Clarion-Clipperton Fracture Zone Research Articles

Preliminary Assessment of Environmentally Friendly Mining Options Based on Various Mineral Resources—A Case Study of the Clarion-Clipperton Fracture Zone in Pacific

Deep-sea polymetallic nodules are associated with rich rare substances, such as rare-earth elements (REEs), Mo, Ti, Te, Li, which are currently in demand and are used in various applications. Deep-sea sediments near nodules are another important source of REEs, which will increase the resource potential of polymetallic nodules. Given the similarity of the mining technologies for deep-sea REEs and polymetallic nodules, this study proposed environmentally friendly mining options and developed a technoeconomic evaluation model by combining deep-sea polymetallic nodules and REEs. Using the Clarion-Clipperton Fracture Zone as an example, this study revealed that the development of polymetallic nodules together with REEs of nearby sediments in the form of by-products will improve the economic and environmental benefits. In addition, the effects of discount rate, cost, and price on the economic benefits of nodule mining were discussed, and a technical development direction was proposed based on scientific and technological needs.

Full radionuclide analysis of polymetallic nodules from the Clarion-Clipperton-Fracture Zone in the NE Pacific

Polymetallic Nodules from the deep sea are currently being targeted for mineral exploration as they are a significant resource for various critical metals. In addition to accumulating such metals, nodules are also known to adsorb naturally occurring radioactive nuclides. With the possibility of exploitation of nodules becoming more likely within the next years, it is important to assess the potential radiation exposures resulting from the handling of polymetallic nodules. In this study we present, for the first time, specific activities of all long-lived alpha, beta and gamma emitters from the natural decay chains of Uranium-238, Uranium-235 and Thorium-232, in bulk and surface material of the same nodules obtained from 10 locations within the Clarion-Clipperton Zone. The results show elevated specific activities for the nuclides Th-230, Ra-226, Pb-210, Po-210, as well as Pa-231 and Ac-227 in accordance with prior reported activities. However, in contrast to assumptions made in previous studies, our analyses show that Pa-231 is not in equilibrium with its daughter nuclide Ac-227. The emanation factor of Rn-222 for dry and water-saturated nodules has also been determined and is higher than previously reported. The results presented here are a key ingredient to assess human radiation exposure during the processes of polymetallic nodule mining, storage and beneficiation.

Correction: Oceanic bottom mixed layer in the Clarion-Clipperton Zone: potential influence on deep-seabed mining plume dispersal

Correction: Oceanic bottom mixed layer in the Clarion-Clipperton Zone: potential influence on deep-seabed mining plume dispersal

Reducing CO2 Emissions through the Strategic Optimization of a Bulk Carrier Fleet for Loading and Transporting Polymetallic Nodules from the Clarion-Clipperton Zone

As global maritime cargo transportation intensifies, managing CO2 emissions from ships becomes increasingly crucial. This article explores optimizing bulk carrier fleets for transporting polymetallic nodules (PMNs) from the Clarion-Clipperton Zone (CCZ) to reduce CO2 emissions. Our analysis shows that larger bulk carriers, despite greater drifting forces from environmental conditions, emit less CO2 over the entire transport mission, including loading and transit. Deploying large ships in global maritime trade could significantly reduce CO2 emissions. This study also introduces a novel artificial neural network (ANN) model to estimate drifting forces during loading operations and proposes a new method for estimating CO2 emissions, considering environmental conditions and ship seakeeping properties. These findings highlight the importance of fleet size optimization and effective operational planning in achieving environmental sustainability in maritime transport.

Flocculation of deep-sea clay from the Clarion Clipperton fracture zone

This article discusses whether or to what extent flocculation plays a role in the saline deep-sea environment and whether sediment plumes generated by deep-sea mining activities are affected by the process of flocculation. The results of our laboratory study demonstrate that deep sea mineral clay with a median floc size of 20μm can flocculate quickly within 2.5 min of mixing to form flocs with a median floc size of about 50–150μm and outliers as large as 500μm in size due to the presence of natural organic matter. At high shear (turbulent mixing), a threshold of about 125s−1 was found above which, organic matter can successfully bind to clay. Above 125s−1, the steady-state floc size is also found to increase linearly with shear. In low energetic conditions (when flocs experience mainly differential settling), the median floc sizes are found to be 2 or 3 times larger than at turbulent mixing. As expected, the rate of flocculation is greater at higher clay concentrations. At long mixing times, the median floc size is found to decrease due to the breaking/reconformation of flocs. Experiments performed to study the ageing of flocs at rest demonstrated that a dynamic process was ongoing between the organic matter and the clay. It is hypothesized that the organic matter present has amphiphilic properties. Over time, the organic matter would rearrange itself such as to maximize its contact area with the mineral clay, resulting in two effects, depending on the structure of the flocs. In the case of flocs formed at high shear, it led to a rupture of flocs. A slow agitation of settled flocs, having previously experienced low shear conditions, on the other hand, led to aggregation. Overall, the results found in the present article show that flocculation likely plays a significant role in deep-sea areas.

Rare earth element enrichment process of bioapatite in deep-sea REY-rich sediments

Rare earth element and yttrium (REY) compositions of bioapatite (e.g., fish tooth and bone) can serve as potential paleoceanographic indicators. However, the REY enrichment of bioapatite and REY transfer from FeMn micronodule to bioapatite remain unclear owing to a lack of comparative study on these processes under variable redox conditions (oxic vs. suboxic), which hampers the utility of these indicators. To address these uncertainties, we conducted in situ geochemical analyses of fish teeth and FeMn micronodules from two REY-rich sediment cores (GC01 and GC02) collected from the Clarion–Clipperton fracture zone in the central equatorial Pacific. We found that the Ce/Ce* ratios of fish teeth from GC01 (sediments ΣREY = 723 ± 274 ppm) and GC02 (sediments ΣREY = 506 ± 65 ppm) gradually increased with depth under oxic conditions, with calculated oxic pore water-derived REY increasing from ∼0–3% on the surface to ∼11–24% at 200 cmbsf. In deep sediment columns (>200 cmbsf), the suboxic pore water contributed a small amount of REY (∼4% to ∼13%) to fish teeth, as evidenced by sharp increases in Ce/Ce* ratios of fish teeth and decreases in Ce/Ce* ratios and increases in YN/HoN ratios of micronodules. Therefore, the REY-patterns of fish teeth in core-deep samples were overprinted by oxic–suboxic pore waters may be unreliable archives of ancient bottom seawater.

A New Species of the Anglerfish Genus Gigantactis (Lophiiformes: Ceratioidei) from the Clarion Clipperton Zone of the Eastern North Pacific Ocean, an Ecosystem Threatened by Deep-Sea Mining

A New Species of the Anglerfish Genus Gigantactis (Lophiiformes: Ceratioidei) from the Clarion Clipperton Zone of the Eastern North Pacific Ocean, an Ecosystem Threatened by Deep-Sea Mining

Industrial mining trial for polymetallic nodules in the Clarion-Clipperton Zone indicates complex and variable disturbances of meiofaunal communities

Following several small-scale benthic disturbance experiments, an industrial polymetallic nodule collector trial was conducted by the company Global Sea mineral Resources (GSR) in their exploration contract area in the Clarion-Clipperton Zone using the pre-prototype vehicle Patania II (PATII). In this study, meiofaunal (i.e., nematode abundance, ASV diversity and genus composition) and environmental (i.e., grain size, total organic carbon/total nitrogen and pigment) properties are compared between disturbance categories (i.e., Pre-impact, Collector Impact and Plume Impact). One week after the trial, proxies for food availability within the Collector Impact sediments were altered with lower total organic carbon (TOC) and pigment (i.e., CPE: sum of Chlorophyll a and phaeopigments) values. Albeit not significant, the observed decrease of nematode abundance and ASV diversity, further indicate the consequences of the removal of the ecologically important surface sediment layer within the PATII tracks. Next to sediment removal, exposed sediments were modified in different ways (e.g., central strips, parallel caterpillar imprints with alternating bands of depressions/ripples and interface patches) and were also subject to heavy collector-induced sediment blanketing. We propose that these cumulative impacts have led to intricate seabed modifications with various levels of disturbance intensity which resulted in the high meiofaunal variability observed. Adjacent nodule-rich areas (i.e., Plume Impact) received considerable levels of sediment deposition (2-3 cm) and were defined by significantly lower food sources (CPE, TOC, carbon to nitrogen ratio) and an observation of meiofaunal enrichment (i.e., higher average nematode abundance and ASV diversity; although statistically non-significant), but mechanisms behind these ecological changes (e.g., suspended material-surface fluxes, passive dispersal of fauna in the plume vs. active upward migration and “viability” of redeposited fauna) remain unresolved. We conclude that complex benthic pressure-response relationships associated with the PATII trial, combined with the high degree of natural spatial and temporal variability in abyssal meiofaunal communities and sedimentary parameters, complicates the quantitative assessment of deep-sea mining associated disturbances.

Bryozoa (Cheilostomata) from polymetallic nodules in the Russian exploration area, Clarion–Clipperton Fracture Zone, eastern Pacific Ocean—taxon novelty and characteristics as macro- and megafaunal elements

Bryozoa (Cheilostomata) from polymetallic nodules in the Russian exploration area, Clarion–Clipperton Fracture Zone, eastern Pacific Ocean—taxon novelty and characteristics as macro- and megafaunal elements

At-sea application of the comet assay to a deep-sea fish

Given the go ahead, deep-sea mining operations are likely to continue for decades on a substantial spatial scale and the resulting sediment plumes combined, are likely to extend beyond the licenced mining areas, and could lead to the chronic exposure of deep-sea organisms to a mixture of metals, even mobile species, such as fish, that could conceivably display avoidance behaviour. The metal concentrations, often substantially below lethal doses, mean that individual mortality is too blunt a measure to allow assessment of “serious harm”. Commonly used cellular biomarkers of exposure in ecotoxicology include DNA damage using the Comet assay. True deep-sea ecotoxicological studies with fish are rare and to our knowledge, there are no published data or method optimizations for deep-sea fish. Coryphaenoides ssp. were collected during SMARTEX expedition 1 (Feb/Mar, 2023) to the Clarion Clipperton Zone (CCZ) in the Eastern Pacific Ocean using a baited trap deployed between 4580–4,732m depth for 24–48 h. Blood and gill tissue were removed and processed for the Comet assay. In order to reduce artefactual DNA damage from cryopreservation observed previously, two sets of samples were prepared: a cryopreservative (10% DMSO) was added to one set of samples and stored at −80 °C; the second set was used to perform a Comet assay within hours of collection. A custom-built gimble table enabled horizontal electrophoresis at sea after which Comet assay slides were dried and stored at room temperature until further analysis. The Comet assay was also assessed in freshly sampled and frozen rainbow trout cells as a proxy control in order to evaluate potential artefacts from the collection and sampling procedure of the deep-sea fish. The blood samples processed at sea had a significantly reduced level of DNA damage compared to the frozen samples. There was no significant difference between the fresh deep-sea and rainbow trout samples. However, the freshly prepared gill samples in Coryphaenoides ssp. showed substantial artefacts, possibly as a consequence of barotrauma. These results represent the first effort at establishing baseline DNA damage data for deep-sea fish, an essential component in understating and quantifying the impact of deep-sea mining.

Integrative taxonomy supports the establishment of a new deep-sea family of Tanaidacea (Peracarida)

Abstract The tanaidacean family Colletteidae is large and exhibits highly diverse morphologies. A significant structural feature, the cephalothorax-cheliped attachment, is one of the sources of this variation but is still poorly understood or resolved in phylogenetic terms. The presence (and wide intrafamily disparities) of a lateral carapacial sclerite associated with this articulation is the main contributor to the diversity and this is investigated by us and shown to have valuable information for paratanaoidean phylogenies. We used integrative taxonomy to evaluate the status of several described colletteid genera, Caudalonga, Macrinella and Pseudoarthrura, based on analysis of COI and 18S genes, comparison with molecular data from ten other paratanaoidean families and detailed morphological study including confocal imaging of whole specimens, with the ‘sclerite’ a prime target for analysis. The results supported the establishment of a new family, Caudalongidae fam. nov., extracted from the overburdened Colletteidae, the narrow-bodied taxa defined principally by the small cheliped sclerite partly covered by a wide membrane and a short one-articled uropodal exopod. Apart from redescriptions/redefinitions of the genera Caudalonga, Macrinella, and Pseudoarthrura, two new genera Facultatotanais gen. nov. and Universitatotanais gen. nov. are erected and six new species are described, Caudalonga kurilensis sp. nov., F. bios sp. nov., U. freie sp. nov., U. gandavensis sp. nov., U. harvardi sp. nov., and U. jagiellonensis sp. nov. The Clarion Clipperton-Fracture Zone appears to support a high diversity of the family.

New xenophyophores (Foraminifera, Monothalamea) from the eastern Clarion-Clipperton Zone (equatorial Pacific).

Xenophyophores are large, agglutinated foraminifera that dominate the benthic megafauna in some parts of the deep sea. Here, we describe an assemblage of largely fragmentary specimens from the Clarion-Clipperton Zone (CCZ), an area of the eastern abyssal Pacific hosting large, commercially significant deposits of polymetallic nodules. We recognised 18 morphospecies of which eight yielded DNA sequences. These include two new genera and three new species, Claraclippia seminuda gen. & sp. nov., Stereodiktyoma mollis gen. & sp. nov., and Aschemonella tani sp. nov., three that are assigned to known species, Abyssalia foliformis, Aschemonella monilis and Shinkaiya contorta, and two assigned to open nomenclature forms Abyssalia aff. foliformis and Stannophyllum aff. granularium. An additional ten forms are represented only by morphology. The following seven are placed in known genera, species and open-nomenclature forms: Aschemonella? sp., Homogammina sp., Psammina multiloculata, P. aff. multiloculata, P. aff. limbata form 1 sensu Gooday et al., 2018, P. aff. limbata form 2 sensu Gooday et al., 2018, and Stannophyllum spp. The other three could not be identified to genus level. This new collection brings the total of described and undescribed species and morphotypes from the CCZ to 27 and 70, respectively, reinforcing the already high diversity of xenophyophores known from this part of the Pacific.

Assigning the unassigned: A signature-based classification of rDNA metabarcodes reveals new deep-sea diversity.

Environmental DNA metabarcoding reveals a vast genetic diversity of marine eukaryotes. Yet, most of the metabarcoding data remain unassigned due to the paucity of reference databases. This is particularly true for the deep-sea meiofauna and eukaryotic microbiota, whose hidden diversity is largely unexplored. Here, we tackle this issue by using unique DNA signatures to classify unknown metabarcodes assigned to deep-sea foraminifera. We analyzed metabarcoding data obtained from 311 deep-sea sediment samples collected in the Clarion-Clipperton Fracture Zone, an area of potential polymetallic nodule exploitation in the Eastern Pacific Ocean. Using the signatures designed in the 37F hypervariable region of the 18S rRNA gene, we were able to classify 802 unassigned metabarcodes into 61 novel lineages, which have been placed in 27 phylogenetic clades. The comparison of new lineages with other foraminiferal datasets shows that most novel lineages are widely distributed in the deep sea. Five lineages are also present in the shallow-water datasets; however, phylogenetic analysis of these lineages separates deep-sea and shallow-water metabarcodes except in one case. While the signature-based classification does not solve the problem of gaps in reference databases, this taxonomy-free approach provides insight into the distribution and ecology of deep-sea species represented by unassigned metabarcodes, which could be useful in future applications of metabarcoding for environmental monitoring.

Enrichment of Smectite in the REY‐Rich Mud of the Clarion‐Clipperton Fracture Zone in the Eastern Pacific and Its Geological Significance

AbstractREY‐rich mud, consisting of deep‐sea sediments with high concentrations of rare‐earth elements and yttrium (REY), holds significant economic potential. Many studies have been conducted on biogenic apatite, ferromanganese micronodule, and phillipsite within these deposits to ascertain the REY enrichment mechanisms. However, the knowledge of clay minerals in REY‐rich mud, which is the predominant component of pelagic sediments, is still limited. In this study, two adjacent gravity cores (core GC02: REY‐rich mud; core GC03: typical sediments of equatorial Pacific) were collected from the Clarion‐Clipperton Fracture Zone (CCFZ) of the Eastern Pacific to study the role of different clay minerals in REY enrichment. The clay minerals in core GC03 and core GC02 are primarily illite (averaging 60%) and smectite (averaging 63%), respectively, and the smectite in core GC02 was mainly Fe‐rich, which was probably formed via the reaction between opal and FeOOH. Moreover, multiple studies have reported similar smectite enrichment in REY‐rich mud, suggesting that it is a common characteristic. The presumed hydrothermal or volcanic origination of smectite in REY‐rich layers of core GC02 indicates the essential role of hydrothermal and volcanic activities in REY‐rich mud formation during the Oligocene in the western CCFZ.

Geochemical Behavior of Shallow Buried Nodules from Clarion–Clipperton Fracture Zone in the East Pacific: A LA-ICP-MS Mapping Analysis Perspective

The Clarion–Clipperton Fracture Zone of the east Pacific contains numerous shallow buried nodules that are in direct contact with pore water in sediment, providing a direct reflection of the interaction between nodules and sediment. However, research on the geochemical behavior of these shallow-buried nodules is limited. This study used laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) to compare mineral and element distribution in shallow buried nodules with surface nodules. The shallow buried nodules are products of nodules entering the burial stage. In comparison to surface nodules, shallowly buried nodules develop a fourth oxidized-suboxic diagenetic growth layer after entering the burial stage, in addition to the three main growth inner layers (L1, L2, L3). We suggest that L4 is not influenced by the bottom water source and that the presence of todorokite and the high flux of Mn2+ in the sediment pore water compete with other metal elements to enter the lattice of manganate, resulting in significantly higher Mn, W, and Li contents in L4 compared to L2. However, the content of Ni, Mg, and other hydrogenetic elements is much lower in L4 compared to L2. We suggest that the instantaneous change in surface primary productivity results in a sudden shift in the redox environment of the upper sediment layer. This reaction leads to the reduction of solid-phase Mn, providing growth opportunities for the buried nodules. Simultaneously, this may also be the reason why the growth layer of the nodules is jointly controlled by the sedimentary processes of hydrogenetic, oxic diagenetic, and suboxic diagenetic processes.

ГЕОЛОГОРАЗВЕДОЧНЫЕ РАБОТЫ НА МЕСТОРОЖДЕНИИ ЖЕЛЕЗОМАРГАНЦЕВЫХ КОНКРЕЦИЙ В ЗОНЕ КЛАРИОН–КЛИППЕРТОН ТИХОГО ОКЕАНА: ИСТОРИЯ И РЕЗУЛЬТАТЫ ИССЛЕДОВАНИЙ

The paper highlights the history of Russian research of manganese nodules in the Pacific Clarion–Clipperton zone, the most promising nodule-bearing province of the World Ocean, and presents the main results of geological exploration work carried out in the Russian license area in the Pacific Ocean – the Russian Exploration Area for Polymetallic nodules. The article provides information about the contractual obligations to the International Seabed Authority (ISBA) that the Russian Federation has in accordance with a fifteen-year contract for the exploration of polymetallic nodules concluded with the ISBA. The paper also presents the main results of studying the baseline environmental characteristics of the natural environment in the Russian Exploration Area for Polymetallic Nodules. Information is provided on the fulfillment of other contractual obligations to the International Seabed Authority: scientific research on the development of exploration and production technologies, processing technologies, training of personnel for the International Seabed Authority, and fulfillment of financial obligations.

Population-level prokaryotic community structures associated with ferromanganese nodules in the Clarion-Clipperton Zone (Pacific Ocean) revealed by 16S rRNA gene amplicon sequencing.

Although deep-sea ferromanganese nodules are a potential resource for exploitation, their formation mechanisms remain unclear. Several nodule-associated prokaryotic species have been identified by amplicon sequencing of 16S rRNA genes and are assumed to contribute to nodule formation. However, the recent development of amplicon sequence variant (ASV)-level monitoring revealed that closely related prokaryotic populations within an operational taxonomic unit often exhibit distinct ecological properties. Thus, conventional species-level monitoring might have overlooked nodule-specific populations when distinct populations of the same species were present in surrounding environments. Herein, we examined the prokaryotic community diversity of nodules and surrounding environments at the Clarion-Clipperton Zone in Japanese licensed areas by 16S rRNA gene amplicon sequencing with ASV-level resolution for three cruises from 2017 to 2019. Prokaryotic community composition and diversity were distinct by habitat type: nodule, nodule-surface mud, sediment, bottom water and water column. Most ASVs (~80%) were habitat-specific. We identified 178 nodule-associated ASVs and 41 ASVs associated with nodule-surface mud via linear discriminant effect size analysis. Moreover, several ASVs, such as members of SAR324 and Woeseia, were highly specific to nodules. These nodule-specific ASVs are promising targets for future investigation of the nodule formation process.

Geochemistry of buried polymetallic nodules from the eastern Pacific Ocean: Implication for the depth-controlled alteration process

Polymetallic nodules are often exposed or semi-buried in surface sediments of abyssal plains, with certain older generations of nodules being deeply buried in the sediment column. Owing to the limitations of sampling, it is unclear whether these nodules have remained intact or have been altered after burial. To explore this question, we carried out a comparative study of the mineralogy and chemistry of polymetallic nodules recovered from the surface sediment and two depth intervals within a sediment column (220–223 cm and 550–555 cm) in the Clarion–Clipperton Zone of the eastern Pacific Ocean. All of the nodules examined have obvious layered structures. The main minerals in the buried nodules are 10 Å vernadite, 7 Å phyllomanganate, and Fe-vernadite, which are characteristic of the hydrogenetic type of polymetallic nodule. However, the in situ Mn/Fe ratios suggest that some microlayers are diagenetic type. With the burial depth, the total content of rare earth elements and yttrium decreased in the bulk nodules, whereas their positive Ce anomalies and diagenetic parts gradually increase. The nodule buried at 220–223 cm sediment depth shows no obvious alterations, whereas the one buried at 550–555 cm has an approximately 200-μm-thick microlayer of continuous diagenetic growth on its surface. Additionally, this GC04_550–555 cm nodule has a microlayer with higher Cu/Ni and Si/Al ratios, located adjacent to its outer diagenetic microlayer, further indicating its alteration after burial. Therefore, the alterations of buried polymetallic nodules may be related to their burial depth. Compared with the sediment layers above and below, the bulk sediment at the 550–555 cm interval has a relatively lower Mn content and higher Fe content, which may be related to the observed alterations in the buried nodule found therein. Our findings on the alterations of polymetallic nodules after burial and the possible impact of the sedimentary environment on those changes provide a theoretical basis for establishing the burial events of these ferromanganese aggregates in the geological history of the study area.

Trace element characteristics of pore water from the deep-sea sediments of the Interoceanmetal exploration area in the Clarion-Clipperton Fracture Zone, NE Pacific

The concentrations of Fe, Mn, Co, Cd, Zn, Cu, Mo, and As were registered in broad intervals and are elevated compared to the mean values for the ocean water. Vertical distributions of the element concentrations in the pore waters along four sediment cores show distinct differences, mainly for the elements Fe, Mn, Cu, and Zn. Bioturbation activities developed in the depth interval 7–15 cm could be a probable reason for the variation trends. The distributions for the elements As, Cd, Co and Zn are conservative type and the patterns for the Mo and Ni – scavenged type. The obtained pore water profiles are similar to the distribution trends for areas in the Eastern Equatorial Pacific and show different patterns from the pore waters from the Western Pacific.

Complete mitochondrial genome of the abyssal coral Abyssoprimnoa gemina Cairns, 2015 (Octocorallia, Primnoidae) from the Clarion-Clipperton Zone, Pacific Ocean

The Clarion-Clipperton Zone (CCZ) in the tropical East Pacific is a region of interest for deep-sea mining due to its underwater deposits of polymetallic nodules containing economically important metals such as nickel, copper, and cobalt. It is also a region of extensive baseline studies aiming to describe the state of the environment, including the biodiversity of the benthic fauna. An abundant component of the abyssal plain ecosystem consists of sessile fauna which encrusts polymetallic nodules and are vulnerable to potential impacts arising from exploitation activities, particularly removal of substrate. Therefore, this fauna is often considered to have key species whose genetic connectivity should be studied to assess their ecological resilience. One such species is Abyssoprimnoa gemina Cairns, 2015, a deep-sea coral from the CCZ whose presence in the Interoceanmetal Joint Organization (IOM) claim area has been confirmed during samplings. In this study, we used next-generation sequencing (NGS) to obtain the 18S nuclear rRNA gene and the complete mitochondrial genome of A. gemina from IOM exploration area. The mitogenome is 18,825 bp long and encodes for 14 protein coding genes, 2 rRNAs, and a single tRNA. The two phylogeny reconstructions derived from these data confirm previous studies and display A. gemina within a highly supported cluster of seven species whose mitogenomes are all colinear and of comparable size. This study also demonstrates the suitability of NGS for DNA barcoding of the benthic megafauna of the CCZ, which could become part of the IOM protocol for the assessment of population diversity and genetic connectivity in its claim area.