Abstract
Abstract. Spatio-temporal variations in the partial pressure of CO2 (pCO2) were studied during eight oceanographic cruises conducted between March 2014 and February 2016 in surface waters of the eastern shelf of the Gulf of Cádiz (SW Iberian Peninsula) between the Guadalquivir river and Cape Trafalgar. pCO2 presents a range of variation between 320.6 and 513.6 µatm with highest values during summer and autumn and lowest during spring and winter. For the whole study, pCO2 shows a linear dependence with temperature, and spatially there is a general decrease from coastal to offshore stations associated with continental inputs and an increase in the zones deeper than 400 m related to the influence of the eastward branch of the Azores Current. The study area acts as a source of CO2 to the atmosphere during summer and autumn and as a sink in spring and winter with a mean value for the study period of -0.18±1.32 mmol m−2 d−1. In the Guadalquivir and Sancti Petri transects, the CO2 fluxes decrease towards offshore, whereas in the Trafalgar transect fluxes increase due to the presence of an upwelling. The annual uptake capacity of CO2 in the Gulf of Cádiz is 4.1 Gg C yr−1.
Highlights
Continental shelves play a key role in the global carbon cycle as this is where the interactions between terrestrial, marine and atmospheric systems take place (Mackenzie et al, 1991; Walsh, 1991; Smith and Hollibaugh, 1993)
A high variability in pressure of CO2 (pCO2) in the Gulf of Cádiz was observed which is associated with its location as a transition zone between coastal and shelf areas, superimposed on the usual seasonal variation due to thermal and biological effects
The mean value of pCO2 found in this study (398.9 ± 15.5 μatm) indicates that the Gulf of Cádiz could be slightly undersaturated in CO2 with respect to the atmosphere (402.1 ± 3.9 μatm)
Summary
Continental shelves play a key role in the global carbon cycle as this is where the interactions between terrestrial, marine and atmospheric systems take place (Mackenzie et al, 1991; Walsh, 1991; Smith and Hollibaugh, 1993). These zones are considered to be among the most dynamic in biogeochemical terms (Wollast, 1991; Bauer et al, 2013) as they are affected by several factors, high rates of primary production, remineralization and organic carbon burial (Walsh, 1988; Wollast, 1993; de Haas et al, 2002). The discrepancies with respect to this estimation derive from the different definitions of the continental shelf domain and the skewed distribution of local studies (Laruelle et al, 2010)
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