Rate Processes for Carbon Capture and Release by Marine Seaweeds

Oregon State University, Corvallis OR

Investigators

Abstract

The rise of greenhouse gases in the Earth’s atmosphere is generally believed to be responsible for global warming and climate change. The dominant greenhouse gas is carbon dioxide (CO2). The world’s oceans are the largest global sink of CO2, capturing over 90 gigatons of this carbon annually from the atmosphere, primarily through growth of photosynthetic plankton and seaweeds in ocean waters. Although much of carbon captured by these organisms goes back to CO2 through a natural cycle, some of the carbon exists in a form that escapes this cycle and remains in the ocean. Seaweeds are large algae that are widely distributed across the globe. Most species of red and brown seaweeds have biological processes that convert their photosynthetic carbon into a form that is not readily degraded, and this recalcitrant carbon gets fed by ocean currents to the deep sea, where it stays there indefinitely. Seaweeds have the potential to accelerate this natural carbon capture process in engineered systems, because they can be sustainably farmed in the ocean to large scale through aquaculture. However, to assess the potential of seaweed-based ocean carbon removal (Ocean CDR), a better understanding of the rate of carbon flow, from CO2 capture to recalcitrant carbon release, is needed. This project will advance fundamental understanding of the connection between CO2 capture and carbon sequestration rates by red and brown marine seaweeds through a combined biological and engineering approach, leading to new models for predicting carbon sequestration potential by seaweeds. The research outcomes will also suggest strategies for development of engineered systems for seaweed-based Ocean CDR. To help stakeholders better understand the research outcomes and move them towards practical application, the project will establish a Red Seaweed Learners Group, which will facilitate outreach, education, and collaborative learning on emerging Ocean CDR processes and their nexus with red seaweed aquaculture. Seaweeds are a potential natural solution for ocean-based carbon removal (Ocean CDR), but the flow of carbon from carbon dioxide (CO2) in the atmosphere to exuded dissolved organic carbon (DOC) available for sequestration by the deep sea is still poorly understood from a rate processes perspective. The overall goal of this proposed research is to provide a fundamental understanding of the rate processes for carbon flow by marine seaweeds under controlled hydrodynamic and environmental conditions in the absence of microbial degradation processes. The project hypothesizes that upstream CO2 uptake, which is driven by hydrodynamic and environmental conditions, is coupled to the downstream exudation of DOC by the seaweed. Therefore, the Research Plan will use clean, clonal seaweed cultures to eliminate microbial degradation processes, so that the upper bound of carbon exudation can be characterized. A recirculating flow system will be used to measure the real-time rates of carbon dioxide capture and dissolved organic carbon release by the model red seaweed Gracilaria and the brown seaweed Sargassum under controlled environmental and hydrodynamic conditions, determine the limiting effects of fluid velocity and environmental stressors such as elevated CO2 gas concentration and hyposaline environments on these rate processes, and develop rate-based models for dynamic prediction of inorganic carbon uptake and dissolved organic carbon release. These studies will advance fundamental understanding of seaweed-based Ocean CDR, and will suggest strategies for harnessing and sustaining these processes within intensified, engineered systems. Research outcomes will also advance the critical role of seaweeds in the development of the Bioeconomy and the Blue Economy, including next-generation aquaculture systems for providing ecosystem services and securing food and valuable products from the sea. Finally, as sustainability, climate change, and marine science aspects of the project are of broad interest to students and the public, the project will engage a diverse range of students in summer research experiences through established programs at Oregon State University, and the project also will establish a Red Seaweed Learners Group. The Learners Group will facilitate outreach, education, and collaborative learning on emerging Ocean CDR processes and their nexus with red seaweed aquaculture though a website, mini workshops, break-out sessions at regional Sea Grant conferences, and presentations to non-governmental organizations. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.