Can the Deep-Sea Mitigate CO2 Rise and Global Warming?

In the last 10 years, the average temperature of the earth as increased by 0.75 degrees Celsius. In less you have not read a newspaper or watched the news in the last 15 years, you would know that a majority of scientists have linked this to increasing C02 emissions from the burning of fossil fuels. Currently those levels are about 7 gigatons of carbon per year (GtC y-1) are expected to reach double that by 2050.

So what do we do with all this extra carbon dioxide?

One phenomenally poor thought out plan is ocean seeding. Another, the superseafloor injection, is direct injection of CO2 into the deep-ocean, where the pressures and temperatures of the deep sea would keep CO2 as a liquid. It is predicted that it would not be reintroduced to the atmosphere (out-gasing) for several centuries remaining in circulation on the seafloor. This concept was first given birth in 1977 by the Italian E. Marchetti. He proposed that gas from power plants be gathered and dumped off the coast of Gibraltar. Here hypersaline Mediterranean water sinks and would potentially carry CO2 into the deep. An economic analysis in 1984, by Steinberg proved this to be an unviable method, which killed interests. However, in the late 1990's interest ensued given the further threat of global warming.
An alternative method is subseabed injection. Again, the proposed mechanism usually involves large-scale industrial CO2 scrubbers that would send emissions to the seabed offshore (3000m) through pipes. Namely, injecting this below the seafloor. In Norway, the petroleum company, Statoil, already utilizes carbon sequestration method to reduce taxes. The Norwegian government has a heavy tax on C02 emmisions and for Statoil this tax could potentially be $53 million a year. The offshore facility pumps atmospheric CO2 to 2600 feet below the seabed to reduce this tax. House and Schrag (Harvard) publish in Proceedings of the National Academy of Sciences, that deep-sea sediments can provide a "unlimited" and "permanent" reservoir to store excess CO2. They calculate that one years of worth of U.S. emissions could be stored in just 80 sq km about the size of Hong Kong Island. "At the high pressures and low temperatures common in deep-sea sediments, CO2 resides in its liquid phase and can be denser than the overlying pore fluid, causing the injected CO2 to be gravitationally stable," the authors argued. Although this sounds reasonable because it would take 3,485,956 years to completely use up the seafloor below 3,000m, there is a glitch. The deep reservoir has to be accessible from the coast, meaning that areas in the center of ocean basins would be potentially inaccessible for this process. Depending on how the 80 sq km is shaped (8km x 10km, 20x4km) you would cover the entire length of California in as little as 60-120 years (just figuring with U.S. emissions). Of course, annually you would also have to add more pipe or eventually move the processing plant.
What effect will all of this have on deep-sea organisms? One potential effect is localized acidification of water. Dissolution of the liquid CO2 into seawater will through the carbonate buffering system of seawater, reduce its ph. One study demonstrated from a test hyperseafloor injection that

"high rates of mortailiy for flagellates, amoebae, and nematodes inhabiting sediments in close proximity to sites of CO2 release." (Barry et al., 2004, Journal of Oceanography)

In another study...

The pteropods [pelagic gastropods] were sealed in jars. The carbon dioxide they exhaled made the water inside more acidic. Though slight, this change in water chemistry ravaged the snails' translucent shells. After 36 hours, they were pitted and covered with white spots....As industrial activity pumps massive amounts of carbon dioxide into the environment, more of the gas is being absorbed by the oceans. As a result, seawater is becoming more acidic, and a variety of sea creatures await the same dismal fate as Fabry's pteropods....At the current rate of increase, ocean acidity is expected, by the end of this century, to be 2 1â2 times what it was before the Industrial Revolution began 200 years ago. Such a change would devastate many species of fish and other animals that have thrived in chemically stable seawater for millions of years...In a matter of decades, the world's remaining coral reefs could be too brittle to withstand pounding waves. Shells could become too fragile to protect their occupants.

As you might already know, Peter conducts research on corals and I on gastropods. If you don't want to put us out of a job and put our families on the street, you should do something now. The better solution is to try to limit CO2 emissions and bolstering sustainable energy production.