CHIRP ACOUSTIC FACIES FROM THE FORMER LARSEN B AREA, NORTH-WESTERN WEDDELL SEA

The breakup of the Larsen B ice shelf in 2002 opened up a new opportunity to study the nature of deposition beneath floating ice shelves, which is as yet poorly known because of the lack of direct observations.

Here we present preliminary results of the high-resolution seismic profiles obtained with the Bathy-2000W system, with CHIRP pulse, during the cruises NBP0107, NBP0603 and with the Knudsen 320 B/R system during the LMG0502 cruise. The acoustic signal was a multi-frequency ping transmission with an average frequency of 3.5 kHz. The echo types were classified, mapped and interpreted and verified using sedimentological data and benthic camera imagery.

The dominant acoustic facies throughout the Larsen B area is a strong, prolonged seabed echo, corresponding to poorly-sorted sediment including very coarse debris; diffuse, prolonged seabed echo with hummocks/hyperbolic diffractions, corresponding to poorly-sorted glacial sediments; and semitransparent facies corresponding to fine grained sediment deposited from suspension or transported by weak bottom currents. Multi-layered sequences of distinct, continuous sub-bottom reflectors are only present in the Crane Glacier through and Hektoria Basin, at depths grater than 800 m.