The Carbon Dioxide Dilemma Promising Technologies and Policies (2003) / Chapter Skim
Currently Skimming:
Sequestration in the Oceans
Sequestration in the Oceans
Pages 41-58
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From page 41... ...
Sequestration in the Oceans
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From page 43... ...
We recognize that the atmosphere then moves across the surface of a large-scale saline "aquifer" containing dissolved carbonate minerals, and we neutralize the CO2 by a reaction with carbonate ion dissolved in seawater, thus converting it to sodium bicarbonate. This aquifer covers 70 percent of the Earth's surface, and the reaction with the alkalinity of surface ocean waters is the primary modifier of the increase of CO2 in the atmosphere.
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From page 44... ...
We have already lowered surface ocean pH by about 0.1 pH units, and, if the Intergovernmental Panel on Climate Control "Business as Usual" scenario is followed, by the end of this century, we will have lowered carbonate ion concentrations in surface ocean waters by >50 percent (Brewer, 1997~. This will significantly affect the calcification process in coral reefs.
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From page 45... ...
45 o to v cM ~ ~-~)
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From page 46... ...
Disposal scenarios that are the focus of current research include droplet plume and dense plume dissolution, dry ice and towed pipe dispersion, and isolation as a dense lake of CO2 on the sea floor. Towed pipe and droplet plume scenarios may offer the best approach in the near future.
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From page 47... ...
The Norwegian study showed that, if the location and depth of release were carefully selected, the water masses labeled with this excess dissolved CO2 would be advected to the North Atlantic deep-water formation regions and transported into the abyssal flows. This would ensure sequestration for >250 years before reventilation of the water masses in the Antarctic circumpolar flows.
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From page 48... ...
Deep ocean waters are approximately 500-fold undersaturated with respect to dissolved CO2. We thus decided to do an experiment to measure directly the oceanic dissolution rates of CO2 hydrates themselves testing the idea of hydrate storage on the ocean floor (Rehder et al., in press)
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From page 49... ...
Thus, in several classic experiments over the course of the last few years, we've determined that CO2 in all forms does dissolve at significantly high rates in the ocean. It reacts quickly with water to form carbonic acid and then with carbonate ion to add to the pool of dissolved bicarbonate in ocean waters.
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From page 50... ...
At a depth of about 300 meters, the ratio of CO2 solubility to nitrogen solubility changes significantly, with strongly preferential dissolution of CO2. Thus, a bubble stream would quickly evolve into a pure nitrogen gas phase and a dense CO2 rich aqueous phase, which could be piped to great depth.
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From page 51... ...
1997. Ocean chemistry of the fossil fuel CO2 signal: the haline signature of "Business as Usual." Geophysical Research Letters 24: 1367-1369.
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From page 53... ...
scenario shows that to stabilize climate at 2°C of warming, if climate sensitivity is at the low end of the accepted range, approximately 75 percent of all power production would have to come from sources free of carbon emissions by the end of this century. If climate sensitivity is at the high end of the accepted range, nearly all of our energy would have to come from carbon-emission-free sources.
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From page 54... ...
The basic idea of iron-based ocean fertilization (see Figure 1) is to add iron to the upper ocean to stimulate biological activity and increase photosynthetic activity, and thus generate more organic carbon removing it from the surface.
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From page 55... ...
carbon placed in the deep ocean eventually mixes back up to the surface; and (2) along with the organic carbon, we sent nutrients down into the deep ocean, thus increasing the deep-ocean nutrient content at the expense of the surface ocean.
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From page 56... ...
My sense is that these are upper bound numbers because in the real world we would probably not fertilize the entire ocean south of 30 degrees, and the areas that were fertilized would probably not perform up to maximum possibilities. It is important to understand that ocean fertilization, insofar as it works and is environmentally and politically acceptable, might become part of a portfolio of responses.
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From page 57... ...
We don't know to what extent adding nutrients to the surface ocean would stimulate marine production of organic carbon or how that would vary from environment to environment. Although we're making progress, we are still not sure what fraction will sink to the deep ocean when organic carbon production is increased.
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From page 58... ...
It might be worth reducing emissions in the short term in anticipation of new energy technologies coming online in the long term.
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