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Multi-year ice

Ice which has survived one or more summer seasons of partial melt is called ‘multi-year ice’ (more than half the ice in the Arctic falls into this category). Growth continues from year to year until the ice thickness reaches a maximum of about 3m, at which point summer melt matches winter growth and the thickness of the ice oscillates through an annual cycle. This old, multi-year ice is much fresher than first-year ice; it has a lower conductivity and a rougher surface. The low salinity of multi-year ice makes it much stronger than first-year ice.

Multi-year ice pushed up to release some of the pressure on the Arctic ice pack

Snow

Snow is generally white because it reflects the full spectrum of light, which we see as white. However, snow can also be red, green, blue or black. This occurs because of the presence of beautifully coloured (if rare) fungi, as well as bacteria, mosses and algae. These can survive in both the Arctic and Antarctic, especially in humid areas: evidence of life in a habitat where it is least expected.