An extreme Antarctic event; 2025 was record low seasonal sea ice and record high iceberg scouring

A profound change in the polar oceans has been the drastic loss of seasonal sea ice. Such marine ice has been recorded daily at Ryder Bay, Adelaide Island (Antarctica) since 1985, and iceberg impacts on the seabed monitored by SCUBA divers annually since 2002. These showed an extreme event of low seasonal sea ice duration in 2007/8 (of just 9 days). However, in 2025, for the first time, zero days seasonal sea ice duration was recorded.Coincident with the 2007/8 extreme low seasonal sea ice event,an extreme high of iceberg scouring of the seabed was also re-corded (53% of seabed at 5–25 m hit). As two decades before,the 2025 extreme low in seasonal sea ice was coincident with a record high of seabed iceberg impact; 68.4% of the seabed at 5–25 m depth was scoured. This was the most extreme of both marine measures and the biggest outlier recorded in the significant (r2 = 57, F = 31.5, p < 0.001) relationship between seasonal sea ice duration versus seabed iceberg scour (anomalies, see Figure 1a). Assessment of iceberg scouring has occurred annually since 2002 (Barnes et al. 2024), but as there are decades more seasonal sea ice duration than ice-scour data, we hind cast the relationship to generate likely past seasonal ice versus ice-scouring data span (grey circles in Figure 1a).