Estuarine CO2 gas transfer kinetics (Corpus Christi Bay, Texas)

Carbon dioxide (CO2) flux across the air-water interface at a location (27.724˚N, 97.341˚W) in Corpus Christi Bay, a subtropical estuary in northwestern Gulf of Mexico, was studied over the course of five weeks from November 16th to December 13th, 2018. CO2 flux was measured using the eddy covariance technique. In addition, CO2 concentration in both the atmosphere and sea surface was obtained. Gas transfer velocities were then mathematically derived from combination of CO2 flux measurements and concentration differences. Gas transfer velocity was modeled as a function of wind speed. Corpus Christi Bay was found to be a net sink of CO2 from the atmosphere for the period of study. Average flux was -0.27 μmol m-2 s-1. Small differences in estuarine and atmospheric CO2 concentrations (<100 ppm) were observed during the study period. Due to limited temporal data coverage, it was not possible to make long-term statements about CO2 movement into and out of Corpus Christi Bay from this study. Gas transfer velocity was modeled as a function of wind speed (3.6 m s-1 < U10 < 12.5 m s−1), where k660 = 0.36U103 (R2 = 0.64). At wind speeds below 3.6 m s-1, wind-induced turbulence contributed only 15% to gas transfer as other factors e.g., surfactant contribution and tidal motion, played a dominant role. Overall gas velocity was high (with a mean k660 of 146 cm hr-1), with average values approximately 10 times those found in other estuarine studies. Bottom-driven turbulence caused by low water depth at the study site in addition to high average wind speeds may have caused the large gas transfer velocities.