Buried Fossil Soil Contains Stocks of Carbon that can Contribute to Global Climate Change

Buried fossil soils could contribute to global climate change as they contain stocks of organic compound, a new study reveals.

Researchers at University of Wisconsin-Madison present a new aspect of the Earth's carbon cycle. They say that fossil soils that formed some thousands of years ago and are currently buried deep down the Earth's surface are rich in organic carbon. When these deep soils reach the surface either through erosion, agriculture, deforestation, mining and other human activities, they can be potential contributors to global climate change.

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

In this study the researchers focused on Brady soil that was formed some 15,000-13,500 years ago in Nebraska, Kansas and other regions of the Great Plains. The soil was present nearly six-and-a-half meters below surface. The soil is an accumulation of thousands of years of windborne dust called loess.  This occurred at the time when the glaciers that blanketed most of North America began to withdraw.

Though the region where Brady Soil was formed was not glaciated, the landscape did undergo some radical change as the Northern Hemisphere's retreating glaciers triggered a sudden and unexpected shift in the climate. This change included vegetation and wildfires that led to separation of carbon as the soil was buried by the loess.

"Most of the carbon (in the Brady soil) was fire derived or black carbon," notes Marin-Spiotta, "It looks like there was an incredible amount of fire."

To analyze the soil, researchers have used a variety of techniques including spectroscopic and isotopic analysis. During the analysis they were surprised to see that the organic matter from the ancient plants had not decomposed completely. Due to the rapid rate at which it got buried the soil didn't undergo any biological process that generally leads to the breakdown of the carbon.

These soils are not just limited to the Great Plains but found everywhere around the world.

The deeply buried fossilized soil offers a glimpse into the changes the environment is undergoing due to the rapid climate change.

 "The world was getting warmer during the time the Brady soil formed," said Mason. "Warm-season prairie grasses were increasing and their expansion on the landscape was almost certainly related to rising temperatures."

The finding was documented in the journal Nature.