EFFECTIVENESS OF CO2 SEQUESTRATION IN THE PREINDUSTRIAL AND POSTINDUSTRIAL OCEANS

Ocean carbon cycle modeling is expected to play a key role in decision s concerning the purposeful sequestration of CO2 in the oceans. Modeli ng is probably the only practical way to know how much good sequestrat ion is doing, or would do if implemented, since even with sequestratio n, atmospheric CO2 would be expected to continue to increase because o f the release of non-sequestered CO2 and the return to the atmosphere of sequestered CO2, We have employed a carbon cycle model based on an ocean general circulation model to estimate the return of sequestered CO2 to the atmosphere for sequestration in the pre-industrial ocean at sites near Tokyo, San Francisco, New York and Miami. Significant diff erences in the effectiveness of sequestration are found. Off the East Coast of the USA, the atmospheric concentration due to the return of s equestered CO2 quickly rises to near the final equilibrium value, for all depths below about 800 m. Off the West Coast of the USA, the CO2 i s effectively hidden from the atmosphere for several hundred years, fo r depths below 800 m. Then the atmospheric concentration rises to larg er values than for sequestration off the East Coast. Sequestration off the coast of Japan at 800 m is similar to sequestration off the West Coast of the USA, but without the time delay. These predicted differen ces are understandable in terms of ocean circulation. Sequestration in the post-industrial ocean beginning in the year 2000 has been modeled also and sites near Tokyo acid New York. This calculation includes ad ditional CO2 from a representation of anthropogenic CO2 for the entire fossil fuel era. No-sequestered CO2 tends to flush the sequestered CO 2 out of the ocean by reducing the concentration of the carbonate ion, with which CO2 reacts. Results are less favorable in the post-industr ial ocean. The pre-industrial ocean model can help in the selection of location and depth, but the post-industrial ocean model is more reali stic. ''Thus human beings are now carrying out a large scale geophysic al experiment of a kind that could not have happened in the past nor b e reproduced in the future. Within a few centuries we are returning to the atmosphere and oceans the concentrated organic carbon stored in s edimentary rocks over hundreds of millions of years'' Roger Revelle an d Hans Suess.(1) (C) 1998 Elsevier Science Ltd. All rights reserved.