Radiocarbon carbon dioxide

Craig, H. (1957b). The natural distribution of radiocarbon and the exchange time of carbon dioxide between atmosphere and sea. Tellus 9,1-17. 

Soon after their creation, the newly formed radiocarbon atoms react with atmospheric oxygen to form radioactive carbon dioxide, molecules of carbon dioxide in which the carbon atom is radiocarbon ... 

The carbon dioxide molecules including a radiocarbon atom are chemically undistinguishable from those of ordinary carbon dioxide, with which it mixes, and eventually, carbon dioxide, including a radiocarbon atom, is homogeneously distributed throughout the earth s atmosphere and hydrosphere. Thus there is a state of constant production, distribution, and decay of radiocarbon, which results in the relative amount of radiocarbon in the atmosphere and hydrosphere remaining constant. In this homogeneously distributed condition, radiocarbon enters the carbon cycle - as the... 

Carbon Dioxide. Carbon dioxide, also a colorless and odorless gas, makes up about 0.03% of dry air. Carbon dioxide is introduced into the atmosphere by several natural processes it is released from volcanoes, from burning organic matter, and from living animals as a byproduct of the respiration process. It is for this latter reason that carbon dioxide plays a vital role in the carbon cycle (see Fig. 62), which makes possible one of the more important scientific tools in archaeology, radiocarbon dating (see Textbox 52). 

Fossil fuel source terms appear not only in equation 1 for atmospheric carbon dioxide fuel/matmco2 but also in equations 6 and 9 for carbon isotopes in the atmosphere fuel/matmco2 defuel or drfuel. The 13C delta value for the fossil fuel source is defuel = — 25, and the radiocarbon value is drfuel = —1000, because fossil carbon is devoid of radiocarbon, rfs = 0, and del = — 1 1000. 

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... 

The chemistry of carbon, and radiocarbon, in the atmosphere represents one of the most important areas of environmental research today. The primary practical reason for this is the increasing attention which must be paid to the critical balance between energy and the environment, especially from the viewpoint of man s perturbations of natural processes and his need to maintain control. Probably more than other species, carbonaceous molecules play a central role in this balance. Some of the deleterious effects of carbonaceous gases and particles in the atmosphere are set down in Table 3. The potential effects of increased local or global concentrations of these species on health and climate have led to renewed interest in the carbon cycle and the "C02 Problem". It should be evident from the table, however, that carbon dioxide is not the only problem. In fact, the so-called "trace gases and particles" in the atmosphere present an important challenge to our interpretation of the climatic effects of carbon dioxide, itself [20]. 

The values of E(t) so computed are listed in Table 4. The correction for fractionation of carbon dioxide at the sea surface is a serious one. It makes the interpretation of 13C/12C variations in wood difficult and militates against the use of the isotope ratio of carbon as a thermometer. This correction, when applied to variations of carbon-14 in wood, is able to explain the Suess radiocarbon "wiggles" of about 100 years duration each, without the need to invoke changes in the neutron flux from the sun [54]. 

Our initial studies on the metabolic pathway of captan in spinach point to similarities with dichlo-fluanid metabolism in strawberries. Preplanting treatment of soil with I C-captan followed by spinach cultivation for 34 days in a closed controlled ventilated cultivating system resulted in a recovery of 87% radiocarbon (Table III). The ma or amount (49%) was found in the soil, 19% in the spinach and 19% as carbon dioxide. Bligh-Dyer extraction of the spinach gave 7.4% of the l c-iabel in the chloroform and metha-... 

Table 2 gives details of some conventional regimes (see British National Formulary, 2008). The efficacy of therapy can be checked by Radiocarbon-labelled urea breath testing (which depends upon release of labelled carbon dioxide by bacterial urease) or by testing gastric biopsy material for persistence of gastric urease, but should only be done after eradication therapy has been discontinued for at least a month, and whilst any anti-secretory treatment has been discontinued (because it tends to suppress but does not eradicate the organism). 

Indeed, this happens every moment in the Earth s atmosphere. The upper atmosphere is bombarded with cosmic rays fast-moving subatomic particles produced by extremely energetic astrophysical processes such as nuclear fusion in the sun. When cosmic rays hit molecules in the atmosphere, they induce nuclear reactions that spit out neutrons. Some of these neutrons react with nitrogen atoms in air, converting them into a radioactive isotope of carbon carbon-14 or radiocarbon , with eight neutrons in each nucleus. This carbon reacts with oxygen to form carbon dioxide. About one in every million million carbon atoms in atmospheric carbon dioxide is C. 

The chemistry of a fourth coenzyme was at least partially elucidated in the period under discussion. F. Lynen and coworkers treated P-methylcrotonyl coenzyme A (CoA) carboxylase with bicarbonate labelled with 14C, and discovered that one atom of radiocarbon was incorporated per molecule of enzyme. They postulated that an intermediate was formed between the enzyme and C02, in which the biotin of the enzyme had become car-boxylated. The carboxylated enzyme could transfer its radiolabelled carbon dioxide to methylcrotonyl CoA more interestingly, they found that the enzyme-COz compound would also transfer radiolabelled carbon dioxide to free biotin. The resulting compound, carboxybiotin [4], was quite unstable, but could be stabilized by treatment with diazomethane to yield the methyl ester of N-carboxymethylbiotin (7) (Lynen et al., 1959). The identification of this radiolabelled compound demonstrated that the unstable material is N-carboxybiotin itself, which readily decarboxylates esterification prevents this reaction, and allows the isolation and identification of the product. Lynen et al. then postulated that the structure of the enzyme-C02 compound was essentially the same as that of the product they had isolated from the reaction with free biotin, but where the carbon dioxide was inserted into the bound biotin of the enzyme (Lynen et al., 1961). Although these discoveries still leave significant questions to be answered as to the detailed mechanism of the carboxylation reactions in which biotin participates as coenzyme, they provide a start toward elucidating the way in which the coenzyme functions. 

Obviously this wide distribution of the 14C formed in the atmosphere lakes time it is believed to require a period of 500-1000 years. This time is not. however, a deterrent to radiocarbon dating because of two factors die long half-life of I4C and the relatively constant rate of cosmic-ray formation of l4C in the earth s atmosphere over the most recent several thousands of years. These considerations lead to the conclusion that the proportion of 14C in the carbon reservoir of the earth is constant, and that the addition by cosmic ray production is in balance with the loss by radioactive decay. If this conclusion is warranted, then the carbon dioxide on earth many centuries ago had the same content of radioactive carbon as the carbon dioxide on earth today, Thus, radioactive carbon in the wood of a tree growing centuries ago had the same content as that in carbon oil earth today. Therefore, if we wish to determine how long ago a tree was cut down to build an ancient fire, all we need to do is to determine the relative 14C content of the carbon in the charcoal remaining, using the value we have determined for llie half life of 14C. If the carbon from Ihe charcoal in an ancient cave has only as much 14C radioactivity as does carbon on earth today, then we can conclude that the tree which furnished llie firewood grew 5730 30 years ago. 

Fractionation and Contamination. The ratio 14C/12C in certain materials may be affected by isotopic fractionation. For example, the uptake of carbon dioxide and its incorporation into plant tissue may be accompanied by substantial fractionation that depends on the plant species. With marine organisms, fractionation may also be important, especially when inorganic carbonate and bicarbonate are involved. Corrections for fractionation must be made for precise radiocarbon dating. 

A living plant contains about the same fraction of carbon-14 as atmospheric carbon dioxide. The observed rate of decay of carbon-14 from a living plant is 15.3 counts per minute per gram of carbon. How many counts per minute per gram of carbon will be measured from a 15,000-yr-old sample Will radiocarbon dating work well for small samples of 10 mg or less ... 

Hesshaimer V., Heimann M., and Levin I. (1994) Radiocarbon evidence for a smaller oceanic carbon-dioxide sink than previously believed. Nature 370, 201-203. 

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