Novel approaches to high resolution studies of calcareous nannofossils

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Hanson, Emma M ORCID: https://orcid.org/0000-0002-7812-7269 (2023). Novel approaches to high resolution studies of calcareous nannofossils. University of Birmingham. Ph.D.

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Abstract

Coccolith carbon isotope ’vital effects’, which are the departure of the coccolith isotopic composition from the expected isotopic signature of inorganic calcite, are proposed to have originated in the late Miocene, between 7 and 5 million years ago. The main control on the size of these vital effects is the degree of carbon limitation experienced by the coccolithophore cell during coccolithogenesis. In culture studies, the main extant species are split into an isotopically ‘heavy’ group of small, lightly calcifying forms, such as Gephyrocapsa oceanica and Emiliania huxleyi, and an isotopically ’light’ group of large, heavily calcifying forms, such as Calcidiscus leptoporus and Coccolithus pelagicus. This division between small, lightly calcifying and large, heavily calcifying forms is also well established in data from the geological record. The application of this understanding to the generation of new proxy measures for past ocean and ecological functioning is, however, hampered by the available size separation protocols that are labour intensive, time consuming and cannot be used to generate the ideal orbital-scale proxy records of environmental change. This thesis addresses this problem with the introduction of a novel size separation technique that allows for the rapid sample preparation of coccolith-rich sediments into very coarse and very fine coccolith size fractions. Using this new technique this thesis presents two new high resolution records of coccolith geochemistry – including oxygen and carbon isotopes and strontium/calcium ratios - with one spanning the Pliocene-Pleistocene Transition (3.01 to 1.38 million years ago) and the second a long-term record from the Miocene to Recent (7.7 to 0.1 million years ago). Both records are based on analyses of sediment from International Ocean Discovery Program Expedition 363, Site U1482, off the northwest margin of Australia. Site U1482 has a continuous sedimentary sequence from the late Miocene to Recent, with well-preserved nannofossil carbonate present throughout. The short term Plio-Pleistocene record provides a reference framework for high-resolution coccolith geochemistry in a stable tropical environment across a long sequence of orbital-scale variability. The long-term Miocene to Recent study records the onset of these coccolith vital effects and how they change with nannofossil evolution and climatic changes. These two records support the use of the new size separation technique and provide the highest resolution coccolith geochemistry records over the two time periods to date.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):