Mineral formation during shipboard ocean alkalinity enhancement experiments in the North Atlantic

作者：Mohammed S. Hashim, Lukas Marx, Frieder Klein, Chloe L. Dean, Emily Burdige, Matthew Hayden, Daniel C. McCorkle, Adam V. Subhas · 发表于：Biogeosciences · 年份：2025 · DOI：10.5194/bg-22-7149-2025 · 被引用次数：6 · 研究领域：CO2 Sequestration and Geologic Interactions、Methane Hydrates and Related Phenomena、Ocean Acidification Effects and Responses

Abstract. Ocean alkalinity enhancement (OAE) is a carbon dioxide (CO2) removal approach that involves the addition of alkaline substances to the marine environment to increase seawater buffering capacity and allow it to absorb more atmospheric CO2. Increasing seawater alkalinity leads to an increase in the saturation state (Ω) with respect to several minerals, which may trigger mineral precipitation, consuming the added alkalinity and thus decreasing the overall efficiency of OAE. 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 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 precipitate phase is aragonite with trace amounts of calcite and magnesium hydroxide (MgOH2, i.e., brucite). Aragonite crystallite size increases and its micro-strain decreases with time, consistent with Ostwald ripening. The precipitation rate (r) in our experiments and those of other OAE-related calcium carbonate precipitation studies correlate with the aragonite saturation stat...