Reverse weathering is the process that forms clay minerals through reactions that involve biologically produced silica. Carbon dioxide is a byproduct of reverse weathering and an important greenhouse gas. As a result, reverse weathering is considered an important process that has regulated global climate over the earth?s natural history. Prior studies that have examined reverse weathering have focused only on abiotic factors (i.e., factors not affected by biology). This research is the first to examine microbial effects on reverse weathering reactions. The project includes laboratory experiments with well-characterized microbial strains. These experiments will provide understanding of this complicated process in a controlled environment. Follow-up experiments and surveys will be conducted in the northern Gulf of Mexico during two field campaigns led by the scientific team. This project contributes to scientific education and development at many levels. The graduate and postgraduate personnel will learn interdisciplinary approaches and collaborate with an international expert in reverse weathering research. Undergraduate trainees from local community colleges will receive paid internships. The project supports high school education in marine science through a partnership with the Dauphin Island Sea Lab Discovery Hall Program. Scientists involved in this study will also work with a non-profit in Birmingham, Alabama, that brings educational opportunities to underserved and underrepresented students in grades 3-8.

This project will take advantage of the passage of Hurricane Ida across the northern Gulf of Mexico shelf in August, 2021 to study important aspects of the cycling of silica in coastal sediments. In coastal systems, water column primary productivity is dominated by diatoms, a group of phytoplankton which produce a shell of amorphous biogenic silica. This biogenic silica can either be buried in its original unaltered form or undergo chemical reactions that convert it to aluminosilicate minerals (e.g. marine clays). This latter process is important in global chemical budgets for many elements, including carbon. One of the factors that influences whether silicon is buried as biogenic silica or converted to aluminosilicates may be the amount of oxygen in the sediments. Storms mix the ocean waters and can add oxygen to sediments in shallow water, potentially changing the silica balance. The investigators collected sediment samples in early August, 2021, two weeks before Hurricane Ida. Sampling through the year after the storm will allow them to test whether storms affect silica cycling. This project will support an early-career investigator and undergraduate student researchers.

A long-standing topic of investigation in the field of chemical oceanography is understanding the processes that deliver elements to, and remove them from, seawater. There has long been a “missing sink” in the global marine silicon (Si) budget in that removal to sediments did not appear to balance the inputs from rivers. Several decades ago, it was postulated that “reverse weathering” in marine sediments could be this missing sink. In this process, the weathering process that takes place on land, whereby silicon is removed from minerals and dissolved in water, would be reversed and these minerals would be reconstituted in marine sediments through the formation of clays. Evidence for this process was very difficult to obtain, and only recently have studies using advanced measurement techniques shown that the global magnitude of marine reverse weathering could account for all the missing sink term in the global Si budget. If validated, this means reverse weathering would represent the largest individual sink for marine Si identified to date, with most of this burial occurring in a relatively small area of the ocean, the land-sea interface. Moreover, the continued upward revision of the marine reverse weathering rate has implications for the sequestration of other elements (e.g. iron, aluminum) and for other coastal processes (e.g. ocean acidification, as carbon dioxide is a byproduct of the reverse weathering process). This project aims to understand the most important factors affecting how fast reverse weathering occurs, and developing new approaches to evaluate this process in the field environment. Beyond the scientific pursuits, this project will support an early career researcher, a postdoctoral investigator, a graduate student, and undergraduate interns. It will also support high school outreach through science fair participation and annual scholarships for students wishing to pursue Marine Science education. This project will develop a community outreach activity to be used annually during the Atlanta Science Festival, Georgia’s biggest science fair that showcases science and technology to the public. Finally, it will build capacity for silicon isotope measurements in the U.S.