Distribution and partitioning of mercury in the Arctic cryosphere: transport across snow-sea ice-water interfaces in the western Arctic Ocean

Abstract

The high toxicity and ability to be transported over long distances and biomagnify up food chains have earned Mercury (Hg) recognition as a contaminant of global concern. The Arctic region is particularly vulnerable to Hg with high levels of Hg being detected in marine mammals. The importance of the cryosphere, especially sea ice, has often been neglected in considerations of the extent to which atmospherically derived Hg impinges on the underlying marine system. This thesis reports the first systematic study of Hg transport in the Arctic cryosphere (sea ice, brine, snow, and melt ponds) conducted in the Amundsen Gulf from February to June 2008. Hg concentrations in bulk first-year sea ice were generally low (0.5 – 4 ng L-1), with the highest concentration in the surface granular ice layer. The highest concentrations of Hg were found in sea ice brine (up to 70 ng L-1). Atmospheric mercury depletion events (AMDEs) appear not to be an important factor in determining Hg in sea ice, with the exception of in frost flowers. Evidence of Hg accumulation during melt – refreezing cycles is seen in multi-year ice. Significant impact of AMDEs is observed on Hg concentrations in snow. Rates of deposition of atmospheric Hg ranged from 200 – 784 ng m-2 into the top 1 cm of snow. Although photo reduction and reemission to the atmosphere does occur, a considerable fraction of deposited Hg is retained in the snowpack due to subsequent burial. At one station it is estimated that less than 50% of the deposited Hg is re-emitted to the atmosphere. It is suggested that in the Beaufort Sea, where AMDEs occur frequently due to dynamic nature of the sea ice environment, a larger than suspected portion of atmospherically deposited Hg can be retained in the snowpack and enter the underlying marine system upon melt later in the season.