Seasonal variability of surface fCO₂ in the Strait of Gibraltar

Abstract:

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 of CO₂ (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 µatm in March to 387 µatm 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.