The South Sandwich Volcanic Arc is one of the most remote and enigmatic arcs on Earth. Sporadic observations from rare cloud-free satellite images—and even rarer in situ reports—provide glimpses into a dynamic arc system characterised by persistent gas emissions and frequent eruptive activity. Our understanding of the state of volcanic activity along this arc is incomplete compared to arcs globally. To fill this gap, we present here detailed geological and volcanological observations made during an expedition to the South Sandwich Islands in January 2020. We report the first in situ measurements of gas chemistry, emission rate and carbon isotope composition from along the arc. We show that Mt. Michael on Saunders Island is a persistent source of gas emissions, releasing 145 ± 59 t day−1 SO2 in a plume characterised by a CO2/SO2 molar ratio of 1.8 ± 0.2. Combining this CO2/SO2 ratio with our independent SO2 emission rate measured near simultaneously, we derive a CO2 flux of 179 ± 76 t day−1. Outgassing from low temperature (90–100 °C) fumaroles is pervasive at the active centres of Candlemas and Bellingshausen, with measured gas compositions indicative of interaction between magmatic fluids and hydrothermal systems. Carbon isotope measurements of dilute plume and fumarole gases from along the arc indicate a magmatic δ13C of − 4.5 ± 2.0‰. Interpreted most simply, this result suggests a carbon source dominated by mantle-derived carbon. However, based on a carbon mass balance from sediment core ODP 701, we show that mixing between depleted upper mantle and a subduction component composed of sediment and altered crust is also permissible. We conclude that, although remote, the South Sandwich Volcanic Arc is an ideal tectonic setting in which to explore geochemical processes in a young, developing arc.
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We are grateful to the crew of the Pelagic Australis—Chris Kobusch, Sophie O’Neill, Thomas Geipel—without whom this fieldwork would never have been possible. We also wish a huge thank you to all other expedition members—Paul Mayewski, Mario Potocki, Gemma Clucas, Jo Feldman, Ruth Peacey, Hamza Yassin and Ted Cheeseman—for their unwavering support in the field and for their sense of humour aboard a small boat for 5 weeks. In particular, we thank Skip Novak—expedition lead—who assisted us ashore on all our sampling excursions. E.J.L. thanks John Smellie for first putting her in contact with T.H., which ultimately led to this study. We acknowledge the support from the Government of South Georgia and the South Sandwich Islands. We thank Yuri Taran and an anonymous reviewer for their helpful reviews, and A. Cannata for editorial comments.
This expedition was funded by public donations raised by Quark Expeditions Ltd., by the Government of South Georgia and the South Sandwich Islands (GSGSSI) and by individual contributions. This work was carried out under RAP 2019/025 issued by GSGSSI. EJL was supported by a Leverhulme Early Career Fellowship. A.A. and M.B. acknowledge funding from Miur (Grant N. 2017LMNLAW). K.W. acknowledges support from the Mount Everest Foundation (20-06).
© 2020, The Author(s).
Copyright 2020 Elsevier B.V., All rights reserved.
- South Sandwich Volcanic Arc
- Volcanic activity
- Volcanic gas emissions