Deconvolving Climate and Biotic Signals from Taphonomic Overprints in Deep-Sea Records of the Paleocene-Eocene Thermal Maximum

• Main Author: Hupp, Brittany N
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2021
• Subjects: Archives & records; Bias; Biogeochemistry; Carbon; Carbon cycle; Climate Change; Earth science; Friendship; Geology; Global warming; Mass spectrometry; Metadata; Paleoclimate Science; Paleoecology; Scientific imaging; Scientists; Sediments; Signatures; Stratigraphy; Trends; Values
• ISBN: 9798516958038

The Paleocene-Eocene Thermal Maximum (PETM), an ancient global warming event that occurred ~56 Ma, was closely associated with a rapid perturbation to the global carbon cycle, making the event an exceptionally-relevant analog for evaluating the future consequences of modern climate change. Here I examine deep-sea, planktic foraminifer records of the PETM from the Weddell Sea (ODP Site 690), southern Indian Ocean (ODP Site 1135), and equatorial Pacific Ocean (ODP Site 865). This dissertation seeks to (1) better characterize geochemical and biotic changes at various latitudes in response to PETM conditions through application of novel techniques, and (2) use the stratigraphic record of the PETM to assess how taphonomic processes such as sediment mixing and diagenesis have distorted deep-sea records of abrupt climate change. In chapters 1 and 2, I use stable carbon (δ13C) and oxygen (δ18O) isotope records constructed with graduated series of size-segregated planktic foraminifer shells to show how size-dependent sediment mixing has distorted the stratigraphic structure of the Site 690 PETM reference section. Chapter 3 demonstrates how the stable isotope signatures of individual foraminifer shells can be used to deconvolve the deleterious effects of sediment mixing on microfossil assemblages associated with abrupt biogeochemical perturbations. Application of this “isotopic filtering” method on the Site 865 PETM record reveals a transient but significant decrease in the diversity of tropical planktic foraminifer communities at the onset of the event, contrary to previous interpretations. Application of the aforementioned isotopic filtering method to high-latitude planktic foraminiferal assemblages of the PETM record of Site 1135 in chapter 4 revealed a similar, short-lived decrease in diversity, previously undetectable in the unfiltered assemblages. Lastly, in chapter 5, I generate parallel δ13C records of the carbon isotope excursion (CIE) marking the PETM in the Site 1135 section using traditional gas source mass spectrometry (GSMS) requiring analysis of whole foraminifer shells and secondary ion mass spectrometry (SIMS) where in-situ δ13C measurements are made on micrometer-scale domains within individual foraminifer shells. Comparison of these parallel δ13C records shows how GSMS analyses fail to capture the full magnitude of the CIE due to incorporated measurement of diagenetic calcite.