Collaborative Research: Disentangling paleoclimate signals with individual foraminiferal analyses from a new record of the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM, 56 million years ago) is an important paleoclimate event used to understand how Earth’s climate system responded to rapid increases in atmospheric methane and carbon dioxide. One approach to study this interval is chemical analysis of microfossils known as foraminifera preserved in deep-sea sediment. Foraminifera grow calcium carbonate shells that record the environmental conditions of the organism’s habitat. However, PETM foraminiferal records suffer from two well-known limitations: first, ocean acidification at the PETM onset can lead to the dissolution of the carbonate shells and, second, vertical sediment mixing (bioturbation) can intermingle shells from different time periods together. Until recently, vertical mixing was a significant drawback because analyses required multiple shells to have sufficient accuracy. This project will remedy those issues by constructing records of individual foraminiferal geochemistry and morphology across the PETM at International Ocean Discovery Program (IODP) Site U1580 located on the Agulhas Plateau in the Southern Ocean. Site U1580 features abundant microfossils that were not dissolved. Cutting-edge analytical techniques will permit measurements on individual foraminifera to disentangle signals affected by bioturbation. Results will produce new estimates of surface and deep-water warming and carbon cycle dynamics across the PETM onset. The proposed work will support a team of three early career researchers plus graduate students and postdoctoral scholars. The project integrates educational outreach; investigators will create an open educational resource on the PETM and its relevance to contemporary climate. The presence of well-preserved foraminifera throughout the PETM onset at IODP Site U1580 offers a unique opportunity to reconstruct the magnitude, pace, and dynamics of climate change during the earliest phases of the PETM. However, pilot data demonstrate extensive vertical mixing of individual foraminifers across the event (as observed at other sites). The investigators will disentangle vertical sediment mixing by applying a series of measurements performed on individual shells. Shells will first be imaged by Scanning Electron Microscopy (SEM) and Computed Tomography (MicroCT) to characterize preservation and document morphology. Shells will then be analyzed for Mg/Ca (a paleotemperature proxy) via Laser Ablation Inductively Coupled Plasma Mass Spectrometry, then finally analyzed for their stable carbon and oxygen isotopic composition using a new CryoFocusing technique adapted for small carbonate samples. The resulting individual foraminifera carbon isotope data will distinguish pre-PETM from PETM individuals, allowing quantification of shell morphology, Mg/Ca-based temperature, hydrologic change, and the carbon isotope shift across the PETM onset. Any observed structure in the geochemical data will provide insight into the pace of change or lead-lag relationships between aspects of the carbon cycle and climate. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.