Ice attached to the beds of streams, lakes, and shallow seas, irrespective of its nature of formation. On clear, cold nights in relatively still water, anchor ice may form directly on submerged objects. It also develops in supercooled water if turbulence is sufficient to maintain uniform temperature at all depths, in which case a spongy mass of frazil accumulates on objects exposed to rapid flow, and later deposition fills in the pores and creates solid ice. When the water temperature increases to above 0°C, the ice rises to the surface, often carrying with it the object on which it had accumulated. Sometimes anchor ice is erroneously called ground ice, a term which should be reserved for bodies of more or less clear ice in frozen ground.
Anchor Ice is described by the World Meteorological Organization as "submerged ice attached or anchored to the bottom, irrespective of the nature of its formation." Anchor ice is most commonly observed in fast-flowing rivers during periods of extreme cold, at the mouths of rivers flowing into very cold seawater, in the shallow sub or intertidal during or after storms when the air temperature is below the freezing point of the water, and in the subtidal in the Antarctic along ice shelves or near floating glacier tongues.
