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In order to better understand the variability of surface CO in the Tropical Atlantic, a CARIOCA sensor has been installed on a PIRATA mooring at 6°S, 10°W in June 2006. The fugacity of CO ( fCO) is recorded hourly from 7 June 2006 to 30 October 2009 with two important data gaps. From July to September, an upwelling develops and a decrease in sea surface temperature (SST) is observed, associated with an fCO increase. However, the highest fCO is observed in October, after the upwelling season, due to the warming of surface waters. The region is a net source of CO to the atmosphere of 2.10 ± 0.69 mol m yr in 2007. The monthly flux is maximum (3.21 ± 0.8 mol m yr) in November (averaged over 2006 and 2008). High frequency variability is observed throughout the time series but is particularly pronounced after the upwelling season. Biological and thermodynamic processes explain the diurnal variability. Dissolved inorganic carbon (DIC) is calculated from (alkalinity) TA and fCO using an empirical TA-salinity relationship determined for the eastern equatorial Atlantic. Net community production (NCP) is calculated from DIC daily changes and ranges from 9 to 41 mmol m d, which is consistent with previous measurements in this region. [ABSTRACT FROM AUTHOR]

Underway fCO has been measured from two merchant ships sailing from France to French Guyana and France to Brazil, and during two zonal cruises from Africa to French Guyana. In the western Tropical Atlantic, the strongest undersaturation is associated with the Amazon discharge near 55°W. In the 5°S-10°N, 65-35°W region, the carbon system is strongly correlated to salinity and robust empirical relationships could be determined. This region is a sink of CO in May-June during the high-flow period of the Amazon river. The eastward propagation of Amazon waters is observed when the retroflection of the North Brazil Current takes place. In August 2008, freshwater is observed as far as 40°W when the North Equatorial Counter Current is quite strong. The Amazon plume, defined as salinities less than 34.9, is a sink of CO of 0.96 mmol m d. Further east, near 27°W, CO undersaturation is recorded thoughout the year between 5°N and 8°N. This is caused by the high precipitation associated with the presence of the intertropical convergence zone (ITCZ). Removing the temperature effect leads to low (high) fCO associated with low (high) salinities in boreal summer (winter), which is consistent with the seasonal migration of the ITCZ. [ABSTRACT FROM AUTHOR]

Shelf seas play an important role in the global carbon cycle, absorbing atmospheric carbon dioxide (CO 2 ) 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 CO 2 fugacity (fCO 2 ) from a single year (2015), to estimate the net influx of atmospheric CO 2 as 26.2 ± 4.7 Tg C yr -1 over the open NW European shelf. CO 2 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 CO 2 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 ).