To limit warming below 2°C, we must implement a robust carbon dioxide reduction (CDR) strategy. Short-term CDR solutions can bridge the gap between the urgent need to reduce atmospheric carbon and the decades needed for permanent CDR technologies to mature. One short-term CDR solution is to use fast-growing macroalgae to capture carbon and sequester biomass in the deep ocean. Macroalgae do not require arable land, water, or added fertilizers, and high production can be achieved in offshore areas of the US EEZ. Recently, novel technologies have been developed to support scalable macroalgal production in offshore areas that can provide the carbon-rich biomass necessary for a directed macroalgal CDR solution. Our objectives are to provide a robust plan to remove up to 0.1 Gt CO2 yr-1 from the atmosphere and sequester it for more than 100 years via ocean farming and injecting the macroalgal crops into the ocean interior, as well as understand the impacts and risks that these perturbations may have to ocean ecosystems and the biogeochemical cycles they help regulate. To meet these objectives, we will provide engineering solutions for transporting macroalgal biomass to the deep ocean, determine the biogeochemical fates of fixed carbon in macroalgae, model the sequestration times of macroalgal carbon over global scales, and assess the risks of these perturbations to the natural system. Understanding the processes and sequestration permanence of macroalgal carbon will provide the information necessary to develop a successful implementation plan in an environment hungry for sound CDR investment.
