Strong Southern Ocean carbon uptake evident in airborne observations
This study employs a novel approach to estimating Southern Ocean air-sea CO2 fluxes, leveraging several aircraft campaigns that measured CO2 in the overlying atmosphere. The authors “calibrate” a relationship between the air-sea flux and the lower-troposphere vertical CO2 gradient in a collection of atmospheric transport models. Combined with the aircraft observations, this relationship indicates that the Southern Ocean remains a strong CO2 sink. The study also examined surface-based atmospheric CO2 measurements, which do not provide as robust constraints on the fluxes as the vertical gradients accessible from aircraft, but suggest a trend of increasing Southern Ocean uptake since 2005. The flux estimates in this study are consistent with ship-board pCO2 observations, but show stronger uptake than suggested by recent float-based pH observations.
Reference: Long, M. C., Stephens, B. B., Mckain, K., et al. (2021). Strong Southern Ocean carbon uptake evident in airborne observations. Science, 374(6572), 1275-1280. https://doi.org/10.1126/science.abi4355.