| Summary: | Recent changes in sea ice type and periodicity are increasing both the spatial and temporal range over which frost flowers can occur, yet their significance to overall ocean-sea ice-atmosphere (OSA) exchange processes remains poorly understood. The climate forcing of the ocean surface, at our winter study site in a polynya-fiord system in NE Greenland, showed that frost flowers form on thin ice when open water becomes available to a cold atmosphere and surface wind conditions are low, allowing for supersaturation of the near-surface boundary layer. The formation of new ice and a frost flower-covered ice surface dramatically changed the photosynthetically available radiation (PAR) and thermal environment of this young OSA interface. A brine skim formed very early, followed almost immediately by clusters of frost flowers. The frost flowers themselves were about 5°C colder than the brine surface, with an approximately linear temperature gradient from the base to the upper tip of the frost flowers. Measured change in 18O values of frost flower vertical dimension and over time indicated that the flowers originated primarily from the surface brine skim, consistent with the model of Style and Worster. Ikaite crystals were observed to form within 1 hour in both frost flowers and thin ice in the artificially opened pond. Average ikaite concentrations in frost flowers were 1013 µmol kg-1 and in the surface slush layer, 1061 µmol kg-1. Chamber flux measurements confirmed an efflux of CO2 at the brine-wetted sea ice surface, in line with expectations of the brine chemistry across this OSA interface. The microbial measurements helped to illuminate the physics of the frost flower formation and how this unique habitat may shape the microbial community. In general, the brinier the frost flower (brine skim or surface slush layer), the higher its concentration of bacteria. Analyses of bacterial densities and dominant members of the community both indicated that a selective process occurs at this OSA interface and also confirmed the general pattern of primary oceanic versus negligible atmospheric deposition. [Submitted to JGR Atmospherest by D. G. Barber, J. K. Ehn1, M. Pucko, S. Rysgaard, J. W. Deming, J. S. Bowman, T. Papakyriakou, R Galley, and D. Sogaard. 2014]
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