T12[Topic] Latest Studies in Sedimentary Geology

entryECS: Early Career Scientist

[T12-P-15] Investigation of CO₂ sequestration through calcification by marine cyanobacteria using stromatolite formation mechanisms★2026年度学生優秀発表賞受賞★

*Ren EINAGA¹, Masahiro HAYASHI², Fumito SHIRAISHI¹ (1. Hiroshima University, Graduate School of Advanced Science and Engineering, Program of Earth and Planetary Systems Science, 2. ENEOS Corporation)

Keywords:

Stromatolite,Calcification,Cyanobacteria,CCS,Microelectrode

As a measure against global warming, the importance of carbon dioxide capture and storage (CCS) is increasing. In the ancient Earth, stromatolites were formed in marine environments by microorganisms such as cyanobacteria that precipitated CaCO₃, fixing large amounts of CO₂. Focusing on this process, this study evaluated the CO₂ sequestration capacity of marine cyanobacteria through calcification (i.e., CaCO₃ precipitation).Marine cyanobacteria Calothrix parasitica (NIES-267) was obtained from the National Institute for Environmental Studies (NIES) and matted on glass filters. This sample was placed in a flow cell filled with artificial seawater and incubated under a light intensity of approximately 1000 µmol/m²/s. pH, O₂ concentration, and Ca²⁺ concentration were measured near the mat surface (within 1 mm from the surface) using microelectrodes. The flux was calculated from the obtained Ca²⁺ concentration gradient. As the evaluation criterion, the Ca²⁺ flux equivalent to the forest CO₂ absorption rate of 10 t-CO₂/ha/year was set as the target value (5.28 × 10⁻⁷ mol/m²/s).The results of experiments revealed that Calothrix formed a thick mat with high adhesion properties, and the Ca²⁺ flux met or exceeded the target value. Indeed, SEM-EDS analysis of recovered Calothrix samples confirmed the presence of CaCO₃ precipitates.Based on these results, it is concluded that Calothrix is highly suitable for calcification and CO₂ sequestration in marine environments.In the future, we plan to conduct long-term experiments using Calothrix under a 12-hour light-dark cycle that more closely approximates natural conditions, aiming to achieve an increase in CaCO₃ precipitation and conduct a quantitative evaluation.