Seagrass meadows are increasingly recognized globally as a natural climate solution due to their significant potential for alkalinity-driven carbon dioxide (CO₂) removal, which may represent an overlooked component of ocean carbon sequestration. This study comprehensively investigated the carbonate chemistry, sediment carbon content, mineral composition, and benthic alkalinity fluxes at two distinct sites with tropical seagrass meadows: one located in organic carbon (OC)-rich reef sediments and the other in OC-poor terrestrial sediments. The results showed that benthic alkalinity fluxes were nearly two orders of magnitude higher in the OC-rich reefs than in the OC-poor sediments (72.8±64.4 vs. 0.53±0.99 mmol m⁻² d⁻¹). This could significantly increase alkalinity levels and reduce the partial pressure of CO₂ in the overlying seawater, thereby enhancing the capacity for CO₂ sequestration. Therefore, we suggest that seagrass meadows on high-OC reef sediments may serve as hotspots for alkalinity generation, thus amplifying the climate change mitigation potential of seagrass restoration initiatives.

blue carbon, seagrass, alkalinity