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.