South Atlantic cruise on "RV Akademik Ioffe" 2009
8 – 14 November
Author: Andrey Gebruk
Shirshov Institute of Oceanology, Russia
After the station at 3000 m at 4°S on the Mid-Atlantic Ridge (SEMS South), benthos was sampled at around 1900 m depth in the same area. Location of sampling was on summit of a seamount. After 1 h 20 min at the bottom, the Sigsbee trawl came badly damaged, with both beams bent, one inside another outside, though with a catch. Together with two large blocks of basalt and numerous gravel, present in the catch were two species of soft sea urchins, Hygrosoma sp. and Phormosoma sp., gastropods, ascidians, ophiuroids, shrimps and fragments of a black coral. The catch and trawl behaviour during trawling with heavy pulls showed that the top of the seamount we worked at lacked the soft sediment.
Benthos sample was also taken at the base of a seamount at 3700-3800 m depth in the northern TMS are, at 18°S. Despite a great depth, this area also lacked soft sediment and the trawl again came damaged, this time much less severely. A catch was small and full of several cm thick iron-manganese crusts indicative of strongly oligotrophic conditions in this area. Tha fauna was represented mainly by various glass sponges, such as Farrea sp. and several species of Rosellidae. Fragments of regular echinoids were also present. Benthos sampling at shallower station in the TMS area was cancelled because of technical problems with wire on the main winch.