labs_title

Caldeira Lab Research:Energy, Global Carbon Cycle, and Climate

Accelerating carbonate dissolution to sequester carbon dioxide in the ocean: Geochemical implications

Ken Caldeira & Greg H. Rau

An often proposed way to curb CO2 emissions is to sequester the gas before it enters the atmosphere and inject it into the deep sea. However, when CO2 is injected into the deep sea, it will eventually leak back into the atmosphere, and can also have severe negative effects on marine life. This is a study of the possibility of sending carbon dioxide through accelerated carbonate dissolution before injection, a method that could be much safer as well as cost-effective.


Caldeira, K., and G.H. Rau, Accelerating carbonate dissolution to sequester carbon dioxide in the ocean: Geochemical implications, Geophysical Research Letters, 27, 225–228, 2000.

Fraction of CO2 leaked into the atmosphere: Although neither would lead to concentrations on the level of direct atmospheric release, the model showed that direct injection of CO2 into the ocean would eventually lead to much higher levels of CO2 in the atmosphere than injection where carbonate dissolution is first applied.

Carbonate dissolution, atmospheric CO2 concentration, and the pH of the ocean: Not only did the model predict lower eventual atmospheric CO2 levels when carbonate dissolution is used before deep sea injection, it showed that such a method would also have less of an effect on ocean water pH. Significant pH reduction could be highly dangerous for marine life.

Abstract

Various methods have been proposed for mitigating release of anthropogenic CO2 to the atmosphere, including deep-sea injection of CO2 captured from fossil-fuel fired power plants. Here, we use a schematic model of ocean chemistry and transport to analyze the geochemical consequences of a new method for separating carbon dioxide from a waste gas stream and sequestering it in the ocean. This method involves reacting CO2-rich power-plant gases with seawater to produce a carbonic acid solution which in turn is reacted on site with carbonate mineral (e.g., limestone) to form Ca2+ and bicarbonate in solution, which can then be released and diluted in the ocean. Such a process is similar to carbonate weathering and dissolution which would have otherwise occurred naturally, but over many millennia. Relative to atmospheric release or direct CO2 injection, this method would greatly expand the capacity of the ocean to store anthropogenic carbon while minimizing environmental impacts of this carbon on ocean biota. This carbonate-dissolution technique may be more cost-effective and less environmentally harmful than previously proposed CO2 capture and sequestration techniques.