Frost flowers

Frost flowers are intricate, often fern-like clusters of ice crystals observed on young, thin sea ice. They have also been reported on frozen freshwater lakes. Despite their name, they are physical ice formations, not plants. The structures are fragile and short-lived, so their abundance and characteristics can vary with local weather and ice conditions.

The formation of frost flowers involves transfers of heat and water vapour between an ice surface and the overlying air. The traditional explanations emphasized vapour condensation or liquid brine moving through porous sea ice. Laboratory experiments and modelling by Style and Worster demonstrated that frost flowers can also grow on solid, pure ice sublimating into a cold, unsaturated atmosphere. This finding shows that one simple formation pathway cannot be assumed for every observed frost flower; the local temperature and humidity regime matters.

On sea ice, frost flowers can carry a coating of brine and have been measured as much saltier than seawater. Their high salt content has made them relevant to research on sea-salt aerosols in polar air. Studies have also examined associations between frost-flower-covered ice and bromine monoxide, a reactive compound involved in polar atmospheric chemistry. These observations motivate investigation of the crystals as a possible influence on aerosol and chemical processes, but do not mean frost flowers alone determine ozone or climate outcomes.

Although they are made of ice, frost flowers can contain saline brine channels and associated organic material, nutrients, and microorganisms. A study of winter frost flowers from the Barents Sea found microbial communities dominated by members of the SAR11 group in both DNA and RNA analyses. The authors also reported signals consistent with active nitrogen- and sulfur-cycling microorganisms. These results describe the sampled environment and do not establish that all frost flowers have the same microbiome.

Frost flowers connect small-scale ice growth with broader questions about sea-ice properties, aerosols, atmospheric chemistry and polar microbial ecology. Their presence and composition may help researchers interpret environmental measurements, including salts preserved in ice cores. Because formation mechanisms and chemical effects depend on conditions, field observations, laboratory experiments and physical models are used together to assess their significance.