A new view of the underside of Arctic sea ice

The Autosub‐II autonomous underwater vehicle (AUV), operating off NE Greenland in August 2004, obtained the first successful swath sonar measurements under sea ice, showing in unprecedented detail the three‐dimensional nature of the under‐ice surface. The vehicle, operated from RRS James Clark Ross , obtained more than 450 track‐km of under‐ice multibeam data. We show imagery from first‐ and multiyear ice, including young ridges, old hummocks and undeformed melting ice. In addition, we show how the combination of other on‐board sensors enabled the vehicle to obtain detailed information about seabed topography, water structure and current fields in an exploratory mode within a region which is seldom visited because of difficult year‐round ice conditions. This included identification of a new current regime in the Norske Trough.