Carbon dioxide in seawater

Murphy et al. [21] have described an infrared based detector method for the determination of carbon dioxide in seawater. 

Fukushi and Hiiro et al. [24] described a method for determining total carbon dioxide in seawater by capillary isotachoelectrophoresis following isolation of the carbon dioxide by membrane permeation. 

Bradshaw A.L. and Brewer P.G. (1988a) High precision measurements of alkalinity and total carbon dioxide in seawater by potentiometric titration - 1. Presence of unknown protolyte(s) Mar. Chem. 23, 69-86. 

Bradshaw, A. L., and Brewer, P. G. (1988) High Precision Measurements of Alkalinity and Total Carbon Dioxide in Seawater by Potentiometric Titration, Mar. Chem. 23, 69-86. 

Describe the chemical processes involving the dissolution of carbon dioxide in seawater. 

The solubility of carbon dioxide in water is given in Figure 1 (11). Over the temperature range 273—393 K, the solubiUties at pressures below 20 MPa (200 atm) decrease with increasing temperature. From 30 to 70 MPa (300—700 atm) a solubiUty minimum is observed between 343 and 353 K, with solubihties increasing as temperature increases to 393 K. Information on the solubiUty of carbon dioxide in pure water and synthetic seawater over the range 268 to 298 K and 101—4,500 kPa pressure (1—44 atm) is available (12,13). 

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 ... 

Weiss, R. F. (1974). Carbon dioxide in water and seawater the solubility of a non-ideal gas. Marine Chem. 2,203-215. 

Various workers have discussed the determination of total alkalinity and carbonate [ 10-12], and the carbonate bicarbonate ratio [ 12] in seawater. A typical method utilises an autoanalyser. Total alkalinity (T milliequivelents per litre) is found by adding a known (excess) amount of hydrochloric acid and back titrating with sodium hydroxide solution a pH meter records directly and after differentiation is used to indicate the end-point. Total carbon dioxide (C milliequivelents per litre of HCO3 per litre) is determined by mixing the sample with dilute sulfuric acid and segmenting it with carbon dioxide-free air, so that the carbon dioxide in the sample is expelled into the air segments. The air... 

Fukishi and Hiiro [222] determined sulfide in seawater by this technique. The method is based on the generation of hydrogen sulfide by the addition of sulfuric acid to the water sample. The gas permeated through a microporous polytetrafluoroethylene (PTFE) tube, and was collected in a sodium hydroxide solution. The carbon dioxide in the permeate was removed by adding a barium cation-exchange resin to the sodium hydroxide solution. Injection into the... 

Carbon dissolved in seawater takes part in fast chemical reactions involving the species dissolved carbon dioxide H2CQ3, bicarbonate ions... 

The chemistry of the carbonic acid system in seawater has been one of the more intensely studied areas of carbonate geochemistry. This is because a very precise and detailed knowledge of this system is necessary to understand carbon dioxide cycling and the deposition of carbonate sediments in the marine environment. A major concept applicable to problems dealing with the behavior of carbonic acid and carbonate minerals in seawater is the idea of a constant ionic medium. This concept is based on the observation that the salt in seawater has almost constant composition, i.e., the ratios of the major ions are the same from place to place in the ocean (Marcet s principle). Possible exceptions can include seawater in evaporative lagoons, pores of marine sediments, and near river mouths. Consequently, the major ion composition of seawater can generally be determined from its salinity. It has been possible, therefore, to develop equations in which the influence of seawater composition on carbonate equilibria is described simply in terms of salinity. 

Weiss, R. (1974) Carbon Dioxide in Water and Seawater. The Solubility of a Nonideal Gas, Mar. Chem. 2, 203-215. 

One of the most important components of the chemical perspective of oceanography is the carbonate system, primarily because it controls the acidity of seawater and acts as a governor for the carbon cycle. Within the mix of adds and bases in the Earth-surface environment, the carbonate system is the primary buffer for the aridity of water, which determines the reactivity of most chemical compoimds and solids. The carbonate system of the ocean plays a key role in controlling the pressure of carbon dioxide in the atmosphere, which helps to regulate the temperature of the planet. The formation rate of the most prevalent authigenic mineral in the environment, CaCOs, is also the major sink for dissolved carbon in the long-term global carbon balance. 

When equilibrium with the atmosphere is reached, approximately 87% of ionic carbonate is present as bicarbonate ion, the remainder being carbonate. In many places, especially close to the surface, seawater is saturated with respect to calcium carbonate, which will precipitate slowly from solution, thus regulating the amount of carbonate in solution. This process is perhaps the most important of all the geological systems since it regulates the amount of carbon dioxide in the atmosphere. 

In the atmosphere, CO2 is affected by processes that operate on different time scales, including interaction with the silicate cycle (for more details, see Bashkin and Howarth, 2002), dissolution in the oceans, and annual cycles of photosynthesis and respiration (see also Section 4). The relative effect of these processes is described below taking into account the interrelationship between sources and sinks of carbon dioxide in the Asian region. Here, it is important to note that carbon dioxide is not reactive with other atmospheric species its MRT is three years (Figure 5). This value is largely determined by exchange with seawater (see below). 

The main gases dissolved in seawater are nitrogen, oxygen, and carbon dioxide. In well-aerated waters, the concentrations of O2 and CO2 are about 5 x 10 " and 10 mol/L, respectively. 

Now, the average pH at the surface layer of seawater is 8.1 [6]. Acidification of the ocean is progressing by an increase in the concentration of carbon dioxide in the air. It may be necessary to revise the pH of a solvent used in the elution test if the pH continues to fall in the future. 

Seawater pH ranges from 7.8-S.3. This narrow pH range is due to reactions that cause the interchange of carbon dioxide in the air with seawater and photosynthesis. Changes in the pH of seawater are buffered by the carbonate system and the presence of undissociated boric acid [7]. The buffering capacity and the constancy of natural waters such as seawater are discussed in Ref 8. 

Solutions include different combinations in which a solid, liquid, or gas acts as either solvent or solute. Usually the solvent is a liquid. For instance, seawater is an aqueous solution of many salts and some gases such as carbon dioxide and oxygen. Carbonated water is a saturated solution of carbon dioxide in water. Solutions are common in nature and are extremely important in all life processes, in all scientific inquiry, and in many industrial processes. Many naturally occurring fluids contain particulate matter suspended in a solution. For example, blood contains a solution (plasma) with suspended blood cells. Seawater contains dissolved substances as well as suspended solids. The body fluids of all life forms are solutions. Variations in concentrations of our bodily fluids, especially those of blood and urine, give physicians valuable clues about a person s health. Solutions in which the solvent is not a liquid are also common. Air is a solution of gases with variable composition. Dental fillings are solid amalgams, or solutions of liquid mercury dissolved in solid metals. Alloys are solid solutions of solids dissolved in a metal. 

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