Simulation of ocean carbon sequestration via direct injection of CO2 at 700 m depth near New York City. This figure represents results from the highest-resolution global simulation of direct injection yet performed. Shown on the figure is the vertically integrated concentration of injected CO2, known as column inventories, after 100 years of continuous injection at the rate of 0.1 PgC per year. At 700 m there is considerable leakage to the atmosphere, but injections at 1500 m or below effectively store the carbon in the ocean for many hundreds of years.

Research Objectives
The research objectives of the DOE Center for Research on Ocean Carbon Sequestration are (1) to understand the efficacy and impacts of various strategies proposed for ocean carbon sequestration; (2) to focus research of other groups on the key uncertainties and/or deficiencies in ocean physics and biogeochemical models; (3) to develop the best numerical simulations of ocean carbon sequestration, both with regard to biological fertilization and direct injection of CO₂ into the deep ocean, by incorporating the research of other groups into an improved model of ocean physics and biogeochemistry.

Computational Approach
For our ocean physics model, we initially used the Lawrence Livermore National Laboratory version of the Geophysical Fluid Dynamics Laboratory's MOM, with a later transition to Los Alamos National Laboratory's POP model. Some modifications to the POP code were made to improve the numerics of handling point sources with high spatial concentration gradients. Because some ocean sequestration strategies involve point sources, and the numerics of the models assume relatively small spatial concentration gradients, we explored a number of techniques for handling these large gradients within the model, including testing various tracer advection schemes and using results from a high-resolution regional model (run at MIT) to initialize the global General Circulation Model.

Accomplishments
We achieved the highest-resolution-ever global simulations of direct injection of CO₂ into the oceans. These simulations indicate that direct injection of CO₂ into the ocean is an effective carbon sequestration strategy. Approximately 80% of the injected carbon remains in the ocean permanently. The approximately 20% of the carbon that leaks back to the atmosphere does so on a time scale of several hundred years. Hence, direct injection of CO₂ into the ocean could play a potentially important role in diminishing anthropogenic climate change. We are now studying our simulation results to better understand possible biotic consequences of adopting this sequestration strategy. Initial results indicate that far-field effects (i.e., hundreds of km from the injection point) may be similar to the effects of CO₂ absorbed passively from the atmosphere. Near-field effects (i.e., < 1 km from the CO₂ source), however, may be acute and significantly impact marine biota in a relatively restricted area.

Significance
We must understand the options available to us to slow the rapid accumulation of CO₂ in the atmosphere and reduce its environmental impacts. It is the primary goal of this research to advance the science necessary to understand the efficacy and impacts of various strategies to sequester carbon in the oceans and away from the atmosphere.

Publications
H. Herzog, K. Caldeira, and E. E. Adams, "Carbon sequestration via direct injection," in Encyclopedia of Ocean Sciences, J. Steele, S. Thorpe and K. Turekian, eds. (Academic Press Ltd., London, in press).

K. Caldeira and P. B. Duffy, "The role of the Southern Ocean in uptake and storage of anthropogenic carbon dioxide," Science 287, 620 (2000).

K. Caldeira and G. H. Rau, "Accelerating carbonate dissolution to sequester carbon dioxide in the ocean: Geochemical implications," Geophys. Res. Lett. 27, 225 (2000).

http://esd.lbl.gov/DOCS