Seasonal and spatial variations in the chemistry of a High Arctic supraglacial snow cover

This paper describes the physical and chemical properties of the snow-pack on John Evans Glacier, Ellesmere Island, Canadian Arctic Archipelago, and investigates the controls on snowpack solute concentrations and atmospheric deposition. The snowpack contains three layers that are traceable across the whole glacier. These represent fall accumulation that has been metamorphosed to depth hoar, winter accumulation mixed with snow reworked by wind from the underlying depth hoar, and spring accumulation mixed with wind-reworked snow. The seasonal cycle in snow chemistry closely reflects changes in the composition of the atmospheric aerosol at Alert, with some modification of NO3- concentrations by post-depositional processes. Mean water-weightcd solute concentrations in the snowpack are largely independent of accumulation, while atmospheric deposition tends to increase with accumulation. This suggests that, for most species, wet deposition is the dominant depositional process throughout the year. However, concentrations of Ca2+ and K+ increase with both accumulation and elevation, implying an enhanced input from dry deposition of soil dust above 800 m elevation. Concentrations of SO42- are inversely related to accumulation, especially in the winter layer, suggesting a significant input from non-precipitating events, such as dry deposition or riming, during this period of very limited snowfall.