Internships

Sara Akiba ’26

Major

Geosciences

Project Title

A Revised Pleistocene View of the Effect of Climate on North Pacific Oxygenation From Foraminifera-bound Nitrogen Isotopes

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 oxygen-deficient 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 paleo-oceanography and research processes, which has inspired me to do further research on this topic.