January Dinner Meeting and Speaker: Dr. Elizabeth K. Thomas (SUNY Buffalo) I Can See Clearly Now: Improving our ability to reconstruct past rain and snowfall by monitoring seasonal trends of hydrogen isotopes in environmental water and sedimentary leaf wa

Dr. Elizabeth K. Thomas (SUNY Buffalo)

I Can See Clearly Now: Improving our ability to reconstruct past rain and snowfall by monitoring seasonal trends of hydrogen isotopes in environmental water and sedimentary leaf waxes

University at Buffalo Department of Geology

Summer 2016 was an abnormally dry season in parts of upstate New York. In Syracuse, the past five winters have been less snowy than the long-term average, but the previous five years were snowier than average. What factors cause droughts? Why does precipitation behave so differently during different years? How much rain and snowfall will we get during the next decade? Records of past climate can help us answer these questions by providing insights into precipitation behavior. This talk will share new research from the University at Buffalo Organic and Stable Isotope Biogeochemistry group that aims to calibrate climate proxies, the methods that we use to reconstruct past climate.

The climate proxy that we are calibrating in this study is the hydrogen isotope ratio of leaf waxes, d²H_wax. Leaf waxes are n-alkyl lipids produced by plants as a protective coating on their leaves. Environmental water d²H is recorded ind²H_wax, allowing for past climate to be determined from these compound-specific isotopes. However, there are still many details of this proxy that are unknown, such as seasonal signals contained in leaf waxes preserved in sediment archives. This study aims to understand the relationship between climate, environmental water d²H and sedimentary d²H_wax throughout the growing season. We collected precipitation, lake water, and lake sediment samples at regular intervals throughout the year at a site in Central New York. Water and sediment samples were collected weekly using sediment traps deployed both near the surface and near the bottom of the studied lakes. Precipitation samples were taken in close proximity to the lakes after a rain or snow event. A Picarro L2130-i water isotope analyzer was used to measure d²H and d¹⁸O of precipitation and lake water samples. The δ²H of n-alkyl lipids was determined using gas chromatography-pyrolysis-isotope ratio mass spectrometry. We find that precipitation and lake water d²H change seasonally due to changing lake water evaporation, temperature and precipitation source and transport history. We will also present seasonal trends ofd²H_wax. A comparison of year-round environmental water δ²H and d²H_wax will elucidate the seasonal signal that is preserved in sedimentary leaf waxes under current climate conditions. Once these current seasonality trends are fully determined, they can be used to provide more precise interpretations of d²H_wax records of past climate, and ultimately help us understand why and how precipitation will change in the future.

This research is the work of UB Honors Undergraduate Megan C. Corcoran, in collaboration with Dr. David Boutt, Department of Geosciences, UMass Amherst, with logistical support from George M. Thomas, Kathy Lyons, and the Buffalo Audubon Society.