Nitrogen abundances

The interpretation of the factors mentioned above in the context of palaeodietary research is not straightforward a lack of nitrogen isotope data in relevant plant species makes the situation even more complicated. The observed variability in plants, even within ecosystems, is so extensive and so unpredictable that modelling of the behaviour of natural nitrogen abundances in plants is fraught with difficulties because there are no simple, universal laws governing the site-specific details of the N cycle, there will be no simple, universal laws of 8 N (in plants) (Handley and Raven 1992 Handley and Scrimgeour 1996). 

Various spectral features can be used to derive the nitrogen abundance in dwarfs. Unfortunately weak high excitation (x=10.34 eV) near-infrared NI lines at 7468.31, 8216.34, 8683.4, 8703.25 and 8718.83 A disappear at metallicities [Fe/H] < -1 and for the analysis of N in metal-poor stars we are left with the CN and NH molecular bands at 3883 and 3360 A, respectively. It must be mentioned... 

Theoretical models for nucleosynthesis in asymptotic giant branch stars predict a large contribution to the cosmic nitrogen abundance from intermediate-mass stars [1], In particular, hot-bottom-burning in stars above a certain mass produces [C/N] —1 [2]. However, observations of C and N abundances in C-rich, metal-poor stars, usually using the CH and CN bands, show [C/N] values that vary between —0.5 and 1.5. (Fig. 1). If any of these stars have been polluted by intermediate mass AGB stars, then they should have lower [C/N] ratios. However, most of the CH stars with detailed abundances have [C/Fe] > 1.0, and it is more likely than stars mildly enhanced in C have been polluted by N-rich stars. 

Kung CC, Clayton RN (1978) Nitrogen abundances and isotopic compositions in stony meteorites. Earth Planet Sci Lett 38 421 35... 

CFCs) and halons over the next decade, as mandated by the Montreal Protocol for the Protection of the Ozone Layer, will affect the chlorine burden of the stratosphere. Hydrochlorofluorocarbons (HCFCs) can be used as substitutes for the CFCs for a few decades without having a substantial impact on the chlorine burden of the stratosphere because they are primarily destroyed in the troposphere by reactions with OH before they are able to deliver the chlorine to the stratosphere. The elimination of CFCs and the temporary use of HCFCs into the early part of the next century must be carefully orchestrated to minimize the peak chlorine loading and promote the most rapid reduction of the chlorine burden of the stratosphere (56, 87). Another issue is the effects that perturbations to the reactive nitrogen abundances will have on the abundances of reactive chlorine. A better understanding and clarification of the direct heterogeneous conversions of chlorine species on both PSCs and sulfate aerosols are also needed. 

Figure 1. Nitrogen abundance in diamonds from various meteorite types.

Carbon isotopic studies alone are not able to resolve the source of such carbon isotopic variability and the relative importance of these competing models. Thus, current approaches are to combine carbon isotopic studies with nitrogen abundance, aggregation, isotopic composition and even age determinations on the same diamonds (e.g., Hauri et al, 1999, 2002). 

Fitzsimons 1. C. W., Harte B., Chinn 1. L., Gurney J. J., and Taylor W. R. (1999) Extreme chemical variation in complex diamonds from George Creek, Colorado a SIMS study of carbon isotope composition and nitrogen abundance. Min. Mag. 63(6), 857-878. 

Harte B., Fitzsimons I. C. W., Harris J. W., and Otter M. L. (1999a) Carbon isotope ratios and nitrogen abundances in relation to cathodoluminescence characteristics for some diamonds from the Kaapvaal Province S. Africa. Mineral. Mag. 63(6), 829-856. 

Nitrogen abundances in the atmospheres of Earth and Venus are comparable, being much higher than that of Mars. Meteoritic 8 N values overlap the terrestrial-atmosphere and the lower-mantle values, while that of Mars atmosphere is much higher. Planetary N/ Ar ratios fall between meteorite and solar ratios. While much of the terrestrial nitrogen at the surface is in the atmosphere with = o%o (where =... 

For main sequence secondary stars in massive close binary systems, a strong boron depletion must also be expected due to the transfer of nuclear processed matter however, a very noticeable CNO-signature is always present in this case (cf. e.g. de Loore De Greve, 1992). Therefore, the existence of boron depleted stars with a roughly normal nitrogen abundance would be a clear indication of rotational mixing. 

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