Beijing, July 29 (IANS): Besides our oceans and plants, the world's deserts may be storing a large portion of carbon dioxide emitted by human activities, a new study suggests.

About 40 percent of carbon dioxide emitted by humans stays in the atmosphere and roughly 30 percent enters the ocean, according to the US University Corporation for Atmospheric Research.

Scientists thought the remaining carbon was taken up by plants on land, but measurements show plants do not absorb all of the leftover carbon.

Scientists have been searching for a place on land where the additional carbon is being stored - the so-called "missing carbon sink."

The new study suggests that massive aquifers underneath deserts could hold a large portion of this missing carbon - more carbon than all the plants on land.

Any carbon dissolved in the water makes its way through the aquifer to the centre of the desert, where it remains for thousands of years, the findings showed.

"The carbon is stored in these geological structures covered by thick layers of sand, and it may never return to the atmosphere," said lead author of the study Yan Li from Chinese Academy of Sciences in Urumqi, Xinjiang.

For the study, the scientists examined the flow of water through the Tarim Desert in China and found that carbon from the atmosphere is being absorbed by crops, released into the soil and transported underground in groundwater.

They found that the amount of carbon entering the desert aquifer in the Tarim Desert jumped around the time the Silk Road, which opened the region to farming, begin to flourish.

The researchers estimated that the world's desert aquifers contain roughly one trillion metric tonnes of carbon--about a quarter more than the amount stored in living plants on land.

The findings will be published in Geophysical Research Letters, a journal of the American Geophysical Union.