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Development and application of speleothem-based proxies for past climate change

This thesis develops and applies new techniques for reconstructing past environments from the speleothem archive. Chapter 3 introduces Ca isotopes as a novel palaeo-aridity proxy. Recent dripwater, farmed calcite and bedrock data show that, in the modern environment, 36% of initial dripwater Ca is removed by prior calcite precipitation at the HS4 dripsite (Heshang Cave, Central China). A speleothem record spanning the 8.2kyr event suggests this value increased to 60% during the event, in response to a decrease in effective rainfall of approximately a third. Modern Ca isotope systematics, and the cycling of other Group II metals, are studied further in Chapter 4. Data from Heshang Cave monitoring samples explore the temporal and spatial controls on these proxy systems. Results highlight the importance of secondary calcite as a potential source of dripwater metals, as well as the significant contribution of particulate calcite to bulk dripwater chemistry. At the HS4 dripsite, over a third of bulk dripwater Ca is present as particulate calcite. This influences bulk dripwater Ca concentrations and isotopes, as well as potentially impacting speleothem growth and chemistry. Chapters 5 introduces CaveCalc, a new numerical model for dripwater and speleothem chemistry and isotopes based on PHREEQC. Key strengths of CaveCalc include its ability to model multiple proxy systems in a single framework, the ability to quantify the extent of open-system dissolution, and the extensible nature of its design. Chapter 6 applies CaveCalc to disentangling the controls on dripwater and speleothem &delta;<sup>13</sup>C values. Model results are compared with speleothem data. At Heshang Cave, anomalously high &delta;<sup>13</sup>C is quantitatively explained as the result of CO<sub>2</sub> degassing and prior calcite precipitation, an interpretation made possible by the availability of coupled &delta;<sup>13</sup>C, a<sup>14</sup>C and Ca isotope data. This approach provides a powerful tool to help researchers better interpret dripwater and speleothem &delta;<sup>13</sup>C data.

Identiferoai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:729867
Date January 2017
CreatorsOwen, Robert
ContributorsDay, Chris ; Henderson, Gideon
PublisherUniversity of Oxford
Source SetsEthos UK
Detected LanguageEnglish
TypeElectronic Thesis or Dissertation
Sourcehttps://ora.ox.ac.uk/objects/uuid:0a44a913-7c28-40ac-9a5e-76811a393a8e

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