Lethal by Design? Resolving Differences Between Experimental and Real‐World Alkalinity Perturbations in Ocean Alkalinity Enhancement

Abstract

Ocean alkalinity enhancement (OAE) aims to mitigate climate change by increasing the chemical capacity of seawater to store anthropogenic CO ₂ . OAE can be implemented through multiple pathways, each of which intentionally modifies marine carbonate chemistry through increases in total alkalinity (TA). Experimental research has only recently begun to assess how such TA perturbations (ΔTA) and associated carbonate chemistry changes affect ocean ecosystems. Meaningful assessments need context on how ΔTA‐induced by different OAE pathways would evolve over time and in magnitude. Here, we use a dilution equation, a regional model, and a global model to explore how marine organisms would be exposed to ΔTA under realistic constraints. We find that a more extreme ΔTA of>1,000 μmol kg ⁻¹ , a perturbation common in OAE experiments, only occurs for minutes in a minuscule fraction of the OAE‐perturbed seawater volume. In contrast, ΔTA between 1 and 100 μmol kg ⁻¹ is a ubiquitous perturbation range for OAE under real‐world constraints, yet are not commonly in focus of environmental OAE assessments. These results suggest that there is a disconnect between real‐world ΔTA that can plausibly be invoked by OAE and the experimental ΔTA range frequently used in the environmental OAE assessment. While “unrealistic” ΔTA can provide mechanistic insights into an organism or ecosystem response to carbonate chemistry changes, they can also cause overestimation of OAE effects, if the unrealistic ΔTA is not contextualized appropriately. Our results can be used to improve the contextualization of OAE studies, thereby making the interpretation of ΔTA effects on the environment more robust.