The thinning of Arctic sea ice

During the first half of the 20th century, the Arctic sea-ice cover was thought to be in a near-steady seasonal cycle, reaching an area of roughly 15millionkm2 each March and retreating to 7millionkm2 each September. Ice thick enough to survive the melt season, termed perennial or multiyear ice (MYI), adds to the ice cover. A large fraction of MYI typically remained in the Arctic Basin for several years and grew to an equilibrium thickness of about 3.5 m - melting half a meter at the surface from June through August and growing by about half a meter at the bottom from October through March. In the late 1970s, MYI occupied more than two-thirds of the surface area of the Arctic Basin, with first-year ice (FYI) covering the remaining one-third. FYI is the thinner, seasonal ice that fills cracks in the ice cover and grows on the open ocean with the southward advance of the ice edge at the end of each summer. © 2011 American Institute of Physics.