Forget gases, carbon in deeper soil threatening our climate

Deep soils can contain long-buried stocks of organic carbon which could, through erosion, agriculture, deforestation, mining and other human activities, contribute to global climate change.

"There is a lot of carbon at depths where nobody is measuring," said Erika Marin-Spiotta, assistant professor of geography at University of Wisconsin-Madison in the US.

It was assumed that there was little carbon in deeper soils and so most studies so far focused only the top 30 centimetres.

"Our study is showing that we are potentially grossly underestimating carbon in soils," Marin-Spiotta added.

The soil studied by Marin-Spiotta and her colleagues, known as the Brady soil, formed between 15,000 and 13,500 years ago in what is now Nebraska, Kansas and other parts of the Great Plains.

It lies up to six-and-a-half metres below the present-day surface and was buried by a vast accumulation of windborne dust known as loess beginning about 10,000 years ago, when the glaciers that covered much of North America began to retreat.

The study appeared in the journal Nature Geoscience.