Ocean, sequestration

Although ocean sequestration is promising in terms of carbon sequestration capacity, the environmental impact may limit the acceptability of ocean storage since the strategy is predicated on the notion that the impacts on the ocean will be less than the avoided impact of these emissions to the atmosphere. Environmental concerns in ocean sequestration focus... 

Feasibility of Large-Scale CO2 Ocean Sequestration. This project, operated by the Monterey Bay Aquarium Research Institute will usea Remotely Operated Vehicle (ROV) to deploy small quantities of liquid CO2 in the deep ocean. Below about 10,000 feet the density of liquid CO2 exceeds that of seawater, and the liquid CO2 is quickly converted into a solid hydrate by reacting with the surrounding water. Using a Raman spectrometer, scientists will assess the impact that the CO2 hydrate material has on the ocean floor and ecosystem. 

The key question is where to put the co2. The largest potential physical reservoir is the deep oceans. Flowever, ocean sequestration poses serious environmental risks and is unlikely to be a viable climate mitigation strategy. Tens of millions of tons of co2 are already injected into oil fields to enhance recovery. This strategy can be expanded for early, low-cost sequestration efforts, but oil fields are limited in size and location, and transporting co2 over long dis-... 

Takeuchi, K., Fujioka, Y., Kawasaki, Y., Shirayama, Y. (1997). Impacts of high concentrations of COj on marine organisms a modification of COj ocean sequestration, Energy Conversion Management 38, S337-S341. 

The environmental impacts will also need to be fully understood. This will involve assessment of localised impacts as well as the regional and global impacts, particularly in the case of the innovative, ocean sequestration options. The results of these studies must also be communicated widely, so that properly informed decisions can be taken. 

On a geological time scale, the important biologically mediated, permanent sequestration of C02 does not occur on land. It is in the oceans where limestone is formed that we would naturally seek the massive reservoirs of sequestered C02. Because the oceans will eventually be the natural sink for C02, concepts for directly sequestering C02 in the oceans have been proposed. But ocean sequestration and ocean fertilization have proven to be extremely controversial and politically unpopular. Proposed demonstration experiments to show the feasibility of C02 ocean sequestration... 

CO2 concentration in the water drops back to the normal levels. Since 1977, when Marchetti first introduced the concept of direct ocean sequestration of CO2, significant research effort has taken place, and now the cost for the direct disposal of CO2 in the oceans is estimated to range from as low as US 1-6 per ton of 002, ° to a more realistic estimate of US 5-15 per ton of 002. ... 

Other methods proposed for ocean sequestration may lower costs but present significant obstacles. One scenario envisions fertilization of the oceans with iron. However, studies of this method have indicated that only about 10 percent of the carbon fixed remains in the ocean. Also, the unintended ecological consequences of this method, such as abyssal nitrogen anoxia and risks to fisheries, may far exceed the benefit derived from carbon sequestration. 

Ocean sequestration of CO2 by direct injection assumes that a relatively pure CO2 stream has been generated at a power plant or chemical factory and transported to an injection point. To better understand the role the ocean can play, we address the capacity of the ocean to sequester CO2, its effectiveness at reducing atmospheric CO2 levels, how to inject the CO2, and possible environmental consequences and issues of public perception. 

Carbon dioxide is constantly exchanged between the ocean and atmosphere. Each year the ocean and atmosphere exchange about 350 Gt CO2, with a net ocean uptake currently of about 8 Gt CO2. Because of this exchange, questions arise as to how effective ocean sequestration will be at keeping the CO2 out of the atmosphere. Specifically, is the sequestration permanent, and if not, how fast does the CO2 leak back to the atmosphere. Because there has been no long-term CO2 direct-injection experiment in the ocean, the long-term effectiveness of direct CO2 injection must be predicted based on observations of other oceanic tracers (e.g., radiocarbon) and on computer models of ocean circulation and chemistry. 

Golomb D, Pennell S, Ryan D, Barry E, and Swett P (2007) Ocean sequestration of carbon dioxide Modeling the deep ocean release of a dense emulsion of liquid C02-in-water stabilized by pulverized limestone... 

Ozaki M, Minamiura J, Kitajima Y, Mizokami S, Takeuchi K, and Hatakenka K (2001) CO2 ocean sequestration by moving ships. Journal of Marine Science and Technology 6 51-58. 

Sato T and Sato K (2002) Numerical prediction of the dilution process and its biological impacts in CO2 ocean sequestration. Journal of Marine Science and Technology 6(4) 169-180. 

Deep ocean sequestration A proposal that might reduce atmospheric CO2 and protect life in the upper ocean is to liquefy the CO2 and pump it deep under water, a process known as deep ocean sequestration. It is thought that the extreme pressure at depths greater than 3000 m will cause the CO2 to form a hydrate. The hydrate will dissolve into the deep ocean water, but the CO2 will remain trapped for hundreds of years far from the upper ocean and atmosphere. 

Brainstorm a list of questions that must be addressed through research before deep ocean sequestration is attempted. Visit qlencoe.coiti for more information on CO2 sequestration. 

Over the past 200 years, the cumulative ocean sequestration of anthropogenic carbon is estimated to be <100 PgC. This sequestration is small (<0.5%) compared to the total carbon inventory in the ocean. To the lowest order, oceanic uptake of anthropogenic CO2 is a small physical-chemical perturbation and does not involve alteration of marine biology, as long as the ocean circulation remains the same. 

This chapter provides a comprehensive overview of the fundamentals and applications of CO2 hydrates. Section 10.2 focuses on the microscopic perspective, looking into how gas hydrates form, the three structures of gas hydrates, and the characteristics of CO2 hydrates. From there onwards, the text focuses specifically on CO2 hydrates. The physical properties of CO2 hydrates are considered in Sect. 10.3. Section 10.4 deals with the phase equihbrium of CO2 hydrate. Experimental methods and the phase diagram are showed in this section. The last section covers the applications of CO2 hydrates, including the formation and dissociation of CO2 hydrates, ocean sequestration, the CH4 replacement in hydrates by CO2, and the use of CO2 hydrates in the refrigeration process. 

Based on its formation and dissociation, CO2 hydrate has many potential applications. As described in detail later, ocean sequestration and CH4/CO2 replacement... 

Oceanic sequestration is possible, and perhaps important, but I omit discussion of it here. 

Dave Cole, Oak Ridge National Laboratory I wonder if you might elaborate on two points regarding the environmental aspect. First, elaborate a little bit on this issue of ocean sequestration and then on geologic storage of CO2. Where do the environmentalists stand on these issues ... 

I should add that not only has there been a huge Japanese research investment in oceanic sequestration, but there is a project that will run next year, funded by (I think) the Canadians, the Americans, and Japanese that will actually attempt to inject CO2 at a rate of a kilogram per second. The project will run off Hawaii and will be used to model plume formation and so on. This experiment has got environmental groups to think about, and critique the idea of ocean sequestration. 

Dave Cole Just one quick comment to follow on that. The federal government is spending a fair bit of money examining the issue of ocean sequestration in terms of the geoenvironment. 

David Keith We just don t know because it is so early, but I think the answer is yes, but not as much for terrestrial as for oceanic CO2 sequestration. At Carnegie Mellon, we had done a preliminary open-ended elicitation of knowledge and opinions about sequestration, with about 10 non-technical members of the community. While it is not representative, we found divergent views on geological sequestration where we found strong resistance to ocean sequestration. 

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