Scientists Link Climate Events in Last Glacial Period to Rapid Changes

Large Icebergs float away as the sun rises near Kulusuk, Greenland, on Aug. 16, 2019. (AP Photo/Felipe Dana)

(CN) — An international team of scientists have connected a number of rapid climate change events from the last glacial period in new research that may help future work in climate chronology.

Their findings link 25 major rapid cycles of warming and cooling recorded in Greenland’s ice cores during the last glacial cycle, which occurred 115,000 to 11,700 years ago, to other known climate changes in the Asian Monsoon, South American Monsoon, and parts of Europe and the Mediterranean. Those 25 abrupt changes are known as the Dansgaard-Oschger events, or D-O events.

“Each of these events were characterized by very abrupt warming over Greenland, of up to 16 degrees Celsius, sometimes within decades,” said Ellen Corrick, a researcher at the University of Melbourne and lead author of the study published Thursday in the journal Science. “These warmer conditions lasted for several hundred to several thousands of years before a more gradual cooling occurred.”

The globe’s climate was starkly different during that last glacial age: ice sheets covered Northern Europe, Asia and roughly half of North America. Sea levels were lower across the world, and the climate was colder and drier.

During this period, Corrick said, Europe experienced temperature and rainfall changes in sync with the D-O climate events. The tropics’ monsoon systems also saw changing rainfall patterns associated with the fluctuating temperature over Greenland.

“We found that abrupt climate changes during Dansgaard-Oeschger events occurred simultaneously across a region extending from the Arctic to the southern sub-tropics, within decades in some cases,” Corrick said in an interview. “We have also determined exactly when the abrupt changes occurred, much more precisely than ever before.”

To determine whether these changes were synchronous, or if they exceeded or lagged behind the Greenland temperature oscillations, Corrick led an appropriately globe-spanning team of 10 researchers from institutions in Australia, China, Denmark, France, Germany, Switzerland, and the U.K. 

“This is something that has been really difficult to test, until now. This is because we need very precisely dated records, in order to know exactly when the climate events occurred. Such records are rare,” Corrick said. “Remember we are talking about events that occurred many tens of thousands of years ago, so determining timing to within decades requires state-of-the-art records.”

The major difference, Corrick said, is that the team could take advantage of 63 published stalagmite records that helped date climactic events as recorded in cave stalagmites all over the world.

“Stalagmites form layer-by-layer, and as they grow they preserve a record of the climate and environmental conditions above the cave in their geochemical signatures. By making measurements on the stalagmites, we can obtain a record of how climate changed during the past,” Corrick said.

The scientists were able to use stalagmite records from European, Asian and South American cave sites — records collected over two decades by teams across the globe — with confidence, because stalagmites can be dated with accurate radiometric methods.

“As a stalagmite grows, minute amounts of uranium are trapped in the crystals. Over time, this uranium slowly undergoes radioactive decay to other isotopes, whose accumulation acts as a sort of ‘clock,’” Corrick said. “Using mass spectrometry, we can measure the relative abundance of these isotopes in a piece of the stalagmite. This enables us to determine the age of the stalagmite very precisely.”

Their findings also help future climate research, because accurately dated measurements and observations work as a check or a grading rubric for climate models’ projections.

“Studying past climates is important, because it enables us to validate these models. For example, in our study we compared the data from the stalagmites to the climate model output,” Corrick said.

While the methods for dating the stalagmites is very precise, dating the Greenland ice cores is much more difficult. Because Corrick and her team could pinpoint synchronous events, those precise dates can be transferred to the ice-core record, enhancing its accuracy for future researchers’ sake.

Corrick hopes to bring these studies ever further south.

“In the future this research can also be extended to regions further south, to the southern limits of the South American, African and Australasian land masses. We currently know very little about how the climate of these regions responded to Arctic warming events,” Corrick said. “High-quality stalagmite records such as the ones we used in our study will be critical for this.”

In other Greenland climate news, its ice sheet recorded a record melt in 2019, according to German climatologists’ findings also published Thursday in Communications Earth & Environment. 

The previous record melt, recorded in 2012, lags last year’s by 15%. The researchers attribute the sheet’s swift melt — one of the largest contributors to global sea level rise — to a return from 2017 and 2018’s unusually cold summers in western Greenland and snow winters in eastern Greenland, which resulted in low loss of ice those years.

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