EAR-PF: Seeing through carbonate diagenesis using the triple oxygen isotope system

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An NSF EAR Postdoctoral Fellowship has been granted to Dr. Jordan Wostbrock to carry out research and educational activities at Yale University under the mentorship of Dr. Noah J. Planavsky. This project investigates how well carbonate rocks preserve the initial environmental conditions under which the rock formed. Carbonates that form in marine settings are commonly used to reconstruct past ocean temperatures to see how oceans change between glacial and interglacial cycles (greenhouse/icehouse climates). The ratios of oxygen isotopes in carbonate rocks are used to calculate the temperature in which these rocks formed. However, using traditional measurements of the oxygen isotope ratios (i.e. using only the Oxygen-18/Oxygen-16 ratio) makes it difficult to figure out if the oxygen isotope ratios measured in the rock are from the initial deposition or if the oxygen isotope ratios have changed after deposition. A novel oxygen isotope measurement technique that looks at an additional oxygen isotope ratio (the Oxygen-17/Oxygen-16 ratio) will be used to better constrain the depositional environments of marine carbonate rocks. This additional variable will enable marine scientists to better determine the conditions of ancient marine environments using the rock record. For example, biologists and paleontologists might be able to use this tool to look at micro-environmental changes that affect coral survivability or that might have impacted evolution. As a female in a STEM field, Dr. Jordan Wostbrock will actively seek female engagement in STEM by recruiting an undergraduate woman as an assistant in the laboratory, mentor undergraduate research experiences, and serve as a mentor for the Women in Science at Yale program. This project will use the triple oxygen isotope composition (combined 17O/16O and 18O/16O measurements) of carbonates to examine how oxygen isotope values change during alteration. It will be the first in-depth application of the triple oxygen isotope system of carbonates in a marine setting and will focus on two main tasks: 1) Measure the triple oxygen isotope compositions of a known diagenetic environment of the Bahama Platform to create a triple oxygen isotope equipped reaction transport model and 2) Measure the triple oxygen isotope compositions of Archean through Cretaceous carbonate rocks to explore whether the observed increase in oxygen isotope values is related to changing ocean isotopic composition, temperature, or preservation quality. Dr. Wostbrock will combine other geochemical systems such as Sr and Ca as well as hydrologic conditions to predict how carbonate oxygen isotope composition changes in the shallow marine environment. A better understanding of diagenesis in shallow marine settings will change our understanding of how the rock record preserves ocean geochemistry. Better understanding of ocean dynamics will assist in the prediction of how oceans respond to external forces during a changing climate. This study will try to address the 50-year-old question as to whether the secular change seen in the carbonate record is a preservation issue, a change in oxygen isotope composition of the ocean, or a change in ocean temperature.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.