Collaborative Research: Tapping an unused biomarker for insights of past evaporation

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Changes to the hydrological cycle, including precipitation and evaporation, have impacts on society and ecosystems at local to global scales. Therefore, it is critical to understand how the hydrological cycle responds to changes in climate as warming forces documented and projected changes in precipitation and extreme events. However, the effects of warming on evaporation are more challenging to anticipate, and without the evaporation term, the complete water budget cannot be constrained. By utilizing various existing proxies preserved in lake sediments, it is possible to track past precipitation and temperature, however there are few proxies that record evaporation. This project will help fill in this gap by developing the use of a group of biologically produced organic compounds called highly branched isoprenoids (HBIs). These HBIs are produced by diatoms and should contain a chemical signal of the lake water the diatoms live in. This project will focus on this connection between the HBIs and the signal of evaporation through a series of field-based modern calibrations and apply these calibrations to recent lake sediment archives to test their ability to reproduce evaporation. The goal of this work is to advance evaporation reconstruction both temporally and spatially, ultimately improving paleohydrologic reconstructions and future predictions of hydrologic change. The national health, prosperity and welfare can be safeguarded with a more complete understating of the evolution of the hydrological cycle. This collaborative project with The College of Wooster will provide research opportunities to undergraduate students while developing mentoring skills and experience for the UC graduate students. The Browns Lake field site in Ohio will be used in to help students gain field and lab experiences during summer programs at Wooster designed to recruit STEM students into the geosciences from underrepresented groups. This project will provide training in project design, data synthesis, interpretation and dissemination for graduate students. This research will also increase broader public knowledge and awareness of climate change by creating hands-on activities at the Northside Farmer’s Market in Cincinnati. This project will advance the use of hydrogen isotopes to reconstruct lake evaporation and hence contribute to the understanding of past hydrologic balance. Specifically, this work will consider diatom-derived highly branched isoprenoids (HBIs) as a paleohydrology proxy. If the hydrogen isotopes of HBIs record lake water hydrogen isotopes, then, when combined with other proxies, past records of lake water evaporation can be generated to constrain the complete hydrologic cycle. To accomplish this, this project will first investigate how diatom growth habitat, water chemistry, and timing of HBI synthesis influences the hydrogen isotopic composition of HBIs. Diatom HBIs will be collected from pelagic and benthic habitats across a suite of lakes that vary in water chemistry (i.e., pH, salinity), as this influences diatom species composition. The timing of seasonality of HBI production will be determined by collection of bimonthly sediment trap samples from Brown’s Lake in northeastern Ohio over two years. Once these controls on HBI hydrogen isotopes are addressed, this project will then determine the sensitivity of HBI hydrogen isotopes in sediment archives to known changes in local hydroclimate. This will be completed by examining HBIs in lake sediments where established records of evaporation and precipitation already exist. The development of HBIs proposed here will provide site selection criteria and necessary calibration information to use hydrogen isotopes of HBIs as a proxy for lake water evaporation, ultimately improving paleohydrological reconstructions from lake sediments. The project broader impacts will benefit society by 1) establishing a partnership with the College of Wooster, a primarily undergraduate institution, by creating research experiences for undergraduate students that will further the research proposed here; 2) creating a unique opportunity for undergraduate students to gain advanced and critical research skills, beyond the classroom, and preparing them for careers in the geosciences or STEM fields; 3) providing training in project design, data synthesis, interpretation and dissemination for graduate and undergraduate students in addition to mentoring students to enhance educational and career development; 4) encouraging the inclusion of and increasing the number of women in STEM by providing support for, and the training of the Ph.D. student, along with support for the training of undergraduate students; and 5) public outreach in the form of geoscience hands-on activities at the Northside Farmer’s Market in Cincinnati, a unique venue to help increase broader public knowledge and awareness of climate change.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.