EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Towards inferring the variability in oceanic CO2 fluxes at high latitudes using atmospheric O2 observations

Nicolas Mayot1, Corinne Le Quéré1, Andrew Manning1, Ralph Keeling2, and Christian Rödenbeck3
Nicolas Mayot et al.
  • 1School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom
  • 2Scripps Institution of Oceanography, University of California, La Jolla, CA, USA
  • 3Max Planck Institute, Jena, Germany

The oceanic CO2 sink displays year-to-year to decadal variabilities which are not fully reproduced by global ocean biogeochemistry models, especially in the high-latitude oceans. Oceanic CO2 is influenced by the same climate variability and the same ecosystem processes as oceanic oxygen (O2), although in different proportions. Unlike for CO2, oceanic O2 flux is not influenced directly by the rise in atmospheric CO2, and therefore its variability reflects purely climatic and biogeochemical variability and trends. Therefore, natural climate variability and changes in oceanic processes controlling air-sea exchanges of CO2 can be studied by focusing on oxygen (O2), where the signal is unencumbered by direct anthropogenic influence. A global time series of oceanic O2 flux was obtained by building a global O2 budget, with an approach similar to the one used for the global carbon budget. The global O2 budget is based on atmospheric O2 observations and fossil fuel statistics, and infers the partitioning of the land and ocean fluxes using constant C:O2 ratios for land processes. One key result of this analysis is that air-sea O2 exchange induced significant year-to-year variability in observed atmospheric O2. Estimates of regional oceanic O2 fluxes were obtained from an atmospheric transport inversion analysis that inferred air-sea O2 exchange based on global atmospheric O2 observations and a global atmospheric transport model. For the Southern Ocean, a comparison was made between time series of winter oceanic O2 fluxes from this inversion method and winter mixed layer depths from Argo floats. Results from this comparison confirmed the previously suggested relationship between the winter ocean mixing and air-sea O2 exchange, which might be controlled by the climate variability induced by the Southern Annular Mode. Finally, these global and regional air-sea O2 fluxes were compared with outputs from six global ocean biogeochemistry models to examine their current skills in simulating O2 variability. Preliminary results suggested that all models underestimated the interannual variability in oceanic O2 fluxes, however they were able to simulate some of the observed multi-annual variability in O2 fluxes at high latitudes. We discuss the implications for the model’s representation of the variability in CO2 fluxes.

How to cite: Mayot, N., Le Quéré, C., Manning, A., Keeling, R., and Rödenbeck, C.: Towards inferring the variability in oceanic CO2 fluxes at high latitudes using atmospheric O2 observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13682,, 2021.


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