Carbon dioxide oceanic, dissolved

Figure 3.10 Schematic representation of ocean storage options. In dissolution type ocean storage, the carbon dioxide rapidly dissolves in the ocean water, whereas in lake type ocean storage, the carbon dioxide is initially a liquid on the sea floor, soon crystallizing as a hydrate. Given sufficient time, all forms of carbon dioxide - gas, liquid, hydrate - will dissolve in the water.

The carbon dioxide (physically) dissolved in water - we denote it as C02 aq) -is in equilibrium with gaseous atmospheric carbon dioxide C02(g). There is no way to separate non-ionic dissolved C02 aq) and H2CO3 therefore, it is often lumped into C02 aq). Analytically, DIC can be measured by acidifying the water sample, extracting the CO2 gas produced and measuring. The marine carbonate system represents the largest carbon pool in the atmosphere, biosphere and ocean, meaning it is of primary importance for the partition of atmospheric excess carbon dioxide produced by human activity. 

Gases can dissolve in liquids. In fact, liquid/gas solutions are important to us. One example is a soft drink, which has carbon dioxide gas dissolved in water. Another example is the ocean, where the solubility of oxygen is crucial to fish and other animal life, and the solubility of carbon dioxide is important for algae and other plant life. In fact, the ability of the oceans to dissolve gases is largely unknown but is thought to be a major factor in the weather conditions of the troposphere (the layer of the atmosphere closest to the surface of the earth). 

Solutions are everywhere around us. Most of the gases, liquids, and solids we see are mixtures of at least one substance dissolved in another. There are different types of solutions. The air we breathe is a solution that is primarily oxygen and nitrogen gases. Carbon dioxide gas dissolved in water makes carbonated drinks. When we make solutions of coffee or tea, we use hot water to dissolve substances from coffee beans or tea leaves. The ocean is also a solution, consisting of many salts such as sodium chloride dissolved in water. In your medicine cabinet, the antiseptic tincture of iodine is a solution of iodine dissolved in ethanol. 

Carbonic acid is an important natural component of the environment because it is formed whenever carbon dioxide dissolves in lake water or seawater. In fact, the oceans provide one of the critical mechanisms for maintaining a constant concentration of carbon dioxide in the atmosphere. Carbonic acid takes part in two successive proton transfer equilibria ... 

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 ... 

An important example of non-linearity in a biogeochemical cycle is the exchange of carbon dioxide between the ocean surface water and the atmosphere and between the atmosphere and the terrestrial system. To illustrate some effects of these non-linearities, let us consider the simplified model of the carbon cycle shown in Fig. 4-12. Ms represents the sum of all forms of dissolved carbon (CO2, H2CO3, HCOi" and... 

Fig. 11-9 (a) The vertical distributions of alkalinity (Aik) and dissolved inorganic carbon (DIC) in the world oceans. Ocean regions shown are the North Atlantic (NA), South Atlantic (SA), Antarctic (AA), South Indian (SI), North Indian (NI), South Pacific (SP), and North Pacific (NP) oceans. (Modified with permission from T. Takahashi et ah, The alkalinity and total carbon dioxide concentration in the world oceans, in B. Bolin (1981). Carbon Cycle Modelling," pp. 276-277, John Wiley, Chichester.)... 

Yong Suk Choi et al. [26] used a carbonate-selective electrode to determine dissolved carbon dioxide in the oceans. 

Carbon dioxide plays a key role in climate, in biological processes, in weathering reactions, and in marine chemistry. I shall next describe how the partial pressure of this gas in the atmosphere may be calculated. Because there is a rapid exchange of carbon dioxide between ocean and atmosphere, we must consider the fate of dissolved carbon. 

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 error results in the following way. The amount of organic carbon dissolved in the oceans is 0.14 gm/cm2, about equal to the amount of carbon in atmospheric carbon dioxide of 0.13 g C/cm2. Since the organic carbon is 2.7 percent depleted in carbon-13, the atmospheric reservoir is correspondingly enriched by 2.7 percent. 

If global warming raises the temperature of surface waters and carbon dioxide continues to build up in the atmosphere, the carbon dioxide is less soluble in warmer water. The dissolved carbon dioxide can easily move back into the atmosphere unless it is taken up by marine plants or combines with a molecule of carbonate. But, the ocean s supply of carbonate is limited and is replenished only slowly as it is washed into the oceans by rivers that erode carbonate-containing rocks such as limestone. By absorbing two billion tons of carbon from the atmosphere each year, the ocean is depleting its buffer carbonate supply. 

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. 

What can lower the pH of an entire ocean An acid, of course.The earth s atmosphere naturally contains a small amount of carbon dioxide. Carbon dioxide in the atmosphere isn t an acid, but when it dissolves in water, it makes a weak acid called carbonic acid. Burning fossil fuels releases more carbon dioxide into the atmosphere to dissolve in water. 

Weathering is the process by which rock is broken down into smaller and smaller particles. It involves both mechanical and chemical breakdowns. The mechanical breakdown into smaller and smaller pieces occurs as a result of exposure to freeze-thaw cycles and to the action of wind and water. Chemical breakdown occurs as a result of exposure to air and water and other chemicals that may be dissolved in water, such as acids. Weathering by exposure to atmosphere results in some of the carbon dioxide being removed from the atmosphere along with the broken-down rock and eventually washed into the ocean. 

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. 

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. 

In the course of the carbon cycle, carbon moves from the atmosphere, where it mostly exists in the form of carbon dioxide, into biological molecules—the molecules that make up living things and the wastes and remains. The incorporation of atmospheric carbon into living organisms begins with the process of photosynthesis. Some atmospheric carbon dioxide is also removed from the atmosphere when it dissolves in the cold ocean waters at the north and south poles. 

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