Deep seabed mining (DSM) is an emerging industry that could carry significant risks for the marine environment. Mining operations will cause biodiversity loss (Van Dover et al., 2017; Niner et al., 2018) and knock-on effects on the food web (Stratmann et al., 2018; Stratmann et al., 2021) due to habitat destruction (Vanreusel et al., 2016; Volz et al., 2020), sediment plumes (Muñoz-Royo et al., 2022) and noise and light pollution (Williams et al., 2022). In aiming to reduce those environmental risks through an ecosystem-based and precautionary approach (ITLOS, 2011), the International Seabed Authority (ISA), which regulates and manages all DSM-related activities on the international seabed “Area”, ¹ requires mining operators to apply Best Environmental Practice (BEP). ² In this context, BEP means ‘the most appropriate combination of environmental control measures and strategies’ at any given point in time. ³ BEP, by definition, improves over time depending on upcoming environmental challenges as well as advances in knowledge and technology, including Traditional Knowledge by Indigenous Peoples and local communities. ⁴

Identifying BEP is never an easy task but may be particularly difficult for an emerging industry that does not yet have a proven track record of safe operations and that uses nascent technologies which are largely untested in the deep ocean environment. Because of these challenges, identifying BEP for DSM will initially have to rely on experience from other offshore industries as well as on long-term experience gained from small-scale scientific disturbance experiments and mining tests. To that effect, this paper seeks to identify elements of preliminary BEP for polymetallic nodule mining, based on a review of scientific recommendations from the literature. This can only be a first approximation, as a multitude of additional, in particular experimental process research (Weaver et al., 2022) and extended test mining with full-size equipment will be necessary to provide knowledge on short- and long-term environmental effects of DSM from in situ operational practices (Amon et al., 2022; Singh and Christiansen, 2022; Weaver et al., 2022).

Identifying BEP is important for at least three actors: the ISA as the regulator, the mining companies, States or State enterprises as contractors, and the sponsoring State of the contractor. The ISA is obligated to ensure effective protection of the marine environment from harmful effects of DSM, ⁵ with BEP being one important element in achieving this obligation, as specifically recognized in the draft regulations for mineral exploitation which the ISA is currently developing. ⁶ Identifying BEP prior to the start of commercial mining is key to enable the ISA to assess whether an applicant has indeed been following BEP. The applicant, in turn, needs to demonstrate that its proposed plan for mineral exploration ⁷ or exploitation ⁸ applies BEP as well as best available techniques (BAT). ⁹ Lastly, the sponsoring State is required to apply BEP both as a direct obligation ¹⁰ and as part of its due diligence obligation to ensure that the contractor complies with its obligations. ¹¹ Clarity on what constitutes BEP at any given point in time is thus fundamental for the ISA, its contractors, and sponsoring States to be able to comply with their respective obligations.

Despite the importance of BEP, there is no agreed understanding on what constitutes BEP in the Area. Indeed, in the absence of respective environmental standards, the ISA’s current approach entrusts individual ISA contractors with identifying project-specific and area-specific impact thresholds ¹² to determine BEP and other standards based on their baseline data collection. These may be guided by (non-binding) guidelines issued by the ISA (Brown, 2018). However, a common understanding of current BEP, and its links to good industry practice and best available technology, ¹³ may be essential to articulate ISA standards, and to help contractors optimize their technology to meet those standards, while reducing financial and legal risks for contractors. Lastly, BEP may help the ISA to assess and compare applications for mineral exploration or exploitation.

Indeed, in 2017, the Netherlands proposed for the ISA Council to develop an assessment and approval methodology to evaluate mining equipment, operational procedures and processes in relation to their impact on the marine environment. ¹⁴ The proposal was for the ISA to develop technical standards and minimum environmental requirements. Only certified technology would receive approval in prior Environmental Impact Assessments. Certification could be considered early in the technological and operational design process, offering a degree of certainty to mining contractors. In addition, once the criteria exist, the assessment and certification process for equipment could be delegated to external bodies, as is customary for ships and other offshore equipment. Alternatively, an independent advisory body or the future inspection unit of the ISA could fulfil this role.

While no such methodology is being developed yet, the ISA Council has recently decided to take a more active approach and develop environmental thresholds for permissible levels of toxicity, noise, light, and turbidity as well as settling of resuspended sediments from DSM. ¹⁵ This will be an important step towards identifying what levels of environmental harm are deemed acceptable, which in turn supports the identification of BEP to meet these thresholds.

This paper starts by outlining the methodology (section 2), followed by a brief overview of potential nodule mining operations (section 3). The paper then addresses the key effects of nodule mining on relevant ocean layers, from the seafloor (section 4), benthic boundary layer (section 5), water column and surface waters (section 6) and noise and light pollution (section 7). Each section discusses the main risks and recommendations for BEP. Section 8 offers overarching recommendations, while section 9 formulates suggestions for a future ISA Standard on BEP, and section 10 offers concluding thoughts.

This paper offers a non-exhaustive list of preliminary recommendations for BEP in nodule mining, expressed as such in relevant scientific publications. The study draws on a broad range of recent studies which provide direct recommendations for managing DSM. Indirect or implied recommendations from the literature were not considered. Overall, the recommendations largely build on each other, although in some cases differences exist, which are reflected in this paper.

We purposefully do not attempt to rank these recommendations in importance, ease of attainability, scales of effects or cost. This will require a broader range of expertise to systematically assess risks and consider all available options for keeping the short- and long-term impacts on of DSM within the limits to be formulated by the ISA in the future. The present paper merely presents a starting point for developing BEP.

Of the three minerals, the ISA is concerned with since its creation, polymetallic nodules have been studied most extensively. Polymetallic nodules in the Area are generally between 1 and 12 cm in diameter and lie half-buried in the sediment in abundances amounting up to more than 20 kg/m² in some parts of the Clarion-Clipperton Fracture Zone, CCZ, in the Eastern Tropical Pacific. In certain biogeographic regions of all oceans, the nodules can occur in contiguous fields of similar-sized nodules interspersed with low abundance regions or areas that are almost devoid of nodules (Kuhn et al., 2020). The metal content of the nodules varies with location, size, formation process and weathering state (Kuhn et al., 2020). Nodule abundance and nodule size affect biological communities directly and indirectly (Vanreusel et al., 2016; Smet et al., 2017; Kuhn et al., 2020; Simon-Lledó et al., 2020).

Harvesting nodules means retrieving them from the seafloor and pumping the collected material to a surface vessel through a vertical riser pipe (Jones et al., 2017; Miller et al., 2018). All proposed seabed mineral mining operations are based on a similar concept, which encompasses four major components: (1) extraction tool, (2) riser system, (3) surface platform, and (4) disposal system. Most proposed seabed collection systems envisage the use of remotely operated vehicles, which would extract the nodules from the seabed using mechanical rakes or pressurized water. Although less invasive collection technologies are in the design phase, ¹⁶ the nodule collection techniques that are currently being tested all involve self-propelled heavy machinery (with up to 100 t weight under water) operating on the seafloor, and removing up to 10-50 cm of the upper sediment (e.g. reviewed by Paul et al., 2018). So far, the nodule collectors will either consist of one large machine with one or several hydraulic sucking, or raking (e.g. India) intake units, or of several identical modules (e.g. DEME-GSR), mounted together or operating in isolation (Deepak et al., 2001; Handschuh et al., 2001; GSR, 2018; Government of India, 2020). The type of collector will determine the width of the collector path. The machine(s) will strip-mine in a lawnmower pattern, with software ensuring the continuous clearing of nodules (Volkmann and Lehnen, 2017). In most cases, the maximum terrain angle that can be cleared of nodules is 3-4% (Kuhn et al., 2011), any steeper or rougher terrain will remain inaccessible. These figures have not changed since the early pilot mining tests, when the National Oceanographic and Atmospheric Administration of the USA (NOAA, 1981) calculated that a nodule collector will traverse 1.9 km² per day, of which 0.8 km² are not mineable.

The future exploitation contracts for minerals in the Area are likely to be valid for a period of three decades. ¹⁷ Van Nijen et al. (2018) assume a mine life of 25 years. The “BlueMining” nodule mining concept presented by (Volkmann and Lehnen, 2017) assumes an annual production of 1.5-2 Mio t (dry weight, DW) of nodules and expects mining operations to be operational 250 days per year and 20 hours per day. To achieve this production capacity, the nodule collection must reach 400 t DW per hour, and the lifting capacity must achieve 150 kg DW per second. For a mine life of 20 years, the German contractor, BGR, calculates that at a conservative resource abundance of 10 kg of dry material per m² would result in the extraction of nodules from 100 and 200 km² per year or 2300-3600 km² (equivalent to the surface area of Luxemburg) over 20 years (Volkmann and Lehnen, 2017).

However, the total seafloor area impacted by individual mining projects will be much larger than suggested by the above figures, particularly as the mine site will rarely be one contiguous area but rather a patchwork of mineable and non-mineable sites (Kuhn et al., 2020). In case of the French contract area in the CCZ, individual mining blocks are expected to be no larger than 100 km² of variable shape (Lenoble, pers com. in Thiel et al., 2005). Estimates for the total area directly impacted by one 20-year mining operation range from to 6500-14,000 km² (Volkmann and Lehnen, 2017), to 28,000-56,000 km² when considering the sediments plumes generated by the collector vehicle (Sharma et al., 2001). ¹⁸ The overall benthic footprint of a single mine over 20 years may be at least 2 to 4 times larger than the mined area itself (Smith et al., 2020). The cumulative impact of several mines in a biogeographic subregion, for example in the eastern CCZ, could degrade substantial portions of the approx. 500,000 km² nodule habitat in the CCZ (Smith et al., 2020).

The nodules collected are separated from the cohesive sediment, both while entering the collector, and inside the collector. Finally, the sediment slurry – possibly ejected by the collector through an exhaust pipe several meters above the seafloor – creates an operational plume of which the larger particle fraction is likely to resettle on the seafloor, while the fine fraction will drift away and remain in the water column for a long time (Baeye et al., 2021; Purkiani et al., 2021; Muñoz-Royo et al., 2022; Weaver et al., 2022).

The nodules may be crushed to be transported as a slurry up to the surface vessel for dewatering, pre-processing and transport to land. Several technologies are under discussion for lifting the ore slurry to the surface ship (Ma et al., 2017), some of which require underwater pumps (Verichev et al., 2012; Ma et al., 2017) likely to cause vibration and noise pollution. The non-mechanical transport systems (pneumatic or hydraulic lifting) require pipes of several kilometers length where the turbulence will cause nodule degradation through particle fragmentation, chipping, attrition, and/or abrasion (Kim et al., 2021). Particles smaller than 8 µm in diameter will be unlikely to be technically recoverable from the slurry and thus likely to be discharged after pre-processing at sea (Van Wijk and De Hoog, 2020; Kim et al., 2021). As an alternative, Ma et al. (2017) propose a mechanical collection and riser system in open or closed containers, though with a lower production capacity in deep water.

It is yet unclear, whether contractors are aiming at beneficiation of the nodules only, i.e., after dewatering of the nodule slurry for storage, with unrecoverable fractions being discharged at certain depths, or whether a partial treatment of the nodules by chemical and physical means is considered to produce a concentrated intermediate product at sea. A third option would be to carry out the full processing or refining at sea, which seems rather unlikely given the energy requirements.

The ore might have to be watered again for transshipment (inter-ship transfer onto transport barges). This would result in more excess water to be discharged from the transport vessel (likely to surface waters and this time most likely of different physical and chemical composition). A recent publication indicates potential health risks for humans when handling nodule material owing to substantial alpha radiation being emitted from stored and dewatered nodules (Volz et al., 2023).

In addition to vessel-generated noise, the entire mining process from the seafloor to the support vessel will create noise pollution. This includes acoustic telemetry which is employed for positioning, locating, equipment steering and controlling remotely operated vessels (ROV) to support extraction operations. Sound is also used, for example, to communicate with landers, AUVs and other equipment.

An overview of environmental pressures resulting from the excavation process is provided in ISBA/23/C/5, Annex and other reviews (e.g., ICES, 2015; Kaikkonen et al., 2018; Leal Filho et al., 2021, Table 3). In the following, we provide a summary of the currently known likely effects of nodule mining on relevant layers of the ocean, as well as recommendations for BEP from the literature.

In addition to the direct effects of nodule removal from the seafloor, the operation of the mining equipment will have 3-dimensional impacts on the seafloor and water column through plumes, vibrations, noise and lighting (Weaver and Billett, 2019). In particular, the effects of increased turbidity from mining plumes may be the most substantial in the benthic boundary layer (BBL), usually the water layer immediately above the seafloor up to a density stratification at approximately 50 m above the seafloor, which is probably the least known deep sea ecosystem (Christiansen et al., 2020). The BBL hosts specialised benthopelagic organisms such as scavenging amphipods, benthopelagic fish and plankton (Christiansen et al., 2010; Vecchione, 2016; Leitner et al., 2017), is an important region for the dispersal of larvae from benthic organisms (Kersten et al., 2017; Kersten et al., 2019; Patel et al., 2020), and is home to a large number of gelatinous organisms (Childress et al., 1989). Bentho-pelagic coupling is crucial to ecosystem functions from nutrient cycling to energy transfer in food webs and thus particularly sensitive to anthropogenic stressors (Griffiths et al., 2017; Christiansen et al., 2020).

The water column extends from the sunlit upper 200 m (epipelagial) and the mesopelagial (including the faintest light levels down to ca. 1000 m) to the completely dark regions of bathy-, abysso- and benthopelagic waters. The deep pelagic fauna may comprise the largest reservoir of animal diversity on Earth and has crucial roles in ecosystem functioning while providing essential ecosystem services. The deep pelagic habitats have been a comparatively predictable environment for millions of years, and its physical and biological patterns have led to distinct adaptations of its communities (Robison, 2009, quoting Koslow, 2007). Therefore, in bathy-, abysso- and benthopelagic waters, organisms are considered least adapted to environmental changes such as increased turbidity, changes in temperature, food supply as well as light and noise pollution, and small absolute increases may lead to acute effects (van der Grient and Drazen, 2022). Epi- and mesopelagial generate the main organic turn-over and production, feeding the entire foodweb. Surface waters are not only the place where the mining platforms and related vessels operate, but has an ecosystem of its own, the neuston, is the interface to air chemistry and wind forcing, and important for avifauna feeding and all air-breathing animals.

The natural environment of the deep oceans may be cold, clear, and dark, but certainly not silent as animals communicate over short and large distances and other geophysical events cause noise (Stocker, 2002; Duarte et al., 2021). Marine animals produce sounds between 10 Hz and 20 kHz for intra- and interspecies purposes, including navigation, foraging, agonistic displays, territorial defense, mate attraction, and reproductive courtship (Duarte et al., 2021). For example, some deep sea fish species use low sound frequencies to communicate (Miller et al., 2018, quoting Rountree et al., 2012), and benthopelagic invertebrates are suspected to use sound to detect food falls up to 100 m away (Stocker, 2002). However, Duarte et al. (2021) demonstrate, that today in many parts of the ocean the sound produced by anthropogenic sources overrules the natural soundscape, affecting marine animals at multiple levels, including their behaviour, physiology, and, in extreme cases, survival.

Natural light only occurs in the upper layers, where it is very dim, monochromatic, and downwelling, and affects vertical migration (Aksnes et al., 2017). Deeper down many taxa produce their own light. Bioluminescence and olfaction are, among other senses, important means of communication in the lightless depths. Bioluminescence has now been detected throughout the oceans (Heger et al., 2008) and is important for mate finding, camouflage, prey attraction and fending off predators (Robison, 2004). Sensing sound, scent and electromagnetic fields also appears to be common in deep pelagic organisms, but little is known about their functions, and there is urgent need for more studies (Robison, 2004). Most organisms inhabiting this environment possess highly sensitive visual systems, for example, predatory mid-water fish and squid frequently have highly developed eyes, to be functional in even the dimmest illumination (Robison, 2009), which makes them vulnerable to e.g. bright artificial lights of deep sea operations.

Overall, a highly precautionary, ecosystem approach to regulating mining operations is essential, focusing on the collection of additional knowledge while avoiding harm as much as possible (Martin et al., 2021; Williams et al., 2022). The authors recommend an iterative approach to noise regulation starting with highly cautious thresholds enabling rapid management responses and full transparency. Acceptable exposure to sediment plumes should also start with concentrations close to background levels (van der Grient and Drazen, 2022). The thresholds relate to the risks posed to fauna by all mining-related stressors individually and combined (Wedding et al., 2022). This requires strategic environmental goal setting by the ISA, an adaptive governance and a strong scientific programme to reduce scientific and management uncertainties (Jaeckel, 2016; Jaeckel, 2017; Jaeckel, 2020). Existing standards and practices from other offshore industries, e.g. for noise pollution, while indicative, need to be thoroughly tested in the deep sea and offshore context, but may only be applicable to a limited extent (Hitchin et al., 2022).

Before any relevant environmental standards for nodule mining in the Area can be developed, scientifically meaningful and robust environmental baselines have to be established for each contract area and the corresponding region (Billett et al., 2019; Amon et al., 2022; Christiansen et al., 2022a), including the mapping of background noise levels (Martin et al., 2021). Therefore, baseline investigations need to inform the location of the mining area and its corresponding representative reference areas, used to determine mining impacts from the very start of operations in their full ecological context (Jones et al., 2018a; Hao et al., 2020; International Seabed Authority, 2020c). Baselines should also determine habitats, species and ecosystem functions to be preserved. The criteria developed by FAO (2009) and Secretariat of the Convention on Biological Diversity (2009) can guide the positioning of additional no-mining areas of the region(s) and contract areas, in order to preserve essential habitats and communities (Christiansen et al., 2022b). For all BEP standards, it is of utmost importance to observe the pelagic and benthic heterogeneity of the regions in question, e.g. the CCZ, which do not constitute one homogenous region and thus cannot be managed as such (Leitner et al., 2017; Drazen et al., 2021; Leitner et al., 2021; Simon-Lledó et al., 2023).

Temporal or spatial avoidance of certain areas by DSM-related activities as well as the avoidance of especially harmful gear was pointed out as an important precautionary mechanism to deal with uncertainty and as a tool for passive adaptive management (Billett et al., 2019). For example, Cuvelier et al. (2018); Haeckel et al. (2020); Hauquier et al. (2019) and Vanreusel et al. (2016) strongly advocate for the incorporation of additional no-mining sites within each of the contract areas (supplementing the PRZ) for the sole purpose of buffering the inevitable loss of biodiversity. Outside contract areas, the network of ‘Areas of Particular Environmental Interest, APEI, in the CCZ has recently been updated to better cover the spectrum of regional and local habitats across the CCZ, ²⁷ including the core oxygen minimum zone currently not covered by the APEIs (Perelman et al., 2021).

Wagner et al. (2020) suggest that in line with a precautionary approach to ensuring effective protection, mining activities should not be allowed to proceed as long as it cannot be demonstrated that vulnerable marine ecosystems (VME, FAO, 2009) will not be subjected to lasting harm. For example, VMEs such as corals and sponges occur on hard substrate including nodules, rugged terrain, and seamounts within the contract areas. Such habitats will not be directly mined, however may suffer from activities and sediment blanketing. Therefore, a VME definition adapted to the risks of deep seabed mining is required (Christiansen et al., 2019).

In addition, Cuvelier et al. (2018) propose to identify seasons or periods during which mining should be restricted or avoided. These “resting periods” (no noise, light and sediment plumes) might help to maintain life functions for the pelagic fauna during critical periods.

Tilot (2019) points to the high importance of preserving the very distinct oldest water masses located in the North-East Pacific between 1800 and 3500 m depth (quoting Talley et al., 2011), which have unique properties due to their perpetual circulation in the deep ocean. The unique biogeochemistry and microbial flora in these waters are presumed to have an impact on the nodule ecosystem (Tilot, 2019). Mining might pollute these waters, for example, through accidents or unregulated leakages from the riser pipes, as well as through wastewater discharge plumes.

Billett et al. (2019) suggest that the full environmental costs should be considered when designing mining equipment, to minimise harm from the start. Additionally, Billett et al. (2019) advocate for the equipment design process to consider mitigation measures at the earliest possible point in time, alongside best available technologies and practices, and cooperation among contractors to advance industry standards and protocols.

Once mining starts, mechanisms should be in place to meticulously observe the intensity and scale of the disturbances, in order to be able to adapt the respective environmental standards and activities to prevent risks and harm to the marine environment (Cormier and Lonsdale, 2020).

We recommend the ISA to use the scientific recommendations compiled above for starting the development of a first Best Environmental Practice Standard for polymetallic nodule mining operations in the Area. At present, most knowledge and recommendations exist for the Clarion-Clipperton Zone and the Peru Basin. Substantial scientific investigations will be needed for other regions. An ISA Standard for BEP should include operational best practice, maximum permissible emissions, and the environmental framework conditions to be maintained. It would thus build on the environmental goals and objectives to be formulated by the ISA globally and regionally, and the corresponding environmental thresholds, a first set of which are currently being developed. ²⁸ A first BEP standard should be available prior to the first applications for exploitation being received, to allow the ISA to assess an applicant’s ability to meet BEP. The BEP Standard should be periodically reviewed, based on results from DSM monitoring programmes and scientific progress.

Building on the scientific recommendations on BEP for polymetallic nodule mining cited above, we compile in Box 1  a preliminary list of elements for a management framework that can underlie a future BEP standard (the “what”). This list is probably not exhaustive, but we hope it provides a starting point for developing a detailed and scientifically sound understanding of the BEP for polymetallic nodule mining in the Area.

Using best environmental practice for mineral exploration and exploitation in the Area is a legal obligation for the ISA, contractors, and sponsoring states. Whereas environmental standards such as BEP, BAT and GIP, ³⁰ are frequently referred to in the ISA draft exploitation regulations (as of 2023) ³¹ , there is still no agreed understanding of what constitutes current BEP in relation to deep seabed mining, nor are there any agreed processes at ISA to arrive at some (preliminary) conclusions in parallel with the development of the exploitation regulations. This may prevent that the ISA can apply uniform standards to all applications for exploitation contracts. In addition, the development of BEP in the Area and its regions is tightly linked to the as yet undefined global and regional environmental goals and objectives within the ISA to guide the development of a system of precautions in order to avoid unintended, uncontrolled and unnoticed environmental degradation.

Science has a key role to play in informing the development of BEP prior to the commencement of commercial mining. Biological responses to small-scale experimental disturbance events over several decades (Gollner et al., 2017; Jones et al., 2017) provide invaluable indications of what limits need to be set for mining-related interferences in the deep sea. Scientific monitoring and assessment of test mining ³² (Boetius and Haeckel, 2018; Haeckel et al., 2020; Amon et al., 2022) brings this knowledge to a new scale with more informed recommendations for a first set of BEPs. To close current gaps in knowledge, Amon et al. (2022) propose a road map for scientific exploration, including better access to contractor environmental data. However, BEP development will also require effective stakeholder participation, e.g. for fisheries (van der Grient and Drazen, 2021) and the cable industry (International Seabed Authority, 2015) as well as harmonization with existing maritime regulation (International Seabed Authority, 2020a).

If mining commences, the monitoring of operations and related environmental effects on various scales are crucial to verify compliance but also to check the appropriateness of the à priori determined environmental standards to provide for effective environmental protection. Gerber and Grogan (2020) assume it unlikely that the environmental impacts of mining activities, once commenced, can be fully verified by independent monitoring. They propose a staged monitoring approach with a highly intensive, real-time ‘validation monitoring’ in the early phases of the project to ascertain that environmental standards are maintained. In this early phase of mining, uncertainties are highest (Smith et al., 2020), which makes it imperative to validate the à priori determined contract conditions (Ginzky et al., 2020), including a review of the appropriateness of the first set of BEP. Subject to the monitoring and assessment results of commercial-scale mining, the standards may need to be adjusted to maintain the desired in situ conditions. An alternative approach would be to require an in situ test of the mining system of significant scale and duration on the basis of which the standards and BEP can be set. Another alternative would be for contractors to only be allowed to commence with a small-scale project where monitoring should demonstrate the effective protection of the environment.

Unlike in traditional industries, Gerber and Grogan (2020) recommend that required standards for e.g. BEP be limited to those “adopted, approved, or issued by the ISA from time to time.” This allows for some flexibility in adopting new standards. In this way, standards can be applied uniformly to all contractors, while the ISA and sponsoring states can maintain oversight and due diligence. This requires a corresponding highly precautionary and adaptive ISA governance system (Jaeckel, 2016; Craik, 2020), which in effect establishes a management cycle that requires contractors to adapt their operations to regularly updated environmental performance standards.

Such an ecosystem-based environmental management framework does not exist yet, and the future standards and thresholds remain vague at present. Yet it is high time to have a discussion about what constitutes BEP and how to get there given that some exploration contractors are considering to venture into commercial-scale mineral exploitation. By offering a review of the recommendations made by scientists on possible BEP in all ocean layers, we hope to set a starting point for a science-based process to developing a BEP Standard for polymetallic nodule mining.

With so much scientific uncertainty remaining about the environmental impacts of seabed mining (Amon et al., 2022), States, NGOs, scientists and others have called for a pause on DSM ³³ to give effect to the precautionary principle and improve our understanding of deep ocean ecosystems and their vulnerability to the effects of DSM. One might argue that if and when widespread support for postponing DSM exists, such a delay or pause may itself be regarded as BEP.

SC conceived and created the manuscript and researched the literature. All authors contributed to the article and approved the submitted version.