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The part of a pressure ridge that extends below the water’s surface. Reaching up to 50 metres below the surface, keels extend farther than the surrounding sea ice.

A brittle, shiny crust of ice that forms on a calm surface by direct freezing or from grease ice, usually in water with low salinity. The crust has a thickness of up to ca. 5 cm and can be easily brok

The ocean is described as ice-free in the absence of sea ice. The entire Arctic Ocean is considered to be ice-free when there are less than one million square kilometres of sea ice. When this is the c

Refers to the dynamic motion of sea ice in one main direction. In the Arctic, this chiefly involves major drift systems. In the Beaufort Gyre off the north coast of Alaska, the ice circulates clockwis

Sea-ice thickness is a central parameter in sea-ice observation. Knowing the thickness is important so that, with the aid of the sea-ice extent, the total sea-ice volume can be calculated. In water, s

A collection of spongy white ice clumps measuring a few centimetres wide. These clumps usually form from grease ice and occasionally from pieces of anchor ice rising to the surface of the water.

Ice cores are important climate archives, allowing information to be gleaned from melted water samples (isotope hydrology), the ions and dust particles they contain, and from pockets of trapped air (p

Icebergs can take a variety of forms and extend more than 5 m above the water’s surface (freebord). Formed when large pieces of ice shelves or glaciers break away or calve and land in the water. Icebe