Postdoctoral Fellowship: EAR-PF: Water Stress Across the Paleocene-Eocene Thermal Maximum: Applying Triple Oxygen Isotopes as an Aridity Proxy in the Bighorn Basin

Allen, Matthew L, Lawrence KS

Investigators

Abstract

Today, global warming is causing changes in the Earth’s water cycle. Some places are having bigger and more frequent flood events. Elsewhere, droughts have become longer and more common. It's important to learn how water availability might change in the future. Some computer models suggest warming will cause more drying. Others predict wetter conditions. It is possible to test these models by studying Earth’s past climate using the chemistry of rocks and fossils. The new “triple oxygen” method may be able to detect changes between wet and dry climates in Earth’s distant past. This project will be the first test of the triple oxygen method. It will be used on fossils from around 55 million years ago during a period of intense global warming called the PETM (Paleocene-Eocene Thermal Maximum). If the triple oxygen method works, scientists can use it on fossils from other places and times. With enough triple oxygen data and better models, nations can make informed decisions about how to adapt to a changing water cycle. Also, the project includes science outreach programs. These are through the University of Michigan Museum of Paleontology. The project will also increase young, diverse student engagement in Earth science. It will do this through the University of Michigan Earth Camp program. The goal of this project is to test if triple oxygen isotopes will detect a change in aridity across the PETM. The PETM section of the Willwood Formation at Polecat Bench in the Bighorn Basin of Wyoming is an ideal testbed for this proxy because robust, high resolution chronostratigraphic, paleontological, and paleoenvironmental records are already available from this section and locality. Spatially and stratigraphically resolved fossil teeth from multiple taxa will be microsampled and the powders will be treated and then analyzed for triple oxygen isotope composition. Pedogenic carbonates will also be sampled and analyzed. Distributions of delta 17O will be evaluated for sample aggregates from each of three time slices: one immediately below the PETM interval (Cf-3), one spanning the PETM (Wa-0), and one immediately above the PETM (Wa-1). If aridity increased during the PETM in the Bighorn Basin, the range in delta 17O values should be significantly greater in the sample aggregate from the Wa-0 interval relative to the aggregates from the intervals immediately preceding and following the PETM. If delta 17O suggests a significant change in aridity (increase or decrease) across the PETM, this will encourage widespread testing of the proxy to the deep time record, potentially allowing unprecedented spatiotemporal reconstructions of effective water availability in ancient terrestrial ecosystems. 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.