Observation and modeling of wave-ice interactions in the MIZ: the relative importance of turbulent processes compared to other attenuation mechanisms

Luc Barast1, Peter Sutherland1, Dany Dumont2 and Jeremy Baudry3, (1)IFREMER, Univ. Brest, CNRS, IRD, IUEM, Laboratoire d’Océanographie Physique et Spatiale (LOPS), Brest, France, (2)Université du Québec à Rimouski (UQAR), Institut des sciences de la mer de Rimouski (ISMER), Rimouski, QC, Canada, (3)Université du Québec à Rimouski (UQAR), Institut des sciences de la mer de Rimouski, Rimouski, QC, Canada
Interactions between surface waves and sea ice in marginal ice zones (MIZ) have been studied for more than half a century, but we still lack quantitative descriptions of the underlying physical processes in many cases. Near-surface turbulence due to small-scale wave-ice interactions is believed to be important in the wave energy balance. To estimate the relative importance of each phenomenon, we study wave attenuation in sea ice in a natural laboratory in the St. Lawrence Estuary through direct measurements and modeling. During field experiments, wave attenuation is estimated using an array of wave buoys deployed on the ice, and water column turbulence under the ice is measured using a downwards-looking pulse-coherent acoustic Doppler profiler. We are able to observe wave energy attenuation across the MIZ over three orders of magnitude, and find wave energy to decrease exponentially as a function of distance into the ice. Turbulent kinetic energy (TKE) dissipation is calculated using the structure function method, and the fraction of wave attenuation directly attributable to TKE dissipation under the ice is estimated. To close the wave energy budget in the study area, we use the WAVEWATCH III® (WW3) wave-modeling framework to model wave attenuation in sea-ice. The domain is separated into two regions: the first part, covering the experiment site, is modeled at high resolution; the second part is wider and coarser, and is used to generate the wave field boundary conditions. Scattering, ice flexure and break-up, as well as TKE dissipation are implemented in WW3 source terms to estimate the relative impact of each phenomenon in wave attenuation. The implications of these results, as well as future planned work on this subject, will be discussed.