The most recent transition, from a greenhouse to an icehouse climate state, occurred during the Eocene-Oligocene transition (~34 Ma) and is thought to have been driven by a long-term decline in carbon dioxide concentrations and/or changes in ocean heat redistribution as a result of tectonic gateway reorganisation. In order to determine the primary driving mechanisms responsible, this thesis reconstructs long-term terrestrial and marine temperature change during the Eocene (56.0-33.9 Ma) using an organic biomarker approach. During the descent towards the icehouse (48-34 Ma), high-latitudes (>55°) are characterised by gradual surface water cooling (~6.5 0c). During the same interval, low-latitude settings exhibit ~2.5 °C of cooling. An ensemble of fixed-C02 climate model simulations that span the Eoc'ene indicate that only a small percentage (~5 to 15%) of this reconstructed temperature change can be ascribed to ocean gateway reorganisation or paleogeographic change. As such, this indicates that atmospheric carbon dioxide was the most likely driver of surface water cooling during the middle and late Eocene (48-34 Ma). To explore this further, new terrestrial temperature records were obtained from marginal marine settings and terrestrial lignite deposits. During the early Eocene, terrestrial temperatures remain stable and warm and coincide with a long-term maximum in global surface water temperatures and atmospheric carbon dioxide. Insights from lignite deposits indicate that additional carbon cycle feedback mechanisms (e.g. methane cycling) may have also been important in regulating early Eocene warmth. During the middle and late Eocene, terrestrial temperatures remain stable or exhibit a gradual decline (~3 °C). The magnitude of terrestrial cooling is much smaller than observed in the marine realm and implies significant changes in ocean heat redistribution during the middle and late Eocene. Although changes in ocean heat redistribution are consistent with C02 drawdown, tectonic gateway reorganisation may have also been important in some regions.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:685351 |
| Date | January 2015 |
| Creators | Inglis, Gordon Neil |
| Publisher | University of Bristol |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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