page_title: Sea ice microbial communities
section_title: Sea ice formation and physical properties
hierarchical_section_title: Sea ice microbial communities / Habitat / Sea ice matrix: chemical and physical properties / Sea ice formation and physical properties
caption_attribution_description: English: Frost flowers growing on young sea ice in the Arctic.
context_page_description: Sea Ice Microbial Communities refer to groups of microorganisms living within and at the interfaces of sea ice at the poles. The ice matrix they inhabit has strong vertical gradients of salinity, light, temperature and nutrients. Sea ice chemistry is most influenced by the salinity of the brine which affects the pH and the concentration of dissolved nutrients and gases. The brine formed during the melting sea ice creates pores and channels in the sea ice in which these microbes can live. As a result of these gradients and dynamic conditions, a higher abundance of microbes are found in the lower layer of the ice, although some are found in the middle and upper layers. Despite this extreme variability in environmental conditions, the taxonomical community composition tends to remain consistent throughout the year, until the ice melts.
  Much of the knowledge concerning the community diversity of the sea ice is known through genetic analyses and next-generation sequencing. In both the Arctic and Antarctic, Alphaproteobacteria, Gammaproteobacteria and Flavobacteriia are the common bacterial classes found.
context_section_description: The autumnal decrease in atmospheric temperatures in the Arctic and Antarctic leads to the formation of a surface layer of ice crystals called frazil ice. A mixture of salts, nutrients and dissolved organic matter (DOM) known as brine is expelled when frazil ice solidifies to form sea ice. Brine permeates through the ice cover and creates a network of channels and pores. This process forms an initial semisolid matrix of approximately 1 meter in thickness with strong temperature, salinity, light and nutrient gradients.
  Since thickening of the sea ice during winter months results in more salts being expelled from the frazil ice, atmospheric temperatures are strongly and negatively correlated to brine salinity. The sea ice-seawater interface temperature is maintained at the freezing point of seawater (~1.8 °C) while the sea ice-air interface reflects more the current atmospheric temperature. Brine salinity can increase to as much as 100 PSU when sea ice temperature reaches ~3 °C below the freezing point of seawater. Brine temperature typically ranges from -1.9 to -6.7 °C in the winter. Sea ice temperatures fluctuate in response to irradiance and atmospheric temperatures, but also change in response to the volume of snowfall. Accumulating snow on the ice cover combined with harsh atmospheric conditions can lead to the formation of a snowpack layer that absorbs UV radiations and provides insulation to the bottom ice layer. The fraction of irradiance reaching the sea ice matrix is thus also controlled by the amount of snowfall and varies from <0.01% to 5% depending on the thickness and density of the snowpack.
  The surface of sea ice also allows the formation of frost flowers, which have their own unique microbial communities.
caption: Frost flowers growing on sea ice in the Arctic.
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