Sea ice formation depends on atmospheric conditions, but initially begins with frazil ice crystal formation (2-15cm x 2mm platelets or needles). These crystals clump together to form grease ice which has no solid structure.
In calm seas the ice will form flat sheets known as nilas ice, which are between 1 and 10cm thick (Figure 2) (Thomas et al. 2008).
In wind mixed conditions (the norm) the frazil ice forms in wave convergences as the crystals are driven by the wind and forms pancake ice that can be up to 3m in diameter; the pancake ice eventually rafts together to form a continuous sheet (Figure 2) (Thomas et al. 2008).
Pancake ice will increase in thickness with the addition of columnar ice crystals that are added in layers under the frazil ice; the ratio of frazil ice to columnar ice is greatest in more turbulent waters and can be up to 80% in Antarctic pack ice (Thomas et al. 2008).
There is a labyrinth of structures through the pack ice, demonstrating the dynamic nature of the sea ice environment; organisms must be able to withstand these rapid changes in habitat that most organisms would find extreme (Figure 3). These are semi-enclosed environments (other than the sea/ice interface) and hence nutrient cycling has to be efficient in order to prevent exhaustion of nutrients and sustain the high biomass present (Kattner et al. 2004).