Is it safe to store CO2 beneath the seafloor?

What comes up might go back down.

Pete Markham

As we transition away from fossil fuels, one way for us to have our cake and eat it too is to capture the CO₂ before it reaches the atmosphere and stick it back down in the ground. That can be done by pumping it into the same reservoirs that once held oil and gas or into deep, saline aquifers. While that CO₂ will gradually dissolve and eventually form carbonate minerals, in the meantime, you’re relying on the integrity of the rocks to provide the container that keeps the CO₂ locked away.

Injecting CO₂ beneath the seafloor is also an attractive option, but questions have remained about the ecological effects of a CO₂ leak on the ocean floor. A newly published study created an artificial leak off Scotland’s western coast to measure its impact; the work was done by a large group of researchers led by Plymouth Marine Laboratory’s Jerry Blackford, the Scottish Association for Marine Science’s Henrik Stahl, and the University of Southampton’s Jonathan Bull.

They drilled a horizontal borehole out to a point 11 meters (slightly more than 36 feet) below the seafloor, beneath twelve meters of water. They monitored and sampled that area while injecting CO₂ for about five weeks. The injection started out slow, increasing over time. Without a barrier to keep it below the seafloor, some of the CO₂ escaped upward.