Prehistoric Climate Change Clues Unearthed in Ancient Caves

Scientists are learning a bit more about prehistoric climate change. It turns out that the steady drip of water deep underground can reveal quite a bit of information about the constantly changing cycles of heat and cold and precipitation and drought in the atmosphere above.

As water seeps through the ground, it picks up minerals, the most common of which is calcium carbonate. When this mineral-rich water drips into caves, it leaves mineral deposits behind that form layers which grow during wet periods and form dusty skins when the water dries up.

Today, researchers can date these layers with extreme precision based on the radioactive decay of uranium into its daughter product thorium. Variations in the thickness of the layers is determined by a combination of the amount of water seeping into the cave and the concentrations of carbon dioxide in the cave's atmosphere. When conditions are right, this means that the layers can tell scientists about the precipitation in the environment.

In this latest study, the researchers looked at a cave in north east India. They made a detailed record of the last 50 years of growth of a stalagmite that formed in the cave. This revealed that during El Niño Modoki events, when drought was occurring in central India, the mineral chemistry suggested more localized storm events occurred above the cave, while during the El Niño periods, the water that seeped into the cave had traveled much farther before it fell, which is the typical monsoon pattern.

"Now that we have shown that the Mawmluh cave record agrees with the instrumental record for the last 50 years, we hope to use it to investigate relationships between the Indian monsoon and El Niño during prehistoric times such as the Holocene," said Jessica Oster, one of the researchers, in a news release.

The findings are published in the journal Geophysical Research Letters.

For more great science stories and general news, please visit our sister site, Headlines and Global News (HNGN).