New ice core data tracks climate-changing eruptions

Newswise — Understanding events that changed the global climate thousands of years ago can help scientists predict how the climate changes moving forward. However, those predictions are only as good as the data upon which they are based, according to South Dakota State University chemistry professor Jihong Cole-Dai.

He is part of an international team of scientists that analyzed chemicals in an ice core from West Antarctica to compile a comprehensive record of 426 large volcanic eruptions that occurred during the last 11,000 years. A chronology of these eruptions is available on Open PRAIRIE.

This is the most accurate chronology of volcanic eruptions produced thus far, according to Cole-Dai, who has been doing ice core research for more than 20 years. “This is the highest-quality volcanic record because of the high-resolution chemical measurements and exceptionally accurate time scale—this has never been done before.”

Cole-Dai is the lead author on an article in the March issue of the Journal of Geophysical Research that describes their findings and how that data can help climate scientists and anthropologists. Two SDSU doctoral students also worked on the data analysis.

Tracking large volcanic eruptions that affected the global climate can help scientists predict how the atmosphere and oceans will respond to variables, such as volcanic aerosols and increased carbon dioxide, and thereby develop accurate ways to forecast climate change.

Cole-Dai leads the SDSU Ice Core and Environmental Chemistry Lab, which specializes in measuring trace chemicals in polar ice cores, and has secured nearly $3.5 million in National Science Foundation funding for ice core research. He and his team have worked on projects in Greenland and Antarctica, including the West Antarctic Ice Sheet Divide Ice Core Project, which involved more than 20 universities and national laboratories.

Examining eruptions

“One of the most important objectives was to lay out a record that goes back 11,000 years,” Cole-Dai said. Using the improved data, the researchers looked at whether the frequency of volcanic eruptions was changing. “We did not see a trend—about the same number of eruptions happen within each millennium,” he explained.

Other researchers have suggested that more eruptions have occurred in the last 1,000 years. However, Cole-Dai said, “Our conclusion is different because our data is higher quality.”

About 8,200 years ago, the Earth experienced a mini-ice age, known as the 8.2 ka event, which lasted about 160 years. Scientists have been trying to figure out what caused this, Cole-Dai explained. “Because our records are so good, we were able to place three large (volcanic) eruptions at the time when 8.2 ka was happening.” These eruptions may have contributed to the cooling.

More importantly, scientists use the data for climate modeling. “What is interesting to those predicting future climate is how much a given amount of aerosols (in the upper atmosphere) cools the climate,” Cole-Dai said. “If they know how big an eruption was 1,000 years ago and how much temperatures cooled, they can apply that to their climate models.” This data can help scientists calibrate and adjust the sensitivity of their models.

By using models of calibrated sensitivity, the scientists can also calculate, for instance, how a given amount of carbon dioxide in the atmosphere might contribute to global warming.

Constructing ancient timelines

The record of volcanic eruptions can also be helpful to archeologists and anthropologists. Those studying early civilizations often need a common timeline to determine how civilizations might have influenced another, but each civilization had its own way of keeping track of time, Cole-Dai explained. “You need a common event that appears in all the histories.”

The Thera eruption that blew up the middle of the Greek island now known as Santorini is one such event. “Scientists have been unable to determine exactly which year that eruption happened,” Cole-Dai said. One group of scholars has narrowed the eruption to a 50-year interval—from 1600 to1650 B.C., while another group has evidence that it happened 100 years later.

“In ice core data from 1600 to 1650 B.C., we do not find evidence of the Thera eruption,” Cole-Dai said. Therefore, the eruption is more likely to have occurred in the later period. “That is how our science is able to contribute to this debate.”