Aquafarming seaweed in the open ocean reduces pressure on coastal ecosystems, while creating new productive biodiverse habitats off-shore. Implementation poses huge engineering challenges and potential benefits. From all seaweeds, there is one that is particularly suited for open-ocean aquaculture. Holopelagic sargassum is a free-floating brown seaweed that rapidly divides by fragmentation, is very efficient at carbon uptake per unit of nutrient provided and creates a nursery habitat for diverse species. Its biomass is already converted into fossil-fuel replacing products (eg. fertilizers, emulsifiers and bioplastic). Aquafarming sargassum in nutrient replete areas will provide a stable feedstock for this nascent industry. To upscale production to the Gt scale, giant off-shore aquafarms can be created in the subtropical gyres. For fertilization, we investigated artificial upwelling of nutrient-rich deep water by harnessing salinity and temperature gradients. Our recent engineering advances on aquafarming barriers, model-based understanding of artificial upwelling pipes, and new discoveries on sargassums nutrient requirements, confirm the feasibility of sargassum aquafarming. Our study shows that combining artificial upwelling with seaweed aquafarming can alleviate some of the environmental impacts such as nutrient robbing. The formation of low oxygen areas in the deep sea, can be mitigated by processing and baling the biomass before sinking. Predicted environmental benefits include long-term carbon dioxide removal, enhanced open ocean biodiversity, and increased albedo.

Primary Presenter: Mar Fernandez Mendez, Alfred Wegener Institute (mar.fernandez-mendez@awi.de)

Authors:

Mar Fernández-Méndez, Alfred Wegener Institute / Seafields  (mar.fernandez-mendez@awi.de)

Miriam Philippi, Alfred Wegener Institute  (miriam.philippi@awi.de)

Julia Schnetzer, Alfred Wegener Institute  (julia.schnetzer@awi.de)

Franziska Elmer, Seafields Solutions  (franziska.elmer@seafields.eco)

Nicola Schwehm, Seafields Solutions  (nicola.schwehm@seafields.eco)

Tom Newton, Seafields Solutions  (tomnewton18@gmail.com)

Jason Cole, Carbonwave  (jcole@carbonwave.com)

Jost Kemper, Fachhochschule Kiel  (jkemper@geomar.de)

Jan Mense, Fachhochschule Kiel / GEOMAR   (jmense@geomar.de)

Brigitta van Tussenbroek, UNAM  (vantuss@cmarl.unam.mx)

Ulf Riebesell, GEOMAR  (uriebesell@geomar.de)

Victor Smetacek, Alfred Wegener Institute  (victor.smetacek@awi.de)