The ocean-climate-biodiversity nexus and marine carbon dioxide removal (mCDR)

Topic updates

28 September 2025
Flash information on proposal numbers

Call HORIZON-CL6-2025-02 has closed on 16/09/2025.

396 proposals have been submitted.

The breakdown per topic is:

HORIZON-CL6-2025-02-CLIMATE-01: 5 proposals 

Evaluation results are expected to be communicated in January 2026.

11 June 2025
Please note that due to a technical issue, during the first days of publication of this call, the topic page did not display the description of the corresponding destination. This problem is now solved. In addition to the information published in the topic page, you can always find a full description of the 7 destinations (Biodiversity and ecosystem services; Fair, healthy and environment-friendly food systems from primary production to consumption; Circular economy and bioeconomy sectors; Clean environment and zero pollution; Land, ocean and water for climate action; Resilient, inclusive, healthy and green rural, coastal and urban communities; Innovative governance, environmental observations and digital solutions in support of the Green Deal) that are relevant for the call in the Work Programme 2025 part for “Food, Bioeconomy, Natural Resources, Agriculture and Environment”. Please select from the work programme the destination relevant to your topic and take into account the description and expected impacts of that destination for the preparation of your proposal

The ocean-climate-biodiversity nexus and marine carbon dioxide removal (mCDR)

TOPIC ID: HORIZON-CL6-2025-02-CLIMATE-01

Type of grant: Call for proposals

General information

Programme:

Call: Cluster 6 Call 02 - single stage (HORIZON-CL6-2025-02)

Type of action: HORIZON-RIA HORIZON Research and Innovation Actions

Type of MGA: HORIZON Lump Sum Grant [HORIZON-AG-LS]

Status: Open for submission

Deadline model: single-stage

Opening Date: 06 May 2025

Deadline dates: 16 September 2025 17:00 (Brussels time)

Topic description

Expected Outcome:

In line with the European and global biodiversity and climate objectives, successful proposals should further the European efforts in achieving both climate–neutrality and ocean sustainability by improving the scientific understanding of ocean climate interventions and their short, medium and long term effects, impacts and risks, and developing monitoring and response measures guided by the precautionary principle and supporting decision-making at regional, European and global levels.

Project results are expected to contribute to several of the following expected outcomes:

• advanced knowledge on scientific aspects, environmental, legal, socio-political and governance considerations for Ocean Alkalinity Enhancement (OAE);
• advanced modelling, monitoring and simulation capabilities (including AI methods and tools) needed for the monitoring, reporting and verification of marine carbon dioxide removal (mCDR) and further improved Earth System Models (ESMs), including the Carbon Dioxide Removal Model Intercomparison Project (CDRMIP);
• enabled evidence-based European and global decision–making on mCDR, sustained European leadership in ocean–climate–biodiversity science nexus, and significant contribution to global scientific assessments.

Scope:

Environmentally safe, socially acceptable, and economically viable carbon dioxide removal (CDR) is needed to support the realisation of European and worldwide climate policies. There is considerable uncertainty regarding scalability and the short, medium and long-term effectiveness and impacts on marine ecosystems and human health. Mindful of the precautionary approach, legitimate, responsible, multi and trans-disciplinary, transparent, and inclusive scientific research to evaluate mCDR techniques is urgently needed.

The London Protocol also calls for certain activities other than legitimate scientific research to be deferred (LC 45/LP 18^[1]). The Convention on Biological Diversity (CBD^[2]) recognizes the importance of biodiversity in the context of climate-related geoengineering. Decision X/33 of the CBD^[3] emphasizes the need for a cautious approach, specifying that no climate-related geoengineering activities that may affect biodiversity should take place until there is an adequate scientific basis to justify such activities and that small-scale scientific research studies are allowed if conducted in controlled settings and justified by the need for specific scientific data. The CBD also requests the compilation of scientific information on the impacts of geoengineeringon biodiversity and the study of gaps in existing mechanisms.

Whether the ocean has a potential to help achieve the required extent of additional carbon dioxide removal (beyond the ocean sink driven by increasing atmospheric CO2 concentrations), while maintaining its integrity and health, requires further research.

Among the greatest challenges associated with mCDR technologies is the ability to measure, monitor and verify the amount of additional carbon removed over time, and to assess the environmental effects of the mCDR technology. This is particularly challenging in the ocean environment, an open system with high inertia, globally connected food-webs and high difference in life traits of species in marine life assemblages, for which safety margins need to be considered, and when considering scale up of these technologies would likely require significant additions in hydrodynamically optimum sites, potentially leading to overlaps with repeated, cumulative and/or transboundary exposures and impacts.

Principled ocean CDR research must be precautionary, inclusive, and well-planned, conducted with a view to ensure these technologies are effective, without harming the environment and people. The research conducted under the topic is to be grounded in the Guide to Best Practices in Ocean Alkalinity Enhancement Research^[4].

The topic is guided by a focus on integrated climate stabilization and biosphere stewardship for the resilience of the entire Earth system. From this perspective, a comprehensive approach to climate and biosphere stewardship is needed, as well as considering all the sustainability dimensions to guide future decisions.

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

Option A: Ocean Alkalinity Enhancement (OAE): biogeochemical and physiological responses and impacts on marine ecosystems

The project is expected to:

• elucidate many unknowns that remain about the efficacy, effectiveness, feasibility, covering both technological readiness and lead time until full potential effectiveness, effectiveness to increase net carbon uptake, effectiveness to reduce ocean warming, ocean acidification, scalability, duration of effects, termination effects, Energy Return on Energy Invested (EROEI), environmental and ecological risk (intended, unintended, undesirable consequences at scale), co-benefits, disbenefits, risks, cost effectiveness, externalities, trade-offs, and competing interests, weighing the impact on reducing climate change by OAE against its negative environmental effects, etc. The actions should use a Life Cycle Assessment (LCA) methodology and consider all the sustainability dimensions (in particular SDGs 3, 6, 9, 12, 13, 14, 15, 16 and 17), across different temporal and spatial scales;
• cover the desirability, ethical considerations, social and political considerations and governability from an international perspective, conducting comprehensive and responsible research to inform decision making under climate inertia about OAE and its potential application;
• carry out comprehensive assessment of the Ocean Alkalinity Enhancement (OAE) and its short, medium and long term impacts on ocean biogeochemistry (including acidification), on pelagic, coastal and deep ocean ecosystems, their assemblages and trophic webs, on marine organisms that are not able to concentrate carbon within their cells under conditions of increased alkalinity, potentially strong fluctuations in pH and seawater pCO2 impacting plankton and microbiome populations dynamics, species competition and assemblages of connected trophic webs, and calcium hydroxide precipitation threatening coral reefs, plants, periphyton and cyanobacteria due to sensitivity to high levels of turbidity, on primary and second production, on seasonal changes in biogeochemistry and plankton dynamics;
• conduct an assessment and evaluation of the rate and severity of the local impacts and compare multiple datasets to deliver a greater holistic understanding of OAE’s biological and ecological impacts regionally and globally, on human wellbeing linked to the degree to which the overall changes in primary and secondary production may result in change of species assemblage on which coastal livelihoods depend; the increased accumulation of contaminants within food chains via the release of minerals such as cadmium, nickel, chromium, iron and silicon, with potential implications for human health; the environmental impacts associated with extensive calcium carbonate mining operations, mineral distribution, the energy-intensive oxy-calcination process, dispersion operations, impact on resource scarcity due to high electric consumption, assessment and evaluation of additional resources needed;
• numerical modelling should be used to assess the scale of the consequences under various scenarios, experimental work in-situ like in mesocosms and benthocosms and ex-situ like in large flow through experimental chambers can help to improve parametrization of geo-biochemical processes. Field experiments are out of scope. The action should improve the precision of predictions and inform ESMs, IAMs and the Carbon Dioxide Removal Model Intercomparison Project (CDRMIP);
• advance the knowledge related to cost and challenges of carbon accounting, cost of environmental monitoring and the need to track impacts beyond carbon cycle on marine ecosystems.

Option B: Monitoring the global ocean for safe, verifiable and sustainable potential marine carbon dioxide removal (mCDR)

The project is expected to:

• establish building blocks and capabilities towards realistic, long-term, sustainable, rigorous, standardized monitoring of potential marine carbon dioxide removal and sequestration, including operational system requirements, and cover aspects of detection, attribution and determination;
• advance empirical approaches and new data needed for data-based ocean modelling (vs. numerical simulations) and develop ocean simulation capabilities based on integrated physical, biogeochemical and ecological oceanic components;
• develop the monitoring capability for quantifying the effectiveness and durability of carbon sequestration, especially in the offshore mesopelagic water column, and identify environmental and ecological short-, medium- and long-term impacts (days to 100s of years) on the ocean and marine ecosystems functioning and the ecosystem services they naturally provide (e.g., biological carbon pump), accounting for climate inertia;
• enable monitoring the multiple components of the carbonate system and, especially in coastal zones, at appropriate spatial and temporal resolution, and considering existing monitoring schemes and databases, such as the Copernicus Marine Environment Monitoring Service (CMEMS), Global Ocean Data Analysis Project (GLODAP) or the Surface Ocean CO2 Atlas (SOCAT);
• utilise enhanced data from observing/modelling to advance scientific knowledge of the ocean-climate-biodiversity nexus and potential impacts of deliberate perturbations (i.e. mCDR). in the ocean, particularly the deep-sea and coastal environments (speed and magnitude of change, thresholds and tipping points), marine ecosystems functioning and the ecosystem services they provide, including carbon and nutrients cycling, climate regulation and fisheries, for future ocean sustainability and decision-making about active climate remediation, trade-offs and policy needs for decision-making under climate inertia.

For both options A&B, the actions funded under this topic should have a strong collaboration mechanism. Proposals should include a dedicated task, appropriate resources, and a plan on how they will collaborate and ensure synergies with relevant activities carried out under other initiatives.

The actions should build on existing observing platforms, e.g. in the context of the Copernicus programme, and strengthen and expand the current capacities in an inter and multidisciplinary and ecosystem-based approach.

The research carried out should also include SSH perspectives and gender, and the research on desirability, benefits and disbenefits should also be done in relation to desirability for whom, benefits and disbenefits for whom, adding a comprehensive justice perspective on the call, including intergenerational aspects. International cooperation is essential.

A strong linkage should be ensured with the activities under the UN Decade of Ocean Science and ongoing Horizon projects, the Copernicus marine service (CMEMS), GOOS, the Ocean Biogeographic Information System (OBIS), MBON of GEOBON, ICOS, GCOS, and other relevant international Ocean Observing Initiatives. All in-situ data collected should follow INSPIRE principles and be available through open access repositories supported by the European Commission (Copernicus, and EMODnet). Synergies with the Horizon Europe Mission Restore our Ocean and waters is encouraged. The projects outputs may contribute to the European Digital Twin of the Ocean and the Destination Earth initiative and outline specific plans to this effect.

This topic is part of a coordination initiative between ESA and the European Commission on Earth System Science and should towards this end include sufficient means and resources for effective coordination. Projects should leverage the data and services available through European Research Infrastructures federated under the European Open Science Cloud, Copernicus, as well as data from relevant data spaces in the data-driven analyses. Projects could additionally benefit from access to infrastructure and relevant FAIR data by collaborating with projects funded under the topics HORIZON-INFRA-2022-EOSC-01-03: FAIR and open data sharing in support of healthy oceans, seas, coastal and inland waters and HORIZON-INFRA-2024- EOSC-01-01: FAIR and open data sharing in support of the mission adaptation to climate change. Collaboration with the relevant existing European Research Infrastructures such as those prioritised by the European Strategy Forum on Research Infrastructures (ESFRI)^[5]is encouraged.

[1] 45th Consultative Meeting of Contracting Parties to the London Convention and the 18th Meeting of Contracting Parties to the London Protocol (LC 45/LP 18) (imo.org)

[2] XI/20. Climate-related geoengineering (cbd.int)

[3] Microsoft Word - COP 10 Decision X (cdrlaw.org)

[4] Oschlies, A., Stevenson, A., Bach, L. T., Fennel, K., Rickaby, R. E. M., Satterfield, T., Webb, R., and Gattuso, J.-P. (Eds.): Guide to Best Practices in Ocean Alkalinity Enhancement Research, Copernicus Publications, State Planet, 2-oae2023, https://doi.org/10.5194/sp-2-oae2023, 2023

[5] The catalogue of European Strategy Forum on Research Infrastructures (ESFRI) research infrastructures portfolio can be browsed from ESFRI website https://ri-portfolio.esfri.eu/.

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