The oceanic cycle of carbon monoxide and its emissions to the atmosphere

The ocean is a source of atmospheric carbon monoxide (CO), a key component for the oxidizing capacity of the atmosphere. It constitutes a minor source at the global scale, but could play an important role far from continental anthropized emission zones. To date, this natural source is estimated with large uncertainties, especially because the processes driving the oceanic CO are related to the biological productivity and can thus have a large spatial and temporal variability. Here we use the NEMO-PISCES (Nucleus for European Modelling of the Ocean, Pelagic Interaction Scheme for Carbon and Ecosystem Studies) ocean general circulation and biogeochemistry model to dynamically assess the oceanic CO budget and its emission to the atmosphere at the global scale. The main biochemical sources and sinks of oceanic CO are explicitly represented in the model. The sensitivity to different parameterizations is assessed. In combination to the model, we present here the first compilation of literature reported in situ oceanic CO data, collected around the world during the last 50 years. The main processes driving the CO concentration are photoproduction and bacterial consumption and are estimated to be 19.1 and 30.0 Tg C yr(-1) respectively with our best-guess modeling setup. There are, however, very large uncertainties on their respective magnitude. Despite the scarcity of the in situ CO measurements in terms of spatiotemporal coverage, the proposed best simulation is able to represent most of the data (similar to 300 points) within a factor of 2. Overall, the global emissions of CO to the atmosphere are 4.0 TgC yr(-1), in the range of recent estimates, but are very different from those published by Erickson in (1989), which were the only gridded global emission available to date. These oceanic CO emission maps are relevant for use by atmospheric chemical models, especially to study the oxidizing capacity of the atmosphere above the remote ocean.