Higher CO2 absorption in the Southern Ocean

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.