Andvord drift: A new type of inner shelf, glacial marine deposystem from the Antarctic Peninsula

Hemipelagic, sediment drift deposits have been discovered and mapped on the Antarctic Peninsula shelf in 300-500 m water depth. The drift located adja cent to Andvord Bay covers 44.5 km(2) and exhibits continuous and discontin uous parallel reflections that conform to peaks and valleys in the acoustic basement as observed in deep-tow boomer and sparker seismic records. This style of drift deposit is a common feature of deep oceanic sediments, but i s not normally found in continental shelf environments. Measured sedimentat ion rates of 1-3 mm/yr on the Andvord drift indicate that the total 40 m dr ift thickness observed in the seismic records is probably postglacial. The drift contrasts with the basin-fill style of sedimentation that is normally associated with the Antarctic continental shelf and may play an important role in the carbon cycle. On the basis of an isopach map of drift sediments and previously published core information, the rate of carbon accumulation in the Andvord drift is estimated to be about 1.7 g/cm(2)/k.y., which is c omparable to the highest rates reported for the southwestern Ross Sea.