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Bacteriogenic iron oxides in natural environments are characterized by an abundance of ferrihydrite precipitates intermixed with bacterial structures that commonly resemble those produced by the lithoautotrophic microorganisms Gallionella ferruginea and Leptohtrix ochracea. These species have been inferred to play a causal role in the formation of bacteriogenic iron oxides, providing a pathway for the reduction of C[O.sub.2] and the depletion of [sup.13]C in the organic constituents of bacteriogenic iron oxides. In this study, stable carbon isotope fractionation was determined for bacteriogenic iron oxide samples collected from submarine hydrothermal vents (Axial Volcano, Juan de Fuca Ridge), subterranean (Aspo Hard Rock Laboratory, Sweden) and surficial (Chalk River, Canada) groundwater seeps, and cultures of G. ferruginea. Data were also collected from ferrihydrite samples lacking evidence of bacteria from Bounty Seamount in the vicinity of Pitcairn Island. The mean [delta][sup.13]C ([per thousand]) of ferrihydrite was determined to be -15.87 [per thousand] [+ or -] 4.96 [per thousand] for the samples from Axial Volcano, -24.97 [per thousand] [+ or -] 0.43 [per thousand] for Aspo, -27.80 [per thousand] [+ or -] 0.85 [per thousand] for Chalk River, -29.3 [per thousand] [+ or -] 0.2 [per thousand] for the microbial culture, and -8.43 [per thousand] [+ or -] 1.89 [per thousand] for the samples from Pitcairn. Samples with the highest concentration of organic carbon also had the lightest [delta][sup.13]C in a logarithmic relationship. The consistency of carbon isotope values in relation to the presence of iron-oxidizing bacteria from natural and laboratory samples is interpreted as the ability of these microorganisms to fractionate carbon. The potential of this fractionation to serve as a biosignature holds promise when the resistance of carbon and bacteriogenic ferrihydrite to diagenesis is taken into consideration. doi: 10.1130/G30986.1

[C.sub.4] plants are widely successful in the grass-dominated ecosystems of tropical, subtropical, and warm-temperate regions, largely as a result of their ability to limit photorespiration and improve water-use efficiency. A widely held paradigm is that low ( doi: 10.1130/G31117.1

Radiocarbon ([sup.14]C) is a radioactive isotope that is useful for determining the age and cycling of carbon-based materials in the Earth system. Compound specific radiocarbon analysis (CSRA) provides powerful insight into the turnover of individual components that make up the carbon cycle. Extraneous or nonspecific background carbon ([C.sub.ex]) is added during sample processing and subsequent isolation of CSRA samples. Here, we evaluate the quantity and radiocarbon signature of [C.sub.ex] added from two sources: preparative capillary gas chromatography (PCGC, [C.sub.PCGC] and chemical preparation of CSRA of black carbon samples ([C.sub.chemistry]). We evaluated the blank directly using process blanks and indirectly by quantifying the difference in the isotopic composition between processed and unprocessed samples for a range of sample sizes. The direct and indirect assessment of [C.sub.chemistry+PCGC] agree, both in magnitude and radiocarbon value (1.1 [+ or -] 0.5 [micro]g of C, fraction modern = 0.2). Half of the [C.sub.ex] is introduced before PCGC isolation, likely from coeluting compounds in solvents used in the extraction method. The magnitude of propagated uncertainties of CSRA samples are a function of sample size and collection duration. Small samples collected for a brief amount of time have a smaller propagated [sup.14]C uncertainty than larger samples collected for a longer period of time. CSRA users are cautioned to consider the magnitude of uncertainty they require for their system of interest, to frequently evaluate the magnitude of [C.sub.ex] added during sampling processing, and to avoid isolating samples [less than or equal to] 5 [micro]g of carbon. 10.1021/ac901922s

Stratigraphic fluctuations of carbon isotope values of terrestrial organic matter within the Upper Cretaceous (Cenomanian--Santonian) sequence in the Obira area of Hokkaido, Japan, record distinctive [delta][sup.13]C fluctuations for the Cenomanian--Turonian boundary, the Middle Turonian, the upper Turonian--lower Coniacian, and the Santonian. A biostratigraphic framework of the age-diagnostic taxa (ammonoids, bivalves and planktic foraminifers) indicates that these [delta][sup.13]C fluctuation events are comparable with those recorded in [delta][sup.13]C data of terrestrial organic matter in Japan and marine carbonates in Europe. These correlations reinforce the utility of these [delta][sup.13]C events in terms of global chemostratigraphy. In particular, the [delta][sup.13]C patterns within the overall positive interval of the Cenomanian--Turonian boundary event are highly conformable between marine and terrestrial records. The consistent nature of these different records of [delta][sup.13]C fluctuation patterns demonstrates that the terrestrial organic [delta][sup.13]C data mirror the global-scale [delta][sup.13]C patterns in the carbon reservoir of ocean--atmosphere--terrestrial biosphere during the Cenomanian--Turonian boundary event. In addition, global correlation of short-term marine and terrestrial organic [delta][sup.13]C fluctuations of the Upper Cretaceous sequence indicate that the magnitude of several terrestrial organic [delta][sup.13]C events appears more amplified than that of coeval marine carbonate [delta][sup.13]C events. This correlation is interpreted to mean that the effects of local C[O.sub.2] emission into the atmosphere by release of terrestrial methane hydrate or biomass burning of terrestrial vegetation in the hinterland of the NE Asian region have been superimposed on the global [delta][sup.13]C trend and resulted in the terrestrial organic [delta][sup.13]C records of the Yezo Group. Keywords: carbon isotope stratigraphy, Hokkaido, Japan, terrestrial organic matter, Upper Cretaceous.

Methylated metal(loid) compounds are formed in the environment by abiotic as well as enzymatically catalyzed transfer of a methyl group. Due to the increased mobility and toxicity in comparison to the inorganic precursors, the investigation of the formation process is of high relevance. Though the natural abundance carbon isotope ratio can give important insights toward their origin as well as the biochemical methyl transfer process, so far, these species have not been investigated by carbon isotope ratio mass spectrometry (IRMS). This is due to the analytical challenge to precisely determine the natural isotope distribution of trace amounts of metal(loid)-bound carbon in complex organic matrixes. To overcome this problem, we tested the concept of selective derivatization of non-volatile organometal(loid)s by hydride generation (HG) followed by purge and trap (P-T) enrichment, heart-cut gas chromatography (hcGC), and subsequent analysis by GC/IRMS. Parameter optimization of HG/P-T/hcGC was conducted using online coupling to element-sensitive ICPMS (inductively coupled plasma mass spectrometry) detection. The purity of the HG/P-T/hcGC fraction was verified by GC/MS. For the model substance trimethylarsine oxide (TMAsO), an excellent agreement of the [[delta].sup.13]C-value analyzed by HG/P-T/hcGC-GC/IRMS was achieved in comparison to the bulk [[delta].sup.13]C-value, which shows that no significant isotope fractionation occurred during hydride generation and subsequent separation. The optimized method showed good reproducibility and a satisfying absolute detection limit of 4.5 [micro]g TMAsO (1.2 [micro][g.sub.carbon]). This method was applied to the analysis of TMAsO in compost. The low [delta][sup.13]C value of this compound (-48.38 [+ or -] 0.41%[per thousand]) indicates that biomethylation leads to significant carbon fractionation. HG/P-T/hcGC-GC/IRMS is a promising tool for investigation of the biomethylation process in the environment.

The 260-million-year-old Emeishan volcanic province of southwest China overlies and is interbedded with Middle Permian carbonates that contain a record of the Guadalupian mass extinction. Sections in the region thus provide an opportunity to directly monitor the relative timing of extinction and volcanism within the same locations. These show that the onset of volcanism was marked by both large phreatomagmatic eruptions and extinctions amongst fusulinacean foraminifers and calcareous algae. The temporal coincidence of these two phenomena supports the idea of a cause-and-effect relationship. The crisis predates the onset of a major negative carbon isotope excursion that points to subsequent severe disturbance of the ocean-atmosphere carbon cycle.

The purpose of this study was to determine the fractional recovery rate of labeled C[O.sub.2] in the breath of severely burned children. This information is needed to perform tracer studies of substrate oxidation using carbon-labeled fatty acids. Nine children, ages 4-14 yr with massive burns participated in the study. All experiments were performed 7 days post burn after an overnight fast. A primed (60 [micro]mol/kg), constant (2.0 [micro]mol x [kg.sup.-1] x [min.sup.-1]) infusion of [[1,2-.sup.13]C]acetate was given during a 4-h basal period and during a 4-h hyperinsulinemic euglycemic clamp. A priming dose (150 [micro]mol/kg) of Na[H.sup.13]C[O.sub.3] was given at the beginning of the study. Breath samples were collected every 10 min during the last 40 min of each period. Indirect calorimetry was performed during the last 30 min of each period. The isotopic enrichment of [sup.13]C[O.sub.2] was determined by isotope ratio-mass spectrometry, and total C[O.sub.2] excretion was measured by indirect calorimetry. The fractional recovery of acetate label was 0.89 [+ or -] 0.05 and 0.88 [+ or -] 0.04 during the basal state and clamp, respectively. We conclude that the fractional recovery of labeled acetate in severely burned children is approximately three times the recovery of a nonburned adult and similar to the value in exercising adults. The high recovery rate reflects the rapid turnover of the TCA cycle in burned children relative to the rate of exchange reactions. Minimal correction of expired C[O.sub.2] data is needed in this circumstance to quantify fatty acid oxidation using [sup.13]C-labeled fatty acids. acetate correction factor; fatty acid oxidation

Although the Earth's environment is constantly changing, there have been a few unusual episodes over the last c. 200 Ma when change was extreme in terms of its rapidity, severity, long-lasting consequences and unpredictability. The geochemical and biotic records for two of these episodes, the Palaeocene--Eocene thermal maximum and the Toarcian Oceanic Anoxic Event (Early Jurassic), possess many significant similarities. Each event was associated with a major carbon isotope excursion, significant levels of biotic extinctions, severe global warming, an enhanced hydrological cycle, and evidence for widespread seawater anoxia. Both carbon isotope excursions can be subdivided into distinct stages with broadly similar characteristics and durations; based on a detailed comparison, the Palaeocene Eocene thermal maximum may have been an incipient Oceanic Anoxic Event. The geochemical and biotic changes during these two events are most readily explained by the abrupt, large-scale dissociation of methane hydrate that followed a period of more gradual environmental change linked to the emplacement of a large igneous province. Carbon release rates at those times were of the same order of magnitude as the current anthropogenic release rate of carbon to the atmosphere, indicating that ancient events such as these may usefully serve as analogues for present-day environmental change.

Determination of compound-specific carbon isotope values by continuous flow isotope ratio mass spectrometry is impacted by variation in several routine operating parameters of which one of the most important is signal size, or linearity. Experiments were carried out to evaluate the implications of these operating parameters on both reproducibility and accuracy of [delta][sup.13]C measurements. A new method is described for assessing total instrumental uncertainty of routine compound-specific [delta][sup.13]C analysis, incorporating both accuracy and reproducibility. These findings have important implications for application of compound-specific isotope analysis in environmental geochemistry and in particular for the rapidly developing field of isotopic investigation of biodegradation and remediation of organic chemicals in contaminant hydrogeology.

Carbonado diamonds from the Central African Republic were investigated using spectroscopic observations and C-isotopic analysis. Based on photoluminescence (PL) spectra, carbonado samples were classified into two groups: Group-A, which exhibits an intense PL band at 504 nm; and Group-B, which exhibits PL bands at 504, 575, and 638 nm at room temperature. PL spectra measured at 120 K gave well-resolved side-band structures of 504 nm bands. Consequently, the 504 nm band of Group-A can be assigned to the 3H center attributable to self interstitials in diamond, whereas the 504 nm band from Group-B can be assigned to the H3 center attributable to a vacancy ([??]) trapped at nearest-neighbor substitutional nitrogen (N) pairs. The PL band at 575 nm, which is attributable to neutral N-[??] pairs, is known to increase its width with increasing residual stress in diamond aggregates. The average FWHM of the 575 nm band and the standard deviations were 3.80 and 0.54 nm for Group-A carbonado, and 2.80 and 0.38 nm for Group-B carbonado. These values suggest that Group-A carbonado samples have higher residual stress than the Group-B samples. The presence of an H3 center and the lower residual stress in Group-B carbonado both suggest that they originated from higher temperatures compared to Group-A. Radiation halos were observed in cathodoluminescence (CL) images of both Group-A and Group-B samples. The CL halos are traces of radiation damage from radioactive nuclides. The texture of the haloes suggests that the radiation damage was a secondary event after formation of the carbonado diamonds. The average C-isotopic composition of Group-A is -23.6 [+ or -] 0.52 [per thousand] in [[delta].sup.13][C.sub.PDB] and that of Group-B is -26.3 [+ or -] 0.65 [per thousand]. Group-A carbonado was enriched systematically in [sup.13]C compared with Group-B carbonado. Isotopic fractionation might occur as a result of the different thermal history of carbonado. Keywords: Carbonado, cathodoluminescence, photoluminescence, carbon isotope, diamond, radiation damage

Peat bogs have historically represented exceptional carbon (C) sinks because of their extremely low decomposition rates and consequent accumulation of plant remnants as peat. Among the factors favoring that peat accumulation, a major role is played by the chemical quality of plant litter itself, which is poor in nutrients and characterized by polyphenols with a strong inhibitory effect on microbial breakdown. Because bogs receive their nutrient supply solely from atmospheric deposition, the global increase of atmospheric nitrogen (N) inputs as a consequence of human activities could potentially alter the litter chemistry with important, but still unknown, effects on their C balance. Here we present data showing the decomposition rates of recently formed litter peat samples collected in nine European countries under a natural gradient of atmospheric N deposition from [approximately equal to] 0.2 to 2 [g*m.sup.-2]*[yr.sup.-1]. We found that enhanced decomposition rates for material accumulated under higher atmospheric N supplies resulted in higher carbon dioxide (C[O.sub.2]) emissions and dissolved organic carbon release. The increased N availability favored microbial decomposition (i) by removing N constraints on microbial metabolism and (ii) through a chemical amelioration of litter peat quality with a positive feedback on microbial enzymatic activity. Although some uncertainty remains about whether decay-resistant Sphagnum will continue to dominate litter peat, our data indicate that, even without such changes, increased N deposition poses a serious risk to our valuable peatland C sinks. decomposition | global change | litter peat | C[O.sub.2]

The microwave technique is found to be very applicable for the preparation of a-cellulose from wood samples and can be recommended for analyzing the stable carbon isotopes in tree rings. At a reaction temperature of 80 [degrees]C, the extraction time can be decreased from 36 h to 15 min. Microwave-supported prepared cellulose contains more amorphous constituents, resulting in a relatively higher reactivity and amenability for a following nitration with regard to determination of nonexchangeable hydrogen. The [delta][sup.18]O values of microwave-enhanced extracted cellulose remain significantly lighter than reference values, possibly as a result of an increased oxygen isotope exchange between bleaching solution and cellulose under conditions of high energy input. Therefore, this technique cannot be recommended for oxygen isotope analyses in wood cellulose.

The most prominent of the two major global [[delta].sup.13]C excursions in the Ordovician, the Hirnantian [[delta].sup.13]C excursion (HICE), which is previously recorded from the uppermost Ordovician in a few sections in Nevada, Quebec, Arctic Canada, Baltoscandia, Scotland and China, is documented for the first time from the North American Midcontinent. Samples through the Girardeau Limestone and Leemon Formation in Missouri and Illinois show elevated [[delta].sup.13]C values of +4 [per thousand] to +5 [per thousand]. Although not determined precisely, the beginning of the HICE is likely to be in the upper part of the Orchard Creek Shale, and it ends in the upper Leemon Formation. Being extraordinarily useful chronostratigraphically, the presence of the HICE makes it possible to provide a firm dating of the study interval, whose age has long been controversial. Comparison between the study sections and coeval HICE sequences in North America and Europe show striking similarities, especially in sea-level history, indicating that major local lowstands reflect eustatic sea-level changes. A comparison with Hirnantian diamictite successions in North and South Africa and Argentina suggests that these lowstands correspond to two major Gondwanan glacial episodes. Keywords: carbon isotope excursion, Hirnantian, Upper Ordovician, Missouri-Illinois, Gondwana glaciation, sea-level changes.

Carbon stable-isotope variation through the Cenomanian-Santonian stages is characterized using data for 1769 bulk pelagic carbonate samples collected from seven Chalk successions in England. The sections show consistent stratigraphic trends and [[delta].sup.13]C values that provide a basis for high-resolution correlation. Positive and negative [[delta].sup.13]C excursions and inflection points on the isotope profiles are used to define 72 isotope events. Key markers are provided by positive [[delta].sup.13]C excursions of up to + 2 [per thousand]: the Albian/Cenomanian Boundary Event; Mid-Cenomanian Event I; the Cenomanian/Turonian Boundary Event; the Bridgewick, Hitch Wood and Navigation events of Late Turonian age; and the Santonian/Campanian Boundary Event. Isotope events are isochronous within a framework provided by macrofossil datum levels and bentonite horizons. An age-calibrated composite [[delta].sup.13]C reference curve and an isotope event stratigraphy are constructed using data from the English Chalk. The isotope stratigraphy is applied to successions in Germany, France, Spain and Italy. Correlation with pelagic sections at Gubbio, central Italy, demonstrates general agreement between biostratigraphic and chemostratigraphic criteria in the Cenomanian-Turonian stages, confirming established relationships between Tethyan planktonic foraminiferal and Boreal macrofossil biozonations. Correlation of the Coniacian-Santonian stages is less clear cut: magnetostratigraphic evidence for placing the base of Chron 33r near the base of the Upper Santonian is in good agreement with the carbon-isotope correlation, but generates significant anomalies regarding the placement of the Santonian and Campanian stage boundaries with respect to Tethyan planktonic foraminiferal and nannofossil zones. Isotope stratigraphy offers a more reliable criterion for detailed correlation of Cenomanian--Santonian strata than biostratigraphy. With the addition of Campanian [[delta].sup.13]C data from one of the English sections, a composite Cenomanian-Campanian age-calibrated reference curve is presented that can be utilized in future chemostratigraphic studies. The Cenomanian-Campanian carbon-isotope curve is remarkably similar in shape to supposedly eustatic sea-level curves: increasing [[delta].sup.13]C values accompanying sea-level rise associated with transgression, and falling [[delta].sup.13]C values characterizing sea-level fall and regression. The correlation between carbon isotopes and sea-level is explained by variations in epicontinental sea area affecting organic-matter burial fluxes: increasing shallow sea-floor area and increased accommodation space accompanying sea-level rise allowed more efficient burial of marine organic matter, with the preferential removal of [sup.12]C from the marine carbon reservoir. During sea-level fall, reduced seafloor area, marine erosion of previously deposited sediments, and exposure of basin margins led to reduced organic-carbon burial fluxes and oxidation of previously deposited organic matter, causing falling [[delta].sup.13]C values. Additionally, drowning of carbonate platforms during periods of rapid sea-level rise may have reduced the global inorganic relative to the organic carbon flux, further enhancing [[delta].sup.13]C values, while renewed platform growth during late transgressions and highstands prompted increased carbonate deposition. Variations in nutrient supply, changing rates of oceanic turnover, and the sequestration or liberation of methane from gas hydrates may also have played a role in controlling carbon-isotope ratios. Keywords: Cretaceous, carbon isotopes, Chalk, chemostratigraphy, sea-level change.

The distribution of [delta][sup.13]C values from human remains recovered in the eastern Chihuahuan Desert and central Texas demonstrates the existence of at least two distinct coeval dietary populations during the Early and Late Archaic. We employed a novel statistical technique, normal probability plots, to identify distinct dietary populations. [delta][sup.13]C values from one population in the Lower Pecos and Trans-Pecos regions of Texas reflect the long-term use of Chihuahuan Desert [C.sub.4] and CAM plants. A second group, consisting of all the central Texas individuals and some individuals from the Lower Pecos, depended heavily on [C.sub.3] plants more common in the Edwards Plateau or in the oak-pine forests in Mexico. The wide range of stable carbon isotope ratios from the Lower Pecos region of the eastern Chihuahuan Desert forces a reconsideration of hunter-gatherer settlement and social organization models proposed for that region. This study highlights the need to conduct more research on hunter-gatherer prehistoric diets and social organization. Keywords: Texas, Archaic, diet, Lower Pecos, stable isotopes

Open savannah grasslands (dominated by [C.sub.4] plants) became a significant component of northeast African vegetation during the late Neogene. We present molecule-specific carbon isotopic measurements of terrestrial plant biomarkers preserved in marine sediments off northeast Africa that allow reconstruction of orbital-scale vegetation changes in short time windows over the past 9.4 m.y. The biomarker data show large-amplitude vegetation variability as early as 3.8 Ma, with the greatest [C.sub.4] expansion occurring after 3.4 Ma. We sampled orbital-scale oscillations of up to 5% [per thousand], almost as large as the observed late Neogene range of 7 [per thousand], suggesting that large and repeated oscillations between more open and more closed landscapes were an important aspect of northeast African vegetation change during the past 4 m.y. Keywords: [[delta].sup.13]C, carbon isotopes, biomarker, Africa, vegetation, [C.sub.4].

Clarification of the factors involved in the formation of unusual ancient organic carbon--rich deposits (like eastern Mediterranean sapropels) is central in understanding oceanic carbon cycling. The role of oxygenation remains a subject of controversy primarily due to two major uncertainties: (1) it is unknown if ancient organic-rich deposits reflect an accumulation of refractory organic matter (OM) or oxygenation-related aberrant sediment OM recycling, and (2) although marine OM degradation may be slower under anoxic conditions, its ultimate impact on organic carbon ([C.sub.org]) preservation over geological time remains unclear. Here we provide direct experimental evidence that the [C.sub.org] in eastern Mediterranean S1 sapropeis (deposited >5 ka) is still highly reactive and that a shutdown in labile organic matter degradation under anoxic conditions played a key role in the formation of these deposits. Keywords: organic carbon, preservation, remineralization, nitrogen isotopes, carbon isotopes, sapropel.

Carbon isotopes in rodent fecal pellets were measured on packrat (Neotoma spp.) middens from the Grand Canyon, Arizona. The pellet samples reflect the abundance of cold-intolerant C4 and Crassulacean acid metabolism (CAM) plant species relative to the predominant C3 vegetation in the packrat diet. The temporal sequence of isotopic results suggests a temperature decline followed by a sharp increase corresponding to the Bolling/ Allerod-Younger Dryas-early Holocene sequence. This pattern was then tested using the past distribution of Utah agave (Agave utahensis). Spatial analyses of the range of this temperature-sensitive CAM species demonstrate that its upper elevational limit is controlled by winter minimum temperature. Applying this paleotemperature proxy to the past elevational limits of Utah agave suggests that minimum winter temperatures were ~8 [degrees]C below modern values during the Last Glacial Maximum, 4.5-6.5 [degrees]C below modern during the Bolling/Allerod, and 7.5-8.7 [degrees]C below modern during the early Younger Dryas. As the Younger Dryas terminated, temperatures warmed ~4 [degrees]C between ca. 11.8 ka and 11.5 ka. These extreme fluctuations in winter minimum temperature have not been generally accepted for terrestrial paleoecological records from the arid southwestern United States, likely because of large statistical uncertainties of older radiocarbon results and reliance on proxies for summer temperatures, which were less affected. Keywords: Younger Dryas, Grand Canyon, [sup.13]C, packrat middens, Agave utahensis, PleistoceneHolocene transition.

A new high-resolution Paleozoic [delta][sup.13][C.sub.carb], curve from the Great Basin shows an amount of variation that appears transitional between the highly unsettled Neoproterozoic and the increasingly stable Mesozoic to Cenozoic periods. Large positive excursions were common during cool periods (e.g., Late Ordovician-Silurian and Late Devonian-Early Mississippian), but rare during greenhouse climates. Some periods of stability in [delta][sub.13][C.sub.carb] lasted for >[10.sup.7] yr and are interpreted to reflect negative feedbacks on productivity in a nitrogen-limited (low oceanic N/P) ocean in which anoxia led to increased denitrification. Suppression of N fixation, likely due to low levels of essential trace elements, is a requirement of N limitation. In contrast, cool periods that ventilated the oceans switched the ultimate limiting nutrient to P and allowed for [delta][sup.13]C excursions, which signal episodic organic carbon burial that could be sustained by positive feedbacks between productivity and anoxia. Keywords: Paleozoic, carbon isotope, phosphorus, nitrogen, glaciation.

All scientists who study the late Quaternary are confronted by the problem of radio-carbon calibration. Since 1969, numerous high-frequency time series have been developed through the use of several stable isotopes (e.g., [[delta].sup.8]O). Such time series are inefficient as dating methods because too many age possibilities are obtained for a given unique value. However, the Bayesian framework permits incorporation of these time series as a prior assumption on ages in order to improve calibrated ages obtained from a more precise absolute dating approach such as that using radiocarbon. The method is tested on data obtained from the Gigny cave (French Jura). Highly discontinuous posterior distributions are obtained with narrow highest posterior density regions. Thus, when the radiocarbon method alone gives large uncertainties, the incorporation of [[delta].sup.8]O values of meteoric waters largely diminishes these uncertainties. Keywords: isotopes, oxygen, radiocarbon calibration, Bayesian statistic.

Studies were conducted to examine the potential use of stable carbon isotope ratios of lipids for determining substrate usage by sulfate reducing bacteria. It was found that FA delta13C values could be useful to interpret carbon utilization by sulfate reducing bacteria in natural environments.

The first kinetic isotope effect (KIE) measurements for the reactions of CI atoms with saturated non-methane hydrocarbons (NMHC) are presented at room temperature and ambient pressure. It is observed that the [super 13]C-structure reactivity relationship values for alkane-Cl reactions are determined and are similar to earlier reported values for alkane-OH reactions

Estimates of carbon fluxes and turnover times for five terrestrial ecosystems are presented using a modeling approach. It is seen that the parameterization method is useful in the estimation of unknown parameters, and to find variability in carbon turnover in a particular ecosystem.

Comparative and phenotypic selection approaches is used to investigate the importance of leaf ecophysiological traits. Findings suggest that the action of phenotypic selection depended greatly on the genotypic class for three closely related sunflower hybrids grown in a common environment.

The use of 13C direct detection, pursued in 2D experiments to detect broad lines in nuclear magnetic resonance spectra of paramagnetic is reported. Paramagnetic-based restraints, in principle, can be used for solution structure determination of paramagnetic metalloproteins and in copper(II) proteins in particular.

Different population movements, technological inventions and the adoption of agricultural foodstuffs qualify the Neolithic period of South Asia. The human subsistence patterns at three Neolithic sites in Sarawak using stable isotype ratios of carbon and oxygen derived from tooth enamel apatite is explored.