Estimates and Variability of the Air-Sea CO₂ Fluxes in the Gulf of Guinea during the 2005-2007 Period

Abstract

Measurements of CO 2 parameters ( i.e. Total Alkalinity (TA) and Dissolved Inorganic Carbon (DIC)) were made from June 2005 to September 2007 in six EGEE (“Etude de la circulation océanique et de savariabilitédans le Golfe de GuinEE”) cruises to better assess air-sea CO 2 fluxes in the Gulf of Guinea (6 ° N - 10 ° S, 10 ° E - 10 ° W). Two empirical relationships TA-Salinity and DIC-Salinity-Temperature were established. These relationships were then used to estimate the monthly fugacity of CO 2 (fCO 2 ) and air-sea CO 2 fluxes. The monthly mean flux of CO 2 reaches 1.76 ± 0.82 mmol·m -2 ·d -1 (resp. 2.90 ± 1.45 mmol·m -2 ·d -1 ) at the north of the Equator (resp. at the South). The north-south gradient observed as the patterns of the air-sea CO 2 fluxes was mainly driven by the oceanic fCO 2 . This gradient was due to the low values of the CO 2 parameters flowing by the Guinea Current (6 ° N - 0 ° ) from the west to the east while the air-sea CO 2 fluxes increased in the south (10 ° S - 0). In the north, the climatology of Takahashi underestimated the CO 2 fluxes in the Gulf of Guinea when comparing to the estimated fluxes. This was due to the north-south gradient, which did not well reproduce by the climatology of Takahashi.