The deep-sea climate record of the Eocene-Oligocene Transition
Approximately 34 million years ago, at the Eocene-Oligocene Transition (EOT), Earth abruptly transitioned to a climate state in which Antarctica became cool enough to sustain large ice sheets for the first time in tens to hundreds of millions of years. The introduction of this new component in the E...
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| Format: | Thesis |
| Language: | English |
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University of Southampton
2022
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| Online Access: | https://eprints.soton.ac.uk/471870/ https://eprints.soton.ac.uk/471870/1/VTaylor_Thesis_October2022_finaldigitalcopy.pdf https://eprints.soton.ac.uk/471870/2/FINAL_Permission_to_deposit_thesis_VTaylor_v2.pdf |
| Summary: | Approximately 34 million years ago, at the Eocene-Oligocene Transition (EOT), Earth abruptly transitioned to a climate state in which Antarctica became cool enough to sustain large ice sheets for the first time in tens to hundreds of millions of years. The introduction of this new component in the Earth system fundamentally changed the predictability of the climate response to astronomical forcing. Our understanding of EOT climate change and the feedback processes that drove the inception of sustained large-scale Antarctic glaciation, however, remains limited by the paucity of highly resolved and well-dated deep-sea records. Here I present records that address this problem and reappraise the sequence of events leading to the development of sustained large-scale Antarctic glaciation. In Chapter 3, I present bulk sediment stable isotope and carbonate content records from a depth transect of sites in the equatorial Pacific Ocean and one site from the subpolar South Atlantic Ocean, together with a new benthic foraminiferal stable isotope record from the shallowest and most expanded Pacific site. These records are used to reconstruct, in detail, changes in the calcite compensation depth (CCD) at the EOT. My analysis reveals (i) a global carbon cycle perturbation defined by a CCD shoaling and negative carbon isotope excursion at the onset of the EOT and leading directly into the first EOT CCD deepening step, (ii) a distinctive CCD over-deepening and settling pattern in the earliest Oligocene, and (iii) comparable results in both the eastern equatorial Pacific and subpolar South Atlantic suggesting that these CCD changes are likely driven by changes in global deep ocean chemistry. These findings show that the carbon cycle was perturbed prior to the inception of Antarctic glaciation. Once large-scale glaciation was initiated, however, rapid changes in global seawater chemistry forced a transient increase in carbon burial flux in the deep ocean far exceeding the new steady state values. In Chapter 4, I present the first ... |
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