Preprints
https://doi.org/10.5194/egusphere-2023-2868
https://doi.org/10.5194/egusphere-2023-2868
11 Dec 2023
 | 11 Dec 2023

Ocean alkalinity enhancement using sodium carbonate salts does not impact Fe dynamics in a mesocosm experiment

David González-Santana, María Segovia, Melchor González-Dávila, Librada Ramírez, Aridane G. González, Leonardo J. Pozzo, Veronica Arnone, Victor Vázquez, Ulf Riebesell, and J. Magdalena Santana-Casiano

Abstract. The addition of carbonate minerals to seawater through an artificial Ocean Alkalinization Enhancement (OAE) process increases the concentrations of hydroxide, bicarbonate, and carbonate ions. This leads to changes in the pH and the buffering capacity of the seawater. Consequently, OAE could have relevant effects on marine organisms and in the speciation and concentration of trace metals that are essential for their physiology. During September and October 2021, a mesocosm experiment was carried out in the coastal waters of Gran Canaria (Spain), consisting of different levels of total alkalinity (TA). Different concentrations of carbonate salts (NaHCO3 and Na2CO3) previously homogenized were added to each mesocosm to achieve an alkalinity gradient between ∆0 to 2400 μmol L-1. The lowest point of the gradient was 2400 µmol kg-1, being the natural alkalinity of the medium, and the highest point was 4800 µmol kg-1. Iron (Fe) speciation was monitored during this experiment to analyse whether total dissolved iron (TdFe), dissolved iron (dFe), soluble iron (sFe), dissolved labile iron (dFe´), iron-binding ligands (LFe) and their conditional stability constants (K'FeL), could change because of OAE and the experimental conditions in each mesocosm. Observed iron concentrations were within the expected range for coastal waters, with no significant increases due to OAE. However, there were variations in Fe size fractionation during the experiment. This could potentially be due to chemical changes caused by OAE, but such effect being masked by the stronger biological interactions. In terms of size fractionation, sFe was below 1 nmol L-1, dFe concentrations were within 0.5-4.0 nmol L-1, and TdFe within 1.5-7.5 nmol L-1. Our results show that over 99 % of Fe was complexed, mainly by L1 and L2 ligands with k´Fe’L ranging between 10.92±0.11 and 12.68±0.32, with LFe ranging from 1.51±0.18 to 12.3±1.8 nmol L-1. Our data on iron size fractionation, concentration, and iron-binding ligands substantiate that the introduction of sodium salts in this mesocosm experiment did not modify iron dynamics. As a consequence, phytoplankton remained unaffected by alterations in this crucial element.

David González-Santana, María Segovia, Melchor González-Dávila, Librada Ramírez, Aridane G. González, Leonardo J. Pozzo, Veronica Arnone, Victor Vázquez, Ulf Riebesell, and J. Magdalena Santana-Casiano

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2868', Anonymous Referee #1, 18 Jan 2024
    • AC1: 'Reply on RC1', David González-Santana, 20 Feb 2024
  • RC2: 'Comment on egusphere-2023-2868', Anonymous Referee #2, 22 Jan 2024
    • AC2: 'Reply on RC2', David González-Santana, 20 Feb 2024
David González-Santana, María Segovia, Melchor González-Dávila, Librada Ramírez, Aridane G. González, Leonardo J. Pozzo, Veronica Arnone, Victor Vázquez, Ulf Riebesell, and J. Magdalena Santana-Casiano
David González-Santana, María Segovia, Melchor González-Dávila, Librada Ramírez, Aridane G. González, Leonardo J. Pozzo, Veronica Arnone, Victor Vázquez, Ulf Riebesell, and J. Magdalena Santana-Casiano

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Short summary
In a recent experiment off the coast of Gran Canaria (Spain), scientists explored a method called Ocean Alkalinization Enhancement (OAE), where carbonate minerals were added to seawater. This process changed the levels of certain ions in the water, affecting its pH and buffering capacity. The researchers were particularly interested in how this could impact the levels of essential trace metals in the water.