Climatology of the 1979–2007 sea-ice concentration for the combined Chukchi/Beaufort coastal region is shown by the solid black line from May through December. The computed start date for freeze-up and break-up are both marked by solid green lines. The end dates for freeze-up and break-up are marked by solid red lines. Seasonal durations are shown by dark red arrows from “break-up start to freeze-up end” and “break-up end to freeze-up start”. Dates from Markus et al. (2009) for early melt onset and early freeze onset from their Chukchi/Beaufort Seas region are shown by the dotted magenta lines, and melt onset and freeze onset by dotted blue lines. Their “inner” and “outer” seasonal durations are marked by blue arrows.