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Ice cores serve as archives of the Earth’s past atmosphere and are invaluable to improving our understanding of past climate. These cores preserve regional and global volcanic histories. Traditionally, the chemical components associated with volcanic aerosols measured in ice have been used to identify volcanic deposits in ice. However, only a handful of studies have identified sources of low concentration ultra-fine volcanic ash (cryptotephra) layers associated with chemically identified horizons. A pioneering study by Palais et al., [Annals of Glaciology, 14, 216-220 (1990)], identified five cryptotephra intervals in the PS1 firn core from South Pole, Antarctica. Now, some 30 years later and armed with improved technology, refined methodologies, and the recently drilled South Pole Ice Core (SPC14), we revisit these tephra-bearing volcanic intervals. Guided by high-resolution glaciochemical time series data, we were able to extract cryptotephra particles from ice intervals corresponding to the eruptions of Tambora (1815 CE); the unknown 1809 CE event; Huaynaputina (1600 CE); Nevado Del Ruiz (1595 CE); and Samalas (1257 CE) at much finer sampling resolutions than was previously possible. Each sample was prepared using recently developed sample mounting techniques tuned to maximize particle recovery, and analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Both the Tambora and 1809 intervals comprise small (< 2μm) particles ranging in composition from trachyandesitic to rhyolitic. As a whole, cryptotephra particles from the Huaynaputina interval represent largely homogenous rhyolitic particles with minor occurrences of trachyte. The composition of cryptotephra from the Nevado Del Ruiz interval ranges from basaltic trachyandesite to trachyte. Lastly, cryptotephra compositions of the Samalas interval include both rhyodacitic and trachytic particles. We captured a wider range of cryptotephra compositions than previously presented for the selected volcanic intervals and many contain subtropical particles (dacite-rhyolite) and local particles (trachytes). These findings will be informative for understanding volcanic eruption dynamics and atmospheric transport of local and distal tephra. This material is based upon work supported by the USA National Science Foundation under Grants No. PLR-1543454 and 1543361.

This work was supported by funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement 820047 to M.Si.), the Malcolm H. Wiener Foundation (Interdisciplinary Chronology of Civilizations Project to C.P.) and a UKRI Future Leader Fellowship (MR/S035478/1 to P.A). Decades of research have focused on establishing the exact year and climatic impact of the Minoan eruption of Thera, Greece (c.1680–1500 BCE). Ice cores offer key evidence to resolve this controversy, but attempts have been hampered by a lack of multi-volcanic event synchronization between records. In this study, Antarctic and Greenland ice-core records are synchronized using a double bipolar sulfate marker and calendar dates are assigned to each eruption revealed within the ‘Thera period’. From this global scale sequence of volcanic sulfate loading, we derive indications towards each eruption’s latitude and potential to disrupt the climate system. Ultra-fine sampling for sulfur isotopes and tephra conclusively demonstrate a colossal eruption of Alaska’s Aniakchak II as the source of stratospheric sulfate in the now precisely dated 1628 BCE ice layer. These findings end decades of speculation that Thera was responsible for the 1628 BCE event, and place Aniakchak II (52 ± 17 Tg S) and an unknown volcano at 1654 BCE (50 ± 13 Tg S) as two of the largest Northern Hemisphere sulfur injections in the last 4000 years. This opens possibilities to explore widespread climatic impacts for contemporary societies and, in pinpointing Aniakchak II, confirms that stratospheric sulfate can be globally distributed from eruptions outside the tropics. Dating options for Thera are reduced to a series of precisely dated, constrained stratospheric sulfur injection events at 1611 BCE, 1562-1555 BCE and c.1538 BCE which are all below 14 ± 5 Tg S, indicating a climatic forcing potential for Thera well below that of Tambora (1815 CE). Publisher PDF