Amount, Sources, and Dissolution of Aerosol Trace Elements in the Canadian Arctic

Atmospheric deposition is an important source of trace elements (TEs) to the Arctic, including both anthropogenic (e.g., Pb) and micronutrient (e.g., Fe) metals. This study measured TE loadings, Pb isotopes, and dissolution in aerosols collected at Alert, Nunavut, Canada, from spring to summer of 2013 and 2014 and during the Canadian Arctic GEOTRACES Cruises (GN02 and GN03) in the summer of 2015. The aerosol loadings were 5-8 times higher and more enriched with anthropogenic metals (Pb and Cd) in the spring than in the summer consistent with the Arctic haze phenomenon. Pb isotopes reveal that Russia, Europe, and China were the likely source regions of this pollution in spring. Comparison of the Pb and Cd concentrations and Pb isotope data with previous studies suggests that atmospheric pollution in the Canadian Arctic has been relatively stable for the last couple of decades. Dissolution experiments were also performed to estimate the fraction of aerosol TEs that can potentially be dissolved and become bioavailable in seawater. The minimum and maximum dissolution estimates for Fe were 8 +/- 5 and 65 +/- 20%, respectively, which translate to a potential input of 5-40 kT year(-1) of dissolvable Fe to the Canada Basin of the Arctic Ocean, comparable to the riverine Fe input (10-20 kT year(-1)) from Mackenzie River. Thus, aerosols could be an important Fe source to Arctic surface waters, especially with decreasing sea ice coverage, changes in stratification and in places far from shelf and river sources.