The Southern Ocean plays an important role in absorbing CO2 from the atmosphere that is released by human activities - a process that is of crucial importance for climate change. In a new study, an international research group led by the University of East Anglia (UEA) and the Plymouth Marine Laboratory (PML), with the participation of the Alfred Wegener Institute, has found that the Southern Ocean around Antarctica absorbs more carbon dioxide (CO2) than previously thought. The results, which were published in the journal Science Advances, are based on a comprehensive data analysis of seven expeditions with direct CO2 measurements.
Previous approaches and data collected, for example, from measurements on board research vessels or model simulations, lead to large variations in estimates of how much carbon the ocean absorbs from the atmosphere. The international research team, which included researchers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), the Max Planck Institute, the Flanders Marine Institute and the University of Hawai'i, used the new eddy covariance technique to directly measure CO2 fluxes between air and ocean and to evaluate different data sets. The aim of the study was to better assess the magnitude and variability of this flux. Measurement systems were used, which were attached to the foremasts of the ships.
The cruise data includes about 175 days of measurements taken during the Antarctic summer in 2019 and 2020 in the period from November to April. The researchers investigated inconsistencies in existing CO2 flux estimates and concluded that the summer Southern Ocean is a stronger CO2 sink than estimated from indirect observations and model simulations. The measurements showed that 25% more CO2 is absorbed than previous estimates based on ship data suggested.
The authors of the study argue that this difference can be explained by the consideration of temperature fluctuations in the upper ocean and a limited resolution in models and data products. They emphasise that previous model simulations and float data do not take into account small-scale, intensive CO2 uptake events and therefore "significantly underestimate" the actual CO2 uptake.
Original publication:
Dong, Y., Bakker, D. C. E., Bell, T. G., Yang, M., Landschützer, P., Hauck, J., Rödenbeck, C., Kitidis, V., Bushinsky, S. M. and Liss, P. Direct observational evidence of strong CO2 uptake in the Southern Ocean. Science Advances. (2024). DOI: 10.1126/sciadv.adn5781