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Scientific and technical objectives

Scientific Objectives: Better understanding the role of the open ocean in climate and marine ecosystems

The open ocean plays a key role in climate regulation, marine ecosystem dynamics, and the evolution of global weather patterns. Yet, this vast area remains largely unknown due to the lack of a sufficiently dense, long-term, and high-resolution in situ observation system. The global network of around 3,500 Argo floats is still mostly limited to the upper 2,000 meters and restricted in terms of biogeochemical and biological parameters. Its deep-Argo and BGC-Argo extensions rely heavily on open-ocean in situ observations to adjust and validate the data. Furthermore, OHIS networks provide strong local spatio-temporal resolution, enabling exploration of cutting-edge scientific questions such as the influence of submesoscale processes (100 m–5 km) on large-scale dynamics and primary production. This topic is central to the development of the ocean digital twin and will allow us to precisely understand these dynamics, improve weather and climate forecasting, and anticipate the magnitude and nature of climate change impacts. Our primary objective is to define, guide, and assess mitigation and adaptation strategies necessary for the preservation of ecosystems and human societies. The proposed OHIS research infrastructure provides precisely the complementary capacity needed by other marine RIs, delivering multi-parameter, high-resolution, and time-resolved reference observations essential for an integrated understanding of the open ocean.

OHIS sets four major scientific objectives to address this challenge:

 

1. Decipher ocean–atmosphere interactions and their impact on global climate variability

OHIS will actively contribute to analyzing ocean-atmosphere interactions through a multi-platform, multi-scale approach:

  • In-depth study of heat, freshwater, and greenhouse gas (CO₂) exchanges using data from instrumented moorings of the PIRATA program in the tropical Atlantic and OVIDE in the North Atlantic subpolar region, which provide precise and continuous measurements of atmospheric (wind, temperature, humidity, radiation) and oceanic (temperature, salinity, currents, CO₂ fugacity) parameters essential for characterizing air-sea exchanges and their seasonal to interannual variability.
  • Detailed monitoring of the oceanic hydrological cycle using surface salinity measurements from the Sea Surface Salinity (SSS) network. These observations will enable analysis of long-term changes in precipitation and evaporation regimes, which are particularly sensitive to global and regional climate variations, directly feeding climate models and calibrating satellite measurements (e.g. SMOS).

 

2. Precisely quantify the role of the open ocean in the global carbon and nutrient cycles

OHIS will fully integrate biogeochemical data collected by its various services to better understand key processes in the carbon cycle:

  • Detailed characterization of the biological and physical carbon pumps via the CO₂ extension associated with PIRATA moorings, SSS network ships, and COOL campaigns, ensuring systematic monitoring of ocean surface CO₂ fugacity and seasonal/interannual carbon fluxes at the air-sea interface. These observations will help refine estimates of the ocean’s role in mitigating anthropogenic CO₂ emissions.
  • Study of biogeochemical processes in oligotrophic and mesotrophic regions through dedicated OHIS campaigns and measurements from Argo floats and instrumented marine mammals (MEMO, OVIDE, COOL), particularly in the Southern Ocean. Continuous measurements of fluorescence, dissolved oxygen, and other biogeochemical parameters sampled by MEMO in under-observed areas will enhance our understanding of the mechanisms controlling marine productivity and biological carbon storage in regions critical for global climate.

 

3. Analyze the dynamics and evolution of deep and intermediate water masses and global thermohaline circulation

OHIS will leverage the unique capabilities of its observation platforms to monitor and anticipate structural changes in water masses:

  • Accurate monitoring of large-scale temperature and salinity changes using regular data from the SSS network for surface layers, and from PIRATA, OVIDE, COOL, and MEMO for vertical stratification in the Atlantic and Southern Ocean. These observations are essential for identifying long-term trends in intermediate and deep waters linked to global warming, polar ice melt, changes in deep convection, and global thermohaline circulation.
  • Complementary and extended deep sampling via instrumented marine mammals (MEMO), providing unprecedented profiles down to about 1,500 m in regions largely inaccessible to conventional observations, particularly under the Antarctic sea ice. These data will complement the Argo network and provide key information on the state of intermediate and deep waters in the Southern Ocean—a critical region for thermohaline circulation and climate regulation.

 

4. Assess the impact of global and anthropogenic changes on open-ocean ecosystems

By relying on innovative and integrative biological observations, OHIS will address major challenges related to marine biodiversity preservation:

  • Monitoring biodiversity changes and trophic networks using biological data collected during PIRATA and OVIDE campaigns (chlorophyll profiles, nutrients, marine acoustics), complemented by biological measurements (fluorescence, dissolved oxygen) from MEMO platforms. The systematic integration of complementary approaches (fisheries, genomics via eDNA, acoustics, isotopes) will provide a comprehensive view of how pelagic ecosystems respond to increasing climatic and anthropogenic pressures.
  • Analysis of climate change impacts on sensitive open-ocean habitats, notably the expansion of oxygen minimum zones (OMZs), through systematic monitoring of oxygenation in intermediate and deep waters by MEMO, OVIDE, COOL, and PIRATA. These observations will be crucial to anticipate risks to marine resources and develop suitable strategies for sustainable management of open-ocean ecosystems.

  

 

 

 

 

Technical Objectives: Expand, decarbonize, structure, and better interface offshore observation capabilities

In addition to its ambitious scientific goals, OHIS promotes a strong drive for technological and environmental innovation to optimize and sustain offshore observation capabilities in France and Europe.

The technical objectives of the infrastructure for the coming years are structured around four major pillars:

1. Strengthen and expand the autonomous offshore observation network

OHIS aims to enhance autonomous, multi-scale, and multiparameter observation by deploying a robust, coherent, and innovative infrastructure through:

  • The deployment and expansion of a network of long-term instrumented moorings equipped with multiparameter sensors measuring physical (temperature, salinity, currents), biogeochemical (carbon, oxygen, nutrients, acidification), and biological (fluorescence, acoustics, biodiversity) parameters. These moorings will serve as reference platforms for long and high-resolution time series, which are essential to understanding ocean dynamics in detail.
  • The strategic increase and extension of the biogeochemical Argo float network, particularly in under-sampled, hard-to-access ocean regions that are nonetheless critical for the global climate (polar and subpolar regions, Southern Hemisphere, tropical areas).
  • The systematic integration of new autonomous platforms such as underwater gliders, autonomous sailing buoys (Sailbuoys), autonomous surface vehicles (ASVs and USVs), and instrumented marine mammals (MEMO project), enabling extended, flexible, and optimized spatial coverage.
  • The development of innovative, miniaturized, energy-efficient, autonomous sensors that can be easily integrated into all existing platforms (floats, gliders, marine drones) to increase sampling capacity, improve data resolution, and open new avenues for scientific exploration.

2. Significantly reduce the environmental footprint of offshore observation

Aware of the environmental issues associated with oceanographic campaigns and instrument management at sea, OHIS is fully integrating a strategy to reduce the ecological footprint of ocean observations:

  • Optimization and pooling of oceanographic campaigns by developing smart, adaptive sampling plans supported by artificial intelligence to minimize travel, reduce ship speed, and thus significantly cut greenhouse gas emissions from oceanographic vessels.
  • Support for experimental use and the gradual generalization of hybrid, hydrogen, or electric-powered vessels, in collaboration with the French Oceanographic Fleet, to align observation activities with national and European carbon neutrality goals.
  • Deployment of innovative solutions for remote instrument recovery, recycling, and maintenance to limit heavy operations at sea, reduce energy and environmental costs, and extend equipment lifespan.
  • Generalization of eco-design practices for equipment, favoring durable, recyclable, non-toxic materials to significantly reduce waste and pollution related to observation systems.
  • Support for the creation of a national, shared metrology and calibration center bringing together the resources of Ifremer, IUEM, and SHOM to ensure autonomous, reliable, and environmentally responsible management of sensor calibration and validation, while reducing dependence on external manufacturers (particularly North American ones).

3. Ensure strong interoperability and synergy with existing national and international infrastructures

OHIS will be fully integrated into an overarching approach to ocean observation by strengthening cooperation and interconnection with other infrastructures:

  • Strategic integration of OHIS within the Fr-OOS, ensuring a seamless observational continuum with infrastructures dedicated to coastal regions (ILICO), enabling coherent and integrated analysis of oceanographic processes from the shore to the open ocean.
  • Full harmonization and standardization of data formats and flows with major international data centers and operational services such as Copernicus Marine Service (CMEMS), EMODnet, and ODATIS, facilitating broad and effective use by the global scientific community.
  • Rigorous development and application of common protocols for calibration, validation, and intercomparison of data with other national and European infrastructures (Euro-Argo, EMSO, ICOS), ensuring maximum coherence and international traceability of offshore observations.

As a candidate infrastructure, OHIS will play a pivotal role within the Fr-OOS by addressing the specific challenges of offshore oceanic regions in a structured and integrated manner. In close synergy with coastal and nearshore infrastructures (notably ILICO), OHIS will have the following missions:

  • Contribute to the efficient and coherent coordination of offshore ocean observations, thus ensuring—alongside ILICO—a seamless observational continuum that allows for a detailed documentation of marine processes, land-ocean and ocean-atmosphere interactions, and the impacts of human activities on these ecosystems.
  • Provide strategic, reference offshore observations that are indispensable for significantly improving weather, seasonal, and climate forecasting models. These data will help to better understand critical large-scale phenomena, especially the complex interactions between ocean and atmosphere that drive extreme weather events and long-term climate regimes.
  • Help align the long-term ocean observation strategies of different organizations, and convey this strategy to the relevant ministries and the national coordination body of the Intergovernmental Oceanographic Commission (IOC).
  • Actively strengthen collaboration and synergies with major national initiatives within the Fr-OOS (e.g., Argo, EMSO, ILICO infrastructures), European initiatives (e.g., EuroGOOS, Copernicus Marine Service, EMODnet), and international ones (GOOS, GCOS, WMO, CLIVAR), thereby consolidating France’s leadership and influence in global in situ ocean observation.

4. Optimize and accelerate the processing, analysis, and dissemination of ocean data for the scientific and operational community

In collaboration with Data Terra (more specifically the ODATIS marine data hub) and CMEMS, OHIS will continue to develop a powerful, open digital infrastructure incorporating best current practices to ensure rapid, reliable, and comprehensive access to oceanographic data:

  • Implementation of automated processing, validation, and analysis chains in near real-time, providing both a quick response to operational user needs and immediate use of observations by researchers.
  • Development of an open, interoperable digital platform fully aligned with the FAIR principles (Findable, Accessible, Interoperable, Reusable), to ensure optimal use of OHIS data by the international scientific community, policymakers, and ocean-related economic stakeholders.
  • Advanced integration of artificial intelligence and numerical modeling methods to detect weak signals early, quickly identify emerging trends, and effectively anticipate the evolution of complex ocean systems—contributing to the robustness of climate forecasts and environmental scenarios.

By offering operational, technological, and scientific solutions to major identified challenges (understanding climate processes, improving environmental forecasting, reducing the environmental impact of observations), the candidate OHIS infrastructure aspires to become a nationally and internationally recognized reference for in situ offshore ocean observation. OHIS will thus actively contribute to advancing fundamental knowledge of ocean and climate dynamics, while ensuring the sustainable and ambitious structuring of France’s marine observation system.