Temporal variability of atmospheric CO2 of the Spanish Atlantic Coast

The variability of the molar fraction of atmospheric CO2 (xCO(2)(a)) and wind speed and direction were investigated in a coastal embayment located in the west European coast, ria de Vigo, NW Spain, along daily and seasonal time scales. Observations in the ria showed that xCO(2)(a) on a short time scale presented a much wider variability than seawater molar fraction (xCO(2)(w)), in addition, a significant covariation between xCO(2)(a) and wind was found. A sluggish atmospheric renewal due to weak winds was associated with high values of xCO(2)(a), whereas higher oceanic winds renovate the air column with more stable and constrained xCO(2)(a) values (from 350 to 370 ppm). The impact of anomalously high xCO(2)(a) on CO2 air-sea fluxes is practically not significant, due to the kinetic control exerted by wind speed by means of the gas exchange coefficient. A seasonal cycle for the atmospheric molar fraction of CO2 in the Southwest European Coast was obtained. Using this approach for xCO(2)(a) in calculating the air-sea CO2 fluxes avoids under/overestimations of the fluxes on particular short periods of time, whilst using a mean xCO(2)(a) seasonal value for longer time scales has no significant effect on the final net magnitude of the air-sea flux.