Buried Carbon Causes Deep Concern

Geographers in the US have found a new factor in the carbon cycle, and – all too ominously – a new potential source of the greenhouse gas carbon dioxide.  They have identified huge deposits of fossil soils, rich in organic carbon, buried beneath the Great Plains of America.

The discovery is evidence that the subterranean soils could be a rich store, or sink, for ancient atmospheric carbon.  But if the soil is exposed – by erosion, or by human activities such as agriculture, deforestation or mining – this treasure trove of ancient charred vegetation, now covered by wind-blown soils, could blow back into the atmosphere and add to global warming.

Erika Marin-Spiotta, a biogeographer at  the University of Wisconsin-Madison, and her colleagues report in Nature Geoscience that what is known as Brady soil – ancient buried soil - formed more than 13,500 years ago in Nebraska, Kansas and other Great Plains states.

It now lies more than six metres below the surface, and it was buried by a vast deposit of loess – wind-blown dust – about 10,000 years ago, when the glaciers began to retreat from North America.

The significance is not that it survived the end of the Ice Age and the colonization of the Great Plains by grazing animals, but in the fact that it is there at all, at such depths. Calculations about the world stock of soil carbon have focused on the topsoil, and the role of root systems, decaying vegetation, microbes and fungi in the natural carbon cycle.  Now the climate scientists who play with models of the carbon cycle will have to think again.

Buried Carbon Causes Deep Concern