Understanding and estimating the role of large-scale seaweed cultivation for carbon sequestration on a global scale over the past two decades.

Seaweeds, as marine photosynthetic organisms, are harvested by humans from the wild or through cultivation for various production purposes and to provide a range of marine ecosystem services, including nutrient removal, oxygen production, and carbon sequestration. The potential use of cultivated seaweed in mitigating carbon dioxide (CO₂) has been extensively proposed in conjunction with commercial seaweed production worldwide. This study aims to assess the annual potential and benefits of cultivated seaweed in reducing and fixing anthropogenic CO₂. Over the past two decades (2000-2019), global seaweed production has seen significant growth. The total output of cultivated seaweed reached 407.4 × 10⁷ tons (t), with coastal mariculture removing 4.26 × 10⁷ t of carbon annually and wild capture removing 2.24 × 10⁶ t. The recalcitrant dissolved organic carbon (RDOC, 549.88-621.60 × 10⁴ t) plays a significant role in the carbon sinks of seaweed cultivation. The substantial benefits of carbon sink resulting from the formation of RDOC from seaweed make up a considerable proportion in the calculation of carbon sequestration and sink enhancement benefits in large-scale seaweed cultivation. The sizable carbon sink base of seaweed cultivation (8631.90-9567.37 × 10⁴ t) results in significant carbon fixation benefits. The total economic value of carbon sequestration and oxygen production was estimated at $70.36 ± 1.52 billion, with an annual average benefit of $3.52 ± 1.70 billion. Increasing the area and yield available for cultivated seaweed has the potential to enhance biomass production, carbon accumulation, and CO₂ drawdown. It is crucial to emphasize the need for improved communication regarding the essential criteria for the feasibility of CO₂ removal (CDR), with a focus on conducting life cycle assessments (LCA) when utilizing marine processes in the present and future work. The sustainable development of the seaweed cultivation industry not only ensures that Asian-Pacific countries remain leaders in this field but also provides an effective yet overlooked solution to excessive CO₂ emissions worldwide.