Frost flower

Frost flowers are branched or dendritic ice crystals that develop on newly formed, thin sea ice when the ice surface is warmer and moister than the air above it. Water vapour supplied by the brine-wetted surface can supersaturate the near-surface air and crystallize on the ice. Calm conditions help this local environment persist; the structures are fragile and usually short-lived. They are distinct from ordinary frost in that their growth occurs on young sea ice and can involve brine from the ice surface.

As they grow, frost flowers can wick up saline liquid from the brine layer, making them salt-rich compared with ordinary fresh snow or frost. Their salt composition is not simply a miniature copy of seawater: salt precipitation and other processes during sea-ice formation can fractionate ions. Field sampling in northwestern Greenland found enrichment of several sea-salt components in frost flowers and brine, while aerosol concentrations increased during strong winds and blowing-snow conditions. This indicates a possible route for sea-ice surface salts to enter the air, but the magnitude and conditions of emissions depend on local processes.

The brine channels and salts in frost flowers also create a temporary habitat for microorganisms. A study of winter frost flowers from the Barents Sea found distinct bacterial and archaeal community signals in the samples, including abundant SAR11-related sequences, and evidence consistent with active nitrogen and sulfur cycling. Such findings describe particular samples and do not mean all frost flowers have identical communities or biological activity.

Researchers study frost flowers because the crystals sit at the ocean–ice–atmosphere boundary, where heat, moisture, salts and gases are exchanged. Their high surface area and saline chemistry may influence polar aerosol and halogen processes, though details remain an active area of research. Salt originating from sea ice and frost flowers can also complicate interpretations of coastal ice-core chemistry: a strong sodium signal need not arise only from open-water spray. Frost flowers are therefore a relevant, but not exclusive, process to consider when interpreting polar observations.