Barandun, M., C. Bravo, B. Grobety, T. Jenk, L. Fang, K.n Naegeli, A. Rivera, S. Cisternas, T. Münster, M. Schwikowski (2022): Science of the Total Environment, https://doi.org/10.1016/j.scitotenv.2022.155068

Resumen / Abstract.

Light absorbing impurities can lower glacier albedo considerably. Glacier darkening enhances glacier melt. Here, we investigate the source and role of light absorbing impurities (LAI) deposited on the glacier surface in the Olivares catchment, Central Chile. We combined chemical and mineralogical analysis of surface ice samples and field based spectral reactance measured to investigate the nature and properties of light absorbing impurities on the glacier surface. With remote sensing-based albedo maps, we upscale the local information to glacier wide coverage, and using a modelling approach, we evaluate the sensitivity of the surface mass balance towards a change in ice albedo. The across-scale surface sample analysis served as input for interpreting trace element concentrations and reflectance properties of samples from an ice core, revealing a history of over half a century of LAI deposition. We found traces of mining residuals in glacier surface samples. The glaciers with highest mass loss in the catchment showed enhanced concentrations of surface dust particles, particularly enriched in Cu, Mo and Pb, the latter two together with Fe and Ni have significantly increased since the 1920’s. We show evidence based on chemical composition and mineralogical structure that dust particles with strong light absorbing capacity due to enriched iron containing minerals have been mobilized from anthropogenic sources and deposited on the nearby glacier surfaces. This lowers the surface reflectance especially in the visible wavelengths. Large scale assessment from satellite-based observations reveals ice albedo lowering (darkening) at most investigated glacier tongues from 1989 to 2018. However, pixel-based albedo trends are heterogeneous, especially above median glacier elevation. The mass balance is sensitive to possible ice albedo changes, and we highlight that an accelerated winter and spring snow albedo decrease, triggered by surface impurities, might be particularly responsible for the above-average mass balances encountered in the catchment.

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