Ice Breakup Controls Dissipation of Wind Waves Across Southern Ocean Sea Ice

• Published in: Geophysical research letters 2020-07, Vol.47 (13), p.n/a
• Main Authors: Ardhuin, Fabrice, Otero, Mark, Merrifield, Sophia, Grouazel, Antoine, Terrill, Eric
• Format: Article
• Language: English
• Subjects: Atmospheric and Oceanic Physics; Damping; Deformation; Deformation mechanisms; Flexing; Fluxes; Gravitational waves; Gravity waves; Ice; Ice breakup; Ice cover; Ice floes; Ice properties; Ocean mixing; Ocean surface; ocean waves; Oceans; Pack ice; Physics; SAR; Scattering; Sea ice; Sea ice dynamics; Sea ice properties; Surface gravity waves; Upper ocean; Wave action; Wave attenuation; Wave direction; Wave height; Wave measurement; Wave reflection; Wind; Wind waves
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL087699

Sea ice inhibits the development of wind‐generated surface gravity waves which are the dominant factor in upper ocean mixing and air‐sea fluxes. In turn, sea ice properties are modified by wave action. Understanding the interaction of ice and waves is important for characterizing both air‐sea interactions and sea ice dynamics. Current leading theory attributes wave attenuation primarily to scattering by ice floes. Here we use new in situ wave measurements to show that attenuation is dominated by dissipation with negligible effect by scattering. Time series of wave height in ice exhibit an “on/off” behavior that is consistent with switching between two states of sea ice: a relatively unbroken state associated with strong damping (off), possibly caused by ice flexure, and very weak attenuation (on) across sea ice that has been broken up by wave action. Plain Language Summary Waves created by wind at the ocean surface are strongly attenuated when they travel across ice‐covered regions. Until now, this effect was thought to be the result of reflection of waves off pieces of ice. Using new measurements of wave directions, we show that waves do not come from a broad range of directions, and scattering must be weak. Instead, we find that attenuation is highly variable and related to the size of ice floes. We hypothesize that attenuation may be caused by cyclic deformation of the ice. When the waves are large enough to break the ice up, this deformation stops, and the attenuation is much less. This finding is important for forecasting waves in ice‐infested waters as well as predicting seasonal sea ice extent. Key Points Wind waves attenuate across the Antarctic sea ice with a narrow directional distribution Scattering of waves by ice floes plays a negligible role in wave attenuation Observed wave attenuation is consistent with ice breakup modulating the dissipation strength