￼Ecology Versus Technology
“I am actually quite worried”, states marine ecologist Marc Lavaleye of the Deep Sea Science & Technology Center in Texel, the Netherlands. He is referring to the consequences to the environment when regarding the deep sea mining developments. Technology is one half of the equation, how do we get to and extract the manganese nodules and the seafloor massive sulfide deposits (SMS deposits)? The other half is what the effect will be on sea life when we eventually do.
The two variations in mineral retrieval for deep sea mining, SMS deposits and manganese nodules have very different ways of forming. Manganese nodule even grow slow in geological terms several thousands to million years. This is due to the geochemical processes involved, including, amongst others, the precipitation of dissolved metals (mainly zinc, nickel and copper, amongst several others) from the pore water between the sediment particles. The metals are in solution in the geochemicaly reduced deeper sediment horizons but precipitate around a nucleus if the geochemical condition become again oxygen-rich close to the seafloor surface. Layer after layer forms around the nucleus with a growth rate of sometimes only 0.001mm/ky. “Once you have extracted the nodule, it will take several hundreds of thousands of years to form again. So, simply speaking, you take it and it is gone”, explains Jens Greinert, marine geologist at the NIOZ, the Royal Netherlands Institute for Sea Research. Concerning the fauna, it has been shown in the Clarion-Clipperton Fracture Zone in the Pacific near Mexico that an experimental extracting track of only 1.5 metres wide made in 1978 through the manganese nodule field still appeared 26 years later as if it was made yesterday. The deep- sea fauna had hardly recolonized the track. This shows that recolonization in the deep-sea can be a very slow process.
Cold ocean water
SMS deposits occur under very different circumstances. “Around areas of rising magma in the earth lithosphere/asthenosphere new oceanic crust along the mid-ocean ridges is formed, at the same time oceanic plates are subducted again initiating magma to rise towards the earth surface forming volcanoes on land and in the oceans. At both sites, hydrothermal vents occur which form the richest SMS deposits, says Greinert. “These vents occur due to cold dense seawater sinking into the fractured ocean floor where the seawater is heated by the magma- heated rocks and becomes acidic. During the migration of the seawater through the rocks metals are dissolved in the form of ions in the super hot water. If these often 350°C hot fluids reach the seafloor surface it comes in contact with the 2°C cold seawater. The cold temperature causes the dissolved metals to precipitate spontaneously. Chimneys made out of ore minerals grow into the water column and release black smoke, which is why they are called ‘black smokers’. Areas of the size of one or few football fields form which are full of these black smokers, which stop being active and collapse after a while others start growing in the close vicinity. This process together with the sedimenting metal sulfites from the black create the most lucrative deposits to mine.”
Abundant sea life
Lavaleye: “What many people do not realize is that these vents have an abundant community of biological life, varying from one meter long tubeworms without a mouth to blind shrimps and large shells with red meat. Even more striking is that these lush communities exist on the basis of chemosynthesis, instead of photosynthesis. It means that bacteria can make organic material – food – from methane and carbondioxide by using the hydrogen sulfite – smells like rotten eggs – from the black smoke as an energy source. The larger animals either graze these bacteria or incorporate them in their gills or tissues to form a symbiotic association. Lots of special vent species are now known, but every year more new species are described from these vent communities. In contrast the normal deep sea fauna never shows such high concentrations of large animals, as these communities are dependent on the food that rains down from the surface of the ocean. But surprisingly for such a cold, dark and food sparse environment the biodiversity of deep sea life is very high and can be compared with a rain forest or tropical coral reef.” Only about ten percent of the ocean floor has been mapped in detail and even less has been studied thoroughly, which means much more fundamental research is required to fully understand ocean life and its link to life on land and to us.
Effects of deep sea mining
Deep sea mining will affect the environment. There is no doubt. Cees van Rhee, professor of dredging & engineering at TU Delft, says: “We don’t yet know what the effect will be on the environment. The loosening of the in rock solidified minerals causes dust to erupt. What happens to sea life when the water becomes murkier? Will the organisms be able to survive?” The question is what can be done to keep the damage to a minimum? Greinert: “We will have to compromise as there will always be an effect to the environment. You are pulling something out of the ocean, crushing any living thing during extraction. Furthermore, when the slurry is returned to the ocean floor, it will form a layer over the organisms living on the ocean floor, possibly killing them”. With respect to SMS deposits formed from black smokers the affected area is ‘rather small’ compared to the vast areas that would be mined (dredged) to recover manganese nodules. Here the idea is to mine sub-areas in the claims requested by the ISA, the International Sea Authority. You mine one sub-area, which can be recolonised from the adjacent untouched seafloor areas. Respective tests have been made in the 80s during the DISCOL project (Disturbance and Re-colonization of a Manganese Nodule Area in the deep South East Pacific Ocean off Peru). The scientists concluded that the dredged area was more or less re-colonized after 25 years, but that the dredged area was much too small to allow upscaling of these findings to industrial dredging. “This means that we still don’t know what will happen with the deep sea environment when large scale dredging will happen. Very thorough planning and constant monitoring is needed to make sure that we do not destroy something for good of which we still don’t know how important it is also for us. The good thing is that we do know what and how we have to monitor the deep sea if mining indeed begins”, says Greinert.
Marck Smit of the Netherlands Deep Sea Science & Technology Centre says: “ManyDutch companies are now working on deep sea mining technology. I find it promising that many of them are enlisting the help of research institutes like us, it means they are willing to safeguard the environment.” In the current climate, companies are enlisted due to their work, but also on their views on sustainability. This will be no different for the deep sea mining industry; companies who have sustainable, environmentally friendly means of extracting will probably be requested more often. Another thing to consider when entering deep sea mining: “I believe we can connect science and technology to benefit both parties”, says Smit.
Not only marine life will require scientific research, as Jaap de Wilde, senior project manager offshore at MARIN, points out: “Many other factors regarding deep sea mining technology will need to be researched, such as the effect of ocean currents on the suction pipe used to extract the minerals. How will a pipe behave in the water? Will it be controllable? How will the excavated rocks behave when they are being pumped up to the production vessel? Questions that need to be answered and that could well push us to the edge of today’s technological feasibility.” Van Rhee agrees. Currently three PhD researchers are investigating the physical processes related to dredging at large water depth in his group.
Two PhD researchers are employed with the hyperbaric cutting process (cutting of rock in presence of a large hydrostatic pressure due to the extreme water depth. The subject of the third researcher is the vertical hydraulic transport of settling solids which has never been done in practice on this scale.
Time is money
It has been addressed that deep sea mining will involve vast investments. De Wilde comments: “It will be interesting to find out how long equipment can function in such deep water up to 5,000 metres. This could be a deciding factor in the extraction of minerals from the ocean floor. Time will also be an issue and we all know time is money.”
Both MARIN and the Royal Netherlands Institute for Sea Research are geared up and ready to offer their knowledge and advice to companies undertaking deep sea mining. Both organisations feel working together will have the best outcome for technology and ecology. As we approach the boundaries to be tested by deep sea mining, wouldn’t it be the best possible scenario if we can evolve technologically, while safeguarding the ocean and her inhabitants?