Recovery of Paleodictyon patterns after simulated mining activity on Pacific nodule fields

Since the late 1980s, various experiments have been conducted in polymetallic nodule fields of the Pacific Ocean to assess the potential environmental impacts of future mining, specifically in two areas: the Peru Basin and the Clarion-Clipperton Fracture Zone (CCZ). Two expeditions, SO242/2 in 2015 (Peru Basin) and SO268/1 + 2 in 2019 (CCZ), deployed a towed camera system to collect imagery from both areas. These expeditions aimed to assess recovery of fauna in the short (few weeks) and long term (several years) following physical seafloor disturbance actions designed to mimic potential mining, by ploughs, dredges and epibenthic sleds. Within the collected image data, several strikingly hexagonal hole patterns were observed and identified as Paleodictyon nodosum, and an irregular form of Paleodictyon traces, both on undisturbed and disturbed areas of seafloor. Recent forms occur abundantly in various deep-sea regions, but their origin, and how they represent the mode of life of the forming organism, remains unknown. In this study, the imaged occurrences of Paleodictyon traces on disturbed seafloor sheds light on the lifecycle of the forming organism, demonstrating that they can recolonize disturbed habitat and produce the trace network in a few weeks. Nevertheless, the density of these patterns on disturbed substrates was lower than observed on undisturbed substrates in both nodule regions. We therefore hypothesize that, along with other benthic deep-sea fauna, these structures and the forming organism are impacted by physical seafloor disturbance, and even 26 years after disturbance, densities on disturbed sediments have not recovered to undisturbed levels.

Deep-sea polymetallic nodules as opportunity for future supply with critical raw materials

The renewed importance of polymetallic nodules in the context of forecasted increasing demands for metals are discussed. Based on the Interoceanmetal Joint Organization’s (IOM) site-specific data obtained during the exploration activity in the Clarion-Clipperton Fracture Zone, a total of 272.5 Mt of nodules were estimated as economically reasonable for future mining for Ni, Cu, Co, and Mn. Additionally, data for REE and other critical elements in nodules as potential by-products are presented.

RV SONNE Fahrtbericht/Cruise Report SO268 - Assessing the Impacts of Nodule Mining on the Deep-sea Environment: NoduleMonitoring, Manzanillo (Mexico) – Vancouver (Canada), 17.02. – 27.05.2019

Cruise SO268 is fully integrated into the second phase of the European collaborative JPI-Oceans project MiningImpact and is designed to assess the environmental impacts of deep-sea mining of polymetallic nodules in the Clarion-Clipperton Fracture Zone (CCZ). In particular, the cruise aimed at conducting an independent scientific monitoring of the first industrial test of a pre-protoype nodule collector by the Belgian company DEME-GSR. The work includes collecting the required baseline data in the designated trial and reference sites in the Belgian and German contract areas, a quantification of the spatial and temporal spread of the produced sediment plume during the trials as well as a first assessment of the generated environmental impacts. However, during SO268 Leg 1 DEME-GSR informed us that the collector trials would not take place as scheduled due to unresolvable technical problems. Thus, we adjusted our work plan accordingly by implementing our backup plan. This involved conducting a small-scale sediment plume experiment with a small chain dredge to quantify the spatial and temporal dispersal of the suspended sediment particles, their concentration in the plume as well as the spatial footprint and thickness of the deposited sediment blanket on the seabed.

Potential impacts of polymetallic nodule removal on deep-sea meiofauna

Deep seabed mining is potentially imminent in the Clarion Clipperton Fracture Zone (CCFZ; northeast Pacific). Seabed collectors will remove polymetallic nodules and the surrounding surface sediments, both inhabited by meiofauna, along their path. To determine potential impacts of polymetallic nodule removal, we investigated the importance of nodule presence for the abundance, composition and diversity of sediment meiofauna, and evaluated the existence and composition of nodule crevice meiofauna in the Global Sea Mineral Resources (GSR) exploration contract area. Nodule-free and nodule-rich sediments displayed high biodiversity with many singletons and doubletons, potentially representing rare taxa. Nodule presence negatively influenced sediment meiofaunal abundances but did not markedly affect taxonomic composition or diversity. This is the first report on CCFZ nodule crevice meiofauna, whose abundance related positively to nodule dimensions. Though dominated by the same taxa, nodules and sediments differed regarding the taxonomic and trophic composition of the meio- and nematofauna. Nevertheless, there were no taxa endemic to the nodule crevices and nodule crevice meiofauna added only little to total small-scale (~ cm) meiofaunal abundance and diversity. We formulated environmental management recommendations at the contract area and regional (CCFZ) scale related to sampling effort, set-aside preservation and monitoring areas, and potential rehabilitation measures.

Vasopora ceramica n. gen., n. sp.—a new abyssal cyclostome bryozoan from polymetallic nodules in the Russian exploration area, Clarion–Clipperton Fracture Zone, eastern Pacific Ocean

A new abyssal cyclostome bryozoan genus and species, Vasopora ceramica n. gen., n. sp., is described from the eastern Russian exploration area of the Clarion–Clipperton Fracture Zone based on newly collected material from Yuzhmorgeologiya GLD4–19 station 421 (13.23408° N, 134.22180° W, 4809 m depth). Generic characters include an erect pedunculate colony with a distinct boundary between column and flared capitulum, short autozooidal peristomes in a single whorl, numerous alveoli, a central unidirectional sac-like gonozooid covered by a surficial network of crossed ridges continuous with adjacent rims of alveoli, a laterally opening ooeciopore, and the entire capitulum surface being minutely densely granular to subspinulate. Whereas the skeletal microstructure of the capitulum surface comprises irregular imbricated crystallites, the column has a planar-spherulitic fabric of acicular crystallites in fan-like arrays, and there are no pseudopores. The sharp boundary between capitulum and column, with their different microstructure separates Vasopora n. gen. from the two existing genera of Alyonushkidae that are found in the same environment. Vasopora n. gen. has a stalk formed of calcified exterior wall, whereas it is interior-walled in Alyonushka and Calyssopora.

Diversity of Deep-Sea Scale-Worms (Annelida, Polynoidae) in the Clarion-Clipperton Fracture Zone

The polymetallic nodules lying on the seafloor of the Clarion-Clipperton Fracture Zone (CCFZ) represent over 30 billion metric tons of manganese. A single mining operation has potential to directly impact approximately 200 km2 of the seabed per year. Yet, the biodiversity and functioning of the bentho-demersal ecosystem in the CCFZ remain poorly understood. Recent studies indicate a high species diversity in a food-poor environment, although the area remains poorly sampled. Undersampling is aggravated by a combination of low densities of fauna and high habitat heterogeneity at multiple spatial scales. This study examines the Polynoidae, a diverse family of mobile polychaetes. Sampling with an epibenthic sledge and a remotely operated vehicle was performed during the cruise SO239 within the eastern CCFZ. Five areas under the influence of a sea surface productivity gradient were visited. Specimens were identified using morphology and DNA: (i) to provide a more comprehensive account of polynoid diversity within the CCFZ, (ii) to infer factors potentially driving alpha and beta diversity, and (iii) to test the hypothesis that epibenthic polychaetes have low species turnover and large species range. Patterns of species turnover across the eastern CCFZ were correlated with organic carbon fluxes to the seafloor but there was also a differentiation in the composition of assemblages north and south of the Clarion fracture. In contrast to the previous studies, patterns of alpha taxonomic and phylogenetic diversity both suggest that polynoid assemblages are the most diverse at Area of Particular Environmental Interest no. 3, the most oligotrophic study site, located north of the Clarion fracture. Without ruling out the possibility of sampling bias, the main hypothesis explaining such high diversity is the diversification of polynoid subfamily Macellicephalinae, in response to oligotrophy. We propose that macellicephalins evolved under extremely low food supply conditions through adoption of a semi-pelagic mode of life, which enabled them to colonise new niches at the benthic boundary layer and foster their radiation at great depths.

Chemostratigraphic and Textural Indicators of Nucleation and Growth of Polymetallic Nodules from the Clarion-Clipperton Fracture Zone (IOM Claim Area)

The detailed mineralogical and microgeochemical characteristics of polymetallic nodules collected from the Interoceanmetal Joint Organization (IOM) claim area, Eastern Clarion-Clipperton Fracture Zone (CCFZ, Eastern Pacific) were described in this study. The obtained data were applied for the delimitation of nodule growth generations and estimation of the growth ratios (back-stripping using the Co-chronometer method). The applied methods included bulk X-ray powder diffraction (XRD) and electron probe microanalysis (EPMA), providing information about Mn-Fe minerals and clays composing nodules, as well as the geochemical zonation of the growth generations. The analyzed nodules were mostly diagenetic (Mn/Fe > 5), with less influence on the hydrogenous processes, dominated by the presence of 10-Å phyllomanganates represented by todorokite/buserite, additionally mixed with birnessite and vernadite. The specific lithotype (intranodulith), being an integral part of polymetallic nodules, developed as a result of the secondary diagenetic processes of lithification and the cementation of Fe-rich clays (potentially nontronite and Fe-rich smectite), barite, zeolites (Na-phillipsite), bioapatite, biogenic remnants, and detrital material, occurs in holes, microcaverns, and open fractures in between ore colloforms. The contents of ∑(Ni, Cu, and Co) varied from 1.54 to 3.06 wt %. Several remnants of siliceous microorganisms (radiolarians and diatoms) were found to form pseudomorphs. The applied Co-chronometer method indicated that the nodules’ age is mainly Middle Pliocene to Middle Pleistocene, and the growth rates are typical of diagenetic and mixed hydrogenetic–diagenetic (HD) processes. Additionally, few nodules showed suboxic conditions of nucleation. Growth processes in the eastern part of the CCFZ deposit might have been induced with the Plio-Pleistocene changes in the paleooceanographic conditions related to the deglaciation of the Northern Hemisphere.

Extent of impact of deep-sea nodule mining midwater plumes is influenced by sediment loading, turbulence and thresholds

Deep-sea polymetallic nodule mining research activity has substantially increased in recent years, but the expected level of environmental impact is still being established. One environmental concern is the discharge of a sediment plume into the midwater column. We performed a dedicated field study using sediment from the Clarion Clipperton Fracture Zone. The plume was monitored and tracked using both established and novel instrumentation, including acoustic and turbulence measurements. Our field studies reveal that modeling can reliably predict the properties of a midwater plume in the vicinity of the discharge and that sediment aggregation effects are not significant. The plume model is used to drive a numerical simulation of a commercial-scale operation in the Clarion Clipperton Fracture Zone. Key takeaways are that the scale of impact of the plume is notably influenced by the values of environmentally acceptable threshold levels, the quantity of discharged sediment, and the turbulent diffusivity in the Clarion Clipperton Fracture Zone.

Potential Impacts of Polymetallic Nodule Removal On Deep-Sea Meiobenthos

Deep seabed mining is imminent in the Clarion Clipperton Fracture Zone (CCFZ; northeast Pacific). Seabed collectors will remove the polymetallic nodules and the surrounding surface sediments, both inhabited by meiobenthos, along their path. To determine potential impacts of polymetallic nodule removal, we investigated the importance of nodule presence for sediment abundance, composition and diversity of meiobenthos, nematodes and copepods, and evaluated the existence and composition of nodule crevice meiobenthos in the Global Sea Mineral Resources (GSR) exploration contract area. Nodule-free and nodule-rich sediments displayed high biodiversity with many singletons and doubletons, potentially representing rare taxa. Nodule presence negatively influenced sediment meiobenthic abundances but did not markedly affect community composition or diversity. This is the first report on CCFZ nodule crevice meiobenthos, whose abundance related positively to nodule dimensions. Though dominated by the same taxa, the meio- and nematofauna differed between sediments and nodules regarding community and functional composition. Nevertheless, there were no taxa endemic to the nodule crevices and nodule crevice meiobenthos added only little to total small-scale (~ cm) meiobenthic abundance and diversity. We formulated environmental management recommendations at the contract area and regional (CCFZ) scale related to sampling effort, set-aside preservation and monitoring areas, and potential rehabilitation measures.

Comparative Reproductive Biology of Deep-Sea Ophiuroids Inhabiting Polymetallic-Nodule Fields in the Clarion-Clipperton Fracture Zone

Deep-sea mining in the Pacific Clarion-Clipperton Fracture Zone (CCZ), a low-energy sedimentary habitat with polymetallic nodules, is expected to have considerable and long-lasting environmental impact. The CCZ hosts extraordinarily high species diversity across representatives from all Domains of Life. Data on species biology and ecology remain scarce, however. The current study describes the reproductive biology of Ophiosphalma glabrum (Ophiosphalmidae) and Ophiacantha cosmica (Ophiacanthidae), two ophiuroids frequently found in the CCZ. Specimens collected in Spring 2015 and 2019 in four contract areas were examined morphologically and histologically. Size-class frequencies (disc diameter and oocytes feret diameters), sex ratios, gametogenic status, putative reproductive mode, and a simple proxy for fecundity are presented. Habitat use differs in each. While O. glabrum is epibenthic, occurring as single individuals, O. cosmica often forms size-stratified groups living on stalked sponges, suggesting gregarious settlement or retention of offspring (though no brooding individuals were found). Further molecular analyses are needed to establish whether O. cosmica groups are familial. In O. glabrum, for which sample sizes were larger, sex ratios approximated a 1:1 ratio with no size-structuring. In both species, individuals were at various stages of gametogenic maturity, but no ripe females were identified. Based on this, O. glabrum is most probably gonochoric. Reproductive mode remains inconclusive for O. cosmica. Both species are presumptively lecithotrophic, with vitellogenic-oocyte feret diameters exceeding 250 μm. Oocyte feret diameters at times exceeded 400 μm in O. glabrum, indicating substantial yolk reserves. Estimates of instantaneous fecundity (vitellogenic specimens of O. glabrum only) were confounded by interindividual variability in gonad characteristics. The well-furnished lecithotrophic larvae of O. glabrum would be capable of dispersing even under food-impoverished conditions. The current study examines ophiuroid reproductive biology over multiple localities in the CCZ concurrently for the first time, at sites characterised by differing productivity regimes. The reproductive biology of each species is thus discussed with reference to past evolutionary (habitat stability), contemporary (food supply), and future environmental drivers (potential impacts of deep-sea mining).