Seasonal and interannual variability in Fram Strait sea ice ridge statistics during 2006-2019 from the data of Ice Profiling Sonars.

Fram Strait is the major gateway connecting the Arctic Ocean and North Atlantic Ocean, where nearly 90% of the sea ice export from the Arctic Ocean takes place. The transported ice represents a broad range of thicknesses and types and exhibits an integrated history of thermodynamic growth/decay and deformation on its way across the Arctic. The present study utilizes high resolution sea ice draft data from ice profiling sonars (IPS) from the four moorings of the Fram Strait Outflow Observatory at 78.85 N and 3W to 6.5 W over the period 2006-2019. The analysis focuses on the identification of deformed ice/sea ice ridges and analysis of the seasonal and interannual variability in the number, geometry and shape of ridges. The study demonstrates a pronounced seasonal cycle in the number, probability density function of keel drafts and shape of ridges traversing FS with a maximum ridge count in March-April and minimum in August-September. An overall decline found in the annual ridge number is accompanied by a general shallowing of ridge keels. The observed changes are most pronounced in the easternmost mooring at 3W, and linked to continuing sea ice retreat in the FS over the studied period. The results are further compared with previous studies on ridge statistics from the area and placed in the context of the observed changes in Arctic sea ice over the last two decades.