A new constraint on global air‐sea CO 2 fluxes using bottle carbon data

We develop a new observationally derived monthly ocean surface climatology for the partial pressure of CO 2 ( p CO 2 ) that allows an independent data‐based constraint on contemporary air‐sea CO 2 fluxes. Our approach uses a neural network, trained on ~17,800 bottle‐derived measurements of p CO 2 , to diagnose monthly p CO 2 levels from standard ocean hydrographic data. Although the pattern of contemporary air‐sea CO 2 fluxes is generally consistent with the independent underway p CO 2 data network, we find a strong shift in the magnitude of oceanic sources and sinks of CO 2 . In particular, we find a contemporary Southern Hemisphere oceanic CO 2 uptake of 0.93 PgC/year, driven by a prominent CO 2 sink in the subpolar region (25°S–60°S), that is five times the magnitude of the Northern Hemisphere oceanic sink (0.18 PgC/year). Globally, our results suggest a net open‐ocean CO 2 sink of 1.55 ± 0.32 PgC/year for the nominal year of 2000.