Air–sea CO 2 fluxes in the north-eastern shelf of the Gulf of Cádiz (southwest Iberian Peninsula)

Abstract

An intra-annual investigation of the fugacity of CO 2 ( fCO 2) has been conducted in surface waters of the north-eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula) in four cruises made in 2006 and 2007. Intra-annual variability of fCO 2 was assessed and is discussed in terms of mixing, temperature and biology. In the study area of the shelf, thermodynamic control over fCO 2 predominates from early May to late November, and this is opposite and similar in magnitude to the net biological effect. However, biological control over fCO 2 predominates during winter. The results suggest that surface waters in the coastal area are under-saturated with respect to atmospheric CO 2 during most of the year; therefore they represent a sink for atmospheric CO 2 between November and May (− 1.0 mmol m − 2 day − 1 ), but a weak source in June (1.3 mmol m − 2 day − 1 ). In contrast, the coastal ecosystems studied (the lower estuary of Guadalquivir Estuary and Bay of Cádiz) acted as a weak sink for atmospheric CO 2 during February (− 1.3 mmol m − 2 day − 1 ) and as a source between May and November (2.6 mmol m − 2 day − 1 ). The resulting mean annual CO 2 flux in the north-eastern shelf of the Gulf of Cádiz was − 0.07 mol m − 2 year − 1 (− 0.2 mmol m − 2 day − 1 ), indicating that the area acts as a net sink on an annual basis.