Distributed and year-long observations of ice-ocean drag across a range of ice morphologies in the Beaufort Sea

Abstract:

While many advances have been made over the years, there are still fundamental gaps in our knowledge of the role of sea ice in mediating momentum transfer in the atmosphere-ice-ocean system in the Arctic. Realistic parameterizations of ice-ocean stress have shown that our treatment of the stress can have first-order impacts on long term trends of ocean forcing. Despite this potential importance for changes in the coupled ice-ocean system, it is not clear from observations if such trends are occurring, and we have so far been unable to perform basic validation of new model schemes.

We present mooring observations made over an annual cycle in the Beaufort Sea which provide a new look at the relationship between ice morphology and ice-ocean momentum transfer. In particular, we examine the ice-ocean drag coefficient used in a quadratic-drag-law description of momentum transfer. Our study compares inferred drag coefficients based on a force-balance approach with predicted coefficients from the geometry-based parameterization scheme implemented in a sea ice model. These results are useful for model validation, and also provide insight into the drivers underlying variation of the ice-ocean drag coefficient. Observed seasonality in ice-ocean coupling is strongly tied to the growth and melt of ice keels. The presence of ice keels increases the drag coefficients in both the observations and the modeling scheme, but challenges remain in relating ice keel geometries to bulk model parameters. Finally, a comparison across different seasonal ice conditions provides insight into potential future changes in the new Arctic, in which ice keels may be less common.