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

Abstract

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.

Spurious Rollover of Wave Attenuation Rates in Sea Ice Caused by Noise in Field Measurements

“…One such example is Ardhuin et al. (2020), who use GPS velocities as the raw data and thus likely have noise energy with an r = −2 shape.…”

Cyclic strengthening of lake ice

“…The propagation of ocean swells into a floating ice cover has led, in at least a few recorded instances, to the sudden break-up of the ice cover into smaller ice floes (Asplin and others, 2012; Collins and others, 2015; Kohout and others, 2016). In these works, the sudden break-up of first-year and multi-year ice was observed due to wave action which is discussed in Ardhuin and others (2020). These observations raise a question about the effect of cyclic loading on the mechanical behavior of ice.…”

The flexural strength of bonded ice

“…Although the experiments were performed under flexural loading, they provide unique data on the tensile strength of the freeze bonds. Under the loading conditions, the flexural strength of ice is governed by tensile strength (assuming the material is linear-elastic and brittle), although measured strengths are greater by a factor of about 1.7 than strengths measured under pure tensile loading (Ashby and Jones, 2012). The reason is that in bending only a thin layer close to one surface of the sample (and thus a relatively small volume) carries the peak tensile stress, and it is less likely that this volume contains larger flaws, while in tension the entire sample carries the tensile stress, and it is more likely that it will contain larger flaws.…”