Carbonate chemistry of competitive dissolution experiment

The archived dataset was collected during a laboratory experiment, conducted between April 2021 and April 2022 at McGill University, in which we tested the competitive carbonate dissolution hypothesis. A mixture of biogenic and synthetic carbonates was reacted with acidified, natural seawater to simulate the progressive acidification of ocean waters by anthropogenic carbon dioxide (CO2). The biogenic material (Goniolithon, a high-magnesium (Mg) calcite red algae, and Halimeda, an aragonitic green algae) was collected off the coast of Andros, Bahamas in November 2019, whereas the ACS-grade synthetic calcite was purchased from Fisher Scientific®. The natural seawater was collected at ~400 m depth in the Gulf of St. Lawrence. The reaction was conducted in 350 mL of natural seawater with 0.3133 g of Goniolithon, 0.3020 g of Halimeda and 0.3068 g of synthetic calcite in a 500 mL water-jacketed glass reaction vessel maintained at 25.0 °C by recirculating water from a constant temperature bath through the reactor jacket. Results of this study confirm the hypothesis that carbonates will dissolve sequentially according to their respective solubility. They also reveal that the dissolution of high Mg-calcites proceeds incongruently. The originality of this contribution rests with the demonstration that the presence of a single high Mg-calcite will generate, like in a sediment of mixed mineralogy, a continuum of transient states as lower Mg-calcites of greater stability are precipitated and dissolved.