Seaweed farms enhance alkalinity production and carbon capture

Seaweed aquaculture is increasingly being explored as a sustainable source of food and industrial processing feedstock, as well as a potential climate solution through carbon dioxide removal. In this study, we use a sediment diagenetic model to quantify how elevated organic carbon fluxes beneath seaweed farms enhance sedimentary alkalinity fluxes, contributing to long-term carbon dioxide sequestration. Our stochastic simulations suggest that enhanced alkalinity production under seaweed farms could remove an average of ~0.85 tonnes of carbon dioxide per hectare per year (range: ~0.1–2 tonnes per hectare per year). These findings highlight a previously underappreciated mechanism of ocean-based carbon dioxide removal associated with seaweed farming. Monetizing this carbon removal—through voluntary carbon markets, policy incentives, or supply-chain insetting—could provide an additional income stream, supporting both the economic viability of seaweed aquaculture and its potential to scale as a climate mitigation strategy. Increased organic carbon fluxes beneath seaweed farms can enhance sedimentary alkalinity fluxes, contributing to long-term carbon dioxide sequestration, according to the results from sediment diagenetic modelling.