A laboratory study of frost flower growth on the surface of young sea ice

Abstract

Frost flowers are fragile ice crystals containing salt which grow to a height of 10–30 mm on the surface of young sea ice. Such flowers are observed all over the Arctic. The importance of the flowers and their accompanying slush layer is that they provide a rapid way to change the surface albedo and increase the surface roughness of young sea ice. This paper describes a laboratory technique for growing frost flowers and the physical processes which accompany the growth. The study was carried out in a saltwater tank located in a cold room. To grow frost flowers, we alternately cool the surface of the growing sea ice with a fan, then supply it with water vapor from a vaporizer. For these conditions and a room temperature of −22°C, the frost flowers begin to grow when the ice thickness reaches 5–8 mm. The flowers form at random locations on the ice and grow vertically to a height of 10–15 mm while spreading laterally from their original sites. Beneath the flowers, the surface is initially dry; then as the flowers spread laterally, a high‐salinity slush layer forms beneath them. This layer, which forms only under the flowers, grows to a thickness of 5 mm in 48 hours and has a characteristic lateral scale of 100–200 mm. The salinity of the slush layer is about 80 psu, compared with a frost flower salinity of 100 psu. Within 24 hours of their appearance, the flowers grow to cover 75–90% of the surface. A surface water budget for the flowers and slush layer shows that most of the water in the flowers and slush layer comes from the ice interior, not from the vaporizer. This implies that an external vapor source may be important in determining the initial growth of the flowers but not in their subsequent development.