PDB standard

Table All.l. Carbon isotope and protein content of experimental diets used for modeling in this paper. The values are 5 C in %o with reference to the PDB standard, except for protein content (by weight) which is in %. The type of diet corresponds to the Ambrose and Norr (1993) and Tieszen and Fagre (1993)...

Methods for pretreatment of samples for 13C analysis had been described in Chen et al. (2002a). After pretreatment, soil samples and plant debris were sent to the State Key Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences (CAS), for 13C analyses. The 13C analyses were conducted using a Finnigan MAT-251 mass spectrometer manufactured by Finnigan-Mat Company, with a precision of 0.2%o. Results are reported as 513C, in parts per thousand of the 13C/12C ratio from that of the International Pee Dee belemnite (PDB) standard, where ... 

The internationally accepted value for C/ Cstandm-d is 0.0112372 from a belemnite fossil from the Pee Dee formation in South Carolina (PDB standard). Naturally occurring C/ C ratios range from about 8 C = -50 to +5 %c. 

As the commonly used international reference standard PDB has been exhausted for several decades, there is a need for introducing new standards. Even though several different standards are in use today, the international standard the 5-values are referred to remains to be the PDB-standard (Table 2.2). 

These delta values (read delta C-13 , or delta carbon-13 ) are typically given in parts per thousand ( permil , %o). For historical reasons, carbon stable isotopes are reported relative to the PDB (Pee Dee Belemnite, a fossil) or the equivalent VPDB (Vienna PDB) standard. Oxygen and hydrogen stable isotopes are reported relative to SMOW (Standard Mean Ocean Water) or the equivalent VSMOW (Vienna SMOW). The VPDB and VSMOW standards are preferred, not only because the original standards, PDB and SMOW, are no longer available, but also because they imply that the measurements have been calibrated according to international conventions. 

It has an I80 / 160 ratio of 2005.20 ( 0.45) x 106 (Baertschi, 1976). In many studies involving carbonates, PDB is the standard relative to which values are reported. The PDB standard is based on the oxygen isotope ratio of a Cretaceous belemnite from the Peedee formation in South Carolina. Because it was composed of calcite, many limestones have isotopic ratios close to it. Values ("X") reported relative to the two standards are related by equation 3.16. 

Figure 5.24. Isotopic composition relative to PDB standard of suspended sediment in whitings compared to the fine fraction of bottom sediment. (After Shinn et al., 1989.)...

Stable carbon isotope ratios have been measured for a variety of samples of each type. Data are quoted as 513C values relative to the PDB standard (Pee Dee Belemnite) where... 

Precambrian carbonates is much lower than that of Quaternary sediments (respectively — 11.39 and — 1.18%, PDB standard). 

The use of the stable isotope as a tracer in biological research has become increasingly common as evidenced by recent bibliographies (1,2), The effective use of this isotope has been established in the field of nutrition, where it has been applied in human clinical studies (3,4), in food science research and in ecological studies of animal food habits (6,7) Many nutrition studies are carried out at natural abundance levels of C Because these levels are low and because differences in the content of natural materials are small, stable carbon isotope ratios (13q/1 ) expressed in relative terms as 6 values A value represents the per mil (parts per thousand) deviation of the content of the sample from the international PDB limestone standard, the value of which has been set arbitrarily to 0 /oo Thus, a value of -27 0 %o would mean that the sample contained 27 parts per thousand less than the PDB standard Although the PDB standard no... 

The term fossil fuel usually refers to coal and lignite, petroleum and namral gas, and usually includes also the production of cement. Cement is produced from limestone with a value close to zero, because the V-PDB standard itself is derived from limestone. The other fuel components are all derived from organic matter... 

Table 2(a) Carbon dioxide data from polar ice cores. Carbon dioxide concentrations and carbon isotope values (in per mil relative to the PDB standard) are listed for the LGM ( 18-24 ka), the Holocene Epoch (1-10 ka), and the most recent pre-industrial part of the Holocene Epoch (1000-1800 AD). Key references for the CO2 data from each core site are hsted in the right-hand colunrn. The superscript letters in the data table indicate the references from which the indicated values were derived. Values for Vostok (LGM and Holocene)... 

By calibrating the dripwater function with isotope ratios from speleothems deposited at known temperatures, numerical values for the empirical coefficients can be obtained. Under present and similar conditions, Asmow = 0, but must be adjusted for changes in ocean water during periods when glacial ice has modified ocean water. Note that 5 Ow is measured with respect to the SMOW standard while 5 0(, is often measured with respect to the PDB standard. With the use of equations (11) and (12), oxygen isotope ratios determined from speleothem calcite can be converted into actual temperatures. It is important to realize, however, that the calculated temperatures are accurate only to the extent that the empirical coefficients are accurate and that the coefficients have remained constant through time. In reality, this is difficult to know. 

Figure 2. Co-variations of 6 Cct and 8 Oc, (given relative to the PDB standard) for some fossil speleothems (73951 - Igloo Cave, Nahanni Region, NWT, Canada 72040 - El Sotano de Soyate, SLP, Mexico 71003 — El Sotano de la Tinaja, SLP, Mexico 73039 — Crystal Cave, Bermuda 71042 - El Sotano del Arroyo, SLP, Mexico 74019 - Coldwater Cave, lA, USA) illustrating isotopic relationships that characterize deposition under equilibrium and non-equilibrium situations (from Harmon, 1975). Meaningful paleoclimate information can only be retrieved from speleothem calcite deposited under conditions of isotopic equilibrium.

The units of are per mil (%o) and 5 0ct values are commonly reported relative to either the Standard Mean Ocean Water (SMOW) or the Pee Dee belemnite (PDB) standards (Craig, 1957, 1961), where S Osmow = 1.0308645 0pdb + 30.864. A similar expression to Eq. (4) defines C-isotope variations, with values always reported relative to the PDB standard. The values for water cited in this paper are given relative to the SMOW standard 5 0 values for calcite and all values are given relative to the PDB standards for oxygen and carbon respectively. 

Figure 4. Axial 5 0ct-time profile for a stalgamite from Aven d Orgnao, France deposited from o. 130,000 to 90,000 years B. P. (after Duplessey et al., 1971)., O-isotope compositions are given relative to the PDB standard. Times of enrichments of speleothem calcite in have been interpreted as episodes of warm climate (Duplessy et al., 1971) and as episodes of cold climate (Emiliani, 1971). See text for discussion.

The carbon in this carbonate carries the isotopic signature of its parent hydrocarbon(s). The carbon of most carbonate minerals is derived from the atmosphere, freshwater or the marine environment and has a C isotopic value of about -10 to +5 per mil relative to the PDB standard (Fairbridge, 1972 Anderson and Arthur, 1983). The C content of most cmde oil ranges from about -20 to -32 per mil, and that of methane ranges from -30 to -90 per mil. Thus carbonate formed from hydrocarbon oxidation... 

Stable carbon Isotopes were analyzed on a Finnigan MAT 250 isotope ratio mass spectrometer according to the procedure of Craig (J5). Results are reported relative to the Chicago PDB standard in terms of 5 c defined as ... 

Similarly, carbon isotope compositions ( - C/ C) are expressed relative to that of the Pee Dee Belemnite (PDB) standard. 

Figure 3t. Isotope age functions of organic carbon (Corg) over 3.8 billion years of recorded Earth s history as compared with the isotopic composition of their progenitor substances in the present environment (marine bicarbonate and biogenic matter of various parentage cf. Right panel). Isotopic compositions are given in values, indicating either a relative increase (+j or decrease (—) in the C7 C ratio of the respective substances (in per mil difference) as compared to that of the Pee Dee Belemnite (PDB) standard with =...

Oxygen and carbon isotopic analyses were made on 166 concretion samples, 34 host rock samples, 54 calcite-cemented beds, 33 veins and 38 mudrock samples. Samples were reacted with 100% phosphoric acid at 25 °C and the extracted gases were analysed on a VG Prism gas-source mass spectrometer. Isotopic values (machine reproducibility 0.02%o are reported relative to the pdb standard. 

Fig. 11-2. Left Geological record for the 13C contents (in permille PDB standard) of carbonates (Ccarb) and organic carbon (Corg) in the sediments. The spread of values is indicated. Right Carbon-13 content in atmospheric C02, marine carbonates, organic material of modern sediments, and various organisms (1) C3 plants, (2) C4 plants, (3) CAM (crassulacean acid metabolism) plants, (4) eukaryotic algae (black bar, range for marine plankton), (5) cyanobacteria from (a) natural communities and (b) culture experiments, (6) several nonoxygenic photosynthetic bacteria, and (7) methanogenic bacteria. [From Schidlowski (1984), with permission.]...

Isotopic composition of carbon C is usually measured by the ratio of stable isotopes and i C. As the standard is used the PDB standard... 

The 5 C values of individual compounds were measured on an HP Model 5890 gas chromatograph equipped with a DB-5 coated fused sihca capillary column (30 m X 0.32 mm i.d., 0.25 jmm film Sickness, J W Scientific) connected to a Finnigan MAT Delta-S mass spectrometer via combustion interface (CuO, NiO and Pt wires) maintained at 940°C. The carrier gas was helium and column injection was applied. The GC oven temperature was programmed as follows injection at 50°C, 30°C/min to 120°C, 5°C/min to 310°C, isothermal for 15 min. Co-injected deuterated n-alkanes C16D34 and C24D50 were employed as isotopic standards. Analyses were generally done in duplicate or triplicate with standard deviations ( 1 s) better than 0.4%c. Carbon isotopic ratios are expressed as 5 C relative to the PDB standard. 

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