Expeditions study environmental impact of mining of deep-sea mining
What would the ecological consequences be if the quantity of polymetallic (e.g. manganese) nodules in the deep sea was reduced? Would sustainable management of our deep-sea resources still be possible? How much time would be needed for affected regions to recover from the extraction of such resources?
These questions were explored during a series of expeditions aboard the new German research vessel SONNE recently.
Scientists from Germany and other European countries revisited a disturbance experiment which was conducted 26 years ago at more than 4,000 metres' depth in the eastern equatorial Pacific.
In 1989, a team of German researchers ploughed an area approximately eleven square kilometres on the ocean floor in the eastern Pacific Ocean. They removed manganese nodules and created sediment plumes, thereby simulating the effects of deep-sea mining on the ecosystem. The site was named DISCOL (Disturbance and Recolonisation Experiment).
Between 1989 and 1996, the researchers returned to DISCOL four times to track the recovery of the ecosystem. This year – after more than two decades – scientists from Germany and several European countries revisited the site to see how fast the communities have recovered. Using the latest robotic technology, the distribution and function of the deep-sea organisms were studied, in both the ploughed and unploughed areas.
Using ABYSS, an autonomous underwater vehicle from GEOMAR, a high-resolution map of the plough tracks, manganese nodule densities, and information about colonisation by key species in the area were collected. In addition, biological samples were also taken to assess the animal biomass distribution and to retrieve samples for further investigation and identification. The remote-controlled underwater vehicle ROV Kiel 6000 was used for targeted sampling to quantify the effects of ploughing of the seafloor on key ecosystem functions, including geochemical fluxes and bacterial activity and density. The robot also conducted experiments on the toxicity of metallic muds with typical deep-sea organisms on the seabed. In addition, a high-resolution camera system was dragged across the ocean floor to photograph and count the presence of small creatures.
“During 23 dives with the ROV Kiel 6000, we conducted in situ experiments and deployed deep-sea observatories,” said Prof. Dr Antje Boetius, from the Alfred Wegener Institute. The initial conclusion was that the removal of nodules had indeed altered the distribution of animals on the seafloor. Many species, such as sponges, corals and sea lilies, grow on the nodules, while other animals in turn attach themselves to these fixed organisms. This pattern is similar to birds and insects and how they come to live in trees.
Scientists have obtained thousands of images and hundreds of samples from the deep sea for chemical and biological analyses of both the ploughed and unploughed areas of the site. “What surprised us a lot was that the onboard geochemical and microbial analyses indicated that even bacterial activity is still low in the plough tracks,” said Boetius, adding that further lab investigations were needed.
Another impact of deep-sea mining was the creation of a sediment plume, said Dr Matthias Haeckel, from GEOMAR. Deep-sea sediments are easily eroded and can form clouds of mud that drift along with the deep-sea currents. They eventually settle a distance away from the site, thus affecting organisms living outside the mining area. However, it is currently unknown whether such plumes are capable of transporting toxic metals, or whether they can affect organisms like corals which filter the seawater to absorb the nutrients.
“We still have a lot to analyse from our very successful expeditions, but it is an enormous motivation to know that the results we produce can directly advise policies for deep-sea environmental protection, including spatial planning for protected areas, and improved mining technology to minimise impact,” said Haeckel.