Ice roughness and momentum transfer in the Arctic marginal ice zone

The interplay between sea ice concentration, sea ice roughness, ocean stratification, and momentum transfer to the ice and ocean is subject to seasonal and decadal variations that are crucial to understanding the present and future air-ice-ocean system in the Arctic. In this study, continuous observations were taken in the Canada Basin from March through December 2014 of wind, ice, and ocean properties from four clusters of drifting instrument systems that were complemented by remote sensing imagery about the clusters as well as drill-hole and NASA operation IceBridge overflights in March. Instruments were embedded within a first-year-ice/multi-year-ice conglomerate with similar thickness and percentage of first-year ice. However, directly estimated ice-ocean drag coefficients varied spatially by a factor of three with rougher ice associated with smaller multi-year ice floe sizes embedded within the first-year-ice/multi-year-ice conglomerate. Temporal differences in the ice-ocean drag coefficient of 20-30% were observed prior to the mixed layer shoaling in summer, and were associated with ice concentrations falling below 100%. The ice-ocean drag coefficient parameterization was found to be invalid in September with low ice concentrations and small ice floe sizes. Maximum momentum transfer to the ice occurred for moderate ice concentrations, and transfer to the ocean for the lowest ice concentrations and shallowest mixed layer. Overall, ice topography, ice concentration, and the shallow summer mixed layer all influenced the transfer of momentum within the air-ice-ocean system. The observed changes in momentum transfer show that care must be taken to determine appropriate parameterizations of momentum transfer, and imply that ice and ocean velocity in the future Arctic system will become increasingly seasonal.