Tackling the gateways-CO2 problem: New insights into Earth’s greenhouse-icehouse transition

Slater-Lewis, Sophie 2024. Tackling the gateways-CO2 problem: New insights into Earth’s greenhouse-icehouse transition. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The Eocene-Oligocene Transition (EOT) was a dramatic climate shift ~33.7 Ma, during which a series of interconnected Earth System components resulted in a new climate state, in a time interval known as the Greenhouse-Icehouse Transition, when Earth went from being free of large-scale ice sheets to having a perennial cryosphere. The EOT is marked by a plethora of changes to the marine and terrestrial environments, and identifiable in the marine sediment record as a ~1.3 ‰ increase in the benthic foraminiferal δ18O record. The causes and feedbacks of this Greenhouse-Icehouse Transition are not fully understood. but may include a combination of internal (e.g. carbon cycle) and external drivers (e.g. orbital configuration). In order to advance our understanding of this transition, improved records characterising the nature and timing of both the climate change itself, and the associated climate system feedbacks, are required. This thesis addresses both of these, by investigating a long-standing conundrum surrounding the nature of deep-sea temperature change, and by exploring the interactions between ocean circulation, climate, and the carbon cycle in the Southern Ocean at the EOT. This was achieved by a three-pronged approach: (1) a boron isotope analytical methodology on a Nu Plasma II MC-ICP-MS was developed to enable future pCO2 reconstructions at Cardiff University. (2) SEM, EPMA, and laser ablation ICP-MS analyses of benthic foraminifera from classic EOT ODP Site 1218 demonstrated that enhanced dissolution in the late Eocene masked a cooling signal in the published Mg/Ca record. (3) Paired stable isotope and trace element data from thermocline species S. utilisindex at ODP Site 1138 (Kerguelen Plateau) show that as the ice sheet grew, the Polar Front moved past the study site, producing a local cooling and freshening not observed at other sites in the same region. Furthermore, nutrients were delivered to the site, likely through weathering associated with a highly dynamic Antarctic Ice Sheet, which prompted orbitally-paced intervals of enhanced export productivity. No evidence was found for a direct role of Southern Ocean gateways. Overall, this thesis provides new insights into a complex period in Earth History, and contributes towards the gateways-CO2 problem by finding evidence to suggest orbitally paced changes in environmental records.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Earth and Environmental Sciences
Subjects:	Q Science > QE Geology
Funders:	NERC GW4+ DTP
Date of First Compliant Deposit:	3 January 2025
Last Modified:	03 Jan 2025 11:03
URI:	https://orca.cardiff.ac.uk/id/eprint/174954

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