Carbon Storage Under The Sea: Could We Lock Greenhouse Gases Safely Away?

Could injecting carbon emissions in rocks underneath the ocean be a safe way to store greenhouse gases?

All of the ways that we burn fossil fuels have the side effect of belching out carbon dioxide. In a paper published Tuesday in the journal Geophysical Research Letters, a group of scientists from the University of Southampton say they’ve found places beneath the oceans where we might sequester carbon safely away from the atmosphere for generations.

"We have found regions that have the potential to store decades to hundreds of years of industrial carbon dioxide emissions, although the largest regions are far off shore,” lead author Chiara Marieni said in a statement. “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."

Marieni and colleagues think that certain regions off the coasts of Japan, Australia, Siberia, South Africa and Bermuda have the right mix of temperature, pressure and rock composition to lock stored carbon dioxide down. When brought deep below the ocean’s surface, carbon dioxide turns into a liquid that is denser than seawater, so theoretically it should stay down. Plus, CO2 injected into the open spaces underneath the sea floor may react with calcium carbonate in the rocks around it, thus trapping it away chemically.

Some carbon dioxide is already being stored under the ocean – the Norwegian national petroleum company Statoil injects CO2 into a layer of sand and saltwater that sits beneath 800 meters (about half a mile) of rock, all below the icy waters of the North Sea.

But can we be sure the carbon stays put?

In Japan, a company named INPEX has been testing underground carbon storage in wells outside the coastal city of Nagaoka. The CO2 has stayed put, even after a 2004 earthquake that registered 6.8 on the Richter scale, according to Miller-McCune magazine. Japan’s government is investigating carbon sequestration in several areas under both land and sea, but many locals are still wary. Kazuya Kaneda, the head of a fishermen’s association in Teradomari, which is near one of the proposed sequestration sites, told Miller-McCune magazine in 2010 that he still had some deep concerns.

“Nobody can guarantee that such a project would not cause an earthquake,” Kaneda said. “This kind of project would never have public support here because people would worry too much about leakage."

If sequestered carbon did escape, many scientists worry about how it might contribute to the ongoing process of ocean acidification.

“If the carbon dioxide were to leave the igneous rocks and be released to the deep sea, it would have similar chemical and biological impacts as ocean acidification,” UC Davis geologist Tessa Hill wrote in an email.

When carbon dioxide dissolves in seawater, some of it reacts with the water to form carbonic acid. Over time, this process can raise the pH of the ocean, which has a range of effects on marine life. A more acidic ocean makes it harder for creatures like oysters, mussels, and corals to maintain their shells. It may also change the acoustic properties of seawater, making the ocean a noisier place that could impact echolocating sea animals like whales and dolphins. There could be a myriad of ways that a more acidic environment could upset ecological conditions under the sea.

Other concerns abound.

“Here is a question - how much per ton of carbon does capturing CO2 and transporting it into the deep ocean bed cost?” Stanford University marine ecologist Stephen Palumbi wrote in an email. “At what point is it just cheaper not to burn the fossil fuels to begin with? What is the balance point?”

SOURCE: Marieni et al. “Geological storage of CO2 within the oceanic crust by gravitational trapping.” Geophysical Research Letters 3 December 2013.