Buried Fossil Soils Lock Carbon into the Earth: Possible Climate Change Implications

Scientists are learning a bit more about our planet's carbon cycle. They've discovered soils that formed on the Earth's surface thousands of years ago that are now deeply buried features of vanished landscapes are rich in carbon.

"There is a lot of carbon at depths where nobody is measure," said Erika Marin-Spiotta, one of the researchers, in a news release. "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 case, the researchers studied soil known as the Brady soil, which formed between 15,000 and 13,500 years ago in what is now Nebraska, Kansas, and other parts of the Great Plains. These days, the soil is located up to six-and-a-half meters below the Earth's surface; windborne dust and sediment slowly buried the soil over time. By studying the soil, the researchers can learn more about the past climate.

The region where the Brady soil formed was actually not glaciated. Instead, it underwent radical change as retreating glaciers sparked an abrupt shift in climate, including changes in vegetation and a regime of wildfire. This, in particular, contributed to carbon sequestration as the soil was rapidly buried.

The findings reveal that fossil organic carbon in buried soils is widespread. As humans increasingly disturb landscapes, this could be a potential contributor to climate change as carbon that has been locked away for thousands of years is reintroduced into the environment.

The findings don't just reveal that this could be a source of climate change, though. The soils also show a time of intense environmental change in the past due to a shifting climate.

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

The findings are published in the journal Nature Geoscience.