Life and Global Climate Change on Earth

Geochimica Et Cosmochimica Acta, 1953

Several hundred samples of carbon from various geologic sources have been analyzed in a new survey of the variation of the ratio C13/C12 in nature. Mass spectrometric determinations were made on the instruments developed by H. C. Urey and his co-workers utilizing two complete feed systems with magnetic switching to determine small differences in isotope ratios between samples and a standard gas. With this procedure variations of the ratio C13/C12 can be determined with an accuracy of ±0.01% of the ratio.The results confirm previous work with a few exceptions. The range of variation in the ratio is 4.5%. Terrestrial organic carbon and carbonate rocks constitute two well defined groups, the carbonates being richer in C13 by some 2%. Marine organic carbon lies in a range intermediate between these groups. Atmospheric CO2 is richer in C13 than was formerly believed. Fossil wood, coal and limestones show no correlation of C13/C12 ratio with age. If petroleum is of marine organic origin a considerable change in isotopic composition has probably occurred. Such a change seems to have occurred in carbon from black shales and carbonaceous schists. Samples of graphites, diamonds, igneous rocks and gases from Yellowstone Park have been analyzed. The origin of graphite cannot be determined from C13/C12 ratios. The terrestrial distribution of carbon isotopes between igneous rocks and sediments is discussed with reference to the available meteoritic determinations. Isotopic fractionation between iron carbide and graphite in meteorites may indicate the mechanism by which early fractionation between deep seated and surface terrestrial carbon may have occurred.

Global Biogeochemical Cycles, 2002

1] Global data sets of the stable carbon isotope composition of plant leaves, of CO 2 in canopy air, and of CO 2 in the background atmosphere were compiled and compared to results of a global vegetation model (BIOME4) that simulated, at these three scales, the magnitude, direction, and timing of fluxes of CO 2 and 13 C between the biosphere and the atmosphere. Carbon isotope data on leaves were classified into 12 Plant Functional Types (PFTs), and measurements from canopy flasks were assigned to 16 biomes, for direct comparison to model results. BIOME4 simulated the observed leaf d 13 C values to within 1 standard deviation of the measured mean for most PFTs. Modeled d 13 C for C 3 grasses, tundra shrubs, and herbaceous plants of cold climates deviated only slightly more from measurements, perhaps as a result of the wide geographic range and a limited set of measurements of these PFTs. Modeled ecosystem isotopic discrimination against 13 C (D e ) averaged 18.6 globally when simulating potential natural vegetation and 18.1 when an agricultural crop mask was superimposed. The difference was mainly due to the influence of C 4 agriculture in areas that are naturally dominated by C 3 vegetation. Model results show a gradient in D e among C 3 -dominated biomes as a result of stomatal responses to aridity; this model result is supported by canopy air measurements. At the troposphere scale, BIOME4 was coupled to a matrix representation of an atmospheric tracer transport model to simulate seasonally varying concentrations of CO 2 and 13 C at remote Northern Hemisphere measuring stations. Ocean CO 2 and 13 C flux fields were included, using the HAMOCC3 ocean biogeochemistry model . Model results and observations show similar seasonal cycles, and the model reproduces the inferred latitudinal trend toward smaller isotopic discrimination by the biosphere at lower latitudes. These results indicate that biologically mediated variations in 13 C discrimination by terrestrial ecosystems may be significant for atmospheric inverse modeling of carbon sources and sinks, and that such variations can be simulated using a process-based model.

a b s t r a c t Pyrogenic carbon (PC; also known as biochar, charcoal, black carbon and soot) derived from natural and anthropogenic burning plays a major, but poorly quantified, role in the global carbon cycle. Isotopes provide a fundamental fingerprint of the source of PC and a powerful tracer of interactions between PC and the environment. Radiocarbon and stable carbon isotope techniques have been widely applied to studies of PC in aerosols, soils, sediments and archaeological sequences, with the use of other isotopes currently less developed. This paper reviews the current state of knowledge regarding (i) techniques for isolating PC for isotope analysis and (ii) processes controlling the carbon ( 13 C and 14 C), nitrogen, oxygen, hydrogen and sulfur isotope composition of PC during formation and after deposition. It also reviews the current and potential future applications of isotope based studies to better understand the role of PC in the modern environment and to the development of records of past environmental change.

2020

Total length of time required for lesson: 1 hr. 30 min. (or two class periods) with an optional 50 min. supplemental activity. Key words, vocabulary: the following definitions are modified from Google Dictionary. Carbon (C)-belonging to group 14 on the Periodic Table of Elements, it is one of the most abundant elements on Earth, with atomic number 6 and atomic mass 12.011. Isotope-each of two or more forms of the same element that contain equal numbers of protons, but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties. Carbon-12 (12 C)-the most common natural carbon isotope of mass 12, with a nucleus containing six protons and six neutrons. It is the basis for the accepted scale of atomic mass units. Carbon-13 (13 C)-a natural, stable isotope of carbon with a nucleus containing six protons and seven neutrons. As one of the environmental isotopes, it makes up about 1.1% of all natural carbon on Earth. Carbon-14 (14 C)-a long-lived, naturally occurring radioactive carbon isotope of mass 14, its nucleus contains six protons and eight neutrons. C-14 is used in carbon dating and as a tracer in biochemistry. As one of the environmental isotopes, it makes up less than 0.1% of all natural carbon on Earth. Atomic number-the number of protons in the nucleus of an atom, which determines the chemical properties of an element and its place on the Periodic Table of Elements. Atomic mass-the mass of an atom of a chemical element expressed in atomic mass units. It is approximately equivalent to the number of protons and neutrons in the atom (the mass number) or to the average number allowing for the relative abundances of different isotopes. Radioactive decay-spontaneous breakdown of an atomic nucleus resulting in the release of energy and matter from the nucleus. Remember that a radioisotope has unstable nuclei that does not have enough binding energy to hold the nucleus together. Half-life-the time taken for the radioactivity of a specified isotope to fall to half its original value. Isotope ratio mass spectrometry (irMS)-measures relative abundance of isotopes in an environmental sample using mass-to-charge ratio of ions. Mass-to-charge ratio-in mass spectroscopy, the mass-to-charge ratio of a cation is equal to the mass of the cation divided by its charge.

Pyrogenic carbon (PC; also known as biochar, charcoal, black carbon and soot) derived from natural and anthropogenic burning plays a major, but poorly quantified, role in the global carbon cycle. Isotopes provide a fundamental fingerprint of the source of PC and a powerful tracer of interactions between PC and the environment. Radiocarbon and stable carbon isotope techniques have been widely applied to studies of PC in aerosols, soils, sediments and archaeological sequences, with the use of other isotopes currently less developed. This paper reviews the current state of knowledge regarding (i) techniques for isolating PC for isotope analysis and (ii) processes controlling the carbon ( 13 C and 14 C), nitrogen, oxygen, hydrogen and sulfur isotope composition of PC during formation and after deposition. It also reviews the current and potential future applications of isotope based studies to better understand the role of PC in the modern environment and to the development of records of past environmental change.

Geologische Rundschau, 1982

Die Entdeckung des atomar gelSsten Kohlenstoffs in Olivinen aus Mantelgesteinen fiihrt zu neuen Vorstellungen fiber die Zusammensetzung der Uratmosph~ire und Entwicklungsbedingungen des Lebens. Atomarer Kohlenstoff im MgO ist in der Lage, in einer O2-freien Atmosph/ire mit dem Gittersauerstoff zu CO9 zu reagieren und mit dem aus OH-stammendeu Gitterwasserstoff eine gro13e Vielfalt yon organischen Verbindungen zu bilden.

… Transactions of the Royal Society of …, 2002

Biogeosciences, 2004

We report that the most abundant C 1 units of terrestrial plants, the methoxyl groups of pectin and lignin, have a unique carbon isotope signature exceptionally depleted in 13 C. Plant-derived C 1 volatile organic compounds (VOCs) are also anomalously depleted in 13 C compared with C n+1 VOCs. The results confirm that the plant methoxyl pool is 5 20

Eos, Transactions American Geophysical Union, 2012

Oecologia, 1994

Estimates of the extent of the discrimination against 13CO 2 during photosynthesis (AA) on a global basis were made using gridded data sets of temperature, precipitation, elevation, humidity and vegetation type. Stomatal responses to leaf-to-air vapour mole fraction difference (D, leaf-to-air vapour pressure difference divided by atmospheric pressure) were first determined by a literature review and by assuming that stomatal behaviour results in the optimisation of plant water use in relation to carbon gain. Using monthly time steps, modelled stomatal responses to D were used to calculate the ratio of stomatal cavity to ambient CO 2 mole fractions and then, in association with leaf internal conductances, to calculate A a. Weighted according to gross primary productivity (GPR annual net CO 2 asimilation per unit ground area), estimated A A for C 3 biomes ranged from 12.9%o for xerophytic woods and shrub to 19.6%o for cool/cold deciduous forest, with an average value for C 3 plants of 17.8%o. This is slightly less than the commonly used values of 18-20%o. For C 4 plants the average modelled discrimination was 3.6%o, again slightly less than would be calculated from C 4 plant dry matter carbon isotopic composition (yielding around 5%o). From our model we estimate that, on a global basis, 21% of GPP is by C 4 plants and for the terrestrial biosphere as a whole we calculate an average isotope discrimination during photosynthesis of 14.8%o. There are large variations in 21A across the globe, the largest of which are associated with the precence or absence of C 4 plants. Due to longitudinal variations in AA, there are problems in using latitudinally averaged terrestrial carbon isotope discriminations to calculate the ratio of net oceanic to net terrestrial carbon fluxes.