Frost flowers – implications for tropospheric chemistry and ice core interpretation

This paper discusses the chemical composition of frost flowers and their accompanying slush layers and the evidence for their role as a salt source in processes important to atmospheric chemistry and ice core interpretation. Analysis of Antarctic frost flowers shows that they are highly saline and fractionated in sea-salt ions, with sulfate being depleted strongly relative to sodium. Because frost flowers give a bright return on satellite scatterometer images, the times and places of their formation can be identified. When winds blow towards an aerosol sampling station from areas identified by the scatterometer as covered with flowers, the collected aerosol is also depleted in sulfate. Because the flowers have a large salinity, bromide concentrations are elevated in frost flowers relative to seawater. With their high surface area, it is possible that bromine is released to the atmosphere from frost flowers, with consequent implications for tropospheric ozone depletion. The finding that quantities of fractionated sea salt are available at the sea–ice interface in the winter months and may be transported inland as aerosol also has implications for the interpretation of ice core records. Analysis of one near-coastal core shows that the majority of the sodium comes from a fractionated source rather than from open water. Hitherto, strong sea-salt signals in ice cores have been attributed to increased open water and more efficient transport inland, perhaps due to stormier weather. At least in coastal regions, however, these signals may be related instead to the increased formation of sea ice and frost flowers.

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