Concerns about protecting the environment during exploration and mining for deep seabed minerals will not be addressed by a ‘one size fits all’ solution.
Dr Malcolm Clark, Principal Scientist (Deepwater Fisheries) at the National Institute of Water and Atmospheric Research (NIWA) Wellington, New Zealand, expressed this opinion during the international workshop on Environmental Management Needs for Exploration and Exploitation of Deep Seabed Minerals.
The workshop, jointly organised by SOPAC a division of the Secretariat of the Pacific Community and the International Seabed Authority, took place in Nadi, Fiji, during December 2011, as a part of the European Union funded, four-year Deep Seabed Minerals Project.
Dr Clark said that the more we learn about the deep sea the more we realise that parts of it are split up into smaller environmental packages, and we don’t have a good understanding of how large these package-like “ecosystems” are, or the degree of connectivity between them.
“Although it is out of sight, the deep sea has complex topography just like on land, and there are different deep-sea environments that have different fauna (animals) and different mineral deposits. These differences in the structure and content of the sea floor would call for different exploration and mining techniques. These mining operations, in turn, would have a correspondingly different effect on the surrounding fauna, and require different management responses,” explained Dr Clark.
There are three types of deep seabed deposits that are being considered as potential resources to be mined: massive sulfide deposits cobalt crusts, and manganese nodules.
“Although our knowledge is still incomplete, we are rapidly learning about the ecosystems and effects of human activities on them, and can be positive for a future in which a balance can be achieved between mining and conservation.”
The massive sulfide deposits have formed around hydrothermal vents that typically are found in areas where there is movement of the earth’s tectonic plates, such as along the mid-ocean ridges, which are underwater mountain chains that weave around the earth where mid-ocean ridge spreading occurs, and in back-arc areas in the western South Pacific where the seafloor is being “consumed”.
Hydrothermal vents are commonly associated with underwater volcanic activity. Deep below the seafloor, through openings in the earth’s crust, sea water interacts with the molten magma layer under the earth’s crust, and spews back in a super heated form, bringing with it minerals in solution that become solid particles as they come into contact with the near freezing sea water. Over thousands of years, massive sulfide deposits have formed, containing gold, silver, copper, zinc, lead, and other trace elements.
The hydrothermal system also brings energy-rich, reduced chemicals that are used by bacteria that form the base of the food web for the fauna living in the depths around vents.
“These hydrothermal vent communities are adapted to the particular chemical and temperature conditions of that particular venting system. These chemosynthetic communities do not rely on sunlight, but utilize the hydrogen sulphide in the water-this is toxic to most life forms, but animals in the vent areas have adapted and evolved for those specific conditions and have quite high levels of unique species,” explained Dr Clark.
“If that vent turns off, which happens naturally, or if the volcanic activity moves, is mined out, or in some way disrupted during mining, the more specialized animals will die out unless they can find exactly the same conditions in a nearby vent field. “This is why the protection of a similar area close to the mined one is important so that the same communities as at the mined site are able to survive.”
Cobalt crusts exist on the sides and tops of mountains under the sea. The creatures that live here are adapted to the rocky seamount environment, which is kept sediment free by the swirling currents, common around seamounts.
With mining the cobalt crust, there could be devastation to much of the upper region of the seamount, as the crust needs to be stripped off over large areas. Dr Clark explained, because of the oceanographic currents around seamounts, the sediment created during mining could also cover a large area, and would be harmful to the fauna that are adapted to living on rocky surfaces, smothering small animals, and clogging the feeding mechanisms of filter-feeders which are common on seamounts (such as corals and sponges).
“We would have to find another seamount with similar communities to be a protected area, far enough away to not be affected. This is a spatial scale of tens of kilometres, compared with just kilometres when dealing with hydrothermal vent communities,” said Dr Clark.
The third kind of mineral deposit, in which there is interest in mining, are manganese nodules. These are found at depths of 4,000 to 5000 metres on the abyssal plains, the flat areas beneath the sea that cover nearly 50% of the earth’s surface. The growth of manganese nodules is one of the slowest geological processes, at the rate of a centimeter over several million years.
“The abyssal plains occur for hundreds to thousands of kilometres, so their geographical extent is huge,” said Dr Clark. Mining of the nodules, which occur on the surface of the seafloor as well as partially buried in the sediment, may extend for a large area, much larger again than on cobalt-rich seamounts.
Life in these depths is not as obvious as on the shallower seamounts. The almost microscopic animals living on the nodules, called Foraminifera, are almost microscopic, while the dominant animals in these areas are types of worm (nematodes and polychaetes) found living under the surface, in the sediment, raising the question as to how large an area would be needed to provide these creatures with an alternative, protected marine environment.
“The spatial scales, and the time things take to happen, vary between the three types of mining situation. The distinctly different environments with their own faunal communities, and different mining operations, will require different management responses for each,” said Dr Clark.