Vertical profiles of bromoform in snow, sea ice, and seawater in the Canadian Arctic

Authors

  • William T. Sturges,

  • Glenn F. Cota,

  • Paul T. Buckley


Abstract

Bromoform (CHBr3) was measured in vertical profiles from the snow surface through the snowpack, sea ice, and water column to the seafloor at Resolute Bay, Canada, in the spring of 1992. Elevated concentrations of bromoform were observed in both the ice (32–266 ng L−1 by liquid water volume) and seawater (∼20 ng L−1) at the ice-water interface, associated with bromoform emission from ice microalgae. A surprising finding was a second horizon of high bromoform concentrations (336–367 ng L−1) in sea ice at the snow-ice interface. Chlorophyll and salinity were also elevated in this upper ice layer, although chlorophyll was much lower than in the basal ice microalgal layer. We speculate that this upper bromoform-enriched layer may have originated from scavenging of the surface water layer by frazil ice during initial ice formation in the preceding autumn. Equally unexpected was the occurrence of yet higher bromoform concentrations in snowpack immediately overlying the sea ice (492–1260 ng L−1), declining in concentration (by about a factor of 2 or more) toward the snow surface. Snow of very recent origin, however, contained as little as 2 orders of magnitude less bromoform than the older snowpack. Possible origins for elevated bromoform in the snowpack include diffusion out of the bromoform-enriched upper ice layer and gradual concentration of bromoform out of the atmosphere by adsorption on to ice crystals. These are considered in turn. In one scenario, photolysis of bromoform from snow is considered, which might help account for atmospheric bromine-ozone chemistry. The possible contributions from snow, sea ice, and seawater to atmospheric bromoform levels during both the winter and spring are also considered, and it is concluded that surface seawater presents the most significant reservoir for atmospheric bromoform.

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