73 / 2024-09-05 15:30:33

Direct observational evidence of strong CO2 uptake in the Southern Ocean

Ocean carbon cycle,Southern Ocean,Eddy covariance

The Southern Ocean is the primary region for the uptake of anthropogenic CO₂ and is, therefore, crucial for Earth’s climate. However, the Southern Ocean CO₂ flux estimates reveal substantial uncertainties and lack direct validation. Using seven directly measured air-sea CO₂ flux datasets, we identify a 25% stronger CO₂ uptake in the Southern Ocean than previously thought. Accounting for upper ocean temperature gradients and insufficient temporal resolution of flux products can bridge this flux gap. The gas transfer velocity parameterization is not the main reason for the flux disagreement. The profiling float data-based flux products and biogeochemistry models considerably underestimate the observed CO₂ uptake, which may be due to the lack of representation of small-scale high-flux events. Our study suggests the need to account for the temperature effects, and fine-scale observations and flux estimates.