Impact of an isolated summer storm on sea ice and ocean conditions in the Canadian Basin

The Arctic Ocean has undergone a rapid decrease of sea ice extent for decades and studies have shown that the storm activity has increased in the Arctic. Regions that are seasonally ice-opened experience a greater forcing at the surface, which affects the upper-ocean through mixing, turbulence and air-sea interactions. Previous studies have shown the local and short term impacts of wind and waves on sea ice through negative or positive feedback mechanisms. For instance, increased air-sea flux during the freezing season can lead to a cooling of the upper-ocean and favor ice formation, while an increase in wind forcing can modify the vertical profile of the mixed layer, leading to melting or formation of ice. Given the potential of the mixed layer properties to be modified locally by an increased wind/wave forcing, we question whether this type of forcing could have a seasonal effect on the mixed layer and therefore on the sea ice.

We thus use a 1D coupled ocean-sea ice model (NEMO1D-SI³) to study, in the seasonal ice zone of the Beaufort Sea, the immediate change and the seasonal evolution of the mixed layer when forced by an idealized summer storm. The response of sea ice is also examined. We conduct the experiment for a range of storms varying in intensity, duration and date of forcing. Compared to a situation with no increased forcing, we first find that summer storms thicken the mixed layer through mixing which increases the upper-ocean heat content. In the fall, ice formation is consequently delayed for a maximum of 2 weeks compared to a situation with no increased forcing. Secondly, we show that storm-induced thick mixed layers isolate the sea ice from sub-surface warm waters, allowing for efficient ice growth. Ice is consequently thicker at the end of winter compared to a situation with no increased forcing (maximum difference of 10 cm). Thirdly, we find that these results are amplified for storms that happen earlier in summer and have a strong momentum input to the ocean. Our results suggest that localized storms could be a significant driver of the seasonal evolution of the mixed layer and the sea ice.