Environmental Internship Program - 2023 Booklet

Rebecca Cho ’26
GEOSCIENCES
OCEANS AND
ATMOSPHERE
PROJECT TITLE
Reconstructing the Marine
Environmental Changes
Across the Cretaceous-
Paleogene Mass
Extinction With Nitrogen
Isotopes in Planktonic
Foraminifera
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;
Crystal Rao, Ph.D.
candidate, Geosciences
Reconstructions of how marine environments
responded to past global disturbances can
improve our understanding of the modern ocean.
Foraminifera, marine microorganisms with
calcium carbonate shells, preserve records of past
ocean conditions in their shells. Approximately
66 million years ago, the Cretaceous-Paleogene
mass extinction event caused significant
ecological turnover and impacted the ocean’s
biogeochemical cycling. Analyzing the nitrogen
isotopic signatures of organic matter bound in
foraminiferal shells from this period allows us
to infer how this event impacted the marine
nitrogen cycle and oxygenation. I assisted in
generating the nitrogen isotope records of fossil
planktonic foraminifera shells preserved in deep
ocean sediment from western North Atlantic
Ocean Drilling Program sites by washing and
sieving bulk sediment to collect foraminifera
shells and assisted with chemical cleaning
and subsequent isotope analysis. I developed
skills for the preparation of geologic marine
sediments, foundational laboratory procedures
in geochemistry, and a novel method for nitrogen
isotope analysis developed in the Sigman
Laboratory and its application to marine nitrogen
cycling dynamics. This experience solidified my
interest in paleoceanography and geochemical
reconstruction with biological proxies and I
plan to pursue research of similar significance
to ascertain historical associations between the
ocean and environmental perturbations.
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