Abstract
Abstract. The impact of volcanic ash on seasonal snow and glacier mass balance has been much less studied than that of carbonaceous particles and mineral dust. We present here the first field measurements on the Argentinian Andes, combined with snow albedo and glacier mass balance modeling. Measured impurity content (1.1 mg kg−1 to 30 000 mg kg−1) varied abruptly in snow pits and snow and firn cores, due to high surface enrichment during the ablation season and possibly local or regional wind-driven resuspension and redeposition of dust and volcanic ash. In addition, we observed high spatial heterogeneity, due to glacier topography and the prevailing wind direction. Microscopic characterization showed that the major component was ash from recent Calbuco (2015) and Cordón Caulle (2011) volcanic eruptions, with a minor presence of mineral dust and black carbon. We also found a wide range of measured snow albedo (0.26 to 0.81), which reflected mainly the impurity content and the snow and firn grain size (due to aging). We updated the SNow, ICe, and Aerosol Radiation (SNICAR) albedo model to account for the effect of cloudiness on incident radiation spectra, improving the match of modeled and measured values. We also ran sensitivity studies considering the uncertainty in the main measured parameters (impurity content and composition, snow grain size, layer thickness, etc.) to identify the field measurements that should be improved to facilitate the validation of the snow albedo model. Finally, we studied the impact of these albedo reductions on Alerce Glacier using a spatially distributed surface mass balance model. We found a large impact of albedo changes on glacier mass balance, and we estimated that the effect of observed ash concentrations can be as high as a 1.25 m water equivalent decrease in the annual surface mass balance (due to a 34 % increase in the melt during the ablation season).
Highlights
Since glaciers are highly sensitive to climate fluctuations, their unprecedented rates of retreat observed during the last few decades represent one of the most unambiguous signals of climate change (Zemp et al, 2015; IPCC, 2019)
particulate matter (PM) concentrations in samples obtained in both field campaigns in the accumulation and the ablation zones are depicted in Fig. 2 as a function of pit or core depth
Further chemical studies will be performed on the PM samples to refine the representation of LAPs in the snow albedo model, since optical properties can be very different for black carbon (BC), mineral dust, volcanic ash, etc
Summary
Since glaciers are highly sensitive to climate fluctuations, their unprecedented rates of retreat observed during the last few decades represent one of the most unambiguous signals of climate change (Zemp et al, 2015; IPCC, 2019). Some studies have used point measurements of LAP content (ice cores) together with a snow albedo model to estimate potential melting, using a radiative transfer model to calculate the additional absorbed energy by BC and mineral dust (Ginot et al, 2014; Zhang et al, 2018) or perturbing a glacier mass balance model to include BC forcing (Painter et al, 2013). A more recent study along the Southern Andes of Chile found a mean albedo reduction due to light-absorbing particles in the snow, with its corresponding mean radiative forcing increase (Rowe et al, 2019) They conclude that in the north (dusty, vegetation-sparse Atacama Desert), BC plays a smaller role than non-BC, whereas near Santiago and in the south (vegetation-rich), the BC contribution is higher. This study is the first field study of the impact of LAPs on Argentinian glaciers and one of the few studies of the long-term impact of volcanic ash on snow albedo
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