Hydrogen isotopes ocean water

A difficnlty in measnring D/H isotope ratios is that, along with the H2+ and HD+ formation in the ion source, H3+ is produced as a by-prodnct of ion-molecule collisions. Therefore, a H3+ correction has to be made. The amonnt of H3+ formed is directly proportional to the number of H2 molecules and H+ ions. Generally the H3+ current measured for hydrogen from ocean water is on the order of 16% of the total mass 3. The relevant procedures for correction have been evaluated by Brand (2002). 

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

In the marine environment oxygen and hydrogen isotope compositions of pore waters may be inherited from ocean water or inflnenced by diagenetic reactions in the sediment or nnderlying basement. Knowledge of the chemical composition of sedimentary pore waters has increased considerably since the beginning of the Deep-Sea-Drilling-Project. From numerous drill sites, similar depth-dependent trends in the isotopic composition have been observed. 

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. 

Various isotope standards are used for reporting isotopic compositions the composition of each of the standards has been defined as 0 per mil. Oxygen and hydrogen isotopic compositions are commonly reported relative to standard mean ocean water (SMOW or V-SMOW) (17). 

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). 

CSIA yields data of the isotopic composition of a single compound relative to an international standard that is usually expressed as delta notation (S) values in parts per thousand (%o) according to Eq. 1. The most common ones, the carbon and hydrogen isotopic compositions (R), are reported as and relative to Vienna Pee Dee Belemnite standard (V-PDB) and Vienna Standard Mean Ocean Water (V-SMOW), respectively [20] ... 

A O and AD values of vent fluids (Table 1) can best be understood in terms of water-rock interaction within the ocean crust. Field studies, experimental studies, and isotopic exchange computations (Muehlenbachs 1972 Stakes and O Neil 1982 Bowers and Taylor 1985 Cole et al. 1987 Bowers 1989 Bohlke and Shanks 1994 Shanks et al. 1995) have clearly shown that both A 0 and AD increase due to water-rock interaction with igneous crust. Oxygen and hydrogen isotope values of end-member vent fluids (Fig. 6) follow a calculated seawater-basalt reaction vector (within AD error of 1.5%o ), due to fluid evolution to decreasing water/rock mass ratios (Shanks et al. 1995). 

Stille P, Chaudhuri S, Kharaka YK, and Clauer N (1992) Neodymium, strontium, oxygen and hydrogen isotope compositions of waters in present and past oceans a... 

Standard Mean Ocean Water — the standard used in oxygen and hydrogen stable isotopic measurements Spark Source Mass Spectrometry syn-COLlisional Granite... 

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 ... 

FIGURE 15.2 Potential variation in the hydrogen isotopic composition of a range of different materials. Reprinted from T.B. Coplen et al. [16], with permission from Coplen. SLAP, Standard Light Antarctic Precipitation GISP, Greenland Ice Sheet Precipitation VSMOW, Vienna Standard Mean Ocean Water NBS, National Bureau of Standards NGS, natural gas standards. 

The relative mass difference between the two stable isotopes and (deuterium, D) is larger than for any other isotope pair. Because of that hydrogen shows the greatest isotopic fractionation. The content of heavy water HDO in ocean water corresponds to 0.015 atomic% and a 8D-value near 0. light water, H O, has the higher vapor pressure and is to some extent enriched in the vapor. The difference becomes greatest when the temperature is low. Measurements of precipitation show that water near the equator has a hydrogen isotopic composition near that of ocean water whereas snow near the poles may have 6°-values below -300%o. 

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