Only the deep ocean stores more carbon than soils. Barring deforestation or dust bowls, "pools" of carbon in soil are remarkably stable, cycling back into the atmosphere only after hundreds or thousands of years.
 Carbon-14 is one of the isotopes researchers use to determine the age and chemistry of soil in core samples like these. |
How important are minerals to this storage capacity? To find out, Margaret
Torn used radiocarbon analysis to measure differences in carbon storage
in soils of the Hawaiian Islands.
Moving from southeast to northwest, the islands have soils ranging from
a few hundred years old to 4 million years old, all starting from the
same volcanic parent material, a plume of magma that rises from the Earth's
mantle.
As soils age, mineral composition changes dramatically. Lava first weathers to noncrystalline (amorphous) materials and much later to fine crystalline clays. The abundance of noncrystalline minerals also increases with rainfall.
Finding that noncrystalline soils stabilize much more carbon than crystalline soils, Torn and her colleagues concluded that the ability of soils to store carbon "across landscapes and over long timescales" greatly depends on their mineralogy. She is now investigating details of that relationship over a range of soil types and climates.
- More
on how minerals stabilize carbon in soils
| The
carbon clock One atom out of a trillion of the carbon taken up by living things
is radioactive carbon-14, "radiocarbon," which decays
at a slow, steady rate. Since organic carbon gets into soil through falling leaves and the deaths of plants and other organisms, radiocarbon dating can measure the age of soils. The relationship isn't straightforward, however; the intensity of cosmic ray bombardment, which produces carbon-14 in the atmosphere, has varied over time. And other sources of radiocarbon — notably atmospheric nuclear weapons tests in the 1950s and 60s — also distort the ratio. Knowledge of these variations helps scientists sharpen their age estimates.
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