Carbon Dioxide in the Ocean: Hidden Uncertainties

5 September 2023, by Franziska Neigenfind

Photo: Paridhi Rustogi et al.

Carbon fluxes between the ocean and atmosphere in the Southern Ocean (0-360°, 35-65°S)

The Southern Ocean has absorbed ca. 40 percent of the global anthropogenic carbon emissions, providing a substantial buffer to climate change. How will carbon flows between the ocean and atmosphere change in the future? The majority of studies provide an annual mean estimate for these fluxes. A team led by Paridhi Rustogi, who is meanwhile a researcher at Princeton University, and Prof. Johanna Baehr has analyzed flows in individual seasons, using the example of the Southern Ocean – and revealed previously hidden uncertainties in the tools used to evaluate these fluxes.

The figure shows the Southern Hemisphere, with Antarctica in the middle. The two rows represent the annual mean carbon fluxes (far left) and the seasonal progression. The top row is based on observational data; the bottom row, on simulations. As the top left and bottom left figures show, the values for the annual mean fluxes match up relatively well. Yet, if we take a closer look at the individual seasons, there are clearly recognizable differences between the observational data and simulations.

These findings show how important uncertainties can be overlooked in the annual mean values. For example, based on the observational data, the Southern Ocean is an important CO₂ sink year-round. In contrast, the bottom row, based on simulations, shows increased uptake in the spring and summer and more pronounced outgassing in the autumn and winter. In order to reliably project how overall carbon uptake in the Southern Ocean will be affected by climate change, reducing uncertainties is of tremendous importance.

Rustogi, P., Landschützer, P., Brune, S. et al. The impact of seasonality on the annual air-sea carbon flux and its interannual variability. npj Clim Atmos Sci 6, 66 (2023). https://doi.org/10.1038/s41612-023-00378-3