The Physiological Response of Contrasting Coccolithophore Species to Ocean Alkalinity Enhancement

Journal article

Plain Language Summary: The marine Carbon Dioxide Removal industry is expanding rapidly, highlighting the need for a better understanding of its environmental impacts. One underexplored area is the effect of Ocean Alkalinity Enhancement (OAE) on marine calcifiers. This study investigates the effects of OAE on two coccolithophore species, Gephyrocapsa huxleyi and Coccolithus braarudii, which play significant roles in carbon cycling. Our findings indicate that the rate of CO2 supply, correlated with bicarbonate concentration, is the primary factor influencing growth and calcification rates in both species. Notably, the larger, heavily calcified C. braarudii had a higher carbon demand than the smaller G. huxleyi, which could explain their differing responses to OAE treatments. Both species growth faster with increasing total alkalinity, suggesting they could thrive under air‐equilibrated OAE conditions. However, higher total alkalinity levels constrained calcification rates for faster‐growing cells, leading to malformations. While our experimental conditions exceed typical field trial parameters, this study provides important insights into safe operational boundaries and the likely impacts on major calcifying organisms in marine ecosystems.

Authors: Gill, S; Ge, J; Zhang, Q; Henderson, GM; Rickaby, REM

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Geophysical Union
• Journal: Journal of Geophysical Research: Biogeosciences
• Volume: 130
• Issue: 11
• Article number: e2025JG009103
• Publication date: 2025-11-17
• Acceptance date: 2025-10-30
• DOI: 10.1029/2025jg009103
• EISSN: 2169-8961
• ISSN: 2169-8953
• Language: English
• Keywords: ocean alkalinity enhancement; growth; coccolithophore; photosynthesis; calcification; marine carbon dioxide removal