Cave Drawings and Ancient: Surprise Climate Learnings

Graffiti scribbled inside a cave in China has revealed how drought affected the local population over the past 500 years. 

Researchers from the University of Cambridge discovered that these unique inscriptions inside that country's Dayu Cave contain valuable information. Paired with a detailed chemical analysis of the stalagmites in the cave, we now know how local populations were affected and how to develop the means for dealing with future climate changes, according to a release.

"In addition to the obvious impact of droughts, they have also been linked to the downfall of cultures -- when people don't have enough water, hardship is inevitable and conflict arises," Dr. Sebastian Breitenbach of Cambridge, one of the paper's co-authors, said in the statement. "In the past decade, records found in caves and lakes have shown a possible link between climate change and the demise of several Chinese dynasties during the last 1800 years, such as the Tang, Yuan and Ming Dynasties."

The inscriptions indicated that during times of drought, residents would come to the cave to get water and pray for rain. An inscription from 1891 reads, "On May 24th, 17th year of the Emperor Guangxu period, Qing Dynasty, the local mayor, Huaizong Zhu led more than 200 people into the cave to get water. A fortune-teller named Zhenrong Ran prayed for rain during the ceremony," the release noted. 

Researchers removed sections of mineral formations, or speleothems (the broader term for stalagmites, stalactites, and similar), to analyze present stable isotopes and trace elements. Concentrations of certain elements that were found were correlated to periods of drought. They verified their findings by cross-referencing the chemical profile of the cave with the writing on the walls. Their findings were recently published in the journal Scientific Reports. 

"There are examples of things like human remains, tools and pottery being found in caves, but it's exceptional to find something like these dated inscriptions," Dr. Liangcheng Tan of the Chinese Academy of Sciences in Xi'an and the paper's lead author, said in the statement. "Combined with the evidence found in the physical formations in the cave, the inscriptions were a crucial way for us to confirm the link between climate and the geochemical record in the cave, and the effect that drought has on a landscape."

Generally, speleothems reveal a series of layers when cut open. These layers record annual growth. By using mass spectrometry, the researchers were able to analyze and dated the ratios of the stable isotopes of oxygen, carbon, as well as concentrations of uranium and other elements. From this they found that higher oxygen and carbon isotope ratios, in particular, corresponded with lower rainfall levels, the release said.

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