Underneath an Antarctic ice shelf

Around much of Antarctica, the ice sheet extends out into the Southern Ocean to form floating ice shelves. Such shelves can be more than 1500 m thick and can have areas of several hundred thousand square kilometers. Interactions between the shelves and the water beneath them can have globally significant effects, since melted ice can cool and freshen the deep ocean waters. To learn more about the largely unexplored water cavities underneath ice shelves, a British team sent an autonomous underwater vehicle on a 53-km roundtrip excursion underneath the Fimbul Ice Shelf along the Princess Martha Coast. The researchers’ analysis of the data they collected on the topography of the shelf base, the local current, and the water’s temperature and salinity reveals a complex environment. Among their findings is that the base of the ice shelf—long assumed to be smooth, based on the shelf’s surface features—shows regions of pronounced roughness, as seen in the figure. The team also concluded that the cavity under the shelf is exposed periodically to warmer, saltier water that could produce significant melting of the shelf’s base. Team leader Keith Nicholls expects that similar missions will be undertaken to further explore the cavities beneath Antarctic ice shelves and to better understand the role the cavities play in Earth’s climate system. (K. W. Nicholls et al., Geophys. Res. Lett. 33 , L08612, 2006 .)