Distribution of CO2 parameters in the Western Tropical Atlantic Ocean

•We subdivided our region of study into four sub regions according to the thermohaline condition.•High variability of TA and CT have been observed during boreal summer in the Amazon plume.•We observed strong correlation of TA and CT with SSS in the WTA.•After determine 0.9 ± 0.3 μmol kg−1 yr−1 as the trend on CT in the WTA, we determine a new relationship for CT.•High correlation is obtained with our computed pCO2 from our relationships with observed pCO2.

The variability of sea surface Total Alkalinity (TA) and sea surface Total Inorganic Carbon (CT) is examined using all available data in the western tropical Atlantic (WTA: 20°S-20°N, 60°W-20°W). Lowest TA and CT are observed for the region located between 0°N-15°N/60°W-50°W and are explained by the influence of the Amazon plume during boreal summer. In the southern part of the area, 20°S-10°S/40°W-60°W, the highest values of TA and CT are linked to the CO2-rich waters due to the equatorial upwelling, which are transported by the South Equatorial Current (SEC) flowing from the African coast to the Brazilian shore. An increase of CT of 0.9 ± 0.3 μmol kg−1yr−1 has been observed in the SEC region and is consistent with previous published estimates. A revised CT-Sea Surface Salinity (SSS) relationship is proposed for the WTA to take into account the variability of CT at low salinities. This new CT-SSS relationship together with a published TA-SSS relationship allow to calculate pCO2 values that compare well with observed pCO2 (R2 = 0.90).