A seamless ensemble-based reconstruction of surface ocean p CO 2 and air–sea CO 2 fluxes over the global coastal and open oceans

• Published in: Biogeosciences
• Main Authors: T. T. T. Chau, M. Gehlen, F. Chevallier
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Ecology; QH540-549.5; Life; QH501-531; Geology; QE1-996.5; Arctic; Southern Ocean; Pacific; Indian
• Online Access: https://doi.org/10.5194/bg-19-1087-2022; https://doaj.org/article/4b1dfe91d52b40849d4586954f9592d0

We have estimated global air–sea CO 2 fluxes ( fg CO 2 ) from the open ocean to coastal seas. Fluxes and associated uncertainty are computed from an ensemble-based reconstruction of CO 2 sea surface partial pressure ( p CO 2 ) maps trained with gridded data from the Surface Ocean CO 2 Atlas v2020 database. The ensemble mean (which is the best estimate provided by the approach) fits independent data well, and a broad agreement between the spatial distribution of model–data differences and the ensemble standard deviation (which is our model uncertainty estimate) is seen. Ensemble-based uncertainty estimates are denoted by ±1 σ . The space–time-varying uncertainty fields identify oceanic regions where improvements in data reconstruction and extensions of the observational network are needed. Poor reconstructions of p CO 2 are primarily found over the coasts and/or in regions with sparse observations, while fg CO 2 estimates with the largest uncertainty are observed over the open Southern Ocean (44 ∘ S southward), the subpolar regions, the Indian Ocean gyre, and upwelling systems. Our estimate of the global net sink for the period 1985–2019 is 1.643±0.125 PgC yr −1 including 0.150±0.010 PgC yr −1 for the coastal net sink. Among the ocean basins, the Subtropical Pacific (18–49 ∘ N) and the Subpolar Atlantic (49–76 ∘ N) appear to be the strongest CO 2 sinks for the open ocean and the coastal ocean, respectively. Based on mean flux density per unit area, the most intense CO 2 drawdown is, however, observed over the Arctic (76 ∘ N poleward) followed by the Subpolar Atlantic and Subtropical Pacific for both open-ocean and coastal sectors. Reconstruction results also show significant changes in the global annual integral of all open- and coastal-ocean CO 2 fluxes with a growth rate of <math xmlns="http://www.w3.org/1998/Math/MathML" id="M26" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>+</mo><mn mathvariant="normal">0.062</mn><mo>±</mo><mn ...