Abstract
The seasonal and spatial variability of the CO2 system and air-sea fluxes were studied in surface waters of the Strait of Gibraltar between February 2019 and March 2021. High-resolution data was collected by a surface ocean observation platform aboard a volunteer observing ship. The CO2 system was strongly influenced by temperature and salinity fluctuations forced by the seasonal and spatial variability in the depth of the Atlantic–Mediterranean Interface layer and by the tidal and wind-induced upwelling. The changes in seawater CO2 fugacity (fCO2,sw) and fluxes were mainly driven by temperature despite the significant influence of non-thermal processes in the southernmost part. The thermal to non-thermal effect ratio (T/B) reached maximum values in the northern section (>1.8) and minimum values in the southern section (<1.30). The fCO2,sw increased with temperature by 9.02 ± 1.99 μatm °C–1 (r2 = 0.86 and ρ = 0.93) and 4.51 ± 1.66 μatm °C–1 (r2 = 0.48 and ρ = 0.69) in the northern and southern sections, respectively. The annual cycle of total inorganic carbon normalized to a constant salinity of 36.7 (NCT) was assessed. Net community production processes described 93.5–95.6% of the total NCT change, while air-sea exchange and horizontal and vertical advection accounted for <4.6%. The fCO2,sw in the Strait of Gibraltar since 1999 has been fitted to an equation with an interannual trend of 2.35 ± 0.06 μatm year–1 and a standard error of estimate of ±12.8 μatm. The seasonality of the air-sea CO2 fluxes reported the behavior as a strong CO2 sink during the cold months and as a weak CO2 source during the warm months. Both the northern and the southern sections acted as a net CO2 sink of −0.82 and −1.01 mol C m–2 year–1, respectively. The calculated average CO2 flux for the entire area was −7.12 Gg CO2 year–1 (−1.94 Gg C year–1).
Highlights
Coastal and transition to open-ocean areas are biogeochemically active regions which play a key role in the global carbon cycle by assembling multiple diverse ecosystems and linking the terrestrial, oceanic, and atmospheric carbon reservoirs
The greatest seasonal change occurs from winter to summer: the SST, f CO2,sw, and FCO2 increased in the northern section by 4.79 ± 1.97◦C, 40.75 ± 28.83 μatm, and 5.52 ± 4.19 mmol m−2 d−1, respectively, leading to a pH in total scale (pHT) decrease of 0.039 ± 0.028 U
The spatio-temporal variability of the CO2 system and fluxes in the Strait of Gibraltar was assessed with a high-resolution dataset in this study
Summary
Coastal and transition to open-ocean areas are biogeochemically active regions which play a key role in the global carbon cycle by assembling multiple diverse ecosystems and linking the terrestrial, oceanic, and atmospheric carbon reservoirs. These regions are characterized by primary production, carbon fixation, and remineralization ratios significantly higher than in the open oceans due to higher supplies of organic and inorganic carbon (Walsh, 1991; Mackenzie et al, 1998; Borges et al, 2005; Muller-Karger et al, 2005) and show a high spatio-temporal variability. The recent IPCC report 2021 (IPCC, 2021) together with the 2007 report (IPCC, 2007), highlighted the need of study of marginal seas, continental shelves, and semienclosed seas due to the variability on the biogeochemical cycles as well as the human pressure
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
