Understanding indirect controls on silicon isotope distribution in surface marine sediments

The National Science Foundation's Division of Ocean Sciences awarded $589,519 under the Geosciences program (CFDA 47.050) to the Marine Environmental Sciences Consortium, operating as Dauphin Island Sea Lab, for a three-year project (October 1, 2025–September 30, 2028) investigating reverse weathering processes in marine sediments. The primary deliverables include novel scientific data and insights on silicon isotope cycling in the Mississippi River Plume through laboratory and ship-based experiments that examine the roles of microbial activity, oxygen availability, and sediment composition in reverse weathering—a critical early diagenetic process affecting ocean pH, metal availability, and the long-term carbon cycle. Research outputs will contribute to the geosciences knowledge base regarding elemental cycling in marine environments and inform understanding of fundamental Earth system processes.

In addition to research findings, the project delivers substantial educational and workforce development products, including experiential learning activities for undergraduate students, graduate student training, and two high school outreach initiatives: scholarships supporting participation in a six-week intensive marine science course at Dauphin Island Sea Lab and a field experience program introducing rural Missouri high school students to the Mobile Bay ecosystem and marine science careers. These educational components align with the Geosciences program's emphasis on strengthening the national scientific workforce across multiple educational levels.

Abstract

Reverse weathering is a chemical process that forms clay minerals from dissolved silica and positively charged ions in marine sediments. This process is important because IT impacts ocean PH, the availability of important metals (e.g. iron, lithium), and the long-term carbon cycle. In this project, the researchers plan to use stable and radioactive silicon isotopes to track reverse weathering processes in sediments of the mississippi river plume. The research includes laboratory and ship-based experiments exploring the role of microbial activity in sediment silicon cycling and reverse weathering. The experiments will also study how the presence or absence of oxygen and different sediment types influence these processes. The project will produce novel data and key insights about the cycling of silicon in marine sediments. Education and outreach activities focus on training the next generation of scientists at multiple levels. These include experiential learning activities for college undergraduates and training for a graduate student. This project will also provide two opportunities for high school students: 1) support scholarships for students to take an immersive six-week marine science class offered at the dauphin island sea lab and 2) provide support for high school students in rural missouri to visit the mobile BAY ecosystem where they will be introduced to marine science. Reverse weathering (RW) reactions are the collection of early diagenetic processes which produce authigenic clay in marine sediments. Reverse weathering is important because IT releases CO2 and is thought to be a quantitatively important sink in the geochemical cycle of multiple elements in the marine environment (e.g. SI, FE, k, MG). Until recently, RW has been considered a geochemical process, but new work has indicated the potential importance of microbes in the RW process. In this project, the research team will use a combination of laboratory and field experiments to quantify the signature of microbial activity on silicon isotopic composition in surface sediments in a subtropical deltaic environment (the mississippi river plume). Specifically, the research team seeks to address three key knowledge gaps associated with these processes: the roles of seasonality, redox state, and sediment characteristics. This research uses a powerful combination of radioisotope 32SI and ?30SI tracer approaches to test hypotheses that aim to understand sediment processes in the field. In addition to providing new information and novel data, this project includes activities focused on training the next generation of scientists through experiential learning opportunities for high school students, research experiences for undergraduates, and training for a graduate student. Beyond the science objectives, the project will also contribute to redeveloping US domestic infrastructure for analysis of silicon stable isotopes in oceanographic systems. 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.- subawards are not planned for this award.