Wave energy propagating into the Antarctic marginal ice zone affects 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. Sea ice is 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 in 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  α = 4 · 10 to 7 · 10 m in spring, and approximately five-fold larger in winter. The attenuation coefficients show a power law frequency dependence, with power coefficient 3.3 in spring and 4 in winter. The in-situ data also shows a change in wave direction, where wave direction tends to be more perpendicular to the ice edge farther into the sea ice. A possible explanation for this might be a change in the dispersion relation caused by changing sea ice composition. These observations can help shed further light on the influence of sea ice on waves propagating into the Marginal Ice Zone, aiding development of coupled wave-sea ice models.

<p>Antarctic sea ice has an important impact on the global climate, affecting albedo, global circulation and heat- and gas exchange between the ocean and the atmosphere. Wave energy propagating into the sea ice can affect the quality and extent of the sea ice, and wave attenuation in sea ice is therefore an important factor for understanding changes in the ice cover. Yet in-situ observations of wave activity in the Antarctic marginal ice zone are scarce, due to the extreme conditions of the region.</p><p>We estimate attenuation of significant wave height in the Antarctic marginal ice zone using in-situ data from two drifting Surface Wave Instrument Float with Tracking (SWIFT) buoys deployed in the Southern Ocean for two days in the Antarctic winter and two weeks in the Antarctic spring. The buoy location ranges from open water to more than 200 km into the sea ice. The extent of the sea ice coverage is determined using satellite sea ice concentration from AMSR-E and SAR imagery from Sentinel-1. Waves were observed more than 150 km into the sea ice, and in higher than 85 % sea ice concentration. Significant wave height and wave direction measured by the buoys in open water agreed well with ERA5 reanalysis data. We find that the significant wave height decayed exponentially in sea ice, which is consistent with physical experiments and other field observations in the Arctic and Antarctic marginal ice zones. </p>