During the glacial-interglacial cycles of the Pleistocene, coral reefs likely experienced a range of stressful conditions. Understanding what factors cause reefs to survive or perish is critical for mitigating modern climate change.

Fossil reef terraces off the island of Hawai'i preserve several glacial-interglacial cycles. As a member of the science party for IODP Expedition 389, I am using the geochemistry of corals to study nitrogen and phosphorus cycling in the coral reef environment during these climate fluctuations.

First, I used coral-skeleton nitrogen isotopes to measure the d15N signatures of organic material trapped in the coral skeleton. This material is thought to come from the coral organism itself, reflecting the balance of nutrients it obtained from the environment versus from its endosymbionts. Using snapshots of CS-d15N from different coral samples from different locations around Hawai'i during the penultimate glacial interval, I am reconstructing coral N sources and how they may have been affected by climate change.

I am also analyzing phosphorus cycling during this interval using carbonate-associated phosphate (CAP). This measures the amount of PO4 contained in the coral's carbonate skeleton, which is thought to correlate with PO4 in seawater. Given the array of local, regional, and global changes associated with warming and cooling, I expected to find changes in P cycling recorded in these corals.

Stay tuned for the publication of this work!