Carbon dioxide, seawater

Hydrate Carbon dioxide + seawater Reference Ohgaki et al. (1993)... 

In a similar vein, mean seawater temperatures can be estimated from the ratio of 0 to 0 in limestone. The latter rock is composed of calcium carbonate, laid down from shells of countless small sea creatures as they die and fall to the bottom of the ocean. The ratio of the oxygen isotopes locked up as carbon dioxide varies with the temperature of sea water. Any organisms building shells will fix the ratio in the calcium carbonate of their shells. As the limestone deposits form, the layers represent a chronological description of the mean sea temperature. To assess mean sea temperatures from thousands or millions of years ago, it is necessary only to measure accurately the ratio and use a precalibrated graph that relates temperatures to isotope ratios in sea water. 

An alternative pretreatment for seawater is acidification of the bicarbonate followed by degasification to remove the carbon dioxide generated. The precipitation step for the seawater process is given by (76) ... 

The selection of boiler-water treatment is also dependent on the type of cooling water. When cooling water reaches the boiler, various compounds precipitate before others. For instance, seawater contains considerable magnesium chloride. When the magnesium precipitates as the hydroxide, hydrochloric acid remains. In some lake waters, calcium carbonate is a significant impurity. When it reaches the boiler, carbon dioxide is driven off in the... 

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). 

For the solubility in seawater of oxygen, nitrogen and carbon dioxide at various temperatures and chlorinities refer to Tables 21.21 and 21.22. 

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 ... 

Carbon dioxide is likewise an inert material. As a result, its only known sinks are photosynthesis and solubility in seawater. The cycle of carbon dioxide through the atmosphere will be a major focal point in Chapter 11. 

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... 

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

Neill et al. [22] have described a headspace gas chromatographic method for the determination of carbon dioxide (fugacity) in seawater. This method requires a small water sample (60 ml), and provides for rapid analysis (2 min). 

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. 

Tabacco et al. [25] have described a method based on emission spectrometry at an excitation wavelength of 488 nm for the telemetric measurements of carbon dioxide tensions in seawater. 

Williams [176] has studied the rate of oxidation of C-labelled glucose in seawater by persulfate. After the oxidation, carbon dioxide was blown off and residual activity was measured. For glucose concentrations of 2000, 200, and 20 xg/l, residual radioactivities (as percentage of total original radioactivity) were 0.04, 0.05, and 0.025, respectively, showing that biochemical compounds are extensively oxidised by persulfate. With the exception of change of temperature, modifications of conditions had little or no effect. Oxidation for 2.5 h at 100 °C was the most efficient. 

In this method volatile organic matter in seawater is concentrated on a Tenax GC solid adsorbent trap and dry-ice trap in series. The trapped organic material is then desorbed and oxidised to carbon dioxide, which is measured with a non-dispersive infrared analyser. A dynamic headspace method was used for the extraction with the assistance of nitrogen purging. Dynamic headspace analysis [184] is an efficient extraction procedure. The efficiency of extraction... 

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

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... 

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