Polar oceans are distinct from other oceanic environments in a number of ways, but the presence of sea ice is a major habitat difference. Sea ice affects polar microbial communities by limiting light penetration into the upper ocean and by providing a unique sea-surface habitat (Figures 1 and 2). Sea ice serves as a support matrix for a diverse and dynamic assemblage of microbes, including phytoplankton and prokaryotes, often referred to as the sea-ice microbial community, or SIMCO. Growth of ice-associated microalgae can lead to extreme carbon enrichment in the ice, fueling microbial production and providing a food supply for herbivorous metazoa. Brine exclusion during the formation of sea ice, coupled with summer melting, contributes to significant and persistent water-column stratification. This is especially the case in the Arctic Ocean where permanent ice cover constrains wind mixing and the land-locked geography of the basin restricts exchange with lower-latitude waters. Other characteristics of polar oceans, such as low temperature and intense seasonal variation in primary production and carbon flux, are often more extreme than in other oceanic habitats.

Hollibaugh, J.T., C. Lovejoy, and A.E. Murray. 2007. Microbiology in polar oceans. Oceanography 20(2):140–145, https://doi.org/10.5670/oceanog.2007.59.