Observations of a geoclutter feature in the straits of Sicily

Several persistent sonar clutter features were observed in 2002 during an experiment in the Straits of Sicily (Malta Plateau) in a region that is nominally flat and thickly sedimented. High frequency sidescan and seismic reflection data from the region indicated that mud volcanoes were present and were possibly expelling clouds of methane bubbles. In 2004 the region was revisited with oceanographic equipment including a multibeam sonar, an acoustic Doppler current profiler (ADCP), CTD’s, temperature loggers, a methane sensor, and a video camera. The visual observations at one site show carbonate mounds comprised of large heterogeneous blocks that suggest the presence of mud volcanism. A multibeam sonar survey of the area shows that the carbonate mounds are of order 5–10 m in height and 10–100 m in lateral dimension, and that they form in clusters. The multibeam backscatter data show high amplitudes in the region surrounding the carbonate mounds, possibly indicating the surficial extent of the carbonate material. High levels of methane were observed in the water column above the mounds, although conclusive evidence of the presence of methane bubble clouds was not found. However, high frequency backscatter recorded on the ADCP above multiple carbonate mounds showed plume‐like features that may be bubble clouds, suspended fine‐grained sediment, and/or schools of fish.