Mind the seafloor

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Science  05 Jan 2018:
Vol. 359, Issue 6371, pp. 34-36
DOI: 10.1126/science.aap7301

As human use of rare metals has diversified and risen with global development, metal ore deposits from the deep ocean floor are increasingly seen as an attractive future resource. Japan recently completed the first successful test for zinc extraction from the deep seabed, and the number of seafloor exploration licenses filed at the International Seabed Authority (ISA) has tripled in the past 5 years. Seafloor-mining equipment is being tested, and industrial-scale production in national waters could start in a few years. We call for integrated scientific studies of global metal resources, the fluxes and fates of metal uses, and the ecological footprints of mining on land and in the sea, to critically assess the risks of deep-sea mining and the chances for alternative technologies. Given the increasing scientific evidence for long-lasting impacts of mining on the abyssal environment, precautionary regulations for commercial deep-sea mining are essential to protect marine ecosystems and their biodiversity.

Remote and Unknown

The seabed covers 70% of Earth's surface and is home to a virtually uncharted diversity of marine life. The ocean floor, at an average depth of 4 km, is characterized by pressures of several hundred bars, temperatures around the freezing point of water, and no sunlight for photosynthetic productivity. For humans, this environment is inhabitable, barely accessible, and extreme. Yet, the relatively stable environmental conditions of the deep sea have promoted a vast biodiversity of taxa that are not found in shallow waters or on land.

Because of its remoteness and the technical challenges associated with reaching the deep seabed, much less than one-thousandth of its area has been studied (1). As a result, little is known about how much deep-sea species contributed to the evolution of life and biodiversity on Earth, how they can tap into unusual energy sources, how the sparse populations maintain enough standing stock in this vast realm, and how they adapt to perturbations. No country sustains the necessary amount of deep-sea observations required to answer such questions. The lack of long-term ecological time series is particularly problematic, making it difficult to decipher natural dynamics and anthropogenic perturbations (2). Recent findings suggest a tight coupling between the dynamics of surface and deep-sea processes and confirm that effects of climate change and pollution propagate quickly. But little is known about the resilience and recovery of deep-sea communities in the context of activities such as mining (3).

Hazards of Deep-Sea Mining

Critical metal resources in the deep sea include arsenic, copper, cobalt, nickel, lithium, platinum, tellurium, zinc, and many rare earth elements (4). The exploitable resources of the potentially prolific, 40-million-km2 deep-sea area (5) could be worth $20 trillion to $30 trillion, considering current metal prices. However, these resources are not renewable, because polymetallic nodules and crusts grow very slowly over millions of years. Furthermore, mining is highly invasive, damaging the surface seafloor and entailing considerable risks for deep-sea life (6, 7). Even in shallow seas, there is no efficient governance for monitoring, managing, and protecting the oceans. The extensive seafloor damage caused by benthic trawling or by accidents such as the 2010 Deepwater Horizon oil spill in the Gulf of Mexico shows that ecological impacts on the deep sea remain literally out of sight in ocean resource management. Even in national waters, no system is in place to repair, restore, and compensate for loss of seafloor habitat.

On land, metal mining is highly destructive to the environment and can put the health of miners and local communities at risk, if not carefully regulated and managed. Mitigation actions such as habitat compensation, restoration, and adaptive management are expensive, but can minimize the damage to biodiversity and help to restore terrestrial landscapes within a few decades. However, it remains questionable whether any land-based mitigation mechanisms can serve as a blueprint for regulations of deep-sea mining (8). The high economic costs of ecological impact on land (9) are often used as an argument for deep-sea mining. Yet, such a “not-in-my-backyard” drive toward seafloor uses would violate the internationally affirmed precautionary approach, as reflected in principle 15 of the 1992 Rio Declaration on Environment and Development.

(Top) Holothurian in a polymetallic nodule field of the Clarion-Clipperton Fracture Zone of the Pacific Ocean. (Bottom) ROV Kiel 6000 push coring disturbed surface sediment of the 26-year old plow track of the DISCOL experiment in the Pacific Peru Basin.


The ISA, which is responsible for controlling the exploitation of mineral resources in international waters, adopts this principle in its draft regulation, published on 8 August 2017 (10). However, concrete environmental objectives for protecting and conserving the deep-sea environment, including its biological diversity and ecological integrity, have not been agreed upon yet. To be economical, any single operation would have to mine several hundred square kilometers of deep seafloor per year, but this estimate does not include the costs of environmental management. At the anticipated scale of seafloor damage, monitoring, compensation, and restoration techniques would be extremely expensive to implement. But without such measures, the use of deep-sea mineral resources to sustain further global economic growth would endanger the deep sea's genetic resources, which are a long-term target for biotechnology and medicine (11).

The Research Basis

Several countries are currently funding a range of activities connected to deep-sea mining, from developing technologies for deep-sea raw materials extraction to researching the ecological consequences of deep-sea mining, but there is no central synthesis platform to bring together arising knowledge.

The MiningImpact project (a part of the Joint Programming Initiative Healthy and Productive Seas and Oceans) has brought together 11 European countries to study the environmental impacts of seafloor mining, with a focus on polymetallic nodules. The researchers revisited benthic impact experiments in the Pacific Peru Basin and in ISA contract areas in the Clarion-Clipperton Fracture Zone in the Pacific Ocean (see the photos). Some of these experiments were initiated up to 40 years ago and have now been studied with state-of-the-art methods (12). Key conclusions were that deep-sea ecosystems associated with polymetallic resources support a diverse fauna with high spatial and temporal variability and largely unknown connectivity; that the loss of seafloor integrity by mining reduces population densities and ecosystem functions for many decades; and that sediment plumes will likely blanket the seafloor up to several tens of kilometers outside the mined area (13). On the basis of current scientific knowledge, the long-term risks of industrial-scale deep-sea mining to the marine environment seem unmanageable from both the economical and the ecological perspective.

However, predicting impacts on the basis of small-scale benthic impact experiments is associated with many uncertainties. Benthic trawling provides a rough analog for large-scale impact on seafloor integrity. In shelf seas, recovery of seafloor communities from benthic trawling can take less than a decade depending on the substrate (14), but decades to centuries are needed in deep-water habitats (15). In 2016, the European Union banned seabed trawling on continental slopes below 800 m to reduce risks for deep-sea life.

Dark, cold, energy-poor deep-sea ecosystems are particularly vulnerable to mechanical disruption of the surface seafloor, which contains most of the food and microbial communities on which benthic fauna depend. Biogeochemical investigations as part of the MiningImpact experiments confirm that even the soft sediment seafloor would take many decades to hundreds of years to recover from the disturbance caused by nodule removal (13). The nodules and crusts themselves, which provide habitats to many deep-sea species, would need millions of years to grow back (4).

Careful Ocean Governance

Strict environmental regulations need to be formulated by the ISA as they finalize their regulations (10). Before any industrial activities could begin, long-term studies with realistic analogs to mining technologies would be needed. Conservation areas must closely match ecosystem characteristics of mined areas to safeguard abyssal biodiversity. Technologies for baseline studies and monitoring need to be standardized and regularly revised to reflect state-of-the-art science. Indicator sets for deep-sea ecosystem status and threshold values for harmful effects must be defined. Environmental management plans need to address uncertainties of sediment-plume dispersal. Finally, transparent and independent international scientific assessment of environmental management plans needs to be in place before any deep-sea mining operations can start. Transparency also needs to be increased in the ISA's decision-making process for issuing contracts, as has become obvious by the latest approval of a 10,000-km2 claim at the Mid-Atlantic Ridge (16) that includes the hydrothermal-vent systems of Lost City, Trans-Atlantic Geotraverse, and Broken Spur, which are key scientific research sites.

Before taking any risk to destroy deep-sea habitats and endanger marine species, metal resources on land could be fully mapped and explored. Technological and social innovations could improve the way metals are used and recycled, and international politics could foster metal-market stability. In all of this, holistic science projects and stakeholder dialogue could help in finding solutions to the development of metal resources, uses, and fates. This would also provide the necessary time to valorize ocean life and its genetic resources (11). A new kind of international deep-sea science and policy, in which knowledge and governance of mineral and genetic resources as well as other ocean ecosystem services are integrated and channeled into international policy, would allow humanity to sustain the full range of options for the deep sea.

References and Notes

  1. Announced to stakeholders at the project's final conference at the Natural History Museum in London on 18 to 20 October 2017.
Acknowledgments: We acknowledge funding by Joint Programming Initiative Healthy and Productive Seas and Oceans (JPI Oceans) “MiningImpact” (Fkz 03F0707A) of the Federal Ministry of Education and Research (BMBF), the EU project Managing Impacts of Deep Sea Resource Exploitation (MIDAS) (GA 603418), and by the German Research Foundation (DFG) Excellence Clusters “Future Ocean” and “MARUM—The Ocean in the Earth System.”
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