| Summary: | Ice cores are amongst best resolved records of past climate change and volcanism for the Late Quaternary period. For the Common Era, counting errors on annual layers can been “zeroed” intermittently though the presence of precisely-dated cryptotephras. Here we report on the identification and analysis of a cryptotephra that is concurrent in the NEEM-2011-S1 with an acid layer previously attributed to the historically recorded eruption of Vesuvius in 79 CE. The cryptotephra has a major and trace element geochemistry that is clearly differentiable from that of Vesuvius, and from all other major eruptions currently thought to have erupted within two centuries of Vesuvius. Its geochemistry is instead consistent with an origin in an active arc, and we find possible correlatives with sources as far afield as the Aleutians, the Kuriles and Mexico, though a robust correlation remains elusive. Using an ash-modelling approach, we estimate the eruption magnitude that would be needed to disperse the tephra from our three candidate sources to northern Greenland. We consider the implications of each of the three scenarios for the approximation of atmospheric sulphate loading, as inferred from the ice core sulphate/sulphur data, and thus for the climate forcing potential of the event. Our study illustrates the difficulties of affirming the sources of volcanic signals in ice cores, and the risks involved with mis-attributing them to well-known eruptions.
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