Carbon isotopes organic matter

The two main terrestrial carbon reservoirs, organic matter and sedimentary carbonates, have distinctly different isotopic characteristics because of the operation of two different reaction mechanisms ... 

Hayes et al. (1999) systematically evaluated the carbon isotope fractionation between carbonates and coeval organic matter for the past 800 Ma. They concluded that earlier assumptions of a constant fractionation between carbonate and organic matter is untenable and that fractionations may vary by about 10%o depending on the dominant biogeochemical pathway as well on environmental conditions. 

Kump LR (1989) Alternative modeling approaches to the geochemical cycles of carbon, sulfur and strontium isotopes. Am J, Sd 289 390-410 Kump LR (2005) Ironing out biosphere oxidation. Science 307 1058-1059 Kump LR, Arthur MA (1999) Interpreting carbon-isotope excursions carbonates and organic matter, Chem Geol, 161 181-198... 

Kump L. R. and Arthur M. A. (1999) Interpreting carbon-isotope excursions carbonates and organic matter. Chem. Geol. 161(1-3), 181-198. 

General Data on Carbon Isotope Composition of Sedimentary Rocks (Carbonates) and Organic Matter from Northeastern Algeria... 

Gas-chromatography-combustion-mass-spectrometry (GC-C-MS) enables the carbon-isotope analysis of n-alkanes of each carbon number, and therefore, the separate analysis of alkanes derived from alga] acterial and vascular plant sources. This ability has previously been utilized to determine the origin of waxy n-alkanes in a variety of sediments 85,86). The carbon-isotope composition of n-alkanes derived fi-om vascular plants can, therefore, be used to determine the relative contributions of C3- and C4-derived carbon to organic matter in marine, terrestrial or composite sediment samples. This approach has been applied in a preliminary manner to representative samples fi om the Amazon Basin (Bird and Summons, unpublished data). 

The quantification of gross root production, rhizodeposition, microbial assimilation, and the production of organic materials in soil has made increasing progress ever since stable ( C) and radioactive ( C) carbon isotopes have been used (see Chap. 12). Measurements of soil organic matter dynamics without these isotopes are difficult due to the large amount present as compared to the smaller rates of input. 

Recurrent is the lack of adequate techniques to assess carbon flows through the plants and microbes into soil organic matter (151). Most important is the development of techniques and protocols to separate rhizosphere from nonrhizosphere soil as well as possibly to facilitate analyses of soil carbon dynamics. The use of carbon isotopes, and, where possible, application of double labeling with C and C, seems inevitable in order to separate the contribution of different substrates to the formation of the soil organic matter pool and to get to an understanding of the ecological advantage of exudates and rhizodeposits. 

D. A. Wedin, L. L. Tieszen, B. Dewey, and J. Pastor, Carbon isotope dynamics during grass decomposition and soil organic matter formation. Ecology 76 1383 (1995). 

---