Approach-dependent Effects of Ocean Alkalinity Enhancement on Particle Sinking Velocities

durch Emily Raab (FB2-BI)

Mittwoch 15.07.2026, 13:15 → 14:30 Europe/Berlin

5-1.213 - PAZIFIK / PACIFIC- Rechte Seite - Großer, unterteilbarer Konferenzraum (GEOMAR - Standort Ostufer / GEOMAR - East Shore)

Abstract:

Mitigating the environmental impacts of global warming requires carbon dioxide removal, e.g., via ocean alkalinity enhancement (OAE). However, before OAE can be deployed on a large scale, our understanding of the environmental impacts of the method must be improved. OAE has been investigated across different experimental settings and application methods to narrow this knowledge gap. Here, we conducted an across-study statistical comparison of three mesocosm experiments, applying liquid or particulate treatment to enhance the alkalinity within the mesocosms using a CO₂-equilibrated or unequilibrated approach. We measured and analyzed particle sinking velocities and export fluxes of particulate inorganic carbon in all studies. Both are drivers of the biological carbon pump, the main mechanism for carbon sequestration in the ocean and are of particular importance for the CO₂ removal efficiency of OAE. Consistent with previous studies, our findings indicate that liquid OAE, regardless of the equilibration state, had no impact on the selected parameters, provided that the precipitation thresholds for calcium carbonate are not crossed. For the particulate OAE approach, enhanced values were observed in both parameters, raising multiple concerns. Dissolution kinetics of the feedstocks and calcium carbonate precipitation were identified as the drivers of the observed changes. In a real-world scenario, the application of particulate OAE or liquid OAE at TA >1,800 μmol kg-1 could lead to alkalinity loss in surface waters caused by either feedstock particles sinking out of the mixed layer or by calcium carbonate precipitation producing CO₂. Consequently, surface waters could become oversaturated and leak CO₂ into the atmosphere.

Our findings suggest that particulate OAE poses a greater risk of reducing the approach’s efficacy than liquid OAE. Both approaches should be further tested in different experimental settings, prioritizing precipitation thresholds and assessing the context-dependency of our findings and their implications for the large-scale deployment of OAE.

Meeting link:
https://geomar.webex.com/geomar/j.php?MTID=ma1a0f968b01c74ed3a49c91d3eb51a04