Abstract
Abstract. 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 (∼300 points) within a factor of 2. Overall, the global emissions of CO to the atmosphere are 4.0 Tg C 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.
Highlights
Atmospheric carbon monoxide (CO) plays an important role in atmospheric chemistry
We describe the oceanic CO cycle as simulated by PISCES using the CO module implemented in this study
The global CO emission to the atmosphere (4.0 Tg C yr−1) is rather small compared to the biochemical source and sink processes
Summary
Atmospheric carbon monoxide (CO) plays an important role in atmospheric chemistry. It indirectly affects the lifetime of greenhouse gases like methane (CH4) as it is the dominant sink for tropospheric hydroxyl radicals (Thompson, 1992; Taylor et al, 1996) and impacts air quality as it is involved in ozone chemistry (Crutzen, 1974; Cicerone, 1988). In 1968, Swinnerton et al conducted in the Mediterranean Sea the first measurements of oceanic CO and reported a supersaturation of a few orders of magnitude in the surface waters with respect to the partial pressure of this gas in the atmosphere. The CO concentration in the surface ocean is a few nanomoles per liter (nmol L−1) and presents large diurnal Subsequent cruises confirmed the supersaturation of oceanic CO concentrations (Seiler and Junge, 1970; Swinnerton et al, 1970; Lamontagne et al, 1971; Swinnerton and Lamontagne, 1973; Linnenbom et al, 1973) and supported the idea that the world oceans serve as a source of CO for the atmosphere.
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