A carbon isotope budget for an anoxic marine sediment

Systematic seasonal variations in the stable carbon isotopic signature of methane gas occur in the anoxic sediments of Cape Lookout Bight, a lagoonal basin on North Carolina's Outer Banks. Values for the carbon isotope ratio (delta 13C) of methane range from -57.3 per mil during summer to -68.5 per mil during winter in gas bubbles with an average methane content of 95%. The variations are hypothesized to result from changes in the pathways of microbial methane production and cycling of key substrates including acetate and hydrogen. The use of stable isotopic signatures to investigate the global methane cycle through mass balance calculations, involving various sediment and soil biogenic sources, appears to require seasonally averaged data from individual sites.

Isotopic signature

Carbon fibers

10.1126/science.11536566

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Citations (123)

Carbon-14 in Methane Sources and in Atmospheric Methane: The Contribution from Fossil Carbon

Science (1989)

M. Wahlen Noriyuki Тanaka Raymond M. Henry B. Deck J. Zeglen

Measurements of carbon-14 in small samples of methane from major biogenic sources, from biomass burning, and in "clean air" samples from both the Northern and Southern hemispheres reveal that methane from ruminants contains contemporary carbon, whereas that from wetlands, pat bogs, rice fields, and tundra is somewhat, depleted in carbon-14. Atmospheric (14)GH(4) seems to have increased from 1986 to 1987, and levels at the end of 1987 were 123.3 +/- 0.8 percent modern carbon (pMC) in the Northern Hemisphere and 120.0 +/- 0.7 pMC in the Southern Hemisphere. Model calculations of source partitioning based on the carbon-14 data, CH(4) concentrations, and delta(13)C in CH(4) indicate that 21 +/- 3% of atmospheric CH(4) was derived from fossil carbon at the end of 1987. The data also indicate that pressurized water reactors are an increasingly important source of (14)CH(4).

Atmospheric methane

Carbon fibers

Atmospheric carbon cycle

10.1126/science.245.4915.286

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Citations (257)

Investigating carbon sources for methane and dissolved organic carbon in a regional confined aquifer using (super 14) C.

Radiocarbon (1991)

Ramón Aravena Leonard I. Wassenaar Jim Barker

Carbon fibers

Carbon-14

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Natural Abundances of Carbon Isotopes in Acetate from a Coastal Marine Sediment

Science (1987)

Neal E. Blair Christopher S. Martens David J. Des Marais

Measurements of the natural abundances of carbon isotopes were made in acetate samples isolated from the anoxic marine sediment of Cape Lookout Bight, North Carolina. The typical value of the total acetate carbon isotope ratio (delta 13C) was -16.1 +/- 0.2 per mil. The methyl and carboxyl groups were determined to be -26.4 +/- 0.3 and -6.0 +/- 0.3 per mil, respectively, for one sample. The isotopic composition of the acetate is thought to have resulted from isotopic discriminations that occurred during the cycling of that molecule. Measurements of this type, which have not been made previously in the natural environment, may provide information about the dominant microbial pathways in anoxic sediments as well as the processes that influence the carbon isotopic composition of biogenic methane from many sources.

Carbon fibers

10.1126/science.11539717

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Citations (62)

FRACTIONATION OF STABLE ISOTOPES OF CARBON AND SULFUR DURING BIOLOGICAL PROCESSES IN THE BLACK SEA

Kluwer Academic Publishers eBooks (2006)

Mikhail Ivanov Alla Yu Lein

δ34S

Mass-independent fractionation

Equilibrium fractionation

Sulfur Cycle

Carbon fibers

10.1007/1-4020-4297-3_15

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Carbon and sulfur isotopic compositions of organic carbon and pyrite in sediments from the Transvaal Supergroup, South Africa

Precambrian Research (1996)

Harald Strauß Nicolas J. Beukes

Carbon fibers

Sedimentary organic matter

Supergroup

10.1016/0301-9268(95)00088-7

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Citations (39)

Radiocarbon in marine dissolved organic matter.

Radiocarbon (1996)

M. le Clercq van der Johannes Plicht Harro A. J. Meijer de Henricus Baar

Absolute dating

Geochronology

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The isotopic composition of particulate organic carbon in mountain rivers: The role of fossil organic carbon

EGU General Assembly Conference Abstracts (2009)

Robert Hilton Αlbert Galy Niels Hovius M. Horng H. Chen

We present a detailed characterisation of POC in the mountain rivers that drain the Central Range, Taiwan. We investigate the range in the stable carbon isotopes, nitrogen to organic carbon ratio and the stable nitrogen isotopes of river suspended sediment, with an aim to determine the processes influencing their variability. We observe considerable heterogeneity in the carbon isotopic composition of fossil organic matter contained in bedrocks and river bed materials. Based on observations from our data, we present an end member mixing model that accounts for a variable fossil POC composition while quantifying the proportion of riverine POC derived from fossil sources and that from the terrestrial biosphere (non-fossil sources). Radiocarbon is used as an independent constraint upon which to test the model. We find that fossil POC dominates the suspended load sediment and induces a 5 permil range in the stable carbon isotopes of riverine POC in Taiwan. We proceed to examine the implications of incomplete oxidation of fossil organic carbon in this landscape on the compositional variability of POC exported to the ocean from Taiwan and discuss its wider implications for the sedimentary record.

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