13C Isotope Ratio Research Articles

Methodological comparison for quantitative analysis of fossil and recently derived carbon in mine soils with high content of aliphatic kerogen

In mine soil, quantification of soil organic carbon (OC) derived recently from biomass decomposition is complicated by the presence of fossil (geogenic) C derived from coal, oil shale, or similar material in the overburden. The only reliable method for such measurement is 14C analysis (i.e. radiocarbon dating) using instrumentation such as accelerator mass spectrometry, which is too expensive for routine laboratory analysis. We tested two previously used and two new methods for recent C quantification and compared them with 14C AMS radiocarbon dating as a reference using a set of soil samples (n=14) from Sokolov, Czech Republic: (i) 13C isotope ratio composition, (ii) cross polarization magic angle spinning 13C nuclear magnetic resonance (CPMAS 13C NMR) spectroscopy, (iii) near infrared spectroscopy (NIRS) coupled with partial least squares regression and (iv) Rock–Eval pyrolysis. Conventional methods for OC determination (dry combustion, wet dichromate oxidation, loss-on-ignition) were also compared to quantify any bias connected with their use. All the methods provided acceptable recent carbon estimates in the presence of mostly aliphatic fossil C from kerogen. However, the most accurate predictions were obtained with two approaches using Rock–Eval pyrolysis parameters as predictors, namely (i) S2 curve components and (ii) oxygen index (OI). The S2 curve approach is based on the lower thermal stability of recent vs. fossil organic matter. The OI approach corresponded well with 13C NMR spectra, which showed that samples rich in recent C were richer in carboxyl C and O-alkyl C. These two methods showed the greatest potential as routine methods for recent C quantification.

13C NMR analysis of cellulose samples from different preparation methods

Alpha-cellulose is a part of the wooden material that preserves isotopic composition during tree-growth, and therefore provides important indirect data for paleoclimatological studies. For this reason, it is exceptionally important to extract the alpha-cellulose component from plants, e.g. from tree rings of wood. Since the cell wall of plant cells consists of multicomponent polysaccharides, the extraction of cellulose from wood is not an obvious task. In this paper, we describe, evaluate and compare nine methods, based on the literature and experimental observations, for obtaining cellulose from tree rings of wood. We show that the distortionless enhancement by polarization transfer (DEPT-135) variant of liquid-state 13C NMR spectroscopy is a powerful analytical method for monitoring the preparation process. Trifluoroacetic acid was applied as solvent for the NMR analysis. We proved that all the preparation methods give pure cellulose samples without hemicellulose and lignin content, and we propose methods resulting in non-fragmented cellulose. 13C and 18O isotope ratio measurements have shown that all the applied extraction methods result in similar isotope ratios, thus they are suitable for paleoclimatological studies.

Discrimination between Ascorbic Acid from Acerola and of Synthetic Origin by Measuring 13C and 18O Stable Isotope Ratios

Abstract We examined the 13C/12C and 18O/16O stable isotope ratios (δ13C, δ18O) of ascorbic acid from acerola and of synthetic origin. Although the obtained δ13C values were partially overlapping for the two species, δ18O values were higher for ascorbic acid from acerola, than values obtained for synthetic ascorbic acid. From this study, it was demonstrated that carbon and oxygen isotopic composition analysis can discriminate ascorbic acid from acerola from that of synthetic origin.

The Impact of Grape Varieties to Wine Isotopic Characterization

This paper highlights the results of a study regarding the impact of geo-climatic conditions, the influence of grape varieties, and harvest year on the isotopic characterization of a wine from a specific vineyard area, using stable isotope ratio analysis by continuous flow mass spectrometry CF-IRMS. This analytical technique has made a significant contribution on wine characterization, by proving the botanical and geographical origin of the wine raw material. A great variability was observed to sap 18O and 2H isotopic ratios for different types of vine (Vitis vinifera plant) from the studied area, Dealu Mare-Valea Calugareasca, reflecting the significant influence of variety on isotopic features. On the other hand, the comparison of stable isotopic fingerprints for rainfall water and sap revealed a close approximation value for 18O isotopic ratio, and an insignificant variation coefficient of 13C isotopic ratio in wine varieties (about 2.85%). The results of isotopic characterization for grape vine sap and original wines for different varieties existing in Dealu Mare-Valea Calugareasca vineyard indicates the relevance of meteorological and viticulture parameters like precipitation, date of vintage, and grape cultivar for wine authentication process.

Dark metabolism and carbon–nitrogen uncoupling in the toxic dinoflagellate Alexandrium catenella (Dinophyceae)

Uptake rates of three potential N-sources (ammonium, nitrate and N-urea) and two potential C-sources (HCO 3 − and C-urea) were estimated during growth of Alexandrium catenella in both light and dark phases. According to the variations observed in 13C-isotopic ratio, A. catenella cells were not able to use C-urea. Furthermore, decreases in 13C cell content during darkness revealed a probably high involvement of C recently fixed in dark respiration. Dark N-uptake capacities of A. catenella were characterized by dark/light uptake ratio of 27%, 43% and 65% for NO 3 −, NH 4 + and N-urea, respectively. An accumulation of C-rich compounds during the light period was highlighted through strong diel variations in C:N ratio and would provide C and energy for these dark uptake processes indicating an uncoupling between N and C metabolism. Total costs in terms of C associated with dark N-uptake and assimilation were estimated and revealed that the main part of those costs may be associated with maintenance metabolism in A. catenella cells. The relatively low C-costs of biosynthesis in darkness suggest that dark uptake and C-storage strategies correspond to a benefit in terms of competitiveness for A. catenella, optimized by the migrating abilities of this species.

Source Evaluation of Diazinon Using Stable Carbon Isotope Ratio

Soil samples were collected between May 27 and October 28, 2005, at sites in Yurihonjo City, Akita Prefecture, Japan. Diazinon, an extensively used organophosphate insecticide, was detected in high concentrations. Recent advances in analytical techniques enabled identification of the source of the high levels of diazinon by measuring the 13C isotope ratio of diazinon. Eight diazinon products primarily used in Akita Prefecture were analyzed. The results show that the isotope ratio of the diazinon products ranged from −31.25 ± 4.07½ to −21.67 ± 2.91½, and the isotope ratio of the diazinon in the soil samples was −24.20 ± 1.23½.

Mapping suitability for Sangiovese wine by means of δ13C and geophysical sensors in soils with moderate salinity

A three year experiment was carried out to test the possibility of using the carbon isotope ratio ( δ 13C) measured in wine, combined with data of proximal and remote soil sensors, to assess viticultural and oenological suitability for Sangiovese. Two specialized vineyards on similar geomorphological conditions were investigated. Twelve plots were positioned differently along slopes. The soils were similar, except for structure, porosity and related hydrological characteristics, and salinity of the deeper horizons. Soil electrical conductivity and resistivity were measured at three different depths, as well as cumulative soil moisture down to the root-limiting layer. Satellite images were analyzed to obtain the NDVI. Soil water content in the plots was monitored at different depths. Yield, phenological phases, and chemical analysis of grapes were determined. Stem water potential was measured during summer. Grapes of each plot were collected for wine making in small barrels. The wines obtained were analyzed and submitted to a blind organoleptic testing. The wine was also analyzed for its δ 13C isotopic ratio. Almost all plots had rather high amounts of transpirable water, even during the driest time of the year. However, only yield components of Sangiovese were influenced by water availability. Wine quality was instead significantly improved by the moderate salinity of the deeper horizons, which increased plant water stress during berry ripening and reduced production. The moderate physiological stress affecting vines was reflected in stem water potentials and δ 13C values. δ 13C was correlated with several viticultural and oenological parameters, and also with panel test evaluations of wine quality. The threshold between good and bad scores corresponded to a δ 13C value of −26.7 ± 1.2‰. Soil salinity affected the geophysical survey and its relationship with the viticultural and oenological result. In particular, the electromagnetic conductivity measured at the beginning of the experiment was functional in distinguishing the two vineyards, but it was not useful for a more detailed prediction of Sangiovese performance. However, electromagnetic resistivity in the first 0.5 m was not influenced by salinity of the deep soil horizons, but only by clay content, and permitted a significant estimation of the Sangiovese anthocyanins content, colour intensity, and must acidity. The outcomes of this study recommend the use of δ 13C in combination with electromagnetic resistivity to map soil suitability for Sangiovese. The favourable performance of Sangiovese in moderately saline soils may encourage diffusion of the cultivar outside its traditional areas of cultivation.

Contribution of trees to soil carbon sequestration under agroforestry systems in the West African Sahel

Consequent to recent recognition of agricultural soils as carbon (C) sinks, agroforestry practices in the West African Sahel (WAS) region have received attention for their C sequestration potential. This study was undertaken in the Segou region of Mali that represents the WAS, to examine the extent of C sequestration, especially in soils, in agroforestry systems. Five land-use systems were selected in farmers’ fields [two traditional parkland systems, two improved agroforestry systems (live fence and fodder bank), and a so-called abandoned land]. Soil samples taken from three depths (0–10 cm, 10–40 cm, and 40–100 cm) were fractionated into three size classes (2,000–250 μm, 250–53 μm, and <53 μm) and their C contents determined. Whole-soil C contents, g kg−1 soil, across three depths ranged from 1.33–4.69 in the parklands, 1.11–4.42 in live fence, 1.87–2.30 in fodder bank, and 3.69–5.30 in abandoned land; and they correlated positively with silt + clay content. Using the 13C isotopic ratio as an indicator of relative contribution of trees (C3 plants) and crops (C4 plants) to soil C, more tree-origin C was found in larger particle size and surface soil and indicated that long-term tree presence promoted storage of protected C in deeper soil. Existing long-standing agroforestry practices of the region such as the parklands seemed to have little advantage for sequestering additional C, whereas improved agroforestry practices such as live fence and fodder bank introduced in treeless croplands seemed to be advantageous.

Natural origin of ascorbic acid: Validation by 13C NMR and IRMS

A new method for the extraction and purification of ascorbic acid from two tropical fruits (acerola and camu-camu) is presented. 13C nuclear magnetic resonance and isotopic ratio mass spectroscopy ( 13C/ 12C) were used to recognize ascorbic acid coming from either natural or industrial sources. A quantitative 13C NMR procedure was optimized to calculate isotopic relative abundances on each molecular site; data were treated by a multivariate method. Samples were also analysed by IRMS coupled with gas-chromatography/combustion and elemental analysis devices. The combined use of these techniques enabled us to validate the origins of ascorbic acid batches issuing from different sources.

Liquid Chromatography Coupled to Isotope Ratio Mass Spectrometry: A New Perspective on Honey Adulteration Detection

A new procedure to determine individual sugar (sucrose, glucose, and fructose) 13C isotope ratios, using liquid chromatography-isotope ratio mass spectrometry (HPLC-IRMS), has been developed to improve isotopic methods devoted to the study of honey authenticity. For this purpose 79 commercial honey samples from various origins were analyzed. Values of delta13Choney ranged from -14.2 to -27.2", and delta13Cprotein ranged from -23.6 to -26.9". A very strong correlation is observed between the individual sugar 13C ratios, which are altered in the event of sugar addition, even at low levels. The use of Deltadelta13C [fruct-glu], Deltadelta13C [fruct-suc], and Deltadelta13C [gluc-suc] systematic differences as an authenticity criterion permits the sugar addition [C3, beet sugar; or C4, cane sugar, cane syrup, isoglucose syrup, and high-fructose corn syrup (HFCS)] to be reliably detected (DL = 1-10%). The new procedure has advantages over existing methods in terms of analysis time and sensitivity. In addition, it is the first isotopic method developed that allows beet sugar addition detection.

Effects of organic effluents from a salmon farm on a fjord system. I. Vertical export and dispersal processes

Vertical flux of organic waste from a Norwegian salmon farm (which produced 2910 tonnes of fish in 19 months) located in 230-m-deep water was measured nine times in the course of 2 years by sediment traps along a transect stretching from the farm and 3 km out towards the sea. The chemical composition of the trapped material and the sediment below the traps were analyzed. The results showed that when the fish farm was empty, sedimentation rates of organic matter were similar all along the transect. Throughout the production cycle high and very variable sedimentation rates of particulate organic matter, particulate organic carbon and particulate organic nitrogen were measured within 250 m from the farm, while between 550 and 3000 m away from the farm sedimentation rates were lower and constant throughout the cycle. During the second year of production, the annual vertical flux of particulate organic carbon to the bottom adjacent to the farm was 365 g m − 2 , nine times as high as what was found 3 km away from the farm. While the sedimentation rates showed that most of the waste matter settled within 250 m of the farm, the fatty acid composition and δ 13C isotope ratio of the material in the bottom traps indicate that some components of the organic waste were transported as far as 550 to 900 m, probably due to resuspension of surface sediment. Despite the high sedimentation rates the content of sedimentary organic matter, total organic carbon and total organic nitrogen was not elevated in the sediment around the farm. However, phosphorus was found in higher concentrations in the sediments close to the farm, indicating that organic matter had settled on the sediment and been decomposed. The unchanged content of organic matter in the sediment during the production cycle showed that at this site the local resuspension and dispersal conditions and the decomposition capacity of the benthos were sufficient to prevent overloading of the locality.

Diet of four rock‐dwelling macropods in the Australian monsoon tropics

Abstract An unusually high diversity of macropods inhabit the rocky areas in the monsoon tropics of the Northern Territory, Australia, yet the mechanisms that allow their niche separation are not clear. Previous studies suggest that the nabarlek, Petrogale concinna, may have a more grazing diet than the short‐eared rock‐wallaby, Petrogale brachyotis, with whom it coexists. Thus, diet may be an important mechanism of niche separation between these species. We examined the diet of the four sympatric species (the black wallaroo Macropus bernardus, common wallaroo Macropus robustus, P. brachyotis and P. concinna) to determine whether there are differences in the dominant plant groups eaten by the species across the landscape and with season. Diets were determined with a macroscopic analysis of the seed and fruit content of scats and an analysis of the 12C to 13C isotope ratios of scats using mass spectrometry. In the dry season the rock‐wallaby species predominantly consumed browse and/or forbs, and the larger wallaroos predominantly consumed grass. However, there was large variation across the landscape in the dry season diets of P. brachyotis, M. bernardus and M. robustus; including high proportions of grass eaten at some sites and high proportions of browse at other sites. In the wet season, greater proportions of grass were eaten by P. brachyotis and M. bernardus than in the dry season. Generally, there was little evidence to support the previous suggestion that P. concinna is more of a grazer than P. brachyotis, but there was some evidence than M. bernardus consumes greater amounts of browse and/or forbs than M. robustus.

Changes in flux pattern of the central carbohydrate metabolism during kernel development in maize

Developing kernels of the inbred maize line W22 were grown in sterile culture and supplied with a mixture of [U– 13C 6]glucose and unlabeled glucose during three consecutive intervals (11–18, 18–25, or 25–32 days after pollination) within the linear phase of starch formation. At the end of each labeling period, glucose was prepared from starch and analyzed by 13C isotope ratio mass spectrometry and high-resolution 13C NMR spectroscopy. The abundances of individual glucose isotopologs were calculated by computational deconvolution of the NMR data. [1,2- 13C 2]-, [5,6- 13C 2]-, [2,3- 13C 2]-, [4,5- 13C 2]-, [1,2,3- 13C 3]-, [4,5,6- 13C 3]-, [3,4,5,6- 13C 4]-, and [U– 13C 6]-isotopologs were detected as the major multiple-labeled glucose species, albeit at different normalized abundances in the three intervals. Relative flux contributions by five different pathways in the primary carbohydrate metabolism were determined by computational simulation of the isotopolog space of glucose. The relative fractions of some of these processes in the overall glucose cycling changed significantly during maize kernel development. The simulation showed that cycling via the non-oxidative pentose phosphate pathway was lowest during the middle interval of the experiment. The observed flux pattern could by explained by a low demand for amino acid precursors recruited from the pentose phosphate pathway during the middle interval of kernel development.

Origin Differentiation of a Heroin Sample and its Acetylating Agent with 13C Isotope Ratio Mass Spectrometry

A novel method for deducing the origins of heroin and the reagent used for acetylation was established based on delta(13)C determinations of heroin and its hydrolysate, morphine, using gas chromatography (13)C isotope ratio mass spectrometry (GC-C-IRMS). The alkaline and acid hydrolysis conditions of heroin were optimized. Both yield and purity of morphine produced could meet the requirement for a GC-C-IRMS analysis. Using (2-diethylaminoethyl-2,2- diphenylvalerate) as internal standard the determinations of heroin and morphine contents were performed with a GC method in a linear range of 0.2 to 2.0 mg ml(1) that was required to gain the isotope ratio results. The hydrolysis and synthesis of heroin did not change the delta(13)C value of morphine. The precision for delta(13)C detection of both heroin and morphine was sufficient for origin differentiation of heroin samples. The information about the origins of acetylation reagents could be deduced from the difference of delta(13)C values between heroin and morphine. The results for origin differentiation of 10 heroin samples grouped into different regions and their acetylating agents were satisfactory.

In situ measurement of seasonal δ18O variations and analysis of isotopic trends in a modern speleothem from southwest Australia

We present a record of seasonal and inter-annual oxygen ( δ 18O) and carbon ( δ 13C) isotope ratios from an 81-year-old stalagmite from Moondyne Cave, southwest Australia. The growth history of stalagmite MND-S1 is known since it grew on a cave boardwalk that was installed in 1911 and removed in 1992. This stalagmite provides an excellent test of speleothem climate proxies because the regional climate is strongly seasonal (wet winter/dry summer) and has experienced a 200 mm (20%) reduction of mean rainfall since the mid-1960s, and a 0.8 °C temperature rise since ∼ 1953. Seasonal variations in calcite δ 18O were measured in situ by high spatial resolution ion microprobe, whilst inter-annual variations of δ 18O and δ 13C were measured by conventional gas-source mass spectrometry. Comparison of the speleothem stable isotopes and instrumental temperature records reveals that δ 18O variations are too large to be driven by temperature alone, and are in the opposite sense. However, daily rainfall δ 18O measurements show that the mean seasonal range in δ 18O of rainfall in southwest Australia is large (2‰) and inversely correlated with rainfall amount. A rainfall driver for the speleothem δ 18O is confirmed by the detection of seasonal shifts of 0.7–1.5‰ in speleothem δ 18O that track rainfall δ 18O, smoothed by storage in the overlying limestone. The seasonal range in speleothem δ 18O is larger than any inter-annual and decadal variation observed in the record. The prominent annual cycles in speleothem δ 18O revealed by ion microprobe analysis indicate that subtle changes in the frequency of intense winter rainfall events, or possibly also moisture sources, could produce significant changes in mean speleothem δ 18O. The ion microprobe results also raise the possibility that the masses of speleothem calcite deposited in winter and summer could vary as a function of the seasonal drip rate and carbonate saturation state of these waters. If this is the case, then small changes in the relative masses of calcite deposited in winter and summer could produce significant shifts in mean δ 18O and δ 13C that have a complex relation to climate. This finding should be generally applicable to the interpretation of long-term trends in speleothem geochemical records for shallow cave sites where seasonal variations in geochemical tracers are relatively large, including most of the sub-tropical monsoon belts and mid to high latitudes with distinct rainfall seasons.

Assessment of cysteine synthesis in very low–birth weight neonates using a [ 13C 6]glucose tracer

Background/Purpose Cysteine is an amino acid necessary for the synthesis of all proteins, the antioxidant glutathione, and the neuromodulator taurine. Whether cysteine is an essential amino acid for premature neonates remains controversial. Using a [ 13C 6]glucose precursor in very-low–birth weight (VLBW) premature neonates, we measured the 13C content of cysteine in hepatically derived apolipoprotein (apo) B-100 and in the plasma to determine whether cysteine synthesis occurs and to relate minimum synthetic capacity to neonatal maturity. Methods Twelve VLBW premature neonates (birth weight, 907 ± 274 [SD] g; gestational age, 26.8 ± 2.4 weeks) were studied on day of life 7.8 ± 4.2 while on total parenteral nutrition (TPN) for 5.6 ± 4.5 days. A 4-hour intravenous infusion of [ 13C 6]glucose was administered. Blood samples were obtained immediately before and at the end of the infusion. Isotopic enrichment of cysteine was determined by gas chromatography/mass spectrometry. Analysis of variance, Student's t test, and linear regression were used for comparisons. Results The 13C isotope ratio of apo B-100–derived cysteine after the [ 13C 6]glucose infusion was significantly higher than baseline (18.57 ± 0.38 [SEM] vs 17.54 ± 0.25 mol%, P < .05). The 13C isotope ratio of plasma cysteine was also significantly higher than baseline (17.36 ± 0.25 vs 16.91 ± 0.16 mol%, P < .05). When expressed as a product/precursor ratio, the mole percent above baseline of [ 13C]apo B-100 cysteine/[ 13C 6]glucose correlated with birth weight ( r = 0.74, P < .01). Conclusions Very low–birth weight neonates are capable of cysteine synthesis as evidenced by incorporation of 13C label into hepatically derived apo B-100 cysteine and plasma cysteine from a glucose precursor. The minimum capacity for intrahepatic cysteine synthesis appears to be directly proportional to the maturity of the neonate and may impact the capabilities of VLBW neonates to counteract oxidative stresses such as bronchopulmonary dysplasia and necrotizing enterocolitis.

The annual cycle of fossil-fuel carbon dioxide emissions in the United States

Time-series of estimated monthly carbon dioxide emissions from consumption of coal, petroleum and natural gas in the United States from 1981 to 2002 have been derived from energy consumption data. The data series for coal and natural gas each reveal a consistent seasonal pattern, with a winter peak for gas and two peaks (summer and winter) for coal. The annual cycle of total emissions has an amplitude of about 20 Tg-C, and is dominated by CO2 released from consumption of natural gas. Summation of the monthly estimates to obtain annual values reveals good agreement with other estimates of CO2 emissions. The varying proportions of CO2emitted from each fuel type over the course of a year lead to an annual cycle in the carbon isotope ratio (δ13C), with a range of about 2 ‰. These monthly carbon emissions estimates should be helpful in understanding the carbon cycle by providing (1) monthly/seasonal input for carbon cycle models, (2) estimates of the annual cycle of the 13C isotope ratio in fossil-fuel CO2 emissions and (3) data at fine enough time intervals to investigate effects of seasonal climate variations and changes in seasonally dependent use patterns of certain appliances (e.g. air conditioners) on fossil-fuel carbon emissions.

Population substructure of North Atlantic minke whales ( Balaenoptera acutorostrata) inferred from regional variation of elemental and stable isotopic signatures in tissues

Information on population structure is essential for estimating population demographics and managing the impacts of exploitation of North Atlantic minke whales ( Balaenoptera acutorostrata). New approaches including assessment of geochemical signatures in tissues can assist in defining such structure. This study determined regional variations in long-term elemental diagnostics of stock differences among 159 minke whales harvested in West Greenland, the Northeast Atlantic Ocean and the North Sea in 1998. The diagnostics tested included mercury (Hg), selenium (Se) and cadmium (Cd) in various tissues, and the trace and major element composition of baleen. Supporting data was also gathered on δ 15N and δ 13C and stable lead isotope ratios. For female whales, significant differences in at least one long-term diagnostic element occurred between several areas. Existence of the following population substructure was inferred: (a) West Greenland, (b) a central group represented by whales from Jan Mayen, (c) a northeastern stock encompassing the Barents Sea, Svalbard and coastal Norway, and (d) the North Sea. These groups were consistent with those defined genetically by Andersen et al. [Mar. Ecol., Prog. Ser. 247 (2003) 263]. Males appeared to fall into similar groupings to females but because of smaller sample sizes fewer significant differences occurred between areas. Stable-isotopic values in minke whales suggested lower trophic-level feeding in this species than hitherto suspected, with significant dietary differences between areas. Variations in feeding habits appeared to explain part of the geographical variation in tissue Cd, but not tissue Hg or Se. Differences among elements with a relatively long biological half-life in specific tissues suggested that groups of minke whales have fidelity to certain summer feeding areas at least for several years.

Paleoenvironmental and diagenetic implications of δ 18O and δ 13C isotope ratios from the Upper Jurassic Plassen limestone (Northern Calcareous Alps, Austria)

The first δ 18O and δ 13C data from the Upper Jurassic of the Northern Calcareous Alps are presented. The interpretation of stable isotope ratios serves as an approach for paleoenvironmental and diagenetic studies of the Plassen carbonate platform, which cannot be obtained by paleontological methods and microfacies analyses alone. The studied part of the Plassen limestone is characterized by (1) lithoclast facies, also called ‘intraformational breccia’; the origin of lithoclasts was formerly unknown; (2) peloid facies; (3) bioclastic facies, composed of peloids, porostromate algae, green algae and red algae; and (4) oncoid facies. Two types of fracturing and four cement generations can be distinguished. Isotope ratios of the matrix, oncoids, three cement generations and whole rock samples revealed that (1) the studied section represents an open marine carbonate platform with high water circulation and high input of cool oceanic waters; (2) the platform was not affected by emersion and fresh water influence; normal marine conditions prevailed; (3) carbonate cements were precipitated in a closed diagenetic system, but burial diagenesis was absent; (4) both fabric-selective and non-fabric-selective fracturing occurred in a normal marine environment, affecting the formation of ‘intraformational breccias’.

Dose-response relationship between fat ingestion and oxidation: quantitative estimation using whole-body calorimetry and 13C isotope ratio mass spectrometry.

To determine dose-dependent relationship between ingested fat and its oxidation in the immediate post-prandial period in humans. Subjects were randomly selected for the study at the Dunn Clinical Nutrition Centre, Cambridge, UK. Subjects ingested naturally enriched 13C corn-oil doses (range 20-140g) in a whole-body indirect calorimeter, and were studied for 8 h. Ingested fat oxidation was estimated from the subject's breath 13C enrichment and total carbon dioxide production. Total fat and carbohydrate oxidation were estimated from non-protein oxygen and carbon dioxide exchanges. Endogenous fat oxidation was estimated as the difference between total fat and ingested fat oxidation. The amount of fat dose oxidized was nonlinearly related to the amount ingested. On average, 25.6+/-2.7% of the mean fat dose was oxidized. A significant (r = - 0.72, P < 0.001) inverse correlation was found between the amount of fat dose and the proportion oxidized. Endogenous carbohydrate oxidation was negatively and significantly correlated to fat dose oxidized (r= -0.61, P < 0.01), but it was not correlated to endogenous fat oxidation. There was a nonlinear relationship between amount of fat dose and its quantity that was oxidized in the immediate post-prandial period. The inverse relationship between the size of the fat load and the proportion that was oxidized post-prandially implies increased dietary fat storage beyond about 50 g in a normal resting adult. This has important implications for 13CO2-based studies.