Temporal variability of atmospheric CO2 of the Spanish Atlantic Coast

The variability of the molar fraction of atmospheric CO2 (xCO(2)(a)) and wi nd speed and direction were investigated in a coastal embayment located in the west European coast, ria de Vigo, NW Spain, along daily and seasonal ti me scales. Observations in the ria showed that xCO(2)(a) on a short time sc ale 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 wit h high values of xCO(2)(a), whereas higher oceanic winds renovate the air c olumn with more stable and constrained xCO(2)(a) values (from 350 to 370 pp m). The impact of anomalously high xCO(2)(a) on CO2 air-sea fluxes is pract ically not significant, due to the kinetic control exerted by wind speed by means of the gas exchange coefficient. A seasonal cycle for the atmospheri c 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 u nder/overestimations of the fluxes on particular short periods of time, whi lst using a mean xCO(2)(a) seasonal value for longer time scales has no sig nificant effect on the final net magnitude of the air-sea flux. (C) 2001 If remer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.