Sediment plumes resulting from deep sea mining

At present there is a keen interest in the recovery of valuable raw materials— polymetallic and phosphorous
nodules, sulphurous deposits and metallic muds – from deep sea environments. These deposits can be
found in depths ranging from several hundred to several thousand meters. The technology being developed
to retrieve these deposits from the sea bed can vary but typically consists of a mining support vessel, a
vertical transport system and a subsea mining tool. The subsea mining tool would vacuum or rake up the
raw materials, grind them and mix them with sea water, creating a slurry of solids and seawater which is
pumped to the surface by the vertical transport system . Processing is undertaken by the mining support
vessel and the discarded sediment/water mixture is returned to the water column, often by a return pipe
which may release the sediment water in the vicinity of the sea bed.
The process of recovery of raw materials from the sea bed and the release of the discarded
sediment/ore/water mixture from the processing stage will inevitably result in the formation of plumes of fine
sediment and release of coarser materials to the bed. Depending on the nature of the deep sea environment
and the extraction process, these have the potential to change the character of the waters immediately
above the bed and the sea bed substrate. These physical changes in turn have the potential, as has been
identified in shallower water environments, to adversely affect the benthic communities existing in this
environment.
This presentation will give an introduction to sediment plume processes and will highlight the main issues
potentially resulting from deep sea mining activities. The presentation will be based upon our research at the
forefront of describing and predicting the behaviour of sediment plumes from seabed disturbance such as
dredging.