Fishing with active bottom-contacting gears is considered one of the greatest sources of anthropogenic disturbance within marine environments with impacts ranging from biodiversity loss, habitat degradation and carbon resuspension. However, there remains strong debate over the global scale of the footprint of this activity primarily driven by uncertainties inherent in the data that underpin such estimates. One major source of uncertainty surrounds global variation in gear width estimates with previous studies applying European relationships to the global fleet, however, the appropriateness of this assumption remains untested. Equally, spatial data on the global fishing fleet has recently become available that separates bottom contacting gears from their mid-water equivalents. In this talk, we will present the latest findings from our investigations into how updated datasets in both of these areas of uncertainty have impacted estimates of the global footprint of bottom-contacting fishing gears and the implications of this for policy and management.

How to cite: Kerry, C., Rickwood, M., Eigaard, O., McLaverty, C., Roberts, C., Sala, A., Godley, B., and Metcalfe, K.: Reducing uncertainty in global carbon emission estimates from active bottom contacting fishing gears, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-25, https://doi.org/10.5194/oos2025-25, 2025.

Anthropogenic activities have caused an increase in greenhouse gas emissions, leading to the alarming rate of global temperature increase and associated climate change impacts. Due to these challenges, nature-based solutions for capturing greenhouse gases, in the form of carbon (C), are becoming of significant interest. Several marine carbon dioxide removal (mCDR) methods are being advanced, including the utilisation of brown macroalgae detritus, such as kelp, as potentially significant contributors to deep-sea C sinks. Although there are several studies that have utilized models to calculate kelp contribution to C sequestration, there is very little observational data to validate these hypotheses. Despite the many unknowns about the role kelp could have in mCDR, many industries are beginning to farm kelp in the open ocean for carbon credit schemes, with little regulation or understanding of the impact these aquaculture farms may have on the open ocean environment. The aim of the present study is to use a multi-methodological approach to quantify kelp contribution to mCDR in Aotearoa New Zealand’s (NZ) submarine canyons and deep-water environments. Multicore sediment samples and water samples were collected for eDNA analyses, bulk stable isotope analyses of C and nitrogen (N), and ¹⁴C and ²¹⁰Pb sediment dating, and the evaluation of environmental factors at 35 sites throughout central New Zealand, to identify the transport mechanisms of kelp detritus from coastal habitats to deep-sea benthic environments. Five genus-specific droplet digital PCR (ddPCR) eDNA assays were developed and applied to 350 sediment and filtered water samples, to identify if kelp contributions to C sequestration are genus-specific and to quantify how much kelp biomass may be transported and deposited from the coast to deep-sea submarine canyons. Bulk stable isotope signatures of sediment were analysed to identify δ¹³C and δ¹⁵N values that are unique to the five target kelp genera. Results from the ddPCR indicate that the amount of kelp detritus deposited in natural C sinks varies between genera and is dependent on geographical location. Although kelp was present in the sediment at some sites, there does not appear to be a significant contribution to deep-sea C stocks, therefore raising questions about the efficacy of macroalgal deposition as an effective mCDR tool.

How to cite: Deinhart, M., Bilewitch, J., Hickson, R., Zuccarello, J., D'Archino, R., Leduc, D., Sutherland, J., Brooks, A., Smith, L., Bury, S., Delgado, J., Kerr-Hislop, O., Frontin-Rollet, G., Alexander, C., and Nodder, S.: Quantifying indigenous kelp contributions to New Zealand’s deep-sea carbon sinks, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-278, https://doi.org/10.5194/oos2025-278, 2025.

In response to the pressing call for climate action, the International Panel on Climate Change (IPCC) has highlighted the key contribution that carbon dioxide removal will play to counterbalance hard-to-abate residual emissions, alongside efforts to reduce and avoid them.

Coastal blue carbon habitats are responsible for supporting up to 71% of carbon storage in oceanic sediments for centuries, outsizing terrestrial ecosystem carbon storage performances. In the Mediterranean Sea, Posidonia oceanica is not only the most widespread but also the most efficient carbon removal.

Under the Paris Agreement, marine ecosystems have been formally recognized as carbon removal, supporting Parties’ commitments to mitigation. Blue carbon habitats such as Posidonia can be included in compliance carbon crediting systems developed under Article 6 of the Agreement, and they also hold promise within the Voluntary Carbon Market (VCM), where coastal ecosystem credits may be sold as offsets.

Despite this potential, the integration of Posidonia oceanica into carbon markets faces several challenges. For the compliance market under the Paris Agreement, definitions and frameworks are still evolving, while VCM integration is hindered by limited historical data and by the need for affordable, and robust technologies and methodologies to establish a baseline. The definition of a baseline is crucial to set the monitoring period, to measure the activity sustainability and even more to ensure the correct accounting of carbon removal units, by avoiding double counting.

This paper presents how Earth Observation (EO) can support blue carbon removal monitoring, reporting and verification (MRV) through the creation of a rating system. Developed in the framework of the ESA-funded Feasibility Study, “SCORE – Scale for Carbon Organic Resilient Ethereal”, this rating system not only is expected to help Marine Protected Areas (MPA) boost coastal conservation and protection but also provides insights into new business models supported by VCM.

How to cite: D'Acunto, F. and Iodice, F.: Leveraging Earth Observation to Enhance Blue Carbon MRV: A Rating System for Posidonia Oceanica in Mediterranean Marine Protected Areas, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-382, https://doi.org/10.5194/oos2025-382, 2025.

Ocean alkalinity enhancement (OAE) aims to increase the CO₂ uptake capacity of the surface ocean by reducing surface water pCO₂ potentially accelerating CO₂ transfer from the atmosphere to the ocean. One such method involves the dissolution of olivine, a naturally occurring silicate mineral, in seawater to sequester excess CO₂. Silicate minerals weather on geological timescales, contributing to the buffering capacity of the ocean, but enhancing this process by adding silicate minerals raises concerns about the potential impact of trace element release from mineral impurities on sensitive marine organisms. In this study we exposed the commercially important Pacific oyster Magallana gigas during critical embryonic and larval development to enhanced alkaline waters derived from olivine dissolution. Two experiments were conducted: (1) batch experiments on embryonic development over a gradient of increasing alkaline water from ambient (2300 µmol kg^-1) to 11000 µmol kg^-1, and (2) a short-term larval experiment from 48 h post-fertilization to 144 h followed by a 15-day recovery period until settlement. For the first time we report that embryonic development collapsed at alkalinity levels above 3500 µmol kg^-1 and that larval development was delayed.  These findings underscore the need for caution in deploying ocean alkalinity enhancement as a geoengineering strategy.

How to cite: miller, C., Koechlin, H., Ducoulombier, L., Gazeau, F., and Pernet, F.: Keeping tabs on ocean alkalinity enhancement: effects of olivine dissolution on the embryonic and larval development of the Pacific oyster Magallana gigas  , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-477, https://doi.org/10.5194/oos2025-477, 2025.

Decarbonization of anthropogenic activities is progressing too slowly, creating an urgent need to actively remove carbon dioxide (CO₂) from our atmosphere if we are to prevent the most severe consequences of a disrupted climate system. The marine environment offers several potential approaches for sequestering carbon, with iron-enhanced biological productivity being the most extensively studied. However, past iron addition studies were not primarily aimed at quantifying the durability of carbon storage, nor did they evaluate how prudent this approach might be as a marine carbon dioxide removal (mCDR) approach. A new generation of field studies is needed to address knowledge gaps and uncertainties regarding the effectiveness, scalability, reproducibility, and cost of iron addition for mCDR. These future field experiments need to be conducted on significantly larger spatial scales (over ten times larger) and longer in duration (multi-seasonal rather than the typical one-month studies) compared to previous mesoscale iron addition studies. Core measurements are required to quantify key factors such as: CO₂ drawdown in the surface ocean, the re-equilibration timescales of atmospheric CO₂ with the surface ocean, the sinking transport of carbon to depth, and the portion of this flux that results in carbon sequestration for 100 years or more. Attention must also be given to the ecological and environmental consequences of iron addition, necessitating a combination of remote sensing, in-situ observations, and modeling. Initial field trials are proposed for the iron-limited high seas of the NE Pacific, chosen for specific reasons outlined in this presentation. These field trials must be developed and conducted in collaboration with social science and governance experts to ensure they are deployed with community engagement, and in an equitable, just, and ethical manner, with the appropriate social safeguards. This presentation reflects the contributions of a diverse group of international and multidisciplinary experts, all of whom are committed to a responsible code of conduct as part of the Exploring Ocean Iron Solutions (ExOIS) consortium. Now is the time for actionable studies to begin. https://oceaniron.org/

How to cite: Buesseler, K., Chai, F., Drysdale, J., Morris, P., Ramakrishna, K., Smith, S., Wells, M., and Yoon, J.-E.: Marine CDR science meets social science – organizing the next generation of ocean iron fertilization field studies, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-487, https://doi.org/10.5194/oos2025-487, 2025.

To reach global climate targets, there is growing attention to novel approaches to draw down atmospheric carbon, such as ocean-based carbon dioxide removal (OCDR) approaches. However, the risks and benefits of deploying OCDR approaches on a large scale, including possible environmental side effects, remain understudied. There is an urgent need to understand these environmental impacts, given that there may be pressure to scale up these approaches quickly as climate issues worsen. A review of the current state of knowledge on the environmental performance of OCDR approaches and their potential is currently lacking. To fill this knowledge gap, we conducted a systematic literature review of the LCAs of OCDR approaches. Life cycle assessment (LCA) is a relevant tool to quantify the environmental performance of a product or a service throughout its life cycle and is already used for CDR approaches.

Our review finds that current practice does not allow for the appropriate assessment of the environmental performance of OCDR approaches. Current OCDR LCAs have a limited scope, often overlooking other environmental impacts than global warming and LCA as an approach is currently limited in capturing impacts in marine environments. We provide guidelines for more consistency and transparency in future environmental assessments of these technologies, such as applying a functional unit related to storage of atmospheric carbon over a specified time horizon and in a specified medium, performing cradle-to-grave analysis, including more (marine) environmental impacts, and estimating uncertainties. We also provide guidance for developing LCA methodology for the marine environment, by notably developing additional marine impact categories in the LCIA and dividing the marine compartment into relevant sub-compartments.

How to cite: Delval, M. H., Thonemann, N., Henriksson, P. J. G., Tanzer, S. E., and Behrens, P. A.: Life cycle assessment of ocean-based carbon dioxide removal approaches: A systematic literature review, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-631, https://doi.org/10.5194/oos2025-631, 2025.

Combined with rapid decarbonization efforts, marine carbon dioxide removal (mCDR) approaches are actively being investigated to offset hard-to-abate and legacy CO₂ emissions in order to limit global warming to 1.5-2°C. These approaches leverage the large surface area and high carbon absorption capacity of the ocean to increase atmospheric drawdown of CO₂. To become effective, timely research, development and assessment of these approaches is necessary.

SeaO₂ is researching and developing an electrochemical direct ocean capture (DOC) approach that has a gigaton-scale removal potential. By using a pH-swing system, SeaO₂’s DOC process captures a pure stream of CO₂ out of seawater without the addition of any chemicals. The captured CO₂ can then be sequestered or utilized, while the CO₂-depleted seawater naturally reabsorbs atmospheric CO₂ over the following months.

Here we present our ongoing collaborative research efforts for assessing environmental impacts to support the ocean safety of our future field trial. We also present our framework for monitoring, reporting, and verification (MRV), which is pivotal for transparent quantification of net carbon removals, environmental monitoring, and third party evaluation. We discuss the combined roles of direct measurements of the carbonate system and model simulations in quantifying the rate of CO₂ re-uptake by decarbonized water. We also discuss how we incorporate emerging community best practices, including public engagement considerations to uphold responsible deployment. 

How to cite: Reijnders, D. and Syed, Z.: Research & MRV framework for SeaO2’s electrochemical Direct Ocean Capture process, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-677, https://doi.org/10.5194/oos2025-677, 2025.

The most recent Emissions Gap Report from the United Nations indicates that the world is on a path towards between 2.5-3.0°C of warming, far from the stated goals of the Paris Agreement of limiting warming to 1.5°C. Such a path poses grave risks to climate stability, biodiversity, and human flourishing on this planet. To close the gap between our existing path and the Paris Agreement, much less a restored climate, requires increased ambition to both decarbonize our society and actively remove greenhouse gases from the atmosphere. Among the options for greenhouse gas removal, marine pathways stand out for their high potential and underinvestment of global time, money, and energy to date.

Ocean Visions, working alongside a network of partners around the world, has a multi-pronged agenda to accelerate progress on marine carbon dioxide removal approaches. Our work is centered on support for accelerated research and development, including field research, to answer the fundamental questions that exist regarding whether or not to deploy any specific marine carbon dioxide removal techniques at climate-relevant scales. We believe this work must be done in a transparent, controlled manner; subject to a code of conduct to govern the research activities; and in consultation and cooperation with local authorities, all affected communities, and rights holders. In our work, we explicitly seek to increase diversity and size of the global community engaged to solve these challenges. Importantly, we believe that it is premature to take positions on whether or not to deploy any of these technologies while the existing science, engineering, and governance gaps remain so large.

We advance this work using two complementary approaches. First, we develop open-access products, such as interactive road maps, research frameworks, field trials databases, site suitability planning tools, and more to help the global community identify and address existing knowledge gaps in science, engineering, policy, governance, and justice. Second, we facilitate, convene, and catalyze conversations to increase collective understanding, attention, and problem solving dedicated to achieving ocean-climate stability, including marine carbon dioxide removal.

We believe that it is critical to generate the base of knowledge this decade that allows us to make informed decisions about the efficacy and impacts of marine carbon dioxide removal approaches. We’ve laid out a course of work that has to happen between now and 2030 to give us information that allows us to take action, or not, on marine carbon dioxide removal approaches as part of a climate solutions portfolio.

This plan of action is highly aligned with the UN Ocean Decade’s motto of “the science we need for the ocean we want”. In this presentation, we will assess how collective progress is shaping up against these stated goals for the end of the decade, assess the gaps, talk about the work that is underway to close these gaps, and highlight critical areas and gaps of needed attention and innovation for the international community and the UN Ocean Decade to direct focus and effort.

How to cite: Koweek, D., Ack, B., Valenzuela-Pérez, L., Neelakantan, N., Mastroni, S., and Driscoll-Lovejoy, R.: Marine Carbon Dioxide Removal: Getting Evidence for Decision Making This Decade, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-765, https://doi.org/10.5194/oos2025-765, 2025.

The settling of zooplankton fecal pellets plays a vital role in transporting particulate organic carbon to the deep ocean, serving as an essential component of the marine biological pump. Here, we present four-year (June 2020 to July 2024) time-series variations of zooplankton fecal pellet flux from two sediment traps respectively at 500 m and 1170 m water depth in the western South China Sea. Of all samples, the numerical flux of fecal pellets was averagely 2.94 and 1.14*10⁴ m^-2 d^-1 at 500 m and 1170 m, respectively, and the carbon flux of fecal pellets was averagely 0.20 and 0.14 mg Cm^-2 d^-1 at 500 m and 1170 m, respectively. Both numerical and carbon flux of fecal pellet decreased with water depth. Three morphological types (spherical, cylindrical, and ellipsoidal) of fecal pellets were identified in this study. Distinct morphological types of fecal pellets contribute differently to the numerical and carbon fluxes. At both water depths, ellipsoidal and spherical pellets accounted for 95% of the numerical flux. Cylindrical pellets were rare in abundance (5%), but accounted for more than 20% of the total fecal pellet carbon flux. During the entire sampling period, the proportion of particulate organic carbon flux attributed to zooplankton fecal pellets ranged from 0.5 to 14.0%, with the average value of 5.1%. From the long-term perspective, both numerical and carbon fluxes varied greatly through time, exhibiting clear seasonal and interannual variations. During 2022 to 2023, the fecal pellet numerical flux was 3 times higher than the other three years. Within each year, fluxes of fecal pellet showed increases when the East Asian monsoon system converted. The contribution of fecal pellet carbon to overall organic carbon indicated that fecal pellets play a quite significant role in transporting organic carbon to the deep sea. The changes of fecal pellet flux were most likely influenced by El Niño and La Niña events in long term and regulated by East Asian monsoon system seasonally. As a result, multiple mechanisms, such as long-term climate event, seasonal monsoon system, zooplankton community structure, and other environmental conditions could be responsible for the production and fate of fecal pellets as well as their contribution to the overall particulate organic carbon. Thus, the settling of fecal pellets could give enlightening insights on the cycle of organic carbon and reveal how climate change influenced the marine biological pump.

How to cite: Cao, J., Liu, Z., Li, J., Zhao, Y., Lin, B., Zhang, X., Zhang, J., Song, H., and Wang, W.: Time-series variations of zooplankton fecal pellet flux in the western South China Sea and their implications for marine biological pump, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-862, https://doi.org/10.5194/oos2025-862, 2025.

In response to the imminent climate crisis and in alignment with the global goals of carbon neutrality and the objectives of the Paris Agreement, the United Nations has recently approved the Global Ocean Negative Carbon Emissions (Global-ONCE). This initiative aims to protect marine biodiversity and ensure the sustainable development of the oceans by harnessing the pivotal role of oceans in regulating greenhouse gas absorption. Within this context, Global ONCE has applied to establish ISO/TC8/WG15, Ocean Negative Carbon Emissions and Carbon Neutrality, under the International Organization for Standardization. The technical scope of this working group encompasses the standardization of technologies and engineering related to ocean negative carbon emissions and carbon neutrality. These standards will facilitate the quantification and assessment of carbon in the marine environment, marine biological carbon, sedimentary carbon, and the application of negative carbon emission technologies in areas such as ocean ranching, alkalization of wastewater treatment, and artificial upwelling. ISO/TC8/WG15 warmly welcomes scientists from around the world to join in international cooperation, aiming to develop innovative technologies, methods, and best practices for harnessing the potential of ocean carbon negative emissions. The ultimate goal is to transform these advancements into international standards and share advanced experiences, technologies, and scientific ideas with humanity at large. Through collaborative efforts, overcoming challenges, and promoting public engagement, this initiative seeks to maximize the role of oceans in mitigating climate change and achieving global carbon neutrality targets.

How to cite: Lei, Y. and Xu, N.: Standardization of Ocean Negative Carbon Emission Technologies and Carbon Neutrality, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-925, https://doi.org/10.5194/oos2025-925, 2025.

Improving our understanding of future ocean carbon uptake requires a nuanced understanding of the value of the annual ocean sink. Here, we combine an abatement cost-based approach and a climate damage-based approach to assess the value of the annual ocean sink. The former shows that the aggregate cost of national climate policies could increase by up to USD 80 billion if the ocean carbon sink weakens by 10 percent. As a complementary perspective, the damage-based approach shows that the annual ocean carbon sink contributes between USD 300 billion and USD 2,332 billion to countries’ inclusive wealth. Despite the conceptual appeal of the damage-based approach for its potential insights into regional wealth redistribution, uncertainties in national social cost of carbon estimates make it less reliable than the abatement cost-based approach, which in turn provides more reliable estimates for a fiscal cost assessment of improved monitoring services of the ocean carbon sink.*

*Rickels, W., et al. The ocean carbon sink enhances countries’ inclusive wealth and reduces the cost of national climate policies. Commun Earth Environ 5, 513 (2024). https://doi.org/10.1038/s43247-024-01674-3

How to cite: Wilfried, R., Grasse, P., Meier, F., Peterson, S., Rühland, S., Thube, S., Kartensen, J., Posern, C., Wolff, C., Vafeidis, A., and Quaas, M.: The ocean carbon sink enhances countries’ inclusive wealth and reduces the cost of national climate policies, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1018, https://doi.org/10.5194/oos2025-1018, 2025.

Combating climate change requires reducing greenhouse gas (GHG) emissions from human activities and enhancing carbon dioxide removal (CDR) through blue carbon ecosystems (BCEs). Progress is measured by international reporting of national GHG inventories under the UNFCCC, following IPCC guidelines. The EU Green Deal, particularly the EU Biodiversity Strategy to 2030, recognizes BCEs’ potential by advocating for the restoration of carbon-rich habitats. However, the IPCC Wetlands Supplement is underutilized in national GHG reporting, and few countries, especially in Europe, include blue carbon in their Nationally Determined Contributions (NDCs) under the Paris Agreement. This is due to limited awareness, the non-mandatory nature of the IPCC Wetlands Supplement, and data gaps. Our research aims to advance blue carbon knowledge, promoting BCEs as nature-based solutions, and addressing key gaps and scientific uncertainties to improve quantification and reporting of blue carbon under the UNFCCC in GHG inventory reporting under the Paris Agreement. The C-BLUES project, part of the Joint EU-China Flagship Initiative on Climate Change & Biodiversity, seeks to enhance the IPCC Wetlands Supplement, increase BCE inclusion in national GHG inventories, and explore additional BCEs like natural and farmed kelp systems. We document best practices for monitoring and verifying BCE actions, model BCE sequestration capacity, and upscale GHG budgets to estimate BCE contributions to EU and Chinese inventories. We assess carbon stock changes, GHG emissions, and removals from various management interventions, and evaluate the integration of BCEs into national reporting mechanisms. We present a roadmap and invite participation with the scientific community, policy makers and the wider civil society to generate knowledge, raise awareness of BCEs and build capacity for BC research, as well as provide guidance on voluntary reporting on BCE.

How to cite: Bellerby, R. and Lindemann, C.:  Monitoring, verifying and reporting of carbon sequestration and greenhouse gas fluxes in blue carbon ecosystems , One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1145, https://doi.org/10.5194/oos2025-1145, 2025.

Ocean Alkalinity Enhancement (OAE) is currently considered as one of the most promising methods for atmospheric carbon dioxide removal (CDR). This process involves adding alkaline substances to seawater to accelerate the ocean’s natural carbon sink.

There are various methods to increase the ocean’s alkalinity locally, but there are concerns regarding the risk for the marine environment and its biodiversity. Indeed, the impact of changes in alkalinity on marine species and ecosystems is poorly understood. Given that some researchers and industrial companies also believe and sell the idea of OAE as a technically and economically feasible global application, it is crucial to assess its potential impacts. This includes evaluating the effects of changing alkalinity alone and in combination with other key trace elements that may be released during implementation, to ensure that any field manipulation does not cause harmful biological effects to the marine environment.

Laboratory experiments, alongside other techniques, play a significant role in addressing these risk assessments. This presentation aims to provide insights into experimental designs, compare the strengths and weaknesses of different approaches, and highlight results from a series of experiments conducted on marine organisms including corals, echinoderms and bivalves.

How to cite: Friedrich, J., Metian, M., and Dupont, S.: Assessing Ocean Alkalinity Enhancement impacts on biodiversity: general considerations to experimental research and first findings, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1151, https://doi.org/10.5194/oos2025-1151, 2025.

Marine carbon dioxide removal (mCDR) refers to the techniques and technologies designed to increase the amount of carbon dioxide the ocean already captures and stores naturally through ecological and physical processes. As such, the deployment of mCDR could contribute to achieving global climate goals. However, many uncertainties and unknowns still surround these technologies, particularly concerning their efficiency and potential impact on ecosystems and societies. Moreover, the governance framework of mCDR is fragmented and falls short in adequately regulating the approaches undergoing development. To assess the status of current knowledge on mCDR, analyse governance challenges, and provide recommendations for mCDR research and potential deployments, we reviewed scientific literature and organised a series of workshops involving researchers and civil society representatives. Our recommendations are discussed and summarised into three key points: (1) the need to prioritise decarbonisation over mCDR deployment and limit the potential negative social and ecological impacts associated with these techniques; (2) the importance for research, based on clear guidelines, to play a crucial role in guiding mCDR development, and in particular on monitoring, reporting, and verification; (3) the urgency to strengthen and harmonise the governance framework of mCDR, which should be done in a way inclusive of civil society, ensuring equity and participation in all decision-making processes. We propose that these findings should guide both research agendas—including the seventh Intergovernmental Panel on Climate Change’s Assessment Report cycle (AR7)—and multilateral processes, in particular the London Convention and Protocol, the Convention on Biological Diversity, the United Nations Framework Convention on Climate Change, the United Nations Convention on the Law of the Sea, and the High Seas Treaty (BBNJ).

How to cite: Brun, V., Lecerf, M., Bopp, L., Le Gouvello, O., Levin, L., Picourt, L., Steenkamp, R., and Claudet, J.: Challenges and opportunities for marine carbon dioxide removal (mCDR), One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1186, https://doi.org/10.5194/oos2025-1186, 2025.

As climate change accelerates, ocean negative carbon emission (ONCE) technologies are emerging as essential tools to enhance carbon sequestration and storage in the ocean. However, effective implementation of ONCE strategies requires technical feasibility, social acceptability, and robust governance. Marine social science offers critical insights into these sociotechnical aspects, facilitating a comprehensive approach to developing ONCE initiatives. This research examines how marine social science can support ONCE strategies through public engagement, ethical frameworks, and interdisciplinary governance.

Understanding public perception is essential to foster support and trust in ONCE efforts. Marine social scientists analyse public attitudes, misconceptions, and concerns, informing outreach strategies that engage communities and enhance public acceptance. Additionally, marine social science highlights the ethical considerations of ONCE, particularly regarding environmental justice issues affecting coastal and marginalised communities. This research emphasises the importance of including impacted communities in decision-making processes by advocating for transparency, fairness, and collaborative engagement.

Marine social science also plays a vital role in shaping policy frameworks for ONCE, addressing regulatory challenges and contributing to adaptive governance models that safeguard both human and environmental interests, such as climate-smart marine spatial planning and ocean multi-use. Through interdisciplinary collaboration, marine social scientists work alongside ecologists, technologists, and policymakers to create responsible strategies grounded in both scientific and social insights. Furthermore, transparent monitoring frameworks supported by social science build credibility and accountability, enabling independent evaluation by multi-stakeholders.

This research underscores that ONCE strategies must integrate the values, ethics, and concerns of affected communities to achieve broad social acceptance and environmental integrity. By facilitating equitable policy, governance and societal understanding, marine social science helps guide these strategies toward responsible and sustainable climate solutions.

How to cite: Li, S., Ning, L., and Zhang, Y.: In What Ways Can Marine Social Science Support Ocean Negative Carbon Emission Strategies, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1349, https://doi.org/10.5194/oos2025-1349, 2025.

To meet global climate targets, carbon dioxide removal (CDR) techniques are essential alongside efforts to reduce greenhouse gas emissions. Among marine CDR (mCDR) approaches, the enhancement of the ocean’s role as a natural "blue carbon" sink, particularly through the cultivation of pelagic macroalgae, is gaining increasing attention for its potential to scale carbon sequestration.

For these approaches to be viable and sustainable, they must undergo rigorous evaluation. This study assesses the potential of scaling up seaweed cultivation, considering environmental effectiveness, durability, and risks. It situates this approach within the broader context of other mCDR strategies, including ocean alkalinity enhancement, enhanced coastal weathering, and coastal blue carbon. In addition, the study explores the role of macroalgae in producing products for defossilisation, contributing to the decarbonisation of industries reliant on fossil-derived materials.

In a future step, the Unified Assessment Framework (ASMASYS), a transdisciplinary tool for evaluating marine CDR options, will be applied to assess the feasibility, sustainability, and risks of pelagic macroalgae in the context of global carbon sequestration efforts. This framework integrates scientific, social, legal, and governance factors, emphasizing sustainability and social acceptability.

This work provides an interim synthesis of pelagic macroalgae's potential for large-scale carbon sequestration and defossilisation products. It also lays the foundation for future research, policy recommendations, and governance frameworks necessary for integrating seaweed cultivation into global climate and defossilisation strategies.

How to cite: Matz, J., Fernández-Méndez, M., and Mengis, N.: Assessing the Potential of Seaweed-Based Carbon Dioxide Removal: Scaling Up and Future Evaluation, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1449, https://doi.org/10.5194/oos2025-1449, 2025.

Giant kelp has been identified as a promising nature-based carbon dioxide removal (CDR) pathway (Pessarrodona et al., 2024) and several scientific studies have analyzed the processes involved both in the different carbon sequestration pathways and the atmospheric carbon dioxide removal (Krause-Jensen and Duarte, 2016). Giant kelp is well-known for its rapid growth of up to tens of centimeters per day, which is fueled by the consumption of nutrients and dissolved inorganic carbon (DIC). As a result, the local concentration of CO2 in the seawater decreases, enabling the uptake of atmospheric CO2. The consumed CO2 is transformed by the kelp to grow and increase its biomass, but a fraction of the carbon is exported to the ocean as dissolved organic carbon (DOC) and particulate organic carbon (POC). Both POC and DOC are transported by ocean currents and can eventually be effectively sequestered for a long time. In the case of POC, fragments of kelp are exported into the deep ocean or are buried in the continental shelf sediment (Pessarrodona et al., 2024). A fraction of the DOC, known as recalcitrant DOC, is highly stable for very long periods of time and is also considered as an effective carbon sequestration pathway (Zhang et al., 2023).

In 2024, Kelp Blue operated a pilot giant kelp farm in Luderitz, Namibia and was selected as a CDR XPRIZE finalist. One of the goals for the project was to assess the ability of kelp farms to remove atmospheric CO2 and sequester carbon for over 100 years.

In this study, we present the results of atdepth’s independent assessment of Kelp Blue’s project. One of the main challenges for marine nature-based solutions is to assess the additionality of CDR and the sequestration of carbon through POC and DOC export. To tackle the problem, we first developed a detailed MRV methodology leveraging prior scientific studies. The methodology combines monitoring data with advanced physical and biogeochemical simulations of the ocean and the kelp. A giant kelp model developed by our collaborators at University of Cambridge was implemented to assess the net primary production of kelp, and the resulting change in surface ocean CO2 and nutrient concentrations.The model was informed by kelp biomass and ocean biogeochemistry data and integrated with a high-resolution physical and biogeochemical model of the ocean using OCM1, a novel simulation code developed by atdepth, that leverages advanced numerical frameworks from MIT and University of Cambridge.

OCM1 integrates data from the project site, and from global ocean and atmospheric data products such as Copernicus’ GLORYSv12, or the European Centre for Medium Range Weather Forecast’s (ECMWF) ERA5 data. The simulation system achieved unprecedented performance compared to legacy ocean modeling systems; the simulation was run on a single NVIDIA A100 GPU, compared to the 1300 CPUs required to run the equivalent simulation using existing ocean modeling codes, which results in a computational cost reduction of over 350x.

About atdepth: atdepth is an MIT spinoff company supported by the U.S. Department of Energy through the SEA-CO2 program and by NASA through the CMS program.

How to cite: Wong, S., Ouillon, R., Castillo Trujillo, C., Ramadhan, A., and Muñoz Royo, C.: Operational assessment of atmospheric carbon dioxide removal and carbon sequestration from a giant kelp farm in Luderitz, Namibia, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1456, https://doi.org/10.5194/oos2025-1456, 2025.

The Sustainable Total Value Chain of Cockle Industry project harnesses environmental resource managements and technological innovations to enhance the sustainability and productivity in the cockle sector. The initiative involves the management of sediment by periodically removing excessive shell accumulation and rotating aquaculture areas; thus, allowing ecological recovery as well as preventing harmful buildup. This approach ensures that only mature cockles are harvested by using machines or tools powered by solar or water wheel-generated energy on boats to enhance resource efficiency and national productivity of cockles. However, the environmental pollution stemming from cockle shells has risen alongside with productivity. Recent research has focused on transforming cockle shell waste into sustainable biological filter media which has shown promising outcomes. This media effectively doubles the alkalinity concentration, stabilizes pH level in aquaculture system, and reduces ammonia content in water. The inherent calcium carbonate in cockle shells helps stabilizing and regulating aquatic pH level which is crucial for maintaining optimal water quality and enhancing the texture of the surface of biological filter media. Also, it is useful in wastewater treatment to reduce ammonia content in aquaculture effluent management, permitting reusability of effluent in aquaculture. Nevertheless, further research is needed to explore the unique structure of cockle shells as biofilter media in promoting microalgal biofilm growth, which could be converted into renewable energy source such as biodiesel and protein source such as fish feed. This innovation repurposes waste, addressing aquaculture's waste management and enhancing sustainability, exemplifying a circular bioeconomy model. Through the development and implementation of biological filter media, the project contributes significantly towards global environmental sustainability efforts, providing a replicable model for ammonia removal in aquatic environments without exuding carbon dioxide. There are initiatives on governance and policy toward carbon dioxide reduction in ocean-related contexts as highlighted in the Fisheries Act 1985, National Climate Change Policy 2.0 and Green Practices Guidelines. The National Fisheries Act 1985, under the Fisheries (Cockles Conservation and Culture) Regulations 2002, focuses on harvesting size restrictions for cockles, permitting harvest and equipment used in the process. The National Climate Change Policy 2.0 reinforces Malaysia's commitment to combat the climate change by integrating policy that measures across various sectors for the transition towards a low-carbon economy while enhancing climate resilience. This policy which aligns with international climate commitments like the Paris Agreement is aiming to achieve a net-zero greenhouse gas emission by 2050. One key policy that focuses is low-carbon development is to reduce the greenhouse gas emission across various key sectors and increase the capacity of carbon sinks. Malaysia's commitment to sustainable development is also underscored by the Green Practices Guidelines, integral to the nation's broader environmental and sustainability efforts under the Twelfth Malaysia Plan. These guidelines advocate for the adoption of sustainable technologies in sectors such as aquaculture, supporting initiatives to improve water quality and reduce environmental impact through innovative filtration methods. This policy framework ensures Malaysia’s economic growth aligns with sustainable, resilient environmental practices by embedding climate considerations throughout national planning and development.

How to cite: Abu Darim, R., Lim, J. W., Mohd Sharif, S. N., Tumin, A. B., Mohd Tahir, K. E., Hamzah, A., Kua, B. C., Harith, H., Rani, A., and Othman, A.: Sustainable Total Value Chain of Cockles: Contributions of Governance and Policy for Industry, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-1006, https://doi.org/10.5194/oos2025-1006, 2025.

Introduction

Ocean alkalinity enhancement (OAE) is a marine-based carbon dioxide removal (CDR) approach, which expedites the natural uptake of CO₂ by the ocean. Due to the key role that CDR now plays in international climate policy, and the ocean’s high CO₂ storage potential, researchers and the private sector are increasingly interested in developing OAE technologies. While there is a growing body of research regarding public perceptions of CDR, research focusing explicitly on OAE is limited, particularly in southern-hemisphere countries. We extend the framing of responsible innovation to understand the roles stakeholders can play in OAE deployment. To do so, we engaged a range of stakeholders to capture their views on the roles they could play in OAE deployment. Identifying the role of stakeholders is important to promote knowledge and resource sharing, build partnerships and enable interested stakeholders to exercise their agency in fostering responsible innovation.

Methods

We conducted a case study on the island state of Tasmania, Australia. We focused on Tasmania primarily due to the prevalence of OAE and other marine CDR (mCDR) research in this state.  In an exploratory study, we interviewed 23 stakeholders using a qualitative approach of inquiry. We adopted a bottom-up mode of engagement, rather than prescriptive, and enquired what role participants assumed they could play in OAE deployment in the state. We recruited participants from the following stakeholder categories: environmental groups, researchers, government agencies, fisheries, tourism, and recreational ocean users.

Findings

Most participants saw value in pursuing OAE to tackle climate change, despite identifying some knowledge gaps to develop an informed understanding of the technology. Participants saw themselves playing active rather than passive roles in OAE deployment. These roles generally depicted stakeholders’ agency not only in working together with decision-makers but also contributing to shaping OAE outcomes. The identified roles were distributed across domains of techno-scientific innovation, procedural fairness, and local governance. For example, fisheries and tourism operators saw their contribution in collecting data for monitoring the effects of OAE. Environmental groups were keen on facilitating community engagement, and partnerships between science and practice. Government representatives foresaw a role in land-use and marine spatial planning, permitting and monitoring.

Conclusion

We found that most stakeholders wish to play an active role in the deployment of OAE, indicating a desire for agency in the implementation and upscaling of these technologies. Early conversation between stakeholders, innovators and policymakers will be essential to understand stakeholders’ interest and capacity, and how their involvement in OAE might be best enabled.

How to cite: Malakar, Y., Brent, K., Jeanneret, T., and Gardner, J.: Local stakeholders can (and should?) play an active role in place-based deployment of Ocean Alkalinity Enhancement (OAE)., One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-228, https://doi.org/10.5194/oos2025-228, 2025.

The Caribbean’s coastal ecosystems—mangroves, seagrass beds, and coral reefs—serve as critical blue carbon sinks, providing coastal protection, supporting biodiversity, and contributing to climate resilience through carbon sequestration. However, these ecosystems face ongoing pressures from coastal development, pollution, and climate-induced stress. The BluEFin Project, in partnership with OECS and the German Corporation for International Cooperation (GIZ), seeks to address these challenges by fostering sustainable blue economy practices and mobilizing new financial resources for marine and coastal conservation.

This initiative could focus on specific technical areas, such as mangrove conservation and restoration, leveraging innovative tools like satellite imaging to assess and monitor carbon sequestration in Small Island Developing States (SIDS). Given the unique scale and ecological challenges faced by SIDS, exploring scalable approaches to ecosystem management through innovation could provide valuable insights and drive policy alignment. Although demonstration projects are currently limited, we aim to present conceptual frameworks and preliminary ideas, particularly around satellite-based monitoring of carbon stocks in mangroves, which have potential application for enhanced conservation and financing efforts.

Through strengthened private sector engagement and the establishment of regionally adapted financial mechanisms, BluEFin supports OECS member states in balancing ecological health with sustainable economic growth. We propose to share early findings and outline policy recommendations to help align MSP training and regional forums with 30x30 goals and CBF’s conservation finance initiatives. This initiative underscores the integration of environmental sustainability into economic frameworks, ensuring the longevity of coastal resources and building resilience against climate impacts.

How to cite: Bervoets, T.: Enhancing Blue Carbon Sequestration in the Caribbean through Sustainable Blue Economy Initiatives, One Ocean Science Congress 2025, Nice, France, 3–6 Jun 2025, OOS2025-560, https://doi.org/10.5194/oos2025-560, 2025.