Dissolved manganese, despite its subnanomolar concentrations, plays a crucial role in co-limiting primary production in the Southern Ocean, yet the physical supply mechanisms during winter—critical for biological consumption in spring and summer—remain underexplored. This study addresses the urgent need to understand how manganese dynamics relate to the broader context of ocean health and climate adaptation. During the austral winter and spring of 2019, two research cruises were conducted in the Atlantic sector of the Southern Ocean to investigate the distribution and supply mechanisms of dissolved manganese in the upper water column. The findings revealed that winter entrainment accounted for an overwhelming majority of the total dissolved manganese flux, averaging 97.26 ± 5.28%, while diapycnal diffusion contributed a mere 4.92 ± 5.14%. Mean dissolved manganese concentrations in the upper water column (<500 m) were consistently low (≤0.34 nmol kg⁻¹; p-value > 0.05), with seasonal mixed layer reservoir sizes averaging 65.21 ± 12.93 μmol m⁻² in winter and 21.64 ± 19.32 μmol m⁻² in spring. Notably, winter supply rates exceeded estimated consumption rates during spring, thus fulfilling phytoplankton’s biological demands and enhancing ecosystem resilience. Conversely, in the subtropical zone, supply rates were insufficient to meet consumption needs, indicating the potential influence of additional mechanisms such as coastal upwelling. These insights into manganese fluxes highlight their importance in sustaining marine ecosystems and their implications for equitable and effective climate adaptation strategies in response to oceanic changes driven by climate variability.

How to cite: Ramalepe, T.: Understanding Manganese Fluxes in the Southern Ocean: Contributions to Climate Adaptation and Ocean Sustainability, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-46, https://doi.org/10.5194/oos2025-46, 2025.

The EBUSs are among the most biologically productive ocean ecosystems in the world and provide more than 20% of the world catch of fish on <1% of the ocean surface. They include the California, Humboldt, Canary, and Benguela Current systems and provide critical ecosystem, economic, and recreational services for over 80 million people who either live along their coasts or near those coasts. This study deals with the analysis of relationships between the Canary Current System, coastal climatology, and fishing activity by adopting a climato-oceano-economic approach along the Moroccan coast. The study points out the phenomenan of upwelling within the Canary system, which have repercussions on peculiarities along the coast that impact marine resources and, hence, have implications for inhabitants of the coastal areas as well as for local economies. Data are from NOAA, chlorophyll, and sea surface temperature, while fisheries data were obtained from official reports provided by the National Fisheries Research Institute and National Fisheries Office. The analysis is then controlled using R and Python programming languages. In this work, one looks for evidence of relevance of the upwelling phenomenon for fisheries production but also forms strategies in the use of marine resources in a sustainable way.

How to cite: Ounacer, F., Lorenzo, C., and Agnaou, M.: Assessing the Impact of Coastal Upwelling on Fisheries: Insights from the Canary Current System, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-82, https://doi.org/10.5194/oos2025-82, 2025.

Understanding and predicting pH distributions through accurate and certified in situ detection is currently crucial. As part of the European BRIDGE Black Sea project, surface pH_T transects were carried out in July 2024 across the Marmara Sea, the Bosphorus Strait and the southern Black Sea. This study compares high-resolution temporal pH_T measurements from 3 sensors deployed in parallel: SAMI-pH^TM (Sunburst Sensors, LLC, colorimetric sensor [1]), SeaFET™ (Sea-Bird Scientific, ion selective field effect transistor (ISFET) [2]) and pHNX (Ifremer Homemade colorimetric sensor). The sensors continuously monitored pH_T distributions of surface seawater passing through a SeaBird Scientific SBE45 thermosalinograph. Data collected by SAMI-pH^TM (n=319), SeaFET™(n=8424) and pHNX (n=488) were corrected from salinity and temperature (data provided by SBE45 thermosalinograph). Additionally, the SeaFET^TM sensor underwent evaluation and correction against robust benchtop measurements, with a one-point correction from the pHNX sensor, ensuring full traceability to international system unit [3]. The three instruments recorded the highest pH_T values (8.2225 for pHNX) at the exit of the Bosphorus Strait, extending in a north-easterly direction into the Black Sea. The lowest surface values were obtained in the northern part of the transect (8.1360 for pHNX, 41°33'04.7"N 29°39'01.1"E) and in the Marmara Sea (8.0623 for pHNX, 40°48'49.3"N 28°53'58.6"E). These findings are in line with a previous study carried out in the same area in June 2023 (data not published yet), and the general trend towards the entry of a pH-enriched flow into a semi-enclosed sea has been observed in other parts of the world [3].

Figure 1: pH_T sensors and sample inlet

Figure 2: Distribution of pH_T from pHNX

[1] A. M. Nightingale, A. D. Beaton, and M. C. Mowlem, “Trends in microfluidic systems for in situ chemical analysis of natural waters,” Sensors Actuators B Chem., vol. 221, pp. 1398–1405, 2015.

[2] T. R. Martz, J. G. Connery, and K. S. Johnson, “Testing the Honeywell Durafet® for seawater pH applications,” Limnol. Oceanogr. Methods, vol. 8, no. MAY, pp. 172–184, 2010.

[3] X. Liu, Z. A. Wang, R. H. Byrne, E. A. Kaltenbacher, and R. E. Bernstein, “Spectrophotometric measurements of pH in-situ: Laboratory and field evaluations of instrumental performance,” Environ. Sci. Technol., vol. 40, no. 16, pp. 5036–5044, 2006.

How to cite: Courson, R., Laës-Huon, A., Davy, R., Salvetat, F., Mamaca, E., Örek, H., Özhan, K., and Yücel, M.: Intercomparison and distribution of pHT in the Bosphorus Strait and Black Sea, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-115, https://doi.org/10.5194/oos2025-115, 2025.

In October 2021, an unusual deviation in the trajectory of a low-pressure system occurred in the Arabian Sea. Typically, low-pressure systems originating in this region follow a northward or northwestward path. However, unexpectedly, a low-pressure system that formed off the Mumbai coast on October 10, 2021, took a southeastward course over the following seven days, ultimately making landfall on the southwest coast of Kerala on October 16, 2021. This exceptional deviation from the usual wind pattern, where most storms in the Arabian Sea follows a west-northwesterly direction toward the Arabian coast or move northward had significant environmental consequences. This atypical shift in the system’s pathway has resulted in severe casualties due to unforeseen heavy rainfall events and subsequent flooding in Kerala. The observed alterations in oceanic and atmospheric warming patterns produce more frequent and intense tropical cyclones in the southeastern Arabian Sea. The trajectory of this low-pressure system serves as a clear indication of the ongoing climate change impacts in the region.

How to cite: Gopurathingal Devassykutty, M.: Latest indication of climate change along the Southwest Coast of India, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-116, https://doi.org/10.5194/oos2025-116, 2025.

The global ocean has warmed substantially over the past century, with far-reaching implications for marine ecosystems. Concurrent with long-term persistent warming, discrete periods of extreme regional ocean warming, known as marine heatwaves (MHWs), have increased in frequency. A comprehensive understanding of the physical processes controlling MHW life cycles is pivotal for improving our knowledge of MHWs, yet such understanding is still lacking in the context of the Philippines. This study seeks to elucidate the mechanisms driving upwelling induced by Ekman pumping and assess the influence of MHWs on this process. Additionally, we have developed a MHW tracker specific to the Philippines, providing daily updates on MHW events across the Philippine seas. This tool is essential for local government units to identify MHW occurrences, helping them to protect marine ecosystems and the communities that rely on them.

To achieve this, we will utilize the OSTIA global sea surface temperature reprocessed product for robust detection of MHWs. This satellite-derived sea surface temperature (SST) will be complemented by available historical in situ data (e.g., from cruises, temperature loggers or moorings) for validation. The dataset offers daily gap-free maps of foundation SST and ice concentration at a horizontal grid resolution of 0.05 degrees, using both in-situ and satellite data, available from October 1, 1981, to the present. Additionally, we will employ the Global Ocean Hourly Reprocessed Sea Surface Wind and Stress dataset, available from January 11, 2007, to March 21, 2024, at a horizontal spatial resolution of 0.125 degrees. This will be used to compute the Ekman pumping velocity to provide an estimate of the upwelling or downwelling proportional to the wind stress curl.

Furthermore, the Global Ocean Physics Analysis and Forecast at 1/12 degree provides 10-day 3D global ocean forecasts updated daily. This includes parameters such as temperature, salinity, currents, sea level, mixed layer depth, and ice from the surface to the ocean floor. This dataset will be used to examine the water column response to wind patterns and the anomalously warm ocean conditions associated with MHW perturbations. Datasets were provided by the E.U. Copernicus Marine Service Information.

How to cite: Repollo, C. L., Francisco, R., and Libatog, C. M.: Marine Heatwave and Its Potential Impacts to Upwelling Regions Around the Philippines, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-206, https://doi.org/10.5194/oos2025-206, 2025.

The high Arctic is one of the most sensitive regions to climate warming, which not only increase temperatures but also causes a substantial increase in freshwater discharge into coastal areas, mainly due to accelerated glacier melting. These meltwater runoffs alter the physical and chemical conditions of the water column, reducing light availability, changing light spectrum, decreasing salinity, and bringing in organic and inorganic particulate and dissolved matter. Effects of glacier meltwater on the structure and the functioning of coastal Arctic plankton communities were assessed by performing an in situ microcosm experiment in the Kongsfjorden, located on the west coast of Spitzbergen in the Svalbard Archipelago in Summer 2022. Two levels of meltwater runoff, moderate and strong, were tested by adding meltwater from two land-terminating glaciers to natural Kongsfjorden coastal waters in microcosms. Throughout the experiment, physical and chemical variables, as well as plankton abundance, diversity and metabolism, were monitored during 11 days. As expected, simulated runoffs significantly decreased salinity and light availability, but also pH, while they enhanced both N:P ratio and silicate concentrations. Meltwater runoffs significantly affected the phytoplankton community structure, favoring microphytoplankton - particularly diatoms - over nanophytoplankton; and increasing diatom diversity while decreasing that of dinoflagellate. The zooplankton community was even more affected than phytoplankton as both proto- and metazooplankton abundances strongly declined. Notably, copepod nauplii, the dominant metazooplankton group in the fjord during the experiment, almost disappeared. This suggests a considerable impact of glacier meltwater runoffs on plankton food web functioning and a weakening of zooplankton’s top-down control on phytoplankton under glacier meltwater runoff conditions. In contrast, the abundances of viruses, bacteria, picophytoplankton, and heterotrophic nanoflagellates were not significantly impacted by the simulated runoffs, suggesting a stronger resistance of these components of the microbial food web. However, based on oxygen measurements, gross primary production was not significantly affected by the treatments, indicating a strong functional resistance of the phytoplankton community and suggesting reduced light induced by the runoffs may have limited any increase in gross phytoplankton photosynthesis. Our findings indicate that the intensification of glacier meltwater runoff due to climate warming could significantly alter the structure of coastal Arctic plankton communities. Reduced zooplankton abundances and their grazing on phytoplankton, could disrupt normal ecosystem functioning, potentially reducing the efficiency of carbon transfer to higher trophic levels. Such changes may have serious consequences for the productivity and health of coastal Arctic ecosystems in the future.

How to cite: Soulié, T., Courboulès, J., Lambert, T., Voron, F., Mas, S., Mostajir, B., and Vidussi, F.: A changing Arctic – Glacier meltwater runoff shifts phytoplankton community structure and collapses zooplankton in a high Arctic fjord (Kongsfjorden, Svalbard), One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-529, https://doi.org/10.5194/oos2025-529, 2025.

Extreme events in the ocean, including marine heatwaves, low pH, and low oxygen events, are among the most severe impacts of climate change, profoundly affecting marine ecosystems, biogeochemical cycles, and the human communities that depend on ocean resources. When these events occur simultaneously or in close sequence leading to compound extremes, their impacts can intensify nonlinearly. Yet, we know very little about these events, especially under scenarios of both rising and declining CO₂ emissions. Using the Max Planck Institute Earth System Model with the emission-driven  SSP5-3.4 overshoot scenario, this study explores how extreme events evolve along a pathway marked by initial rapid emissions increases followed by steep reductions, ultimately reaching net-negative emissions. The emission-driven simulations incorporate an interactive carbon cycle, which in this setup allows for an examination of how CO₂ fluxes between the ocean and the atmosphere respond dynamically to changing emissions. Previous studies have shown that under negative emissions, the ocean may transition from a CO₂ sink to a source. However, it remains unclear how this shift could influence  marine extremes, potentially altering their frequency, intensity, and duration. This is especially relevant for both surface and subsurface extremes, where responses to emission changes may vary considerably. By focusing on the SSP5-3.4 overshoot scenario, this study provides a novel perspective at the implications of emission reductions and negative emissions for marine extreme events. These insights are crucial for understanding the potential risks associated with compound oceanic extremes and their impacts on the ocean’s climate-mitigating functions. The findings of our research will further provide guidance for future climate adaptation and mitigation strategies that consider the ocean’s critical role in a changing climate.

How to cite: Filippou, D., Li, H., and Ilyina, T.: Ocean Compound Extreme Events Under Emission Reduction and Negative CO₂ Pathways, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-534, https://doi.org/10.5194/oos2025-534, 2025.

This study examines the occurrence and impacts of Marine Heat Waves (MHWs) in the Eastern Tropical Atlantic, with a focus on the Gulf of Guinea. Using sea surface temperature (SST) data from OISST (1991-2020) and the PIRATA network (October 2019-March 2020), we identified an average of two MHW events per year over the past few decades. Notably, the frequency of these events has increased since 2015, with the northern coast of the Gulf of Guinea experiencing the most significant rise. We categorize the region into three key zones: the northern Gulf of Guinea, the equatorial zone, and the Congo-Gabon coastal region. Long-duration MHWs are more prevalent in the equatorial zone, while temperature anomalies exceeding 2°C are most intense along the Congo-Gabon coast. In addition, we analyze the impact of MHWs on coastal upwelling, mangroves, and coral reefs within the Grand-Béréby Marine Protected Area in Côte d'Ivoire. Our findings highlight the significant ecological and socio-economic consequences of MHWs on these vital ecosystems. We also address the causes and potential long-term effects of rising sea surface temperatures, particularly the extension of ocean heatwaves into deeper ocean layers, as noted in the 2024 Copernicus report. This study underscores the need for enhanced monitoring and predictive tools to mitigate the impacts of MHWs in the context of climate change and protect vulnerable marine ecosystems.

How to cite: Djakouré, S., Koné, M., Koffi, U., Kouadio, K. Y., Nyadjro, E., Adon, M., and Ta, S.: Impacts of Marine Heat Waves on Coastal Ecosystems in the Eastern Tropical Atlantic: Insights from the Gulf of Guinea and Grand-Béréby Marine Protected Area, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-709, https://doi.org/10.5194/oos2025-709, 2025.

Vietnam's coastal zone extends for 3260 km along the Western Pacific, an area that experiences a high number of tropical cyclones each year.  Approximately 24% of the coastline suffers from moderate to severe erosion. The central region of Vietnam, in particular, experiences a tropical monsoon climate characterized by two distinct seasons: summer monsoon (southwest monsoon) and winter monsoon (northeast monsoon). This climate leads to exceptional morphological evolution, with episodes of accretion and erosion. Understanding and identifying the specific driving force of shoreline change over space and time are crucial for coastal management. This study demonstrates a close relationship between monsoon winds and seasonal shoreline fluctuations. By analysing  shoreline positions extracted using various optical bands of satellite image from different satellite missions such as Sentinel 2, Landsat 5, 7, and 8, from 1993 to 2019, we reveal that seasonal shoreline changes are driven to a great extent by seasonal sea level variations, a direct consequence of monsoon winds. Furthermore, the study also investigated shoreline changes due to sediment transport using an empirical model. The analysis found that in some regions, sediment transport has a relatively minor impact on seasonal shoreline variation compared to the influence of wind setup during the study period.

How to cite: Hai Tran, Y., Marchesiello, P., Almar, R., Hai Thuan, D., and Morvan, G.: Shoreline extraction and analysis of its seasonal evolution under wind effects along the central coast of Vietnam, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-918, https://doi.org/10.5194/oos2025-918, 2025.

Since the beginning of the industrial era, the atmospheric greenhouse gases (GHG) have increased continuously (around +50% for carbon dioxide (CO₂) and +150% for methane (CH₄), for the two most important), causing the current climate change. In November 2023, the World Meteorological Organization (WMO) highlighted once again there are still significant uncertainties about the carbon cycle, its fluxes, and they stressed the importance to follow the non-CO₂ GHG with greater global warming potential.

The ocean plays a crucial role in climate regulation as a sink of anthropogenic CO₂, while surface seawater is naturally supersaturated in CH₄, and shallow coastal waters are a source of CH₄ to the atmosphere. However, the air-sea CO₂ and CH₄ fluxes are driven by different key processes depending on the region of the open or coastal ocean.

To improve the understanding of the processes driving the air-sea exchange of GHG, we investigate the CO₂ and CH₄ concentrations in open ocean and coastal areas affected by sea ice, glacier runoff and riverine inputs within the context of the European project GreenFeedBack. To do so, we measured CO₂ and CH₄ concentrations in surface water during a summer cruise (August 2024) conducted on board the RV Skagerak between Sweden, Norway and the Storfjorden in Svalbard. The data were obtained using a custom-made air-seawater equilibration system, that was connected to the vessel’s non-toxic seawater supply (equilibrator and Cavity Ring Down Spectrometer) and discrete sampling. We also investigated the depth distribution of CH₄ and carbonate system parameters.

Our first results show very high CH₄ concentration in surface seawater near marine-terminated glaciers in the Storfjorden, correlated with salinity gradient (but not the lowest salinity observed in Svalbard). In West-Svalbard, we found minimal CO₂ concentration correlated with low salinity, indicating a potential impact of freshwater discharge from the glaciers systems.

How to cite: Leseurre, C., Delille, B., Theetaert, H., T’Jampens, M., and Gkritzalis, T.: Summer greenhouse gases spatial variability from Svalbard and Norway fjords, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1035, https://doi.org/10.5194/oos2025-1035, 2025.

In the Gulf of Lion (GOL), in the northwestern Mediterranean Sea, a phenomenon known as deep convection often occurs in the late winter / early spring. It occurs when the vertical stability, or stratification, of the ocean is eroded until becoming neutral, allowing the column to overturn. Following these overturning events, there are large phytoplankton blooms, as the mixing evenly distributes oxygen and nutrients throughout the column. Western Mediterranean dense water is also formed by this overturning and aids in the overall Mediterranean Sea thermohaline circulation.

Deep convection is primarily driven by air-sea fluxes on the yearly timescale, forming an annual cycle. When these fluxes turn significantly negative in the fall and winter, cooling the ocean surface, they drive the aforementioned erosion of stratification, leading to deep convection. However, if these fluxes do not provide sufficient cooling, the column retains some stratification and overturning won't occur. Similarly, if enough stratification accumulates during the summer when the air-sea fluxes are positive, typical fall/winter fluxes can be prevented from completely removing it.

Marine heatwaves (MHWs) are anomalously warm sea surface temperature (SST) events, typically identified as extreme SST events above the 90th percentile SST. They are driven either by anomalously warm air-sea fluxes and/or warm advected water masses. These events can significantly affect the local air-sea fluxes and marine biology. One particular impact they can have is increasing the local stratification, by increasing the vertical temperature gradient at/near the surface. For areas with an annual stratification cycle that can result in deep convection, e.g. the GOL, this is a concerning potential consequence of MHWs. For example, in the GOL, 2022 and 2023 saw a significant number of MHWs: 130 and 90 days per year of extreme SSTs, respectively.

In this work, we analyse Infrared Atmospheric Sounding Interferometer (IASI) SST data with in-situ Argo float measurements to observe the co-occurrence of MHWs and extreme stratification events from 2007 to 2024, to evaluate the impact of MHWs on the deep convection cycle in the GOL. During this period, 731 days in the GOL were marked as MHWs, occurring roughly 11.7% of the time. However, of this 11.7%, MHWs only co-occurred roughly half (~45.1%) of the time with an extreme stratification event somewhere in the vertical column. When examining the co-occurrence with extreme stratification per vertical ocean layer, this percentage drops to around 10% for most of the layers.

This means, despite MHWs becoming more frequent with climate change (8 event days in 2010 in the GOL versus 90 in 2023), in the GOL only half of these events co-occur with extreme stratification. While this seems large, to further quantify the impact, the anomalous extreme stratification are small enough in magnitude to be potentially removed by ~2.5 weeks of probable surface cooling (~-100 MJ of integrated, anomalous heat fluxes required, achievable with ~18 days of ~-75 W/m² anomalous heat flux). Therefore, marine heatwaves do not appear to significantly impact the deep convection cycle of the Gulf of Lion, even as they become more frequent.

How to cite: Keller Jr., D., Siriez, D., Capelle, V., and Hartmann, J.-M.: Marine Heatwaves and Stratification Extremes in the Gulf of Lion, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1090, https://doi.org/10.5194/oos2025-1090, 2025.

The CFOSAT (China-France Oceanography SATellite) satellite mission, a successful cooperation between China and France, launched in 28 October 2018 has revealed the importance of directional observations of waves and winds at the ocean surface. The SWIM wave scatterometer provides a detailed description of wave energy in direction and wavelengths of waves ranged from 50 to 1100 m. This presentation summarize the oustanding acchievements of CFOSAT mission on science and operational applications. The assimilation of such observations into the operational wave model has enabled significant correction of significant wave height bias in ocean regions with high wind uncertainties, such as the Southern Ocean. The integrated wave parameters with exceptional accuracy are provided in the Copernicus marine service. In addition, the sea state corrected by CFOSAT observations improves the estimation of physical coupling processes needed for accounting ocean/wave/atmosphere interactions. Among the remarkable results of using CFOSAT observations, we can highlight the improvement of wind-waves forecast in extreme conditions such as cyclones or hurricanes, and consequently a better initial conditions for swell propagation in the oceans. CFOSAT's directional observations are the only satellite mission that can provide the estimation of Stokes drift and improved surface stress, which play an important role in the upper ocean mixed layer. Other achievements concern the capacity of SWIM instrument to provide probability of sea ice in the Marginal Ice Zone, where uncertainties in heat and momentum fluxes are high. Directional wave observations from CFOSAT also contributed to accurate global wave climate as provided in the wave reanalysis WAVERYS produced by the Copernicus Marine Service.

How to cite: Aouf, L., Faugere, Y., Ying, X., Hauser, D., Tourain, C., Hazan, D., Sun, C., Chapron, B., and Fangli, Q.: CFOSAT : A step forward for operational oceanography and better understanding of ocean waves climate, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1092, https://doi.org/10.5194/oos2025-1092, 2025.

The project “deteCtion and threAts of maRinE Heat waves – CAREHeat”, funded by ESA in the framework of the Ocean Health initiative, aims at advancing the understanding of marine heatwaves (MHWs) processes, including the associated physical processes and biogeochemical responses at the global scale. This is achieved by integrating long-term satellite-based climate data records with model-based datasets and high quality in situ observations of key parameters, such as temperature and carbon concentration.

In the frame of the project we assess the sensitivity of standard detection approaches to methodological choices, which we find to be significant across major ocean basins. Dependence on the dataset choices is also a matter of concern, as they can contribute to spread in the detection results. 

Furthermore, we study processes leading to persistent heatwave conditions for selected case studies, such as the Mediterranean Sea, in the last decades. This type of events can have cascading effects on marine ecosystems, such as phytoplankton communities and higher trophic levels, therefore is of paramount importance to understand them and anticipate them to aid adaptation and mitigation.

Perspectives on multivariate compound extremes, whereby heatwaves are associated with e.g. increasing ocean acidification, will also be discussed, to try and disentangle the effects of anthropogenic warming from the modulation due to natural climate variability. 

Further details on the project outcomes can be found at the associated website (https://careheat.org/) and broader context is provided by the ESA Ocean Science Cluster (https://eo4society.esa.int/communities/scientists/esa-ocean-science-cluster/). Key results from the project, such as the heatwave atlas, are publicly disseminated to facilitate research and increase awareness on this pressing problem.

How to cite: Serva, F. and Santoleri, R. and the CAREHeat team members: Characterizing marine temperature extremes and their impacts under climate change: the CAREHeat project, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1287, https://doi.org/10.5194/oos2025-1287, 2025.

Almost the entire amount of planetary heating from climate change is buffered by the ocean. Today, the Earth is out of energy balance from human-induced emissions and consequently, heat is accumulating in Earth’s climate system from which about 90% is stored in the global ocean. Hence, measuring this accumulated heat induced from anthropogenic activities through an estimate of ocean heat content while integrating ocean temperature from the surface down to large depth allows us to track the state of planetary warming. The fraction of this surplus heat of anthropogenic origin that is reaching the deep ocean – i.e., which is not in active communication with the atmosphere – is stored and trapped for hundreds to thousands of years. Hence, the ocean does not only guide us on the current amount of planetary warming, but also on the committed – and even irreversible changes to come. The recent assessment of the Intergovernmental Panel for Climate Change (IPCC) has stated that global heating of the Earth system is unequivocal, and both satellite and in situ observations have shown that heat accumulation and hence the Earth energy imbalance has doubled over the past 2 decades. Detecting an acceleration of Earth heating has remained elusive to date, despite suggestive evidence of a potential increase in heating rates. Studying ocean warming from independent studies also tells us that since 1960, the warming of the world ocean has accelerated at a relatively consistent pace of 0.15 ± 0.05 (W/m²)/decade, while the land, cryosphere, and atmosphere have exhibited an accelerated pace of 0.013 ± 0.003 (W/m²)/decade. This has led to a substantial increase in ocean warming, with a magnitude of 0.91 ± 0.80 W/m² between the decades 1960–1970 and 2010–2020, which overlies substantial decadal-scale variability in ocean warming of up to 0.6 W/m². These findings withstand a wide range of sensitivity analyses and are consistent across different observation-based datasets. The long-term acceleration of Earth warming aligns qualitatively with the rise in CO₂ concentrations and the decline in aerosol concentration during the same period, but further investigations are necessary to properly attribute these changes, and to analyze regional implications and their link to marine extremes which are ongoing under the European project ObsSea4Clim. This global indicator is hence most fundamental for the use of the scientific community and the public to measure of how well the world is doing in the task of bringing anthropogenic climate change under control, which are the committed changes for hundreds to thousands of years, and to track increase and acceleration of planetary warming.

How to cite: Minière, A., von Schuckmann, K., Speich, S., Zegna-Rata, A., Sallée, J.-B., and Vogt, L.: The Ocean – sentinel for planetary warming, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1294, https://doi.org/10.5194/oos2025-1294, 2025.

The role of continental shelves in carbon sequestration is poorly quantified. Riverine inputs present terrestrial inputs of organic carbon and nutrients to the coastal zone. In addition, the strong benthic-pelagic coupling in shallow areas, combined with the large variation in hydrodynamic and hydrographic regimes puts a large uncertainty on vertical carbon export fluxes. Furthermore, ocean-atmosphere interactions close to land are strongly influenced by local conditions such as wind direction and bottom depth, which are key determinants for wave conditions and gas exchange. We use a relatively simple 1D vertical ecosystem model in concert with monitoring data from national monitoring programmes and the ICOS project (Integrated Carbon Observing System; EU infrastructure project) to identify and quantify sources of uncertainty in carbon export fluxes in the southern North Sea. Results are discussed against a background of coastal and latitudinal gradients.

How to cite: Van Engeland, T., Soetaert, K., and Gkritzalis, T.: Is the southern North Sea a carbon source or sink? : a model-data integration exercise, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1296, https://doi.org/10.5194/oos2025-1296, 2025.

Blue carbon ecosystems—such as mangroves, salt marshes, and seagrasses—play a critical role in the ocean-climate nexus by sequestering large amounts of carbon, enhancing coastal resilience, and supporting biodiversity. However, these ecosystems face significant threats from climate change impacts and human activities, which can disrupt their carbon sequestration capacity and resilience. This study examines Brazil’s blue carbon strategies within the framework of climate adaptation and the ocean-climate nexus, focusing on gaps in policy integration, governance, and financing.

Brazil, while advancing its climate adaptation agenda with initiatives like the National Adaptation Plan (PNA), faces challenges in aligning blue carbon policies with broader climate goals, including adaptation and Loss and Damage frameworks outlined by the Warsaw International Mechanism (WIM). Recent research underscores the importance of blue carbon in mitigating losses and damages, especially for vulnerable coastal communities (Polejack et al., 2021). Nonetheless, the current WIM mechanism and related climate financing tools do not fully encompass blue carbon considerations, limiting Brazil’s capacity to harness international support for these critical ecosystems​.

Governance challenges also hinder Brazil’s blue carbon potential. Effective management requires integrating multi-level governance, with the involvement of local and regional entities to address specific vulnerabilities and socio-economic dynamics of coastal regions. However, only a small proportion of Brazilian municipalities have sufficient risk management capabilities, a significant barrier to blue carbon preservation (Melo, 2021). Strengthening local governance and increasing public awareness on climate risks are essential steps to enhance adaptive capacity and secure ecosystem services provided by blue carbon habitats.

The paper further highlights the potential of international partnerships and climate funds to support blue carbon initiatives through tailored funding mechanisms. Recommendations include developing sectoral frameworks for blue carbon, strengthening Brazil’s governance structure for integrated climate and marine policies, and expanding public-private partnerships to support blue carbon resilience efforts.

This analysis underscores that while blue carbon holds significant promise within Brazil’s climate agenda, robust policy integration, targeted financing, and capacity-building initiatives are critical for maximizing its benefits. By advancing blue carbon strategies, Brazil can position itself as a leader in ocean-climate adaptation, leveraging blue carbon ecosystems to foster both national resilience and global climate stability.

How to cite: Moraes Neves, A. F., Maltese Zuffo, M., Mondino, I. C., Duleba, W., and Duleba Marques, I.: Integrating Blue Carbon in Brazil’s Climate Strategy: Policy, Governance, and Financing Challenges within the Ocean-Climate Nexus, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1419, https://doi.org/10.5194/oos2025-1419, 2025.

The midlatitude oceanic front is a zonally elongated domain with a prominent sea surface temperature meridional gradient, which is a key region for the midlatitude air-sea interaction. The synoptic-scale transient eddy activity is prevalent over the midlatitude oceanic front, referred to as storm track, which plays an important role in the midlatitude weather and climate system. Therefore, it is of great significance to investigate the interaction between the midlatitude oceanic front and the storm track , which may help to understand and improve the theory of midlatitude air-sea interaction.

In this study, the relationship between the North Pacific midlatitude oceanic frontal intensity and the storm track is investigated based on the high-resolution oceanic and atmospheric reanalysis datasets. It is found that there exists a close association between the North Pacific storm track and the midlatitude oceanic front. The storm track strengthens (weakens) with the increased (decreased) oceanic front. The impact of the oceanic frontal intensity on the storm track is strongest in winter and spring, followed by autumn, and it is weakest in summer. The seasonal variations of the relationship between the two may be attributed to the near surface baroclinicity and the baroclinic energy conversion anomalies.

Additionally, future changes in the relationship between the North Pacific midlatitude oceanic frontal intensity and the wintertime storm track are projected based on a CMIP6 high-resolution climate model CNRM-CM6-1-HR. By comparing the relationship between the oceanic frontal intensity and the storm track under four different shared socioeconomic pathways (SSPs) with the historical run, it is found that there tends to exist the significant positive correlation under global warming, while the correlation will weaken in the storm track climatology and northern region, with the largest reduction in the high radiation scenarios (SSP5-8.5) and the least reduction in the medium to high radiation scenarios (SSP3-7.0). Further analysis indicates that the positive correlation between the oceanic frontal intensity and the near-surface baroclinicity also exhibits a similar weakened trend, which suggests that the projected changes in the relationship between the oceanic front and the storm track are mainly determined by the future changes in the relationship between the oceanic front and the near-surface baroclinicity.

How to cite: Yao, Y., Zhong, W., He, H., Sun, Y., and Feng, Z.: The relationship between the North Pacific midlatitude oceanic frontal intensity and the storm track and its future changes, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-241, https://doi.org/10.5194/oos2025-241, 2025.

Sea state information is needed for many applications, ranging from safety at sea and on the coast, for which real time data are essential, to planning and design needs for infrastructure that require long time series. The definition of the wave climate and its possible evolution requires high resolution data, and knowledge on possible drift in the observing system. Sea state is also an important climate variable that enters in air-sea fluxes parameterizations. Finally, sea state patterns can reveal the intensity of storms and associated climate patterns at large scales, and the intensity of currents at small scales. A synthesis of user requirements leads to requests for spatial resolution at kilometer scales, and estimations of trends of a few centimeters per decade. Such requirements cannot be met by observations alone in the foreseeable future, and numerical wave models can be combined with in situ and remote sensing data to achieve the required resolution. As today's models are far from perfect, observations are critical in providing forcing data, namely winds, currents and ice, and validation data, in particular for frequency and direction information, and extreme wave heights. In situ and satellite observations are particularly critical for the correction and calibration of significant wave heights to ensure the stability of model time series. A number of developments are underway for extending the capabilities of satellites and in situ observing systems. These include the generalization of directional measurements, an easier exchange of moored buoy data, the measurement of waves on drifting buoys, the evolution of satellite altimeter technology, and the measurement of directional wave spectra from satellite radar instruments. For each of these observing systems, the stability of the data is a very important issue. The combination of the different data sources, including numerical models, can help better fulfill the needs of users.

How to cite: Ardhuin, F.: The seastate Climate Change Initiative project: mapping ocean waves for applications from all existing satellite data, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1384, https://doi.org/10.5194/oos2025-1384, 2025.