Seasonal variability of surface fCO2 in the Strait of Gibraltar

From September 2005 to May 2006 four cruises were performed in the Strait of Gibraltar to study the seasonal variability of carbon dioxide surface waters and assess the air-sea CO2 fluxes. Continuous water measurement of fugacity ofCO2 (fCO2), temperature and salinity was performed along the longitudinal and latitudinal axes of the Strait. Additionally, discrete surface water samples were taken to measure dissolved inorganic carbon (DIC) and oxygen. The spatial distribution of surface fCO2 showed low variability compared to the seasonal scale, with fCO2 values ranging from 329 matm in March to 387 matm in September. Seasonal variability of fCO2 was assessed and discussed in terms of temperature and biology, and the temperature was the main controlling factor. The Strait of Gibraltar is CO2 undersaturated most of the year, except in September, when the annual average CO2 uptake equals 0.28 mol C m 2 yr 1, if behaves as a discreet sink of CO2 on an annual scale