Stratospheric eruptions from tropical and extra-tropical volcanoes constrained using high-resolution sulfur isotopes in ice cores
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The record of volcanic forcing of climate over the past 2500 years is based primarily on sulfate concentrations in ice cores. Of particular interest are large volcanic eruptions with plumes that reached high altitudes in the stratosphere, as these afford sulfate aerosols the longest residence time in the atmosphere, and thus have the greatest impact on radiative forcing. Sulfur isotopes measured in ice cores can be used to identify these large eruptions because stratospheric sulfur is exposed to UV radiation, which imparts a time-evolving mass independent fractionation (MIF) that is preserved in the ice. However, sample size requirements of traditional measurement techniques mean that the MIF signal may be obscured, leading to an inconclusive result. Here we present a new method of measuring sulfur isotopes in ice cores by multi-collector inductively coupled plasma mass spectrometry, which reduces sample size requirements by three orders of magnitude. Our method allows us to measure samples containing as little as 10 nmol of sulfur, with a precision of 0.11‰ for δ34S and 0.10‰ for Δ33S, enabling a high-temporal resolution over ice core sulfate peaks. We tested this method on known tropical (Tambora 1815 and Samalas 1257) and extra-tropical (Katmai/Novarupta 1912) stratospheric eruptions from the Tunu2013 ice core in Greenland and the B40 ice core from Antarctica. These high-resolution sulfur isotope records suggest a distinct difference between the signatures of tropical versus extra-tropical eruptions. Furthermore, isotope mass balance on sulfate from extra-tropical eruptions provides a means to estimate the fraction of sulfate deposited that was derived from the stratosphere. This technique applied to unidentified eruptions in ice cores may thus improve the record of explosive volcanism and its forcing of climate.
Burke , A , Moore , K A , Sigl , M , Nita , D C , McConnell , J R & Adkins , J F 2019 , ' Stratospheric eruptions from tropical and extra-tropical volcanoes constrained using high-resolution sulfur isotopes in ice cores ' , Earth and Planetary Science Letters , vol. 521 , pp. 113-119 . https://doi.org/10.1016/j.epsl.2019.06.006
Earth and Planetary Science Letters
Copyright © 2019 Elsevier B.V. All rights reserved. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1016/j.epsl.2019.06.006
DescriptionThis research was funded by a Foster and Coco Stanback postdoctoral fellowship and a Marie Curie Career Integration Grant (CIG14-631752) to AB and a NSF-OCE grant 1340174 and NSF-EAR grant 1349858 to JFA. MS acknowledges funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 820047). NSF-PLR grant 1204176 to JRM supported collection and analysis of the Tunu2013 core.
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