Kausijäätä

Kausijäätä, often translated as seasonal ice, refers to ice that forms on bodies of water, such as lakes, rivers, and the sea, and melts away within a single year. This is in contrast to multi-year ice, which can persist for more than one annual melt season. The formation and thickness of kausijäätä are primarily influenced by the duration and intensity of sub-zero temperatures during winter.

In freshwater environments, kausijäätä typically forms when the water temperature drops below freezing. The process begins with frazil ice crystals, which can then aggregate to form larger ice sheets. The extent of ice cover and its thickness depend on factors like air temperature, wind, snow cover, and the depth and salinity of the water. In saline environments, such as oceans, the presence of salt lowers the freezing point of water, meaning colder temperatures are required for ice formation. Seawater ice, or kausijäätä on the sea, also tends to be thinner and more fragile than freshwater ice.

The presence and characteristics of kausijäätä have significant implications for ecosystems and human activities. For aquatic life, it can alter oxygen levels and light penetration. For human activities, it affects transportation, fishing, and recreation. The timing of ice formation and melt, as well as the ice's thickness, are important indicators of climate change, with warmer winters leading to later freeze-ups and earlier melts, and consequently, thinner and less extensive seasonal ice cover.