Isotope ratio biological production

Fig. 6-5. The evolution of the lagoon s waters in response to oscillations in biological productivity. The results show the adjustment of the system from an initial composition equal to that of seawater. This figure shows isotope ratios, calcium concentration, the saturation index, and productivity.

In this chapter I explained how isotope ratios may be calculated from equations that are closely related, but not identical, to the equations for the bulk species. Extra terms arise in the isotope equations because isotopic composition is most conveniently expressed in terms of ratios of concentrations. I illustrated the use of these equations in a calculation of the carbon isotopic composition of atmosphere, surface ocean, and deep ocean and in the response of isotope ratios to the combustion of fossil fuels. As an alternative application, I simulated the response of the carbon system in an evaporating lagoon to seasonal changes in biological productivity, temperature, and evaporation rate. With a simulation like the one presented here it is quite easy to explore the effects of various perturbations. Although not done here, it would be easy also to examine the sensitivity of the results to such parameters as water depth and salinity. 

Kumar N, Anderson RF, Mortlock RA, Froelich PN, Kubik P, Dittrich-Hannen B, Suter M (1995) Increased biological productivity and export production in the glacial southern ocean. Nature 378 675-680 Malinovsky D, Stenberg A, Rodushkin I, Andren H, Ingri J, Ohlander B, Baxter DC (2003) Performance of high resolution MC-ICP-MS for Fe isotope ratio measurements in sedimentary geologic materials. J Anal... 

Therefore, biologically mediated kinetic fractionation, where the products will have more of the lighter isotope in them due to differential partitioning from higher energy properties, will result in a net depletion of the heavy isotope in the product and a more negative del value. Moreover, kinetic fractionation occurs in reactions that are unidirectional, where the reaction rates actually depend on the isotopic composition of the substrates and products. Thus, the isotopic ratio of the substrate is related to the amount... 

Complex mixtures of molecules such as biological fluids, natural products, foods, and beverages will result in mass spectra that are quite comphcated, even if soft ionization is used to minimize fragmentation. Mixtures are more commonly analyzed by using GC-MS" or LC-MS" to separate the components of the mixture and to obtain mass spectral information on the separated components. Standards are run, often using isotope dilution and internal standard calibration and the peak intensities or intensity ratios of appropriately selected peaks are used to make a calibration curve from which unknown concentrations in samples can be determined. 

In the estimation of unlabelled metabolites extracted from biological materials, enzymes have been used to convert non-radioactive substrates into labelled derivatives. A labelled co-factor is used in a manner similar to the use of a labelled reagent in isotope derivative analysis. A good example of such methods is the double isotope enzymatic assay for histamine [325]. Samples containing unknown amounts of histamine, tracer amounts of H-histamine and " C-S-adenosylmethionine are incubated with a partially purified preparation of histamine methyl transferase from guinea-pig brain. This enzyme is specific for the methylation of histamine [326]. The product of the reaction, 1,4-methylhistamine, is extracted into chloroform and the ratio of determined by liquid scintillation counting, is directly pro-... 

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