Mapping turbidity layers using seismic oceanography methods

Using a combination of seismic oceanographic and physical oceanographic data acquired across the Faroe- Shetland Channel we present evidence of a turbidity layer that transports suspended sediment along the western bound- ary of the Channel. We focus on reflections observed on seis- mic data close to the sea-bed on the Faroese side of the Chan- nel below 900 m. Forward modelling based on independent physical oceanographic data show that thermohaline struc- ture does not explain these near sea-bed reflections but they are consistent with optical backscatter data, dry matter con- centrations from water samples and from seabed sediment traps. Hence we conclude that an impedance contrast in wa- ter column caused by turbidity layers is strong enough to be seen in seismic sections and this provides a new way to visu- alise this type of current and its lateral structure. By invert- ing the seismic data we estimate a sediment concentration in the turbidity layers, present at the time of the survey, of 45±25mgl−1. We believe this is the first direct observation of a turbidity current using Seismic Oceanography.