King’s Trough is a deep-sea geomorphological feature in the northeastern Atlantic Ocean. Despite its ecological significance, the region remains largely unexplored, and the benthic fauna inhabiting its seamounts is still unknown. Here we present the first characterization of benthic communities inhabiting the seamounts flanking the King’s Trough complex (Axis, Laughton, Adamastor, and Antialtair), based on remotely operated vehicle (ROV) surveys conducted between 1100 and 2200 m depth. Community composition varied markedly among the surveyed seamounts, however, megafaunal densities were generally consistent among seamounts, except at Antialtair, where densities were approximately half those recorded at the other sites. Coral assemblages, comprising several taxonomic groups, dominated hard substrates. Dense whip-like black coral gardens were documented, and extensive sea-pen fields occured on biogenic sediments. Stylasterid aggregations were also recorded, and additional habitat-forming taxa included dense fields of xenophyophores.Multivariate analyses revealed a clear depth-related gradient structuring communities with scleractinian corals predominating at shallower depths and antipatharians becoming more abundant in deeper waters. Substrate type also influenced assemblage composition. However, the measured environmental variables explained only approximately 9% of the observed variation in community structure, suggesting that additional unmeasured environmental factors or biological processes may contribute to shaping these assemblages. This study establishes the first ecological baseline for the King’s Trough seamounts. Their structural complexity, together with the presence of long-lived habitat-forming species, and Vulnerable Marine Ecosystem (VME) indicator taxa, highlights the conservation importance of these seamounts and supports ongoing area-based management and conservation initiatives.

The Central East Atlantic Ocean and its Iberian and Moroccan margins have been affected by intense magmatic activity from the Cretaceous onward. In this study, we present new major and trace element, isotopic (Sr-Nd-HfPb), and geochronological (40Ar/39Ar) data for three seamounts (Rugoso, Jo Cousin, and Pico Pia) located on top of the Madeira-Tore Rise (MTR), a major -1000 km long physiographic feature in the Central East Atlantic Ocean. The alkaline composition of these volcanoes and their ages (0.07-1.39 Ma) contrast with the mid-ocean ridge basalt (MORB) affinity and the -125-130 Ma age of the underlying ridge. This defines the MTR as a complex structure, initially formed during the Atlantic breakup and later overprinted by intraplate magmatism. The reported seamounts are distinct with respect to their degrees of SiO2-undersaturation (Jo Cousin being the least undersaturated) and magma evolution (reaching phonolitic compositions in Rugoso). Additionally, the studied lavas further increase the range of isotopic signatures previously observed for the post-breakup MTR volcanoes, reflecting their derivation from sources either with more time-integrated depletion (Jo Cousin: epsilon Nd up to 10.27 and 206Pb/204Pb down to 18.427) or enrichment (Rugoso and Pico Pia: epsilon Nd down to 4.26 and 206Pb/204Pb up to 20.256) in the most incompatible elements. These signatures can be interpreted in terms of the roles of HIMU and DMM mantle components, as well as different proportions of eclogite/pyroxenite and peridotite mantle lithologies in the magma sources. Despite their similar ages and geographic proximity, Rugoso, Jo Cousin, and Pico Pia seamounts exhibit dual isotopic compositions, with Jo Cousin showing affinities with the Madeira Archipelago, and Rugoso and Pico Pia being isotopically comparable to lavas from the Canary Archipelago. However, considering their ages and geographic positions, these volcanic structures cannot be directly attributed to the activity of mantle plumes at the origin of such hotspot provinces. Instead, we propose that they were produced by independent, small-scale, and ephemeral secondary mantle upwellings that sampled compositional domains similar to those feeding the Madeira and Canary provinces within the Central East Atlantic Anomaly (CEAA), located at the topmost lower mantle.

Abstract Volcanic ocean island collapse is a gravitational process, which means that mass is a key variable. Here we show that small volcanic islands (small mass) usually considered stable can undergo full flank collapse (i.e. full flank plus summit), and we also evaluate the most likely collapse mechanisms by numerical modelling. Santa Maria Island (Azores) is ca. 170 times smaller than Hawaii; however, it has collapsed more than once, as inferred from onshore data and new high-resolution bathymetry and seismic reflection data. Santa Maria is less than 8 Ma old and lies on an oceanic crust ca. 40 Ma old; therefore, several hundred meters of marine sediments lie between the oceanic crust and the base of the volcanic edifice of Santa Maria, which could behave as a weak layer (detachment) under shear. The numerical simulations indicate that, if the volcanic edifice is strong, it does not collapse, even if its base is weak. However, a relatively weak edifice can collapse over a weak base, from which we conclude that small volcanic islands can collapse when both the edifice and its base are weak. The proximity of Santa Maria to the East Azores Fault, active during the lifetime of Santa Maria, may point to the trigger mechanism of flank collapses. Confirmation that the collapses have actually occurred increases both hazard and risk, because the number of recognised collapses increases, and so does the frequency, thus bringing closer the time scales of flank collapses and human life.

The present study provides the first results of the exploratory research campaign to Gloria seamount (summit at 45.03 degrees N, 15.54 degrees W), a newly identified seamount in the NE Atlantic. New multibeam bathymetry and an 8 h remote operated vehicle footage and photography data were compiled and analyzed to give the first insights on the geological nature and benthic megafauna assemblages of Gloria seamount. Footage evidenced three distinct seafloor coverage areas, ranging from unconsolidated fine sediment with ripple marks, to increasingly coarser-grain sediment with large blocks, to outcrops with steep slopes along successive ridges, locally exhibiting vol-canic structures. The deep-sea benthic assemblages differed with depth (2700-2450 m) and seafloor substrate type. In sediment habitats, pink holothurians (Elpidiidae) and brittle stars (Ophiuroidea) were recorded, whereas in hard substrates, sponges (Hexactinellida and Demospongiae) and stalked crinoids (Crinoidea) were mixed with distinct coral specimens, such as bamboo corals (Isidiidae) and Coralliidae (Scleralcyonacea). The integration of these data contribute to the geo-habitats knowledge of an unexplored seamount.

Deep sea mining in the Area (seabed and subsoil beyond national jurisdiction) is regarded by some stakeholders as a threat to the achievement of Goal 14 of the United Nations, 2030 Agenda for sustainable development. However, the availability of metals and mineral resources will be crucial to comply with most Sustainable Development Goals. Despite the need to foster a circular economy and reduce waste to a minimum, it seems unlikely that the decarbonization of the economy could be achieved without primary mining. Future minerals supply, facing significant obstacles, can source from increased primary terrestrial and deep-seabed supply, or deep-seabed displacing terrestrial. This work develops principles and an integrated, holistic framework for deep-seabed mining to play a role in future demand through sustainable global sourcing and collective action on the global commons through the International Seabed Authority. Optimum global welfare requires balancing all the competing uses of the marine environment and their contributions to private and public benefits enjoyed by all Humanity, in both current and future generations, and weighted by equity concerns for a more progressive distribution as required by the United Nations Convention on the Law of the Sea.

The D. João de Castro is a submarine volcano with known hydrothermal activity located in the Terceira ultra-slow spreading rift within the Azores triple junction (ATJ). Several well-known mafic and ultramafic rock-hosted seafloor hydrothermal systems lay along the Mid-Atlantic Ridge, to the north and to the south of the Azores platform, yet little is known about seafloor hydrothermal activity, ore-metal availability, and magmatic–hydrothermal interactions within the ATJ. Here, we investigate multi-phase melt inclusions hosted in early formed phenocrysts (olivine, clinopyroxene and plagioclase), and metallic precipitates found in groundmass vesicles. Combining detailed petrographic observations with geochemical data and thermobarometry calculations, we assess P–T conditions of early formed phenocrysts, melt pathways towards surface, timing of sulfide saturation and composition of immiscible sulfide melts. Results show that D. João de Castro is characterized by a multi-level magmatic system where primary melt segregated from the upper mantle and moved up through the oceanic crust with little residence time. Sulfide saturation with the formation of immiscible magmatic sulfide liquid (Fe–Ni–Cu) occurred early in primitive magmas with clinopyroxene and olivine crystallization and continued during plagioclase crystallization. At shallower levels, the magmatic degassing of volatiles carrying base metals (Cu–Zn–Pb–Co) and Ba have contributed to the element budget of the D. João de Castro hydrothermal system. The study of multi-phase melt inclusions and vesicles at D. João de Castro submarine volcano contributes to the understanding of source to surface magmatic processes at the Terceira Rift and underline the importance of magmatic degassing into seafloor hydrothermal systems.

This work presents a new high-resolution multibeam bathymetric map of a segment of active deep sea-floor spreading in the Atlantic Ocean, the northern Mid-Atlantic Ridge (MAR) at 45–46º N. New high-resolution bathymetry data were acquired using an Atlas multibeam echosounder onboard the research vessel Sarmiento de Gamboa during the EXPLOSEA-2 survey in 2019. The final map of the MAR (50 m cell grid size) at the original scale of 1:200,000 shows a segment of 140 × 35 km of the MAR, at water depths from 715 to 3700 m. This new high-resolution bathymetric map allows to better defining the submarine morphology of the Moytirra hydrothermal active field, the only high-temperature field identified between the Azores Archipelago (Portugal) and Iceland. ROV submarine observations reaching the deepest part of the system for the first time show giant anhydrite-sulfide chimneys up to 20 m high, active strong black smokers and polymetallic massive sulfides.

This work presents the preliminary result of the multidisciplinary cruise EXPLOSEA2 surveying the northern Mid-Atlantic Ridge and Azores Archipelago from 46 degrees 30' N to 38 degrees 30' N aboard the R/V Sarmiento de Gamboa and ROV Luso over 54 days (June 11 to July 27, 2019). In this cruise report, we detail the geophysical, hydrographic, geological, oceanographic, ecological, and microbiological data acquired and a brief of main findings. The cruise addressed the exploration and comprehensive characterization of venting sites, including the water column, the sediments and rocks that host the hydrothermal activity, and the associated mineralizations, biology, and microbiology. Deep hydrothermal chimneys and massive sulfide deposits (up 3,000 m in depth) within the Moytirra hydrothermal active field were identified on slopes that had not been explored previously. Another striking finding made during the EXPLOSEA2 cruise was the field of carbonate chimneys named the "Magallanes-Elcano" field, a potentially relict ultramafic-hosted hydrothermal site sourced by abiotic methane. This field is related to a serpentinite and gabbro rock outcropping on a dome-shaped massif named the "Iberian Massif." An outstanding finding of the EXPLOSEA2 survey was the identification of the first garden of soft corals growing after active submarine eruptions were reported in the Azores Archipelago composed by a high density of soft corals the suborder Alcyoniina at the summit and flanks of a recent volcanic cone at 160 m water depth developed during the 1957-1958 eruption of Capelinhos. Several cold-water coral habitats formed by colonial scleractinians (e.g., Lophelia pertusa and Madrepora oculata), coral gardens composed of mixed assemblages of black corals (Leiopathes sp.), and octocorals and dense aggregations of the glass sponge Pheronema carpenteri that may be classified as vulnerable marine ecosystems (VMEs) have been discovered during the EXPLOSEA2 cruise along the northern Mid-Atlantic Ridge. This work reveals the importance of multidisciplinary surveys to the knowledge of deep-sea environments.

New geochemical, isotopic (Sr-Nd-Hf-Pb) and K-Ar data, are presented here on samples from the Southern Azores Seamount Chain (SASC) located south of the Azores Plateau. The SASC also includes the Great Meteor, Small Meteor and Closs seamounts, morphologically connected by a saddle at −4100m deep. We conclude that the SASC are characterized by a narrow isotopic variability that falls within the Azores isotopic field. Although each seamount has its own isotopic signature, their mantle source must comprise four local mantle end-members, three of which are common to the Azores, e.g. Plato isotopic signature results from the mixing between HIMU and N-MORB while Great Meteor signature results from this mix with the Azores Common Component (AzCC). A fourth end-member with high 208Pb/204Pb and decoupled Th/U ratios (Δ8/4 up to 59.2) is identified on Great Meteor northern flank. New K-Ar ages on Plato (33.4±0.5Ma) and Small Hyeres (31.6±0.4Ma) show nearly coeval volcanism, which is contemporaneous with the E-MORBs erupted at the MAR, drilled on oceanic crust with 30-34Ma (DSDP82). This study endorses the genetic link between the Azores Archipelago and the SASC to the long-term activity of the Azores plume and the large-scale ridge-hotspot interaction, contributing to better constrain the temporal-spatial evolution of this region of the North Atlantic.