SMOW Research Articles

Determination of the absolute density of water at 16 °C and 0,101 325 MPa

The absolute density of pure water was determined with an accuracy better than 1 part in 106. The method used was hydrostatic weighing in which a fused-quartz sphere, whose volume was measured by optical interferometry, was weighed in water. The density obtained in the hydrostatic weighing was corrected for impurity effects using differential densimetry and, using mass spectrometry, was further corrected for isotopic composition. A total of eighteen samples was measured using three spheres. The density of pure water at 16 °C (ITS-90) and 0,101 325 MPa having isotopic composition equal to that of Standard Mean Ocean Water was found to be 998,9468 kg m-3 with a combined standard uncertainty of 0,0006 kg m-3. The maximum density at about 4 °C, as calculated from our previous measurements of thermal expansion, was found to be 999,9756 kg m-3 with an uncertainty of 0,0008 kg m-3.

Secondary K-feldspar at the Precambrian–Paleozoic unconformity, southwestern Ontario

The Precambrian–Paleozoic boundary in the subsurface of southwestern Ontario commonly is characterized by secondary K-feldspar. In the weathered and altered Precambrian granitoid gneisses at the unconformity, secondary K-feldspar has replaced preexisting minerals, and also occurs as discrete crystals of adularia, overgrowths on altered minerals, and microcrystalline veinlets. The K-feldspar is chemically pure (Or99–100) and has high δ18O values (+18.9 to +21.4‰ Vienna Standard Mean Ocean Water), features that indicate crystallization at low temperatures. Secondary K-feldspar also occurs in Cambro-Ordovician clastic and carbonate rocks that immediately overlie the Precambrian basement. K/Ar (453 ± 9 to 412 ± 8 Ma) and Rb/Sr (440 ± 50 Ma) dates obtained for secondary K-feldspar from the Precambrian host rocks suggest that its crystallization is unrelated to Precambrian weathering or early diagenesis of the immediately overlying Cambro-Ordovician strata. Estimated crystallization temperatures for the secondary K-feldspar (≥100 °C) exceed presumed burial temperatures for the Precambrian–Paleozoic boundary in southwestern Ontario during Late Ordovician–Silurian time. We infer that secondary K-feldspar formed from a hot brine that moved preferentially along the Precambrian–Paleozoic unconformity. The wide distribution of secondary K-feldspar of Late Ordovician–Silurian age throughout mid-continental North America at the Precambrian–Paleozoic boundary records the regional extent of this process. Some Cambro-Ordovician rocks elsewhere in the mid-continent also contain secondary K-feldspar and illitic clay of Late Pennsylvanian–Early Permian age, suggesting more than one episode of fluid movement. Major pulses of orogenic activity may have initiated brine migration. We speculate that the brine originated as connate (sea) water trapped in lower Paleozoic strata, and was modified by rock–water interaction at elevated temperatures, and by mixing with meteoric water.

Geochemical studies of the origins and effects of synorogenic crustal fluids in the southern Omineca Belt of British Columbia, Canada

Research Article| September 01, 1995 Geochemical studies of the origins and effects of synorogenic crustal fluids in the southern Omineca Belt of British Columbia, Canada Bruce E. Nesbitt; Bruce E. Nesbitt 1Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E3 Canada Search for other works by this author on: GSW Google Scholar Karlis Muehlenbachs Karlis Muehlenbachs 1Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E3 Canada Search for other works by this author on: GSW Google Scholar Author and Article Information Bruce E. Nesbitt 1Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E3 Canada Karlis Muehlenbachs 1Department of Geology, University of Alberta, Edmonton, Alberta T6G 2E3 Canada Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Geological Society of America GSA Bulletin (1995) 107 (9): 1033–1050. https://doi.org/10.1130/0016-7606(1995)107<1033:GSOTOA>2.3.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Bruce E. Nesbitt, Karlis Muehlenbachs; Geochemical studies of the origins and effects of synorogenic crustal fluids in the southern Omineca Belt of British Columbia, Canada. GSA Bulletin 1995;; 107 (9): 1033–1050. doi: https://doi.org/10.1130/0016-7606(1995)107<1033:GSOTOA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Fluid inclusion and stable isotope investigations of 400+ samples of quartz ± carbonate veins and their zeolite to amphibolite grade host rocks from the southern Omineca Belt of the Canadian Cordillera have been used to determine origins, evolution, and effects of crustal fluids during and after orogenic activity. Correlations between fluid inclusion characteristics and tectonic and lithologic features indicate that salinities and gas compositions (CO2/CH4 ratios) are controlled by host rock lithology. High total gas contents are linked to high inclusion homogenization temperatures, which parallel increasing metamorphic grades.The δD values of the vast majority of vein-forming fluids range from −100% to −150% (Standard Mean Ocean Water [SMOW]), indicating meteoric water as the source of the fluids. The δ18OWater values of the fluids were homogeneous over large sections of the crust, with a typical range of δ18O values of 6% to 11% (SMOW). Homogenization of δ18O values of vein-forming fluids is believed to reflect interaction of the meteoric water with a variety of rock types at temperatures in excess of 350 °C. This process resulted in resetting of δ18O values of both fluids and rock units. The absence of vein formation from low δ18O water requires that mixing of ascending and descending fluids does not occur. Carbon and strontium isotope analyses indicate a strong degree of host rock control on these isotopic ratios.Synthesis of the results yields a model for the hydrogeology of the brittle crust consisting of moderately high permeabilities in fractured brittle rocks with deep convection of surface, meteoric water. The maximum depth of penetration of the fluids is limited by the rheological brittle/ductile transition at temperatures of 350 to 450 °C and depths of 10 km or greater. The vast majority of veins found in greenschist and lower grades of metamorphic rocks are formed on the upflow limbs of the meteoric water convection cells. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Discontinuance of SMOW and PDB

Discontinuance of SMOW and PDB

Determination of Ice-Phase Water Capture Temperatures Using Isotopic Composition and Habits of Ice Crystals—Relevance to Snowpack Augmentation

Abstract The oxygen 18/oxygen 16 (18O/16O) and deuterium/hydrogen (D/H) ratios of snowmelt have been used for estimating the weighted mean temperatures in clouds where ice-phase water capture has occurred during the precipitation-forming process. The isotopic measurements were combined with ice crystal replication and microphotographic observations of primary ice crystal habits and degrees of riming. Measurements from two complete winter seasons have enabled the development of climatological databases of these ice-phase water capture temperatures for the central Sierra Nevada and the Snowy Mountains of Australia. The results are based on the linear relationships between the temperature of formation in the clouds of ice crystals grown by vapor deposition and the departures (δ18O, δD) of the oxygen and hydrogen isotopic ratios in these crystals from the standard mean ocean water values. It was found that precipitation falling from orographic winter storms collects most of its water substance in the lower 1–...

Great Lakes paleohydrology: Complex interplay of glacial meltwater, lake levels, and sill depths

The oxygen isotope record of ostracode and clam shells recovered from Great Lakes cores of known age allows definition of times when meltwaters from the Laurentide ice sheet were important components of lake water in the several lake basins since 12 ka. We find that the lowstands in Lake Huron and Georgian Bay are characterized by isotopically light waters (δ 18 O values of -20‰ to -22‰ relative to SMOW [standard mean ocean water]) and the highstands by isotopically heavy waters of more local origin. These data can be used to determine the degree of hydraulic separation among the early Holocene lakes. Southern Lake Michigan, for instance, may mix with northern-source waters only during times of rising and high water levels. Generally it is characterized by waters of local origin.

Mississippi Valley-type Pb-Zn mineralization in eastern Belgium: Indications for gravity-driven flow

Mississippi Valley-type deposits are widespread in Carboniferous strata in eastern Belgium. Five successive Fe-rich, fracture-filling calcite generations have been recognized in the veins containing the Pb-Zn mineralization of Bleiberg. Fluid-inclusion evidence indicates that all the calcites formed from fluids with salinities between 16.0 and 23.1 equivalent wt% NaCl. The trapping temperature of the fluid inclusions decreases from ∼125 °C in the first two calcite generations to ≤50 °C in the last two vein cements. The δ 13 C values of the calcites vary between -0.1‰ and -8.3‰ relative to PDB (Peedee belemnite). The oxygen isotopic composition of the ambient fluids, calculated from the trapping temperature and the isotopic composition of the calcites, varies between -5.2‰ and +7.6‰ relative to SMOW (standard mean ocean water). The low δ 13 C values of the calcites are explained by the contribution of 12 C from CO 2 released during the oxidation of organic matter in the upper Carboniferous shales and the coupled reduction of sulfate in the mineralizing brine. The highly variable oxygen isotopic composition of the ambient fluids, the low δ 18 C value of the water from which one calcite cement precipitated, and the intense water-rock interaction necessary to leach metals indicate that the original fluids had a low δ 18 C, and that those fluids became enriched in 18 O by water-rock interaction. Waters with such low δ 18 C, values must have had a meteoric origin. Flow of these waters into the deeper subsurface was likely gravity driven and took place from the uplifted parts of the Variscan orogen toward the foreland basin.

Measurement of Absolute Water Density, 1 °C to 40 °C

The absolute density of Standard Mean Ocean Water (SMOW) has been determined over the range 1 °C to 40 °C by weighing a hollow sphere of known volume in air-free water samples of measured isotopic content. The volume of the sphere as a function of temperature is known as a result of a combination of interferometric and mechanical measurements. The measured densities are tabulated. A formula (as proposed by Thiesen et al) and a fifth-order polynomial in temperature have been fitted to the tabulated data by least-squares analysis. The density calculated from the polynomial is estimated to have a standard uncertainty ranging from 0,64 parts in 106 at 15 °C to 1,4 parts in 106 at 1 °C and 40 °C. Comparisons are made with published data.

The δ18O of dissolved O2 in the surface waters of the subarctic Pacific: A tracer of biological productivity

The 18O/16O of dissolved oxygen was measured in the upper ocean of the subarctic Pacific in 1988. In May and August, at stations Papa (50°N, 145°W) and R (53°N, 145°W), the mean δ18O in the mixed layer was 23.84±0.20 and 24.00±0.24 ‰ (versus standard mean ocean water) consistently more depleted than atmospheric saturation levels by about 0.4 ‰. This relative depletion is caused by input of photosynthetically produced O2. A value for the isotopic fractionation effect during respiration (αT) of 0.978±0.006 was determined from the time rate of change of the concentration and δ18O of O2 in the mixed layer measured during August 1988. Below the mixed layer (100–280 m) the O2 concentration decreased with a corresponding increase in δ18O. Model derived values for αT over this depth region ranged from 0.980 to 0.988 and depended on the mixing model. The difference between αT determinations for the surface layer versus upper thermocline likely results from mixing model inaccuracies or different isotope fractionation effects during plankton and bacterial respiration. If the calculated mixed layer αT values apply oceanwide, then photosynthesis and respiration by the marine biota have a similar effect to land plants in maintaining the δ18O of atmospheric O2 at 23.5 ‰.

Cryptic Grain-Scale Heterogeneity of Oxygen Isotope Ratios in Metamorphic Magnetite

Oxygen isotope ratios measured by ion microprobe in magnetite from granulite-facies marble of the Adirondack Mountains, New York, range from +2 to +11 per mil (standard mean ocean water) across a single grain that measures 3 millimeters by 5 millimeters. Low values are concentrated in irregular domains near the grain boundary but also occur in the grain's interior. In contrast, grains 1 millimeter in diameter that are from a second nearby sample show no significant heterogeneity, except within 10 micrometers of the grain boundary. These data, including large gradients of up to 9 per mil per 10 micrometers, provide important new constraints on the nature and origins of intragrain isotopic heterogeneity and on oxygen isotope thermometry. The differences between these magnetite grains result from contrasting mechanisms of isotope exchange with fluids after the peak of regional metamorphism. Volume diffusion of oxygen through the crystal structure of magnetite contributed to isotope exchange in the rims of small grains, but larger grains are crosscut by healed cracks that are not readily detected and that short-circuited diffusion.

Oxygen isotope composition of Holocene dolomite formed in a humid hypersaline setting

Holocene dolomite forming in supratidal carbonate sediments of Bonaire, Netherlands Antilles, is precipitated from hypersaline fluids in which the Mg:Ca ratio is elevated by evaporation and gypsum precipitation. Kinetic effects and water-vapor exchange between the humid atmosphere and hypersaline brines limit the δ18O values of the brines to between +0.7‰ and +2.1‰ standard mean ocean water. The mean δ18O value of dolomite is +1.0‰ Peedee belemnite ( n = 8), which is lower than values of dolomite precipitated from hypersaline brines in less humid environments. Bonaire dolomite is also isotopically lighter than dolomites interpreted to have formed in normal marine waters and mixed marine and/or meteoric waters. Calculated fractionation between dolomite and calcite formed from Bonaire brines is between 1.5‰ and 3.5‰. The high end of this range is consistent with previously proposed mineralogic fractionations of 3‰ ±1‰ and 3.2‰ between dolomite and calcite.

Oxygen-18 Composition of Sphagnum, and Microenvironmental Water Relations

The 180 isotope content of Jive species of Sphagnum from three peatlands in Ontario was analyzed. Sphagnum fuscum and S. capillifolium had significantly more enriched 6'80 values than S. fallax, S. magellanicum, and S. papillosum. The enriched values in the former species indicate that water involved in photosynthesis in hummock species is much more affected by evapotranspiration than in adjacent species situated in depressions. These data suggest that microenvironmental water relations regulate evapotranspiration in Sphagnum species. Environmental isotope analysis (180, 2H) is another technique that may shed light on understanding Sphagnum ecophysiology and water relations along microenvironmental gradients in northern peatlands. The vertical distribution of Sphagnum species along microtopographic gradients has long been noted, indeed, ever since the earliest ecological studies of northern bogs and poor fens (Andrus et al. 1983; Clymo & Hayward 1982; Sj6rs 1948; Vitt et al. 1975). The genus Sphagnum represents a unique group of hydrophytes especially adapted to periodic drought conditions because of large seasonal changes in water supplies reaching peatland surfaces. Ecological factors such as cation exchange capacity, desiccation resistance, water holding capacity, degree of drying, and photosynthetic ability have been found to be important for Sphagnum microenvironmental distribution patterns (Andrus 1986; Clymo & Hayward 1982; Lindholm 1990). Environmental isotopes--oxygen18 (180) and deuterium (2H)-that form part of the water molecules and organic compounds in plant organic matter, have been widely used in ecology and geochemistry (Fritz & Fontes 1980; Rundel et al. 1989). One specific application is in the reconstruction of paleoclimate based on the isotopic composition of fossil wood and peat cellulose (Dupont & Brenninkmeijer 1984; Edwards et al. 1985; Yapp & Epstein 1982). Paleoclimatic inferences are based on the relationship between the 180 and 2H composition of plant cellulose and the isotopic composition of the plant water source and relative humidity (Burk & Stuiver 1981; DeNiro & Epstein 1979; Epstein et al. 1977). We report some results of a project aimed at assessing the relationship between the isotopic composition of bog plant species and environmental factors. The understanding of this relationship is essential if stable isotopes in fossil peat plant cellulose are to be used in paleoclimate studies. This paper proposes that isotopic analysis of Sphagnum mosses may be an important aid in understanding the ecophysiological requirements and microenvironmental distribution of sphagna. MATERIAL AND METHODS Field methods.--Mosses for this study were collected from three peatlands in Ontario. Oliver's Bog is a floating bog and fen complex (sensu Tarnocai et al. 1988) developed in a closed kettle basin 4 km southeast of Cambridge in southwestern Ontario (43019'45N; 80017'15W). An open bog and poor fen mat has a soft bottom closest to the open water area in the centre and is firmly anchored in the treed bog area around the edge of the basin. The mat portion, where mosses were collected for this study, is characterized by oligotrophic lawn and carpet vegetation with some areas periodically in contact with waters of the underlying lake system, and having small ombrotrophic hummocks. Emo Bog is a large ombrotrophic raised bog complex, about 680 ha in size, situated 8 km northeast of Emo in northwestern Ontario, near the Minnesota-Ontario border (48042'N; 93047'W). It is a forested-low shrub bog with Picea mariana, numerous ericaceous shrubs, and welldeveloped hummock microtopography. Rainy River Bog is 40 km west of Emo Bog and 6 km north of the Town of Rainy River (48047'30N; 94034'W). This ombrotrophic bog is developed in a small basin about 10 ha in size with a vegetation cover and microtopography similar to that at Emo Bog. Laboratory procedures. -Representative Sphagnum mosses were collected at each study site for isotope analyses in June or July 1987. Samples that included several moss stems were selected from adjacent paired microsites-hummock top and a position near the bottom of the side of the hummock. Sphagnum nomenclature follows Anderson (1990). Voucher specimens are deposited in the Wetlands Ecology Laboratory at the University of Waterloo. Cellulose was extracted from the living plants 0007-2745/92/445-448$0.55/0 This content downloaded from 157.55.39.54 on Fri, 01 Jul 2016 05:38:50 UTC All use subject to http://about.jstor.org/terms 446 THE BRYOLOGIST [VOL. 95 TABLE 1. Isotopic composition of Sphagnum from three peatlands in Ontario. The sample of S. magellanicum from Emo bog may contain some Polytrichum strictum. Collection sites: OB = Oliver's Bog, a quaking bog, southwestern Ontario; RRB = Rainy River Bog, a raised basin bog, northwestern Ontario; EB = Emo Bog, a raised basin bog, northwestern Ontario; SMOW = standard mean ocean water.

Thermal springs in Lake Baikal

Research Article| June 01, 1992 Thermal springs in Lake Baikal Wayne C. Shanks, III; Wayne C. Shanks, III 1U.S. Geological Survey, 954 National Center, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar Edward Callender Edward Callender 1U.S. Geological Survey, 954 National Center, Reston, Virginia 22092 Search for other works by this author on: GSW Google Scholar Geology (1992) 20 (6): 495–497. https://doi.org/10.1130/0091-7613(1992)020<0495:TSILB>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Wayne C. Shanks, Edward Callender; Thermal springs in Lake Baikal. Geology 1992;; 20 (6): 495–497. doi: https://doi.org/10.1130/0091-7613(1992)020<0495:TSILB>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Pore waters extracted from sediment cores were analyzed for their oxygen and hydrogen isotopic compositions and major ion chemistry to determine the source of water from a vent area for diffuse lake-bottom thermal springs or seeps in Frolikha Bay, northeastern Lake Baikal. The δ18O values of pore waters range from -15.2‰ to -16.7‰, and δD values range from -119‰ to -126‰ (both isotopes determined relative to standard mean ocean water [SMOW]). Bottom water in Lake Baikal has a δ18O value of -5.6‰ and a δD value of -120‰ Pore waters in the vent area are significantly enriched in Mg, B, Ca, and especially Na and have the lowest δD and δ18O values; these pore waters are isotopically and chemically distinct from pore waters in other, more typical parts of the lake. The pore-water isotopic data fall on a local meteoric water line, and covariations in water isotopes and chemistry are not consistent with evaporation or hydrothermal water-rock interaction. The thermal springs represent discharging meteoric waters that have been gently heated during subsurface circulation and are largely unaltered isotopically. Chemical variations are most likely due to dissolution of subsurface evaporites. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Stratospheric profiles of heavy water vapor isotopes and CH3D from analysis of the ATMOS Spacelab 3 infrared solar spectra

Stratospheric volume mixing ratio profiles of H218O, H217O, HDO, and CH3D near latitudes of 30°N and 47°S have been retrieved from ∼0.01‐cm−1 resolution infrared solar occultation spectra recorded by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Fourier transform spectrometer during the Spacelab 3 shuttle mission (April 29 to May 6, 1985). Improved heavy isotope water vapor and CH3D spectroscopic parameters determined from ∼0.005‐ to 0.01‐cm−1 resolution room temperature laboratory spectra have been used in the retrievals. The profiles of the three water vapor isotopes show an increase in the volume mixing ratio with altitude over the range of measurements (20 to 54 km for H218O, 20 to 46 km for H217O, and 20 to 34 km for HDO). Deuterium‐to‐hydrogen and heavy‐to‐normal oxygen isotope ratio profiles have been calculated by dividing the retrieved isotopic profiles by the previously reported profiles of H216O and CH4 obtained from the same spectral data and then referencing these results to the isotopic composition of standard mean ocean water (SMOW). At 20 km the 18O/16O ratio in H2O is slightly (∼8%) depleted relative to SMOW; this ratio increases with altitude and is slightly positive above ∼36 km. No evidence has been found for the large 18O enhancements reported previously. The 17O/16O water vapor results are similar to those for 18O/16O. The ATMOS measurements show depletions of ∼63% in the D/H content of water vapor near 20 km and an increase in this ratio with altitude up to 34 km. The D/H ratio in stratospheric methane is close to the isotopic ratio in SMOW over the 18 to 28 km altitude range. No differences between the water vapor or methane isotopic compositions at 30°N and 47°S were detected. The results are compared with previously reported measurements and calculations.

Oxygen and hydrogen isotope geochemistry of the Star-Morning mine, Coeur d'Alene mining district, Idaho

Oxygen isotope values of vein quartz from the Star-Morning mine range from 13.2{per thousand} to 16.2{per thousand} relative to standard mean ocean water. Calculated isotopic values of water in equilibrium with the vein quartz at 325{degree}C range from 7.2{per thousand} to 10.2{per thousand}. The {delta}{sup 18}O{sub quartz} values decrease with depth in the mine. The {delta}D values of quartz inclusion fluids range from {minus}18{per thousand} to {minus}105{per thousand} and do not significantly correlate with depth. Oxygen isotope values of Belt Supergroup whole-rock samples range from 13.8{per thousand} to 16.8{per thousand}. The data indicate that the fluids were a mix of metamorphic water released from the Belt rocks during low-grade metamorphism, and {sup 18}O-shifted meteoric water.

Use of isotope fractionation of sulfate-sulfur and sulfate-oxygen to assess bacterial desulfurication in a sandy aquifer

The unconfined aquifer of the “Fuhrberger Feld” consists of 20–30m sands and gravelly sands with unevenly distributed reduced sulfur compounds and small lignitic pebbles. In vertical direction two hydrochemically different zones with specific solute transformations are present, an upper portion with bacterial denitrification (with reduced sulfur compounds as electron donors) and a deeper portion with hydrochemical indications of reduction of the aqueous sulfate. In the study area ten multilevel groundwater sampling wells were installed. Sampling and interpretation was based on a two-dimensional vertical-plane groundwater flownet and on the knowledge of the landuse upgradient of the multilevel wells. The concentration and isotopic composition of the sulfate at the entrance into the zone of sulfate reduction is controlled by sulfate of groundwater recharge as well as sulfate formed during denitrification. The recharge-sulfate shows clear landuse specific differences in concentration and isotopic composition: under arable land an average concentration of ≈ 60 mg SO 4l −1 with values of δ 34S close to +3‰ CDT Diablo Meteorite Standard (Can̄on) and of δ 18O about + 8‰ standard mean ocean water (SMOW) was measured, whereas under coniferous forest an average of ∼ 100 mg SO 4l −1 with δ 34 S ≈ + 2‰ and δ 18 O ≈ 4.5‰ was found. In the denitrification zone no significant sulfur isotope fractionation occurs during oxidation of reduced sulfur. The oxygenisotopic composition of the newly formed sulfate (“denitrification-sulfate”) depends on the 18O content of nitrate acting as oxygen donor and on the 18O content of groundwater in which the oxidation occurs; under certain assumptions a δ 18 O = +0.54‰ was calculated for the oxygen of the newly formed sulfate. Consequently, with increasing sulfate concentrations, i.e. with the admixture of “denitrification-sulfate”, a decrease of the δ 18O values from about +8‰ to +2‰ was observed. In the zone of sulfate reduction, both the δ 34S and δ 18O-values of the residual sulfate increase with decreasing sulfate concentrations thus proving the existence of bacterial reduction of the aqueous sulfate. This sulfate reduction follows a Rayleigh process with calculated enrichment factors of ϵ 34 = −9.7‰ for 34S and ϵ 18 ≈ −6‰ for 18O, respectively. A plot of δ 34S vs. δ 18O gives a good linear correlation with a slope close to 1: 1.4. Data on concentration and isotopic composition of sulfate and on the hydraulically derived groundwater age are used for kinetic considerations. The results of a multilevel well for depths between 10 and 17m are given as an example. The bacterial reduction can be considered as first-order reaction with a half-life between 75 and 100 years.

Analysis of the origins and implications of the18O content of stratospheric water vapor

Factors influencing the18O content of stratospheric H2O are reviewed in order to provide a theoretical framework for the interpretation of measurements of this quantity, which are now becoming available. Depletions in18O of 5–10% in stratospheric H2O are expected based on the known correlation between that of D and18O in tropospheric H2O and observed measurements of large (typically 50%) depletions of D in stratospheric H2O. H2O formed in the stratosphere as a result of oxidation of CH4 can be expected to reflect primarily the18O content of stratospheric O2, which is the same as that of tropospheric O2 (slightly enhanced with respect to standard mean ocean water). Thus, a reduction in the18O depletion is expected with increasing altitude, but not a large enhancement in18O in upper stratospheric H2O as found in recent far infrared measurements. The observed large enhancement of18O in stratospheric O3 is not expected to be reflected in stratospheric H2O. Necessary laboratory data for the improved quantification of these effects are reviewed.

Crustal sources involved in continental arc magmatism: A case study of volcan Mocho-Choshuenco, southern Chile

Volcan Mocho-Choshuenco, a Pleistocene-Holocene basaltic andesite to dacite shield volcano located at lat 40°S in the Southern Volcanic Zone (SVZ) of the Andes, is built on the thinnest SVZ continental crust (≈30 km), which consists largely of Paleozoic sedimentary and metamorphic rocks and Mesozoic plutons. Sr, Pb, Nd, and O isotopic ratios of Mocho-Choshuenco lavas ( 87 Sr/ 86 Sr = 0.70399 to 0.70422; 206 Pb/ 204 Pb =18.57 to 18.61; 207 Pb/ 204 Pb = 15.60 to 15.63; 208 Pb/ 204 Pb = 38.45 to 38.57; 143 Nd/ 144 Nd = 0.512787 to 0.512881; δ 18 O = +5.8‰ to +6.8‰ Standard Mean Ocean Water) are similar to those of other SVZ centers and exhibit no correlation with indices of differentiation. However, incompatible trace-element systematics indicate that evolved lavas have been contaminated by crustal plutonic rocks by 5% to 15%. Rb/Ba, K/Ba, Rb/La, and K/La ratios increase with increasing SiO 2 content as a result of assimilation of orogenic calc-alkalic plutonic rocks enriched in Rb and K relative to Ba and La. Xenoliths of plutonic rocks recovered from Mocho-Choshuenco lavas are slightly more radiogenic in 87 Sr/ 86 Sr, less radiogenic in 143 Nd/ 144 Nd, and comparable in Pb isotopic ratios, and they have variable 18 O contents ( 87 Sr/ 86 Sr = 0.70482 to 0.70557; 206 Pb/ 204 Pb = 18.60 to 18.64; 207 Pb/ 204 Pb = 15.60 to 15.62; 208 Pb/ 204 Pb = 38.53 to 38.56; 143 Nd/ 144 Nd = 0.512686; δ 18 O = +3.3‰ to +5.5‰ SMOW). Contamination of Mocho-Choshuenco parental magmas by crustal melts with small isotopic contrast imposed little variation on isotopic heterogeneities existing in the parental compositions. These heterogeneities probably were produced during magma-crust interaction at the crust-mantle boundary or in the lower crust.

Infrared measurements of atmospheric gases above Mauna Loa, Hawaii, in February 1987

Infrared solar absorption spectra recorded at 0.02 cm−1 resolution from the National Oceanic and Atmospheric Administration (NOAA) Geophysical Monitoring for Climate Change (GMCC) program station at Mauna Loa, Hawaii (latitude 19.5°N, longitude 155.6°W, elevation 3.40 km), in February 1987 have been analyzed to determine simultaneous total vertical column amounts for 13 atmospheric gases. Average tropospheric concentrations of CO2, N2O, CH4, and CHClF2 and the daytime diurnal variations of the total columns of NO and NO2 have also been inferred. The retrieved total columns (in molecules cm−2) of the nondiurnally varying gases are 1.6±0.2×1015 for HCl, 5.9±1.2 ×1015 for HNO3, 2.0±0.2×1021 for H216O, 4.4±0.7×1018 for H218O, 2.7±0.1×1017 for HDO, 2.3±0.2×1019 for CH4, 5.0±0.5×1021 for CO2, 6.7±0.8×1018 for O3, 4.3±0.4×1018 for N2O, 1.0±0.2×1016 for C2H6, and 9.7±2.5×1014 for CHClF2. We compare the total column measurements of HCl and HNO3 with previously reported ground‐based, aircraft, and satellite measurements. The results for HCl are of particular interest because of the expected temporal increase in the concentration of this gas in the stratosphere. However, systematic differences among stratospheric HCl total column measurements from 1978 to 1980 and the absence of observations of free tropospheric HCl above Mauna Loa make it impossible to obtain a reliable estimate of the trend in the total burden of HCl. The measured HNO3 total column is consistent with aircraft measurements from ∼12 km altitude. The O3 total column deduced from the IR spectra agrees with correlative Mauna Loa Umkehr measurements within the estimated error limits. The column‐averaged D/H ratio of water vapor is (68±9)×10−6, which is 0.44±0.06 times the reference value of 155.76×10−6 for standard mean ocean water (SMOW). This large depletion in the D content of water vapor is similar to published measurements of the upper troposphere and lower stratosphere. Average tropospheric concentrations deduced for CO2, N2O, and CH4 are in good agreement with correlative NOAA GMCC surface data, indicating consistency between the measurement techniques for determining tropospheric volume mixing ratios. Results of the present study indicate that Mauna Loa is a favorable site for infrared monitoring of atmospheric gases. The site is particularly favorable for monitoring the tropospheric volume mixing ratios of long‐lived gases, since the high altitude of the tropopause reduces corrections required to account for the decrease in volume mixing ratio in the stratosphere.

Extreme 18O depletion in calcite and chert clasts from the Elephant Moraine on the East Antarctic ice sheet

Two large morain es are presently forming near the margin of the East Antarctic ice sheet west of Victoria Land where the flow of the ice sheet is disturbed by subglacial bedrock ridges of the Transantarctic Mountains (Fig. 1). During the 1983–84 search for meteorites in this area several clasts, composed of black acicular calcite crystals, were collected from the Elephant Moraine (76°17'35" S and 157°20'05" E) where they are ablating out of the ice1–3. Additional samples of this calcite were later collected from the Elephant Moraine during the 1984–85 and 1986–87 field seasons, but none were found at the Reckling Moraine at 76° 15' S and 158°40' E4–6. The calcite clasts are strongly depleted in 18O (δ 18O = –20.5 ±0.4%) with reference to standard mean ocean water, SMOW and in 13C (S13C =–22.6 ±0.1% with reference to the PDB standard) in addition to being enriched in radiogenic 87Sr (87Sr/86Sr = 0.71417 ±0.00002) relative to sea water. These results suggest that the calcite precipitated from aqueous solutions discharged by hotsprings under the East Antarctic ice sheet.