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The Silk Road helped form a hidden carbon sink under the desert

Scientists have found a potentially large carbon sink in the most unlikely place on Earth – under the desert. The increase in carbon storage is linked with the rise of farming in arid landscapes.

This surprising conclusion comes from work done in the Tarim Basin of western China by Chinese and American scientists. The results are published in the journal Geophysical Research Letters.

“Basically, people thought the whole arid region is totally negligible to the global carbon budget,” says lead author Yan Li of the Chinese Academy of Sciences in Urumqi. “We are arguing that that’s not the case.”

Li and colleagues measured and dated the carbon content of water samples taken from a salty aquifer beneath the Tarim Basin. They show that the rate at which carbon sunk into the aquifer rose dramatically with the rise of farming and agriculture in the region. Rate of carbon storage increased by more than 12 times previous levels over the past 8000 years with particularly high levels beginning around 2000 years ago when the Silk Road opened.

How it works

The process began when humans started to grow crops on sandy soil. As the plants take in carbon dioxide from the air, some is released into the sand. Farming in desert conditions requires a lot of water to combat rising salinity caused by rapidly evaporating water. This organic carbon dissolves in the water and is transported down through the sand into deed salty aquifers.

Li_etal_2015
A schematic diagram showing the leaching and transport of DIC (dissolved inorganic carbon) in a closed arid basin. Source: Li et al, 2015

Normally these aquifers are tapped by rivers and streams and so the carbon comes back out of storage. But in the Tarim Basin the aquifer is a closed system, meaning that water does not escape, effectively locking away the carbon.

Li expects this process to occur in deserts around the globe but the amount of carbon would vary depending on the pH of the soil and the level of farming activity.

The results from this study will have important implications for the study of the global carbon cycle as desert regions were previously thought to be unimportant for carbon storage.

Read the full study here: http://onlinelibrary.wiley.com/doi/10.1002/2015GL064222/abstract