Distribution and variability of the dissolved inorganic carbon system in the Cariaco Basin, Venezuela

A study was conducted to characterize the variability of dissolved inorganic carbon concentration and speciation in surface waters (upper 100 m) of the southern Caribbean Sea in the Cariaco Basin, located off Venezuela. The spatial distribution of total CO2 (TCO2), partial pressure of CO2 (pCO2), and the saturation state with respect to aragonite (Ωarg) was evaluated by measuring pH and total alkalinity (TA) in transects across the Basin during upwelling (dry season in March 2004 and 2009) and during the rainy season (September 2006 and 2008). Alkalinity was more strongly related to salinity in the western half of the Cariaco Basin (R2 = 0.87 and R2 = 0.80 for September 2008 and March 2009, p < 0.001) than in the eastern sub-basin (R2 = 0.20, p > 0.01 for March 2004, and R2 = 0.37 and R2 = 0.31 for September 2008 and March 2009, p > 0.001). In the western sub-basin, high pH (> 8.1) and low pCO2 (< 380 μatm) were observed near the estuaries of the Tuy and Neveri Rivers. In the eastern sub-basin, pH was low (< 8.0) and pCO2 was high (> 400 μatm) in surface waters during upwelling. The TA-salinity relationship followed a two end-member mixing model (upwelled waters and river input). pCO2 in surface waters ranged from 366 to 525 μatm during upwelling (March), and 385 to 452 μatm during the rainy period (September). Waters were supersaturated with respect to aragonite saturation state throughout the Cariaco Basin. The Basin was typically over-saturated with CO2 with respect to the atmosphere. Under-saturation was only observed near the coast, such as near the mouth of the Tuy River. The flux of CO2 over most of the Cariaco Basin was generally from the ocean to the atmosphere in both seasons. Fluxes tend to remain between 0 and 10 mmol CO2 m− 2 day− 1, with average values for the whole basin of 11.39 ± 17.17 mmol CO2 m− 2 day−1 in March 2004, 7.19 ± 2.17 mmol CO2 m− 2 day−1 in September 2006, 6.32 ± 2.42 mmol CO2 m− 2 day−1 in September 2008 and 4.35 ± 3.97 mmol CO2 m− 2 day−1 in March 2009.