As the years tick by with most of the planet doing little in the way of reducing carbon emissions, researchers are getting increasingly serious about the possibility of carbon sequestration. If it looks like we're going to be burning coal for decades, carbon sequestration offers us the best chance of limiting its impact on climate change and ocean acidification. A paper that will appear in today's PNAS describes a fantastic resource for carbon sequestration that happens to be located right next to many of the US' major urban centers on the East Coast.
Assuming that capturing the carbon dioxide is financially and energetically feasible, the big concern becomes where to put it so that it will stay out of the atmosphere for centuries. There appear to be two main schools of thought here. One is that areas that hold large deposits of natural gas should be able to trap other gasses for the long term. The one concern here is that, unlike natural gas, CO2 readily dissolves in water, and may escape via groundwater that flows through these features. The alternative approach turns that problem into a virtue: dissolved CO2 can react with minerals in rocks called basalts (the product of major volcanic activity), forming insoluble carbonate minerals. This should provide an irreversible chemical sequestration.
The new paper helpfully points out that if we're looking for basalts, the East Coast of the US, home to many of its major urban centers and their associated carbon emissions, has an embarrassment of riches. The rifting that broke up the supercontinent called Pangea and formed the Atlantic Ocean's basin triggered some massive basalt flows at the time, which are now part of the Central Atlantic Magmatic Province, or CAMP. The authors estimate that prior to some erosion, CAMP had the equivalent of the largest basalt flows we're currently aware of, the Siberian and Deccan Traps.
Some of this basalt is on land—anyone in northern Manhattan can look across the Hudson River and see it in the sheer cliffs of the Palisades. But much, much more of it is off the coast under the Atlantic Ocean. The authors provide some evidence in the form of drill cores and seismic readings that indicate there are large basalt deposits in basins offshore of New Jersey and New York, extending up to southern New England.
These areas are now covered with millions of years of sediment, which should provide a largely impermeable barrier that will trap any gas injected into the basalt for many years. The deposits should also have reached equilibrium with the seawater above, which will provide the water necessary for the chemical reactions that precipitate out carbonate minerals.
Using a drill core from an onshore deposit, the authors show that the basalt deposits are also composed of many distinct flows of material. Each of these flows would have undergone rapid cooling on both its upper and lower surface, which fragmented the rock. The core samples show porosity levels between 10 and 20 percent, which should allow any CO2 pumped into the deposits to spread widely.
The authors estimate that New Jersey's Sandy Hook basin, a relatively small deposit, is sufficient to house 40 years' worth of emissions from coal plants that produce 4GW of electricity. And the Sandy Hook basin is dwarfed by one that lies off the Carolinas and Georgia. They estimate that the South Georgia Rift basin covers roughly 40,000 square kilometers.
The authors argue that although laboratory simulations suggest the basic idea of using basalts for carbon sequestration is sound, the actual effectiveness in a given region can depend on local quirks of geology, so pilot tests in the field are absolutely essential for determining whether a given deposit is suitable. So far, only one small-scale test has been performed on any of the CAMP deposits.
Given the area's proximity to significant sources of CO2 and the infrastructure that could be brought into play if full-scale sequestration is attempted, it seems like one of the most promising proposals to date.
PNAS, 2010. DOI: 10.1073/pnas.0913721107