficit of the ambient air accompanied by relatively high firn surface temperatures. Low surface temperatures at night cause condensation of water vapor in the firn pores near the surface and thus inhibit penetration of the isotopically enriched surface front into deeper firn layers. Measuring an isotope profile obtained through detailed sampling between the surface and 38 cm depth proved this mechanism. The observed modification of the isotopic composition at the surface was quantitatively described by a model, which also reproduced the mass loss measured with sublimation pans and calculated from relevant meteorological data. The results of this study suggest that the influence of sublimation on the preserved isotope record of ice cores under comparable environmental conditions is rather limited. In any case, simultaneous measurements of 82H and 8•80 help to identify layers in an ice core which might be effected by sublimation. However, since the mass loss due to sublimation was of the order of 2-4 mm per day during the experiment, important palaeoinformation from an isotope record could be eliminated during extended dry periods.

Understanding snow hydrological processes through the lens of stable water isotopes

“…Sublimation-induced changes on the isotopic composition of a snowpack are similar to the changes induced by evaporation on the isotopic composition of residual water (Earman et al, 2006). If a snowpack undergoes sublimation, the residual snowpack isotopic composition follows the LEL with a reduced d-excess value (Figure 2; Ren et al, 2013;Stichler et al, 2001). It is interesting to note that snow sublimation during the trajectory of snowflakes from the cloud to the ground may not lead to substantial fractionation, presumably as it is an irreversible reaction (Friedman et al, 1992).…”

Isotopic and hydrogeochemical characterization of high-altitude karst aquifers in complex geological settings. The Ordesa and Monte Perdido National Park (Northern Spain) case study

“…The resulting vapour increases its atmospheric deuterium excess at the local scale. The low night temperatures at high elevation cause the atmospheric water vapour to condense on the snow surface, and as a result, the snow cover there increases its deuterium excess (Stichler et al, 2001;Froehlich et al, 2008). This diurnal snow sublimation and nocturnal condensation cycle could explain why the recharge due to high altitude snow melt in autumn, winter and spring has an increased deuterium excess in the PNOMP.…”

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

“…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). The presence of the glacier is somewhat unusual, in that peaks of similar elevation at this latitude are presently deglaciated (Stichler et al, 2001). …”

“…The region's very low humidity, high winds, and high insolation result in high rates of sublimation; field studies indicate 2-4 mm/day water equivalent at Cerro Tapado (Stichler et al, 2001;Kull et al, 2002). In this setting, melting has a negligible impact on mass balance, as meltwater quickly refreezes in the firn: temperatures at depths below ~10 cm during the Cerro Tapado study never exceeded 0º and the daytime air temperature was ~3º during the austral summer period of 11-16 February, 1999(Stichler et al, 2001.…”