Oceans Would Suck Up CO2 in New Plan

Dec. 7, 2007 -- Every year humans send about 8 billion metric tons of carbon into the atmosphere. Reducing fossil fuel use and deforestation can help cut down those emissions, but scientists are also investigating ways to soak up CO2 on a large scale.

One new idea involves building water treatment plants that would enhance the ocean's natural ability to absorb carbon dioxide from the atmosphere. Unlike other methods that propose burying carbon underground or deep in the ocean, this plan mimics natural geochemical reactions that occur between rocks and the ocean but at a much faster rate.

"If you think about global warming, you can do one of three things: You can decrease emissions of CO2; you can do nothing and adapt to whatever changes result; or you can do some kind of large-scale geo-engineering project that would get at the problem through the back door," said Kurt Zenz House, a Ph.D. candidate in earth and planetary sciences at Harvard University.

House and his team are publishing their research in the December 15 issue of the American Chemical Society's journal, Environmental Science & Technology.

To understand how the process works, think of the ocean as a large bucket of saltwater, said House. In other words, imagine a mixture of water (two hydrogen molecules and one oxygen) and salt (one sodium and one chlorine molecule). That solution has a particular pH ("potential of hydrogen") level that describes its acidity or alkalinity.

CO2 is an acid and naturally dissolves in the ocean. The overabundance of CO2 in the atmosphere has decreased the pH level of the ocean, making the water unnaturally acidic. The acid breaks down calcium in the water, which can cause coral reefs and organisms that make shells to become vulnerable or even die.

What House and his team propose is a plan to increase the ocean's pH level -- make it more alkaline -- so that it can better soak up excess CO2.

It would occur at a water treatment plant where first, an electrical current would pass through the saltwater, splitting the water and salt molecules apart. When they recombined, they would make sodium hydroxide, which is not acidic, and hydrochloric acid, which is, of course, an acid.

But that acid can be neutralized, using a process that is similar to what naturally occurs in nature. It turns out that when the magnesium, silicon and oxygen in volcanic rock come into contact with seawater, a chemical reaction occurs that results in plain water and magnesium chloride salt -- neither of which are acidic.