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Which volcanoes impacted ancient climate? Sulphur tells the story

Ice core isotopes ID the big blasts

A staple complaint of the climate sceptic, that it’s impossible to determine the impact of historical volcanic eruptions on the climate, is a step closer to being spiked, courtesy of work at the University of Copenhagen.

The university’s Matthew Johnson, an associate professor in the Department of Chemistry, has published work conducted with the Tokyo Institute of Technology in which he uses the isotopes captured in old sulphur to determine the scale of eruptions.

As explained in the university’s announcement, the work is designed to resolve the often-conflicting dates attached to recorded eruptions. Dating is difficult from ancient records, since historians may have been setting down their accounts years after the event, and there are discrepancies between different calendar systems in use.

Johnson explains that ice cores provide an accurate way to date the chemicals associated with a volcanic eruption, but until now, the scale of the eruption has been difficult to determine. The sulphur isotopes, he says, provide a way “to prove whether a given eruption was so explosive that it entered the stratosphere, affecting global climate and civilizations, or, whether a given eruption was confined to the troposphere and local in its effects”.

Since a large and powerful eruption sends a plume into the stratosphere, it reacts with sunlight to produce a different isotopic signature when the dust finally settles back to Earth. Capturing that signature should allow climate historians to work out whether a major event was associated with volcanism.

Citing some of the more contentious eruptions, he continues: “The Mediterranean island of Santorini blew apart and caused the end of the Minoan culture. But there is a huge debate about when exactly this occurred. 1601 was the 'year without a summer' - but nobody knows where the volcano was that erupted. There is debate over whether there was an eruption on Iceland in 527, or 535, or 541.

"The sulphur isotope trick is a definite method to solve debates like this and get the most information out of the ice core records.” ®

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