| Summary: | In our NSF-funded project InMotion: Influx of Momentum into the Arctic Ocean Changes Associated with Sea Ice Reduction we investigated how the observed thinning and retreat of the sea ice cover affects the amount of wind energy entering the Arctic Ocean. In the Arctic, wind is the dominant driver of sea ice and ocean motion. The momentum flux from the atmosphere into the ocean (a.k.a. ocean surface stress) generally depends the wind speed, the surface roughness, and sea ice conditions. Here, we provide Arctic-wide (49˚-90˚N) daily fields of ocean surface stress based on a simulation with the Pan-arctic Ice-Ocean Modeling and Assimilation System (PIOMAS) for the period 1979-2012. The simulation is forced by atmospheric reanalysis fields and constrained by assimilating satellite-observed sea ice edge position. Our analysis yielded two main results: (i) Over the 34-year period annual mean basin-wide ocean surface stress is increasing, which we link to the significant sea ice thickness decrease and related ice strength loss over the same period. (ii) Momentum flux into the ocean is greatest at an optimal ice concentration of 80-90%. This is because the overall surface roughness increases with increasing ice coverage as sea ice adds roughness but only to a point, the optimal ice concentration, where frictional losses due to high ice compactness reduce the momentum transfer. As summer Arctic sea ice coverage has been shrinking over the past years, our data show decreasing ocean surfaces stress for the summer months (July to September). More details are given in Martin et al. (2014).
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