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.

中文翻译：

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南三明治弧沿线的火山活动和气体排放

南三明治火山弧是地球上最遥远、最神秘的弧之一。来自罕见的无云卫星图像的零星观测——甚至更罕见的现场报告——提供了对以持续气体排放和频繁喷发活动为特征的动态弧系统的一瞥。与全球弧相比，我们对沿该弧的火山活动状态的理解是不完整的。为了填补这一空白，我们在此展示了 2020 年 1 月在南桑威奇群岛探险期间进行的详细地质和火山学观测。我们报告了沿弧线的气体化学、排放率和碳同位素组成的首次原位测量。我们表明，山。桑德斯岛上的迈克尔是一个持续的气体排放源，在以 CO2/SO2 摩尔比为 1 为特征的羽流中释放 145 ± 59 t day−1 SO2。8±0.2。将此 CO2/SO2 比率与我们几乎同时测量的独立 SO2 排放率相结合，我们得出 179 ± 76 t day−1 的 CO2 通量。在 Candlemas 和 Bellingshausen 的活动中心，从低温 (90–100 °C) 喷气孔中排出的气体普遍存在，测量的气体成分表明岩浆流体和热液系统之间的相互作用。沿弧的稀释羽流和喷气孔气体的碳同位素测量表明岩浆 δ13C 为 − 4.5 ± 2.0‰。最简单地解释，该结果表明碳源以地幔衍生碳为主。然而，基于沉积物核心 ODP 701 的碳质量平衡，我们表明耗尽的上地幔与由沉积物和蚀变地壳组成的俯冲成分之间的混合也是允许的。我们得出的结论是，虽然遥远，