VANCOUVER, Wash. -A Washington State University researcher has found that one-fourth of the carbon held by soil is bound to minerals as far as six feet below the surface. The discovery opens a new possibility for dealing with the element as it continues to warm the Earth's atmosphere.

One hitch: Most of that carbon is concentrated deep beneath the world's wet forests, and they won't sequester as much as global temperatures continue to rise.

Marc Kramer, an associate professor of environmental chemistry at WSU Vancouver, drew on new data from soils around the world to describe how water dissolves organic carbon and takes it deep into the soil, where it is physically and chemically bound to minerals. Kramer and Oliver Chadwick, a soil scientist at the University of California Santa Barbara, estimate that this pathway is retaining about 600 billion metric tons, or gigatons, of carbon. That's more than twice the carbon added to the atmosphere since the dawn of the Industrial Revolution.