In line with the European Green Deal and, in particular with the objectives of the European Climate Law^[1], the EU climate adaptation and mitigation strategies, the EU biodiversity strategy for 2030, the EU proposal for a nature restoration law^[2], the Marine Strategy Framework Directive (MSFD), the Birds and Habitats Directives, the Regulation (EU) n. 734/2008 on the protection of vulnerable marine ecosystems in the high seas from the adverse impacts of bottom fishing gears, successful proposals should further the European efforts in achieving climate-neutrality by maintaining and enhancing natural carbon sinks and stocks in marine and polar ecosystems, while preserving and enhancing their biodiversity, including by unfolding the potential of nature-based solutions, where adaptations to climate change are also being fostered for enhanced resilience.

Successful proposals are expected to contribute to all of the following expected outcomes:

• Better understood and enhanced mitigation potential of ecosystems, based on sustainable management of natural resources and climate change mitigation fostered through the maintenance and enhancement of natural carbon sinks and stocks, while preserving or enhancing biodiversity in ecosystems, in support of a sustained European leadership in ocean–climate–biodiversity nexus science;
• Advanced understanding and science in support of adaptation and resilience of natural and managed marine and polar ecosystems in the context of a changing climate, including its interaction with other natural or anthropogenic stressors such as pollutants, invasive species or marine construction, and better understood impacts of climate change on coastal zones (including the associated ecosystems) and improved adaptive capacity of ocean and marine systems, including by unlocking the potential of nature-based solutions;
• Uncovered mitigation opportunities of newly emerging European and polar blue carbon habitats (novel habitats emerging due to the rising atmospheric CO2 that is intensifying climate change but also driving global and particularly polar greening; polar blue carbon increases with losses of marine ice (sea ice, ice shelf and glacier retreat) that generates a valuable negative feedback on (mitigating) climate change);
• Reduced knowledge gaps for enabling the inclusion of carbon- and biodiversity-rich marine habitats and accounting in nationally determined contributions (NDCs) and associated national climate plans and strategies (NAPs), such as additional national data collection, science and technical capacity, as well as significant contributions made to the implementation of the European Green Deal, particularly the climate and biodiversity objectives, the UNFCCC Ocean and Climate Change Dialogue, the Global Biodiversity Framework, and global scientific assessments.

The ocean and coastal ecosystems and habitats play a significant role in the global carbon cycle, representing the largest long-term carbon sink. Over the past decade, research efforts to understand the ocean and blue carbon sinks and utilize their potential in climate mitigation frameworks has increased. There are remaining research gaps for advancing opportunities to incorporate potential ocean and blue carbon ecosystems into climate frameworks. Evaluating and quantifying the broad range of benefits provided by coastal and marine ecosystems should strengthen the ability to account for them in nationally determined contributions (NDCs) and national adaptation plans (NAPs). Avoiding and reversing the loss and degradation and restoring carbon- and species-rich ecosystems in the ocean and coastal waters is highly effective and of highest importance for combined biodiversity protection and climate change mitigation actions with large adaptation co-benefits. If degraded or lost, these ecosystems are likely to release most of their carbon back into the atmosphere.

Actions should aim at developing innovative approaches to address only one of the following options:

• Option A: European and polar blue carbon hotspots and priority areas for climate policy frameworks and effective management (TRL 3-5)

The research actions should map European and polar blue carbon hotspots and priority areas for carbon sequestration and climate change mitigation potential, including an estimate of the area/extent of the habitats. In doing so, the successful proposal should rely on the synergistic use of Earth Observation data (in-situ, airborne, satellite) and models to monitor, evaluate and quantify both carbon fluxes and carbon stocks and stock changes in ocean and coastal reservoirs, to evaluate current trends and improve modelling skills and predictions, including using space and in-situ existing datasets and climate records that can be used as proxy (e.g., Copernicus, EMODnet).

The action should also gather information on organic carbon stocks and accumulation, their characteristics (source, lability, dissolved particulate, living, non-living), and their potential change under pressures from human activities. The action should identify the key characteristics that make the selected ecosystem and habitat a hotspot for blue carbon (i.e. geomorphology, physical-chemical characteristics, anthropogenic manipulation, sea level rise effects, etc.). The action should enable a better understanding of the dynamics of carbon between these reservoirs and the associated timescales involved. A quantification of the approximate amount of carbon (and preferably nutrients) fixed annually by those natural ecosystems in Europe, as well as a quantification of the annual degradation rates of the ecosystems and consequent reduction in carbon sequestration should also be carried out. This knowledge should then be consolidated into a framework for predictive tools to investigate climate-smart management scenarios at appropriate scales, as well as methodologies, methods, and guidance tailored to the specific EU maritime region. The research action will identify and recommend best suited, fit-for-purpose, climate smart and resilient initiatives and activities that are relevant to local communities in order to protect, sustainably manage, restore, and enhance blue carbon habitats. Particular attention should be given to win-win-win solutions and strategies that have multiple benefits for climate mitigation and adaptation, biodiversity gains and benefit to people, including nature-based solutions, ecosystem-based approaches and technological-ecological synergies (TES) (combining technological and nature-based solutions). Where applicable and desirable, socioeconomic aspect of sustainability should also be part of such solutions, in order to make the projects more socially acceptable; e.g. allowing for eco-tourism, recreational activities and/or extraction activities (for example recreational fishing with permits or mussels farming that does not require any feed inputs) could also allow symbiosis with the communities in the coastal areas in which these ecosystems are situated. Where appropriate, this should include technological-ecological synergies (TES) as an integrated systems approach that recognizes the potential co-benefits that exist in combining technological and nature-based solutions. The action should also assess the synergies and trade-offs of combining nature-based solutions and blue infrastructure with grey infrastructure (i.e. hybrid measures), assess the scalability of nature-based solutions and whether the same benefits and effects achieved on a small scale can be achieved by implementing them across larger spatial scales. Actions should keep in mind and address the challenge that several factors may limit the effectiveness of nature-based solutions applied to coastal areas, making the case for more effective long-term strategies and activities (lack of knowledge of the benefits and limitations of nature-based solutions options, poor planning of measures, impacts of extreme weather- and climate-related hazards, emission of CH4 and N2O, and biogenic calcification, risks of slow-onset events, such as increasing temperature and biodiversity loss, and their interaction with multiple drivers (e.g., land use change) and cascading tipping points related to ecosystem degradation). Many of the approaches are conceptually feasible or have been demonstrated in the laboratory, but their consequences for the ocean, including on its biodiversity are uncertain, especially if applied at scale. Any proposed solutions should have to keep the precautionary approach in mind and demonstrate that they are biodiversity positive and have no negative impacts on the marine environment and ecosystem functioning. Particular attention should be given to maladaptation solutions. For each proposed solution, the action should identify the status, costs, potentials, risk & impacts (including tipping points and irreversibility, as well as the challenges posed by the emissions of blue methane, sea level rise, underwater permafrost thaw, coastal nitrate enrichment, etc.), co-benefits, trade-offs and spill over effects, and role in mitigation pathways. In addition, the economic feasibility should be taken into account, as well as the cost/benefit ratio of natural regeneration (rewilding) vs. assisted (e.g., Posidonia beds restoration/protection against trawling) vs. full restoration.

The action should identify and quantify the impact of anthropogenically induced activities that lead to the disturbance, degradation and destruction of these habitats (with estimation of the most and least impactful activities, CO2 release in the atmosphere and the cost of no action) (direct or indirect pressure from human activities, such as bottom-contact fisheries, and climate forcing).

Finally, the action should make policy recommendations for advancing the incorporation of potential blue carbon ecosystems into climate frameworks, transforming science into effective policy and management and significantly contribute to the implementation of the European Green Deal and its climate and biodiversity strategies and objectives, including the Communication on Sustainable Carbon Cycles and the EU proposal for a nature restoration law^[2] which includes targets.

• Option B: Uncover mitigation opportunities of newly emerging European and polar blue carbon habitats (TRL 2-4)

Rising atmospheric CO2 is intensifying climate change but it is also driving global and particularly polar greening. Polar blue carbon increases with losses of marine ice over high latitude continental shelf areas. Marine ice (sea ice, ice shelf and glacier retreat) losses generate a valuable negative feedback on (mitigating) climate change. The research action should conduct exploratory research into potentially new habitats emerging that could yield both mitigation and biodiversity benefits, if appropriately managed. Among the emerging habitats that should be tested in terms of their emerging role in carbon storage and sequestration, with the aim of understanding of carbon sink balances and climate change–feedback variability and reduce uncertainty in model projections, are: blue carbon change with sea ice losses; blue carbon gains from glacier retreat along fjords (fjordic blue carbon, i.e. seabed biological carbon gains as a result of recent rapid glacier retreat along fjords); blue carbon gains from ice shelf losses through opening up of productive new habitat and leaving nutrient-fertilized wakes of enhanced productivity; slight increases in sea temperature may also increase polar blue carbon; blue carbon around Antarctica is increasing with climate change, and the productivity within emerging fjords is likely to further increase with age and seasonal sea ice loss; snow and ice retreat in the subarctic and subantarctic; marine ice losses that create new polar continental shelf habitat across millions of km2 and doubling seabed carbon stocks in 25 years; fjords that have become exposed by glacier retreat (fjords are hotspots for the burial and storage of organic carbon and for their potential to provide an important long-term global climate regulation service); massive coastal embayment emerging as a result of giant iceberg breakout from ice shelves; new and intense phytoplankton blooms around the Southern Ocean which have doubled carbon storage by seafloor organisms in the last 25 years; marine ice loss in the Arctic; macroalgal particulate organic carbon sinks; changes in primary production in open Arctic waters; loss of pagophilic (ice-dependent) species and lower albedo, macroalgae, bivalves; species yet to be discovered in polar and deep-ocean ecosystems; relatively inaccessible habitats; novel approaches to secure carbon stocks in the face of fishing disruption (e.g., through changes in target species, gear, target areas).The action should build on existing and novel datasets (in-situ and satellite) to gather carbon information on stocks and accumulation, carbon characteristics (source, lability), change under pressures from human activities if not protected, the potential for carbon sequestration and associated timescales, understanding of carbon dynamics, framework and criteria to integrate these considerations and predictive tools to investigate management scenarios at appropriate scales, including displacement and trade-offs. The action should identify the key characteristics that led to the selected ecosystem and habitat to be considered a hotspot for blue carbon (i.e. geomorphology, physical-chemical characteristics, anthropogenic manipulation, sea level rise effects, etc.).

The action should also identify and recommend best suited, fit-for-purpose, climate smart and resilient and locally informed actions, initiatives and activities to protect, sustainably manage, restore, and enhance these newly emerging European and polar blue carbon habitats and assess the impact of anthropogenically induced activities that lead to the disturbance, degradation and destruction of these habitats and assess the synergies and trade-offs of protection vs. no action.

For both options (A & B), international cooperation is strongly encouraged, with a strong linkage with the ongoing activities under the All-Atlantic Ocean Research and Innovation Alliance.

Proposals should include a dedicated task, appropriate resources and a plan on how they will collaborate with the other project funded under this topic, and ensure synergy with relevant activities carried out under other initiatives in Horizon Europe, and the EU Polar Cluster. Actions should build upon and link with Horizon projects (in particular project funded under the calls HORIZON-CL6-2022-CLIMATE-01-02:Understanding the oceanic carbon cycle, HORIZON-CL6-2021-BIODIV-01-03: Understanding and valuing coastal and marine biodiversity and ecosystems services, HORIZON-CL6-2022-BIODIV-01-01: Observing and mapping biodiversity and ecosystems, with particular focus on coastal and marine ecosystems, HORIZON-CL6-2021-CIRCBIO-01-09: Unlocking the potential of algae for a thriving European blue bioeconomy, HORIZON-MISS-2021-OCEAN-02-01: European Blue Parks, HORIZON-MISS-2022-OCEAN-01-07: Integration of biodiversity monitoring data into the Digital Twin Ocean, EU PolarNET2), the Copernicus marine service, Sustaining Arctic Observing Networks (SAON), Scientific Committee on Antarctic Research (SCAR) and Southern Ocean Observing System (SOOS), and international Ocean Observing Initiatives. The R&I needs to be conducted in a multidisciplinary and ecosystem-based approach.

This topic is part of a coordination initiative between the European Space Agency and the European Commission on Earth System Science. Under the initiative, both institutions aim at coordinating efforts to support complementarities between the Horizon Europe and the European Space Agency FutureEO programmes, and their projects. Proposals under this topic should address networking and collaborative research activities with relevant European Space Agency actions. In particular, the European Space Agency will contribute to this topic with existing and planned projects focused on enhancing the observation capacity and understanding from satellite EO technology of carbon sinks and stocks in marine and polar ecosystems^[4]. Relevant European Space Agency activities will be implemented under the A) Ocean Science Clusters (eo4society.esa.int/communities/scientists/esa-ocean-science-cluster), B) the Biodiversity Science Clusters (eo4society.esa.int/) and C) the Polar Science Cluster (eo4society.esa.int/communities/scientists/esa-polar-science-cluster). Proposals should address the collaboration with ongoing or future European Space Agency projects, including those that will be funded through dedicated coordinated invitations to tender, and should towards this end include sufficient means and resources for effective coordination. Applicants are encouraged to contact the European Space Agency to organise the joint European Commission - European Space Agency work. Collaboration with the relevant existing European Research Infrastructures is encouraged.

All in-situ data collected through actions funded from this call should follow INSPIRE principles and be available through open access repositories supported by the European Commission (Copernicus, GEOSS, and EMODnet).

Synergies and complementarities with projects funded under topics: HORIZON-CL5-2024-D1-01-07: Quantification of the role of key terrestrial ecosystems on the carbon cycle and related climate effects; HORIZON-CL5-2023-D1-02-02: EU-China international cooperation on blue carbon; Mission Restore our Ocean and Waters by 2030 (HORIZON-MISS-2021-OCEAN-02-01: European Blue Parks, HORIZON-MISS-2021-OCEAN-02-03: Atlantic and Arctic basin lighthouse - restoration of marine and coastal ecosystems and increased climate resilience, HORIZON-MISS-2022-OCEAN-01-01: European Blue Parks – Protection and restoration solutions for degraded coastal and marine habitats, HORIZON-MISS-2022-OCEANCLIMA-01-01: Mission Climate adaptation and Mission Ocean and waters - Joint demonstration for coastal resilience in the Arctic and Atlantic sea basin).

In this topic, the integration of the gender dimension (sex and gender analysis) in research and innovation content is not a mandatory requirement.

[1] Regulation (EU) 2021/1119 of the European Parliament and of the Council of 30 June 2021 establishing the framework for achieving climate neutrality and amending Regulations (EC) No 401/2009 and (EU) 2018/1999, available at: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32021R1119.

[2] Proposal for a Regulation of the European Parliament and of the Council on nature restoration, COM(2022) 304 final, 22.06.2022

[3] Proposal for a Regulation of the European Parliament and of the Council on nature restoration, COM(2022) 304 final, 22.06.2022

[4] Dedicated ESA invitation to tenders to be launched in 2023 and 2024 for each of the clusters will be published in the ESA-STAR Tender publication system (https://esastar-publication-ext.sso.esa.int).