Frost flower surface area and chemistry as a function of salinity and temperature
Frost flowers play a role in air-ice exchange in polar regions, contribute to tropospheric halogen chemistry, and affect ice core interpretation. Frost flowers were observed and collected on the Hudson Bay in March 2008. Their specific surface area (SSA) was measured using CH4 adsorption at 77 K. The Brunauer-Emmett-Teller analysis produced SSA values between 63 and 299 cm(2) g(-1) (mean 162 cm(2) g(-1), accuracy and reproducibility 5%). This range is very similar to that of Domine et al. (2005) but our correlation of results with growth time and chemistry reveals the factors responsible for the wide range of SSA values. Longer growth time leads to higher SSA at low temperatures, so frost flowers are more likely to affect total surface area during colder periods. Chemical analysis was performed on frost flower melt and on local seawater and brine. We examined salinity and sulfate and bromide enrichment. The relationship between growth time and salinity varied spatially because of a freshwater plume from a nearby river and of tidal effects at the coast. Enrichment of certain ions in frost flowers, which affects their contribution to atmospheric chemistry, depends heavily on location, growth time, and temperature. No significant enrichment or depletion of bromide was detected. The low surface area index of frost flowers plus their lack of destruction in wind suggest their direct effect on sea salt mobilization and halogen chemistry may be less than previously thought, but their ability to salinate wind-blown snow may increase their indirect importance.
Authors: Obbard, Rachel W., Roscoe, Howard K., Wolff, Eric W., Atkinson, Helen M.