Sea-ice concentration anomaly (color scale bar) with the annual cycle removed contoured as a Hovmöller diagram from 1979 through 2012 (x-axis). The green line connects dates of break-up start and suggests a quasi bi-annual oscillation. The linear fit (black line connecting black circles) to “early” break-up start dates (see text) has a correlation coefficient of −88. Red symbols mark the beginning and end of break-up. Blue symbols mark the beginning and end of freeze-up. Durations of freeze-up and break-up are marked by the vertical lines.