Enhancement of snowpack inorganic nitrogen by aerosol debris

Abstract

The NO₃^-, Cl^- and Ca₂⁺ loading and provenance of the lower wetted-refrozen part of an Arctic snowpack sampled in spring 1999 is analysed. This wetted-refrozen layer (WRL) formed during rain-on-snow events in early winter 1998, being subsequently buried by later snowfall. It is a unique environment within which to study NO₃^- provenance, since it is effectively sealed off from the atmosphere, and solute is mostly stored in superimposed ice, ice lenses and wetted-refrozen snow. Post-depositional losses/gains of NO₃^- by volatilization/dry deposition are, therefore, minimized. Partitioning of WRL Ca²⁺ and NO₃^- loads into their respective sea salt/atmospheric components and an excess component indicates significant contributions of excess Ca²⁺ (∼80% of total) and NO₃ - (11–64% of total). These excess loads are thought to arise from a combination of preferential elution during lateral meltwater drainage and the release of Ca⁺ and N (as NO₃^- and NH₄⁺) from snowpack debris during wetting. Dissolution experiments on local snowpack debris provide envelopes of Ca²⁺ and NO₃^- release that are in line with the excess loads of these species at most sampling sites and are supportive of the latter hypothesis. This is the first study to date to indicate debris as a possible source of non-atmospheric nitrogen to snow. It has implications for nitrogen cycling in other catchments where snow contains significant aerosol sourced from N-containing lithologies and organic matter