Collaborative Research: Identifying basin-specific controls on isotopic and chronological offsets of lake sediment leaf wax hydrogen isotope records

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To determine how future precipitation might change, it is important to have a baseline of how precipitation changed in the past. However, determining past precipitation, prior to the generation of instrumental records, has remained challenging and necessitates the use of precipitation proxies that are preserved in the geologic record. Biological proxies, such as leaf waxes, hold promise in this regard as the hydrogen isotopic composition of leaf wax primarily reflects that of precipitation. Therefore, leaf waxes preserved in lake sediments are a potential source of high resolution information about how precipitation and the water cycle have changed over geologic time. However, the transfer of modern leaf waxes to lake sediments appears to introduce offsets in hydrogen isotope values. This project will help define these offsets and identify the factors that control them, thus allowing for improved reconstructions of past hydrological conditions. Until these offsets are evaluated, and their influence measured, the quantitative link between sedimentary leaf wax and precipitation will remain limited. Identification of these factors will allow selection of lakes where the effects of these offsets are minimal. This is critical for constraining past changes in hydrology prior to the instrumental record and will help anticipate future hydrologic change. This project will benefit society by creating educational and research experiences for undergraduates through interdisciplinary collaborations with St. Lawrence University, a primarily undergraduate institution. This will improve STEM field retention by providing research and training experiences for undergraduate students to develop advanced research skill sets, expand scientific understanding, and strengthen preparation for graduate studies or a career in the geosciences. Finally, this research will promote a broader public understanding of the geosciences and appreciation of scientific research by expanding on museum exhibits in collaboration with the Cincinnati Museum Center, a large urban cultural institution.Past precipitation remains a challenge to quantify. Biological proxies, such as leaf waxes, hold promise in this regard as the hydrogen isotopic composition of leaf wax primarily reflects plant source water (i.e., precipitation). However, quantitative paleohydrology, as inferred from precipitation hydrogen isotopic composition, is limited by a poor understanding of the taphonomic processes governing the source, integration, and transport of leaf waxes from plants to sediments. This project will address two significant gaps in our understanding of lake sediment leaf waxes. First, the investigators will determine how vegetation proximity influences leaf wax hydrogen isotope signals in lake sediments. Second, they will determine how important reworking of older leaf waxes via fluvial erosion impacts the apparent age of leaf waxes in lake sediments. This project examines these two processes in temperate lakes in the Adirondack Mountains, NY, USA. Research methods will include forest inventorying, modern leaf wax (n-alkane and n-alkanoic acid) molecular and isotope (hydrogen, carbon) characterization, lake sediment coring and dating (210Pb, 137Cs, 14C), and compound-specific radiocarbonanalyses of n-alkanes in lake sediments, catchment soils, and fluvial suspended sediments. The project will benefit society by 1) establishing partnerships with St. Lawrence University, a primarily undergraduate institution, to develop interdisciplinary collaborations and undergraduate research opportunities, create graduate student mentoring opportunities, and provide a hands-on isotope workshop for undergraduates; 2) improving STEM field retention by providing research and training experiences for two undergraduate students per year to develop advanced research skill sets, expand scientific understanding, and strengthen preparation for graduate studies or a career in the geosciences; 3) increasing the number of women in STEM fields by support of a Ph.D. student and an undergraduate students; 4) providing mentoring to enhance the educational and career development of undergraduate and graduate students, and improving the success of mentoring approaches through regular assessment and professional development; and 5) promoting broader public understanding of the geosciences and appreciation of scientific research by expanding on museum exhibits in collaboration with the Cincinnati Museum of Center, a large urban cultural institution.