ORIGINAL PAPER Potential volume for CO 2 deep ocean sequestration: an assessment of the area located on western Pacific Ocean David Ching-Fang Shih • Yih-Min Wu • Jyr-Ching Hu Published online: 10 November 2009 Ó Springer-Verlag 2009 Abstract Captured CO 2 could be deliberately injected into the ocean at great depth, where most of it would remain isolated from the atmosphere for centuries. CO 2 can be transported via pipeline or ship for release in the ocean or on the sea floor. In Taiwan, CO 2 release is preliminarily projected from 2010 to 2030 in an average amount of 6.957 Gt within this duration. If deep sea sequestration for CO 2 can be the possible option in Taiwan, it seems to exists possible potential area delimited between 122.0°E to 122.5°E and 21.8°N to 22.3°N for CO 2 sequestration on account of its isolated and flat topography. Apparently, the area to the southeast of Taiwan is found to reach a depth deeper than -3,000 m and can be taken as a testing area for pilot studies. This study searches the area using the contours from the depth of -4,554 to -5,500 m with 1-m interval; the area, topographic volume, maximum mean height (volume/area), and ocean volume are reported. If the emission rate is kept constantly, for 20-year storage it needs 3 m of thickness reaching the sea ridge at the depth -4,554 m using top-down style; for 100 years of storage it needs 12 m. On the other hand, if it accounts for the bottom the sea floor is taken as the reference and the accumulated CO 2 is stored from the depth at -4,900 m using bottom-up style, it requires about 37 m for the 20-year storage and 61 m for one decade. Keywords Carbon dioxide Á Ocean sequestration Á Regression analysis Á Western Pacific Ocean 1 Introduction Direct ocean injection of CO 2 is one of several approaches under consideration to sequester carbon dioxide in order to stabilize increased atmospheric CO 2 . A potential CO 2 storage option is to inject captured CO 2 directly into the deep ocean at depths deeper than -1,000 m or more, where most of CO 2 would be isolated from the atmosphere for centuries. This can be achieved by transporting CO 2 via pipelines or ships to an ocean storage site, where CO 2 is injected into the water column of the ocean or at the sea floor. At typical pressures and temperatures, CO 2 exists as gas in the ocean at a depth of approximately -500 m and as a liquid below that depth. Between depths of about - 500 and -2,700 m, liquid CO 2 is lighter than sea water (IPCC 2005). Deeper than -3,000 m, liquid CO 2 is denser than sea water. The buoyancy of CO 2 released into the ocean determines whether released CO 2 rises or falls in the ocean column. In the gas phase, CO 2 is lighter than sea water and rises. In the liquid phase CO 2 is a highly com- pressible fluid as compared to sea water. A fully formed crystalline CO 2 hydrate is denser than sea water and will form a sinking mass in mid-depth (Aya et al. 2003); hydrate formation can thus aid ocean CO 2 storage by more rapid transport to depth and by slowing dissolution. At the surface and intermediate depths, hydrate particles have negative buoyancy, and thus they will sink in the ocean (Teng and Yamasaki 1998). However, at a certain depth, called neutral depth, neutral buoyancy will be reached. Teng and Yamasaki (1998) indicate that neutral depth will be around -4,456 m. The hydrate density/seawater density D. C.-F. Shih (&) Institute of Nuclear Energy Research, AEC, P.O. Box 3-7, Longtan 32546, Taiwan, ROC e-mail: cfshih@iner.gov.tw Y.-M. Wu Á J.-C. Hu Department of Geosciences, National Taiwan University, Taipei 10617, Taiwan ROC 123 Stoch Environ Res Risk Assess (2010) 24:705–711 DOI 10.1007/s00477-009-0357-4