Agriculture, Mining Releases Carbon Trapped in Ancient Soils, Researchers Say

University of Wisconsin-Madison researchers said that ancient soils store large amounts of trapped carbon.

The carbon from this soil, which is now being released due to erosion, agriculture and mining could contribute to climate change, researchers said.

"There is a lot of carbon at depths where nobody is measuring," said Erika Marin-Spiotta, a University of Wisconsin-Madison assistant professor of geography and the lead author of the new study. "It was assumed that there was little carbon in deeper soils. Most studies are conducted in only the top 30 centimeters. Our study is showing that we are potentially grossly underestimating carbon in soils."

Marin-Spiotta and her colleagues studied "Brady soil", which was formed some 15,000-13,500 years ago. Modern-day Nebraska, Kansas and other parts of the Great Plains have Brady soil underneath the surface.

Changes in North American climate some 10,000 years ago sparked a series of events that led to the formation of Brady soil in this region. The soil accumulated carbon via wildfires burning vast amount of vegetation. The organic matter then got buried under accumulating loess or dust.

"Most of the carbon (in the Brady soil) was fire derived or black carbon," noted Marin-Spiotta, according to a news release. "It looks like there was an incredible amount of fire."

For the study, researchers examined one-meter-thick layer of dark soil present beneath modern-day surface. They say the soil is like a time-capsule, preserving remnants from ancient times. Researchers used spectroscopic and isotopic analyses to study the soil composition.

In 2012, another group of scientists had warned that global warming is helping forest soil carbon get into the atmosphere. Related studies have said that climate scientists keeping a tab on carbon budgets need to account for carbon present in the form of charcoal as well. Charcoal from wildfire gets deposited in lakes, rivers and oceans.

Joseph Mason, UW-Madison geography Professor and study co-author, said that ancient soils such as Brady aren't unique to the Great Plains. These fossilized soils are found in several areas in the world and are now being disturbed due to human-activities such as mining and agriculture.

The National Science Foundation and the Wisconsin Alumni Research Foundation and was published in the journal Nature Geoscience.