Frans E. Wickman

VARIATIONS IN THE RELATIVE ABUNDANCE OF THE CARBON ISOTOPES IN PLANTS

Abstract The C 12 C 13 ratio of 105 plants representing all the major systematic groups has been determined. Except perhaps for gymnosperms there are in principle no systematic differences between the groups. Characteristic differences occur, however, between plants grown in different biotopes, and these differences are related to the varying intensity of the local carbon-dioxide cycle.

The cycle of carbon and the stable carbon isotopes

The following estimates are used: carbonate carbon (A) 2420 ± 560 grammes, C12C13 = 88·55 ± 0·05; organic sedimentary carbon (B) between 0·1–0·5 per cent C in shales, C12C13 = 91·00 ± 0·1θ. The concept “crustal carbon” is defined, and based on the measurements of the isotope ratios of thirty-seven diamonds, nineteen carbonates from Ivigtut, some other carbonates and some graphites: the isotope ratio of crustal carbon is estimated to be 89·11 ± 0·05. Using these isotope ratios, the ratio AB is found to be 3·45 ± 0·55, and B = 700 ± 200 grammes. All weights are referred to cm2 earth surface, and the isotope ratios to the Stockholm scale.

A contribution to the stable carbon isotope geochemistry of iron meteorites

Abstract For most iron meteorites studied, the carbon isotopic composition of nodular graphite falls in the range −4.8 to −8.2%. vs PDB and shows a mode between −5 and −6%.. Fourteen cohenite analyses from the Magura meteorite fall between −18.1 and −19.2%. with a pronounced clustering around −18.5%.. Carbon of a taenite separate from the same meteorite has an isotopic composition of −18.8%.; compositions between −19.7 and −22.1%. were found for taenite carbon in five other octahedrites. It is suggested that the 12 C enrichment in cohenite and taenite relative to the nodular graphite is a general phenomenon in iron meteorites, and that the study of 13 C abundances in iron meteorites may aid in the elucidation of their history. To this end an experimental study of carbon isotope fractionations in the system Fe-Ni-C is essential. The 13 C content of carbon from several silicate inclusions in the Four Corners and ‘El Taco’ (Campo del Cielo) meteorites is generally similar to the nodular graphite, the 12 C enrichment (−13%.) in one specimen may be interpreted in terms of a mixing model involving an original inclusion carbon and carbon exsolved from the taenite upon cooling.

The “total” amount of sediments and the composition of the “average igneous rock”

Abstract Assuming sediments to derive exclusively from granite-granodiorite and basalt the chemical composition of the “average igneous rock” is found to be almost identical with that of the Appalachian and Cordilleran igneous rocks as determined by A. Knopf (1916). The total amount of weathered igneous rocks is found to be 194 ± 21, the amount of shale 172 ± 28, sandstone 17.3 ± 21, limestone 12.8 ± 4.3, and dolomite 6.8 ± 3.0, all in kg per cm 2 earth surface. The total amount of sediments formed by complete weathering is thus 209 ± 35 in the same unit. The results and their degree of accuracy are discussed and compared with the results of previous calculations.

Wird das Häufigkeitsverhältnis der Kohlenstoffisotopen bei der Inkohlung verändert

Abstract Three series of coal samples representing Pliocene, Wealden, and Carboniferous have been investigated. Metamorphism has no traceable influence on the 12c/13c ratios. Various factors are briefly discussed in order to explain the observed isotope ratios. Often carbonates in coal do not seem to have been formed from plant carbon dioxide which is contrary to common views on their origin.

Natural variations in the relative abundances of the nitrogen isotopes

Abstract Two samples of NH 4 C1, two of caliche, eight of Wealden coal, five of Carboniferous coal, three of living trees and one air sample were studied. The NH 4 C1 samples formed a distinct group about 1 % heavier than the air sample. The other samples showed variations of some parts per thousand from the air sample. The Wealden-coal nitrogen is heavier than the Carboniferous-coal nitrogen, this being contrary to the results found for the carbon isotopes.

The isotopic composition of ‘graphitic’ carbon from iron meteorites and some remarks on the troilitic sulfur of iron meteorites

Abstract The carbon isotopic composition of graphite inclusions and finely dispersed carbon from twelve iron meteorites has been studied. The analyses are given as parts permil deviations from the PDB standard. Forty-five analyses of inclusion-graphites from four coarse-grained octahedrites fall in the range from − 4.8 to − 8.2‰; within some of the inclusions a C 13 depletion toward the rim of the nodules is observed. Finely dispersed, residual carbon from four coarse octahedrites, obtained by dissolving the meteorite, shows distinctly lighter isotopic compositions ranging from −5.6 to −24.1%., probably representing a mixture of small inclusions and flakes as well as carbon contained in carbides or in solid solution in the nickel-iron. Graphite inclusions showing C 13 concentrations outside the above range for inclusion-graphites were found in 1. (1) two octahedrites with silicate inclusions, i.e., Four Corners (− 4.0%.) and Pine River (− 8.7%.). 2. (2) the hexahedrite Kendall County (−13.3 to −14.4%.). 3. (3) the ‘ataxite’ Dayton (−11.5 to −11-8%.). This suggests that the average carbon isotopic composition may not be identical for all iron meteorites. The large variability in the C 13 concentration encountered within individual irons contrasts with the isotopic constancy of sulfur observed in meteorites. It is proposed that the differences in the isotope distribution patterns of the two elements may be understood on the basis of the chemical phase relationships in the system Fe-Ni-S-C. However, while δC 13 variations within a meteorite may be discussed within this framework, little can be said as yet about possible causes for the suggested differences in C 13 concentrations between different meteorites.

A PRELIMINARY INVESTIGATION INTO THE ISOTOPIC COMPOSITION OF CARBON FROM SOME ALKALINE INTRUSIONS

Abstract Twelve samples of carbonate rocks from Alno (Sweden), eight samples from Fen, two from Stjernoy and one from Seiland (Norway), have been investigated. The beforsites from Alno show a lower C12/C13 ratio than the soevites and the alvikites from the same area. In the Fen area there is a difference between the iron-rich and iron-poor rocks. The C12/C13 ratios of the soevites from all four occurrences are quite consistent. Various factors which might influence the ratio are mentioned.

Two notes on the isotopic constitution of carbon in minerals

Abstract Measurements of the C 12 C 13 ratio on two generations of calcite and the matrix from a single specimen are given and discussed. This ratio has also been determined for four examples of graphite and limestone occurring together. The formation of the graphite is briefly discussed in relation to the C 12 C 13 ratios.

A search for variations in the relative abundance of the zinc isotopes in nature

Abstract The ratio Zn 64 Zn/ 68 was studied in 18 samples of 7 different zinc minerals. No variations could be detected. If they exist they are less than 0.1% of the ratio.