Minerals Report - International Seabed Authority

of the sedimentary column, whereas seismic reflection surveys reveal
information about the deeper part of the sedimentary pile. Side-scan sonar
systems that are towed behind the ship obtain information about tectonic
features at the seafloor. Gravity, magnetic, and heat flow surveys are also
routinely run.
On-line real-time observation of the seafloor in the search for
hydrothermal sulphides at oceanic spreading ridges or for cobalt-rich
ferromanganese crusts at seamount flanks is achieved by using deep-towed
camera-systems (rated up to 5.000 m depth) which are equipped with lamps
and flashes in combination with high-resolution colour video cameras and
still cameras for up to 700 colour slides. The data transfer from the seafloor to
the ship is achieved via a fibre optic cable while the energy for cameras, lamps
and flashes is transmitted via a co-axial cable.
Basic sampling devices include various corers (spade, piston and
gravity) and dredges (barrel, box and chain-bag) as well as free-fall grabs
known from manganese nodule exploration. An excellent development is that
of TV-guided grab systems (rated up to 5.000 m depth) for precise large- scale
(up to about 3 tonnes) sampling of rocks, massive sulphides or cobalt crusts.
Due to a high-resolution video camera and several lights mounted in the
centre of the grab, the system can be used for small scale mapping of the
seafloor as well as for sample selection and finally sampling. If the sample is
not sufficient, the grab can be reopened and closed several times before the
batteries are exhausted and need to be recharged. TV-grabs are usually also
operated on a fibre optic cable to enhance the camera signal and to trigger the
closing and opening mechanism of the grab. The power necessary to close
and open the claws, however, is provided by deep-sea batteries.
For water sampling in the search for geochemical signals (methane,
manganese, helium isotopes) of active hydrothermal vents, several CTD
(conductivity-temperature-depth) and rosette sampler systems with up to 24
bottles are in use. Each bottle can be closed remotely at a certain water depth.
Chemical analyses of the water samples are usually performed on board ship
with only limited time delays. In recent years, geochemical scanners (e.g.,
SUAVE: NOAA/USA; ZAPS: Oregon State University/USA; ALCHEMIST:
IFREMER/France) have become available, and are used in the towed mode to
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