Marine carbon dioxide removal (mCDR) is a growing field of research to help address and mitigate climate change. As different strategies move from laboratory experiments to field trials and deployments, it is increasingly important to address knowledge gaps revolving around how to measure and quantify the efficacy and impacts of an intervention.

In several of these strategies, including ocean alkalinity enhancement (OAE) and nutrient fertilization, particles play a critical role in the efficacy of an intervention. For example, in mineral-based OAE, crushed alkaline material is added to seawater that dissolves over time, reacting with carbon dioxide and water to form stable bicarbonate. The dissolution of the alkaline feedstock is governed by its particle size distribution, particle shape, concentration, and other properties along with the local environmental conditions. Measuring these properties is critical to understanding the extent to which the alkaline material dissolves, settles to the seafloor, and/or results in secondary precipitation or other impacts. However, there are few in situ measurements reported for particle properties such as size distribution, and frequently simplifying assumptions about particle properties are used in modeling efforts related to alkalinity dissolution. This knowledge gap must be addressed to improve in situ monitoring efforts related to OAE efficacy and impacts and to help validate and update models used to predict alkalinity dissolution and transport.

Here we will focus on particle measurements as it relates to mineral-based OAE. We will present results from laboratory experiments focused on measuring key particle properties of alkaline feedstock material during dissolution. We will describe the LISST sensors used in this study and the different optical techniques they employ for measuring particle size, concentration, and settling velocity. We will present measurements quantifying key particle properties and how the properties change over time during material dissolution. We will discuss the implications of these measurements for measuring and monitoring an OAE intervention. Finally, we will use the results to provide recommendations for how to study particles in the laboratory and field across different mCDR strategies.

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