Stable Oxygen Isotope Fractionation Research Articles

Kinetic Oxygen Isotope Fractionation between Water and Aqueous OH– during Hydroxylation of CO2

The fractionation of stable oxygen isotopes between water and aqueous hydroxide ions (e18H2O/OH−) is an integral parameter in chemical modeling. Quantum chemical calculations predict thermodynamic ...

Oxygen isotope fractionation between water and the aqueous hydroxide ion

The stable oxygen isotope fractionation factor between water and the aqueous hydroxide ion is a fundamental geochemical parameter widely used in the Earth Sciences and other fields. Studies from the 1960s reported α(H2O(l)-OH-(aq)), the fractionation factor between liquid H2O and aqueous OH−, theoretically as 1.046 and ∼1.048 (46‰ and 48‰ at 15 °C and 25 °C) and experimentally as 1.045 (45‰) at 15 °C. These, or similar values have been used in the literature for almost 60 years. Here I present quantum-chemical (QC) calculations, showing that the above theoretical values are fundamentally wrong as they pertain to free OH− (incorrectly assumed equivalent to aqueous OH−) and ignore intermolecular vibrational modes in solution. As a result, the theoretical values from the 1960s are off by a factor of ∼2 (when expressed in ‰), suggesting that the experimental value is also wrong. QC computations of OH−-water clusters with up to n=22 water molecules demonstrate that hydrogen bonding in solution significantly affects the fundamental vibrational modes associated with OH− and substantially reduces the oxygen isotope fractionation between water and OH-(aq), compared to the fractionation between water and free OH−. The most accurate QC methods tested here yield values for the fractionation factor between H2O and OH− in water clusters with n=7 to 22 water molecules of ∼1.019 to ∼1.024 (19 to 24‰) at 25 °C based on the harmonic approximation. Estimated effects due to anharmonicity (from numerically demanding computations) could add uncertainties of up to ∼3‰ to these values.

Temperature-dependent fractionation of stable oxygen isotopes differs between cuttlefish statoliths and cuttlebones

• The first equation between temperature and δ 18 O values for cephalopod is established. • Carbonate δ 18 O values as a temperature proxy are structure specific. • The variation of δ 18 O values in biogenic carbonates is shown among marine organisms. The recording of oxygen isotope composition (δ 18 O) in biogenic carbonates is a powerful tool for investigating temperature changes in organisms’ habitats, especially in relation to their growth, migration, movement, adaptation, and acclimation. Temperature-dependent equations of δ 18 O values have been established from biogenic carbonates in various organisms, but no equation has yet been validated for cephalopods, thus limiting the application of this approach to the field of cephalopod ecology. In this study, we established a temperature-dependent equation of δ 18 O values in statoliths and cuttlebones of the pharaoh cuttlefish, Sepia pharaonis , through a controlled experiment involving three temperatures (20 °C, 25 °C, and 30 °C). The established equations for statoliths and cuttlebones follow the general trend in inorganic carbonates, fish otoliths, and mollusc shells, revealing that δ 18 O values are lower when the temperature is higher. Noticeably, the intercept and slope of the equations obtained from cuttlebones and statoliths differed even when these two carbonate structures formed within the same individual cuttlefish. The isotopic difference between statoliths and cuttlebones suggests that temperature-dependent fractionation is structure specific and may result from the functional demands and chemistry of the internal fluids surrounding these two biogenic carbonates. The use of δ 18 O values recorded in statoliths and cuttlebones as a temperature proxy can benefit studies of cephalopod ecology and thermal history.

A sulfate conundrum: Dissolved sulfates of deep-saline brines and carbonate-associated sulfates

Sulfates in deeply circulating brines and carbonate-associated sulfates (CAS) within sedimentary units of the Cambrian strata in the Illinois Basin record a complex history. Dissolved sulfate within the Mt. Simon Sandstone brines exhibits average δ34SSO4 values of 35.4‰ and δ18OSO4 values of 14.6‰ and appears to be related to Cambrian seawater sulfate, either original seawater or sourced from evaporite deposits such as those in the Michigan Basin. Theoretical and empirical relationships based on stable oxygen isotope fractionation suggest that sulfate within the lower depths of the Mt. Simon brines has experienced a long period of isolation, possibly several tens of millions of years. Comparison with brines from other stratigraphic units shows the Mt. Simon brines are geochemically unique. Dissolved sulfate from brines within the Ironton-Galesville Sandstone averages 22.7‰ for δ34SSO4 values and 13.0‰ for δ18OSO4 values. The Ironton-Galesville brine has mixed with younger groundwater, possibly of Ordovician to Devonian age and younger. The Eau Claire Formation lies between the Mt. Simon and Ironton-Galesville Sandstones. The carbonate units of the Eau Claire and stratigraphically equivalent Bonneterre Formation contain CAS that appears isotopically related to the Late Pennsylvanian-Early Permian Mississippi Valley-type ore pulses that deposited large sulfide minerals in the Viburnum Trend/Old Lead Belt ore districts. The δ34SCAS values range from 21.3‰ to 9.3‰, and δ18OCAS values range from +1.4‰ to −2.6‰ and show a strong covariance (R2=0.94). The largely wholesale replacement of Cambrian seawater sulfate signatures in these dolomites does not appear to have affected the sulfate signatures in the Mt. Simon brines even though these sulfide deposits are found in the stratigraphically equivalent Lamotte Sandstone to the southwest. On the basis of this and previous studies, greater fluid densities of the Mt. Simon brines may have prevented the less dense Mississippi Valley-type fluids from interacting with these deeply circulating brines. Progressive in situ quartz cementation that occurred in the Mt. Simon Sandstone contemporaneous to the ore pulses may also have precluded fluid migration. The Mt. Simon brines appear to be a mixture of evaporated connate Cambrian seawater, recirculating deep-seated crystalline basement brines, and meteoric water.

Ikaite precipitation in a lacustrine environment – implications for palaeoclimatic studies using carbonates from Laguna Potrok Aike (Patagonia, Argentina)

The monoclinic mineral ikaite (CaCO3 · 6H2O) and its pseudomorphs are potentially important archives for palaeoenvironmental reconstructions. Natural ikaite occurs in a small temperature range near freezing point and is reported mainly from marine and only rarely from continental aquatic environments. Ikaite transforms to more stable anhydrous forms of CaCO3 after an increase in temperature or when exposed to atmospheric conditions. The knowledge about conditions for natural ikaite formation, its stable isotope fractionation factors and isotopic changes during transformation to calcite is very restricted. Here, for the first time, primary precipitation of idiomorphic ikaite and its calcite pseudomorphs are reported from a subsaline lake, Laguna Potrok Aike, in southern Argentina. The calculated stable oxygen isotope fractionation factor between lake water and ikaite-derived calcite (αPAI = 1.0324 at a temperature of 4.1 °C) is close to but differs from that of primarily inorganically precipitated calcite. Pseudomorphs after ikaite rapidly disintegrate into calcite powder that is indistinguishable from μm-sized calcite crystals in the sediment record of Laguna Potrok Aike suggesting an ikaite origin of sedimentary calcites. Therefore, the Holocene carbonates of Laguna Potrok Aike have the potential to serve as a recorder of past hydrological variation.

A new value for the stable oxygen isotope fractionation between dissolved sulfate ion and water

Although the stable oxygen isotope fractionation between dissolved sulfate ion ( SO 4 2 - ) and H 2O (hereafter α ( SO 4 2 - – H 2 O ) ) is of physico-chemical and biogeochemical significance, no experimental value has been established until present. The primary reason being that uncatalyzed oxygen exchange between SO 4 2 - and H 2O is extremely slow, taking ∼ 10 5 years at room temperature. For lack of a better approach, values of 16‰ and 31‰ at 25 °C have been assumed in the past, based on theoretical ‘gas-phase’ calculations and extrapolation of laboratory results obtained at temperatures >75 °C that actually pertain to the bisulfate ( HSO 4 - ) – H 2 O system. Here I use novel quantum-chemistry calculations, which take into account detailed solute–water interactions to establish a new value for α ( SO 4 2 - – H 2 O ) of 23‰ at 25 °C. The results of the corresponding calculations for the bisulfate ion are in agreement with observations. The new theoretical values show that sediment δ 18 O SO 4 2 - -data, which reflect oxygen isotope equilibration between sulfate and ambient water during microbial sulfate reduction, are consistent with the abiotic equilibrium between SO 4 2 - and water.

Oxygen isotope fractionation of dissolved oxygen during abiological reduction by aqueous sulfide

The stable oxygen isotope fractionation factor of dissolved oxygen gas has been measured during abiological reduction by aqueous sulfide at 10–40 °C under circum-neutral conditions in order to understand the stable isotope behavior of oxygen during interaction with sulfide-rich natural waters. The oxygen isotopic composition of O 2 becomes isotopically heavier as the reaction proceeds, with the oxygen isotope enrichment factor ε ranging from − 8.2 to − 9.8‰ at 10 °C, from − 8.8 to − 10.9‰ at 23 °C, and from − 6.0 to − 10.7‰ at 40 °C. Values of ε show little dependence on the initial sulfide concentration, reaction temperature, or salinity in the solutions. In addition to the direct reaction of sulfide with O 2, aqueous sulfide oxidation can also progress through complex and multiple reaction pathways where O 2 can further react with intermediate products of sulfide oxidation such as S 0, S x 2−, S 2O 3 2−, and SO 3 2−. Hence, the measured values of ε are a result of multiple isotope fractionations during O 2 consumption by these sulfur species, where the net measured isotope fractionation factor is dependent upon the relative magnitude of each individual O 2-consuming reaction, and the isotope fractionation factor associated with each of these reactions. Nevertheless, the results will have application to the identification and possible quantification of O 2 consumption by reaction with sulfide in natural environments.

Hydration in solution is critical for stable oxygen isotope fractionation between carbonate ion and water

Various isotope studies require accurate fractionation factors ( α’s) between different chemical compounds in thermodynamic equilibrium. Although numerous isotope systems involve aqueous solutions, the conventional theory is formulated for the gas-phase and predicts incorrect α’s for many compounds dissolved in water. Here I show that quantum-chemistry calculations, which take into account solute–water interactions, accurately predict, for instance, oxygen isotope fractionation between dissolved CO 3 2 - and H 2O (hereafter α ( CO 3 2 - – H 2 O ) ). Simple force field and quantum-chemistry calculations for the ‘gas-phase’ ion CO 3 2 - predict α ( CO 3 2 - – H 2 O ) ≃ 1.015 (15‰) at 25 °C. However, based on CO 3 2 - · ( H 2 O ) n -clusters with up to 22 H 2O molecules, I calculate a value of 25‰, which agrees with the experimental value of 24.5 ± 0.5‰. Effects of geometry and anharmonicity on the calculated α were also examined. The calculations reveal the critical role of hydration in solution, which is ignored in the gas-phase theory. The approach presented provides an adequate framework for calculating fractionation factors involving dissolved compounds; it may also be used to predict α’s that cannot (or have not yet been) determined experimentally.

An expression for the overall oxygen isotope fractionation between the sum of dissolved inorganic carbon and water

Stable oxygen isotope fractionation factors (α's) between individual dissolved carbonate species (CO2(aq.), H2CO3, HCO3−, CO32−) and water, and their sum ( = [CO2(aq.)] + [H2CO3] + [HCO3−] + [CO32−]) and water are fundamental geochemical parameters. While values of , α, and have recently been examined, an overall mass balance for stable oxygen isotopes in the carbonate system still needs to be derived. The theoretical treatment of this mass balance is not trivial (in contrast to, e.g., stable carbon isotopes) because (1) oxygen is exchanged with H2O and (2) complications arise from the nature of the oxygen mole fractions. I use the recently reported individual α's to derive an expression for the overall oxygen isotope fractionation between and water. This allows the calculation of α(−H2O) at any given pH of the solution. The result differs from a relationship published earlier, and implications for previous studies are discussed. Numerical routines in MATLAB and Excel for the present calculation have been developed and are available as auxiliary material (Software S1). Applications of the expression include, for example, examination of biomineralization mechanisms and corrections to isotopic paleotemperature equations. The latter application can significantly alter reconstructions of Phanerozoic climate change.

Temperature-dependent fractionation of stable oxygen isotopes in otoliths of juvenile cod (Gadus morhua L.)

Abstract Analysis of stable oxygen isotopes in otoliths is a promising technique for estimating the ambient temperature experienced by fish, but consistent equations relating temperature and fractionation of stable oxygen isotopes in otoliths among different fish species are lacking. Juvenile cod were reared at constant temperatures from 6 to 20°C and the sagittal otoliths were analysed for oxygen isotope values. We determined that temperature-dependent fractionation of oxygen isotopes in the otoliths was close to that reported for inorganic aragonite at low temperatures, but there were deviations from oxygen isotope fractionation equations for otoliths of other species. The linear relationship between oxygen isotope value in the cod otoliths and temperature was determined to be: 1000 Ln α = 16.75(103 TK−1) − 27.09. Temperature estimates with 1°C precision at the 95% probability level require a sample size of ≥5 otoliths. Only an insignificant amount of the variance in the data was due to variance between left and right otolith, and due to repeated measurements of otolith subsamples. This study confirms that stable isotope values of cod otoliths can give precise and accurate estimates of the ambient temperature experienced by fish.

Oxygen and sulfur isotope fractionation during anaerobic bacterial disproportionation of elemental sulfur

Bacterial disproportionation of elemental sulfur is an important process in the sulfur cycle of natural sediments and leads to the formation of hydrogen sulfide and sulfate. The oxygen atoms in sulfate during this anaerobic process are completely derived from water according to the overall reaction: 4H 2O + 4S 0 → 3H 2S + SO 4 2− + 2H +In the present study, stable oxygen isotope fractionation during formation of sulfate via this reaction was experimentally investigated for a pure culture (Desulfocapsa thiozymogenes) and an enrichment culture (“Kuhgraben”) at 28°C. Synthetic FeCO 3 and FeOOH were used as scavengers for hydrogen sulfide to keep the disproportionation reaction exergonic and to suppress polysulfide formation and isotope exchange between elemental sulfur and hydrogen sulfide. Compared to water, dissolved sulfate was enriched in 18O by +17.4 ± 0.1‰ ( Desulfocapsa thiozymogenes) and +16.6 ± 0.5‰ (Kuhgraben) at cell specific sulfur disproportionation rates of 10 −15.4 ± 0.4 mol S° cell −1 h −1 and 10 −14.4 ± 0.9 mol S° cell −1 h −1, respectively. Oxygen isotope fractionation was not influenced by the type of iron-bearing scavenger used, corroborating earlier findings that H 2S oxidation by FeOOH yields elemental sulfur as the dominant oxidation product. Sulfite is suggested to be formed as a metabolic intermediate to facilitate isotope exchange with water. Due to bacterial disproportionation, dissolved sulfate was also enriched in 34S compared to elemental sulfur by +11.0 to +18.4‰ ( D. thiozymogenes) and +12.7 to +17.9‰ (Kuhgraben). FeS was depleted in 32S compared to elemental sulfur by −3.7 to −5.3‰ ( D. thiozymogenes).

The effects of increased water fertility on tropical spinose planktonic foraminifers in laboratory cultures

Other| July 01, 1992 The effects of increased water fertility on tropical spinose planktonic foraminifers in laboratory cultures Jelle Bijma; Jelle Bijma University of Tuebingen, Institut und Museum fuer Geologie und Palaeontologie, Tubingen, Federal Republic of Germany Search for other works by this author on: GSW Google Scholar Christoph Hemleben; Christoph Hemleben Search for other works by this author on: GSW Google Scholar Hedi Oberhaensli; Hedi Oberhaensli Search for other works by this author on: GSW Google Scholar Michael Spindler Michael Spindler Search for other works by this author on: GSW Google Scholar Author and Article Information Jelle Bijma University of Tuebingen, Institut und Museum fuer Geologie und Palaeontologie, Tubingen, Federal Republic of Germany Christoph Hemleben Hedi Oberhaensli Michael Spindler Publisher: Cushman Foundation for Foraminiferal Research First Online: 03 Mar 2017 Online ISSN: 1943-264X Print ISSN: 0096-1191 GeoRef, Copyright 2008, American Geological Institute. Journal of Foraminiferal Research (1992) 22 (3): 242–256. https://doi.org/10.2113/gsjfr.22.3.242 Article history First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jelle Bijma, Christoph Hemleben, Hedi Oberhaensli, Michael Spindler; The effects of increased water fertility on tropical spinose planktonic foraminifers in laboratory cultures. Journal of Foraminiferal Research 1992;; 22 (3): 242–256. doi: https://doi.org/10.2113/gsjfr.22.3.242 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 SocietyJournal of Foraminiferal Research Search Advanced Search 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.