Bromoform (CHBr3) was measured in vertical profiles from the snow surf
ace 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 wa
ter volume) and seawater (similar to 20 ng L-1) at the ice-water inter
face, associated with bromoform emission from ice microalgae. A surpri
sing finding was a second horizon of high bromoform concentrations (33
6-367 ng L-1) in sea ice at the snow-ice interface. Chlorophyll and sa
linity were also elevated in this upper ice layer, although chlorophyl
l was much lower than in the basal ice microalgal layer. We speculate
that this upper bromoform-enriched layer may have originated from scav
enging of the surface water layer by frazil ice during initial ice for
mation in the preceding autumn. Equally unexpected was the occurrence
of yet higher bromoform concentrations in snowpack immediately overlyi
ng 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 o
rigin, however, contained as little as 2 orders of magnitude less brom
oform 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 atmospher
e by adsorption on to ice crystals. These are considered in turn. In o
ne scenario, photolysis of bromoform from snow is considered, which mi
ght help account for atmospheric bromine-ozone chemistry. The possible
contributions from snow, sea ice, and seawater to atmospheric bromofo
rm levels during both the winter and spring are also considered, and i
t is concluded that surface seawater presents the most significant res
ervoir for atmospheric bromoform.