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In recent years, dynamical seasonal forecast systems have started to incorporate interactive sea ice components, allowing for sea ice forecasts on seasonal (1-12 month) timescales. Previous investigations on the forecast skill in such dynamical forecast systems have mainly focused on area-integrated sea ice quantities, which are of little use to end-users. Here we assess the skill in predictions of ice-free and freeze-up dates - variables that are highly relevant to shipping - in a set of hindcasts performed with the Canadian Seasonal to Interannual Prediction System (CanSIPS).
We find statistically significant skill for both ice-free and freeze-up dates in large parts of the Arctic, including Hudson's Bay, Baffin Bay/Labrador Sea and the Barents, Kara and Chukchi Seas. Skill is particularly large for freeze-up dates with significant skill at lead times up to 6-12 months. While most of the skill of ice-free dates stems from persistence of sea ice concentration anomalies, the longer-lead time skill for freeze-up dates is due to a reemergence mechanism involving ocean temperatures. These results highlight the potential for dynamical forecast systems to provide valuable forecasts of socio-economically relevant sea ice variables on seasonal timescales.