A streams of thoughts contribution by Hayat Nasirova

The deep sea, the largest ecosystem on earth and one of the least explored, is home to high biodiversity and offers an abundance of resources (Ramirez-Llodra et al., 2011).

The Ocean Foundation (https://oceanfdn.org/) defines deep sea mining (DSM) as a commercial industry aimed at mining mineral deposits on the sea floor to extract commercially valuable minerals such as manganese, copper, cobalt, zinc and rare earth elements. Although humans have exploited the oceans for millennia, technological developments now allow the exploitation of fisheries resources, hydrocarbons, and minerals below 2000 m depth (Ramirez-Llodra et al., 2011). The mineral deposits are found in three seafloor habitats: the abyssal plains, seamounts and hydrothermal vents (Gollner et al., 2017). Abyssal plains are large parts of the deep ocean floor covered with deposits of sediment and minerals, also called polymetallic nodules and this is currently the main goal of DSM. With an increasing demand for mineral resources, deep-sea mining brought a critical threshold to the ecosystem (Gollner et al., 2017). This is because the depletion of minerals has irreversible consequences that can lead to the loss of habitats, species, and ecosystem services which are unlikely to recover to their original state (Thompson et al., 2018).

Historically, deep-sea mining projects were already underway in the 1960s and an advanced stage of development by the 1970s, only to be shelved again in the 1980s (Sparenberg, 2019). Although seafloor massive sulfides are likely to be the first deep-sea minerals to be mined in near future (Sparenberg, 2019), this essay focuses on manganese nodules. In the future, the mining of manganese nodules is expected to have a greater impact on global metals markets as well as on the marine environment than the mining of seabed massive sulfides (Sparenberg, 2019). The major issues related to the impacts of deep-sea mining revolve around lack of scientific understanding of deep-sea ecosystems, lack of knowledge about the capabilities of the technology still under development, and lack of a regulatory framework that limits environmental impact.

Deep sea mining for manganese nodules: an overview

Manganese nodules or polymetallic nodules are composed of manganese oxides and iron oxyhydroxides with a size range of 2–8 cm and found widely on the surface of sediment-covered abyssal plains (Sparenberg, 2019). These nodules were first discovered in 1868 in the Kara Sea, in the Arctic Ocean of Siberia, and in 1873 the first manganese nodules were dredged by the early oceanographic ship HMS Challenger (Glover and Smith, 2003). Polymetallic nodules grow at an average rate of 10–20 mm per million years. They are embedded in the sediment surface and therefore provide a hard-substrate habitat in deep-sea plains dominated by sediments. Nodules result from the precipitation of dissolved metals on a hard substrate; typically there is a core of foreign material, such as a shark tooth, and then the nodule surface itself (Glover and Smith, 2003). The occurrence of manganese nodules is known from the Clarion Clipperton Fracture Zone (CCZ), a region that encompasses the NE equatorial Pacific, the Peru Basin in the SE Pacific, the Cook Island region in the SW Pacific, and the Central Indian Ocean Basin, which is the largest known continuous occurrence of nodule fields and covers an area of approximately 4 million square kilometers. Fauna in nodule regions plays a role in situ carbon fixation, cycling and storage, although the mechanisms are not well understood (Orcutt et al., 2020; Molari et al., 2020). Questions remain regarding the appropriate methods to measure and assess ecosystem functions and services in nodule regions, but these regions are likely to host new and important ecosystem processes, pathways and mechanisms, e.g. providing evolutionary potential due to unique biodiversity. 

Environmental Impacts

The methods for mining of manganese nodules are important when environmental impacts are to be considered. The mining of manganese nodules may be the largest human activity directly impacting the deep-sea floor (Glover and Smith, 2003). Manganese nodule mining may not happen for another 10 to 15 years, but it could ultimately be the largest human activity to directly impact the deep-sea floor. The redeposition of sediments suspended from mining activities will disrupt seabed communities in an area perhaps two to five times larger. Therefore, over 15 years, a single mining operation could damage deep-water communities covering an area of 50,000 km² and three mining operations could impact an area of seabed half the size of Germany. 

The movement of the nodule collector and the separation and collection of the nodules from the surrounding sediment produce plumes of sediment on and above the sea floor. It is expected that the sediment resuspended in the near-bottom water will mainly contain very fine clay particles which can remain suspended for a long period. Many of the collector designs propose screening of the associated sediments near the seabed to minimize the amount of unwanted material that is lifted to the surface.

Direct impacts of mining include mortality and destruction of animals living on mined substrates, removal of substrates and habitat loss, habitat fragmentation, habitat modification (i.e. changes in mineral and sediment composition, topography, of the chemical regime) and various other direct effects such as noise and electromagnetic radiation from mining equipment. Indirect impacts include the formation of (potentially toxic) sediment plumes from the activity of crawler vehicles, seabed installations and risers, and the potential release of toxic materials into the water column along the riser system and/or from process material discharged from the ship (return plume) (Glover and Smith, 2003).

Animals in the CCZ, as well as in all manganese nodule areas, occur in the sediment, attached to the nodules, and in the water column above the seafloor. A study on megafauna in the CCZ by Vanreusel et al. (2016) found that epifauna (animals living on the surface of the sediment and nodules) are more abundant and diverse in areas associated with polymetallic nodules than in areas without nodules or with only low nodule counts. Endemic animals such as sponges, worms and even corals colonize and grow on the nodules themselves, while the sediment below and the surrounding waters support life similar to the rest of the abyssal plain, including starfish, sea cucumbers and fish (Amon et al., 2016).

In conclusion, the alluring potential of deep-sea mining for valuable minerals like manganese nodules presents a critical crossroads for humanity. While it promises riches, its ecological impact on the intricate and poorly understood deep-sea ecosystems could be irreversible. The lack of scientific understanding, immature technologies, and regulatory gaps underscore the urgency for cautious and collaborative action. As we peer into the abyss, we must balance our pursuit of resources with the preservation of Earth’s largest and least explored ecosystem, recognizing that our choices today will shape the oceans of tomorrow.

References:

Amon, D.J., Ziegler, A.F., Dahlgren, T.G., Glover, A.G., Goineau, A., Gooday, A.J., Wiklund, H., & Smith, C.R. (2016). Insights into the abundance and diversity of abyssal megafauna in a polymetallic-nodule region in the eastern Clarion-Clipperton Zone. Scientific Reports, 6, 30492. https://doi.org/10.1038/srep30492

Glover, A.G., & Smith, C.R. (2003). The deep-sea floor ecosystem: current status and prospects of anthropogenic change by the year 2025. Environmental Conservation, 30(3), 219–241. https://doi.org/10.1017/s0376892903000225

Gollner, S., Kaiser, S., Menzel, L., Jones, D.O.B., Brown, A., Mestre, N.C., Van Oevelen, D., Menot, L., Colaço, A., Canals, M., Cuvelier, D., Durden, J. M., Gebruk, A., Egho, G., Haeckel, M., Marcon, Y., Mevenkamp, L., Morato, T., Pham, C. K., … & Arbizu, P.M. (2017). Resilience of benthic deep-sea fauna to mining activities. Marine Environmental Research, 129, 76–101. https://doi.org/10.1016/j.marenvres.2017.04.010

Molari, M., Janssen, F., Vonnahme, T.R., Wenzhöfer, F., & Boetius, A. (2020). The contribution of microbial communities in polymetallic nodules to the diversity of the deep-sea microbiome of the Peru Basin (4130–4198 m depth). Biogeosciences, 17(12), 3203–3222. https://doi.org/10.5194/bg-17-3203-2020

Orcutt, B.N., Bradley, J.A., Brazelton, W.J., Estes, E.R., Goordial, J., Huber, J.A., Jones, R.M., Mahmoudi, N., Marlow, J., Murdock, S., & Pachiadaki, M. (2020). Impacts of deep‐sea mining on microbial ecosystem services. Limnology and Oceanography, 65(7), 1489–1510. https://doi.org/10.1002/lno.11403

Ramirez-Llodra, E., Tyler, P.A., Baker, M., Bergstad, O.A., Clark, M.R., Escobar, E., Levin, L.A., Menot, L., Rowden, A.A., Smith, C.R., & Van Dover, C.L. (2011). Man and the Last Great Wilderness: Human Impact on the Deep Sea. PLOS ONE, 6(8), e22588. https://doi.org/10.1371/journal.pone.0022588

Sparenberg, O. (2019). A historical perspective on deep-sea mining for manganese nodules, 1965–2019. The Extractive Industries and Society, 6(3), 842–854. https://doi.org/10.1016/j.exis.2019.04.001

Thompson, K.F., Miller, K., Currie, D., Johnston, P., Santillo, D. (2018). Seabed mining and approaches to governance of the deep seabed. Frontiers in Marine Science, 5. https://doi.org/10.3389/fmars.2018.00480

Vanreusel, A., Hilario, A., Ribeiro, P., Menot, L., Arbizu, P.M. (2016). Threatened by mining, polymetallic nodules are required to preserve abyssal epifauna. Scientific Reports, 6, 26808. https://doi.org/10.1038/srep26808

About the author

Hayat Nasirova is a geographer and teacher with a background in education. She originally completed her Bachelor’s degree in Earth Science from Azerbaijan State Pedagogical University and is currently a Master’s student in Physical Geography: Climate and Environmental Sciences at the University of Bremen. She is an experienced science communicator, especially with respect to the intersection of science and contemporary art, having led masterclasses and workshops integrating and articulating scientific phenomena on art and canvas. She runs a series of courses called “The History of Science” and “Sci-Art”, as part of the Pint of Science festival. 

LinkedIn profile: www.linkedin.com/in/hayat-nasirova