All values in billion tonnes of carbon per year (GtC/yr), for the globe. For values in billion tonnes of carbon dioxide per year (GtCO₂/yr), multiply the numbers below by 3.664.
1 billion tonnes C = 1 petagram of carbon (10^15 gC) = 1 gigatonne C = 3.664 billion tonnes of CO₂
Methods: The ocean sink (uncertainty of ±0.4 GtC/yr on average) is estimated from the average of 10 global ocean biogeochemistry models and 7 fCO₂ data products that reproduce the observed mean ocean sink of the 1990s. UOEx-Watson not used for the fCO₂ data products average.
Cite as: Friedlingstein et al 2023 (see summary tab).
Prior to 1990, the GCB ocean sink estimate is calculated from the GOBM multi-model mean with an offset applied. The offset is calculated as the half of the difference between GOBMs and data products in the period 1990-2001 (inclusive). This ensures no artificial jumps occur in 1990 when the data products are used to estimate the sink in conjunction with the GOBMs.

Note: the surface ocean fCO₂-based data products are adjusted for a pre-industrial steady state source of CO₂ from rivers (of 0.65 GtC/yr) to be comparable with the ocean model results and to satisfy the definition of the ocean carbon sink used in the Global Carbon Budget.

Cite individual estimates as:

Global ocean biogeochemical models:

• NEMO3.6-PISCESv2-gas (CNRM) Berthet, S., Séférian, R., Bricaud, C., Chevallier, M., Voldoire, A., & Ethé, C. ( 2019). Evaluation of an online grid‐coarsening algorithm in a global eddy‐admitting ocean biogeochemical model. Journal of Advances in Modeling Earth Systems, 11, 1759–1783. https://doi.org/10.1029/2019MS001644
• FESOM-2.1-REcoM2 Gürses, Ö., Oziel, L., Karakuş, O., Sidorenko, D., Völker, C., Ye, Y., Zeising, M., Butzin, M., and Hauck, J.: Ocean biogeochemistry in the coupled ocean–sea ice–biogeochemistry model FESOM2.1–REcoM3, Geosci. Model Dev., 16, 4883–4936, https://doi.org/10.5194/gmd-16-4883-2023, 2023.
• NEMO-PISCES (IPSL) Aumont, O., Ethé, Tagliabue, A., Bopp, L., & Gehlen, M. (2015). PISCES-v2: an ocean biogeochemical model for carbon and ecosystem studies.
• MOM6-COBALT (Princeton) Liao, E., Resplandy, L., Liu, J. and Bowman, K. W.: Amplification of the Ocean Carbon Sink During El Niños: Role of Poleward Ekman Transport and Influence on Atmospheric CO 2, Global Biogeochem. Cycles, 34(9), doi:10.1029/2020GB006574, 2020.
• MRI-ESM2-2 Nakano, H., Tsujino, H., Hirabara, M., Yasuda, T., Motoi, T., Ishii, M., and Yamanaka, G.: Uptake mechanism of anthropogenic CO₂ in the Kuroshio Extension region in an ocean general circulation model, J. Oceanogr., 67, 765–783, https://doi.org/10.1007/s10872-011-0075-7, 2011.
• MICOM-HAMOCC (NorESM-OCv1.2) Schwinger, J., Goris, N., Tjiputra, J. F., Kriest, I., Bentsen, M., Bethke, I., Ilicak, M., Assmann, K. M., and Heinze, C.: Evaluation of NorESM-OC (versions 1 and 1.2), the ocean carbon-cycle stand-alone configuration of the Norwegian Earth System Model (NorESM1), Geosci. Model Dev., 9, 2589-2622, 2016.
• NEMO-PlankTOM12 Wright, R. M., Le Quéré, C., Buitenhuis, E., Pitois, S., & Gibbons, M. J. (2021). Role of jellyfish in the plankton ecosystem revealed using a global ocean biogeochemical model. Biogeosciences, 18(4), 1291-1320. https://doi.org/10.5194/bg-18-1291-2021
• CESM-ETHZ Doney, S. C., Lima, I., Feely, R. A., Glover, D. M., Lindsay, K., Mahowald, N., Moore, J. K., and Wanninkhof, R.: Mech- anisms governing interannual variability in upper-ocean inor- ganic carbon system and air–sea CO₂ fluxes: Physical cli- mate and atmospheric dust, Deep-Sea Res. Pt. II, 56, 640–655, https://doi.org/10.1016/j.dsr2.2008.12.006, 2009.
• MPIOM-HAMOCC6 Lacroix F., Tatiana Ilyina, Moritz Mathis, Goulven Laruelle, Pierre Regnier: Historical Increases in Land-Derived Nutrient Inputs May Alleviate Effects from a Changing Physical Climate on the Oceanic Carbon Cycle. Global Change Biology, https://doi.org/10.1111/gcb.15822, 2021
• ACCESS (CSIRO) Law, R. M., Ziehn, T., Matear, R. J., Lenton, A., Chamberlain, M. A., Stevens, L. E., Wang, Y.-P., Srbinovsky, J., Bi, D., Yan, H., and Vohralik, P. F.: The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) – Part 1: Model description and pre-industrial simulation, Geosci. Model Dev., 10, 2567–2590, https://doi.org/10.5194/gmd-10-2567-2017, 2017.

fCO₂-products:

• CMEMS-LSCE-FFNNv2 Chau, T. T. T., Gehlen, M., and Chevallier, F.: A seamless ensemble-based reconstruction of surface ocean pCO₂ and air–sea CO₂ fluxes over the global coastal and open oceans, Biogeosciences, 19, 1087–1109, https://doi.org/10.5194/bg-19-1087-2022, 2022.
• JMA-MLR Iida, Y., Takatani, Y., Kojima, A., and Ishii, M.: Global trends of ocean CO₂ sink and ocean acidification: an observation-based reconstruction of surface ocean inorganic carbon variables. J. Oceanogr. 77, 323–358. https://doi.org/10.1007/s10872-020-00571-5, 2021
• LDEO-HPD Gloege, L., Yan, M., Zheng, T., and McKinley, G. A.: Improved Quantification of Ocean Carbon Uptake by Using Machine Learning to Merge Global Models and pCO₂ Data, J. Adv. Model. Earth Syst., 14, e2021MS002620, https://doi.org/10.1029/2021MS002620, 2022.
• MPI-SOMFFN Landschützer, P., Gruber, N., and Bakker, D. C. E.: Decadal variations and trends of the global ocean carbon sink: decadal air-sea CO₂ flux variability, Global Biogeochem. Cycles, 30, 1396–1417, https://doi.org/10.1002/2015GB005359, 2016.
• NIES-NN Zeng, J., Nojiri, Y., Landschützer, P., Telszewski, M., Nakaoka, S.: A Global Surface Ocean fCO₂ Climatology Based on a Feed-Forward Neural Network. Journal of Atmospheric and Oceanic Technology 31, 1838–1849. https://doi.org/10.1175/JTECH-D-13-00137.1, 2014.
• OS-ETHZ-GRaCER Gregor, L. and Gruber, N.: OceanSODA-ETHZ: a global gridded data set of the surface ocean carbonate system for seasonal to decadal studies of ocean acidification, Earth Syst. Sci. Data, 13, 777–808, https://doi.org/10.5194/essd-13-777-2021, 2021.
• Jena-MLS Rödenbeck, C., DeVries, T., Hauck, J., Le Quéré, C., and Keeling, R. F.: Data-based estimates of interannual sea–air CO₂ flux variations 1957–2020 and their relation to environmental drivers, Biogeosciences, 19, 2627–2652, https://doi.org/10.5194/bg-19-2627-2022, 2022.
• UOEx-Watson Watson, A. J., Schuster, U., Shutler, J. D., Holding, T., Ashton, I. G. C., Landschützer, P., Woolf, D. K. and Goddijn-Murphy, L.: Revised estimates of ocean-atmosphere CO₂ flux are consistent with ocean carbon inventory, Nat. Commun., 11(1), 1–6, doi:10.1038/s41467-020-18203-3, 2020.