Environmental Internship Program - 2023 Booklet

Erin Yoo ’26
GEOSCIENCES
CLIMATE AND
ENVIRONMENTAL SCIENCE
PROJECT TITLE
Ground-truthing Nitrogen
Isotopes in Celtis
(Hackberry) Endocarps as
a Paleoclimate Proxy
ORGANIZATION(S)
Sigman Research
Laboratory, Department
of Geosciences, Princeton
University
LOCATION(S)
Princeton, New Jersey
MENTOR(S)
Daniel Sigman,
Dusenbury Professor of
Geological and
Geophysical Sciences,
Professor of Geosciences;
Mason Scher, Ph.D.
candidate, Geosciences
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 δ 15 N 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.
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