Īt the same time the ocean pH in the deep ocean has been decreasing at a relatively slower rate compared with the surface ocean. This is a higher rate of carbon addition than ever experienced by the earth over a short geological time scale. The total addition of carbon into the atmosphere is expected to be about 5000 PgC – the estimated fossil fuel reserves excluding hydrates - in the next 500 years. To place in a geological perspective, the surface ocean pH (on a total scale) has not been below 8.1 during the past 2.1 million years. If CO 2 emissions continue unabated the subsurface ocean total could decline by 0.7 units by 2300. The oceans have absorbed about one-third of anthropogenic CO 2 (the atmosphere retained about 43%, while the oceans absorbed about 30%), leading to a decrease of surface-ocean total pH by about 0.1 units from about 8.2 to 8.1. By 1994, the total atmospheric release of anthropogenic (i.e., man-made) carbon was about 244 Pg of carbon (PgC) from fossil fuel combustion, and about 140 PgC from land use change (e.g., deforestation).
However, dissolved CO 2 is already causing surface ocean acidification (most productive region of ocean) as it equilibrates with the atmospheric CO 2. The Earth’s oceans cover over 70% of the Earth’s surface, and have an average depth of 3,800 m. The ocean is presently the largest sink of atmospheric CO 2 (about 7 Pg per year). Motivation of Ocean Carbon Sequestration (OCS) Finally, this chapter will address the legal, policy and public outreach issues that have ultimately precluded implementation of OCS using direct injection.ġ.1. It will also include a discussion of the engineering challenges of delivering CO 2 to the water column, including the selection of injection sites to minimize CO 2 outgassing to the atmosphere as well as minimizing marine life impacts. It will summarize past ocean direct injection studies, and outline the effects of increased dissolved CO 2 and locally increased CO 2 partial pressure on marine organisms. This chapter will first describe the physical mechanism by which CO 2 can be stored in the ocean water column at depth. This chapter focuses only on the direct injection as a method of OCS. There are two major methods of OCS – direct injection and ocean fertilization (promoting photosynthetic fixation of CO 2 by ocean organisms). Ocean carbon sequestration (OCS) is a method to distribute CO 2 more evenly throughout ocean depth and minimize surface ocean impacts. Dissolved CO 2 (passively entering the ocean via diffusion from the atmosphere) has already acidified the surface ocean, the most productive region of the ocean. The ocean is the largest sink of atmospheric CO 2 (about 7 petagrams (Pg) per year) (1 Pg = 1 gigaton = 10 15 g).
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