SMOW standard

SMOW. standard mean ocean water (a standard for oxygen and hydrogen isotopes)... 

The Institute of Isotopic and Molecular Technology, Cluj-Napoca, performed all the analyses. The routine isotopic analyses were run on a Thomson THN 202D mass spectrometer, with a working precision of 0.3%o. The uranium method was used to release hydrogen from water. All isotopic data are expressed in conventional 5 notation as the permil deviation of D/H ratios with respect to the V-SMOW standard. 

SMOW = Standard Mean Ocean Water IAEA(AgS) = International Atomic Energy Agency (silver sulfide) SMOC = Standard Mean Ocean Chloride... 

Figure 1. Three isotope plot of O isotopes in Allende inclusions. Deviations are plotted in 6 units which are %o deviations relative to the terrestrial SMOW standard. In a two stage model, normal inclusions had initially a composition close to point A and exchanged with a reservoir poorer in O in the region of point D (Clayton et al. 1973). FUN inclusions underwent an intermediate step along a fractionation line between point A and point C. Then each inclusion exchanged with the same O poor reservoir D (Clayton and Mayeda 1977).

Among the reference samples now used, relatively few meet all of these requirements. For instance, the situation for the SMOW standard is rather confusing. The... 

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. 

The isotopic composition of water, determined by mass spectrometry, is expressed in per mil %o deviations from the SMOW standard. These deviations are written rID for the deuterium, and d180 for lsO ... 

SMOW standard mean ocean water, the reference standard for O isotopes. 

For ancient chemogenic cherts, including cherts from the BIF of Gunflint, Ontario, and Biwabik, Minnesota, Perry (1967) established a functional relationship between the of silica and the time of deposition. On this basis it was concluded that the waters of the ancient ocean were depleted in the heavy oxygen isotope, and that the 5 0 value was about — 10 to — 12%o for the Proterozoic and up to — 18%o for the Archean (compared to the oxygen of recent ocean water, SMOW standard). 

Assuming that the sedimentary rocks were derived from rocks with an original value of +1.0%c (original basalts, meteorites), and that the total amount of oxygen in the ocean is 1.2 10 " g and in sedimentary rocks 0.9 10 " g, the value found for the of the water of the primordial ocean is + 12.0%o (for the water of the present ocean, was taken as 0.0%o — SMOW standard). If granitized rocks are taken into account, then the of the ancient hydrosphere increases to + 16.2%o. These calculations cannot be considered reliable, as Silverman himself remarks, inasmuch as the composition and amount of primary rocks of the Earth s crust remain uncertain nor was juvenile water introduced from the mantle taken into account. 

Stable oxygen and hydrogen isotopic ratios are normally reported relative to the standard mean ocean water (SMOW) standard (Craig, 1961b) or the equivalent Vienna-SMOW (V-SMOW) standard. Carbon, nitrogen, and sulfur stable isotope ratios are reported relative to the Pee Dee Belemnite (PDB) or Vienna-PDB (VPDB), ambient air (AIR), and Canyon Diablo Troilite (CDT) standards, respectively, as defined later. The use of the V before SMOW or PDB indicates that the measurements were calibrated on normalized per mil scales (Coplen, 1996). 

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. 

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 3. Plot of average cave drip water 5 0 values (relative to the SMOW standard) for modem cave seepage water as a function of cave temperature. The non-linear trend in the data closely resembles that recorded by Yurtsever and Gat (1981) for continental rainfall.

The data are expressed as TR (Tritium Ratio 1 TR corresponds to a H/H ratio of 10 or to an activity concentration of 0.118 Bq/kg water). The data are expressed as percent modem carbon (pmc 100 pmc corresponds to 95% of the NBS oxalic acid standard or to an activity concentration of 0.226 Bq/g C). The and data are expressed as deviations(8-values) relative to SMOW (Standard Mean Ocean Water). The data are expressed as deviations relative to PDB (Pee Dee Belemnite) standard. The data are expressed as /qo deviations relative to CDT (Canion Diablo Troilite) standard. 

Monthly samplings were made of eight springs from May 1978 to April 1979. During the same period rain water was also collected. The 5 O determinations were made by the isotopic equilibrium methods between H2O and CO2 (Epstein and Mayeda, 1953), with small modifications. The 5D-values were determined according to the method described by Friedman (1953) and Friedman and Hardcastle (1970). All values are referred to the SMOW standards (Craig, 1961) and the analytical deviation are less than O.2O%o for 51 0 and 2%o for 5D. 

SMOW Standard Mean Ocean Water (Vienna)... 

Hydrogen isotopes are measured in parts per thousand reladve to the SMOW standard and are calculated in an analogous manner to that for oxygen isotopes (see Eqn [7.1]) and expressed as 5D /oo. Precision is between 1 and 2 / . 6D values for the SLAP standard reladve to SMOW are -428 /m. D/H ratios are usually measured on H2 gas which is produced from the reduction of water at high temperatures. 

VSMOW for silicates and water. As for PDB, the original SMOW (Standard Mean Ocean Water) material is no longer available. SMOW was defined as... 

Analytically, the separated gases have to be combusted to form CO2 for measurements and the H2O formed is turned into H2, which is measured for D. The standard for carbon isotopes is usually PDB (Peedee Belemnite, a carbonate) though the oil industry also uses the NBS22 (an oil fraction), whereas the standard is SMOW (Standard Mean Ocean Water). 

Isotope ratios in a sample are measured and expressed relative to internationally accepted standard samples of accurately known isotope ratios. For example, PDB (Pee Dee Belemnite CaCOs) is used as a standard for carbon its ratio is 0.0112372 [29]. Similarly, Vienna SMOW (Standard Mean Ocean Water) is the standard for oxygen and hydrogen, and air is the standard for nitrogen. Following are the commonly accepted definitions for reporting isotope ratios ... 

The 8( 0) value of a water sample is reported as —30.02 against the SMOW standard. Calculate the ratio for the water sample. 

Oxygen SMOW, Standard Mean Ocean Water 180/16Q -2 to +36 -50 to +15... 

---