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Shelf seas play an important role in the global carbon cycle, absorbing atmospheric carbon dioxide (CO2) and exporting carbon (C) to the open ocean and sediments. The magnitude of these processes is poorly constrained, because observations are typically interpolated over multiple years. Here, we used 298500 observations of CO2 fugacity (fCO(2)) from a single year (2015), to estimate the net influx of atmospheric CO2 as 26.2 +/- 4.7 Tg C yr(-1) over the open NW European shelf. CO2 influx from the atmosphere was dominated by influx during winter as a consequence of high winds, despite a smaller, thermally-driven, air-sea fCO(2) gradient compared to the larger, biologically-driven summer gradient. In order to understand this climate regulation service, we constructed a carbon-budget supplemented by data from the literature, where the NW European shelf is treated as a box with carbon entering and leaving the box. This budget showed that net C-burial was a small sink of 1.3 +/- 3.1 Tg C yr(-1), while CO2 efflux from estuaries to the atmosphere, removed the majority of river C-inputs. In contrast, the input from the Baltic Sea likely contributes to net export via the continental shelf pump and advection (34.4 +/- 6.0 Tg C yr(-1)).

The European Research Infrastructure Consortium "Integrated Carbon Observation System" (ICOS) aims at delivering high quality greenhouse gas (GHG) observations and derived data products (e.g., regional GHG-flux maps) for constraining the GHG balance on a European level, on a sustained long-term basis. The marine domain (ICOS-Oceans) currently consists of 11 Ship of Opportunity lines (SOOP - Ship of Opportunity Program) and 10 Fixed Ocean Stations (FOSs) spread across European waters, including the North Atlantic and Arctic Oceans and the Barents, North, Baltic, and Mediterranean Seas. The stations operate in a harmonized and standardized way based on community-proven protocols and methods for ocean GHG observations, improving operational conformity as well as quality control and assurance of the data. This enables the network to focus on long term research into the marine carbon cycle and the anthropogenic carbon sink, while preparing the network to include other GHG fluxes. ICOS data are processed on a near real-time basis and will be published on the ICOS Carbon Portal (CP), allowing monthly estimates of CO2 air-sea exchange to be quantified for European waters. ICOS establishes transparent operational data management routines following the FAIR (Findable, Accessible, Interoperable, and Reusable) guiding principles allowing amongst others reproducibility, interoperability, and traceability. The ICOS-Oceans network is actively integrating with the atmospheric (e.g., improved atmospheric measurements onboard SOOP lines) and ecosystem (e.g., oceanic direct gas flux measurements) domains of ICOS, and utilizes techniques developed by the ICOS Central Facilities and the CP. There is a strong interaction with the international ocean carbon cycle community to enhance interoperability and harmonize data flow. The future vision of ICOS-Oceans includes ship-based ocean survey sections to obtain a three-dimensional understanding of marine carbon cycle processes and optimize t

The fugacity of CO2 (fCO(2)) has been measured underway during three quasi-synoptic cruises in the western tropical Atlantic in March/April 2009 and July/August 2010 in the region 6 degrees S-15 degrees N, 52 degrees W-24 degrees W. The distribution of fCO(2) is related to the main features of the ocean circulation. Temperature exerts a dominant control on the distribution of fCO(2) in March/April whereas salinity plays an important role in July/ August due to the more developed North Equatorial Countercurrent (NECC) carrying Amazon water and to the high precipitation associated with the presence of the Intertropical Convergence Zone (ITCZ). The main surface currents are characterized by different fCO(2). Overall, the NECC carries less saline waters with lower fCO(2) compared to the South Equatorial Current (SEC). The North Equatorial Current (NEC) is usually characterized by CO2 undersaturation in winter and supersaturation in summer. Using empirical fCO(2)-SST-SSS relationships, two seasonal maps of fCO(2) are constructed for March 2009 and July 2010. The region is a sink of CO2 of 0.40 mmol m(-2)d(-1) in March, explained by the winter cooling in the northern hemisphere, whereas it is a source of CO2 of 1.32 mmol m(-2)d(-1) in July. The equatorial region is a source of CO2 throughout the year due to the upwelling supplying CO2-rich waters to the surface. However, the evolution of fCO(2) over time, determined from all the available cruises in a small area, 1 degrees S-1 degrees N, 32 degrees W-28 degrees W, suggests that the source of CO2 has decreased in February-March from 1983 to 2011 or has remained constant in October-November from 1991 to 2010.