OCE-PRF: Constraints on the role of sediment diagenesis in chemical mass balance and Eocene climate using high-resolution pore fluids from IODP Expedition 396

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OCE-PRF Constraints on the role of sediment diagenesis in chemical mass balance and Eocene climate using high-resolution pore fluids from IODP Expedition 396Silicates are important minerals in ocean sediments and Earth’s crust. The chemical changes (or diagenesis) of silicates in marine sediments may play a key role in regulating seawater chemistry at modern and geological timescales. Yet, our understanding of how silicate diagenesis influences specific elements, such as magnesium (Mg), strontium (Sr), lithium (Li) and boron (B), in seawater is incomplete. These elements are important in both the modern ocean and as proxies for understanding changes in the ocean over geologic time. For example, Mg, Sr, Li, and B are used as paleoclimate proxies for temperature (Mg/Ca), weathering (Sr/Ca, Li/Ca), and the carbonate system (B/Ca). PI Clementi will pair chemical analysis of fluids squeezed from new sediment cores from the North Atlantic Ocean with modeling techniques to determine which diagenetic processes are occurring in marine sediments, how these processes influence seawater chemistry, and whether silicate diagenesis has influenced global climate processes over the last 65 million years. The research will be conducted at Rutgers University and Princeton University. Themes from this project (e.g., solute sources and sinks, climate change) will be incorporated into public lectures that the PI will give at New Jersey community colleges. The PI will also develop summer research projects as part of mentoring programs for current Rutgers undergraduate students and students from under-represented groups at colleges across the country.Our ability to reconstruct past climate processes using a range of paleoceanographic proxies (e.g., Mg/Ca, Sr/Ca, Li/Ca, and B/Ca) is reliant on a fundamental understanding of the sources and sinks of elements in the ocean. Despite substantial exchange of these elements during various diagenetic processes, however, constraints on chemical mass balance for Mg, Sr, Li, and B remains incomplete. Further, silicate diagenesis in marine sediments has been suggested to have influenced Paleogene climate, but data-based constraints on these model hypotheses is limited. Using a new suite of high resolution pore fluid samples from recently implemented IODP Expedition 396 to the Mid-Norwegian Margin, combined with numerical modeling, the work proposed here will: (1) identify the mode(s) of silicate diagenesis controlling pore fluid chemistry; (2) use data- and model-based approaches to determine the influence of silicate diagenesis processes (e.g., ash alteration, reverse weathering, marine silicate weathering, and crustal alteration) on the geochemical budgets of Mg, Sr, Li, and B; and (3) elucidate the extent to which silicate diagenesis contributed to climate changes during the Paleogene hothouse. Pore fluids will be analyzed for their isotopic (𝛅26Mg, 87Sr/86Sr, 𝛅7Li, 𝛅11B) composition using the Neptune MC-ICP-MS facilities at Rutgers University and Princeton University. The sampling resolution and proposed analytical plan will offer unprecedented constraints on the extent to which silicate diagenesis in marine sediments regulates seawater chemistry and facilitates environmental change. Importantly, the work will provide critical insight for proxy-based and proxy enabled model-based reconstructions of warmer climates in Earth’s history.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.