This dataset was collected during the iMAR cruise “The Integrated assessment of the distribution of Vulnerable Marine Ecosystem along the Mid-Atlantic Ridge (MAR) in the Azores region”, that took place aboard the Research Vessel Pelagia of the Royal Netherlands Institute for Sea Research (NIOZ) between May 19th and June 2nd 2021. The iMAR cruise aimed to evaluate the role of the MAR in shaping latitudinal and trans-Atlantic patterns in deep-sea biogeography, connectivity and assemblages of deep-sea megafauna. This expedition was funded by the SEA OCEANS program of Eurofleets+ and the H2020 European project iAtlantic, and was led by the University of the Azores (Portugal) in collaboration with the Hydrographic Institute and University of Porto (Portugal), the University of Aarhus (Denmark), the National Oceanography Center (United Kingdom), GEOMAR (Germany), the University Museum of Bergen (Norway), the PP Shirshov Institute of Oceanology (Russia), and the University of Vale do Itajaí (Brazil). The deep-sea benthic communities were mapped using the NIOZ towed camera system. The Hopper system generated a series of high-definition video transects in each area explored, starting from the deepest point (set at 1,200 m approx.) and moving upwards towards the seamount or ridge summit (700 m to 300 m depth). During the iMAR cruise, 22 stations for Hopper video transects were performed (Table 1), mainly in the North portion of the MAR inside the Exclusive Economic Zone around the Azores, which produced approximately 54 hours of bottom time, along 48 km of seafloor.

This dataset was produced during the iMAR cruise “The Integrated assessment of the distribution of Vulnerable Marine Ecosystem along the Mid-Atlantic Ridge (MAR) in the Azores region”, that took place aboard the Research Vessel Pelagia of the Royal Netherlands Institute for Sea Research between May 18th and June 2nd 2021. The iMAR cruise aimed to evaluate the role of the MAR in shaping latitudinal and trans-Atlantic patterns in deep-sea biogeography, connectivity and assemblages of deep-sea megafauna. This expedition was funded by the SEA OCEANS program of Eurofleets+ and the H2020 European project iAtlantic, and was led by the University of the Azores (Portugal) in collaboration with the Hydrographic Institute and University of Porto (Portugal), the University of Aarhus (Denmark), the National Oceanography Center (United Kingdom), GEOMAR (Germany), the University Museum of Bergen (Norway), the PP Shirshov Institute of Oceanology (Russia), and the University of Vale do Itajaí (Brazil). Vertical CTD/Rosette profiles were conducted with the CTD Seabird SBE 32 at 19 stations to measure physical and chemical seawater properties that characterize the dominant water masses described for the North MAR region of the Azores (Table 1). The “.CNV” files of fully processed data contain data of twenty-two parameters interpolated at 1-meter bins, (Table 2), mainly in the North portion of the MAR in the Exclusive Economic Zone around the Azores.

This dataset was produced during the iMAR cruise “The Integrated assessment of the distribution of Vulnerable Marine Ecosystem along the Mid-Atlantic Ridge (MAR) in the Azores region”, that took place aboard the Research Vessel Pelagia of the Royal Netherlands Institute for Sea Research between May 19th and June 2nd 2021. The iMAR cruise aimed to evaluate the role of the MAR in shaping latitudinal and trans-Atlantic patterns in deep-sea biogeography, connectivity and assemblages of deep-sea megafauna. This expedition was funded by the SEA OCEANS program of Eurofleets+ and the H2020 European project iAtlantic, and was led by the University of the Azores (Portugal) in collaboration with the Hydrographic Institute and University of Porto (Portugal), the University of Aarhus (Denmark), the National Oceanography Center (United Kingdom), GEOMAR (Germany), the University Museum of Bergen (Norway), the PP Shirshov Institute of Oceanology (Russia), and the University of Vale do Itajaí (Brazil). Vertical CTD Seabird SBE 32 /Rosette profiles were conducted at 19 stations to generate Sound Velocity Profiles (Table 1), mainly in the North portion of the MAR in the Exclusive Economic Zone around the Azores. The “.cnv” files contain the sound velocity data binned to 1 m depth intervals using the “bin average”.

This dataset contain the metadata for all stations conducted during the iMAR cruise “The Integrated assessment of the distribution of Vulnerable Marine Ecosystem along the Mid-Atlantic Ridge (MAR) in the Azores region”, that took place aboard the Research Vessel Pelagia of the Royal Netherlands Institute for Sea Research between May 19th and June 2nd 2021. This expedition was funded by the SEA OCEANS program of Eurofleets+ and the H2020 European project iAtlantic, and was led by the University of the Azores (Portugal) in collaboration with the Hydrographic Institute and University of Porto (Portugal), the University of Aarhus (Denmark), the National Oceanography Center (United Kingdom), GEOMAR (Germany), the University Museum of Bergen (Norway), the PP Shirshov Institute of Oceanology (Russia), and the University of Vale do Itajaí (Brazil). Statistics: Cruise duration was 17 days, 2,500 km of transits, 6 areas visited, 5,500 km2 of mapped seabed (mainly in the North portion of the MAR in the EEZ around the Azores), 19 dives with the NIOZ video system that resulted in 54 hours of deep-sea images over 48 km of the seabed, 13 stations for the analysis of water mass properties and to collect sediments, which resulted in 380 samples for environmental DNA, 280 samples for nutrient analyses, 27 sediment samples for geological analyses, 24 for microplastic analyses, 10 samples for bacteriological, and 10 samples meiofauna analyses.

This dataset was produced during the iMAR cruise “The Integrated assessment of the distribution of Vulnerable Marine Ecosystem along the Mid-Atlantic Ridge (MAR) in the Azores region”, that took place aboard the Research Vessel Pelagia of the Royal Netherlands Institute for Sea Research between May 19th and June 2nd 2021. The iMAR cruise aimed to evaluate the role of the MAR in shaping latitudinal and trans-Atlantic patterns in deep-sea biogeography, connectivity and assemblages of deep-sea megafauna. This expedition was funded by the SEA OCEANS program of Eurofleets+ and the H2020 European project iAtlantic, and was led by the University of the Azores (Portugal) in collaboration with the Hydrographic Institute and University of Porto (Portugal), the University of Aarhus (Denmark), the National Oceanography Center (United Kingdom), GEOMAR (Germany), the University Museum of Bergen (Norway), the PP Shirshov Institute of Oceanology (Russia), and the University of Vale do Itajaí (Brazil). ADCP data was collected at 34 stations during the iMAR cruise, mainly in the North portion of the MAR in the EEZ around the Azores (Table 1). This dataset contain the “.ENR” and another 9 file types with the same name structure but different extensions (.ENS; .ENX; .TXT; .LTA; .N1R; .N2R; .NMS; .STA; .VMO). VmDas Quick Start Guide: “.ENR” raw ADCP data file; “.ENS” ADCP data after having been screened for RSSI and correlation by VmDas; “.ENX” ADCP single-ping data (plus NAV) after having been bin-mapped, transformed to Earth coordinates, and screened for error velocity, vertical velocity, and false targets. “.LTA” ADCP (plus NAV) data that has been averaged using the long time period; “.N1R” and “.N2R” Raw NMEA data files; includes ADCP time stamps; “.N1R” extension is used for single-port NMEA data collection, or for GPS position data (Nav) in dual-port collection mode. The “.N2R” extension is used for Roll/Pitch/Heading (RPH) data collection when using two serial ports for NMEA data collection. “.NMS” Binary format NAV data file after having been screened and pre-averaged. “.STA” ADCP (plus NAV) data that has been averaged using the short time period; “.VMO” the option settings used for collecting the data (text file).

This dataset was produced during the iMAR cruise “The Integrated assessment of the distribution of Vulnerable Marine Ecosystem along the Mid-Atlantic Ridge (MAR) in the Azores region”, that took place aboard the Research Vessel Pelagia of the Royal Netherlands Institute for Sea Research between May 18th and June 2nd 2021. The iMAR cruise aimed to evaluate the role of the MAR in shaping latitudinal and trans-Atlantic patterns in deep-sea biogeography, connectivity and assemblages of deep-sea megafauna. This expedition was funded by the SEA OCEANS program of Eurofleets+ and the H2020 European project iAtlantic, and was led by the University of the Azores (Portugal) in collaboration with the Hydrographic Institute and University of Porto (Portugal), the University of Aarhus (Denmark), the National Oceanography Center (United Kingdom), GEOMAR (Germany), the University Museum of Bergen (Norway), the PP Shirshov Institute of Oceanology (Russia), and the University of Vale do Itajaí (Brazil). Nutrient analysis was performed according to Grasshoff et al, adopted for a 5 channel continues flow analyzer (Skalar San Plus, Skalar Analytical B. V., Breda, The Netherlands). Nitrite and nitrate+nitrite was measured using an ammonia buffer and sulfanilamide/alpha-Naphthylethylene diamine dihydrochloride colour reagent in phosphoric acid, with reduction of nitrate to nitrite by cadmium column of at least 80% measured reduction capacity (90-100% achieved), followed by quantification with spectrophotometric determination of the nitrite-azo dye at 540 nm. Nitrate was determined as the difference between nitrate+nitrite and nitrite measurements. Ammonia was measured using a citrate/tartrate buffer and phenol color reagent, catalyzed by hypochlorite and nitroprusside , followed by quantification with spectrophotometric determination of the phenol-ammonia complex at 630 nm. Phosphate samples reacted with antimo nytartrate and ammonium molybdate solution in sulfuric acidified solution, the resulting complex wasreduced by ascorbic acid to a deep blue dye, followed by quantification with spectrophotometric determination of the reduced antimony-phospho-molybdate complex at 880 nm. Silicate samples was acidified with sulfuric acid and reacted with ammonium molybdate solution, reduced by ascorbic acid to a blue dye with oxalic acid to remove phosphate interference , followed by quantification with spectrophotometric determination of the reduced molybdo-silicate complex at 810 nm. Methods used are accredited with expected detection limit of 0,04 µM for nitrite, 0,1 µM for nitrate, 0,3 µM for ammonia, 0,06 µM for Phosphate and 0,2 µM for silicate, with expected RSD between 4 and 7%for the individual nutrients. Certified reference materials (VKI type QC RW1 for ammonia, phosphate and nitrate) and internal reference materials for Nitrite and silicate was spiked at two levels to natural low nutrient seawater sample for quality assurance, recovering 91-109% of the spike for nitrite, nitrate, phosphate and silicate at with RSD% of 1 to 5%, and recovery of 84-91% for ammonia, with RSDs up to 15%. No corrections was performed on data the recoveries. Except for ammonia, all results was within the acceptance limits for accredited analysis. Analysis was performed over two runs, one with triplicates and then a fourth spare sample was included to investigate the ammonia instability, but it could not be determined if this was due to storage/transport or instrument The “.CSV” files of fully processed data contain data collected mainly in the North portion of the MAR in the Exclusive Economic Zone around the Azores.

The iMAR cruise “The Integrated assessment of the distribution of Vulnerable Marine Ecosystem along the Mid-Atlantic Ridge (MAR) in the Azores region” took place aboard the Research Vessel Pelagia of the Royal Netherlands Institute for Sea Research (NIOZ) between May 19th and June 2nd 2021. This expedition was funded by the SEA OCEANS program of Eurofleets+ and the H2020 European project iAtlantic, and was led by the University of the Azores (Portugal) in collaboration with the Hydrographic Institute and University of Porto (Portugal), the University of Aarhus (Denmark), the National Oceanography Center (United Kingdom), GEOMAR (Germany), the University Museum of Bergen (Norway), the PP Shirshov Institute of Oceanology (Russia), and the University of Vale do Itajaí (Brazil). During the iMAR cruise we performed 28 stations for multibeam surveys, summing 171:30 hours of surveys, 5,500 km2 of mapped seabed (mainly in the North portion of the MAR in the Exclusive Economic Zone around the Azores), in 8 main areas and during many of the 2,500 km of transits All multibeam data processing was treated by Leonor Neves de Sousa (Instituto Hidrográfico) with the software “CARIS HIPS & SIPS”.These are the .all files of multibeam row data about 28 stations, between 18 May and 2 June, with information about seamounts, ridges and depressions of the Mid-Atlantic Ridge in the Azores.

Knowledge of the strength of submarine volcaniclastic deposits is important for assessing the stability of slopes of such materials and their geohazards but is dif cult to measure. An opportunity for an alternative evaluation has been presented by an earthquake swarm under a volcanic seamount in the Azores. Attenuation relationships applied to earthquake data suggest that a cone eld and anks of the seamount experienced horizontal accel- erations of >0.3 g during the swarm. However, multibeam sonar data collected before and after the swarm suggest that no slope failures occurred. Furthermore, in backscatter data collected after the swarm, low in- tensities below slopes suggest that muddy aprons were undisturbed by landslide debris. The swarm overlies cones with slopes near typical repose angles of non-cohesive particles. During earthquake shaking, the direction of maximum acceleration deviates from that due to gravity alone. We show that cone slopes effectively experienced much steeper gradients than their repose angles during the swarm. As they survived the shaking without failing, they were effectively stronger than non-cohesive sediment. We use a pseudo-static analysis to investigate the implied sediment strength, nding a ratio of undrained shear strength to vertical stress of >0.4–0.5. This implies shear strength of >24–30 kPa at 10 m depth below seabed. We speculate that carbonate cements and/or compaction may be responsible. If shallow areas are more widely strengthened, slope failure may then be less likely during moderate (ML ~ 4.0 or less) seismic shaking and hence be less hazardous than if the slopes comprised wholly non-cohesive materials.