Calcium distribution in the subtropical Atlantic Ocean: Implications for calcium excess and saturation horizons

• Published in: Journal of Marine Systems
• Main Authors: Rosón, Gabriel, Fernández-Guallart, E., Pérez, Fiz F., Ríos, Aida F.
• Other Authors: Ministerio de Economía y Competitividad (España)
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2016
• Subjects: Calcium; Alkalinity; Aragonite; Calcite; Seawater; North Atlantic; Arctic
• Online Access: http://hdl.handle.net/10261/129516; https://doi.org/10.1016/j.jmarsys.2016.01.011; https://doi.org/10.13039/501100003329

7 páginas, 1 tabla, 4 figuras This study constituted the first attempt to measure dissolved calcium ([Ca2 +]meas) in the subtropical North Atlantic, during a zonal transoceanic cruise along 24.5°N (WOCE A05 section), in summer 1992. [Ca2 +]meas was obtained in 20 full-depth equidistant stations along the section, showing that their gradients are rather sensitive to horizontal and vertical water mass distribution. Deep waters along 24.5°N systematically show a positive calcium excess of 20 ± 14 μmol·kg− 1, i.e., more [Ca2 +] than expected by CaCO3 dissolution and organic matter oxidation (estimated by total alkalinity and nitrate). CaCO3 settling and benthic dissolution accounts for 70% and the North Atlantic plus Arctic riverine inputs of HCO3− for the remaining 30%. Combining [Ca2 +]meas and CO2 data sets, carbonate mineral saturation states distributions for aragonite and calcite can be obtained. The two solubility ratios resulted, on average, 0.5% smaller than if conservative behavior for Ca2 + was assumed (an approach widely followed when [Ca2 +]meas is unknown). As a result, shallower saturation horizon depths for both carbonate states (19 dbar for aragonite and 10 dbar for calcite) are yielded if [Ca2 +]meas is taken into account instead than estimated from salinity This work has been performed under the project BOCATS (CTM2013-41048-P) supported by the Spanish Government and co-founded by the European Regional Development Fund (FEDER) Peer reviewed