Whodunit? Determining the source and climatic forcing of unidentified volcanic eruptions from ice core archives.

The impact and frequency of large volcanic events is important to our society, with implications for global climate, governments, and industries such as aviation and agriculture. The cooling effect of volcanic sulfate aerosol emissions in the atmosphere is prolonged if the volcanic plume reaches the stratosphere and is globally circulated (Robock 2000). Therefore, having an accurate, high resolution record of past volcanism is important to understanding the frequency and climatic impact of large volcanic events which can significantly affect our society. We can understand more about the magnitude and location of large volcanic events from the ice core record, which can preserve sulfate and ash layers from local and distal eruptions (eg: Sigl et al. 2015). This continuous, high resolution ice record is therefore invaluable to the understanding past volcano-climate links.
This project aims to use both sulfur isotope analysis of volcanic sulfate deposits, and geochemical characterisation of tephra shards from ice core records to determine the plume height, source volcano and climatic forcing of large eruptions from the recent geological past (<200,000 years).
Multiple sulfur isotope analysis will be done using column chemistry and Multi Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICP-MS). Isotopic signature will help determine stratospheric or tropospheric plume height by the presence (or absence) of a mass independent fractionation (Baroni et al. 2007, 2008), and latitude of source volcano from comparison of isotopic data and SO4 concentration curves across the ice core eruption record (Burke et al. 2019).
Tephra from large unknown eruptions will be geochemically characterised using Electron Probe Micro Analysis, providing a unique fingerprint that can be used to determine potential sources for large eruptions, aided by latitudinal information given by S isotope data. Interpretation of tephra results will also aid understanding of dispersal of ash from past eruptions (Watson et al. 2016).
Once source location and magnitude of past eruptions are evaluated using these techniques, the climatic impact can be assessed. These characteristics have a strong control on the spatial extent and residence time of the sulfate aerosols in the atmosphere, allowing the global climatic impact of past eruptions to be evaluated.

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