Summary

Ocean carbon is one of only two observational constraints within global carbon assessments. The OC4C project aims to initiate preliminary activities towards the long-term generation of ocean carbon Climate Data Records (CDRs) which will provide and use multiple Essential Climate Variables (ECVs).

Our objectives are to improve, advance and further constrain current estimates of the uptake of atmospheric carbon dioxide (CO2) and its exchange with the ocean (air-sea CO2 fluxes), and to fully characterise and reduce the uncertainties of these estimates. Within this, we will generate a global climate quality time series dataset of ocean carbon air-sea CO2 fluxes which will provide an estimate of the ocean carbon sink from 1980 to present day. This effort involves a diverse group of internationally recognised ocean carbon scientists from across the community.

Carbon dioxide continually exchanges between the atmosphere and oceans, either into the ocean (blues) or out of the ocean (reds). The balance of these continually exchanges leads to a net movement of carbon from the atmosphere to the oceans. Data used in
Carbon dioxide continually exchanges between the atmosphere and oceans, either into the ocean (blues) or out of the ocean (reds). The balance of these continually exchanges leads to a net movement of carbon from the atmosphere to the oceans. Data used in the figure was submitted to the Global Carbon Budget 2024 (Friedlingstein et al., 2024) by the University of Exeter following the methods of Ford et al. (2024)

Project background

Observation-based estimates of the annual ocean carbon uptake (sink) have now become a key component within global carbon budget assessments used to guide policy. Ocean and atmosphere observations form the two key observational pillars and constraints within these annual carbon budget assessments, with their uncertainties directly impacting the closure of the total budget. The policy relevance of these annual carbon assessments cannot be underestimated; they provide information about the impact of mitigation policies and they also enable updates on the so called “remaining carbon budget”, which identifies how much CO2 can be emitted in the coming decades without overshooting specific climate targets. Thus, efforts to increase understanding of, as well as improve the quantification of the ocean carbon sink, will strengthen its constraint on the remaining components of the budget within annual assessments, and increase the strength of any resulting policy guidance.

Aims and Objectives

The aim of the OC4C project is to improve our understanding of the physical and biogeochemical aspects inherent to the ocean carbon uptake, and how they are related to the climate change, both on a global and regional basis. To achieve this, the work on this project sets out to address eight key objectives. These are to:

  1. Improve and upgrade the state-of-the-art Earth observation (EO)-based estimation of carbon fluxes through the assessment of different reference SST (at their related ocean depths), and refine the ocean carbon fluxes uncertainty estimates.
  2. Improve and upgrade the state-of-the-art EO-based estimation of carbon fluxes through the assessment of the relevance of marine biology, and refine the ocean carbon fluxes uncertainty estimates.
  3. Begin to reconcile/recalibrate the currently diverging Global carbon Budget (GCB) model estimates with these upgraded EO Carbon sink datasets.
  4. Explore carbon sink variability in relation to climate indexes (e.g., ENSO) occurrence and phasing.
  5. Assess carbon sink variability at different temporal scales (seasonal, inter-annual) and in challenging ocean basins (e.g. the Arctic Ocean)
  6. Perform a model versus EO sampling sensitivity analysis to assess the inherent sampling-driven differences.
  7. Provide both global and regional estimates; for the latter, assess the options for regionalization (extrapolation, downscaling, etc.) and the guidance provided by biogeochemical provinces and biomes.
  8. Draft a scientific roadmap for channelling the relevant upgraded EO carbon fluxes estimates for the future wider context of Global Stocktake reporting for the Paris Agreement.

Project plan

Professor Jamie Shutler (university of Exeter) is responsible for guiding the project’s scientific and technical activity. Project Manager Ruth Wilson (Space ConneXions Ltd) is responsible for the management and execution of the work to be performed, and for the coordination of the consortium’s work. The project draws on the scientific expertise of the partners, UoE, PML, VLIZ, AWI, LSCE and UC (see image ‘Team Roles’).

The project work is broken down into 6 Tasks. These are:

OC4C work breakdown
OC4C project work breakdown

Task 1: Requirements Baseline

All the available satellite, in-situ and model datasets that serve the scope of the project, together with plans to acquire them will be identified and assessed, along with the best candidate test site for the development of the regional experimental products. A clear description of the added value of the proposed work with respect to existing activities and identification of potential areas for collaboration will also be made.

Task 2: Algorithm Development

Via numerous algorithm updates and assessments of data sources, masks and interpolation schemes, a high quality, global, multi-mission, consistent time-series of relevant ocean carbon datasets within an experimental data package will be generated, for further exploitation and reference by the user community.

Task 3: Validation

Validation metrics will be generated and compared with the accuracy, precision and stability requirements specified in the requirement baseline. Product uncertainties will be characterised, through direct or indirect methods, paying attention to the spatial and temporal representation errors.

Task 4: Impact Assessment and Model Intercomparison

Differences between observation-based and model-based CO₂ flux estimates, and the closeness to which the two estimates come with the inclusion of uncertainties/error bars on the observation-based estimates, will be assessed. The correlation of ocean carbon sinks to major climate indexes (e.g. ENSO) will be evaluated. Modelled pCO₂ data at the same spatial and temporal locations as the in-situ data will be sampled, and the EO-model spatial and temporal consistencies or discrepancies, once devoid of the sampling effect, will be evaluated. GOBMs models at EO spatial and temporal resolution, once devoid of the representation error, will be upscaled and assessed.

Task 5: Scientific Roadmap

Major achievements and related shortcoming/bottlenecks of the project will be assessed for future ocean carbon climatic perspectives, and a community workshop will be hosted.

Task: User Engagement and Outreach

Work shall be complementary with related activities, both within and outside ESA