[1] 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.

[1] We describe in situ measurements of the compaction of Antarctic snow. At three different sites in Antarctica, the rate of compaction was measured hourly, over various depth intervals, for up to two years. These measurements show that compaction at each of the sites occurs through slow, viscous deformation of the snowpack, with no significant contribution from sudden collapse of weak layers. The measured rates of compaction at the coldest site exhibit a strong seasonality, consistent with a temperature-dependent sintering mechanism having activation energy of 70 kJ mol −1 . At the two warmer sites, activation energies of 80 and 120 kJ mol −1 provide slightly better agreement with the observations. Published models of snow compaction underestimate the temperature sensitivity. A good match to our observations is provided by a semi-empirical model, based on rate equations for lattice-diffusion (Nabarro-Herring) creep of material around pores, combined with normal grain growth. This model also provides a theoretical basis for a widely used empirical model of snow compaction. The rate coefficient for lattice-diffusion inferred from our measurements is considerably higher than published values, however, and other creep mechanisms cannot be ruled out.

Frost flowers grow on newly‐formed sea ice from a saturated water vapour layer. They provide a large effective surface area and a reservoir of sea salt ions in the liquid phase with triple the ion concentration of sea water. Recently, frost flowers have been recognised as the dominant source of sea salt aerosol in the Antarctic, and it has been speculated that they could be involved in processes causing severe tropospheric ozone depletion events during the polar sunrise. These events can be explained by heterogeneous autocatalytic reactions taking place on salt‐laden ice surfaces which exponentially increase the reactive gas phase bromine (“bromine explosion”). We analyzed tropospheric bromine monoxide (BrO) and the sea ice coverage both measured from satellite sensors. Our model based interpretation shows that young ice regions potentially covered with frost flowers seem to be the source of bromine found in bromine explosion events.