A new constraint on global air-sea CO2 fluxes using bottle carbon data

We develop a new observationally derived monthly ocean surface climatology for the partial pressure of CO2 (pCO2) that allows an independent data-based constraint on contemporary air-sea CO2 fluxes. Our approach uses a neural network, trained on similar to 17,800 bottle-derived measurements of pCO2, to diagnose monthly pCO2 levels from standard ocean hydrographic data. Although the pattern of contemporary air-sea CO2 fluxes is generally consistent with the independent underway pCO2 data network, we find a strong shift in the magnitude of oceanic sources and sinks of CO2. In particular, we find a contemporary Southern Hemisphere oceanic CO2 uptake of 0.93 PgC/year, driven by a prominent CO2 sink in the subpolar region (25 degrees S60 degrees 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 CO2 sink of 1.55 +/- 0.32 PgC/year for the nominal year of 2000.