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[1] The partial pressure of carbon dioxide (pCO 2 ) in surface seawater on the South Atlantic Bight (SAB) of the United States was measured during six cruises from January 2005 to May 2006. The high-resolution pCO 2 data allow us to create the first maps of the sea surface pCO 2 over the SAB for all seasons. Contrary to an earlier study that was based on limited spatial and seasonal coverage, this study shows that the SAB is a net sink of atmospheric CO 2 on an annual basis (À0.48 ± 0.21 mol m À2 a À1 ). The inner shelf is a source of +1.20 ± 0.24 mol m À2 a À1 , while the middle and outer shelves are sinks of À1.23 ± 0.19 and À1.37 ± 0.21 mol m À2 a À1 , respectively. Seasonally, the SAB shifts from a sink for atmospheric CO 2 in winter to a source in summer. The annual cycle of sea surface temperature plays a dominant role in controlling the seasonal variation of the pCO 2 . Wind speeds are seasonally anti-correlated with the air-sea pCO 2 differences, and this is an important factor in contributing to the net annual air-sea CO 2 exchange. Factors related to the estimates of CO 2 fluxes in the coast ocean, such as the choice of wind speeds, the correction of gas transfer equations with nonlinearity coefficients, the effect of diel variations of pCO 2 , the spatial extrapolation of the pCO 2 to the nearshore area, and the seasonal interpolation are also discussed.

Abstract. Here we present monthly, basin-wide maps of the partial pressure of carbon dioxide (pCO2) for the North Atlantic on a 1° latitude by 1° longitude grid for years 2004 through 2006 inclusive. The maps have been computed using a neural network technique which reconstructs the non-linear relationships between three biogeochemical parameters and marine pCO2. A self organizing map (SOM) neural network has been trained using 389 000 triplets of the SeaWiFS-MODIS chlorophyll-a concentration, the NCEP/NCAR reanalysis sea surface temperature, and the FOAM mixed layer depth. The trained SOM was labelled with 137 000 underway pCO2 measurements collected in situ during 2004, 2005 and 2006 in the North Atlantic, spanning the range of 208 to 437 μatm. The root mean square error (RMSE) of the neural network fit to the data is 11.6 μatm, which equals to just above 3 per cent of an average pCO2 value in the in situ dataset. The seasonal pCO2 cycle as well as estimates of the interannual variability in the major biogeochemical provinces are presented and discussed. High resolution combined with basin-wide coverage makes the maps a useful tool for several applications such as the monitoring of basin-wide air-sea CO2 fluxes or improvement of seasonal and interannual marine CO2 cycles in future model predictions. The method itself is a valuable alternative to traditional statistical modelling techniques used in geosciences.

[1] The results of 1 year of automated pCO 2 measurements in 2002/2003 onboard the car carrier M/V Falstaff are presented and analyzed with regard to the driving forces that change the seawater pCO 2 in the midlatitude North Atlantic Ocean. The pCO 2 in surface seawater is controlled by thermodynamics, biology, air-sea gas exchange, and physical mixing. Here we estimate the effects on the annual cycle of pCO 2 and relate this property to parameters like SST, nitrate, and chlorophyll. On the basis of the amplitude in seawater pCO 2 for all 4°Â 5°grid boxes, this region can be separated into an eastern and western basin. The annual pCO 2 cycle in the eastern basin (10°W-35°W) is less variable, which can be related to the two counteracting effects of temperature and biology; air-sea gas exchange plays a minor role when using climatological MLD. In the western basin (36°W-70°W) the pCO 2 amplitude is more variable and strongly follows the thermodynamic forcing, since the biological forcing (as derived from nitrate concentrations) is decreased. Biology and air-sea exchange strongly depend on the MLD and therefore also include physical mixing effects. The pCO 2 data of the analyzed region between 34°N and 52°N compare well to the Takahashi et al. [2002] climatology except for regions north of 45°N during the wintertime where the bias is significant.