Testor, Pierre, Wagener, Thibaut, Bosse, Anthony, Asselot, Remy, Thierry, Virginie, Karstensen, Johannes , Thomsen, Soeren, Carracedo, Lidia, von Schnuckmann, Karina and Telszewski, Maciej (2022) Estimate of magnitude and drivers of regional carbon variability for both regions. . EuroSea Deliverable, D7.3 . EuroSea, 37 pp. DOI 10.3289/eurosea_d7.3.

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Abstract

This deliverable provides an overview of EuroSea outcomes related to interior ocean carbon variability in deep convection areas in order to assess the linkage of these processes for the use in national climate action (NCA) plans delivered in the framework of the Paris Agreement. In summary, large-scale connectivity in the ocean does not allow clear delineation of patterns of regional carbon uptake across national boundaries, limiting an assessment of the Exclusive Economic Zones (EEZ) in light of NCA plans. This problem becomes already clear by a simple scale estimation: considering sluggish, open ocean (away from continental boundaries) advection speeds of 2 cm/s result in a “relocation” of any water parcel by roughly 630 km per year (or 3150 km in 5 years Paris Agreement carbon auditing period) and crossing national borders easily.
Knowing changes in the global ocean carbon uptake is of great importance for the preparation of NCA plans. This is because the NCA plans are motivated by the globally averaged atmospheric CO2 concentration, which is the sum of all sources and sinks and including the ocean sink. In case of decrease in the oceanic sink (e.g., IPCC, 2021), more CO2 will remain in the atmosphere and consequently nations will need to formulate their NCA plans with increased ambition in order to meet the CO2 target defined in the Paris Agreement. In this deliverable key approaches for the assessment of the global ocean carbon uptake have been applied to ocean areas. The observational requirements for applying statistical approaches (i.e., artificial neural networks, Fourrier et al., 2020) to reconstruct dissolved inorganic carbon (DIC) from oxygen, nutrient and hydrographic data are analysed. It is shown that even small changes in the DIC content determined in this way can be linked to anthropogenic increases in atmospheric carbon (Cant). Furthermore, it has been shown that multilinear regression techniques can be used to produce maps of ocean surface carbon fluxes at very high spatial resolution, which in turn can provide a much more accurate estimate of regional CO2 uptake (or release). Finally, a quantification of the redistribution of dissolved gases in boundary current systems could be investigated by following recommendations for observational methods stemming from this deliverable.
This deliverable recommends improvement of carbon sampling in all nations EEZ regions and following global standards. Because the objective targets a global assessment, the data must be disseminated rapidly and in a FAIR fashion to enable further global integration (e.g., global carbon budget). A need for defining responsibilities for such global integration and the resourcing is required. It is recommended to make use of statistical methods to create surface and interior carbon parameter distributions via multiparameter approaches with a sufficient amount of reference data (e.g., co-located DIC, oxygen, nutrients, chlorophyll-a, hydrography). In the light of the ongoing crisis related to global availability of the Certified Reference Materials (CRMs) for carbonate system measurements, provision of European-produced material becomes critical to enable traceability of future measurements. Nations should be encouraged to provide appropriate resources by means of corresponding European directives. Example for such national commitments is the collection of reference data in the framework of the Common Fisheries Policy.

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