7th December 2013

Regions identified where centuries of industrial CO2 could be stored

Researchers at the University of Southampton have identified regions beneath the oceans where igneous rocks of the upper ocean crust could safely store huge volumes of carbon dioxide.

The burning of fossil fuels such as coal, oil, and natural gas has led to dramatically increased levels of CO2 in our planet's atmosphere. These industrial emissions reached 36 billion tonnes annually in 2013 – over 100 times greater than natural CO2 output from all of the world's volcanoes, according to the US Geological Survey. The overwhelming majority of climate scientists agree this is causing climate change and ocean acidification. Although technologies are now being developed to capture CO2 from power stations and other sources, this will only avoid further warming if that CO2 is then safely locked away from the atmosphere for centuries.

Chiara Marieni, PhD, from the National Oceanography Centre in Southampton, investigated the physical properties of CO2 to develop global maps of the ocean floor and estimate where CO2 can be safely stored.

At high pressures and low temperatures, like those in deep oceans, CO2 occurs as a liquid that is denser than seawater. Estimating temperatures in the upper ocean crust, Chiara and her colleagues identified regions where it may be possible to stably store large volumes of CO2 in the basalts. These fractured rocks have high proportions of open space and over time may also react with the CO2 so it becomes locked into solid calcium carbonate – permanently preventing its release back into the oceans or atmosphere. As a precaution, Chiara refined her locations to areas that have the additional protection of thick blankets of impermeable sediments to prevent gas escape.

The team identified five potential regions in off-shore Australia, Japan, Siberia, South Africa and Bermuda, ranging in size from ½ million square kilometres to almost four million square kilometres.

"We found regions that have the potential to store decades to hundreds of years of industrial carbon dioxide emissions," said Chiara, "although the largest regions are far off-shore. However, further work is needed in these regions to accurately measure local sediment conditions and sample the basalt beneath before this potential can be confirmed."

Her work, published this week in Geophysical Research Letters, shows that previous studies, which concentrated on the effects of pressure to liquefy CO2 – but ignored temperature – pointed to the wrong locations, where high temperatures mean the CO2 will have a low density, and thus be more likely to escape.

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