As commercial interest in deep-sea minerals grows, decisions by governments on whether to allow deep-sea mining (DSM) will have long-lasting consequences for the global ocean. Grasping the potential implications of DSM is complex due to the wide range of issues and knowledge gaps spanning natural and social sciences. In this paper, we present a comprehensive overview of political, economic, social, technological, environmental, and legal (PESTEL) factors that could influence the initiation of commercial DSM exploitation or the adoption of a moratorium on DSM. To this end, we propose a transdisciplinary approach combining a literature survey and a stakeholder consultation aimed at integrating expert knowledge (science, industry, NGOs, policy-makers) into the PESTEL analysis, setting the scene for an in-depth exploration of opportunities and risks associated with different scenarios regarding the future of the DSM industry and trade-offs involved. We highlight issues of interest to stakeholders that are not yet well developed in the academic literature as well as differences in perception across stakeholder groups. We conclude by a discussion of the implication of our results for problem framing in transdisciplinary science needed to inform a societal debate on DSM. 

How to cite: Bellanger, M.: Implementing a transdisciplinary approach for the strategic assessment of different scenarios for the emerging deep-sea mining industry and the protection of deep-sea ecosystems, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-104, https://doi.org/10.5194/oos2025-104, 2025.

The deep sea holds a wealth of unique and diverse habitats that are still largely unexplored and vulnerable. At the same time, the deep ocean poses a great potential for resources, which requires scientific understanding to achive sustainable development. The UN Ocean Decade endorsed programme “Digital Deep-sea Typical Habitats" (Digital DEPTH) focuses on investigating the deep-sea habitats, such as seamounts, mid-ocean ridges, submarine slopes, and abyssal plains, that are vulnerable to natural and climate changes, as well as human activities. Scientific studies are jointly made over 40 countries with more than 70 institutes to develop long-term intelligent monitoring technologies for the deep ocean. The programme targets to enhance the prediction ability of typical deep-sea habitats to respond to disturbances, such as climate change and deep-sea mining, and construct a digital platform for the habitats, as well as formulating solutions for deep-sea governance. In particular, a 2024 West Pacific International Cruises was carried out over 45 days where the Jiaolong manned submersible successfully completed the 18 dives during the expedition. A total of 8 foreign scientists and 3 scientists from Hong Kong, China, took the Jiaolong to dive in this voyage, covering 6 seamounts and 1 basin in the Western Pacific. The Digital DEPTH serves as a great platform for fostering international collaboration on studying the deep-sea habitat and achieving sustainable development.

How to cite: Li, J., Wang, Y., Xu, X., Sun, Q., and Lu, Z.: Exploring Deep-sea Typical Habitats for achieving sustainable development, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-244, https://doi.org/10.5194/oos2025-244, 2025.

The oceans host essential information to understand climate change (sea level rise, ocean warming) and natural hazards (tsunamis, earthquakes) but monitoring them is difficult and costly. Current initiatives aim at leveraging the millions of kilometers of submarine telecommunication fiber optic cables to enable worlwide real-time observation of the oceans at modest incremental costs. A Joint Task Force (JTF) sponsored by three United Nations agencies leads the initiative to realize Science Monitoring And Reliable Telecommunications (SMART) Cables, which integrate sensors into undersea telecommunications cables to measure seafloor temperature, pressure and seismic acceleration. Distributed Acoustic Sensing (DAS) is a complementary technology that converts the fiber optic cable itself into a dense array of tens of thousands of vibration and temperature sensors, up to 150 km from the coast. This new generation of sensors will provide fundamental ocean data to adequately model and understand climate change processes, and to improve the speed and reliability of global tsunami and earthquake warning systems, without interfering with telecommunicatons. Moreover, these sensors can contribute to monitor other signals of interest, such as ship traffic and marine mammals.

How to cite: Ampuero, J. P. and Howe, B.: Monitoring the Oceans with SMART and DAS Sensors on Submarine Cables, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-489, https://doi.org/10.5194/oos2025-489, 2025.

Understanding the dynamics of thermohaline intrusions is crucial for predicting changes in water masses and their impact on marine ecosystems, especially in highly stratified semi-enclosed seas and other coastal environments. We use high-resolution (up to 1-2 m) Argo profiling float data collected over 15 years in the Black Sea, an excellent test area for studying thermohaline intrusions. Our analysis challenges the conventional view of stagnant intermediate and deep waters, revealing active mixing processes that reshape the thermohaline structure. We identified two main mechanisms driving these intrusions, related to dense water inflows from the Marmara Sea and boundary mixing enhansed by frontal instabilities. Argo data also allowed us to identify areas with favorable conditions for double-diffusive processes. The variability of intrusions is due to changes in the thermohaline state of the upper ocean as well as to quasi-periodic changes in the inflow caused by local conditions. Trends in the intensity and frequency of intrusions indicate shifts in water mass properties that are likely to be associated with climate variability and extreme weather events. Such trends can affect nutrient cycling, oxygen distribution and the overall stability of the water column, thereby affecting biogeochemical cycles and the resilience of marine ecosystems. Similar ventilation mechanisms may operate in other highly stratified marine systems, such as the Baltic Sea and the Arctic Ocean, so our findings may have wider implications for understanding climate-induced changes in water masses at regional and global scales.

How to cite: Stanev, E., Gramcianinov, C., Staneva, J., and Slabakova, V.: Thermohaline intrusions as Seen by Argo Floats: the Case of the Black Sea  , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-493, https://doi.org/10.5194/oos2025-493, 2025.

Long-term environmental monitoring of the deep ocean environment is crucial for better understanding the feedback processes between the oceans and Earth’s climate in the face of global warming. However, obtaining in-situ observations from the deep seafloor is difficult and costly. Use of laser reflectometry in optical fibers using existing submarine telecommunication cables can help bridge this knowledge gap. We performed distributed thermal sensing (using the Brillouin Optical Time Domain Reflectometry technique) on a network of commercially operating telecom cables connecting the islands of the Guadeloupe archipelago in water depths of 10 - 700 m. Monitoring at regular 6 month intervals over the past 2.5 years reveals a temperature change (delta T) of +1.3°C  between June 2022 and late-May 2024 on the shallow carbonate platform (10 - 40 m water depth) south of Grande-Terre (Saint François), Guadeloupe. These sea-floor measurements are corroborated by satellite observations of the Sea-Surface-Temperature (SST) during the past three years, which document a similar (+1.3°C) temperature increase at the sea surface, in the same location (offshore Saint François). A smaller temperature increase (0.2 - 1.0°C) is observed in deeper waters (300 - 700 m) between the islands over the same period (June 2022 - late-May 2024). These results can open the path for widespread use of submarine cables for long-term environmental monitoring of the seafloor.

How to cite: Gutscher, M.-A., Cappelli, G., Quetel, L., Philippon, M., LeBrun, J.-F., Nativelle, C., Quillin, J.-G., and Autret, E.: Submarine cables feel the heat from global warming, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-526, https://doi.org/10.5194/oos2025-526, 2025.

As their tropical analogues, cold-water colonial corals are engineer species that create complex habitats among the richest in deep-sea biodiversity (Rogers 1999). Although living in deeper waters than tropical corals (from 5 m to over 3,000 m depth), cold-water corals will soon face the cumulative threats of ocean warming and acidification (Foley et al. 2010). As their tropical counterparts, specific host-bacteria associations have been highlighted (Neulinger et al. 2008, Meistertzheim et al. 2016, Kellog et al. 2017). But due to the difficulty of deep-sea sampling, detailed knowledge of the ecology and physiology of cold-water corals is still lacking to forecast the response of the coral holobiont to climate change.

Thus, we conducted an in-depth description of the coral holobiont, including growth and anatomy of the host to the localization and function of the associated bacteria. The study focused on the cold-water coral species Desmophylum pertusum present in the Lampaul canyon, Bay of Biscay (North-East Atlantic). In situ experiments using calcein staining and epifluorescence microscopy revealed particularly low polyp growth rates of D. pertusum in this canyon (2.9±1.3 mm/year) compared to the literature. A morphological description of different coral host tissues and the localization of the bacterial microbiome within these tissues, was carried out, using respectively histological stains and electron microscopy approaches. These approaches have enabled us to gain a better understanding of the tissues’ deep structure and the occurrence of bacteria within them. In order to study climate change-related effects on cold-water-corals, coral colonies were maintained in pressurized aquaria for 5 months, at +3°C and a reduced pH of 0.3 units, in line with the IPCC predictions for 2100 in the NE Atlantic. The effect of rising temperature and decrease in pH on skeletal growth and tissues’ structure has been studied using the same techniques as described above.

[The present work was supported by a grant (Project-ANR-20-CE02-0006) from French National Research Agency]

How to cite: Robbe, J., Zbinden, M., and Lartaud, F.: Effects of water temperature and pH on skeletal growth and micro-anatomy of cold-water coral holobiont of one of the main reef-building species Desmophyllum pertusum, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-645, https://doi.org/10.5194/oos2025-645, 2025.

On the continental shelf, the sediments are the only possibility to better understand the marine ecosystem, because of the material they contain (micropalaeontological tracers, i.e. pollen, microfossils, geochemical and mineralogical tracers, i.e. dust...). The physical, chemical, and biological characteristics of ocean sediments are not the only elements that determine their character; the source from which they originate also influences the nature of these deposits.

A missions aboard the scientific vessel "Amir Moulay Abdellah and Al Hassan Al Marrakchi, the oceanographic and environmental monitoring program (INRH)" and "Dr. Fridtjof Nansen, EAF-Nansen Programme/FAO" were carried out to collect a superficial sediment from continental shelf in the south Moroccan Atlantic coast.

This study investigates the mineralogical and geochemical composition of 38 surface sediment samples, between Cap Boujdour and Cap Blanc. Using a multi-pronged approach, the sedimentological characteristics were assessed through direct observation, grain size analysis, measurements of calcium carbonate (CaCO3) and organic carbon content, as well as geochemical and mineralogical composition analyzed using X-ray diffraction (XRD) and X-ray fluorescence (XRF).

The results indicate that the inner-shelf sediments are predominantly mud, characterized by abundant quartz grains and elevated concentrations of terrigenous elements such as Fe, Si, Rb, and K, likely originating from coastal erosion with minor contributions from aeolian dust. In contrast, the middle and outer shelf regions are dominated by biogenic carbonate, with calcium carbonate (CaCO3) levels approaching to 65%, and elevated Ca and Sr content. The mineralogy in these areas is primarily composed of calcite and aragonite. Slope sediments are enriched with mud and montmorillonite clay minerals.

The sediments in the middle-, outer-shelf, and slope regions are interpreted as relict deposits from previous glacial periods of lower sea levels. Aeolian contributions are more pronounced south of Dakhla and are particularly related to the Saharan Air Layer.

How to cite: Nait Hammou, H., El Khalidi, K., Khalfaoui, O., Makaoui, A., Chierici, M., Jamal, C., and Zourarah, B.: Geochemical and Grain Size Characterization of Surface Sediments on the Southern Continental Shelf of Morocco, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-807, https://doi.org/10.5194/oos2025-807, 2025.

With the world’s growing demand for metals, Seafloor Massive Sulfides (SMS) deposits are now seen as a possible mineral resource that could contributes to secure metal supply for human needs. Although inactive or extinct SMS deposits are likely to be the main target for potential exploitation, only few studies have been devoted to them so far. Relict SMS deposits in Trans-Atlantic Geotraverse (TAG) hydrothermal field are known since the mid-1980s but these so-called inactive sites have only been recently further investigated [1,2,3]. High-resolution acoustic surveys and extensive human occupied vehicle (HOV) dive operations performed during four different expeditions led to the discovery of thirteen new SMS deposits including six large (i.e > 5000 m2) deposits making the TAG hydrothermal field the largest accumulation of SMS deposits (i.e. 21.1 Mt) known on the seafloor. However, copper and zinc grades of the largest SMS deposits remain low (i.e. < 1.4 wt.%) even compared to on-land volcanogenic massive sulfides. Additionally, eight areas of diffuse hydrothermal fluid flow were identified challenging the presumed inactivity of these SMS deposits and, for the first time, emphasizing the importance of low temperature (LT) hydrothermal activity in the whole TAG field.

Some authors [4] classified the TAG field as hydrothermally active. This recommendation is relevant, particularly now knowing that all hydrothermal zones in the TAG field exhibit temperature anomalies. Other inactive sulfide deposits might be discovered further east. However, considering knowledge gaps (e.g. patterns of hydrothermal circulation) and based on a precautionary approach, all to-be-discovered deposits belonging to TAG area should be grouped within a single area classified as active and thus protected from exploitation.

References:

[1]. Murton, B.J., et al., 2019. Geological fate of seafloor massive sulphides at the TAG hydrothermal field (Mid-Atlantic Ridge). Ore Geology Reviews 107, 903–925. https://doi.org/10.1016/j.oregeorev.2019.03.005

[2]. Graber, S., et al., 2020. Structural Control, Evolution, and Accumulation Rates of Massive Sulfides in the TAG Hydrothermal Field. Geochemistry, Geophysics, Geosystems 21, e2020GC009185. https://doi.org/10.1029/2020GC009185

[3].      Pelleter E., et al., 2024. Diversity, spatial distribution and evolution of inactive and weakly active hydrothermal deposits in the TAG hydrothermal field . Frontiers In Earth Science , 12, 1304993 (25p.) . Publisher's official version : https://doi.org/10.3389/feart.2024.1304993

[4]. Jamieson, J.W., Gartman, A., 2020. Defining active, inactive, and extinct seafloor massive sulfide deposits. Marine Policy 117, 103926. https://doi.org/10.1016/j.marpol.2020.103926

How to cite: Pelleter, E.-L., Principaud, M., Alix, A.-S., Boissier, A., Cheron, S., Guerin, C., Gaillot, A., Pierre, D., Rospabé, M., Giunta, T., Grenet, L., Cathalot, C., Cambon, M.-A., and Fouquet, Y.: Should inactive seafloor massive sulfide deposits from the TAG hydrothermal field be protected?, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1001, https://doi.org/10.5194/oos2025-1001, 2025.

Increasing exploration and industrial exploitation of the vast and fragile deep-ocean environment for a wide range of resources (e.g., oil, gas, fisheries, new molecules, and soon, minerals) raises global concerns about potential ecological impacts. BathyBot is a multi-instrumented deep-sea crawler deployed from a dock, at 2500m depth, 40 km off the French coast (Mediterranean Sea), at the EMSO-LO station. BathyBot is connected to a deep sea cabled observatory allowing real-time observations of the deep sea. The deployment of this benthic internet operated vehicle complements the ALBATROSS-MII mooring line in the pelagic, multi-instrumented with oceanographic sensors. Two cameras are installed on BathyBot for real time imaging of the deep sea, as well as an Underwater Video Profiler on its dock, and a biocamera closeby the vehicle. Such instrumentation allowed: 1) to better understand the biodiversity in the deep Mediterranean Sea over time and to detect months where some organisms have a higher activity at this deep station 2) to involve citizen through the diffusion of images acquired by BathyBot through a citizen science platform “Ocean Spy – Mediterranean Spy”.

How to cite: martini, S., Gojak, C., Tamburini, C., Lefèvre, D., Bernardet, K., Mahiouz, K., and Laus, C.: BathyBot: a deep-sea crawler to see the unseen of the NW Mediterranean Sea, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1072, https://doi.org/10.5194/oos2025-1072, 2025.

 ARMOR3D is a 3D product based on a statistical approach that merges satellite and in situ observations to retrieve temperature, salinity, mixed layer depth and geostrophic velocities from 0 to 1500m depth and based on seasonal climatic temperature and salinity from 1500 to 5500m. This product is part of the Copernicus Marine Service catalog (https://doi.org/10.48670/moi-00052) and its resolution has been increased to reach a daily temporal resolution and 1/8° spatial resolution. Here, we’ll present the different steps of the methods used and the main results of the in-depth validation that was carried out on this new high-resolution version. Thermosteric and halosteric trends will be discussed. 

How to cite: Zunino, P., Verbrugge, N., and Greiner, E.: ARMOR3D: a 3D high-resolution temperature, salinity, mixed layer depth and geostrophic velocities product based on satellite and in situ observations , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1122, https://doi.org/10.5194/oos2025-1122, 2025.

Phytoplankton, ubiquitous microorganisms in the world’s oceans, play a fundamental role in marine ecosystems. These organisms synthesize organic matter from sunlight, supporting the entire marine food web and driving oceanic life. Through photosynthesis, phytoplankton absorb atmospheric carbon dioxide, making them integral to the biological carbon pump—a natural mechanism sequestering carbon in the ocean’s depths. In the context of climate change, understanding phytoplankton’s contribution to carbon cycling is critical, as their rate of carbon assimilation, or net primary production (NPP), is a key metric for assessing ecosystem health and carbon sequestration potential.

Traditionally, global NPP estimates have relied on satellite observations that detect chlorophyll-a—a green pigment essential for photosynthesis. However, satellite imagery can only capture surface-level data, assuming most NPP occurs in the upper ocean layers. This approach overlooks subsurface processes, potentially underestimating the true extent of phytoplankton productivity. In response, the Biogeochemical Argo floats network—a global fleet of autonomous profiling floats—now provides unprecedented, depth-resolved measurements of chlorophyll, carbon proxies, and light availability. These observations enable estimates of NPP at greater depths, offering a more comprehensive view of phytoplankton’s role across the ocean.

In this study, we leverage Biogeochemical Argo Argo float data and a modified carbon-based productivity model to quantify subsurface phytoplankton contributions to global NPP. Our findings reveal a significant portion of NPP occurring below the ocean’s surface, extending down to depths exceeding 200 meters. This subsurface productivity is particularly pronounced in regions spanning from the equator to 45 degrees latitude—areas previously considered low in productivity. Our results highlight an overlooked reservoir of organic matter, available for deeper marine organisms and representing an unquantified carbon export pathway.

These insights redefine our understanding of oceanic carbon cycling, emphasizing the critical role of subsurface phytoplankton in sustaining deeper ecosystems. Our findings also stress the importance of modern observation systems, like Biogeochemical Argo floats, in capturing the full depth and complexity of ocean productivity. This research not only contributes to a deeper understanding of carbon pathways but also has implications for the broader marine food web, influencing the availability of resources for higher trophic levels, including commercially important fish species.

How to cite: Cornec, M. and Claustre, H.: Subsurface ocean is blooming, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1189, https://doi.org/10.5194/oos2025-1189, 2025.

The deep ocean is vast and challenging to observe; however, it is key to knowledge of the sea and its impact on global climate. Fixed sea observing points (such as the EMSO observing nodes) provide a limited view and are complemented by expensive oceanographic campaigns with systems demanding high logistical requirements such as deep-sea ROVs.  These costs not only limit our capability for key ocean data collection in the deep but also introduce their own environmental costs.

Emerging challenges in knowledge and pressure on the exploration of the deep ocean demand new technological solutions for monitoring and safeguarding the marine ecosystem.

Innovative robotic technologies such as the TURTLE robotic deep-sea landers can combine long-term permanence at the seabed with mobility and dynamic reconfigurability in spatial and temporal deep-sea observation.

Robotic systems of a heterogeneous nature (from conventional gliders, AUVs, or robotic landers) can be combined with standard and new sensing systems, such as bottom-deployed sensor nodes, moored systems, and cabled points when feasible.

These systems can provide underwater localization services for the different assets, energy supply and high bandwidth data transfer with robotic docking stations for other mobile elements. An example of the synergy obtained with these new systems is the possibility of using robotic landers as carriers of EGIM (EMSO Generic Instrument Module) sensor payloads, providing power and data storage and flexibility in the deployment and recovery process.

This approach, partly taken in the EU-funded Trident project to develop technical solutions for cost-effective and efficient observation of environmental impacts on deep seabed environments, allows for a substantial reduction in the operational and logistic requirements for deep-sea observation, greatly reducing the need for costly oceanographic campaigns or the use of expensive (economic and logistical) deep sea ROV systems.

In this work, we present some of the new developments and discuss the transition from existing technological solutions to new ones integrating these recent developments.

How to cite: Martins, A., Almeida, J., Almeida, C., and Silva, E.: From fixed bottom nodes to mobile long term seabed robotic systems: the future of deep ocean observation, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1191, https://doi.org/10.5194/oos2025-1191, 2025.

The deep ocean, defined as waters below 200 meters, is a vital component of global ecosystems. It represents 93% of the world’s living space by volume, supports immense biodiversity and biomass, offers unique genetic resources, and plays a key role in ecosystem services and climate regulation. However, its vast and remote nature poses significant challenges for sampling and research, which can particularly limit early-career ocean professionals (ECOPs) from engaging in deep ocean science. Surveys conducted by the Deep Ocean Observing Strategy (DOOS), a decade-endorsed programme, in 2023 highlighted that (1) many early-career researchers are eager to engage in deep ocean science and policy, and (2) there is a need for a dedicated early-career deep ocean program to provide training and entry points into the deep ocean decade community. In response, the Deep Ocean ECOP Task Team was created in 2024. The objectives of this Task Team are (1) to connect ECOPs with ongoing deep ocean decade programs and projects, (2) provide tailored training, workshops, and mentorship, and (3) form topical working groups based on community needs and scientific knowledge gaps. Our aim is to share the vision and mission of the Deep Ocean ECOP Task Team, outline our strategic plan for the coming year, and highlight opportunities for individuals to become involved and integrate into existing early-career networks. By fostering a collaborative, inclusive network, this task team will support the next generation of deep ocean professionals, empowering ECOPs to advance scientific knowledge and contribute to deep ocean science and policy through the UN Ocean Decade and beyond.

How to cite: Hetherington, E., Annasawmy, P., Olusola, A., Maroni, P., and Smith, L.: Introducing the Deep Ocean Early Career Ocean Professional (ECOP) Task Team, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1530, https://doi.org/10.5194/oos2025-1530, 2025.

Anthropogenic disturbances are drastically affecting marine biodiversity across diverse ecosystems, including the deep sea. However, the relative inaccessibility of the deep sea poses difficulties in assessing the biodiversity of vulnerable habitats such as chemosynthetic environments. Chemosynthetic cold seeps host distinct macrofaunal communities adapted to living in harsh environmental conditions and contribute significantly to productivity and nutrient cycling of the barren seafloor. Traditionally, biodiversity of deep-sea macrofauna has been assessed via morphological approaches, in which sediment samples are collected and animals sorted and identified—a time-consuming process that relies heavily on taxonomic expertise. Technological advancements in eDNA metabarcoding may now provide a rapid means for the analysis and monitoring of these remote habitats. However, few studies have compared metabarcoding methods to traditional approaches and baseline genetic data are needed prior to its use in biomonitoring. The vulnerability of dense macrofaunal communities in seeps make them an ideal habitat for evaluating metabarcoding’s effectiveness in estimating taxa abundance and diversity. Sediment macrofaunal communities were examined in core samples collected via ROV from cold seeps in Astoria Canyon, located on the Cascadia margin off the coasts of Oregon and Washington, USA. For traditional morphology-based analyses, cores were preserved, sieved, and sorted, and macrofauna were identified to the lowest possible taxonomic level. Additional sediment cores were collected, preserved, and processed for eDNA metabarcoding methods; this processing included isolating the fauna via Ludox density gradient separation, followed by DNA extraction, amplification of the 18S rRNA gene, and sequencing (Illumina NextSeq 2x300 bp). Here we compare the community metrics (e.g., abundance estimates, taxa richness, Shannon diversity index, community structure) resulting from both approaches, while also describing the macrofaunal communities across various depths and seep habitats of Astoria Canyon. The role of environmental variables (e.g., organic carbon, total nitrogen, C:N ratios, δ13C and δ15N stable isotopes, redox potential, and grain size) in shaping these communities was examined for both methodologies. These findings will inform future experimental designs and biomonitoring efforts for macrofaunal communities vulnerable to human-induced disturbances, while also broadening the knowledge of biodiversity in these deep-sea cold seeps.

How to cite: McCowen, P., Behringer, D., Bourque, J., Pereira, T., Bik, H., and Demopoulos, A.: Assessing biodiversity of remote deep-sea chemosynthetic environments: a case study comparing morphological and metabarcoding analysis of seep macrofauna from the U.S. Cascadia margin, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1543, https://doi.org/10.5194/oos2025-1543, 2025.