| Summary: | The world’s oceans are facing unprecedented challenges in response to a rapidly changing climate. Understanding Earth system response through time can enable better predictions of the future trajectory of Earth systems. The calcium carbonate shells of planktonic foraminifera encapsulate biogeochemical fingerprints of the oceans in which they formed, by proxy recording ocean, atmosphere, and climate conditions of the past. This thesis furthers our understanding and application of planktonic foraminifera in palaeoceanography through four experimental geochemical studies. Electron backscatter diffraction analysis (EBSD) was used to investigate foraminiferal test microstructure and preservation. Three processes of post-depositional modification were identified, namely: 1) dissolution; 2) interface-coupled fluid-mediated replacement reactions of dissolution and re-precipitation; and 3) inorganic overgrowth. Paired with electron microprobe analysis (EMPA) of Mg/Ca distribution, these processes were found to affect foraminiferal geochemistry to differing degrees; with implications for microfossil utility in palaeoclimate reconstructions. Single-specimen stable isotope analysis enabled refined understanding of “Globorotalia” ecology; challenging broader assumptions of ecological niche conservatism within foraminifera clades. Recommendations are made on the assignment and application of foraminiferal functional groups in palaeoceanography, and best practice using stable isotope analysis for palaeoclimate reconstructions. S/Ca in foraminifera is hypothesised as a proxy for seawater carbonate ion concentration (as a function of seawater [SO₄²-] / [CO3²-]), which is intrinsically linked with atmospheric CO2. This thesis finds the relationship between seawater [SO₄²-] / [CO3²-] and planktonic foraminiferal S/Ca more complex than first hypothesised. Potential controls on S incorporation were investigated, with recommendations for further research using this study as a foundation. The isotopic composition of neodymium (εNd) in ...
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