Carbon isotope signatures

As is the case for hydrogen, carbon isotope signatures in Martian meteorites present evidence for different carbon reservoirs. Wright et al. (1990) and Ro-manek et al. (1994) distingnished three carbon compounds one component released... 

Martens C. S., Blair N. E., Green C. D., and Des Marais D. J. (1986) Seasonal variations in the stable carbon isotope signature of biogenic methane in a coastal sediment. Science 233, 1300-1303. 

Kerogenous filaments in cherts from within the Apex basalt sequence in the Pilbara Craton, western Australia, became famous in the late 1980s as the world s oldest microfossils. They were described by Schopf and Packer (1987) and Schopf (1993) and have, until recently, been widely accepted as authentic, because of their supposed good preservation state. The kerogenous filaments are divided into cell-like compartments and have carbon isotope signatures as low as (S13C = —30%o) -all the hallmarks of microfossils (Schopf, 1993 Schopf et al., 2002). 

Table 6.4 Major sources of methane, their mean carbon isotopic signatures and estimated contribution to total methane flux entering the atmosphere (after Whiticar 1990)...

The total annual input of methane from all sources to the atmosphere shown in Table 6.4 is 540 Mt, while the estimated output from atmosphere to sinks is 500 Mt. The potential inaccuracies in flux data can be seen by comparing the observed carbon isotopic signature of atmospheric methane of —47%o with that calculated from the data in Table 6.4 of c— 54%o (the latter is actually equivalent to —58%o upon correcting for the kinetic isotope effect (see Box 1.3) that operates during the hydroxyl abstraction reaction). There are clearly major gaps in our understanding of the pathways of methane into and out of the atmosphere and the fluxes involved, as there are for many anthropogenic substances (see Chapter 7). 

Cook et al. 1997 Cook and Bowman 2000). The fluids carry a magmatic oxygen and carbon isotope signature. Hence the fluid source is probably the crystallizing magma of the Alta stock. 

Stern, L. A., Johnson, G. D., and Chamberlain, C. P. (1994). Carbon isotope signature of environmental change found in fossil ratite eggshells from a South Asian Neogene sequence. Geology 22, 419-422. ... 

Wilcke, W., Krauss, M., and Amelung, W., Carbon isotope signature of polycyclic aromatic hydrocarbons (PAHs) evidence for different sources in tropical and temperate environments ... 

The Julia oil sample from 30/7a-10 is markedly different from the Judy/Joanne samples it has a much higher maturity and wax content and a light carbon isotope signature. The oil in the Palaeocene in Julia probably resulted from leakage from an underlying Triassic accumulation, possibly associated with hydraulic fracturing. 

Finally, differences in the carbon isotopic ratio between organic and inorganic carbon, as well as atmospheric CO2, allow the construction of yet a third mass budget for the euphoric zone. There is a clear carbon isotope signature that can be modeled... 

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