From below the ground it may soon be called for carbon dioxide. There it remains bound as 'mineral water'.
Read aloud Carbon dioxide can be stored underground for many millions of years: the greenhouse gas dissolves in the pore water of the rock, where it remains virtually frozen as mineral water. Researchers led by Stuart Gilfillan from the University of Manchester found this out in analyzes on natural gas wells. They studied the ratio of carbon dioxide to other materials in these wells and were able to infer how the naturally occurring carbon dioxide has behaved underground for long geological periods. The results could provide new impetus for the partly controversial, large-scale landfilling of carbon dioxide in disused natural gas fields. The data may also help to improve computer models of metabolic exchange in the Earth's interior. The researchers studied samples from nine natural gas fields in the US, China and Hungary, where carbon dioxide naturally occurs in large quantities in addition to natural gas. From the ratio of carbon dioxide to the noble gases helium and neon, geologists have determined that the greenhouse gas must have dissolved predominantly in water. In addition, the water in the rock spores comes into question.

In addition, the researchers determined the ratio of two carbon isotopes in the samples. Isotopes are atoms of the same chemical element, which differ in the amount of the core building blocks and thus their mass. From the isotope ratio, the researchers deduce that carbon dioxide was not fixed by formation of new carbonate rock. This confirms the first finding: carbon dioxide dissolves almost exclusively in the pore water of the rock.

The industrial landfill of carbon dioxide in disused reservoirs is considered by climatologists as an option to delay greenhouse gas emissions. So far, however, it was unclear how the carbon dioxide reacts underground and whether it is safely disposed of there for a long time, without coming back to the earth's surface. The findings of geologists Gilfillan now show that carbon dioxide can remain dissolved in pore water for thousands to millions of years underground. The so-called carbon dioxide sequestration is however controversial among experts, because too little is known about the ecological effects. Critics see the necessary investment in alternative energy sources better invested, as the carbon dioxide in coal-fired power plants laboriously separate and then pump into gas deposits.

Stuart Gilfillan (University of Manchester) et al: Nature (Vol. 458, p. 614) ddp / Martin Schäfer advertisement


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