EAGER: Unraveling riverine sulfate using minor oxygen isotopes

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Over geological timescales, weathering reactions involving minerals on the land surface have regulated the amounts of important gases such as oxygen and carbon dioxide in Earth's atmosphere. This award funds research that will explore the potential for a new method to provide constraints on one such reaction in Earth history: the oxidation of the mineral pyrite. Over the geological past, global variation in the amount of pyrite that has been oxidized provides a critical link between Earth's carbon and sulfur cycles, while a record of this history may be preserved by sulfate minerals in marine sediments. The researchers will generate a proof-of-concept data set that takes advantage of information that can be gathered from a rare and difficult-to-measure stable isotope in dissolved and mineral sulfate: 17-oxygen. This novel method will be applied to previously collected and well-characterized water samples from a major river system draining the Himalaya Range. This pilot data set will provide important information about the mechanisms that control the isotopic composition of dissolved sulfate and will help to unravel the record that is preserved in marine sediments. The award will also provide mentoring for a postdoctoral fellow who has contributed to the design and planning of this project and will provide the individual with opportunities for leadership roles within the research group.This award funds the exploration of the potential for a new proxy to quantify geological rates of pyrite oxidation, based on the minor oxygen stable isotope (17-O) preserved in sulfate produced by pyrite oxidation. Because pyrite oxidation both consumes oxygen and generates acidity that dissolves carbonate rocks and produces CO2, it has been suggested that changes in pyrite oxidation rates may have acted to stabilize fluctuations in atmospheric CO2. Although pyrite oxidation is a critical link between Earth's carbon and sulfur cycles, the application of a 17-O proxy in marine sulfate is limited by our understanding of sulfate generation and translation through fluvial systems. This work would begin to narrow this gap by generating a proof-of-concept data set from well-characterized river samples from a major river system draining the Himalaya Range that has already been measured for 34-S and 18-O composition of dissolved sulfate. The researchers will add measurements of the 17O composition of dissolved sulfate from these samples to investigate the potential sources and subsequent recycling of sulfate in downstream floodplains. The riverine 17-O-sulfate data set will provide a rigid framework with which to interpret 17-O records in the marine sulfate record.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.