Speleothem Archives of New Zealand Volcanism: In Search of theTaupō Eruption of 232 ± 10 CE

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dc.contributor.advisor Baker, J en
dc.contributor.advisor Baker, S en
dc.contributor.author Gampell, Nicholas en
dc.date.accessioned 2019-12-05T00:22:05Z en
dc.date.issued 2019 en
dc.identifier.uri http://hdl.handle.net/2292/49296 en
dc.description Full Text is available to authenticated members of The University of Auckland only. en
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. en
dc.publisher ResearchSpace@Auckland en
dc.relation.ispartof Masters Thesis - University of Auckland en
dc.relation.isreferencedby UoA99265208213502091 en
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. en
dc.rights Restricted Item. Full Text is available to authenticated members of The University of Auckland only. en
dc.rights.uri https://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm en
dc.title Speleothem Archives of New Zealand Volcanism: In Search of theTaupō Eruption of 232 ± 10 CE en
dc.type Thesis en
thesis.degree.discipline Earth Sciences en
thesis.degree.grantor The University of Auckland en
thesis.degree.level Masters en
dc.rights.holder Copyright: The author en
pubs.elements-id 788632 en
pubs.org-id Science en
pubs.org-id School of Environment en
pubs.record-created-at-source-date 2019-12-05 en


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