CAREER: New insights into the ancient carbon cycle from siliceous deep-sea sediments

When silicate minerals in rocks are exposed to air and water, a “chemical weathering” reaction occurs that consumes carbon dioxide from the atmosphere. This process acts as a feedback on Earth’s climate – past, present, and future. Microscopic fossils preserved in deep-sea sediment record ancient warming events and their recoveries. This project will analyze fossils from two distinct events in Earth history to understand how weathering rates respond to warm climates. The results will help predict the role of silicate weathering in regulating future climate. Education and Outreach activities will engage students from K-12 through the PhD level through novel classroom and field experiences at Utah State University. An interactive museum exhibit at the Loveland Living Planet Aquarium will introduce visitors to plankton and deep-sea fossils. Three intersecting approaches will apply the Germanium/Silicon ratio of siliceous microfossils to constrain ancient silicate weathering rates. Approach 1 will develop and calibrate this proxy in modern siliceous sediments, focusing on radiolarians, which are common in Early Cenozoic marine sediment but whose Ge/Si ratios are understudied. Approach 2 will generate new down-core records from legacy International Ocean Discovery Program cores spanning two key climate events: the Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) and the Middle Eocene Climatic Optimum (MECO, 40 million years ago). These events provide a contrast: the PETM is easily reconciled with a strong silicate weathering feedback driving its recovery, while several aspects of the MECO apparently contradict a dynamic silicate weathering response. Pilot data already document clear and opposing Ge/Si trends over the two events, indicating contrasting behavior of silicate weathering and demonstrating the utility of Ge/Si to resolve ancient weathering changes. Complementary siliceous microfossil-hosted datasets (isotopes of oxygen, silicon, and boron) will be measured on PETM and MECO samples shared with collaborators, which will assist in more fully understanding these events, and demonstrate the potential of siliceous sediments as powerful records for reconstructing paleoceanography and paleoclimate. Approach 3 will develop and apply a numerical model of the coupled carbon and Si cycles equipped with Ge/Si tracers to interrogate downcore records, quantify changes in silicate weathering implied by Ge/Si shifts across the PETM and MECO, and test hypothesized mechanisms for climate and carbon cycle change during these events. 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. NSF Award ID: 2543576 | Program: 01002930DB NSF RESEARCH & RELATED ACTIVIT,01003031DB NSF RESEARCH & RELATED ACTIVIT,01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Donald Penman | Institution: Utah State University, LOGAN, UT | Award Amount: $362,421 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2543576 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2543576.html