In line with the European Green Deal and, in particular with the objectives of the European Climate Law, the EU climate adaptation and mitigation strategies, the EU biodiversity strategy for 2030, the EU proposal for a nature restoration law^[1], the Marine Strategy Framework Directive (MSFD), successful proposals should further the European efforts in achieving climate–neutrality by advancing the understanding and science to support adaptation and resilience of natural and managed ecosystems in the context of a changing climate and biodiversity loss and by efficiently monitoring, assessment and projections related to climate change impacts, mitigation, and adaptation potential to deliver solutions for tackling emerging threats and support decision-making at regional, European and global levels.

Successful proposal results are expected to contribute to all of the following expected outcomes:

• Further developed key ocean monitoring indicators, Essential Climate Variables (ECVs from GCOS), Essential Ocean Variables (EOVs from GOOS) in compliance with international programmes (IPCC, WOA, IPBES, CMIP, CLIVAR, Ocean Health Index, UN Decade, ARGO) that support international global assessments and foster the development of a regional approach to ocean climate monitoring and reporting, overcoming current limitations and gaps;
• Further improved Earth System Models (ESMs) representing key physical, biogeochemical and biological processes in the ocean with reduced uncertainty of climate change projections at regional scales, and reduced biases (i.e. in the WCRP Coupled Model Intercomparison Project (CMIP7) models for ocean and polar regions);
• Better understood links between ocean physical, biogeochemical and biodiversity (including microbes and macro-organisms) variability over time, and the impacts of environmental stressors (e.g., warming, extreme events, ocean deoxygenation, and acidification) on ocean health, GHG sources and sinks, biology and ecosystems, as well as 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 like pollutants;
• Strengthened development of common, agreed standards for climate records content, format, quality and validation methodology;
• Enabled evidence-based decision–making (e.g., developing early warning ocean climate indicators); Sustained European leadership in ocean–climate–biodiversity science nexus supporting EU programmes e.g., the Copernicus climate service, marine service, EEA / JRC reporting and complementing other relevant European programmes (e.g., science programme of the European Space Agency); Significant contribution to the implementation of the European Green Deal and its climate and biodiversity objectives, the EU maritime strategy, to the development of the European Digital Twin of the Ocean^[2] (both data and models components), and to global scientific assessments, such as the IPCC, IPBES and WOA, as well as to the UNFCCC Ocean and Climate Change Dialogue, UN Decade of Ocean Science and UN SDGs 13 and 14.

To be able to deliver ocean forecasts and early warnings, climate projections and assessments and protect ocean health and its benefits, it is vital to measure Essential Ocean Variables (EOVs). The Essential Climate Variables and Essential Ocean Variables form the basis of the Global Climate Indicators that contain key information for the most relevant areas of climate change. The physics, chemistry, biology and biodiversity (including microbes and macro-organisms) of the ocean system are irrevocably interlinked. Ocean ecosystems are subject to a multitude of stressors, including changes in ocean physics and biogeochemistry, and direct anthropogenic influences. Implementation of protective and adaptive measures for ocean ecosystems sustainable management and conservation requires a combination of ocean observations with analysis and prediction tools that can guide assessments of the current state of ocean ecosystems, elucidate ongoing trends and shifts, anticipate impacts of climate change and management policies and provide decision makers and the public with the necessary information to assess the impact of policy decisions. In physical oceanography, essential variables have been collected globally in a standardized manner providing valuable input to the IPCC. Expansion of biogeochemical and ecological observation systems should allow for significant advances in the development and application of analysis and prediction tools for ocean biogeochemistry and ecosystems, production of biodiversity essential variables and associated climate records, with multiple societal benefits. This requires further standardisation and improved utilisation of existing sensors, as well as exploration and development of new sensor technology, suitable for ships, mooring and autonomous platforms, increased use of emerging remote sensing technologies at higher resolution.

One of the major roles of the research conducted under this topic should be to deliver integrated multidisciplinary ocean science by means of the physical, biogeochemical and biological/ecosystem research communities coming together and joining forces for development of Essential Ocean Variables, integration of observations from the different oceanographic disciplines into models for multidisciplinary analysis and reporting.

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

• Option A: Improving the monitoring, understanding, reporting (Essential Variables) and projections of essential physical oceanic processes related to climate and changes over time, and production of related Essential Ocean Variables and indicators, at regional or sea basin scale (sea state, ocean surface stress, sea ice, ocean surface heat fluxes, sea surface and subsurface salinity, sea surface height, sea surface and subsurface temperature, ocean circulation and surface and subsurface currents, ocean layering and density gradient, upwelling) (including GHG fluxes) (TRL 7-8).

The research action is expected to further develop essential physical ocean monitoring indicators, EOVs, ECVs, improve their performances (e.g. resolution, uncertainties) and support their integration in climate models in order to improve the understanding of important feedbacks (e.g., cryosphere–ocean interactions such as: permafrost thawing–ocean feedbacks, ocean–ice sheet coupling, wind– and wave–ice coupling and sea ice formation, carbon–climate feedbacks). The activity should improve monitoring and reporting in specific ocean areas such as at depth and in marginal areas, over the continental shelf slopes, coastal zones and polar areas. The action should combine observation analyses and models over different time scales (by making use of instrumental and proxy data), benefiting from latest advances in satellite measurements and in-situ, to improve the scientific understanding of the change and variability of ocean circulation and ocean heat content change, sea surface and subsurface conditions (temperature, salinity, sea ice, currents, deep convection), and the short- and long-term variability, as well as improve projections at regional scales.

The action should advance the scientific understanding of the projected decrease of Antarctic ice and Arctic sea ice and contribute to improving model projections of future changes, particularly at the regional level; of the potential connections between Arctic polar warming and sea ice loss and mid-latitude atmospheric variability; and the understanding and sea level long term prediction better considering the response of the ice sheets on multi-decadal to centennial timescales.

The action should advance in improving the characterisation of ice sheets and glaciers contribution in sea level monitoring, and projections, and advance our understanding and prediction of the multi-decadal reversibility. The action should contribute to the development of a more quantitative understanding and predictability of the processes that cause and maintain ocean extremes, and the conditions that are conducive for the generation of extremes.

• Option B: Improving the monitoring, understanding, reporting (Essential Variables) and projections of essential biogeochemical oceanic processes related to climate and changes over time at regional or sea basin scale (oxygen, nutrients, inorganic carbon, transient tracers, nitrous oxide, ocean colour, particulate matter, dissolved organic carbon, elemental and isotopic tracers, stable carbon isotopes, marine debris) (TRL 7-8).

The action should further develop essential biogeochemical ocean monitoring indicators, EOVs and ocean ECVs. The action should support the development of the ocean component of climate models through a better representation of essential biogeochemical processes, microbe biomass and diversity and enable a better understanding of the links between ocean physical and biogeochemical variability. The action should combine GHG measurements in regions especially critical for GHG fluxes (the polar oceans, main open-ocean convection areas like the North Atlantic, southern hemisphere, coastal and marginal seas, or coastal upwelling zones) with relevant biogeochemical measurements (e.g., oxygen, nutrients, carbon) to support GHG data analyses and model simulations. The action should improve the understanding of ocean biogeochemical fluxes and turnover of carbon and nitrogen in the ocean using state of the art autonomous observation technology combined with remote-sensing. This includes quantifying fluxes between basins/regimes (e.g. Arctic to North Atlantic, or coastal to oceanic) and across boundaries (air-sea, water-sediment), as well as between chemical phases (such as inorganic to organic, particulate to dissolved). Focus should be on quantifying GHG reservoir size and change, and potential subsequent impact on GHG fluxes, ocean productivity, carbon sequestration, oxygen demand and carbonate system.

The action should further inform models and improve predictions of the Earth system response to ocean acidification and to the ocean biological pump, including the long-term trends in ocean chemistry, beyond the observational record (paleo-ocean acidification), for a better understanding of the multi-decadal reversibility or the hysteresis of ocean processes (like the AMOC). Links should be made with ocean stratification that acts as barrier for water mixing or carbon sequestration.

The action should improve observations for the interplay between carbonate chemistry and a variety of biogeochemical and physical processes, including eutrophication and freshwater inflow and outflow in coastal zones, and increase the robustness of future assessments of ocean acidification. The action should improve our understanding of changes in water mass ventilation associated with climate change and variability to gain further insights into future trends in ocean acidification.

The action should further research the net response of natural ocean CH4 and N2O sources to future warming, including permafrost, and predict the magnitude and timing of the responses of each individual process.

The action should make use of the recent developments, such as the Biogeochemical ARGO, to investigate extreme conditions, and extreme or compound events below the surface of the ocean, and their link to biogeochemical processes.

The action should further contribute towards the integration of more biogeochemical parameters, assimilation techniques, models and assessment strategies into ESMs.

• Option C: Improving the monitoring, understanding, reporting (Essential Variables) and projections of essential biological and ecosystem oceanic processes related to climate and changes over time at regional or sea basin scale (marine habitat properties, calcifying organisms, phytoplankton, zooplankton, fish, nekton migration, marine turtles, birds and mammals, hard coral, seagrass, mangrove, macroalgal canopy, microbe, invertebrate, ocean sound) (TRL 5-6).

The research action should further develop the essential biological and ecosystem ocean monitoring variables and indicators, and the development of early warning systems based on biological indicators (like marine calcifying organisms, coral reefs or plankton lifecycle).

The action should develop the integration (e.g., forcing, assimilation of boundary conditions, coupling, etc.) between climate models (physics and biogeochemistry) and ecosystem/marine habitat models to support ocean biodiversity variables and ECV development, in particular, quantifying the sensitivity of regional ecosystems responses to poorly-resolved, global, physical & biogeochemical inputs at model boundaries. The action should also identify & quantify the propagation of non-linear errors through the ecosystem models (from physics through biogeochemistry and to the highest trophic levels), including through better integration of numerical & statistical approaches allowing improved forecasting.

The action should further develop observation processing for biological and ecosystem EOVs and ECVs production, and assess needs for additional observations in support of biological EOVs and ECV development and validation. The action should support the development of common approaches and standards for the development of biological and ecosystem variables and ECVs for the oceans by strengthening the use of observation networks and relevant biogeochemistry, biological and ecological measurements; an increase use of high-resolution remote sensing technologies, and the development of inter-calibrated protocols, notably for macroalgae, coral reefs, mangroves, tidal marshes, saltmarshes and seagrass. Particularly, it should extend the physical, biogeochemical, and ecological data records needed to develop, initialize, and validate marine ecosystem forecasts.

The action should assess the integration of the whole model chain (ESM + biology) on some specific test cases to evaluate uncertainties and potential use of such a modelling capacity for climate scenarios development and policy - management: e.g., evaluation of impacts of overshoot on ecosystems due to extreme climate change scenarios, perturbation of the biological carbon pump in a changing ocean or tipping point effect, surpassing the physiological tolerance limits beyond which the resilience of the ecosystem is compromised.

Particular attention should be paid to impacts of warming and acidity, or changes in the frequency and intensity of disturbance regimes, as they may lead to the collapse or transition of ecosystems to a new ecological state, with a loss or altered biodiversity and ecosystem services. The action should advance our scientific understanding of how extremes affect organisms and ecosystems, in particular for the effect of dual- or triple-compound events, by better understanding the cumulative effects on biota of the multifaceted characteristics—from abruptness to recurrence—associated with individual extremes; and the role of the compounding effect of the different hazards, leading to a complex matrix of often new conditions. Furthermore, advances should be made with regard to closing gaps in our understanding of the factors controlling biological, genetic and functional diversity, food-web interactions and relationships between different ecosystem constituents (trophic links, symbiosis, parasitism, etc.), and, also with regard to the physiological states and trophic modes (mixotrophy) of populations, before these models can be made operational in future forecasting and impact projection applications.

The action should establish protocols for the scientific validation of forecasts to validate results and build trust in forecasts, and ensure forecasts have the necessary spatiotemporal resolution for analysis and application to marine resource management, or to force downscaled regional forecasts.

The action should contribute towards the integration of more ecosystem parameters, assimilation techniques, models and assessment strategies into ESMs.

For all three options (A, B & C), actions should result in better scientific understanding and quantification of tipping points and abrupt system changes, and associated impacts, including aspects of irreversibility and compound events. Actions should support a regional approach to ECVs, EOVs, ocean monitoring indicators and climate change / ocean health assessment, taking into account sea basin specificities. The action should result in spatially and temporally explicit information about physical, biological, and chemical properties of the ocean. Actions should also advance the understanding of the impacts caused by the crossing of tipping elements and develop early warning indicators. Where appropriate, the combination of multiple drivers and/or hazards that contribute to societal and/or environmental risk should be assessed. Actions should identify safe operating spaces for the ocean to provide life-support systems for humanity, accompanied – where relevant – with long-term strategies for preventing or mitigating impacts. To better monitor significant changes in physical and biogeochemical environments and their impacts on ecosystems and society, actions should enable further integration of multidisciplinary observation systems (in-situ, airborne, satellite) and improved models. The assessments of cumulative effects should look at existing and past activities in the marine environment but should also allow for foresight in order to inform planning of future activities and support management that is adaptive to future conditions and sustains ecosystems and human well-being.

The actions funded under this topic should have a strong collaboration element and mechanism in order to ensure that the topic delivers on its key research priorities and help characterize the interplay and dependence between the biological, chemical, and physical properties of the ocean environment. The actions should build on existing observing platforms, Copernicus, and strengthen and expand the current capacities in a multidisciplinary and ecosystem-based approach. This multidisciplinary approach is key to comprehensively understand the variety of effects of global change on the ocean and its ecosystems. This topic provides for the opportunity to strengthen the interaction between biological and physical and biogeochemical platforms and research communities. To this end, proposals should include a dedicated task, appropriate resources and a plan on how they will collaborate with the other projects funded under this topic, and ensure synergy with relevant activities carried out under other initiatives in Horizon Europe. Relevant activities of the plan will be set out and carried out in close cooperation with relevant Commission services, ensuring coherence with related policy initiatives.

International cooperation will be essential in integrating and coordinating these different scaled approaches. A strong linkage should be ensured with the ongoing activities under the All-Atlantic Ocean Research and Innovation Alliance, UN Decade of Ocean Science, and GOOS bio-eco panel. Actions under this topic will build upon and link with Horizon projects (COMFORT, PolarRES, CrIceS, EuroSea, AtlantOS, EPOC, OCEAN ICE, OceanICU, Jetzon, DOOS, etc.), the Copernicus marine service, GOOS, the Ocean Biogeographic Information System (OBIS), MBON of GEOBON, ICOS, GCOS, and other relevant international Ocean Observing Initiatives. 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).

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 the relevant ocean processes^[3]. 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 ESA 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 ESA to organise the joint European Commission-European Space Agency work.

Projects shall 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 is encouraged.

Synergies and complementarities: HORIZON-CL6-2024-CLIMATE-01-6: Ocean models for seasonal to decadal and local to regional climate predictions, and Cluster 5 topics: HORIZON-CL5-2024-D1-01-02: Inland ice, including snow cover, glaciers, ice sheets and permafrost, and their interaction with climate change, HORIZON-CL5-2024-D1-01-01: Enhanced quantification and understanding of natural and anthropogenic methane emissions and sinks, and HORIZON-CL5-2023-D1-01-02: Climate-related tipping points.

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

[2] European Digital Twin of the Ocean (European DTO) | European Commission (europa.eu).

[3] 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).