The effects of ice formation on wave-driven upper-ocean turbulence and air-sea exchanges.

Surface waves and wave-driven turbulence are primary mechanisms controlling air-sea exchanges over the majority of the world’s oceans. Historically, this was less true in the Arctic due to extensive ice cover, but that ice cover has been decreasing both spatially and temporally since the beginning of satellite records. As a result, open water dynamics, notably surface waves, are becoming increasingly important in the Arctic basin. Waves and wave-driven turbulence are known to inhibit ice skin-over, modifying air-sea energy, momentum, and mass transfer. A key aspect of this modification is the creation of frazil ice, small ice crystals suspended in water, that allow ice to form without creating a physical barrier between the atmosphere and the ocean. The presence of frazil ice, even in relatively low concentrations, is known to attenuate small waves, resulting in smooth “oily”-looking patches at the sea surface. This smoothing is expected to decrease wind input to the wave field. In this presentation, results from ongoing in situ measurements and airborne remote sensing campaigns, designed to study the evolution of the surface wave field and wave-driven turbulence in the presence of frazil ice formation, will be analyzed. Observed high wave growth rates suggest that frazil either suppresses wave attenuation or increases wind input to the wave field. These two processes have opposite implications for the energetic structure of the upper ocean, and will be explored. Specific foci will be on the effects of frazil on wave-modulated air-sea fluxes, and on the development of large coherent structures, such as Langmuir circulations, which are capable of vertically mixing the upper ocean.