CO2 Removal from Oceans through Sargassum Macroalgae

Alyson Myers, Organization Not Listed, Washington, DC, United States, Margaux Filippi, Fearless Fund, Washington, DC, United States and Zach Moscicki, Fearless Fund, United States
Surplus concentrations of CO2 in our atmosphere require carbon removal to reduce the impact of climate change. While much attention has focused on land-based strategies (reforestation, storage in soils, etc), marine taxa can play a significant role. Floating macroalgae Sargassum Natans and S. Fluitans, for instance, have a carbon content of approximately 30% and can be farmed for the purpose of carbon removal. Currently, natural CDR processes remove an estimated 22 Gt of CO2 from the atmosphere annually, moderating the climate effects of the current 41 Gt per year of emissions. The target for removal prices is currently at $100 per tonne.

Since 2011, massive blooms of Sargassum macroalgae have increasingly occurred in the Caribbean Sea, the Gulf of Mexico and the Atlantic Ocean, beaching onto the coast and causing significant nuisance for the environment, for public health and for local economies, especially for tourism-dependent island nations. This team, funded by the U.S. Department of Energy’s ARPA-E MARINER program, has focused on a dual-pronged strategy for these macroalgae. Initially, the team harvests nuisance Sargassum in offshore waters before they cause economic and environmental hardship. Second, if feasible, the team shall conduct controlled farming of these same plants to accelerate CO2 uptake. Both of these strategies have the potential to lower ocean acidification locally--an added benefit. Using remote sensing, satellite imaging and ocean modeling, the goal is to target mats of Sargassum before they beach.
Utilization of the biomass will focus on long term carbon storage. The team’s current CO2 removal price averages $300 per ton but can potentially fall with efficiencies in logistics. Preliminary techno-economic analyses for the Quintana Roo coast, Mexico, for example, revealed that the harvest cost estimates could be less than $100 per dry tonne of algae.