Thinning of Arctic sea ice observed in Fram Strait: 1990-2011

[1] Time series (1990–2011) of sea ice thickness observed by moored sonars in the Transpolar Drift in Fram Strait are examined. Contrasting the post-2007 years against the 1990s, three remarkable changes in the monthly ice thickness distributions are highlighted: (1) The thickness of old level ice (modal thickness) is reduced by 32%, (2) the old ice modal peak width is reduced by 25%, and (3) the fraction of (ridged) ice thicker than 5 m is reduced by 50%. The combined effect on the mean ice thickness is a reduction from an annual average of 3.0 m during the 1990s to 2.2 m during 2008–2011. Most of the thinning took place after 2005–2006. While the old ice modal thickness and peak width show signs of recovery after 2008, the decreasing trend in fraction of ridged ice and mean ice thickness persists until the end of the record in 2011. The ice observed in Fram Strait carries an integrated signal of Arctic change due to the advection of ice from many sites in the Arctic. Based on concurrence in timing, we conclude that much of the thinning quantified here is reflecting recent change in the age composition of the Arctic ice cover toward younger ice. The old level ice remains thin, and as such the ice cover remains preconditioned for new summers of very low sea ice extent.