Mapping the seabed beneath Larsen C Ice Shelf

The shape of the seabedbeneath Larsen C Ice Shelfturns out to be much more rugged than was thought previously. New topographic mapping of the ice shelfhas changed our picture of the seafloor beneath it; some deep troughs in the seabedare deeper than expected, others are shallower, and some of the seafloor ridges are higher, even rising high enough to touch the base of the floating icecover above. This new mapping helps oceanographers understand the flow of water underneath the iceand its resulting contribution to the world’s oceans. The shape of the bed topography controls the circulation of seawater under the ice shelf, the amount of icethat melts off it into the ocean and also the more-unusual places where water freezes back onto the ice. These interactions between iceand ocean are unique to iceshelves and are the source of cold, fresh water packets that are known to come from the polar regions. This water from beneath Larsen Ice Shelfflows into the nearby Weddell Sea and eventually northwards into the Global ocean system, helping to drive currents around the Planet. Iceshelves are an important, integral part of the polar icesheets; they hold back the flow of the inland glaciers and they contribute cold, fresh water masses to the Global oceans, and the shape of the underlying seabedcan be an important factor controlling both of these. Very few techniques are capable of mapping the shape of the sea floor beneath iceshelves. The most reliable method is seismic surveys and these were done at nearly 100 new locations on the ice shelf. With these we were able to correct and improve earlier maps made by interpolations from less-reliable methods. In some places, those earlier maps were found to be correct, elsewhere large errors were found that can now be corrected. Larsen C Ice Shelfis the largest ice shelfon the Antarctic Peninsula. During the last 20 years, its two neighbours to the North, Larsen A and Larsen B, completely disintegrated; Larsen C Ice Shelfis itself thinning over time and its eventual breakup is beginning to seem likely.