dc.contributor.advisor |
Baker, J |
en |
dc.contributor.advisor |
Baker, S |
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dc.contributor.author |
Gampell, Nicholas |
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dc.date.accessioned |
2019-12-05T00:22:05Z |
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dc.date.issued |
2019 |
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dc.identifier.uri |
http://hdl.handle.net/2292/49296 |
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dc.description |
Full Text is available to authenticated members of The University of Auckland only. |
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dc.description.abstract |
This study examined whether New Zealand speleothems preserved the 232 ± 10 CE Taupō eruption (VEI 7). A stalagmite, TR-990218B (TR-B), from Te Reinga Cave in the eastern North Island was subjected to various geochemical techniques to search for evidence of the eruption, which deposited ~10-20 cm of volcanogenic material over the cave site. High-precision uranium-series ages revealed a significant increase in growth rate shortly after the eruption (a factor of ~4 for ~35-40 yr). Trace element profiles obtained by laser-ablation-inductively-coupled-plasma-mass-spectrometry exhibited two concentration peaks in S at 214 ± 27 CE (lasting ~7 yr) and 243 ± 23 CE. Field-emission-scanning-electronmicroscopy with energy-dispersive-spectroscopy observations at 214 ± 27 CE revealed particulate/colloidal material with elevated Si, K, Na, Mg, Al, S, Cl, and Ti contents, but not consistent with rhyolitic cryptotephra. High-resolution stable C-O isotopic analyses show decoupling for ~11 yr from 214 ± 27 CE, as compared to other parts of the stalagmite record. These observations strongly suggest TR-B preserved a fingerprint of the Taupō eruption. Growth rate increases can be ascribed to: (1) de-vegetation above the cave site due to ashfall, which perturbed normal evapotranspiration processes, and thus increased water flow into the cave; (2) the enhanced acidity of the percolating groundwater (due to increases in inorganic/organic acids) increasing karst dissolution and subsequent delivery of Ca (for stalagmite growth) into the cave; and (3) regenerating vegetation as new plant root systems and bacterial colonies thrive on surplus nutrients in the soil enhancing carbonic acid production, and thus stalagmite growth. Lower Mg/Ca ratios at this time can also be accounted for by these processes, as a decrease in prior-calcite-precipitation due to evapotranspiration decrease above the cave (i.e., effectively causing wetter conditions) would decrease stalagmite Mg/Ca ratios. Moreover, this process is consistent with stable isotope decoupling, due to vegetation destruction above the cave site. The patterns in S can be explained by volcanically sourced aerosols being deposited above the cave and then by immediate leaching from the volcanic ash deposited above the cave, which persisted for more than ~20 yr due to biogeochemical cycling. In summary, this study suggests that New Zealand speleothems preserve evidence of volcanic eruptions, which can be used to refine eruption ages using U-series dating techniques and also assess the nature and duration of environmental change produced by eruptions. |
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dc.publisher |
ResearchSpace@Auckland |
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dc.relation.ispartof |
Masters Thesis - University of Auckland |
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dc.relation.isreferencedby |
UoA99265208213502091 |
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dc.rights |
Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated. Previously published items are made available in accordance with the copyright policy of the publisher. |
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dc.rights |
Restricted Item. Full Text is available to authenticated members of The University of Auckland only. |
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dc.rights.uri |
https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm |
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dc.title |
Speleothem Archives of New Zealand Volcanism: In Search of theTaupō Eruption of 232 ± 10 CE |
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dc.type |
Thesis |
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thesis.degree.discipline |
Earth Sciences |
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thesis.degree.grantor |
The University of Auckland |
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thesis.degree.level |
Masters |
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dc.rights.holder |
Copyright: The author |
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pubs.elements-id |
788632 |
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pubs.org-id |
Science |
en |
pubs.org-id |
School of Environment |
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pubs.record-created-at-source-date |
2019-12-05 |
en |
dc.identifier.wikidata |
Q112948507 |
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