Anthropogenic Influence on Surface Changes at Olivares Glaciers, Central Chile

We have investigated the source and role of light absorbing impurities (LAI) deposited on the glaciers of the Olivares catchment, in Central Chile. LAI can considerably darken (lower ice albedo) the glacier surface, enhancing their melting. We combined chemical and mineralogical analyses of surface ice samples with field-based spectral reflectance measurements and laboratory analysis to investigate the nature and properties of LAI on the glacier surface. Using remote sensing-based albedo maps, we upscaled local information to glacier-wide coverage. We then used a model to evaluate the sensitivity of surface mass balance to a change in ice albedo. The across-scale surface sample analysis revealed 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 present enhanced concentrations of surface dust particles with low reflectance properties. Our results indicate that dust particles with strong light-absorbing capacity have been mobilized from anthropogenic sources and deposited on the nearby glacier surfaces, thus lowering their surface reflectance. Large scale assessment from satellite-based observations revealed darkening (ice albedo lowering) at most investigated glacier tongues from 1989 to 2018. Mass balance is sensitive to ice albedo changes. However, we believe that an accelerated winter and spring snow albedo decrease, triggered by surface impurities, might be responsible for the above-average mass balances encountered in this catchment.