Hydrothermal Metal Fluxes over the Cenozoic

Hydrothermal vents are underwater geysers that spew about as much water into the ocean as rivers. These vents can change the chemistry of seawater and change the climate on million-year timescales. However, how much water circulates through these vents or how it has changed over time is unknown. During eruptions, metals like iron and manganese are erupted from the vents, transported within the deep ocean, and deposited in the marine sediment. These deposits serve as evidence of past eruptions in the geologic record. This project will gather, expand, compare, and analyze multiple chemical clues found in marine sediments. The goal is to figure out how the flow of these vents has changed over millions of years. Ultimately, the project will calculate the flow of metals from hydrothermal vents and create maps that show where these metals are deposited now and in the past. The seafloor distribution of these metals such as manganese, cobalt, copper, and zinc are critical to modern technology and renewable energy. Additionally, the project supports K-12 outreach activities involving communities underrepresented in the geosciences. With the entire ocean volume cycling through the underlying ocean crust every few thousand years, the global hydrothermal fluid flux is comparable to the global riverine flux to the ocean. Hydrothermal circulation significantly affects the chemical balance of seawater chemistry, long-term climate, biogeochemical cycles, paleo-seawater compositions, and the composition of crust subducted into the mantle. Despite the importance, hydrothermal fluxes are poorly constrained. This project will compile, expand, compare, and synthesize tracers of hydrothermal metal deposition in marine sediment to reconstruct variations in the basin-wide spatial distribution of hydrothermal fluxes over million-year timescales. Focusing on the Pacific Plate, four tracers of hydrothermal deposition will be compared: Fe-Mn oxide abundances from smear slides, multivariate modeling of element concentrations, Pb isotopes, and rare earth element patterns. The project tests the hypothesis that marine sediment records tracing metal deposition from hydrothermal vents can be combined and expanded across ocean basins to reconstruct changes in hydrothermal fluxes for the modern back through much of the Cenozoic. Along with estimating fluxes, the project will produce maps of present and past hydrothermal metal deposition that will illustrate where and how far hydrothermal plumes are transported away from mid-ocean ridges. The outcome has implications for the cycling of micronutrients (iron) in the past as well as adding constraints to novel isotope systems affected by hydrothermalism. Given that Mn, Co, Cu, and Zn will be investigated, the project is pertinent to critical minerals research. The project supports early career scientists and K-12 outreach activities involving people from communities underrepresented in the geosciences as well. 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.