Impact of physical processes on the seasonal distribution of the fugacity of CO2 in the western tropical Atlantic

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.

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Lefevre Nathalie, Urbano Domingos F., Gallois Francis, Diverres Denis (2014). Impact of physical processes on the seasonal distribution of the fugacity of CO2 in the western tropical Atlantic. Journal Of Geophysical Research-oceans. 119 (2). 646-663.,

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