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Sample records for oxygen isotope record

  1. What does the oxygen isotope composition of rodent teeth record?

    NASA Astrophysics Data System (ADS)

    Royer, Aurélien; Lécuyer, Christophe; Montuire, Sophie; Amiot, Romain; Legendre, Serge; Cuenca-Bescós, Gloria; Jeannet, Marcel; Martineau, François

    2013-01-01

    Oxygen isotope compositions of tooth phosphate (δ18Op) were measured in 107 samples defined on the basis of teeth obtained from 375 specimens of extant rodents. These rodents were sampled from pellets collected in Europe from 38°N (Portugal) to 65°N (Finland) with most samples coming from sites located in France and Spain. Large oxygen isotopic variability in δ18Op is observed both at the intra- and inter-species scale within pellets from a given location. This isotopic variability is partly explained by heterochrony in tooth formation related to the short time of mineralization for all rodent species as well as the duration of mineralization that is species-dependent. Consequently, tooth phosphate of rodents records a short seasonal interval in the oxygen isotope compositions of meteoric waters (δ18Omw). In addition, inter-species isotopic variability observed in the same pellets suggests behavioural differences implying distinct isotopic compositions for species living in the same location. At the scale of Europe, a robust linear oxygen isotope fractionation equation was determined for Muroidea between the midrange δ18Op values and δ18Omw values: δ18Op=1.21(±0.20)δ18Omw+24.76(±2.70) with R2=0.79 (n=9; p<0.0001).

  2. Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes

    NASA Astrophysics Data System (ADS)

    Frei, Robert; Gaucher, Claudio; Poulton, Simon W.; Canfield, Don E.

    2009-09-01

    Geochemical data suggest that oxygenation of the Earth's atmosphere occurred in two broad steps. The first rise in atmospheric oxygen is thought to have occurred between ~2.45 and 2.2Gyr ago, leading to a significant increase in atmospheric oxygen concentrations and concomitant oxygenation of the shallow surface ocean. The second increase in atmospheric oxygen appears to have taken place in distinct stages during the late Neoproterozoic era (~800-542Myr ago), ultimately leading to oxygenation of the deep ocean ~580Myr ago, but details of the evolution of atmospheric oxygenation remain uncertain. Here we use chromium (Cr) stable isotopes from banded iron formations (BIFs) to track the presence of Cr(VI) in Precambrian oceans, providing a time-resolved picture of the oxygenation history of the Earth's atmosphere-hydrosphere system. The geochemical behaviour of Cr is highly sensitive to the redox state of the surface environment because oxidative weathering processes produce the oxidized hexavalent [Cr(VI)] form. Oxidation of reduced trivalent [Cr(III)] chromium on land is accompanied by an isotopic fractionation, leading to enrichment of the mobile hexavalent form in the heavier isotope. Our fractionated Cr isotope data indicate the accumulation of Cr(VI) in ocean surface waters ~2.8 to 2.6Gyr ago and a likely transient elevation in atmospheric and surface ocean oxygenation before the first great rise of oxygen 2.45-2.2Gyr ago (the Great Oxidation Event). In ~1.88-Gyr-old BIFs we find that Cr isotopes are not fractionated, indicating a decline in atmospheric oxygen. Our findings suggest that the Great Oxidation Event did not lead to a unidirectional stepwise increase in atmospheric oxygen. In the late Neoproterozoic, we observe strong positive fractionations in Cr isotopes (δ53Cr up to +4.9‰), providing independent support for increased surface oxygenation at that time, which may have stimulated rapid evolution of macroscopic multicellular life.

  3. Chromium Isotopes Record Fluctuations in Precambrian Biospheric Oxygenation

    NASA Astrophysics Data System (ADS)

    Frei, R.; Gaucher, C.; Poulton, S. W.; Canfield, D. E.

    2009-12-01

    There is a direct relationship between life, oxygen, and the surface chemistry of the Earth. Geochemical data suggest that oxygenation of the Earth's atmosphere occurred in two broad steps, near the beginning and the end of the Proterozoic Eon (2500 to 542 million years ago), but the details of this history are unclear. The geochemical behaviour of chromium (Cr) is highly sensitive to the redox state of the surface environment as oxidative weathering processes produce the oxidised hexavalent [Cr(VI)] form. Oxidation of reduced trivaltent [Cr(III)] chromium on land is accompanied by an isotopic fractionation, leading to enrichment of the mobile hexavalent form in the heavier isotope. The fractionated Cr isotope signature is then tranfered by riverine transport to the sea. Here, we use Cr stable isotopes from banded iron formations (BIFs) to track the presence of Cr(VI) in Precambrian oceans, providing a time-resolved picture of the oxygenation history of Earth’s atmosphere-hydrosphere system. Fractionated Cr isotopes indicate the accumulation of Cr(VI) in ocean surface waters ~2.8 to 2.6 billion years (Gyr) ago and a likely transient elevation in atmospheric and surface ocean oxygen prior to the first great rise of oxygen 2.45-2.2 Gyr ago (the Great Oxidation Event; GOE). In contrast, Cr isotopes in ~1.88 Gyr old BIFs are not fractionated, indicating a major decline in atmospheric oxygen and demonstrating that the GOE did not lead to a unidirectional stepwise increase in atmospheric oxygen. In the late Neoproterozoic, ~800 to 542 million years (Myr) ago, we observe strong positive fractionations in Cr isotopes (δ53Cr up to +4.9 ‰) providing independent support for increased surface oxygenation at this time. This may have stimulated rapid evolution of macroscopic multicellular life. Our chromium isotope data thus provide new insights into the oxygenation history of the Earth, and highlight its use as a powerful redox tracer in aquatic systems.

  4. Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes.

    PubMed

    Frei, Robert; Gaucher, Claudio; Poulton, Simon W; Canfield, Don E

    2009-09-10

    Geochemical data suggest that oxygenation of the Earth's atmosphere occurred in two broad steps. The first rise in atmospheric oxygen is thought to have occurred between approximately 2.45 and 2.2 Gyr ago, leading to a significant increase in atmospheric oxygen concentrations and concomitant oxygenation of the shallow surface ocean. The second increase in atmospheric oxygen appears to have taken place in distinct stages during the late Neoproterozoic era ( approximately 800-542 Myr ago), ultimately leading to oxygenation of the deep ocean approximately 580 Myr ago, but details of the evolution of atmospheric oxygenation remain uncertain. Here we use chromium (Cr) stable isotopes from banded iron formations (BIFs) to track the presence of Cr(VI) in Precambrian oceans, providing a time-resolved picture of the oxygenation history of the Earth's atmosphere-hydrosphere system. The geochemical behaviour of Cr is highly sensitive to the redox state of the surface environment because oxidative weathering processes produce the oxidized hexavalent [Cr(VI)] form. Oxidation of reduced trivalent [Cr(III)] chromium on land is accompanied by an isotopic fractionation, leading to enrichment of the mobile hexavalent form in the heavier isotope. Our fractionated Cr isotope data indicate the accumulation of Cr(VI) in ocean surface waters approximately 2.8 to 2.6 Gyr ago and a likely transient elevation in atmospheric and surface ocean oxygenation before the first great rise of oxygen 2.45-2.2 Gyr ago (the Great Oxidation Event). In approximately 1.88-Gyr-old BIFs we find that Cr isotopes are not fractionated, indicating a decline in atmospheric oxygen. Our findings suggest that the Great Oxidation Event did not lead to a unidirectional stepwise increase in atmospheric oxygen. In the late Neoproterozoic, we observe strong positive fractionations in Cr isotopes (delta(53)Cr up to +4.9 per thousand), providing independent support for increased surface oxygenation at that time, which may

  5. Fluctuations in Precambrian atmospheric oxygenation recorded by chromium isotopes.

    PubMed

    Frei, Robert; Gaucher, Claudio; Poulton, Simon W; Canfield, Don E

    2009-09-10

    Geochemical data suggest that oxygenation of the Earth's atmosphere occurred in two broad steps. The first rise in atmospheric oxygen is thought to have occurred between approximately 2.45 and 2.2 Gyr ago, leading to a significant increase in atmospheric oxygen concentrations and concomitant oxygenation of the shallow surface ocean. The second increase in atmospheric oxygen appears to have taken place in distinct stages during the late Neoproterozoic era ( approximately 800-542 Myr ago), ultimately leading to oxygenation of the deep ocean approximately 580 Myr ago, but details of the evolution of atmospheric oxygenation remain uncertain. Here we use chromium (Cr) stable isotopes from banded iron formations (BIFs) to track the presence of Cr(VI) in Precambrian oceans, providing a time-resolved picture of the oxygenation history of the Earth's atmosphere-hydrosphere system. The geochemical behaviour of Cr is highly sensitive to the redox state of the surface environment because oxidative weathering processes produce the oxidized hexavalent [Cr(VI)] form. Oxidation of reduced trivalent [Cr(III)] chromium on land is accompanied by an isotopic fractionation, leading to enrichment of the mobile hexavalent form in the heavier isotope. Our fractionated Cr isotope data indicate the accumulation of Cr(VI) in ocean surface waters approximately 2.8 to 2.6 Gyr ago and a likely transient elevation in atmospheric and surface ocean oxygenation before the first great rise of oxygen 2.45-2.2 Gyr ago (the Great Oxidation Event). In approximately 1.88-Gyr-old BIFs we find that Cr isotopes are not fractionated, indicating a decline in atmospheric oxygen. Our findings suggest that the Great Oxidation Event did not lead to a unidirectional stepwise increase in atmospheric oxygen. In the late Neoproterozoic, we observe strong positive fractionations in Cr isotopes (delta(53)Cr up to +4.9 per thousand), providing independent support for increased surface oxygenation at that time, which may

  6. Oxygenation of Ediacaran Ocean recorded by iron isotopes

    NASA Astrophysics Data System (ADS)

    Fan, Haifeng; Zhu, Xiangkun; Wen, Hanjie; Yan, Bin; Li, Jin; Feng, Lianjun

    2014-09-01

    The increase in atmospheric oxygen during the late Neoproterozoic Era (ca. 800-542 Ma) may have stimulated the oxygenation of the deep oceans and the evolution of macroscopic multicellular organisms. However, the mechanism and magnitude of Neoproterozoic oxygenation remain uncertain. We present Fe isotopes, Fe species and other geochemical data for two sections of the Doushantuo Formation (ca. 635-551 Ma) deposited after the Nantuo glacial episode in the Yangtze Gorge area, South China. It is highlighted that highly positive δ56Fe values reflect a lower oxidation rate of Fe(II)aq under ferruginous conditions, and in turn near zero δ56Fe values indicate oxidizing conditions. Our study suggests that during the deposition of the bottom of Member II of the Doushantuo Formation the shallow seawater was oxic, but the deep water was characterized by ferruginous conditions, which is consistent with a redox chemical stratification model. Subsequent anoxic conditions under shallow seawater, represented by positive δ56Fe and negative δ13Ccarb excursions, should be ascribed to the upwelling of Fe(II)aq and dissolved organic carbon (DOC)-rich anoxic deep seawater. The oxidation of Fe (II)aq and DOC-rich anoxic deep seawater upon mixing with oxic shallow water provides an innovative explanation for the well-known negative δ13Ccarb excursions (ENC2) and positive δ56Fe excursions in the middle of Doushantuo Formation. Meanwhile, the upwelling Fe (II)aq- and DOC-rich anoxic deep seawater could increase photosynthetic activity. The balance between oxygen consumption and production was most important criteria for the oxygenation of Early Ediacaran Ocean and diversity of eukaryotic organisms.

  7. Oxygen Isotope Records in Modern Oyster Shells from Chi Ku, Tainan and Their Implication of Seasonality

    NASA Astrophysics Data System (ADS)

    Chen, Y. C.; Mii, H. S.; Li, K. T.

    2015-12-01

    To exam whether oxygen isotope records of Crassostrea gigasoysters can be used as proxies of environment, 133 cultivated oysters and 21 water samples were collected from Chi Ku area, Tainan City, southern Taiwan in December of 2012, and from March, 2013 to July, 2014. Instrumental air and water temperatures and precipitation records were obtained from a nearest Central Weather Bureau (CWB) station roughly 16 km north of Chi Ku. The oxygen and carbon isotope values of the ligamental area of the modern oyster shells are from -6.92‰ to -0.08‰ (-3.05 ± 1.17‰, N = 2280; 1σ; VPDB) and from -5.57‰ to 0.63‰ (-1.88 ± 0.81‰), respectively. Oxygen isotope values of the water samples are mainly between -0.28‰ and 0.74‰ (0.18 ± 0.29‰, N = 20; 1σ; VSMOW). However, water oxygen isotope value of -2.75‰ was observed for the water sample collected immediately after a typhoon heavy rainfall. Seasonal temperature fluctuation pattern of estimated oxygen isotope temperatures from modern shells is similar to that of CWB instrumental records. However, the oxygen isotope temperatures are respectively about 3 °C and 10°C higher than those of instrumental records for winter and summer. Higher estimated oxygen isotope temperatures are most likely caused by underestimated fraction of freshwater. We analyzed 5 archaeological oyster shells of Siraya culture (500~250B.P.) collected from Wu Chien Tuso North (WCTN) archaeological site of Tainan branch of Southern Taiwan Science Park to infer the harvest season of mollusks. Oxygen isotope values of the ligamental area of the archaeological oyster shells are between -5.98‰ and -1.26‰ (-3.34 ± 1.37‰, N = 60; 1σ), and carbon isotope values are between -3.21‰ and 0.60‰ (-2.04‰ ± 0.55‰). The oxygen isotope records of archaeological oyster shells also showed clear seasonality. Most of the oysters were collected in autumn and winter. Oxygen isotope values of archaeological oyster shells was 1‰ greater than that

  8. Oxygen Isotopes in Bivalve Shells record Hydrological Changes in the Siberian Land-Shelf Connection on Annual Timescales

    NASA Astrophysics Data System (ADS)

    Mueller-Lupp, T.; Bauch, H. A.; Erlenkeuser, H.

    2003-04-01

    It is now widely accepted that changes in surface ocean hydrology at northern high latitudes is a major forcing mechanism that can strongly perturbate a particular climate mode. Given the variability on subdecadal and on centennial to millennial timescales, the dispersal and fate of arctic riverine water discharge and its role on the ice regime as well as on surface water properties are central issues in the understanding of Holocene climate change in the arctic marginal seas, the Arctic Ocean, and beyond. Oxygen isotope profiles from living and fossil bivalves were investigated in order to trace modern and past hydrographical changes in the strongly coupled land-shelf system of the Laptev Sea. Detailed oxygen isotope measurements were executed on the shells along their axis of maximum growth and provide an isotopic record of hydrological and environmental changes for the lifespan of the individual bivalves. The oxygen isotopic records exhibit amplitude cycles interpreted as recording annual cycles. Based on the well-known relationship between the oxygen isotope ratio in the bivalves carbonate, the temperature and the isotopic composition of water, it is possible to relate phases of more negative (lighter) oxygen isotope values indicating summer and more positive (heavier) oxygen isotope values indicating the winter season. The main forcing factor of the oxygen isotope variations is the variability of the isotopic composition of the bottom water. Measurements of the oxygen isotope ratio in surface and bottom waters of the Laptev Sea show a linear relation of salinity and oxygen isotope ratio of the water with a coefficient of 0.50 per mill per salinity unit and document the mixing of freshwater and seawater. The oxygen isotope cycles from growing profiles of the living bivalves indicate a correspondence to seasonal hydrographic changes and can be compared with runoff data and circulation patterns in the Laptev Sea. Given the seasonal cycles in living bivalves

  9. Fidelity of Stable Oxygen Isotope Ratios as Environmental Recorders Using Multiple Coral Cores From Coastal Kenya

    NASA Astrophysics Data System (ADS)

    Naish, T.; Carter, B.; Abbott, S.; Field, B.; Zhu, H.; Wilson, G.; Alloway, B.; Edwards, S.; Pillans, B.; Barker, A.; Niessen, F.; Maslen, G.; Beu, A.; Fleitmann, D.; Dunbar, R. B.; Mucciarone, D. A.

    2004-12-01

    Climate variability in the western equatorial Indian Ocean reflects the combined influence of seasonally changing sea surface temperature (SST), ocean currents, and monsoon circulation, as well as inter-annual to -decadal variability associated with ENSO in the Pacific. However, the Indian Ocean also exhibits variability that appears unrelated to ENSO in the Pacific. The nature of interactions between air-sea variability in the Indian and Pacific oceans is not yet fully resolved, in part because of the lack of long-term, high-resolution SST records from key localities in the Indian Ocean. Such records are now being obtained using oxygen isotope profiles measured on corals from East Africa, Indonesia, Australia, and Indian Oceania (Maldives, Seychelles), with the longest coral-based time series from Malindi, Kenya, covering the last 300 years at near-monthly resolution. The value of these developing coral records depends on the fidelity with which they record regional climate variability. In order to assess the fidelity of oxygen isotope ratios (\\delta18O) in Indian Ocean corals as a proxy for sea surface temperature, we have generated stable isotopic time series from multiple Porites lutea coral heads collected along the coast of Kenya. Coral-based isotopic paleoclimatology is labor and time-intensive so detailed analyses using multiple coral heads from different sites within a region are extremely rare. Most published records are produced from a single coral head, yet questions have been raised about the accuracy of such records. To address such concerns, near-monthly resolution isotopic profiles, spanning 10 to 50 years prior to 1997, were measured on a total of 8 cores from five sites along a north-south transect between 2° and 4° S (Kiwayu: 2° 2'S, 41° 2'E, Malindi: 3° 14'S, 40° 8'E, Watamu: 3° 23'S, 39° 52'E, Mombasa: 3° 59'S, 39° 5'E, and Kisite: 4° 43'S, 39° 23'E. Correlations among individual \\delta18O time series (r values range from 0.65 to

  10. Oxygen isotope records of Holocene climate variability in the Pacific Northwest

    NASA Astrophysics Data System (ADS)

    Steinman, Byron A.; Pompeani, David P.; Abbott, Mark B.; Ortiz, Joseph D.; Stansell, Nathan D.; Finkenbinder, Matthew S.; Mihindukulasooriya, Lorita N.; Hillman, Aubrey L.

    2016-06-01

    Oxygen isotope (δ18O) measurements of authigenic carbonate from Cleland Lake (southeastern British Columbia), Paradise Lake (central British Columbia), and Lime Lake (eastern Washington) provide a ∼9000 year Holocene record of precipitation-evaporation balance variations in the Pacific Northwest. Both Cleland Lake and Paradise Lake are small, surficially closed-basin systems with no active inflows or outflows. Lime Lake is surficially open with a seasonally active overflow. Water isotope values from Cleland and Paradise plot along the local evaporation line, indicating that precipitation-evaporation balance is a strong influence on lake hydrology. In contrast, Lime Lake water isotope values plot on the local meteoric water line, signifying minimal influence by evaporation. To infer past hydrologic balance variations at a high temporal resolution, we sampled the Cleland, Paradise, and Lime Lake sediment cores at 1-60 mm intervals (∼3-33 years per sample on average) and measured the isotopic composition of fine-grained (<63 μm) authigenic CaCO3 in each sample. Negative δ18O values, which indicate wetter conditions in closed-basin lakes, occur in Cleland Lake sediment from 7600 to 2200 years before present (yr BP), and are followed by more positive δ18O values, which suggest drier conditions, after 2200 yr BP. Highly negative δ18O values in the Cleland Lake record centered on ∼2400 yr BP suggest that lake levels were high (and that the lake may have been overflowing) at this time as a result of a substantially wetter climate. Similarly, Paradise Lake sediment δ18O values are relatively low from 7600 to 4000 yr BP and increase from ∼4000 to 3000 yr BP and from ∼2000 yr BP to present, indicating that climate became drier from the middle through the late Holocene. The δ18O record from Lime Lake, which principally reflects changes in the isotopic composition of precipitation, exhibits less variability than the closed-basin lake records and follows a

  11. Model based paleoclimate interpretations of Holocene oxygen isotope records from the Pacific Northwest

    NASA Astrophysics Data System (ADS)

    Steinman, B. A.; Pompeani, D. P.; Abbott, M. B.; Ortiz, J. D.; Stansell, N.; Mihindukulasooriya, L. N.; Hillman, A. L.; Finkenbinder, M. S.

    2015-12-01

    Oxygen isotope measurements of authigenic carbonate from Cleland Lake (British Columbia), Paradise Lake (British Columbia), and Lime Lake (Washington) provide an ~9,000 year Holocene record of precipitation-evaporation balance variations in the Pacific Northwest. Both Cleland Lake and Paradise Lake are small, surficially closed-basin systems with no active inflows or outflows. Lime Lake is surficially open with a seasonally active overflow. We sampled the lake sediment cores at 1-60 mm intervals (~3-33 years per sample on average) and measured the isotopic composition of fine-grained, authigenic CaCO3 in each sample. Negative δ18O values, which indicate wetter conditions in closed-basin lakes, occur in Cleland Lake and Paradise Lake sediment during the mid-Holocene and are followed by more positive δ18O values, which suggest drier conditions, in the late Holocene. The δ18O record from Lime Lake, which principally reflects changes in the isotopic composition of precipitation, exhibits less variability than the closed-basin lake records and follows an increasing trend from the mid-Holocene to present. Power spectrum analysis of the Cleland Lake δ18O data from 1,000 yr BP to present demonstrates significant periodicities of ~6 and ~67 years that likely reflect the enhancement of El Niño Southern Oscillation (ENSO) variability in the late Holocene with an associated multidecadal (i.e., 50 to 70 yr) component of the Pacific Decadal Oscillation. Results from mid-Holocene (6,000 yr BP) climate model simulations conducted as part of the Paleoclimate Modeling Intercomparison Project Phase 3 (PMIP3) indicate that in much of western North America, the cold season was wetter, and the warm season (April-September) was considerably drier (relative to the late Holocene), leading to an overall drier climate in western North America but with enhanced hydroclimatic seasonality. This is consistent with inferences from the Cleland and Paradise Lake δ18O records, which lake

  12. Survivor or opportunist? Oxygen isotope records from Stylaster miniata in the Florida Straits

    NASA Astrophysics Data System (ADS)

    Rosenheim, B. E.; Adamic, J. F.; Reed, J. K.; Rosenberg, A. D.; Grasmueck, M.; Swart, P. K.; Eberli, G. P.; Correa, T. S.

    2009-12-01

    Deep on the flanks of the Florida Straits, several reefs exist with numerous colonies of standing-dead coral interspersed with species of Stylasterid corals. The Stylasterids appear to either be survivors of widespread die-off or opportunistic species that are occupying a recently vacated niche. In the former scenario, the environmental records within their skeletons may be helpful in determining the cause of death of other species of corals. Timing and cause of death from surrounding corals can be approached by 1. dates from the standing dead corals and 2. environmental records and dates from the living Stylasterids. The latter has proven difficult due to the paucity of knowledge of growth habits and rates of the Stylasterids. Here we present stable oxygen isotope records from Stylaster miniata collected in 2007 from a depth of 156 m at the summit of a Stylasterid-dominated deep-water coral bioherm on Pourtales Terrace in the Florida Straits. Cyclical trends in δ18O of 1 ‰ VPDB are observed in the base of the coral skeleton and suggest a growth rate of approximately 18mm/y if they are assumed to be annual in nature. Extrapolated over the length of the entire coral, this growth rate suggests an age approximately 10 years, and suggests that Stylasterids only recently inhabited the reef. However, radiocarbon and U/Th dating of coral rubble suggests a sustained rate of death on adjacent reefs.

  13. Coral oxygen isotope records of interdecadal climate variations in the South Pacific Convergence Zone region

    NASA Astrophysics Data System (ADS)

    Bagnato, Stefan; Linsley, Braddock K.; Howe, Stephen S.; Wellington, Gerard M.; Salinger, Jim

    2005-06-01

    The South Pacific Convergence Zone (SPCZ), a region of high rainfall, is a major feature of subtropical Southern Hemisphere climate and contributes to and interacts with circulation features across the Pacific, yet its past temporal variability and forcing remain only partially understood. Here we compare coral oxygen isotopic (δ18O) series (spanning A.D. 1997-1780 and A.D. 2001-1776) from two genera of hermatypic corals in Fiji, located within the SPCZ, to examine the fidelity of these corals in recording climate change and SPCZ interdecadal dynamics. One of these coral records is a new 225-year subannually resolved δ18O series from the massive coral Diploastreaheliopora. Diploastrea's use in climate reconstructions is still relatively new, but this coral has shown encouragingly similar interannual variability to Porites, the coral genus most commonly used in Pacific paleoclimate studies. In Fiji we observe that interdecadal δ18O variance is also similar in these two coral genera, and Diploastrea contains a larger-amplitude interdecadal signal that more closely tracks instrumental-based indices of Pacific interdecadal climate change and the SPCZ than Porites. Both coral δ18O series record greater interdecadal variability from ˜1880 to 1950, which is consistent with the observations of Folland et al. (2002), who reported higher variability in SPCZ position before 1945. These observations indicate that Diploastrea will likely provide a significant new source of long-term climate information from the SPCZ region.

  14. Oxygen Isotopes in Meteorites

    NASA Astrophysics Data System (ADS)

    Clayton, R. N.

    2003-12-01

    types of stellar sources, corresponding to the r-process, s-process, and p-process. Presolar silicon carbide grains, extracted from primitive meteorites, contain molybdenum that has been subject to s-process neutron capture in red-giant stars, resulting in large enrichments of isotopes at masses 95, 96, 97, 98, and severe depletions (up to 100%) of isotopes at masses 92 and 94 (p-process) and 100 (r-process) (Nicolussi et al., 1998). Complementary patterns have been found in whole-rock samples of several meteorites, with >1,000-fold smaller amplitude, suggesting the preservation of a small fraction of the initial isotopic heterogeneity ( Yin et al., 2002; Dauphas et al., 2002). Oxygen is another element for which primordial isotopic heterogeneity might be preserved. This is discussed further below.It would be highly desirable to have samples of oxygen-rich mineral grains that have formed in stellar atmospheres and have recorded the nucleosynthetic processes in individual stars. Similar samples are already available for carbon-rich grains, in the form of SiC and graphite, primarily from asymptotic giant branch (AGB) stars and supernovae (Anders and Zinner, 1993). These presolar grains have provided a wealth of detailed information concerning nucleosynthesis of carbon, nitrogen, silicon, calcium, titanium, and heavier elements (see Chapter 1.02). It is thought that such carbon-rich minerals should form only in environments with C/O>1, as in the late stages of AGB evolution, or in carbon-rich layers of supernovae. By analogy, one would expect to form oxide and silicate minerals in environments with C/O<1, as is common for most stars. Indeed there is evidence in infrared spectra for the formation of Al2O3 (corundum) and silicates, such as olivine (Speck et al., 2000) around evolved oxygen-rich stars. However, searches for such grains in meteorites have yielded only a very small population of corundum grains, a few grains of spinel and hibonite, and no silicates ( Nittler et

  15. Sulfur Isotope Trends in Archean Microbialite Facies Record Early Oxygen Production and Consumption

    NASA Astrophysics Data System (ADS)

    Zerkle, A.; Meyer, N.; Izon, G.; Poulton, S.; Farquhar, J.; Claire, M.

    2014-12-01

    The major and minor sulfur isotope composition (δ34S and Δ33S) of pyrites preserved in ~2.65-2.5 billion-year-old (Ga) microbialites record localized oxygen production and consumption near the mat surface. These trends are preserved in two separate drill cores (GKF01 and BH1-Sacha) transecting the Campbellrand-Malmani carbonate platform (Ghaap Group, Transvaal Supergroup, South Africa; Zerkle et al., 2012; Izon et al., in review). Microbialite pyrites possess positive Δ33S values, plotting parallel to typical Archean trends (with a Δ33S/δ34S slope of ~0.9) but enriched in 34S by ~3 to 7‰. We propose that these 34S-enriched pyrites were formed from a residual pool of sulfide that was partially oxidized via molecular oxygen produced by surface mat-dwelling cyanobacteria. Sulfide, carrying the range of Archean Δ33S values, could have been produced deeper within the microbial mat by the reduction of sulfate and elemental sulfur, then fractionated upon reaction with O2 produced by oxygenic photosynthesis. Preservation of this positive 34S offset requires that: 1) sulfide was only partially (50­­-80%) consumed by oxidation, meaning H2S was locally more abundant (or more rapidly produced) than O2, and 2) the majority of the sulfate produced via oxidation was not immediately reduced to sulfide, implying either that the sulfate pool was much larger than the sulfide pool, or that the sulfate formed near the mat surface was transported and reduced in another part of the system. Contrastingly, older microbialite facies (> 2.7 Ga; Thomazo et al., 2013) appear to lack these observed 34S enrichments. Consequently, the onset of 34S enrichments could mark a shift in mat ecology, from communities dominated by anoxygenic photosynthesizers to cyanobacteria. Here, we test these hypotheses with new spatially resolved mm-scale trends in sulfur isotope measurements from pyritized stromatolites of the Vryburg Formation, sampled in the lower part of the BH1-Sacha core. Millimeter

  16. Changes in ENSO Frequency and Character as Recorded in NE Indian Speleothem Oxygen Isotopes

    NASA Astrophysics Data System (ADS)

    Oster, J. L.; Myers, C. G.; Breitenbach, S. F. M.; Sharp, W. D.

    2014-12-01

    Oxygen isotopes (δ18O) from speleothems in monsoon regions such as NE India have provided important records of monsoon strength on decadal to multi-millennial timescales. However, recent precipitation and cave drip water studies suggest that regional rain and drip water δ18O variability may be driven by changes in moisture sources and transport pathways rather than mainly reflecting changes in rainfall amount. Hence, we compare a modern δ18O speleothem time-series with historical meteorological records and global climate indices to identify dominant influences on speleothem δ18O.We have constructed a high resolution (7-8 samples per year) δ18O time-series using a stalagmite (MAW 02-01) from Mawmluh Cave in NE India that grew during the ~50 years preceding collection in 2013. U-series dates (±1-2 years) provide an age model and confirm that visible stalagmite laminations are approximately annual. We compared the stalagmite time-series with local meteorologic records and indices of the El Niño/Southern Oscillation (Niño3, Niño4) and the Indian Ocean Dipole (IOD). Our record shows no significant correlation with rainfall amount and reveals the same seasonal signal observed in local rain and drip water δ18O. We observe significant positive correlations, with a 6 month lag, between our dataset and the Niño4 Sea Surface Temperature (SST) index (r = 0.49, p < 0.001) and the IOD (r = 0.41, p < 0.001). A cross-wavelet analysis between MAW 02-01 δ18O and Niño4 highlights a shared 4-6 year frequency throughout and a strong in-phase 8-12 year frequency beginning in 1990 and persisting for the duration of the record. The latter may reflect an increase in strength and frequency of central Pacific (CP) El Niño events since 1990. Such events, with stronger SST anomalies in the central Pacific, are more likely to restrict Indian Summer Monsoon (ISM) strength through enhanced westward migration of the descending arm of the Walker Cell. HYSPLIT back-trajectory analysis

  17. Controlling factors on a paleo-lake oxygen isotope record (Yammoûneh, Lebanon) since the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Develle, Anne-Lise; Herreros, Julien; Vidal, Laurence; Sursock, Alexandre; Gasse, Françoise

    2010-04-01

    Late Quaternary paleoclimatic changes in the Levant are difficult to extract from carbonate oxygen isotope records partly because the factors controlling the terrestrial δ 18O signals are not fully understood in this region characterized by sharp climatic gradients. Here, we address this purpose by presenting the first 14C-dated isotope record from the northern Levant. The record is based on oxygen isotopes from ostracod shells from lacustrine-palustrine deposits accumulated in a small karstic, hydrologically open basin (Yammoûneh), located on the eastern flank of Mount Lebanon. We have first constructed a composite isotopic record obtained from three different ostracod taxa. This yields an oxygen isotope record of ostracods (δ ost) related to the most widespread species ( Ilyocypris inermis), and converted to δ 18O values coeval with calcite precipitated in equilibrium (δ C) with the lake water (δ L). As with other records from the Mediterranean region, the Yammoûneh profile shows maximum and minimum δ C values during the LGM and the early Holocene, respectively, and a slight late Holocene increase. In order to discuss the potential causes of the observed δ 18O values fluctuations (e.g., changes in the isotopic composition of the moisture source, temperature, precipitation minus evaporation (P-E) balance, or atmospheric circulation), we tentatively reconstruct the lake water isotope composition by correcting the δ C values for lake water temperature using regional paleotemperature estimates. Inferred δ L values were then corrected for the isotopic composition of the Eastern Mediterranean sea surface water (the moisture source) derived from planktonic foraminifera δ 18O values corrected for alkenone-based sea surface temperature. Our study suggests that Holocene δ L fluctuations are primarily linked to changes in the sea surface water composition (source effect) amplified by enhanced inland rainfall during the early Holocene. During the LGM, low δ L

  18. Shallow marine carbon and oxygen isotope and elemental records indicate icehouse-greenhouse cycles during the Early Jurassic

    NASA Astrophysics Data System (ADS)

    Korte, Christoph; Hesselbo, Stephen P.

    2011-12-01

    For much of the Mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences. We present a carbon and oxygen isotope and elemental record for part of the Early Jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the Cleveland Basin, UK. The invertebrate isotope record is supplemented with carbon isotope data from fossil wood, which samples atmospheric carbon. New data elucidate two major global carbon isotope events, a negative excursion of ˜2‰ at the Sinemurian-Pliensbachian boundary, and a positive excursion of ˜2‰ in the Late Pliensbachian. The Sinemurian-Pliensbachian boundary event is similar to the slightly younger Toarcian Oceanic Anoxic Event and is characterized by deposition of relatively deepwater organic-rich shale. The Late Pliensbachian strata by contrast are characterized by shallow marine deposition. Oxygen isotope data imply cooling locally for both events. However, because deeper water conditions characterize the Sinemurian-Pliensbachian boundary in the Cleveland Basin the temperature drop is likely of local significance; in contrast a cool Late Pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions. Both the large-scale, long-term and small-scale, short-duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy. Isotope events and the sea level cycles are concluded to reflect processes of global significance, supporting the idea of an Early Jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 Ma.

  19. Oxygen isotopes in tree rings record variation in precipitation δ18O and amount effects in the south of Mexico

    PubMed Central

    Brienen, Roel J W; Hietz, Peter; Wanek, Wolfgang; Gloor, Manuel

    2013-01-01

    [1] Natural archives of oxygen isotopes in precipitation may be used to study changes in the hydrological cycle in the tropics, but their interpretation is not straightforward. We studied to which degree tree rings of Mimosa acantholoba from southern Mexico record variation in isotopic composition of precipitation and which climatic processes influence oxygen isotopes in tree rings (δ18Otr). Interannual variation in δ18Otr was highly synchronized between trees and closely related to isotopic composition of rain measured at San Salvador, 710 km to the southwest. Correlations with δ13C, growth, or local climate variables (temperature, cloud cover, vapor pressure deficit (VPD)) were relatively low, indicating weak plant physiological influences. Interannual variation in δ18Otr correlated negatively with local rainfall amount and intensity. Correlations with the amount of precipitation extended along a 1000 km long stretch of the Pacific Central American coast, probably as a result of organized storm systems uniformly affecting rainfall in the region and its isotope signal; episodic heavy precipitation events, of which some are related to cyclones, deposit strongly 18O-depleted rain in the region and seem to have affected the δ18Otr signal. Large-scale controls on the isotope signature include variation in sea surface temperatures of tropical north Atlantic and Pacific Ocean. In conclusion, we show that δ18Otr of M. acantholoba can be used as a proxy for source water δ18O and that interannual variation in δ18Oprec is caused by a regional amount effect. This contrasts with δ18O signatures at continental sites where cumulative rainout processes dominate and thus provide a proxy for precipitation integrated over a much larger scale. Our results confirm that processes influencing climate-isotope relations differ between sites located, e.g., in the western Amazon versus coastal Mexico, and that tree ring isotope records can help in disentangling the processes

  20. Oxygen isotopes in tree rings record variation in precipitation δ18O and amount effects in the south of Mexico

    NASA Astrophysics Data System (ADS)

    Brienen, Roel J. W.; Hietz, Peter; Wanek, Wolfgang; Gloor, Manuel

    2013-12-01

    Natural archives of oxygen isotopes in precipitation may be used to study changes in the hydrological cycle in the tropics, but their interpretation is not straightforward. We studied to which degree tree rings of Mimosa acantholoba from southern Mexico record variation in isotopic composition of precipitation and which climatic processes influence oxygen isotopes in tree rings (δ18Otr). Interannual variation in δ18Otr was highly synchronized between trees and closely related to isotopic composition of rain measured at San Salvador, 710 km to the southwest. Correlations with δ13C, growth, or local climate variables (temperature, cloud cover, vapor pressure deficit (VPD)) were relatively low, indicating weak plant physiological influences. Interannual variation in δ18Otr correlated negatively with local rainfall amount and intensity. Correlations with the amount of precipitation extended along a 1000 km long stretch of the Pacific Central American coast, probably as a result of organized storm systems uniformly affecting rainfall in the region and its isotope signal; episodic heavy precipitation events, of which some are related to cyclones, deposit strongly 18O-depleted rain in the region and seem to have affected the δ18Otr signal. Large-scale controls on the isotope signature include variation in sea surface temperatures of tropical north Atlantic and Pacific Ocean. In conclusion, we show that δ18Otr of M. acantholoba can be used as a proxy for source water δ18O and that interannual variation in δ18Oprec is caused by a regional amount effect. This contrasts with δ18O signatures at continental sites where cumulative rainout processes dominate and thus provide a proxy for precipitation integrated over a much larger scale. Our results confirm that processes influencing climate-isotope relations differ between sites located, e.g., in the western Amazon versus coastal Mexico, and that tree ring isotope records can help in disentangling the processes

  1. High-resolution conodont oxygen isotope record of Ordovician climate change

    NASA Astrophysics Data System (ADS)

    Chen, J.; Chen, Z.; Algeo, T. J.

    2013-12-01

    The Ordovician Period was characterized by several major events, including a prolonged 'super greenhouse' during the Early Ordovician, the 'Great Ordovician Biodiversification Event (GOBE)' of the Middle and early Late Ordovician, and the Hirnantian ice age and mass extinction of the latest Ordovician (Webby et al., 2004, The Great Ordovician Biodiversification Event, Columbia University Press). The cause of the rapid diversification of marine invertebrates during the GOBE is not clear, however, and several scenarios have been proposed including widespread development of shallow cratonic seas, strong magmatic and tectonic activity, and climate moderation. In order to investigate relationships between climate change and marine ecosystem evolution during the Ordovician, we measured the oxygen isotopic composition of single coniform conodonts using a Cameca secondary ion mass spectrometer. Our δ18O profile shows a shift at the Early/Middle Ordovician transition that is indicative of a rapid 6 to 8 °C cooling. This cooling event marks the termination of the Early Ordovician 'super greenhouse' and may have established cooler tropical seawater temperatures that were more favorable for invertebrate animals, setting the stage for the GOBE. Additional cooling episodes occurred during the early Sandbian, early Katian, and Hirnantian, the last culminating in a short-lived (<1-Myr) end-Ordovician ice age. The much cooler conditions that prevailed at that time may have been an important factor in the end-Ordovician mass extinction. Our results differ from those of Trotter et al. (2008, 'Did cooling oceans trigger Ordovician biodiversification? Evidence from conodont thermometry,' Science 321:550-554). Instead of a slow, protracted cooling through the Early and Middle Ordovician, our high-resolution record shows that cooling occurred in several discrete steps, with the largest step being at the Early/Middle Ordovician transition.

  2. Does Oxygen Isotopic Heterogeneity in Refractory Inclusions and Their Wark-Lovering Rims Record Nebular Repressing?

    NASA Technical Reports Server (NTRS)

    Simon, J. I.; Matzel, J. E. P.; Simon, S. B.; Weber, P. K.; Grossman, L.; Ross, D. K.; Hutcheon, I. D.

    2013-01-01

    Large systematic variations in O-isotopic compositions found within individual mineral layers of rims surrounding Ca-, Al-rich inclusions (CAIs) and at the margins of some CAIs imply formation from distinct environments [e.g., 1-3]. The O-isotope compositions of many CAIs preserve a record of the Solar nebula gas believed to initially be O-16-rich (delta O-17 less than or equal to -25%0) [4-5]. Data from a recent study of the compact Type A Allende CAI, A37, preserve a diffusion profile in the outermost 70 micrometers of the inclusion and show greater than 25%0 variations in delta O-17 within its 100 micrometer-thick Wark-Lovering rim (WL-rim) [3]. This and comparable heterogeneity measured in several other CAIs have been explained by isotopic mixing between the O-16-rich Solar reservoir and a second O-16-poor reservoir (probably nebular gas) with a planetary-like isotopic composition, e.g., [1,2,3,6]. However, there is mineralogical and isotopic evidence from the interiors of CAIs, in particular those from Allende, for parent body alteration. At issue is how to distinguish the record of secondary reprocessing in the nebula from that which occurred on the parent body. We have undertaken the task to study a range of CAI types with varying mineralogies, in part, to address this problem.

  3. Climatic dependence of stable carbon and oxygen isotope signals recorded in speleothems: From soil water to speleothem calcite

    NASA Astrophysics Data System (ADS)

    Dreybrodt, Wolfgang; Scholz, Denis

    2011-02-01

    Understanding the relationship between stable isotope signals recorded in speleothems (δ 13C and δ 18O) and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability. Here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open-closed conditions with respect to CO 2. The water entering the cave flows as a thin film towards the drip site. CO 2 degasses from this film within approx. 10 s by molecular diffusion. Subsequently, chemical and isotopic equilibrium is established on a time scale of several 10-100 s. The δ 13C value of the drip water is mainly determined by the isotopic composition of soil CO 2. The evolution of the δ 18O value of the carbonate species is determined by the long exchange time Tex, between oxygen in carbonate and water of several 10,000 s. Even if the oxygen of the CO 2 in soil water is in isotopic equilibrium with that of the water, dissolution of limestone delivers oxygen with a different isotopic composition changing the δ 18O value of the carbonate species. Consequently, the δ 18O value of the rainwater will only be reflected in the drip water if it has stayed in the rock for a sufficiently long time. After the water has entered the cave, the carbon and oxygen isotope composition of the drip water may be altered by CO 2-exchange with the cave air. Exchange times, τexCO, of about 3000 s are derived. Thus, only drip water, which drips in less than 3000 s onto the stalagmite surface, is suitable to imprint climatic signals into speleothem calcite deposited from it. Precipitation of calcite proceeds with time constants, τp, of several 100 s. Different rate constants and equilibrium concentrations for the heavy and light isotopes, respectively, result in isotope fractionation during calcite precipitation. Since Tex ≫ τp, exchange with the

  4. Coordinated Oxygen Isotopic and Petrologic Studies of CAIS Record Varying Composition of Protosolar

    NASA Technical Reports Server (NTRS)

    Simon, Justin I.; Matzel, J. E. P.; Simon, S. B.; Weber, P. K.; Grossman, L.; Ross, D. K.; Hutcheon, I. D.

    2012-01-01

    Ca-, Al-rich inclusions (CAIs) record the O-isotope composition of Solar nebular gas from which they grew [1]. High spatial resolution O-isotope measurements afforded by ion microprobe analysis across the rims and margin of CAIs reveal systematic variations in (Delta)O-17 and suggest formation from a diversity of nebular environments [2-4]. This heterogeneity has been explained by isotopic mixing between the O-16-rich Solar reservoir [6] and a second O-16-poor reservoir (probably nebular gas) with a "planetary-like" isotopic composition [e.g., 1, 6-7], but the mechanism and location(s) where these events occur within the protoplanetary disk remain uncertain. The orientation of large and systematic variations in (Delta)O-17 reported by [3] for a compact Type A CAI from the Efremovka reduced CV3 chondrite differs dramatically from reports by [4] of a similar CAI, A37 from the Allende oxidized CV3 chondrite. Both studies conclude that CAIs were exposed to distinct, nebular O-isotope reservoirs, implying the transfer of CAIs among different settings within the protoplanetary disk [4]. To test this hypothesis further and the extent of intra-CAI O-isotopic variation, a pristine compact Type A CAI, Ef-1 from Efremovka, and a Type B2 CAI, TS4 from Allende were studied. Our new results are equally intriguing because, collectively, O-isotopic zoning patterns in the CAIs indicate a progressive and cyclic record. The results imply that CAIs were commonly exposed to multiple environments of distinct gas during their formation. Numerical models help constrain conditions and duration of these events.

  5. An 8,000 year oxygen isotope record of hydroclimatic change from Paradise Lake, central British Columbia

    NASA Astrophysics Data System (ADS)

    Hillman, A. L.; Abbott, M. B.; Steinman, B. A.; Pompeani, D. P.; Cwiklik, J. P.

    2013-12-01

    Climate in the Pacific Northwest over the Holocene has primarily been controlled by the position of the Aleutian Low (AL), which is interconnected to the Pacific Decadal Oscillation (PDO) and the El Nino Southern Oscillation (ENSO). Stable isotopes of authigenic calcite precipitated from lake water and archived as lake sediment can be used to reconstruct changes in precipitation/evaporation (P/E) balance over timescales ranging from individual years to millennia. Several records of this type from southern British Columbia and northern Washington (e.g., Castor and Cleland Lakes), as well as from the southern Yukon Territory (e.g., Marcella and Rantin Lakes) have been produced, but few records from between these two regions exist. Here, we present a record of δ18O and δ13C measurements of authigenic calcite from Paradise Lake, British Columbia (54.68259°N, 122.61154°W), a surficially closed basin, groundwater throughflow lake located in the central interior of British Columbia. A total of 14 AMS radiocarbon dates were used to provide age control for the Paradise Lake record. In sediment from 8,000-4,500 years BP, oxygen isotope values vary around a mean value of -18.0‰. From 4,500-2,000 years BP, a general trend towards more positive oxygen isotope values occurs, with increased variability in both δ18O and δ13C. A gradual shift of ~2‰ in δ18O measurements (to a mean value of -16.0‰) occurs over the last 2,000 years of the record, likely due to lower lake levels. The large magnitude mean state shifts in oxygen isotopes over the last 8,000 years are similar to that observed in the Marcella Lake record (Anderson et al., 2007), although they are of a smaller magnitude. We hypothesize that significant groundwater throughflow at Paradise Lake likely causes a muted hydrologic and isotopic response to climate forcing relative to Marcella Lake, which has more isotopically enriched water and loses a greater proportion of water via evaporation. The Paradise lake

  6. Relative Humidity Recorded in the hydrogen and oxygen isotopic compositions of treerings

    NASA Astrophysics Data System (ADS)

    Shu, Y.; Feng, X.

    2002-12-01

    Many paleoclimate proxies have been developed to reconstruct continental surface temperatures. Examples are oxygen or hydrogen isotope ratios in ice cores, groundwater, and treerings, oxygen isotopes in stalagmites, tree-ring width and density, and pollen distributions in lake sediment cores. Several proxies listed above are also indicative of amount of precipitation. However, to our knowledge, a proxy indicator for air humidity does not yet exist. Humidity is related to the moisture content in the atmosphere, which plays an important role in the energy budget determining the planetary climate. Here we describe a study of oxygen and hydrogen isotopic compositions in modern treerings collected from trees growing along a transect of precipitation in Olympic Peninsula, Washington, USA. We are consciously optimistic that reconstruction of relative humidity may be possible if both oxygen and hydrogen isotopic compositions in tree cellulose are determined. Douglas-fir (Pseudotsuga menziesii) and subalpine fir (Abies lasiocarpa) trees were sampled at five sites within the Olympic Mountains. Among these sites, the annual precipitation varies from over three meters on the westside of the mountains to less than one meter on the eastside. The δ18O and δD in the surface water of these sites follow the trend of precipitation, decreasing from west to east. Annual treerings from seven trees were analyzed for δ18O and δD values. The number of rings from each tree ranges from 23 (1963-1985) to 48 (1949-1996). No significant correlation was found between the δD and δ18O values within each tree. This is expected because the range of variation in the isotopic ratios of source water at a given site is limited, and other factors such as humidity and soil hydrology may upset the one-to-one relationship between the δD and δ18O in the source water and those in treerings. However, the mean δD and δ18O values from each tree are weakly correlated with a slope of 19. This slope is

  7. Oxygen Isotopes in Bivalve Shells Record Hydrological Changes in the Siberian Land-Shelf Connection on Annual Timescales

    NASA Astrophysics Data System (ADS)

    Mueller-Lupp, T.; Bauch, H. A.; Erlenkeuser, H.

    2002-12-01

    It is now widely accepted that changes in surface ocean hydrology at northern high latitudes is a major forcing mechanism that can strongly perturbate a particular climate mode. Given the variability on subdecadal and on centennial to millennial timescales, the dispersal and fate of arctic riverine water discharge and its role on the ice regime as well as on surface water properties are central issues in the understanding of Holocene climate change in the arctic marginal seas, the Arctic Ocean, and beyond. Oxygen isotope profiles from living and fossil bivalves were investigated in order to trace modern and past hydrographical changes in the strongly coupled land-shelf system of the Laptev Sea. Detailed oxygen isotope measurements were executed on the shells along their axis of maximum growth and provide an isotopic record of hydrological and environmental changes for the lifespan of the individual bivalves. The oxygen isotopic records exhibit amplitude cycles interpreted as recording annual cycles. Based on the well-known relationship between the carbonate δ18O, temperature and the isotopic composition of water, it is possible to relate phases of more negative (lighter) δ18O values indicating summer and more positive (heavier) δ18O values indicating the winter season. The main forcing factor of the δ18O variations is the variability of the isotopic composition of the bottom water. Measurements of δ18O in surface and bottom waters of the Laptev Sea show a linear relation of salinity and water δ18O with a coefficient of 0.50 \\permil salinity-1 and document the mixing of freshwater and seawater. The δ18O cycles from growing profiles of the living bivalves indicate a correspondence to seasonal hydrographic changes and can be compared with runoff data and circulation patterns in the Laptev Sea. Given the seasonal cycles in living bivalves, oxygen isotope profiles of fossil, radiocarbon-dated, and well-preserved bivalve shells from sediment cores are used to

  8. Geochemistry of brachiopods: Oxygen and carbon isotopic records of Paleozoic oceans

    NASA Astrophysics Data System (ADS)

    Veizer, Ján; Fritz, Peter; Jones, Brian

    1986-08-01

    Combined trace element and isotope studies of 319 brachiopods, covering the Ordovician to Permian time span, show that δ 13C and δ 18O in well preserved specimens varied during the Paleozoic. The overall δ 13C secular trend is in accord with the previously published observations, but its details are obscured by vital isotopic fractionation effects at generic level. Nonetheless, the results suggest that the negative correlation between marine δ 13C carbonate and δ 34S sulphate deteriorates at time scales of ⩽ 10 6 years, due to the long residence time, and thus slow response, of SO 42- in the ocean. For oxygen isotopes, all Devonian and older specimens have δ 18O of ⩽ -4%, while the well preserved Permian samples have near-present day δ 18O of about -1% (PDB). This isotopic dichotomy is probably not due to post-depositional phenomena, salinity, or biogenic fractionation effects. This leaves open the perennial arguments for a change in 18O /16O of sea water versus warmer ancient oceans. The present data are difficult to explain solely by the temperature alternative. The coincidence of the proposed shift in δ 18O with the large Late Paleozoic changes in marine 87Sr /86Sr , 13C /12C , 34S /32S , and "sea level stands" argues for a tectonic cause and for a change in 18O /16O of sea water, although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites. Whatever the precise cause, or combination of causes, the implications for tectonism and/or paleoclimatology are of first order significance.

  9. Correlation of stable oxygen isotope temperature record with light attenuation profiles in reef-dwelling Tridacna shells

    NASA Astrophysics Data System (ADS)

    Pätzold, J.; Heinrichs, J. P.; Wolschendorf, K.; Wefer, G.

    1991-06-01

    Molluscs are known to record environmental changes in their carbonate shells in detail. This paper reports the findings of a high-resolution analysis of stable oxygen isotopic compositions and light transmission properties of a shell of the reef-dwelling Pacific giant clam Tridacna gigas. Our findings reveal that the annual growth rates and the longevity of Tridacna specimens can be readily determined by measuring the annual light attenuation pattern within the shell. Annual seasonal changes in water temperature are reflected with high resolution in the stable oxygen isotope ratios and in the light attenuation values of the aragonite shell. The inner shell of T. gigas deposited below the pallial line revealing undisturbed shell accretion with high growth rates shows the maximum seasonal oxygen isotope range and the highest resolution in light attenuation changes. We suggest that this is the best part of the shell to reconstruct former seasonal surface water temperatures in tropical environments. Scanning electron microscopy (SEM) studies suggest that the annual growth patterns observed in transmitted light are generated by a complex pattern of daily growth increments with varying sizes of skeletal crystallites and varying amounts of organic carbon.

  10. A High-resolution Detrital and Oxygen Isotope Record from Flemish Pass, Labrador Sea

    NASA Astrophysics Data System (ADS)

    deJesus, E.; Hoffman, J. S.; Clark, P. U.; Mix, A. C.

    2014-12-01

    High-resolution records of deglacial paleoceanographic change along the Labrador shelf are scarce. However, they are required in order to characterize and understand possible ice-ocean interactions involving the eastern sector of the Laurentide Ice Sheet (LIS). We have generated a high-resolution stable isotope and detrital stratigraphic record for core HU2001043-008 (990m, 48° N, 45° W) from Flemish Pass, Labrador Sea, to better understand the role of LIS ice-rafting events in abrupt climate changes during the last glaciation. Samples at two-centimeter resolution were disaggregated, washed, and picked for Neogloboquandrina pachyderma (sinistral) for stable isotope and radiocarbon analysis. The δ18O signal in foraminiferal calcite allows us to examine surface-ocean changes that may indicate an influx of freshwater, which may or may not be related to an LIS ice-rafting event. Our results will help in developing a better understanding of the source of LIS ice-rafting events, precursory indicators of the events, and how these events are associated with changes in deep-water formation in the Labrador Sea.

  11. Stable carbon and oxygen isotope record of central Lake Erie sediments

    USGS Publications Warehouse

    Tevesz, M.J.S.; Spongberg, A.L.; Fuller, J.A.

    1998-01-01

    Stable carbon and oxygen isotope data from mollusc aragonite extracted from sediment cores provide new information on the origin and history of sedimentation in the southwestern area of the central basin of Lake Erie. Sediments infilling the Sandusky subbasin consist of three lithologic units overlying glacial deposits. The lowest of these is a soft gray mud overlain by a shell hash layer containing Sphaerium striatinum fragments. A fluid mud unit caps the shell hash layer and extends upwards to the sediment-water interface. New stable isotope data suggest that the soft gray mud unit is of postglacial, rather than proglacial, origin. These data also suggest that the shell hash layer was derived from erosional winnowing of the underlying soft gray mud layer. This winnowing event may have occurred as a result of the Nipissing flood. The Pelee-Lorain moraine, which forms the eastern boundary of the Sandusky subbasin, is an elevated area of till capped by a sand deposit that originated as a beach. The presence of both the shell hash layer and relict beach deposit strengthens the interpretation that the Nipissing flood was a critical event in the development of the southwestern area of the central basin of Lake Erie. This event, which returned drainage from the upper lakes to the Lake Erie basin, was a dominant influence on regional stratigraphy, bathymetry, and depositional setting.

  12. The correlation between the magnetic paleoclimatic record of the Chinese eolian sequences and the marine benthic oxygen isotope record during the past 6 Myr

    NASA Astrophysics Data System (ADS)

    Nie, J.; King, J. W.

    2012-12-01

    Global cooling in the Cenozoic, leading to the growth of large continental ice sheets in both hemispheres, may have been caused by the uplift of the Tibetan Plateau and the positive feedbacks initiated by it. However, the details remain to be clarified. An ideal place to study detailed sedimentary and climatic processes associated with Tibetan uplift is the Chinese Loess Plateau (CLP), which is immediately adjacent to northeastern Tibet. Here we review recent progresses in correlating the magnetic susceptibility record of the eolian sequences on the CLP with the benthic oxygen isotope records over the past 6 Myr. Magnetic susceptibility of the eolian sequences on the CLP and the benthic oxygen isotope reflect intensity of the East Asian summer monsoon (EASM) and global ice volume, respectively. We then present new results about correlation patterns between the magnetic grain size records and the benthic oxygen isotope records over the past 6 Myr. We found a good correlation between the magnetic susceptibility record and the benthic oxygen isotope record in the past 6 Myr except during 4.5-2.7 Ma. We attributed this lack of correlation between these two records at the interval to closure of the Panama Seaway and uplift of the Tibetan Plateau. We also found that the 400-kyr eccentricity signals intensified at around 4 Ma in the Chinese eolian sequences. This intensification synchronizes with intensification of the 400-kyr signals in ice volume records. We proposed that the EASM system and ice volume probably crossed a rainfall amount threshold and a low temperature threshold, respectively, crossing which the two systems have a clipped response to insolation forcing. Thus, 400-kyr signals got intensified in these two kinds of sedimentary records. We hypothesize that uplift of the Tibetan Plateau is the required forcing for pushing these two systems to cross these two thresholds at ~4 Ma. In addition to the 400-kyr cycles, we also examined the 100-kyr cycles in the

  13. Stable oxygen and hydrogen isotope analyses of bowhead whale baleen as biochemical recorders of migration and arctic environmental change

    NASA Astrophysics Data System (ADS)

    deHart, Pieter A. P.; Picco, Candace M.

    2015-06-01

    An analysis of the stable isotopes of oxygen (δ18O) and hydrogen (δD) was used to examine the linkage between sea ice concentration and the migration of western arctic bowhead whales (Balaena mysticetus; WABW). We compared δ18O and δD variability along the length of WABW baleen with isotopic values of zooplankton prey from different WABW habitat, with published δ13C and δ15N data, and with historical sea ice records. Zooplankton signatures varied widely (δ18O = -13‰-56‰; δD = -220‰ to -75‰), with regional separation between winter (Bering Sea) and summer (eastern Beaufort Sea) habitats of WABW observable in δD. The δ18O and δD of WABW varied significantly along the length of baleen (δ18O = 8-18‰; δD = -180 to -80‰), confirming seasonal migration and reflecting distinct regional dietary variation in isotopes. WABW migration appears to have varied concomitant with temporal sea ice concentration (SIC) changes; in years with high SIC, the difference in δD of WABW baleen between seasonal habitats was significantly greater than low SIC periods. This work shows that SIC is not only a determinant of habitat accessibility for WABW, but baleen may also be a record of historical SIC and Arctic climate.

  14. Characterizing seawater oxygen isotopic variability in a regional ocean modeling framework: Implications for coral proxy records

    NASA Astrophysics Data System (ADS)

    Stevenson, S.; Powell, B. S.; Merrifield, M. A.; Cobb, K. M.; Nusbaumer, J.; Noone, D.

    2015-11-01

    Reconstructions of the El Niño-Southern Oscillation (ENSO) are often created using the oxygen isotopic ratio in tropical coral skeletons (δ18O). However, coral δ18O can be difficult to interpret quantitatively, as it reflects changes in both temperature and the δ18O value of seawater. Small-scale (10-100 km) processes affecting local temperature and seawater δ18O are also poorly quantified and contribute an unknown amount to intercoral δ18O offsets. A new version of the Regional Ocean Modeling System capable of directly simulating seawater δ18O (isoROMS) is therefore presented to address these issues. The model is used to simulate δ18O variations over the 1979-2009 period throughout the Pacific at coarse (O(50 km)) resolution, in addition to 10 km downscaling experiments covering the central equatorial Pacific Line Islands, a preferred site for paleo-ENSO reconstruction from corals. A major impact of downscaling at the Line Islands is the ability to resolve fronts associated with tropical instability waves (TIWs), which generate large excursions in both temperature and seawater δ18O at Palmyra Atoll (5.9°N, 162.1°W). TIW-related sea surface temperature gradients are smaller at neighboring Christmas Island (1.9°N, 157.5°W), but the interaction of mesoscale features with the steep island topography nonetheless generates cross-island temperature differences of up to 1°C. These nonlinear processes alter the slope of the salinity:seawater δ18O relationship at Palmyra and Christmas, as well as affect the relation between coral δ18O and indices of ENSO variability. Consideration of the full physical oceanographic context of reef environments is therefore crucial for improving δ18O-based ENSO reconstructions.

  15. A cryptic record of magma mixing in diorites revealed by high-precision SIMS oxygen isotope analysis of zircons

    NASA Astrophysics Data System (ADS)

    Appleby, S. K.; Graham, C. M.; Gillespie, M. R.; Hinton, R. W.; Oliver, G. J. H.; EIMF

    2008-05-01

    High-precision in-situ ion microprobe (SIMS) oxygen isotope analysis of zircons from two diorite intrusions associated with the late Caledonian Lochnagar pluton in Scotland has revealed large differences in the degree of heterogeneity in zircon δ18O between the diorites. Zircon crystals from the Cul nan Gad diorite (CnG) show a unimodal distribution of oxygen isotope values ( δ18O = 6.0 ± 0.6‰ (2 σ)) and no or only minor grain-scale variation. Those from the Allt Darrarie diorite (AD1) show a large range in δ18O and an apparent bimodal distribution with modes of 6.6 ± 0.4‰ and 7.3 ± 0.4‰. Variations of up to 1.2‰ occur between and within grains; both an increase and decrease in δ18O with zircon growth has been observed. The δ18O composition of growing zircon can only change if open-system processes affect the magma composition, i.e. if material of contrasting δ18O composition is added to the magma. The variability in AD1 is interpreted to represent a cryptic record of magma mixing. A 'deep crustal hot zone' is a likely site for generation of the dioritic magmas which developed by mixing of residual melts and crustal partial melts or by melting of mafic lower crustal rocks. The overall small number of zircons with mantle-like δ18O values (5.3 ± 0.6‰ (2 σ)) in the Lochnagar diorites is largely the product of crustal differentiation rather than crustal growth. The δ18O of quartz from the CnG and AD1 diorites shows only minor variation (CnG: 10.9 ± 0.5‰ (2 σ), AD1: 11.7 ± 0.6‰ (2 σ)) within single populations, with no evidence of mixing. Quartz-zircon isotopic disequilibrium is consistent with later crystallisation of quartz from late magmatic fluids, and in case of the AD1 diorite after the inferred magma mixing from a homogenised, higher δ18O melt. High-precision SIMS oxygen isotope analysis of zircon provides a new approach to identifying and resolving previously undetected early-stage magma mixing and constraining the compositions

  16. Oxygen Isotope Speleothem record of Decadal and Multidecadal Atlantic Oscillations over the last millennium in Southwestern Morocco

    NASA Astrophysics Data System (ADS)

    Ait Brahim, Yassine; Sha, LiJuan; Sifeddine, Abdelfettah; Cheng, Hai; Bouchaou, Lhoussaine; Da Cruz Junior, Francisco William; Khodri, Myriam; Peerbocus, Nawaaz; Mariller, Alexandre; Apaestegui, James; Guyot, Jean-Loup; Auler, Augusto; Hassane Beraaouz, El

    2016-04-01

    In this work, we present a stable oxygen isotope (δ18O) speleothem record from Ifoulki cave located South-West of Morocco (N 30°42'29'', W 09°19'39'' and 1267 meters above sea level). The age model, based on eighteen U-Th dates, reveals that the record covers the AD 790-1953 period with a data resolution of ~1.7 years. Stable oxygen isotope variations show substantial decadal to multi-decadal swings between dry and humid periods. The Medieval Climate Anomaly (MCA) is characterized by the longest period with δ18O values above the average, suggestive of pronounced drying possibly as a response to positive North Atlantic Oscillation (NAO) phases and increased volcanic activity during this period. However, at least two short wet phases are recognized during the MCA in Morocco, with peaks centered on the years AD 1040 and AD 1190 and seem to overlap with negative NAO phases as recorded in a recently published NAO reconstruction for the last millennium. During the next centuries, the NAO again depicts predominantly negative values and the δ18O drops below the average during the Little Ice Age (LIA). Furthermore, a striking resemblance is observed between our record and another recently published stalagmite record from the Piste cave in Northeastern Morocco, which is quite remarkable given the different type of tracers (δ18O vs. Mg and Sr) obtained from different environments (Western High Atlas vs. Northeastern Middle Atlas and ~634 km away). Comparison with regional paleorecords from other studies also reveals the replication of many characteristic climate features from the last millennium, first detected in Northern Morocco and the Iberian Peninsula. In particular, the evidence of generally dry conditions during the MCA and wetter conditions in the LIA, which is confirmed by all the paleorecords. These similarities indicate coherent climate variability in Northwest Africa and the Iberian Peninsula and suggest a strong regional control of the NAO during the last

  17. Paleomagnetic record from Academician Ridge, Lake Baikal: a reversal excursion at the base of marine oxygen isotope stage 6

    NASA Astrophysics Data System (ADS)

    Oda, H.; Nakamura, K.; Ikehara, K.; Nakano, T.; Nishimura, M.; Khlystov, O.

    2002-08-01

    Paleomagnetic and rock-magnetic studies on a hydraulic piston core (Ver98-1, St.6) from Academician Ridge, Lake Baikal showed the occurrence of a reversal excursion at 670-696 cm depth, which is at the base of marine oxygen isotope stage 6. A correlation of X-ray CT values, as a proxy of relative density, to the marine oxygen isotope record provides an age of 177-183 ka for this reversal excursion. It can be correlated with other excursion records from Lake Baikal, found in Core 287-K2 from Academician Ridge [King et al., Russ. Geol. Geophys. 34 (1993) 148-162] and in core BDP93-1 drilled on the Buguldeika saddle [BDP-93, Quat. Int. 37 (1997) 3-17]. We correlate the Lake Baikal reversal excursion with a well documented excursion in the Brunhes Chron, the Iceland Basin event (186-189 ka) from ODP Sites 983 and 984 in the North Atlantic [Channell, J. Geophys. Res. 104 (1999) 22937-22951]. Also the relative paleointensity record agrees well with that from ODP Site 983 [Channell, J. Geophys. Res. 104 (1999) 22937-22951]. The Lake Baikal excursion and the Iceland Basin event correspond to the minimum of relative intensity at 188 ka in Sint-800 [Guyodo and Valet, Nature 399 (1999) 249-252]. We argue that it is distinct from the Jamaica/Pringle Falls excursion, estimated at 205-215 ka [Langereis et al., Geophys. J. Int. 129 (1997) 75-94]. This is supported by the recalibration of the age of another excursion found in Core St.16 in Lake Baikal [Sakai et al., Bull. Nagoya Univ. Furukawa Mus. 13 (1997) 11-22] with an age of ˜223 ka, which is close to the age of the Jamaica/Pringle Falls excursion, as suggested earlier [King et al., Russ. Geol. Geophys. 34 (1993) 148-162]. The VGP path of the reversal excursion (177-183 ka) consists of a southward swing through the North Atlantic, followed by a loop through Africa and the Indian Ocean. The path morphology is similar to that of the Iceland Basin event from the North Atlantic [Channell, J. Geophys. Res. 104 (1999) 22937-22951].

  18. Patterns of moisture source and climate variability in the southeastern United States: a four-century seasonally resolved tree-ring oxygen-isotope record

    NASA Astrophysics Data System (ADS)

    Labotka, D. M.; Grissino-Mayer, H. D.; Mora, C. I.; Johnson, E. J.

    2016-04-01

    This study presents a climate reconstruction utilizing a seasonally resolved 417-year oxygen-isotope record of tree rings from southern Georgia, United States (1580-1997 CE). Oxygen isotopes within the cellulose predominately reflect moisture source observed on a seasonal scale between earlywood and latewood growth. Signatures of large climate oscillations were captured in modern and subfossil wood. Spectral and wavelet transform analyses of seasonally resolved oxygen isotopes showed distinct periodicities coinciding with the Atlantic multidecadal oscillation and other major climate oscillation phenomena. Oxygen-isotope values in latewood growth revealed a significant correlation with North Atlantic sea surface temperature anomalies. This correlation suggests that the precipitation source was strongly influenced by fluctuations in the Atlantic multidecadal oscillation and teleconnections with other major climate phenomena such as the North Atlantic subtropical high-pressure system, El Niño Southern Oscillation, and Pacific Decadal Oscillation. These results emphasize the utility of oxygen isotopes in tree rings for revealing seasonal influences associated with major climate drivers over centuries and enhance our understanding of long-term climate behavior on a detailed scale.

  19. Carbon and Oxygen Isotope Records from Tridacna derasa Shells: Toward Establishing a Reliable Proxy for Sea Surface Environments

    PubMed Central

    Yamanashi, Junpei; Takayanagi, Hideko; Isaji, Ayaka; Asami, Ryuji

    2016-01-01

    We report the carbon (δ13C) and oxygen (δ18O) isotope records of three modern Tridacna derasa shells from Ishigaki-jima, southwestern Japan. The high-resolution δ13C profiles of samples from the inner shell layer on cross-sections fall within similar narrow ranges and display no regular variations or trends, such as an ontogenetic trend or abrupt short-term drops likely to be related to reproductive activity. This suggests that the calcification site of this species is not likely affected by photosynthetic CO2 uptake or CO2 incorporation during respiration. The δ18O profiles show distinct seasonal cycles. The intraspecific variability in the δ18O values is small in parts of the shell precipitated in the adult stage, but is not negligible in the juvenile and senescent stages. The differences in the monthly and seasonally resolved δ18O values among shells are less than 0.51‰ and 0.76‰, respectively. The shell δ18O values are nearly identical or close to the δ18O values for aragonite precipitated in oxygen isotope equilibrium with ambient seawater (δ18OEA). The largest differences between the shell δ18O and δ18OEA values calculated from the monthly and seasonally resolved data correspond to an overestimate of the seawater temperature by as much as 1.7°C and 2.3°C, respectively. However, these differences are smaller in the adult stage (<0.25‰) than in the other stages. This small difference allows an accurate reconstruction of the seawater temperature with an error of <1.1°C. Consequently, we recommend that multiple shell records be obtained because of the non-negligible intraspecific variations in their δ18O values. Growth banding, composed of alternating narrow white bands and wide light-grey bands, is discernible on cross-sections of the inner shell layer. The δ18Oshell data indicate that they were formed in winter and the other seasons, respectively. PMID:27327430

  20. Carbon and Oxygen Isotope Records from Tridacna derasa Shells: Toward Establishing a Reliable Proxy for Sea Surface Environments.

    PubMed

    Yamanashi, Junpei; Takayanagi, Hideko; Isaji, Ayaka; Asami, Ryuji; Iryu, Yasufumi

    2016-01-01

    We report the carbon (δ13C) and oxygen (δ18O) isotope records of three modern Tridacna derasa shells from Ishigaki-jima, southwestern Japan. The high-resolution δ13C profiles of samples from the inner shell layer on cross-sections fall within similar narrow ranges and display no regular variations or trends, such as an ontogenetic trend or abrupt short-term drops likely to be related to reproductive activity. This suggests that the calcification site of this species is not likely affected by photosynthetic CO2 uptake or CO2 incorporation during respiration. The δ18O profiles show distinct seasonal cycles. The intraspecific variability in the δ18O values is small in parts of the shell precipitated in the adult stage, but is not negligible in the juvenile and senescent stages. The differences in the monthly and seasonally resolved δ18O values among shells are less than 0.51‰ and 0.76‰, respectively. The shell δ18O values are nearly identical or close to the δ18O values for aragonite precipitated in oxygen isotope equilibrium with ambient seawater (δ18OEA). The largest differences between the shell δ18O and δ18OEA values calculated from the monthly and seasonally resolved data correspond to an overestimate of the seawater temperature by as much as 1.7°C and 2.3°C, respectively. However, these differences are smaller in the adult stage (<0.25‰) than in the other stages. This small difference allows an accurate reconstruction of the seawater temperature with an error of <1.1°C. Consequently, we recommend that multiple shell records be obtained because of the non-negligible intraspecific variations in their δ18O values. Growth banding, composed of alternating narrow white bands and wide light-grey bands, is discernible on cross-sections of the inner shell layer. The δ18Oshell data indicate that they were formed in winter and the other seasons, respectively. PMID:27327430

  1. On the Use of Biomineral Oxygen Isotope Data to Identify Human Migrants in the Archaeological Record: Intra-Sample Variation, Statistical Methods and Geographical Considerations.

    PubMed

    Lightfoot, Emma; O'Connell, Tamsin C

    2016-01-01

    Oxygen isotope analysis of archaeological skeletal remains is an increasingly popular tool to study past human migrations. It is based on the assumption that human body chemistry preserves the δ18O of precipitation in such a way as to be a useful technique for identifying migrants and, potentially, their homelands. In this study, the first such global survey, we draw on published human tooth enamel and bone bioapatite data to explore the validity of using oxygen isotope analyses to identify migrants in the archaeological record. We use human δ18O results to show that there are large variations in human oxygen isotope values within a population sample. This may relate to physiological factors influencing the preservation of the primary isotope signal, or due to human activities (such as brewing, boiling, stewing, differential access to water sources and so on) causing variation in ingested water and food isotope values. We compare the number of outliers identified using various statistical methods. We determine that the most appropriate method for identifying migrants is dependent on the data but is likely to be the IQR or median absolute deviation from the median under most archaeological circumstances. Finally, through a spatial assessment of the dataset, we show that the degree of overlap in human isotope values from different locations across Europe is such that identifying individuals' homelands on the basis of oxygen isotope analysis alone is not possible for the regions analysed to date. Oxygen isotope analysis is a valid method for identifying first-generation migrants from an archaeological site when used appropriately, however it is difficult to identify migrants using statistical methods for a sample size of less than c. 25 individuals. In the absence of local previous analyses, each sample should be treated as an individual dataset and statistical techniques can be used to identify migrants, but in most cases pinpointing a specific homeland should not

  2. On the Use of Biomineral Oxygen Isotope Data to Identify Human Migrants in the Archaeological Record: Intra-Sample Variation, Statistical Methods and Geographical Considerations

    PubMed Central

    Lightfoot, Emma; O’Connell, Tamsin C.

    2016-01-01

    Oxygen isotope analysis of archaeological skeletal remains is an increasingly popular tool to study past human migrations. It is based on the assumption that human body chemistry preserves the δ18O of precipitation in such a way as to be a useful technique for identifying migrants and, potentially, their homelands. In this study, the first such global survey, we draw on published human tooth enamel and bone bioapatite data to explore the validity of using oxygen isotope analyses to identify migrants in the archaeological record. We use human δ18O results to show that there are large variations in human oxygen isotope values within a population sample. This may relate to physiological factors influencing the preservation of the primary isotope signal, or due to human activities (such as brewing, boiling, stewing, differential access to water sources and so on) causing variation in ingested water and food isotope values. We compare the number of outliers identified using various statistical methods. We determine that the most appropriate method for identifying migrants is dependent on the data but is likely to be the IQR or median absolute deviation from the median under most archaeological circumstances. Finally, through a spatial assessment of the dataset, we show that the degree of overlap in human isotope values from different locations across Europe is such that identifying individuals’ homelands on the basis of oxygen isotope analysis alone is not possible for the regions analysed to date. Oxygen isotope analysis is a valid method for identifying first-generation migrants from an archaeological site when used appropriately, however it is difficult to identify migrants using statistical methods for a sample size of less than c. 25 individuals. In the absence of local previous analyses, each sample should be treated as an individual dataset and statistical techniques can be used to identify migrants, but in most cases pinpointing a specific homeland should

  3. The carbon and oxygen isotope records of reef-dwelling foraminifers subjected to five varied pCO2 seawater

    NASA Astrophysics Data System (ADS)

    Hikami, M.; Ishimura, T.; Suzuki, A.; Nojiri, Y.; Kawahata, H.

    2013-12-01

    Ocean acidification (OA) in response to rising atmospheric pCO2 is generally expected to reduce rates of calcification by reef calcifying organisms, with potentially severe implications for coral reef ecosystems. Reef dwelling foraminifera is one of the most important primary and carbonate producers in coral reef environments. Their shells are composed of high-Mg calcite and they are host to algal endosymbionts. In our previous culture experiment with two algal reef dwelling foraminifers, Amphisorus kudakajimensis and Calcarina gaudichaudii in the seawater of five different pCO2 conditions, net calcification of A. kudakajimensis was reduced under higher pCO2, whereas net calcification of C. gaudichaudii showed continued increasing trend with pCO2. These contrasting responses between the two species are possibly due to differences in calcification mechanisms and to links between calcification by the foraminifers and photosynthesis by the algal endosymbionts. But the factors affecting these calcification mechanisms are poorly understood. In this study, to get a better understanding of the effect of OA on their calcification, we cultured three reef dwelling foraminifers: Amphisorus hemprichii, belong to imperforate species, Baculogypsina sphaerulata, and C. gaudichaudii belong to perforate species, in the seawater of five different pCO2 conditions and we address the response of carbon and oxygen isotopes of the carbonate shells of foraminifers. The oxygen isotope ratio of cultured foraminiferal tests under five varied pCO2 seawater indicated no significant correlation to pCO2 values. On the other hand, the carbon isotope ratio of foraminiferal tests indicated heavy trend with rising pCO2 in all species. Alteration of carbonate chemistry result from ocean acidification may be effect strongly on carbon isotope composition relate to metabolic system (i.e. photosynthesis and respiration). In perforate species, both of oxygen and carbon isotope ratio were lighter than that

  4. Early Cenomanian "hot greenhouse" revealed by oxygen isotope record of exceptionally well-preserved foraminifera from Tanzania

    NASA Astrophysics Data System (ADS)

    Ando, Atsushi; Huber, Brian T.; MacLeod, Kenneth G.; Watkins, David K.

    2015-11-01

    The search into Earth's mid-Cretaceous greenhouse conditions has recently been stimulated by the Tanzania Drilling Project (TDP) which has recovered exceptionally well-preserved biogenic carbonates from subsurface pre-Neogene marine sediments in the eastern margin of central Africa. Published Tanzanian oxygen isotope records measured on exquisitely preserved foraminiferal tests, dating to as old as ~93 Ma, provided evidence for a Turonian "hot greenhouse" with very high and stable water-column temperatures. We have generated a comparable data set of exceptionally well-preserved foraminifera from a lower Cenomanian interval of TDP Site 24 spanning 99.9-95.9 Ma (planktonic foraminiferal Thalmanninella globotruncanoides Zone; nannofossil Corollithion kennedyi to Lithraphidites eccentricus Zones), thereby extending the age coverage of the Tanzanian foraminiferal δ18O record back by ~7 million years. Throughout the interval analyzed, the new foraminiferal δ18O data are consistently around -4.3‰ for surface-dwelling planktonic taxa and -1.9‰ for benthic Lenticulina spp., which translate to conservative paleotemperature estimates of >31°C at the surface and >17°C at the sea floor (upper bathyal depths). Considering the ~40°S Cenomanian paleolatitude of TDP Site 24, these estimates are higher than computer simulation results for accepted "normal" greenhouse conditions (those with up to 4X preindustrial pCO2 level) and suggest that the climate mode of the early Cenomanian was very similar to the Turonian hot greenhouse. Taking account of other comparable data sources from different regions, the hot greenhouse mode within the normal mid-Cretaceous greenhouse may have begun by the latest Albian, but the precise timing of the critical transition remains uncertain.

  5. Triple oxygen isotopes and clumped isotopes in modern vertebrate and dinosaur biominerals: Records of paleoecology, paleoaridity, and paleo-carbon-cycling

    NASA Astrophysics Data System (ADS)

    Hu, H.; Passey, B. H.; Lehmann, S. B.; Levin, N. E.; Montanari, S.; Chin, K.; Johnson, B. J.

    2015-12-01

    The parameter Δ17O describes the departure of δ17O from an expected equilibrium relationship with δ18O, which can be caused by factors such as evaporation of parent waters, and photochemical reactions among oxygen-bearing gases in stratosphere. Hence, the Δ17O of water records information about environmental aridity, and the Δ17O of atmospheric O2 is related to atmospheric concentrations of CO2 and O2, and gross primary productivity (GPP). Vertebrates incorporate Δ17O signals of input water (e.g. drinking water and free food water) and atmospheric O2 into body water through respiration, and biominerals forming in equilibrium with body water can preserve this signal over geological timescales. The preservation of fossil biominerals can be evaluated by clumped isotopes as they record the temperature of mineralization, be it primary mineralization in the living animal (at body temperature), or secondary mineralization during diagenesis. We can distinguish the alteration of samples from the deviation between observed clumped isotope temperatures and plausible body temperatures. Meanwhile, diagenesis tends to moderate Δ17O of biominerals towards Δ17O of meteoric waters, such that measured Δ17O values reflect the minimum anomaly in fossil samples. Thus, preservation of anomalous Δ17O indicates at least partial preservation of the original signal. We present Δ17O data from both modern vertebrate and fossil dinosaur biominerals. We use a 17O-enabled body water model to explore the influence of aridity and dietary ecology on animal Δ17O, and to predict the degree of dilution of the atmospheric O2 Δ17O signal by other sources of oxygen to the animal. We observe: 1) animals consuming more leaf water than drinking water are "evaporation sensitive" (ES) animals, and have lower Δ17O relative to "evaporation insensitive" animals in the same climates; 2) ES animals from arid climates have lower Δ17O values compared to ES animals from humid climates, which forms the

  6. Oxygen isotope geospeedometry by SIMS

    NASA Astrophysics Data System (ADS)

    Bonamici, C. E.; Valley, J. W.

    2013-12-01

    Geospeedometry, a discipline closely related and complimentary to thermochronology, exploits the phenomenon of diffusion in order to extract rate and duration information for segments of a rock's thermal history. Geospeedometry data, when anchored in absolute time by geochronologic data, allow for the construction of detailed temperature-time paths for specific terranes and geologic processes. We highlight the developing field of SIMS-based oxygen isotope geospeedometry with an application from granulites of the Adirondack Mountains (New York) and discuss potential future applications based on a recently updated and expanded modeling tool, the Fast Grain Boundary diffusion program (FGB; Eiler et al. 1994). Equilibrium oxygen isotope ratios in minerals are a function of temperature and bulk rock composition. In dynamic systems, intragrain oxygen isotope zoning can develop in response to geologic events that affect the thermal state of a rock and/or induce recrystallization, especially tectonic deformation and fluid infiltration. As an example, titanite grains from late-Grenville shear zones in the northwestern Adirondack Mountains exhibit a range of δ18O zoning patterns that record post-peak metamorphic cooling, episodic fluid infiltration, and deformation-facilitated recrystallization. Many titanite grains preserve smooth, core-to-rim decreasing, diffusional δ18O profiles, which are amenable to diffusion modeling. FGB models that best fit the measured δ18O profiles indicate cooling from ~700-500°C in just 2-5 m.y., a rapid thermal change signaling the final gravitational collapse of the late-Grenville orogen. Titanite can also be utilized as a U-Pb chronometer, and comparison of δ18O and U-Pb age zoning patterns within the Adirondack titanites pins the episode of rapid cooling inferred from the δ18O record to some time between 1054 and 1047 Ma. The expanded capabilities of FGB also allow for evaluation of a range of heating-cooling histories for the

  7. Isotopic and hydrologic responses of small, closed lakes to climate variability: Comparison of measured and modeled lake level and sediment core oxygen isotope records

    NASA Astrophysics Data System (ADS)

    Steinman, Byron A.; Abbott, Mark B.; Nelson, Daniel B.; Stansell, Nathan D.; Finney, Bruce P.; Bain, Daniel J.; Rosenmeier, Michael F.

    2013-03-01

    Simulations conducted using a coupled lake-catchment isotope mass balance model forced with continuous precipitation, temperature, and relative humidity data successfully reproduce (within uncertainty limits) long-term (i.e., multidecadal) trends in reconstructed lake surface elevations and sediment core oxygen isotope (δ18O) values at Castor Lake and Scanlon Lake, north-central Washington. Error inherent in sediment core dating methods and uncertainty in climate data contribute to differences in model reconstructed and measured short-term (i.e., sub-decadal) sediment (i.e., endogenic and/or biogenic carbonate) δ18O values, suggesting that model isotopic performance over sub-decadal time periods cannot be successfully investigated without better constrained climate data and sediment core chronologies. Model reconstructions of past lake surface elevations are consistent with estimates obtained from aerial photography. Simulation results suggest that precipitation is the strongest control on lake isotopic and hydrologic dynamics, with secondary influence by temperature and relative humidity. This model validation exercise demonstrates that lake-catchment oxygen isotope mass balance models forced with instrumental climate data can reproduce lake hydrologic and isotopic variability over multidecadal (or longer) timescales, and therefore, that such models could potentially be used for quantitative investigations of paleo-lake responses to hydroclimatic change.

  8. Long-distance relationship between large-scale tropical SSTs and ice core-derived oxygen isotopic records in the Third Pole Region

    NASA Astrophysics Data System (ADS)

    Thompson, L. G.; Yao, T.; Mosley-Thompson, E. S.; Lin, P.

    2012-12-01

    The tropical hydrological cycle is a key factor coupling isotopic records from ice core, speleothem and lake records with tropical SSTs and the vertical amplification of temperature in the Tropics. Stable isotopic ratios, particularly of oxygen, preserved in glacier ice provide high resolution records of climate changes over long time periods. In polar ice sheets the isotopic signal is driven primarily by temperature while in low-latitudes it depends on a variety of hydrologic and thermal influences in the broad geographic region that supplies moisture to the mountain glaciers. The strong correlation between ice core-derived isotopic records throughout the low- and mid-latitudes and tropical SSTs likely reflects the dominance of tropical evaporation in the flux of water vapor to the atmosphere and provides a possible explanation for the large-scale isotopic links among low- and mid-latitude paleoclimate records. Many low- to mid-latitude ice fields provide continuous, annually-resolved proxy records of climatic and environmental variability recorded by many preserved and measurable parameters including oxygen and hydrogen isotopic ratios and net mass balance (accumulation). These records present an opportunity to examine the nature of climate variability in these regions in greater detail and to extract new information about long-distance relationships in the climate system. Understanding these relationships is essential for proper interpretation of the isotopic records archived in glaciers, lakes, speleothems and other paleo-archives in the Third Pole (TP) Region. Here we compare high resolution records from Dasuopu Glacier in the Himalaya, a speleothem record from Wanxiang Cave in Gansu Province on the TP and the annually resolved ice core records from the Quelccaya Ice Cap in the tropical Andes of South America. The purpose is to explore the role of long-distance processes in determining the isotopic composition of paleo archives on the TP. Running correlations

  9. Punctuated evolution of global climate cooling during the late middle to early late Miocene: High-resolution planktonic foraminiferal and oxygen isotope records from the Mediterranean

    NASA Astrophysics Data System (ADS)

    Turco, E.; Hilgen, F. J.; Lourens, L. J.; Shackleton, N. J.; Zachariasse, W. J.

    High-resolution planktonic foraminiferal and oxygen isotope records are presented from a Mediterranean deep marine succession, dated astronomically between 12.12 and 9.78 Ma. Planktonic and benthic oxygen isotope records are punctuated by two episodes of δ18O increase, which have astronomical ages of 11.4 and 10.4 Ma and correspond to the Mi5 and Mi6 events of Miller et al. [1991a]. These ice growth events coincide with low-amplitude variations in the 1.2 Myr obliquity cycle and are accompanied by significant faunal changes in the Mediterranean, such as the arrival of neogloboquadrinids, the increase in abundance of the G. apertura-G. obliquus group, and the areal differentiation between N. atlantica and N. acostaensis. Short-term variations in the planktonic foraminiferal and oxygen isotope records correspond to dominantly precession-controlled sedimentary cycles. Features of the sapropel/gray marl layers indicate that the short-term astronomically controlled circum-Mediterranean climate changes remained basically the same over the last 12 Myr.

  10. Living on the edge: The oxygen isotope record of Eocene Basins at the margin of the Cenozoic North American plateau

    NASA Astrophysics Data System (ADS)

    Methner, Katharina; Mulch, Andreas; Chamberlain, Page

    2013-04-01

    Topography has a strong impact on atmospheric circulation and precipitation patterns and is a key element in reconstructing the dynamics of mountain building processes. The topographic evolution of the world's major orogens remains one of the most important questions when discussing the interactions among tectonics, climate, and Earth surface processes. Here, we focus on the spatial and temporal development of topography and relief in the western North American Cordillera and how changes in the topography may have affected precipitation patterns and vice versa. In this context, we sampled more than 20 sections in Eocene to Oligocene terrestrial (intermontane?) basins (Chumstick, Swauk, and Chuckanut) in western and central Washington (USA) to the W and E of the modern Cascades. Oxygen isotope analysis of pedogenic carbonate in these sections allows us to reconstruct the isotopic composition of ancient soilwater or groundwater, and ultimately precipitation. Oxygen isotope measurements of pedogenic concretions and calcic horizons interestingly yield uniformly low δ18O values of 10 to 13‰ SMOW despite the proximity of all sections to the Pacific moisture source. These extremely low oxygen isotope values can result from (1) highly 18O-depleted meteoric waters (soil- or groundwater), (2) burial diagenesis at moderate temperatures and interaction with 18O-depleted (ground)water, and (3) high burial temperatures and and exchange with basins brines. Vitrinite reflectance data and preservation of primary soil structures such as rootlets, root casts, burrows, or even preserved wood fragments clearly show that some of the low-d18O sections were not affected by high degrees of burial diagenesis. Thus, we believe that the primary isotopic signal of ancient soil- or groundwater is preserved at least in parts (if not in all) of these basins. Low δ18O values of pedogenic carbonate require highly 18O-depleted meteoric water, which in turn, would require high elevation either at

  11. Spatial and temporal oxygen isotope variability in northern Greenland - implications for a new climate record over the past millennium

    NASA Astrophysics Data System (ADS)

    Weißbach, S.; Wegner, A.; Opel, T.; Oerter, H.; Vinther, B. M.; Kipfstuhl, S.

    2015-06-01

    We present for the first time all 12 δ18O records obtained from ice cores drilled in the framework of the North Greenland Traverse (NGT) between 1993 and 1995 in northern Greenland between 74 to 80° N, 36 to 49° W and 2000 to 3200 m a.s.l. The cores cover an area of 680 km × 317 km, ~200 000 km2 or 10 % of the area of Greenland. Depending on core length (100-175 m) and accumulation rate (90-200 kg m-2 a-1) the records reflect an isotope-temperature history over the last 500-1100 years. The δ18O signal in northern Greenland is influenced by temperature, accumulation and the topography of the North Greenland ice sheet between 72 and 80° N. About 12 % of the variability can be attributed to the position of the single drill sites in relation to the ice sheet topography. Lowest δ18O mean values occur north of summit and east of the main divide. In general, ice cores drilled on the main ice divide show different results than those drilled east of the main ice divide that might be influenced by secondary regional moisture sources. A stack of all 12 NGT records and the NGRIP record is presented with improved signal-to-noise ratio. This stack represents the mean δ18O signal for northern Greenland that is interpreted as proxy for temperature. Our northern Greenland δ18O stack indicates isotopically enriched periods compared to their average during medieval times, about 1420 ± 20 AD and from 1870 AD onwards. The period between 1420 AD and 1850 AD was isotopically depleted compared to the average for the entire millennium and represents the Little Ice Age. The 20th century has isotopic values higher than the 1000 years mean and is comparable to the medieval period but lower than about 1420 AD.

  12. Punctuated Evolution of Global Climate Cooling during the late Middle to early Late Miocene: High-Resolution Planktonic Foraminiferal and Oxygen Isotope Records from the Mediterranean

    NASA Astrophysics Data System (ADS)

    Turco, E.; Hilgen, F. J.; Lourens, L. J.; Shackleton, N. J.; Zachariasse, W. J.; Kruk, R. W.

    2001-05-01

    High-resolution planktonic foraminiferal and oxygen isotope records are presented from a deep marine succession of late Middle to early Late Miocene age in the Mediterranean, dated astronomically between 12.12 and 9.78 Ma. Long-term changes in the faunal composition reflect the overall late Neogene cooling trend. The planktonic and benthic oxygen isotope records are punctuated by two episodes of δ 18O increase, which have astronomical ages of 11.4 and 10.4 Ma and correspond to the Mi5 and Mi6 events of Miller et al. (1991a). The first-order comparison with the astronomical time series for the variations in the tilt of the Earth's axis revealed that these ice growth events coincide with low amplitude variations in the 1.2 myr obliquity cycle. This phase relation is different from that found during the last 5 myr, pointing to a fundamentally different response of the ice sheets to long-term obliquity induced variations in insolation. The inferred global cooling during Mi5 and Mi6 is accompanied by significant faunal changes in the Mediterranean, such as the arrival of neogloboquadrinids, the increase in abundance of the G. apertura-G. obliquus group, and the areal differentiation between N. atlantica and N. acostaensis. Other faunal events, such as the disappearance of P. mayeri and the coiling changes in neogloboquadrinids are not related to these glacial episodes, but may have been controlled by short-term climate fluctuations superimposed on long-term astronomically and/or tectonically induced climate changes. Short-term variations in the planktonic foraminiferal and oxygen isotope records correspond to dominantly precession-controlled sedimentary cycles. The micropaleontological and stable isotopic features of sapropel/grey marl layers are identical to those observed for Late Miocene to Pleistocene sapropels, indicating that the short-term astronomically controlled circum-Mediterranean climate changes remained basically the same over the last 12 myr.

  13. Stable carbon isotopes of C3 plant resins and ambers record changes in atmospheric oxygen since the Triassic

    NASA Astrophysics Data System (ADS)

    Tappert, Ralf; McKellar, Ryan C.; Wolfe, Alexander P.; Tappert, Michelle C.; Ortega-Blanco, Jaime; Muehlenbachs, Karlis

    2013-11-01

    Estimating the partial pressure of atmospheric oxygen (pO2) in the geological past has been challenging because of the lack of reliable proxies. Here we develop a technique to estimate paleo-pO2 using the stable carbon isotope composition (δ13C) of plant resins-including amber, copal, and resinite-from a wide range of localities and ages (Triassic to modern). Plant resins are particularly suitable as proxies because their highly cross-linked terpenoid structures allow the preservation of pristine δ13C signatures over geological timescales. The distribution of δ13C values of modern resins (n = 126) indicates that (a) resin-producing plant families generally have a similar fractionation behavior during resin biosynthesis, and (b) the fractionation observed in resins is similar to that of bulk plant matter. Resins exhibit a natural variability in δ13C of around 8‰ (δ13C range: -31‰ to -23‰, mean: -27‰), which is caused by local environmental and ecological factors (e.g., water availability, water composition, light exposure, temperature, nutrient availability). To minimize the effects of local conditions and to determine long-term changes in the δ13C of resins, we used mean δ13C values (δ13Cmeanresin) for each geological resin deposit. Fossil resins (n = 412) are generally enriched in 13C compared to their modern counterparts, with shifts in δ13Cmeanresin of up to 6‰. These isotopic shifts follow distinctive trends through time, which are unrelated to post-depositional processes including polymerization and diagenesis. The most enriched fossil resin samples, with a δ13Cmeanresin between -22‰ and -21‰, formed during the Triassic, the mid-Cretaceous, and the early Eocene. Experimental evidence and theoretical considerations suggest that neither change in pCO2 nor in the δ13C of atmospheric CO2 can account for the observed shifts in δ13Cmeanresin. The fractionation of 13C in resin-producing plants (Δ13C), instead, is primarily influenced by

  14. Oxygen and carbon isotopic growth record in a reef coral from the florida keys and a deep-sea coral from blake plateau

    USGS Publications Warehouse

    Emiliani, C.; Harold, Hudson J.; Shinn, E.A.; George, R.Y.

    1978-01-01

    Carbon and oxygen isotope analysis through a 30-year (1944 to 1974) growth of Montastrea annularis from Hen and Chickens Reef (Florida Keys) shows a strong yearly variation in the abundances of both carbon-13 and oxygen-18 and a broad inverse relationship between the two isotopes. Normal annual dense bands are formed during the summer and are characterized by heavy carbon and light oxygen. "Stress bands" are formed during particularly severe winters and are characterized by heavy carbon and heavy oxygen. The isotopic effect of Zooxanthellae metabolism dominates the temperature effect on the oxygen-18/oxygen-16 ratio. The isotopic results on the deep-sea solitary coral Bathypsammia tintinnabulum, where Zooxanthellae are nonexistent, indicates that the abundance of the heavy isotopes carbon-13 and oxygen-18 is inversely related to the growth rate, with both carbon and oxygen approaching equilibrium values with increasing skeletal age.

  15. Oxygen isotope heterogeneity of arc magma recorded in plagioclase from the 2010 Merapi eruption (Central Java, Indonesia)

    NASA Astrophysics Data System (ADS)

    Borisova, Anastassia Y.; Gurenko, Andrey A.; Martel, Caroline; Kouzmanov, Kalin; Cathala, Annick; Bohrson, Wendy A.; Pratomo, Indyo; Sumarti, Sri

    2016-10-01

    Chemical and isotopic compositions of magmatic crystals provide important information to distinguish between deep juvenile and crustal contributions. In this work, high-resolution multicollector secondary ion mass spectrometry data reveal strong variations of δ18O values in three plagioclase crystals (800-1700 μm) from two representative basaltic andesite samples of the 2010 Merapi eruption (Central Java, Indonesia). The δ18O values (from 4.6‰ to 7.9‰) are interpreted to reflect oxygen isotope heterogeneity in the melt composition during plagioclase growth. The lowest δ18O values (4.6-6.6‰) are found in anorthite-rich cores (An82-97), whereas higher δ18O values (5.7-7.9‰) are found in anorthite-poorer zones (An33-86), typically in crystal rims. Combining these new plagioclase δ18O data with δ18O of calc-silicate crustal xenoliths erupted between 1994 and 1998, the composition of glass inclusions hosted by the anorthite-rich plagioclase (An82-92), available experimental data, and the results of thermodynamic modeling using the Magma Chamber Simulator code, we conclude that the abundant anorthite-rich cores crystallized from a mantle-derived hydrous basaltic to basaltic trachyandesite melt that recharged a deeper (200-600 MPa) magma storage zone, whereas lower anorthite zones crystallized at shallower levels (100-200 MPa). The oxygen isotope variations in the plagioclase are explained by a two-stage model of interaction of the hydrous, mafic mantle-derived magma (1) with old crustal rocks depleted in 18O due to high temperature alteration that yielded the low δ18O values in the anorthite-rich cores at deep levels (13-20 km), and later (2) with 18O-enriched carbonate material that yielded the high δ18O values in anorthite-poorer zones at shallow levels (∼4.5-9 km). Thermodynamic modeling is consistent with ∼18 wt.% assimilation of crustal calc-silicate material at 925-950 °C and 100-200 MPa by the 2010 Merapi basaltic andesite magma prior to

  16. Spatial and temporal oxygen isotope variability in northern Greenland - implications for a new climate record over the past millennium

    NASA Astrophysics Data System (ADS)

    Weißbach, S.; Wegner, A.; Opel, T.; Oerter, H.; Vinther, B. M.; Kipfstuhl, S.

    2016-02-01

    We present for the first time all 12 δ18O records obtained from ice cores drilled in the framework of the North Greenland Traverse (NGT) between 1993 and 1995 in northern Greenland. The cores cover an area of 680 km × 317 km, 10 % of the Greenland ice sheet. Depending on core length (100-175 m) and accumulation rate (90-200 kg m-2 a-1) the single records reflect an isotope-temperature history over the last 500-1100 years. Lowest δ18O mean values occur north of the summit and east of the main divide as a consequence of Greenland's topography. In general, ice cores drilled on the main ice divide show different results than those drilled east of the main ice divide that might be influenced by secondary regional moisture sources. A stack of all NGT records and the NGRIP record is presented with improved signal-to-noise ratio. Compared to single records, this stack represents the mean δ18O signal for northern Greenland that is interpreted as proxy for temperature. Our northern Greenland δ18O stack indicates distinctly enriched δ18O values during medieval times, about AD 1420 ± 20 and from AD 1870 onwards. The period between AD 1420 and AD 1850 has depleted δ18O values compared to the average for the entire millennium and represents the Little Ice Age. The δ18O values of the 20th century are comparable to the medieval period but are lower than that about AD 1420.

  17. An oxygen isotope record of prograde and retrograde subduction fluids preserved in garnets from eclogite and related rocks from California and Greece

    NASA Astrophysics Data System (ADS)

    Page, F.; Strickland, A.; Essene, E. J.; Valley, J. W.

    2012-12-01

    In situ analysis of oxygen isotopes in garnet formed during subduction metamorphism offers a powerful new tool to unravel fluid histories of eclogite and related rocks. Slow intracrystalline diffusion rates in garnet allow it to preserve primary oxygen isotope ratios, and its utility in thermobarometry and geochronology allows oxygen isotope ratios to be tied to a P-T-t-fluids path. These paths can be used to identify when, in the history of a rock, fluid infiltration took place. Application of this method to orogenic eclogites has demonstrated external fluid interaction during prograde metamorphism (Russell et al., 2012 CMP in press). Analyses of garnets from metamafic and metasedimentary blocks in mélange-type subduction environments reveal a greater diversity in the timing of fluid infiltration events than those found in continental collision zones. Garnets from two glaucophane eclogites from Syros, Greece were found to be homogeneous within analytical uncertainty (δ18O=3.6±0.5‰ 2SD; 4.6±0.4‰). This result is consistant with existing studies in the region demonstrating limited fluid flow in eclogite blocks during metamorphism. Cation and oxygen isotope zoning in garnet from tectonic blocks of eclogite and garnet hornblendite from the Franciscan Formation reveals separate prograde and retrograde fluid histories. Garnet cores preserve a homogeneous prograde δ18O history with both high (11‰) and low (4‰) values in different samples. Multiple episodes of garnet resorption and regrowth record a dramatically changing bulk oxygen composition resulting in 6-7‰ neoformed garnet rims in both samples. Thermobarometry of inclusions (grt+cpx+phg) in eclogite garnet rims yields lower pressure blueschist-facies PT, requiring that low-δ18O fluid infiltration and garnet rim growth post-dates substantial exhumation. Tectonic blocks of metamafic and metasedimentary rocks are found in mélange on Santa Catalina Island. Samples of garnet hornblendite and garnet

  18. A High Resolution Absolute-dated Oxygen Isotope Record of the Past 7000 Years from Spring Valley Caverns, Southeastern MN, USA

    NASA Astrophysics Data System (ADS)

    Dasgupta, S.; Edwards, R. L.; Alexander, E. C.; Cheng, H.; Dorale, J. A.

    2005-12-01

    Two stalagmites, SV982 (3 thousand years (kyr)-present) and SV983 (7.8 kyr-present), from Spring Valley Caverns, southeastern Minnesota, USA contain records of oxygen isotopic variation in that cave for the past 7 kyr, which have been measured with an average time resolution of 10 years. The two stalagmites show similar patterns of stable isotopic variations for the overlapping portions of the records. An absolute chronology was constructed for stalagmite SV983 using 36 230Th dates (typical 2σ relative error of 2%) coupled with annual band counting. For SV982, only the past 270 years were studied and part of the record from 1998 to 1900 A.D. was compared with instrumental climate record from the nearby town of Spring Valley, Minnesota. The δ 18 values correlate positively with the local mean annual temperature but show no apparent correlation with mean annual precipitation. The δ 18 agree closely with other climate records from the region (Dorale J.A. et al. 1992 Science 258, 1626-1630; Laird K.R. et al. 1996 LO 41, 890-902) demonstrating their significance as regional palaeoclimatic indicators. Several abrupt decadal to centennial scale shifts in δ 18 values are found ranging in magnitude from 0.6‰ to 2.7‰. Preliminary dating shows that these abrupt shifts in δ 18 values are centered at 6.5 (2.7‰), 4.6 (1.9‰), 3.4 (1.8‰) and 0.5 kyr (1.3‰). The 3.4 kyr event shows heavier δ 18 values corresponding to increase in temperature while all the other events are associated with decrease in δ 18 values and hence, decrease in temperature. The 6.5 kyr event was a shift from a several-century long cooling trend to an equally long warming trend. Comparing our record with the GISP2 δ 18 record (Grootes, P.M. et al. 1997 JGR 102, 26455-26470) from Greenland we find notable similarities in the decadal and centennial scale events, while the long term trends are more pronounced in our record. The δ 18 record from Spring Valley Caverns appears to be the best

  19. Sea surface temperatures in the central southern Indian Ocean over the period 1790 to 2007 inferred from two monthly resolved Sr/Ca and oxygen isotope records

    NASA Astrophysics Data System (ADS)

    Zinke, J.; Wassenburg, J.; Hardman, E.

    2009-04-01

    We obtained two monthly resolved Sr/Ca records from Rodrigues island (Mauritius) located in the trade wind belt of the central southern Indian Ocean. The longest core was obtained at a nearshore fringing reef and covers the period 1790-2005. This coral records surface air temperatures from the local weather station available from 1950 to the present. The most remarkable signal is a slight cooling after the 1950's. The second core was obtained from the open ocean and records a long-term warming trend between 1947 to 2007. The warming accelerated after the late 1970's in agreement with instrumental data. The oxygen isotope record is affected by salinity variations and shows a strong freshening trend after the late 1970's. The freshening trend is probably related to advection of low salinity waters with the South Equatorial Current and/or increased cyclonicity. We will discuss our results in light of interannual and decadal variability and present long-term seawater monitoring data.

  20. Late Pleistocene paleoclimatic history documented by an oxygen isotope record from carbonate sediments in Qarhan Salt Lake, NE Qinghai-Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Fan, QiShun; Ma, HaiZhou; Wei, HaiCheng; Shan, FaShou; An, FuYuan; Xu, LiMing; Madsen, David B.

    2014-05-01

    Late Pleistocene paleoclimatic variability on the northeastern Qinghai-Tibetan Plateau (NE QTP) was reconstructed using a chronology based on AMS 14C and 230Th dating results and a stable oxygen isotopic record. These are derived from lake carbonates in a 102-m-long Qarhan sediment core (ISL1A) collected from the eastern Qaidam Basin. Previous research indicates that the δ18O values of lacustrine carbonates are mainly controlled by the isotopic composition of lake water, which in turn is a function of regional P/E balance and the proportion of precipitation that is monsoon-derived on the NE QTP. Modern isotopic observations indicate that the δ18O values of lake carbonates in hyper-arid Qaidam Basin are more positive during the warm and wet period. Due to strong evaporation and continental effect in this basin, the positive δ18O values in the arid region indicate drier climatic conditions. Based on this interpretation and the δ18O record of fine-grained lake carbonates and dating results in ISL1A, the results imply that drier climatic conditions in the Qarhan region occurred in three intervals, around 90-80 ka, 52-38 ka and 10-9 ka, which could correspond to late MIS 5, middle MIS 3 and early Holocene, respectively. These three phases were almost coincided with low lake level periods of Gahai, Toson and Qinghai Lakes (to the east of Qarhan Lake) influenced by ASM on the orbital timescales. Meanwhile, there was an episode of relatively high δ18O value during late MIS 3, suggesting that relatively dry climatic condition in this period, rather than “a uniform Qarhan mega-paleolake” spanning the ˜44 to 22 ka period. These results insight into the understanding of “the Greatest Lake Period” on the QTP.

  1. A 430 year record of hydroclimate variability for NE-Germany based on stable carbon and oxygen isotopes from pine and oak tree rings

    NASA Astrophysics Data System (ADS)

    Helle, Gerhard; Baschek, Heiko; Heinrich, Ingo; Navabzadeh, Nadia; Riedel, Frank; Wilmking, Martin; Heußner, Karl-Uwe

    2016-04-01

    European lowlands experience many direct and indirect influences of global warming, particularly related to the hydrological cycle which lately faces increasing flood and drought events. Although important for humans and the ecosystems in which they live, little is known about the long-term spatiotemporal hydrological changes in various European regions. Here we present the first 430-year stable carbon and oxygen chronologies from tree ring cellulose in lowland oak and pine trees (P. sylvestris, Q. petraea) for the region of NE-Germany and provide annually resolved high quality hydroclimatic reconstructions. When compared to ring width data isotope data can be used with only minor adjustments to their means (besides correction of short juvenile trends) and sample depths of 4-5 trees are normally enough for a significant expressed population signal being representative for a site. For this study more than 20 individual tree ring sub-samples for isotopic analyses were obtained from well replicated tree ring chronologies built using living trees as well as historical timber originating from four different lowland sites (50-90m asl.). By a calibration and verification approach we have evaluated the response to instrumental climate and trends of atmospheric partial pressure of CO2 (13C, only) data. While ring widths shows strong correlation to winter temperature, highly significant correlations with summer (JJA) hydroclimate conditions were found for both tree ring 13C and 18O. Strongest relationships were found with summer water vapour pressure deficit (13C and 18O) and Tmax (JJA). Although significant, relationships between 13C and climate data were found considerably weaker than climate/18O relations. On the other hand, the 13C record reveals high similarity with solar irradiance, whereas 18O does not. Based on this profound calibration the presentation will show and discuss annually resolved hydroclimatic variability of the region from our multi-centennial isotope

  2. Oxygen isotope studies and compilation of isotopic dates from Antarctica

    SciTech Connect

    Grootes, P.M.; Stuiver, M.

    1986-01-01

    The Quaternary Isotope Laboratory, alone or in collaboration with other investigators, is currently involved in a number of oxygen-isotope studies mainly in Antarctica. Studies of a drill core from the South Pole, seasonal oxygen-18 signals preserved in the Dominion Range, isotope dating of the Ross Ice Shelf, oxygen-18 profiles of the Siple Coast, McMurdo Ice Shelf sampling, and a data compilation of radiometric dates from Antarctica are discussed.

  3. Spatial and temporal variation in tree-ring α-cellulose oxygen and hydrogen isotope values as a record of water availability in the Atacama Desert

    NASA Astrophysics Data System (ADS)

    Olson, E. J.; Dodd, J. P.

    2015-12-01

    Previous studies have documented that tree ring oxygen and hydrogen isotopes primarily reflect source water; however, biosynthetic fractionation processes modify this signal and can have a varied response to environmental conditions. The degree to which source water contributes to δ2H and δ18O values of plant α-cellulose is species-specific and modern calibration studies are necessary. Here we present a calibration data set of P. tamarugo α-cellulose δ2H and δ18O values from the Atacama Desert in Northern Chile. P. tamarugo trees are endemic to the region and have adapted to the extremely arid environment where average annual precipitation is < 5mm/yr. This modern isotope chronology has been constructed from living P. tamarugo trees (n=12) from the Pampa del Tamarugal Basin in the northern Atacama. Generally, the tree-ring α-cellulose δ18O values are poorly correlated with meteorological data from coastal stations (i.e. Iquique); however, there is good agreement between regional groundwater depth and α-cellulose δ18O values. Most notably, average α-cellulose δ18O values increase by >2 ‰ over the past 20 years associated with a ~1.1 m lowering of the local groundwater table throughout the area. The correlation between a-cellulose isotope values and hydrologic conditions in modern times provides a baseline for interpretation of tree-ring isotope chronologies from the past 9.5 kya. A high-resolution Holocene (1.8-9.1 kya) age record of Prosopis sp. tree ring α-cellulose δ18O values provides a proxy for climatic and hydrologic conditions. During the early Holocene δ18O values range from 31 to 35‰ (2σ=0.58‰), while during the late Holocene values are much more variable (27.4 to 41‰; 2σ=2.64‰). Anthropogenic demand on local water sources is the most significant environmental factor affecting the variation in modern α-cellulose δ18O values; however, climate induced changes in regional water availability are the dominant driver of variability

  4. Device and method for separating oxygen isotopes

    DOEpatents

    Rockwood, Stephen D.; Sander, Robert K.

    1984-01-01

    A device and method for separating oxygen isotopes with an ArF laser which produces coherent radiation at approximately 193 nm. The output of the ArF laser is filtered in natural air and applied to an irradiation cell where it preferentially photodissociates molecules of oxygen gas containing .sup.17 O or .sup.18 O oxygen nuclides. A scavenger such as O.sub.2, CO or ethylene is used to collect the preferentially dissociated oxygen atoms and recycled to produce isotopically enriched molecular oxygen gas. Other embodiments utilize an ArF laser which is narrowly tuned with a prism or diffraction grating to preferentially photodissociate desired isotopes. Similarly, desired mixtures of isotopic gas can be used as a filter to photodissociate enriched preselected isotopes of oxygen.

  5. Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

    USGS Publications Warehouse

    Anderson, Lesleigh; Max Berkelhammer,; Barron, John A.; Steinman, Byron A.; Finney, Bruce P.; Abbott, Mark B.

    2016-01-01

    Lake sediment oxygen isotope records (calcium carbonate-δ18O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean–atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ18O records along with a new compilation of lake water δ18O and δ2H that are used to characterize lake sediment sensitivity to precipitation-δ18O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ18O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north–south precipitation-δ18O patterns that is evidence for a highly non-stationary influence by Pacific ocean–atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ18O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ18O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean–atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north–south precipitation-δ18O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean–atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ18O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the

  6. Lake oxygen isotopes as recorders of North American Rocky Mountain hydroclimate: Holocene patterns and variability at multi-decadal to millennial time scales

    NASA Astrophysics Data System (ADS)

    Anderson, Lesleigh; Berkelhammer, Max; Barron, John A.; Steinman, Byron A.; Finney, Bruce P.; Abbott, Mark B.

    2016-02-01

    Lake sediment oxygen isotope records (calcium carbonate-δ18O) in the western North American Cordillera developed during the past decade provide substantial evidence of Pacific ocean-atmosphere forcing of hydroclimatic variability during the Holocene. Here we present an overview of 18 lake sediment δ18O records along with a new compilation of lake water δ18O and δ2H that are used to characterize lake sediment sensitivity to precipitation-δ18O in contrast to fractionation by evaporation. Of the 18 records, 14 have substantial sensitivity to evaporation. Two records reflect precipitation-δ18O since the middle Holocene, Jellybean and Bison Lakes, and are geographically positioned in the northern and southern regions of the study area. Their comparative analysis indicates a sequence of time-varying north-south precipitation-δ18O patterns that is evidence for a highly non-stationary influence by Pacific ocean-atmosphere processes on the hydroclimate of western North America. These observations are discussed within the context of previous research on North Pacific precipitation-δ18O based on empirical and modeling methods. The Jellybean and Bison Lake records indicate that a prominent precipitation-δ18O dipole (enriched-north and depleted-south) was sustained between ~ 3.5 and 1.5 ka, which contrasts with earlier Holocene patterns, and appears to indicate the onset of a dominant tropical control on North Pacific ocean-atmosphere dynamics. This remains the state of the system today. Higher frequency reversals of the north-south precipitation-δ18O dipole between ~ 2.5 and 1.5 ka, and during the Medieval Climate Anomaly and the Little Ice Age, also suggest more varieties of Pacific ocean-atmosphere modes than a single Pacific Decadal Oscillation (PDO) type analogue. Results indicate that further investigation of precipitation-δ18O patterns on short (observational) and long (Holocene) time scales is needed to improve our understanding of the processes that drive

  7. A deglacial and Holocene record of climate variability in south-central Alaska from stable oxygen isotopes and plant macrofossils in peat

    USGS Publications Warehouse

    Jones, Miriam C.; Wooller, Matthew J.; Peteet, Dorothy M.

    2014-01-01

    We used stable oxygen isotopes derived from bulk peat (δ18OTOM), in conjunction with plant macrofossils and previously published carbon accumulation records, in a ∼14,500 cal yr BP peat core (HT Fen) from the Kenai lowlands in south-central Alaska to reconstruct the climate history of the area. We find that patterns are broadly consistent with those from lacustrine records across the region, and agree with the interpretation that major shifts in δ18OTOM values indicate changes in strength and position of the Aleutian Low (AL), a semi-permanent low-pressure cell that delivers winter moisture to the region. We find decreased strength or a more westerly position of the AL (relatively higher δ18OTOM values) during the Bølling-Allerød, Holocene Thermal Maximum (HTM), and late Holocene, which also correspond to warmer climate regimes. These intervals coincide with greater peat preservation and enhanced carbon (C) accumulation rates at the HT Fen and with peatland expansion across Alaska. The HTM in particular may have experienced greater summer precipitation as a result of an enhanced Pacific subtropical high, a pattern consistent with modern δ18O values for summer precipitation. The combined warm summer temperatures and greater summer precipitation helped promote the observed rapid peat accumulation. A strengthened AL (relatively lower δ18OTOM values) is most evident during the Younger Dryas, Neoglaciation, and the Little Ice Age, consistent with lower peat preservation and C accumulation at the HT Fen, suggesting less precipitation reaches the leeward side of the Kenai Mountains during periods of enhanced AL strength. The peatlands on the Kenai Peninsula thrive when the AL is weak and the contribution of summer precipitation is higher, highlighting the importance of precipitation seasonality in promoting peat accumulation. This study demonstrates that δ18OTOM values in peat can be applied toward understand large-scale shifts in atmospheric circulation

  8. Oxygen stable isotope ratios from British oak tree-rings provide a strong and consistent record of past changes in summer rainfall

    NASA Astrophysics Data System (ADS)

    Young, Giles H. F.; Loader, Neil J.; McCarroll, Danny; Bale, Roderick J.; Demmler, Joanne C.; Miles, Daniel; Nayling, Nigel T.; Rinne, Katja T.; Robertson, Iain; Watts, Camilla; Whitney, Matthew

    2015-12-01

    United Kingdom (UK) summers dominated by anti-cyclonic circulation patterns are characterised by clear skies, warm temperatures, low precipitation totals, low air humidity and more enriched oxygen isotope ratios (δ18O) in precipitation. Such conditions usually result in relatively more positive (enriched) oxygen isotope ratios in tree leaf sugars and ultimately in the tree-ring cellulose formed in that year, the converse being true in cooler, wet summers dominated by westerly air flow and cyclonic conditions. There should therefore be a strong link between tree-ring δ18O and the amount of summer precipitation. Stable oxygen isotope ratios from the latewood cellulose of 40 oak trees sampled at eight locations across Great Britain produce a mean δ18O chronology that correlates strongly and significantly with summer indices of total shear vorticity, surface air pressure, and the amount of summer precipitation across the England and Wales region of the United Kingdom. The isotope-based rainfall signal is stronger and much more stable over time than reconstructions based upon oak ring widths. Using recently developed methods that are precise, efficient and highly cost-effective it is possible to measure both carbon (δ13C) and oxygen (δ18O) isotope ratios simultaneously from the same tree-ring cellulose. In our study region, these two measurements from multiple trees can be used to reconstruct summer temperature (δ13C) and summer precipitation (δ18O) with sufficient independence to allow the evolution of these climate parameters to be reconstructed with high levels of confidence. The existence of long, well-replicated oak tree-ring chronologies across the British Isles mean that it should now be possible to reconstruct both summer temperature and precipitation over many centuries and potentially millennia.

  9. Combined oxygen- and carbon-isotope records through the Early Jurassic: multiple global events and two modes of carbon-cycle/temperature coupling

    NASA Astrophysics Data System (ADS)

    Hesselbo, S. P.; Korte, C.

    2010-12-01

    The Jurassic comprises some 55 million years of Earth history. However, within the Jurassic, only one major environmental change (hyperthermal) event is really well known - the Early Toarcian Oceanic Anoxic Event (OAE) at ~183 Ma - and until very recently the extent to which the accompanying environmental changes were global has been strongly debated. Nevertheless, partly as a result of the international effort to define Global Stratotype Sections and Points (GSSPs), much more is now being discovered about environmental changes taking place at and around the other Jurassic Age (Stage) boundaries, to the extent that meaningful comparisons between these events can begin to be made. Here we present new carbon and oxygen isotope data from mollusks (bivalves and belemnites) and brachiopods collected through the marine Early Jurassic succession of NE England, including the Sinemurian-Plienbachian boundary GSSP. All materials have been screened by chemical analysis and scanning electron microscopy to check for diagenetic alteration. Analysis of carbon isotopes from marine calcite is supplemented by analysis of carbon-isotope values from fossil wood collected through the same section. It is demonstrated that both long-term and short-term carbon-isotope shifts from the UK Early Jurassic represent global changes in carbon cycle balances. The Sinemurian-Pliensbachian boundary event is an event of global significance and shows several similarities to the Toarcian OAE (relative sea-level change, carbon-isotope signature), but also some significant contrasts (oxygen-isotope based paleotemperatures which provide no evidence for warming). Significant contrast in oxygen- and carbon-isotope co-variation also occurs on a long timescale. There appear to be two modes in the co-variation of carbon and oxygen isotopes through this time interval: mode 1 shows positive correlation and may be explained by conventional sources and sinks for carbon-dioxide; mode 2, representing negative

  10. Interdecadal-decadal climate variability from multicoral oxygen isotope records in the South Pacific Convergence Zone region since 1650 A.D.

    NASA Astrophysics Data System (ADS)

    Linsley, Braddock K.; Zhang, Peipei; Kaplan, Alexey; Howe, Stephen S.; Wellington, Gerard M.

    2008-06-01

    In the South Pacific, interdecadal-decadal oceanic and atmospheric variability, referred to as the Interdecadal Pacific Oscillation (IPO), is most pronounced in the South Pacific Convergence Zone (SPCZ) salinity front region. Here we have used annual average oxygen isotope (δ18O) time series from five coral cores collected from Fiji and Tonga in this region to construct a Fiji-Tonga Interdecadal-Decadal Pacific Oscillation (F-T IDPO) index of low-frequency (>9 and <55 years) climate variability back to 1650 A.D. We first demonstrate the consistency between this F-T IDPO index and a mean sea level (MSL) pressure-based SPCZ position index (SPI) (1891-2000), thus verifying the ability of coral δ18O to record past interdecadal-decadal climatic variations in this region back to 1891. The F-T IDPO index is then shown to be synchronous with the IPO index (1856-2000), suggesting that this coral-based index effectively represents the interdecadal-decadal scale climate variance back to 1650. The regularity of the F-T IDPO index indicates that interdecadal-decadal variability in the SPCZ region has been relatively constant over the past 350 years with a mean frequency of ˜20 years (variance peaks near 11 and 35 years). There is a consistent antiphase correlation of the F-T IDPO index and the interdecadal-decadal components in equatorial Pacific coral δ18O series from Maiana and Palmyra. This observation indicates that the eastward expansion (westward contraction) of the eastern salinity front of the Western Pacific Warm Pool (WPWP) occurs simultaneously (±<1 year) with the westward (eastward) shift of the SPCZ salinity front during positive IPO (negative IPO) phases. This is the same relationship observed during the phases of the El Niño Southern Oscillation.

  11. A continuous 250,000 yr record of oxygen and carbon isotopes in ostracode and bulk-sediment carbonate from Bear Lake, Utah-Idaho

    USGS Publications Warehouse

    Bright, Jordon; Kaufman, D.S.; Forester, R.M.; Dean, W.E.

    2006-01-01

    Oxygen and carbon isotopes from a continuous, 120-m-long, carbonate-rich core from Bear Lake, Utah-Idaho, document dramatic fluctuations in the hydrologic budget of the lake over the last 250,000 yr. Isotopic analyses of bulk sediment samples capture millennial-scale variability. Ostracode calcite was analyzed from 78 levels, mainly from the upper half of the core where valves are better preserved, to compare the isotopic value of purely endogenic carbonate with the bulk sediment, which comprises both endogenic and detrital components. The long core exhibits three relatively brief intervals with abundant endogenic aragonite (50??10%) and enriched ??18O and ??13C. These intervals are interpreted as warm/dry periods when the lake retracted into a topographically closed basin. We correlate these intervals with the interglacial periods of marine oxygen-isotope stages 1, 5e, and 7a, consistent with the presently available geochronological control. During most of the time represented by the core, the lake was fresher than the modern lake, as evidenced by depleted ??18O and ??13C in bulk-sediment carbonate. ?? 2006 Elsevier Ltd. All rights reserved.

  12. Oxygen isotope relationships in iron meteorites

    NASA Technical Reports Server (NTRS)

    Clayton, R. N.; Mayeda, T. K.; Olsen, E. J.; Prinz, M.

    1983-01-01

    Iron meteorites with oxygen-bearing phases can be classified in terms of their oxygen isotopic abundances. These iron meteorite classes are isotopically similar to various stony meteorite classes, which may indicate a common origin. The group IAB and IIICD irons may be related to the winonaites; group IIE irons may be related to H chondrites; group IVA irons may be related to L or LL chondrites.

  13. Normalization of oxygen and hydrogen isotope data

    USGS Publications Warehouse

    Coplen, T.B.

    1988-01-01

    To resolve confusion due to expression of isotopic data from different laboratories on non-corresponding scales, oxygen isotope analyses of all substances can be expressed relative to VSMOW or VPDB (Vienna Peedee belemnite) on scales normalized such that the ??18O of SLAP is -55.5% relative to VSMOW. H3+ contribution in hydrogen isotope ratio analysis can be easily determined using two gaseous reference samples that differ greatly in deuterium content. ?? 1988.

  14. Position-specific measurement of oxygen isotope ratios in cellulose: Isotopic exchange during heterotrophic cellulose synthesis

    NASA Astrophysics Data System (ADS)

    Waterhouse, John S.; Cheng, Shuying; Juchelka, Dieter; Loader, Neil J.; McCarroll, Danny; Switsur, V. Roy; Gautam, Lata

    2013-07-01

    We describe the first reported method for the measurement of oxygen isotope ratios at each position in the glucose units of the cellulose molecule. The overall process comprises a series of synthetic organic sequences, by which α-cellulose is hydrolysed to glucose, and oxygen atoms at specific positions in the glucose molecule are removed in samples of benzoic acid for measurement of δ18O. Values of δ18O at specific positions in cellulose are calculated from these δ18O values and the overall δ18O value of the cellulose. We apply the method to determine the degree to which oxygen atoms at each position undergo isotopic exchange with water during heterotrophic cellulose synthesis, such as occurs in the cambium of trees. To do this we extract α-cellulose from wheat seedlings germinated in the dark in aqueous media of differing oxygen isotope ratios. Results indicate that oxygen atoms at positions 5 and 6 (O-5 and O-6 respectively) undergo around 80% exchange with medium water, O-3 undergoes around 50% exchange, and O-2 and O-4 do not undergo isotopic exchange. The results have important implications for extracting palaeoclimatic records from oxygen isotope time series obtained from tree ring cellulose. As O-5 and O-6 undergo significant exchange with medium water during heterotrophic cellulose synthesis, oxygen isotopes at these positions in tree ring cellulose should carry a predominantly trunk (source) water signal. On the other hand, O-2 and O-4 should retain the isotopic signature of leaf water in tree ring cellulose. Our method therefore potentially enables the separate reconstruction of past temperature and humidity data from oxygen isotope ratios of tree ring cellulose - something that has hitherto not been possible. The measured degrees of isotopic exchange are to some extent unexpected and cannot be fully explained using current biochemical mechanisms, suggesting that knowledge of these processes is incomplete.

  15. Oxygen isotope perspective on crustal evolution on early Earth: A record of Precambrian shales with emphasis on Paleoproterozoic glaciations and Great Oxygenation Event

    NASA Astrophysics Data System (ADS)

    Bindeman, I. N.; Bekker, A.; Zakharov, D. O.

    2016-03-01

    We present stable isotope and chemical data for 206 Precambrian bulk shale and tillite samples that were collected mostly from drillholes on all continents and span the age range from 0.5 to 3.5 Ga with a dense coverage for 2.5-2.2 Ga time interval when Earth experienced four Snowball Earth glaciations and the irreversible rise in atmospheric O2. We observe significant, downward shift of several ‰ and a smaller range of δ18 O values (7 to 9‰) in shales that are associated with the Paleoproterozoic and, potentially, Neoproterozoic glaciations. The Paleoproterozoic samples consist of more than 50% mica minerals and have equal or higher chemical index of alteration than overlying and underlying formations and thus underwent equal or greater degrees of chemical weathering. Their pervasively low δ18 O and δD (down to - 85 ‰) values provide strong evidence of alteration and diagenesis in contact with ultra-low δ18 O glacial meltwaters in lacustrine, deltaic or periglacial lake (sikussak-type) environments associated with the Paleoproterozoic glaciations. The δDsilicate values for the rest of Precambrian shales range from -75 to - 50 ‰ and are comparable to those for Phanerozoic and Archean shales. Likewise, these samples have similar ranges in δ13Corg values (-23 to - 33 ‰ PDB) and Corg content (0.0 to 10 wt%) to Phanerozoic shales. Precambrian shales have a large range of δ18 O values comparable to that of the Phanerozoic shales in each age group and formation, suggesting similar variability in the provenance and intensity of chemical weathering, except for the earliest 3.3-3.5 Ga Archean shales, which have consistently lower δ18 O values. Moreover, Paleoproterozoic shales that bracket in age the Great Oxidation Event (GOE) overlap in δ18 O values. Absence of a step-wise increase in δ18 O and δD values suggests that despite the first-order change in the composition of the atmosphere, weathering cycle was not dramatically affected by the GOE at ∼2

  16. A Deglacial and Holocene Record of Climate Variability in South-Central Alaska from Stable Oxygen Isotopes and Plant Macrofossils in Peat

    NASA Technical Reports Server (NTRS)

    Jones, Miriam C.; Wooller, Matthew; Peteet, Dorothy M.

    2014-01-01

    We used stable oxygen isotopes derived from bulk peat (delta-O-18(sub TOM) in conjunction with plant macrofossils and previously published carbon accumulation records, in a approximately14,500 cal yr BP peat core (HT Fen) from the Kenai lowlands in south-central Alaska to reconstruct the climate history of the area. We find that patterns are broadly consistent with those from lacustrine records across the region, and agree with the interpretation that major shifts in delta-O-18(sub TOM) values indicate changes in strength and position of the Aleutian Low (AL), a semi-permanent low-pressure cell that delivers winter moisture to the region. We find decreased strength or a more westerly position of the AL (relatively higher delta-O-18(sub TOM) values) during the Bolling-Allerod, Holocene Thermal Maximum (HTM), and late Holocene, which also correspond to warmer climate regimes. These intervals coincide with greater peat preservation and enhanced carbon (C) accumulation rates at the HT Fen and with peatland expansion across Alaska. The HTM in particular may have experienced greater summer precipitation as a result of an enhanced Pacific subtropical high, a pattern consistent with modern delta-O-18 values for summer precipitation. The combined warm summer temperatures and greater summer precipitation helped promote the observed rapid peat accumulation. A strengthened AL (relatively lower delta-O-18(sub TOM) values) is most evident during the Younger Dryas, Neoglaciation, and the Little Ice Age, consistent with lower peat preservation and C accumulation at the HT Fen, suggesting less precipitation reaches the leeward side of the Kenai Mountains during periods of enhanced AL strength. The peatlands on the Kenai Peninsula thrive when the AL is weak and the contribution of summer precipitation is higher, highlighting the importance of precipitation seasonality in promoting peat accumulation. This study demonstrates that delta-O-18(sub TOM) values in peat can be applied

  17. Age and origin of post collision Baltoro granites, south Karakoram, North Pakistan: Insights from in-situ U-Pb, Hf and oxygen isotopic record of zircons

    NASA Astrophysics Data System (ADS)

    Mahar, Munazzam Ali; Mahéo, Gweltaz; Goodell, Philip C.; Pavlis, Terry L.

    2014-09-01

    Origin of post collision plutonism is critical to understand the tectonothermal evolution of the over thickened continental crust in collision zones. This has proven difficult to reconcile with the conventional whole rock geochemical and field based studies alone. We report in-situ study of zircon U-Pb, Hf and O isotopes from five samples of the Baltoro Plutonic Unit (BPU) in south Karakoram. The plutonic unit is the western part of the southern Asian margin of the India-Asia convergent zone. Baltoro granites and a biotite-rich enclave yielded similar and overlapping U-Pb ages ranging from 26 to 15 Ma. Hafnium isotopic composition (εHf (0)) is very heterogeneous ranging from - 17.1 to + 4.4 while the oxygen isotopic composition of the granites is homogeneous with mean δ18O ranging from 7.2 to 9.4‰. Based on U-Pb geochronology and Hf-O isotopic composition, the involvement of two main sources is suggested (1) Cretaceous calc-alkaline Karakoram crust and (2) Karakoram gneisses. Moreover, possible involvement of metasomatized Asian lithospheric mantle is supported by elevated oxygen composition of granites and identical Hf composition of biotite-rich enclave to the mantle derived Baltoro lamprophyre. However, direct contribution from juvenile pristine mantle is unlikely as no juvenile mantle type Hf and oxygen values were obtained. This also precludes the involvement of southward juvenile arc related component of Kohistan-Ladakh batholith. Our new U-Pb and Hf data are comparable to the Mesozoic Karakoram batholith, Miocene two-mica leucogranites in the Pangong Range and magmatism from the Lhasa terrane in south Tibet, suggesting a genetic link between the Karakoram and the rocks to the east. This magmatic event is best explained by lower crust partial melting promoted by both thermal equilibration following crustal thickening and heat advection by ultrapotassic magmas associated with the breakoff of the Indian continental margin.

  18. Variations in groundwater availability during the past 9,000 years in the Atacama Desert, Chile: A subannual record of oxygen isotope values from Prosopis tamarugo tree rings

    NASA Astrophysics Data System (ADS)

    Dodd, J. P.; Rivera, M.

    2012-12-01

    The Atacama Desert is among the driest regions on Earth; therefore, access to water is critical to human populations throughout the Pampa del Tamarugal region of northern Chile (20° to 22°S, 69° to 70°W). Presently, the region receives <5 mm of precipitation annually, and seasonal runoff and groundwater recharge from higher altitudes in the Andes Mountains is the primary source of water in the Pampa del Tamarugal. Oxygen isotope data from Prosopis tamarugo tree rings indicate that the region has become increasingly arid over the past 9ka, likely as a result of decreased water transport from these recharge areas. Oxygen isotope values from α-cellulose of P. tamarugo tree rings from the Llamara Basin (9130 ±145 and 7910 to 7870 ±10 Cal BP), Ramaditas (2615 ±135 Cal BP), and La Tirana Refresco (modern) record sub-annual variations in groundwater availability in the Pampa del Tamarugal. Low δ18O values (23.8 to 32.8‰) in the P. tamarugo samples from the Llamara Basin indicate wetter conditions prior to 7.8 ka; however, sub-annual variability in the δ18O values remains relatively high with an average range in intra-ring values of 3.0‰ (2σ=1.1‰). P. tamarugo logs that were used as building materials and grown in agricultural fields at Ramaditas (~2.6ka), an archeological site in the Pampa del Tamarugal, have a wider range of δ18O values (17.5 to 35.6‰) and greater intra-ring variability (ave. 4.5‰, 2σ=3.2‰). The greater range in interannual and subannual δ18O values most likely reflects a period with highly variable fluxes of runoff/recharge water. The development and eventual abandonment of Ramaditas and other settlements appear to coincide with changes in the availability of water in the region. Modern P. tamarugo from La Tirana Refresco collected in 2008 have δ18O values that are consistently higher (33.1 to 36.3‰) with much lower intra-ring variability (1.5‰, 2σ=0.9‰), indicating persistently drier conditions and greater evaporative

  19. The oxygen isotope evolution of parent body aqueous solutions as recorded by multiple carbonate generations in the Lonewolf Nunataks 94101 CM2 carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Lee, M. R.; Sofe, M. R.; Lindgren, P.; Starkey, N. A.; Franchi, I. A.

    2013-11-01

    The CM2 carbonaceous chondrite LON 94101 contains aragonite and two generations of calcite that provide snapshots of the chemical and isotopic evolution of aqueous solutions during parent body alteration. Aragonite was the first carbonate to crystallize. It is rare, heterogeneously distributed within the meteorite matrix, and its mean oxygen isotope values are δ18O 39.9 ± 0.6‰, Δ17O -0.3 ± 1.0‰ (1σ). Calcite precipitated soon afterwards, and following a fall in solution Mg/Ca ratios, to produce small equant grains with a mean oxygen isotope value of δ18O 37.5 ± 0.7‰, Δ17O 1.4 ± 1.1‰ (1σ). These grains were partially or completely replaced by serpentine and tochilinite prior to precipitation of the second generation of calcite, which occluded an open fracture to form a millimetre-sized vein, and replaced anhydrous silicates within chondrules and the matrix. The vein calcite has a mean composition of δ18O 18.4 ± 0.3‰, Δ17O -0.5 ± 0.5‰ (1σ). Petrographic and isotopic results therefore reveal two discrete episodes of mineralisation that produced calcite generations with contrasting δ18O, and mean Δ17O values. The aragonite and equant calcite crystallized over a relatively brief period early in the aqueous alteration history of the parent body, and from static fluids that were evolving chemically in response to mineral dissolution and precipitation. The second calcite generation crystallized from solutions of a lower Δ17O, and a lower δ18O and/or higher temperature. As two generations of calcite whose petrographic characteristics and oxygen isotopic compositions are similar to those in LON 94101 occur in at least one other CM2, multiphase carbonate mineralisation could be the typical outcome of the sequence of chemical reactions during parent body aqueous alteration. It is equally possible however that the second generation of calcite formed in response to an event such as impact fracturing and concomitant fluid mobilisation that affected

  20. Oxygen isotopes in deep sea spherules

    NASA Technical Reports Server (NTRS)

    Mayeda, T. K.; Clayton, R. N.; Brownlee, D. E.

    1984-01-01

    The determination of the genetic relationships between the dust and small particles in the solar system, and the meteorites and larger bodies are examined. Oxygen isotopes proved useful in the identification of such relationships between one meteorite group and another. Of the various samples of submillimeter extraterrestrial particles available for laboratory study, only the deep sea spherules are abundant enough for precise oxygen isotope analysis using existing techniques. Complications arise in interpretation of the isotopic data, since these particles were melted during passage through the Earth's atmosphere, and have been in contact with seawater for prolonged periods. Spherules that were originally silicates are considered with the originally metallic ones to deduce their preterrestrial isotopic compositions. The type 1 spherules which enter the atmosphere as metallic particles, contain only atmospheric oxygen. The type S spherules contain a mixture of atmospheric oxygen and their original extraterrestrial oxygen. It is suggested that the Earth's mesosphere is strongly enriched in heavy isotopes of oxygen at altitudes near 90 km at which the iron particles are oxidized. Fractionation due to the combined diffusion of O atoms and O2 molecules may be responsible.

  1. The isotopic composition of atmospheric oxygen

    NASA Astrophysics Data System (ADS)

    Luz, Boaz; Barkan, Eugeni

    2011-09-01

    Atmospheric O2 is almost 24‰ more enriched in 18O than seawater, and this enrichment is known as the Dole effect. For a long time it has been accepted that there is no oxygen isotope fractionation in photosynthesis, and thus the Dole effect should be the result of preferential terrestrial and marine respiratory consumption of 16O over 18O, and also several permil enrichment of leaf water from which terrestrial photosynthesis produces 18O enriched O2. This concept has led to the understanding that the record of past Dole effect variations was strongly affected by changes in the ratio of photosynthetic production between land and sea. However, recent studies in our lab have led to two major new observations: (1) O2 produced by certain marine phytoplankton, representing important groups of primary producers, is significantly enriched (up to 6‰) in 18O with respect to the substrate seawater and (2) effective oxygen isotope fractionation in soil respiration is considerably smaller than the intrinsic respiratory fractionation. Here we take these two observations into account and show that the magnitudes of the terrestrial and marine components of the Dole effect are close, and both are close to the measured Dole effect. As a result, the magnitude of the global Dole effect should not be sensitive to past changes in the ratio of land-to-sea photosynthetic rates. Instead of the land-sea control, variations in low-latitude hydrology, and possibly changes of fractionations in the marine biosphere, are more important in regulating the magnitude of the Dole effect and its past variations.

  2. Oxygen isotope record of oceanic and high-pressure metasomatism: a P-T-time-fluid path for the Monviso eclogites (Italy)

    NASA Astrophysics Data System (ADS)

    Rubatto, Daniela; Angiboust, Samuel

    2015-12-01

    Fluids are considered a fundamental agent for chemical exchanges between different rock types in the subduction system. Constraints on the sources and pathways of subduction fluids thus provide crucial information to reconstruct subduction processes. The Monviso ophiolitic sequence is composed of mafic, ultramafic and minor sediments that have been subducted to ~80 km depth. In this sequence, both localized fluid flow and channelized fluids along major shear zones have been documented. We investigate the timing and source of the fluids that affected the dominant mafic rocks using microscale U-Pb dating of zircon and oxygen isotope analysis of mineral zones (garnet, zircon and antigorite) in high-pressure rocks with variable degree of metasomatic modification. In mafic eclogites, Jurassic zircon cores are the only mineralogical relicts of the protolith gabbros and retain δ18O values of 4.5-6 ‰, typical of mantle melts. Garnet and metamorphic zircon that grew during prograde to peak metamorphism display low δ18O values between 0.2 and 3.8 ‰, which are likely inherited from high-temperature alteration of the protolith on the sea floor. This is corroborated by δ18O values of 3.0 and 3.6 ‰ in antigorite from surrounding serpentinites. In metasomatized eclogites within the lower shear zone, garnet rim formed at the metamorphic peak shows a shift to higher δ18O up to 6 ‰. The age of zircons in high-pressure veins and metasomatized eclogites constrains the timing of fluid flow at high pressure at around 45-46 Ma. Although the oxygen data do not contradict previous reports of interaction with serpentinite-derived fluids, the shift to isotopically heavier oxygen compositions requires contribution from sediment-derived fluids. The scarcity of metasediments in the Monviso sequence suggests that such fluids were concentrated and fluxed along the lower shear zone in a sufficient amount to modify the oxygen composition of the eclogitic minerals.

  3. The stable oxygen and carbon isotopic record from a coral growing in Florida Bay: a 160 year record of climatic and anthropogenic influence

    USGS Publications Warehouse

    Swart, Peter K.; Healy, Genevieve F.; Dodge, Richard E.; Kramer, Philip; Hudson, J. Harold; Halley, Robert B.; Robblee, Michael B.

    1996-01-01

    A 160 year record of skeletal δ13C and δ18O was examined in a specimen of the coral Solenastrea bournonigrowing in Florida Bay. Variations in the δ18O of the skeleton can be correlated to changes in salinity while changes in the δ13C reflect cycling of organic material within the Bay. Based on the correlation between salinity and skeletal δ18O, we have concluded that there has been no long term increase in salinity in this area of Florida Bay over the past 160 years. Using salinity correlations between the various basins obtained from instrumental data, we have been able to extend our interpretations to other parts of Florida Bay reaching similar conclusions. In contrast to current ideas which have focused on changes in Florida Bay water quality over the past 20-yr history of the Bay as causative in its decline, we have determined that changes in water quality in this basin were already set in motion between 1905 and 1912 by the construction of the Florida East Coast Railway from Miami to Key West. The construction of the railway resulted in the restriction of the exchange of water between the Florida reef tract and the Gulf of Mexico causing Florida Bay to become more eutrophic. Evidence of this process is observed in the sudden shift to relatively lower δ13C values coincident with railway construction. Natural events also appear to have influenced the water in the Bay. Between 1912 and 1948 frequent hurricanes had the effect of increasing exchange of water between the Bay and reef tract and removing large quantities of organic rich sediments. However, since 1948 the number of hurricanes affecting the area has decreased and the products of the oxidation of organic material have been increasingly retained within the basin promoting the initiation of eutrophic conditions.

  4. Oxygen Isotopes in the Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Clayton, R. N.

    2004-12-01

    Mechanisms that may account for oxygen isotope heterogeneity in meteorites on the microscopic scale do not seem adequate for explaining the similarities and differences in isotopic composition on a planetary scale. In chondrites, most of the isotopic variability can be attributed to photochemical enrichment of the two rare heavy isotopes with respect to the 16O-rich solar composition In the CO, CM, CI, and CR chondrites, an additional low-temperature aqueous alteration leads to mass-dependent further enrichment of the heavy isotopes. If the photochemical origin of the isotopic variation in chondrites is correct, then only a small fraction, represented primarily in CAIs, has the solar oxygen isotopic composition, and all other meteoritic components must have undergone photochemical processing. In addition, since the bulk isotopic compositions of the terrestrial planets and of the achondrite parent bodies are similar to those of chondrites, they too must be made of photochemically enriched matter. The photochemical reactions produce a non-equilibrium assemblage of gases, probably leading to a non-equilibrium assemblage of solids, particularly with respect to their oxidation state. These issues emphasize the importance of the measurement of oxygen isotopes in the Genesis solar wind mission. Within the Earth, oxygen isotope variations are due almost entirely to mass-dependent fractionation effects, giving a line of slope 0.52 on the three-isotope plot. The average crustal composition is 3 to 4 permil higher in delta-18O than the upper mantle. This difference is too large to be due to igneous fractionation effects alone, and reflects the larger, low-temperature isotope fractionation associated with aqueous weathering reactions at the Earth's surface. Similar effects are not observed in the intraplanetary isotopic variations in the Moon or in the parent bodies of the HED and SNC meteorites. The bulk oxygen isotopic compositions of Earth and Mars (assumed to be the SNC

  5. Oxygen isotope ratios in eclogites from kimberlites.

    PubMed

    Garlick, G D; Macgregor, I D; Vogel, D E

    1971-06-01

    The oxygen isotope compositions (delta(18)O) of eclogitic xenoliths from the Roberts Victor kimberlite range from 2 to 8 per mil relative to SMOW (standard mean ocean water). This surprising variation appears to be due to fractional crystallization: the eclogites rich in oxygen-18 represent early crystal accumulates; the eclogites poor in oxygen-18 represent residual liquids. Crystal-melt partitioning probably exceeded 3 per mil and is interpreted to be pressure-dependent. Anomalous enrichment of oxygen-18 in cumulate eclogites relative to ultramafic xenoliths suggests that crystal-melt partitioning increased after melt-formation but prior to crystallization.

  6. Oxygen isotope ratios in eclogites from kimberlites.

    PubMed

    Garlick, G D; Macgregor, I D; Vogel, D E

    1971-06-01

    The oxygen isotope compositions (delta(18)O) of eclogitic xenoliths from the Roberts Victor kimberlite range from 2 to 8 per mil relative to SMOW (standard mean ocean water). This surprising variation appears to be due to fractional crystallization: the eclogites rich in oxygen-18 represent early crystal accumulates; the eclogites poor in oxygen-18 represent residual liquids. Crystal-melt partitioning probably exceeded 3 per mil and is interpreted to be pressure-dependent. Anomalous enrichment of oxygen-18 in cumulate eclogites relative to ultramafic xenoliths suggests that crystal-melt partitioning increased after melt-formation but prior to crystallization. PMID:17798552

  7. Carbon and oxygen isotopic records from Lake Tuosu over the last 120 years in the Qaidam Basin, Northwestern China: The implications for paleoenvironmental reconstruction

    NASA Astrophysics Data System (ADS)

    Li, Xiangzhong; Zhou, Xin; Liu, Weiguo; Wang, Zheng; He, Yuxin; Xu, Liming

    2016-06-01

    Isotopic compositions of total organic carbon (TOC) and authigenic carbonate in lakes have been widely used to reconstruct paleoclimatic changes and the depositional environments of lake sediments. However, since these proxies are often controlled by multiple environmental factors, detailed examinations of modern environmental processes is necessary before further applying them into paleoclimatic studies, especially in arid/semi-arid northwestern China. Here we generate High-resolution multi-proxy sedimentary records from Lake Tuosu, a hydrologically closed, saline and alkaline lake located at the north margin of the Qaidam Basin, through analysis of carbon isotope of TOC, and δ18O and δ13C values of ostracods over the last 120 years. Together with the meteorological data (precipitation and temperature), lake area record, and other tree-ring evidence, we examine how these sedimentary indices respond to changes in hydrologic balance and climate at interannual to decadal timescales. We found that sedimentary δ13Corg values resemble the variation of lake areas of Lake Tuosu over the last 40 years, suggesting that δ13Corg values would be an ideal indicator of lake area/level fluctuations and thus effective moisture variations (precipitation vs. evaporation). However, ostracod δ18O, which was previously used as proxies of effective precipitation, is not well correlated with δ13Corg values in Lake Tuosu. Therefore, the changes of ostracod δ18O values cannot be straightforwardly explained as the effective precipitation. Instead, the isotopic composition of carbonate would be additionally controlled by other factors including isotopic compositions of input water and drainage pattern.

  8. Oxygen isotope fractionation in double carbonates.

    PubMed

    Zheng, Yong-Fei; Böttcher, Michael E

    2016-01-01

    Oxygen isotope fractionations in double carbonates of different crystal structures were calculated by the increment method. Synthesis experiments were performed at 60 °C and 100 °C to determine oxygen and carbon isotope fractionations involving PbMg[CO3]2. The calculations suggest that the double carbonates of calcite structure are systematically enriched in (18)O relative to those of aragonite and mixture structures. Internally consistent oxygen isotope fractionation factors are obtained for these minerals with respect to quartz, calcite and water at a temperature range of 0-1200 °C. The calculated fractionation factors for double carbonate-water systems are generally consistent with the data available from laboratory experiments. The experimentally determined fractionation factors for PbMg[CO3]2, BaMg[CO3]2 and CaMg[CO3]2 against H2O not only fall between fractionation factors involving pure carbonate end-members but are also close to the calculated fractionation factors. In contrast, experimentally determined carbon isotope fractionation factors between PbMg[CO3]2 and CO2 are much closer to theoretical predictions for the cerussite-CO2 system than for the magnesite-CO2 system, similar to the fractionation behavior for BaMg[CO3]2. Therefore, the combined theoretical and experimental results provide insights into the effects of crystal structure and exchange kinetics on oxygen isotope partitioning in double carbonates.

  9. Laboratory constraints on the stability of oxygen isotopes in sulfate

    NASA Astrophysics Data System (ADS)

    Turchyn, A. V.; Rennie, V.

    2012-12-01

    The oxygen isotopic composition of sulfate (δ18OSO4) is a powerful new tool for exploring the transformations of sulfur in laboratory experiments and the natural environment. The δ18OSO4 is central to our understanding of bacterial sulfate reduction because variations in δ18OSO4 reflect differences in the rates of various metabolic steps. Additionally, the δ18OSO4 provides key information on the pathways of both biotic and abiotic sulfide oxidation. If preserved in the geological record, the δ18OSO4, along with the sulfur isotope composition of sulfate, provides unique insight into the long-term variability of the sulfur cycle. Use of the δ18OSO4 rests on the assumption that there is minimal abiotic exchange between sulfate-oxygen and water-oxygen during the variety of conditions imposed by sample storage and laboratory processing. Previous work has shown that oxygen isotope exchange between sulfate and water does occur at high temperatures (>100°C) and/or at low pH values (<1). Estimates of the timescales for exchange under laboratory temperatures and pH values have been extrapolated from highly dissimilar conditions. The controls on abiotic oxygen isotope exchange between sulfate and water under laboratory conditions thus remain enigmatic. We explore two mechanisms that could allow for isotope exchange and thus interfere with the interpretation of δ18OSO4: oxygen isotope exchange under low pH and oxygen isotope exchange in the presence of sulfide by the formation and subsequent reaction of thiosulfate complexes. Our results definitively rule out short and medium-term exchange of sulfate-oxygen with water-oxygen over a range of acidic conditions. Furthermore, although it has been suggested that thiosulfate complexes will form from coexisting aqueous sulfide and sulfate, we demonstrate that this mechanism does not facilitate sulfate-oxygen isotope exchange at low temperatures. Our results confirm that the δ18OSO4 is robust to standard laboratory conditions.

  10. Isotopic Composition of Oxygen in Lunar Zircons

    NASA Technical Reports Server (NTRS)

    Nemchin, A. A.; Whitehouse, M. J.; Pidgeon, R. T.; Meyer, C.

    2005-01-01

    The recent discovery of heavy oxygen in zircons from the Jack Hills conglomerates Wilde et al. and Mojzsis et al. was interpreted as an indication of presence of liquid water on the surface of Early Earth. The distribution of ages of Jack Hills zircons and lunar zircons appears to be very similar and therefore analysis of oxygen in the lunar grains may provide a reference frame for further study of the early history of the Earth as well as give additional information regarding processes that operated on the Moon. In the present study we have analysed the oxygen isotopic composition of zircon grains from three lunar samples using the Swedish Museum of Natural History CAMECA 1270 ion microprobe. The samples were selected as likely tests for variations in lunar oxygen isotopic composition. Additional information is included in the original extended abstract.

  11. A 1000-year record of dry conditions in the eastern Canadian prairies reconstructed from oxygen and carbon isotope measurements on Lake Winnipeg sediment organics

    USGS Publications Warehouse

    Buhay, W.M.; Simpson, S.; Thorleifson, H.; Lewis, M.; King, J.; Telka, A.; Wilkinson, Philip M.; Babb, J.; Timsic, S.; Bailey, D.

    2009-01-01

    A short sediment core (162 cm), covering the period AD 920-1999, was sampled from the south basin of Lake Winnipeg for a suite of multi-proxy analyses leading towards a detailed characterisation of the recent millennial lake environment and hydroclimate of southern Manitoba, Canada. Information on the frequency and duration of major dry periods in southern Manitoba, in light of the changes that are likely to occur as a result of an increasingly warming atmosphere, is of specific interest in this study. Intervals of relatively enriched lake sediment cellulose oxygen isotope values (??18Ocellulose) were found to occur from AD 1180 to 1230 (error range: AD 1104-1231 to 1160-1280), 1610-1640 (error range: AD 1571-1634 to 1603-1662), 1670-1720 (error range: AD 1643-1697 to 1692-1738) and 1750-1780 (error range: AD 1724-1766 to 1756-1794). Regional water balance, inferred from calculated Lake Winnipeg water oxygen isotope values (??18Oinf-lw), suggest that the ratio of lake evaporation to catchment input may have been 25-40% higher during these isotopically distinct periods. Associated with the enriched d??18Ocellulose intervals are some depleted carbon isotope values associated with more abundantly preserved sediment organic matter (d??13COM). These suggest reduced microbial oxidation of terrestrially derived organic matter and/or subdued lake productivity during periods of minimised input of nutrients from the catchment area. With reference to other corroborating evidence, it is suggested that the AD 1180-1230, 1610-1640, 1670-1720 and 1750-1780 intervals represent four distinctly drier periods (droughts) in southern Manitoba, Canada. Additionally, lower-magnitude and duration dry periods may have also occurred from 1320 to 1340 (error range: AD 1257-1363), 1530-1540 (error range: AD 1490-1565 to 1498-1572) and 1570-1580 (error range: AD 1531-1599 to 1539-1606). ?? 2009 John Wiley & Sons, Ltd.

  12. The deep sea oxygen isotopic record: Significance for tertiary global ice volume history, with emphasis on the latest Miocene/early Pliocene

    SciTech Connect

    Prentice, M.L.

    1988-01-01

    Planktonic and benthic isotopic records as well as carbonate sedimentation records extending from 6.1 to 4.1 Ma for eastern South Atlantic Holes 526A and 525B are presented. These data suggest ice volume variations about a constant mean sufficient to drive sea level between 10 m and 75 m below present. Isotopic records at the deeper (2500 m) site have been enriched by up to 0.5% by dissolution. Carbonate accumulation rates at both sites quadrupled at 4.6 Ma primarily because of increased production and, secondarily, decreased dissolution. The second part presents a Cenozoic-long composite {delta}{sup 18}O curve for tropical shallow-dwelling planktonic foraminifers and the benthic foraminifer Cibicides at 2-4 km depths. Surface {delta}{sup 18}O gradients between various low-and-mid latitude sites reflect: (1) widespread SST stability through the Cenozoic and (2) significant change in Tasman Sea SST through the Tertiary. Assuming average SST for tropical non-upwelling areas was constant, the planktonic composite suggest that global ice volume for the last 40 my has not been significantly less than today. Residual benthic {delta}{sup 18}O reflect relatively warm and saline deep water until the early Miocene after which time deep water progressively cooled. The third part presents {delta}{sup 18}O for Recent Orbulina universa from 44 core-tops distributed through the Atlantic and Indian Oceans. The purpose was to test the hypothesis that Orbulina calcifies at constant temperature and so records only ice volume changes. Orbulina commonly calcifies at intermediate depths over a wide range of temperatures salinities, and densities. These physical factors are not the primary controls on the spatial and vertical distribution of Orbulina.

  13. The effect of rising atmospheric oxygen on carbon and sulfur isotope anomalies recorded in the Neoproterozoic Johnnie Formation, Death Valley, USA

    NASA Astrophysics Data System (ADS)

    Kaufman, A. J.; Corsetti, F. A.

    2004-12-01

    Carbonates within the Rainstorm Member in the terminal Neoproterozoic Johnnie Formation of Death Valley, California record a remarkable negative δ 13C anomaly to a nadir of near -11‰ , accompanied by a dramatic rise in trace sulfate abundance (>500 ppm) and drop in carbonate associated sulfate δ 34S values from 26.6‰ to 15.8‰ . The carbonates, including the laterally extensive Johnnie Oolite, were deposited during marine flooding atop a sequence boundary best observed in cratonward sections. A similarly dramatic carbon isotope anomaly is recorded in broadly equivalent successions that post-date known Marinoan glacial deposits and pre-date the Precambrian-Cambrian boundary in Oman, India, China, Australia, and Namibia. The cause of the carbon and sulfur isotopic excursions was likely associated with a rise in atmospheric O2, which resulted in 1) the oxidation of exposed continental shelf sediments rich in fossil organic matter and sulfides, providing a source of 12C, 32S, and sulfate; and 2) the ventilation of the oceans. Large metazoan fossils (Ediacaran animals) first appear directly above this anomaly, suggesting that a critical threshold with respect to atmospheric O2 had been crossed at this time. A negative δ 13C excursion of similar magnitude occurs in overlying strata at the Precambrian-Cambrian boundary, which may reflect similar processes.

  14. Tree-ring isotope records of tropical cyclone activity

    PubMed Central

    Miller, Dana L.; Mora, Claudia I.; Grissino-Mayer, Henri D.; Mock, Cary J.; Uhle, Maria E.; Sharp, Zachary

    2006-01-01

    The destruction wrought by North Atlantic hurricanes in 2004 and 2005 dramatically emphasizes the need for better understanding of tropical cyclone activity apart from the records provided by meteorological data and historical documentation. We present a 220-year record of oxygen isotope values of α-cellulose in longleaf pine tree rings that preserves anomalously low isotope values in the latewood portion of the ring in years corresponding with known 19th and 20th century landfalling/near-coastal tropical storms and hurricanes. Our results suggest the potential for a tree-ring oxygen isotope proxy record of tropical cyclone occurrence extending back many centuries based on remnant pine wood from protected areas in the southeastern U.S. PMID:16984996

  15. Tree-ring isotope records of tropical cyclone activity.

    PubMed

    Miller, Dana L; Mora, Claudia I; Grissino-Mayer, Henri D; Mock, Cary J; Uhle, Maria E; Sharp, Zachary

    2006-09-26

    The destruction wrought by North Atlantic hurricanes in 2004 and 2005 dramatically emphasizes the need for better understanding of tropical cyclone activity apart from the records provided by meteorological data and historical documentation. We present a 220-year record of oxygen isotope values of alpha-cellulose in longleaf pine tree rings that preserves anomalously low isotope values in the latewood portion of the ring in years corresponding with known 19th and 20th century landfalling/near-coastal tropical storms and hurricanes. Our results suggest the potential for a tree-ring oxygen isotope proxy record of tropical cyclone occurrence extending back many centuries based on remnant pine wood from protected areas in the southeastern U.S.

  16. Oxygen isotopic anomalies in Allende inclusion HAL

    NASA Astrophysics Data System (ADS)

    Lee, T.; Mayeda, T. K.; Clayton, R. N.

    1980-07-01

    An oxygen isotopic study which demonstrates the Allende inclusion HAL is a FUN object is discussed; the hibonite core, black inner rim and fine-grained outer rim have beem sampled. The oxygen in HAL is found to be heterogeneous, the rim samples having oxygen compositions similar to that of melilites and alteration products in other Allende inclusions including the FUN inclusion EK1-4-1, while the oxygen in the hibonite core shows the most extreme deviation from the AD line so far observed. The oxygen in HAL hibonite, in ED1-4-1 spinel and in spinels of usual Allende inclusions form an approximate linear array with a slope close to 1/2. With regard to the fractionation process, it is noted that the fractionation per amu for various elements does not correlate inversely with mass and that fractionation is elementally selective, probably according to volatility.

  17. A 200,000-Year Record of Change in Oxygen Isotope Composition of Sulfate in a Saline Sediment Core, Death Valley, California

    NASA Astrophysics Data System (ADS)

    Yang, Wenbo; Krouse, H. Roy; Spencer, Ronald J.; Lowenstein, Tim K.; Hutcheon, Ian E.; Ku, Teh-Lung; Li, Jianren; Roberts, Sheila M.; Brown, Christopher B.

    1999-03-01

    δ 18O values of sulfate minerals from a 186-m core (past 200,000 years) in Death Valley varied from +9 to +23‰ (V-SMOW). Sulfates that accumulated in the past ephemeral saline lake, salt pans, and mud flats have relatively low δ 18O values similar to those of present-day local inflows. Sulfates that accumulated during two perennial lake intervals, however, have higher δ 18O values, reflecting changes in temperature, lake water levels, and/or sulfur redox reactions. Over the same time interval, the δ 18O record for sulfate had excursions that bear similarities to those found for carbonate in the Death Valley core, marine carbonate (SPECMAP), and polar ice in the Summit ice core, Greenland. The δ 18O record differed considerably from the records reported for carbonate at Owens Lake and Devils Hole, which probably relates to different water sources. Death Valley, Owens Lake, and Devils Hole are responding to the same climatic changes but manifesting them differently. In Death Valley sediments, the isotopic composition of sulfate may have potential as an indicator of paleoenvironmental changes.

  18. Triple Oxygen Isotopes: Fundamental Relationships and Applications

    NASA Astrophysics Data System (ADS)

    Bao, Huiming; Cao, Xiaobin; Hayles, Justin A.

    2016-06-01

    The element oxygen has three stable isotopes: 16O, 17O, and 18O. For a defined process, a change in 18O/16O scales with the corresponding change in 17O/16O, or the fractionation factors 18α and 17α have a relationship of θ = ln17α/ln18α, in which the triple oxygen isotope exponent θ is relatively fixed but does vary with reaction path, temperature, and species involved. When the small variation is of interest, the distinction of three concepts—θ, S (a slope through data points in δ17O-δ18O space), and C (an arbitrary referencing number for the degree of 17O deviation)—becomes important. Triple oxygen isotope variations can be measured by modern instruments and thus offer an additional line of information on the underlying reaction processes and conditions. Analytical methods and Earth science applications have recently been developed for air oxygen, carbon dioxide, water, silicates, oxides, sulfates, carbonates, and phosphates.

  19. Triple Oxygen Isotopes: Fundamental Relationships and Applications

    NASA Astrophysics Data System (ADS)

    Bao, Huiming; Cao, Xiaobin; Hayles, Justin A.

    2016-06-01

    The element oxygen has three stable isotopes: 16O, 17O, and 18O. For a defined process, a change in 18O/16O scales with the corresponding change in 17O/16O, or the fractionation factors 18α and 17α have a relationship of θ = ln17α/ln18α, in which the triple oxygen isotope exponent θ is relatively fixed but does vary with reaction path, temperature, and species involved. When the small variation is of interest, the distinction of three concepts—θ, S (a slope through data points in δ17O–δ18O space), and C (an arbitrary referencing number for the degree of 17O deviation)—becomes important. Triple oxygen isotope variations can be measured by modern instruments and thus offer an additional line of information on the underlying reaction processes and conditions. Analytical methods and Earth science applications have recently been developed for air oxygen, carbon dioxide, water, silicates, oxides, sulfates, carbonates, and phosphates.

  20. How the oxygen isotope ratio of rain water influences the isotope ratio of chicken eggshell carbonate

    NASA Astrophysics Data System (ADS)

    Price, Gregory; Grimes, Stephen

    2015-04-01

    The stable oxygen isotope ratio of chicken eggshell carbonate was analysed from chicken eggs laid under free range, and organic farming regimes from across the UK. The eggshell carbonate oxygen isotope data shows a clear depletion in delta18O distribution from the southwest to the northeast. Although consistently offset by around 1 permil, the same isotopic distribution as that seen in eggshell carbonate is observed in the delta18O ratio of rainfall and groundwater from across the UK. This distribution is related to the Rayleigh distillation of rainfall driven by westerly winds across the UK landmass. The clear relationship observed between eggshell delta18O values and that of rainwater presumably reflects the nature of free range chickens which must be drinking locally derived rainwater and supplementing their diet and water intake with locally derived food. These results suggest that the oxygen isotope value of chicken eggshells can be used as a forensic tool to identify the locality that free range and organic eggs were laid within the UK. Furthermore, if suitable material is preserved in the archaeological and geological record then such a relationship can potentially be used to establish the oxygen isotope value of rainwater from which ancient and / or ancestral birds lived.

  1. Oxygen Isotope Systematics of Almahata Sitta

    NASA Technical Reports Server (NTRS)

    Kita, N. T.; Goodrich, C. A.; Herrin, J. S.; Shaddad, M. H.; Jenniskens, P.

    2011-01-01

    The Almahata Sitta (hereafter "AHS") meteorite was derived from an impact of asteroid 2008TC3 on Earth and is classified as an anomalous polymict ureilite. More than 600 meteorite fragments have been recovered from the strewnfield. Previous reports indicate that these fragments consist mainly of ureilitic materials with textures and compositions, while some fragments are found to be chondrites of a wide range of chemical classes. Bulk oxygen three isotope analyses of ureilitic fragments from AHS fall close to the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line similar to ureilites. In order to further compare AHS with known ureilites, we performed high precision SIMS (Secondary Ion Mass Spectrometer) oxygen isotope analyses of some AHS samples

  2. Oxygen Isotope Trajectories of Crystallizing Arc Magmas

    NASA Astrophysics Data System (ADS)

    Bucholz, C. E.; Jagoutz, O. E.; VanTongeren, J. A.; Wang, Z.

    2014-12-01

    Oxygen isotopes are essential to quantify mantle-derived versus 'recycled' crustal contributions to arc magmas. High δ18O values in igneous rocks (i.e., δ18OSMOW > ~5.7) are generally used to identify supra-crustal inputs, but a melt can also become enriched in 18O due to magmatic differentiation [1,2]. To assess magmatic δ18O values of plutonic rocks, δ18Ozircon values, which are resilient to secondary alteration, are often used. Thus, to disentangle the effects of assimilation versus fractionation, both the absolute increase in melt δ18O due to differentiation and ∆18O(WR-zircon) must be determined. However, existing constraints on the effect of magmatic fractionation on melt δ18O are model-based [2] and calculated relationships between WR SiO2, δ18Ozircon, and δ18Omelt do not incorporate complex melt SiO2, H2O, and temperature (T) relationships [3]. To build upon these initial constraints, we combine the first high-precision δ18O data set on natural samples documenting changes in δ18O melt values with increasing extent of differentiation and modeling which incorporates experimentally constrained melt SiO2, H2O, and T relationships. We analyzed 55 mineral separates with infrared laser-fluorination [4] across large fractionation intervals of two well-studied cumulate sequences: (I) a relatively dry (~1 wt.% H2O initial) tholeiitic sequence (analyzed minerals include plag, opx, cpx, & Fe-rich ol) from the Bushveld Complex and (II) a hydrous high-K sequence (analyzed minerals include ol, cpx, bt, fsp, & qtz) from the Dariv paleoarc in Mongolia. Our results indicate that multiple per mil increases in melt δ18O can occur during magmatic fractionation that in detail depend strongly on melt composition and T. Calculated relationships between WR SiO2 and δ18Ozircon for experimental melt compositions show that wet, 'cool' and dry, 'hot' melts are characterized by larger and smaller ∆18O (melt-zircon) fractionations, respectively. Applying our results to

  3. Oxygen isotope partitioning between phosphate and carbonate in mammalian apatite

    NASA Astrophysics Data System (ADS)

    Daniel Bryant, J.; Koch, Paul L.; Froelich, Philip N.; Showers, William J.; Genna, Bernard J.

    1996-12-01

    The oxygen isotope compositions of phosphate and structural carbonate in mammalian enamel and bone apatite are linked to that of body water at constant body temperature near 37°C, but the isotope systematics of oxygen in structural carbonate are not well understood. Using coupled measurements of the oxygen isotope composition of structural carbonate and phosphate from horse tooth enamel, the apparent oxygen isotope fractionation factor between structural carbonate and body water is estimated to be 1.0263 ± 0.0014. These estimates provide a quantitative basis for using the oxygen isotope composition of structural carbonate in mammalian biogenic apatite for ecological, climatological, and physiological reconstruction.

  4. Oxygen and hydrogen isotope geochemistry of zeolites

    NASA Technical Reports Server (NTRS)

    Karlsson, Haraldur R.; Clayton, Robert N.

    1990-01-01

    Oxygen and hydrogen isotope ratios for natural samples of the zeolites analcime, chabazite, clinoptilolite, laumontite, mordenite, and natrolite have been obtained. The zeolite samples were classified into sedimentary, hydrothermal, and igneous groups. The ratios for each species of zeolite are reported. The results are used to discuss the origin of channel water, the role of zeolites in water-rock interaction, and the possibility that a calibrated zeolite could be used as a low-temperature geothermometer.

  5. 100,000-year-long terrestrial record of millennial-scale linkage between eastern North American mid-latitude paleovegetation shifts and Greenland ice-core oxygen isotope trends

    NASA Astrophysics Data System (ADS)

    Litwin, Ronald J.; Smoot, Joseph P.; Pavich, Milan J.; Markewich, Helaine W.; Brook, George; Durika, Nancy J.

    2013-09-01

    We document frequent, rapid, strong, millennial-scale paleovegetation shifts throughout the late Pleistocene, within a 100,000+ yr interval (~ 115-15 ka) of terrestrial sediments from the mid-Atlantic Region (MAR) of North America. High-resolution analyses of fossil pollen from one core locality revealed a continuously shifting sequence of thermally dependent forest assemblages, ranging between two endmembers: subtropical oak-tupelo-bald cypress-gum forest and high boreal spruce-pine forest. Sedimentary textural evidence indicates fluvial, paludal, and loess deposition, and paleosol formation, representing sequential freshwater to subaerial environments in which this record was deposited. Its total age-depth model, based on radiocarbon and optically stimulated luminescence ages, ranges from terrestrial oxygen isotope stages (OIS) 6 to 1. The particular core sub-interval presented here is correlative in trend and timing to that portion of the oxygen isotope sequence common among several Greenland ice cores: interstades GI2 to GI24 (≈ OIS2-5 d). This site thus provides the first evidence for an essentially complete series of 'Dansgaard-Oeschger' climate events in the MAR. These data reveal that the ~ 100,000 yr preceding the Late Glacial and Holocene in the MAR of North America were characterized by frequently and dynamically changing climate states, and by vegetation shifts that closely tracked the Greenland paleoclimate sequence.

  6. Oxygen isotope composition of trinitite postdetonation materials.

    PubMed

    Koeman, Elizabeth C; Simonetti, Antonio; Chen, Wei; Burns, Peter C

    2013-12-17

    Trinitite is the melt glass produced subsequent the first nuclear bomb test conducted on July 16, 1945, at White Sands Range (Alamagordo, NM). The geological background of the latter consists of arkosic sand that was fused with radioactive debris and anthropogenic materials at ground zero subsequent detonation of the device. Postdetonation materials from historic nuclear weapon test sites provide ideal samples for development of novel forensic methods for attribution and studying the chemical/isotopic effects of the explosion on the natural geological environment. In particular, the latter effects can be evaluated relative to their spatial distribution from ground zero. We report here δ(18)O(‰) values for nonmelted, precursor minerals phases (quartz, feldspar, calcite), "feldspathic-rich" glass, "average" melt glass, and bulk (natural) unmelted sand from the Trinity site. Prior to oxygen isotope analysis, grains/crystals were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to determine their corresponding major element composition. δ(18)O values for bulk trinitite samples exhibit a large range (11.2-15.5‰) and do not correlate with activity levels for activation product (152)Eu; the latter levels are a function of their spatial distribution relative to ground zero. Therefore, the slow neutron flux associated with the nuclear explosion did not perturb the (18)O/(16)O isotope systematics. The oxygen isotope values do correlate with the abundances of major elements derived from precursor minerals present within the arkosic sand. Hence, the O isotope ratios documented here for trinitite melt glass can be attributed to a mixture of the respective signatures for precursor minerals at the Trinity site prior to the nuclear explosion.

  7. Oxygen isotope composition of trinitite postdetonation materials.

    PubMed

    Koeman, Elizabeth C; Simonetti, Antonio; Chen, Wei; Burns, Peter C

    2013-12-17

    Trinitite is the melt glass produced subsequent the first nuclear bomb test conducted on July 16, 1945, at White Sands Range (Alamagordo, NM). The geological background of the latter consists of arkosic sand that was fused with radioactive debris and anthropogenic materials at ground zero subsequent detonation of the device. Postdetonation materials from historic nuclear weapon test sites provide ideal samples for development of novel forensic methods for attribution and studying the chemical/isotopic effects of the explosion on the natural geological environment. In particular, the latter effects can be evaluated relative to their spatial distribution from ground zero. We report here δ(18)O(‰) values for nonmelted, precursor minerals phases (quartz, feldspar, calcite), "feldspathic-rich" glass, "average" melt glass, and bulk (natural) unmelted sand from the Trinity site. Prior to oxygen isotope analysis, grains/crystals were examined using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to determine their corresponding major element composition. δ(18)O values for bulk trinitite samples exhibit a large range (11.2-15.5‰) and do not correlate with activity levels for activation product (152)Eu; the latter levels are a function of their spatial distribution relative to ground zero. Therefore, the slow neutron flux associated with the nuclear explosion did not perturb the (18)O/(16)O isotope systematics. The oxygen isotope values do correlate with the abundances of major elements derived from precursor minerals present within the arkosic sand. Hence, the O isotope ratios documented here for trinitite melt glass can be attributed to a mixture of the respective signatures for precursor minerals at the Trinity site prior to the nuclear explosion. PMID:24304329

  8. 1.8 billion years of fluid-crust interaction: A zircon oxygen isotope record for the lower crust, western Churchill Province, Canadian Shield

    NASA Astrophysics Data System (ADS)

    Petts, Duane C.; Moser, Desmond E.; Longstaffe, Frederick J.; Davis, William J.; Stern, Richard A.

    2014-04-01

    The western Churchill Province of the Canadian Shield experienced a prolonged and complex formation history (ca. 4.04 to 1.70 Ga), with evidence for multiple episodes of orogenesis and regional magmatic activity. Here we report on the oxygen isotopic compositions of garnet and zircon recovered from lower crustal xenoliths, which have U-Pb ages between ca. 3.5 and 1.7 Ga. Overall, zircon from four metabasite xenoliths from the Rankin Inlet sample suite have δ18O values ranging from + 5.5 to + 8.6‰. Zircon from three metatonalite/anorthosite xenoliths and five metabasite xenoliths from the Repulse Bay sample suite have δ18O values of + 5.6 to + 8.3‰. High δ18O values (> + 6.0‰) for the oldest igneous zircon cores (ca. 3.5 Ga and 3.0-2.6 Ga) indicate that their metatonalite/anorthosite protolith magmas were generated from, or had assimilated, supracrustal rocks that interacted previously with surface-derived fluids. Igneous zircon cores (ca. 2.9-2.6 Ga) from one metabasite xenolith have δ18O values of + 5.6 to + 6.4‰, which suggests a formation from a mantle-derived basaltic/gabbroic magma. Metamorphic zircon cores (ca. 2.0-1.9 Ga) from one metabasite xenolith commonly have δ18O values between + 6.0 and + 6.3‰, which is indicative of a basalt/gabbro protolith and localized reworking of the lower crust caused by regional-scale plate convergence. The wide range of δ18O values (+ 5.5 to + 8.3‰) for ca. 1.75-1.70 Ga metamorphic zircon rims (identified in all xenoliths) indicates regional transient heating and reworking of mantle- and supracrustal-derived crust, induced by magmatic underplating along the crust-mantle boundary.

  9. Oxygen isotopes in nitrite: Analysis, calibration, and equilibration

    USGS Publications Warehouse

    Casciotti, K.L.; Böhlke, J.K.; McIlvin, M.R.; Mroczkowski, S.J.; Hannon, J.E.

    2007-01-01

    Nitrite is a central intermediate in the nitrogen cycle and can persist in significant concentrations in ocean waters, sediment pore waters, and terrestrial groundwaters. To fully interpret the effect of microbial processes on nitrate (NO3-), nitrite (NO2-), and nitrous oxide (N2O) cycling in these systems, the nitrite pool must be accessible to isotopic analysis. Furthermore, because nitrite interferes with most methods of nitrate isotopic analysis, accurate isotopic analysis of nitrite is essential for correct measurement of nitrate isotopes in a sample that contains nitrite. In this study, nitrite salts with varying oxygen isotopic compositions were prepared and calibrated and then used to test the denitrifier method for nitrite oxygen isotopic analysis. The oxygen isotopic fractionation during nitrite reduction to N2O by Pseudomonas aureofaciens was lower than for nitrate conversion to N2O, while oxygen isotopic exchange between nitrite and water during the reaction was similar. These results enable the extension of the denitrifier method to oxygen isotopic analysis of nitrite (in the absence of nitrate) and correction of nitrate isotopes for the presence of nitrite in "mixed" samples. We tested storage conditions for seawater and freshwater samples that contain nitrite and provide recommendations for accurate oxygen isotopic analysis of nitrite by any method. Finally, we report preliminary results on the equilibrium isotope effect between nitrite and water, which can play an important role in determining the oxygen isotopic value of nitrite where equilibration with water is significant. ?? 2007 American Chemical Society.

  10. Oxygen Isotope Measurements of a Rare Murchison Type A CAI and Its Rim

    NASA Technical Reports Server (NTRS)

    Matzel, J. E. P.; Simon, J. I.; Hutcheon, I. D.; Jacobsen, B.; Simon, S. B.; Grossman, L.

    2013-01-01

    Ca-, Al-rich inclusions (CAIs) from CV chondrites commonly show oxygen isotope heterogeneity among different mineral phases within individual inclusions reflecting the complex history of CAIs in both the solar nebula and/or parent bodies. The degree of isotopic exchange is typically mineral-specific, yielding O-16-rich spinel, hibonite and pyroxene and O-16-depleted melilite and anorthite. Recent work demonstrated large and systematic variations in oxygen isotope composition within the margin and Wark-Lovering rim of an Allende Type A CAI. These variations suggest that some CV CAIs formed from several oxygen reservoirs and may reflect transport between distinct regions of the solar nebula or varying gas composition near the proto-Sun. Oxygen isotope compositions of CAIs from other, less-altered chondrites show less intra-CAI variability and 16O-rich compositions. The record of intra-CAI oxygen isotope variability in CM chondrites, which commonly show evidence for low-temperature aqueous alteration, is less clear, in part because the most common CAIs found in CM chondrites are mineralogically simple (hibonite +/- spinel or spinel +/- pyroxene) and are composed of minerals less susceptible to O-isotopic exchange. No measurements of the oxygen isotope compositions of rims on CAIs in CM chondrites have been reported. Here, we present oxygen isotope data from a rare, Type A CAI from the Murchison meteorite, MUM-1. The data were collected from melilite, hibonite, perovskite and spinel in a traverse into the interior of the CAI and from pyroxene, melilite, anorthite, and spinel in the Wark-Lovering rim. Our objectives were to (1) document any evidence for intra-CAI oxygen isotope variability; (2) determine the isotopic composition of the rim minerals and compare their composition(s) to the CAI interior; and (3) compare the MUM-1 data to oxygen isotope zoning profiles measured from CAIs in other chondrites.

  11. Stable isotopes of oxygen and carbon compositions in the Neoproterozoic of South Gabon (Schisto-Calcaire Subgroup, Nyanga Basin): Are cap carbonates and lithoherms recording a particular destabilization event after the Marinoan glaciation?

    NASA Astrophysics Data System (ADS)

    Préat, Alain; Prian, Jean-Pierre; Thiéblemont, Denis; Obame, Rolf Mabicka; Delpomdor, Franck

    2011-06-01

    Geologic evidence of tropical sea level glaciation in the Neoproterozoic remains a matter of debate in the Snowball Earth hypothesis. The Niari Tillite Formation and the cap carbonates record the late Neoproterozoic Marinoan glaciation in South Gabon. These cap carbonates are located at the base of the Schisto-Calcaire Subgroup a predominantly carbonate succession that rests with sharp contact on top of the Niari Tillite. Integrating sedimentological and stable isotope data, a consistent sequence of precipitation events is proposed, with strongly negative δ 13C values pointing to a particular event in the cap carbonates (average δ 13C value = -3.2‰ V-PDB) and in a further newly defined lithohermal unit (average δ 13C value = -4.6‰ V-PDB). Subsequent shallow evaporitive platform carbonates display carbon and oxygen isotopic compositions indicative of relatively unaltered seawater values. Strongly negative δ 18O values in the lithoherms and replacement of aragonite fans by equigranular calcite suggest flushing of meteoric water derived from glacial meltwater.

  12. The influence of oxygen exchange between sulfite and water on the oxygen isotope composition of sulfate

    NASA Astrophysics Data System (ADS)

    Müller, I. A.; Brunner, B.

    2012-12-01

    Sulfate does not exchange oxygen with the water under most environmental conditions. Therefore, its oxygen isotope composition serves as an archive of past oxidative sulfur cycling. Studies on the oxygen isotope signature of sulfate produced from reduced sulfur compounds show varying relative contributions of two possible oxygen sources; molecular oxygen and water, and variable isotope fractionations relative to these two compounds. These discrepancies could be due to differences in the production and consumption of sulfuroxy intermediates which exchange oxygen with water. Thereby, the rate of oxygen exchange as well as the rate of oxidation depends on the pH. Studies on the oxygen isotope exchange effects between sulfuroxy intermediates and water and on the oxygen isotope effects during the oxidation of sulfuroxy intermediates are scarce, severely limiting the interpretability of oxygen isotope signatures in sulfate. Sulfite is often considered to be the last/final sulfuroxy intermediate in the oxidation of reduced sulfur compounds to sulfate and may, therefore, be pivotal in shaping the oxygen isotope signature of sulfate. We determined the oxygen isotope equilibrium fractionation between sulfite and water and used the obtained equilibrium value to determine the oxygen isotope effects in abiotic sulfite oxidation experiments. Our results demonstrate that natural variations in the oxygen isotope composition of sulfate produced by oxidative processes can be explained by differences in the interplay of the sulfite oxidation rate and oxygen isotope exchange rate between sulfite and water which both depend on pH conditions and availability of oxidizing agents (e.g. molecular oxygen or ferric iron). Our findings contribute to a more detailed mechanistic understanding of the oxidation of reduced sulfur compounds and underline the importance of sulfite as the final sulfuroxy intermediate in oxidative sulfur cycling.

  13. Cyclostratigraphy and eccentricity tuning of the early Oligocene through early Miocene (30.1-17.1 Ma): Cibicides mundulus stable oxygen and carbon isotope records from Walvis Ridge Site 1264

    NASA Astrophysics Data System (ADS)

    Liebrand, Diederik; Beddow, Helen M.; Lourens, Lucas J.; Pälike, Heiko; Raffi, Isabella; Bohaty, Steven M.; Hilgen, Frederik J.; Saes, Mischa J. M.; Wilson, Paul A.; van Dijk, Arnold E.; Hodell, David A.; Kroon, Dick; Huck, Claire E.; Batenburg, Sietske J.

    2016-09-01

    Few astronomically calibrated high-resolution (≤5 kyr) climate records exist that span the Oligocene-Miocene time interval. Notably, available proxy records show responses varying in amplitude at frequencies related to astronomical forcing, and the main pacemakers of global change on astronomical time-scales remain debated. Here we present newly generated X-ray fluorescence core scanning and benthic foraminiferal stable oxygen and carbon isotope records from Ocean Drilling Program Site 1264 (Walvis Ridge, southeastern Atlantic Ocean). Complemented by data from nearby Site 1265, the Site 1264 benthic stable isotope records span a continuous ∼13-Myr interval of the Oligo-Miocene (30.1-17.1 Ma) at high resolution (∼3.0 kyr). Spectral analyses in the stratigraphic depth domain indicate that the largest amplitude variability of all proxy records is associated with periods of ∼ 3.4 m and ∼ 0.9 m, which correspond to 405- and ∼110-kyr eccentricity, using a magnetobiostratigraphic age model. Maxima in CaCO3 content, δ18O and δ13C are interpreted to coincide with ∼110 kyr eccentricity minima. The strong expression of these cycles in combination with the weakness of the precession- and obliquity-related signals allow construction of an astronomical age model that is solely based on tuning the CaCO3 content to the nominal (La2011_ecc3L) eccentricity solution. Very long-period eccentricity maxima (∼2.4-Myr) are marked by recurrent episodes of high-amplitude ∼110-kyr δ18O cycles at Walvis Ridge, indicating greater sensitivity of the climate/cryosphere system to short eccentricity modulation of climatic precession. In contrast, the responses of the global (high-latitude) climate system, cryosphere, and carbon cycle to the 405-kyr cycle, as expressed in benthic δ18O and especially δ13C signals, are more pronounced during ∼2.4-Myr minima. The relationship between the recurrent episodes of high-amplitude ∼110-kyr δ18O cycles and the ∼1.2-Myr amplitude

  14. Oxygen isotope corrections for online δ34S analysis

    USGS Publications Warehouse

    Fry, B.; Silva, S.R.; Kendall, C.; Anderson, R.K.

    2002-01-01

    Elemental analyzers have been successfully coupled to stable-isotope-ratio mass spectrometers for online measurements of the δ34S isotopic composition of plants, animals and soils. We found that the online technology for automated δ34S isotopic determinations did not yield reproducible oxygen isotopic compositions in the SO2 produced, and as a result calculated δ34S values were often 1–3‰ too high versus their correct values, particularly for plant and animal samples with high C/S ratio. Here we provide empirical and analytical methods for correcting the S isotope values for oxygen isotope variations, and further detail a new SO2-SiO2 buffering method that minimizes detrimental oxygen isotope variations in SO2.

  15. A model predicting hydrogen and oxygen isotopes of mammalian hair at the landscape scale

    NASA Astrophysics Data System (ADS)

    Ehleringer, J.; Podlesak, D.; Cerling, T.; Chesson, L.; Bowen, G.

    2006-12-01

    A model has been developed to predict hydrogen and oxygen isotope ratios of keratin in hair of mammalian herbivores and omnivores, incorporating the influences of drinking water and dietary input. The isotopic composition of carbohydrates in food sources and the water in blood and tissues are predicted as intermediate components linking drinking water and dietary sources (environment) with hair (environmental recorder). This model is scaled to landscape and regional levels using geographic information system map predictions of the hydrogen and oxygen isotope ratios of drinking waters and anticipated hydrogen and oxygen isotope ratios of carbohydrate food sources. The model was tested using isotope ratios of human hair (an omnivore) from across the USA. We discuss the application of this model as a tool for providing spatially integrated information about the quality of primary productivity relevant to mammalian herbivores over time, through the effects of varying primary productivity on protein nitrogen balance of the herbivore.

  16. A Test of Carbon and Oxygen Stable Isotope Ratio Process Models in Tree Rings.

    NASA Astrophysics Data System (ADS)

    Roden, J. S.; Farquhar, G. D.

    2008-12-01

    Stable isotopes ratios of carbon and oxygen in tree ring cellulose have been used to infer environmental change. Process-based models have been developed to clarify the potential of historic tree ring records for meaningful paleoclimatic reconstructions. However, isotopic variation can be influenced by multiple environmental factors making simplistic interpretations problematic. Recently, the dual isotope approach, where the variation in one stable isotope ratio (e.g. oxygen) is used to constrain the interpretation of variation in another (e.g. carbon), has been shown to have the potential to de-convolute isotopic analysis. However, this approach requires further testing to determine its applicability for paleo-reconstructions using tree-ring time series. We present a study where the information needed to parameterize mechanistic models for both carbon and oxygen stable isotope ratios were collected in controlled environment chambers for two species (Pinus radiata and Eucalyptus globulus). The seedlings were exposed to treatments designed to modify leaf temperature, transpiration rates, stomatal conductance and photosynthetic capacity. Both species were grown for over 100 days under two humidity regimes that differed by 20%. Stomatal conductance was significantly different between species and for seedlings under drought conditions but not between other treatments or humidity regimes. The treatments produced large differences in transpiration rate and photosynthesis. Treatments that effected photosynthetic rates but not stomatal conductance influenced carbon isotope discrimination more than those that influenced primarily conductance. The various treatments produced a range in oxygen isotope ratios of 7 ‰. Process models predicted greater oxygen isotope enrichment in tree ring cellulose than observed. The oxygen isotope ratios of bulk leaf water were reasonably well predicted by current steady-state models. However, the fractional difference between models that

  17. The oxygen isotope equilibrium fractionation between sulfite species and water

    NASA Astrophysics Data System (ADS)

    Müller, Inigo A.; Brunner, Benjamin; Breuer, Christian; Coleman, Max; Bach, Wolfgang

    2013-11-01

    Sulfite is an important sulfoxy intermediate in oxidative and reductive sulfur cycling in the marine and terrestrial environment. Different aqueous sulfite species exist, such as dissolved sulfur dioxide (SO2), bisulfite (HSO3-), pyrosulfite (S2O52-) and sulfite sensu stricto (SO32-), whereas their relative abundance in solution depends on the concentration and the pH. Conversion of one species into another is rapid and involves in many cases incorporation of oxygen from, or release of oxygen to, water (e.g. SO2 + H2O ↔ HSO3- + H+), resulting in rapid oxygen isotope exchange between sulfite species and water. Consequently, the oxygen isotope composition of sulfite is strongly influenced by the oxygen isotope composition of water. Since sulfate does not exchange oxygen isotopes with water under most earth surface conditions, it can preserve the sulfite oxygen isotope signature that it inherits via oxidative and reductive sulfur cycling. Therefore, interpretation of δO values strongly hinges on the oxygen isotope equilibrium fractionation between sulfite and water which is poorly constrained. This is in large part due to technical difficulties in extraction of sulfite from solution for oxygen isotope analysis.

  18. Oxygen and hydrogen isotope fractionation during cellulose metabolism in Lemna gibba L

    SciTech Connect

    Yakir, D.; DeNiro, M.J. )

    1990-05-01

    Lemna gibba L. B3 was grown under heterotrophic, photoheterotrophic, and autotrophic conditions in water having a variety of hydrogen and oxygen isotopic compositions. The slopes of the linear regression lines between the isotopic composition of water and leaf cellulose indicated that under the three growth conditions about 40, 70, and 100% of oxygens and carbon-bound hydrogens of cellulose exchanged with those of water prior to cellulose formation. Using the equations of the linear relationships, we estimated the overall fractionation factors between water and the exchanged oxygen and carbon bound-hydrogen of cellulose. At least two very different isotope effects must determine the hydrogen isotopic composition of Lemna cellulose. One reflects the photosynthetic reduction of NADP, while the second reflects exchange reactions that occur subsequent to NADP reduction. Oxygen isotopic composition of cellulose apparently is determined by a single type of exchange reaction with water. Under different growth conditions, variations in metabolic fluxes affect the hydrogen isotopic composition of cellulose by influencing the extent to which the two isotope effects mentioned above are recorded. The oxygen isotopic composition of cellulose is not affected by such changes in growth conditions.

  19. Hydrogen and oxygen in brine shrimp chitin reflect environmental water and dietary isotopic composition

    NASA Astrophysics Data System (ADS)

    Nielson, Kristine E.; Bowen, Gabriel J.

    2010-03-01

    Hydrogen and oxygen isotope ratios of the common structural biopolymer chitin are a potential recorder of ecological and environmental information, but our understanding of the mechanisms of incorporation of H and O from environmental substrates into chitin is limited. We report the results of a set of experiments in which the isotopic compositions of environmental water and diet were varied independently in order to assess the contribution of these variables to the H and O isotopic composition of Artemia franciscana chitin. Hydrogen isotope ratios of chitin were strongly linearly correlated with both food and water, with approximately 26% of the hydrogen signal reflecting food and approximately 38% reflecting water. Oxygen isotopes were also strongly correlated with the isotopic composition of water and food, but whereas 69% of oxygen in chitin exchanged with environmental water, only 10% was derived from food. We propose that these observations reflect the position-specific, partial exchange of H and O atoms with brine shrimp body water during the processes of digestion and chitin biosynthesis. Comparison of culture experiments with a set of natural samples collected from the Great Salt Lake, UT in 2006 shows that, with some exceptions, oxygen isotope compositions of chitin track those of water, whereas hydrogen isotopes vary inversely with those of lake water. The different behavior of the two isotopic systems can be explained in terms of a dietary shift from allochthonous particulate matter with relatively higher δ 2H values in the early spring to autochthonous particulate matter with significantly lower δ 2H values in the late summer to autumn. These results suggest oxygen in chitin may be a valuable proxy for the oxygen isotopic composition of environmental water, whereas hydrogen isotope values from the same molecule may reveal ecological and biogeochemical changes within lakes.

  20. Oxygen isotope geochemistry of The Geysers reservoir rocks, California

    SciTech Connect

    Gunderson, Richard P.; Moore, Joseph N.

    1994-01-20

    Whole-rock oxygen isotopic compositions of Late Mesozoic graywacke, the dominant host rock at The Geysers, record evidence of a large liquid-dominated hydrothermal system that extended beyond the limits of the present steam reservoir. The graywackes show vertical and lateral isotopic variations that resulted from gradients in temperature, permeability, and fluid composition during this early liquid-dominated system. All of these effects are interpreted to have resulted from the emplacement of the granitic "felsite" intrusion 1-2 million years ago. The {delta}{sup 18}O values of the graywacke are strongly zoned around a northwest-southeast trending low located near the center of and similar in shape to the present steam system. Vertical isotopic gradients show a close relationship to the felsite intrusion. The {delta}{sup 18}O values of the graywacke decrease from approximately 15 per mil near the surface to 4-7 per mil 300 to 600 m above the intrusive contact. The {delta}{sup 18}O values then increase downward to 8-10 per mil at the felsite contact, thereafter remaining nearly constant within the intrusion itself. The large downward decrease in {delta}{sup 18}O values are interpreted to be controlled by variations in temperature during the intrusive event, ranging from 150{degree}C near the surface to about 425{degree}C near the intrusive contact. The upswing in {delta}{sup 18}O values near the intrusive contact appears to have been caused by lower rock permeability and/or heavier fluid isotopic composition there. Lateral variations in the isotopic distributions suggests that the effects of temperature were further modified by variations in rock permeability and/or fluid-isotopic composition. Time-integrated water:rock ratios are thought to have been highest within the central isotopic low where the greatest isotopic depletions are observed. We suggest that this region of the field was an area of high permeability within the main upflow zone of the liquid

  1. Local origins of interdecadal Pacific variability in the tropical and North Pacific Ocean: evidence from a comparative study of coral oxygen isotope records

    NASA Astrophysics Data System (ADS)

    Deng, Wenfeng; Wei, Gangjian

    2014-08-01

    Interdecadal Pacific variability (IPV) is commonly observed in both the tropical and mid-latitude Pacific Ocean, and has a widespread influence on surface climate in the Pan-Pacific Basin. This variability is recorded by climate proxies such as geochemical parameters preserved in corals. However, the origins of IPV remain uncertain. To shed light on this, interdecadal variations in two long coral δ18O records from Nauru Island and the South China Sea (SCS), respectively located in the tropical Pacific and the mid-latitude North Pacific Ocean, were investigated. The interdecadal fluctuations in the δ18O series from Nauru Island (tropical Pacific) match those of the NINO3.4 index reasonably well (r=-0.30, n=96, p=0.0015), but are not correlated with those of the Pacific decadal oscillation (PDO) index (r=-0.17, n=96, p=0.05). The δ18O time series from the SCS (northwestern Pacific), by contrast, co-vary with the PDO index (r=-0.30, n=156, p=0.0007), but are out of phase with the NINO3.4 index at the interdecadal timescale (r=0.04, n=156, p=0.31). The impact on the interdecadal variability of processes occurring outside the growth region of corals is generally weak. The results thus do not support a tropical origin of IPV, but demonstrate that the interdecadal variability in the tropical Pacific and the North Pacific originates predominantly from local coupled ocean-atmosphere processes within these regions. The results also suggest that tropical-extratropical interactions played a role in IPV between 1920 and 1940, which indicates that IPV is a complex climatic phenomenon that involves multiple forcing mechanisms.

  2. Oxygen Isotope Variability within Nautilus Shell Growth Bands

    PubMed Central

    2016-01-01

    Nautilus is often used as an analogue for the ecology and behavior of extinct externally shelled cephalopods. Nautilus shell grows quickly, has internal growth banding, and is widely believed to precipitate aragonite in oxygen isotope equilibrium with seawater. Pieces of shell from a wild-caught Nautilus macromphalus from New Caledonia and from a Nautilus belauensis reared in an aquarium were cast in epoxy, polished, and then imaged. Growth bands were visible in the outer prismatic layer of both shells. The thicknesses of the bands are consistent with previously reported daily growth rates measured in aquarium reared individuals. In situ analysis of oxygen isotope ratios using secondary ion mass spectrometry (SIMS) with 10 μm beam-spot size reveals inter- and intra-band δ18O variation. In the wild-caught sample, a traverse crosscutting 45 growth bands yielded δ18O values ranging 2.5‰, from +0.9 to -1.6 ‰ (VPDB), a range that is larger than that observed in many serial sampling of entire shells by conventional methods. The maximum range within a single band (~32 μm) was 1.5‰, and 27 out of 41 bands had a range larger than instrumental precision (±2 SD = 0.6‰). The results from the wild individual suggest depth migration is recorded by the shell, but are not consistent with a simple sinusoidal, diurnal depth change pattern. To create the observed range of δ18O, however, this Nautilus must have traversed a temperature gradient of at least ~12°C, corresponding to approximately 400 m depth change. Isotopic variation was also measured in the aquarium-reared sample, but the pattern within and between bands likely reflects evaporative enrichment arising from a weekly cycle of refill and replacement of the aquarium water. Overall, this work suggests that depth migration behavior in ancient nektonic mollusks could be elucidated by SIMS analysis across individual growth bands. PMID:27100183

  3. Oxygen Isotope Variability within Nautilus Shell Growth Bands.

    PubMed

    Linzmeier, Benjamin J; Kozdon, Reinhard; Peters, Shanan E; Valley, John W

    2016-01-01

    Nautilus is often used as an analogue for the ecology and behavior of extinct externally shelled cephalopods. Nautilus shell grows quickly, has internal growth banding, and is widely believed to precipitate aragonite in oxygen isotope equilibrium with seawater. Pieces of shell from a wild-caught Nautilus macromphalus from New Caledonia and from a Nautilus belauensis reared in an aquarium were cast in epoxy, polished, and then imaged. Growth bands were visible in the outer prismatic layer of both shells. The thicknesses of the bands are consistent with previously reported daily growth rates measured in aquarium reared individuals. In situ analysis of oxygen isotope ratios using secondary ion mass spectrometry (SIMS) with 10 μm beam-spot size reveals inter- and intra-band δ18O variation. In the wild-caught sample, a traverse crosscutting 45 growth bands yielded δ18O values ranging 2.5‰, from +0.9 to -1.6 ‰ (VPDB), a range that is larger than that observed in many serial sampling of entire shells by conventional methods. The maximum range within a single band (~32 μm) was 1.5‰, and 27 out of 41 bands had a range larger than instrumental precision (±2 SD = 0.6‰). The results from the wild individual suggest depth migration is recorded by the shell, but are not consistent with a simple sinusoidal, diurnal depth change pattern. To create the observed range of δ18O, however, this Nautilus must have traversed a temperature gradient of at least ~12°C, corresponding to approximately 400 m depth change. Isotopic variation was also measured in the aquarium-reared sample, but the pattern within and between bands likely reflects evaporative enrichment arising from a weekly cycle of refill and replacement of the aquarium water. Overall, this work suggests that depth migration behavior in ancient nektonic mollusks could be elucidated by SIMS analysis across individual growth bands. PMID:27100183

  4. Triple oxygen isotopes in biogenic and sedimentary carbonates

    NASA Astrophysics Data System (ADS)

    Passey, Benjamin H.; Hu, Huanting; Ji, Haoyuan; Montanari, Shaena; Li, Shuning; Henkes, Gregory A.; Levin, Naomi E.

    2014-09-01

    The 17O anomaly (Δ17O) of natural waters has been shown to be sensitive to evaporation in a way analogous to deuterium excess, with evaporated bodies of water (e.g., leaf waters, lake waters, animal body waters) tending to have lower Δ17O than primary meteoric waters. In animal body water, Δ17O relates to the intake of evaporated waters, evaporative effluxes of water, and the Δ17O value of atmospheric O2, which itself carries signatures of global carbon cycling and photochemical reactions in the stratosphere. Carbonates have the potential to record the triple oxygen isotope compositions of parent waters, allowing reconstruction of past water compositions, but such investigations have awaited development of methods for high-precision measurement of Δ17O of carbonate. We describe optimized methods based on a sequential acid digestion/reduction/fluorination approach that yield Δ17O data with the high precision (∼0.010‰, 1σ) needed to resolve subtle environmental signals. We report the first high-precision Δ17O dataset for terrestrial carbonates, focusing on vertebrate biogenic carbonates and soil carbonates, but also including marine invertebrates and high-temperature carbonates. We determine apparent three-isotope fractionation factors between the O2 analyte derived from carbonate and the parent waters of the carbonate. These in combination with appropriate temperature estimates (from clumped isotope thermometry, or known or estimated body temperatures) are used to calculate the δ18O and Δ17O of parent waters. The clearest pattern to emerge is the strong 17O-depletion in avian, dinosaurian, and mammalian body water (from analyses of eggshell and tooth enamel) relative to meteoric waters, following expected influences of evaporated water (e.g., leaf water) and atmospheric O2 on vertebrate body water. Parent waters of the soil carbonates studied here have Δ17O values that are similar to or slightly lower than global precipitation. Our results suggest

  5. Simulating oxygen isotope ratios in tree ring cellulose using a dynamic global vegetation model

    NASA Astrophysics Data System (ADS)

    Keel, Sonja G.; Joos, Fortunat; Spahni, Renato; Saurer, Matthias; Weigt, Rosemarie B.; Klesse, Stefan

    2016-07-01

    Records of stable oxygen isotope ratios in tree rings are valuable tools to reconstruct past climatic conditions and investigate the response of trees to those conditions. So far the use of stable oxygen isotope signatures of tree rings has not been systematically evaluated in dynamic global vegetation models (DGVMs). DGVMs integrate many hydrological and physiological processes and their application could improve proxy-model comparisons and the interpretation of oxygen isotope records. Here we present an approach to simulate leaf water and stem cellulose δ18O of trees using the LPX-Bern DGVM (LPX-Bern). Our results lie within a few per mil of measured tree ring δ18O of 31 different forest stands mainly located in Europe. Temporal means over the last 5 decades as well as interannual variations for a subset of sites in Switzerland are captured. A sensitivity analysis reveals that relative humidity, temperature, and the water isotope boundary conditions have the largest influence on simulated stem cellulose δ18O, followed by all climatic factors combined, whereas increasing atmospheric CO2 and nitrogen deposition exert no impact. We conclude that simulations with LPX-Bern are useful for investigating large-scale oxygen isotope patterns of tree ring cellulose to elucidate the importance of different environmental factors on isotope variations and therefore help to reduce uncertainties in the interpretation of δ18O of tree rings.

  6. Oxygen and hydrogen isotope signatures of Northeast Atlantic water masses

    NASA Astrophysics Data System (ADS)

    Voelker, Antje H. L.; Colman, Albert; Olack, Gerard; Waniek, Joanna J.; Hodell, David

    2015-06-01

    Only a few studies have examined the variation of oxygen and hydrogen isotopes of seawater in NE Atlantic water masses, and data are especially sparse for intermediate and deep-water masses. The current study greatly expands this record with 527 δ18O values from 47 stations located throughout the mid- to low-latitude NE Atlantic. In addition, δD was analyzed in the 192 samples collected along the GEOTRACES North Atlantic Transect GA03 (GA03_e=KN199-4) and the 115 Iberia-Forams cruise samples from the western and southern Iberian margin. An intercomparison study between the two stable isotope measurement techniques (cavity ring-down laser spectroscopy and magnetic-sector isotope ratio mass spectrometry) used to analyze GA03_e samples reveals relatively good agreement for both hydrogen and oxygen isotope ratios. The surface (0-100 m) and central (100-500 m) water isotope data show the typical, evaporation related trend of increasing values equatorward with the exception for the zonal transect off Cape Blanc, NW Africa. Off Cape Blanc, surface water isotope signatures are modified by the upwelling of fresher Antarctic Intermediate Water (AAIW) that generally has isotopic values of 0.0 to 0.5‰ for δ18O and 0 to 2‰ for δD. Along the Iberian margin the Mediterranean Outflow Water (MOW) is clearly distinguished by its high δ18O (0.5-1.1‰) and δD (3-6‰) values that can be traced into the open Atlantic. Isotopic values in the NE Atlantic Deep Water (NEADW) are relatively low (δ18O: -0.1 to 0.5‰; δD: -1 to 4‰) and show a broader range than observed previously in the northern and southern convection areas. The NEADW is best observed at GA03_e Stations 5 and 7 in the central NE Atlantic basin. Antarctic Bottom Water isotope values are relatively high indicating modification of the original Antarctic source water along the flow path. The reconstructed δ18O-salinity relationship for the complete data set has a slope of 0.51, i.e., slightly steeper than the 0

  7. The clumped isotopic record of Neoproterozoic carbonates, Sultanate of Oman

    NASA Astrophysics Data System (ADS)

    Bergmann, K. D.; Eiler, J. M.; Fischer, W. W.; Osburn, M. R.; Grotzinger, J. P.

    2011-12-01

    The Huqf Supergroup of the Sultanate of Oman records several important events in latest Precambrian time, including two glaciations in the Abu Mahara Group (ca. 725 - <645 Ma), the enigmatic Shuram carbon isotope excursion in the Nafun Group (ca. <645-547 Ma), and the Precambrian-Cambrian boundary in the Ara Group (ca. 547-540 Ma). This interval contains several extreme isotopic excursions, hypothesized to record perturbations of the surficial Earth carbon cycle or post-depositional diagenetic processes. Rigorous interpretation of these records requires a more thorough assessment of diagenetic processes. To better understand the significance and cause of these large amplitude isotopic excursions, we employed carbonate clumped isotope thermometry. This method allows us to estimate the absolute temperature of carbonate precipitation, including recrystallization, based on the temperature dependent abundance of carbonate ions containing both 13C and 18O. These estimates are accompanied by a measurement of carbonate δ18O, which in conjunction with temperature, can be used to calculate the oxygen isotopic composition of the fluid from which the carbonate precipitated. We analyzed stratigraphically constrained samples from a range of paleoenvironments with differing burial histories (1 - >10km maximum burial depth) to constrain the temperature and fluid composition of recrystallization. Clumped isotope temperatures from Huqf Supergroup samples range from 35-175°C. The isotopic composition of the fluid these rocks equilibrated with ranges from -3.7 to 15.7% VSMOW. This large range in temperature and fluid composition separates into distinct populations that differ systematically with independent constraints on petrography, stratigraphy and burial history. The data indicate the Abu Mahara, Nafun and Ara groups have unique diagenetic histories. In central Oman, the post-glacial Abu Mahara cap dolostone shows high temperature, rock buffered diagenesis (Tavg = 176°C; δ18

  8. Meteorites and their parent bodies: Evidence from oxygen isotopes

    NASA Technical Reports Server (NTRS)

    Clayton, R. N.

    1978-01-01

    Isotopic abundance variations among meteorites are used to establish genetic associations between meteorite classes. Oxygen isotope distributions between group II E irons with H-group ordinary chondrites and enstatic meteorites indicate that the parent bodies were formed out of pre-solar material that was not fully mixed at the time condensation occurred within the solar nebula.

  9. Galena oxidation investigations on oxygen and sulphur isotopes.

    PubMed

    Heidel, Claudia; Tichomirowa, Marion

    2011-06-01

    Batch experiments with the lead sulphide ore mineral galena were carried out in order to get information about the oxidation mechanisms and to contribute to the understanding of field data, especially those obtained from the mining-affected sites. Results indicate that oxygen and sulphur isotopes of dissolved sulphate may be useful tools for the investigation of galena oxidation mechanisms. However, some methodological modifications are necessary to obtain sufficient sulphate yields, which are a prerequisite for the reduction of the analytical uncertainty. Surface and hydrochemical investigations indicated that galena was dissolved non-oxidatively during the experiment at initial pH 2, whereas the oxidative dissolution of galena dominated in experiments at initial pH 6 and 8. No isotope results could be obtained from the experiment at initial pH 2 due to the low sulphate production. The oxidative dissolution of galena resulted in somewhat higher sulphate yields. Thus, the oxygen isotope composition of sulphate produced from galena oxidation could be determined for the first time. Oxygen in sulphate derived largely from water molecules; but minor amounts of molecular oxygen could be also observed. Both molecular oxygen and ferric iron may act as oxidants of galena. A variety of intermediate reactions allow for a variable oxygen isotope composition of sulphate. Sulphur isotopes of sulphate showed an enrichment of (32)S in sulphate (relative to galena), which increases with increasing pH. Sulphur isotope enrichment processes may be associated with the formation of anglesite.

  10. Oxygen isotope fractionation in stratospheric CO2

    NASA Technical Reports Server (NTRS)

    Thiemens, M. H.; Jackson, T.; Mauersberger, K.; Schueler, B.; Morton, J.

    1991-01-01

    A new cryogenic collection system has been flown on board a balloon gondola to obtain separate samples of ozone and carbon dioxide without entrapping major atmospheric gases. Precision laboratory isotopic analysis of CO2 samples collected between 26 and 35.5 km show a mass-independent enrichment in both O-17 and O-18 of about 11 per mil above tropospheric values. Ozone enrichment in its heavy isotopes was 9 to 16 percent in O3-50 and 8 to 11 percent in O3-49, respectively (Schueler et al., 1990). A mechanism to explain the isotope enrichment in CO2 has been recently proposed by Yung et al. (1991). The model is based on the isotope exchange between CO2 and O3 via O(1D), resulting in a transfer of the ozone isotope enrichment to carbon dioxide. Predicted enrichment and measured values agree well.

  11. Identifying Oxygen Isotopic Signatures of ENSO Dynamics Through Isotope-Enabled Regional Ocean Modeling

    NASA Astrophysics Data System (ADS)

    Stevenson, S.; Powell, B.; Merrifield, M. A.; Cobb, K. M.; Nusbaumer, J. M.; Noone, D. C.

    2015-12-01

    Coral oxygen isotope (δ18O) records provide important constraints on past variability in the El Nino/Southern Oscillation (ENSO). However, the relationship between ENSO activity and δ18O anomalies is subject to a high degree of uncertainty owing to both observational limitations and poorly understood dynamical processes. The isotope-enabled Regional Ocean Modeling System (isoROMS) is designed to address some of these uncertainties; isoROMS is a flexible modeling framework capable of simulating δ18O over an arbitrary domain at a variety of spatial resolutions. Initial results for isoROMS simulations at the central equatorial Pacific Line Islands chain over the 1979-2009 period are presented, using water isotopologue fluxes taken from the isotope-enabled NCAR Community Atmosphere Model (iCAM). Mesoscale ocean processes can significantly impact temperature and seawater δ18O variability under certain conditions, particularly during strong La Nina events. The variability in the ENSO/δ18O relationship is then investigated over the 20th century using a suite of isoROMS simulations conducted with combinations of atmosphere and ocean reanalysis products, in an effort to determine the optimal form of 'forward models' for predicting δ18O given local conditions. Implications for our ability to quantitatively reconstruct ENSO amplitude and the properties of El Nino/La Nina events are discussed.

  12. Behaviour of Structural Carbonate Stable Carbon and Oxygen Isotope Compositions in Bioapatite During Burning of Bone

    NASA Astrophysics Data System (ADS)

    Munro, L. E.; Longstaffe, F. J.; White, C. D.

    2003-12-01

    about 8-10‰ below 500° C, 5-6‰ between 500-700° C, and 8-10‰ above 700° C. CI and oxygen isotopic compositions of carbonate and phosphate are not well correlated. Only modest CI changes are recorded from 25-675° C, compared with much larger changes in oxygen isotopic composition, especially above 300° C. On average, original isotopic compositions are largely preserved for both phosphate (+/-1‰ ) and carbonate (+/-2‰ ) oxygen at <300° C. At higher temperatures, however, both phosphate and carbonate oxygen in the bioapatite are systematically depleted of oxygen-18 relative to original values.

  13. Holocene precipitation seasonality captured by a dual hydrogen and oxygen isotope approach at Steel Lake, Minnesota

    NASA Astrophysics Data System (ADS)

    Henderson, Anna K.; Nelson, David M.; Hu, Feng Sheng; Huang, Yongsong; Shuman, Bryan N.; Williams, John W.

    2010-12-01

    Middle-Holocene (8 to 4 ka BP) warmth and aridity are well recorded in sediment archives from midcontinental North America. However, neither the climatic driver nor the seasonal character of precipitation during this period is well understood because of the limitations of available proxy indicators. For example, an important challenge is to distinguish among the interacting effects of evaporation, temperature, or precipitation seasonality in existing δ 18O records from the region. Here we combine hydrogen isotopes of palmitic acid and oxygen isotopes of carbonate to derive lake-water isotopic values during the Holocene at Steel Lake in north-central Minnesota. In combination, these data enable us to separate variations in evaporation from variations in the isotopic composition of input-waters to lake. Variations in evaporation are used as a proxy for aridity and lake-water input isotopic values are used as a proxy for the isotopic values of meteoric precipitation. Our results suggest that lake-water input isotopic values were more negative during the middle Holocene than at present. To test whether these more negative values are related to temperature or precipitation seasonality, we compare pollen-inferred temperatures and the expected isotopic value of precipitation resulting from these temperatures to the reconstructed precipitation isotopic values. Results suggest that middle Holocene warmth and aridity were associated with increased evaporation rates and decreased summer precipitation. These inferences are consistent with climate simulations that highlight the role of seasonal insolation and sea surface temperatures in driving variations in precipitation seasonality during the Holocene. Results also suggest that changes in Holocene precipitation seasonality may have influenced the expansion of the prairie-forest border in Minnesota as well as regional variations in grassland community composition. This study demonstrates the efficacy of the dual hydrogen and

  14. Hydrogen burning of the rare oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Buckner, Matthew Quinn

    2014-10-01

    At the Laboratory for Experimental Nuclear Astrophysics (LENA), two rare oxygen isotope proton capture studies were performed at low energies--- 18O(p,gamma)19F and 17O( p,gamma)18F. The goal of each study was to improve thermonuclear reaction rates at stellar plasma temperatures relevant to 18O and 17O destruction, respectively. The stellar nucleosynthesis temperature regime corresponds to very low proton bombarding energies. At these low energies, the Coulomb barrier suppresses the reaction yield in the laboratory, and environmental backgrounds dominate the detected signal, making it difficult to differentiate the gamma-cascade from background. At LENA, the electron cyclotron resonance (ECR) ion source produces intense, low-energy proton beam, and these high currents boost the reaction yield. LENA, a ``sea-level" facility dedicated to nuclear astrophysics, also has a coincidence detector setup that reduces environmental background contributions and boosts signal-to-noise. The sensitivity afforded by gammagamma-coincidence and high beam current allowed these rare oxygen isotope reactions to be probed at energies that correspond to stellar plasma temperatures. For stars with masses between 0.8 solar masses < M < 8.0 solar masses, nucleosynthesis enters its final phase during the asymptotic giant branch (AGB) stage. This is an evolutionary period characterized by grain condensation that occurs in the stellar atmosphere; the star also experiences significant mass loss during this period of instability. Presolar grain production can often be attributed to this unique stellar environment. A subset of presolar oxide grains features dramatic 18O depletion that can not be explained by the standard asymptotic giant star burning stages and dredge-up models. An extra mixing process for low-mass asymptotic giant branch stars, known as cool bottom processing (CBP), was used in the literature to explain this and other anomalies. Cool bottom processing can also occur during the

  15. Foraminifera isotopic records... with special attention to high northern latitudes and the impact of sea-ice distillation processes

    NASA Astrophysics Data System (ADS)

    Hillaire-Marcel, Claude

    2011-05-01

    Since the reassessment of oxygen isotope paleotemperatures by N. Shackleton in the late 60s, most papers using isotopic records from planktic or benthic foraminifers imply a direct relationship between oxygen isotopes in seawater and the ice/ocean volume, thus some linkage with salinity, sea level, etc. Such assumptions are also made when incorporating "isotopic modules" in coupled models. Here, we will further examine the linkages between salinity and oxygen isotope ratios of sea-water recorded by foraminifers, and their potential temporal and spatial variability, especially in the northern North Atlantic and the Arctic oceans. If temporal and spatial changes in the isotopic composition of precipitations and ice meltwaters tune the isotopic properties of the fresh water end-member that dilutes the ocean, rates of sea-ice formation and evaporation at the ocean surface play a further role on the salt and oxygen isotope contents of water masses. Thus, the oxygen 18-salinity relationship carries a specific isotopic signature for any given water mass. At the ocean scale, residence time and mixing of these water masses, as well as the time dependent-achievement of proxy-tracer equilibrium, will also result in variable recordings of mass transfers into the hydrosphere, notable between ice-sheets and ocean. Since these records in water mass may vary in both amplitude and time, direct correlations of isotopic records will potentially be misleading. Implications of such issues on the interpretation of oxygen isotope records from the sub-arctic seas will be discussed, as well as the inherent flaws of such records due to sedimentological and or ecological parameters.

  16. Silicon and oxygen isotopic trends in Mesozoic radiolarites

    NASA Astrophysics Data System (ADS)

    Bôle, Maximlien; Baumgartner Peter, O.; Lukas, Baumgartner; Anne-Sophie, Bouvier; Rie, Hori; Masayuki, Ikeda

    2016-04-01

    Silicon and oxygen isotopes (δ30Si and δ18O) of siliceous tests (diatoms, sponges and radiolarians) preserve environmental signatures in unconsolidated sediments, but few studies show such signatures for ancient biosilicieous rocks. In Precambrian cherts from greenstone belts, small scaled isotopic variations were interpreted as a primary diagenetic feature. They were used, coupled to mean δ18O, to reconstruct seawater temperature at which cherts precipitated. Here, we examine stable isotopes in Mesozoic biogenic cherts that may also preserve an environmental signature. We measured δ30Si and δ18O in situ by SIMS, in the chalcedony of individual radiolarian tests preserved in Mesozoic radiolarites. Microanalysis of chalcedony, rather than the bulk rock isotopic composition, is likely to reveal a palaeoenvironmental signal, since it is derived from biogenic opal, the most mobile silica phase during earliest diagenesis. Our data reveal clear trends through several Mesozoic radiolarite sections from Panthalassa (Kiso River, Japan) and Western Tethys (Sogno, Italy). δ18O records measured in radiolarites show a relatively good correlation to δ18O-variations of Mesozoic low magnesium calcite shells, which are commonly used as a palaeotemperature proxy. Once these variations, attributed to seawater temperature, are removed, the residual δ18O trends are opposite to the δ30Si trends. δ30Si increases from Middle Triassic to Early Jurassic in the Kiso River sections and decrease during the Middle Jurassic in the Sogno section. The observed d30Si-trends are likely to represent a palaeoenvironmental signal, because they are not compatible with simple models of progressive diagenesis along P/T-paths (or depth below sea bottom in drill holes). Among the palaeoenvironmental factors that may have influenced these trends are the oceanic silica cycle changing though time, oceanic circulation and/or the palaeogeographic location of each studied site. Siliceous organisms are

  17. Oxygen isotopic composition of relict olivine grains in cosmic spherules: Links to chondrules from carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Rudraswami, N. G.; Prasad, M. Shyam; Nagashima, K.; Jones, R. H.

    2015-09-01

    Most olivine relict grains in cosmic spherules selected for the present study are pristine and have not been disturbed during their atmospheric entry, thereby preserving their chemical, mineralogical and isotopic compositions. In order to understand the origin of the particles, oxygen isotope compositions of relict olivine grains in twelve cosmic spherules collected from deep sea sediments of the Indian Ocean were studied using secondary ion mass spectrometry. Most of the data lie close to the CCAM (Carbonaceous Chondrite Anhydrous Mineral) line, with Δ17O ranging from -5‰ to 0‰. The data overlap oxygen isotopic compositions of chondrules from carbonaceous chondrites such as CV, CK, CR and CM, which suggests that chondrules from carbonaceous chondrites are the source of relict grains in cosmic spherules. Chemical compositions of olivine in cosmic spherules are also very similar to chondrule olivine from carbonaceous chondrites. Several olivine relict grains in three cosmic spherules are 16O-rich (Δ17O -21.9‰ to -18.7‰), similar to oxygen isotopic compositions observed in calcium aluminum rich inclusions (CAIs), amoeboid olivine aggregates (AOAs), and some porphyritic chondrules from carbonaceous chondrites. These grains appear to have recorded the initial oxygen isotopic composition of the inner solar nebula. Three olivine grains from two cosmic spherules have δ18O values >+20‰, which could be interpreted as mixing with stratospheric oxygen during atmospheric entry.

  18. Oxygen-isotope fractionation between marine biogenic silica and seawater

    SciTech Connect

    Matheney, R.K.; Knauth, L.P. )

    1989-12-01

    A stepwise fluorination technique has been used to selectively react away the water component of hydrous silica in order to better investigate the oxygen-isotope fractionation between biogenic opal and seawater, and to determine whether all taxa produce opal which is suitable for oxygen isotope paleothermometry. {delta}{sup 18}O of the tetrahedrally coordinated silicate oxygen of siliceous sponge spicules grown at a wide variety of temperatures varies independently of temperature. {delta}{sup 18}O from an Eocene radiolarian ooze sample is much more enriched than would be expected from any reasonable isotopic temperature curve, given the probable growing temperature of the sample. {delta}{sup 18}O of diatom samples seems to vary systematically with temperature and to conform approximately to the isotopic temperature curve for diatom frustules obtained by Labeyrie and coworkers using an entirely different analytical technique. Sponges appear to precipitate silica in isotopic disequilibrium with seawater oxygen, and old radiolarian silica may exchange readily with could oceanic bottom water. Neither will apparently be useful for paleoclimate reconstructions. Diatoms maybe useful in deducing ancient surface-water temperatures, but the systematic variation of {alpha} with temperature for diatoms may not be related to the quartz-H{sub 2}O equilibrium isotope fractionation.

  19. The rate of oxygen isotope exchange between nitrate and water

    NASA Astrophysics Data System (ADS)

    Kaneko, Masanori; Poulson, Simon R.

    2013-10-01

    The oxygen isotope exchange rate between nitrate and water was measured at a temperature of 50-80 °C and pH -0.6 to 1.1. Oxygen isotope exchange is a first-order reaction, with the exchange rate being strongly affected by both reaction temperature and pH, with increased rates of isotope exchange at higher temperatures and lower pH values. The rate of oxygen isotope exchange under natural conditions is extremely slow, with an estimated half-life for isotope exchange of 5.5 × 109 years at 25 °C and pH 7. The extremely slow rate of oxygen isotope exchange between nitrate and water under typical environmental conditions illustrates that nitrate-δ18O signatures (and also nitrate δ17O and Δ17O signatures) associated with various nitrate sources, as well as isotope compositions produced by biogeochemical processes, will be preserved. Hence, it is valid to use the value of nitrate-δ18O to investigate the sources and biogeochemical behavior of nitrate, in a similar manner to the use of sulfate-δ18O signatures to study the sources and biogeochemical behavior of sulfate. Equilibrium oxygen isotope fractionation factors have been determined, although quantification of the nitrate-water equilibrium fractionation factor is not possible due to the presence of nitrate as both protonated (i.e. HNO3) and unprotonated forms (i.e. NO3-) under the experimental conditions, and the difficulty in accurately calculating nitrate speciation in low pH, high ionic strength solutions.

  20. Oxygen Isotopes in Early Solar System Materials: A Perspective Based on Microbeam Analyses of Chondrules from CV Carbonaceous Chondrites

    NASA Technical Reports Server (NTRS)

    Jones, R. H.; Leshin, L. A.; Guan, Y.

    2004-01-01

    Some of the biggest challenges to understanding the early history of the solar system include determining the distribution of oxygen isotopes amongst materials that existed in the solar nebula, and interpreting the processes that might have resulted in the observed isotopic distributions. Oxygen isotope ratios in any individual mineral grain from a chondritic meteorite may be the cumulative product of a variety of processes, including stellar nucleosynthetic events, gas/solid interactions in the molecular cloud, mixing of independent isotopic reservoirs in the nebula, mass-independent processing in the nebula, and mass-dependent fractionation effects in various environments. It is not possible to unravel this complex isotopic record unless the distribution of oxygen isotope ratios in chondritic materials is fully understood.

  1. Baseline shifts in coral skeletal oxygen isotopic composition: a signature of symbiont shuffling?

    NASA Astrophysics Data System (ADS)

    Carilli, J. E.; Charles, C. D.; Garren, M.; McField, M.; Norris, R. D.

    2013-06-01

    Decades-long records of the stable isotopic composition of coral skeletal cores were analyzed from four sites on the Mesoamerican Reef. Two of the sites exhibited baseline shifts in oxygen isotopic composition after known coral bleaching events. Changes in pH at the calcification site caused by a change in the associated symbiont community are invoked to explain the observed shift in the isotopic composition. To test the hypothesis that changes in symbiont clade could affect skeletal chemistry, additional coral samples were collected from Belize for paired Symbiodinium identification and skeletal stable isotopic analysis. We found some evidence that skeletal stable isotopic composition may be affected by symbiont clade and suggest this is an important topic for future investigation. If different Symbiodinium clades leave consistent signatures in skeletal geochemical composition, the signature will provide a method to quantify past symbiont shuffling events, important for understanding how corals are likely to respond to climate change.

  2. The isotopic homogeneity in the early solar system: Revisiting the CAI oxygen isotopic anomaly

    NASA Astrophysics Data System (ADS)

    Ozima, M.; Yamada, A.

    2009-12-01

    Since the first discovery of the mass-independently fractionated oxygen isotopes in anhydrous, high temperature Ca-Al rich inclusion minerals in carbonaceous meteorites (CAIs) by Clayton et al. (1), their common occurrence in primitive meteorites has generally been regarded to reflect some fundamental process prevalent in the early solar nebula. The CAI oxygen isotopic composition is uniquely characterized by (i) large mass independent isotopic fractionation and (ii) their isotopic data in an oxygen three isotope plot (δ17O - δ18O (δ17O ≡ {(17O/16O)/(17O/16O)SMOW - 1} × 1000) yield nearly a straight line with a slope 1.0. In establishing these characteristics, ion microprobe analyses has played a central role, especially an isotopic mapping technique (isotopography) was crucial (e.g., 2). The extraordinary oxygen isotopic ratio in CAIs is widely attributed to the self-shielding absorption of UV radiation in CO, one of the dominant chemical compounds in the early solar nebula (3). However, the self-shielding scenario necessarily leads to the unusual prediction that a mean solar oxygen isotopic composition differs from most of planetary bodies including Earth, Moon, and Mars. If the self-shielding process were indeed responsible to the CAI oxygen isotopic anomaly, this would require a fundamental revision of the current theory of the origin of the solar system, which generally assumes the initial total vaporization of nebula material to give rise to isotopic homogenization. The GENESIS mission launched in 2001(4), which collected oxygen in the solar wind was hoped to resolve the isotopic composition of the Sun. However, because of difficulties in correcting for instrumental and more importantly for intrinsic isotopic fractionation between the SW and the Sun, a final answer is yet to be seen (5). Here, we show on the basis of the oxygen isotopic fractionation systematics that the self shielding hypothesis cannot explain the key characteristics of the CAI oxygen

  3. Leaf water oxygen isotope measurement by direct equilibration.

    PubMed

    Song, Xin; Barbour, Margaret M

    2016-08-01

    The oxygen isotope composition of leaf water imparts a signal to a range of molecules in the atmosphere and biosphere, but has been notoriously difficult to measure in studies requiring a large number of samples as a consequence of the labour-intensive extraction step. We tested a method of direct equilibration of water in fresh leaf samples with CO2 , and subsequent oxygen isotope analysis on an optical spectrometer. The oxygen isotope composition of leaf water measured by the direct equilibration technique was strongly linearly related to that of cryogenically extracted leaf water in paired samples for a wide range of species with differing anatomy, with an R(2) of 0.95. The somewhat more enriched values produced by the direct equilibration method may reflect lack of full equilibration with unenriched water in the vascular bundles, but the strong relationship across a wide range of species suggests that this difference can be adequately corrected for using a simple linear relationship.

  4. Oxygen isotope variability within Nautilus shell growth bands

    DOE PAGES

    Linzmeier, Benjamin J.; Kozdon, Reinhard; Peters, Shanan E.; Valley, John W.

    2016-04-21

    Nautilus is often used as an analogue for the ecology and behavior of extinct externally shelled cephalopods. Nautilus shell grows quickly, has internal growth banding, and is widely believed to precipitate aragonite in oxygen isotope equilibrium with seawater. Pieces of shell from a wild-caught Nautilus macromphalus from New Caledonia and from a Nautilus belauensis reared in an aquarium were cast in epoxy, polished, and then imaged. Growth bands were visible in the outer prismatic layer of both shells. The thicknesses of the bands are consistent with previously reported daily growth rates measured in aquarium reared individuals. In situ analysis ofmore » oxygen isotope ratios using secondary ion mass spectrometry (SIMS) with 10 μm beam-spot size reveals inter- and intra-band δ18O variation. In the wild-caught sample, a traverse crosscutting 45 growth bands yielded δ18O values ranging 2.5‰, from +0.9 to -1.6 ‰ (VPDB), a range that is larger than that observed in many serial sampling of entire shells by conventional methods. The maximum range within a single band (~32 μm) was 1.5‰, and 27 out of 41 bands had a range larger than instrumental precision (±2 SD = 0.6‰). The results from the wild individual suggest depth migration is recorded by the shell, but are not consistent with a simple sinusoidal, diurnal depth change pattern. In addition, to create the observed range of δ18O, however, this Nautilus must have traversed a temperature gradient of at least ~12°C, corresponding to approximately 400 m depth change. Isotopic variation was also measured in the aquarium-reared sample, but the pattern within and between bands likely reflects evaporative enrichment arising from a weekly cycle of refill and replacement of the aquarium water. Overall, this work suggests that depth migration behavior in ancient nektonic mollusks could be elucidated by SIMS analysis across individual growth bands.« less

  5. Genetic algorithm as a correlation tool - speleothems stable isotope records example

    NASA Astrophysics Data System (ADS)

    Pawlak, J.; Hercman, H.

    2012-04-01

    The isotopic composition of oxygen and carbon in cave speleothems is a valuable source of paleoenvironmental information. Oxygen isotopic composition reflects the mean annual temperature at the cave area and the isotopic composition of the infiltering water. Carbon isotopic composition reflects the level of development of soil and vegetation type at the surface. Calcites from cave speleothems can be usually dated by U- series method but U-series method has limitations. One of the most critical is cleanest of analysed calcite. Any detrital admixtures make contamination by initial thorium and dating results are not reliable. In such a situation there is a problem with the time scale estimation of isotopic data. Oxygen stratigraphy of carbonate marine sediments base on the correlation of oxygen isotopic sequence from studied profile with the global standard curve. Similar solution could be applied to the isotopic profiles obtained from cave speleothems. In this case any isotopic record can be correlated with a record which has well defined age. Such correlations can be made on the basis of arbitrary decisions of the researcher however, such procedure may be suffered by subjectively evaluation. Therefore we decided to develop a tool that will enable the correlation of isotopic profiles. Cave speleothems grown with a variable crystallization rate, so similar stretch of time can be represented by the sediments of varying thickness. The process of correlation of isotope curves consists on free shifting of data points ( accordance with the rule of superposition ) belonging to the record with undetermined age, relative to the record with well defined age. Each generated position is evaluated. The best position is accepted as a true position. Such procedure requires the use of an algorithm, which is able to efficient search of large (almost infinite) set of possible positions. Genetic algorithm is a tool that could find the optimal solution in a set of large number of

  6. Oxygen Isotope Signatures of Water Masses and Planktonic Carbonate Shells of Southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Venancio, I. M.; Belem, A. L.; Albuquerque, A.; Azevedo, A. G.; Barbosa, C. F.; Capilla, R.; Water Hunters

    2011-12-01

    The continental shelf of southeastern Brazil around Cabo Frio is an important region connecting the Campos and Santos basin, two main oil producing areas, characterized by the occurrence of three main water masses: the (1) warm surface Tropical Water (TW) with temperature ranging between 24-28°C and salinities higher then 36.8, carried by the Brazil Current; overlaying (2) the cooler South Atlantic Central Water (SACW) with temperatures below 18°C; and (3) Coastal Water (CW) which results from mixing of shelf waters with continental drainage showing low salinity values (<34). Eddy-induced and wind-driven upwelling zones can be found during specific meteorological and oceanographic conditions, when SACW can be found at the surface and TW far away from the coast. Oxygen isotopic ratio (δ18O) can be used as a proxy when the transfer rate between water and planktonic carbonate shells can be coupled to these oceanographic conditions. In this study water samples from different water masses and conditions as well as living species of planktonic foraminifera and pteropods were collected using plankton tows for analyses of oxygen isotope composition. We established ranges of oxygen isotope ratio values together with hydrographic data for the different water masses present in the region. First range between 1.0 and 0.75 was characterized as TW; second range with values below 0.75 and higher than 0.6 showed CW and mixing zones; and values below 0.6 indicated the SACW. These ranges are related to those found in literature and well correlated to the oceanographic conditions found in the region. Isotope records of both foraminifera and pteropods shells showed distinct patterns for the different water masses where they were sampled, due to inter-specific oxygen isotope transfer function. This study demonstrates the use of combined water and planktonic carbonate shells oxygen isotope analysis for generating more reliable paleo-oceanographic proxies to use in marine sediment

  7. Atmospheric methane isotope records during MIS 4

    NASA Astrophysics Data System (ADS)

    Sowers, Todd; Bock, Michael; Mitchell, Hailey

    2014-05-01

    The long-term δ13CH4record has led to a new paradigm in our thinking of the biogeochemistry of atmospheric CH4 (Möller et al. 2013). Throughout the last glacial period, abrupt D/O CH4changes appear to be decoupled from δ13CH4, while for δDCH4 we are still missing the big picture. The lack of a clear long-term relationship between loading changes and the isotopic composition of atmospheric CH4suggests multiple sources/sinks were responsible for the observed changes and/or that the characteristic isotope value for some of these sources may have changed over time. During the early part of MIS 4, we observed a ~4o increase in δ13CH4during a period when CH4changes were less than 50 ppb. We measured 12 ice core samples from the NEEM core for δDCH4 covering DO 8 and the MIS 5-4 transition. These new δDCH4 data compliment previously published δDCH4 data from EDML covering the same period (Möller et al. 2013). Replicate analyses of NEEM ice from DO 8 agreed with previously measured samples from NGRIP (Bock et al., 2010). External precision of the analyses based on replicate air standards run throughout each analytical day were ±1.8‰These data were overlain on previously measured δ13CH4data from the Vostok and EDML ice cores from the same periods. The δ13CH4data for the MIS4 start at ~ -48o around 75ka and increase to -44o at 65ka and then decrease to -46o by 59ka. In contrast, NEEM δDCH4 values start at -90o at 70ka and decrease to -97o at 64ka before increasing to -92o by 59ka. These two records appear to be roughly in phase with one another but opposite in the sign of their changes. Comparison between NEEM and EDML δDCH4 data for MIS4 suggest the interpolar δDCH4 difference increases somewhat during the δ13CH4transition. We plan to discuss these records in terms of constraints on the biogeochemistry of atmospheric methane during MIS 4. Bock, M., J. Schmitt, L. Möller, R. Spahni, T. Blunier and H. Fischer (2010). "Hydrogen Isotopes Preclude Marine

  8. Oxygen isotope fractionation in divalent metal carbonates

    USGS Publications Warehouse

    O'Neil, J.R.; Clayton, R.N.; Mayeda, T.K.

    1969-01-01

    Equilibrium fractionation factors for the distribution of 18O between alkaline-earth carbonates and water have been measured over the temperature range 0-500??C. The fractionation factors ?? can be represented by the equations CaCO3-H2O, 1000 ln??=2.78(106 T-2)-3.39, SrCO3-H 2O, 1000 ln??=2.69(106 T-2)-3.74, BaCO3-H2O, 1000 ln??=2.57(106 T -2)-4.73. Measurements on MnCO3, CdCO3, and PbCO3 were made at isolated temperatures. A statistical-mechanical calculation of the isotopic partition function ratios gives reasonably good agreement with experiment. Both cationic size and mass are important in isotopic fractionation, the former predominantly in its effect on the internal vibrations of the anion, the latter in its effect on the lattice vibrations.

  9. Microbial cycling, oxidative weathering, and the triple oxygen isotope consequences for marine sulfate

    NASA Astrophysics Data System (ADS)

    Johnston, D. T.; Cowie, B.; Turchyn, A. V.; Antler, G.; Gill, B. C.; Berelson, W.

    2015-12-01

    Microorganisms are responsible for most geochemical sulfur cycling in the ocean. On both modern and geological time scales, stable isotope ratios often serve as a mechanism to track conspicuous or coupled microbial processes, which in turn inform burial fluxes. The most common example of this approach is the use of sulfur isotopes in sulfate and sulfide (both aqueous and in mineral form) to track everything from rates of microbial processes through to the presence/absence of certain metabolic processes in a given environment. The use of oxygen isotope ratios in sulfate has developed in a similar fashion, providing complementary information to that of sulfur isotopes. Through our current work, we will extend the application of oxygen isotopes to include the trace stable oxygen isotope, 17O. These data are facilitated by a new laser F2 fluorination technique running at Harvard, and accompanied by the calibration of a suite of common sulfate standards. At first blush, 16O - 17O - 18O systematics should carry mass-dependent microbial fractionations with process-specific mass laws that are resolvable at the level of our analytical precision. We look to calibrate these biogeochemical effects through the integrated picture captured in marine pore water sulfate profiles, where the 18O/16O is known to evolve. In compliment, riverine sulfate (the sulfate input to the ocean) is an oxidative weathering product and is posited to carry a memory effect of tropospheric O2. Interestingly, the 17O/16O of that O2 carries a mass-independent signal reflecting the balance between stratospheric reactions and Earth surface biospheric fluxes. Through this presentation, we look to calibrate the controls on the balance between biospheric and atmospheric contributions to the marine sulfate reservoir. This is enabled by a series of isotope mass-balance models and with the ultimate goal of developing the geological triple oxygen isotope records of sulfate as a new environmental proxy for paleo

  10. Photosynthetic fractionation of the stable isotopes of oxygen and carbon

    SciTech Connect

    Guy, R.D. ); Fogel, M.L.; Berry, J.A. )

    1993-01-01

    Isotope discrimination during photosynthetic exchange of O[sub 2] and CO[sub 2] was measured using enzyme, thylakoid, and whole cell preparations. Evolved oxygen from isolated spinach thylakoids was isotopically identical (within analytical error) to its source water. Similar results were obtained with Anacystis nidulans Richter and Phaeodactylum tricornutum Bohlin cultures purged with helium. For consumptive reactions, discrimination ([triangle], where 1 + [triangle]/1000 equals the isotope effect, k[sup 16]/k[sup 18] or k[sup 12]/k[sup 13]) was determined by analysis of residual substrate (O[sub 2] or CO[sub 2]). The [triangle] for the Mehler reaction, mediated by ferredoxin or methylviologen, was 15.3[per thousand]. Oxygen isotope discrimination during oxygenation of ribulose-1,5-bisphosphate (RuBP) catalyzed by RuBP carboxylase/oxygenase (Rubisco) was 21.3[per thousand] and independent of enzyme source, unlike carbon isotope dicrimination: 30.3[per thousand] for spinach enzyme and 19.6 to 23[per thousand] for Rhodospirillum rubrum and A. nidulans enzymes, depending on reaction conditions. The [triangle] for O[sub 2] consumption catalyzed by glycolate oxidase was 22.7[per thousand]. Consistent with this, when Asparagus sprengeri Regel mesopyll cells approached the compensation point within a sealed vessel, the [delta][sup 18]O of dissolved O[sub 2] came to a steady-state value of about 21.5[per thousand] relative to the source water. The results provide improved estimates of discrimination factors in several reactions prominent in the global oxygen cycle and indicate that photorespiration plays a significant part in determining the isotopic composition of atmospheric oxygen. 47 refs., 8 figs., 2 tabs.

  11. Calcium and Oxygen Isotopic Composition of Calcium Carbonates

    NASA Astrophysics Data System (ADS)

    Niedermayr, Andrea; Eisenhauer, Anton; Böhm, Florian; Kisakürek, Basak; Balzer, Isabelle; Immenhauser, Adrian; Jürgen Köhler, Stephan; Dietzel, Martin

    2016-04-01

    Different isotopic systems are influenced in multiple ways corresponding to the crystal structure, dehydration, deprotonation, adsorption, desorption, isotope exchange and diffusion processes. In this study we investigated the structural and kinetic effects on fractionation of stable Ca- and O-isotopes during CaCO3 precipitation. Calcite, aragonite and vaterite were precipitated using the CO2 diffusion technique[1]at a constant pH of 8.3, but various temperatures (6, 10, 25 and 40° C) and precipitation rates R (101.5 to 105 μmol h-1 m-2). The calcium isotopic fractionation between solution and vaterite is lower (Δ44/40Ca= -0.10 to -0.55 ‰) compared to calcite (-0.69 to -2.04 ‰) and aragonite (-0.91 to -1.55 ‰). In contrast the fractionation of oxygen isotopes is highest for vaterite (32.1 ‰), followed by aragonite (29.2 ‰) and calcite (27.6 ‰) at 25° C and equilibrium. The enrichment of 18O vs. 16O in all polymorphs decreases with increasing precipitation rate by around -0.7 ‰ per log(R). The calcium isotopic fractionation between calcite/ vaterite and aqueous Ca2+ increases with increasing precipitation rate by ˜0.45 ‰ per log(R) and ˜0.1 ‰ per log(R) at 25° C and 40° C, respectively. In contrast the fractionation of Ca-isotopes between aragonite and aqueous Ca2+ decreases with increasing precipitation rates. The large enrichment of 18O vs. 16O isotopes in carbonates is related to the strong bond of oxygen to the small and highly charged C4+-ion. In contrast equilibrium isotopic fractionation between solution and calcite or vaterite is nearly zero as the Ca-O bond length is similar for calcite, vaterite and the hydrated Ca. Aragonite incorporates preferentially the lighter 40Ca isotope as it has very large Ca-O bonds in comparison to the hydrated Ca. At the crystal surface the lighter 40Ca isotopes are preferentially incorporated as dehydration and diffusion of lighter isotopes are faster. Consequently, the surface becomes enriched in 40

  12. Calcium and Oxygen Isotopic Composition of Calcium Carbonates

    NASA Astrophysics Data System (ADS)

    Niedermayr, Andrea; Eisenhauer, Anton; Böhm, Florian; Kisakürek, Basak; Balzer, Isabelle; Immenhauser, Adrian; Jürgen Köhler, Stephan; Dietzel, Martin

    2016-04-01

    Different isotopic systems are influenced in multiple ways corresponding to the crystal structure, dehydration, deprotonation, adsorption, desorption, isotope exchange and diffusion processes. In this study we investigated the structural and kinetic effects on fractionation of stable Ca- and O-isotopes during CaCO3 precipitation. Calcite, aragonite and vaterite were precipitated using the CO2 diffusion technique[1]at a constant pH of 8.3, but various temperatures (6, 10, 25 and 40° C) and precipitation rates R (101.5 to 105 μmol h‑1 m‑2). The calcium isotopic fractionation between solution and vaterite is lower (Δ44/40Ca= -0.10 to -0.55 ‰) compared to calcite (-0.69 to -2.04 ‰) and aragonite (-0.91 to -1.55 ‰). In contrast the fractionation of oxygen isotopes is highest for vaterite (32.1 ‰), followed by aragonite (29.2 ‰) and calcite (27.6 ‰) at 25° C and equilibrium. The enrichment of 18O vs. 16O in all polymorphs decreases with increasing precipitation rate by around -0.7 ‰ per log(R). The calcium isotopic fractionation between calcite/ vaterite and aqueous Ca2+ increases with increasing precipitation rate by ˜0.45 ‰ per log(R) and ˜0.1 ‰ per log(R) at 25° C and 40° C, respectively. In contrast the fractionation of Ca-isotopes between aragonite and aqueous Ca2+ decreases with increasing precipitation rates. The large enrichment of 18O vs. 16O isotopes in carbonates is related to the strong bond of oxygen to the small and highly charged C4+-ion. In contrast equilibrium isotopic fractionation between solution and calcite or vaterite is nearly zero as the Ca-O bond length is similar for calcite, vaterite and the hydrated Ca. Aragonite incorporates preferentially the lighter 40Ca isotope as it has very large Ca-O bonds in comparison to the hydrated Ca. At the crystal surface the lighter 40Ca isotopes are preferentially incorporated as dehydration and diffusion of lighter isotopes are faster. Consequently, the surface becomes enriched in

  13. Extreme crustal oxygen isotope signatures preserved in coesite in diamond.

    PubMed

    Schulze, Daniel J; Harte, Ben; Valley, John W; Brenan, James M; Channer, Dominic M De R

    2003-05-01

    The anomalously high and low oxygen isotope values observed in eclogite xenoliths from the upper mantle beneath cratons have been interpreted as indicating that the parent rock of the eclogites experienced alteration on the ancient sea floor. Recognition of this genetic lineage has provided the foundation for a model of the evolution of the continents whereby imbricated slabs of oceanic lithosphere underpin and promote stabilization of early cratons. Early crustal growth is thought to have been enhanced by the addition of slab-derived magmas, leaving an eclogite residuum in the upper mantle beneath the cratons. But the oxygen isotope anomalies observed in eclogite xenoliths are small relative to those in altered ocean-floor basalt and intermediate-stage subduction-zone eclogites, and this has hindered acceptance of the hypothesis that the eclogite xenoliths represent subducted and metamorphosed ocean-floor basalts. We present here the oxygen isotope composition of eclogitic mineral inclusions, analysed in situ in diamonds using an ion microprobe/secondary ion mass spectrometer. The oxygen isotope values of coesite (a polymorph of SiO2) inclusions are substantially higher than previously reported for xenoliths from the subcratonic mantle, but are typical of subduction-zone meta-basalts, and accordingly provide strong support for the link between altered ocean-floor basalts and mantle eclogite xenoliths. PMID:12721625

  14. Rapid biologically mediated oxygen isotope exchange between water and phosphate

    NASA Astrophysics Data System (ADS)

    Paytan, Adina; Kolodny, Yehoshua; Neori, Amir; Luz, Boaz

    2002-03-01

    In order to better constrain the rate of oxygen isotope exchange between water and phosphate via biochemical reactions a set of controlled experiments were conducted in 1988 at the Aquaculture Plant in Elat, Israel. Different species of algae and other organisms were grown in seawater tanks under controlled conditions, and the water temperature and oxygen isotopic composition (δ18Ow) were monitored. The oxygen isotopic composition of phosphate (δ18Op) in the organisms' food source, tissues, and the δ18Op of dissolved inorganic phosphate (DIP) were measured at different stages of the experiments. Results indicate that intracellular oxygen isotope exchange between phosphorus compounds and water is very rapid and occurs at all levels of the food chain. Through these reactions the soft tissue δ18Op values become 23-26‰ higher than δ18Ow, and δ18Op values of DIP become ~20‰ higher than δ18Ow. No correlation between δ18Op values and either temperature or P concentrations in these experiments was observed. Our data imply that biogenic recycling and intracellular phosphorus turnover, which involves kinetic fractionation effects, are the major parameters controlling the δ18Op values of P compounds dissolved in aquatic systems. This information is fundamental to any application of δ18Op of dissolved organic or inorganic phosphate to quantify the dynamics of phosphorus cycling in aquatic systems.

  15. Oxygen Isotopes and Origin of Opal in an Antarctic Ureilite

    NASA Astrophysics Data System (ADS)

    Downes, H.; Beard, A. D.; Franchi, I. A.; Greenwood, R. C.

    2016-08-01

    Fragments of opal (SiO2.nH2O) in several internal chips of a single Antarctic polymict ureilite meteorite Elephant Moraine (EET) 83309 have been studied by NanoSIMS to determine their oxygen isotope compositions and hence constrain their origin.

  16. Nitrogen and Oxygen Isotopic Studies of the Marine Nitrogen Cycle.

    PubMed

    Casciotti, Karen L

    2016-01-01

    The marine nitrogen cycle is a complex web of microbially mediated reactions that control the inventory, distribution, and speciation of nitrogen in the marine environment. Because nitrogen is a major nutrient that is required by all life, its availability can control biological productivity and ecosystem structure in both surface and deep-ocean communities. Stable isotopes of nitrogen and oxygen in nitrate and nitrite have provided new insights into the rates and distributions of marine nitrogen cycle processes, especially when analyzed in combination with numerical simulations of ocean circulation and biogeochemistry. This review highlights the insights gained from dual-isotope studies applied at regional to global scales and their incorporation into oceanic biogeochemical models. These studies represent significant new advances in the use of isotopic measurements to understand the modern nitrogen cycle, with implications for the study of past ocean productivity, oxygenation, and nutrient status.

  17. Nitrogen and Oxygen Isotopic Studies of the Marine Nitrogen Cycle

    NASA Astrophysics Data System (ADS)

    Casciotti, Karen L.

    2016-01-01

    The marine nitrogen cycle is a complex web of microbially mediated reactions that control the inventory, distribution, and speciation of nitrogen in the marine environment. Because nitrogen is a major nutrient that is required by all life, its availability can control biological productivity and ecosystem structure in both surface and deep-ocean communities. Stable isotopes of nitrogen and oxygen in nitrate and nitrite have provided new insights into the rates and distributions of marine nitrogen cycle processes, especially when analyzed in combination with numerical simulations of ocean circulation and biogeochemistry. This review highlights the insights gained from dual-isotope studies applied at regional to global scales and their incorporation into oceanic biogeochemical models. These studies represent significant new advances in the use of isotopic measurements to understand the modern nitrogen cycle, with implications for the study of past ocean productivity, oxygenation, and nutrient status.

  18. Oxygen isotopes and the moon-forming giant impact.

    PubMed

    Wiechert, U; Halliday, A N; Lee, D C; Snyder, G A; Taylor, L A; Rumble, D

    2001-10-12

    We have determined the abundances of 16O, 17O, and 18O in 31 lunar samples from Apollo missions 11, 12, 15, 16, and 17 using a high-precision laser fluorination technique. All oxygen isotope compositions plot within +/-0.016 per mil (2 standard deviations) on a single mass-dependent fractionation line that is identical to the terrestrial fractionation line within uncertainties. This observation is consistent with the Giant Impact model, provided that the proto-Earth and the smaller impactor planet (named Theia) formed from an identical mix of components. The similarity between the proto-Earth and Theia is consistent with formation at about the same heliocentric distance. The three oxygen isotopes (delta17O) provide no evidence that isotopic heterogeneity on the Moon was created by lunar impacts.

  19. Nitrogen and Oxygen Isotopic Studies of the Marine Nitrogen Cycle.

    PubMed

    Casciotti, Karen L

    2016-01-01

    The marine nitrogen cycle is a complex web of microbially mediated reactions that control the inventory, distribution, and speciation of nitrogen in the marine environment. Because nitrogen is a major nutrient that is required by all life, its availability can control biological productivity and ecosystem structure in both surface and deep-ocean communities. Stable isotopes of nitrogen and oxygen in nitrate and nitrite have provided new insights into the rates and distributions of marine nitrogen cycle processes, especially when analyzed in combination with numerical simulations of ocean circulation and biogeochemistry. This review highlights the insights gained from dual-isotope studies applied at regional to global scales and their incorporation into oceanic biogeochemical models. These studies represent significant new advances in the use of isotopic measurements to understand the modern nitrogen cycle, with implications for the study of past ocean productivity, oxygenation, and nutrient status. PMID:26747521

  20. Constraints on the vital effect in coccolithophore and dinoflagellate calcite by oxygen isotopic modification of seawater

    NASA Astrophysics Data System (ADS)

    Hermoso, Michaël; Horner, Tristan J.; Minoletti, Fabrice; Rickaby, Rosalind E. M.

    2014-09-01

    dinoflagellate Thoracosphaera heimii exhibits different behaviour for both isotopic systems, in particular with respect to its very negative carbon isotope composition, owing to coeval intra and extracellular biomineralisation in this group. In this study, we also investigate the sensitivity of 18O/16O fractionation to varying ambient oxygen isotope composition of the medium for inorganic, coccolithophore, and dinoflagellate calcite precipitated under controlled laboratory conditions. The varying responses of different taxa to increased oxygen isotope composition of the growth medium may point to a potential bias in sea surface temperature reconstructions that are based on the oxygen isotopic compositions of sedimentary calcite, especially during times of changing seawater oxygen isotopic composition. Overall, this study represents an important step towards establishing a mechanistic understanding of the “vital effect” in coccolith and dinoflagellate calcite, and provides valuable information for interpreting the geochemistry of the calcareous nannofossils in the sedimentary record, at both monospecific and interspecies levels.

  1. Photosynthetic Fractionation of the Stable Isotopes of Oxygen and Carbon.

    PubMed Central

    Guy, R. D.; Fogel, M. L.; Berry, J. A.

    1993-01-01

    Isotope discrimination during photosynthetic exchange of O2 and CO2 was measured using enzyme, thylakoid, and whole cell preparations. Evolved oxygen from isolated spinach thylakoids was isotopically identical (within analytical error) to its source water. Similar results were obtained with Anacystis nidulans Richter and Phaeodactylum tricornutum Bohlin cultures purged with helium. For consumptive reactions, discrimination ([delta], where 1 + [delta]/1000 equals the isotope effect, k16/k18 or k12/k13) was determined by analysis of residual substrate (O2 or CO2). The [delta] for the Mehler reaction, mediated by ferredoxin or methylviologen, was 15.3[per mille (thousand) sign]. Oxygen isotope discrimination during oxygenation of ribulose-1,5-bisphosphate (RuBP) catalyzed by RuBP carboxylase/oxygenase (Rubisco) was 21.3[per mille (thousand) sign] and independent of enzyme source, unlike carbon isotope discrimination: 30.3[per mille (thousand) sign] for spinach enzyme and 19.6 to 23[per mille (thousand) sign] for Rhodospirillum rubrum and A. nidulans enzymes, depending on reaction conditions. The [delta] for O2 consumption catalyzed by glycolate oxidase was 22.7[per mille (thousand) sign]. The expected overall [delta] for photorespiration is about 21.7[per mille (thousand) sign]. Consistent with this, when Asparagus sprengeri Regel mesophyll cells approached the compensation point within a sealed vessel, the [delta]18O of dissolved O2 came to a steady-state value of about 21.5[per mille (thousand) sign] relative to the source water. The results provide improved estimates of discrimination factors in several reactions prominent in the global O cycle and indicate that photorespiration plays a significant part in determining the isotopic composition of atmospheric oxygen. PMID:12231663

  2. Impact of flood events on lacustrine carbonate isotope records

    NASA Astrophysics Data System (ADS)

    Kämpf, Lucas; Plessen, Birgit; Lauterbach, Stefan; Nantke, Carla; Meyer, Hanno; Chapligin, Bernhard; Höllerer, Hannes; Brauer, Achim

    2016-04-01

    Stable oxygen (δ 18O) and carbon (δ 13C) isotope compositions of lacustrine carbonates are among the most frequently used proxies in palaeolimnological / -environmental studies. Stable isotope analyses are often carried out on bulk carbonate samples, which are prone to contamination with detrital carbonates, transported into the lake by runoff processes and carrying the isotopic signal of catchment rocks, thus hampering the interpretation of the data in terms of past climatic and/or environmental changes. Despite the awareness of a likely detrital bias, the degree of contamination in most cases remains unknown and discrete contaminated samples undetected due to a lack of methods to disentangle endogenic and detrital carbonates in sediment records. To address this issue and provide more comprehensive insights into effects of flood-related detrital input on the bulk carbonate isotopic composition, we conducted stable isotope measurements on sediments trapped on a 3-12 day basis over a three-year period (January 2011 to November 2013) at two locations in pre-Alpine Lake Mondsee, close to the inflow of the main tributary and in the deepest part of the lake basin. Lake Mondsee was chosen for the monitoring since the pelagic sediments are annually laminated consisting of couplets of light calcite layers and dark layers made up by a mixture of detrital clastic and organic matter. Maximum calcite flux rates >1.5 g m2 d-1 were trapped between May and September, indicating the seasonal endogenic precipitation of calcite crystals. The comparison of the δ 18O composition of trapped carbonates, rain and epilimnion lake water revealed equilibrium calcite precipitation, allowing us to infer purely endogenic δ 18O (-9 to -11.3‰ VPDB) and δ 13C values (-6 to -9‰ VPDB) throughout the summer season. The endogenic calcite precipitation was interrupted by 14 peaks in carbonate flux (4 to 175 g m2 d-1) triggered by runoff events of different magnitudes (10-110 m3 s-1 peak

  3. Oxygen Isotope Signatures of Biogenic Manganese(III/IV) Oxides

    NASA Astrophysics Data System (ADS)

    Sutherland, K. M.; Hansel, C. M.; Wankel, S. D.

    2015-12-01

    Manganese (Mn) oxide minerals are pervasive throughout a number of surface earth environments as rock varnishes, ferromanganese nodules, crusts around deep-sea vents, and cave deposits among many other marine, freshwater, and terrestrial deposits. Mn(III,IV) oxides are also among the strongest sorbents and oxidants in surface earth environments and are crucial to understanding the fate of organic matter in sedimentary environments. The precipitation of Mn oxide minerals proceeds via both abiotic and biotic oxidation pathways, the latter due to the indirect or direct activity of Mn(II)- oxidizing microorganisms, including bacteria and fungi. Although the precipitation of Mn oxides is believed to be primarily controlled by Mn(II)-oxidizing organisms in most surface earth environments, confirmation of this generally held notion has remained illusive and limits our understanding of their formation on Earth and beyond (e.g., Mars). Previous work provided evidence that O atom incorporation by specific Mn oxidation pathways may exhibit unique and predictable isotopic fractionation. In this study, we expand upon this evidence by measuring the oxygen isotope signature of several biogenic and abiogenic Mn oxide minerals synthesized under a range of oxygen-18 labeled water. These results allow us to determine the relative amount oxygen atoms derived from water and molecular oxygen that are incorporated in the oxide and shed light on corresponding isotope fractionation factors. Additionally, we show that, once precipitated, Mn oxide isotope signatures are robust with respect to aqueous oxygen isotope exchange. The study provides a foundation on which to study and interpret Mn oxides in natural environments and determine which environmental controls may govern Mn(II) oxidation.

  4. Oxygen Isotope Constraints on the Origin of Georgia Tektites

    NASA Astrophysics Data System (ADS)

    Albin, E. F.

    1997-07-01

    Georgia tektites ("georgiaites") are North American tektites that occur in east-central Georgia. In this investigation small chips of tektite material was separated from 24 individual specimens for oxygen isotope analysis. Results have an analytical precision of 0.2% based on duplicate analysis of a NIST silicate standard (NBS-28) and tektites. Oxygen isotope ratios (i.e., delta (18) O - SMOW) range from + 6.9 to + 10.7 parts per mil. The mean delta (18) O for Georgia tektites is + 9.1 parts per mil. These results are consistent with a delta (18) O value reported previously on a single georgiaite [1]. It appears that the tektites have oxygen isotope ratios similar to igneous and/or metamorphic rocks. Blum and Chamberlain [2] argue that since sea water has a relatively low delta (18) O value, its addition to isotopically heavier sedimentary rocks could account for the relatively low oxygen isotope ratios determined for the tektites. Such a model would require vaporization of the target material in order to exchange oxygen between the water and silicates. However, vaporization is not a popular theory of tektite petrogenesis, and since tektites contain very little water, it is difficult to reconcile the low delta (18) O values due to mixing with sea water. An alternative explanation may be that the low delta (18) O values are derived from a crystalline basement or it may be that the sedimentary target rocks at the proposed source crater (i.e., Chesapeake Bay crater) have delta (18) O values similar to that of the tektites. To resolve the issue, it will be necessary to melt samples of the proposed target material and make delta (18) O measurements on the resulting glass and then compare the results to the tektites. References: [1] Taylor, H.P. and Epstein, S. (1969) J. Geophys. Res., 74, 6834-6844. [2] Blum J.D. and Chamberlain C.D. (1992) Science, 257, 1104-1107.

  5. Unified picture of the oxygen isotope effect in cuprate superconductors

    PubMed Central

    Chen, Xiao-Jia; Struzhkin, Viktor V.; Wu, Zhigang; Lin, Hai-Qing; Hemley, Russell J.; Mao, Ho-kwang

    2007-01-01

    High-temperature superconductivity in cuprates was discovered almost exactly 20 years ago, but a satisfactory theoretical explanation for this phenomenon is still lacking. The isotope effect has played an important role in establishing electron–phonon interaction as the dominant interaction in conventional superconductors. Here we present a unified picture of the oxygen isotope effect in cuprate superconductors based on a phonon-mediated d-wave pairing model within the Bardeen–Cooper–Schrieffer theory. We show that this model accounts for the magnitude of the isotope exponent as functions of the doping level as well as the variation between different cuprate superconductors. The isotope effect on the superconducting transition is also found to resemble the effect of pressure on the transition. These results indicate that the role of phonons should not be overlooked for explaining the superconductivity in cuprates. PMID:17360421

  6. Clumped-Isotope Thermometry and Oxygen Isotope Systematics in Speleothem Calcite From a Near Cave-Entrance Environment

    NASA Astrophysics Data System (ADS)

    Carlson, P. E.; Banner, J.; Breecker, D.; Affek, H. P.

    2015-12-01

    Speleothems that grow in well-ventilated zones of caves have not been widely used in paleoclimate studies, yet may provide paleotemperature records. These zones are characterized by low CO2 concentrations year-round and, in temperate climates, large seasonal temperature fluctuations. They are typically avoided for paleoclimate reconstruction due to concerns about kinetic isotope effects (KIE). However, speleothems in general seem to be sensitive to KIE, even in non-ventilated areas and can nonetheless provide useful paleoclimate records. At Westcave Preserve (Westcave), a shallow, well-ventilated cave in central Texas, we have found seasonal temperature differences recorded in both the oxygen isotope and clumped isotope compositions of speleothem calcite grown on glass-plate substrates harvested from active drips. Although growth rates in this cave are relatively rapid, speleothem analogs in Westcave are growing near oxygen-isotopic equilibrium with their drip waters (between the calibrations of Kim and O'Neil, 1997 and Coplen, 2007). We have tested the compatibility of the Zaarur et al. (2013) clumped isotope bulk solution thermometer calibration to glass-substrate calcite in the cave collected during various months. This technique can provide absolute temperatures, but is sensitive to kinetic isotope effects, often significantly overestimating growth temperatures of speleothems. When this thermometer was applied to calcite collected from near where the plates were impacted by drip water, it overestimated measured temperatures by 7.7 ± 4.3°C, showing moderate KIE. When applied to calcite away from the drip impact, it overestimated temperatures by 18.7 ± 4.2°C, showing KIE increasing away from the drip. Measured monthly average temperatures in the cave ranged seasonally between 8 and 28°C, and daily temperatures vary significantly. At Westcave, calcite growth rates increase with temperature, and the calcite may therefore preferentially record warmer daily or

  7. Local and regional oscillations of carbon and oxygen isotopes in terestrial carbonates

    NASA Astrophysics Data System (ADS)

    Skipitytė, Raminta; Stančikaitė, Miglė

    2014-05-01

    Stable isotope ratios of carbon and oxygen in sediment carbonates are used as a tool to identify climatic changes in the past [1], [2]. Carbon is more related to humidity whereas oxygen is thought to respond the temperature [2]. Nevertheless number of questions about local, regional and global scale impacts to these records is left. In this research work carbon and oxygen isotope ratios in lacustrine carbonates are used to identify palaeoenvironmental dynamics of different locations. Samples of lacutrine carbonates were obtained from 8 sequences of different sites in Lithuania (4), Poland (1), Belarus (1) and Kaliningrad (1). Every sequence was divided into 2 cm intervals. The study showed differences in average carbon and oxygen isotope ratios between Lithuania and other countries (Poland, Belarus and Kaliningrad). Carbon and oxygen isotope ratios in 4 sites in Lithuania are: ¯U la δ13C -4.72± 2.11, o and δ18O -9.46± 1.9, o ; Zervynos δ13C -4.79± 1.82, o and δ18O -9.57± 1.69, o ; Rudnia δ13C -4.94± 7.53, o and δ18O -9.3± 3.92, o ; Pauliai δ13C -4.15± 0.67, o and δ18O -9.94± 1.07, o : In other countries: Poland δ13C -1.07± 1.94, o and δ18O -7.69± 0.95, o ; Belarus δ13C 0.97± 1.94, o and δ18O -7.61± 1.42, o ; Kaliningrad δ13C -1.14± 1.43, o and δ18O -6.51± 1.00, o : Average stable carbon and oxygen isotope values from four sites in Lithuania were -4.65 o for carbon and -9.51 o for oxygen. Despite homogeneity of average isotope signals in these four sites there are relatively large oscillations of isotopic values in Rudnia and relatively small in Pauliai. These oscillations could be related to local characteristics of particular place such as environmental conditions, water balance, input of terrigenous materials into basin, etc. Total amount of CaCO3 could also play a significant role in reconstructing palaeoenvironment from stable isotopes and creating isomaps. The comparison of isotope records from different locations could enable to

  8. Oxygen isotope variations of phosphate in mammalian bone and tooth enamel

    NASA Astrophysics Data System (ADS)

    Delgado Huertas, Antonio; Iacumin, Paola; Stenni, Barbara; Sánchez Chillón, Begoña; Longinelli, Antonio

    1995-10-01

    About eighty specimens from ten different species of mammals, collected from different areas under different climatic and environmental conditions, were measured for the oxygen isotopic composition of their bone and tooth phosphate. The equations relating these values to the mean oxygen isotopic composition of local meteoric water were also derived. The same equation can be used for goats, roe-bucks, and mouflons, despite the biological differences among these species. Measurements were made on about fourty different specimens of rabbit and hare from Europe, Africa, and Canada, but in this case the data obtained clearly show no direct relationship between the oxygen isotopic composition of local meteoric water and the isotopic composition of the skeletal phosphate. However, there seems to be an inverse relationship between the relative humidity of the studied areas and the δ 18O(PO 43-) of the skeletal phosphate, thus suggesting the use of fossil bones of these mammal species as recorders of palaeoenvironmental relative humidity. Finally, a new equation was derived for the isotopic scale for horses, on the basis of all the previous data and of a few newly obtained results.

  9. Oxygenation of a Cryogenian ocean (Nanhua Basin, South China) revealed by pyrite Fe isotope compositions

    NASA Astrophysics Data System (ADS)

    Zhang, Feifei; Zhu, Xiangkun; Yan, Bin; Kendall, Brian; Peng, Xi; Li, Jin; Algeo, Thomas J.; Romaniello, Stephen

    2015-11-01

    was likely responsible for the return of lighter, seawater-like Fe isotope compositions in pyrite. Our pyrite Fe isotope profile thus records increased oxygenation in the Nanhua Basin between the Sturtian and Marinoan glaciations. The increased oxygenation of Nanhua Basin seawater deduced from pyrite Fe isotopes could have resulted from either local or global controls. Further work will be needed to determine whether this increasing oxygenation extended to the global scale.

  10. Oxygen isotope fractionation in phosphates: the role of dissolved complex anions in isotope exchange.

    PubMed

    Zheng, Yong-Fei

    2016-01-01

    Oxygen isotope fractionation factors for phosphates were calculated by means of the increment method. The results suggest that Ag3PO4 and BiPO4 are enriched in (18)O relative to AgPO4, and the three phosphates are consistently depleted in (18)O relative to Ba3[PO4]2; fluorapatite and chlorapatite exhibit a similar behaviour of oxygen isotope fractionation with consistent enrichment of (18)O relative to hydroxyapatite. The valence, radii and coordination of metal cations play a quantitative role in dictating the (18)O/(16)O partitioning in these phosphates of different compositions. The calculated fractionation factors for the Ag3PO4-H2O system are in agreement with experimental determinations derived from enzyme-catalysed isotope exchange between dissolved inorganic phosphate and water at the longest reaction durations at low temperatures. This demonstrates that the precipitated Ag3PO4 has completely captured the oxygen isotope fractionation in the dissolved inorganic phosphate. The calculated fractionation factors for the F/Cl-apatite-water systems are in agreement with the enzyme-catalysed experimental fractionations for the dissolved phosphate-water system at the longest reaction durations but larger than fractionations derived from bacteria-facilitated exchange and inorganic precipitation experiments as well as natural observations. For the experimental calibrations of oxygen isotope fractionation involving the precipitation of dissolved phosphate species from aqueous solutions, the fractionation between precipitate and water is primarily dictated by the isotope equilibration between the dissolved complex anions and water prior to the precipitation. Therefore, the present results provide a quantitative means to interpret the temperature dependence of oxygen isotope fractionation in inorganic and biogenic phosphates.

  11. Planetary Accretion, Oxygen Isotopes and the Central Limit Theorem

    NASA Technical Reports Server (NTRS)

    Nuth, Joseph A., III; Hill, Hugh G. M.; Vondrak, Richard R. (Technical Monitor)

    2001-01-01

    The accumulation of presolar dust into increasingly larger aggregates (CAIs and Chondrules, Asteroids, Planets) should result in a very drastic reduction in the numerical spread in oxygen isotopic composition between bodies of similar size, in accord with the Central Limit Theorem. Observed variations in oxygen isotopic composition are many orders of magnitude larger than would be predicted by a simple, random accumulation model that begins in a well-mixed nebula - no matter which size-scale objects are used as the beginning or end points of the calculation. This discrepancy implies either that some as yet unspecified process acted on the solids in the Solar Nebula to increase the spread in oxygen isotopic composition during each and every stage of accumulation or that the nebula was heterogeneous and maintained this heterogeneity throughout most of nebular history. Large-scale nebular heterogeneity would have significant consequences for many areas of cosmochemistry, including the application of some well-known isotopic systems to the dating of nebular events or the prediction of bulk compositions of planetary bodies on the basis of a uniform cosmic abundance.

  12. Oxygen Isotopic Analyses of Water Extracted from Lunar Samples

    NASA Astrophysics Data System (ADS)

    Nunn Martinez, M.; Thiemens, M. H.

    2014-12-01

    Oxygen exists in lunar materials in distinct phases having unique sources and equilibration histories. The oxygen isotopic composition (δ17O, δ18O) of various components of lunar materials has been studied extensively, but analyses of water in these samples are relatively sparse [1-3]. Samples collected on the lunar surface reflect not only the composition of their source reservoirs but also contributions from asteroidal and cometary impacts, interactions with solar wind and cosmic radiation, among other surface processes. Isotopic characterization of oxygen in lunar water could help resolve the major source of water in the Earth-Moon system by revealing if lunar water is primordial, asteroidal, or cometary in origin [1]. Methods: A lunar rock/soil sample is pumped to high vacuum to remove physisorbed water before heating step-wise to 50, 150, and 1000°C to extract extraterrestrial water without terrestrial contamination. The temperature at which water is evolved is proportional to the strength with which the water is bound in the sample and the relative difficulty of exchanging oxygen atoms in that water. This allows for the isolated extraction of water bound in different phases, which could have different source reservoirs and/or histories, as evidenced by the mass (in)dependence of oxygen compositions. A low blank procedure was developed to accommodate the low water content of lunar material [4]. Results: Oxygen isotopic analyses of lunar water extracted by stepwise heating lunar basalts and breccias with a range of compositions, petrologic types, and surface exposure ages will be presented. The cosmic ray exposure age of these samples varies by two orders of magnitude, and we will consider this in discussing the effects of solar wind and cosmic radiation on the oxygen isotopic composition (Δ17O). I will examine the implications of our water analyses for the composition of the oxygen-bearing reservoir from which that water formed, the effects of surface

  13. Silicon and oxygen isotopes in selected Allende inclusions

    NASA Technical Reports Server (NTRS)

    Becker, R. H.; Epstein, S.

    1982-01-01

    Silicon and oxygen data are presented for a number of Allende samples. It is found that based on oxygen and silicon isotopes, Allende samples EGG-1, EGG-6, BG1a, and 3529Yc are typical, unfractionated Allende inclusions. Where magnesium data are available, they indicate the same thing. EGG-3 is fractionated in both oxygen and silicon, as it is in magnesium. Sample D7 melilite is fractionated in oxygen by several per mil along the C2-matrix line, away from typical Allende melilites. Inclusion BG10a is a FUN inclusion with an inferred original oxygen isotopic fractionation of 8-9 per mille/amu relative to the Allende line. Silicon data for two density fractions of inclusion 3A with different mineralogies show a difference of about 2 per mille, which indicates that silicon, like oxygen, has been added to at least some mineral phases in Allende inclusions from a reservoir other than the one in which the inclusion first began to form.

  14. Oxygen Isotopes in Chondritic Interplanetary Dust: Parent-Bodies and Nebular Oxygen Reservoirs

    SciTech Connect

    Aleon, J; McKeegan, K D; Leshin, L

    2006-02-14

    Planetary objects have preserved various amounts of oxygen issued from isotopically different oxygen reservoirs reflecting their origin and physico-chemical history. An {sup 16}O-rich component is preserved in refractory inclusions (CAIs) whereas meteorites matrices are enriched in an {sup 16}O-poor component. The origin of these components is still unclear. The most recent models are based on isotope selective photodissociation of CO in a {sup 16}O-rich nebula/presolr cloud resulting in a {sup 16}O-poor gas in the outer part of the nebula. However because most meteorite components are thought to be formed in the inner 3AU of the solar nebula, the precise isotopic composition of outer solar system components is yet unknown. In that respect, the oxygen isotopic composition of cometary dust is a key to understand the origin of the solar system. The Stardust mission will bring back to the Earth dust samples from comet Wild2, a short period comet from the Jupiter family. A precise determination of the oxygen isotope composition of Wild2 dust grains is essential to decipher the oxygen reservoirs of the outer solar system. However, Stardust samples may be extremely fragmented upon impact in the collector. In addition, interplanetary dust particles (IDPs) collected in the stratosphere are likely to contain comet samples. Therefore, they started to investigate the oxygen isotopic composition of a suite of chondritic interplanetary dust particles that includes IDPs of potential cometary origin using a refined procedure to increase the lateral resolution for the analysis of Stardust grains or IDP subcomponents down to {approx} 3 {micro}m. High precision data for 4 IDPs were previously reported, here they have measured 6 additional IDPs.

  15. Oxygen and carbon isotope disequilibria in Galapagos corals: isotopic thermometry and calcification physiology

    SciTech Connect

    McConnaughey, T.A.

    1986-01-01

    Biological carbonate skeletons are built largely from carbon dioxide, which reacts to form carbonate ion within thin extracellular solutions. The light isotopes of carbon and oxygen react faster than the heavy isotopes, depleting the resulting carbonate ions in /sup 13/C and /sup 18/O. Calcium carbonate precipitation occurs sufficiently fast that the skeleton remains out of isotopic equilibrium with surrounding fluids. This explanation for isotopic disequilibrium in biological carbonates was partially simulated in vitro, producing results similar to those seen in non-photosynthetic corals. Photosynthetic corals have higher /sup 13/C//sup 12/C ratios due to the preferential removal of /sup 12/C (as organic carbon) from the reservoir of dissolved inorganic carbon. The oxygen isotopic variations in corals can be used to reconstruct past sea surface temperatures to an accuracy of about 0.5/sup 0/C. The carbon isotopic content of photosynthetic corals provides an indication of cloudiness. Using isotopic data from Galapagos corals, it was possible to construct proxy histories of the El Nino phenomenon. The physiology of skeletogenesis appears to be surprisingly similar in calcium carbonate, calcium phosphate, and silica precipitating systems.

  16. Chromium Isotopes in Carbonate Rocks: New Insights into Proterozoic Atmospheric Oxygenation

    NASA Astrophysics Data System (ADS)

    Kah, L. C.; Gilleaudeau, G. J.; Frei, R.; Kaufman, A. J.; Azmy, K.; Bartley, J. K.; Chernyavskiy, P.; Knoll, A. H.

    2015-12-01

    There has been a long-standing debate in geobiology about the role that Earth's oxygenation played in the evolution of complex life. Temporal linkages exist between the Great Oxidation Event (GOE) and the evolution of eukaryotes, as well as Neoproterozoic rise in oxygen and the diversification of metazoans. Further advances have been hampered, however, by the lack of direct proxies that mark specific levels of atmospheric pO2 in the geologic past. Chromium (Cr) isotopes show promise in this regard because the oxidation of Cr during terrestrial weathering—which results in isotopic fractionation—is dependent on a specific threshold of atmospheric pO2 (0.1-1% of the present atmospheric level [PAL]). This threshold value broadly coincides with recent estimates of the oxygen requirements of early animals. Here we report new Cr-isotope data from four late Mesoproterozoic carbonate-dominated successions. Samples were collected from the Turukhansk Uplift (Siberia), the El Mreiti Group (Mauritania), the Vazante Group (Brazil), and the Angmaat Formation (Canada). We emphasize the application of Cr-isotopes to carbonate rocks because the broad temporal range of this lithology in the geologic record provides an opportunity to significantly expand our understanding of Proterozoic oxygenation on shorter time scales. Our data indicate that pO2 levels required to support early animals were attained long before Neoproterozoic metazoan diversification, although the large degree of isotopic heterogeneity in our dataset may indicate that pO2 > 0.1-1% PAL was only a transient phenomenon in the Mesoproterozoic. This study demonstrates the utility of Cr-isotopes as an atmospheric redox proxy in carbonate rocks and helps inform future avenues of research on Proterozoic pO2 thresholds.

  17. Oxygen Isotope Character of the Lake Owyhee Volcanic Field, Oregon

    NASA Astrophysics Data System (ADS)

    Blum, T.; Strickland, A.; Valley, J. W.

    2012-12-01

    Oxygen isotope analyses of zircons from lavas and tuffs from the Lake Owyhee Volcanic Field (LOVF) of east central Oregon unequivocally demonstrate the presence of mid-Miocene low-δ18O magmas (δ18Ozrc<4.7 ‰). Despite the growing data set of low-δ18O melts within, and proximal to, the Snake River Plain (SRP) Large Igneous Province, debate persists regarding both the mechanisms for low-δ18O magma petrogenesis, and their relative influence in the SRP. The LOVF is associated with widespread silicic volcanism roughly concurrent with the eruption of the Steens-Columbia River Basalt Group between ~17-15Ma. Silicic activity in the LOVF is limited to 16-15Ma, when an estimated 1100km3 of weakly peralkaline to metaluminous rhyolitic lavas and ignimbrites erupted from a series of fissures and calderas. Geographically, the LOVF overlaps the Oregon-Idaho Graben (OIG), and straddles the 87Sr/86Sr= 0.704 line which, together with the 0.706 line to the east, delineate the regional transition from the North American Precambrian continental crust to the east to younger Phanerozoic accreted terranes to the west. Here we report high accuracy ion microprobe analyses of δ18O in zircons using a 10-15μm spot, with average spot-to-spot precision ±0.28‰ (2SD), to investigate intra-grain and intra-unit δ18Ozrc trends for LOVF rhyolites. Due to its high closure temperature, chemical and physical resistance, and slow oxygen diffusion rates, zircon offers a robust record of magmatic oxygen isotope ratios during crystallization and provides constraints on the petrogenesis of Snake River Plain (SRP) low-δ18O melts. Individual zircons from LOVF rhyolites show no evidence of core-rim δ18O zoning, and populations exhibit ≤0.42‰ (2SD) intra-unit variability. Unit averages range from 2.2 to 4.3‰, with the lowest values in caldera-forming ignimbrites, but all units show evidence of crystallization from low-δ18O melts. Quartz and feldspar analyses by laser fluorination (precision

  18. Oxygen isotope fractionation between analcime and water: An experimental study

    SciTech Connect

    Karlsson, H.R.; Clayton, R.N. )

    1990-05-01

    The fractionation of oxygen isotopes between natural analcime ({approximately}100 {mu}m) and water has been determined at 300, 350, and 400{degree}C at fluid pressures ranging from 1.5 to 5.0 kbar. Isotope ratios were obtained for the analcime framework, the channel water, and bulk water. Analcimes from Surtsey (145{degree}C), DSDP Hole 417A (30 to 55{degree}C), and Guam (25{degree}C) were used to constrain the fractionation factors below 300{degree}C. Analcime channel water exchanged completely with external water in all runs. Although some retrograde exchange may have occurred during quenching, the results indicate that the channel water is depleted in {sup 18}O relative to bulk water by a constant value of {approximately}5{per thousand}, nearly independent of temperature. Analcime is the first hydrated mineral found to have water of hydration depleted in {sup 18}O. Analcime framework oxygen exchanged 80, 90, and 96% at 300{degree}C for 412 h, 350{degree}C for 178 h, and 400{degree}C for 120 h, respectively. Equilibrium {Delta}{sup 18}O ({per thousand}) are as follows: 2.9 (400{degree}C), 4.5 (350{degree}C), and 5.8 (300{degree}C) for the experimental runs and 12.2 (145{degree}C) and 24.2 to 28.2 (30-55{degree}C) for the empirical data. The analcime-water fractionation curve is within experimental error of that of calcite-water. The exchange had little effect on grain morphology and does not involve recrystallization. This is the fastest exchange observed for a silicate. The rapid exchange rates indicate that zeolites in active high-temperature geothermal areas are in oxygen isotopic equilibrium with ambient fluids. Once calibrated, zeolites may be among the best low-temperature oxygen isotope geothermometers.

  19. Coupled silicon-oxygen isotope fractionation traces Archaean silicification

    NASA Astrophysics Data System (ADS)

    Abraham, K.; Hofmann, A.; Foley, S. F.; Cardinal, D.; Harris, C.; Barth, M. G.; André, L.

    2011-01-01

    Silica alteration zones and cherts are a conspicuous feature of Archaean greenstone belts worldwide and provide evidence of extensive mobilisation of silica in the marine environment of the early Earth. In order to understand the process(es) of silicification we measured the silicon and oxygen isotope composition of sections of variably silicified basalts and overlying bedded cherts from the Theespruit, Hooggenoeg and Kromberg Formations of the Barberton Greenstone Belt, South Africa. The δ30Si and δ18O values of bulk rock increase with increasing amount of silicification from unsilicified basalts (-0.64‰ < δ30Si < -0.01‰ and + 8.6‰ < δ18O < + 11.9‰) to silicified basalts (δ30Si and δ18O values as high as + 0.81‰ and + 15.6‰, respectively). Cherts generally have positive isotope ratios (+ 0.21‰ < δ30Si < + 1.05‰ and + 10.9 < δ18O < + 17.1), except two cherts, which have negative δ30Si values, but high δ18O (up to + 19.5‰). The pronounced positive correlations between δ30Si, δ18O and SiO2 imply that the isotope variation is driven by the silicification process which coevally introduced both 18O and 30Si into the basalts. The oxygen isotope variation in the basalts from about 8.6‰ to 15.6‰ is likely to represent temperature-dependent isotope fractionation during alteration. Our proposed model for the observed silicon isotope variation relies on a temperature-controlled basalt dissolution vs. silica deposition process.

  20. Oxygen isotope constraints on the petrogenesis of Aleutian arc magmas

    SciTech Connect

    Singer, B.S.; O'Neil, J.R. ); Brophy, J.G. )

    1992-04-01

    The first measurement of {sup 18}O/{sup 16}O ratios of plagioclase, clinopyroxene, orthopyroxene, and titanomagnetite phenocrysts from modern Aleutian island-arc lavas provides new insight and independent constraints on magma sources and intracrustal processes. Basalts are heterogeneous on the scale of the entire arc and individual volcanic centers. Combined with Sr isotope and trace element data {delta}{sup 18}O{sub plag} values suggest a variable magma source characterized by differences in the mantle wedge or the subducted sediment component along the volcanic front. Seven tholeiitic basalt to rhyodacite lavas from the Seguam volcanic center have nearly identical {delta}{sup 18}O{sub plag} values of 6.0{per thousand} {plus minus} 0.2{per thousand}, reflecting extensive closed-system plagioclase-dominated crystal fractionation. Oxygen isotope thermometry and pyroxene and oxide equilibria indicate that differentiation occurred between 1,150 {plus minus} 100C (basalt) and 950 {plus minus} 100C (rhyodacite). In contrast, {delta}{sup 18}O{sub plag} values of 12 calc-alkalic basaltic andesites and andesites from the smaller Kanaga volcanic center span a broader range of 5.9{per thousand}-6.6{per thousand}, and consist of mostly higher values. Isotopic disequilibrium in the Kanaga system is manifest in two ways: two types of basaltic inclusions with contrasting {delta}{sup 18}O values occur in one andesite, and in two other andesites plagioclase-titanomagnetite and clinopyroxene-titanomagnetite oxygen isotope temperatures are inconsistent.

  1. Leaf water oxygen isotope measurement by direct equilibration.

    PubMed

    Song, Xin; Barbour, Margaret M

    2016-08-01

    The oxygen isotope composition of leaf water imparts a signal to a range of molecules in the atmosphere and biosphere, but has been notoriously difficult to measure in studies requiring a large number of samples as a consequence of the labour-intensive extraction step. We tested a method of direct equilibration of water in fresh leaf samples with CO2 , and subsequent oxygen isotope analysis on an optical spectrometer. The oxygen isotope composition of leaf water measured by the direct equilibration technique was strongly linearly related to that of cryogenically extracted leaf water in paired samples for a wide range of species with differing anatomy, with an R(2) of 0.95. The somewhat more enriched values produced by the direct equilibration method may reflect lack of full equilibration with unenriched water in the vascular bundles, but the strong relationship across a wide range of species suggests that this difference can be adequately corrected for using a simple linear relationship. PMID:27147584

  2. Lake isotope records of the 8200-year cooling event in western Ireland: Comparison with model simulations

    NASA Astrophysics Data System (ADS)

    Holmes, Jonathan A.; Tindall, Julia; Roberts, Neil; Marshall, William; Marshall, Jim D.; Bingham, Ann; Feeser, Ingo; O'Connell, Michael; Atkinson, Tim; Jourdan, Anne-Lise; March, Anna; Fisher, Elizabeth H.

    2016-01-01

    The early Holocene cooling, which occurred around 8200 calendar years before present, was a prominent abrupt event around the north Atlantic region. Here, we investigate the timing, duration, magnitude and regional coherence of the event as expressed in carbonate oxygen-isotope records from three lakes on northwest Europe's Atlantic margin in western Ireland, namely Loch Avolla, Loch Gealáin and Lough Corrib. An abrupt negative oxygen-isotope excursion lasted about 200 years. Comparison of records from three sites suggests that the excursion was primarily the result of a reduction of the oxygen-isotope values of precipitation, which was likely caused by lowered air temperatures, possibly coupled with a change in atmospheric circulation. Comparison of records from two of the lakes (Loch Avolla and Loch Gealáin), which have differing bathymetries, further suggests a reduction in evaporative loss of lake water during the cooling episode. Comparison of climate model experiments with lake-sediment isotope data indicates that effective moisture may have increased along this part of the northeast Atlantic seaboard during the 8200-year climatic event, as lower evaporation compensated for reduced precipitation.

  3. Oxygen isotope exchange between refractory inclusion in Allende and solar nebula gas.

    PubMed

    Yurimoto, H; Ito, M; Nagasawa, H

    1998-12-01

    A calcium-aluminum-rich inclusion (CAI) from the Allende meteorite was analyzed and found to contain melilite crystals with extreme oxygen-isotope composition (approximately 5 percent oxygen-16 enrichment relative to terrestrial oxygen-16). Some of the melilite is also anomalously enriched in oxygen-16 compared with oxygen isotopes measured in other CAIs. The oxygen isotopic variation measured among the minerals (melilite, spinel, and fassaite) indicates that crystallization of the CAI started from oxygen-16-rich materials that were probably liquid droplets in the solar nebula, and oxygen isotope exchange with the surrounding oxygen-16-poor nebular gas progressed through the crystallization of the CAI. Additional oxygen isotope exchange also occurred during subsequent reheating events in the solar nebula.

  4. Oxygen isotope exchange between refractory inclusion in allende and solar nebula Gas

    PubMed

    Yurimoto; Ito; Nagasawa

    1998-12-01

    A calcium-aluminum-rich inclusion (CAI) from the Allende meteorite was analyzed and found to contain melilite crystals with extreme oxygen-isotope compositions ( approximately 5 percent oxygen-16 enrichment relative to terrestrial oxygen-16). Some of the melilite is also anomalously enriched in oxygen-16 compared with oxygen isotopes measured in other CAIs. The oxygen isotopic variation measured among the minerals (melilite, spinel, and fassaite) indicates that crystallization of the CAI started from oxygen-16-rich materials that were probably liquid droplets in the solar nebula, and oxygen isotope exchange with the surrounding oxygen-16-poor nebular gas progressed through the crystallization of the CAI. Additional oxygen isotope exchange also occurred during subsequent reheating events in the solar nebula.

  5. The use of the oxygen isotopes from diatom silica as a proxy for North Atlantic Oscillation reconstruction

    NASA Astrophysics Data System (ADS)

    Hernández, Armand; Leng, Melanie J.; Trigo, Ricardo M.; Vázquez-Loureiro, David; Bao, Roberto; Sloane, Hilary J.; Rubio-Inglés, Maria J.; Sánchez-López, Guiomar; Gonçalves, Vitor; Raposeiro, Pedro M.; Sáez, Alberto; Giralt, Santiago

    2015-04-01

    The North Atlantic Oscillation (NAO) is the main atmospheric circulation mode controlling climate variability in the Northern Hemisphere. Instrumental records of the NAO are relatively short, and therefore proxy approaches are essential to understand its evolution over longer time periods. Diatom oxygen isotope ratios are increasingly being used for palaeoclimatic reconstructions in lacustrine sedimentary records. However, application of this proxy to annual-to-decadal resolution lacustrine records is still in its infancy. To our knowledge, oxygen isotope ratios from diatoms at annual-to-decadal resolution has not been attempted, mainly due to the difficulty in obtaining large enough samples suitable for analysis at this temporal scale. Here we present a high-resolution, ca. 200-year-long, proxy record based on 56 oxygen isotope measurements from Lake Santiago (37° 50' N - 25° 47'W, Azores Archipelago, Portugal). This record will be compared to instrumental data of precipitation and NAO index values to test its robustness to conduct an ancient NAO reconstruction. In detail the oxygen isotope data shows an isotope depletion trend (-3o), with several interannual oscillations, from 1830 cal yr AD until present. The entire record can be divided into two intervals. The interval, from 1830 to 1938 cal yr AD, displays values above the average (+33o), whereas the interval from 1939 to 2012 cal yr AD shows values below the mean. Since Lake Santiago is a hydrologically closed lake, the oxygen isotope variations are mostly related to the precipitation-evaporation ratio. These results exhibit a good agreement with the rainfall instrumental data with an increase of net rainfall amount through the last decades in the Azores archipelago. Besides this, the short-term recorded isotope excursions (±3.5o) are related to the rainfall interannual variability. These patterns suggest that the isotope data from diatom silica in Lake Santiago sediments are directly linked to past

  6. Hydrogen and Oxygen Isotope Ratios in Body Water and Hair: Modeling Isotope Dynamics in Nonhuman Primates

    PubMed Central

    O’Grady, Shannon P.; Valenzuela, Luciano O.; Remien, Christopher H.; Enright, Lindsey E.; Jorgensen, Matthew J.; Kaplan, Jay R.; Wagner, Janice D.; Cerling, Thure E.; Ehleringer, James R.

    2012-01-01

    The stable isotopic composition of drinking water, diet, and atmospheric oxygen influence the isotopic composition of body water (2H/1H, 18O/16O expressed as δ2H and δ18O). In turn, body water influences the isotopic composition of organic matter in tissues, such as hair and teeth, which are often used to reconstruct historical dietary and movement patterns of animals and humans. Here, we used a nonhuman primate system (Macaca fascicularis) to test the robustness of two different mechanistic stable isotope models: a model to predict the δ2H and δ18O values of body water and a second model to predict the δ2H and δ18O values of hair. In contrast to previous human-based studies, use of nonhuman primates fed controlled diets allowed us to further constrain model parameter values and evaluate model predictions. Both models reliably predicted the δ2H and δ18O values of body water and of hair. Moreover, the isotope data allowed us to better quantify values for two critical variables in the models: the δ2H and δ18O values of gut water and the 18O isotope fractionation associated with a carbonyl oxygen-water interaction in the gut (αow). Our modeling efforts indicated that better predictions for body water and hair isotope values were achieved by making the isotopic composition of gut water approached that of body water. Additionally, the value of αow was 1.0164, in close agreement with the only other previously measured observation (microbial spore cell walls), suggesting robustness of this fractionation factor across different biological systems. PMID:22553163

  7. Nitrogen Isotope Tracing of Eutrophication Sources on a Watershed Scale: Nitrogen and Oxygen Isotopes of Nitrate

    NASA Astrophysics Data System (ADS)

    Showers, W. J.; Genna, B.; Karr, J.

    2001-05-01

    Nitrate contamination of shallow aquifers and surface waters associated with agricultural activities has become a major concern in river basins, like the Neuse, where significant agricultural land use is coupled with growing numbers of intensive animal operations (ILO's). The development of effective management practices to preserve water quality, or remediation strategies for basins already polluted requires source identification. The stable isotopes of nitrogen and oxygen in nitrate has been used as tracers to evaluate nitrogen sources on small scales, such as agricultural fields, or small watersheds with one dominate land use. This discrimination is possible because of the large fractionation associated with the volatilization of ammonia from animal wastes. Using stable isotopes on larger scales to evaluate nutrient sources is complicated by multiple sources, overlapping point and non-point sources, and co-existing biogeochemical processes that alter nitrate concentrations. To evaluate the potential of stable isotopes to determine the character of nutrient fluxes on larger scales, the isotopic/discharge relationship was examined for a watershed with little agricultural activity, an urban watershed, a watershed with mixed urban and agricultural land use, a watershed dominated by swine ILO's, and a watershed dominated by poultry ILO's. The watershed with little agricultural activity and the poultry watershed have similar isotope/discharge relationships with isotopic values at natural background levels and no change in concentration or isotopic composition in different discharge states. The urban watershed is dominated by point source isotopic values at all flow levels, the mixed urban and agricultural watershed is dominated by point source values during low flow conditions, and fertilizer non-point source values during high flow conditions. In this watershed nutrient concentrations also increase during low flow conditions. The swine watershed is dominated by

  8. Online Method for Oxygen Triple Isotope Analyses of Nitrate

    NASA Astrophysics Data System (ADS)

    Kaiser, J.; Hastings, M. G.; Houlton, B.; Roeckmann, T.; Sigman, D. M.

    2004-12-01

    Combined 17O/16O and 18O/16O isotope ratio analyses of nitrate in ground and surface waters help to understand the partitioning between atmospheric and terrestrial nitrate sources because only terrestrial nitrate shows mass-dependent relative enrichments in 17O and 18O, whereas atmospheric nitrate displays an anomalous enrichment in 17O. The 17O isotope anomaly of nitrate is therefore a sensitive tracer of fresh water pollution. Furthermore, isotope measurements of atmospheric nitrate in aerosols and precipitation provide insight into the partitioning between atmospheric NOx cycling pathways via ozone or hydroxy/peroxy radicals because only ozone has a significant non-mass dependent enrichment in 17O. Previous methods to analyze the oxygen triple isotope composition of nitrate rely on offline thermal decomposition of AgNO3 amounts in the µ mol range. We have recently developed an online (coupled gas chromatography-mass spectrometry) method that requires two to three orders of magnitude less material to achieve essentially the same analytical precision: 30 nmol of nitrate give a 1σ uncertainty of 1.0 ‰ for the δ ^{18}O value and 0.3 \\permil for the ^{17}O anomaly (\\Delta17O). The method uses a strain of bacterial denitrifiers to convert nitrate to N2O [Casciotti et al., 2002], which is then quantitatively converted to elemental nitrogen and oxygen in a gold furnace at 800° C. Both gases are separated on a molecular sieve capillary column and introduced into the isotope ratio mass spectrometer. There is no significant memory effect, but calibration via nitrate or N2O standards is required for scale normalization. This novel method was used to analyze nitrate isotopes in rain water and streams and, thanks to the low sample size requirements, will also be suitable for ice core samples, which have very low nitrate concentrations. A tight correlation between Δ 17O and δ 18O in rain water was found with a slope of about 0.3 (R2 = 0.86), which reflects the

  9. Oxygen-isotope variations in post-glacial Lake Ontario

    NASA Astrophysics Data System (ADS)

    Hladyniuk, Ryan; Longstaffe, Fred J.

    2016-02-01

    The role of glacial meltwater input to the Atlantic Ocean in triggering the Younger Dryas (YD) cooling event has been the subject of controversy in recent literature. Lake Ontario is ideally situated to test for possible meltwater passage from upstream glacial lakes and the Laurentide Ice Sheet (LIS) to the Atlantic Ocean via the lower Great Lakes. Here, we use the oxygen-isotope compositions of ostracode valves and clam shells from three Lake Ontario sediment cores to identify glacial meltwater contributions to ancient Lake Ontario since the retreat of the LIS (∼16,500 cal [13,300 14C] BP). Differences in mineralogy and sediment grain size are also used to identify changes in the hydrologic regime. The average lakewater δ18O of -17.5‰ (determined from ostracode compositions) indicates a significant contribution from glacial meltwater. Upon LIS retreat from the St. Lawrence lowlands, ancient Lake Ontario (glacial Lake Iroquois) lakewater δ18O increased to -12‰ largely because of the loss of low-18O glacial meltwater input. A subsequent decrease in lakewater δ18O (from -12 to -14‰), accompanied by a median sediment grain size increase to 9 μm, indicates that post-glacial Lake Ontario received a final pulse of meltwater (∼13,000-12,500 cal [11,100-10,500 14C] BP) before the onset of hydrologic closure. This meltwater pulse, which is also recorded in a previously reported brief freshening of the neighbouring Champlain Valley (Cronin et al., 2012), may have contributed to a weakening of thermohaline circulation in the Atlantic Ocean. After 12,900 cal [11,020 14C] BP, the meltwater presence in the Ontario basin continued to inhibit entry of Champlain seawater into early Lake Ontario. Opening of the North Bay outlet diverted upper Great Lakes water from the lower Great Lakes causing a period (12,300-8300 cal [10,400-7500 14C] BP) of hydrologic closure in Lake Ontario (Anderson and Lewis, 2012). This change is demarcated by a shift to higher δ18Olakewater

  10. Stable isotope record of Holocene climate and ecological change from brine shrimp cyst chitin for the Great Salt Lake, UT

    NASA Astrophysics Data System (ADS)

    Nielson, K. E.; Bowen, G. J.

    2009-12-01

    We present a record of oxygen and hydrogen isotopes in brine shrimp cysts from the Great Salt Lake, a terminal lake in the Great Basin, US. Water balance for the region is influenced by strength of the El Niño in Pacific and by the strength of the summer monsoon. Brine shrimp cysts are a novel proxy for isotope reconstruction, and allow reconstruction of water isotopes (oxygen, hydrogen) and ecology (hydrogen). Oxygen isotopes in chitin respond to water, while both diet and growth water contribute to hydrogen isotopes, allowing reconstruction of both environmental and ecological information from a single molecule. Values of δ18O decrease from about +15‰ to about +11‰ over course of the 8000 year record. This may suggest the importance of snow melt increased over the Holocene, or it may suggest lake is larger today than it was in mid-Holocene. Hydrogen isotopes are relatively stable for most of record, fluctuating around -140‰. Modeled hydrogen isotopes in food, also stable in the beginning of the record at about -150‰, become much heavier, shifting toward about -75‰ starting about 5000 ybp. This may suggest a shift from a primarily aquatic diet in the Mid-Holocene to a diet with a greater contribution of terrestrial material later in the Holocene. These observations agree broadly with previous inferences of a warm Mid-Holocene and associated low terrestrial productivity, followed by a more moist, and consequently more productive Late Holocene.

  11. Fractionation of oxygen isotopes by root respiration: Implications for the isotopic composition of atmospheric O 2

    NASA Astrophysics Data System (ADS)

    Angert, Alon; Luz, Boaz

    2001-06-01

    The ratio of 18O/ 16O in atmospheric oxygen depends on the isotopic composition of the substrate water used in photosynthesis and on discrimination against 18O in respiratory consumption. The current understanding of the composition of air O 2 attributes the magnitude of the respiratory fractionation to biochemical mechanisms alone. Thus the discrimination against 18O is assumed as 18‰ in normal dark respiration and 25‰ to 30‰ in cyanide resistant respiration. Here we report new results on the fractionation of O 2 isotopes in root respiration. The isotopic fractionation was determined from the change in δ 18O of air due to partial uptake by roots in closed containers. The discrimination in these experiments was in the range of 11.9‰ to 20.0‰ with an average of 14.5‰. This average is significantly less than the known discrimination in dark respiration. A simple diffusion-respiration model was used to explain the isotopic discrimination in roots. Available data show that O 2 concentration inside roots is low due to slow diffusion. As a result, due to diffusion and biological uptake at the consumption site inside the root, the overall discrimination is small. Root respiration is an important component of the global oxygen uptake. Our new result that the discrimination against 18O is less than generally thought indicates that the mechanisms affecting δ 18O of atmospheric oxygen should be re-evaluated.

  12. Oxygen isotope variation in primitive achondrites: The influence of primordial, asteroidal and terrestrial processes

    NASA Astrophysics Data System (ADS)

    Greenwood, R. C.; Franchi, I. A.; Gibson, J. M.; Benedix, G. K.

    2012-10-01

    similar oxygen isotope compositions to the brachinites. It remains unclear whether the brachinites and related olivine-rich achondrites are from a single or multiple parent bodies. The primitive achondrites and related samples represent material from at most only 18 parent bodies, compared to an estimated 65 for the iron meteorites. This suggests that asteroidal mantle material is underrepresented in the meteorite record. Early fragmentation of differentiated asteroids, followed by preferential destruction of their silicate-rich mantles, offers a possible explanation for this discrepancy. On an oxygen three-isotope diagram, primitive chondrule-bearing winonaites (Dho 1222, NWA 725, NWA 1052, NWA 1463, Mt. Morris (Wisconsin)) plot close to the Young & Russell (Y&R) slope 1 line, with more evolved samples extending away from it towards the CCAM line. A similar relationship is shown by the CR chondrites. The acapulcoite-lodranite clan plots between the slope 1 and CCAM lines. However, the precursor material to the clan may have had a composition close to the slope 1 line prior to parent body processing. These relationships support the view that primordial oxygen isotope variation in the early solar system is best represented by the slope 1 (Y&R) line.

  13. Constraining the oxygen isotope composition of early Cretaceous seawater

    NASA Astrophysics Data System (ADS)

    Price, Gregory; VanDeVelde, Justin; Passey, Ben; Grimes, Stephen

    2015-04-01

    The oxygen isotopic composition of well-preserved marine fossils fundamentally underpins our understanding of the evolution of the Earth's climate. However, a lack of constraint on the delta18O of seawater provides a major challenge. In this study new analyses of sub-Arctic and Boreal Cretaceous (Berriasian-late Valanginian, ca. 145-134 Ma) fossil molluscs (belemnites) have been undertaken using carbonate clumped isotopes, an approach based on the "clumping" of 13C and 18O in the carbonate mineral lattice into bonds with each other. From our analyses we infer Early Cretaceous marine temperatures ranging from 10 °C to 20 °C. We identify a cooler late Valanginian interval with temperatures consistent with regions a few degrees above freezing. Our combined temperature and delta18O belemnite data imply seawater delta18O values that have a remarkably modern profile in that they are similar to modern high-latitude seawater and much more positive than values typically assumed for Cretaceous seawater. These high oxygen isotope ratios suggest a hydrological cycle similar to the modern rather than a substantial increase towards a more vigorous hydrological cycle. Our results argue for generally warm but dynamic polar climates during Cretaceous greenhouse intervals that were punctuated by periods of ice growth.

  14. The bound coherent neutron scattering lengths of the oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Fischer, Henry E.; Simonson, J. Mike; Neuefeind, Jörg C.; Lemmel, Hartmut; Rauch, Helmut; Zeidler, Anita; Salmon, Philip S.

    2012-12-01

    The technique of neutron interferometry was used to measure the bound coherent neutron scattering length bcoh of the oxygen isotopes 17O and 18O. From the measured difference in optical path between two water samples, either H217O or H218O versus H2natO, where nat denotes the natural isotopic composition, we obtain bcoh,17O = 5.867(4) fm and bcoh,18O = 6.009(5) fm, based on the accurately known value of bcoh,natO = 5.805(4) fm which is equal to bcoh,16O within the experimental uncertainty. Our results for bcoh,17O and bcoh,18O differ appreciably from the standard tabulated values of 5.6(5) fm and 5.84(7) fm, respectively. In particular, our measured scattering-length contrast of 0.204(3) fm between 18O and natO is nearly a factor of 6 greater than the tabulated value, which renders feasible neutron diffraction experiments using 18O isotope substitution and thereby offers new possibilities for measuring the partial structure factors of oxygen-containing compounds, such as water.

  15. The bound coherent neutron scattering length of the oxygen isotopes

    SciTech Connect

    Fischer, Henry E; Simonson, J Michael {Mike}; Neuefeind, Joerg C; Lemmel, Hartmut; Rauch, Helmut; Zeidler, Anita; Salmon, Phil

    2012-01-01

    The technique of neutron interferometry was used to measure the bound coherent neutron scattering length bcoh of the oxygen isotopes 17O and 18O. From the measured difference in optical path between two water samples, either H2 17O or H2 18O versus H2 natO, where nat denotes the natural isotopic composition, we obtain bcoh , 17O = 5.867(4) fm and bcoh , 18O = 6.009(5) fm, based on the accurately known value of bcoh , natO = 5.805(4) fm which is equal to bcoh , 16O within the experimental uncertainty. Our results for bcoh , 17O and bcoh , 18O differ appreciably from the standard tabulated values of 5.6(5) fm and 5.84(7) fm, respectively. In particular, our measured scattering length contrast of 0.204(3) fm between 18O and natO is nearly a factor of 6 greater than the tabulated value, which renders feasible neutron diffraction experiments using 18O isotope substitution and thereby offers new possibilites for measuring the partial structure factors of oxygen-containing compounds, such as water.

  16. Uranium Stable Isotopes: A Proxy For Productivity Or Ocean Oxygenation?

    NASA Astrophysics Data System (ADS)

    Severmann, S.

    2015-12-01

    Uranium elemental abundances in sediments have traditionally been used to reconstruct primary productivity and carbon flux in the ocean. 238U/235U isotope compositions, in contrast, are currently understood to reflect the extent of bottom water anoxia in the ocean. A review of our current understanding of authigenic U enrichment mechanism into reducing sediments suggests that a revision of this interpretation is warranted. Specifically, the current interpretation of U isotope effects in suboxic vs. anoxic deposits has not taken into account the well-documented linear relationship with organic C burial rates. Although organic C rain rates (i.e., surface productivity) and bottom water oxygenation are clearly related, distinction between these two environmental controls is conceptually important as it relates to the mechanism of enhanced C burial and ultimately the strength of the biological pump. Here we will review new and existing data to test the hypothesis that the isotope composition of authigenic U in reducing sediments are best described by their relationship with parameters related to organic carbon delivery and burial, rather than bottom water oxygen concentration.

  17. Oxygen Isotope Fractionation During Evaporation of Mg- and Si-rich CMAS-Liquids in Vacuum

    NASA Astrophysics Data System (ADS)

    Mendybaev, R. A.; Richter, F. M.; Spicuzza, M. J.; Valley, J. W.; Davis, A. M.

    2010-03-01

    We report oxygen isotope data for the residues produced by evaporation of Mg- and Si-rich CMAS-liquids. The results on oxygen together with Mg- and Si-isotopes in the experimental run products are used to estimate the isotopic compositions of natural FUN CAIs.

  18. Evaluation of sampling resolution in coral stable isotope records: A case study using records from New Caledonia and Tarawa

    NASA Astrophysics Data System (ADS)

    Quinn, Terrence M.; Taylor, Frederick W.; Crowley, Thomas J.; Link, Suzanne M.

    1996-10-01

    We have generated a 40-year-long, monthly stable isotope record from a Porites lutea coral collected offshore of Amedee, New Caledonia (22°S, 167°E) to investigate the relation between sampling resolution in coral isotope studies and retrieval of sea-surface environmental information. We interpret the high correlation between our oxygen isotope record and a twenty-year long sea-surface temperature record at the monthly timescale (r=0.88) to indicate that our coral isotope record is an accurate monitor of environmental conditions offshore of Amedee. The character of the signal and the percent variance explained in the record at the annual band, at the quasi-biennial oscillation band ((QBO) 2.0-2.4 years), and at the El Nino-Southern Oscillation band ((ENSO) 3-8 years) changes little in response to a reduction in sampling density from monthly to bimonthly to quarterly. Similar results have been obtained in a reanalysis of a coral isotope record from Tarawa, Kiribati. Our results indicate that a significant amount of the information obtained from high-density sampling can also be retrieved from lower-density sampling. In particular, bimonthly sampling yields virtually no drop-off in variance explained, and quarterly sampling is satisfactory for resolving interannual and decadal-scale trends in time series. The proposed sampling approach may enable a more rapid filling in of numerous spatial holes in coral sampling sites needed for reconstruction of long-term decadal-scale variations in climate.

  19. Does the Shuram δ13C excursion record Ediacaran oxygenation?

    NASA Astrophysics Data System (ADS)

    Husson, J. M.; Maloof, A. C.; Schoene, B.; Higgins, J. A.

    2013-12-01

    The most negative carbon isotope excursion in Earth history is found in carbonate rocks of the Ediacaran Period (635-542 Ma). Known colloquially as the the 'Shuram' excursion, workers have long noted its tantalizing, broad concordance with the rise of abundant macro-scale fossils in the rock record, variously interpreted as animals, giant protists, macro-algae and lichen, and known as the 'Ediacaran Biota.' Thus, the Shuram excursion has been interpreted by many in the context of a dramatically changing redox state of the Ediacaran oceans - e.g., a result of methane cycling in a low O2 atmosphere, the final destruction of a large pool of recalcitrant dissolved organic carbon (DOC), and the step-wise oxidation of the Ediacaran oceans. More recently, diagenetic interpretations of the Shuram excursion - e.g. sedimentary in-growth of very δ13C depleted authigenic carbonates, meteoric alteration of Ediacaran carbonates, late-stage burial diagenesis - have challenged the various Ediacaran redox models. A rigorous geologic context is required to discriminate between these explanatory models, and determine whether the Shuram excursion can be used to evaluate terminal Neoproterozoic oxygenation. Here, we present chemo-stratigraphic data (δ13C, δ18O, δ44/42Ca and redox sensitive trace element abundances) from 12 measured sections of the Ediacaran-aged Wonoka Formation (Fm.) of South Australia that require a syn-depositional age for the extraordinary range of δ13C values (-12 to +4‰) observed in the formation. In some locations, the Wonoka Fm. is ~700 meters (m) of mixed shelf limestones and siliclastics that record the full 16 ‰ δ13C excursion in a remarkably consistent fashion across 100s of square kilometers of basin area. Fabric-altering diagenesis, where present, occurs at the sub-meter vertical scale, only results in sub-permil offsets in δ13C and cannot be used to explain the full δ13C excursion. In other places, the Wonoka Fm. is host to deep (1 km

  20. Oxygen isotope ratios of cellulose-derived phenylglucosazone: An improved paleoclimate indicator of environmental water and relative humidity

    NASA Astrophysics Data System (ADS)

    Sternberg, Leonel da S. L.; Pinzon, Maria C.; Vendramini, Patricia F.; Anderson, William T.; Jahren, A. Hope; Beuning, Kristina

    2007-05-01

    Oxygen atoms within fossil wood provide high-resolution records of climate change, particularly for the Quaternary. However, current analysis methods of fossil cellulose do not differentiate between different positions of the oxygen atoms. Here, we propose a refinement to tree-cellulose paleoclimatology modeling, using the cellulose-derived compound phenylglucosazone as the isotopic substrate. Stem samples from trees were collected at northern latitudes as low as 24°37'N and as high as 69°00'N. We extracted stem water and cellulose from each stem sample and analyzed them for their 18O content. In addition, we derived the cellulose to phenylglucosazone, a compound which lacks the oxygen attached to the second carbon of the cellulose-glucose moieties. Oxygen isotope analysis of phenylglucosazone allowed us to calculate the 18O content of the oxygen attached to the second carbon of the cellulose-glucose moieties. By way of these analyses, we tested two hypotheses: first, that the 18O content of the oxygen attached to second carbon will more closely reflect the 18O content of the stem water, and will not resemble the 18O content of either cellulose or its derivative phenylglucosazone. Second, tree-ring models that incorporate the variable oxygen isotope fractionation shown here and elsewhere are more accurate than those that do not. Our first hypothesis was rejected on the basis that the oxygen isotope ratios of the oxygen attached to the second carbon of the glucose moieties had a noisy isotopic signal with a large standard deviation and gave the poorest correlation with the oxygen isotope ratios of stem water. Related to this isotopic noise, we observed that the correlation between oxygen isotope ratios of phenylglucosazone with both stem water and relative humidity were higher than those observed for cellulose. Our hypothesis about tree-ring models which account for changes in the oxygen isotopic fractionation during cellulose synthesis was consistent only for the

  1. Triple oxygen isotope evidence for elevated CO2 levels after a Neoproterozoic glaciation.

    PubMed

    Bao, Huiming; Lyons, J R; Zhou, Chuanming

    2008-05-22

    Understanding the composition of the atmosphere over geological time is critical to understanding the history of the Earth system, as the atmosphere is closely linked to the lithosphere, hydrosphere and biosphere. Although much of the history of the lithosphere and hydrosphere is contained in rock and mineral records, corresponding information about the atmosphere is scarce and elusive owing to the lack of direct records. Geologists have used sedimentary minerals, fossils and geochemical models to place constraints on the concentrations of carbon dioxide, oxygen or methane in the past. Here we show that the triple oxygen isotope composition of sulphate from ancient evaporites and barites shows variable negative oxygen-17 isotope anomalies over the past 750 million years. We propose that these anomalies track those of atmospheric oxygen and in turn reflect the partial pressure of carbon dioxide (P(CO2)) in the past through a photochemical reaction network linking stratospheric ozone to carbon dioxide and to oxygen. Our results suggest that P(CO2) was much higher in the early Cambrian than in younger eras, agreeing with previous modelling results. We also find that the (17)O isotope anomalies of barites from Marinoan (approximately 635 million years ago) cap carbonates display a distinct negative spike (around -0.70 per thousand), suggesting that by the time barite was precipitating in the immediate aftermath of a Neoproterozoic global glaciation, the P(CO2) was at its highest level in the past 750 million years. Our finding is consistent with the 'snowball Earth' hypothesis and/or a massive methane release after the Marinoan glaciation. PMID:18497821

  2. Triple oxygen isotope evidence for elevated CO2 levels after a Neoproterozoic glaciation.

    PubMed

    Bao, Huiming; Lyons, J R; Zhou, Chuanming

    2008-05-22

    Understanding the composition of the atmosphere over geological time is critical to understanding the history of the Earth system, as the atmosphere is closely linked to the lithosphere, hydrosphere and biosphere. Although much of the history of the lithosphere and hydrosphere is contained in rock and mineral records, corresponding information about the atmosphere is scarce and elusive owing to the lack of direct records. Geologists have used sedimentary minerals, fossils and geochemical models to place constraints on the concentrations of carbon dioxide, oxygen or methane in the past. Here we show that the triple oxygen isotope composition of sulphate from ancient evaporites and barites shows variable negative oxygen-17 isotope anomalies over the past 750 million years. We propose that these anomalies track those of atmospheric oxygen and in turn reflect the partial pressure of carbon dioxide (P(CO2)) in the past through a photochemical reaction network linking stratospheric ozone to carbon dioxide and to oxygen. Our results suggest that P(CO2) was much higher in the early Cambrian than in younger eras, agreeing with previous modelling results. We also find that the (17)O isotope anomalies of barites from Marinoan (approximately 635 million years ago) cap carbonates display a distinct negative spike (around -0.70 per thousand), suggesting that by the time barite was precipitating in the immediate aftermath of a Neoproterozoic global glaciation, the P(CO2) was at its highest level in the past 750 million years. Our finding is consistent with the 'snowball Earth' hypothesis and/or a massive methane release after the Marinoan glaciation.

  3. Oxygen isotope variations in phosphate of deer bones

    NASA Astrophysics Data System (ADS)

    Luz, Boaz; Cormie, Allison B.; Schwarcz, Henry P.

    1990-06-01

    Variations of δ 18O of bone phosphate (δ p) of white tailed deer were studied in samples with wide geographic distribution in North America. Bones from the same locality have similar isotopic values, and the difference between specimens (0.4‰) is not large relative to the measurement error (0.3‰). The total range of δ p values is about 12‰. This indicates that deer use water from a relatively small area, and thus their δ p indicates local environmental conditions. Multiple regression analysis between oxygen isotope composition of deer bone phosphate and of local relative humidity and precipitation (δ w) yields a high correlation coefficient (0.95). This correlation is significantly better than the linear correlation (0.81) between δ p and δ w of precipitation alone. Thus δ p depends on both isotopic composition of precipitation and on relative humidity. This is because deer obtain most of their water from leaves, the isotopic composition of which is partly controlled by relative humidity through evaporation/transpiration.

  4. Extending the calibration of marine barite Pb isotope records

    NASA Astrophysics Data System (ADS)

    Erhardt, A. M.; Paytan, A.

    2010-12-01

    Lead isotopes in marine barite have been emerging as a new proxy for intermediate water conditions. Marine barite forms at intermediate water depths and incorporates Pb into its matrix at ~2ppm. The isotopic composition of this Pb is retained as the barite settles in the water column, allowing us to reconstruct the Pb isotopic ratios of intermediate water. Lead and its isotopes are introduced into the ocean primarily through the weathering of continental rock. These rocks may have distinct isotopic signatures, depending on the age of the eroded material and weathering style. Lead has a short residence time in the ocean. As a result of these characteristics, different water masses have distinct lead isotope signatures that depend on the Pb sources (riverine and atmospheric) to the water mass at the point of origin. Since anthropogenic pollution has irrevocably altered Pb concentrations and isotope ratios, calibration of Pb proxies relies on data collected from other sources. Currently, ferromanganese nodules have been utilized for seawater Pb reconstructions. As nodules form at the seafloor, for intermediate water depth these records are limited to isolated seamounts in the open ocean. As a result, the calibration of intermediate water column Pb isotopes requires the characterization of signatures using barite form a whole spectrum of regions. This study reports Pb isotopes in barite from a broad range of locations and extends the current core top data from the equatorial Pacific.

  5. Kinetic theory of oxygen isotopic exchange between minerals and water

    USGS Publications Warehouse

    Criss, R.E.; Gregory, R.T.; Taylor, H.P.

    1987-01-01

    Kinetic and mass conservation equations are used to describe oxygen isotopic exchange between minerals and water in "closed" and open hydrothermal systems. In cases where n coexisting mineral phases having different reaction rates are present, the exchange process is described by a system of n + 1 simultaneous differential equations consisting of n pseudo first-order rate equations and a conservation of mass equation. The simultaneous solutions to these equations generate curved exchange trajectories on ??-?? plots. Families of such trajectories generated under conditions allowing for different fluid mole fractions, different fluid isotopic compositions, or different fluid flow rates are connected by positive-sloped isochronous lines. These isochrons reproduce the effects observed in hydrothermally exchanged mineral pairs including 1) steep positive slopes, 2) common reversals in the measured fractionation factors (??), and 3) measured fractionations that are highly variable over short distances where no thermal gradient can be geologically demonstrated. ?? 1987.

  6. Lightning and Mass Independent Oxygen Isotopic Fractionation in Nebular Silicates

    NASA Technical Reports Server (NTRS)

    Nuth, Joseph A.

    2009-01-01

    Lightning has long been postulated as the agent of Chondru|e formation in the solar nebula, but it may have an additional role to play as well. Lightning bolts of almost any scale will both vaporize dust and liberate oxygen atoms that will then interact with both nebular gases as well as the refractory silicate vapor as it re-condenses. Such processes should result in the addition of the heavy oxygen isotopes to the growing silicate grains while the light oxygen-16 becomes part of the gas phase water. This process will proceed to some extent throughout the history of any turbulent nebula and will result in the gradual increase of O-16 in the gas phase and in a much larger relative increase in the O-17 and O-18 content of the nebular dust. Laboratory experiments have demonstrated the production of such "heavy oxygen enriched", non-mass-dependently-fractionated dust grains in a high voltage discharge in a hydrogen rich gas containing small quantities of silane, pentacarbonyl iron and oxygen.

  7. An orbital origin for large oxygen isotopic shifts and sea-level changes during the Oligocene

    NASA Astrophysics Data System (ADS)

    Pekar, S. F.; Christie-Blick, N.

    2004-12-01

    Recently, it was shown that a relatively rare orbital congruence involving low-amplitude variance in obliquity and a minimum in eccentricity coincides at the Miocene/Oligocene boundary with a large increase in oxygen isotopes (Mi1 event) and ice volume, suggesting a possible causal mechanism for such events at the million-year timescale. We tested this idea against the Oligocene oxygen isotopic and sea-level records and the astronomical timescale of Shackleton et al. (1999). As in the Miocene, large isotopic shifts (Oi events; δ 18O >0.5\\permil, with maximum values >2.7\\permil) and sea-level changes (30-70 m) occurred in the Oligocene at the million-year timescale. Smaller variations in sea level (and corresponding isotopic values) characterize obliquity (104 years) and eccentricity (105 years) timescales: 15-20 m and 20-30 m, respectively. Our analysis shows that, as with the Mi1 event, Oi events relate to the anticipated orbital congruence - resolving one of the outstanding conundrums of the late Paleogene paleoclimate. It also provides support for the robustness of the astronomical time scale of Shackleton et al. (1999) for the Oligocene Epoch.

  8. Climatic forcing of carbon-oxygen isotopic covariance in temperate-region marl lakes

    NASA Technical Reports Server (NTRS)

    Drummond, C. N.; Patterson, W. P.; Walker, J. C.

    1995-01-01

    Carbon and oxygen stable isotopic compositions of lacustrine carbonate from a southeastern Michigan marl lake display linear covariance over a range of 4.0% Peedee belemnite (PDB) in oxygen and 3.9% (PDB) in carbon. Mechanisms of delta 13 C-delta 18 O coupling conventionally attributed to lake closure in arid-region basins are inapplicable to hydrologically open lake systems. Thus, an alternative explanation of isotopic covariance in temperate region dimictic marl lakes is required. We propose that isotopic covariance is a direct record of change in regional climate. In short-residence-time temperate-region lake basins, summer meteoric precipitation is enriched in 18O relative to winter values, and summer organic productivity enriches epilimnic dissolved inorganic carbon in 13C. Thus, climate change toward longer summers and/or shorter winters could result in greater proportions of warm-month meteoric precipitation, longer durations of warm-month productivity, and net long-term enrichment in carbonate 18O and 13C. Isotopic covariance observed in the Michigan marl lake cores is interpreted to reflect postglacial warming from 10 to 3 ka followed by cooler mean annual temperature, a shift toward greater proportions of seasonal summer precipitation, a shortening of the winter season, or some combination of these three factors.

  9. Oxygen and carbon isotopic compositions of gases respired by humans

    SciTech Connect

    Epstein, S.; Zeiri, L. )

    1988-03-01

    Oxygen-isotope fractionation associated with respiration in human individuals at rest is linearly related to the fraction of the O{sub 2} utilized in the respiration process. The slope of this relationship is affected by a history of smoking, by vigorous exercise, and by the N{sub 2}/O{sub 2} ratio of the inhaled gas. For patients who suffer anemia-related diseases, the slope of this relationship is directly proportional to their level of hemoglobin. These results introduce a new approach for studying the mechanisms of O{sub 2} consumption in human respiration and how they are affected by related diseases.

  10. Neutron decay spectroscopy of neutron-rich oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Frank, N.; Baumann, T.; Bazin, D.; Brown, B. A.; Brown, J.; DeYoung, P. A.; Finck, J. E.; Gade, A.; Hinnefeld, J.; Howes, R.; Lecouey, J.-L.; Luther, B.; Peters, W. A.; Scheit, H.; Schiller, A.; Thoennessen, M.; Tostevin, J.

    2008-12-01

    Neutron decay spectroscopy of neutron-rich oxygen isotopes has been performed using the two-proton knock-out reaction 9Be( 26Ne, X) 24,23,22O. A combination of the knock-out of valence and core protons can explain the three observed spectra. These knock-out processes are selective and preferentially populate hole states. The observed narrow resonance state in 23O at an excitation energy of 2.8(1) MeV was assigned to the 5/2 state.

  11. Carbonate Ion Effects on Coccolith Carbon and Oxygen Isotopes

    NASA Astrophysics Data System (ADS)

    Ziveri, P.; Probert, I.; Stoll, H. M.

    2006-12-01

    The stable oxygen and carbon isotopic composition of biogenic calcite constitutes one of the primary tools used in paleoceanographic reconstructions. The δ18O of shells of ocean floor microfossils and corals reflects the composition of the paleo-seawater as they use the oxygen to build up their calcite and aragonite shells. The δ13C is used to reconstruct variations in the carbon isotopic composition of dissolved inorganic carbon in the ocean, which is controlled by biological productivity through the removal of isotopically light carbon in organic matter. To be effective and sensitive tools for understanding photic zone processes it is first necessary to understand the various biological fractionations associated with carbonate precipitation. To date, isotopic fractionation models are mainly based on foraminifera and corals but not on coccoliths, tiny plates produced by coccolithophore algae, which are often the most dominant carbonate contributors to pelagic sediments. As photosynthetic organisms, their chemistry can provide a sensitive tool for understanding photic zone processes. Coccoliths may be the most important carbonate phase for geochemical analysis in sediments where foraminifera are less common and/or core material is limited, such as in subpolar regions and for Early Cenozoic and Mesozoic sediments. Here we report experimental results on a common living coccolithophore species showing that the 13C/12C and 18O/16O ratios decrease with the increase of HCO^{3-} (CO32-). The selected species are among the heaviest calcifying extant coccolithophores and are major contributors to present coccolith carbonate export production. Because coccolithophores are photosynthetic organisms that calcify intracellularly in specialized vesicles, the challenge lies in ascertaining how kinetic and thermodynamic processes of isotopic fractionation are linked to cellular carbon "transport" and carbonate precipitation. This is a daunting challenge since studies have not

  12. Syntheses with stable isotopes of carbon, nitrogen, and oxygen

    SciTech Connect

    Ott, D.G.

    1981-01-01

    Methods, techniques, ideas, information, and references to prepare compounds labeled with stable isotopes of carbon, nitrogen, and oxygen are presented, which can be used in selecting or devising synthetic schemes. By studying and comparing methods that other investigators have applied to problems in isotopic labeling, the task of deciding on suitable syntheses for incorporating isotopes into various other compounds can be considerably simplified. The major portion of the book is devoted to synthetic procedures that have been used for preparation of specific labeled compounds. The descriptions are often given in sufficient detail that they can be applied or modified without necessity for recourse to the original literature. Methods can be compared, feasibility for extensions to other isotope isomers or to related compounds can be assessed, and requirements for apparatus, materials, time, effort, and skills can be evaluated. Additional methods and speculations are presented for a number of other compounds whose syntheses are not given in detail. A few biosynthetic preparations, which afford specific products in good isotopic yield, are described; certain other applications of biological methods are considered briefly. Arrangement of the procedures into chapters according to functional groups is somewhat arbitrary; that is, not all preparations of carboxylic acids will be found in the chapter dealing with acids and derivatives; certain alcohols appear as components in multistep syntheses in the chapter on hydrocarbons; some compounds could just as well have been placed elsewhere; and so on. Thus it is important to use the index. Following the introductory chapter, the contents of this book are as follows: (1) acids, anhydrides, amids, esters, and nitriles; (2) aldehydes and ketones; (3) alcohols, ethers, and phenols; (4) amines, and hydrocarbons; (5) heterocyclic compounds; and (6) other compounds.

  13. Unlocking the ice house: Oligocene-Miocene oxygen isotopes, eustasy, and margin erosion

    SciTech Connect

    Miller, K.G. Columbia Univ., Palisades, NY ); Wright, J.D.; Fairbanks, R.G. )

    1991-04-10

    Benthic foraminiferal {delta}{sup 18}O records place limits on the history of glaciation, suggesting the presence of ice sheets at least intermittently since the earliest Oligocene. The best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic {delta}{sup 18}O records. Although planktonic isotope records from the western equatorial regions are limited, subtropical planktonic foraminifera may also record such ice volume changes. It is difficult to apply these established principles to the Cenozoic {delta}{sup 18}O record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events. The authors improved Oligocene to Miocene correlations of {delta}{sup 18}O records and erected eight oxygen isotope zones (Oi1-Oi2, Mi1-Mi6). Benthic foraminiferal {delta}{sup 18}O increases which can be linked with {delta}{sup 18}O increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near Antarctica. These new correlations of middle Miocene benthic and western equatorial planktonic {delta}{sup 18}O records show remarkable agreement in timing and amplitude. They interpret benthic-planktonic covariance to reflect substantial ice volume increases near the bases of Zones Mi2 (circa 16.1 Ma), Mi3 (circa 13.6 Ma), and possibly Mi5 (circa 11.3 Ma). Possible glacioeustatic lowerings are associated with the {delta}{sup 18}O increases which culminated with the bases of Zone Mi4 (circa 12.6 Ma) and Mi6 (circa 9.6 Ma), although low-latitude planktonic {delta}{sup 18}O records are required to test this. These inferred glacioeustatic lowerings can be linked to seismic and rock disconformities.

  14. Dentine oxygen isotopes (δ (18)O) as a proxy for odontocete distributions and movements.

    PubMed

    Matthews, Cory J D; Longstaffe, Fred J; Ferguson, Steven H

    2016-07-01

    Spatial variation in marine oxygen isotope ratios (δ (18)O) resulting from differential evaporation rates and precipitation inputs is potentially useful for characterizing marine mammal distributions and tracking movements across δ (18)O gradients. Dentine hydroxyapatite contains carbonate and phosphate that precipitate in oxygen isotopic equilibrium with body water, which in odontocetes closely tracks the isotopic composition of ambient water. To test whether dentine oxygen isotope composition reliably records that of ambient water and can therefore serve as a proxy for odontocete distribution and movement patterns, we measured δ (18)O values of dentine structural carbonate (δ (18) OSC) and phosphate (δ (18) OP) of seven odontocete species (n = 55 individuals) from regional marine water bodies spanning a surface water δ (18)O range of several per mil. Mean dentine δ (18) OSC (range +21.2 to +25.5‰ VSMOW) and δ (18) OP (+16.7 to +20.3‰) values were strongly correlated with marine surface water δ (18)O values, with lower dentine δ (18) OSC and δ (18) OP values in high-latitude regions (Arctic and Eastern North Pacific) and higher values in the Gulf of California, Gulf of Mexico, and Mediterranean Sea. Correlations between dentine δ (18) OSC and δ (18) OP values with marine surface water δ (18)O values indicate that sequential δ (18)O measurements along dentine, which grows incrementally and archives intra- and interannual isotopic composition over the lifetime of the animal, would be useful for characterizing residency within and movements among water bodies with strong δ (18)O gradients, particularly between polar and lower latitudes, or between oceans and marginal basins. PMID:27547302

  15. Dentine oxygen isotopes (δ (18)O) as a proxy for odontocete distributions and movements.

    PubMed

    Matthews, Cory J D; Longstaffe, Fred J; Ferguson, Steven H

    2016-07-01

    Spatial variation in marine oxygen isotope ratios (δ (18)O) resulting from differential evaporation rates and precipitation inputs is potentially useful for characterizing marine mammal distributions and tracking movements across δ (18)O gradients. Dentine hydroxyapatite contains carbonate and phosphate that precipitate in oxygen isotopic equilibrium with body water, which in odontocetes closely tracks the isotopic composition of ambient water. To test whether dentine oxygen isotope composition reliably records that of ambient water and can therefore serve as a proxy for odontocete distribution and movement patterns, we measured δ (18)O values of dentine structural carbonate (δ (18) OSC) and phosphate (δ (18) OP) of seven odontocete species (n = 55 individuals) from regional marine water bodies spanning a surface water δ (18)O range of several per mil. Mean dentine δ (18) OSC (range +21.2 to +25.5‰ VSMOW) and δ (18) OP (+16.7 to +20.3‰) values were strongly correlated with marine surface water δ (18)O values, with lower dentine δ (18) OSC and δ (18) OP values in high-latitude regions (Arctic and Eastern North Pacific) and higher values in the Gulf of California, Gulf of Mexico, and Mediterranean Sea. Correlations between dentine δ (18) OSC and δ (18) OP values with marine surface water δ (18)O values indicate that sequential δ (18)O measurements along dentine, which grows incrementally and archives intra- and interannual isotopic composition over the lifetime of the animal, would be useful for characterizing residency within and movements among water bodies with strong δ (18)O gradients, particularly between polar and lower latitudes, or between oceans and marginal basins.

  16. Unlocking the Ice House: Oligocene-Miocene oxygen isotopes, eustasy, and margin erosion

    NASA Astrophysics Data System (ADS)

    Miller, Kenneth G.; Wright, James D.; Fairbanks, Richard G.

    1991-04-01

    Oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on Antarctica since the earliest Oligocene (circa 35 Ma). The growth and decay of ice sheets during the Oligocene to modern "ice house world" caused glacioeustatic sea level changes. The early Eocene was an ice-free "greenhouse world," but it is not clear if ice sheets existed during the middle to late Eocene "doubt house world." Benthic foraminiferal δ18O records place limits on the history of glaciation, suggesting the presence of ice sheets at least intermittently since the earliest Oligocene. The best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic δ18O records. Although planktonic isotope records from the western equatorial regions are limited, subtropical planktonic foraminifera may also record such ice volume changes. It is difficult to apply these established principles to the Cenozoic δ18O record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events. We improved Oligocene to Miocene correlations of δ18O records and erected eight oxygen isotope zones (Oi1-Oi2, Mi1-Mi6). Benthic foraminiferal δ18O increases which are associated with the bases of Zones Oil (circa 35.8 Ma), Oi2 (circa 32.5 Ma), and Mil (circa 23.5 Ma) can be linked with δ18O increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near Antarctica. Our new correlations of middle Miocene benthic and western equatorial planktonic δ18O records show remarkable agreement in timing and amplitude. We interpret benthic-planktonic covariance to reflect substantial ice volume increases near the bases of Zones Mi2 (circa 16.1 Ma), Mi3 (circa 13.6 Ma), and possibly Mi5 (circa 11.3 Ma). Possible glacioeustatic lowerings are associated with the δ18O increases which culminated with the bases of Zone Mi4 (circa 12.6 Ma) and Mi6 (circa 9

  17. Three-Body Forces and the Limit of Oxygen Isotopes

    SciTech Connect

    Otsuka, Takaharu; Suzuki, Toshio; Holt, Jason D.; Schwenk, Achim; Akaishi, Yoshinori

    2010-07-16

    The limit of neutron-rich nuclei, the neutron drip line, evolves regularly from light to medium-mass nuclei except for a striking anomaly in the oxygen isotopes. This anomaly is not reproduced in shell-model calculations derived from microscopic two-nucleon forces. Here, we present the first microscopic explanation of the oxygen anomaly based on three-nucleon forces that have been established in few-body systems. This leads to repulsive contributions to the interactions among excess neutrons that change the location of the neutron drip line from {sup 28}O to the experimentally observed {sup 24}O. Since the mechanism is robust and general, our findings impact the prediction of the most neutron-rich nuclei and the synthesis of heavy elements in neutron-rich environments.

  18. Authigenic Molybdenum Isotopes Record Lake Baikal in the Past

    NASA Astrophysics Data System (ADS)

    Yu, E.; Liu, H.; Lee, D.

    2013-12-01

    Authigenic molybdenum isotope signatures in marine sediments reflect the mechanisms of deposits under both oxic and reducing conditions. The studies are mainly focusing on marine environment, and the application on lake record is rare. A three-meters long gravity core (GC-99; 52°05'23'N, 105°50'24'E; water depth 201m) from Lake Baikal is studied for Mo isotopes and concentration. The result is using to examine the sources of material or/and the changes in conditions of Lake Baikal with climate changes. To approach on extracting Mo isotope signal directly related to lake water, a sequential leaching technique to extract the Mo isotopes coating on the Fe-Mn oxides and a robust chromatography technique to purify molybdenum isotopes is modified and used for all lake sediment samples. Then, Mo isotope composition is measured by applying double spike method with Multi-Collector Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS). According to the Mo concentration and its isotope composition δ98/95Mo relative to NIST-SRM-3134, the results imply Lake Baikal stayed oxic condition over the last 24 ka. Moreover, the sediment core GC-99 from Lake Baikal imply two stages fluctuations of the lake environment separated at core depth of 100cm (around 12ka); and the shifting of δ98/95Mo isotope composition shows that the lake during interglacial period was more oxic than the last glacial period due to absence of ice cover.

  19. Turnover of oxygen and hydrogen isotopes in the body water, CO 2, hair, and enamel of a small mammal

    NASA Astrophysics Data System (ADS)

    Podlesak, David W.; Torregrossa, Ann-Marie; Ehleringer, James R.; Dearing, M. Denise; Passey, Benjamin H.; Cerling, Thure E.

    2008-01-01

    Oxygen and hydrogen isotope signatures of animal tissues are strongly correlated with the isotope signature of local precipitation and as a result, isotope signatures of tissues are commonly used to study resource utilization and migration in animals and to reconstruct climate. To better understand the mechanisms behind these correlations, we manipulated the isotope composition of the drinking water and food supplied to captive woodrats to quantify the relationships between drinking water ( δdw), body water ( δbw), and tissue ( δt). Woodrats were fed an isotopically constant food but were supplied with isotopically depleted or enriched water. Some animals were switched between these waters, allowing simultaneous determination of body water turnover, isotope change recorded in teeth and hair, and fractional contributions of atmospheric O 2, drinking water, and food to the oxygen and hydrogen budgets of the animals. The half-life of the body water turnover was 3-6 days. A mass balance model estimated that drinking water, atmospheric O 2, and food were responsible for 56%, 30%, and 15% of the oxygen in the body water, respectively. Drinking water and food were responsible for 71% and 29% of the hydrogen in the body water, respectively. Published generalized models for lab rats and humans accurately estimated δbw, as did an updated version of a specific model for woodrats. The change in drinking water was clearly recorded in hair and tooth enamel, and multiple-pool and tooth enamel forward models closely predicted these changes in hair and enamel, respectively. Oxygen and hydrogen atoms in the drinking water strongly influence the composition of the body water and tissues such as hair and tooth enamel; however, food and atmospheric O 2 also contribute oxygen and/or hydrogen atoms to tissue. Controlled experiments allow researchers to validate models that estimate δt based on δdw and so will increase the reliability of estimates of resource utilization and climate

  20. Assessment of the clumped isotope composition of fossil bone carbonate as a recorder of subsurface temperatures

    NASA Astrophysics Data System (ADS)

    Suarez, Marina B.; Passey, Benjamin H.

    2014-09-01

    Bone is susceptible to early diagenesis, and its carbon and oxygen isotopic compositions have been suggested to reflect conditions in the soil environment and shallow subsurface during fossilization. This implies open-system recrystallization involving mass exchange of carbon and oxygen among bioapatite, soil water, and DIC. Such recrystallization would also redistribute isotopic clumping (including 13C-18O bonds), leading to the possibility that the carbonate clumped isotope compositions of fossil bone record ground temperature during early diagenesis. We assess this possibility by studying Quaternary mammalian fossil bone from subtropical to polar latitudes: if recrystallization is early and pervasive, clumped isotope derived temperatures, T(Δ47), should closely mirror latitudinal gradients in ground temperature. Excluding results from a mummified specimen yielding T(Δ47) = 38 °C (that is, indistinguishable from mammalian body temperature), we find that T(Δ47) values are intermediate between mammalian body temperature and ground temperature, suggesting partial recrystallization of bone carbonate. XRD analyses show that the nature and extent of diagenesis varies among the samples and does not relate in a straightforward manner to T(Δ47). No clear correlation exists between T(Δ47) and mean annual temperature or mean warm season temperature. Furthermore, bone tends to retain the 18O-enriched signature of body water, suggesting incomplete oxygen isotope exchange with meteoric waters. Incomplete carbon and oxygen isotope exchange between bone carbonate and soil waters is also indicated for a set of late Miocene bone-enamel pairs from a sequence of stacked paleosols in northern China. Analysis of bone as old as Early Cretaceous shows that bone carbonate is susceptible to later diagenesis at elevated burial temperatures, although T(Δ47) does not closely conform to maximum burial temperature, again suggesting partial recrystallization, or recrystallization during

  1. Kinetic oxygen isotope effects during dissimilatory sulfate reduction: A combined theoretical and experimental approach

    NASA Astrophysics Data System (ADS)

    Turchyn, Alexandra V.; Brüchert, Volker; Lyons, Timothy W.; Engel, Gregory S.; Balci, Nurgul; Schrag, Daniel P.; Brunner, Benjamin

    2010-04-01

    Kinetic isotope effects related to the breaking of chemical bonds drive sulfur isotope fractionation during dissimilatory sulfate reduction (DSR), whereas oxygen isotope fractionation during DSR is dominated by exchange between intercellular sulfur intermediates and water. We use a simplified biochemical model for DSR to explore how a kinetic oxygen isotope effect may be expressed. We then explore these relationships in light of evolving sulfur and oxygen isotope compositions (δ 34S SO4 and δ 18O SO4) during batch culture growth of twelve strains of sulfate-reducing bacteria. Cultured under conditions to optimize growth and with identical δ 18O H2O and initial δ 18O SO4, all strains show 34S enrichment, whereas only six strains show significant 18O enrichment. The remaining six show no (or minimal) change in δ 18O SO4 over the growth of the bacteria. We use these experimental and theoretical results to address three questions: (i) which sulfur intermediates exchange oxygen isotopes with water, (ii) what is the kinetic oxygen isotope effect related to the reduction of adenosine phosphosulfate (APS) to sulfite (SO 32-), (iii) does a kinetic oxygen isotope effect impact the apparent oxygen isotope equilibrium values? We conclude that oxygen isotope exchange between water and a sulfur intermediate likely occurs downstream of APS and that our data constrain the kinetic oxygen isotope fractionation for the reduction of APS to sulfite to be smaller than 4‰. This small oxygen isotope effect impacts the apparent oxygen isotope equilibrium as controlled by the extent to which APS reduction is rate-limiting.

  2. Carbon and oxygen isotope variations of the Middle-Late Triassic Al Aziziyah Formation, northwest Libya

    NASA Astrophysics Data System (ADS)

    Moustafa, Mohamed S. H.; Pope, Michael C.; Grossman, Ethan L.; Mriheel, Ibrahim Y.

    2016-06-01

    This study presents the δ13C and δ18O records from whole rock samples of the Middle-Late Triassic (Ladinian-Carnian) Al Aziziyah Formation that were deposited on a gently sloping carbonate ramp within the Jifarah Basin of Northwest Libya. The Al Aziziyah Formation consists of gray limestone, dolomite, and dolomitic limestone interbedded with shale. The Ghryan Dome and Kaf Bates sections were sampled and analyzed for carbon and oxygen isotope chemostratigraphy to integrate high-resolution carbon isotope data with an outcrop-based stratigraphy, to provide better age control of the Al Aziziyah Formation. This study also discusses the relation between the facies architecture of the Al Aziziyah Formation and the carbon isotope values. Seven stages of relative sea level rise and fall within the Ghryan Dome were identified based on facies stacking patterns, field observations and carbon stable isotopes. The Al Aziziyah Formation δ13C chemostratigraphic curve can be partially correlated with the Triassic global δ13C curve. This correlation indicates that the Al Aziziyah Formation was deposited during the Ladinian and early Carnian. No straight-forward relationship is seen between δ13C and relative sea level probably because local influences complicated systematic environmental and diagenetic isotopic effects associated with sea level change.

  3. Oxygen isotope variations in granulite-grade iron formations: constraints on oxygen diffusion and retrograde isotopic exchange

    USGS Publications Warehouse

    Sharp, Z.D.; O'Neil, J.R.; Essene, E.J.

    1988-01-01

    The oxygen isotope ratios of various minerals were measured in a granulite-grade iron formation in the Wind River Range, Wyoming. Estimates of temperature and pressure for the terrane using well calibrated geothermometers and geobarometers are 730??50?? C and 5.5??0.5 kbar. The mineral constraints on fluid compositions in the iron formation during retrogression require either very CO2-rich fluids or no fluid at all. In the iron formation, isotopic temperature estimates from quartz-magnetite fractionations are controlled by the proximity to the enclosing granitic gneiss, and range from 500?? C (??qz - mt=10.0???) within 2-3 meters of the orthogneiss contact to 600?? C (??qz - mt=8.0???) farther from the contact. Temperature estimates from other isotopic thermometers are in good agreement with those derived from the quartz-magnetite fractionations. During prograde metamorphism, the isotopic composition of the iron formation was lowered by the infiltration of an external fluid. Equilibrium was achieved over tens of meters. Closed-system retrograde exchange is consistent with the nearly constant whole-rock ??18Owr value of 8.0??0.6???. The greater ??qz-mt values in the iron formation near the orthogneiss contact are most likely due to a lower oxygen blocking temperature related to greater exchange-ability of deformed minerals at the contact. Cooling rates required to preserve the quartz-magnetite fractionations in the central portion of the iron formation are unreasonably high (???800?? C/Ma). In order to preserve the 600?? C isotopic temperature, the diffusion coefficient D (for ??-quartz) should be two orders of magnitude lower than the experimentally determined value of 2.5??10-16 cm2/s at 833 K. There are no values for the activation energy (Q) and pre-exponential diffusion coefficient (D0), consistent with the experimentally determined values, that will result in reasonable cooling rates for the Wind River iron formation. The discrepancy between the diffusion

  4. Interpreting the Ca isotope record of marine biogenic carbonates

    NASA Astrophysics Data System (ADS)

    Sime, Neil G.; De La Rocha, Christina L.; Tipper, Edward T.; Tripati, Aradhna; Galy, Albert; Bickle, Michael J.

    2007-08-01

    An 18 million year record of the Ca isotopic composition (δ 44/42Ca) of planktonic foraminiferans from ODP site 925, in the Atlantic, on the Ceara Rise, provides the opportunity for critical analysis of Ca isotope-based reconstructions of the Ca cycle. δ 44/42Ca in this record averages +0.37 ± 0.05 (1 σ SD) and ranges from +0.21‰ to +0.52‰. The record is a good match to previously published Neogene Ca isotope records based on foraminiferans, but is not similar to the record based on bulk carbonates, which has values that are as much as 0.25‰ lower. Bulk carbonate and planktonic foraminiferans from core tops differ slightly in their δ 44/42Ca (i.e., by 0.06 ± 0.06‰ ( n = 5)), while the difference between bulk carbonate and foraminiferan values further back in time is markedly larger, leaving open the question of the cause of the difference. Modeling the global Ca cycle from downcore variations in δ 44/42Ca by assuming fixed values for the isotopic composition of weathering inputs (δ 44/42Ca w) and for isotope fractionation associated with the production of carbonate sediments (Δ sed) results in unrealistically large variations in the total mass of Ca 2+ in the oceans over the Neogene. Alternatively, variations of ±0.05‰ in the Ca isotope composition of weathering inputs or in the extent of fractionation of Ca isotopes during calcareous sediment formation could entirely account for variations in the Ca isotopic composition of marine carbonates. Ca isotope fractionation during continental weathering, such as has been recently observed, could easily result in variations in δ 44/42Ca w of a few tenths of permil. Likewise a difference in the fractionation factors associated with aragonite versus calcite formation could drive shifts in Δ sed of tenths of permil with shifts in the relative output of calcite and aragonite from the ocean. Until better constraints on variations in δ 44/42Ca w and Δ sed have been established, modeling the Ca 2+ content

  5. Oxygen isotope ratios in the shell of Mytilus edulis: archives of glacier meltwater in Greenland?

    NASA Astrophysics Data System (ADS)

    Versteegh, E. A. A.; Blicher, M. E.; Mortensen, J.; Rysgaard, S.; Als, T. D.; Wanamaker, A. D., Jr.

    2012-09-01

    Melting of the Greenland Ice Sheet (GrIS) is accelerating and will contribute significantly to global sea level rise during the 21st century. Instrumental data on GrIS melting only cover the last few decades, and proxy data extending our knowledge into the past are vital for validating models predicting the influence of ongoing climate change. We investigated a potential meltwater proxy in Godthåbsfjord (West Greenland), where glacier meltwater causes seasonal excursions with lower oxygen isotope water (δ18Ow) values and salinity. The blue mussel (Mytilus edulis) potentially records these variations, because it precipitates its shell calcite in oxygen isotopic equilibrium with ambient seawater. As M. edulis shells are known to occur in raised shorelines and kitchen middens from previous Holocene warm periods, this species may be ideal in reconstructing past meltwater dynamics. We investigate its potential as a palaeo-meltwater proxy. First, we confirmed that M. edulis shell calcite oxygen isotope (δ18Oc) values are in equilibrium with ambient water and generally reflect meltwater conditions. Subsequently we investigated if this species recorded the full range of δ18Ow values occurring during the years 2007 to 2010. Results show that δ18Ow values were not recorded at very low salinities (< ~19), because the mussels appear to cease growing. This implies that M. edulis δ18Oc values are suitable in reconstructing past meltwater amounts in most cases, but care has to be taken that shells are collected not too close to a glacier, but rather in the mid region or mouth of the fjord. The focus of future research will expand on the geographical and temporal range of the shell measurements by sampling mussels in other fjords in Greenland along a south-north gradient, and by sampling shells from raised shorelines and kitchen middens from prehistoric settlements in Greenland.

  6. Observations of nitrogen and oxygen isotopes in the low energy cosmic rays. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Vidor, S. B.

    1975-01-01

    The isotopic composition of low-energy nitrogen and oxygen cosmic rays was measured with an electron/isotope spectrometer aboard the IMP-7 satellite to determine the possible source of the particles. Instrument calibration showed the standard range-energy tables to be inadequate to calculate the isotope response, and corrections were obtained. The low-energy nitrogen and oxygen cosmic rays were found to be primarily 14N and 16O. Upper limits were obtained for the abundances of the other stable nitrogen and oxygen isotopes. The nitrogen composition differs from higher energy measurements which indicate that 15N, which is thought to be secondary, is the dominant isotope.

  7. Chemostratigraphies of carbon, oxygen and strontium isotopes and oxygen contents across the Precambrian-Cambrian boundary

    NASA Astrophysics Data System (ADS)

    Komiya, T.; Sawaki, Y.; Ishikawa, T.

    2007-12-01

    The Precambrian-Cambrian (PC-C) boundary is one of the most important intervals for evolution of life. However, the scarcity of well-preserved outcrops through the boundary makes it ambiguous to decode change of the surface environment and biological evolution. In south China, strata through the PC-C boundary are continuously exposed and contain many fossils, suitable for study of environmental and biological change. In addition, we conducted excavations at four sites of Three Gorge area to obtain continuous and fresh samples. We measured the delta13C, delta18O and 87Sr/86Sr values of the drill core samples and REE compositions of fresh carbonate rocks, respectively. We identified two positive and two negative isotope excursions of delta13Ccarb within this interval: a moderate increase from 0 to +2 permil and a subsequent dramatic drop to -7 permil at the PC-C boundary, and a continuous increase to +5 permil at the upper part of the Nemakit-Daldynian (ND) stage and the subsequent sharp decrease to -9 permil just below the basal Tommotian unconformity, respectively. The continuous pattern of the delta13C shift is irrespective of lithotype and is comparable to fragmented records of other sections within and outside of the Yangtze Platform, indicating that the profile represents global change of seawater chemistry. A chemostratigraphy of 87Sr/86Sr ratios of the drilled samples also displays a smooth curve and its large positive anomaly just below the PC-C boundary. The estimate of oxygen content of seawater from REE composition of carbonate minerals shows significant decreases around PC-C and ND-Tommotian boundaries, respectively. The combination of chemostratigraphies of delta13C, 87Sr/86Sr and pO2 indicates that the 87Sr/86Sr excursions preceded the delta13C negative excursion at PC-C boundary, and suggests that global regression or formation of the Gondwana supercontinent, evident in increase of influx of continental materials, caused biological depression together

  8. Oxygen isotope thermometry of basic lavas and mantle nodules

    USGS Publications Warehouse

    Kyser, T.K.; O'Neil, J.R.; Carmichael, I.S.E.

    1981-01-01

    Measurements have been made of the oxygen isotope and chemical composition of glass and phenocrysts in lavas and coexisting minerals in mantle nodules. Temperatures of formation of these assemblages have been estimated from various chemical thermometers and range from 855?? to 1,300?? C. The permil fractionations between coexisting orthopyroxene and clinopyroxene in the lavas and nodules are all near zero. The fractionations between pyroxene and olivine vary from +1.2 to -1.4 and are a smooth function of temperature over the entire range. This function is given by T(?? C)=1151-173?? (px-d)-68??2(px-d) and has an uncertainty of ??60?? (2??). At temperatures above 1,150?? C, olivine in the nodules becomes more18O-rich than coexisting clinopyroxene, orthopyroxene, and plagioclase. In combination with the experimental work of Muehlenbachs and Kushiro (1974), the olivine-pyroxene fractionations indicate that olivine also becomes substantially more18O-rich than basaltic liquids above 1,200?? C. Geothermometers based on the oxygen isotope equilibration of basaltic liquid with olivine, pyroxene, and plagioclase are presented. ?? 1981 Springer-Verlag.

  9. New views on the isotopic composition of atmospheric oxygen

    NASA Astrophysics Data System (ADS)

    Luz, B.

    2001-05-01

    Air oxygen is enriched in O-18 with respect to ocean water by about 23 permil. This enrichment is named "Dole effect" after its discoverer. Air oxygen originates from marine and terrestrial photosynthesis that produces oxygen gas without fractionation with respect to the substrate water. The O-18 enrichment results primarily from preferential removal of O-16 during respiratory uptake. However, the discrimination against O-18 in ordinary dark respiration is only 18 permil, and cannot account for the entire magnitude of the Dole effect. Part of the discrepancy may be explained by enrichment of the substrate water in terrestrial evapo-transpiration. But the existing evidence on the magnitude of this enrichment shows that this mechanism alone cannot explain the discrepancy. In an attempt to better understand the Dole effect we have studied the overall fractionation in soil and aquatic oxygen uptake. Due to slow gas diffusion in soils and roots the discrimination is smaller than in respiration. This result thus increases the discrepancy. On the other hand, our new estimates show that discrimination in aquatic oxygen uptake is considerably greater than previously assumed. Oxygen uptake in the surface waters of oceans and lakes takes place by ordinary dark respiration as well as by cyanide resistant respiration in both dark and light conditions, and by photorespiration and Mehler reaction that occur only during illumination. Thus in order to study the overall discrimination in aquatic systems it is necessary to evaluate its effects in both light and dark conditions and to separate the effect of photosynthetic production of oxygen. Such separation is possible if gross rates of oxygen production and consumption are known. We have estimated these rates from in situ incubation experiments and from the natural distribution of O-16, O-17, O-18 and the ratio of dissolved oxygen/argon. We have used isotopic and elemental budgets to derive the overall respiratory fractionation in

  10. The Oxygen Isotope Composition of Dark Inclusions in HEDs, Ordinary and Carbonaceous Chondrites

    NASA Technical Reports Server (NTRS)

    Greenwood, R. C.; Zolensky, M. E.; Buchanan, P. C.; Franchi, I. A.

    2015-01-01

    Dark inclusions (DIs) are lithic fragments that form a volumetrically small, but important, component in carbonaceous chondrites. Carbonaceous clasts similar to DIs are also found in some ordinary chondrites and HEDs. DIs are of particular interest because they provide a record of nebular and planetary processes distinct from that of their host meteorite. DIs may be representative of the material that delivered water and other volatiles to early Earth as a late veneer. Here we focus on the oxygen isotopic composition of DIs in a variety of settings with the aim of understanding their formational history and relationship to the enclosing host meteorite.

  11. The influence of pH on the oxygen isotope equilibrium fractionation between sulfite and water

    NASA Astrophysics Data System (ADS)

    Müller, Inigo; Brunner, Benjamin; Ferdelman, Timothy

    2010-05-01

    Currently, the value for the oxygen isotope equilibrium fractionation between water and sulfite in solution is poorly constrained. Sulfite is an important intermediate in the oxidative/reductive sulfur cycle and oxygen isotope exchange between sulfite and water is expected to leave an imprint on the isotope composition of sulfate affected by sulfur cycling. One reason for the lack of accurate information about isotope fractionation between sulfite and water are technical difficulties in extraction of sulfite from solution for oxygen isotope analysis. The pH dependent presence of multiple S(IV) species in solution, i.e. sulfur dioxide (SO2), bisulfite (HSO3-), pyrosulfite (S2O52-) and sulfite (SO32-) complicates data interpretation. For example, the oxygen isotope equilibrium fractionation between water and SO32- may be different than that between water and any of the other sulfite species in solution. We exposed sodium sulfite (Na2SO3) solutions to different pH conditions and monitored oxygen isotope exchange between sulfite and water, until isotope equilibrium was reached. The equilibrium value is determined by using two isotopically different sodium sulfite starting materials, one with a starting value lighter than the equilibrium value and one with a starting composition heavier than the equilibrium value. In this manner oxygen isotope equilibrium is approached from two directions. Sulfite from solution was precipitated as BaSO3 with a set of Ba(OH)2 solutions containing different oxygen isotope compositions. This procedure allows us to disentangle the oxygen isotope contribution from water incorporated during the precipitation from the oxygen isotope composition of sulfite in solution. We present the first results from this experimental approach and discuss the applicability of determining isotope equilibrium fractionations between water and distinct S(IV) species.

  12. Oxygen isotope perspective on Precambrian crustal growth and maturation

    SciTech Connect

    Peck, W.H.; King, E.M.; Valley, J.W.

    2000-04-01

    In this study the authors contrast insights on Precambrian crustal growth and maturation from radiogenic and oxygen isotope systematics in the Superior (3.0--2.7 Ga) and Grenville (1.3--1.0 Ga) Provinces of the Canadian shield. Oxygen isotope ratios in zircon provide the best evidence of supracrustal input into ancient orogens. Archean Superior Province zircons have relatively low {delta}{sup 18}O values and a limited range (5.7{per_thousand} {+-} 0.6{per_thousand}), while Proterozoic Grenville Province zircons have elevated {delta}{sup 18}O values and a wider range (8.2{per_thousand} {+-} 1.7{per_thousand}). These data reflect fundamental differences in crustal evolution and maturation between the Superior and the Grenville Provinces. In the Grenville Province, radiogenically juvenile supracrustal material with high {delta}{sup 18}O values was buried (or subducted) to the base of the crust within 150 m.y. of initial crust production, causing high magmatic {delta}{sup 18}O values ({delta}{sup 18}O [zircon] {ge} 8{per_thousand}) in anorthosite suite and subsequent plutons. Information about large volumes and rapid recycling of Grenville crust is not accessible from radiogenic isotope data alone. The Grenville data contrast with the restricted {delta}{sup 18}O values of Superior Province magmatism, where subtle ({approximately}1{per_thousand}) elevation in {delta}{sup 18}O occurs only in volumetrically minor, late to postorogenic (sanukitoid) plutons. Differences in sediment {delta}{sup 18}O values between the Superior and Grenville Provinces are predominantly a function of the {delta}{sup 18}O of source materials, rather than differences in chemical maturity or erosion styles. This study shows that zircon is a robust reference mineral to compare igneous processes in rocks that have undergone radically different histories.

  13. A non-mass-dependent oxygen isotope effect in the production of ozone from molecular oxygen - The role of molecular symmetry in isotope chemistry

    NASA Technical Reports Server (NTRS)

    Heidenreich, J. E., III; Thiemens, M. H.

    1986-01-01

    It was previously reported that the reaction products from the synthesis of ozone in an electric discharge through molecular oxygen display a nonmass-dependent (NoMaDic) oxygen isotope effect. In this paper, a detailed characterization of the isotope effect, including the effect of molecular oxygen pressure, and the presence of a chemically inert third body (helium), is reported. The NoMaDic effect is due to an isotopically selective stabilization of the O3 formation reaction intermediate, possibly resulting from the ability of the different isotopomers to exhibit different molecular symmetries.

  14. Palaeoclimate signal recorded by stable isotopes in cave ice: a modeling approach

    NASA Astrophysics Data System (ADS)

    Perşoiu, A.; Bojar, A.-V.

    2012-04-01

    Ice accumulations in caves preserve a large variety of geochemical information as candidate proxies for both past climate and environmental changes, one of the most significant being the stable isotopic composition of the ice. A series of recent studies have targeted oxygen and hydrogen stable isotopes in cave ice as proxies for past air temperatures, but the results are far from being as straightforward as they are in high latitude and altitude glaciers and ice caps. The main problems emerging from these studies are related to the mechanisms of cave ice formation (i.e., freezing of water) and post-formation processes (melting and refreezing), which both alter the original isotopic signal in water. Different methods have been put forward to solve these issues and a fair understanding of the present-day link between stable isotopes in precipitation and cave ice exists now. However, the main issues still lays unsolved: 1) is it possible to extend this link to older ice and thus reconstruct past changes in air temperature?; 2) to what extent are ice dynamics processes modifying the original climatic signal and 3) what is the best method to be used in extracting a climatic signal from stable isotopes in cave ice? To respond to these questions, we have conducted a modeling experiment, in which a theoretical cave ice stable isotope record was constructed using present-day observations on stable isotope behavior in cave ice and ice dynamics, and different methods (presently used for both polar and cave glaciers), were used to reconstruct the original, known, isotopic values. Our results show that it is possible to remove the effects of ice melting and refreezing on stable isotope composition of cave ice, and thus reconstruct the original isotopic signal, and further the climatic one.

  15. Oxygen isotope constraints on the origin of island arc granitoids

    NASA Astrophysics Data System (ADS)

    Perez, R. J.; Cavosie, A. J.; Valley, J. W.

    2007-12-01

    Granitic intrusions in island arcs constitute additions of juvenile crust from oceanic environs that ultimately get accreted to continents. The genesis of island arc granitoids is thus important to studies of the growth of oceanic and continental crust. Puerto Rico (USA) is a composite island arc terrane that preserves a record of plutonism from 85 Ma to 38 Ma (Cavosie et al., 2007 AGU). Mid-crustal granitoid plutons are exposed (~1 to 500 km2), but their origins are unknown, as no suspected parental magmas associated with the plutons (e.g., gabbro) are exposed. This study uses petrography, WR major elements, and oxygen isotopes of WR and zircon from granitoids and xenoliths to place better constraints on the origin of granitoid in the Greater Antilles island arc. WR δ18O analyses were made with laser fluorination by IRMS at the Univ. of Wisconsin (uncertainties = 0.10 to 0.20‰, 2sd). The main plutons (Caguas, Rio Blanco, San Lorenzo, Utuado, Vieques) yield primitive δ18O(WR) values, ranging from 6.24 to 7.72‰ over a range of wt.% SiO2= 58.03 to 66.54. Smaller stocks (<20 km2) yield higher δ18O(WR) values, ranging from 7.47 to 10.27‰. Qualitative petrographic analysis reveals that granitoids with δ18O(WR) >~7.5‰ are partially to pervasively altered. Zircon preserves magmatic δ18O and is used here to quantitatively evaluate the measured δ18O(WR) values. If δ18O(Zrc) and wt.% SiO2 are known, a comparison of measured vs. predicted δ18O(WR) can be made (Valley et al., 2005, CMP). The measured δ18O(WR) values record variable amounts of alteration, ranging from virtually undetectable, to WR δ18O elevations of ~4‰, indicative of low-T subsolidus alteration. The Δ18O (WR-Zrc) values using calculated δ18O(WR) yield the following fractionations: -1.57 to 1.00‰ for granodiorites (wt.% SiO2=66 to 57); -0.85‰ for diorite (wt.% SiO2=55); and -0.56‰ for the only gabbro analyzed (wt.% SiO2=50). Mafic xenoliths (53-57 wt.% SiO2) from 4 granitoids yield

  16. The triple isotopic composition of oxygen in leaf water

    NASA Astrophysics Data System (ADS)

    Landais, A.; Barkan, E.; Yakir, D.; Luz, B.

    2006-08-01

    The isotopic composition of atmospheric O 2 depends on the rates of oxygen cycling in photosynthesis, respiration, photochemical reactions in the stratosphere and on δ17O and δ18O of ocean and leaf water. While most of the factors affecting δ17O and δ18O of air O 2 have been studied extensively in recent years, δ17O of leaf water—the substrate for all terrestrial photosynthesis—remained unknown. In order to understand the isotopic composition of atmospheric O 2 at present and in fossil air in ice cores, we studied leaf water in field experiments in Israel and in a European survey. We measured the difference in δ17O and δ18O between stem and leaf water, which is the result of isotope enrichment during transpiration. We calculated the slopes of the lines linking the isotopic compositions of stem and leaf water. The obtained slopes in ln( δ17O + 1) vs. ln( δ18O + 1) plots are characterized by very high precision (˜0.001) despite of relatively large differences between duplicates in both δ17O and δ18O (0.02-0.05‰). This is so because the errors in δ18O and δ17O are mass-dependent. The slope of the leaf transpiration process varied between 0.5111 ± 0.0013 and 0.5204 ± 0.0005, which is considerably smaller than the slope linking liquid water and vapor at equilibrium (0.529). We further found that the slope of the transpiration process decreases with atmospheric relative humidity ( h) as 0.522-0.008 × h, for h in the range 0.3-1. This slope is neither influenced by the plant species, nor by the environmental conditions where plants grow nor does it show strong variations along long leaves.

  17. Oxygen and Nitrogen Isotopes in the Sun and Solar Nebula

    NASA Astrophysics Data System (ADS)

    Lyons, J. R.

    2014-12-01

    The record of light stable isotope signatures in early solar system materials provides key constraints on the formation environment, mixing processes, and loss processes that influenced the solar nebula. Considering first the Sun, the NASA Genesis mission showed that the solar wind has a 17O depletion that is slightly more negative than the isotopically lightest CAIs (McKeegan et al. 2011), but still only yields an inferred photospheric (and bulk) solar O isotope composition. Recent reanalysis of astronomical measurement of O isotopes from infrared CO lines (Ayres et al. 2013) argues for a similarity in d18O for the directly observed photosphere and the inferred photosphere from Genesis, in contrast to the wildly divergent astronomical values previously reported. The accuracy of the Ayres et al. results are limited by the accuracy of the IR oscillator strength models; I will report on the impact of new oscillator strength models for CO. Turning to the CAIs, the Genesis O isotope results are consistent with CO self-shielding as the mechanism for producing the CAI mixing line from a mixture of photo-produced H2O (17O-enriched) and solar-like initial material (Clayton 2002; Lyons and Young 2005). Two other mechanisms have been proposed: 17O enrichment from 1) high temperature SiO reactions with OH (Chakraborty et al. 2013), and 2) transfer from low temperature O3 formation on dust. I will critique both of these suggested mechanisms. Finally, N isotope ratios, which span a range in d15N values from ~-400 permil for the Sun (Marty et al. 2011) and solar nebula, to +1000s permil for hotspots in CB chondrites, are influenced by low temperature ion-molecule reactions, and potentially by photoprocesses. Heays et al. (2014) have shown that N2 photolysis can produce very large 15N enrichments in product HCN in a static protoplanetary disk. I will present similar calculations for a turbulently mixed disk. Implications for cometary isotopic composition will be presented.

  18. Crustal evolution reflected in seawater Sr and Nd isotope records

    NASA Astrophysics Data System (ADS)

    Peucker-Ehrenbrink, B.

    2013-12-01

    Radiogenic isotope ratios record time-integrated parent-daughter ratios, and are thus sensitive to chemical composition and time. The oceans recieve the integrated runoff from the continental surface and preserve these signals in marine sedimentary records. Radiogenic isotope records of seawater and marine sediments have been reconstructed over the past five decades for many of the radiogenic isotope systems. For some systems (Sr) excellent records do exist that integrate seawater signals for the entire ocean. In contrast, globally averaged records of radiogenic isotopes with short marine residence times (Nd, Pb) are much more difficult to establish. Here, I attempt to link long-term (Phanerozoic) records of marine radiogenic isotope systems to records of the evolution of the continental surface that interacts with the hydrologic cycle. For the present we can show that the dissolved and particulate loads from the continents integrate different portions of the continental surface (Peucker-Ehrenbrink et al., 2010, G-cubed 11, doi: 10.1029/2009GC002869). For instance, the areas generating the dissolved load are characterized by significantly older bedrock (~400 Myr) than those generating the particulate load (~320 Myr). The fact that both are younger than the mean bedrock age of the non-glaciated, exorheic portion of the continental surface (~450 Myr) reflects the disproportionate role active margins, high-standing ocean island, and weathering and erosion of young sedimentary strata play in exporting dissolved matter and sedimnent to the oceans. Using present-day systematics as a guide, I argue that the first-order trough-like shape of the Phanerozoic marine Sr isotope record reflects the rejuvenation of the continental surface involved in exporting Sr to the ocean from the early Phanerozoic to the mid Jurassic that is followed by an 'aging' that continues into the Quaternary. This long-term evolution of the continental surface is mirrored by a similar - though more

  19. Isotopic records in CM hibonites: Implications for timescales of mixing of isotope reservoirs in the solar nebula

    NASA Astrophysics Data System (ADS)

    Liu, Ming-Chang; McKeegan, Kevin D.; Goswami, Jitendra N.; Marhas, Kuljeet K.; Sahijpal, Sandeep; Ireland, Trevor R.; Davis, Andrew M.

    2009-09-01

    The magnesium isotopic compositions of 26 hibonite-bearing inclusions from the CM chondrite Murchison, as well as isotopic measurements on a subset of these samples for oxygen, titanium, and lithium-beryllium-boron are reported along with oxygen isotopic data for an additional 13 hibonites that were previously investigated for other isotope systems (magnesium, potassium, calcium, and titanium) and rare earth element concentrations. Magnesium isotopic compositions divide CM hibonites into two distinct populations which correlate perfectly with their mineralogy and morphology, as previously discovered by Ireland [Ireland T. R. (1988) Correlated morphological, chemical, and isotopic characteristics of hibonites from the Murchison carbonaceous chondrite. Geochim. Cosmochim. Acta52, 2827-2839]: Spinel-HIBonite spherules (SHIBs) bear evidence of in situ26Al decay, whereas PLAty-Crystals (PLACs) and Blue AGgregates (BAGs) either lack resolvable 26Mg-excesses or exhibit 26Mg deficits by up to ˜4‰. High precision, multiple collector SIMS analyses show that 6 of 7 SHIBs investigated fall on a single correlation line implying 26Al/ 27Al = (4.5 ± 0.2) × 10 -5 at the time of isotopic closure, consistent with the "canonical" 26Al abundance characteristic of internal isochrons in many calcium-aluminum-rich inclusions (CAIs). One SHIB sample exhibits Δ 26Mg ∗ consistent with a "supracanonical" 26Al/ 27Al ratio of (6.4 ± 0.5) × 10 -5. The PLAC hibonites contain highly anomalous titanium isotopic compositions, with δ 50Ti values ranging from -80‰ to almost +200‰, whereas SHIBs generally lack large Ti isotopic anomalies. Eight out of 11 26Al-free PLAC hibonite grains record 10B/ 11B excesses that correlate with Be/B; the inferred initial 10Be/ 9Be ratio of (5.1 ± 1.4) × 10 -4 is lower than the best-constrained 10Be/ 9Be of (8.8 ± 0.6) × 10 -4 in a CV CAI. The data demonstrate that 10Be cannot be used as a relative chronometer for these objects and that most of the

  20. Oxygen Isotope Anomalies in Orgueil Corundum: Confirmation of Presolar Origin

    NASA Astrophysics Data System (ADS)

    Huss, G. R.; Hutcheon, I. D.; Fahey, A. J.; Wasserburg, G. J.

    1993-07-01

    In a study of Mg isotopes in oxide grains from an Orgueil SiC-spinel-rich residue, [1] reported a corundum grain with ^26Mg*/^27Al = 8.9 x 10^-4, a value ~18 times greater than the canonical 5 x 10^-5 value characteristic of refractory phases formed in the solar nebula. Comparable ratios had previously been found only in carbon-rich interstellar materials, SiC and graphite, [2] leading [1] to suggest that Orgueil corundum B is a pre-solar oxide grain. Subsequently, [3] discovered Murchison corundum 83-5 with a sirnilar ^26Mg*/^27Al of 8.7 x 10^-4; the very unusual oxygen isotope composition (delta^17O = 1072 +- 59 per mil, delta^18O = -244 per mil) led [3] to conclude 83-5 is an interstellar oxide grain. The Panurge ion probe was used to determine ^170/^160 and ^180/^160 ratios in 27 Orgueil oxide grains--16 corundum, 2 hibonite, and 9 spinel--and in 6 Allende spinels. Orgueil corundum B has an extreme ^17O excess (delta^17O = 1394 +- 178 per mil (2sigma(mean)) and a hint of an ^18O depletion (delta^18O = -65 +- 64 per mil) (Fig. 1). The extraordinary enrichments in ^26Mg* and ^17O identify Orgueil B as an interstellar oxide grain. Orgueil B and Murchison 83-5 have remarkably similar O- and Mg-isotope compositions. Red giant stars are enriched in ^17O with ^17O/^18O >~ 1 [4], suggesting these stars are a likely source of the interstellar corundum. Production of ^26Al during H-burning in AGB stars also appears to account for the ^26Mg* excess [5,6]. Condensation of corundum in the circumstellar envelope must occur before dredge up of processed material from the stellar interior decreases ^17O/^16O and creates a C-rich atmosphere. The oxygen isotope compositions of the remaining oxide grains fall into three groups (Fig. 1). All but six corundums and one Orgueil spinel exhibit ^16O excesses and lie along the ^16O-mixing line with compositions similar to those of corundum and spinel from Murchison LS, LU, and CFO(sub)c [7]. Data from Allende spinels cluster about a

  1. Oxygen Isotopic Composition of Seawater Sulfate in the past 5 Ma

    NASA Astrophysics Data System (ADS)

    Markovic, S.; Paytan, A.; Wortmann, U. G.

    2012-12-01

    The oxygen isotopic composition of sulfate (δ18OSO4) is distinctively different from the δ18O of ambient seawater. It is generally believed that this isotopic offset is caused by continuous redox cycling of sulfur in the benthic boundary layer, where microbially mediated sulfate reduction first reduces sulfate to sulfide, which subsequently is re-oxidized to sulfate. The reoxidation step is controlled by a variety of microbial and inorganic processes, the balance of which being a function of the respective sedimentary environments. Previously published δ18OSO4 record shows a 5 ‰ drop over the last 3 Ma. Here we complement this record with new high resolution data covering the last 5 Ma. Our data supports the notion that the marine δ18OSO4 values declined during the Quaternary, but only by about 2 ‰. While a 2 ‰ change appears small, it must be viewed relative to the long residence time of oxygen in marine sulfate (>1Ma) which implies a fairly large change in the fluxes controlling seawater sulfate oxygen isotope ratios. These fluxes include erosional input from pyrite and evaporite weathering on continents and internal recycling of sulfate. Weathering of pyrite produces sulfate with a δ18O ratio close to that of ambient water (on average ~0 ‰), whereas evaporite weathering releases sulfate with the δ18O ratio which represents the seawater sulfate value at the time of formation (~10 ‰). The O-isotope effect of S-cycling in the benthic boundary layer depends on the balance between inorganic (δ18O=~0 ‰) and microbial sulfide reoxidation pathways (δ18O~8-16 ‰). Previous models suggested that change of seawater δ18OSO4 was caused by a complete breakdown of microbial sulfur cycling in the benthic boundary layer. However, S-isotope data suggests that the last 3 million years saw an increasing flux of isotopically light S from pyrite weathering. If we account for this process, the observed δ18O signal can be explained with a 35% reduction of the

  2. Miocene benthic foraminiferal isotope records: A synthesis

    USGS Publications Warehouse

    Savin, S.M.; Douglas, R.G.; Keller, G.; Killingley, J.S.; Shaughnessy, L.; Sommer, M.A.; Vincent, E.; Woodruff, F.

    1981-01-01

    18O 16O and 13C 12C ratios of Miocene benthic foraminifera from a number of Atlantic, Pacific and Indian Ocean DSDP sites (71, 77B, 206, 208, 238, 279, 289, 296, 329, 357 and 366A) have been compiled. These provide a rather detailed history of Miocene deep water especially in the Pacific Ocean. Bottom-water temperatures rose during the early Miocene and then declined rapidly during the middle Miocene. This decline was accompanied by an increase in Antarctic glaciation. Late Miocene bottom temperatures and Antarctic ice volumes are inferred to be similar to today's, but exhibited some fluctuation. The early Miocene ocean was less thermally stratified at intermediate and abyssal depths while the late Miocene deep ocean had a thermal structure generally similar to the modern ocean. Foraminiferal carbon isotope ratios at most of the sites varied quasi-sympathetically throughout the Miocene. These variations must reflect comparable variations in the mean 13C 12C of marine HCO3-. However, the causes of such variations are not yet clear. ?? 1981.

  3. Oxygen isotopes in tree rings are a good proxy for Amazon precipitation and El Nino-Southern Oscillation variability.

    PubMed

    Brienen, Roel J W; Helle, Gerd; Pons, Thijs L; Guyot, Jean-Loup; Gloor, Manuel

    2012-10-16

    We present a unique proxy for the reconstruction of variation in precipitation over the Amazon: oxygen isotope ratios in annual rings in tropical cedar (Cedrela odorata). A century-long record from northern Bolivia shows that tree rings preserve the signal of oxygen isotopes in precipitation during the wet season, with weaker influences of temperature and vapor pressure. Tree ring δ(18)O correlates strongly with δ(18)O in precipitation from distant stations in the center and west of the basin, and with Andean ice core δ(18)O showing that the signal is coherent over large areas. The signal correlates most strongly with basin-wide precipitation and Amazon river discharge. We attribute the strength of this (negative) correlation mainly to the cumulative rainout processes of oxygen isotopes (Rayleigh distillation) in air parcels during westward transport across the basin. We further find a clear signature of the El Niño-Southern Oscillation (ENSO) in the record, with strong ENSO influences over recent decades, but weaker influence from 1925 to 1975 indicating decadal scale variation in the controls on the hydrological cycle. The record exhibits a significant increase in δ(18)O over the 20th century consistent with increases in Andean δ(18)O ice core and lake records, which we tentatively attribute to increased water vapor transport into the basin. Taking these data together, our record reveals a fresh path to diagnose and improve our understanding of variation and trends of the hydrological cycle of the world's largest river catchment.

  4. Episodic growth of the Gondwana supercontinent from hafnium and oxygen isotopes in zircon.

    PubMed

    Kemp, A I S; Hawkesworth, C J; Paterson, B A; Kinny, P D

    2006-02-01

    It is thought that continental crust existed as early as 150 million years after planetary accretion, but assessing the rates and processes of subsequent crustal growth requires linking the apparently contradictory information from the igneous and sedimentary rock records. For example, the striking global peaks in juvenile igneous activity 2.7, 1.9 and 1.2 Gyr ago imply rapid crustal generation in response to the emplacement of mantle 'super-plumes', rather than by the continuous process of subduction. Yet uncertainties persist over whether these age peaks are artefacts of selective preservation, and over how to reconcile episodic crust formation with the smooth crustal evolution curves inferred from neodymium isotope variations of sedimentary rocks. Detrital zircons encapsulate a more representative record of igneous events than the exposed geology and their hafnium isotope ratios reflect the time since the source of the parental magmas separated from the mantle. These 'model' ages are only meaningful if the host magma lacked a mixed or sedimentary source component, but the latter can be diagnosed by oxygen isotopes, which are strongly fractionated by rock-hydrosphere interactions. Here we report the first study that integrates hafnium and oxygen isotopes, all measured in situ on the same, precisely dated detrital zircon grains. The data reveal that crust generation in part of Gondwana was limited to major pulses at 1.9 and 3.3 Gyr ago, and that the zircons crystallized during repeated reworking of crust formed at these times. The implication is that the mechanisms of crust formation differed from those of crustal differentiation in ancient orogenic belts. PMID:16452978

  5. Episodic growth of the Gondwana supercontinent from hafnium and oxygen isotopes in zircon.

    PubMed

    Kemp, A I S; Hawkesworth, C J; Paterson, B A; Kinny, P D

    2006-02-01

    It is thought that continental crust existed as early as 150 million years after planetary accretion, but assessing the rates and processes of subsequent crustal growth requires linking the apparently contradictory information from the igneous and sedimentary rock records. For example, the striking global peaks in juvenile igneous activity 2.7, 1.9 and 1.2 Gyr ago imply rapid crustal generation in response to the emplacement of mantle 'super-plumes', rather than by the continuous process of subduction. Yet uncertainties persist over whether these age peaks are artefacts of selective preservation, and over how to reconcile episodic crust formation with the smooth crustal evolution curves inferred from neodymium isotope variations of sedimentary rocks. Detrital zircons encapsulate a more representative record of igneous events than the exposed geology and their hafnium isotope ratios reflect the time since the source of the parental magmas separated from the mantle. These 'model' ages are only meaningful if the host magma lacked a mixed or sedimentary source component, but the latter can be diagnosed by oxygen isotopes, which are strongly fractionated by rock-hydrosphere interactions. Here we report the first study that integrates hafnium and oxygen isotopes, all measured in situ on the same, precisely dated detrital zircon grains. The data reveal that crust generation in part of Gondwana was limited to major pulses at 1.9 and 3.3 Gyr ago, and that the zircons crystallized during repeated reworking of crust formed at these times. The implication is that the mechanisms of crust formation differed from those of crustal differentiation in ancient orogenic belts.

  6. Oxygen isotope activities and concentrations in aqueous salt solutions at elevated temperatures: Consequences for isotope geochemistry

    USGS Publications Warehouse

    Truesdell, A.H.

    1974-01-01

    Studies of the effect of dissolved salts on the oxygen isotope activity ratio of water have been extended to 275??C. Dehydrated salts were added to water of known isotope composition and the solutions were equilibrated with CO2 which was sampled for analysis. For comparison similar studies were made using pure water. Results on water nearly coincide with earlier calculations. Salt effects diminish with increasing temperature only for solutions of MgCl2 and LiCl. Other salt solutions show complex behavior due to the temperature-dependent formation of ion pairs of changing character. Equilibrium fractionations (103 ln ??) between 1 molal solutions and pure water at 25, 100, and 275??C are: NaCl 0.0, -1.5, +1.0; KCl 0.0, -1.0, +2.0; LiCl -1.0, -0.6, -0.5; CaCl2 -0.4, -1.8, +0.8; MgCl2 -1.1, -0.7, -0.3; MgSO4 -1.1, +0.1, -; NaF (0.8 m) 0.0, -1.5, -0.3; and NH4Cl (0.55 m) 0.0, -1.2, -1.3. These effects are significant in the isotope study of hot saline fluids responsible for ore deposition and of fluids found in certain geothermal systems. Minor modification of published isotope geothermometers may be required. ?? 1974.

  7. Evidence for rapid climate change in North America during the latest Paleocene thermal maximum: oxygen isotope compositions of biogenic phosphate from the Bighorn Basin (Wyoming)

    NASA Astrophysics Data System (ADS)

    Fricke, Henry C.; Clyde, William C.; O'Neil, James R.; Gingerich, Philip D.

    1998-07-01

    Oxygen isotope records of Cenozoic sea water temperatures indicate that a rapid warming event known as the Latest Paleocene Thermal Maximum (LPTM) occurred during the otherwise gradual increase in world temperatures during the Late Paleocene and Early Eocene. Oxygen isotope analysis of the carbonate and phosphate components of hydroxyapatite found in mammalian tooth enamel and body scales of river-dwelling fish from the Bighorn Basin in Wyoming were made to investigate corresponding changes in the terrestrial climate. A comparison of carbonate and phosphate isotope data from modern and fossil material indicates that some diagenetic alteration of the fossil material has occurred, although systematically larger intra-tooth ranges in the oxygen isotope composition of carbonate indicate that it is more likely to have been affected than phosphate. Carbonate and phosphate from the ecologically diverse mammals and fishes both record a shift to higher oxygen isotope ratios at the same time and of the same duration as the LPTM. These shifts reflect a change in the isotopic composition of regional precipitation, which in turn provides the first evidence for continental climate change during the LPTM. Assuming the present-day relation between the oxygen isotope composition of precipitation and temperature applies to conditions in the past, and that animal physiology and behavior is relatively invariant over time, the isotopic shift is equivalent to an increase of surface temperature in western North America of several degrees. This result is consistent with the magnitude of high-latitude ocean warming, and provides a basis for relating marine and terrestrial oxygen isotope records to records of terrestrial biotic change.

  8. Oxygen isotope values of precipitation and the thermal climate in Europe during the middle to late Weichselian ice age

    NASA Astrophysics Data System (ADS)

    Arppe, L.; Karhu, J. A.

    2010-05-01

    The oxygen isotope compositions of 28 mammoth tooth enamel samples from Estonia, Latvia, Lithuania, Poland and Denmark provide new quantitative records of the middle to late Weichselian climate in northern Europe. The new δ18O data was combined with records of oxygen isotope values from earlier investigations on European mammoth tooth enamel and palaeogroundwaters to study the spatial patterns and temporal variations in the oxygen isotope composition of precipitation and the thermal climate over much of Europe. The reconstructed geographical distribution of δ18O in precipitation during 52-24 ka reflects the progressive isotopic depletion of air masses moving northeast, consistent with a westerly source of moisture for the entire region, and a circulation pattern similar to that of the present-day. Regional long-term average δ18O w values were 0.6-4.1‰ lower than at present, the largest changes recorded for the currently maritime influenced southern Sweden and the Baltic region. The application of regionally varied δ/ T-slopes, estimated from palaeogroundwater data and modern correlations, yield reasonable estimates of glacial surface temperatures in Europe and imply 2-9 °C lower long-term mean annual surface temperatures during the glacial period.

  9. Vertical distribution of triple oxygen isotopic composition of dissolved oxygen in the northwestern Pacific

    NASA Astrophysics Data System (ADS)

    Abe, Osamu; Honda, Makio; Saino, Toshiro

    2013-04-01

    Oxygen-17 excess of dissolved oxygen calculated from δ18O and δ17O is not affected by oxygen consumption process but controlled only by processes of primary production and air-water gas transfer. Evaluating gross primary productivity using the 17O-excess in ocean surface water are one of the most advanced geochemical researches for last 10 years. Oxygen-17 excess below ocean mixed/photic layer has not been much investigated because it might be out of focus for estimating present primary productivity, except for the purpose to correct diapycnal mixing effect on surface water. In principle, water mass which has not been affected both by photosynthesis and gas transfer after its separation from ocean surface could preserve 17O-excess value where the water mass was at the surface. The purpose of this study is to determine the vertical distribution of 17O-excess from the surface to the bottom of northwestern Pacific to know whether 17O-excess could really preserve its "original" value after the long and dark travel. Near stations K2 and KNOT, water mass which has a density of 26.8 ?? is observed at depth between 100 and 300 m. This water mass is mainly originated from bottom water in the Okhotsk Sea and spreading widely to entire northwestern Pacific, which is called North Pacific Intermediate Water (NPIW). NPIW is found at depth of 700 m at station S1. Samplings were conducted by two R/V Mirai cruises (MR10-06, Oct-Nov 2010; MR11-02, Feb-Mar 2011). Dissolved oxygen gas was purified by the method of Sarma et al. (2003) and its isotopic composition was determined by dual-inlet isotope ratio mass spectrometer (Thermo Scientific Delta Plus). Gross primary productivities at mixed layer estimated by 17O-excess were well consistent with those by conventional light and dark bottle incubations for stations K2 and S1.

  10. Do foraminifera accurately record seawater neodymium isotope composition?

    NASA Astrophysics Data System (ADS)

    Scrivner, Adam; Skinner, Luke; Vance, Derek

    2010-05-01

    Palaeoclimate studies involving the reconstruction of past Atlantic meridional overturning circulation increasingly employ isotopes of neodymium (Nd), measured on a variety of sample media (Frank, 2002). In the open ocean, Nd isotopes are a conservative tracer of water mass mixing and are unaffected by biological and low-temperature fractionation processes (Piepgras and Wasserburg, 1987; Lacan and Jeandel, 2005). For decades, benthic foraminifera have been widely utilised in stable isotope and geochemical studies, but have only recently begun to be exploited as a widely distributed, high-resolution Nd isotope archive (Klevenz et al., 2008), potentially circumventing the difficulties associated with other methods used to recover past deep-water Nd isotopes (Klevenz et al., 2008; Rutberg et al., 2000; Tachikawa et al., 2004). Thus far, a single pilot study (Klevenz et al., 2008) has indicated that core-top sedimentary benthic foraminifera record a Nd isotope composition in agreement with the nearest available bottom seawater data, and has suggested that this archive is potentially useful on both millennial and million-year timescales. Here we present seawater and proximal core-top foraminifer Nd isotope data for samples recovered during the 2008 "RETRO" cruise of the Marion Dufresne. The foraminifer samples comprise a depth-transect spanning 3000m of the water column in the Angola Basin and permit a direct comparison between high-resolution water column and core-top foraminiferal Nd isotope data. We use these data to assess the reliability of both planktonic and benthic foraminifera as recorders of water column neodymium isotope composition. Frank, M., 2002. Radiogenic isotopes: Tracers of past ocean circulation and erosional input, Rev. Geophys., 40 (1), 1001, doi:10.1029/2000RG000094. Klevenz, V., Vance, D., Schmidt, D.N., and Mezger, K., 2008. Neodymium isotopes in benthic foraminifera: Core-top systematics and a down-core record from the Neogene south Atlantic

  11. Oxygen isotope evidence for shallow emplacement of Adirondack anorthosite

    USGS Publications Warehouse

    Valley, J.W.; O'Neil, J.R.

    1982-01-01

    Oxygen isotopic analysis of wollastonites from the Willsboro Mine, Adirondack Mountains, New York reveals a 400-ft wide zone of 18O depletion at anorthosite contacts. Values of ??18O vary more sharply with distance and are lower (to -1.3) than any yet reported for a granulite fades terrain. Exchange with circulating hot meteoric water best explains these results and implies that the anorthosite was emplaced at relatively shallow depths, <10 km, in marked contrast to the depth of granulite fades metamorphism (23 km). These 18O depletions offer the first strong evidence for shallow emplacement of anorthosite within the Grenville Province and suggest that regional metamorphism was a later and tectonically distinct event. ?? 1982 Nature Publishing Group.

  12. Oxygen isotopes and emerald trade routes since antiquity

    PubMed

    Giuliani; Chaussidon; Schubnel; Piat; Rollion-Bard; France-Lanord; Giard; de Narvaez D; Rondeau

    2000-01-28

    Oxygen isotopic compositions of historical emerald artifacts from the Gallo-Roman period to the 18th century indicate that during historical times, artisans worked emeralds originating from deposits supposedly discovered in the 20th century. In antiquity, Pakistani and Egyptian emeralds were traded by way of the Silk Route. Together with Austrian stones, they were the only source of gem-quality emeralds. Immediately after the discovery of the Colombian mines by Spaniards in the 16th century, a new trade route was established, first via Spain to Europe and India and then directly via the Philippines to India. Since then, Colombian emeralds have dominated the emerald trade, and most of the high-quality emeralds cut in the 18th century in India originated from Colombia. PMID:10649992

  13. Thermophysiology of Tyrannosaurus rex: Evidence from Oxygen Isotopes.

    PubMed

    Barrick, R E; Showers, W J

    1994-07-01

    The oxygen isotopic composition of vertebrate bone phosphate (delta(p)) is related to ingested water and to the body temperature at which the bone forms. The delta(p) is in equilibrium with the individual's body water, which is at a physiological steady state throughout the body. Therefore, intrabone temperature variation and the mean interbone temperature differences of well-preserved fossil vertebrates can be determined from the deltap variation. Values of delta(p) from a well-preserved Tyrannosaurus rex suggest that this species maintained homeothermy with less than 4 degrees C of variability in body temperature. Maintenance of homeothermy implies a relatively high metabolic rate that is similar to that of endotherms.

  14. Oxygen isotopes and emerald trade routes since antiquity

    PubMed

    Giuliani; Chaussidon; Schubnel; Piat; Rollion-Bard; France-Lanord; Giard; de Narvaez D; Rondeau

    2000-01-28

    Oxygen isotopic compositions of historical emerald artifacts from the Gallo-Roman period to the 18th century indicate that during historical times, artisans worked emeralds originating from deposits supposedly discovered in the 20th century. In antiquity, Pakistani and Egyptian emeralds were traded by way of the Silk Route. Together with Austrian stones, they were the only source of gem-quality emeralds. Immediately after the discovery of the Colombian mines by Spaniards in the 16th century, a new trade route was established, first via Spain to Europe and India and then directly via the Philippines to India. Since then, Colombian emeralds have dominated the emerald trade, and most of the high-quality emeralds cut in the 18th century in India originated from Colombia.

  15. Oxygen Isotopes and Emerald Trade Routes Since Antiquity

    NASA Astrophysics Data System (ADS)

    Giuliani, Gaston; Chaussidon, Marc; Schubnel, Henri-Jean; Piat, Daniel H.; Rollion-Bard, Claire; France-Lanord, Christian; Giard, Didier; de Narvaez, Daniel; Rondeau, Benjamin

    2000-01-01

    Oxygen isotopic compositions of historical emerald artifacts from the Gallo-Roman period to the 18th century indicate that during historical times, artisans worked emeralds originating from deposits supposedly discovered in the 20th century. In antiquity, Pakistani and Egyptian emeralds were traded by way of the Silk Route. Together with Austrian stones, they were the only source of gem-quality emeralds. Immediately after the discovery of the Colombian mines by Spaniards in the 16th century, a new trade route was established, first via Spain to Europe and India and then directly via the Philippines to India. Since then, Colombian emeralds have dominated the emerald trade, and most of the high-quality emeralds cut in the 18th century in India originated from Colombia.

  16. Oxygen and hydrogen isotope evidence for a temperate climate 3.42 billion years ago.

    PubMed

    Hren, M T; Tice, M M; Chamberlain, C P

    2009-11-12

    Stable oxygen isotope ratios (delta(18)O) of Precambrian cherts have been used to establish much of our understanding of the early climate history of Earth and suggest that ocean temperatures during the Archaean era ( approximately 3.5 billion years ago) were between 55 degrees C and 85 degrees C (ref. 2). But, because of uncertainty in the delta(18)O of the primitive ocean, there is considerable debate regarding this conclusion. Examination of modern and ancient cherts indicates that another approach, using a combined analysis of delta(18)O and hydrogen isotopes (deltaD) rather than delta(18)O alone, can provide a firmer constraint on formational temperatures without independent knowledge of the isotopic composition of ambient waters. Here we show that delta(18)O and deltaD sampled from 3.42-billion-year-old Buck Reef Chert rocks in South Africa are consistent with formation from waters at varied low temperatures. The most (18)O-enriched Buck Reef Chert rocks record the lowest diagenetic temperatures and were formed in equilibrium with waters below approximately 40 degrees C. Geochemical and sedimentary evidence suggests that the Buck Reef Chert was formed in shallow to deep marine conditions, so our results indicate that the Palaeoarchaean ocean was isotopically depleted relative to the modern ocean and far cooler (

  17. Oxygen and hydrogen isotope evidence for a temperate climate 3.42 billion years ago.

    PubMed

    Hren, M T; Tice, M M; Chamberlain, C P

    2009-11-12

    Stable oxygen isotope ratios (delta(18)O) of Precambrian cherts have been used to establish much of our understanding of the early climate history of Earth and suggest that ocean temperatures during the Archaean era ( approximately 3.5 billion years ago) were between 55 degrees C and 85 degrees C (ref. 2). But, because of uncertainty in the delta(18)O of the primitive ocean, there is considerable debate regarding this conclusion. Examination of modern and ancient cherts indicates that another approach, using a combined analysis of delta(18)O and hydrogen isotopes (deltaD) rather than delta(18)O alone, can provide a firmer constraint on formational temperatures without independent knowledge of the isotopic composition of ambient waters. Here we show that delta(18)O and deltaD sampled from 3.42-billion-year-old Buck Reef Chert rocks in South Africa are consistent with formation from waters at varied low temperatures. The most (18)O-enriched Buck Reef Chert rocks record the lowest diagenetic temperatures and were formed in equilibrium with waters below approximately 40 degrees C. Geochemical and sedimentary evidence suggests that the Buck Reef Chert was formed in shallow to deep marine conditions, so our results indicate that the Palaeoarchaean ocean was isotopically depleted relative to the modern ocean and far cooler (

  18. Oxygen-18 Carbon Dioxide Isotope Ratio in Mars Atmosphere

    NASA Astrophysics Data System (ADS)

    Kostiuk, T.; Livengood, T. A.; Hewagama, T.; Smith, R.; Fast, K. E.; Annen, J.; Sonnabend, G.; Sornig, M.

    2012-09-01

    The determination of isotopic ratios on Mars is important to the study of atmospheric evolution [1]. The relative abundance of isotopes of CO2 provides insight into the loss of Mars' primordial atmosphere. Isotopic ratios also provide markers in the study of geochemistry of Mars meteorites and future returned samples formed in equilibrium with ambient atmosphere, and are probes of biogenic and abiotic chemistry, which differ in isotope fractionation. Due to its lesser gravity and relatively thin residual atmosphere, Mars' atmosphere should be enriched in heavy isotopes [1]. However Viking [2] results indicated an Earth-like singly substituted oxygen-18 CO2 isotopic ratio, 18OCO/OCO, with δ18O = 0±50‰ relative to Vienna Standard Mean Ocean Water (VSMOW). By comparison, isotopic ratios in Earth atmospheric CO2 are not uniquely defined due to seasonal and biotic variability, but have a range 0-41‰ relative to VSMOW [3, 4]. Phoenix lander TEGA [3] measurements found a modest enrichment of δ18O = 31.0±5.7‰. Only the Viking and Phoenix landers have carried a mass spectrometer to Mars, so far, until the arrival of Mars Science Laboratory in August 2012. Using ground-based spectroscopic techniques Krasnopolsky et al. [5] also found modest enrichment δ18O = 18±18‰. We present results from fully resolved spectroscopic measurements near 10.6 μm of both the normal and singly substituted oxygen- 18 CO2 lines, taken with the Goddard Space Flight Center Heterodyne Instrument for Planetary Winds And Composition (HIPWAC) at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Measurements with spectral resolving power λ/Δλ=107 were obtained in October 2007 with an instantaneous field-of-view on the planet of ~1 arcsec, at the locations shown in Fig. 1 as open squares. The solid and broken line tracks show Mars SPICAM measurements of ozone corresponding to ozone measurements also obtained with HIPWAC and shown as hatched and solid regions [6]. Figure 1

  19. SIMS Oxygen Isotope Study of Chondrules in the Least Metamorphosed CV3 Chondrite Kaba

    NASA Astrophysics Data System (ADS)

    Hertwig, A.; Defouilloy, C.; Kita, N. T.

    2016-08-01

    High-precision SIMS oxygen three isotope analyses of chondrules in Kaba CV3 show that most chondrules are internally homogeneous in oxygen isotopes and dominated by high Mg# (≥98) and Δ17O from –6‰ to –4‰.

  20. Constraints on Phanerozoic paleotemperature and seawater oxygen isotope evolution from the carbonate clumped isotope compositions of Late Paleozoic marine fossils (Invited)

    NASA Astrophysics Data System (ADS)

    Henkes, G. A.; Passey, B. H.; Grossman, E. L.; Pérez-Huerta, A.; Shenton, B.; Yancey, T. E.

    2013-12-01

    of burial. Consideration of the thermal history of samples is essential for identifying the possibility of clumped isotope alteration via C-O bond reordering. Our experimental results further suggest that even nascent reordering (<5-10%) is enough to measurably bias reconstructed paleotemperatures (and calculated seawater oxygen isotope compositions) to higher values. We also investigate the use of electron backscatter diffraction (EBSD), which resolves crystallographic orientation at high spatial resolution, as an alternative method for identifying sub-microstructural diagenesis in calcite. Preliminary results of EBSD on the experimental and natural Paleozoic brachiopod shells will be presented and discussed with respect to their clumped isotope compositions and the Phanerozoic record.

  1. Oxygen isotopic composition of opaline phytoliths: Potential for terrestrial climatic reconstruction

    SciTech Connect

    Shahack-Gross, R.; Weiner, S.; Shemesh, A.; Yakir, D.

    1996-10-01

    Opaline mineralized bodies are produced by many terrestrial plants and accumulate in certain soils and archaeological sites. Analyses of the oxygen isotopic compositions of these so-called phytoliths from stems and leaves of wheat plants grown in a greenhouse showed a linear relationship with stem and leaf water isotopic compositions and hence, indirectly, rain water isotopic composition. Analyses of wheat plants grown in fields showed that stem phytoliths isotopic composition directly reflects the seasonal air temperature change, whereas leaf phytoliths isotopic composition reflects both temperature and relative humidity. Temperature and the oxygen isotopic composition of stem phytoliths were related by an equation similar to that proposed for marine opal. Oxygen isotopic compositions of fossil phytoliths, and in particular those from stems, could be valuable for reconstructing past terrestrial climate change.

  2. Oxygen isotope heterogeneity in chondrules from the Mokoia CV3 carbonaceous chondrite

    NASA Astrophysics Data System (ADS)

    Jones, Rhian H.; Leshin, Laurie A.; Guan, Yunbin; Sharp, Zachary D.; Durakiewicz, Tomasz; Schilk, Alan J.

    2004-08-01

    We report a study of the oxygen isotope ratios of chondrules and their constituent mineral grains from the Mokoia, oxidized CV3 chondrite. Bulk oxygen isotope ratios of 23 individual chondrules were determined by laser ablation fluorination, and oxygen isotope ratios of individual grains, mostly olivine, were obtained in situ on polished mounts using secondary ion mass spectrometry (SIMS). Our results can be compared with data obtained previously for the oxidized CV3 chondrite, Allende. Bulk oxygen isotope ratios of Mokoia chondrules form an array on an oxygen three-isotope plot that is subparallel to, and slightly displaced from, the CCAM (carbonaceous chondrite anhydrous minerals) line. The best-fit line for all CV3 chondrite chondrules has a slope of 0.99, and is displaced significantly (by δ 17O ˜ -2.5‰) from the Young and Russell slope-one line for unaltered calcium-aluminum-rich inclusion (CAI) minerals. Oxygen isotope ratios of many bulk CAIs also lie on the CV-chondrule line, which is the most relevant oxygen isotope array for most CV chondrite components. Bulk oxygen isotope ratios of most chondrules in Mokoia have δ 18O values around 0‰, and olivine grains in these chondrules have similar oxygen isotope ratios to their bulk values. In general, it appears that chondrule mesostases have higher δ 18O values than olivines in the same chondrules. Our bulk chondrule data spread to lower δ 18O values than any ferromagnesian chondrules that have been measured previously. Two chondrules with the lowest bulk δ 18O values (-7.5‰ and -11.7‰) contain olivine grains that display an extremely wide range of oxygen isotope ratios, down to δ 17O, δ 18O around -50‰ in one chondrule. In these chondrules, there are no apparent relict grains, and essentially no relationships between olivine compositions, which are homogeneous, and oxygen isotopic compositions of individual grains. Heterogeneity of oxygen isotope ratios within these chondrules may be the

  3. Climatic influences on the oxygen isotopic composition of biogenic silica in prairie grass

    NASA Astrophysics Data System (ADS)

    Webb, Elizabeth A.; Longstaffe, Fred J.

    2002-06-01

    Samples of Calamovilfa longifolia were collected from across the North American prairies to investigate the relationship between the oxygen-isotope composition of biogenic silica (phytoliths) deposited in this grass and relative humidity, temperature, and the oxygen-18 enrichment of soil water relative to local precipitation. The δ 18O values of silica in nontranspiring tissues were controlled by soil-water composition and temperature, whereas the oxygen-18 content of silica formed in leaf and inflorescence tissues was enriched further by transpiration. Accurate calculation of growing temperature was possible only when the oxygen-isotope compositions of both stem silica and soil water were known. However, the oxygen-isotope values of stem phytoliths can be used to calculate the variation in the isotopic composition of soil water across a North American temperature gradient. As plant organic matter decays and phytoliths are transferred to the soil, the temperature and soil-water signals carried by the oxygen-isotope composition of silica from nontranspiring tissues can be masked by the oxygen-18 enrichment of phytoliths from transpiring tissues. However, the overall oxygen-isotope composition of a soil-phytolith assemblage can be related to temperature using an empirical relationship based on temperature and the difference between soil-phytolith and estimated soil-water oxygen-isotope compositions.

  4. Oxygen-18 Carbon Dioxide Isotope Ratio in Mars Atmosphere

    NASA Astrophysics Data System (ADS)

    Kostiuk, T.; Livengood, T. A.; Hewagama, T.; Smith, R.; Fast, K. E.; Annen, J.; Sonnabend, G.; Sornig, M.

    2012-09-01

    The determination of isotopic ratios on Mars is important to the study of atmospheric evolution [1]. The relative abundance of isotopes of CO2 provides insight into the loss of Mars' primordial atmosphere. Isotopic ratios also provide markers in the study of geochemistry of Mars meteorites and future returned samples formed in equilibrium with ambient atmosphere, and are probes of biogenic and abiotic chemistry, which differ in isotope fractionation. Due to its lesser gravity and relatively thin residual atmosphere, Mars' atmosphere should be enriched in heavy isotopes [1]. However Viking [2] results indicated an Earth-like singly substituted oxygen-18 CO2 isotopic ratio, 18OCO/OCO, with δ18O = 0±50‰ relative to Vienna Standard Mean Ocean Water (VSMOW). By comparison, isotopic ratios in Earth atmospheric CO2 are not uniquely defined due to seasonal and biotic variability, but have a range 0-41‰ relative to VSMOW [3, 4]. Phoenix lander TEGA [3] measurements found a modest enrichment of δ18O = 31.0±5.7‰. Only the Viking and Phoenix landers have carried a mass spectrometer to Mars, so far, until the arrival of Mars Science Laboratory in August 2012. Using ground-based spectroscopic techniques Krasnopolsky et al. [5] also found modest enrichment δ18O = 18±18‰. We present results from fully resolved spectroscopic measurements near 10.6 μm of both the normal and singly substituted oxygen- 18 CO2 lines, taken with the Goddard Space Flight Center Heterodyne Instrument for Planetary Winds And Composition (HIPWAC) at the NASA Infrared Telescope Facility on Mauna Kea, Hawaii. Measurements with spectral resolving power λ/Δλ=107 were obtained in October 2007 with an instantaneous field-of-view on the planet of ~1 arcsec, at the locations shown in Fig. 1 as open squares. The solid and broken line tracks show Mars SPICAM measurements of ozone corresponding to ozone measurements also obtained with HIPWAC and shown as hatched and solid regions [6]. Figure 1

  5. Delineating the effect of El-Nino Southern Oscillations using oxygen and sulfur isotope anomalies of sulfate aerosols

    NASA Astrophysics Data System (ADS)

    Shaheen, R.; Abaunza Quintero, M. M.; Jackson, T.; McCabe, J.; Savarino, J. P.; Thiemens, M. H.

    2013-12-01

    Sulfate aerosols, unlike greenhouse gases, contribute to global cooling by acting as cloud condensation nuclei in the troposphere and by directly reflecting solar radiation in the stratosphere. To understand the long-term effect of natural and anthropogenic sulfate aerosol on the climate cycle, it is critical to obtain a clear picture of the factors controlling the transport and transformation of sulfate aerosols. We have employed both oxygen triple isotopes and sulfur quadruple isotopes on sulfates from Antarctic ice samples to define the oxidation history, long range transport dynamics, and sources of sulfate aerosols over time. The measurements are used to deconvolve the impact of natural and anthropogenic aerosols on the stratospheric sulfate aerosol composition. Sulfate aerosols were extracted from a snow pit at the South Pole (1979-2002) with a high resolution temporal (6 month) record of the winter and summer seasons covering two largest volcanic events, Pinatubo and El-chichon and three largest ENSO events of the century. All three oxygen and four sulfur isotopes were measured on the extracted sulfate (Shaheen et al., 2013). The high temperature pyrolysis (1000oC) of silver sulfate yielded O2 and SO2. The oxygen triple isotopic composition of the O2 gas was used to determine the oxidation history of sulfate aerosol and SO2 gas obtained during this reaction was utilized to measure sulfur quadruple isotopes following appropriate reaction chemistry (Farquhar et al., 2001). The data revealed that oxygen isotope anomalies in Antarctic aerosols (Δ17O = 0.8-3.7‰) from 1990 to 2001 are strongly linked to the variation in ozone levels in the upper stratosphere/lower stratosphere. The variations in ozone levels are reflective of the intensity of the ENSO events and changes in relative humidity in the atmosphere during this time period. Sulfate concentrations and sulfur quadruple isotopic composition and associated anomalies were used to elucidate the sources of

  6. Oxygen isotope systematics in magmatic and subsolidus epidote

    NASA Astrophysics Data System (ADS)

    Morrison, J.; Anderson, J. L.

    2003-04-01

    Magmatic epidote in broadly granitic plutonic rocks can be used to quantify parameters such as depth of crystallization and rates of pluton ascent. However, the textural criteria used to distinguish magmatic epidote from epidote grown at temperatures and pressures below the solidus can be equivocal. Oxygen isotope systematics of epidote and associated minerals in 6 broadly granitic lithologies have been used to 1) evaluate available calibrations of the temperature dependent fractionations involving epidote and 2) constrain the magmatic versus subsolidus origins of epidote in a variety of well characterized lithologies. Oxygen isotope compositions of epidote (Ep), quartz (Qt), plagioclase (Pl) and biotite (Bt) were measured using a CO_2 laser microprobe system. We measured Δ18O values in 2 distinct rapidly-cooled or "quenched" lithologies: a biotite rhyolite of the Pleistocene Sutter Buttes volcano of California and Late Cretaceous rhyodacite dikes from Boulder County, Colorado. The biotite rhyolite contains phenocrysts of magmatic epidote, quartz, plagioclase and biotite and is virtually devoid of alteration minerals. Discrete but spatially related Ep, Qt, Pl and Bt from 6 samples yield an average ΔQt-Ep of 3.10±0.12 ppm (n=5), DletaPl-Ep = 1.75 ppm, and ΔEp-Bt = -0.44 ppm. In the rhyodacite, ΔQt-Ep = 3.12±0.06 ppm and ΔEp-Bt = 1.47±0.34 ppm. Both of these lithologies likely crystallized at temperatures of ˜750^oC. Temperatures inferred from these ΔQt-Ep values are ˜550^oC. In contrast, the 3 Late Cretaceous tonalitic plutons in which Zen and Hammarstrom (1984) originally documented magmatic epidote, plus the Ordovician Ellicott City granodiorite, yield distinct values: ΔQt-Ep = 4.19±0.17 ppm, ΔPl-Ep = 1.64±0.19 ppm, ΔEp-Amph = 0.54±0.25 ppm, and ΔEp-Bt = 0.85±0.24 ppm. All 4 of these lithologies underwent slow, post-crystallization cooling. Cation exchange thermometry indicates that these plutons crystallized at temperatures from ˜680^o to

  7. Determination and application of the equilibrium oxygen isotope effect between water and sulfite

    NASA Astrophysics Data System (ADS)

    Wankel, Scott D.; Bradley, Alexander S.; Eldridge, Daniel L.; Johnston, David T.

    2014-01-01

    The information encoded by the two stable isotope systems in sulfate (δ34SSO4 and δ18OSO4) has been widely applied to aid reconstructions of both modern and ancient environments. Interpretation of δ18OSO4 records has been complicated by rapid oxygen isotope equilibration between sulfoxyanions and water. Specifically, the apparent relationship that develops between δ18OSO4 and δ18Owater during microbial sulfate reduction is thought to result from rapid oxygen isotope equilibrium between intracellular water and aqueous sulfite - a reactive intermediate of the sulfate reduction network that can back-react to produce sulfate. Here, we describe the oxygen equilibrium isotope effect between water and sulfite (referring to all the sum of all S(IV)-oxyanions including sulfite and both isomers and the dimer of bisulfite). Based on experiments conducted over a range of pH (4.5-9.8) and temperature (2-95 °C), where ε = 1000 * (α - 1), we find εSO3-H2O=13.61-0.299∗pH-0.081∗T °C. Thus, at a pH (7.0) and temperature (25 °C) typifying commonly used experimental conditions for sulfate reducing bacterial cultures, sulfite is enriched in 18O by 9.5‰ (±0.8‰) relative to ambient water. We examine the implication of these results in a sulfate reduction network that has been revised to reflect our understanding of the reactions involving oxygen. By evaluating previously published data within this new architecture, our results are consistent with previous suggestions of high reversibility of the sulfate reduction biochemical network. We also demonstrate that intracellular exchange rates between SO32- and water must be on average 1-3 orders of magnitude more rapid than intracellular fluxes of sulfate reduction intermediates and that kinetic isotope effects upstream of SO32- are required to explain previous laboratory and environmental studies of δ18OSO4 resulting as a consequence of sulfate reduction.

  8. What processes control the oxygen isotopes of soil bio-available phosphate?

    NASA Astrophysics Data System (ADS)

    Gross, Avner; Angert, Alon

    2015-06-01

    The biological availability of phosphorus (P) is considered to be the limiting factor for plant growth in many natural and agricultural soils. Recent studies demonstrated that valuable information on soil P dynamics can be gained from the stable oxygen isotopes of soil phosphate (δ18OP). However, to interpret this information correctly, our understanding of the processes that controls soil phosphate δ18OP values needs to be improved since most of the current data is based primarily on laboratory studies of pure microbial cultures and enzymatic assays and may not be relevant to soils. Here we designed a series of controlled soil incubation experiments to study the actual isotopic effects induced by abiotic reactions, biological uptake, microbial turnover and organic-P mineralization on soil phosphate δ18OP values. We used this data to estimate the role of these processes in mediating soil P availability. Our study was conducted on Mediterranean soils sampled from the same site during winter, spring and summer. The soils were incubated with various mineral and organic-P compounds and their bioavailable phosphate concentrations and δ18OP values were measured. We confirmed that the role of abiotic reactions on phosphate δ18OP values was negligible and that the δ18OP values of the added phosphate were rapidly driven towards isotopic equilibrium with soil water. We suggest this process was mediated by rapid microbial phosphate turnover. Yet, we did not detect the expected isotopic enrichment effect associated with phosphate biological uptake. In another set of incubation experiments we demonstrated that mineralization of phosphate from organic compounds, such as phospho-mono-ester (PME) and phosphor-di-ester (PDE), produced an offset from isotopic equilibrium, as a result of the strong isotopic fractionation associated with the mineralization process. However, the δ18OP values recorded by the mineralized phosphate were gradually driven back towards isotopic

  9. Preliminary results of oxygen isotope ratio measurement with a particle-gamma coincidence method

    NASA Astrophysics Data System (ADS)

    Borysiuk, Maciek; Kristiansson, Per; Ros, Linus; Abdel, Nassem S.; Elfman, Mikael; Nilsson, Charlotta; Pallon, Jan

    2015-04-01

    The possibility to study variations in the oxygen isotopic ratio with photon tagged nuclear reaction analysis (pNRA) is evaluated in the current work. The experiment described in the article was performed at Lund Ion Beam Analysis Facility (LIBAF) with a 2 MeV deuteron beam. Isotopic fractionation of light elements such as carbon, oxygen and nitrogen is the basis of many analytical tools in hydrology, geology, paleobiology and paleogeology. IBA methods provide one possible tool for measurement of isotopic content. During this experimental run we focused on measurement of the oxygen isotopic ratio. The measurement of stable isotopes of oxygen has a number of applications; the particular one driving the current investigation belongs to the field of astrogeology and specifically evaluation of fossil extraterrestrial material. There are three stable isotopes of oxygen: 16O, 17O and 18O. We procured samples highly enriched with all three isotopes. Isotopes 16O and 18O were easily detected in the enriched samples, but no significant signal from 17O was detected in the same samples. The measured yield was too low to detect 18O in a sample with natural abundances of oxygen isotopes, at least in the current experimental setup, but the spectral line from the reaction with 16O was clearly visible.

  10. Kangaroo tooth enamel oxygen and carbon isotope variation on a latitudinal transect in southern Australia: implications for palaeoenvironmental reconstruction.

    PubMed

    Brookman, Tom H; Ambrose, Stanley H

    2013-02-01

    Tooth enamel apatite carbonate carbon and oxygen isotope ratios of modern kangaroos (Macropus spp.) collected on a 900-km latitudinal transect spanning a C(3)-C(4) transition zone were analysed to create a reference set for palaeoenvironmental reconstruction in southern Australia. The carbon isotope composition of enamel carbonate reflects the proportional intake of C(3) and C(4) vegetation, and its oxygen isotope composition reflects that of ingested water. Tooth enamel forms incrementally, recording dietary and environmental changes during mineralisation. Analyses show only weak correlations between climate records and latitudinal changes in δ(13)C and δ(18)O. No species achieved the δ(13)C values (~-1.0 ‰) expected for 100 % C(4) grazing diets; kangaroos at low latitudes that are classified as feeding primarily on C(4) grasses (grazers) have δ(13)C of up to -3.5 ‰. In these areas, δ(13)C below -12 ‰ suggests a 100 % C(3) grass and/or leafy plant (browse) diet while animals from higher latitude have lower δ(13)C. Animals from semi-arid areas have δ(18)O of 34-40 ‰, while grazers from temperate areas have lower values (~28-30 ‰). Three patterns with implications for palaeoenvironmental reconstruction emerge: (1) all species in semi-arid areas regularly browse to supplement limited grass resources; (2) all species within an environmental zone have similar carbon and oxygen isotope compositions, meaning data from different kangaroo species can be pooled for palaeoenvironmental investigations; (3) relatively small regional environmental differences can be distinguished when δ(13)C and δ(18)O data are used together. These data demonstrate that diet-isotope and climate-isotope relationships should be evaluated in modern ecosystems before application to the regional fossil record.

  11. Stable oxygen isotopes (delta18(O)) in Austrocedrus chilensis tree rings reflect climate variability in northwestern Patagonia, Argentina.

    PubMed

    Roig, F A; Siegwolf, R; Boninsegna, J A

    2006-11-01

    The stable oxygen isotope (delta (18)O) composition of Austrocedrus chilensis (D. Don) Endl. (Cupressaceae) tree rings potentially provide retrospective views of changes in environment and climate in the semi-arid lands of Patagonia. We report the development of the first annually resolved delta (18)O tree-ring chronology obtained from natural forests of the foothills of the northwestern Patagonian Andes. The isotope record spans between 1890 and 1994 AD. We explore the probable links between this record and the climate of the region. Air temperatures during summer conditions are significantly, but not strongly, inversely correlated with annual delta (18)O values from Austrocedrus tree rings. The strongest correlations are between the southern oscillation index (SOI) and the tree rings. The existence of millennial-age Austrocedrus trees in northern Patagonia provides interesting possibilities for examining these climate-related isotopic signals over most of the last 1,000 years.

  12. Developing stable isotopic records from organic material preserved in speleothems

    NASA Astrophysics Data System (ADS)

    Blyth, A.; Baker, A.

    2011-12-01

    Speleothems form excellent archives of environmental change as they are easy to date and preserve multiple environmental records. However, although the stable isotopic composition of speleothem calcite is well characterised, the isotopic composition of organic matter in speleothems has not been investigated in-depth. The approach has considerable potential value in providing isotopic records directly linked to the overlying ecosystem. For stable carbon isotopes, this will provide records independent of the calcite signal, and enable identification of the local primary controls (vegetation type, climate, soil conditions). However, the detailed measurement of isotopic records in speleothem organic matter is hindered by methodological constraints, including extraction of sufficient material, and recovery without adding carbon contamination. Here we present results from a number of methodological techniques and discuss which show most potential for future palaeoenvironmental work. Isotopic records in organic matter can be divided into two main types - analyses of the bulk organic fraction, and compound-specific analyses of molecules of interest (e.g. plant waxes, bacterial lipids etc.). From the point of view of sample size, bulk analysis is the most amenable. Our work shows that TOC in stalagmites can be as low as <0.1 mg/g calcite. However, this is still sufficient to produce bulk organic signals at a sample size of between 100 and 500 mg of calcite powder, which provides a workable temporal resolution at a decadal-centennial scale on many samples. The main obstacle is the recovery of bulk organics without carbon contamination, but whilst avoiding excess acid salts which might damage the instrumentation. One method we propose is the use of an iTOC-CDRS analyser, which measures total organic carbon, and also 12C and 13C isotopes. The approach has the advantage of requiring minimal sample preparation, with drilled powders simply being dissolved in acid. The major

  13. Stable Isotopic Variations in Columnar Cacti: are Responses to Climate Recorded in Spines?

    NASA Astrophysics Data System (ADS)

    English, N. B.; Dettman, D. L.; Williams, D. G.

    2004-12-01

    The behavior of the North American monsoon (NAM), particularly with respect to times of continental drought and its relationship to the Pacific-North American (PNA) teleconnection pattern and the El Nino/Southern Oscillation (ENSO) is of great interest to paleoclimatologists and water managers. Long-term instrumental precipitation and tree ring records in the southwestern United States and northwestern Mexico at low elevations are sparse and this has hindered research on NAM variability at interannual timescales. Saguaro cacti (Carnegiea gigantea) and other columnar cacti in North and South America are long-lived and have the potential to record climate variability on land with high temporal and spatial resolution. The vertical sequence of spines on the saguaro's exterior represents a high resolution (4 to 6 per year), and long (over 150 years) record of environmental change. We present results from an experiment where we tracked the oxygen isotopic values in the source waters, stem tissue waters and spine tissue for three treatments over the course of three months. These data are then compared to a previously developed mechanistic model of isotopic variation that reflects the physiological responses of Saguaro to climate variation over seasonal to century long time-scales. We also present the rationale for a new method to determine the growth rate of columnar cacti using the radiocarbon bomb spike. Our measurements reveal that oxygen and hydrogen isotopic variation among the sequentially produced and persistent spines covering the saguaro body record fluctuations in saguaro water balance. The model successfully predicts isotopic variation in spines and constrains controlling variables, yielding a powerful and high-resolution stable isotope index of water stress in the low desert. The development and refinement of an isotopic model for saguaro will serve as the basis for models applied to other species of columnar cacti in North and South America. The role of the

  14. Holocene climate change in Newfoundland reconstructed using oxygen isotope analysis of lake sediment cores

    NASA Astrophysics Data System (ADS)

    Finkenbinder, Matthew S.; Abbott, Mark B.; Steinman, Byron A.

    2016-08-01

    Carbonate minerals that precipitate from open-basin lakes can provide archives of past variations in the oxygen isotopic composition of precipitation (δ18Oppt). Holocene δ18Oppt records from the circum- North Atlantic region exhibit large fluctuations during times of rapid ice sheet deglaciation, followed by more stable conditions when interglacial boundary conditions were achieved. However, the timing, magnitude, and climatic controls on century to millennial-scale variations in δ18Oppt in northeastern North America are unclear principally because of a dearth of paleo-proxy data. Here we present a lacustrine sediment oxygen isotope (δ18O) record spanning 10,200 to 1200 calendar years before present (cal yr BP) from Cheeseman Lake, a small, alkaline, hydrologically open lake basin located in west-central Newfoundland, Canada. Stable isotope data from regional lakes, rivers, and precipitation indicate that Cheeseman Lake water δ18O values are consistent with the isotopic composition of inflowing meteoric water. In light of the open-basin hydrology and relatively short water residence time of the lake, we interpret down-core variations in calcite oxygen isotope (δ18Ocal) values to primarily reflect changes in δ18Oppt and atmospheric temperature, although other factors such as changes in the seasonality of precipitation may be a minor influence. We conducted a series of climate sensitivity simulations with a lake hydrologic and isotope mass balance model to investigate theoretical lake water δ18O responses to climate change. Results from these experiments suggest that Cheeseman Lake δ18O values are primarily controlled by temperature and to a much lesser extent, the seasonality of precipitation. Increasing and more positive δ18Ocal values between 10,200 and 8000 cal yr BP are interpreted to reflect the waning influence of the Laurentide Ice Sheet on atmospheric circulation, warming temperatures, and rapidly changing surface ocean δ18O from the input of

  15. Skeletal isotope records of growth perturbations in Porites corals during the 1997-1998 mass bleaching event

    NASA Astrophysics Data System (ADS)

    Suzuki, A.; Gagan, M.; Fabricius, K.; Isdale, P.; Yukino, I.; Kawahata, H.

    2003-04-01

    Severe coral bleaching occurred throughout the tropics in 1997/98. We report skeletal UV fluorescence, oxygen isotope, and carbon isotope evidence for perturbations in coral skeletal growth due to bleaching at Ishigaki Island, Japan, and Pandora Reef, Great Barrier Reef. Bleached corals showed abrupt reductions in skeletal extension rate immediately after summer temperature maxima, indicating that bleaching inhibits coral calcification. A colony growing at the low tide line in Ishigaki exhibited clear blue UV fluorescent bands associated with recurrent growth interruptions. Based on the length of time-gaps observed in the annual isotopic cycle, the typical time required for a coral to recover from bleaching is estimated to be about 5--6 months. The effect of bleaching on the oxygen isotope ratio -- temperature relationship was negligible. However, the Ishigaki corals showed lower carbon isotope ratios during bleaching indicating depressed coral metabolism associated with a reduction in calcification. In contrast, skeletal carbon isotope ratios in the Pandora Reef corals exhibited little change in response to bleaching. This is because the records for Pandora Reef were derived from the shaded sides of coral colonies, where algal photosynthesis was particularly slow prior to bleaching, thus subduing the carbon isotope response to bleaching. Taken together, the isotopic and UV fluorescence signals can be used to reconstruct past bleaching events.

  16. Petrologic and oxygen isotopic study of ALH 85085-like chondrites

    NASA Astrophysics Data System (ADS)

    Prinz, M.; Weisberg, M. K.; Clayton, R. N.; Mayeda, T. K.; Ebihara, M.

    1994-07-01

    Four meteorites (PAT 91546, PCA 91328, PCA 91452, PCA 91467) petrologically similar to ALH 85085 chondrite have now been found. Previous studies of ALH 85085 showed it be a new kind of CR-related microchondrule-bearing chondrite, although one called it a sub-chondrite. The purpose of this study is to learn more about ALH 85085-like meteorites and their relationship to CR and CR-related (LEW 85332, Acfer 182, Bencubbin) chondrites. The methods used included petrology, INA bulk chemical analysis (PAT 91546, PCA 91467), and O isotopic analyses of the whole rocks and separated chondrules and dark inclusions (DIs) from PAT 91546. Since microchondrules and fragments are approximately 20 microns it was necessary to analyze composite samples for O; one was of approximately 100 chondrules, and another was of 5 DIs. Petrologically, the four meteorites are similar to ALH 85085, and there is no basis for determining if all of them, or any combinations, are paired. Mineralogically, olivine and pyroxene are highly magnesian FeNi metal generally has 3-10% Ni, and has a positive Ni-Co correlation similar to that in CR and CR-related chondrites. Refractory inclusions are similar in size to the chondrules and have the following assemblages: (1) hibonite-perovskite, (2) melilite-fassaite-forsterite, (3) grossite (Ca-dialuminate)-melilite-perovskite, (4) spinel-melilite, and (5) spinel-pyroxene aggregates. Chemically, INA analyses indicate that PAT 91546 and PCA 91467 are generally similar to ALH 85085. Oxygen isotopic analyses of the four whole-rock compositions fall along the CR mixing line as does ALH 85085; they are also close to LEW 85332, Acfer 182, and Bencubbin. This supports the concept that these are all CR-related chondrites. Even stronger support is found in the compositions of the chondrules and DIs in PAT 91546, which also plot on or near the CR line.

  17. Oxygen and iron isotope studies of magnetite produced by magnetotactic bacteria

    USGS Publications Warehouse

    Mandernack, K.W.; Bazylinski, D.A.; Shanks, Wayne C.; Bullen, T.D.

    1999-01-01

    A series of carefully controlled laboratory studies was carried out to investigate oxygen and iron isotope fractionation during the intracellular production of magnetite (Fe3O4) by two different species of magnetotactic bacteria at temperatures between 4??and 35??C under microaerobic and anaerobic conditions. No detectable fractionation of iron isotopes in the bacterial magnetites was observed. However, oxygen isotope measurements indicated a temperature-dependent fractionation for Fe3O4 and water that is consistent with that observed for Fe3O4 produced extracellularly by thermophilic Fe3+-reducing bacteria. These results contrast with established fractionation curves estimated from either high-temperature experiments or theoretical calculations. With the fractionation curve established in this report, oxygen-18 isotope values of bacterial Fe3O4 may be useful in paleoenvironmental studies for determining the oxygen-18 isotope values of formation waters and for inferring paleotemperatures.

  18. Mass-independent oxygen isotopic partitioning during gas-phase SiO2 formation.

    PubMed

    Chakraborty, Subrata; Yanchulova, Petia; Thiemens, Mark H

    2013-10-25

    Meteorites contain a wide range of oxygen isotopic compositions that are interpreted as heterogeneity in solar nebula. The anomalous oxygen isotopic compositions of refractory mineral phases may reflect a chemical fractionation process in the nebula, but there are no experiments to demonstrate this isotope effect during particle formation through gas-phase reactions. We report experimental results of gas-to-particle conversion during oxidation of silicon monoxide that define a mass-independent line (slope one) in oxygen three-isotope space of (18)O/(16)O versus (17)O/(16)O. This mass-independent chemical reaction is a potentially initiating step in nebular meteorite formation, which would be capable of producing silicate reservoirs with anomalous oxygen isotopic compositions. PMID:24159043

  19. Recent planktic foraminifers in the Fram Strait (Arctic Ocean): carbon and oxygen stable isotope composition

    NASA Astrophysics Data System (ADS)

    Pados, T.; Spielhagen, R. F.; Bauch, D.; Meyer, H.; Segl, M.

    2012-12-01

    In paleoceanographic reconstructions the carbon isotopic compositions (δ13C) of fossil foraminifers refer to, e.g., paleoproductivity and stratification, while oxygen isotopic (δ18O) records provide information about variations in sea surface temperatures and salinities in the past. However, for a correct interpretation of the fossil data it is important to improve our understanding of the correlation between recent oceanic variability and the composition of shells of living calcareous microorganisms. For this, the upper water column and sediment surface in the Fram Strait (Arctic Ocean, 78°50'N, 5°W-8°E) were sampled for planktic foraminifer species Neogloboquadrina pachyderma (sin.) and Turborotalita quinqueloba with a large-diameter multinet and a multicorer, respectively. The δ13C and δ18O values of the shells are compared to the stable isotope composition of the ambient water and to equilibrium calcite values to define the preferred calcification depths of the foraminifers and to determine the factors controlling the isotopic signature of these calcareous microorganisms. The study area was chosen because of its high oceanographic variability: in the eastern Fram Strait the northward flowing West Spitsbergen Current (WSC) carries Atlantic Water, with a thin mixed layer on top, while in the west the upper 200 m consists of cold, low-saline Arctic outflow waters of the East Greenland Current (EGC) and warmer, saline waters of Atlantic origin underneath. Despite this variable oceanographic regime along the studied transect, the stable carbon isotope ratios of the shells do not show major differences according to their horizontal but to their vertical distribution: the δ13C values of N. pachyderma (sin.) from plankton tow samples vary roughly between -1 and -0.1‰ depending on the water depth, while the δ18O values of the tests differ more between the stations.

  20. Oxygen isotope mass balance of atmospheric nitrate at Dome C, East Antarctica, during the OPALE campaign

    NASA Astrophysics Data System (ADS)

    Savarino, Joël; Vicars, William C.; Legrand, Michel; Preunkert, Suzanne; Jourdain, Bruno; Frey, Markus M.; Kukui, Alexandre; Caillon, Nicolas; Gil Roca, Jaime

    2016-03-01

    Variations in the stable oxygen isotope composition of atmospheric nitrate act as novel tools for studying oxidative processes taking place in the troposphere. They provide both qualitative and quantitative constraints on the pathways determining the fate of atmospheric nitrogen oxides (NO + NO2 = NOx). The unique and distinctive 17O excess (Δ17O = δ17O - 0.52 × δ18O) of ozone, which is transferred to NOx via oxidation, is a particularly useful isotopic fingerprint in studies of NOx transformations. Constraining the propagation of 17O excess within the NOx cycle is critical in polar areas, where there exists the possibility of extending atmospheric investigations to the glacial-interglacial timescale using deep ice core records of nitrate. Here we present measurements of the comprehensive isotopic composition of atmospheric nitrate collected at Dome C (East Antarctic Plateau) during the austral summer of 2011/2012. Nitrate isotope analysis has been here combined for the first time with key precursors involved in nitrate production (NOx, O3, OH, HO2, RO2, etc.) and direct observations of the transferrable Δ17O of surface ozone, which was measured at Dome C throughout 2012 using our recently developed analytical approach. Assuming that nitrate is mainly produced in Antarctica in summer through the OH + NO2 pathway and using concurrent measurements of OH and NO2, we calculated a Δ17O signature for nitrate on the order of (21-22 ± 3) ‰. These values are lower than the measured values that ranged between 27 and 31 ‰. This discrepancy between expected and observed Δ17O(NO3-) values suggests the existence of an unknown process that contributes significantly to the atmospheric nitrate budget over this East Antarctic region. However, systematic errors or false isotopic balance transfer functions are not totally excluded.

  1. Zircon megacrysts from kimberlite: oxygen isotope variability among mantle melts

    NASA Astrophysics Data System (ADS)

    Valley, John W.; Kinny, Peter D.; Schulze, Daniel J.; Spicuzza, Michael J.

    The oxygen isotope ratios of Phanerozoic zircons from kimberlite pipes in the Kaapvaal Craton of southern Africa and the Siberian Platform vary from 4.7 to 5.9‰ VSMOW. High precision, accurate analyses by laser reveal subtle pipe-to-pipe differences not previously suspected. These zircons have distinctive chemical and physical characteristics identifying them as mantle-derived megacrysts similar to zircons found associated with diamond, coesite, MARID xenoliths, Cr-diopside, K-richterite, or Mg-rich ilmenite. Several lines of evidence indicate that these 18O values are unaltered by kimberlite magmas during eruption and represent compositions preserved since crystallization in the mantle, including: U/Pb age, large crystal size, and the slow rate of oxygen exchange in non-metamict zircon. The average 18O of mantle zircons is 5.3‰, 0.1 higher and in equilibrium with values for olivine in peridotite xenoliths and oceanic basalts. Zircon megacrysts from within 250 km of Kimberley, South Africa have average 18O=5.32+/-0.17 (n=28). Small, but significant, differences among other kimberlite pipes or groups of pipes may indicate isotopically distinct reservoirs in the sub-continental lithosphere or asthenosphere, some of which are anomalous with respect to normal mantle values of 5.3+/-0.3. Precambrian zircons (2.1-2.7 Ga) from Jwaneng, Botswana have the lowest values yet measured in a mantle zircon, 18O=3.4 to 4.7‰. These zircon megacrysts originally crystallized in mafic or ultramafic rocks either through melting and metasomatism associated with kimberlite magmatism or during metamorphism. The low 18O zircons are best explained by subduction of late Archean ocean crust that exchanged with heated seawater prior to underplating as eclogite and to associated metasomatism of the mantle wedge. Smaller differences among other pipes and districts may result from variable temperatures of equilibration, mafic versus ultramafic hosts, or variable underplating. The narrow

  2. Recent variability in the hydrological cycle of tropical Asia from oxygen isotopes of tree cellulose

    NASA Astrophysics Data System (ADS)

    Zhu, Mengfan

    This dissertation investigates hydrological variability within tropical Asia over the past several few centuries as reflected in the stable oxygen isotope composition of atmospheric moisture. High-resolution water isotope records are developed from trees collected from northern Thailand, southern Cambodia, and eastern part of the Tibetan Plateau. These records are examined to assess whether and how the 20th century is unique in terms of the hydrological conditions in tropical Asia under the influences of both monsoon and ENSO with the observed temperature changes. In northern Thailand, the oxygen isotopic composition (δ 18O) of tree cellulose samples of Pinus kesiya from a montane forest has been analyzed in subannual resolution for the past 80 years. The cellulose δ18O values exhibit a distinctive annual cycle with an amplitude of up to 12 ‰, which is interpreted to reflect primarily the seasonal cycle of precipitation δ18 O. The cellulose δ18O annual mean values correlate significantly with the amount of summer monsoon precipitation over the India subcontinent, corroborating recent studies that suggest the so-called "isotope amount effect" in the tropical precipitation δ18O reflects the hydrological processes of the upstream or the moisture source regions instead of the rainfall amount at the local site. No obvious trend in the summer monsoon precipitation is detected from the cellulose δ 18O record. However, the record does suggest a temporal weakening relationship between the Indian Monsoon and ENSO over the 20th century. The annual maxima in the cellulose δ18O values are representative of the moisture balance during the winter dry season, and possibly document a decreasing trend in the isotopically-distinct fog water input during the dry season because of the warming in the 20th century. Isotope chronologies of Pinus merkusii from a coastal lowland forest in Cambodia have been generated to investigate hydrological variability over the Indo

  3. Reconstructing a Hot and High Eocene Sierra Nevada Using Oxygen and Hydrogen Isotopes in Kaolinite

    NASA Astrophysics Data System (ADS)

    Mix, H.; Ibarra, D. E.; Mulch, A.; Graham, S. A.; Chamberlain, C. P.

    2014-12-01

    Despite the broad interest in determining the topographic and climatic histories of mountain ranges, the evolution of California's Sierra Nevada remains actively debated. Prior stable isotope-based studies of Sierra Nevada have relied exclusively on hydrogen isotopes in kaolinite, hydrated volcanic glass and leaf n-alkanes. Additional constraints from the oxygen isotope composition of phyllosilicates increase the robustness of findings from a single isotope system and allow for the reconstruction of paleotemperatures. Here, we reconstruct the temperature and elevation of the Early Eocene Sierra Nevada using the oxygen isotope composition of kaolinitized granite clasts from the ancestral Yuba and American Rivers. We evaluate the possible contributions of hydrogen isotope exchange by direct comparison with more robust oxygen isotope measurements. Next, we utilize differences in the hydrogen and oxygen isotope fractionation in kaolinite to constrain paleotemperature. Oxygen isotope geochemistry of in-situ kaolinites indicates upstream (eastward) depletion of 18O in the northern Sierra Nevada. δ18O values ranging from 11.4 - 14.4 ‰ at the easternmost localities correspond to paleoelevations as high as 2400 m when simulating the orographic precipitation of moisture from a Pacific source using Eocene boundary conditions. This finding is consistent with stable isotope studies of the northern Sierra, but oxygen isotope based paleoelevation estimates are systematically ~500 - 1000 m higher than those from hydrogen-based estimates from the same samples. Kaolinite geothermometry from 16 samples measured in duplicate or triplicate produce an average Early Eocene temperature of 24.2 ± 2.0 °C (1s). This kaolinite temperature reconstruction is in agreement with paleofloral and geochemical constraints and general circulation model simulations from Eocene California. Our results confirm prior hydrogen isotope-based paleoelevations and further substantiate the existence of a

  4. A Delayed Noeproterozoic Oceanic Oxygenation: Evidence from the Mo Isotope of the Cryogenian Datangpo Formation

    NASA Astrophysics Data System (ADS)

    Cheng, M.; Li, C.; Algeo, T. J.; Zhou, L.; Liu, X. D.; Feng, L. J.

    2015-12-01

    The onset of the Neoproterozoic oxygenation event (NOE) is usually considered to be at 750-800Ma, which was supposed to have triggered the subsequent oxygenation of the earth's atmosphere-ocean system, thus removing the barrier for the emergence and rapid diversification of animals. However, the subsequent oceanic redox responses in the Cryogenian are poorly constrained. Here, we conducted an integrated Fe-S-C-Mo biogeochemical study on black shales of the Cryogenian Datangpo Formation (~660Ma, Nanhua Basin, South China). Iron speciation data indicate that these black shales were deposited under euxinic water conditions. Co-variation between Mo and TOC suggests an increasing isolation of the basin from open ocean during the deposition of the black shales. Correspondingly, the Datangpo black shales show higher δ98Mo values (+0.97‰ to +1.12‰) for the lower part (0-10m) and lower δ98Mo values (+0.44‰ to +0.53‰) for the upper part (10-20m) consistent with a global scale seawater δ98Mo recorded in the lower part but only a basin scale seawater δ98Mo recorded in the upper part. Accordingly, we estimate the seawater Mo isotope closed to +1.1‰ at ~660 Ma, which suggests substantial oceanic anoxia compared to modern oceans (+2.3‰). The seawater δ98Mo reconstructed by the Datangpo black shales is exactly the same to previously reported seawater δ98Mo at ~750 Ma and ~640 Ma, indicating a continuous oceanic anoxia throughout the Cryogenian although widespread oceanic oxygenation was suggested for the subsequent Ediacaran by multiple geochemical records. Thus, in light of previous studies, our findings indicate a delayed oceanic oxygenation relative to the onset of NOE, which may help to explain the first presence of metazoa in Cryogenian but rapid diversification occurred in Ediacaran.

  5. Bioapatite Recrystallization During Burning and its Effects on Phosphate Stable Oxygen Isotope Composition

    NASA Astrophysics Data System (ADS)

    Munro, L. E.; Longstaffe, F. J.; White, C. D.

    2003-04-01

    Stable oxygen isotopic compositions of phosphate from mammal bones are commonly used in palaeoenvironmental reconstructions. However, preservation of the primary bone oxygen isotopic composition is of concern during post-mortem alteration. Particularly in studies of archaeological interest, bone samples are often obtained from contexts where they have been heated, either in middens, or near hearths. Hence, in addition to alteration resulting from natural diagenetic processes, burning may also have contributed to modification of the primary oxygen isotopic signal. Various techniques can be employed to evaluate the degree of preservation of bone during burning. Anthropologists commonly use colour comparisons (Munsell Colour Chart) to assess the temperature of burning. Recrystallization of the carbonated hydroxyapatite, i.e., bioapatite, in bone is more rigorously assessed using X-ray diffraction and infra-red spectroscopy. In this study, freshly deceased (6<8 months) white-tailed deer leg bones (Odocoileus virginianus) were collected from Pinery Provincial Park, Ontario, Canada. Each long bone was sectioned, incrementally burned, colour-typed, ground to a standardized grain-size (45<63mm), and analysed using differential thermal analysis (DTA), thermogravimetric analysis (TGA), rotating anode X-ray diffraction (XRD), and Fourier transform infra-red spectroscopy (FTIR). Heating temperatures ranged from 25 to 900^oC, increasing in intervals of 25^oC. Two major stages of weight loss were recorded in the DTA/TGA data, 25-260^oC representing dehydration, and 270-600^oC reflecting incineration of organic matter. The end-product (900^oC) resembled pure hydroxyapatite. XRD patterns of the bioapatite remained virtually unchanged from 25-250^oC, after which peak intensity, sharpness and the XRD crystallinity index (XRD CI) increased from 0.80 at 250^oC to 1.26 at 900^oC. FTIR patterns showed analogous behaviour, demonstrating minimal fluctuations in the FTIR crystallinity

  6. Variation in oxygen isotope fractionation during cellulose synthesis: intramolecular and biosynthetic effects.

    PubMed

    Sternberg, Leonel; Pinzon, Maria Camila; Anderson, William T; Jahren, A Hope

    2006-10-01

    The oxygen isotopic composition of plant cellulose is commonly used for the interpretations of climate, ecophysiology and dendrochronology in both modern and palaeoenvironments. Further applications of this analytical tool depends on our in-depth knowledge of the isotopic fractionations associated with the biochemical pathways leading to cellulose. Here, we test two important assumptions regarding isotopic effects resulting from the location of oxygen in the carbohydrate moiety and the biosynthetic pathway towards cellulose synthesis. We show that the oxygen isotopic fractionation of the oxygen attached to carbon 2 of the glucose moieties differs from the average fractionation of the oxygens attached to carbons 3-6 from cellulose by at least 9%, for cellulose synthesized within seedlings of two different species (Triticum aestivum L. and Ricinus communis L.). The fractionation for a given oxygen in cellulose synthesized by the Triticum seedlings, which have starch as their primary carbon source, is different than the corresponding fractionation in Ricinus seedlings, within which lipids are the primary carbon source. This observation shows that the biosynthetic pathway towards cellulose affects oxygen isotope partitioning, a fact heretofore undemonstrated. Our findings may explain the species-dependent variability in the overall oxygen isotope fractionation during cellulose synthesis, and may provide much-needed insight for palaeoclimate reconstruction using fossil cellulose.

  7. Variation in oxygen isotope fractionation during cellulose synthesis: intramolecular and biosynthetic effects.

    PubMed

    Sternberg, Leonel; Pinzon, Maria Camila; Anderson, William T; Jahren, A Hope

    2006-10-01

    The oxygen isotopic composition of plant cellulose is commonly used for the interpretations of climate, ecophysiology and dendrochronology in both modern and palaeoenvironments. Further applications of this analytical tool depends on our in-depth knowledge of the isotopic fractionations associated with the biochemical pathways leading to cellulose. Here, we test two important assumptions regarding isotopic effects resulting from the location of oxygen in the carbohydrate moiety and the biosynthetic pathway towards cellulose synthesis. We show that the oxygen isotopic fractionation of the oxygen attached to carbon 2 of the glucose moieties differs from the average fractionation of the oxygens attached to carbons 3-6 from cellulose by at least 9%, for cellulose synthesized within seedlings of two different species (Triticum aestivum L. and Ricinus communis L.). The fractionation for a given oxygen in cellulose synthesized by the Triticum seedlings, which have starch as their primary carbon source, is different than the corresponding fractionation in Ricinus seedlings, within which lipids are the primary carbon source. This observation shows that the biosynthetic pathway towards cellulose affects oxygen isotope partitioning, a fact heretofore undemonstrated. Our findings may explain the species-dependent variability in the overall oxygen isotope fractionation during cellulose synthesis, and may provide much-needed insight for palaeoclimate reconstruction using fossil cellulose. PMID:16930314

  8. Controls on ostracod valve geochemistry: Part 2. Carbon and oxygen isotope compositions

    NASA Astrophysics Data System (ADS)

    Decrouy, Laurent; Vennemann, Torsten Walter; Ariztegui, Daniel

    2011-11-01

    The stable carbon and oxygen isotope compositions of fossil ostracods are powerful tools to estimate past environmental and climatic conditions. The basis for such interpretations is that the calcite of the valves reflects the isotopic composition of water and its temperature of formation. However, calcite of ostracods is known not to form in isotopic equilibrium with water and different species may have different offsets from inorganic precipitates of calcite formed under the same conditions. To estimate the fractionation during ostracod valve calcification, the oxygen and carbon isotope compositions of 15 species living in Lake Geneva were related to their autoecology and the environmental parameters measured during their growth. The results indicate that: (1) Oxygen isotope fractionation is similar for all species of Candoninae with an enrichment in 18O of more than 3‰ relative to equilibrium values for inorganic calcite. Oxygen isotope fractionation for Cytheroidea is less discriminative relative to the heavy oxygen, with enrichments in 18O for these species of 1.7 to 2.3‰. Oxygen isotope fractionations for Cyprididae are in-between those of Candoninae and Cytheroidea. The difference in oxygen isotope fractionation between ostracods and inorganic calcite has been interpreted as resulting from a vital effect. (2) Comparison with previous work suggests that oxygen isotope fractionation may depend on the total and relative ion content of water. (3) Carbon isotope compositions of ostracod valves are generally in equilibrium with DIC. The specimens' δ 13C values are mainly controlled by seasonal variations in δ 13C DIC of bottom water or variation thereof in sediment pore water. (4) Incomplete valve calcification has an effect on carbon and oxygen isotope compositions of ostracod valves. Preferential incorporation of CO32- at the beginning of valve calcification may explain this effect. (5) Results presented here as well as results from synthetic carbonate

  9. Oxygen isotopic composition and U-Pb discordance in zircon

    USGS Publications Warehouse

    Booth, A.L.; Kolodny, Y.; Chamberlain, C.P.; McWilliams, M.; Schmitt, A.K.; Wooden, J.

    2005-01-01

    We have investigated U-Pb discordance and oxygen isotopic composition of zircon using high-spatial resolution ??18O measurement by ion microprobe. ??18O in both concordant and discordant zircon grains provides an indication of the relationship between fluid interaction and discordance. Our results suggest that three characteristics of zircon are interrelated: (1) U-Pb systematics and concomitant age discordance, (2) ??18O and the water-rock interactions implied therein, and (3) zircon texture, as revealed by cathodoluminescence and BSE imaging. A key observation is that U-Pb-disturbed zircons are often also variably depleted in 18O, but the relationship between discordance and ??18O is not systematic. ??18O values of discordant zircons are generally lighter but irregular in their distribution. Textural differences between zircon grains can be correlated with both U-Pb discordance and ??18O. Discordant grains exhibit either a recrystallized, fractured, or strongly zoned CL texture, and are characteristic of 18O depletion. We interpret this to be a result of metamictization, leading to destruction of the zircon lattice and an increased susceptibility to lead loss. Conversely, grains that are concordant have less-expressed zoning and a smoother CL texture and are enriched in 18O. From this it is apparent that various stages of water-rock interaction, as evidenced by systematic variations in ??18O, leave their imprint on both the texture and U-Pb systematics of zircon. Copyright ?? 2005 Elsevier Ltd.

  10. Herbivore tooth oxygen isotope compositions: Effects of diet and physiology

    NASA Astrophysics Data System (ADS)

    Kohn, Matthew J.; Schoeninger, Margaret J.; Valley, John W.

    1996-10-01

    The applicability of rapid and precise laser probe analysis of tooth enamel for δ18O has been verified, and the method has been applied to different modern herbivores in East Africa. Sampling and pretreatment procedures involve initial bleaching and grinding of enamel to <75 μm, and elimination of adsorbed water and organic compounds with BrF 5. Typical analytical reproducibilities for 0.5-2 mg samples are ±0.08‰ (± 1σ). Chemical and spectroscopic characterization of pretreated but unanalyzed samples show no alteration compared to fresh enamel. Solid reaction products are nearly pure CaF 2 with little evidence for residual O 2. Because laser probe fluorination extracts oxygen from all sites in the apatite structure (phosphate, structural carbonate, and hydroxyl), only unaltered tooth enamel (>95% apatite) can be analyzed reliably. Different East African herbivores exhibit previously unsuspected compositional differences. Average enamel δ18O values (V-SMOW) are approximately: 25‰ (goat), 27‰ (oryx), 28‰ (dikdik and zebra), 29‰ (topi), 30‰ (gerenuk), and 32‰ (gazelle). These compositions differ from generalized theoretical models, but are broadly consistent with expected isotope effects associated with differences in how much each animal (a) drinks, (b) eats C3 vs. C4 plants, and (c) pants vs. sweats. Consideration of diet, water turnover, and animal physiology will allow the most accurate interpretation of ancient teeth and targeting of environmentally-sensitive animals in paleoclimate studies.

  11. Spatial Variability in Instantaneous Photosynthetic Carbon and Oxygen Isotope Discrimination

    NASA Astrophysics Data System (ADS)

    Barbour, M. M.

    2007-12-01

    Stable carbon and oxygen isotope ratios of CO2 are useful tracers in studies of carbon and water cycling between the terrestrial biosphere and the atmosphere. Interpretation of variation in 13CO2 and C16O18O relies on models describing physical and biochemical processes and their associated fractionations. A layer of complexity not currently quantified or accounted for in canopy models is spatial variation in photosynthetic discrimination within a single leaf. A new measurement technique, employing tunable diode laser absorption spectrometry coupled to an open gas exchange system, enables online measurement of photosynthetic discrimination at high temporal resolution. Using this system, photosynthetic 13C and 18O discrimination was measured along leaves of a C3 monocot. For the forage cereal Triticale, 13C discrimination increased by 2‰ and 18O by 20‰ from the base to the tip of mature leaves when measured at saturating irradiance. The increase in 13C discrimination was associated with an increase in the leaf internal conductance of CO2, and 18O discrimination with carry-forward of evaporative enrichment along the leaf. When numerical averages are compared to flux- and area-weighted averages, the portion of the leaf approximately one third of the way from the base can be shown to provide the most representative area for scaling up.

  12. Isotopic record of Pleistocene glacial/interglacial cycles in pelagic carbonates: Revisiting historical data from the Caribbean Sea

    NASA Astrophysics Data System (ADS)

    Hermoso, Michaël

    2016-04-01

    The glacial/interglacial cycles of the Pleistocene were first recognised by variations in the oxygen isotopic composition of planktonic foraminifera from cores in the Caribbean Sea. Since this pioneering work by Emiliani, this proxy has been extensively applied to a variety of carbonate biominerals over the entirety of the Meso-Cenozoic. However, palaeoceanographic studies have overwhelmingly focused on foraminifera compared to other calcifying microorganism fossils, such as the coccoliths. In this study, I revisit coccolith stable isotopic data obtained from the classic P6304-4 core in light of recent developments in the biogeochemistry of coccolithophores. In particular, I show that the coccolith stable isotope record of the last 13 Marine Isotope Stages (∼480 kyrs) is significantly biased by large vital effects. The magnitude of coccolith carbon and oxygen isotope vital effects is not uniform, but shows remarkable co-variance with the Vostok CO2 ice record. During periods of relatively elevated CO2 (interstadials), the expression of the vital effect is relatively small, whereas it can as high as +3‰ for the oxygen isotopes during glacial stadials, which I argue is a result of enhanced CO2 limitation of coccolithophores. Using this paradigm, I propose that coccolithophore vital effects are not a complicating factor, but rather the signal of interest. As the magnitude of the coccolith vital effect is shown to scale with pCO2, coccolith carbon and oxygen isotopes may be used in conjunction with foraminifera data to reconstruct and refine aqueous CO2 concentrations in the past.

  13. Multiple oxygen and sulfur isotopic analyses on water-soluble sulfate in bulk atmospheric deposition from the southwestern United States

    USGS Publications Warehouse

    Bao, H.; Reheis, M.C.

    2003-01-01

    Sulfate is a major component of bulk atmospheric deposition (including dust, aerosol, fog, and rain). We analyzed sulfur and oxygen isotopic compositions of water-soluble sulfate from 40 sites where year-round dust traps collect bulk atmospheric deposition in the southwestern United States. Average sulfur and oxygen isotopic compositions (??34S and ??18O) are 5.8 ?? 1.4 (CDT) and 11.2 ?? 1.9 (SMOW) (n = 47), respectively. Samples have an oxygen 17 anomaly (?? 17O), with an average value of 1.0 ?? 0.6???. Except for a weak positive correlation between ??18O and ??17O values (r2 ??? 0.4), no correlation exists for ??18O versus ??34S, ?? 17O versus ??34S, or any of the three isotopic compositions versus elevation of the sample site. Exceptional positive ?? 17O values (up to 4.23???) are found in samples from sites in the vicinity of large cities or major highways, and near-zero ?? 17O values are found in samples close to dry lakes. Comparison of isotopic values of dust trap sulfate and desert varnish sulfate from the region reveals that varnish sulfate has average isotopic values that are ???4.8??? lower for ??18O, ???2.1??? higher for ??34S , and ???0.3??? lower for ?? 17O than those of the present-day bulk deposition sulfate. Although other factors could cause the disparity, this observation suggests a possibility that varnish sulfate may have recorded a long-term atmospheric sulfate deposition during the Holocene or Pleistocene, as well as the differences between sulfur and oxygen isotopic compositions of the preindustrial bulk deposition sulfate and those of the industrial era.

  14. Multiple oxygen and sulfur isotopic analyses on water-soluble sulfate in bulk atmospheric deposition from the southwestern United States

    NASA Astrophysics Data System (ADS)

    Bao, Huiming; Reheis, Marith C.

    2003-07-01

    Sulfate is a major component of bulk atmospheric deposition (including dust, aerosol, fog, and rain). We analyzed sulfur and oxygen isotopic compositions of water-soluble sulfate from 40 sites where year-round dust traps collect bulk atmospheric deposition in the southwestern United States. Average sulfur and oxygen isotopic compositions (δ34S and δ18O) are 5.8 ± 1.4 (CDT) and 11.2 ± 1.9 (SMOW) (n = 47), respectively. Samples have an oxygen 17 anomaly (Δ17O), with an average value of 1.0 ± 0.6‰. Except for a weak positive correlation between δ18O and Δ17O values (r2 ≈ 0.4), no correlation exists for δ18O versus δ34S, Δ17O versus δ34S, or any of the three isotopic compositions versus elevation of the sample site. Exceptional positive Δ17O values (up to 4.23‰) are found in samples from sites in the vicinity of large cities or major highways, and near-zero Δ17O values are found in samples close to dry lakes. Comparison of isotopic values of dust trap sulfate and desert varnish sulfate from the region reveals that varnish sulfate has average isotopic values that are ˜4.8‰ lower for δ18O, ˜2.1‰ higher for δ34S, and ˜0.3‰ lower for Δ17O than those of the present-day bulk deposition sulfate. Although other factors could cause the disparity, this observation suggests a possibility that varnish sulfate may have recorded a long-term atmospheric sulfate deposition during the Holocene or Pleistocene, as well as the differences between sulfur and oxygen isotopic compositions of the preindustrial bulk deposition sulfate and those of the industrial era.

  15. Oxygen isotope composition of diatoms as Late Holocene climate proxy at Two-Yurts Lake, Central Kamchatka, Russia

    NASA Astrophysics Data System (ADS)

    Meyer, Hanno; Chapligin, Bernhard; Hoff, Ulrike; Nazarova, Larisa; Diekmann, Bernhard

    2015-11-01

    Especially in combination with other proxies, the oxygen isotope composition of diatom silica (δ18Odiatom) from lake sediments is useful for interpreting past climate conditions. This paper presents the first oxygen isotope data of fossil diatoms from Kamchatka, Russia, derived from sediment cores from Two-Yurts Lake (TYL). For reconstructing Late Holocene climate change, palaeolimnological investigations also included diatom, pollen and chironomid analysis. The most recent diatom sample (δ18Odiatom = + 23.3‰) corresponds well with the present day isotopic composition of the TYL water (mean δ18O = - 14.8‰) displaying a reasonable isotope fractionation in the system silica-water. Nonetheless, the TYL δ18Odiatom record is mainly controlled by changes in the isotopic composition of the lake water. TYL is considered as a dynamic system triggered by differential environmental changes closely linked with lake-internal hydrological factors. The diatom silica isotope record displays large variations in δ18Odiatom from + 27.3‰ to + 23.3‰ from about ~ 4.5 kyr BP until today. A continuous depletion in δ18Odiatom of 4.0‰ is observed in the past 4.5 kyr, which is in good accordance with other hemispheric environmental changes (i.e. a summer insolation-driven Mid- to Late Holocene cooling). The overall cooling trend is superimposed by regional hydrological and atmospheric-oceanic changes. These are related to the interplay between Siberian High and Aleutian Low as well as to the ice dynamics in the Sea of Okhotsk. Additionally, combined δ18Odiatom and chironomid interpretations provide new information on changes related to meltwater input to lakes. Hence, this diatom isotope study provides further insight into hydrology and climate dynamics of this remote, rarely investigated area.

  16. 500,000-year stable carbon isotopic record from Devils Hole, Nevada

    USGS Publications Warehouse

    Coplen, T.B.; Winograd, I.J.; Landwehr, J.M.; Riggs, A.C.

    1994-01-01

    The record of carbon-13 (??13C) variations in DH-11 vein calcite core from Devils Hole, Nevada, shows four prominent minima near glacial terminations (glacial-interglacial transitions) V to II. The ??13C time series is inversely correlated with the DH-11 oxygen isotope ratio time series and leads it by as much as 7000 years. The ??13C variations likely record fluctuations in the ??13C of dissolved inorganic carbon of water recharging the aquifer. How such variations are transported 80 kilometers to Devils Hole without obliteration by waterrock reaction remains an enigma. The record may reflect (i) global variations in the ??13C of atmospheric CO2 and, hence, the ??13C of continental biomass or (ii) variations in extent and density of vegetation in the southern Great Basin. In the latter case, ??13C minima at 414, 334, 246, and 133 thousand years ago mark times of maximum vegetation.

  17. A model of oxygen transport in Pt/ceria catalysts from isotope exchange

    SciTech Connect

    Holmgren, A.; Andersson, B.; Duprez, D.

    1999-03-10

    From isotope oxygen exchange reactions and simulations of these experiments, the important steps in oxygen transport in Pt/ceria were distinguished and their rates were estimated. A Pt/alumina sample was also experimentally investigated for comparison. Oxygen surface diffusion as well as oxygen spillover from Pt to ceria was found to be fast in comparison with adsorption/desorption of oxygen on the metal and oxygen bulk diffusion. The exchange rate was found to be higher on a very-low-Pt-dispersion sample than on a high-dispersion sample, which in the model was explained by the different adsorption properties of oxygen.

  18. Uranium Isotope Evidence for Temporary Ocean Oxygenation Following the Sturtian Glaciation

    NASA Astrophysics Data System (ADS)

    Lau, K. V.; Maher, K.; Macdonald, F. A.; Payne, J.

    2015-12-01

    The link between widespread ocean oxygenation in the Neoproterozoic and the rise of animals has long been debated, largely because the timing and nature of oxygenation of the oceans remain poorly constrained. Strata deposited during the Cryogenian non-glacial interlude (660 to 635 Ma), between the Sturtian and Marinoan Snowball Earth glaciations, contain the earliest fossil evidence of animals. To quantitatively estimate patterns of seafloor oxygenation during this critical interval, we present uranium isotope (δ238U) data from limestone of the Taishir Formation (Fm) in Mongolia in two stratigraphic sections that are separated by ~75 km across the basin. The Taishir Fm hosts two large δ13C excursions that co-vary in total organic and inorganic (carbonate) carbon: a basal carbonate δ13C excursion to -4‰ in the Sturtian cap carbonate, followed by a rise to enriched values of +8‰, a second negative δ13C excursion to -7‰ referred to as the Taishir excursion, followed by a second rise to +10‰. Above the Sturtian glacial deposits, in the stratigraphic interval below the Taishir excursion, δ238U compositions have a mean value that is similar to that of modern seawater. After the Taishir excursion, the δ238U record exhibits a step decrease of ~0.3‰, and δ238U remains approximately constant until the erosional unconformity at the base of the Marinoan glacial deposits. We use a box model to constrain the uranium cycle behavior that best explains our observations. In the model, the best explanation for the less negative post-Sturtian values of δ238U is extensive oxygenation of the seafloor. Moreover, the model demonstrates that the higher δ238U values of the post-Sturtian limestones are inconsistent with an increased flux of uranium to the oceans due to post-Snowball weathering as the primary driver of the excursion. Thus, we favor a scenario in which there was a rise in oxygen levels following the Sturtian glaciation followed by a decrease in seafloor

  19. Oxygen-18 content of atmospheric oxygen does not affect the oxygen isotope relationship between environmental water and cellulose in a submerged aquatic plant, Egeria densa Planch

    SciTech Connect

    Cooper, L.W.; DeNiro, M.J. )

    1989-10-01

    We determined that the oxygen isotopic composition of cellulose synthesized by a submerged plant, Egeria densa Planch., is related to the isotopic composition of environmental water by a linear function, {delta}{sup 18}O cellulose = 0.48 {delta}{sup 18}O water + 24.1{per thousand}. The observation of a slope of less than 1 indicates that a portion of cellulose oxygen is derived from an isotopically constant source other than water. We tested whether this source might be molecular oxygen by growing plants in the presence of high concentrations of {sup 18}O in the form of O{sub 2} bubbled into the bottom of an aquarium. Cellulose synthesized during this experiment did not have significantly different oxygen isotope ratios than that synthesized by control plants exposed to O{sub 2} of normal {sup 18}O abundance. We propose that oxygen in organic matter recycled from senescent portions of the plant is incorporated into cellulose. Our findings indicate that paleoclimatic models linking the oxygen isotope composition of environmental water to cellulose from fossil plants will have to be modified to account for contributions of oxygen from this or other sources besides water.

  20. Phosphorus Speciation and Phosphate Oxygen Isotope Systematics of Type Euxinic Marine Deposits from Middle Devonian North America

    NASA Astrophysics Data System (ADS)

    Carney, C. P.; Arthur, M. A.

    2010-12-01

    Perturbation to the P cycle is thought to be an important forcing in episodes of ocean oxygen depletion and enhanced organic C burial, but this relationship remains underconstrained by geochemical data. This geochemical study applies sequential P extraction and subsequent phase-specific PO4-oxygen isotope analyses to the Marcellus Shale Formation - a type euxinic marine unit. Analysis of sedimentary P is assimilated with bulk geochemical data and detailed lithostratigraphy to capture the relationship of P-cycling with evolving sediment inputs, sea level, water column redox conditions, and water column stratification. It is also possible to study the effects of variable thermal history on lithified sediments, as the thermal history of the Marcellus Shale Formation is known throughout the basin. Thermal maturity is compared to variability in P-speciation and PO4-oxygen isotopic composition to control for the effects of secondary diagenesis. A high-resolution oxygen isotope-derived temperature record is important in paleoceanographic reconstruction. In the Middle Devonian, and the Paleozoic in general, diagenetically-robust PO4-oxygen has begun to supplant the CO3-oxygen isotope system in paleothermometry applications due to near pervasive signal overprinting. Conodont elements are the typical source of PO4 for these analyses, but the spatio-temporal distribution of these fossils is limited, and collection from non-carbonate facies is prohibitively labor-intensive. Oxygen isotope analyses of specific fractions of bulk sedimentary phosphate provide a feasible, but relatively unproven alternative. Two recent studies have demonstrated that a large fraction of authigenic P is precipitated in isotopic equilibrium with seawater and that phase partitioning of P can be preserved on hundred-Myr timescales. These results suggest that a PO4 isotope paleoproxy is viable. This study expands the scope of application to paleosediments with high-resolution data and complimentary

  1. A new isotopic reference material for stable hydrogen and oxygen isotope-ratio measurements of water—USGS50 Lake Kyoga Water

    USGS Publications Warehouse

    Coplen, Tyler B.; Wassenaar, Leonard I; Mukwaya, Christine; Qi, Haiping; Lorenz, Jennifer M.

    2015-01-01

    This isotopic reference material, designated as USGS50, is intended as one of two reference waters for daily normalization of stable hydrogen and oxygen isotopic analysis of water with an isotope-ratio mass spectrometer or a laser absorption spectrometer, of use especially for isotope-hydrology laboratories analyzing freshwater samples from equatorial and tropical regions.

  2. A refined method for calculating paleotemperatures from linear correlations in bamboo coral carbon and oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Saenger, Casey; Watkins, James M.

    2016-06-01

    Bamboo corals represent an emerging paleoclimate archive with the potential to record variability at intermediate depths throughout much of the global ocean. Realizing this potential has been complicated by biologically mediated vital effects, which are evident in linear correlations of skeletal carbon (δ13C) and oxygen (δ18O) isotope composition. Previous efforts to develop a bamboo coral δ18O paleothermometer by accounting for such vital effects have not been completely successful as they still rely on empirical calibrations that are offset from the temperature dependence of abiogenic experiments. Here we describe an approach that better corrects for bamboo coral vital effects and allows paleotemperatures to be calculated directly from the abiogenic temperature dependence. The success of the method lies in calculating apparent equilibrium carbon and oxygen isotope fractionation at the temperature, pH, and growth rate of each coral, as well as in the use of model II regressions. Rigorous propagation of uncertainty suggests typical errors of ±2-3°C, but in select cases errors as low as ±0.65°C can be achieved for densely sampled and strongly correlated data sets. This lower limit approaches the value attributed to uncertainty in pH and growth rate estimates alone, as predicted by a series of pseudoproxy experiments. The incorporation of isotopically light metabolic CO2 appears to be negligible in most Pacific corals, but may be significant in Atlantic specimens, potentially requiring an additional correction. The success of the method therefore hinges on how well complex environmental systems and biomineralization strategies are constrained, with the most reliable temperatures occurring when calcifying fluid pH, growth rate, and incorporation of metabolic carbon into skeletal calcite are constrained using multiple geochemical proxies.

  3. Carbon and Oxygen Isotopic Ratios for Nearby Miras

    NASA Astrophysics Data System (ADS)

    Hinkle, Kenneth H.; Lebzelter, Thomas; Straniero, Oscar

    2016-07-01

    Carbon and oxygen isotopic ratios are reported for a sample of 46 Mira and SRa-type variable asymptotic giant branch (AGB) stars. Vibration-rotation first and second-overtone CO lines in 1.5-2.5 μm spectra were measured to derive isotopic ratios for 12C/13C, 16O/17O, and 16O/18O. Comparisons with previous measurements for individual stars and with various samples of evolved stars, as available in the extant literature, are discussed. Models for solar composition AGB stars of different initial masses are used to interpret our results. We find that the majority of M-stars have main sequence masses ≤2 M ⊙ and have not experienced sizable third dredge-up (TDU) episodes. The progenitors of the four S-type stars in our sample are slightly more massive. Of the six C-stars in the sample three have clear evidence relating their origin to the occurrence of TDU. Comparisons with O-rich presolar grains from AGB stars that lived before the formation of the solar system reveal variations in the interstellar medium chemical composition. The present generation of low-mass AGB stars, as represented by our sample of long period variables (LPVs), shows a large spread of 16O/17O ratios, similar to that of group 1 presolar grains and in agreement with theoretical expectations for the composition of mass 1.2-2 M ⊙ stars after the first dredge-up. In contrast, the 16O/18O ratios of present-day LPVs are definitely smaller than those of group 1 grains. This is most probably a consequence of the the decrease with time of the 16O/18O ratio in the interstellar medium due to the chemical evolution of the Milky Way. One star in our sample has an O composition similar to that of group 2 presolar grains originating in an AGB star undergoing extra-mixing. This may indicate that the extra-mixing process is hampered at high metallicity, or, equivalently, favored at low metallicity. Similarly to O-rich grains, no star in our sample shows evidence of hot bottom burning, which is expected for

  4. The Divnoe meteorite: Petrology, chemistry, oxygen isotopes and origin

    NASA Technical Reports Server (NTRS)

    Petaev, M. I.; Barsukova, L. D.; Lipschultz, M. E.; Wang, M.-S.; Ariskin, A. A.; Clayton, R. N.; Mayeda, T. K.

    1994-01-01

    The Divnoe meteorite is an olivine-rich primitive achondrite with subchondritic chemistry and mineralogy. It has a granoblastic, coarse-grained, olivine groundmass (CGL: coarse-grained lithology) with relatively large pyroxene-plagioclase poiklitic patches (PP) and small fine-grained domains of an opaque-rich lithology (ORL). Both PP and ORL are inhomogeneously distributed and display reaction boundaries with the groundmass. Major silicates, olivine Fa(20-28) and orthopyroxyene Fs(20-28 Wo(0.5-2.5), display systematic differences in composition between CGL and ORL as well as a complicated pattern of variations within CGL. Accessory plagioclase has low K content and displays regular igneous zoning with core compositions An(40-45) and rims An(32-37). The bulk chemical composition of Divnoe is similar to that of olivine-rich primitive achondrites, except for a depletion of incompatible elements and minor enrichment of refractory siderophiles. Oxygen isotope compositions for whole-rock and separated minerals from Divnoe fall in a narrow range, with mean delta O-18 = +4.91, delta O-17 = +2.24, and Delta O-17 = -0.26 +/- 0.11. The isotopic composition is not within the range of any previously recognized group but is very close to that of the brachinites. To understand the origin of Divnoe lithologies, partial melting and crystallization were modelled using starting compositions equal to that of Divnoe and some chondritic meteorites. It was found that the Divnoe composition could be derived from a chondritic source region by approximately 20 wt% partial melting at Ta approximately 1300 C and log(fO2) = IW-1.8, followed by approximtely 60 wt% crystallization of the partial melt formed, and removal of the still-liquid portion of the partial melt. Removal of the last partial melt resulted in depletion of the Divnoe plagioclase in Na and K. In this scenario, CGL represents the residue of partial melting, and PP is a portion of the partial melt that crystallized in situ. The

  5. Carbon and Oxygen Isotopic Ratios for Nearby Miras

    NASA Astrophysics Data System (ADS)

    Hinkle, Kenneth H.; Lebzelter, Thomas; Straniero, Oscar

    2016-07-01

    Carbon and oxygen isotopic ratios are reported for a sample of 46 Mira and SRa-type variable asymptotic giant branch (AGB) stars. Vibration–rotation first and second-overtone CO lines in 1.5–2.5 μm spectra were measured to derive isotopic ratios for 12C/13C, 16O/17O, and 16O/18O. Comparisons with previous measurements for individual stars and with various samples of evolved stars, as available in the extant literature, are discussed. Models for solar composition AGB stars of different initial masses are used to interpret our results. We find that the majority of M-stars have main sequence masses ≤2 M ⊙ and have not experienced sizable third dredge-up (TDU) episodes. The progenitors of the four S-type stars in our sample are slightly more massive. Of the six C-stars in the sample three have clear evidence relating their origin to the occurrence of TDU. Comparisons with O-rich presolar grains from AGB stars that lived before the formation of the solar system reveal variations in the interstellar medium chemical composition. The present generation of low-mass AGB stars, as represented by our sample of long period variables (LPVs), shows a large spread of 16O/17O ratios, similar to that of group 1 presolar grains and in agreement with theoretical expectations for the composition of mass 1.2–2 M ⊙ stars after the first dredge-up. In contrast, the 16O/18O ratios of present-day LPVs are definitely smaller than those of group 1 grains. This is most probably a consequence of the the decrease with time of the 16O/18O ratio in the interstellar medium due to the chemical evolution of the Milky Way. One star in our sample has an O composition similar to that of group 2 presolar grains originating in an AGB star undergoing extra-mixing. This may indicate that the extra-mixing process is hampered at high metallicity, or, equivalently, favored at low metallicity. Similarly to O-rich grains, no star in our sample shows evidence of hot bottom burning, which is expected

  6. Oxygen and hydrogen isotope ratios in tree rings: how well do models predict observed values?

    NASA Astrophysics Data System (ADS)

    Waterhouse, J. S.; Switsur, V. R.; Barker, A. C.; Carter, A. H. C.; Robertson, I.

    2002-07-01

    We have measured annual oxygen and hydrogen isotope ratios in the α-cellulose of the latewood of oak ( Quercus robur L.) growing on well-drained ground in Norfolk, UK. We compare the observed values of isotope ratios with those calculated using equations that allow for isotopic fractionation during the transfer of oxygen and hydrogen from source water taken by the tree to cellulose laid down in the cambium. The equations constitute a model in which isotopic fractionation occurs during evaporative enrichment within the leaf and during isotopic change between carbohydrates and water in the trunk during cellulose synthesis. From the relationship between isotope ratios in precipitation and α-cellulose, we deduce that the source water used by the tree comprises a constant mixture of groundwater and precipitation, chiefly from the months of May, June and July of the growth year. By selection of isotopic fractionation factors and the degree of isotope exchange within the trunk, we are able to model the observed annual values of oxygen isotope ratios of α-cellulose to a significant level ( r=0.77, P<0.01). When we apply the same model to hydrogen isotope ratios, however, we find that, although we can predict the average value over the time series, we can no longer predict the year-to-year variation. We suggest that this loss of environmental signal in the hydrogen isotopes is caused by differences in the kinetic isotope effects of the biochemical reactions involved in the fixation of hydrogen in different positions of the glucose molecule. Owing to these effects, the hydrogen isotope ratios of cellulose can vary in a way not anticipated in current models and hence may induce non-climatic 'noise' in the hydrogen isotope time series.

  7. Carbon, Hydrogen, and Oxygen Isotope Ratios of Cellulose from Plants Having Intermediary Photosynthetic Modes 1

    PubMed Central

    Sternberg, Leonel O'Reilly; Deniro, Michael J.; Ting, Irwin P.

    1984-01-01

    Carbon and hydrogen isotope ratios of cellulose nitrate and oxygen isotope ratios of cellulose from species of greenhouse plants having different photosynthetic modes were determined. When hydrogen isotope ratios are plotted against carbon isotope ratios, four clusters of points are discernible, each representing different photosynthetic modes: C3 plants, C4 plants, CAM plants, and C3 plants that can shift to CAM or show the phenomenon referred to as CAM-cycling. The combination of oxygen and carbon isotope ratios does not distinguish among the different photosynthetic modes. Analysis of the carbon and hydrogen isotope ratios of cellulose nitrate should prove useful for screening different photosynthetic modes in field specimens that grew near one another. This method will be particularly useful for detection of plants which show CAM-cycling. PMID:16663360

  8. Oxygen isotopes as a tracer of phosphate sources and cycling in aquatic systems (Invited)

    NASA Astrophysics Data System (ADS)

    Young, M. B.; Kendall, C.; Paytan, A.

    2013-12-01

    The oxygen isotopic composition of phosphate can provide valuable information about sources and processes affecting phosphorus as it moves through hydrologic systems. Applications of this technique in soil and water have become more common in recent years due to improvements in extraction methods and instrument capabilities, and studies in multiple aquatic environments have demonstrated that some phosphorus sources may have distinct isotopic compositions within a given system. Under normal environmental conditions, the oxygen-phosphorus bonds in dissolved inorganic phosphate (DIP) can only be broken by enzymatic activity. Biological cycling of DIP will bring the phosphate oxygen into a temperature-dependent equilibrium with the surrounding water, overprinting any existing isotopic source signals. However, studies conducted in a wide range of estuarine, freshwater, and groundwater systems have found that the phosphate oxygen is often out of biological equilibrium with the water, suggesting that it is common for at least a partial isotopic source signal to be retained in aquatic systems. Oxygen isotope analysis on various potential phosphate sources such as synthetic and organic fertilizers, animal waste, detergents, and septic/wastewater treatment plant effluents show that these sources span a wide range of isotopic compositions, and although there is considerable overlap between the source groups, sources may be isotopically distinct within a given study area. Recent soil studies have shown that isotopic analysis of phosphate oxygen is also useful for understanding microbial cycling across different phosphorus pools, and may provide insights into controls on phosphorus leaching. Combining stable isotope information from soil and water studies will greatly improve our understanding of complex phosphate cycling, and the increasing use of this isotopic technique across different environments will provide new information regarding anthropogenic phosphate inputs and

  9. Oxygen and sulfur isotope fractionation during sulfide oxidation by anoxygenic phototrophic bacteria

    NASA Astrophysics Data System (ADS)

    Brabec, Michelle Y.; Lyons, Timothy W.; Mandernack, Kevin W.

    2012-04-01

    Sulfide-mediated anoxygenic photosynthesis (SMAP) carried out by anaerobic phototrophic bacteria may have played an important role in sulfur cycling, formation of sulfate, and, perhaps, primary production in the Earth’s early oceans. Determination of ε34SSO4-Sulfide- and ε18OSO4-H2O values for bacterial sulfide oxidation will permit more refined interpretation of the δ34S and δ18OSO4 values measured in modern anoxic environments, such as meromictic lakes where sulfide commonly extends into the photic zone, and in the ancient rock record, particularly during periods of the Precambrian when anoxic and sulfidic (euxinic) conditions were believed to be more pervasive than today. Laboratory experiments with anaerobic purple and green sulfur phototrophs, Allochromatium vinosum and Chlorobaculum tepidum, respectively, were conducted to determine the sulfur and oxygen isotope fractionation during the oxidation of sulfide to sulfate. Replicate experiments were conducted at 25 °C for A. vinosum and 45 °C for C. tepidum, and in duplicate at three different starting oxygen isotope values for water to determine sulfate-water oxygen isotope fractionations accurately (ε18OSO4-H2O). ε18OSO4-H2O values of 5.6 ± 0.2‰ and 5.4 ± 0.1‰ were obtained for A. vinosum and C. tepidum, respectively. Temperature had no apparent effect on the ε18OSO4-H2O values. By combining all data from both cultures, an average ε18OSO4-H2O value of 5.6 ± 0.3‰ was obtained for SMAP. This value falls between those previously reported for bacterial oxidation of sphalerite and elemental sulfur (7-9‰) and abiotic and biotic oxidation of pyrite and chalcopyrite (2-4‰). Sulfur isotope fractionation between sulfide and sulfate formed by A.vinosum was negligible (0.1 ± 0.2‰) during all experiments. For C. tepidum an apparent fractionation of -2.3 ± 0.5‰ was observed during the earlier stages of oxidation based on bulk δ34S measurements of sulfate and sulfide and became smaller (-0.7

  10. Oxygen isotope mass balance of atmospheric nitrate at Dome C, East Antarctica, during the OPALE campaign

    NASA Astrophysics Data System (ADS)

    Savarino, J.; Vicars, W. C.; Legrand, M.; Preunkert, S.; Jourdain, B.; Frey, M. M.; Kukui, A.; Caillon, N.; Gil Roca, J.

    2015-09-01

    Variations in the stable oxygen isotope composition of atmospheric nitrate act as novel tools for studying oxidative processes taking place in the troposphere. They provide both qualitative and quantitative constraints on the pathways determining the fate of atmospheric nitrogen oxides (NO + NO2 = NOx). The unique and distinctive 17O-excess (Δ17O = δ17O - 0.52 × δ18O) of ozone, which is transferred to NOx via oxidation, is a particularly useful isotopic fingerprint in studies of NOx transformations. Constraining the propagation of 17O-excess within the NOx cycle is critical in polar areas where there exists the possibility of extending atmospheric investigations to the glacial/interglacial time scale using deep ice core records of nitrate. Here we present measurements of the comprehensive isotopic composition of atmospheric nitrate collected at Dome C (East Antarctic plateau) during the austral summer of 2011/12. Nitrate isotope analysis has been here combined for the first time with key precursors involved in nitrate production (NOx, O3, OH, HO2, RO2, etc.) and direct observations of the transferrable Δ17O of surface ozone, which was measured at Dome C throughout 2012 using our recently developed analytical approach. Assuming that nitrate is mainly produced in Antarctica in summer through the OH + NO2 pathway and using concurrent measurements of OH and NO2, we calculated a Δ17O signature for nitrate in the order of (21-22 ± 3) ‰. These values are lower than the measured values that ranged between 27 and 31 ‰. This discrepancy between expected and observed Δ17O(NO3-) values suggests the existence of an unknown process that contributes significantly to the atmospheric nitrate budget over this east Antarctic region.

  11. Herbivore tooth oxygen isotope compositions: Effects of diet and physiology

    SciTech Connect

    Kohn, M.J.; Valley, J.W.; Schoeninger, M.J.

    1996-10-01

    The applicability of rapid and precise laser probe analysis of tooth enamel for {delta}{sup 18}O has been verified, and the method has been applied to different modern herbivores in East Africa. Sampling and pretreatment procedures involve initial bleaching and grinding of enamel to <75 {mu}m, and elimination of adsorbed water and organic compounds with BrF{sub 5}. Typical analytical reproducibilities for 0.5-2 mg samples are {+-}0.08{per_thousand} ({+-} 1{sigma}). Chemical and spectroscopic characterization of pretreated but unanalyzed samples show no alteration compared to fresh enamel. Solid reaction products are nearly pure CaF{sub 2} with little evidence for residual O{sub 2}. Because laser probe fluorination extracts oxygen from all sites in the apatite structure (phosphate, structural carbonate, and hydroxyl), only unaltered tooth enamel ( >95% apatite) can be analyzed reliably. Different East African herbivores exhibit previously unsuspected compositional differences. Average enamel {delta}{sup 18}O values (V-SMOW) are approximately: 25{per_thousand} (goat). 27{per_thousand} (oryx), 28{per_thousand} (dikdik and zebra), 29{per_thousand} (topi), 30{per_thousand} (gerenuk), and 32{per_thousand} (gazelle). These compositions differ from generalized theoretical models, but are broadly consistent with expected isotope effects associated with differences in how much each animal (a) drinks, (b) eats C3 vs. C4 plants, and (c) pants vs. sweats. Consideration of diet, water turnover. and animal physiology will allow the most accurate interpretation of ancient teeth and targeting of environmentally-sensitive animals in paleoclimate studies. 66 refs., 2 figs., 2 tabs.

  12. Soil phosphate stable oxygen isotopes across rainfall and bedrock gradients.

    PubMed

    Angert, Alon; Weiner, Tal; Mazeh, Shunit; Sternberg, Marcelo

    2012-02-21

    The stable oxygen isotope compositions of soil phosphate (δ(18)O(p)) were suggested recently to be a tracer of phosphorus cycling in soils and plants. Here we present a survey of bioavailable (resin-extractable or resin-P) inorganic phosphate δ(18)O(p) across natural and experimental rainfall gradients, and across soil formed on sedimentary and igneous bedrock. In addition, we analyzed the soil HCl-extractable inorganic δ(18)O(p), which mainly represents calcium-bound inorganic phosphate. The resin-P values were in the range 14.5-21.2‰. A similar range, 15.6-21.3‰, was found for the HCl-extractable inorganic δ(18)O(p), with the exception of samples from a soil of igneous origin that show lower values, 8.2-10.9‰, which indicate that a large fraction of the inorganic phosphate in this soil is still in the form of a primary mineral. The available-P δ(18)O(p) values are considerably higher than the values we calculated for extracellular hydrolysis of organic phosphate, based on the known fractionation from lab experiments. However, these values are close to the values expected for enzymatic-mediated phosphate equilibration with soil-water. The possible processes that can explain this observation are (1) extracellular equilibration of the inorganic phosphate in the soil; (2) fractionations in the soil are different than the ones measured at the lab; (3) effect of fractionation during uptake; and (4) a flux of intercellular-equilibrated inorganic phosphate from the soil microbiota, which is considerably larger than the flux of hydrolyzed organic-P.

  13. An oxygen isotope study of Wark-Lovering rims on type A CAIs in primitive carbonaceous chondrites

    NASA Astrophysics Data System (ADS)

    Bodénan, Jean-David; Starkey, Natalie A.; Russell, Sara S.; Wright, Ian P.; Franchi, Ian A.

    2014-09-01

    Calcium-aluminium-rich Inclusions (CAIs) and the thin Wark-Lovering (WL) rims of minerals surrounding them offer a record of the nature of changing conditions during the earliest stages of Solar System formation. Considerable heterogeneity in the gas composition in the immediate vicinity of the proto-Sun had previously been inferred from oxygen isotopic variations in the WL rim of a CAI from Allende (Simon et al., 2011). However, high precision and high spatial resolution oxygen isotope measurements presented in this study show that WL rim and pristine core minerals of individual CAIs from meteorites that had experienced only low degrees of alteration or low grade metamorphism (one from Léoville (reduced CV3), two in QUE 99177 (CR3.0) and two in ALHA 77307 (CO3.0)) are uniformly 16O-rich. This indicates that the previously observed variations are the result of secondary processes, most likely on the asteroid parent body, and that there were no temporal or spatial variations in oxygen isotopic composition during CAI and WL rim formation. Such homogeneity across three groups of carbonaceous chondrites lends further support for a common origin for the CAIs in all chondrites. 16O-poor oxygen reservoirs such as those associated with chondrule formation, were probably generated by UV photo-dissociation involving self-shielding mechanisms and must have occurred elsewhere in outer regions of the solar accretion disk.

  14. Contrasting behavior of oxygen and iron isotopes in banded iron formation revealed by in situ analysis

    NASA Astrophysics Data System (ADS)

    Beard, B.; Li, W.; Kita, N.; Valley, J. W.; Johnson, C.

    2012-12-01

    Banded iron formations (BIFs) record a period of dramatic secular change in Earth's geologic history, when abundant aqueous Fe(II) was removed from Archean and Proterozoic oceans by oxidation. BIFs are characterized by co-existing of quartz and iron minerals, including oxides and carbonates, and alternating iron-rich and iron-poor layers range from m to isotope ratios in minerals in BIFs provide valuable information about the origin of BIFs, as well as diagenetic and metamorphic effects that were superimposed on primary layering. We analyzed O and Fe isotope compositions of magnetite and hematite in BIFs from the 2.5 Ga Dales Gorge Member of the Brockman Iron Formation, Hamersley Group, Western Australia. Oxygen isotope ratios were measured by Secondary Ion Mass Spectrometry (SIMS), and Fe isotope ratios were measured by femtosecond Laser ablation Multi-Collector ICP-MS (fs-LA-MC-ICP-MS), with spatial resolutions of 15 mm (O) and 30-50 mm (Fe), and external precisions (2s) of +0.7 ‰ for δ18O and +0.2 ‰ for δ56Fe, respectively. Analysis of δ18O in iron oxides by SIMS employed special tuning with a 3kV primary beam to minimize orientation effects (Huberty et al. 2010 ). For hematite, δ18O values range from -7.1 ‰ to -0.6 ‰, with the majority of data clustering around -4.5 ‰, and δ56Fe values range from -0.50 ‰ to +1.53‰. Magnetite has a δ18O range of -5.6 ‰ to +5.6 ‰ and a δ56Fe range of -0.76 ‰ to +1.33 ‰. Notably, magnetite shows significant O isotope heterogeneity at a mineral grain scale, and the highest δ18O values were commonly measured from Si-rich (1-3 wt% SiO2) magnetite overgrowths or magnetite grains that have a recrystallization texture. In contrast, lowest δ18O values were measured from magnetite that contains less than 1 wt% SiO2. Individual magnetite grains can have up to 6 ‰ variation in δ18O values between low-Si core and Si-rich overgrowth. Iron

  15. Oxygen Isotope Mass-Balance Constraints on Pliocene Sea Level and East Antarctic Ice Sheet Stability

    NASA Astrophysics Data System (ADS)

    Winnick, M. J.; Caves, J. K.

    2015-12-01

    The mid-Pliocene Warm Period (MPWP, 3.3-2.9 Ma), with reconstructed atmospheric pCO2 of 350-450 ppm, represents a potential analogue for climate change in the near future. Current highly cited estimates place MPWP maximum global mean sea level (GMSL) at 21 ± 10 m above modern, requiring total loss of the Greenland (GIS) and marine West Antarctic Ice Sheets (WAIS) and a substantial loss of the East Antarctic Ice Sheet (EAIS), with only a concurrent 2-3 ºC rise in global temperature. Many estimates of Pliocene GMSL are based on the partitioning of oxygen isotope records from benthic foraminifera (δ18Ob) into changes in deep-sea temperatures and terrestrial ice sheets. These isotopic budgets are underpinned by the assumption that the δ18O of Antarctic ice (δ18Oi) was the same in the Pliocene as it is today, and while the sensitivity of δ18Ob to changing meltwater δ18O has been previously considered, these analyses neglect conservation of 18O/16O in the ocean-ice system. Using well-calibrated δ18O-temperature relationships for Antarctic precipitation along with estimates of Pliocene Antarctic surface temperatures, we argue that the δ18Oi of the Pliocene Antarctic ice sheet was at minimum 1‰-4‰ higher than present. Assuming conservation of 18O/16O in the ocean-ice system, this requires lower Pliocene seawater δ18O (δ18Osw) without a corresponding change in ice sheet mass. This effect alone accounts for 5%-20% of the δ18Ob difference between the MPWP interglacials and the modern. With this amended isotope budget, we suggest that Pliocene GMSL was likely 9-13.5 m and very likely 5-17 m above modern, which suggests the EAIS is less sensitive to radiative forcing than previously inferred from the geologic record.

  16. Spatial and Temporal Trends in Stable Carbon and Oxygen Isotope Ratios of Juvenile Winter Flounder

    EPA Science Inventory

    Isotopic ratios of fish otoliths have been used in numerous studies as natural tags or markers to aid the study of connectivity among fish populations. We investigated the use of spatial and temporal changes in the stable carbon and oxygen isotope ratios of otoliths to different...

  17. Carbon and oxygen isotopes in apatite CO/sub 2/ and co-existing calcite

    SciTech Connect

    Kolodny, Y.; Kaplan, I. R.

    1981-04-01

    Carbon and oxygen isotopes were analyzed in carbonate apatite CO/sub 2/ and in co-existing calcite. Both C and O in apatite CO/sub 2/ are enriched in the respective light isotopes relative to calcite. These results confirm the proposition that carbonate is part of the apatite structure.

  18. Oxygen Isotope in Phosphate an Indicator of Phosphorous Cycling in the Ocean - Controls, and Applications

    NASA Astrophysics Data System (ADS)

    Paytan, A.; Roberts, K.; Defforey, D.; McLaughlin, K.; Lomas, M. W.; Church, M. J.; Mackey, K. R.

    2012-12-01

    In order to better constrain the parameters affecting oxygen isotope exchange between water and phosphate via biochemical reactions a set of culture experiments were conducted. Different species of phytoplankton were grown in seawater at various temperatures, light levels, and phosphate concentrations. The oxygen isotopic composition in the phosphate source, algal cells, and the isotopic composition oxygen in the dissolved inorganic phosphate (DIP) were measured. Results showing the effect of species, temperature, light and P availability on intracellular oxygen isotope exchange between phosphorus compounds and water will be presented. The effect of these parameters on the utility of the oxygen isotopic composition of phosphate as a tracer of phosphate utilization rate in the ocean will be discussed. This information is fundamental to any application of isotopic composition of oxygen of dissolved inorganic or organic phosphate to quantify the dynamics of phosphorus cycling in aquatic systems. The data will be utilized to investigate seasonal changes in phosphate sources and cycling in the open ocean and how these relate to phytoplankton abundance, hydrography, and nutrient concentrations.

  19. Forward Modeling of Carbonate Proxy Data from Planktonic Foraminifera using Oxygen Isotope Tracers in a Global Ocean Model

    NASA Technical Reports Server (NTRS)

    Schmidt, Gavin A.

    1999-01-01

    The distribution and variation of oxygen isotopes in seawater are calculated using the Goddard Institute for Space Studies global ocean model. Simple ecological models are used to estimate the planktonic foraminiferal abundance as a function of depth, column temperature, season, light intensity, and density stratification. These models are combined to forward model isotopic signals recorded in calcareous ocean sediment. The sensitivity of the results to the changes in foraminiferal ecology, secondary calcification, and dissolution are also examined. Simulated present-day isotopic values for ecology relevant for multiple species compare well with core-top data. Hindcasts of sea surface temperature and salinity are made from time series of the modeled carbonate isotope values as the model climate changes. Paleoclimatic inferences from these carbonate isotope records are strongly affected by erroneous assumptions concerning the covariations of temperature, salinity, and delta (sup 18)O(sub w). Habitat-imposed biases are less important, although errors due to temperature-dependent abundances can be significant.

  20. Short-Term Coral Bleaching Is Not Recorded by Skeletal Boron Isotopes

    PubMed Central

    Schoepf, Verena; McCulloch, Malcolm T.; Warner, Mark E.; Levas, Stephen J.; Matsui, Yohei; Aschaffenburg, Matthew D.; Grottoli, Andréa G.

    2014-01-01

    Coral skeletal boron isotopes have been established as a proxy for seawater pH, yet it remains unclear if and how this proxy is affected by seawater temperature. Specifically, it has never been directly tested whether coral bleaching caused by high water temperatures influences coral boron isotopes. Here we report the results from a controlled bleaching experiment conducted on the Caribbean corals Porites divaricata, Porites astreoides, and Orbicella faveolata. Stable boron (δ11B), carbon (δ13C), oxygen (δ18O) isotopes, Sr/Ca, Mg/Ca, U/Ca, and Ba/Ca ratios, as well as chlorophyll a concentrations and calcification rates were measured on coral skeletal material corresponding to the period during and immediately after the elevated temperature treatment and again after 6 weeks of recovery on the reef. We show that under these conditions, coral bleaching did not affect the boron isotopic signature in any coral species tested, despite significant changes in coral physiology. This contradicts published findings from coral cores, where significant decreases in boron isotopes were interpreted as corresponding to times of known mass bleaching events. In contrast, δ13C and δ18O exhibited major enrichment corresponding to decreases in calcification rates associated with bleaching. Sr/Ca of bleached corals did not consistently record the 1.2°C difference in seawater temperature during the bleaching treatment, or alternatively show a consistent increase due to impaired photosynthesis and calcification. Mg/Ca, U/Ca, and Ba/Ca were affected by coral bleaching in some of the coral species, but the observed patterns could not be satisfactorily explained by temperature dependence or changes in coral physiology. This demonstrates that coral boron isotopes do not record short-term bleaching events, and therefore cannot be used as a proxy for past bleaching events. The robustness of coral boron isotopes to changes in coral physiology, however, suggests that reconstruction of

  1. Short-term coral bleaching is not recorded by skeletal boron isotopes.

    PubMed

    Schoepf, Verena; McCulloch, Malcolm T; Warner, Mark E; Levas, Stephen J; Matsui, Yohei; Aschaffenburg, Matthew D; Grottoli, Andréa G

    2014-01-01

    Coral skeletal boron isotopes have been established as a proxy for seawater pH, yet it remains unclear if and how this proxy is affected by seawater temperature. Specifically, it has never been directly tested whether coral bleaching caused by high water temperatures influences coral boron isotopes. Here we report the results from a controlled bleaching experiment conducted on the Caribbean corals Porites divaricata, Porites astreoides, and Orbicella faveolata. Stable boron (δ11B), carbon (δ13C), oxygen (δ18O) isotopes, Sr/Ca, Mg/Ca, U/Ca, and Ba/Ca ratios, as well as chlorophyll a concentrations and calcification rates were measured on coral skeletal material corresponding to the period during and immediately after the elevated temperature treatment and again after 6 weeks of recovery on the reef. We show that under these conditions, coral bleaching did not affect the boron isotopic signature in any coral species tested, despite significant changes in coral physiology. This contradicts published findings from coral cores, where significant decreases in boron isotopes were interpreted as corresponding to times of known mass bleaching events. In contrast, δ13C and δ18O exhibited major enrichment corresponding to decreases in calcification rates associated with bleaching. Sr/Ca of bleached corals did not consistently record the 1.2°C difference in seawater temperature during the bleaching treatment, or alternatively show a consistent increase due to impaired photosynthesis and calcification. Mg/Ca, U/Ca, and Ba/Ca were affected by coral bleaching in some of the coral species, but the observed patterns could not be satisfactorily explained by temperature dependence or changes in coral physiology. This demonstrates that coral boron isotopes do not record short-term bleaching events, and therefore cannot be used as a proxy for past bleaching events. The robustness of coral boron isotopes to changes in coral physiology, however, suggests that reconstruction of

  2. Oxygen isotope fractionation during N2O production by soil denitrification

    NASA Astrophysics Data System (ADS)

    Lewicka-Szczebak, Dominika; Dyckmans, Jens; Kaiser, Jan; Marca, Alina; Augustin, Jürgen; Well, Reinhard

    2016-02-01

    The isotopic composition of soil-derived N2O can help differentiate between N2O production pathways and estimate the fraction of N2O reduced to N2. Until now, δ18O of N2O has been rarely used in the interpretation of N2O isotopic signatures because of the rather complex oxygen isotope fractionations during N2O production by denitrification. The latter process involves nitrate reduction mediated through the following three enzymes: nitrate reductase (NAR), nitrite reductase (NIR) and nitric oxide reductase (NOR). Each step removes one oxygen atom as water (H2O), which gives rise to a branching isotope effect. Moreover, denitrification intermediates may partially or fully exchange oxygen isotopes with ambient water, which is associated with an exchange isotope effect. The main objective of this study was to decipher the mechanism of oxygen isotope fractionation during N2O production by soil denitrification and, in particular, to investigate the relationship between the extent of oxygen isotope exchange with soil water and the δ18O values of the produced N2O. In our soil incubation experiments Δ17O isotope tracing was applied for the first time to simultaneously determine the extent of oxygen isotope exchange and any associated oxygen isotope effect. We found that N2O formation in static anoxic incubation experiments was typically associated with oxygen isotope exchange close to 100 % and a stable difference between the 18O / 16O ratio of soil water and the N2O product of δ18O(N2O / H2O) = (17.5 ± 1.2) ‰. However, flow-through experiments gave lower oxygen isotope exchange down to 56 % and a higher δ18O(N2O / H2O) of up to 37 ‰. The extent of isotope exchange and δ18O(N2O / H2O) showed a significant correlation (R2 = 0.70, p < 0.00001). We hypothesize that this observation was due to the contribution of N2O from another production process, most probably fungal denitrification. An oxygen isotope fractionation model was used to test various scenarios with

  3. Stable Carbon Isotope Record in a Palau Sclerosponge

    NASA Astrophysics Data System (ADS)

    Grottoli, A. G.

    2002-12-01

    The ratio of stable carbon isotopes (δ13C) deposited in the calcium carbonate skeleton of marine sclerosponges appears to record the carbon isotopic composition of seawater mixed-layer dissolved inorganic carbon (δ13CDIC). Thus the δ13C signature chronicled in sclerosponge skeletons offers a promising multi-century proxy record of seawater mixed-layer δ13CDIC throughout the tropics. Here, a high-resolution (0.1 mm) δ13C record for a 7.7 cm Acanthocheatetes wellsi sclerosponge from Palau (7N, 134W) is presented. At a published growth rate of 0.45 mm per year, this record spans ~s170 years beginning in July 2001 and going back to 1831. The δ13C values for a definitive 10-year A. wellsi record spanning 1989-1998 were similar to δ13C values here for the first 4.7 mm of the record providing supporting evidence for the growth rate. The sclerosponge δ13C shows a distinct Seuss Effect. At the time this abstract was submitted, the analysis of the first 16 mm of the sclerosponge revealed a significant decrease in δ13C with time [δ13C = 0.02 (distance) + 2.64, r2 = 0.73, p < 0.0001, where time is marked by distance in millimeters from the growing edge] corresponding to a decrease in δ13C of 0.076‰ per decade. For comparison, published low-frequency measurements in Australian, New Caledonian and Jamaican sclerosponges have yielded decreases in δ13C of ~s0.05 to 0.08 ‰ per decade over the past 40 years. Preliminary interpretation of the data indicates that the amount of atmospheric CO2 contributing to the seawater δ13CDIC at Palau is intermediate to Australia and Jamaica. In addition, visual examination of the δ13C record reveals regular fluctuation in δ13C that may correspond to annual variability in δ13CDIC. This research presents the first century or longer sclerosponge δ13C record from the northwester equatorial Pacific.

  4. Oxygen isotopes in tree rings show good coherence between species and sites in Bolivia

    NASA Astrophysics Data System (ADS)

    Baker, Jessica C. A.; Hunt, Sarah F. P.; Clerici, Santiago J.; Newton, Robert J.; Bottrell, Simon H.; Leng, Melanie J.; Heaton, Timothy H. E.; Helle, Gerhard; Argollo, Jaime; Gloor, Manuel; Brienen, Roel J. W.

    2015-10-01

    A tree ring oxygen isotope (δ18OTR) chronology developed from one species (Cedrela odorata) growing in a single site has been shown to be a sensitive proxy for rainfall over the Amazon Basin, thus allowing reconstructions of precipitation in a region where meteorological records are short and scarce. Although these results suggest that there should be large-scale (> 100 km) spatial coherence of δ18OTR records in the Amazon, this has not been tested. Furthermore, it is of interest to investigate whether other, possibly longer-lived, species similarly record interannual variation of Amazon precipitation, and can be used to develop climate sensitive isotope chronologies. In this study, we measured δ18O in tree rings from seven lowland and one highland tree species from Bolivia. We found that cross-dating with δ18OTR gave more accurate tree ring dates than using ring width. Our "isotope cross-dating approach" is confirmed with radiocarbon "bomb-peak" dates, and has the potential to greatly facilitate development of δ18OTR records in the tropics, identify dating errors, and check annual ring formation in tropical trees. Six of the seven lowland species correlated significantly with C. odorata, showing that variation in δ18OTR has a coherent imprint across very different species, most likely arising from a dominant influence of source water δ18O on δ18OTR. In addition we show that δ18OTR series cohere over large distances, within and between species. Comparison of two C. odorata δ18OTR chronologies from sites several hundreds of kilometres apart showed a very strong correlation (r = 0.80, p < 0.001, 1901-2001), and a significant (but weaker) relationship was found between lowland C. odorata trees and a Polylepis tarapacana tree growing in the distant Altiplano (r = 0.39, p < 0.01, 1931-2001). This large-scale coherence of δ18OTR records is probably triggered by a strong spatial coherence in precipitation δ18O due to large-scale controls. These results

  5. Molybdenum isotope records as a potential new proxy for paleoceanography

    NASA Astrophysics Data System (ADS)

    Siebert, Christopher; Nägler, Thomas F.; von Blanckenburg, Friedhelm; Kramers, Jan D.

    2003-06-01

    New high-precision isotope ratios of dissolved Mo in seawater from different ocean basins and depths show a homogeneous isotope composition ('mean ocean water 98Mo/ 95Mo' (MOMO)), as expected from its long ocean residence time (800 kyr). This composition appears to have been constant for the past 60 Myr at a 1-3 Myr time resolution as indicated from thick sections of Fe-Mn crusts from the Atlantic and Pacific. These records yield a constant offset from MOMO (average of -3.1 and -2.9‰). They are similar to our new data on recent oxic Mo sinks: pelagic sediments and six Fe-Mn crust surface layers range from -2.7 to -2.9‰ and -2.7 to -3.1‰, respectively. Recent suboxic Mo sinks from open ocean basins display heavier and more variable isotope ratios (-0.7 to -1.6‰ relative to MOMO). Crustal Mo sources were characterized by measuring two granites (and a mild acid leach of one granite), seven volcanic rocks and two clastic sediments. All show a narrow range of compositions (-2.0 to -2.3‰). These data indicate that isotope fractionation by chemical weathering and magmatic processes is insignificant on a global scale. They therefore represent good estimates of the composition of dissolved Mo input to the oceans and that of the average continental crust. Thus, the Mo input into the oceans appears to be distributed into lighter oxic sinks and heavier reducing sinks. This is consistent with steady-state conditions in the modern ocean. The constant isotope offset between oxic sediments and seawater suggests that the relative amounts of oxic and reducing Mo removal fluxes have not varied by more than 10% over the last 60 Myr. An equilibrium fractionation process is proposed assuming that Mo isotope fractionation occurs between (dominant) MoO 42- and (minor) Mo(OH) 6 species in solution, of which the latter is preferentially scavenged.

  6. Oxygen isotope effects as probes of electron transfer mechanisms and structures of activated O2.

    PubMed

    Roth, Justine P

    2009-03-17

    Competitively determined oxygen ((18)O) isotope effects can be powerful probes of chemical and biological transformations involving molecular oxygen as well as superoxide and hydrogen peroxide. They play a complementary role to crystallography and spectroscopy in the study of activated oxygen intermediates by forging a link between electronic/vibrational structure and the bonding that occurs within ground and transition states along the reaction coordinate. Such analyses can be used to assess the plausibility of intermediates and their catalytic relevance in oxidative processes. This Account describes efforts to advance oxygen kinetic isotope effects ((18)O KIEs) and equilibrium isotope effects ((18)O EIEs) as mechanistic probes of reactive, oxygen-derived species. We focus primarily on transition metal mediated oxidations, outlining both advances over the past five years and current limitations of this approach. Computational methods are now being developed to probe transition states and the accompanying kinetic isotope effects. In particular, we describe the importance of using a full-frequency model to accurately predict the magnitudes as well as the temperature dependence of the isotope effects. Earlier studies have used a "cut-off model," which employs only a few isotopic vibrational modes, and such models tend to overestimate (18)O EIEs. Researchers in mechanistic biological inorganic chemistry would like to differentiate "inner-sphere" from "outer-sphere" reactivity of O(2), a designation that describes the extent of the bonding interaction between metal and oxygen in the transition state. Though this problem remains unsolved, we expect that this isotopic approach will help differentiate these processes. For example, comparisons of (18)O KIEs to (18)O EIEs provide benchmarks that allow us to calibrate computationally derived reaction coordinates. Once the physical origins of heavy atom isotope effects are better understood, researchers will be able to apply

  7. Oxygen isotopic abundances in calcium- aluminum-rich inclusions from ordinary chondrites: implications for nebular heterogeneity.

    PubMed

    McKeegan, K D; Leshin, L A; Russell, S S; MacPherson, G J

    1998-04-17

    The oxygen isotopic compositions of two calcium-aluminum-rich inclusions (CAIs) from the unequilibrated ordinary chondrite meteorites Quinyambie and Semarkona are enriched in 16O by an amount similar to that in CAIs from carbonaceous chondrites. This may indicate that most CAIs formed in a restricted region of the solar nebula and were then unevenly distributed throughout the various chondrite accretion regions. The Semarkona CAI is isotopically homogeneous and contains highly 16O-enriched melilite, supporting the hypothesis that all CAI minerals were originally 16O-rich, but that in most carbonaceous chondrite inclusions some minerals exchanged oxygen isotopes with an external reservoir following crystallization.

  8. Paleoclimatic Study of the West Pacific Warm Pool using Oxygen Isotope Variations in a Stalagmite from Guam

    NASA Astrophysics Data System (ADS)

    Moore, M. W.; Hardt, B. F.; Partin, J. W.; Banner, J. L.; Jenson, J. W.; Sinclair, D. J.; Taylor, F.

    2011-12-01

    The West Pacific Warm Pool (WPWP) is a region of the Pacific with mean seasonal sea surface temperatures > 28°C, and is a major driver of global climate. While the past ˜150 years have been instrumented and conditions have been recorded, it is unclear how much of the changes observed are due to anthropogenic effects or natural variability. In addition, this time frame may not include events that are natural but infrequent. This study investigates climate of the WPWP using oxygen isotope variations in speleothem calcite as a proxy for changes in rainfall on the island of Guam. The temperature effect on oxygen isotope ratios is relatively small in the tropics when compared to the effects of rainfall at Guam, and speleothem oxygen isotope ratios are more likely to vary in response to changes in storm tracks or rainfall amount. Previous research in the area has shown a correlation (r2 of .57) between rainfall amount and stable isotopic composition. The speleothem sample "Stumpy" being used for this study was collected in 2005 from Jinapsan Cave on Guam (13° 38' N, 144° 53' E), where annual rainfall is connected to the state of the WPWP. Samples were milled at 1 millimeter resolution, representing an average resolution of 50 years per sample. U-series analyses show that the 33-cm-long Stumpy grew from ˜18,000 ka up to present day. Oxygen isotope values range from -9.4 to -4.5 per mille, and exhibit oscillations of approximately 0.5 per mille. At 27 cm, the record shows a 3.8 per mille shift to higher values, coincident with the occurrence of a dark brown growth layer. This shift may represent a change in rainfall across a growth hiatus. The range in oxygen isotope values of 4.9 per mille in Stumpy corresponds to a difference in rainfall of 350 +/- 74 mm/month, based on previous study of rainfall in the modern system.

  9. Oxygen isotope signatures of transpired water vapor: the role of isotopic non-steady-state transpiration under natural conditions.

    PubMed

    Dubbert, Maren; Cuntz, Matthias; Piayda, Arndt; Werner, Christiane

    2014-09-01

    The oxygen isotope signature of water is a powerful tracer of water movement from plants to the global scale. However, little is known about the short-term variability of oxygen isotopes leaving the ecosystem via transpiration, as high-frequency measurements are lacking. A laser spectrometer was coupled to a gas-exchange chamber directly estimating branch-level fluxes in order to evaluate the short-term variability of the isotopic composition of transpiration (δE ) and to investigate the role of isotopic non-steady-state transpiration under natural conditions in cork-oak trees (Quercus suber) during distinct Mediterranean seasons. The measured δ(18) O of transpiration (δE ) deviated from isotopic steady state throughout most of the day even when leaf water at the evaporating sites was near isotopic steady state. High agreement was found between estimated and modeled δE values assuming non-steady-state enrichment of leaf water. Isoforcing, that is, the influence of the transpirational δ(18) O flux on atmospheric values, deviated from steady-state calculations but daily means were similar between steady state and non-steady state. However, strong daytime isoforcing on the atmosphere implies that short-term variations in δE are likely to have consequences for large-scale applications, for example, partitioning of ecosystem fluxes or satellite-based applications.

  10. Multidecadal climate variability in Brazil's Nordeste during the last 3000 years based on speleothem isotope records

    NASA Astrophysics Data System (ADS)

    Novello, Valdir F.; Cruz, Francisco W.; Karmann, Ivo; Burns, Stephen J.; Stríkis, Nicolás M.; Vuille, Mathias; Cheng, Hai; Lawrence Edwards, R.; Santos, Roberto V.; Frigo, Everton; Barreto, Eline A. S.

    2012-12-01

    We present the first high resolution, approximately ∼4 years sample spacing, precipitation record from northeastern Brazil (hereafter referred to as ‘Nordeste’) covering the last ∼3000 yrs from 230Th-dated stalagmites oxygen isotope records. Our record shows abrupt fluctuations in rainfall tied to variations in the intensity of the South American summer monsoon (SASM), including the periods corresponding to the Little Ice Age (LIA), the Medieval Climate Anomaly (MCA) and an event around 2800 yr B.P. Unlike other monsoon records in southern tropical South America, dry conditions prevailed during the LIA in the Nordeste. Our record suggests that the region is currently undergoing drought conditions that are unprecedented over the past 3 millennia, rivaled only by the LIA period. Using spectral, wavelet and cross-wavelet analyses we show that changes in SASM activity in the region are mainly associated with variations of the Atlantic Multidecadal Oscillation (AMO) and to a lesser degree caused by fluctuations in tropical Pacific SST. Our record also shows a distinct periodicity around 210 years, which has been linked to solar variability.

  11. Possible evidence for fluid-rock oxygen isotope disequilibrium in hydrothermal systems

    SciTech Connect

    Cole, D.R.

    1992-01-01

    There is ample evidence from geothermal systems that isotope temperatures estimated from the oxygen isotope fractionation between alteration phases and coexisting aquifer fluids agree closely with measured bore-hole temperatures. Similar, but limited evidence is found in epithermal vein deposits where isotopes temperature agree well with fluid inclusion homogenization temperature. Conversely, many hydrothermal systems exhibit varying degrees of fluid-rock oxygen isotope equilibration. There appears to be a crude relationship between increasing degree of equilibrium and increasing temperature and salinity. The observed variations in the degree of exchange may have resulted from local, self-sealing of the fracture network prior to equilibration. The ability for fracture to remain open or to propogate allowing continued fluid flow may be the deciding factor in the attainment of isotopic equilibration.

  12. Possible evidence for fluid-rock oxygen isotope disequilibrium in hydrothermal systems

    SciTech Connect

    Cole, D.R.

    1992-04-01

    There is ample evidence from geothermal systems that isotope temperatures estimated from the oxygen isotope fractionation between alteration phases and coexisting aquifer fluids agree closely with measured bore-hole temperatures. Similar, but limited evidence is found in epithermal vein deposits where isotopes temperature agree well with fluid inclusion homogenization temperature. Conversely, many hydrothermal systems exhibit varying degrees of fluid-rock oxygen isotope equilibration. There appears to be a crude relationship between increasing degree of equilibrium and increasing temperature and salinity. The observed variations in the degree of exchange may have resulted from local, self-sealing of the fracture network prior to equilibration. The ability for fracture to remain open or to propogate allowing continued fluid flow may be the deciding factor in the attainment of isotopic equilibration.

  13. Atmospheric oxygen levels in the precambrian: a review of isotopic and geological evidence

    NASA Astrophysics Data System (ADS)

    Lambert, I. B.; Donnelly, T. H.

    1991-12-01

    The significant change in the sulfur isotope record in the early Proterozoic implies global scale oxidation of the previously reduced and sulfate-poor hydrosphere. Changes in the nature/abundance of uranium, iron and manganese deposits are consistent with the evolution of significant oxygen levels in the atmosphere in this period. It is suggested that global oxidation occurred in the early Proterozoic as a result of widespread development of sedimentary environments favourable for the proliferation of phytosynthetic organisms, coupled with steadily decreasing availability of ferrous iron, an important oxygen buffer, because of generally declining igneous and hydrothermal activity. There is a predominance of positive δ34S values for sulfides in Proterozoic carbonaceous strata and sediment-hosted mineral deposits, although the uncommonly preserved evaporitic sulfate deposits do not provide evidence of unusual 34S-enrichment in contemporaneous seawater. These data can be explained in terms of a supercontinent on which there was extensive sedimentation in major intracratonic troughs and platforms. This model is consistent with geological and palaeomagnetic data for this era. In the many sedimentary basins which had only occasional, or no, access to the open ocean, variably 34S-enriched sulfides accumulated by high rates and high degrees of biological sulfate reduction, and also by hydrothermal processes. Pyrite in Proterozoic open marine strata should have had mainly variable negative δ34S values, but few examples of such sequences occur in the geological record for this era. Late Proterozoic carbonates (ca. 900-600 m.y.) from different regions are characterised by mainly positive δ13C values. These are explained as the result of long-term global oceanic anoxia, which may have been a function of prolonged crustal stability preceding continental dispersion around the Proterozoic-Cambrian boundary. Significant rises in atmospheric oxygen levels would have resulted

  14. Oxygen Isotopes Reveal Attenuation in Latitudinal Ocean Temperature Gradient during the Permian Icehouse to Hothouse Transition

    NASA Astrophysics Data System (ADS)

    Shultis, A. I.; Frank, T. D.; Fielding, C. R.

    2011-12-01

    To assess changes in paleolatitudinal temperature gradient in the Permian ocean system during the demise of the Late Paleozoic Ice Age (LPIA), we analyzed the oxygen isotope composition of high latitude brachiopod and bivalve shells and compared them to published low latitude isotope records. We selected brachiopods and Eurydesma bivalves of Early to Middle Permian age that lie along a transect extending from temperate paleolatitudes in Queensland to polar paleolatitudes in Tasmania. Using cathodoluminescence (CL) microscopy and elemental analyses, diagenically altered samples were separated from well-preserved samples for isotopic analysis. Samples that were nonluminescent were prepared for elemental screening, and brachiopod and bivalve samples that passed both CL and trace element screening methods were analyzed for oxygen and carbon isotopes. The δ18O values reveal a long-term decrease in the paleolatitudinal temperature gradient from Early Permian (Sakmarian) and late Middle Permian (Capitanian), which parallels the trend in climate associated with the demise of LPIA. Transient decreases from glacial to non-glacial epochs are also evident. The δ18O values from well-preserved samples are as high as 0.1% during glacial epoch P2 (287-280 Ma: late Sakmarian to mid-Artinskian) and drop to -3.0% in the nonglacial interval between P2 and glacial epoch P3 (273-268 Ma: late Kungurian to latest Roadian). High-latitude δ18O values then rise to -1.5% during P3 and drop to -3.8% during the subsequent nonglacial interval. Low latitude δ18O values from the literature are as high as -2.3% during the P2 and drop to -2.9% in the nonglacial interval between P2 and the P3. δ18O values then rise to -1.6% during P3. Low latitude δ18O values drop to -4.4% between P3 and P4 and rise again to -2.4% during the P4 glacial epoch (267-260 Ma: late Wordian to late Capitanian). This comparison of high and low latitude δ18O suggests that meridional sea surface temperature gradients

  15. Non-destructive measurement of carbonic anhydrase activity and the oxygen isotope composition of soil water

    NASA Astrophysics Data System (ADS)

    Jones, Sam; Sauze, Joana; Ogée, Jérôme; Wohl, Steven; Bosc, Alexandre; Wingate, Lisa

    2016-04-01

    Carbonic anhydrases are a group of metalloenzymes that catalyse the hydration of aqueous carbon dioxide (CO2). The expression of carbonic anhydrase by bacteria, archaea and eukarya has been linked to a variety of important biological processes including pH regulation, substrate supply and biomineralisation. As oxygen isotopes are exchanged between CO2 and water during hydration, the presence of carbonic anhydrase in plants and soil organisms also influences the oxygen isotope budget of atmospheric CO2. Leaf and soil water pools have distinct oxygen isotope compositions, owing to differences in pool sizes and evaporation rates, which are imparted on CO2during hydration. These differences in the isotopic signature of CO2 interacting with leaves and soil can be used to partition the contribution of photosynthesis and soil respiration to net terrestrial CO2 exchange. However, this relies on our knowledge of soil carbonic anhydrase activity and currently, the prevalence and function of these enzymes in soils is poorly understood. Isotopic approaches used to estimate soil carbonic anhydrase activity typically involve the inversion of models describing the oxygen isotope composition of CO2 fluxes to solve for the apparent, potentially catalysed, rate of oxygen exchange during hydration. This requires information about the composition of CO2 in isotopic equilibrium with soil water obtained from destructive, depth-resolved soil water sampling. This can represent a significant challenge in data collection given the considerable potential for spatial and temporal variability in the isotopic composition of soil water and limited a priori information with respect to the appropriate sampling resolution and depth. We investigated whether we could circumvent this requirement by constraining carbonic anhydrase activity and the composition of soil water in isotopic equilibrium with CO2 by solving simultaneously the mass balance for two soil CO2 steady states differing only in the

  16. Theoretical and Experimental Approaches to Understanding the Anomalous Distribution of Oxygen Isotopes in the Solar System

    NASA Astrophysics Data System (ADS)

    Dominguez, Gerardo; Christensen, Elizabeth; Boyer, Charisa; Park, Manesseh; Benitez, Ezra; Nunn, Morgan; Thiemens, Mark H.; Jackson, Terri

    2016-06-01

    Decades of careful laboratory analysis of primitive meteorites have revealed an intriguing and unexplained pattern in the distribution of oxygen isotopes in the solar system. With the recent analysis of solar wind oxygen by NASA’s Genesis mission, it appears that the Sun has a distinct oxygen isotopic composition from the terrestrial planets, asteroids, and comets. These differences cannot be explained by mass-dependent diffusion and require a physical-chemical mechanism or mechanisms that separate oxygen isotopes in a non-mass dependent manner.Several hypothesis have been proposed to explain the anomalous distribution. Photochemical self-shielding of CO may explain the anomalous distribution, however, this mechanism has key weaknesses including the requirement of a very fine tuned timescale to explain the isotopic differences between the Sun and bulk of the terrestrial planets. Recently, attention has been directed at understanding specific chemical reactions that occur on interstellar dust grains due to their similarities with non-equilibrium photochemical reactions believed to be responsible for the mass-independent isotopic fractionation patterns observed in Earth’s atmosphere. A specific focus has been directed towards understanding the formation of H2O because some of its precursor (HO2, and O3) are well-known to acquire mass-independent isotopic signatures when formed in the gas-phase.In this presentation, I describe a series of laboratory astrophysical experiments whose goal is to understand the distribution of oxygen isotopes in the solar system and perhaps, by extension, the distribution in other planetary systems. Preliminary results for the isotopic composition of O3 formed at 5K will be presented as well as the first, to our knowledge, measurements of the isotopic composition of H2O (18O/16O, 17O/16O, D/H) formed at 32K. We find that H2O formed in the astrophysical conditions we simulated acquired an anomalous isotopic composition with a triple-oxygen

  17. Making an honest measurement scale out of the oxygen isotope delta-values.

    PubMed

    Gat, Joel R; DeBievre, Paul

    2002-01-01

    The differential measurement of the abundance of oxygen isotopes based on reference materials, such as VSMOW for the case of water, was used because the precision of the absolute mass-spectrometric determination of the abundance fell short of the differences to be measured. Since then these measurements have been much improved, so that a calibration scheme of the oxygen isotope abundance in water, carbonates, silica, phosphates, sulfates, nitrates and organic materials is suggested, based on an accredited primary standard of oxygen in air and using standard fluorination and O(2) to CO(2) conversion techniques. PMID:12442297

  18. Divergent Biochemical Fractionation, Not Convergent Temperature, Explains Cellulose Oxygen Isotope Enrichment across Latitudes

    PubMed Central

    Sternberg, Leonel; Ellsworth, Patricia Fernandes Vendramini

    2011-01-01

    Recent findings based on the oxygen isotope ratios of tree trunk cellulose indicate that the temperature of biomass production in biomes ranging from boreal to subtropical forests converge to an average leaf temperature of 21.4°C. The above conclusion has been drawn under the assumption that biochemically related isotopic fractionations during cellulose synthesis are not affected by temperature. Here we test the above assumption by heterotrophically generating cellulose at different temperatures and measuring the proportion of carbohydrate oxygen that exchange with water during cellulose synthesis and the average biochemical fractionation associated with this exchange. We observed no variation in the proportion of oxygen that exchange with different temperatures, which averaged 0.42 as it has been observed in other studies. On the other hand, the biochemical oxygen isotope fractionation during cellulose synthesis is affected by temperature and can be described by a 2nd order polynomial equation. The biochemical fractionation changes little between temperatures of 20 and 30°C averaging 26‰ but increases at lower temperatures to values of 31‰. This temperature sensitive biochemical fractionation explains the pattern of cellulose oxygen isotope ratios of aquatic plants encompassing several latitudes. The observed temperature sensitive biochemical fractionation also indicates that divergent biochemical fractionation and not convergent leaf temperature explains the increase in oxygen isotope enrichment of cellulose across several biomes. PMID:22132203

  19. Oxygen isotopic transport and exchange during fluid flow: One-dimensional models and applications

    SciTech Connect

    Bowman, J.R. ); Willett, S.D. ); Cook, S.J. Environ Corp., Houston, TX )

    1994-01-01

    In this work the authors investigate the consequences of fluid flow and fluid-rock interaction to the isotopic evolution of fluids and rock with one-dimensional transport models of fluid flow and oxygen isotope exchange. Transport models dealing with stable isotopes are well established in recent geochemical literature. The authors extend previous treatments by presenting the derivation of both analytical and numerical solutions to the transport equations incorporating simultaneously advection, diffusion and hydrodynamic dispersion, and kinetics of isotopic exchange. The increased generality of numerical solutions allows the incorporation of other effects which control the spatial patterns of [delta][sup 18]O values developed in rocks and fluids including multiple reactive species and temperature gradients. The authors discuss the effects of flow parameters, conditions of isotopic exchange, and temperature gradients on the spatial patterns of isotopic shifts produced in rock sequences subjected to fluid flow, and on conventionally calculated W/R ratios for these rock sequences. Finally, the authors examine the implications of oxygen isotope transport for two natural systems where isotopic shifts or gradients could be interpreted in terms of unidirectional fluid infiltration. Solutions of one-dimensional transport equations including the mechanisms of advection, diffusion, hydrodynamic dispersion, and non-equilibrium exchange between water and rock indicate that the time-space evolution of oxygen isotopic compositions of rock and infiltrating fluid is dependent on (1) the rate of fluid infiltration, (2) the diffusive and dispersive properties of the rock matrix, (3) the rate of isotopic exchange, and (4) the rock-water mass oxygen ratio in a unit volume of water-saturated, porous rock. 56 refs., 18 figs., 2 tabs.

  20. Sulfur cycling in contaminated aquifers: What can we learn from oxygen isotopes in sulfate? (Invited)

    NASA Astrophysics Data System (ADS)

    Knoeller, K.; Vogt, C.; Hoth, N.

    2009-12-01

    Bacterial reduction of dissolved sulfate (BSR) is a key process determining the natural attenuation in many contaminated aquifers. For example, in groundwater bodies affected by acid mine drainage (AMD) BSR reduces the contaminant load by producing alkalinity and facilitating a sustainable fixation of sulfur in the sediment. In aquifers contaminated with petroleum hydrocarbons sulfate may act as a terminal electron acceptor for the anaerobic oxidation of the organic contaminants to carbon dioxide and water. Due to the isotope selectivity of sulfate reducing bacteria, BSR shows the most pronounced isotope fractionation within the sulfur cycle. While sulfur displays a straightforward kinetic enrichment in the residual sulfate described by the enrichment factor epsilon (ɛ), the mechanism of oxygen isotope fractionation is still being discussed controversially. Nevertheless, it is agreed on that oxygen isotope exchange between ambient water and residual sulfate occurs during BSR in natural environments. With respect to this potential isotope exchange, the fractionation parameter theta (θ) is introduced instead of the kinetic enrichment factor epsilon (ɛ). The dual isotope system considering both sulfate-sulfur and sulfate-oxygen isotope fractionation and the respective fractionation parameters ɛ and θ provides an excellent tool for the recognition and quantification of BSR. Beyond that, the dual isotope approach may help identify and estimate interfering sulfur transformations such as re-oxidation and disproportionation processes which is especially vital for the understanding of the overall natural attenuation potential of the investigated aquifers. We present two examples from different field studies showing the benefits of applying the combination of sulfur and oxygen isotopes in dissolved sulfate to reveal the details of the sulfur cycle. The first case study is concerned with the evaluation of the potential for BSR in an AMD-affected aquifer close to an

  1. Oxygen isotopes and hydroclimatic change in the Yukon Flats National Wildlife Refuge, northeast Alaska (Invited)

    NASA Astrophysics Data System (ADS)

    Anderson, L.; Finney, B. P.; Guldager, N.; Rover, J. A.; Shapley, M.; van Sistine, D. R.

    2010-12-01

    The Yukon Flats is the region surrounding the confluence of the Porcupine, Sheenjek, Christian, Chandalar, and Yukon Rivers including approximately 20,000 lakes. It is a diverse boreal mosaic landscape (~23,000 km2) that provides spring and summer habitat for over 150 bird species. The climate of the area is continental with severe winter temperatures and warm summers. High effective moisture deficits relative to most boreal environments lead to the unique occurrence of evaporite mineral deposits as well as the highest incidence of naturally occurring wildfires in Alaska. Lake levels are dynamic, and frequently localized, because of subdued topography, varying lake ages and surficial geologic substrates, permafrost extent, and corresponding surface and groundwater flow paths. To better understand the relationships between climate and hydro-environmental change, we are sampling oxygen isotope ratios spatially and temporally. Here we present preliminary GIS-spatial analyses from 108 water bodies and a late Holocene sediment oxygen isotope record from Twelve Mile Lake. We find that the first-order wetland water chemistry relation is with geographic location and hydrologic linkages. A 1.45-m sediment core from 8.8-m water depth was retrieved from Twelve Mile Lake because lake-water δ18O values indicate that evaporation dominates the lake’s hydrologic balance and because it is sufficiently alkaline to generate bioinduced endogenic carbonate sedimentation. The sediment δ18O trends during the last millennia have decade-to-century scale temporal resolution and similarities with paleoclimatic trends documented by other lakes in interior regions of Alaska and the Yukon Territory. Results from these preliminary studies reinforce that 1) wetland and lake sensitivity to climate-induced changes in hydrology varies spatially in the Yukon Flats because of dynamic hydrogeographic factors, and 2) recent hydro-environmental changes are better evaluated within a long-term context

  2. Stable isotope analysis of molecular oxygen from silicates and oxides using CO2 laser extraction

    NASA Technical Reports Server (NTRS)

    Perry, Eugene

    1996-01-01

    A laser-excited system for determination of the oxygen isotope composition of small quantities of silicate and oxide minerals was constructed and tested at JSC. This device is the first reported to use a commercially available helium cryostat to transfer and purify oxygen gas quantitatively within the system. The system uses oxygen gas instead of the conventional CO2 for mass spectrometer analyses. This modification of technique permits determination of all three stable oxygen isotopes, an essential requirement for oxygen isotope analysis of meteoritic material. Tests of the system included analysis of standard silicate materials NBS 28 and UWMG2 garnet, six SNC meteorites, and inclusions and chondrules from the Allende meteorite. Calibration with terrestrial standards was excellent. Meteorite values are close to published values and show no evidence of terrestrial oxygen contamination. The one limitation observed is that, in some runs on fine-grained SNC matrix material, sample results were affected by other samples in the sample holder within the reaction chamber. This reemphasizes the need for special precautions in dealing with fine-grained, reactive samples. Performance of the JSC instrument compares favorably with that of any other instrument currently producing published oxygen isotope data.

  3. Gradients in seasonality and seawater oxygen isotopic composition along the early Permian Gondwanan coast, SE Australia

    NASA Astrophysics Data System (ADS)

    Beard, J. Andrew; Ivany, Linda C.; Runnegar, Bruce

    2015-09-01

    Oxygen isotope compositions of marine carbonates are commonly employed for understanding ancient temperatures, but this approach is complicated in the very distant past due to uncertainties about the effects of diagenesis and the isotopic composition of seawater, both locally and globally. Microsampled accretionary calcite from two species of the fossil bivalve Eurydesma Sowerby and Morris 1845 collected from sediments of Cisuralian age in high latitude marine sediments along the SE coast of Australia records cyclic seasonal fluctuations in shell δ18O values during growth, demonstrating the primary nature of the isotope signal and thus allowing investigation of early Permian seawater isotopic composition and water temperature in the high southern latitudes. The mean and seasonal range of δ18Ocarb decreases poleward across about 10° of paleolatitude (∼67°S-77°S). The presence of co-occurring dropstones and stratigraphically associated glendonites constrains winter temperatures across the region to near-freezing, thus permitting calculation of realistic estimates of water composition and summer temperatures. Summer δ18Ocarb values indicate water temperatures between 5 °C and 12 °C, with warmer values at lower latitudes. The decrease in both mean sea surface temperature and seasonal amplitude with increasing latitude on the Gondwanan coast is much like that observed along high-latitude coastlines today. Calculated δ18Owater decreases toward the pole, likely associated with an increasing contribution of isotopically light fresh water derived from summer snow-melt. The gradient in δ18Owater is similar to that documented over a similar span of latitude on the modern SE Greenland coast. We infer the presence of a north-flowing coastal current of cold, O18-depleted water that entrains progressively greater amounts of more typical seawater as it moves away from the pole. δ18O values in SE Australia, however, are about 3‰ lower than those off Greenland

  4. Miocene to Pleistocene osmium isotopic records of the Mediterranean sediments

    NASA Astrophysics Data System (ADS)

    Kuroda, Junichiro; Jiménez-Espejo, Francisco J.; Nozaki, Tatsuo; Gennari, Rocco; Lugli, Stefano; Manzi, Vinicio; Roveri, Marco; Flecker, Rachel; Sierro, Francisco J.; Yoshimura, Toshihiro; Suzuki, Katsuhiko; Ohkouchi, Naohiko

    2016-01-01

    In the late Miocene the Mediterranean Sea experienced a salinity crisis and thick sequences of evaporites precipitated across the deep and marginal basins. In this study we report Os isotopic records from Deep Sea Drilling Project and Ocean Drilling Project cores in the Mediterranean: the Balearic Sea (Site 372), the Tyrrhenian Sea (Site 654), the Ionian Basin (Site 374), and the Florence Rise (Sites 375-376), as well as Integrated Ocean Drilling Project Site U1387 in Gulf of Cadiz, North Atlantic. Pliocene-Pleistocene sediments at all sites show 187Os/188Os values close to that of the coeval ocean water, indicating that the Mediterranean was connected to the North Atlantic. Evaporitic sediments deposited during the latest Miocene, however, have 187Os/188Os values significantly lower than coeval ocean water values. The offset of the Mediterranean evaporite 187Os/188Os is attributed to limited exchange with the North Atlantic during the Messinian salinity crisis. The source of unradiogenic Os is likely to be weathering of ultramafic rocks (ophiolites) cropping out in the Mediterranean's drainage basins. Based on a box model we estimated the amount of unradiogenic Os and the Atlantic-Mediterranean exchange rate to explain this offset. Os isotopic ratios of the pre-evaporite sediments in the western Mediterranean are almost identical to that of the coeval ocean water. In contrast, equivalent sediments from the Florence Rise have significantly lower 187Os/188Os values. The offset in the Os isotopic ratio on the Florence Rise is attributed either to limited water exchange between eastern and western Mediterranean or to local effects associated with exhumation of the Troodos ophiolites (Cyprus).

  5. Silicon isotope composition of diagenetic quartz: A record of Precambrian weathering

    NASA Astrophysics Data System (ADS)

    Pollington, A. D.; Kozdon, R.; Valley, J. W.

    2013-12-01

    The genesis of quartz cements, which modify the porosity and permeability of many sedimentary rocks, is widely studied to determine the origin, flux, pathways and timing of water-rich fluids. Stable isotope ratios provide evidence of fluid/rock interactions. So called 'non-traditional stable isotope' ratios such as silicon may record processes such as chemical weathering, whereas aqueous fluid dominates the source of oxygen during precipitation. Silicon may be derived internally to a rock such as from pressure solution or recrystallization, or introduced by fluids. Silicon isotope ratios of diagenetic quartz reflect the source of dissolved chemical components; if δ30Si values of overgrowth quartz (OQ) and neighboring detrital quartz (DQ) are similar, the cations may be locally sourced from detrital grains. Alternatively, if the δ30Si of overgrowth quartz is significantly different than that of nearby detrital grains, then the silicon in those overgrowths is dominated by material derived from outside the formation. Here we present high-resolution in situ silicon isotope data, measured by secondary ion mass spectrometry from 10 μm spots, for the Mt Simon Sandstone, the basal Cambrian unit in the Midcontinent of North America. Silicon and oxygen isotope ratios have been measured in detrital quartz grains and quartz overgrowths from outcrops and deeply buried samples from drill core. Overgrowths from drill cores and most outcrops studied have δ30Si values close to 0‰ NBS-28, which is the same as values measured for adjacent detrital grains and δ18O values between 18 and 33‰ VSMOW, reflecting different temperatures of precipitation. However, in multiple samples from an outcrop on the Wisconsin Dome, adjacent to the Precambrian-Cambrian unconformity, quartz overgrowths have a wide range of δ30Si, with values as low as -5.4‰ and paired δ18O values as low as 18.5‰. Using the high spatial resolution afforded by SIMS analyses, we have measured isotopic

  6. Palaeoclimatology: the record for marine isotopic stage 11.

    PubMed

    Raynaud, Dominique; Barnola, Jean-Marc; Souchez, Roland; Lorrain, Reginald; Petit, Jean-Robert; Duval, Paul; Lipenkov, Vladimir Y

    2005-07-01

    The marine isotopic stage 11 (MIS 11) is an extraordinarily long interglacial period in the Earth's history that occurred some 400,000 years ago and lasted for about 30,000 years. During this period there were weak, astronomically induced changes in the distribution of solar energy reaching the Earth. The conditions of this orbital climate forcing are similar to those of today's interglacial period, and they rendered the climate susceptible to other forcing--for example, to changes in the level of atmospheric carbon dioxide. Here we use ice-core data from the Antarctic Vostok core to reconstruct a complete atmospheric carbon dioxide record for MIS 11. The record indicates that values for carbon dioxide throughout the interglacial period were close to the Earth's pre-industrial levels and that both solar energy and carbon dioxide may have helped to make MIS 11 exceptionally long. Anomalies in the oceanic carbonate system recorded in marine sediments at the time, for example while coral reefs were forming, apparently left no signature on atmospheric carbon dioxide concentrations.

  7. High Resolution Carbon and Oxygen Isotope Measurements of Laminations in Pedogenic Carbonate

    NASA Astrophysics Data System (ADS)

    Breecker, D.; Sharp, Z.

    2005-12-01

    Stable carbon and oxygen isotope ratios in pedogenic carbonate from buried soils provide a proxy for low-resolution Quaternary climate and environmental conditions. Samples of carbonate are taken from clast rinds, nodules or filaments in calcic soils. Most clast rinds exhibit micro-laminations that may preserve isotopic ratios of formation. The techniques typically utilized to sample pedogenic carbonate, however, are too coarse to sample individual laminations and likely result in time averages and therefore limit temporal resolution. We investigated the heterogeneity of both carbon and oxygen isotopes ratios in clast rinds at a 100 μm scale using a rapid CO2 laser extraction technique (Sharp and Cerling, 1996). A single 20 msec burst at low power releases CO2 from polished carbonate slabs and the CO2 is then analyzed using continuous flow GC-IRMS. Analyses take less than 5 minutes with a reproducibility of better than ±0.3‰ (δ13C) and ±0.4‰ (δ18O). We have made a two dimensional map of a thick carbonate rind on a limestone clast from a stage V soil to explore the potential for preservation of isotopic ratios in well developed soils and plan to analyze additional rinds from less well developed calcic horizons for comparison. The isotopic map reveals heterogeneities in δ13C of up to 4‰ at a sub-millimeter scale, possibly corresponding to 30% changes in the fraction of C4 plants. Also imaged are abrupt changes in δ13C of approximately 2‰ across sub-100 μm scale boundaries. One well-defined carbon isotope boundary is sub parallel to, but crosses, the lamination boundaries. Oxygen isotope compositions do not change systematically across the same boundary and generally appear more random. These observations are most easily explained by alteration of initial isotopic compositions. Alteration may preferentially affect oxygen isotope ratios leaving carbon isotope distributions relatively intact. It is also possible that both carbon and oxygen isotopes

  8. Miocene to Pliocene osmium isotopic records of Mediterranean sediments

    NASA Astrophysics Data System (ADS)

    Kuroda, Junichiro; Jiménez-Espejo, Francisco J.; Nozaki, Tatsuo; Gennari, Rocco; Lugli, Stefano; Manzi, Vinicio; Roveri, Marco; Flecker, Rachel; Suzuki, Katsuhiko; Yoshimura, Toshihiro; Sierro, Francisco; Ohkouchi, Naohiko

    2015-04-01

    In the late Miocene the Mediterranean Sea experienced a salinity crisis and thick sequences of evaporites precipitated across the basin. In this study we report Os isotopic records from drilled cores in the Mediterranean; the Balearic Sea, the Tyrrhenian Sea, the Ionian Basin and the Florence Rise. Pliocene sediments at all sites show 187Os/188Os values close to that of the coeval ocean water, indicating that the Mediterranean was connected to the North Atlantic. Evaporitic sediments deposited during the late Miocene however, have 187Os/188Os values lower than coeval ocean water values and samples from the eastern Mediterranean and Ionian basins are particularly low. Os isotopic ratios of the pre-evaporite sediments in the western Mediterranean are almost identical to that of the coeval ocean water. In contrast, equivalent sediments from the Florence Rise have significantly lower 187Os/188Os values. The offset of Mediterranean evaporite 187Os/188Os is attributed to limited exchange with the North Atlantic during the Messinian Salinity Crisis (MSC). The source of unradiogenic Os is likely to be weathering of ultramafic rocks (ophiolites) cropping out in the Mediterranean's drainage basins. The offset in the Os ratio on the Florence Rise is attributed either to limited water exchange between eastern and western Mediterranean, or to local effects associated with exhumation of ophiolites around the eastern Mediterranean Sea.

  9. Hydrogen Isotope Ratios of Leaf Waxes in C3 and C4 Grasses Record Meteoric Water and Aridity Signatures

    NASA Astrophysics Data System (ADS)

    Smith, F. A.; Freeman, K. H.; Ehleringer, J. R.; Helliker, B.

    2004-12-01

    Hydrogen isotope ratios of sedimentary n-alkanes (C27-C33) from vascular plants potentially provide a valuable record of past hydrologic conditions. To explore this, we analyzed grasses grown in a greenhouse and calculated fractionation factors (epsilon) between source water and n-alkane for each sample. An average difference of 21 permil is observed between C3 and C4 grasses, which is comparable to that determined for grasses collected from the Great Plains. The more positive isotope values in C4 grasses likely reflects smaller interveinal distance compared to C3 grass leaves, allowing greater back-diffusion of transpirationally enriched water from stomata, as documented with the oxygen isotope ratios of grass leaf water and cellulose by Helliker and Ehleringer (2000). The oxygen isotope difference is magnified at low relative humidity, when transpiration rates are higher. A similar effect is expected in hydrogen isotope ratios of leaf water and plant compounds. However, preliminary results from grasses grown hydroponically at different relative humidities suggest that there may be a decoupling of the hydrogen isotope ratio of leaf-wax n-alkanes and the oxygen isotope ratio of leaf water and cellulose. To examine the effects of source water delta D and climate on n-alkane delta D values, we analyzed grasses collected from the Great Plains. We use river water delta D values as a proxy for source water and the epsilon values determined in the greenhouse experiments, to predict expected values for C3 and C4 grass lipids. Measured values compare well to predicted values, with the exception of two semi-arid sites where evapotranspiration may have led to leaf-waters that are enriched in deuterium. Residual delta D values (measured-expected) correspond strongly with measures of aridity, such as annual precipitation and recipitation/evaporation ratios.

  10. Distinguishing phosphate from fertilizers and wastewater treatment plant effluents in Western Canada using oxygen isotope measurements

    NASA Astrophysics Data System (ADS)

    Fau, Veronique; Nightingale, Michael; Tamburini, Frederica; Mayer, Bernhard

    2014-05-01

    The successful application of oxygen isotope ratios as a tracer for phosphate in aquatic ecosystems requires that different sources of phosphate are isotopically distinct. The objective of this study was to determine whether the oxygen isotope ratios of phosphate from fertilizers and effluents from wastewater treatment plants in Western Canada are isotopically distinct. Therefore, we carried out oxygen isotope analyses on phosphate in effluent from five different wastewater treatment plants (WWTP) in the Bow River watershed of Alberta, Canada. Samples were collected directly from the final effluent (post-UV) in Banff and Canmore upstream of Calgary, and from effluents of Calgary's WWTPs at Bonnybrook, Fish Creek and Pine Creek. We also carried out oxygen isotope analyses on a variety of phosphate-containing fertilizers that are widely used in Western Canada. Historically, most of the phosphate contained in manufactured fertilizers sold in Alberta came from two distinct deposits: 1) a weathered Pliocene igneous carbonatite located in eastern Canada, and 2) the Permian Phosphoria Formation in the western USA. Phosphate (PO43-) contained in the water or the fertilizer was concentrated and quantitatively converted to pure silver phosphate (Ag3PO4). The silver phosphate was then reduced with carbon in an oxygen free environment using a TC/EA pyrolysis reactor linked to a mass spectrometer where 18O/16O ratios of CO were measured in continuous flow mode. Preparation of samples for δ18OPO4 analyses was conducted using the Magnesium Induced Coprecipitation (MAGIC) method. Expected oxygen isotope ratios for phosphate in equilibrium with water (δ18Oeq) were calculated using the Longinelli and Nuti equation: T (° C) = 111.4 - 4.3 (δ18Oeq - δ18Owater). Measured δ18O values of phosphate for fertilizer samples varied from 8 to 25 oÈ®n average, fertilizer samples of sedimentary origin had higher δ18O values (15.8) than those of igneous origin (11.5). Phosphate isotopic

  11. Understanding Cellulose-Water Oxygen Isotopic Fractionation in Tropical African Lakes: Implications for Paleoclimatic and Paleohydrologic Reconstruction

    NASA Astrophysics Data System (ADS)

    Beuning, K. R.; Anderson, B.

    2001-12-01

    Paleohydrologic reconstructions from lake sedimentary archives have provided insight into Earth's changing climate. One such archive, sediment cellulose, provides paleohydrologic information by preserving a record of changing oxygen isotopic composition of the lake water. Paleohydrologic interpretation is possible because the cellulose-water oxygen isotopic fractionation is both species and temperature independent. Yet, recent analyses of modern macrophytes in several African lakes suggest that potential species and temperature effects might induce more variability in cellulose-water oxygen isotopic fractionation than once thought. Oxygen isotopic analysis of aquatic macrophytes and associated water samples from tropical East African lakes suggests a reduced mean cellulose-water fractionation (mean: +25 per mil) in these tropical environments as opposed to temperate freshwater aquatic ecosystems (mean: +28 per mil). To test a possible temperature effect associated with cellulose-water fractionation in tropical lake environments, four aquatic macrophyte taxa (Lemna, Ceratophyllum, Egeria and Vallisneria) were grown in replicate tanks at 21, 23, 25, 28 and 30° C. All four taxa currently live in tropical East African lakes. The results demonstrate a negative linear relationship between temperature and cellulose-water fractionation in Ceratophyllum with fractionation values of +30 +/- 0.5 per mil at 21° C and +26 +/- 0.2 per mil at 30° C. A similar, though less significant, relationship is observed between temperature and cellulose-water fractionation in Egeria with values of +29.5 +/- 0.4 per mil at 21° C and +28.5 +/- 0.1 per mil at 30° C. Measurements of Vallisneria and Lemna are ongoing. These preliminary results suggest that at temperatures characteristic of tropical aquatic lakes, cellulose-water fractionation may be reduced as compared to such fractionation in colder/temperate lake environments.

  12. A molecular organic carbon isotope record of miocene climate changes.

    PubMed

    Schoell, M; Schouten, S; Damsté, J S; de Leeuw, J W; Summons, R E

    1994-02-25

    The difference in carbon-13 ((13)C) contents of hopane and sterane biomarkers in the Monterey formation (Naples Beach, California) parallels the Miocene inorganic record of the change in (18)O (delta(18)O), reflecting the Miocene evolution from a well-mixed to a highly stratified photic zone (upper 100 meters) in the Pacific. Steranes (delta(13)C = 25.4 +/- 0.7 per mil versus the Pee Dee belemnite standard) from shallow photic-zone organisms do not change isotopically throughout the Miocene. In contrast, sulfur-bound C(35) hopanes (likely derived from bacterial plankton living at the base of the photic zone) have systematically decreasing (13)C concentrations in Middle and Late Miocene samples (delta(13)C = -29.5 to -31.5 per mil), consistent with the Middle Miocene formation of a carbon dioxide-rich cold water mass at the base of the photic zone.

  13. Oxygen isotope fractionation in the vacuum ultraviolet photodissociation of carbon monoxide: Wavelength, pressure and temperature dependency.

    SciTech Connect

    Chakraborty, Subrata; Davis, Ryan; Ahmed, Musahid; Jackson, Teresa L.; Thiemens, Mark H.

    2012-01-03

    Several absorption bands exist in the VUV region of Carbon monoxide (CO). Emission spectra indicate that these bands are all predissociative. An experimental investigation of CO photodissociation by vacuum ultraviolet photons (90 to 108 nm; ~13 to 11 eV) from the Advanced Light Source Synchrotron and direct measurement of the associated oxygen isotopic composition of the products are presented here. A wavelength dependency of the oxygen isotopic composition in the photodissociation product was observed. Slope values (δ'{sup 18}O/ δ'{sup 17}O) ranging from 0.76 to 1.32 were observed in oxygen three-isotope space (δ'{sup 18}O vs. δ'{sup 17}O) which correlated with increasing synchrotron photon energy, and indicate a dependency of the upper electronic state specific dissociation dynamics (e.g., perturbation and coupling associated with a particular state). An unprecedented magnitude in isotope separation was observed for photodissociation at the 105 and 107 nm synchrotron bands and are found to be associated with accidental predissociation of the vibrational states ({nu} = 0 and 1) of the upper electronic state E{sup 1}Π. For each synchrotron band, a large (few hundred per mil) extent of isotopic fractionation was observed and the range of fractionation is a combination of column density and exposure time. A significant temperature dependency in oxygen isotopic fractionation was observed, indicating a rotational level dependency in the predissociation process.

  14. High Precision Oxygen Three Isotope Analysis of Wild-2 Particles and Anhydrous Chondritic Interplanetary Dust Particles

    NASA Technical Reports Server (NTRS)

    Nakashima, D.; Ushikubo, T.; Zolensky, Michael E.; Weisberg, M. K.; Joswiak, D. J.; Brownlee, D. E.; Matrajt, G.; Kita, N. T.

    2011-01-01

    One of the most important discoveries from comet Wild-2 samples was observation of crystalline silicate particles that resemble chondrules and CAIs in carbonaceous chondrites. Previous oxygen isotope analyses of crystalline silicate terminal particles showed heterogeneous oxygen isotope ratios with delta(sup 18)O to approx. delta(sup 17)O down to -50% in the CAI-like particle Inti, a relict olivine grain in Gozen-sama, and an olivine particle. However, many Wild-2 particles as well as ferromagnesian silicates in anhydrous interplanetary dust particles (IDPs) showed Delta(sup 17)O values that cluster around -2%. In carbonaceous chondrites, chondrules seem to show two major isotope reservoirs with Delta(sup 17)O values at -5% and -2%. It was suggested that the Delta(sup 17)O = -2% is the common oxygen isotope reservoir for carbonaceous chondrite chondrules and cometary dust, from the outer asteroid belt to the Kuiper belt region. However, a larger dataset with high precision isotope analyses (+/-1-2%) is still needed to resolve the similarities or distinctions among Wild-2 particles, IDPs and chondrules in meteorites. We have made signifi-cant efforts to establish routine analyses of small particles (< or =10micronsm) at 1-2% precision using IMS-1280 at WiscSIMS laboratory. Here we report new results of high precision oxygen isotope analyses of Wild-2 particles and anhydrous chondritic IDPs, and discuss the relationship between the cometary dust and carbonaceous chondrite chondrules.

  15. The effect of phosphomonoesterases on the oxygen isotope composition of phosphate

    NASA Astrophysics Data System (ADS)

    von Sperber, Christian; Kries, Hajo; Tamburini, Federica; Bernasconi, Stefano M.; Frossard, Emmanuel

    2014-01-01

    Plants and microorganisms under phosphorus (P) stress release extracellular phosphatases as a strategy to acquire inorganic phosphate (Pi). These enzymes catalyze the hydrolysis of phosphoesters leading to a release of Pi. During the enzymatic hydrolysis an isotopic fractionation (ε) occurs leaving an imprint on the oxygen isotope composition of the released Pi which might be used to trace phosphorus in the environment. Therefore, enzymatic assays with acid phosphatases from wheat germ and potato tuber and alkaline phosphatase from Escherichia coli were prepared in order to determine the oxygen isotope fractionation caused by these enzymes. Adenosine 5‧ monophosphate and glycerol phosphate were used as substrates. The oxygen isotope fractionation caused by acid phosphatases is 20-30‰ smaller than for alkaline phosphatases, resulting in a difference of 5-7.5‰ in δ18O of Pi depending on the enzyme. We attribute the enzyme dependence of the isotopic fractionation to distinct reaction mechanisms of the two types of phosphatases. The observed difference is large enough to distinguish between the two enzymatic processes in environmental samples. These findings show that the oxygen isotope composition of Pi can be used to trace different enzymatic processes, offering an analytical tool that might contribute to a better understanding of the P-cycle in the environment.

  16. The geochemical record of the ancient nitrogen cycle, nitrogen isotopes, and metal cofactors.

    PubMed

    Godfrey, Linda V; Glass, Jennifer B

    2011-01-01

    The nitrogen (N) cycle is the only global biogeochemical cycle that is driven by biological functions involving the interaction of many microorganisms. The N cycle has evolved over geological time and its interaction with the oxygen cycle has had profound effects on the evolution and timing of Earth's atmosphere oxygenation (Falkowski and Godfrey, 2008). Almost every enzyme that microorganisms use to manipulate N contains redox-sensitive metals. Bioavailability of these metals has changed through time as a function of varying redox conditions, and likely influenced the biological underpinnings of the N cycle. It is possible to construct a record through geological time using N isotopes and metal concentrations in sediments to determine when the different stages of the N cycle evolved and the role metal availability played in the development of key enzymes. The same techniques are applicable to understanding the operation and changes in the N cycle through geological time. However, N and many of the redox-sensitive metals in some of their oxidation states are mobile and the isotopic composition or distribution can be altered by subsequent processes leading to erroneous conclusions. This chapter reviews the enzymology and metal cofactors of the N cycle and describes proper utilization of methods used to reconstruct evolution of the N cycle through time.

  17. Toward forward modeling for paleoclimatic proxy signal calibration: A case study with oxygen isotopic composition of tropical woods

    NASA Astrophysics Data System (ADS)

    Evans, M. N.

    2007-07-01

    A forward model of the oxygen isotopic composition (δ18O) of wood cellulose is parameterized for time series prediction in tropical environments and driven with meteorological data observed at La Selva Biological Research Station, Costa Rica, for 1985-2001. Monthly-resolution model results correlate modestly (r = 0.34, p < 0.05) with observed isotopic data, with higher correlation (r = 0.45, p < 0.01) over the earliest 10 years of comparison and nonsignificant correlation over the most recent 6 years of record. Analysis of model output for La Selva suggests that isotopic variations are strongly controlled by rainfall amount. The model simulates an analogous but stronger than observed negative isotopic anomaly associated with positive July-September rainfall anomalies during El Niño-Southern Oscillation (ENSO) warm phase event years. Simulated tree isotope data for the global tropics suggest that a network of well-replicated data series from selected locations may resolve the large-scale precipitation anomaly pattern associated with ENSO.

  18. Variability in magnesium, carbon and oxygen isotope compositions, and trace element contents of brachiopod shells: implications for paleoceanographic studies

    NASA Astrophysics Data System (ADS)

    Rollion-Bard, Claire; Saulnier, Ségolène; Vigier, Nathalie; Schumacher, Aimryc; Chaussidon, Marc; Lécuyer, Christophe

    2016-04-01

    Magnesium content in the ocean is ≈ 1290 ppm and is one of the most abundant elements. It is involved in the carbon cycle via the dissolution and precipitation of carbonates, especially Mg-rich carbonates as dolomites. The Mg/Ca ratio of the ocean is believed to have changed through time. The causes of these variations, i.e. hydrothermal activity change or enhanced precipitation of dolomite, could be constrained using the magnesium isotope composition (δ26Mg) of carbonates. Brachiopods, as marine environmental proxies, have the advantage to occur worldwide in a depth range from intertidal to abyssal, and have been found in the geological record since the Cambrian. Moreover, as their shell is in low-Mg calcite, they are quite resistant to diagenetic processes. Here we report δ26Mg, δ18O, δ13C values along with trace element contents of one modern brachiopod specimen (Terebratalia transversa) and one fossil specimen (Terebratula scillae, 2.3 Ma). We combined δ26Mg values with oxygen and carbon isotope compositions and trace element contents to look for possible shell geochemical heterogeneities in order to investigate the processes that control the Mg isotope composition of brachiopod shells. We also evaluate the potential of brachiopods as a proxy of past seawater δ26Mg values. The two investigated brachiopod shells present the same range of δ26Mg variation (up to 2 ‰)). This variation cannot be ascribed to changes in environmental parameters, i.e. temperature or pH. As previously observed, the primary layer of calcite shows the largest degree of oxygen and carbon isotope disequilibrium relative to seawater. In contrast, the δ26Mg value of this layer is comparable to that of the secondary calcite layer value. In both T. scillae and T. transversa, negative trends are observable between magnesium isotopic compositions and oxygen and carbon isotopic compositions. These trends, combined to linear relationships between δ26Mg values and REE contents, are best

  19. Intramolecular oxygen isotope ratios of a global stem cellulose sample set: insight into a climate proxy.

    NASA Astrophysics Data System (ADS)

    Sternberg, L.; Pinzon, M. C.; Vendramini, P.; Anderson, W.; Jahren, H.; Beuning, K.

    2006-12-01

    Oxygen isotope ratios of cellulose have been used to interpret current and paleo-climate. However, our knowledge of biochemical processes leading to cellulose oxygen isotope ratios is limited. We have previously developed a technique to determine the oxygen isotope ratio of the oxygen attached to the second carbon separate from the average oxygen isotope ratio of the oxygen attached to carbon 3, 4, 5 and 6 of the cellulose glucose moieties. Cellulose, representing the average δ18O value of oxygen attached to carbon 2, 3, 4, 5 and 6, is hydrolyzed to glucose, followed by the synthesis of phenylglucosazone, which represents the average δ18O value of oxygen attached to carbon 3, 4, 5 and 6. With the δ18O values of cellulose and phenyglucosazone it is possible to calculate the δ18O value of oxygen attached to the second carbon of the cellulose glucose moieties. We use this technique to elucidate biochemical processes causing oxygen isotopic fractionation during cellulose synthesis. We show here with stem samples from several areas of the world that the changes in the δ18O value of cellulose is non linear relative to those of stem water and this lack of linearity is in part caused by changes in the biochemical fractionation during cellulose synthesis. The biochemical cause of this non-linearity is confirmed by a compilation of previously published oxygen isotope ratios of aquatic plant cellulose in relation to that of lake water showing a curvilinear relationship parallel to the δ18O value of stem cellulose vs stem water in terrestrial plants. This non linearity is, in part, caused by the large variation in the δ18O value of the oxygen attached to the second carbon which super-imposes isotopic noise on the stem cellulose isotopic signals. This conclusion is supported by examining the three best fit multiple linear regression equations between oxygen isotope ratios of stem water and relative humidity as independent factors with either δ18O values of (1) cellulose

  20. Temperature and Oxygen Isotope Composition of The Ediacaran Ocean: Constraints From Clumped Isotope Carbonate Thermometry

    NASA Astrophysics Data System (ADS)

    Bonifacie, M.; Eiler, J. M.; Fike, D. A.

    2008-12-01

    The temperature and chemical variations of the early oceans on Earth are highly debated, particularly for periods associated with significant evolutionary change and/or extinction. The temperature of past oceans has been estimated based on conventional carbonate-water and/or silicate-water stable oxygen isotope thermometry. Precambrian carbonates and silicates both exhibit a long-term secular trend of increasing δ18O values with decreasing age. This trend has been used to support two opposite - though related - interpretations: the Earth's oceans gradually cooled over the course of the Proterozoic eon, from a maximum of ~ 60-90°C at ~ 2.5Ga (and were, on average, relatively warm during much of the Paleozoic era) [1]. This interpretation has been supported by Si-isotope proxies and the thermal tolerances of proteins in various classes of microbial organisms [2-3]. Alternatively, the δ18O value of the oceans has gradually increased through time [4-5], and mean Earth surface temperatures varied over a narrow range similar to modern conditions. In other terms, one either assumes an ocean of constant δ18O and infers that climate varied dramatically, or vise versa. Finally, it is possible that post- depositional processes (e.g., diagenesis, burial metamorphism, weathering) has modified the δ18O values of all or most Precambrian sedimentary carbonates and silicates, overprinting any paleoclimatic variations. Carbonate 'clumped isotope' thermometry provides a new way to independently test these hypotheses because it allows one to determine the apparent growth temperatures of carbonate minerals based on their abundances of 13C-18O bonds, as reflected by the 'Δ47' value of CO2 extracted by phosphoric acid digestion [6]. This method is thermodynamically based and independent of the δ18O of water from which the carbonate grew. We will report the initial results of measurements of 'Δ47 for a suite of carbonates from the Sultanate of Oman. This Ediacaran age (~ 635 to

  1. Carbon and oxygen isotope variations in Precambrian cherts

    SciTech Connect

    Robert, F. )

    1988-06-01

    Isotopic compositions of O in bulk Precambrian cherts and of C in the insoluble organic matter trapped in the silica have been determined. A general negative correlation relates these two variables and indicates that post-depositional alteration may have markedly modified the pristine isotopic ratios of the C compounds and their hosts. This interpretation is in good agreement with the expected isotopic trends for C and O resulting from secondary geological thermal events. Based on this correlation, a maximum {delta}{sup 13}C value of ca. {minus}33{per thousand}/PDB is proposed for the Precambrian kerogen. The difference between Proterozoic and Phanerozoic ({minus}27{per thousand}) {delta}{sup 13}C values could be linked to the flowering of life at the end of the Precambrian.

  2. Oxygen isotope biogeochemistry of phosphate in brackish marginal seas: I. The Black Sea

    NASA Astrophysics Data System (ADS)

    Isensee, Kirsten; Hille, Sven; Dellwig, Olaf; Blake, Ruth; Böttcher, Michael E.

    2010-05-01

    Phosphorus (P) is an important limiting nutrient for primary production in aquatic ecosystems. Therefore, it is important to understand the sources and biogeochemical cycling of different P species. Biotic and abiotic processes, like the uptake and metabolism of inorganic and organic P compounds, enzymatic regeneration of P, redox controlled sorption and release of phosphates and precipitation of apatite or other P containing solids can alter the isotopic composition of oxygen in dissolved and particulate phosphorus matter. The Black Sea is known as the world's largest permanently modern euxinic basin - the Type System for anoxia in Earth's history. Strong gradients for dissolved species are observed across the redoxcline and a zonation of the biogeochemical processes occurs along the stratified water column and further within the sediments. Oxygen isotope analyses of phosphate were carried out as a additional tool to allow the evaluation of biotic and abiotic influences on the P cycle. We analyzed for the first time, the oxygen isotope composition of DIP (d18OP) in the water column of the Black Sea and compared the results to inorganic P extracted from laminated brackish and limnic sediments. Samples were recovered during two cruises (M51/4, M72/5) of the research vessel RV METEOR. Besides hydrographical and physical parameters, particulate P and Fe, as well as dissolved constituents, like DIP, O2 and H2S, were analyzed for water column samples. Oxygen isotope compositions of phosphate were measured after conversion to silver phosphate, and then results were compared with published values for oxygen isotope compositions of water. In addition, oxygen isotope compositions of inorganic phosphate bound to laminated brackish (MUC sample) and bioturbated (formerly limnic) sediments were determined. We found an increase in δ18OP from the redoxcline down to the deep anoxic waters. The isotope values even exceed the calculated equilibrium composition. The increase in d18

  3. Comparison of oxygen isotope values from bulk lake sediment and ostracod valves

    NASA Astrophysics Data System (ADS)

    Teng, J.; Blisniuk, P.

    2012-12-01

    The oxygen isotope composition of the water in a lake is largely controlled by the isotopic composition of precipitation in the lake's catchment area, which is, in turn, controlled by a variety of geographic and climatic factors. Accordingly, the potential to reconstruct past isotopic compositions of lake water using authigenic minerals formed in isotopic equilibrium with the lake water makes lake sediments a promising target for paleoclimate reconstructions. Several different materials can be utilized to reconstruct the oxygen isotope composition of paleo-lake water. These include biogenic carbonates, such as shells of macrofossils (e.g., clams and snails), microfossils, (e.g., ostracods) and chemically precipitated carbonates in bulk lake sediment. To evaluate the suitability of different materials for the reconstruction of oxygen isotope values of past precipitation, we compared the oxygen isotope values of bulk lake sediments and ostracod microfossils that were extracted from an 800 meters thick sequence of sediments in the Zada Basin, southwestern Tibet. The sediment was wet-sieved for grain size separation, and the <63 um size fraction was used for the analysis of the bulk lake sediment. The ostracod microfossils were typically separated from the 125-500 um size fraction. Ostracod valves were cleaned using deionized water and ultrasound. When this did not successfully clean them, we used a brush under a microscope. Preliminary results of our work yielded oxygen isotope values of -2 to -22 permil for bulk lake sediment and a narrower range of -4 to -15 permil for ostracod valves (relative to PDB). In some stratigraphic levels, the oxygen isotope values differed by as much as 10 permil. These differences are significantly higher than offsets of several permil which are commonly observed as the result of species specific vital effects during biogenic calcite precipitation. A plausible explanation for this is that the lake sediment contains a significant portion

  4. Timing and extent of early marine oxygen isotope stage 2 alpine glaciation in Skagit Valley, Washington

    NASA Astrophysics Data System (ADS)

    Riedel, Jon L.; Clague, John J.; Ward, Brent C.

    2010-03-01

    Twenty-two new radiocarbon ages from Skagit valley provide a detailed chronology of alpine glaciation during the Evans Creek stade of the Fraser Glaciation (early marine oxygen isotope stage (MIS) 2) in the Cascade Range, Washington State. Sediments at sites near Concrete, Washington, record two advances of the Baker valley glacier between ca. 30.3 and 19.5 cal ka BP, with an intervening period of glacier recession about 24.9 cal ka BP. The Baker valley glacier dammed lower Skagit valley, creating glacial Lake Concrete, which discharged around the ice dam along Finney Creek, or south into the Sauk valley. Sediments along the shores of Ross Lake in upper Skagit valley accumulated in glacial Lake Skymo after ca. 28.7 cal ka BP behind a glacier flowing out of Big Beaver valley. Horizontally laminated silt and bedded sand and gravel up to 20 m thick record as much as 8000 yr of deposition in these glacially dammed lakes. The data indicate that alpine glaciers in Skagit valley were far less extensive than previously thought. Alpine glaciers remained in advanced positions for much of the Evans Creek stade, which may have ended as early as 20.8 cal ka BP.

  5. Determination of fractionation of oxygen isotopes between rice grain and environmental water

    NASA Astrophysics Data System (ADS)

    Kaushal, R.; Ghosh, P.

    2013-12-01

    Oxygen isotopic composition (δ18O) of plant organic matter (POM) serves as a valuable proxy for paleoclimatic studies [1].The δ18O of POM emulates the isotopic composition of the source water [2]. Rice crop cultivation goes back to 12,000 years, when rice was first domesticated in China and the earliest cultivation of rice observed in India was during 3000- 2500 BC. Presently rice is cultivated in many countries around the world including India where the prerequisite of saturated soil water condition for optimum growth of rice crop is provided by the South west monsoons. Earlier studies on δ18O of rice have been limited to its geographic characterization [3]. However, detailed investigations to determine fractionation of oxygen isotopes in water, in different parts of a rice plant, with rice seed organic matter is the primary objective of this work. This is important for understanding the mechanism responsible for the transfer of source water signature to the seed organics and can facilitate understanding of past monsoonal regime using well preserved rice grain remains from archaeological sites. Water from the leaves and culms was extracted by means of heating and cryogenic distillation in a vacuum extraction system [4]. The source water and the water extracted from plant parts were analysed by CO2 equilibration method using Gas Bench peripheral. Rice seed powder, after removal of husk, is composed primarily of starch and were analysed using High Temperature Conversion-Elemental Analyser. Both these peripherals were coupled to an Isotope Ratio Mass spectrometer- MAT253 (Thermo Finnigan). Experimental results discussed here were based on greenhouse and field based studies of water and seed organic composition. The water fed to the plant in the green house showed an average δ18O value of -0.50‰ whereas the field water from irrigation covering the time of grain filling ranges between -1.03‰ and -3.08‰. Figure 1 displays the extent of enrichment recorded in

  6. Oxygen isotope diffusion and zoning in diopside: The importance of water fugacity during cooling

    SciTech Connect

    Edwards, K.J.; Valley, J.W.

    1998-07-01

    The oxygen isotope ratio of diopside correlates with crystal size in many high grade marbles, permitting the intracrystalline self-diffusion rate of oxygen in diopside to be empirically evaluated. Small (75--300 {micro}m) and large (1.2--1.5 mm) diopside grains were analyzed in bulk for their oxygen isotope ratios by laser extraction. Cooling histories were calculated using the Fast Grain Boundary diffusion model, assuming equilibrium at peak metamorphic temperatures (700--800 C), slow cooling of 1.5--4 C/Ma, and experimentally determined diffusion coefficients for oxygen in minerals. Measurements and calculations to predict differences in {delta}{sup 18}O between large and small diopside grains lead to the following conclusions. (1) Natural diopsides in this study exhibit variations in oxygen isotope ratios between grains of different size, which are related to the peak temperature, cooling rate, and water fugacity during cooling. Diffusion distances are properly modeled by the size of an entire grain; there is no evidence for subdomains. (2) In slowly cooled high grade metamorphic terrains, water fugacity can be highly variable from rock to rock during cooling. For many rocks, water fugacity is the most important constraint on the degree of oxygen isotope retrograde exchange.

  7. Oxygen and Sulfur Isotope Composition of Dissolved Sulfate in Interstitial Waters of the Great Australian Bight, ODP Leg 182.

    NASA Astrophysics Data System (ADS)

    Bernasconi, S. M.; Böttcher, M. E.; Wormann, U. G.

    2005-12-01

    We measured the sulfur and oxygen isotope composition of dissolved sulfides and sulfate at ODP Sites 1129, 1130, 1131 and 1132 in the Great Australian Bight (GAB). At all Sites, a saline brine is present in the subsurface as indicated by increasing chloride concentrations with depth to reach contents up to 3 times seawater. Sulfate also increases with depth but the concentrations are reduced by intense microbial sulfate reduction. The sulfur isotope fractionation between coexisting dissolved sulfate and sulfide is very large and reaches up to 70 ‰ at all studied Sites. Due to the high sulfide concentrations and the lack of a significant source of oxidants we consider that the large sulfur isotope fractionations are induced by sulfate reducing bacteria alone without a significant contribution of elemental sulfur disproportionation and sulfide oxidation processes. The oxygen isotope composition of dissolved sulfate reaches maximum values of approximately +27 ‰ vs. VSMOW at all sites, close to the equilibrium isotope fractionation between sulfate and water. The oxygen isotope composition of dissolved sulfate positively correlates with the sulfur isotope fractionation between sulfate and sulfide. These oxygen isotope data thus support the hypothesis that that the high sulfur isotope fractionation are related to a single step fractionation by sulfate reducing bacteria and do not involve significant sulfide oxidation reactions and/or elemental sulfur disproportionation. Sulfide oxidation processes would lead to a lowering of the oxygen isotope composition of residual sulfate. Elemental sulfur disproportionation has been shown to increase the oxygen isotope composition of sulfate but to a smaller extent than that that observed in the GAB. The patterns of the oxygen isotope increase with progressive sulfate reduction indicate a predominant influence of isotope exchange rather than a kinetic isotope fractionation controlling the oxygen isotope composition of sulfate

  8. Oxygen Isotope Composition of Evapotranspiration and its Relation to C4 Photosynthetic Discrimination

    NASA Astrophysics Data System (ADS)

    Griffis, T. J.; Lee, X.; Sargent, S.; Baker, J. M.; Billmark, K.; Schultz, N.; Erickson, M.; Zhang, X.; Fassbinder, J.; Xiao, W.; Hu, N.

    2009-12-01

    The oxygen isotope composition (δ18O) of atmospheric water vapor (H2O) and carbon dioxide (CO2) is an important signal of global change and has been used to diagnose the palaeoclimate record, elucidate plant-water relations, and constrain regional carbon sinks/sources. At the present time there is very limited capacity to quantify the δ18O of H2O and CO2 exchange between the land and atmosphere. Of particular interest to carbon cycle studies that use δ18O as a tracer is the need to determine the isotope composition of leaf water at the sites of evaporation (δL,e). δL,e can not be measured directly, but represents a critical boundary condition for determining C18O16O discrimination. Here we use simultaneous observations of the δ18O composition of water vapor and carbon dioxide exchange using a combination of eddy covariance (EC), automated chambers, and tunable diode laser spectroscopy to investigate the relation between canopy leaf water enrichment and photosynthetic discrimination in a C4 (Zea mays L.) ecosystem. The objectives of the study were to: 1) present new results of isotopic water vapor flux measurements based on the EC methodology; 2) examine the influence of evapotranspiration on the isotopic composition of the atmosphere (isoforcing); 3) evaluate the extent of H218O-C18O16O equilibration at the canopy scale; and 4) refine our understanding regarding the role of C4 ecosystems in the budgets of C18O16O and H218O. Data and analyses are presented from experiments that were conducted in the laboratory and in the field at the University of Minnesota over the period August 8, 2008 to August 31, 2009. Our preliminary results indicate that the oxygen isotope composition of evapotranspiration (δET) ranged from about -20‰ (VSMOW scale) in the early morning to -5‰ after midday. These values were used to estimate δL,e and to evaluate the steady state/non-steady behavior of C4 vegetation. δL,e showed a strong diurnal pattern with typical values ranging

  9. Hydrogen and oxygen isotope exchange reactions between clay minerals and water

    USGS Publications Warehouse

    O'Neil, J.R.; Kharaka, Y.K.

    1976-01-01

    The extent of hydrogen and oxygen isotope exchange between clay minerals and water has been measured in the temperature range 100-350?? for bomb runs of up to almost 2 years. Hydrogen isotope exchange between water and the clays was demonstrable at 100??. Exchange rates were 3-5 times greater for montmorillonite than for kaolinite or illite and this is attributed to the presence of interlayer water in the montmorillonite structure. Negligible oxygen isotope exchange occurred at these low temperatures. The great disparity in D and O18 exchange rates observed in every experiment demonstrates that hydrogen isotope exchange occurred by a mechanism of proton exchange independent of the slower process of O18 exchange. At 350?? kaolinite reacted to form pyrophyllite and diaspore. This was accompanied by essentially complete D exchange but minor O18 exchange and implies that intact structural units in the pyrophyllite were inherited from the kaolinite precursor. ?? 1976.

  10. Oxygen and iron isotope constraints on near-surface fractionation effects and the composition of lunar mare basalt source regions

    NASA Astrophysics Data System (ADS)

    Liu, Yang; Spicuzza, Michael J.; Craddock, Paul R.; Day, James M. D.; Valley, John W.; Dauphas, Nicolas; Taylor, Lawrence A.

    2010-11-01

    Oxygen and iron isotope analyses of low-Ti and high-Ti mare basalts are presented to constrain their petrogenesis and to assess stable isotope variations within lunar mantle sources. An internally-consistent dataset of oxygen isotope compositions of mare basalts encompasses five types of low-Ti basalts from the Apollo 12 and 15 missions and eight types of high-Ti basalts from the Apollo 11 and 17 missions. High-precision whole-rock δ 18O values (referenced to VSMOW) of low-Ti and high-Ti basalts correlate with major-element compositions (Mg#, TiO 2, Al 2O 3). The observed oxygen isotope variations within low-Ti and high-Ti basalts are consistent with crystal fractionation and match the results of mass-balance models assuming equilibrium crystallization. Whole-rock δ 56Fe values (referenced to IRMM-014) of high-Ti and low-Ti basalts range from 0.134‰ to 0.217‰ and 0.038‰ to 0.104‰, respectively. Iron isotope compositions of both low-Ti and high-Ti basalts do not correlate with indices of crystal fractionation, possibly owing to small mineral-melt iron fractionation factors anticipated under lunar reducing conditions. The δ 18O and δ 56Fe values of low-Ti and the least differentiated high-Ti mare basalts are negatively correlated, which reflects their different mantle source characteristics (e.g., the presence or absence of ilmenite). The average δ 56Fe values of low-Ti basalts (0.073 ± 0.018‰, n = 8) and high-Ti basalts (0.191 ± 0.020‰, n = 7) may directly record that of their parent mantle sources. Oxygen isotope compositions of mantle sources of low-Ti and high-Ti basalts are calculated using existing models of lunar magma ocean crystallization and mixing, the estimated equilibrium mantle olivine δ 18O value, and equilibrium oxygen-fractionation between olivine and other mineral phases. The differences between the calculated whole-rock δ 18O values for source regions, 5.57‰ for low-Ti and 5.30‰ for high-Ti mare basalt mantle source regions

  11. Oxygen and strontium isotope tracing of human migration at the Bell Beaker site Le Tumulus des Sables, France.

    NASA Astrophysics Data System (ADS)

    Willmes, Malte; James, Hannah; Boel, Ceridwen; Courtaud, Patrice; Chancerel, Antoine; McMorrow, Linda; Armstrong, Richard; Kinsley, Les; Aubert, Maxime; Eggins, Stephen; Moffat, Ian; Grün, Rainer

    2014-05-01

    Oxygen (δ18O) and strontium (87Sr/86Sr) isotopes were used as tools to investigate human migration at the early Bell Beaker site (2500-2000 BC) Le Tumulus des Sables, Saint-Laurent-Médoc, south-west France. The O and Sr isotope ratios measured in tooth enamel record the average dietary isotope signature ingested by that individual during their childhood. When this data is compared to the isotope signature of the burial site it can be used to indicate if the individual migrated into this area during their lifetime. The O isotopic composition of meteoric water changes depending on climate, temperature and quantity of precipitation. O isotope ratios in skeletal and dental remains are related to body water, which in turn is influenced by diet, physiology and climate. Most of the water consumed by large mammals comes from drinking water, typically sourced locally. Sr isotope ratios on the other hand vary between different geologic regions, depending on their age and composition. Sr is released through weathering and transported into the soil, ground and surface water, where it becomes available for uptake by plants, enters the food cycle and eventually ends up in skeletal and dental tissue where it substitutes for calcium. We analysed the teeth of 18 adult and 8 juvenile disarticulated skeletons from Le Tumulus des Sables. O isotopes were analysed in-situ by Sensitive High Resolution Ion Micro Probe (SHRIMP).The Sr isotope analysis involved drilling a 0.2-0.5 mg sample of enamel from the tooth. The Sr was then chemically separated and analysed by Thermal Ionization Mass Spectrometry (TIMS). These results were then compared to the O isoscape of Europe and bioavailable Sr isotope data (fauna, plants, soils) from the IRHUM database. We found that most of the individuals at Le Tumulus des Sables show O and Sr isotope ratios corresponding to the local environmental signal and we interpret these as part of the local population. 3 adults however show slightly higher 87Sr/86

  12. Multiple taxon multiple locality approach to providing oxygen isotope evidence for warm-blooded theropod dinosaurs

    NASA Astrophysics Data System (ADS)

    Fricke, Henry C.; Rogers, Raymond R.

    2000-09-01

    Oxygen isotope ratios of fossil remains of coexisting taxa from several different localities can be used to help investigate dinosaur thermoregulation. Focusing on the Late Cretaceous, oxygen isotope ratios of crocodile tooth enamel from four separate localities exhibit less of a decrease with latitude than do ratios of tooth enamel from coexisting theropod dinosaurs. A shallower latitudinal gradient for crocodiles is consistent with how oxygen isotope ratios should vary for heterothermic animals having body temperatures coupled with their environments (“cold blooded”), while a steeper gradient for theropods is consistent with how these ratios should vary for homeothermic animals having constant body temperatures independent of their environments (“warm blooded”). This inferred homoethermy in theropods is likely due to higher rates of metabolic heat production relative to crocodiles and is not an artifact of body size.

  13. The abiotic disproportionation of sulfur dioxide (SO2) produces sulfate with an oxygen isotope signature close to the isotope composition of seawater sulfate

    NASA Astrophysics Data System (ADS)

    Müller, Inigo A.; Brunner, Benjamin; Max, Thomas; Breuer, Christian; Reeves, Eoghan P.; Thal, Janis; Bernasconi, Stefano M.; Bach, Wolfgang

    2013-04-01

    Whereas the sulfur isotope effects during the abiotic disproportionation of SO2 were thoroughly investigated in the last years, data on the oxygen isotope signature of produced sulfate is scarce. To fill in this gap in knowledge, we performed laboratory experiments which simulated the abiotic SO2 disproportionation at temperatures ranging from 150°C to 320°C. In our experiments SO2 disproportionated rapidly into sulfate and elemental sulfur. The oxygen isotope fractionation between produced sulfate and water is in the range of the observed oxygen isotope offset between seawater sulfate and seawater. The isotope fractionations observed for the experiments is likely composed of an initial kinetic oxygen isotope fractionation, which is rapidly overprinted by equilibrium oxygen isotope between sulfate and water (reaching completion probably within a time frame of ½ to 1 hour. Our observations raise the questions if disproportionation of magmatic SO2 in submarine hydrothermal vent systems is an important control for today's seawater sulfate isotope composition, and if so, if marine hydrothermal SO2 disproportiantion shaped the oxygen isotope signature of marine sulfate over geological times.

  14. No oxygen isotope exchange between water and APS-sulfate at surface temperature: Evidence from quantum chemical modeling and triple-oxygen isotope experiments

    NASA Astrophysics Data System (ADS)

    Kohl, Issaku E.; Asatryan, Rubik; Bao, Huiming

    2012-10-01

    In both laboratory experiments and natural environments where microbial dissimilatory sulfate reduction (MDSR) occurs in a closed system, the δ34S ((34S/32S)sample/(34S/32S)standard - 1) for dissolved SO42- has been found to follow a typical Rayleigh-Distillation path. In contrast, the corresponding δ18O ((18O/16O)sample/(18O/16O)standard) - 1) is seen to plateau with an apparent enrichment of between 23‰ and 29‰ relative to that of ambient water under surface conditions. This apparent steady-state in the observed difference between δ18O and δ18OO can be attributed to any of these three steps: (1) the formation of adenosine-5'-phosphosulfate (APS) from ATP and SO42-, (2) oxygen exchange between sulfite (or other downstream sulfoxy-anions) and water later in the MDSR reaction chain and its back reaction to APS and sulfate, and (3) the re-oxidation of produced H2S or precursor sulfoxy-anions to sulfate in environments containing Fe(III) or O2. This study examines the first step as a potential pathway for water oxygen incorporation into sulfate. We examined the structures and process of APS formation using B3LYP/6-31G(d,p) hybrid density functional theory, implemented in the Gaussian-03 program suite, to predict the potential for oxygen exchange. We conducted a set of in vitro, enzyme-catalyzed, APS formation experiments (with no further reduction to sulfite) to determine the degree of oxygen isotope exchange between the APS-sulfate and water. Triple-oxygen-isotope labeled water was used in the reactor solutions to monitor oxygen isotope exchange between water and APS sulfate. The formation and hydrolysis of APS were identified as potential steps for oxygen exchange with water to occur. Quantum chemical modeling indicates that the combination of sulfate with ATP has effects on bond strength and symmetry of the sulfate. However, these small effects impart little influence on the integrity of the SO42- tetrahedron due to the high activation energy required for

  15. Sulfur- and oxygen-isotopes in sediment-hosted stratiform barite deposits

    USGS Publications Warehouse

    Johnson, C.A.; Emsbo, P.; Poole, F.G.; Rye, R.O.

    2009-01-01

    Sulfur- and oxygen-isotope analyses have been obtained for sediment-hosted stratiform barite deposits in Alaska, Nevada, Mexico, and China to examine the environment of formation of this deposit type. The barite is contained in sedimentary sequences as old as Late Neoproterozoic and as young as Mississippian. If previously published data for other localities are considered, sulfur- and oxygen-isotope data are now available for deposits spanning a host-rock age range of Late Neoproterozoic to Triassic. On a ??34S versus ??18O diagram, many deposits show linear or concave-upward trends that project down toward the isotopic composition of seawater sulfate. The trends suggest that barite formed from seawater sulfate that had been isotopically modified to varying degrees. The ??34S versus ??18O patterns resemble patterns that have been observed in the modern oceans in pore water sulfate and water column sulfate in some anoxic basins. However, the closest isotopic analog is barite mineralization that occurs at fluid seeps on modern continental margins. Thus the data favor genetic models for the deposits in which barium was delivered by seafloor seeps over models in which barium was delivered by sedimentation of pelagic organisms. The isotopic variations within the deposits appear to reflect bacterial sulfate reduction operating at different rates and possibly with different electron donors, oxygen isotope exchange between reduction intermediates and H2O, and sulfate availability. Because they are isotopically heterogeneous, sediment-hosted stratiform barite deposits are of limited value in reconstructing the isotopic composition of ancient seawater sulfate.

  16. Sulfur- and oxygen-isotopes in sediment-hosted stratiform barite deposits

    NASA Astrophysics Data System (ADS)

    Johnson, Craig A.; Emsbo, Poul; Poole, Forrest G.; Rye, Robert O.

    2009-01-01

    Sulfur- and oxygen-isotope analyses have been obtained for sediment-hosted stratiform barite deposits in Alaska, Nevada, Mexico, and China to examine the environment of formation of this deposit type. The barite is contained in sedimentary sequences as old as Late Neoproterozoic and as young as Mississippian. If previously published data for other localities are considered, sulfur- and oxygen-isotope data are now available for deposits spanning a host-rock age range of Late Neoproterozoic to Triassic. On a δ 34S versus δ 18O diagram, many deposits show linear or concave-upward trends that project down toward the isotopic composition of seawater sulfate. The trends suggest that barite formed from seawater sulfate that had been isotopically modified to varying degrees. The δ 34S versus δ 18O patterns resemble patterns that have been observed in the modern oceans in pore water sulfate and water column sulfate in some anoxic basins. However, the closest isotopic analog is barite mineralization that occurs at fluid seeps on modern continental margins. Thus the data favor genetic models for the deposits in which barium was delivered by seafloor seeps over models in which barium was delivered by sedimentation of pelagic organisms. The isotopic variations within the deposits appear to reflect bacterial sulfate reduction operating at different rates and possibly with different electron donors, oxygen isotope exchange between reduction intermediates and H 2O, and sulfate availability. Because they are isotopically heterogeneous, sediment-hosted stratiform barite deposits are of limited value in reconstructing the isotopic composition of ancient seawater sulfate.

  17. Ground Based Observation of Isotopic Oxygen in the Martian Atmosphere Using Infrared Heterodyne Spectroscopy

    NASA Technical Reports Server (NTRS)

    Smith, R. L.; Kostiuk, T.; Livengood, T. A.; Fast, K. E.; Hewagama, T.; Delgado, J. D.; Sonnabend, G.

    2010-01-01

    Infrared heterodyne spectra of isotopic CO2 in the Martian atmosphere were obtained using the Goddard Heterodyne Instrument for Planetary Wind and Composition, HIPWAC, which was interfaced with the 3-meter telescope at the NASA Infrared Telescope Facility- Spectra were colle cted at a resolution of lambda/delta lambda=10(exp 7). Absorption fea tures of the CO2 isotopologues have been identified from which isotop ic ratios of oxygen have been determined. The isotopic ratios O-17/O -16 and O-18/O-16 in the Martian atmosphere can be related to Martian atmospheric evolution and can be compared to isotopic ratios of oxyg en in the Earth's atmosphere. Isotopic carbon and oxygen are importa nt constraints on any theory for the erosion of the Martian primordia l atmosphere and the interaction between the atmosphere and surface o r subsurface chemical reservoirs. This investigation explored the pr esent abundance of the stable isotopes of oxygen in Mars' atmospheric carbon dioxide by measuring rovibrational line absorption in isotop ic species of CO2 using groundbased infrared heterodyne spectroscopy in the vicinity of the 9.6 micron and 10.6 micron CO2 lasing bands. T he target transitions during this observation were O-18 C-12 O-16 as well as O-178 C-12 O-16 and O-16 C-113 O-16 at higher resolving power of lambda/delta lambda=10(exp 7) and with high signal-to-noise ratio (longer integration time) in order to fully characterize the absorpt ion line profiles. The fully-resolved lineshape of both the strong n ormal-isotope and the weak isotopic CO2 lines were measured simultane ously in a single spectrum.

  18. Uranium and molybdenum isotope evidence for an episode of widespread ocean oxygenation during the late Ediacaran Period

    NASA Astrophysics Data System (ADS)

    Kendall, Brian; Komiya, Tsuyoshi; Lyons, Timothy W.; Bates, Steve M.; Gordon, Gwyneth W.; Romaniello, Stephen J.; Jiang, Ganqing; Creaser, Robert A.; Xiao, Shuhai; McFadden, Kathleen; Sawaki, Yusuke; Tahata, Miyuki; Shu, Degan; Han, Jian; Li, Yong; Chu, Xuelei; Anbar, Ariel D.

    2015-05-01

    To improve estimates of the extent of ocean oxygenation during the late Ediacaran Period, we measured the U and Mo isotope compositions of euxinic (anoxic and sulfidic) organic-rich mudrocks (ORM) of Member IV, upper Doushantuo Formation, South China. The average δ238U of most samples is 0.24 ± 0.16‰ (2SD; relative to standard CRM145), which is slightly higher than the average δ238U of 0.02 ± 0.12‰ for restricted Black Sea (deep-water Unit I) euxinic sediments and is similar to a modeled δ238U value of 0.2‰ for open ocean euxinic sediments in the modern well-oxygenated oceans. Because 238U is preferentially removed to euxinic sediments compared to 235U, expanded ocean anoxia will deplete seawater of 238U relative to 235U, ultimately leading to deposition of ORM with low δ238U. Hence, the high δ238U of Member IV ORM points to a common occurrence of extensive ocean oxygenation ca. 560 to 551 Myr ago. The Mo isotope composition of sediments deposited from strongly euxinic bottom waters ([H2S]aq >11 μM) either directly records the global seawater Mo isotope composition (if Mo removal from deep waters is quantitative) or represents a minimum value for seawater (if Mo removal is not quantitative). Near the top of Member IV, δ98Mo approaches the modern seawater value of 2.34 ± 0.10‰. High δ98Mo points to widespread ocean oxygenation because the preferential removal of isotopically light Mo to sediments occurs to a greater extent in O2-rich compared to O2-deficient marine environments. However, the δ98Mo value for most Member IV ORM is near 0‰ (relative to standard NIST SRM 3134 = 0.25‰), suggesting extensive anoxia. The low δ98Mo is at odds with the high Mo concentrations of Member IV ORM, which suggest a large seawater Mo inventory in well-oxygenated oceans, and the high δ238U. Hence, we propose that the low δ98Mo of most Member IV ORM was fractionated from contemporaneous seawater. Possible mechanisms driving this isotope fractionation include

  19. Genetic relations among basic lavas and ultramafic nodules: Evidence from oxygen isotope compositions

    USGS Publications Warehouse

    Kyser, T.K.; O'Neil, J.R.; Carmichael, I.S.E.

    1982-01-01

    ??18O values of unaltered basic lavas range from 4.9 to 8.3 but different types of basalts are usually restricted to narrow and distinct ranges of isotopic composition. The average ??18O values for Hawaiian tholeiites, mid-ocean ridge tholeiites, and alkali basalts are 5.4, 5.7, and 6.2 permil, respectively. Potassic lavas and andesites tend to be more 18O rich with ??18O values between 6.0 and 8.0 permil. The differences among the oxygen isotopic compositions of most of these lavas can be attributed to partial melting of isotopically distinct sources. The oxygen isotope compositions of the sources may be a function of prior melting events which produce 18O-depleted partial melts and 18O-enriched residues as a consequence of relatively large isotopic fractionations that exist at high temperatures. It is proposed that lavas with relatively low ??18O values are derived from primitive, 18O-depleted sources whereas 18O-rich basalts are produced from refractory sources that have already produced partial melts. High temperature fractionations among silicate liquids and coexisting minerals can be used in conjunction with the oxygen isotope compositions of ultramafic nodules to place constraints on the genetic relations between some nodules and different types of basic lavas. ?? 1982 Springer-Verlag.

  20. Lake Louise Water (USGS47): A new isotopic reference water for stable hydrogen and oxygen isotope measurements

    USGS Publications Warehouse

    Qi, Haiping; Lorenz, Jennifer M.; Coplen, Tyler B.; Tarbox, Lauren V.; Mayer, Bernhard; Taylor, Steve

    2014-01-01

    RESULTS: The δ2H and δ18O values of this reference water are –150.2 ± 0.5 ‰ and –19.80 ± 0.02 ‰, respectively, relative to VSMOW on scales normalized such that the δ2H and δ18O values of SLAP reference water are, respectively, –428 and –55.5 ‰. Each uncertainty is an estimated expanded uncertainty (U = 2uc) about the reference value that provides an interval that has about a 95-percent probability of encompassing the true value. CONCLUSION: This isotopic reference material, designated as USGS47, is intended as one of two isotopic reference waters for daily normalization of stable hydrogen and stable oxygen isotopic analysis of water with a mass spectrometer or a laser absorption spectrometer. "

  1. Oxygen isotope calibration of the onset of ice-rafting and history of glaciation in the North Atlantic region

    USGS Publications Warehouse

    Shackleton, N.J.; Backman, J.; Zimmerman, H.; Kent, D.V.; Hall, M.A.; Roberts, David G.; Schnitker, D.; Baldauf, J.G.; Desprairies, A.; Homrighausen, R.; Huddlestun, P.; Keene, J.B.; Kaltenback, A.J.; Krumsiek, K.A.O.; Morton, A.C.; Murray, J.W.; Westberg-Smith, J.

    1984-01-01

    We report here that DSDP Site 552A, cored with the hydraulic piston corer on the west flank of Rockall Bank, recovered an undisturbed sequence of alternating white deep-sea carbonate oozes and dark-coloured layers that are rich in glacial debris. Oxygen isotope analysis of the sequence together with detailed nannofossil and palaeomagnetic stratigraphy shows that the first major horizon of ice-rafting occurred at about 2.4 Myr, and was preceded by a minor pulse of ice-rafting at about 2.5 Myr. The carbon isotope record shows that the site has been bathed by a water mass of similar characteristics to present-day North Atlantic deep water at least since 3.5 Myr. ?? 1984 Nature Publishing Group.

  2. Geologic implications of the oxygen isotope profile of the Toa Baja drill hole, Puerto Rico

    SciTech Connect

    Smith, B.M. )

    1991-03-01

    The whole-rock O-isotopic compositions of volcanic and volcaniclastic samples from the Toa Baja drill hole demonstrate that low-temperature (< 200C) processes have strongly enriched the island arc materials in {sup 18}O. Subsequent to eruption, processes such as subaerial weathering, alteration during transport and deposition in volcaniclastic aprons, submarine weathering, burial diagenesis, and prograde regional metamorphism through the beginning of the prehnite-pumpellyite facies have raised average whole-rock {delta}{sup 18}O values by {approximately}4% for basalt and andesite lava flows, and by {approximately}8% for volcaniclastic sandstones. These O-isotopic disturbances were probably caused by oxygen exchange with regionally circulating seawater under rather high-water/rock conditions. The processes associated with ageing' of volcanic and volcaniclastic materials in the oceanic environment are probably more important to the global budgets of the oxygen isotopes than has been assumed in the past. Integration of these results into global models for the oxygen isotopes awaits analysis of more varied oceanic terranes, to determine the generality of the O-isotopic conclusions proferred here, and to more carefully evaluate the relative sizes of volcanic, volcaniclastic, and oceanic oxygen reservoirs and their variabilities in time.

  3. Enhancement of ferromagnetism by oxygen isotope substitution in strontium ruthenate SrRuO3

    NASA Astrophysics Data System (ADS)

    Kawanaka, Hirofumi; Aiura, Yoshihiro; Hasebe, Takayuki; Yokoyama, Makoto; Masui, Takahiko; Nishihara, Yoshikazu; Yanagisawa, Takashi

    2016-10-01

    The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3 with a Curie temperature Tc of 160 K is studied. We observed for the first time a shift of ∆Tc ~ 1 K by oxygen isotope substitution of 16O → 18O in SrRuO3 by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient α = ‑∂ lnTc/∂ lnM. The Raman spectra indicate that the main vibration frequency of 16O at 363 cm‑1 shifts to 341 cm‑1 following oxygen isotope substitution 18O. This shift is remarkably consistent with the Debye frequency being proportional to ∝ 1√M where M is the mass of an oxygen atom. The positive isotope shift of ∆Tc can be understood by taking account of the electron-phonon interaction.

  4. Enhancement of ferromagnetism by oxygen isotope substitution in strontium ruthenate SrRuO3

    PubMed Central

    Kawanaka, Hirofumi; Aiura, Yoshihiro; Hasebe, Takayuki; Yokoyama, Makoto; Masui, Takahiko; Nishihara, Yoshikazu; Yanagisawa, Takashi

    2016-01-01

    The oxygen isotope effect of the ferromagnetic transition in itinerant ferromagnet strontium ruthenate SrRuO3 with a Curie temperature Tc of 160 K is studied. We observed for the first time a shift of ∆Tc ~ 1 K by oxygen isotope substitution of 16O → 18O in SrRuO3 by precise measurements of DC and AC magnetizations. The results surprisingly lead to the noteworthy inverse isotope effect with negative coefficient α = −∂ lnTc/∂ lnM. The Raman spectra indicate that the main vibration frequency of 16O at 363 cm−1 shifts to 341 cm−1 following oxygen isotope substitution 18O. This shift is remarkably consistent with the Debye frequency being proportional to ∝ 1√M where M is the mass of an oxygen atom. The positive isotope shift of ∆Tc can be understood by taking account of the electron-phonon interaction. PMID:27739475

  5. Recrystallization-induced oxygen isotope changes in inclusion-hosted water of speleothems - paleoclimatological implications

    NASA Astrophysics Data System (ADS)

    Demény, Attila; Czuppon, György; Leél-Őssy, Szabolcs; Németh, Péter; Szabó, Máté; Tóth, Mária; Németh, Tibor

    2016-04-01

    Stable hydrogen and oxygen isotope data of water trapped in fluid inclusions were collected for recently forming stalagmites and flowstones in order to determine how dripwater compositions are reflected and preserved in the inclusion water compositions. The samples were collected from different cave sites (with temperatures around 10 ± 1 °C) from the central and north-eastern parts of Hungary. Hydrogen isotope compositions were found to reflect dripwater values, whereas the oxygen isotope data were increasingly shifted from the local dripwater compositions with the time elapsed after deposition. The δ18O data are correlated with X-Ray diffraction full width at half maximum values (related to crystal domain size and lattice strain), suggesting that the oxygen isotope shift is related to recrystallization of calcite. Transmission electron microscope analyses detected the presence of nanocrystalline (<50 nm) calcite, whose crystallization to coarser-grained calcite crystals (>200 nm) may have induced re-equilibration between the carbonate and the trapped inclusion water. Additional data indicated that amorphous calcium carbonate (ACC) may have formed as a precursor of nanocrystalline calcite. ACC-calcite transformation followed by Ostwald ripening process provides an explanation for unexpectedly low oxygen isotope compositions in the inclusion water, especially in cold caves where carbonate may form first as an amorphous phase. This research was supported by the National Office for Research and Technology of Hungary (GVOP-3.2.1-2004-04-0235/3.0), the Hungarian Scientific Research Fund (OTKA CK 80661 and OTKA NK 101664).

  6. Influences on the stable oxygen and carbon isotopes in gerbillid rodent teeth in semi-arid and arid environments: Implications for past climate and environmental reconstruction

    NASA Astrophysics Data System (ADS)

    Jeffrey, Amy; Denys, Christiane; Stoetzel, Emmanuelle; Lee-Thorp, Julia A.

    2015-10-01

    The stable isotope composition of small mammal tissues has the potential to provide detailed information about terrestrial palaeoclimate and environments, because their remains are abundant in palaeontological and archaeological sites, and they have restricted home ranges. Applications to the Quaternary record, however, have been sparse and limited by an acute lack of understanding of small mammal isotope ecology, particularly in arid and semi-arid environments. Here we document the oxygen and carbon isotope composition of Gerbillinae (gerbil) tooth apatite across a rainfall gradient in northwestern Africa, in order to test the relative influences of the 18O/16O in precipitation or moisture availability on gerbil teeth values, the sensitivity of tooth apatite 13C/12C to plant responses to moisture availability, and the influence of developmental period on the isotopic composition of gerbil molars and incisors. The results show that the isotopic composition of molars and incisors from the same individuals differs consistent with the different temporal periods reflected by the teeth; molar teeth are permanently rooted and form around the time of birth, whereas incisors grow continuously. The results indicate that tooth choice is an important consideration for applications as proxy Quaternary records, but also highlights a new potential means to distinguish seasonal contexts. The oxygen isotope composition of gerbil tooth apatite is strongly correlated with mean annual precipitation (MAP) below 600 mm, but above 600 mm the teeth reflect the oxygen isotope composition of local meteoric water instead. Predictably, the carbon isotope composition of the gerbil teeth reflected C3 and C4 dietary inputs, however arid and mesic sites could not be distinguished because of the high variability displayed in the carbon isotope composition of the teeth due to the microhabitat and short temporal period reflected by the gerbil. We show that the oxygen isotope composition of small

  7. Climate forcings of changes in paleoprecipitation patterns in Brazil from oxygen isotope ratios on speleothems

    NASA Astrophysics Data System (ADS)

    da Cruz, F.; Cheng, H.; Barreto, E. S.; Wang, X.; Vuille, M.; Edwards, R.; Karmann, I.; Burns, S. J.; Auler, A.

    2009-12-01

    Stable oxygen isotope records in speleothems have provided new insights into changes in the tropical precipitation patterns over South America during Holocene. This is evident in the antiphasing observed between rainfall in northeastern Brazil and in areas affected by the South American Summer Monsoon (SASM), such as southern Brazil, the Amazon and the tropical Andes on orbital time-scales (Cruz et al., 2009). This pattern is attributed to changes in the strength of both Hadley and Walker-cells due to the influence of insolation on the global summer monsoons. A higher incoming austral summer insolation can intensify the SASM by favoring moisture convergence in the Amazon Basin and promote a substantial increase in monsoon precipitation in southern Brazil. Simultaneously, northeastern Brazil experiences arid conditions because of increased west-east upper-level subsidence induced by the convection in the monsoon core. A new speleothem record from Bahia State in NE Brazil confirms this antiphasing pattern of long-term precipitation for last 90 ky B.P. in Brazil, but in contrast with what is seen in southern Brazil, the records from the NE part of the country are mostly in phase with the Chinese speleothem records. Besides, it also shows that insolation exerts a strong forcing during MIS 5c to 5a, which is not as apparent during the MIS 4, 3 and 2. We suggest that the glacial boundary conditions play an important role in the SASM intensification between 60 and 20 ky during the latter marine isotope stages triggering wetter and drier conditions in southern and northeastern Brazil, respectively. On the other hand, the abrupt increases in precipitation during Heinrich events indicate a similar rainfall pattern everywhere in Brazil and suggest a more direct response from changes in oceanic conditions on millennial time-scales, which is relatively independent of monsoon activity in South America. References Cruz, F.W; Vuille, M.; Burns, S.J.; Wang, X.; Cheng H; Werner M

  8. Oxygen isotopic evidence for vigorous mixing during the Moon-forming giant impact.

    PubMed

    Young, Edward D; Kohl, Issaku E; Warren, Paul H; Rubie, David C; Jacobson, Seth A; Morbidelli, Alessandro

    2016-01-29

    Earth and the Moon are shown here to have indistinguishable oxygen isotope ratios, with a difference in Δ'(17)O of -1 ± 5 parts per million (2 standard error). On the basis of these data and our new planet formation simulations that include a realistic model for primordial oxygen isotopic reservoirs, our results favor vigorous mixing during the giant impact and therefore a high-energy, high-angular-momentum impact. The results indicate that the late veneer impactors had an average Δ'(17)O within approximately 1 per mil of the terrestrial value, limiting possible sources for this late addition of mass to the Earth-Moon system.

  9. The Oxygen Isotopic Composition of MIL 090001: A CR2 Chondrite with Abundant Refractory Inclusions

    NASA Technical Reports Server (NTRS)

    Keller, Lindsay P.; McKeegan, K. D.; Sharp, Z. D.

    2012-01-01

    MIL 090001 is a large (>6 kg) carbonaceous chondrite that was classified as a member of the CV reduced subgroup (CVred) that was recovered during the 2009-2010 ANSMET field season [1]. Based on the abundance of refractory inclusions and the extent of aqueous alteration, Keller [2] suggested a CV2 classification. Here we report additional mineralogical and petrographic data for MIL 090001, its whole-rock oxygen isotopic composition and ion microprobe analyses of individual phases. The whole rock oxygen isotopic analyses show that MIL 090001 should be classified as a CR chondrite.

  10. Carbon dioxide and oxygen isotope anomalies in the mesosphere and stratosphere

    SciTech Connect

    Thiemens, M.H.; Jackson, T.; Zipf, E.C.

    1995-11-10

    Isotopic ({delta}{sup 17}O and {delta}{sup 18}O) measurements of stratospheric and mesospheric carbon dioxide (CO{sub 2}) and oxygen (O{sub 2}), along with trace species concentrations (N{sub 2}O, CO, and CO{sub 2}), were made in samples collected from a rocket-borne cryogenic whole air sampler. A large mass-independent isotopic anomaly was observed in CO{sub 2}, which may in part derive from photochemical coupling to ozone (O{sub 3}). The data also require an additional isotopic fractionation process, which is presently unidentified. Mesospheric O{sub 2} isotope ratios differed from those in the troposphere and stratosphere. The cause of this isotopic variation in O{sub 2} is presently unknown. The inability to account for these observations represents a fundamental gap in the understanding of the O{sub 2} chemistry in the stratosphere and mesosphere. 28 refs., 2 figs., 1 tab.

  11. Ultrafiltration by a compacted clay membrane-I. Oxygen and hydrogen isotopic fractionation

    USGS Publications Warehouse

    Coplen, T.B.; Hanshaw, B.B.

    1973-01-01

    Laboratory experiments were carried out to determine the magnitude of the isotopic fractionation of distilled water and of 0.01 N NaCl forced to flow at ambient temperature under a hydraulic pressure drop of 100 bars across a montmorillonite disc compacted to a porosity of 35 per cent by a pressure of 330 bars. The ultrafiltrates in both experiments were depleted in D by 2.5%. and in O18 by 0.8%. relative to the residual solution. No additional isotopic fractionation due to a salt filtering mechanism was observed at NaCl concentrations up to 0.01 N. Adsorption is most likely the principal mechanism which produces isotopic fractionation, but molecular diffusion may play a minor role. The results suggest that oxygen and hydrogen isotopic fractionation of ground water during passage through compacted clayey sediments should be a common occurrence, in accord with published interpretations of isotopic data from the Illinois and Alberta basins. ?? 1973.

  12. Changes in Oxygen Isotopes Composition of Precipitation over Tibetan Plateau during Cenozoic

    NASA Astrophysics Data System (ADS)

    Botsyun, S.; Sepulchre, P.; Donnadieu, Y.; Risi, C. M.; Fluteau, F.

    2014-12-01

    Despite the increasing role of the stable oxygen isotopes measurements for reconstructing mountains belts paleoelevation, some issues remain that lead to a large uncertainty in paleoelevation estimationes. Among them, the use of modern isotopic lapse rate with no account of climate change linked to lower topography can lead to misinterpretation of uplift rates. In this study, we use the atmospheric general circulation model LMDZ-iso to simulate changes in isotopic composition of precipitation due to uplift of the Himalayas and Tibetan plateau. Various scenarios of TP growth have been applied together with Paleocene, Eocene, Oligocene and Miocene boundary conditions. Our simulations allow us to estimate the magnitude of precipitation, temperature and wind field changes related to the spatial and temporal evolution of the Tibetan Plateau and Himalayas. Such changes affected the isotopic composition of precipitation during the Cenozoic.We investigate the impact of these changes on the isotopic lapse rate and the implications for paleoelevation estimates.

  13. Late Eocene Antarctic glacial events revealed by radiogenic isotope records from the Kerguelen Plateau

    NASA Astrophysics Data System (ADS)

    Smith, B. W.; Munn, G. H.; Bohaty, S. M.; Scher, H. D.

    2011-12-01

    Oxygen isotope measurements of benthic foraminifera in ODP Hole 738B (Kerguelen Plateau, Southern Ocean) show a 0.6% shift toward more positive values at ca. 37.1 Ma, near the middle/late Eocene boundary. The δ18O values during this cool event reach 2.2%, which may reflect a combination of both intermediate deep-water cooling and partial glaciation of East Antarctica. We conducted neodymium (Nd) isotope measurements of the terrigenous detrital fraction (i.e., decarbonated and leached) from the same samples used to construct the stable isotope record. Our results reveal a shift in the Nd isotope composition of fine-grained material deposited on Kerguelen Plateau that coincides with the δ18O excursion. The background ɛNd values (i.e., before and after the δ18O shift) are -12 ɛNd, consistent with regionally sourced sediment from along the East Antarctica margin (e.g., Wilkes Land, Prydz Bay). During the δ18O excursion at 37.1 Ma, there is transient decrease in ɛNd values to -15.5. These results strongly indicate that Kerguelen Plateau received an influx of detrital material from ancient sediment sources (i.e., with low ɛNd values), such as those found in nearby Prydz Bay. Our results support an increase in continental ice volume in East Antarctica during this event, resulting in enhanced rates of mechanical weathering. We have also documented a second cool event ca. 36.7 Ma, approximately 400 kyr after the 37 Ma event. Future efforts will focus on determining the timing of middle-to-late Eocene cooling episoides and further documenting changes in weathering during each of these events.

  14. Intracellular phosphorous compounds and the reversibility of dissimilatory sulfate reduction: what do we learn from oxygen isotopes?

    NASA Astrophysics Data System (ADS)

    Brunner, B.

    2012-12-01

    Dissimilatory sulfate reduction (DSR) leads to an overprint of the oxygen isotope composition of sulfate by the oxygen isotope composition of water. This overprint is assumed to occur via cell-internally formed sulfuroxy intermediates in the sulfate reduction pathway. Unlike sulfate, the sulfuroxy intermediates can readily exchange oxygen isotopes with water. Subsequent to the oxygen isotope exchange, these intermediates, e.g. sulfite, are re-oxidized by reversible enzymatic reactions to sulfate, incorporating the oxygen used for the re-oxidation of the sulfur intermediates. Consequently, the rate and expression of DSR-mediated oxygen isotope exchange between sulfate and water depends not only on the oxygen isotope exchange between sulfuroxy intermediates and water, but also on cell-internal forward and backward reactions. The latter are the very same processes that control the extent of sulfur isotope fractionation expressed by DSR. In the stepwise reduction of sulfate to sulfide, intracellular phosphorous compounds are pivotal for the conversion of intracellular sulfate to sulfite. Because of thermodynamics, the concentration of thereby produced intracellular phosphorous compounds affects the reversibility of this reduction step and thereby impacts the oxygen isotope composition of sulfate. Consequently, there should be a link between cell-internal management of phosphorous pools and the expression of sulfur and oxygen isotope effects. The measurement of multiple sulfur isotope fractionation has successfully been applied to obtain information on the reversibility of individual enzymatically catalyzed steps in DSR. Similarly, also the oxygen isotope signature of sulfate reveals information on the reversibility of DSR. High reversibility (i.e. large isotope effects) is generally assumed to be tied to low energy availability. This raises the question if and how cell-internal management of phosphorous pools could be tied to survival strategies under energy limitation.

  15. Kinetic isotope effect in CO2 degassing: Insight from clumped and oxygen isotopes in laboratory precipitation experiments

    NASA Astrophysics Data System (ADS)

    Affek, Hagit P.; Zaarur, Shikma

    2014-10-01

    Laboratory precipitation experiments provide the basis for the common calibration of both the oxygen isotope and the clumped isotope thermometers. These focus on CaCO3 crystals that form deep in the bulk of the solution, often by the bubbling of N2(g) through a saturated Ca(HCO3)2 solution, following the classic experiments on McCrea (1950). Here we examine oxygen and clumped isotopes in CaCO3 that was precipitated at the surface of a solution that undergoes passive CO2 degassing. This CaCO3 is affected by enhanced disequilibrium that is associated with degassing, and has therefore higher δ18O and lower Δ47 values than those of the accepted thermometer calibrations. These offsets from the common thermometers calibrations increase with decreasing temperature for Δ47 but decrease with decreasing temperature for δ18O. The Δ47-δ18O co-variance is therefore strongly temperature dependent, in contrast to theoretical predictions. This suggests an influence of additional fractionation in fast growing minerals, between DIC and calcite, that affects δ18O and counteracts some of the degassing related enrichment. This effect seems not to influence Δ47. The physical setup of CaCO3 minerals growing at the solution surface is analogous to the degassing and precipitation processes that occur in stalagmites, such that these laboratory experiments may help shed light on the isotopic disequilibrium that is observed in speleothems.

  16. The cause of the seasonal variation in the oxygen isotopic composition of precipitation along the western U.S. coast

    NASA Astrophysics Data System (ADS)

    Buenning, N. H.; Stott, L. D.; Yoshimura, K.; Berkelhammer, M. B.

    2012-12-01

    This study seeks to find the primary influence on the seasonal cycle of the oxygen isotopic composition of precipitation (δ18Op) along the western U.S. coast. Observed long-term mean seasonal variations of δ18Op from 16 different stations along the west coast are presented. The most robust features in the observations are high values in the summer and a drop in δ18Op during the winter, a feature observed at many mid-latitude locations. The Isotope-incorporated Global Spectral Model (IsoGSM) also simulates this wintertime drop in δ18Op along the west coast of the U.S. To better understand the cause of this seasonal variation, sensitivity experiments are performed with IsoGSM where individual oxygen isotope fractionation processes are turned off. These simulations reveal that the primary control on the seasonal variations is equilibrium oxygen isotopic fractionation during vapor condensation. There is almost no influence of the temperature dependence of equilibrium fractionation on the seasonal δ18Op cycle for both ocean evaporation and vapor condensation. Additional experiments (including tagging simulations) are performed to better understand why Rayleigh distillation causes the seasonal variation in δ18Op. Tagging results suggest no strong influence of seasonal moisture source variations on the seasonal δ18Op cycle, though the seasonal cycle of column-integrated water vapor δ18O values is in phase with the monthly shifts in moisture sources (in IsoGSM). The tagging simulations did however reveal that vertical oxygen isotope gradients and variations in condensation height cause the seasonal cycle in δ18Op. This results from seasonal changes in the polar jet, and subsequent changes to divergence and vertical velocities, which affects the uplift of moisture. These findings suggest that δ18Op in the western U.S. is a tracer of condensation height on seasonal timescales. The large influence of condensation height on δ18Op seasonality complicates

  17. Seasonal variation in kangaroo tooth enamel oxygen and carbon isotopes in southern Australia

    NASA Astrophysics Data System (ADS)

    Brookman, Tom H.; Ambrose, Stanley H.

    2012-09-01

    Serial sampling of tooth enamel growth increments for carbon and oxygen isotopic analyses of Macropus (kangaroo) teeth was performed to assess the potential for reconstructing paleoseasonality. The carbon isotope composition of tooth enamel apatite carbonate reflects the proportional intake of C3 and C4 vegetation. The oxygen isotopic composition of enamel reflects that of ingested and metabolic water. Tooth enamel forms sequentially from the tip of the crown to the base, so dietary and environmental changes during the tooth's formation can be detected. δ13C and δ18O values were determined for a series of enamel samples drilled from the 3rd and 4th molars of kangaroos that were collected along a 900 km north-south transect in southern Australia. The serial sampling method did not yield pronounced seasonal isotopic variation patterns in Macropus enamel. The full extent of dietary isotopic variation may be obscured by attenuation of the isotopic signal during enamel mineralisation. Brachydont (low-crowned) Macropus teeth may be less sensitive to seasonal variation in isotopic composition due to time-averaging during mineralisation. However, geographic variations observed suggest that there may be potential for tracking latitudinal shifts in vegetation zones and seasonal environmental patterns in response to climate change.

  18. Laboratory chalcopyrite oxidation by Acidithiobacillus ferrooxidans: Oxygen and sulfur isotope fractionation

    USGS Publications Warehouse

    Thurston, R.S.; Mandernack, K.W.; Shanks, Wayne C.

    2010-01-01

    Laboratory experiments were conducted to simulate chalcopyrite oxidation under anaerobic and aerobic conditions in the absence or presence of the bacterium Acidithiobacillus ferrooxidans. Experiments were carried out with 3 different oxygen isotope values of water (??18OH2O) so that approach to equilibrium or steady-state isotope fractionation for different starting conditions could be evaluated. The contribution of dissolved O2 and water-derived oxygen to dissolved sulfate formed by chalcopyrite oxidation was unambiguously resolved during the aerobic experiments. Aerobic oxidation of chalcopyrite showed 93 ?? 1% incorporation of water oxygen into the resulting sulfate during the biological experiments. Anaerobic experiments showed similar percentages of water oxygen incorporation into sulfate, but were more variable. The experiments also allowed determination of sulfate-water oxygen isotope fractionation, ??18OSO4-H2O, of ~ 3.8??? for the anaerobic experiments. Aerobic oxidation produced apparent ??SO4-H2O values (6.4???) higher than the anaerobic experiments, possibly due to additional incorporation of dissolved O2 into sulfate. ??34SSO4 values are ~ 4??? lower than the parent sulfide mineral during anaerobic oxidation of chalcopyrite, with no significant difference between abiotic and biological processes. For the aerobic experiments, a small depletion in ??34SSO4 of ~- 1.5 ?? 0.2??? was observed for the biological experiments. Fewer solids precipitated during oxidation under aerobic conditions than under anaerobic conditions, which may account for the observed differences in sulfur isotope fractionation under these contrasting conditions. ?? 2009 Elsevier B.V.

  19. Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record

    NASA Astrophysics Data System (ADS)

    Leavitt, William D.; Halevy, Itay; Bradley, Alexander S.; Johnston, David T.

    2013-07-01

    Phanerozoic levels of atmospheric oxygen relate to the burial histories of organic carbon and pyrite sulfur. The sulfur cycle remains poorly constrained, however, leading to concomitant uncertainties in O2 budgets. Here we present experiments linking the magnitude of fractionations of the multiple sulfur isotopes to the rate of microbial sulfate reduction. The data demonstrate that such fractionations are controlled by the availability of electron donor (organic matter), rather than by the concentration of electron acceptor (sulfate), an environmental constraint that varies among sedimentary burial environments. By coupling these results with a sediment biogeochemical model of pyrite burial, we find a strong relationship between observed sulfur isotope fractionations over the last 200 Ma and the areal extent of shallow seafloor environments. We interpret this as a global dependency of the rate of microbial sulfate reduction on the availability of organic-rich sea-floor settings. However, fractionation during the early/mid-Paleozoic fails to correlate with shelf area. We suggest that this decoupling reflects a shallower paleoredox boundary, primarily confined to the water column in the early Phanerozoic. The transition between these two states begins during the Carboniferous and concludes approximately around the Triassic-Jurassic boundary, indicating a prolonged response to a Carboniferous rise in O2. Together, these results lay the foundation for decoupling changes in sulfate reduction rates from the global average record of pyrite burial, highlighting how the local nature of sedimentary processes affects global records. This distinction greatly refines our understanding of the S cycle and its relationship to the history of atmospheric oxygen.

  20. Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record.

    PubMed

    Leavitt, William D; Halevy, Itay; Bradley, Alexander S; Johnston, David T

    2013-07-01

    Phanerozoic levels of atmospheric oxygen relate to the burial histories of organic carbon and pyrite sulfur. The sulfur cycle remains poorly constrained, however, leading to concomitant uncertainties in O2 budgets. Here we present experiments linking the magnitude of fractionations of the multiple sulfur isotopes to the rate of microbial sulfate reduction. The data demonstrate that such fractionations are controlled by the availability of electron donor (organic matter), rather than by the concentration of electron acceptor (sulfate), an environmental constraint that varies among sedimentary burial environments. By coupling these results with a sediment biogeochemical model of pyrite burial, we find a strong relationship between observed sulfur isotope fractionations over the last 200 Ma and the areal extent of shallow seafloor environments. We interpret this as a global dependency of the rate of microbial sulfate reduction on the availability of organic-rich sea-floor settings. However, fractionation during the early/mid-Paleozoic fails to correlate with shelf area. We suggest that this decoupling reflects a shallower paleoredox boundary, primarily confined to the water column in the early Phanerozoic. The transition between these two states begins during the Carboniferous and concludes approximately around the Triassic-Jurassic boundary, indicating a prolonged response to a Carboniferous rise in O2. Together, these results lay the foundation for decoupling changes in sulfate reduction rates from the global average record of pyrite burial, highlighting how the local nature of sedimentary processes affects global records. This distinction greatly refines our understanding of the S cycle and its relationship to the history of atmospheric oxygen.

  1. Influence of sulfate reduction rates on the Phanerozoic sulfur isotope record

    PubMed Central

    Leavitt, William D.; Halevy, Itay; Bradley, Alexander S.; Johnston, David T.

    2013-01-01

    Phanerozoic levels of atmospheric oxygen relate to the burial histories of organic carbon and pyrite sulfur. The sulfur cycle remains poorly constrained, however, leading to concomitant uncertainties in O2 budgets. Here we present experiments linking the magnitude of fractionations of the multiple sulfur isotopes to the rate of microbial sulfate reduction. The data demonstrate that such fractionations are controlled by the availability of electron donor (organic matter), rather than by the concentration of electron acceptor (sulfate), an environmental constraint that varies among sedimentary burial environments. By coupling these results with a sediment biogeochemical model of pyrite burial, we find a strong relationship between observed sulfur isotope fractionations over the last 200 Ma and the areal extent of shallow seafloor environments. We interpret this as a global dependency of the rate of microbial sulfate reduction on the availability of organic-rich sea-floor settings. However, fractionation during the early/mid-Paleozoic fails to correlate with shelf area. We suggest that this decoupling reflects a shallower paleoredox boundary, primarily confined to the water column in the early Phanerozoic. The transition between these two states begins during the Carboniferous and concludes approximately around the Triassic–Jurassic boundary, indicating a prolonged response to a Carboniferous rise in O2. Together, these results lay the foundation for decoupling changes in sulfate reduction rates from the global average record of pyrite burial, highlighting how the local nature of sedimentary processes affects global records. This distinction greatly refines our understanding of the S cycle and its relationship to the history of atmospheric oxygen. PMID:23733944

  2. Stable iron isotope fractionation between aqueous Fe(II) and model Archean ocean Fe-Si coprecipitates and implications for iron isotope variations in the ancient rock record

    NASA Astrophysics Data System (ADS)

    Wu, Lingling; Percak-Dennett, Elizabeth M.; Beard, Brian L.; Roden, Eric E.; Johnson, Clark M.

    2012-05-01

    Iron isotope fractionation between aqueous Fe(II) (Fe(II)aq) and two amorphous Fe(III) oxide-Si coprecipitates was investigated in an aqueous medium that simulated Archean marine conditions, including saturated amorphous silica, low sulfate, and zero dissolved oxygen. The equilibrium isotope fractionation (in 56Fe/54Fe) between Fe(II)aq and Fe(III)-Si coprecipitates at circum-neutral pH, as inferred by the three-isotope method, was -3.51 ± 0.20 (2σ)‰ and -3.99 ± 0.17 (2σ)‰ for coprecipitates that had Fe:Si molar ratios of 1:2 and 1:3, respectively. These results, when combined with earlier work, indicate that the equilibrium isotope fractionation factor between Fe(II)aq and Fe(III)-Si coprecipitates changes as a function of Fe:Si ratio of the solid. Isotopic fractionation was least negative when Fe:Si = 1:1 and most negative when Fe:Si = 1:3. This change corresponds with changes in the local structure of iron, as revealed by prior spectroscopic studies. The kinetics of isotopic exchange was controlled by movement of Fe(II) and Si, where sorption of Fe(II) from aqueous to solid phase facilitated atom exchange, but sorption of Si hindered isotopic exchange through blockage of reactive surface sites. Although Fe(II)-Fe(III) isotopic exchange rates were a function of solid and solution compositions in the current study, in all cases they were much higher than that determined in previous studies of aqueous Fe(III) and ferrihydrite interaction, highlighting the importance of electron exchange in promoting Fe atom exchange. When compared to analogous microbial reduction experiments of overlapping Fe(II) to Fe(III) ratios, isotopic exchange rates were faster in the biological experiments, likely due to promotion of atom exchange by the solid-phase Fe(II) produced in the biological experiments. These results provide constraints for interpreting the relatively large range of Fe isotope compositions in Precambrian marine sedimentary rocks, and highlight important

  3. Variability of oxygen isotopes in water vapor, soil and leaf water and leaf cellulose along a steep environmental gradient in Hawaii

    NASA Astrophysics Data System (ADS)

    Kahmen, A.; Sachse, D.; Arndt, S.; Farrington, H.; Vitousek, P. M.; Dawson, T. E.

    2008-12-01

    The stable oxygen isotope ratio (δ18O) of plant organic mater (OM) has been shown to contain essential information on the ecophysiological performance of plants and for the understanding of water and carbon fluxes at the plant and ecosystem scales. The primary source of δ18O variability in plant OM is the isotopic composition of leaf water. In general, the isotopic composition of leaf water depends on the isotopic signature of the plant's source water, the isotopic composition of atmospheric vapor surrounding the leaf, the leaf to atmosphere vapor pressure gradient, the leaf's stomatal conductance and transpiration rates as well as leaf hydraulic properties. The combined influence of all these factors on isotopic leaf water enrichment clearly complicates the interpretation of plant δ18O signatures. However, significant recent improvements in mechanistic leaf water models have much advanced our understanding of the interplay of all these factors and their combined effects on isotopic leaf water enrichment. These models now give the theoretical background to constrain which of the multiple factors that potentially drive the isotopic enrichment of leaf water are finally recorded in plant OM. Along one of the steepest moisture gradients in the world - the eastern slope of the 4200 m volcano Mauna Loa (Hawaii) we tested the applicability of these models to constrain which environmental factors drive the isotopic variability in leaf water and OM of Metrosideros polymorpha, a tree species that inhabits the entire moisture gradient. On seven sites along the eastern slope of the 4200 m volcano Mauna Loa, we determined the isotopic signature of source water, leaf water and leaf cellulose. In addition, we also determined the diurnal isotopic enrichment of leaf water, the diurnal variability of the plant's stomatal conductance and transpiration rates and well as air temperature and humidity and the isotopic composition of atmospheric vapor on three core sites along the

  4. A 6000 year, quantitative reconstruction of precipitation variability in central Washington from lake sediment oxygen isotopes and predictive models

    NASA Astrophysics Data System (ADS)

    Steinman, B. A.; Abbott, M.; Rosenmeier, M. F.; Stansell, N.

    2010-12-01

    Oxygen isotope (δ18O) records from lake sediment have long been used to provide qualitative and/or semi-quantitative information on past hydroclimatic and glacial conditions. Strict quantitative interpretations of lake sediment δ18O records, that is, the estimation of specific values for past precipitation (P), temperature (T), and relative humidity (RH) from oxygen isotope ratios, have not yet been developed, although recent advances in the use of models designed to simulate lake hydrologic and isotopic responses to climate change have helped to define the range of climatic states capable of producing observed sediment core δ18O variations. For example, water budgets and isotopic mass balances within small, closed-basin lakes in semi-arid environments have been shown to respond most significantly over the short-term (i.e., transiently, over just a few years) to changes in P. At steady state (i.e., over multiple decades or longer) changes in T and RH (in addition to P) become important. Closed-basin lakes, however, are often subject to considerable inter-annual variability in climate (e.g., stochastic, year-to-year changes in P), and hence never truly exist in an equilibrium state. As a consequence, transient isotopic responses to stochastic (i.e., random), inter-annual climate change are typically more important (relative to steady state responses) in determining short term variability in the isotopic composition of lake sediment. Over the long term, transient responses can be averaged to produce isotopic values that are primarily a function of mean state (i.e., the long term average) climate conditions and to a lesser extent the stochastic state of climate (which, e.g., affects lake hydrologic balance through non-linear catchment runoff responses to P). Quantitative interpretation of sediment δ18O records therefore requires determination of stochastic and mean state changes in hydroclimatic variables. This necessity is complicated by the equifinality inherent

  5. Evaluation of Speleothem Oxygen Isotope Fractionation from a Tropical Cave on the Island of Guam

    NASA Astrophysics Data System (ADS)

    Moore, M. W.; Hardt, B. F.; Banner, J. L.; Jenson, J. W.

    2013-12-01

    Recent studies in the tropics apply oxygen isotope variations in speleothems as proxies for changes in past hydroclimate, yet little work has been done to study the modern tropical cave environment. Oxygen isotope time series in speleothems are commonly used to interpret past climate based on the assumption of equilibrium fractionation. When re-constructing paleoclimate, there are limited tools available to assess potential non-equilibrium isotope effects. One approach is to test for agreement of oxygen isotope values between parallel-milled tracks from a stalagmite. A stalagmite collected from Jinapsan Cave on the island of Guam supports the argument for equilibrium as multiple overlapping transects along the growth axis show consistent replication. However, to fully evaluate the fractionation processes relating to calcite growth, we have also studied the relationship between modern drip water and modern speleothem calcite. To accomplish this, we collected monthly dripwater samples and deployed artificial substrates under active drips to measure calcite growth rates and to assess the state of isotopic equilibrium between speleothem calcite and drip water. We evaluate the processes controlling the δ18O values of calcite formed on substrates relative to values for the dripwater feeding the site of the speleothem in Jinapsan Cave. The studied drip site shows seasonal variability in dripwater δ18O of ~1‰, with more negative composition occurring during the wet season. The δ18O of the substrate calcite sampled at the point of first growth (analogous to the growth axis in a speleothem) also shows a seasonal cycle of about 1‰, yet the values are more positive than predicted by the equilibrium equation of Kim & O'Neil 1997. In addition, carbon and oxygen isotopic composition between substrates strongly covary. Correlation of carbon and oxygen isotopes between substrates at the point of first growth may be explained by prior calcite precipitation. Carbon isotope

  6. Seasonal variability of soil phosphate stable oxygen isotopes in rainfall manipulation experiments

    NASA Astrophysics Data System (ADS)

    Angert, Alon; Weiner, Tal; Mazeh, Shunit; Tamburini, Federica; Frossard, Emmanuel; Bernasconi, Stefano M.; Sternberg, Marcelo

    2011-08-01

    Phosphorus (P) availability limits productivity in many ecosystems worldwide. As a result, improved understanding of P cycling through soil and plants is much desirable. The use of the oxygen isotopes associated to phosphate can be used to study the cycle of P in terrestrial systems. However, changes with time in the oxygen isotopes associated to available P have not yet been evaluated under field conditions. Here we present the variations in available-P oxygen isotopes, based on resin extractions, in a semi-arid site that included plots in which the amount of rainfall reaching the soil was modified. In addition, the oxygen isotopes in the less dynamic fraction which is extractable by HCl, were also measured. The δ 18O of the HCl-extractable phosphate shows no seasonal pattern and corresponds to the average value of the available phosphate of 16.5‰. This value is in the expected range for equilibration with soil water at the prevailing temperatures in the site. The δ 18O values of resin-extractable P showed a range of 14.5-19.1‰ (SMOW), and evidence of seasonal variability, as well as variability induced by rainfall manipulation experiments. We present a framework for analyzing the isotopic ratios in soil phosphate and explain the variability as mainly driven by phosphate equilibration with soil water, and by the isotopic effects associated with extracellular mineralization. Additional isotopic effects result from fractionation in uptake, and the input to the soil of phosphate equilibrated in leaves. These results suggest that the δ 18O of resin-extractable P is an interesting marker for the rate of biological P transformations in soil systems.

  7. Oxygen Isotope Systematics of Chondrules from the Least Equilibrated H Chondrite

    NASA Technical Reports Server (NTRS)

    Kita, N. T.; Kimura, M.; Ushikubo, T.; Valley, J. W.; Nyquist, L. E.

    2008-01-01

    Oxygen isotope compositions of bulk chondrules and their mineral separates in type 3 ordinary chondrites (UOC) show several % variability in the oxygen three isotope diagram with slope of approx.0.7 [1]. In contrast, ion microprobe analyses of olivine and pyroxene phenocrysts in ferromagnesian chondrules from LL 3.0-3.1 chondrites show mass dependent isotopic fractionation as large as 5% among type I (FeO-poor) chondrules, while type II (FeO-rich) chondrules show a narrow range (less than or equal to 1%) of compositions [2]. The .Delta(exp 17)O (=delta(exp 17)O-0.52xdelta(exp 18)O) values of olivine and pyroxene in these chondrules show a peak at approx.0.7% that are systematically lower than those of bulk chondrule analyses as well as the bulk LL chondrites [2]. Further analyses of glass in Semarkona chondrules show .17O values as high as +5% with highly fractionated d18O (max +18%), implying O-16-poor glass in chondrules were altered as a result of hydration in the parent body at low temperature [3]. Thus, chondrules in LL3.0-3.1 chondrites do not provide any direct evidence of oxygen isotope exchange between solid precursor and O-16-depleted gas during chondrule melting events. To compare the difference and/or similarity between chondrules from LL and H chondrites, we initiated systematic investigations of oxygen isotopes in chondrules from Yamato 793408 (H3.2), one of the least equilibrated H chondrite [4]. In our preliminary study of 4 chondrules, we reported distinct oxygen isotope ratios from dusty olivine and refractory forsterite (RF) grains compared to their host chondrules and confirmed their relict origins [5].

  8. The oxygen isotopic composition of captured solar wind: first results from the Genesis mission

    NASA Astrophysics Data System (ADS)

    McKeegan, K. D.; Coath, C. D.; Heber, V.; Jarzebinski, G.; Kallio, A.; Kunihiro, T.; Mao, P. H.; Burnett, D.

    2008-12-01

    Oxygen is the major constituent of rocky planets and the third most abundant element comprising the Sun, yet the solar oxygen isotopic composition has remained essentially unknown. One reason is that the usual appeal to primitive meteorites does not work because oxygen is isotopically distinct in all different classes of meteorites. The cause of this premier "isotopic anomaly" (first discovered in 1973) has been variously ascribed to nucleosynthetic input, e.g. from a nearby supernova, or to exotic isotope-selective chemistry in the solar nebula, e.g. based on molecular symmetry or UV photolysis. Knowledge of the average starting composition of the solar system, which is preserved in the Sun, would provide a baseline from which one could interpret the oxygen isotopic compositions of planetary materials. To this end, NASA flew the Genesis Mission to capture samples of the solar wind (SW) in ultra-pure target materials and return them to Earth for laboratory analysis. At UCLA, we have designed and constructed a hybrid secondary ion and accelerator mass spectrometer (SIMS/AMS), called the "MegaSIMS", specifically to tackle the unique analytical challenges posed by the Genesis samples: dilute elemental concentrations, limited sample material, and close proximity of likely surface contamination to the implanted solar wind ions. Three years after the crash- landing of the sample return capsule in the Utah desert, we have succeeded in making oxygen isotopic measurements on SW captured in a SiC target from the Genesis SW concentrator. Our preliminary data indicate that the Sun is enriched in 16O by at least 5% relative to Earth and meteorites. Implications for planetary science will be discussed.

  9. Oxygen isotopes in the early protoplanetary disk inferred from pyroxene in a classical type B CAI

    NASA Astrophysics Data System (ADS)

    Aléon, Jérôme

    2016-04-01

    A major unanswered question in solar system formation is the origin of the oxygen isotopic dichotomy between the Sun and the planets. Individual Calcium-Aluminum-rich inclusions (CAIs) from CV chondrites exhibit almost the full isotopic range, but how their composition evolved is still unclear, which prevents robust astrochemical conclusions. A key issue is notably the yet unsolved origin of the 16O-rich isotopic composition of pyroxene in type B CAIs. Here, I report an in-situ oxygen isotope study of the archetypal type B CAI USNM-3529-Z from Allende with emphasis on the isotopic composition of pyroxene and its isotopic and petrographic relationships with other major minerals. The O isotopic composition of pyroxene is correlated with indicators of magmatic growth, indicating that the pyroxene evolved from a 16O-poor composition and became progressively enriched in 16O during its crystallization, contrary to the long held assumption that pyroxene was initially 16O-rich. This variation is well explained by isotopic exchange between a 16O-poor partial melt having the isotopic composition of melilite and a 16O-rich gas having the isotopic composition of spinel, during pyroxene crystallization. The isotopic evolution of 3529-Z is consistent with formation in an initially 16O-rich environment where spinel and gehlenitic melilite crystallized, followed by a 16O-depletion associated with melilite partial melting and recrystallization and finally a return to the initial 16O-rich environment before pyroxene crystallization. This strongly suggests that the environment of CAI formation was globally 16O-rich, with local 16O-depletions systematically associated with high temperature events. The Al/Mg isotopic systematics of 3529-Z further indicates that this suite of isotopic changes occurred in the first 150 000 yr of the solar system, during the main CAI formation period. A new astrophysical setting is proposed, where the 16O-depletion occurs in an optically thin surface

  10. Nitrogen cycling in shallow low-oxygen coastal waters off Peru from nitrite and nitrate nitrogen and oxygen isotopes

    NASA Astrophysics Data System (ADS)

    Hu, Happy; Bourbonnais, Annie; Larkum, Jennifer; Bange, Hermann W.; Altabet, Mark A.

    2016-03-01

    O2 deficient zones (ODZs) of the world's oceans are important locations for microbial dissimilatory nitrate (NO3-) reduction and subsequent loss of combined nitrogen (N) to biogenic N2 gas. ODZs are generally coupled to regions of high productivity leading to high rates of N-loss as found in the coastal upwelling region off Peru. Stable N and O isotope ratios can be used as natural tracers of ODZ N-cycling because of distinct kinetic isotope effects associated with microbially mediated N-cycle transformations. Here we present NO3- and nitrite (NO2-) stable isotope data from the nearshore upwelling region off Callao, Peru. Subsurface oxygen was generally depleted below about 30 m depth with concentrations less than 10 µM, while NO2- concentrations were high, ranging from 6 to 10 µM, and NO3- was in places strongly depleted to near 0 µM. We observed for the first time a positive linear relationship between NO2-δ15N and δ18O at our coastal stations, analogous to that of NO3- N and O isotopes during NO3- uptake and dissimilatory reduction. This relationship is likely the result of rapid NO2- turnover due to higher organic matter flux in these coastal upwelling waters. No such relationship was observed at offshore stations where slower turnover of NO2- facilitates dominance of isotope exchange with water. We also evaluate the overall isotope fractionation effect for N-loss in this system using several approaches that vary in their underlying assumptions. While there are differences in apparent fractionation factor (ɛ) for N-loss as calculated from the δ15N of NO3-, dissolved inorganic N, or biogenic N2, values for ɛ are generally much lower than previously reported, reaching as low as 6.5 ‰. A possible explanation is the influence of sedimentary N-loss at our inshore stations which incurs highly suppressed isotope fractionation.

  11. Evaluation of Community Respiratory Mechanisms With Oxygen Isotopes

    NASA Astrophysics Data System (ADS)

    Luz, B.; Barkan, E.

    Oxygen uptake in the surface waters of oceans and lakes takes place by ordinary dark respiration as well as by cyanide resistant respiration in both dark and light conditions, and by photorespiration and Mehler reaction that occur only during illumination. Thus in order to study the overall discrimination in aquatic systems it is necessary to eval- uate its effects in both light and dark conditions and to separate the effect of photo- synthetic production of oxygen. Such separation is possible if gross rates of oxygen production and consumption are known. We have estimated these rates from in situ incubation experiments and from the natural distribution of O-16, O-17, O-18 and the ratio of dissolved oxygen/argon. We have studied the respiration mechanisms in L. Kinneret, in the Atlantic Ocean near Bermuda and in the Southern Ocean. The over- all respiratory fractionation, which represents both light and dark consumption, was greater than the fractionation found in dark incubations of surface waters. We suggest that the only mechanism that can explain the strong overall fractionation is significant O2 uptake by cyanide resistant respiration in illuminated plankton. Our study shows that cyanide resistant respiration, which is known to strongly fractionate against O-18, is widespread in aquatic systems.

  12. A molecular organic carbon isotope record of miocene climate changes

    SciTech Connect

    Schoell, M. ); Schouten, S.; Sinninghe Damste', J.S.; Leeuw, J.W. de ); Summons, R.E. )

    1994-02-25

    The difference in carbon-13 ([sup 13]C) contents of hopane and sterane biomarkers in the Monterey formation (Naples Beach, California) parallels the Miocene inorganic record of the change in [sup 18]O ([delta][sup 18]O), reflecting the Miocene evolution from a well-mixed to a highly stratified photic zone (upper 100 meters) in the Pacific. Steranes ([delta][sup 13]C = 25.4 [+-] 0.7 per mil versus the Pee Dee belemnite standard) from shallow photic-zone organisms do not change isotopically throughout the Miocene. In contrast, sulfur-bound C[sub 35] hopanes (likely derived from bacterial plankton living at the base of the photic zone) have systematically decreasing [sup 13]C concentrations in Middle and Late Miocene samples ([delta][sup 13]C = 2