Organic-inorganic carbon coupling shapes carbon dioxide fluxes in seagrass ecosystems

Abstract

Seagrass meadows can remove atmospheric carbon dioxide through organic carbon production and storage, but they also alter seawater chemistry through calcium carbonate formation and dissolution. Most blue carbon assessments focus on organic carbon burial and overlook how inorganic carbon cycling regulates carbon dioxide exchange. This Perspective presents a framework linking organic carbon metabolism, carbonate cycling, and sedimentary processes to explain when seagrass ecosystems function as net carbon dioxide sinks or sources. We introduce a compensation ratio that defines the balance between organic carbon uptake and calcification-driven carbon dioxide release and show how this balance changes with environmental conditions and sediment carbon sources. Using the Dongsha Island lagoon as a case study, we show how seagrass metabolism coupled to dissolution of geologically derived carbonate sediments can sustain alkalinity generation and long-term carbon dioxide uptake. Together, this framework provides a more complete basis for evaluating blue carbon and the climate mitigation potential of carbonate-rich coastal ecosystems.