AUTHOR=Curbelo-Hernández David , González-Dávila Melchor , Santana-Casiano J. Magdalena 

TITLE=The carbonate system and air-sea CO2 fluxes in coastal and open-ocean waters of the Macaronesia

JOURNAL=Frontiers in Marine Science

VOLUME=10

YEAR=2023

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2023.1094250

DOI=10.3389/fmars.2023.1094250

ISSN=2296-7745

ABSTRACT=<p>The CO<sub>2</sub> system, anthropogenic carbon (C<sub>ant</sub>) inventory and air-sea CO<sub>2</sub> fluxes (FCO<sub>2</sub>) were analysed in the archipelagic waters of the Macaronesian region. The (sub)surface data were collected during POS533 (February and March, 2019) in coastal areas leeward of Cape Verde (CV), Canary Islands (CA) and Madeira (MA) and through the vessel track. The CO<sub>2</sub> variability was controlled by changes in temperature, biological activity and advection processes forced by spatial heterogeneities in the Canary Upwelling System, the mixed layer depth, the mesoscale activity and the circulation patterns. The surface <italic>f</italic>CO<sub>2,sw</sub> variability was driven by biological production and CO<sub>2</sub>-rich water injection in tropical waters and by temperature fluctuations in subtropical waters. The factors controlling the upper ocean changes in the total inorganic carbon normalized to a constant salinity (NC<sub>T</sub>) were assessed. The uptake and storage of anthropogenic carbon, calculated by using the TrOCA 2007 approach described, as an upper limit, &gt; 60% (&gt;90% above the MLD) of the NC<sub>T</sub> increase from preformed values. The organic carbon pump accounted 36.6-40.9% for tropical waters and lose importance for subtropical waters (7.5-11.6%), while the carbonate pump has a minimal contribution (&lt;4.2%). The upper-ocean C<sub>ant</sub> inventory in coastal areas of CV (8,570 Km<sup>2</sup>), CA (7.960 Km<sup>2</sup>) and MA (1,250 Km<sup>2</sup>) was 7.57 x 10<sup>3</sup>, 9.26 x 10<sup>3</sup> and 8.86 x 10<sup>3</sup> µmol kg<sup>-1</sup>, respectively (0.51, 0.58 and 0.09 Tg C, respectively). In terms of FCO<sub>2</sub>, the CV, CA and MA behaved as a winter CO<sub>2</sub> sink (-4.74, -3.90 and -8.34 mmol m<sup>-2</sup>d<sup>-1</sup>, respectively) while a strong outgassing was detected over the Cape Blanc filament (20-25 mmol m<sup>-2</sup>d<sup>-1</sup>). The total average FCO<sub>2</sub> for the ocean area of the three archipelagos (371,250 Km<sup>2</sup>) was -28.27 Gg CO<sub>2</sub> d<sup>-1</sup>. The POS533 data were compared and compilated with SOCAT and GLODAP data and a new set of equations was provided to calculate the <italic>f</italic>CO<sub>2,sw</sub>, C<sub>ant</sub> and FCO<sub>2</sub> in the Macaronesian region based on physical and biogeochemical properties.</p>