Sequestration and storage of carbon in the sea through Sargassum aquafarms: Open ocean seaweed aquafarming has a high potential for large scale natural carbon dioxide removal. Pelagic Sargassum is of particular interest due to its fast reproduction by fragmentation and high carbon to nutrient ratio. Originally from the Sargasso Sea, nowadays it grows across the tropical Atlantic and causes problems to coastal ecosystems and tourism-based economies when it reaches the coast in large quantities. Companies valorising this biomass, face the problems of a highly variable supply. Therefore, aquafarming Sargassum could benefit this nascent industry and contribute to mitigate climate change. To expand the areas where Sargassum can grow and cultivate it in large quantities, the currently unproductive subtropical gyres will need to be irrigated by artificial upwelling. To sequester carbon in seaweed biomass for long time scales, the harvested biomass can be converted to durable, alternative plastics, or it can be processed and compacted into bales, stored on the abyssal plain providing safe and long-lasting carbon dioxide sequestration.