Erin Yoo ’26



Project Title

Ground-truthing Nitrogen Isotopes in Celtis (Hackberry) Endocarps as a Paleoclimate Proxy

Hackberry trees are a deciduous group that have had widespread distribution across the Americas and Mediterranean since at least the Paleocene epoch (56-66 million years ago). Hackberry trees are a useful model for reconstructing the historical climate because of the structure of their endocarps, a hard layer of the seed. Hackberry endocarps are made of calcium carbonate, a mineral commonly used to reconstruct the historical climate, and they also trap organic matter as they form. My project examined the potential for using the isotopic nitrogen composition of Hackberry endocarps as a paleoclimate proxy. I measured the nitrogen isotopic composition of modern U.S. hackberries and analyzed their composition in relation to mean annual temperature and precipitation. I found that high δ15N endocarp values correlated with hotter and drier sample regions, indicating that fossil hackberries have promising potential to be paleoclimate proxies. Climate reconstructions based on hackberries could provide insight into modern-day global warming. Through my internship, I learned how to use new lab equipment, including a sonicator, aspirator, muffle oven and mass spectrometer. I realized that I love pipetting to a surprising degree. I enjoyed learning about the natural world and I plan to continue studying geosciences at Princeton.

Internship Year


Project Category

Climate and Environmental Science


Sigman Research Laboratory, Department of Geosciences, Princeton University - Princeton, New Jersey


Daniel Sigman, Dusenbury Professor of Geological and Geophysical Sciences, Professor of Geosciences; Mason Scher, Ph.D. candidate, Geosciences