Direct Observations of Wave-Sea Ice Interactions in the Antarctic Marginal Ice Zone

Wave energy propagating into the Antarctic marginal ice zone effects the quality and extent of the sea ice, and wave propagation is therefore an important factor for understanding and predicting changes in sea ice cover. Wave-sea ice interactions are notoriously hard to model and in situ observations of wave activity in the Antarctic marginal ice zone are scarce, due to the extreme conditions of the region. Here, we provide new in situ data from two drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys deployed in the Weddell Sea in the austral winter and spring of 2019. The buoy location ranges from open water to more than 200 km into the sea ice. We estimate the attenuation of swell with wave periods 8-18 s, and find an attenuation coefficient alpha = 4 center dot 10-6 to 7 center dot 10-5 m-1 in spring, and approximately five-fold larger in winter. The attenuation coefficients show a power law frequency dependence, with power coefficient close to literature. The in situ data also shows a change in wave direction, where wave direction tends to be more perpendicular to the ice edge in sea ice compared to open water. A possible explanation for this might be a change in the dispersion relation caused by sea ice. These observations can help shed further light on the influence of sea ice on waves propagating into marginal ice zones, aiding development of coupled wave-sea ice models. Changes in the sea ice extent around Antarctica affects the global climate, and it is therefore important to accurately represent sea ice in climate models. One feature that is generally missing in climate models is the interaction between ocean waves and sea ice. Ocean waves change the sea ice, for example, by breaking up ice floes into smaller ones. At the same time, the sea ice reduces the strength of the waves so that the wave height decreases and eventually disappears far into the sea ice. How far into the sea ice waves reach depends both on the size of the waves and on the sea ice, and can be very different depending on for example, ice thickness, size of floes and age. In order to better represent the wave-sea ice interactions in climate models, simple but accurate models of how fast sea ice reduces the strength of waves is needed. Using wave buoys, we measured the wave activity in the Antarctic sea ice during two expeditions in 2019. We found a notable difference between spring and winter, where the waves were reduced much faster in winter than in spring. This can help to improve predictions of sea ice cover. SWIFT buoy data show that frequency dependence of wave attenuation in Antarctic sea ice follows a power lawBoth wave attenuation and the frequency dependence of attenuation were stronger in austral winter than in springObservations suggest a change in wave direction in sea ice compared to open water

Automated summary

Wave energy has an impact on the quality and extent of sea ice in the Antarctic marginal ice zone, and understanding wave propagation is crucial for predicting changes in sea ice cover. In this study, new in situ data collected from drifting buoys in the Weddell Sea reveal season-dependent attenuation of swell and a change in wave direction in sea ice compared to open water. These observations provide valuable insights into wave-sea ice interactions and can aid the development of accurate models for representing the influence of sea ice on wave propagation.