Synergistic CO2 Removal via Enhanced Olivine Weathering and Diatom Growth in the Ocean

Abstract

Enhancing the alkalinity of the ocean is a promising approach for CO2 removal by promoting marine carbon sequestration. Olivine is a key candidate material for enhancing alkalinity owing to its release of silicates when dissolved in seawater. These released compounds serve as crucial nutrients for phytoplankton such as diatoms to foster their growth, which in turn accelerates olivine dissolution and further enhances carbon sequestration. In this study, we investigated the short-term synergistic CO2 removal effects of an olivine–diatom coculture system. Over a 6-day incubation period, the olivine dissolution was 92% to 144% higher in the olivine–diatom groups compared with the olivine-only groups. The olivine-only groups achieved a CO2 removal efficiency of 5.15% to 5.49%, while the olivine–diatom groups achieved a CO2 removal efficiency of 8.84% to 14.44%. Adding olivine was found to increase the total alkalinity by 70 to 100 μM and the diatom abundance by 26.4% to 58.4%. Diatom growth and the fixed carbon content were greatly enhanced, particularly during the later silicate-depleted stage when the Si:C ratio significantly exceeded that of groups without olivine. This mutually beneficial olivine–diatom coculture system offers a highly efficient CO2 removal strategy for addressing climate change. The results of this study contribute to our understanding of carbonate and biological carbon pump processes.