Does sea ice retreat reduce or increase the momentum flux into the Arctic Ocean?

Vast areas of the Arctic Ocean have changed from perennially to merely seasonally ice-covered. It may seem obvious that sea ice retreat enables greater momentum influx to the ocean, similar to heat and mass fluxes. Accordingly, observations show enhanced upper ocean shear and inertial internal wave formation in summer. However, the observations are still rather inconclusive as to what exactly happens in areas of reduced but non-negligible ice concentration. These areas in fact comprise a large fraction of the Arctic Ocean area. Recent findings based on observations and model simulations indicate that (1) sea ice damps ocean surface stress when very compact but (2) it acts as an amplifier when in free drift, due to its greater roughness. Also, (3) ice surface roughness changes seasonally with a maximum in summer, while (4) open water roughness is reduced by the presence of surprisingly low ice concentrations. How these factors affect the ocean surface momentum budget is our focus. Our results suggest that the Marginal Ice Zone (MIZ) is likely a place of enhanced momentum transfer. This is important because during recent summers, most of the Arctic Ocean featured MIZ-typical conditions. Further, the summer season has begun to expand into what used to be considered spring and fall months.