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British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
We present the first images of sub-seabed structure to be obtained from beneath the Ronne Ice Shelf. Single-fold profiles totalling 158 km were recorded using a new form drag cable with explosives as source. The survey was conducted in an area lying 100 km SE of the Orville Coast, Antarctic Peninsula. The ice shelf at this location is about 350 m thick and the seabed undulates gently between 650 and 675 m below sealevel. In the western part of the area, acoustic basement outcrops at the seabed. In the eastern part, a set of open folds were observed with wavelengths of 5–6 km, amplitudes of 200–300 m and a NNE-SSW strike direction. These features match those observed on previous marine data obtained in the narrow shore lead at the front of the ice shelf and allow the strike of the structures to be traced for 70 km to the SW of the original observations. Existing models of the plate tectonic development of West Antarctica have anticipated major dextral strike-slip motion between the Antarctic Peninsula and the Weddell Sea but the new data shows no evidence for this, indeed the structures can be interpreted as resulting from an episode of sinistral motion.
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