grease ice

Because of the salt content, seawater begins to freeze at about –1.8o C, a lower temperature than for fresh water. Ice formation begins at the surface with the formation of small needle-like ice crystals called frazil, which accumulate and make the water appear slushy and cloudy; this stage is referred to as grease ice (Figure 14.1.2 A). In calmer water these small crystals can freeze together into a thin surface layer called nilas, which can reach a thickness of up to 10 cm (Figure 14.1.2 B).

14.1 Types of Ice 2025