Characterization of the seafloor at the SYSTCO stations based on video observations and ground truthing sedimentology

An underwater camcorder mounted on a lander frame was used to image the sedimentary conditions and the epibenthic fauna at the seafloor along the SYSTCO transect. Four stations were monitored; on the lower shelf (600 m), continental slope (2000 m), abyssal plain (5300 m), and on top of a seamount (2100 m). The sediment surface was filmed for different time lengths between 3 and 19 min, while the camera was towed over distances ranging from 11 to 187 m, resulting in areas filmed between 4 and 71 m2 per station. From the gathered images, epifauna was counted and identified to the lowest possible taxonomic level. For ground truthing, two to three replicate multicorer samples per station were vertically sectioned per centimeter down to 5 cm depth and analyzed for sediment granulometry. Differences in the sedimentary characteristics could be related to both water depth and topography according to the multicorer samples. The video footage from each station showed a range of different sediment surface types and widely varying epifaunal abundance, the lowest number of readily identifiable organisms being present on the abyssal plain and the highest on the lower shelf.