It is often thicker than 3 meters. As sea ice ages, it loses salt. Meltwater ponds forming on sea ice several years old may have water fresh enough to drink. First-year sea ice covers much of the Arctic and surrounding seas in winter. In summer, this ice melts, thins, and moves offshore.
Multiyear ice covers the central Arctic and eastern Greenland areas.
Winds and ocean currents keep most of the ice in constant motion. As a result, the ice is broken up into floes, with open water spaces, called leads, between the floes. The two main ice circulation systems are the clockwise Beaufort Gyre in the Amerasian Arctic, and the west-flowing Transpolar Drift Stream in the Eurasian Arctic. Much of the Arctic sea ice forms in winter in the marginal seas, especially in the wide Siberian shelf seas, such as the Kara and Laptev. A region of open water, called a polynya or a flaw lead, often exists between the fast-ice zone and the drift ice.