February 12, 2013
Chemistry ‘Trick’ Helps Settle Volcano Controversy
Brett Smith for redOrbit.com - Your Universe Online
Volcanic eruptions have been known to cause global cooling, although the extent of this cooling has been a topic of scientific controversy. Now a team of atmosphere chemists from the Tokyo Institute of Technology and the University of Copenhagen has devised a method for determining which historical cooling periods are the results of volcanic eruptions.When a large volcano erupts, it can propel gases high into the stratosphere where they can impact the global climate for a year or more. Smaller eruptions tend to have a shorter more localized effect on climate.
The high gas plumes of a large eruption end up spending longer in the harsh sunlight of the stratosphere, resulting in changes to the chemical signature of the gaseous volcanic sulfur. The changes can be detected be analyzing the balance of various isotopes found in volcanic samples.
"Historical records are not always so accurate. Some may have been written down long after the fact, or when a different calendar was in use by a different culture. But the chemistry does not lie,” said study co-author Matthew Johnson, an associate professor at the Department of Chemistry in the University of Copenhagen.
"Using our method we can determine whether a given eruption was powerful enough for the plume to enter the stratosphere affecting global climate. If we can find material from ancient eruptions it can now be used to give an accurate record of global volcanic events extending many hundreds of thousands of years back in time,” Johnson added.
Ironically, ice cores are the best places to find sample traces of volcanic activity. As annual snowfalls adds layers of ice in places like Greenland or Antarctica, they record a variety of events that occur in the atmosphere.
"With the sulfur isotope method, we now have 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" explained Johnson. "There are many controversial eruptions. 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.”
Johnson also noted that, “1601 was the 'year without a summer', and yet to this day no one knows where the volcano was that erupted. There's debate over whether there was an eruption on Iceland in 527, or 535, or 541. The sulfur isotope trick is a definite method to solve debates like this and get the most information out of the ice core records.”
Since Denmark has no volcanoes, Johnson collaborate with other researchers based on the opposite side of the globe.
"The Tokyo Institute of Technology specializes in analysis of the patterns of sulfur isotopes found in samples in nature, and was able to synthesize the isotopically labeled samples,” Johnson said. “The University of Copenhagen has a strong group in atmospheric chemistry and spectroscopy; the laboratory measurements were carried out in Copenhagen.”
“Together we were able to do the experiments and build the atmospheric chemical model that demonstrated the stratospheric photoexcitation mechanism,” he said.