Talk by Guy Williams, University of Tasmania

Institute of Marine and Antarctic Studies
Antarctic Climate and Ecosystems Cooperative Research Centre

Very thick and heavily deformed Antarctic sea ice mapped by autonomous underwater vehicle

Abstract
Sea ice is a fundamental component of the polar climate system and there is an urgent need to advance our ability to monitor its thickness (and hence volume) from space and to model its response 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 3D floe-scale maps of sea ice draft. Here we present such observations from ten floes (up to 400m2) surveyed during two recent AUV expeditions to the near-coastal regions of the Weddell/Bellingshausen Sea and Wilkes Land in early spring. We find the thickest observations of Antarctic sea ice to date, with mean drafts ranging from 1.4— 5.5 m, and maxima up to 17m and deformed ice contributing an average of 76% to the volume.  These data deliver a complete statistical characterisation of sea ice draft morphology, providing new insights into the role of deformation processes in controlling total Antarctic sea ice volume.  Similarly ‘thick’ ice is being reported from new remote sensing products in areas outside of these near-coastal regions, prompting the question: ‘Have we underestimated Antarctic sea ice thickness?’