High-frequency near-bottom acoustic reflection signatures of hydrocarbon seeps on the Northern Gulf of Mexico continental slope

Acoustic reflection signatures of four hydrocarbon seeps were classified us ing near-bottom 25-kHz echosounder profiles. Echo patterns were compared wi th ground-truth data obtained by submersible observations and shallow corin g. Six echo types were distinguished: strong reflections from (1) exposed o r (2) buried hard substrates, such as authigenic carbonate or gas hydrate; acoustic scattering in (3) unlayered or (4) layered sediments owing to gas, shells, or disseminated carbonates; (5) attenuation caused by gas; and (6) undisturbed sediments. Echo type distributions suggest that high spatial v ariability indicates a younger, vigorous seep, whereas extensive hard subst rate implies an older, encrusted seep.