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Abstract. The Arctic is one of the most rapidly warming regions of the Earth, with predicted temperature increases of 5–7 ∘C and the accompanying extensive retreat of Arctic glacial systems by 2100. Retreating glaciers will reveal new land surfaces for microbial colonisation, ultimately succeeding to tundra over decades to centuries. An unexplored dimension to these changes is the impact upon the emission and consumption of halogenated organic compounds (halocarbons). Halocarbons are involved in several important atmospheric processes, including ozone destruction, and despite considerable research, uncertainties remain in the natural cycles of some of these compounds. Using flux chambers, we measured halocarbon fluxes across the glacier forefield (the area between the present-day position of a glacier's ice-front and that at the last glacial maximum) of a high-Arctic glacier in Svalbard, spanning recently exposed sediments (<10 years) to approximately 1950-year-old tundra. Forefield land surfaces were found to consume methyl chloride (CH3Cl) and methyl bromide (CH3Br), with both consumption and emission of methyl iodide (CH3I) observed. Bromoform (CHBr3) and dibromomethane (CH2Br2) have rarely been measured from terrestrial sources but were here found to be emitted across the forefield. Novel measurements conducted on terrestrial cyanobacterial mats covering relatively young surfaces showed similar measured fluxes to the oldest, vegetated tundra sites for CH3Cl, CH3Br, and CH3I (which were consumed) and for CHCl3 and CHBr3 (which were emitted). Consumption rates of CH3Cl and CH3Br and emission rates of CHCl3 from tundra and cyanobacterial mat sites were within the ranges reported from older and more established Arctic tundra elsewhere. Rough calculations showed total emissions and consumptions of these gases across the Arctic were small relative to other sources and sinks due to the small surface area represented by glacier forefields. We have demonstrated that glacier forefields can consume and emit halocarbons despite their young age and low soil development, particularly when cyanobacterial mats are present.

Supraglacial debris cover regulates the melt rates of many glaciers in mountainous regions around the world, thereby modifying the availability and quality of downstream water resources. However, the influence of supraglacial debris is often poorly represented within glaciological models, due to the absence of a technique to provide high-precision, spatially continuous measurements of debris thickness. Here, we use high-resolution UAV-derived thermal imagery, in conjunction with local meteorological data, visible UAV imagery and vertically profiled debris temperature time series, to model the spatially distributed debris thickness across a portion of Llaca Glacier in the Cordillera Blanca of Peru. Based on our results, we simulate daily sub-debris melt rates over a 3-month period during 2019. We demonstrate that, by effectively calibrating the radiometric thermal imagery and accounting for temporal and spatial variations in meteorological variables during UAV surveys, thermal UAV data can be used to more precisely represent the highly heterogeneous patterns of debris thickness and sub-debris melt on debris-covered glaciers. Additionally, our results indicate a mean sub-debris melt rate nearly three times greater than the mean melt rate simulated from satellite-derived debris thicknesses, emphasising the importance of acquiring further high-precision debris thickness data for the purposes of investigating glacier-scale melt processes, calibrating regional melt models and improving the accuracy of runoff predictions.

Abstract. The Arctic is one of the most rapidly warming regions of the Earth, with predicted temperature increases of 5–7 °C and the accompanying extensive retreat of Arctic glacial systems by 2100. This will reveal new proglacial land surfaces for microbial colonisation, ultimately succeeding to tundra over decades to centuries. An unexplored dimension to these changes is the impact upon the emission and consumption of halogenated organic compounds (halocarbons) from proglacial land surfaces. Halocarbons are involved in several important atmospheric processes, including ozone destruction, and despite considerable research, uncertainties remain in the natural cycles of some of these compounds. Using flux chambers, we measured halocarbon fluxes from proglacial land surfaces spanning recently-exposed sediments (

This study presents an empirical method for identifying and monitoring acidic lakes impacted by acid rock drainage (ARD) processes in the Cordillera Blanca, Peru, using Landsat 8 images. ARD poses a threat to water security for downstream populations and has been associated with glacier retreat in various river catchments in the region. Previous research has linked water source acidification to the progressive exposure of the sulphide-rich Chicama Formation (Js-Chic), previously covered by perennial ice. However, traditional identification methods rely on labor-intensive ground-based field campaigns, limiting the scope of studies and hindering future predictions. Upon correlating the Landsat 8-derived pH proxies with the Js-Chic map, a higher Js-Chic exposure was observed near highly acidic lakes. Notably, Js-Chic exposure areas exceeding 60 hectares coincided with highly acidic lakes (pH < 4). We also analyzed glacial retreat in the study basins through a time series of the Normalized Difference Snow Index (NDSI) from 1986 to 2019, finding greater glacial retreat in basins with acidic lakes. We also compared vegetation quality in these basins over the same period using the average Normalized Difference Vegetation Index (NDVI) and observed higher vegetation quality in acidic-lake basins. We then developed a methodology to assess lake acidity based on the spectral signatures of 28 lakes in the Cordillera Blanca. These results suggest that a greater Js-Chic exposure area near a lake may indicate acidity. We applied this methodology on 267 lakes in the Cordillera Blanca and found 60 lakes to be highly acidic with a pH < 4 (22.5%), and 207 lakes (77.5%) with a pH > 4. However, these findings should be supplemented with more complex analyses, as there is currently limited in situ monitoring data on lake pH.