Apr 22, 2021 - Science

The quest to put carbon to rest at sea

Illustration of an anchor holding three carbon dioxide molecules underwater.

Illustration: Aïda Amer/Axios

The Earth's ocean acts as a global climate regulator, and scientists are increasingly studying its chemistry and geology to find potential ways to store carbon dioxide captured from emissions or removed from the air.

The big picture: Oceans are bearing some of the brunt of climate change — they're acidifying, warming at the surface and experiencing other damaging effects. But deploying wind and solar energy offshore, restoring coastal ecosystems and other efforts could turn the seas into a solution, Axios' Andrew Freedman reports.

Vast, and far from humans, offshore sites are being studied by researchers for capturing and storing carbon.

  • Half of the roughly 10-20 trillion tons of CO2 storage capacity in the Earth's geology is located offshore, says Julio Friedmann of the Center on Global Energy Policy at Columbia University.

Background: One approach is to sequester carbon as part of enhanced oil recovery operations, in which CO2 is injected into reservoirs in the sea floor to push out remaining oil or gas, leaving the carbon dioxide stored within the porous rocks.

What's new: Saline formations are found around the world but basalt rock lines most of the oceanic crust and converts carbon dioxide into new minerals — a chemical reaction researchers are investigating to store carbon.

  • Unlike storing CO2 in a reservoir from where it might one day leak, "this removes it from the carbon cycle entirely," says geoscientist Rachel Lauer of the University of Calgary, who is part of a group of researchers studying the approach at a site off the coast of British Columbia.
  • 95% of the CO2 injected in basalt at a site on land in Iceland — where the lava rocks form the land above the sea — turned into minerals within two years.
  • Lauer and her colleagues geochemist Benjamin Tutolo and postdoctoral fellow Adedapo Awolayo are studying how fast mineralization of CO2 can happen in the undersea basalt formation off western Canada. They're looking at whether adding water to CO2 can speed the process and how to use seismic surveys to track the mineralization, which would occur in basalt buried under hundreds of meters of sediment on the ocean floor.

If CO2 injection can move offshore wherever there are basalt or saline formations, that could open up the possibility of pulling CO2 out of the air directly, anywhere, says Friedmann.

  • Yes, but: Direct air capture and negative emissions technologies don't currently operate at scale, in part because of the hefty price tag, so depending on them for climate change mitigation carries risk, whereas other solutions like cutting emissions and solar and wind power are already cost-competitive.
  • But models suggest negative emissions will be required to help keep the climate below red lines, and supporters of carbon removal technologies say the price pales in comparison to the cost of carbon emissions to society, something governments struggle to put a number on and that some economists argue has been historically low.
  • "There’s a need for [the technology] that isn’t priced by the market," says Laura Singer, an economist at the Colorado School of Mines.

The team working off the coast of western Canada is looking to bring together renewable energy sources — mostly offshore wind — to provide energy to machines that pull carbon dioxide from the air or ocean and then inject it into the basalt.

  • Operating machinery at sea typically introduces inefficiencies, more maintenance and higher costs.
  • For direct air carbon capture, "the advantage, however, is its co-location with offshore wind power and storage. Doing these activities close together eliminates transport of power and CO2, plus the entire operation remains remote," says David Goldberg of Columbia University's Lamont-Doherty Earth Observatory, who is working on the project.
  • It also helps that the seafloor is typically owned by one entity — federal or state governments — which eases regulatory hurdles.

What to watch: Researchers are also studying ways to harness marine chemistry to remove carbon dioxide and reduce the acidity of the ocean, which is rising due to CO2 dissolving in the water and threatening ocean life.

  • Planetary Hydrogen, a startup based in Nova Scotia, is developing a system that uses electrolysis to split sea water molecules into hydrogen and oxygen, creating ions that bind to carbon dioxide. The resulting bicarbonate can raise the pH of the ocean — while producing a potentially revenue-generating hydrogen fuel in the process.
  • The U.S. National Academy of Sciences recently convened a series of workshops to set research priorities for answering scientific, environmental and governance questions about the potential use of ocean alkalinity enhancement and other technologies along the coasts and at sea.

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