UCLA

Temperature reconstructions of past oceanic conditions and climates are vital to our understanding of the earth system. Foraminiferal tests are one of the most widely used archives of past climate. Several studies have previously reported that the clumped isotope composition (Δ47) of core-top foraminifera record seawater temperatures, and this proxy is increasingly being applied to foraminifera. In this thesis, I examine multiple aspects of foraminiferal clumped isotope thermometry that are less well constrained and apply this proxy to early Cenozoic samples for temperature reconstructions in a hothouse climate. The first chapter presents an investigation of thermal and non-thermal effects on core-top foraminifera that includes both new data and a meta-analysis of published data. It shows that foraminiferal Δ47-temperature regressions are indistinguishable from inorganic calcite. It also reports possible effects of bottom water carbonate saturation on both planktic and benthic foraminifera. The second chapter is an investigation of the potential impacts of dissolution on foraminiferal Δ47. We report data for multiple species from a core-top transect at the Ontong Java Plateau and from dissolution impacts. It shows evidence that in some species, dissolution elevates Δ47, and biases Δ47-temperatures to colder values. Multiple mechanisms for dissolution impacts on ∆47 and correction methods are explored. The third chapter applies clumped isotope paleothermometry to constrain temperatures across the Paleocene-Eocene Thermal Maximum (PETM) in the South Atlantic. We report planktic foraminiferal and fine fraction isotopic data and derive sea surface temperature and seawater composition estimates and compare this record to published proxy-based temperature estimates and climate model predictions. Chapter 4 investigates clumped isotope changes across the PETM but over a suite of global oceanic sites. Non-thermal influences, especially recrystallization and dissolution, contribute variably to each site, and this chapter systematically explores the possible impacts of each of these factors to the interpretation of clumped isotope temperature estimates, and comparisons with other proxy reconstructions and model temperatures. These reconstructions are used to evaluate equator-to-pole temperature and seawater δ18O gradients, and climate sensitivities to forcing, and could be used for model parameterization.