Environmental Internship Program - 2023 Booklet

OCEANS AND
ATMOSPHERE
Sara Akiba ’26
GEOSCIENCES
PROJECT TITLE
A Revised Pleistocene
View of the Effect of
Climate on North Pacific
Oxygenation From
Foraminifera-bound
Nitrogen Isotopes
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;
Matthew Lacerra, Ph.D.
candidate, Geosciences
My project examined the effect of climate on
ocean oxygenation in the Eastern Tropical North
Pacific (ETNP), a region that is home to one of the
ocean’s largest oxygen-deficient zones due to the
region’s high productivity and slow circulation.
When oxygen is depleted, organisms rely instead
on nitrate for respiration via water column
denitrification. During denitrification, the
lighter nitrogen-14 is preferentially lost, which
leads to increases in the ratio of nitrogen-15
to nitrogen-14. This signal of denitrification
is incorporated into organic matter via
nitrate assimilation in the surface ocean and
preserved through burial on the seafloor. Fossil
foraminifera-bound organic matter thus provides
a record of the extent of denitrification in oxygendeficient
zones over glacial-interglacial periods.
I prepared and analyzed foraminifera samples
to extend an existing record of denitrification
in the ETNP back to ~180,000 years before the
present. I prepared samples by washing sediment
material and selectively sorting two species of
foraminifera for analysis. I also assisted in the
wet chemistry stages of preparing the samples
for mass spectrometry. This experience has
strengthened my microscopy and laboratory
skills and enhanced my understanding of paleooceanography
and research processes, which has
inspired me to do further research on this topic.
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