The Ocean plays a critical role in sustaining life on Earth. However, the Ocean’s ability to continue supporting life is under threat. We therefore need to better understand what is happening in the Ocean, how it connects to the wider Earth System, and how its degradation can be mitigated.

Navigating the Future VI (NFVI) is the latest edition of the flagship European Marine Board marine science-policy foresight series. NFVI discusses the Ocean and its place in the wider Earth system. It presents the most recent trends and highlights the needed breakthroughs in marine (natural and social) science research to help address the challenges facing the planet. It looks beyond the Ocean community to identify with whom we need to collaborate to develop and implement solutions. The publication is the result of a two-year collaborative effort from October 2022-2024. The Working Group comprised 33 experts from 16 European countries, covering a wide range of marine natural and social science backgrounds and career levels, including ECOPs.

NFVI’s four main chapters align with pressing global challenges, covering Ocean and People, Ocean and Climate, Ocean and Fresh Water, and Ocean and Biodiversity. The Ocean and People Chapter focuses on the myriad links between the Ocean and people and presents a vision for a future where Ocean stakeholders are better able to work together. The Ocean and Climate Chapter highlights the need for better understanding the multitude of links between the Ocean and climate to better equip us to live alongside a changing Ocean. The Ocean and Fresh Water Chapter presents the connections between terrestrial and marine water systems and outlines the need to manage these holistically to ensure clean and safe water for all. The Ocean and Biodiversity Chapter puts a spotlight on how biodiversity will evolve as the Ocean changes and stresses the need to be better able to identify and study species so they can be protected. NFVI closes by identifying the infrastructure, financial, training and other requirements needed to underpin and enable the recommendations.

This presentation will outline the main messages and research recommendations arising from NFVI, advising future strategic research programming.

How to cite: Heymans, J. J., Lericolais, G., Kellett, P., Muñiz Piniella, A., Alexander, B. E., Rodriguez-Perez, A., and Bayo Ruiz, F. and the Navigating the Future VI Working Group: Navigating the Future VI: Ocean Science for Earth Challenges, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-133, https://doi.org/10.5194/oos2025-133, 2025.

Life and Earth Sciences and Human and Social Sciences can be brought together under the umbrella of biogeography to guide us in explaining the order and disorder of a world in perpetual motion. We are currently experiencing accelerating climate change, which is calling into question the foundations of many civilisations. The subject of Fernand Braudel's pioneering geohistorical work, the Mediterranean and the Mediterranean world offer a concrete space for renewed reflection on Time and its rhythms. Extending the Braudelian concept of the '3 Times' of History, our reflection opens onto the '5 Times' of the Biosphere, a concept born of biogeohistorical reflection committed to responding to the major challenges of climate disruption and the upheavals of the Earth, which overdetermine the life of living communities, of which humanity is a part. Geology and Climatology have to be crossed with legacy of History to understand the way Mediterranean sea is on : Red alert on the Big Blue. 

How to cite: Degron, R.:  The 5 Times of the Biosphere – Beyond Braudel Legacy Red : Alert on the Big Blue, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-158, https://doi.org/10.5194/oos2025-158, 2025.

Observing the ocean is vital for met-ocean forecasting, supplying essential insights for understanding the ocean’s current state and predicting future patterns. Modern forecasting systems rely on numerical models of ocean dynamics and data-assimilation techniques that incorporate real-time observations. Key parameters like temperature, salinity, currents, and atmospheric conditions significantly enhance model accuracy by connecting model simulations with actual ocean conditions.

A wide network of research institutions, governmental bodies, and private organizations contributes to these observations, using a range of sensors deployed on research vessels, submarines, aircraft, moorings, drifting buoys, gliders, floats, fixed platforms, and satellites. These sensors capture data across physical, chemical, biological, geological, and geophysical domains, forming a comprehensive basis for informed ocean management.

Near Real-Time (NRT) data, updated hourly to weekly, supports immediate forecasting needs, while Delayed Mode (DM) data serves reanalysis, climate monitoring, and seasonal forecasting. To ensure quality, NRT data typically undergoes automated control procedures, while DM data benefits from offline expert review and rigorous quality checks, ensuring the data’s robustness for longer-term scientific studies and climate assessments.

In Europe, two principal programs drive ocean data observation and dissemination: the Copernicus Marine Service and the European Marine Observation and Data Network (EMODnet). Together with the Marine In Situ Collaboration (MIC)—a partnership among EMODnet, CMEMS, and EuroGOOS—these initiatives coordinate ocean data collection, quality control, and accessibility, directly supporting the goals of ocean prediction and action. This collaboration exemplifies vibrant science in action, equipping decision-makers with critical insights to guide sustainable ocean stewardship.

How to cite: Novellino, A. and Gorringe, P.: European Marine Observations and Data netowrk: Science-Driven Insights for Sustainable Action, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-168, https://doi.org/10.5194/oos2025-168, 2025.

Coastal marine ecosystems play a central role in hosting biodiversity and providing crucial ecosystem services for human societies. In tropical regions, biodiversity levels reach their climax in coral reefs, seagrass meadows, and mangroves, highly productive ecosystems that have long supported human wellbeing. While these ecosystems suffer growing impacts from local and global environmental changes and are declining rapidly, not all ecosystems show the same level of exposure and vulnerability to the various human and climate stressors. In this context, understanding how changing environmental conditions shape ecosystems can help elucidate the mechanisms underlying ecosystem resilience and define safe management pathways. We report a country-scale collaborative-science initiative bringing together scientific protagonists from various sectors, including research academics, coastal management officials, private consulting companies and environmental agencies, and participative-science civilians, to characterize the response of New Caledonia’s exceptional coastal system representing 6% of the world’s coral reef habitats, 0.25% of known seagrass meadows, and 0.26% of mangrove forest on the planet. Our evaluations produce environmental diagnostics of ecosystem health and current management efforts, and characterize socio-ecosystem resilience mechanisms and thresholds to define safe maneuvering spaces towards sustainable biodiversity-climate-human pathways.

How to cite: Kayal, M.: Identifying paths towards coastal sustainability through collaborative-science assessments of system responses to environmental changes, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-294, https://doi.org/10.5194/oos2025-294, 2025.

Sargassum, a floating brown algae, has caused significant environmental and socioeconomic impacts in the Caribbean region since 2011. Understanding the complex interplay of hydrodynamic processes and coastal morphology that govern Sargassum stranding events is crucial for effective mitigation and adaptation strategies. This study leverages high-resolution satellite imagery from VENµS-VM5 and Sentinel-2 to develop a robust method for monitoring Sargassum at unprecedented spatial and temporal scales. By applying the Normalized Floating Algae Index (NFAI) to daily VENµS-VM5 observations, we generate detailed maps and time series of Sargassum distribution. The method incorporates advanced atmospheric, cloud, and land mask corrections to ensure accurate detection and quantification. Preliminary results demonstrate the potential of this approach to provide early warnings of Sargassum strandings at fine spatial (4m) and temporal (~daily) resolutions. This high-resolution monitoring will enable the identification of key hydrodynamic factors and coastal features that influence stranding patterns. By assessing Sargassum residence times and quantifying stranded biomass, we can better understand the impacts on coastal ecosystems and human activities. The applications of this research are far-reaching. It can inform decision-making on marine conservation, and waste management. By providing timely and accurate information, this study contributes to the development of effective strategies to mitigate the negative consequences of Sargassum strandings and promote sustainable coastal management.

How to cite: Pitek, L., Brilouet, P.-E., Jouanno, J., and Graffin, M.: High-Resolution Satellite Monitoring of Sargassum Strandings for Enhanced Coastal Management in the West Indies, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-456, https://doi.org/10.5194/oos2025-456, 2025.

Climate action-oriented aquaculture is a production that integrates adaptation practices and mitigation efforts that reduce greenhouse gas emissions. We have developed a 10-step guide for how to include climate action in aquaculture across all species, from seaweed to fish.

Species diversification is one of the main adaptation strategies in aquaculture, suggested to make the sector more robust to impacts from climate change, as it will make the industry more robust to withstand challenging conditions, relieve the pressure on over-exploited wild populations, and if done correctly, can be used to reduce emissions. Unfortunately, there is a lack of climate action driven aquaculture production at present, and efforts should be made to emphasize both the importance of this for sustained production as well as for aquacultures potential to pave the way for more sustainable food production.

Establishing a new commercial aquaculture species takes time, effort, knowledge and resources. To ensure implementation of climate action, we developed the Aquaculture Readiness Levels (ARL®). The ARL® involves 10 levels across four stages: Research (1-3), Development (4-6), Commercialization (7-9), and Adaptation (10). ‘Research’ includes fundamental knowledge of biology, requirements of species under aquaculture, ‘Development’ includes trials to harvest size in production environment, and ‘Commercialization’ the commercial success, products to market, and production at large scale.  At the highest ARL®, level 10, where climate action is embedded within all production strategies.

Taking a fast track to market and skipping some of the steps in development of new species for commercialization may seem an attractive option. Skipping steps may however make that sector less flexible and more vulnerable to shocks, as the foundational knowledge and experience may be lacking. ARL® 10 is the Climate Action stage, and this demands strategies that make climate adaptation and mitigation strategies central to all decisions. Climate change should be considered at each ARL® stage, but what sets ARL® 10 apart from the others is that it is a deliberate scaling up of efforts to address the climate emergency by acting against climate change and its impacts, aligning with Sustainable Development Goal 13, Climate Action.

All species developed for aquaculture purposes should therefore aim for ARL® 10, where climate action permeates everything in the business model.

How to cite: Ytteborg, E. and Falconer, L.: Pushing Boundaries in Species Diversification for Climate Action with Aquaculture Readiness Levels (ARL®), One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-537, https://doi.org/10.5194/oos2025-537, 2025.

The increase of atmospheric CO₂ levels by as much as about 10% since the beginning of 21st century and its impact on the Earth’s climate and the biosphere represent a major concern. Based on a compilation of in situ data extrapolated over the global coastal ocean, previous studies indicate that the world’s coastal shelves absorb about 0.25 Pg C/year (~17% of oceanic CO2 influx), although these areas represent only 7% of the oceanic surface area. However, large uncertainties in coastal carbon fluxes and stocks exists due to their under sampling in both space and time. Moreover, all of the methods used to assess the land carbon sink rely upon accurate estimate of oceanic carbon as a key constraint or input. In this context, satellite remote sensing of ocean colour play a central role, as this Essential Climate Variables is currently the only ones for monitoring coastal and open ocean waters globally and systematically, at high spatial and temporal resolutions. Based on the development of recent algorithms performed in the frame of several research projects funded by CNES, EUMETSAT, ANR, and the COPERNICUS marine service, we present and discuss the first global vision of key aquatic carbon components over the global coastal ocean at high spatial resolution. The different algorithms developed to assess the particulate organic carbon, POC, dissolved organic carbon, DOC, and the in-water partial pressure of CO₂, pCO₂w, from ocean colour remote sensing will be presented with their quantified uncertainties. Theses algorithms will then be applied to the remote sensing reflectances obtained from the ESA Data User Element Project GlobColour to assess the spatio-temporal patterns of POC, DOC, and pCO2w over the global coastal waters from 1998 to 2024. The main temporal patterns will be presented and discussed and the global coastal carbon hot spots of long-term significative changes will be identified.

How to cite: Loisel, H., El Hourany, R., Vantrepotte, V., S.F. Jorge, D., monterro, M., Duforet-Gaurier, L., Bretagnon, M., Bryère, P., and Mangin, A.: Remote sensing monitoring of the spatio-temporal dynamics of the marine carbon polls of the global coastal ocean over the two last decades, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-577, https://doi.org/10.5194/oos2025-577, 2025.

Since the year 2011 the Caribbean region has seen a massive seasonal influx of pelagic Sargassum. The proliferation of this algae adversely affects the island nations by deteriorating their coastal and marine ecosystems, like coral reefs; decreasing biodiversity, and lowering water quality, while also diminishing tourism revenue, which may be the economic backbone of most countries in this region.  The proliferation of Sargassum seaweed and its effects on Guadalupe and Dominican Republic are directly linked to Sustainable Development Goal (SDG) 14, which seeks to "conserve and sustainably use the oceans, seas and marine resources for sustainable development". The impact from the seasonal assault on both nations has led to different mitigation, usage, and conservation strategies that can be developed into a comprehensive program for the management and valorization of sargassum, which in turn can become an opportunity for sustainable development.

This work will present the strategies followed by a group of universities within the Dominican Republic’s interuniversity Sargassum research network which tackle the arrivals through four fundamental research lines:

- Monitoring and prediction: The Dominican Republic is developing a prediction model based on aerial and satellite imagery, GPS tracking and ocean current models which will try and identify sargassum accumulation from trajectories through monitoring of sargassum windrows. This work includes the deployment of a nanosatellite focused on sargassum monitoring in coastal waters.

- Containment and collection: the group has made advances in sargassum containment through sea barriers and water collection in order to guarantee high quality biomass for value aggregated processing.

- Valorization: Sargassum is being processed through modular systems to obtain biomass that can be converted into energy (via anaerobic digestion or gasification), biofertilizers, biochars, activated carbon (through both conventional and microwave pyrolysis), alginate, and biocomposites of fibers and biopolymers.

- Impact assessment and management: experiences in management research will be shared, especially in the analysis of risk perception and the development of a comprehensive management model for sargassum in the Dominican Republic, which guarantees compliance with SDG 14 by 2030, as proposed by the United Nations.

How to cite: Jauregui Haza, U. J., Núñez-Sellés, A., Rodríguez, A., Sanlley, C., Christelle Yacou, C., Sánchez, E., Gandini, G., Polaert, I., Jiménez, I., Rodríguez de Francisco, L. E., Brehm, N., de la Cruz Iturbides, R., Liranzo Gómez, R., Gaspard, S., Rodríguez-Rodríguez, Y., Alvarez, Y., and Castro, Y. A.: Addressing the Massive Influx of Sargassum in the Dominican Republic: Transforming an Environmental Challenge into a Sustainable Development Opportunity, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-902, https://doi.org/10.5194/oos2025-902, 2025.

Effective monitoring of Dissolved Organic Carbon (DOC) from space is crucial for tracking carbon stocks and understanding fluctuations in both coastal and open ocean environments. As part of the OCROC project, founded by the Copernicus Marine Service, we have enhanced the existing Ocean and Land Color Instrument (OLCI) DOC algorithm, designed to leverage data from both historical and current ocean color sensors. This algorithm initially used four key inputs: the absorption coefficient of Colored Dissolved Organic Matter (a_cdom), chlorophyll-a concentration, Sea Surface Temperature (SST), and Mixed Layer Depth (MLD), each at varied time lags to account for water mass dynamics.

Our updated version introduces two optimized Artificial Neural Network models, a specialized approach for coastal areas affected by terrestrial influences, and reanalysis data for SST and MLD from COPERNICUS. We also assess the algorithm's adaptability for MODIS and VIIRS missions, requiring wavelength adjustments to ensure accurate a_cdom estimation—a process undergoing further calibration. By incorporating MODIS and VIIRS data, we aim to expand our dataset significantly, creating a new baseline for the algorithm.

The final weekly DOC product, spanning from 1998 to 2022 with a 4 km resolution, is available for community evaluation and feedback. This dataset supports in-depth studies of DOC variations, the identification of significant spatial and temporal patterns, and long-term time series analyses and tendencies, thereby advancing our understanding of carbon dynamics in coastal and open ocean waters.

How to cite: Montero, M., Elhourany, R., S.F. Jorge, D., Bretagnon, M., Vantrepotte, V., Cauvin, A., Prat, A., Bonelli, A. G., Duforêt-Gaurier, L., Mangin, A., and Loisel, H.: Estimating and Monitoring Dissolved Organic Carbon (DOC) Concentrations from Space across the Global Ocean, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1050, https://doi.org/10.5194/oos2025-1050, 2025.

Flood risk management and land use governance have become critical areas of study within environmental governance, particularly in low-lying coastal regions that are both highly urbanized and vulnerable to hydrological extremes. In riverine and estuarine systems, the interplay between water management, spatial planning, and the environment has significant implications. Historically, floods have played a central role in shaping delta landscapes; structural interventions like dikes and land reclamation enabled living conditions in flood-prone areas such as the Netherlands and parts of Flanders. While water infrastructure has contributed greatly to societal welfare, it has also encountered criticism due to its economic, social, and environmental impacts. Especially in response to growing ecological concerns, water management underwent a paradigm shift, marked by an “ecological turn” that began in the mid-20th century. This shift redefined nature as an intrinsically valuable component, highlighting the ecological debts incurred by prior civil engineering efforts. This environmental awareness, however, primarily influenced political and cultural attitudes, while the technical aspects of water management, especially hard engineering solutions, remained largely unquestioned until recently. The ecological awareness owned however the merit of prompting the use of nature-based solutions to achieve water safety while promoting ecological values and enhancing socio-economic functions. Yet, despite the growing advocacy for NBS, their integration into traditional hydraulic engineering systems has remained a challenge.

By adopting an evolutionary governance perspective, this research provides a comparative account of the evolution of flood governance over the past 25 years in the Scheldt estuary. The influence of institutional, material, discursive, goal, path dependencies, and interdependencies on flood risk governance and their implications for flood safety and nature conservation in the estuary is unraveled. This study places significant emphasis on the science-policy interface by exploring how scientific insights have been embedded within governance processes and decision-making. Institutional dependencies are assessed through formal and informal regulatory frameworks, while material dependencies cover natural and human development patterns that can impact policy effectiveness. Discursive dependencies are crucial, as they highlight the role of framing, semantics, and narrative in promoting the adoption of science-based policies. Goal dependencies are examined to understand how evolving governance objectives integrate scientific evidence, while path dependencies reveal how past decisions constrain or enable current policy shifts. Finally, interdependencies map the interconnectedness among governance actors, emphasizing collaborative pathways for science-informed policy implementation.

By taking a longitudinal and comparative approach, this research not only maps the distinct trajectories of flood governance in both regions in the Scheldt Estuary; the research findings also demonstrate the necessity for cross-border cooperation and underscores the critical need for science to consistently inform policy and decision-making to mitigate future hazards. A well-functioning science-policy interface helps bridge the gap between research and real-world application, promoting policies that are more effective, transparent, and aligned with long-term societal and environmental goals. This is particularly important when it comes to increasing flood hazards where timely and evidence-based decision-making is essential. This contribution enriches the academic and societal conversation on adaptive governance in the face of the escalating challenges posed by climate change.

How to cite: Vitale, C., Meijerink, S., Crabbé, A., Fletcher, C., Wiering, M., and Nijamdeen, F. M.: Unraveling 25 Years of Flood Governance in the Scheldt Estuary: A Comparative Study Through an Evolutionary Governance Lens, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1088, https://doi.org/10.5194/oos2025-1088, 2025.

The 4DBALTDYN ESA project is at the forefront of advancing our understanding of the Baltic Sea's dynamics by integrating state-of-the-art technologies. While modern satellite data excels in global monitoring, its focus on surface phenomena limits our holistic view of the marine environment. Although numerical modeling is a crucial tool, challenges persist in replicating complex environmental interactions. Acknowledging this, the project adopts a complementary approach, combining numerical modeling, AI, ML, and Earth Observation data for a comprehensive Baltic Sea overview. Specialized products, analyzing biochemical exchanges, and employing Earth Observation and modeling contribute to a 4D reconstruction in 2016-2023. Addressing the inadequacy of traditional methods, the project covers key variables like ocean color, sea surface temperature, open ocean, coastal sea level, and salinity. By characterizing surface circulation patterns and integrating AI models, the project aims to transcend limitations and make significant contributions to marine research. Interdisciplinary Science Case Studies address key questions and knowledge gaps, emphasizing a holistic approach. The project envisions a robust 4D reconstruction of Baltic waters, enhancing insights into physical and biogeochemical parameters through the integration of EO data, models, and AI. As the project commenced in April 2024, this presentation provides an overview, outlining aims, structure, developed products, validation processes and case studies outline.

How to cite: Bulczak, A. and Darecki, M. and the 4DBaltdyn team: Baltic Sea Dynamics through 4D Modelling and Integrated Earth Observation (4DBALTDYN), One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1187, https://doi.org/10.5194/oos2025-1187, 2025.

  National Marine Environmental Forecasting Center (NMEFC) in China has made a series of contributions in the field of marine environmental forecasting, with a strong emphasis on attaining the goals set for UN Ocean decade and one global ocean. Since the 1980s, NMEFC has been at the forefront of innovation. It established the Z-coordinate model for sea surface temperature forecasting in the China Seas and Northwest Pacific, which was a significant step forward in regional forecasting capabilities. Subsequently, in the 1990s and 2000s, it independently developed storm surge and tsunami numerical prediction models respectively, enhancing the ability to forecast and mitigate the impacts of natural disasters. In 2013, the Chinese Global Operational Oceanography Forecasting System (CGOFS) was launched, covering global temperature, salinity, and current parameters. Notably, the milestone achievement with the Mass Conservation Ocean Model (MaCOM) independently developed by NMEFC has significantly enhanced the capabilities of marine environmental forecasting since 2023. NMEFC's focus areas are extensive and crucial. It plays a vital role in modelling global and regional 3D temperature, salinity, current, and polar ice conditions. It also addresses various threats and challenges, including storm surges, tsunamis, and ecological environmental elements. Additionally, it is actively involved in responding to oil spills and pollutant leaks, as well as search and rescue operations. Moreover, its efforts in climate prediction are continuously advancing.

  In terms of research and development, NMEFC emphasizes a multi-faceted approach. It focuses on data, models (such as the mass conservation ocean model and finite volume model), and system products. It utilizes advanced methods like AI forecasting and GPU & CPU parallel I/O acceleration to enhance the accuracy and efficiency of forecasting.

  Looking towards 2030 of UN Ocean decade, NMEFC is dedicated to fulfilling strategic ambitions. This includes prioritizing the unlocking and generation of key datasets, establishing effective indicators to measure progress, and concentrating on capacity development and resource partnerships. It also aims to promote knowledge sharing, technological innovation, and the development of infrastructure for data and knowledge generation. By aligning with the objectives of the one global ocean, NMEFC is committed to making substantial contributions to creating a safe, sustainable, and well-understood ocean environment for future generations.

How to cite: Liu, G.:  Advancements in Marine Environmental Forecasting for one global ocean, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-919, https://doi.org/10.5194/oos2025-919, 2025.

The self-potential (SP) method based on the measurement of electrical potential changes occurring naturally in fresh and saltwater environments has become used as an auxiliary technique in marine geophysics research over the past few decades. Although the method is straightforward to apply on land, its application in aquatic environments requires a more precise dynamic measurement system for both data acquisition and processing. In this study, we present a self-potential data acquisition system design and demonstrate its applicability through measurements conducted in the laboratory and inshore areas of Kepez, Strait of Çanakkale.  A gradient array was designed, with two silver-silver chloride (Ag-AgCl) electrodes towed by a floating platform (buoy) connected via a few meters of cable to a recording unit. The recorder was equipped with a GPS for position fixing, a high-sensitivity analog-to-digital converter, and a data storage unit.  The buoy was horizontally framed with a 2-meter separation between the fore and aft tips to prevent sinking while being towed along the stern of the vessel. Chirp profiles were concurrently obtained at the self-potential target positions. Post-processing and interpretation of the trial data demonstrate that the designed system is well-suited for marine research. The SP data allowed us to distinguish both morphological changes, verified by chirp sonar imagery, and freshwater inflow into the marine environment, corroborated by multi-parameter data collected at the initial points of the profiles. Future studies will focus on freshwater surveys to investigate the impact of these observed variations.

How to cite: Önder, Ş., Öztekin, A., and Ulugergerli, E.: Self-Potential survey on marine environment: an example form the Strait of Çanakkale, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1071, https://doi.org/10.5194/oos2025-1071, 2025.

The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the Earth’s climate. According to the last IPCC reports, it is expected to weaken as the mean atmosphere temperature increases, with considerable impact around the world. There are few long time series of observations of the AMOC, and the study of the mechanisms driving its variability depends mainly on numerical simulations. Understanding the seasonal to decadal variability is required to properly detect a trend in the observed AMOC timeseries. Here, we use four ocean circulation estimates produced by different data-driven approaches of increasing complexity to analyse the seasonal to decadal variability of the subpolar AMOC across the Greenland–Portugal OVIDE (Observatoire de la Variabilité Interannuelle à DÉcennale, GO-SHIP line A25) line since 1993. We decompose the MOC strength variability into a velocity-driven component due to circulation changes and a volume-driven component due to changes in the depth of the overturning maximum isopycnal. We show that the variance of the time series is dominated by seasonal variability, which is due to both seasonal variability in the volume of the AMOC limbs and to seasonal variability in the transport of the Eastern Boundary Current. The decadal variability of the subpolar AMOC is mainly caused by changes in velocity, which after the mid-2000s are partly offset by changes in the volume of the AMOC limbs. This compensation means that the decadal variability of the AMOC is weaker and therefore more difficult to detect than the decadal variability of its velocity-driven and volume-driven components.

How to cite: Lherminier, P., Mercier, H., Desbruyères, D., Velo, A., Carracedo, L., Fontela, M., and Pérez, F. F.: Variability of the eastern subpolar North Atlantic meridional overturning circulation, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1570, https://doi.org/10.5194/oos2025-1570, 2025.