Carbon dioxide deep ocean

Alternatives to fossil fuels, such as hydrogen, are explored in Box 6.2 and Section 14.3. Coal, which is mostly carbon, can be converted into fuels with a lower proportion of carbon. Its conversion into methane, CH4, for instance, would reduce C02 emissions per unit of energy. We can also work with nature by accelerating the uptake of carbon by the natural processes of the carbon cycle. For example, one proposed solution is to pump C02 exhaust deep into the ocean, where it would dissolve to form carbonic acid and bicarbonate ions. Carbon dioxide can also be removed from power plant exhaust gases by passing the exhaust through an aqueous slurry of calcium silicate to produce harmless solid products ... 

The difference between the total dissolved carbon in the surface and in deep-sea reservoirs depends on productivity. And the difference between the alkalinity in these reservoirs depends on productivity and also corat, the calcium-carbonate-to-organic-carbon ratio. The carbon dioxide partial pressure depends on the difference between total carbon and alkalinity in the surface reservoir, and all these depend on the total amount of carbon and alkalinity at the start of the calculation in the three reservoirs combined. By adjusting the values of these various parameters and repeating the calculation, I arrive at the following values for a steady-state system that is close to the present-day ocean with a preindustrial level of atmospheric carbon dioxide ... 

The radiocarbon ratio also evolves very rapidly from its initial value of -50 to an average value of about -8 per mil. This evolution is not a consequence of evaporative concentration but, instead, of an approach to equilibrium with atmospheric carbon dioxide. Average surface seawater contains significantly less radiocarbon than does the atmosphere because its isotopic composition is affected by exchange with the deep ocean as... 

Pumping the carbon dioxide produced at industrial plants into the deep ocean is another technique that could reduce and delay the rise of carbon dioxide in the atmosphere. But, it would not prevent an eventual warming as some made its way back into the atmosphere. Reforestation could be used as a carbon bank to capture carbon from the atmosphere, but the decay or burning of harvested trees decades later would add some carbon. 

Carbon could be filtered from power plant emissions, compressed into a liquid, and pumped into ocean depths of ten thousand feet. Here, the water pressure would compress liquid carbon dioxide to a high enough density to pool on the seafloor before dissolving. At shallower depths it would just disperse. However, injecting vast quantities of carbon dioxide could acidify the deep ocean and harm marine life. Protesters have forced scientists to cancel experiments to test the scheme in Hawaii and Norway. 

Carbon enters the atmosphere mainly as the result of respiration and burning of any kind. The oceans provide a slower, smaller pathway for carbon to enter the atmosphere. Dissolved carbon dioxide moves through the oceans waters in currents. At some places on the planet, mainly near the equator, currents bring cold water rich in carbon dioxide from deep in the ocean to the sea surface, where the Sun warms it. These warm surface waters naturally release carbon dioxide into the atmosphere. 

Carbon dioxide mainly enters the oceans from the atmosphere. It dissolves in the cold surface waters around the north and south poles. When these cold waters sink, they carry the carbon deep into the oceans where it can be stored for hundreds of years. Because of their ability to store carbon, the oceans are known as a carbon sink. The sea as a carbon sink has become increasingly important in recent decades because human activity is adding increasing amounts of carbon dioxide to the atmosphere, and much of it ends up in the sea. According to the National Aeronautics and Space Administration (NASA), almost half of the carbon added to the atmosphere hy fossil fuel burning ends up sequestered in the ocean. 

Another way to increase Earth s ability to store carbon is by creating new, artificial carbon sinks that would trap excess carbon gas produced by human activity before it enters the atmosphere. The carbon dioxide would be collected and placed in a new location for controllable, long-term storage. Scientists have already experimented with two new carbon sink locations, one deep in the ocean, the other underground. In each case, carbon is forcefully injected into its new reservoir for long-term storage. 

In the ocean experiments, scientists pump carbon dioxide into the deep ocean, where it forms giant lakes of liquid carbon dioxide. Eventually, the carbon dioxide dissolves into the surrounding waters. However, it is unclear how such increased amounts of oceanic carbon would affect sea life and water chemistry. 

Carbon dioxide oversaturation is important only in fresh water. Not a single example of oversaturation with C02 has been reported from the sea, presumably a result of an efficient buffering system. In the ocean, the partial pressure of C02 varies within a narrow range, from 1.7 x 10-4 near the surface to 9.9 x 10 4 at 5000 m depth. In enclosed seas, the range is wider. For example, in the Black Sea these values are 3-3.9 x 10"4 in near-surface water and 20-25.8 x 10-4 in deep water (Alekin, 1966). 

Clathrate hydrates have been found to occur naturally in large quantities. Around 120 X 10 m (at STP) of methane is estimated to be trapped in deposits of the deep ocean floor [10]. Clathrate hydrates are also suspected to occur in large quantities on some outer planets, moons, and trans-Neptunian objects [11]. In the petroleum industry, hydrocarbon clathrate hydrates are a cause of problems because they can form inside gas pipelines, often resulting in plugging. Deep sea deposition of carbon dioxide clathrate hydrate has been proposed as a method to remove this greenhouse gas from the atmosphere and control climate change [12]. 

Recent pelagic sediments containing over 30% calcium carbonate, by dry weight, cover a quarter of the surface of the earth (see Figure 1). These sediments make up a vast and chemically reactive carbonate reservoir which has a major influence on the chemistry of the oceans and atmosphere. In order to have a predictive understanding of the natural carbon dioxide system and the influence of man on it, the chemical dynamics of calcium carbonate deposition in the deep ocean basins must be known in detail. 

The balance between calcium carbonate production and dissolution is the major pH buffering mechanism of seawater over periods of time at least on the order of thousands of years ( ). The atmospheric carbon dioxide reservoir is less than 2 percent the size of the seawater reservoir ( ) and there is active exchange between these two reservoirs across the air-water interface. Consequently, the carbon dioxide content of the atmosphere and accumulation of calcium carbonate in the deep oceans are closely coupled. 

Estimation of Uncertainty in The determination of the total ion molal concentration of calcium from salinity measurement is relatively precise with a probable error of less than 0.3% under open ocean conditions. Dickson and Riley (37) have recently discussed the effect of analytical errors on the evaluation of the components of the aquatic carbon-dioxide system for seawater at 25°C and 1 atmosphere total pressure. Their conclusions Indicate that if alkalinity and total carbon dioxide are the measured parameters a probable combined uncertainty in the total carbonate ion molal concentration from 3 to 6 percent results, depending on Fco2 If pH and alkalinity are the measured parameters the uncertainty is approximately 4 percent. In addition to the probable error introduced by analytical precision, the absolute accuracy of the measurements introduces an error which is difficult to evaluate. The results of the GEOSECS intercalibration study (38) were indicative of this problem. A conservative guess is that accuracy introduces at least a one percent further uncertainty. It is also difficult to determine exactly what error is introduced through temperature and pressure corrections to situ conditions. For the deep sea this may introduce a further uncertainty of at least... 

Bates, N. R., Michaels, A. P., and Knap, A. H. (1996). Seasonal and interannual variability of oceanic carbon dioxide species at the U.S. JGOFS Bermuda Atlantic Time-series study (BATS) site. Deep Sea Res. f/43, 347-383. 

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