Very thick and heavily deformed Antarctic sea ice captured in 3-D by autonomous underwater vehicle

Sea-ice thickness is a fundamental component of the polar climate system and there is an urgent need to advance our capability to monitor it from space and to model its response and feedback to climate change. Whereas previous in situ observations in support of these efforts have been restricted to point measurements, a new generation of autonomous underwater vehicles (AUV) are delivering unique 3-D floe-scale maps of sea ice draft. Here we present sea ice draft observations from ten floes (up to 400 m2) during two recent AUV expeditions to the near-coastal regions of Weddell/Bellingshausen and Wilkes Land sectors in early spring. These data provide the first complete statistical characterisation of sea ice draft morphology, providing new insights into ecosystem habitats and the role of deformation processes in controlling total sea ice volume. We find mean drafts ranging from 1.4 m to 5.5 m, with maximum drafts up to 17 m and drafts >5 m accounting for 10–30% of the mean, these are the thickest observations of Antarctic sea ice to date. Similarly ‘thick’ ice is being reported from new remote sensing products in areas outside of these near-coastal regions, prompting the question: ‘Are we underestimating Antarctic sea ice thickness?’.