Thermogravimetric analysis (TGA) for precipitate from shipboard ocean alkalinity enhancement (OAE) experiments in the North Atlantic on R/V Atlantic Explorer cruise AE2320 in September 2023

To explore mineral formation due to alkalinity addition, we present results from shipboard experiments in which an aqueous solution of NaOH was added to unfiltered seawater collected from the surface ocean in the Sargasso Sea. Alkalinity addition ranged from 500 to 2000 micromoles per kilogram (µmol.kg-1) and the carbonate chemistry was monitored through time by measuring total alkalinity (TA) and dissolved inorganic carbon (DIC), which were used to calculate Ω. The amount of precipitate and its mineralogy were determined throughout the experiments. Mineral precipitation took place in all experiments over a timescale of hours to days. The dominant mineralogy of precipitate is aragonite with trace amounts of calcite and brucite. Aragonite crystallite size increases and its micro-strain decreases with time, consistent with Ostwald ripening. This dataset contains TGA analysis for precipitate from an experiment where TA was enhanced by 2000 µmol.kg-1.