Substantial Limitations of Ocean Alkalinity Enhancement in Mitigating the Negative Impacts of Ocean Acidification on Marine Calcifiers
Hanna van de Mortel, Nina Bednaršek, Greg Pelletier, Richard A. Feely, Jens D. Müller, Nicolas Gruber
TL;DR
Ocean Alkalinity Enhancement may not fully restore marine calcifier health despite its potential to reduce ocean acidification.
Contribution
Quantifies the limited effectiveness of OAE in reversing calcification losses in marine calcifiers under various scenarios.
Findings
Historical calcification losses in marine calcifiers range from 7% to 44% due to ocean acidification.
Restoring calcification rates via OAE requires large alkalinity additions (up to 104 μmol kg–1) and is limited to 0–52.2% recovery.
Higher CO2 drawdown efficiency reduces the potential for biological ocean acidification mitigation.
Abstract
Ocean Alkalinity Enhancement (OAE) is increasingly considered as a marine carbon dioxide removal (mCDR) strategy with the potential cobenefit of mitigating ocean acidification (OA), but this remains poorly constrained. Here, we evaluate these biological cobenefits for 27 marine calcifiers whose calcification has declined under OA, by quantifying both historical OA-driven calcification losses and the potential of OAE to reverse them under scenarios with and without air–sea equilibration. Regression models describing calcification as a function of TA-DIC reveal substantial declines since preindustrial times, particularly in linear responders (mean 22%, range 7–44%), such as gastropods and pteropods, while threshold responders show minimal decline (∼3%). A realistic addition of 50 μmol kg–1 of OAE alkalinity restores species-specific calcification rates maximally only between 0 and 52.2%,…
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Taxonomy
TopicsOcean Acidification Effects and Responses · CO2 Sequestration and Geologic Interactions · Methane Hydrates and Related Phenomena