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Sample records for abiotic marine calcite

  1. The δ18O record of phanerozoic abiotic marine calcite cements

    NASA Astrophysics Data System (ADS)

    Lohmann, Kyger C.; Walker, James C. G.

    Monomineralic, abiotic marine cements formed in low-latitude Phanerozoic reefs provide the direction and amplitude of secular variation of δ13C and δ18O in marine calcite and defines two end member compositions — 580 to 360 my (-7 to -5‰ δ18OPDB) and 360 to present (-3 to 0‰ δ18OPDB). Sampling of the Devono-Carboniferous transition (375-320 my) at several global sites reveals a rapid change in carbonate isotopic compositions. Bracketed within Fammenian to Early Visean-aged strata, a 7 to 15 my time interval, this shift corresponds to a 2‰ offset in mean δ13C and 3-4‰ offset in δ18O. The abruptness of such change, and its overall correlation with variations in 87Sr/86Sr, δ34S, δ13C, and Li/Al ratios in marine sediments suggests a primary offset in marine water composition.

  2. The. delta. sup 18 O record of Phanerozoic abiotic marine calcite cements

    SciTech Connect

    Lohmann, K.C.; Walker, J.C.G. )

    1989-04-01

    Monomineralic, abiotic marine cements formed in low-latitude Phanerozoic reefs provide the direction and amplitude of secular variation of {delta}{sup 13}C and {delta}{sup 18}O in marine calcite and defines two end member compositions - 580 to 360 my ({minus}7 to {minus}5{per thousand}{delta}{sup 18}O{sub PDB}) and 360 to present ({minus}3 to 0{per thousand}{delta}{sup 18}O{sub PDB}). Sampling of the Devono-Carboniferous transition (375-320 my) at several global sites reveals a rapid change in carbonate isotopic compositions. Bracketed within Fammenian to Early Visean-aged strata, a 7 to 15 my time interval, this shift corresponds to a 2% offset in mean {delta}{sup 13}C and 3-4% offset in {delta}{sup 18}O. The abruptness of such change, and its overall correlation with variations in {sup 87}Sr/{sup 86}Sr, {delta}{sup 34}S, {delta}{sup 13}C, and Li/Al ratios in marine sediments suggests a primary offset in marine water composition.

  3. δ 18O values, 87Sr /86Sr and Sr/Mg ratios of Late Devonian abiotic marine calcite: Implications for the composition of ancient seawater

    NASA Astrophysics Data System (ADS)

    Carpenter, Scott J.; Lohmann, K. C.; Holden, Peter; Walter, Lynn M.; Huston, Ted J.; Halliday, Alex N.

    1991-07-01

    Late Devonian (Frasnian) abiotic marine calcite has been microsampled and analyzed for 87Sr /86Sr ratios, δ 18O and δ 13C values, and minor element concentrations. Portions of marine cement crystals from the Alberta and Canning Basins have escaped diagenetic alteration and preserve original marine δ 18O values (-4.8%. ± 0.5, PDB), δ 13C values (+2.0 to +3.0%., PDB), 87Sr /86Sr ratios (0.70805 ± 3), and Sr/Mg weight ratios (0.04 to 0.05). Marine 87Sr /86Sr ratios are globally consistent and can be correlated within the Alberta Basin, and among the Alberta, Canning, and Williston Basins. Correlation of isotopic and chemical data strengthen the conclusion that marine cements from the Leduc Formation preserve original marine δ 18O values which are 3 to 4%. lower than those of modern marine cements. These low δ 18O values are best explained by precipitation from 18O-depleted seawater and not by elevated seawater temperature or diagenetic alteration. For comparison with Devonian data, analogous data were collected from Holocene Mg-calcite and aragonite marine cements from Enewetak Atoll, Marshall Islands. Mg-calcite and aragonite marine cements are in isotopic equilibrium with ambient seawater, and Mg-calcite cements are homogeneous with respect to Sr and Mg contents. Empirically derived homogeneous distribution coefficients for Mg and Sr in modern, abiotic Mg-calcite from Enewetak Atoll are 0.034 and 0.15, respectively. An equation describing the dependence of DSr on Mg content was based on a compilation of Sr and Mg data from Holocene abiotic marine calcite ( DSr = 3.52 × 10 -6 (ppm Mg) + 6.20 × 10 -3). Unlike that derived from experimental data, this Sr-Mg relation is consistent over a range of 4 to 20 mol% MgCO 3 and may represent precipitation phenomena which are minimally controlled by kinetic effects. Comparison of Sr and Mg contents of analogous Devonian and Holocene marine cements suggests that the Mg/Ca ratio of Late Devonian seawater was

  4. Search for past life on Mars: Physical and chemical characterization of calcite minerals of biotic and abiotic origin

    NASA Astrophysics Data System (ADS)

    Stalport, S.; Coll, C.; Cabane, C.; Navarro González, N. G.; Raulin, R.; Vaulay, V.; Ausset, A.; Szopa, S.; McKay, M.

    Several lines of evidence suggest that early Mars once had liquid water on its surface a denser atmosphere and a mild climate Similar environmental conditions led to the origin of life on the Earth more than 3 5 billion years ago consequently life might also have originated on Mars We contend that inorganic compounds could give us interesting clues as to the existence of possible biological activity in future astrobiological missions to Mars Consequently we have investigated the physical and chemical properties of calcite which could be expected on Mars because liquid water was certainly present on the surface of early Mars and carbon dioxide was abundant in its atmosphere Calcite is interesting because on Earth this mineral is produced by abiotic processes as well as by biological activity One may suppose that crystalline defects and trace element in the crystal lattice and the growth speed of biotic calcites must indicate a difference between them and pure abiotic calcites We investigated twelve different terrestrial calcite samples from various origins biotic diagenetic and abiotic The minerals were studied by X-ray diffraction and electron scanning microscopy to determine their mineralogical and chemical composition and differential thermal analysis coupled to thermogravimetric analysis DTA-TG to determine their thermal behavior Our results show that the thermal degradation of abiotic calcite starts at a temperature at least 40oC higher than the degradation temperature of any biotic calcite investigated Consequently in the case of a Martian in-situ

  5. Search For Past Life On Mars: Physical And Chemical Characterization Of Calcite Minerals Of Biotic And Abiotic Origin

    NASA Astrophysics Data System (ADS)

    Stalport, Fabien; Coll, P.; Cabane, M.; Person, A.; Navarro-Gonzales, R.; Raulin, F.; Valay, M.; Ausset, P.; Szopa, C.; McKay, C. P.

    2006-09-01

    Several lines of evidence suggest that early Mars once had liquid water on its surface, a denser atmosphere and a mild climate. Similar environmental conditions led to the origin of life on the Earth more than 3.5 billion years ago; consequently, life might also have originated on Mars. We contend that inorganic compounds could give us interesting clues as to the existence of possible biological activity in future astrobiological missions to Mars. Consequently, we have investigated the physical and chemical properties of calcite, which could be expected on Mars because liquid water was certainly present on the surface of early Mars and carbon dioxide was abundant in its atmosphere. Calcite is interesting because on Earth this mineral is produced by abiotic processes as well as by biological activity. One may suppose that crystalline defects and trace element in the crystal lattice and the growth speed of biotic calcites must indicate a difference between them and pure abiotic calcites. We investigated twelve different terrestrial calcite samples from various origins: biotic, diagenetic and abiotic. The minerals were studied by X-ray diffraction and electron scanning microscopy to determine their mineralogical and chemical composition, and differential thermal analysis coupled to thermogravimetric analysis (DTA-TG) to determine their thermal behavior. Our results show that the thermal degradation of abiotic calcite starts at a temperature at least 40°C higher than the degradation temperature of any biotic calcite investigated. Consequently, in the case of a Martian in-situ study or in a sample return mission, the analysis of Martian minerals by DTA-TG represents a promising approach to detect evidence of past biological activity on Mars.

  6. Search for past life on Mars: Physical and chemical characterization of minerals of biotic and abiotic origin: part 1 - Calcite

    NASA Astrophysics Data System (ADS)

    Stalport, Fabien; Coll, Patrice; Cabane, Michel; Person, Alain; González, Rafael Navarro; Raulin, Francois; Vaulay, Marie Jo; Ausset, Patrick; McKay, Chris P.; Szopa, Cyril; Zarnecki, John

    2005-12-01

    Several lines of evidence suggest that early Mars once had liquid water on its surface, a denser atmosphere and a mild climate. Similar environmental conditions led to the origin of life on the Earth more than 3.5 billion years ago; consequently, life might also have originated on Mars. The Viking landers searched for evidence of organic molecules on the surface of Mars, and found that the Martian soil is depleted in organics at ppb levels at the landing sites. We contend that inorganic compounds could give us interesting clues as to the existence of possible biological activity in future astrobiological missions to Mars. Consequently, we have investigated the physical and chemical properties of calcite, which could be expected on Mars because liquid water was certainly present on the surface of early Mars and carbon dioxide was abundant in its atmosphere. Calcite is interesting because on Earth this mineral is produced by abiotic processes as well as by biological activity. One may suppose that crystalline defects and trace element in the crystal lattice and the growth speed of biotic calcites must indicate a difference between them and pure abiotic calcites. We investigated twelve different terrestrial calcite samples from various origins: biotic, diagenetic and abiotic. The minerals were studied by X-ray diffraction and electron scanning microscopy to determine their mineralogical and chemical composition, and differential thermal analysis coupled to thermogravimetric analysis (DTA-TG) to determine their thermal behavior. Our results show that the thermal degradation of abiotic calcite starts at a temperature at least 40°C higher than the degradation temperature of any biotic calcite investigated. Consequently, in the case of a Martian in-situ study or in a sample return mission, the analysis of Martian minerals by DTA-TG represents a promising approach to detect evidence of past biological activity on Mars.

  7. Planktic foraminiferal sedimentation and the marine calcite budget

    NASA Astrophysics Data System (ADS)

    Schiebel, Ralf

    2002-12-01

    The vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal CaCO3 budget is presented. Test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples. Modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget, highlighting the importance of ecological, autecological (e.g., reproduction), and biogeochemical conditions that determine the presence or absence of species. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccolithophores, pteropods, and calcareous dinophytes is discussed. Based on the studied regions, the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1.3-3.2 Gt yr-1, equivalent to 23-56% of the total open marine CaCO3 flux. The preservation of tests varies on a regional and temporal scale, and is affected by local hydrography and dissolution. During most of the year (off-peak periods), many tests dissolve above 700-m water depth while settling through the water column, with on average only 1-3% of the initially exported CaCO3 reaching the deep-seafloor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of tests to the formation of deep-sea sediments. On average, ˜25% of the initially produced planktic foraminiferal test CaCO3 settles on the seafloor. The total planktic foraminiferal contribution of CaCO3 to global surface sediments amounts to 0.36-0.88 Gt yr-1, ˜32-80% of the total deep-marine calcite budget.

  8. Planktic Foraminiferal Contribution To The Marine Calcite Budget

    NASA Astrophysics Data System (ADS)

    Schiebel, R.

    The vertical flux and sedimentation of planktic foraminiferal tests is quantified and a global planktic foraminiferal CaCO3 budget is presented. The eastern North Atlantic, the Arabian Sea, and the Caribbean were identified as key areas for this investiga- tion, covering a wide spectrum of ecological conditions and faunal compositions. Test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples. Population dynamics of modern plank- tic foraminifers are discussed as a prerequesite for the quantification of the calcite budget, highlighting the importance of ecological, autecological (e.g., reproduction), and biogeochemical conditions that determine the presence or absence of species. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccol- ithophores, pteropods, and calcareous dinophytes is discussed. It is assumed that the global planktic foraminiferal calcite flux at 100 m depth amounts to 1.3-3.2 Gigatons per year, equivalent to 23-56% of the total open marine CaCO3 flux. The preservation of tests varies on a regional and temporal scale, and is affected by local hydrogra- phy and dissolution susceptibility of planktic foraminiferal tests. Throughout most of the year (off-peak periods) a major portion of tests is dissolved above 700 m water depth while individually settling through the water column, with on average only 1- 3% of the initially exported CaCO3 reaching the deep sea floor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of the tests to the formation of deep-sea sediments. On an annual average, about one fourth of the ini- tially produced planktic foraminiferal test CaCO3 may settle on the sea floor. The total planktic foraminiferal contribution of CaCO3 to global deep-marine surface sediments amounts to 0.36-0.88 Gt per year, which is 32-80% of the total CaCO3 budget that is estimated at 1.1 Gt per year (e

  9. Marine diagenesis of Lower Ordovician carbonate sediments (Dumugol Formation), Korea: cementation in a calcite sea

    NASA Astrophysics Data System (ADS)

    Kim, Jeong Chan; Lee, Yong Il

    1996-09-01

    The Lower Ordovician Dumugol Formation exhibits many features that indicate early lithification, such as calcite nodules, hardgrounds, mud-mounds and intraclasts. Detailed observations of these early-lithified features reveal that rapid marine cementation was instrumental in their formation. Marine lithification took place in a low-energy subtidal environmental that was influenced by intermittent storms. Marine cements include syntaxial overgrowth, bladed calcite, fibrous calcite and fine-crystalline equant calcite cements. Syntaxial overgrowths precipitated on echinoderm grains and contributed to rapid marine lithification of echinoderm-bearing sediments. Bladed, fibrous, and fine-crystalline equant calcite cements precipitated in locally suitable sites but their occurrence is limited, and thus played a minor role in marine lithification. Microcrystalline calcites also precipitated in lime mud-rich, fine-grained sediments and participated in rapid marine lithification of the Dumugol sediments. The absence of aragonite allochems and cement, and the predominance of calcite cement, suggest that the Dumugol sea was undersaturated with respect to aragonite, but supersaturated with respect to calcite, which is indicative of a 'calcite sea'.

  10. Review: geological and experimental evidence for secular variation in seawater Mg/Ca (calcite-aragonite seas) and its effects on marine biological calcification

    NASA Astrophysics Data System (ADS)

    Ries, J. B.

    2010-09-01

    Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time are believed to have been caused by tectonically induced variations in the Mg/Ca ratio of seawater (molar Mg/Ca>2="aragonite seas", <2="calcite seas"). Here, I assess the geological evidence in support of secular variation in seawater Mg/Ca and its effects on marine calcifiers, and review a series of recent experiments that investigate the effects of seawater Mg/Ca (1.0-5.2) on extant representatives of calcifying taxa that have experienced variations in this ionic ratio of seawater throughout the geologic past. Secular variation in seawater Mg/Ca is supported by synchronized secular variations in (1) the ionic composition of fluid inclusions in primary marine halite, (2) the mineralogies of late stage marine evaporites, abiogenic carbonates, and reef- and sediment-forming marine calcifiers, (3) the Mg/Ca ratios of fossil echinoderms, molluscs, rugose corals, and abiogenic carbonates, (4) global rates of tectonism that drive the exchange of Mg2+ and Ca2+ along zones of ocean crust production, and (5) additional proxies of seawater Mg/Ca including Sr/Mg ratios of abiogenic carbonates, Sr/Ca ratios of biogenic carbonates, and Br concentrations in marine halite. Laboratory experiments have revealed that aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibit higher rates of calcification and growth in experimental seawaters formulated with seawater Mg/Ca ratios that favor their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification within the bryopsidalean

  11. Biomineralization processes of calcite induced by bacteria isolated from marine sediments

    PubMed Central

    Wei, Shiping; Cui, Hongpeng; Jiang, Zhenglong; Liu, Hao; He, Hao; Fang, Nianqiao

    2015-01-01

    Biomineralization is a known natural phenomenon associated with a wide range of bacterial species. Bacterial-induced calcium carbonate precipitation by marine isolates was investigated in this study. Three genera of ureolytic bacteria, Sporosarcina sp., Bacillus sp. and Brevundimonas sp. were observed to precipitate calcium carbonate minerals. Of these species, Sporosarcina sp. dominated the cultured isolates. B. lentus CP28 generated higher urease activity and facilitated more efficient precipitation of calcium carbonate at 3.24 ± 0.25 × 10−4 mg/cell. X-ray diffraction indicated that the dominant calcium carbonate phase was calcite. Scanning electron microscopy showed that morphologies of the minerals were dominated by cubic, rhombic and polygonal plate-like crystals. The dynamic process of microbial calcium carbonate precipitation revealed that B. lentus CP28 precipitated calcite crystals through the enzymatic hydrolysis of urea, and that when ammonium ion concentrations reached 746 mM and the pH reached 9.6, that favored calcite precipitation at a higher level of 96 mg/L. The results of this research provide evidence that a variety of marine bacteria can induce calcium carbonate precipitation, and may influence the marine carbonate cycle in natural environments. PMID:26273260

  12. Biomineralization processes of calcite induced by bacteria isolated from marine sediments.

    PubMed

    Wei, Shiping; Cui, Hongpeng; Jiang, Zhenglong; Liu, Hao; He, Hao; Fang, Nianqiao

    2015-06-01

    Biomineralization is a known natural phenomenon associated with a wide range of bacterial species. Bacterial-induced calcium carbonate precipitation by marine isolates was investigated in this study. Three genera of ureolytic bacteria, Sporosarcina sp., Bacillus sp. and Brevundimonas sp. were observed to precipitate calcium carbonate minerals. Of these species, Sporosarcina sp. dominated the cultured isolates. B. lentus CP28 generated higher urease activity and facilitated more efficient precipitation of calcium carbonate at 3.24 ± 0.25 × 10(-4) mg/cell. X-ray diffraction indicated that the dominant calcium carbonate phase was calcite. Scanning electron microscopy showed that morphologies of the minerals were dominated by cubic, rhombic and polygonal plate-like crystals. The dynamic process of microbial calcium carbonate precipitation revealed that B. lentus CP28 precipitated calcite crystals through the enzymatic hydrolysis of urea, and that when ammonium ion concentrations reached 746 mM and the pH reached 9.6, that favored calcite precipitation at a higher level of 96 mg/L. The results of this research provide evidence that a variety of marine bacteria can induce calcium carbonate precipitation, and may influence the marine carbonate cycle in natural environments.

  13. Differential kinetics and temperature dependence of abiotic and biotic processes controlling the environmental fate of TNT in simulated marine systems.

    PubMed

    Chappell, Mark A; Porter, Beth E; Price, Cynthia L; Pettway, Brad A; George, Robert D

    2011-08-01

    This work seeks to understand how the balance of abiotic and biotic kinetic processes in sediments control the residual concentration of TNT in marine systems after release from ocean-dumped source. Kinetics of TNT disappearance were followed using marine sediments at different temperatures and under both biotic and presumably abiotic conditions (through sodium azide addition). Sediments exhibiting the highest rate of TNT disappearance under biotic conditions also exhibited the highest sorption affinity for TNT under abiotic conditions. Significant temperature dependence in the abiotic processes was observed in the diffusion coefficient of TNT and not sediment sorption affinity. At higher temperature, kinetics of biotic processes outpaced abiotic processes, but at low temperature, kinetics of abiotic processes were much more significant. We concluded that the differential influence of temperature on the kinetics of abiotic and biotic processes could provide distinguishing predictions for the potential residual concentration of TNT contamination in marine-sediment systems.

  14. Abiotic Racemization Kinetics of Amino Acids in Marine Sediments

    PubMed Central

    Steen, Andrew D.; Jørgensen, Bo Barker; Lomstein, Bente Aa.

    2013-01-01

    The ratios of d- versus l-amino acids can be used to infer the sources and composition of sedimentary organic matter. Such inferences, however, rely on knowing the rates at which amino acids in sedimentary organic matter racemize abiotically between the d- and the l-forms. Based on a heating experiment, we report kinetic parameters for racemization of aspartic acid, glutamic acid, serine, and alanine in bulk sediment from Aarhus Bay, Denmark, taken from the surface, 30 cm, and 340 cm depth below seafloor. Extrapolation to a typical cold deep sea sediment temperature of 3°C suggests racemization rate constants of 0.50×10−5–11×10−5 yr−1. These results can be used in conjunction with measurements of sediment age to predict the ratio of d:l amino acids due solely to abiotic racemization of the source material, deviations from which can indicate the abundance and turnover of active microbial populations. PMID:23951211

  15. Seawater fluid inclusions preserved within Cambrian-Ordovician marine cements indicate Cambrian-Ordovician seawater precipitated low-magnesium calcite

    SciTech Connect

    Johnson, W.J.; Goldstein, R.H. . Dept. of Geology)

    1992-01-01

    The San Saba Member of the Wilberns Formation (Llano Uplift, Texas) contains a series of Late Cambrian-Early Ordovician hardgrounds. Bladed low-Mg calcite cements are truncated at hardground surfaces and overlain by shallow marine limestones, indicating a syndepositional shallow marine origin. Primary one-phase fluid inclusions within bladed cements have marine salinities, suggesting that these low-Mg calcite cements formed as a precipitate from Late Cambrian and Early Ordovician seawater and have not undergone recrystallization. Stable isotope analysis of the bladed cement yields delta O-18 values that cluster between [minus]5.6--[minus]6.0 ([per thousand] PDB) which is comparable to those previously reported for Early Ordovician marine calcite. The delta C-13 values are more positive than those reported for this time interval (0.6--1.3 [per thousand] PDB). Trace element analysis indicates that strontium content ranges from 200 to 2,200 ppm. Iron ranges from below detection by electron microprobe to 800 ppm. Mg is generally below detection, however, cements in one hardground display Mg contents that increase progressively toward pore centers. Trace element data lack covariance that would suggest recrystallization. In addition, closed system recrystallization cannot be supported here due to a lack of microdolomite inclusions. Stable isotope, trace element, and fluid inclusion data are consistent with submarine cementation at or below the sediment-water interface. These cements have not undergone significant recrystallization and preserve a primary low Mg calcite mineralogy. These data suggest that early Paleozoic seawater differed chemically from modern seawater. Moreover, preservation of ancient seawater, within fluid inclusions, may provide a direct means of determining those differences.

  16. Abiotic proxies for predictive mapping of nearshore benthic assemblages: implications for marine spatial planning.

    PubMed

    McHenry, Jennifer; Steneck, Robert S; Brady, Damian C

    2017-03-01

    Marine spatial planning (MSP) should assist managers in guiding human activities toward sustainable practices and in minimizing user conflicts in our oceans. A necessary first step is to quantify spatial patterns of marine assemblages in order to understand the ecosystem's structure, function, and services. However, the large spatial scale, high economic value, and density of human activities in nearshore habitats often makes quantifying this component of marine ecosystems especially daunting. To address this challenge, we developed an assessment method that employs abiotic proxies to rapidly characterize marine assemblages in nearshore benthic environments with relatively high resolution. We evaluated this assessment method along 300 km of the State of Maine's coastal shelf (<100 m depth), a zone where high densities of buoyed lobster traps typically preclude extensive surveys by towed sampling gear (i.e., otter trawls). During the summer months of 2010-2013, we implemented a stratified-random survey using a small remotely operated vehicle that allowed us to work around lobster buoys and to quantify all benthic megafauna to species. Stratifying by substrate, depth, and coastal water masses, we found that abiotic variables explained a significant portion of variance (37-59%) in benthic species composition, diversity, biomass, and economic value. Generally, the density, diversity, and biomass of assemblages significantly increased with the substrate complexity (i.e., from sand-mud to ledge). The diversity, biomass, and economic value of assemblages also decreased significantly with increasing depth. Last, demersal fish densities, sessile invertebrate densities, species diversity, and assemblage biomass increased from east to west, while the abundance of mobile invertebrates and economic value decreased, corresponding mainly to the contrasting water mass characteristics of the Maine Coastal Current system (i.e., summertime current direction, speed, and temperature

  17. Protective function of nitric oxide on marine phytoplankton under abiotic stresses.

    PubMed

    Li, Peifeng; Liu, Chun-Ying; Liu, Huanhuan; Zhang, Qiang; Wang, Lili

    2013-09-01

    As an important signaling molecule, nitric oxide (NO) plays diverse physiological functions in plants, which has gained particular attention in recent years. We investigated the roles of NO in the growth of marine phytoplankton Platymonas subcordiforms and Skeletonema costatum under abiotic stresses. The growth of these two microalgae was obviously inhibited under non-metal stress (sodium selenium, Na2SeO3), heavy metal stress (lead nitrate, Pb(NO3)2), pesticide stress (methomyl) and UV radiation stress. After the addition of different low concentrations of exogenous NO (10(-10)-10(-8) mol L(-1)) twice each day during cultivation, the growth of these two microalgae was obviously promoted. Results showed that NO could relieve the oxidative stresses to protect the growth of the two microalgae. For different environmental stress, there is a different optimum NO concentration for marine phytoplankton. It is speculated that the protective effect of NO is related to its antioxidant ability.

  18. Suboxic to anoxic diagenesis of platform-marginal ooids and bladed-to-fibrous calcite from the middle Ordovician Ottosee Formation (east Tennessee)

    SciTech Connect

    Tobin, K.J.; Walker, K.R.; Srinivasan, K.; Steinhauff, D.M.

    1996-02-01

    The oolite member of the Ottosee Formation (early Caradoc) has bladed-to-fibrous calcite cement that formed under oxygen-depleted conditions atypical of most abiotic marine precipitates. The sequence of early diagenetic events was as follows: (1) ooid formation, (2) precipitation of rare turbid marine cement, (3) minor dissolution of ooids and initial marine cement, (4) precipitation of translucent bladed-to-fibrous calcite, and (5) stabilization of metastable components, such as ooids and turbid marine cements. Ooids and turbid marine cements precipitated from oxic fluids. Minor dissolution of ooids and turbid marine cements was associated with aerobic degradation of organic material, which decreased alkalinity through generation of CO{sub 2}. Translucent bladed-to-fibrous calcite precipitated from suboxic to anoxic marine fluids that were modified by bacterially mediated Mn{sup 4+}, Fe{sup 3+}, and SO{sub 4}{sup 2-} reduction. Translucent bladed-to-fibrous cement was originally low-magnesian calcite and has {delta}{sup 13}C and {delta}{sup 18}O values near other Caradoc marine values. Conversely, ooids and turbid marine calcite had a metastable magnesian calcite mineralogy. These components were dramatically altered by stabilization as reflected by negative {delta}{sup 13}C and {delta}{sup 18}O ooid values. Mineralogical stabilization of ooids and turbid marine cements mainly postdated bladed-to-fibrous calcite formation. 64 refs., 8 figs., 2 tabs.

  19. The Effect of Abiotic Factors on Marine Animal Body Size Evolution

    NASA Astrophysics Data System (ADS)

    Wang, X. F.; Wong, W.; Heim, N.; Payne, J.

    2015-12-01

    While there is evidence of a general increase in body size over time, there has been no comprehensive attempt to determine the influence of abiotic factors on body size. Although an increase in maximum body size has been observed during and after the Precambrian oxidation events in the Late Archean and at the onset of the Cambrian, these observations took into account the appearance of eukaryotic life and multicellular life respectively. Using a database of marine animal body sizes spanning the Phanerozoic, we conducted a series of Pearson product-moment correlation tests with igneous rock weathering (Strontium-87: Strontium-86), rate of carbon cycle (δ13C), temperature (δ18O), CO2 concentration, sulfate mineral weathering (δ34S), atmospheric oxygen concentration, and sea level as independent variables, and mean body size as the dependent variable. Our test yielded a correlation coefficient of 0.81 between δ18O and body size, and -0.78 between rCO2 and body size; since δ18O is inversely correlated with temperature, these results indicate that both temperature and CO2 have strong inverse relationships with body size. Atmospheric oxygen yielded a correlation coefficient of 0.09, demonstrating that it ceased to play an influential role in shaping body sizes following the start of the Phanerozoic.

  20. Early diagenetic high-magnesium calcite and dolomite indicate that coal balls formed in marine or brackish water: Stratigraphic and paleoclimatic implications

    NASA Astrophysics Data System (ADS)

    Raymond, Anne

    2016-04-01

    Coal balls are carbonate and pyrite permineralizations of peat that contain three-dimensional plant fossils preserved at the cellular level. Coal balls, which occur in Pennsylvanian and earliest Permian equatorial coals, provide a detailed record of terrestrial ecology and tropical climate during the Late Paleozoic Ice Age; yet their depositional environment remains controversial. The exquisite preservation of some coal-ball fossils, e.g. pollen with pollen tubes and leaves with mesophyll, indicates rapid formation. The presence of abundant, cement-filled, void spaces within and between the plant debris in most coal balls indicates that they formed in uncompacted peat, near the surface of the mire. Botanical, taphonomic and isotopic evidence point to a freshwater origin for coal balls. The nearest living relatives of coal ball plants (modern lycopsids, sphenopsids, marratialean ferns and conifers) grow in fresh water. Coal-ball peat contains a high percentage of aerial debris, similar to modern freshwater peat. The stable oxygen isotopes of coal-ball carbonate (δ18O = 16 to 3 per mil) suggest a freshwater origin. However, the widespread occurrence of marine invertebrates and early diagenetic framboidal pyrite in coal balls suggests that many formed in close proximity to marine water. Indeed, carbonate petrology points to a marine or brackish water origin for the first-formed carbonate cements in coal balls. Petrographic and geochemical (microprobe) analysis of coal-ball carbonates in Pennsylvanian coals from the midcontinent of North America (Western Interior Basin, West Pangaea) and the Ruhr and Donets Basins (East Pangaea) indicate that the first formed carbonate is either radaxial, nonstochiometric dolomite or high magnesium calcite (9 - 17 mol % MgCO3, indicating precipitation in marine or brackish water. Although both primary dolomite and high magnesium calcite can form in lacustrine settings, the lakes in which these minerals form occur in carbonate terranes

  1. Origin and timing of siderite and calcite concretions in late Palaeogene non- to marginal-marine facies of the Te Kuiti Group, New Zealand

    NASA Astrophysics Data System (ADS)

    Middleton, Heather A.; Nelson, Campbell S.

    1996-05-01

    The Late Eocene-earliest Miocene Te Kuiti Group represents an overall transgressive sequence of formations ranging upwards from non-marine coal measure facies through marginal-marine low-energy shoreline siliciclastic sediments to fully-marine mixed siliciclastic-carbonate deposits. Concretionary structures are common in the lowest formations of the group, being dominantly sideritic in the non-marine to brackish sediment facies (Waikato Coal Measures and Glen Afton Claystone) and calcitic in the more marine-influenced sediments (Rotowaro Siltstone). The geochemistry of the carbonate cements within these early diagenetic concretions records the change from carbonate precipitation from purely meteoric fluids to precipitation from marine fluids, and a shifting source of carbonate carbon across this transition. Siderite precipitation in the Waikato Coal Measures concretions and hardpans was initiated and often largely completed in the methanogenic zone, within the upper 20 m of the sediment pile over a period possibly lasting 100-300 ka. Precipitation continued at a reduced rate to burial depths of 300 m or more when septarian cracking occurred in some siderite concretions and was healed by calcite vein cements that probably derived carbonate from the oxidation of methane ascending from the maturing coal seams directly below. Siderite precipitation in the concretions and hardpans of the overlying brackish-marine Glen Afton Claystone was completed in the topmost few metres of sediment, possibly a few 10 ka. Stable-isotope values near zero support a marine carbonate carbon source, suggested to be from remobilised shell material as evidenced by the common occurrence of shell casts in the formation and the high degree of Mg and Ca substitution in the siderites. The overlying marginal-marine to low-energy marine Rotowaro Siltstone contains calcite concretions precipitated from pore waters enriched in bicarbonate derived from the sulphate-reduction zone, largely within the

  2. The effects of atmospheric [CO2] on carbon isotope fractionation and magnesium incorporation into biogenic marine calcite

    NASA Technical Reports Server (NTRS)

    Vieira, Veronica

    1997-01-01

    The influences of atmospheric carbon dioxide on the fractionation of carbon isotopes and the magnesium incorporation into biogenic marine calcite were investigated using samples of the calcareous alga Amphiroa and benthic foraminifer Sorites grown in the Biosphere 2 Ocean system under variable atmospheric CO2 concentrations (approximately 500 to 1200 ppm). Carbon isotope fractionation was studied in both the organic matter and the skeletal carbonate. Magnesium analysis was to be performed on the carbonate removed during decalcification. These data have not been collected due to technical problems. Carbon isotope data from Amphiroa yields a linear relation between [CO2] and Delta(sup 13)C(sub Corg)values suggesting that the fractionation of carbon isotopes during photosynthesis is positively correlated with atmospheric [CO2]. [CO2] and Delta(sup 13)C(sub Corg) values for Sorites produce a relation that is best described by a hyperbolic function where Delta(sup 13)C(sub Corg) values increase between 300 and 700 ppm and decrease from 700 to 1200 ppm. Further investigation of this relation and Sorites physiology is needed.

  3. Strontium stable isotope behaviour in foraminiferal calcite and the retrieval of marine records

    NASA Astrophysics Data System (ADS)

    Stevenson, E.; Burton, K.; Rickaby, R.; Parkinson, I. J.; Anand, P.; Hathorne, E.

    2009-12-01

    The stable strontium (88Sr/86Sr) isotope composition of seawater recorded in sedimentary foraminifera potentially provides key information on variations in the composition of material delivered by continental weathering to the oceans and on changes in carbonate productivity over time. However, recent studies suggest a significant temperature dependent fractionation of Sr stable isotopes during the precipitation of calcium carbonate, which must be quantified before seawater records can be accurately retrieved [1, 2]. This study presents high-precision stable Sr isotope data (±10 ppm 2 s.d.) for core-top planktonic foraminifera from sites in the South Atlantic with a range of annual sea surface temperatures of 18 - 28°C, and preliminary data for quaternary marine foraminiferal records from the SE Indian Ocean. These results indicate that there is no signficiant variation in the stable isotope composition of an individual species across the temperature range studied here, but there are resolvable differences in the offset from seawater between species. In this case, seawater stable Sr isotope records can be reconstructed without the necessity of a temperature correction. The preliminary results for a glacial-interglacial planktonic foraminifera record indicate that there are no resolvable variations in the stable isotope ratios over this time interval, indicating that there are no significant variations in the Sr isotope composition of continental runoff or carbonate productivity in the oceans over this time interval. [1] Fietzke, J., Eisenhauer, A. (2006), Geochem. Geophys. Geosyst., 7, (8), 1-6 . [2] Ruggerburg, A., Fietzke, J., Liebetrau, V. Eisenhauer, A., Dullo, W-C., Freiwald, A. (2008). Earth Plan. Sci. Lett. 269, 570-575

  4. Microbiological and abiotic processes in modelling longer-term marine corrosion of steel.

    PubMed

    Melchers, Robert E

    2014-06-01

    Longer term exposure of mild steel in natural (biotic) waters progresses as a bimodal function of time, both for corrosion mass loss and for pit depth. Recent test results, however, found this also for immersion in clean fresh, almost pure and triply distilled waters. This shows chlorides or microbiological activity is not essential for the electrochemical processes producing bimodal behaviour. It is proposed that the first mode is aerobic corrosion that eventually produces a non-homogeneous corroded surface and rust coverage sufficient to allow formation of anoxic niches. Within these, aggressive autocatalytic reduction then occurs under anoxic abiotic conditions, caused by sulfide species originating from the MnS inclusions typical in steels. This is consistent with Wranglen's model for abiotic anoxic crevice and pitting corrosion without external aggressive ions. In biotic conditions, metabolites from anaerobic bacterial activity within and near the anoxic niches provides additional (sulfide) species to contribute to the severity of corrosion. Limited observational evidence that supports this hypothesis is given but further investigation is required to determine all contributor(s) to the cathodic current for the electrochemical reaction. The results are important for estimating the contribution of microbiological corrosion in infrastructure applications.

  5. Growth rate controlled barium partitioning in calcite and aragonite

    NASA Astrophysics Data System (ADS)

    Goetschl, Katja Elisabeth; Mavromatis, Vasileios; Baldermann, Andre; Purgstaller, Bettina; Dietzel, Martin

    2016-04-01

    The barium (Ba) content and the Ba/Ca molar ratios in biogenic and abiotic carbonates have been widely used from the scientific community as a geochemical proxy especially in marine and early diagenetic settings. The Ba content of carbonate minerals has been earlier associated to changes in oceanic circulation that may have been caused by upwelling, changes in weathering regimes and river-runoff as well as melt water discharge. The physicochemical controls of Ba ion incorporation in the two most abundant CaCO3 polymorphs found in Earth's surface environments, i.e. calcite and aragonite, have adequately been studied only for calcite. These earlier studies (i.e. [1]) suggest that at increasing growth rate, Ba partitioning in calcite is increasing as well. In contrast, to date the effect of growth rate on the partitioning of Ba in aragonite remains questionable, despite the fact that this mineral phase is the predominant carbonate-forming polymorph in shallow marine environments. To shed light on the mechanisms controlling Ba ion uptake in carbonates in this study we performed steady-state Ba co-precipitation experiments with calcite and aragonite at 25°C. The obtained results for the partitioning of Ba in calcite are in good agreement with those reported earlier by [1], whereas those for aragonite indicate a reduction of Ba partitioning at elevated aragonite growth rates, with the partitioning coefficient value between solid and fluid to be approaching the unity. This finding is good agreement with the formation of a solid solution in the aragonite-witherite system, owing to the isostructural crystallography of the two mineral phases. Moreover, our data set provides new insights that are required for reconstructing the evolution of the Ba content of pristine marine versus diagenetically altered carbonate minerals commonly occurring in marine subfloor settings, as the thermodynamically less stable aragonite will transform to calcite enriched in Ba, whilst affecting

  6. Molecular evidence for abiotic sulfurization of dissolved organic matter in marine shallow hydrothermal systems

    NASA Astrophysics Data System (ADS)

    Gomez-Saez, Gonzalo V.; Niggemann, Jutta; Dittmar, Thorsten; Pohlabeln, Anika M.; Lang, Susan Q.; Noowong, Ann; Pichler, Thomas; Wörmer, Lars; Bühring, Solveig I.

    2016-10-01

    recirculation in Milos seafloor. The four most effective potential sulfurization reactions were those exchanging an O atom by one S atom in the formula or the equivalent + H2S reaction, correspondingly exchanging H2O, H2 and/or O2 by a H2S molecule. Our study reveals novel insights into DOS dynamics in marine hydrothermal environments and provides a conceptual framework for molecular-scale mechanisms in organic sulfur geochemistry.

  7. Seawater Mg/Ca controls polymorph mineralogy of microbial CaCO3: a potential proxy for calcite-aragonite seas in Precambrian time.

    PubMed

    Ries, J B; Anderson, M A; Hill, R T

    2008-03-01

    A previously published hydrothermal brine-river water mixing model driven by ocean crust production suggests that the molar Mg/Ca ratio of seawater (mMg/Ca(sw)) has varied significantly (approximately 1.0-5.2) over Precambrian time, resulting in six intervals of aragonite-favouring seas (mMg/Ca(sw) > 2) and five intervals of calcite-favouring seas (mMg/Ca(sw) < 2) since the Late Archaean. To evaluate the viability of microbial carbonates as mineralogical proxy for Precambrian calcite-aragonite seas, calcifying microbial marine biofilms were cultured in experimental seawaters formulated over the range of Mg/Ca ratios believed to have characterized Precambrian seawater. Biofilms cultured in experimental aragonite seawater (mMg/Ca(sw) = 5.2) precipitated primarily aragonite with lesser amounts of high-Mg calcite (mMg/Ca(calcite) = 0.16), while biofilms cultured in experimental calcite seawater (mMg/Ca(sw) = 1.5) precipitated exclusively lower magnesian calcite (mMg/Ca(calcite) = 0.06). Furthermore, Mg/Ca(calcite )varied proportionally with Mg/Ca(sw). This nearly abiotic mineralogical response of the biofilm CaCO3 to altered Mg/Ca(sw) is consistent with the assertion that biofilm calcification proceeds more through the elevation of , via metabolic removal of CO2 and/or H+, than through the elevation of Ca2+, which would alter the Mg/Ca ratio of the biofilm's calcifying fluid causing its pattern of CaCO3 polymorph precipitation (aragonite vs. calcite; Mg-incorporation in calcite) to deviate from that of abiotic calcification. If previous assertions are correct that the physicochemical properties of Precambrian seawater were such that Mg/Ca(sw) was the primary variable influencing CaCO3 polymorph mineralogy, then the observed response of the biofilms' CaCO3 polymorph mineralogy to variations in Mg/Ca(sw), combined with the ubiquity of such microbial carbonates in Precambrian strata, suggests that the original polymorph mineralogy and Mg/Ca(calcite )of well

  8. Sensitivity of air-sea CO2-exchange and calcite saturation depth to the remineralization depth of marine particulate organic and inorganic carbon

    NASA Astrophysics Data System (ADS)

    Schneider, B.; Bopp, L.; Gehlen, M.

    2009-04-01

    The present study addresses the question of what would happen to air-sea CO2 exchange and the depth of the calcite saturation horizon (CSH) if the remineralization depth of particulate organic and inorganic carbon (POC, PIC) was changing. Therefore, a biogeochemical ocean circulation model (PISCES) was run with four different parameterizations for vertical particle fluxes, starting from the same initial conditions. Particle fluxes undergo strong changes induced by a combination of the respective mechanistic formulation of the vertical particle flux and the resulting ecosystem response. Reorganizations in dissolved properties are caused by (i) changed fluxes of POC and PIC; (ii) advection; (iii) air-sea CO2 exchange (DIC). The results show that the more (less) efficient the vertical transport of POC (PIC) from the surface toward depth, the lower the surface ocean pCO2, the higher the air-sea CO2 flux, and the stronger the increase in the oceanic inventory of DIC, and vice versa. Consequently, in one experiment the ocean is turning into a CO2 source to the atmosphere, in two cases it becomes a weak sink and in one simulation it turns into a strong sink. Surprisingly, results for changes in the CSH are more similar among the simulations at larger scale with a general deepening in the North Pacific and a shoaling elsewhere. In most areas the readjustment of the CSH is controlled by DIC and alkalinity acting both towards the simulated CSH shifts, however, in some cases DIC (alkalinity) is overcompensating for an effect that would occur due to changes in alkalinity (DIC), alone. In detail, the differences found between the experiments can be well explained by the respective particle flux responses. The current study shows that reorganizations in the vertical flux of particulate matter in the ocean may have immediate and longer-term effects on the marine carbon cycle which could potentially feedback on the climate system.

  9. Effect of organic ligands on Mg partitioning and Mg isotope fractionation during low-temperature precipitation of calcite

    NASA Astrophysics Data System (ADS)

    Mavromatis, Vasileios; Immenhauser, Adrian; Buhl, Dieter; Purgstaller, Bettina; Baldermann, Andre; Dietzel, Martin

    2016-04-01

    Calcite growth experiments have been performed at 25 oC and 1 bar pCO2 in the presence of aqueous Mg and six organic ligands in the concentration range from 10-5 to 10-3 M. These experiments were performed in order to quantify the effect of distinct organic ligands on the Mg partitioning and Mg stable isotope fractionation during its incorporation in calcite at similar growth rates normalized to total surface area. The organic ligands used in this study comprise of (i) acetate acid, (ii) citrate, (iii) glutamate, (iv) salicylate, (v) glycine and (vi) ethylenediaminetetraacetic acid (EDTA), containing carboxyl- and amino-groups. These fuctional groups are required for bacterial activity and growth as well as related to biotic and abiotic mineralization processes occurring in sedimentary and earliest diagenetic aquatic environments (e.g. soil, cave, lacustrine, marine). The results obtained in this study indicate that the presence of organic ligands promotes an increase in the partition coefficient of Mg in calcite (DMg = (Mg/Ca)calcite (Mg/Ca)fluid). This behaviour can be explained by the temporal formation of aqueous Mg-ligand complexes that are subsequently adsorbed on the calcite surfaces and thereby reducing the active growth sites of calcite. The increase of DMg values as a function of the supersaturation degree of calcite in the fluid phase can be described by the linear equation LogDMg =0.3694 (±0.0329)×SIcalcite - 1.9066 (±0.0147); R2=0.92 In contrast, the presence of organic ligands, with exception of citrate, does not significantly affect the Mg isotope fractionation factor between calcite and reactive fluid (Δ26Mgcalcite-fluid = -2.5 ±0.1). Citrate likely exhibits larger fractionation between the Mg-ligand complexes and free aqueous Mg2+, compared to the other organic ligands studied in this work, as evidenced by the smaller Δ26Mgcalcite-fluid values. These results indicate that in Earth's surface calcite precipitating environments that are

  10. Fibrous calcite from the Middle Ordovician Holston Formation (east Tennessee)

    SciTech Connect

    Tobin, K.J.; Walker, K.R. . Dept. of Geological Sciences)

    1993-03-01

    Fibrous calcite from buildups, which occur near the top of the Middle Ordovician Holston Formation, were examined from two localities near Knoxville, TN (Alcoa Highway and Deanne Quarry). Buildups at these localities were deposited under open-marine conditions, slightly down-slope from the platform edge. Fibrous calcite (mainly radiaxial fibrous) occur most commonly as cements in mainly stromatactis structures present in bioherms and intergranular porosity in beds that flank bioherms. Fibrous calcite is interpreted to have been precipitated in a marine setting. Fibrous calcite is uniformly turbid or banded with interlayered turbid and clearer cement. Fibrous calcite most commonly shows patchy or blotchy dull-non-luminescence under cathodoluminescence. Bands of uniformly non-luminescent and relatively bright luminescent calcite are present. [delta][sup 13]C compositions of fibrous calcite vary little (0.6 to 1.0%) but [delta][sup 18]O values are highly variable ([minus]4.8 to [minus]7.1%). Post-marine cement consists of ferroan and non-ferroan, dull luminescent equant calcite ([delta][sup 13]C = 0.3 to 0.8; [delta][sup 18]O = [minus]8.6 to [minus]11.5) and is interpreted as precipitated in a deep meteoric or burial setting. Depleted [delta][sup 18]O compositions of fibrous calcite reflect addition of post-depositional calcite during stabilization. Most enriched [delta][sup 13]C and [delta][sup 18]O fibrous calcite composition are similar to enriched values from other Middle Ordovician southern Appalachian buildups (other localities of Holston (TN) and Effna (VA) formations) ([delta][sup 13]C = 0.3 to 0.8; [delta][sup 18]O = [minus]3.9 to [minus]4.8) and may reflect fibrous calcite precipitated in isotopic equilibrium with Middle Ordovician sea water.

  11. High surface area calcite

    NASA Astrophysics Data System (ADS)

    Schultz, L. N.; Andersson, M. P.; Dalby, K. N.; Müter, D.; Okhrimenko, D. V.; Fordsmand, H.; Stipp, S. L. S.

    2013-05-01

    Calcite (CaCO3) is important in many fields—in nature, because it is a component of aquifers, oil reservoirs and prospective CO2 storage sites, and in industry, where it is used in products as diverse as paper, toothpaste, paint, plastic and aspirin. It is difficult to obtain high purity calcite with a high surface area but such material is necessary for industrial applications and for fundamental calcite research. Commercial powder is nearly always contaminated with growth inhibitors such as sugars, citrate or pectin and most laboratory synthesis methods deliver large precipitates, often containing vaterite or aragonite. To address this problem, we (i) adapted the method of carbonating a Ca(OH)2 slurry with CO2 gas to develop the first simple, cheap, safe and reproducible procedure using common laboratory equipment, to obtain calcite that reproducibly had a surface area of 14-17 m2/g and (ii) conducted a thorough characterization of the product. Scanning electron microscopy (SEM) revealed nanometer scale, rhombohedral crystals. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR) confirmed highly crystalline, pure calcite that more closely resembles the dimensions of the biogenic calcite produced by algae in coccoliths than other methods for synthesizing calcite. We suggest that this calcite is useful when purity and high surface area are important.

  12. The origin of carbon isotope vital effects in coccolith calcite

    PubMed Central

    McClelland, H. L. O.; Bruggeman, J.; Hermoso, M.; Rickaby, R. E. M.

    2017-01-01

    Calcite microfossils are widely used to study climate and oceanography in Earth's geological past. Coccoliths, readily preserved calcite plates produced by a group of single-celled surface-ocean dwelling algae called coccolithophores, have formed a significant fraction of marine sediments since the Late Triassic. However, unlike the shells of foraminifera, their zooplankton counterparts, coccoliths remain underused in palaeo-reconstructions. Precipitated in an intracellular chemical and isotopic microenvironment, coccolith calcite exhibits large and enigmatic departures from the isotopic composition of abiogenic calcite, known as vital effects. Here we show that the calcification to carbon fixation ratio determines whether coccolith calcite is isotopically heavier or lighter than abiogenic calcite, and that the size of the deviation is determined by the degree of carbon utilization. We discuss the theoretical potential for, and current limitations of, coccolith-based CO2 paleobarometry, that may eventually facilitate use of the ubiquitous and geologically extensive sedimentary archive. PMID:28262764

  13. The origin of carbon isotope vital effects in coccolith calcite

    NASA Astrophysics Data System (ADS)

    McClelland, H. L. O.; Bruggeman, J.; Hermoso, M.; Rickaby, R. E. M.

    2017-03-01

    Calcite microfossils are widely used to study climate and oceanography in Earth's geological past. Coccoliths, readily preserved calcite plates produced by a group of single-celled surface-ocean dwelling algae called coccolithophores, have formed a significant fraction of marine sediments since the Late Triassic. However, unlike the shells of foraminifera, their zooplankton counterparts, coccoliths remain underused in palaeo-reconstructions. Precipitated in an intracellular chemical and isotopic microenvironment, coccolith calcite exhibits large and enigmatic departures from the isotopic composition of abiogenic calcite, known as vital effects. Here we show that the calcification to carbon fixation ratio determines whether coccolith calcite is isotopically heavier or lighter than abiogenic calcite, and that the size of the deviation is determined by the degree of carbon utilization. We discuss the theoretical potential for, and current limitations of, coccolith-based CO2 paleobarometry, that may eventually facilitate use of the ubiquitous and geologically extensive sedimentary archive.

  14. Defects in Calcite.

    DTIC Science & Technology

    1991-05-13

    AD-A245 645 A TRIDENT SCHOLAR PROJECT REPORT NO. 181 "DEFECTS IN CALCITE " DTTC %N FEB 5-1912 UNITED STATES NAVAL ACADEMY ANNAPOLIS, MARYLAND 92-02841...report; no. 181 (1991) "DEFECTS IN CALCITE " A Trident Scholar Project Report by Midshipman Anthony J. Kotarski, Class of 1991 U. S. Naval Academy Annapolis...REPORT TYPE AND DATES COVERED 13 May 1991 Final 1990/91 . TITLE AND SUBTITLE s. FUNDING NUMBERS DEFECTS IN CALCITE 6. AUTHOR(S) Anthony J. Kotarski 7

  15. Planktic Foraminiferal Sedimentation and Calcite Budget

    NASA Astrophysics Data System (ADS)

    Schiebel, R.

    2002-12-01

    Vertical flux and sedimentation rate of planktic foraminiferal tests is quantified on a global scale. The planktic foraminiferal test flux is a consequence of the population dynamics, and the differential settling modes for different species are a precondition for the differences in the regional flux rates. The average planktic foraminiferal calcite flux rate at the 100-m depth-level is estimated at 50% of the global-marine calcite flux and 6% of the total carbon flux. The most significant decrease in the planktic foraminiferal test flux rates between 100-700 m water depth possibly results from increased bacterially-mediated decomposition of cytoplasm and a decreasing pH in microenvironments within foraminiferal tests. Throughout most of the year, on average only 1-3% of the initially exported CaCO3 reaches the deep sea floor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of tests to the formation of deep-sea sediments. On a global average, ~25% of the total calcite produced by planktic foraminifers arrives in the deep ocean and at the sediment surface. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccolithophores, pteropods, and calcareous dinophytes is discussed. The global planktic foraminiferal calcite flux rate at 100 m depth amounts to 23-56% of the total open marine CaCO3 flux. The total planktic foraminiferal contribution of CaCO3 to global surface sediments is estimated at 0.36-0.88 Gt per year, ~30-80% of the total deep-marine calcite budget.

  16. Microbially-Mediated Subsurface Calcite Precipitation for Removal of Hazardous Divalent Cations

    SciTech Connect

    Colwell, Frederick S.; Smith, R.W.; Ferris, F. Gratn; Ingram, Jani C.; Reysenbach, A.-L.; Fujita, Yoshiko; Tyler, T.L.; Taylor, J.L.; Banta, A.; Delwiche, M.E.; McLing, T.; Cortez, Marnie, M.; Watwood, M.E.

    2003-03-27

    We are investigating microbially-mediated acceleration of calcite precipitation and co-precipitation of hazardous divalent cations (e.g., 90Sr) in calcite saturated subsurface systems. In theory, the addition of urea to an aquifer or vadose zone and its subsequent hydrolysis by indigenous microbes will cause an increase in alkalinity, pH and calcite precipitation. Lab studies indicated the ability of various bacteria to precipitate calcite through urea hydrolysis and that incorporation of strontium in biogenically-formed calcite is greater than in abiotically formed calcite. Results from a field experiment in a pristine location in the Snake River Plain aquifer involving the phased addition of molasses and then urea showed increases in total cell numbers, rate of urea hydrolysis and calcite formation during the study. The combined diagnostic approaches of microbiology, molecular ecology and analytical chemistry demonstrate the feasibility of this biogeochemical manipulation for subsurface remediation at arid Western DOE sites such as Hanford and INEEL.

  17. Strontium Incorporation into Calcite Generated by Bacterial Ureolysis

    SciTech Connect

    Yoshiko Fujita; George D. Redden; Jani C. Ingram; Marnie M. Cortez; Robert W. Smith

    2004-08-01

    Strontium incorporation into calcite generated by bacterial ureolysis was investigated as part of an assessment of a proposed remediation approach for 90Sr contamination in groundwater. Urea hydrolysis produces ammonium and carbonate and elevates pH, resulting in the promotion of calcium carbonate precipitation. Urea hydrolysis by the bacterium Bacillus pasteurii in a medium designed to mimic the chemistry of the Snake River Plain Aquifer in Idaho resulted in a pH rise from 7.5 to 9.1. Measured average distribution coefficients (DEX) for Sr in the calcite produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic calcites (0.02–0.4). They were also higher than values for calcite produced abiotically by ammonium carbonate addition (0.3). The precipitation of calcite in these experiments was verified by X-ray diffraction. Time-of-flight secondary ion mass spectrometry (ToF SIMS) depth profiling (up to 350 nm) suggested that the Sr was not merely sorbed on the surface, but was present at depth within the particles. X-ray absorption near edge spectra showed that Sr was present in the calcite samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of calcite precipitation, where faster precipitation was associated with greater Sr uptake into the solid. The presence of bacterial surfaces as potential nucleation sites in the ammonium carbonate precipitation treatment did not enhance overall precipitation or the Sr distribution coefficient. Because bacterial ureolysis can generate high rates of calcite precipitation, the application of this approach is promising for remediation of 90Sr contamination in environments where calcite is stable over the long term.

  18. Unusual calcite stromatolites and pisoids from a landfill leachate collection system

    NASA Astrophysics Data System (ADS)

    Maliva, Robert G.; Missimer, Thomas M.; Leo, Kevin C.; Statom, Richard A.; Dupraz, Christophe; Lynn, Matthew; Dickson, J. A. D.

    2000-10-01

    Low-magnesium calcite stromatolites and pisoids were found to have precipitated within the leachate collection system piping of a Palm Beach County, Florida, landfill. The stromatolites and pisoids formed in an aphotic and anoxic environment that was at times greatly supersaturated with calcite. The stromatolites are composed of branching cylindrical bundles of concentrically laminated radial fibrous crystals. The pisoids consist of concentric layers of radial fibrous and microcrystalline calcite. Bacteria, likely sulfate reducing, appear to have acted as catalysts for calcite crystal nucleation, and thus the formation of the stromatolites and pisoids. The leachate system stromatolites provide a recent example of stromatolites that formed largely by cement precipitation. By acting as catalysts for calcite nucleation, bacteria may cause more rapid cementation than would have occurred under purely abiotic conditions. Rapid calcite precipitation catalyzed by bacteria has interfered with the operation of the Palm Beach County landfill leachate collection by obstructing pipes and may be an unrecognized problem at other landfill sites.

  19. Application of calcite Mg partitioning functions to the reconstruction of paleocean Mg/Ca

    NASA Astrophysics Data System (ADS)

    Hasiuk, Franciszek J.; Lohmann, Kyger C.

    2010-12-01

    Calcite Mg/Ca is usually assumed to vary linearly with solution Mg/Ca, that a constant partition coefficient describes the relationship between these two ratios. Numerous published empirical datasets suggests that this relationship is better described by a power function. We provide a compilation of these literature data for biotic and abiotic calcite in the form of Calcite Mg/Ca = F(Solution Mg/Ca) H, where F and H are empirically determined fitting parameters describing the slope and deviation from linearity, respectively, of the function. This is equivalent to Freundlich sorption behavior controlling Mg incorporation in calcite. Using a power function, instead of a partition coefficient, lowers Phanerozoic seawater Mg/Ca estimates based on echinoderm skeletal material by, on average, 0.5 mol/mol from previous estimates. These functions can also be used to model the primary skeletal calcite Mg/Ca of numerous calcite phases through geologic time. Such modeling suggests that the Mg/Ca of all calcite precipitated from seawater has varied through the Phanerozoic in response to changing seawater Mg/Ca and that the overall range in Mg/Ca measured among various calcite phases would be greatest when seawater Mg/Ca was also high (e.g., "aragonite seas") and lowest when seawater Mg/Ca was low (e.g., "calcite seas"). It follows that, during times of "calcite seas" when the seawater Mg/Ca is presumed to have been lower, deposition of calcite with low Mg contents would have resulted in a depressed drive for diagenetic stabilization of shelfal carbonate and, in turn, lead to greater preservation of crystal and skeletal microfabrics and primary chemistries in biotic and abiotic calcites.

  20. A novel determination of calcite dissolution kinetics in seawater

    NASA Astrophysics Data System (ADS)

    Subhas, Adam V.; Rollins, Nick E.; Berelson, William M.; Dong, Sijia; Erez, Jonathan; Adkins, Jess F.

    2015-12-01

    We present a novel determination of the dissolution kinetics of inorganic calcite in seawater. We dissolved 13 C -labeled calcite in unlabeled seawater, and traced the evolving δ13 C composition of the fluid over time to establish dissolution rates. This method provides sensitive determinations of dissolution rate, which we couple with tight constraints on both seawater saturation state and surface area of the dissolving minerals. We have determined dissolution rates for two different abiotic calcite materials and three different grain sizes. Near-equilibrium dissolution rates are highly nonlinear, and are well normalized by geometric surface area, giving an empirical dissolution rate dependence on saturation state (Ω) of: This result substantiates the non-linear response of calcite dissolution to undersaturation. The bulk dissolution rate constant calculated here is in excellent agreement with those determined in far from equilibrium and dilute solution experiments. Plots of dissolution versus undersaturation indicates the presence of at least two dissolution mechanisms, implying a criticality in the calcite-seawater system. Finally, our new rate determination has implications for modeling of pelagic and seafloor dissolution. Nonlinear dissolution kinetics in a simple 1-D lysocline model indicate a possible transition from kinetic to diffusive control with increasing water depth, and also confirm the importance of respiration-driven dissolution in setting the shape of the calcite lysocline.

  1. Alginic Acid Accelerates Calcite Dissolution

    NASA Astrophysics Data System (ADS)

    Perry, T. D.; Duckworth, O. W.; McNamara, C. J.; Martin, S. T.; Mitchell, R.

    2003-12-01

    Accelerated carbonate weathering through biological activity affects both geochemical cycling and the local pH and alkalinity of terrestrial and marine waters. Microbes affect carbonate dissolution through metabolic activity, production of acidic or chelating exudates, and cation binding by cell walls. Dissolution occurs within microbial biofilms - communities of microorganisms attached to stone in an exopolymer matrix. We investigated the effect of alginic acid, a common biological polymer produced by bacteria and algae, on calcite dissolution using a paired atomic force microscopy/flow-through reactor apparatus. The alginic acid caused up to an order of magnitude increase in dissolution rate at 3 < pH < 12. Additionally, the polymer preferentially binds to the obtuse pit steps and increases step velocity. We propose that the polymer is actively chelating surficial cations reducing the activation energy and increasing dissolution rate. The role of biologically produced polymers in mineral weathering is important in the protection of cultural heritage materials and understanding of marine and terrestrial systems.

  2. Elastic constants of calcite

    USGS Publications Warehouse

    Peselnick, L.; Robie, R.A.

    1962-01-01

    The recent measurements of the elastic constants of calcite by Reddy and Subrahmanyam (1960) disagree with the values obtained independently by Voigt (1910) and Bhimasenachar (1945). The present authors, using an ultrasonic pulse technique at 3 Mc and 25??C, determined the elastic constants of calcite using the exact equations governing the wave velocities in the single crystal. The results are C11=13.7, C33=8.11, C44=3.50, C12=4.82, C13=5.68, and C14=-2.00, in units of 1011 dyncm2. Independent checks of several of the elastic constants were made employing other directions and polarizations of the wave velocities. With the exception of C13, these values substantially agree with the data of Voigt and Bhimasenachar. ?? 1962 The American Institute of Physics.

  3. Strontium Incorporation Into Calcite Generated by Bacterial Ureolysis

    NASA Astrophysics Data System (ADS)

    Fujita, Y.; Ingram, J. A.; Cortez, M. M.; Redden, G. D.; Smith, R. W.

    2002-12-01

    Strontium incorporation into calcite generated by bacterial ureolytic activity was investigated as part of a larger effort to evaluate the use of in situ urea hydrolysis for accelerating co-precipitation of trace metals and radionuclides in contaminated aquifers. 90Sr, a uranium fission product with a half-life of 29 years, is a significant subsurface contaminant at several Department of Energy facilities and could be immobilized using this remediation strategy. Experiments were conducted in a medium designed to simulate the groundwater of the Snake River Plain Aquifer in eastern Idaho, amended with strontium. Initially the solution was undersaturated with respect to calcite. As a model ureolytic organism, we used Bacillus pasteurii, a well-characterized bacterium known for high urease activity and previously shown to induce calcite precipitation in urea-amended medium. To gain information on the effect of the bacterial surfaces, we also looked at precipitation in the presence of a bacterial species that did not hydrolyze urea, as well as in the absence of bacteria. In the absence of bacterial ureolysis, carbonate precipitation was induced by addition of ammonium carbonate. All products were identified as calcite by X-ray diffraction. Strontium uptake was observed in all cases, but was greatest in the system including bacterial ureolysis. Sputter depth element profiling by time-of-flight secondary ion mass spectrometry (TOF-SIMS) confirmed this finding, showing highest Sr:Ca ratios in the bacterially generated calcite throughout the depth (~350 nm) investigated. Environmental Scanning Electron Microscopy (ESEM) of the solids revealed regular crystals containing the outlines of embedded or entombed bacterial cells, suggesting that calcite precipitated directly on the cell surfaces when present. Analysis by X-ray Absorption Near Edge Spectroscopy (XANES) indicated that in both the biotically and abiotically generated calcites the Sr was incorporated into the calcite

  4. in situ Calcite Precipitation for Contaminant Immobilization

    SciTech Connect

    Yoshiko Fujita; Robert W. Smith

    2009-08-01

    in situ Calcite Precipitation for Contaminant Immobilization Yoshiko Fujita (Yoshiko.fujita@inl.gov) (Idaho National Laboratory, Idaho Falls, Idaho, USA) Robert W. Smith (University of Idaho-Idaho Falls, Idaho Falls, Idaho, USA) Subsurface radionuclide and trace metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of DOE’s greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide strontium-90, is co-precipitation in calcite. Calcite, a common mineral in the arid western U.S., can form solid solutions with trace metals. The rate of trace metal incorporation is susceptible to manipulation using either abiotic or biotic means. We have previously demonstrated that increasing the calcite precipitation rate by stimulating the activity of urea hydrolyzing microorganisms can result in significantly enhanced Sr uptake. Urea hydrolysis causes the acceleration of calcium carbonate precipitation (and trace metal co-precipitation) by increasing pH and alkalinity, and also by liberating the reactive cations from the aquifer matrix via exchange reactions involving the ammonium ion derived from urea: H2NCONH2 + 3H2O ? 2NH4+ + HCO3- + OH- urea hydrolysis >X:2Ca + 2NH4+ ? 2>X:NH4 + Ca2+ ion exchange Ca2+ + HCO3- + OH- ? CaCO3(s) + H2O calcite precipitation where >X: is a cation exchange site on the aquifer matrix. This contaminant immobilization approach has several attractive features. Urea hydrolysis is catalyzed by the urease enzyme, which is produced by many indigenous subsurface microorganisms. Addition of foreign microbes is unnecessary. In turn the involvement of the native microbes and the consequent in situ generation of reactive components in the aqueous phase (e.g., carbonate and Ca or Sr) can allow dissemination of the reaction over a larger volume and/or farther away from an amendment injection point, as compared to direct addition of the reactants at

  5. On the complex conductivity signatures of calcite precipitation

    SciTech Connect

    Wu, Yuxin; Hubbard, Susan; Williams, Kenneth Hurst; Ajo-Franklin, Jonathan

    2009-11-01

    Calcite is a mineral phase that frequently precipitates during subsurface remediation or geotechnical engineering processes. This precipitation can lead to changes in the overall behavior of the system, such as flow alternation and soil strengthening. Because induced calcite precipitation is typically quite variable in space and time, monitoring its distribution in the subsurface is a challenge. In this research, we conducted a laboratory column experiment to investigate the potential of complex conductivity as a mean to remotely monitor calcite precipitation. Calcite precipitation was induced in a glass bead (3 mm) packed column through abiotic mixing of CaCl{sub 2} and Na{sub 2}CO{sub 3} solutions. The experiment continued for 12 days with a constant precipitation rate of {approx}0.6 milimole/d. Visual observations and scanning electron microscopy imaging revealed two distinct phases of precipitation: an earlier phase dominated by well distributed, discrete precipitates and a later phase characterized by localized precipitate aggregation and associated pore clogging. Complex conductivity measurements exhibited polarization signals that were characteristic of both phases of calcite precipitation, with the precipitation volume and crystal size controlling the overall polarization magnitude and relaxation time constant. We attribute the observed responses to polarization at the electrical double layer surrounding calcite crystals. Our experiment illustrates the potential of electrical methods for characterizing the distribution and aggregation state of nonconductive minerals like calcite. Advancing our ability to quantify geochemical transformations using such noninvasive methods is expected to facilitate our understanding of complex processes associated with natural subsurface systems as well as processes induced through engineered treatments (such as environmental remediation and carbon sequestration).

  6. Morphology Controls on Calcite Recrystallization.

    PubMed

    Heberling, Frank; Paulig, Leonie; Nie, Zhe; Schild, Dieter; Finck, Nicolas

    2016-11-01

    Environmental scientists and geoscientists working in different fields regard the reactivity of calcite and corresponding changes in its trace elemental- or isotopic composition from diametrically opposed points of view. As one extreme, calcite based environmental remediation strategies rely on the fast recrystallization of calcite and the concurrent uptake and immobilization of pollutants. Paleo-ecological investigations denote the other extreme, and rely on the invariability of calcite composition over geological periods of time. We use long-term radiotracer experiments to quantify recrystallization rates of seven types of calcite powder with diverse morphology and particle size distribution. On the one hand our results demonstrate the long-term metastability of calcite with equilibrated crystal surfaces even at isotopic dis-equilibrium. On the other hand, we document the extremely high reactivity and interfacial free energy of freshly ground, rough calcite. Our results indicate that bulk calcite recrystallization is an interfacial free energy driven Ostwald-ripening process, in which particle roughness effects dominate over the effect of crystal habitus and particle size. We confirm that the dynamic equilibrium exchange of crystal constituents between kink sites involves an activation barrier of about 25 kJ/mol. At room temperature the equilibrium exchange is limited to a near surface region and proceeds at a rate of (3.6 ± 1.4)·10(-13) mol/(m(2)·s).

  7. Review: the effects of secular variation in seawater Mg/Ca on marine biocalcification

    NASA Astrophysics Data System (ADS)

    Ries, J. B.

    2009-07-01

    Synchronized transitions in the polymorph mineralogy of the major reef-building and sediment-producing calcareous marine organisms and abiotic CaCO3 precipitates (ooids, marine cements) throughout Phanerozoic time is believed to have been caused by tectonically-induced variations in seawater molar Mg/Ca (>2="aragonite seas"; <2="calcite seas"). Here, I review a series of experiments in which extant calcifying taxa were reared in experimental seawater formulated over the range of mMg/Ca ratios (1.0 to 5.2) that occurred throughout their geologic history. Aragonite-secreting bryopsidalean algae and scleractinian corals and calcite-secreting coccolithophores exhibited higher rates of calcification and growth in the experimental seawaters that favored their skeletal mineral. These results support the assertion that seawater Mg/Ca played an important role in determining which hypercalcifying marine organisms were the major reef-builders and sediment-producers throughout Earth history. The observation that primary production increased along with calcification in mineralogically-favorable seawater is consistent with the hypothesis that calcification promotes photosynthesis within autotrophs through the liberation of CO2. The Mg/Ca ratio of calcite secreted by the coccolithophores, coralline algae and reef-dwelling animals (crustacea, urchins, calcareous tube worms) declined with reductions in seawater Mg/Ca. Calcifying microbial biofilms varied their mineral polymorph with seawater Mg/Ca (mMg/Ca<2=low Mg calc; mMg/Ca>2=arag+high Mg calc), suggesting a nearly abiotic mode of calcification. These results indicate that biomineralogical control can be partially overridden by ambient seawater Mg/Ca and suggests that modern high Mg calcite organisms probably secreted low Mg calcite in calcite seas of the past. Notably, Mg fractionation in autotrophic organisms was more strongly influenced by changes in seawater Mg/Ca, a probable consequence of them inducing a less controlled

  8. Magnesium incorporation in calcite in the presence of organic ligands

    NASA Astrophysics Data System (ADS)

    Mavromatis, Vasileios; Baldermann, Andre; Purgstaller, Bettina; Dietzel, Martin

    2015-04-01

    The formation of authigenic Mg-calcites in marine early diagenetic environments is commonly driven by a bio-induced process, the anaerobic oxidation of methane (AOM), which provides inorganic carbon required for the precipitation of such authigenic carbonates. In such settings the availability of major and/or trace divalent metal cations (Me2+) incorporated in calcite and their aqueous speciation are controlled by the presence of aqueous organic molecules that are produced either as (by-)products of biological activity (i.e. exopolymeric substances) or during degradation of allochthonous organic matter in the sediments. Despite the fact that the presence of aqueous organic ligands strongly affects the growth rates and the mineralogy of precipitating CaCO3 polymorphs, till now no study addresses the role of Me2+-ligand aqueous complexes on the extent of Mg and/or other trace element content of Mg-calcites. In order to shed light on this process, relevant to authigenic calcite formation in organic-rich marine sediments and continental soils, we precipitated calcite in the presence of aqueous Mg and a variety of low molecular weight carboxylic- and aminoacids. Our experimental data indicate that the presence of organic ligands augments significantly the saturation state of calcite in the parent fluid during its precipitation. Moreover, they suggest that the higher the ligand concentration, the higher the obtained distribution coefficient of Mg in calcite. The latter is directly proportional to the ratio of Mg2+/Ca2+ aqueous ions for all ligands used. Hydrogeochemical modelling of the aqueous fluids indicate that the observed correlation can be explained by the stronger complexation of Ca2+ with organic ligands compared to Mg2+, which results in higher availability of Mg2+ vs. Ca2+ aqueous ions. Overall the obtained results suggest that the higher the organic ligand aqueous concentration the higher the Mg content of calcite forming from this fluid. These findings are

  9. Radiaxial-fibrous calcites of shallow subsurface diagenetic origin

    SciTech Connect

    Mazzullo, S.J.; Bischoff, W.D.; Lobitzer, H.

    1989-03-01

    Radiaxial-fibrous calcites (RFC) in marine carbonates are generally considered syndepositional cements. In Upper Triassic and basal Liassic reef and platform limestones in Austria (Steinplatte complex), however, isopachous RFC is demonstrably a postdepositional diagenetic component that precipitated in shallow-burial phreatic environments during a time of periodic meteoric exposure. Isopachous RFC occurs solely within solution cavities and is interlayered with internal red sediment; discontinuities due to leaching separate sequential generations of RFC in the rocks. Accordingly, one possibility is that the RFC was originally low-magnesium calcite that precipitated in the meteoric phreatic zone during lowstands. Such calcites contain relatively low magnesium concentrations (average 0.87 mole % MgCO/sub 3/) and are /sup 18/O depleted (average - 5.81 /per thousand/ PDB). However, most other RFC cements in the sequence average slightly higher magnesium comparable to crinoidal calcites (1.13 mole % MgCO/sub 3/), are less depleted in /sup 18/O (average - 1.88 /per thousand/ PDB), and are partly dolomitized. Additionally, all the RFC cements are enriched in /sup 13/C to values similar to that of Triassic and Jurassic seawater (+ 2.86 /per thousand/ PDB) and are nonluminescent. Trace element studies indicate alteration of the rocks in partly closed, rock-dominated diagenetic systems. By these facts, the authors favor a precursor high-magnesium calcite mineralogy for the RFC cements, which possibly precipitated during highstands when meteoric pore waters were replaced by marine fluids. Thus, the geochemical trends observed are likely due to variations in the degree of meteoric alteration of high-magnesium calcite RFC rather than to differences in original mineralogy.

  10. Scleractinian corals produce calcite, and grow more slowly, in artificial Cretaceous seawater

    NASA Astrophysics Data System (ADS)

    Ries, Justin B.; Stanley, Steven M.; Hardie, Lawrence A.

    2006-07-01

    The mineralogies of most biotic and abiotic carbonates have alternated in synchroneity between the calcite (hexagonal) and aragonite (orthorhombic) polymorphs of CaCO3 throughout the Phanerozoic Eon. These intervals of calcite and aragonite production, or calcite seas and aragonite seas, are thought to be caused primarily by secular variation in the molar magnesium/calcium ratio of seawater (mMg/Ca > 2 = aragonite + high-Mg calcite; mMg/Ca < 2 = low-Mg calcite), a ratio that has oscillated between 1.0 and 5.2 throughout the Phanerozoic. In laboratory experiments, we show that three species of scleractinian corals, which produce aragonite in modern seawater and which have flourished as important reef builders primarily during aragonite seas of the past, began producing calcite in artificial seawater with an ambient mMg/Ca ratio below that of modern seawater (5.2). The corals produced progressively higher percentages of calcite and calcified at lower rates with further reduction of the ambient mMg/Ca ratio. In artificial seawater of imputed Late Cretaceous composition (mMg/Ca = 1.0), which favors the precipitation of the calcite polymorph, scleractinian corals produced skeletons containing >30% low-Mg calcite (skeletal mMg/Ca < 0.04). These results indicate that the skeletal mineral used by scleractinian corals is partially determined by seawater chemistry. Furthermore, slow calcification rates, resulting from the production of largely aragonitic skeletons in chemically unfavorable seawater (mMg/Ca < 2), probably contributed to the scleractinians' diminished reef-building role in the calcite seas of Late Cretaceous and early Cenozoic time.

  11. Aragonite / Calcite seas and the evolution of biomineralization

    NASA Astrophysics Data System (ADS)

    Balthasar, Uwe

    2015-04-01

    The vast majority of marine invertebrate skeletons are composed of the CaCO3 polymorphs aragonite and calcite, yet the influence of seawater composition on the evolution of calcareous skeletal composition is poorly understood. The main theoretical framework in which the evolution of CaCO3 shell mineralogy is assessed is the aragonite-calcite sea hypothesis with conventional thinking suggesting that a threshold in the marine Mg:Ca ratio determines CaCO3 polymorph formation. I present data from CaCO3 precipitation experiments to show that the concept of a distinct threshold is misleading because Mg:Ca ratio and temperature combined result in a Phanerozoic continuum of co-existing aragonite-calcite seas with aragonite-facilitating conditions existing throughout the Phanerozoic in shallow warm-water (>20° C) environments. The stable reservoir of aragonite-favouring conditions in shallow warm water environments potentially explains the trend of increasing occurrences of skeletal aragonite throughout the Phanerozoic, particularly in the context of the 'out of the tropics' hypothesis. By contrast, the most prominent fluctuations with respect to aragonite-calcite sea conditions can be expected to have occurred in mid- to high latitudes.

  12. Removal of organic magnesium in coccolithophore calcite

    NASA Astrophysics Data System (ADS)

    Blanco-Ameijeiras, S.; Lebrato, M.; Stoll, H. M.; Iglesias-Rodriguez, M. D.; Méndez-Vicente, A.; Sett, S.; Müller, M. N.; Oschlies, A.; Schulz, K. G.

    2012-07-01

    Coccolithophore calcite refers to the plates of calcium carbonate (CaCO3) produced by the calcifying phytoplankton, coccolithophores. The empirical study of the elemental composition has a great potential in the development of paleoproxies. However, the difficulties to separate coccolithophore carbonates from organic phases hamper the investigation of coccoliths magnesium to calcium ratios (Mg/Ca) in biogeochemical studies. Magnesium (Mg) is found in organic molecules in the cells at concentrations up to 400 times higher than in inorganically precipitated calcite in present-day seawater. The aim of this study was to optimize a reliable procedure for organic Mg removal from coccolithophore samples to ensure reproducibility in measurements of inorganic Mg in calcite. Two baseline methods comprising organic matter oxidations with (1) bleach and (2) hydrogen peroxide (H2O2) were tested on synthetic pellets, prepared by mixing reagent grade CaCO3 with organic matter from the non-calcifying marine algae Chlorella autotrophica and measured with an ICP-AES (inductively coupled plasma-atomic emission spectrometer). Our results show that treatments with a reductive solution [using hydroxylamine-hydrochloride (NH2OH·HCl + NH4OH)] followed by three consecutive oxidations (using H2O2) yielded the best cleaning efficiencies, removing >99% of organic Mg in 24 h. P/Ca and Fe/Ca were used as indicators for organic contamination in the treated material. The optimized protocol was tested in dried coccolithophore pellets from batch cultures of Emiliania huxleyi, Calcidiscus leptoporus and Gephyrocapsa oceanica. Mg/Ca of treated coccolithophores were 0.151 ± 0.018, 0.220 ± 0.040, and 0.064 ± 0.023 mmol/mol, respectively. Comparison with Mg/Ca literature coccolith values, suggests a tight dependence on modern seawater Mg/Ca, which changes as a consequence of different seawater origins (<10%). The reliable determination of Mg/Ca and Sr/Ca, and the low levels of organic contamination

  13. Calcite formation in soft coral sclerites is determined by a single reactive extracellular protein.

    PubMed

    Rahman, M Azizur; Oomori, Tamotsu; Wörheide, Gert

    2011-09-09

    Calcium carbonate exists in two main forms, calcite and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called "calcite and aragonite seas." Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce calcite despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form calcitic skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces calcite formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single crystals generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of calcite instead of aragonite in the biocalcification process and that -OH, secondary structures (e.g. α-helices and amides), and other necessary chemical groups are distributed over the center of the calcite crystals. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of crystal formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different calcite-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the crystal structure of calcite in nature.

  14. Calcite Formation in Soft Coral Sclerites Is Determined by a Single Reactive Extracellular Protein*

    PubMed Central

    Rahman, M. Azizur; Oomori, Tamotsu; Wörheide, Gert

    2011-01-01

    Calcium carbonate exists in two main forms, calcite and aragonite, in the skeletons of marine organisms. The primary mineralogy of marine carbonates has changed over the history of the earth depending on the magnesium/calcium ratio in seawater during the periods of the so-called “calcite and aragonite seas.” Organisms that prefer certain mineralogy appear to flourish when their preferred mineralogy is favored by seawater chemistry. However, this rule is not without exceptions. For example, some octocorals produce calcite despite living in an aragonite sea. Here, we address the unresolved question of how organisms such as soft corals are able to form calcitic skeletal elements in an aragonite sea. We show that an extracellular protein called ECMP-67 isolated from soft coral sclerites induces calcite formation in vitro even when the composition of the calcifying solution favors aragonite precipitation. Structural details of both the surface and the interior of single crystals generated upon interaction with ECMP-67 were analyzed with an apertureless-type near-field IR microscope with high spatial resolution. The results show that this protein is the main determining factor for driving the production of calcite instead of aragonite in the biocalcification process and that –OH, secondary structures (e.g. α-helices and amides), and other necessary chemical groups are distributed over the center of the calcite crystals. Using an atomic force microscope, we also explored how this extracellular protein significantly affects the molecular-scale kinetics of crystal formation. We anticipate that a more thorough investigation of the proteinaceous skeleton content of different calcite-producing marine organisms will reveal similar components that determine the mineralogy of the organisms. These findings have significant implications for future models of the crystal structure of calcite in nature. PMID:21768106

  15. Paleozoic Mg calcite preserved: Implications for the Carboniferous ocean

    NASA Astrophysics Data System (ADS)

    Dickson, J. A. D.

    1995-06-01

    Modern Mg calcite echinoderm skeletons are thought to lose Mg so rapidly that no pre-Pleistocene ossicles retain their original Mg concentrations; however, Carboniferous echinoderm skeletons from the Imo Formation of Arkansas and the Holder Formation of New Mexico are reported herein that are still composed of Mg calcite (7.8 to 14.5 mol% MgCO3). Their Sr concentration is also high (620 to 3710 ppm). The pore system in these echinoderm skeletons is filled with ferroan calcite or siderite that has not grown in optical continuity with the skeleton. The discovery of Carboniferous Mg calcite confirms an interpretation already made from their diagenetic replacements. Marine Mg calcite has been associated with proposed icehouse conditions, and although the Carboniferous echinoderm skeletons are compatible with this as they formed during Gondwana glaciation, they are too few to be of significance. Also they are organic secretions and so can override secular mineral trends based on inorganic precipitates. The Carboniferous echinoderm skeletons, produced in tropical waters, have a concentration of Mg similar to values for modern echinoderms. The simplest explanation for this similarity is that both precipitated by similar processes from oceans of similar composition. This does not support predictions, based on mass-balance modeling, that the Mg/Ca ratio of the Carboniferous ocean was half that of today's. The Sr content of Carboniferous echinoderms is less than that for modern echinoderms, leading to a prediction of 6 ppm Sr concentration for the Carboniferous ocean. Further examples of Mg calcite are required to substantiate these interpretations.

  16. Corrosion Protection by Calcite-Type Coatings

    DTIC Science & Technology

    1989-10-01

    CORROSION PROTECTION BY CALCITE -TYPE COATINGS OCTOBER, 1989 Prepared by: OCEAN CITY RESEARCH CORPORATION Tennessee Avenue & Beach Thorofare Ocean...REPORT DATE OCT 1989 2. REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE Corrosion Protection by Calcite -Type Coatings 5a. CONTRACT... calcite -type coatings to segregated seawater ballast tanks. If perfected, a calcite coating approach could substantially reduce the cost of corrosion

  17. Kinetic and thermodynamic factors controlling the distribution of SO 32- and Na + in calcites and selected aragonites

    NASA Astrophysics Data System (ADS)

    Busenberg, Eurybiades; Niel Plummer, L.

    1985-03-01

    Significant amounts of SO 42-, Na +, and OH - are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO 42-. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na +, but very low concentrations of SO 42-. The SO 42- content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na + and SO 42- increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO 42- beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO 42- is the same as that of aragonite. Na + appears to have very little effect on the solubility product of calcites. The amounts of Na + and SO 42- incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient ( D) of SO 42- in calcite at 25.0°C and 0.50 molal NaCl is described by the equation D = k 0 + k 1R where k 0 and k 1 are constants equal to 6.16 × 10 -6 and 3.941 × 10 -6, respectively, and R is the rate of crystal growth of calcite in mg·min -1·g -1 of seed. The data on Na + are consistent with the hypothesis that a significant amount of Na + occupies interstitial positions in the calcite structure. The distribution of Na + follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na + distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na + contents of calcites are not very accurate indicators of environmental salinities.

  18. Kinetic and thermodynamic factors controlling the distribution of SO32- and Na+ in calcites and selected aragonites

    USGS Publications Warehouse

    Busenberg, E.; Niel, Plummer L.

    1985-01-01

    Significant amounts of SO42-, Na+, and OH- are incorporated in marine biogenic calcites. Biogenic high Mg-calcites average about 1 mole percent SO42-. Aragonites and most biogenic low Mg-calcites contain significant amounts of Na+, but very low concentrations of SO42-. The SO42- content of non-biogenic calcites and aragonites investigated was below 100 ppm. The presence of Na+ and SO42- increases the unit cell size of calcites. The solid-solutions show a solubility minimum at about 0.5 mole percent SO42- beyond which the solubility rapidly increases. The solubility product of calcites containing 3 mole percent SO42- is the same as that of aragonite. Na+ appears to have very little effect on the solubility product of calcites. The amounts of Na+ and SO42- incorporated in calcites vary as a function of the rate of crystal growth. The variation of the distribution coefficient (D) of SO42- in calcite at 25.0??C and 0.50 molal NaCl is described by the equation D = k0 + k1R where k0 and k1 are constants equal to 6.16 ?? 10-6 and 3.941 ?? 10-6, respectively, and R is the rate of crystal growth of calcite in mg??min-1??g-1 of seed. The data on Na+ are consistent with the hypothesis that a significant amount of Na+ occupies interstitial positions in the calcite structure. The distribution of Na+ follows a Freundlich isotherm and not the Berthelot-Nernst distribution law. The numerical value of the Na+ distribution coefficient in calcite is probably dependent on the number of defects in the calcite structure. The Na+ contents of calcites are not very accurate indicators of environmental salinities. ?? 1985.

  19. Subaerial meteoric calcitization and lithification of high-magnesian calcite muds, Belize

    SciTech Connect

    Mazzullo, S.J.; Bischoff, W.D. )

    1991-03-01

    Holocene ({lt}1000-1500 yrs old) high-magnesian calcite-dominated muddy sediments (1 m thick) on subaerially exposed cays in northern Belize are in the process of being converted to low-magnesian calcite micrite. Mineralogic stabilization and attendant lithification result from interaction of the sediments with meteoric fluids believed to be derived from seasonal upward discharge through subjacent Pleistocene limestones. The initial marine-derived sediments, composed of {gt}85% HMC (and minor skeletal aragonite), consist of mud and associated soritid and miliolid foraminifera both with MgCO{sub 3} content of 11-15 mol%, and isotopic compositions of -1.0 to -2.5{per thousand} PDB (O), 0 to +1.5{per thousand} PDB (C). With depth, lithified LMC crusts appear in the section, and the Mg concentration of the sediments and associated crusts decreases rapidly to 3 mol% or less, with a corresponding isotopic depletion to values approaching -7.0{per thousand} (O) and -5.8{per thousand} (C). Concomitantly there is progressive dissolution of skeletal aragonite in the sediments, reduction of porosity due to cementation by LMC, and in the muds, a decrease in Sr and increase in Mn contents. The resultant petrofabric of these lithified LMC deposits, derived from the alteration of HMC-dominated muds, is characterized by micrite with patches of pore-filling micritic and microsparitic LMC cements. Such a fabric is similar to and can be confused easily with calcitized aragonite-dominated precursor muds, except for the relative rarity in the samples examined of aragonite relicts in component microspar and/or pseudospar.

  20. Diagnosing Abiotic Degradation

    EPA Science Inventory

    The abiotic degradation of chlorinated solvents in ground water can be difficult to diagnose. Under current practice, most of the “evidence” is negative; specifically the apparent disappearance of chlorinated solvents with an accumulation of vinyl chloride, ethane, ethylene, or ...

  1. Abiotic origin of biopolymers

    NASA Technical Reports Server (NTRS)

    Oro, J.; Stephen-Sherwood, E.

    1976-01-01

    A variety of methods have been investigated in different laboratories for the polymerization of amino acids and nucleotides under abiotic conditions. They include (1) thermal polymerization; (2) direct polymerization of certain amino acid nitriles, amides, or esters; (3) polymerization using polyphosphate esters; (4) polymerization under aqueous or drying conditions at moderate temperatures using a variety of simple catalysts or condensing agents like cyanamide, dicyandiamide, or imidazole; and (5) polymerization under similar mild conditions but employing activated monomers or abiotically synthesized high-energy compounds such as adenosine 5'-triphosphate (ATP). The role and significance of these methods for the synthesis of oligopeptides and oligonucleotides under possible primitive-earth conditions is evaluated. It is concluded that the more recent approach involving chemical processes similar to those used by contemporary living organisms appears to offer a reasonable solution to the prebiotic synthesis of these biopolymers.

  2. Isotopic composition of a calcite-cemented layer in the Lower Jurassic Bridport Sands, southern England: Implications for formation of laterally extensive calcite-cemented layers

    SciTech Connect

    Bjoerkum, P.A. ); Walderhaug, O. )

    1993-07-01

    [delta][sup 18]O[sub PDB] and [delta][sup 13]C[sub PDB] values have been measured on 107 calcite cement samples from a laterally extensive (> 3 km) and continuous calcite-cemented layer 0.5 m thick in the coastal exposures of the Lower Jurassic shallow-marine Bridport Sands in Dorset, southern England. The samples were taken from a two-dimensional grid with 10-cm horizontal and vertical spacing between samples and along individual vertical lines across the calcite-cemented layer, [delta][sup 18]O[sub PDB] values vary between [minus]4.8% and [minus]9.2% and decrease radially outwards from points with lateral spacings on the order of 0.5-1 m in the middle of the calcite-cemented layer. The [delta][sup 18]O[sub PDB] values therefore indicate that the calcite-cemented layer was formed by merging of concretions. All [delta][sup 13]C[sub PDB] values measured are in the narrow range [minus]2.2% to [minus]0.5%, which suggests that the dominant source of calcite cement in the layer was biogenic carbonate.

  3. Shock-induced devolatilization of calcite

    NASA Technical Reports Server (NTRS)

    Boslough, M. B.; Ahrens, T. J.; Vizgirda, J.; Becker, R. H.; Epstein, S.

    1982-01-01

    Experimental measurements of the release adiabats by Vizgirda (1981) indicate that substantial vaporization takes place upon release from shock pressures of 37 GPa for calcite and 14 GPa for aragonite. The present investigation includes the first controlled partial vaporization experiments on calcite. The experiments were conducted to test the predictions of the release adiabat experiments. The quantities of the gaseous species produced from shocked calcite and their carbon and oxygen isotopic compositions were determined, and the shock-induced effect on the Mn(2+) electron spin resonance spectrum in the shock-recovered calcite was observed. On the basis of the obtained results, it is concluded that shock stresses at the 17-18 GPa level give rise to volatilization of 0.03-0.3 (mole) percent of calcite to CO2 and CO. The devolatilization of calcite occurs at low pressure at significantly lower entropy densities than predicted on the basis of thermodynamic continuum models.

  4. Preliminary Results of Bacteria Distribution in Chinese Loess and Their Control on the Calcite Formation

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Lian, B.; Hu, Q.; Teng, H. H.; Wu, T.; Ji, J.; Chen, J.

    2005-12-01

    Continuous loess-paleosol sequences on the Chinese Loess Plateau are viewed as one of best continental archives of paleoclimatic and paleoenvironmental changes of the Late Cenozoic era. Carbonate, mainly calcite, commonly occurs throughout the entire sequence; though some are detrital, most are in-situ pedogenic. TEM studies have shown various morphologies of calcites in Chinese loess, especially nano-rod calcite widely occurring in loess and paleosols which are biogenic. In this study, we collected fresh and undisturbed loess and paleosol samples and successfully separated dominant microbial communities. These microbes are mainly bacteria, especially Bacillus anthracis, and a few fungi. The amount of bacteria decreases sharply with the depth. Then we added the bacteria into the near saturated solution of CaCl2 and Na2CO3. It is interesting that the original calcite crystals formed under abiotic conditions changed from quadrilateral face to pentagonal or hexagonal and the crystal size enlarged almost twice. SEM and AFM observations display bacteria control on the growth of calcite, which cause the lighter carbon isotopic ratios.

  5. Mg-calcite dissolution in carbonate sediments: role in ocean acidification

    NASA Astrophysics Data System (ADS)

    Drupp, P. S.; De Carlo, E. H.; Mackenzie, F. T.

    2014-12-01

    An array of porewater wells at two locations on Hawaiian reefs have been utilized to obtain interstitial pore fluid from various depths in permeable sandy sediments. The total alkalinity (AT) and pH (total scale) were measured for each sample (depths 0, 2, 4, 6, 8, 12, 16, 20, 30, 40, and 60 cm) as well as calcium, magnesium, and strontium concentrations. Ca2+ and Mg2+ concentrations co-vary and appear to be directly related to AT and pH. The ratio of the change in calcium and magnesium (ΔCa, ΔMg) between the overlying water column and the porewater indicates that an 18 mol % Mg-calcite phase is dissolving within the sediment column. This could represent the dissolution of coralline algae such as Porolithon or Lithothamnion both of which produce ~18% Mg-calcite skeletons and are present on Hawaiian reefs. The small changes in Mg concentrations from dissolution/precipitation of high Mg-calcites is typically difficult to measure against the high background matrix of seawater and to our knowledge these data represent some of the first magnesium concentrations measured in permeable sediments. Saturation state (Ω) for Mg-calcites was calculated using both sets of stoichiometric solubility products (K) widely accepted in the literature. Depending on the K used, most of the porewater was undersaturated with respect to the high Mg calcites (>12%). Saturation states were determined using an ion activity product (IAP) calculated from the measured values of calcium and magnesium. This produces a more accurate Ω than assuming calcium and magnesium concentrations based on salinity, as is typically done in surface waters. As surface water becomes more corrosive to carbonate minerals due to enhanced ocean acidification through the next century, it is expected that dissolution of both biogenic high Mg-calcites and abiotic Mg-calcite cements will increase, potentially destabilizing reef framework and altering the biogeochemical cycling of carbon in these environments.

  6. Direct observation of microbial inhibition of calcite dissolution.

    PubMed

    Lüttge, Andreas; Conrad, Pamela G

    2004-03-01

    Vertical scanning interferometry (VSI) provides a method for quantification of surface topography at the angstrom to nanometer level. Time-dependent VSI measurements can be used to study the surface-normal retreat across crystal and other solid surfaces during dissolution or corrosion processes. Therefore, VSI can be used to directly and nondestructively measure mineral dissolution rates with high precision. We have used this method to compare the abiotic dissolution behavior of a representative calcite (CaCO(3)) cleavage face with that observed upon addition of an environmental microbe, Shewanella oneidensis MR-1, to the crystal surface. From our direct observations, we have concluded that the presence of the microbes results in a significant inhibition of the rate of calcite dissolution. This inhibition appears to be a 2nd-order effect that is related to the formation of etch pits. The opening of etch pits was greatly inhibited in the presence of added bacteria, suggesting that the bacterial cells exert their effect by inhibiting the formation of etch pits at high-energy sites at the crystal surface caused by lattice defects, e.g., screw or point dislocations. The experimental methodology thus provides a nondestructive, directly quantifiable, and easily visualized view of the interactions of microbes and minerals during weathering (or corrosion) processes or during mineral precipitation.

  7. Stabilities of calcite and aragonite

    USGS Publications Warehouse

    Christ, C.L.; Hostetler, P.B.; Siebert, R.M.

    1974-01-01

    A revaluation of the 25° C activity-product constants of calcite (KC) and aragonite (KA) was made on the basis of the known solubilities of these phases for which the activity of total dissolved calcium was corrected for the presence of the ion pair CaHCO3+ in the aqueous phase. The value of the dissociation constant of CaHCO3+ was taken to be 10-1.225±0.02. This value, combined with values of the analytical concentrations in solutions with partial pressure PCO2 =0.97 atmosphere, leads to KC=l0-8.52±0.04 and KA= 10-8.36±0.04. Based on these K values, standard free energies of formation of calcite and aragonite were calculated to be -270,144±375 and -269,926±375 calories mole-1, (-1,130,282±1,569 and -1,129,370±1,569 joules mole-1), respectively. From the 25°C K values, using appropriate entropy and heat capacity data, values of KC and KA were calculated over the temperature range 0° to 200°C. Possible errors in interpretation of measured pH values and inferred PCO2values and the bearing of these errors on calculations of K values are discussed.

  8. Crystal lattice tilting in prismatic calcite.

    PubMed

    Olson, Ian C; Metzler, Rebecca A; Tamura, Nobumichi; Kunz, Martin; Killian, Christopher E; Gilbert, Pupa U P A

    2013-08-01

    We analyzed the calcitic prismatic layers in Atrina rigida (Ar), Haliotis iris (Hi), Haliotis laevigata (HL), Haliotis rufescens (Hrf), Mytilus californianus (Mc), Pinctada fucata (Pf), Pinctada margaritifera (Pm) shells, and the aragonitic prismatic layer in the Nautilus pompilius (Np) shell. Dramatic structural differences were observed across species, with 100-μm wide single-crystalline prisms in Hi, HL and Hrf, 1-μm wide needle-shaped calcite prisms in Mc, 1-μm wide spherulitic aragonite prisms in Np, 20-μm wide single-crystalline calcite prisms in Ar, and 20-μm wide polycrystalline calcite prisms in Pf and Pm. The calcite prisms in Pf and Pm are subdivided into sub-prismatic domains of orientations, and within each of these domains the calcite crystal lattice tilts gradually over long distances, on the order of 100 μm, with an angle spread of crystal orientation of 10-20°. Furthermore, prisms in Pf and Pm are harder than in any other calcite prisms analyzed, their nanoparticles are smaller, and the angle spread is strongly correlated with hardness in all shells that form calcitic prismatic layers. One can hypothesize a causal relationship of these correlated parameters: greater angle spread may confer greater hardness and resistance to wear, thus providing Pf and Pm with a structural advantage in their environment. This is the first structure-property relationship thus far hypothesized in mollusk shell prisms.

  9. Do organic ligands affect calcite dissolution rates?

    NASA Astrophysics Data System (ADS)

    Oelkers, Eric H.; Golubev, Sergey V.; Pokrovsky, Oleg S.; Bénézeth, Pascale

    2011-04-01

    Steady state Iceland-spar calcite dissolution rates were measured at 25 °C in aqueous solutions containing 0.1 M NaCl and up to 0.05 M dissolved bicarbonate at pH from 7.9 to 9.1 in the presence of 13 distinct dissolved organic ligands in mixed-flow reactors. The organic ligands considered in this study include those most likely to be present in either (1) aquifers at the conditions pertinent to CO 2 sequestration or (2) soil/early diagenetic environments: acetate, phthalate, citrate, EDTA 4-, succinate, D-glucosaminate, L-glutamate, D-gluconate, 2,4-dihydroxybenzoate, 3,4-dihydroxybenzoate, fumarate, malonate, and gallate. Results show that the presence of <0.05 mol/kg of these organic anions changes calcite dissolution rates by less than a factor of 2.5 with the exception of citrate and EDTA 4-. The presence of 0.05 mol/kg citrate and EDTA 4- increases calcite dissolution rates by as much as a factor of 35 and 500, respectively, compared to rates in organic anion-free solutions. Further calcite dissolution experiments were performed in the presence of organic polymers similar to bacterial exudates, cell exopolysaccharides, and analogs of microbial cell envelopes: alginate, lichen extract, humic acid, pectin, and gum xanthan. In no case did the presence of <100 ppm of these organics change calcite dissolution rates by more than a factor of 2.5. Results obtained in this study suggest that the presence of aqueous organic anions negligibly affects calcite forward dissolution rates in most natural environments. Some effect on calcite reactivity may be observed, however, by the presence of organic anions if they change substantially the chemical affinity of the fluid with respect to calcite.

  10. Diffusion of Ca and Mg in Calcite

    SciTech Connect

    Cygan, R.T.; Fisler, D.K.

    1999-02-10

    The self-diffusion of Ca and the tracer diffusion of Mg in calcite have been experimentally measured using isotopic tracers of {sup 25}Mg and {sup 44}Ca. Natural single crystals of calcite were coated with a thermally-sputtered oxide thin film and then annealed in a CO{sub 2} gas at one atmosphere total pressure and temperatures from 550 to 800 C. Diffusion coefficient values were derived from the depth profiles obtained by ion microprobe analysis. The resultant activation energies for Mg tracer diffusion and Ca self-diffusion are respectively: E{sub a}(Mg) = 284 {+-} 74 kJ/mol and E{sub a}(Ca) = 271 {+-} 80 kJ/mol. For the temperature ranges in these experiments, the diffusion of Mg is faster than Ca. The results are generally consistent in magnitude with divalent cation diffusion rates obtained in previous studies and provide a means of interpreting the thermal histories of carbonate minerals, the mechanism of dolomitization, and other diffusion-controlled processes. The results indicate that cation diffusion in calcite is relatively slow and cations are the rate-limiting diffusing species for the deformation of calcite and carbonate rocks. Application of the calcite-dolomite geothermometer to metamorphic assemblages will be constrained by cation diffusion and cooling rates. The direct measurement of Mg tracer diffusion in calcite indicates that dolomitization is unlikely to be accomplished by Mg diffusion in the solid state but by a recrystallization process.

  11. Abiotic stresses and endophyte effects

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Abiotic stresses consist of nonorganismal, nonpathogenic factors that inhibit plant function. Tall fescue [Lolium arundinaceum (Schreb.) Darbysh.] is widely symbiotic with a naturally occurring endophytic fungus [Neotyphodium coenophialum (Morgan-Jones and Gams) Glenn, Bacon, and Hanlin], which con...

  12. Abiotic tooth enamel

    NASA Astrophysics Data System (ADS)

    Yeom, Bongjun; Sain, Trisha; Lacevic, Naida; Bukharina, Daria; Cha, Sang-Ho; Waas, Anthony M.; Arruda, Ellen M.; Kotov, Nicholas A.

    2017-03-01

    Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix. This structural motif is unusually consistent across all species from all geological eras. Such invariability—especially when juxtaposed with the diversity of other tissues—suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels—we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that light-weight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial portion to macroscale deformations along the tooth’s normal is maximized when the architecture is columnar, suggesting an evolutionary advantage of the columnar motif in the enamel of living species. We expect our findings to apply to all columnar composites and to lead to the development of high-performance load-bearing materials.

  13. Abiotic tooth enamel.

    PubMed

    Yeom, Bongjun; Sain, Trisha; Lacevic, Naida; Bukharina, Daria; Cha, Sang-Ho; Waas, Anthony M; Arruda, Ellen M; Kotov, Nicholas A

    2017-03-01

    Tooth enamel comprises parallel microscale and nanoscale ceramic columns or prisms interlaced with a soft protein matrix. This structural motif is unusually consistent across all species from all geological eras. Such invariability-especially when juxtaposed with the diversity of other tissues-suggests the existence of a functional basis. Here we performed ex vivo replication of enamel-inspired columnar nanocomposites by sequential growth of zinc oxide nanowire carpets followed by layer-by-layer deposition of a polymeric matrix around these. We show that the mechanical properties of these nanocomposites, including hardness, are comparable to those of enamel despite the nanocomposites having a smaller hard-phase content. Our abiotic enamels have viscoelastic figures of merit (VFOM) and weight-adjusted VFOM that are similar to, or higher than, those of natural tooth enamels-we achieve values that exceed the traditional materials limits of 0.6 and 0.8, respectively. VFOM values describe resistance to vibrational damage, and our columnar composites demonstrate that light-weight materials of unusually high resistance to structural damage from shocks, environmental vibrations and oscillatory stress can be made using biomimetic design. The previously inaccessible combinations of high stiffness, damping and light weight that we achieve in these layer-by-layer composites are attributed to efficient energy dissipation in the interfacial portion of the organic phase. The in vivo contribution of this interfacial portion to macroscale deformations along the tooth's normal is maximized when the architecture is columnar, suggesting an evolutionary advantage of the columnar motif in the enamel of living species. We expect our findings to apply to all columnar composites and to lead to the development of high-performance load-bearing materials.

  14. Controls on variation of calcite content in arkose beds of the Sangre de Cristo Formation, (Pennsylvanian-Permian) Colorado

    SciTech Connect

    Wysong, J.R.; Bain, R.J. . Dept. of Geology)

    1994-04-01

    Arkosic conglomerates and sandstones of the Pennsylvanian-Permian Sangre de Cristo Formation of south-central Colorado were deposited on alluvial plains and nearshore marine shelves adjacent to the highlands of the Ancestral Rocky Mountains. Thin limestone units occur locally, however calcite content of arkoses varies independent of these limestones. The thinly bedded to laminated arkoses contain abundant detrital orthoclase and plagioclase feldspars, micas and quartz. Authigenic clay (kaolinite) and calcite occur both as void-filling cement and replacement of feldspars. Fine-grained arkoses possess more calcite and authigenic clay than their coarse-grained counterparts. Calcite occurs as plagioclase replacement in fine-grained samples whereas in coarse-grained rocks it fills interstitial voids. Calcite content in fine-grained arkoses is low where laminae are preserved and increases with the presence of bioturbation. Diagenetic processes responsible for calcite and clay content of these arkoses were controlled by several factors including original sediment texture, composition, and grain orientation. Plagioclase has been altered to produce calcite and clay more than orthoclase. Permeability of coarse-grained rocks was higher and resulted in primarily void-filling cement. In fine-grained arkoses, permeability was less and water remained in contact with grains longer thereby altering plagioclase. Aligned mica grains of laminae retarded flow and impeded diagenetic alteration whereas bioturbation disrupted grain orientation thereby enhancing diagenesis.

  15. Calcite dissolution in two deep eutrophic lakes

    SciTech Connect

    Ramisch, F.; Dittrich, M.; Mattenberger, C.; Wehrli, B.; Wueest, A.

    1999-10-01

    The calcium cycle, in particular carbonate dissolution, was analyzed in two deep eutrophic lakes, Lago di Lugano (288 m maximum depth) and Sempachersee (87 m) located in Switzerland. A box model approach was used to calculate calcite dissolution in the water column and at the sediment-water interface based on various lake monitoring data such as sediment traps, sediment cores, water and pore-water interface based on various lake monitoring data such as sediment traps, sediment cores, water and pore-water analysis. A model for stationary conditions allowing the calculation of calcite dissolution in the water column for a given particle size distribution was developed. The relative values of the simulated flux were consistent with sediment trap observations. The best fit of the dissolution rate constant of sinking calcite in Lago di Lugano was on the same order of magnitude (3 {center{underscore}dot} 10{sup {minus}10} kg{sup 1/3} s{sup {minus}1}) as published laboratory values for this surface controlled process. Both lakes show a similar specific calcite precipitation rate of 170 g Ca m{sup {minus}2} a{sup {minus}1}. The diffusive flux across the sediment-water interface amounts to about 15 and 10% of total calcite precipitation in Sempachersee and Lago di Lugano, respectively. However, 61% of the precipitated calcite is dissolved in the water column of Lago di Lugano compared to only 13% in Sempachersee. These results point towards the importance of grain size distributions and settling times in stratified deep waters as the two most important factors determining calcite retention in sediments of hard water lakes.

  16. Environmental controls on the Emiliania huxleyi calcite mass

    NASA Astrophysics Data System (ADS)

    Horigome, M. T.; Ziveri, P.; Grelaud, M.; Baumann, K.-H.; Marino, G.; Mortyn, P. G.

    2014-04-01

    Although ocean acidification is expected to impact (bio) calcification by decreasing the seawater carbonate ion concentration, [CO32-], there is evidence of nonuniform response of marine calcifying plankton to low seawater [CO32-]. This raises questions about the role of environmental factors other than acidification and about the complex physiological responses behind calcification. Here we investigate the synergistic effect of multiple environmental parameters, including seawater temperature, nutrient (nitrate and phosphate) availability, and carbonate chemistry on the coccolith calcite mass of the cosmopolitan coccolithophore Emiliania huxleyi, the most abundant species in the world ocean. We use a suite of surface (late Holocene) sediment samples from the South Atlantic and southwestern Indian Ocean taken from depths lying above the modern lysocline (with the exception of eight samples that are located at or below the lysocline). The coccolith calcite mass in our results presents a latitudinal distribution pattern that mimics the main oceanographic features, thereby pointing to the potential importance of seawater nutrient availability (phosphate and nitrate) and carbonate chemistry (pH and pCO2) in determining coccolith mass by affecting primary calcification and/or the geographic distribution of E. huxleyi morphotypes. Our study highlights the importance of evaluating the combined effect of several environmental stressors on calcifying organisms to project their physiological response(s) in a high-CO2 world and improve interpretation of paleorecords.

  17. Calibration of the calcite-water oxygen-isotope geothermometer at Devils Hole, Nevada, a natural laboratory

    USGS Publications Warehouse

    Coplen, T.B.

    2007-01-01

    The ??18O of ground water (-13.54 ?? 0.05 ???) and inorganically precipitated Holocene vein calcite (+14.56 ?? 0.03 ???) from Devils Hole cave #2 in southcentral Nevada yield an oxygen isotopic fractionation factor between calcite and water at 33.7 ??C of 1.02849 ?? 0.00013 (1000 ln ??calcite-water = 28.09 ?? 0.13). Using the commonly accepted value of ???(??calcite-water)/???T of -0.00020 K-1, this corresponds to a 1000 ln ??calcite-water value at 25 ??C of 29.80, which differs substantially from the current accepted value of 28.3. Use of previously published oxygen isotopic fractionation factors would yield a calcite precipitation temperature in Devils Hole that is 8 ??C lower than the measured ground water temperature. Alternatively, previously published fractionation factors would yield a ??18O of water, from which the calcite precipitated, that is too negative by 1.5 ??? using a temperature of 33.7 ??C. Several lines of evidence indicate that the geochemical environment of Devils Hole has been remarkably constant for at least 10 ka. Accordingly, a re-evaluation of calcite-water oxygen isotopic fractionation factor may be in order. Assuming the Devils Hole oxygen isotopic value of ??calcite-water represents thermodynamic equilibrium, many marine carbonates are precipitated with a ??18O value that is too low, apparently due to a kinetic isotopic fractionation that preferentially enriches 16O in the solid carbonate over 18O, feigning oxygen isotopic equilibrium.

  18. The Alkaline Dissolution Rate of Calcite.

    PubMed

    Colombani, Jean

    2016-07-07

    Due to the widespread presence of calcium carbonate on Earth, several geochemical systems, among which is the global CO2 cycle, are controlled to a large extent by the dissolution and precipitation of this mineral. For this reason, the dissolution of calcite has been thoroughly investigated for decades. Despite this intense activity, a consensual value of the dissolution rate of calcite has not been found yet. We show here that the inconsistency between the reported values stems mainly from the variability of the chemical and hydrodynamic conditions of measurement. The spreading of the values, when compared in identical conditions, is much less than expected and is interpreted in terms of sample surface topography. This analysis leads us to propose benchmark values of the alkaline dissolution rate of calcite compatible with all the published values, and a method to use them in various chemical and hydrodynamic contexts.

  19. Impact of amorphous precursor phases on magnesium isotope signatures of Mg-calcite

    NASA Astrophysics Data System (ADS)

    Mavromatis, Vasileios; Purgstaller, Bettina; Dietzel, Martin; Buhl, Dieter; Immenhauser, Adrian; Schott, Jacques

    2017-04-01

    Various marine calcifiers form exoskeletons via an amorphous calcium carbonate (ACC) precursor phase and magnesium plays an important role in the temporary stabilization of this metastable phase. Thus, the use of Mg isotope ratios of marine biogenic carbonates as a proxy to reconstruct past seawater chemistry calls for a detailed understanding of the mechanisms controlling Mg isotope signatures during the formation and transformation of ACC to the final crystalline carbonate mineral. For this purpose we have investigated the Mg isotope fractionation between (Ca,Mg)CO3 solids and aqueous fluids at 25 °C and pH = 8.3 during (i) the direct precipitation of crystalline Mg-calcite and (ii) the formation of Mg-rich ACC (Mg-ACC) and its transformation to Mg-calcite. The outcome documents that the small Mg isotope fractionation between Mg-ACC and reactive fluid (ΔMg26ACC-fluid = - 1.0 ± 0.1 ‰) is not preserved during the transformation of the ACCs into Mg-calcite. Following a pronounced isotopic shift accompanying the transformation of Mg-ACC into Mg-calcite, Δ26Mgcalcite-fluid progressively decreases with reaction progress from ∼ - 3.0 ‰ to - 3.6 ‰, reflecting both the approach of isotopic equilibrium and the increase of calcite Mg content (to near 20 mol % Mg). In contrast the crystalline Mg-calcite precipitated directly from the reacting fluid, i.e. lacking a discernable formation of an amorphous precursor, exhibits only small temporal variations in Δ26Mgcalcite-fluid which overall is affected by the precipitation kinetics. The values found in this study at the onset of Mg-ACC precipitation for Mg isotope fractionation between Mg-ACC and the fluid (ΔMg26ACC-fluid = - 1.0 ‰) and between Mg-ACC and Mg2+(aq) (Δ(aq) 26 Mg ACC-Mg2+ = + 2.0 ‰) are consistent with the formation of a hydrated Ca nanoporous solid accommodating Mg bicarbonate/carbonate species in combination with hydrated magnesium. This material crossed by percolating channels filled with the

  20. Coccolithophore responses to environmental variability in the South China Sea: species composition and calcite content

    NASA Astrophysics Data System (ADS)

    Jin, Xiaobo; Liu, Chuanlian; Poulton, Alex J.; Dai, Minhan; Guo, Xianghui

    2016-08-01

    Coccolithophore contributions to the global marine carbon cycle are regulated by the calcite content of their scales (coccoliths) and the relative cellular levels of photosynthesis and calcification rates. All three of these factors vary between coccolithophore species and with response to the growth environment. Here, water samples were collected in the northern basin of the South China Sea (SCS) during summer 2014 in order to examine how environmental variability influenced species composition and cellular levels of calcite content. Average coccolithophore abundance and their calcite concentration in the water column were 11.82 cells mL-1 and 1508.3 pg C mL-1, respectively, during the cruise. Water samples can be divided into three floral groups according to their distinct coccolithophore communities. The vertical structure of the coccolithophore community in the water column was controlled by the trophic conditions, which were regulated by mesoscale eddies across the SCS basin. The evaluation of coccolithophore-based calcite in the surface ocean also showed that three key species in the SCS (Emiliania huxleyi, Gephyrocapsa oceanica, Florisphaera profunda) and other larger, numerically rare species made almost equal contributions to total coccolith-based calcite in the water column. For Emiliania huxleyi biometry measurements, coccolith size positively correlated with nutrients (nitrate, phosphate), and it is suggested that coccolith length is influenced by light and nutrients through the regulation of growth rates. Larger-sized coccoliths were also linked statistically to low pH and calcite saturation states; however, it is not a simple cause and effect relationship, as carbonate chemistry was strongly co-correlated with the other key environmental factors (nutrients, light).

  1. Interaction of alcohols with the calcite surface.

    PubMed

    Bovet, N; Yang, M; Javadi, M S; Stipp, S L S

    2015-02-07

    A clearer understanding of calcite interactions with organic molecules would contribute to a range of fields including harnessing the secrets of biomineralisation where organisms produce hard parts, increasing oil production from spent reservoirs, remediating contaminated soils and drinking water aquifers and improving manufacturing methods for industrial products such as pigments, soft abrasives, building materials and optical devices. Biomineralisation by some species of blue green algae produces beautifully elaborate platelets of calcite where the individual crystals are of nanometer scale. Controlling their growth requires complex polysaccharides. Polysaccharide activity depends on the functionality of OH groups, so to simplify the system in order to get closer to a molecular level understanding, we investigated the interaction of OH from a suite of alcohols with clean, freshly cleaved calcite surfaces. X-ray photoelectron spectroscopy (XPS) provided binding energies and revealed the extent of surface coverage. Molecular dynamics (MD) simulations supplemented with information about molecule ordering, orientation and packing density. The results show that all alcohols studied bond with the calcite surface through the OH group, with their carbon chains sticking away in a standing-up orientation. Alcohol molecules are closely packed and form a well-ordered monolayer on the surface.

  2. Cyclic Cratonic Carbonates and Phanerozoic Calcite Seas.

    ERIC Educational Resources Information Center

    Wilkinson, Bruce H.

    1982-01-01

    Discusses causes of cyclicity in cratonic carbonate sequences and evidence for and potential significance of postulated primary calcite sediment components in past Paleozoic seas, outlining problems, focusing on models explaining existing data, and identifying background. Future sedimentary geologists will need to address these and related areas…

  3. Alternate deposition of oriented calcite and amino acid layer on calcite substrates.

    PubMed

    Qiao, Li; Feng, Qingling; Li, Zhuo; Lu, Shanshan

    2008-10-30

    Material synthesis inspired by novel nacre architecture and mechanism is popular and has attracted more and more attention. In this paper, iso-oriented calcite tablets/layers and amino acid layers were formed alternately on calcite wafers. It is interesting that the neonatal calcite tablets/layers have the same crystal orientation with their inorganic substrates through amino acid layers. It is quite possible that the amino acid layers in this study could transfer crystal orientation from formed inorganic layers to neighboring neonatal layers due to their fixed and appropriate structures, which may imply the process of nacre formation, and the role of aligned organic matrix sheets in nacre. Moreover, it could provide a new way to produce oriented calcite tablets/layers.

  4. Abiotic Organic Chemistry in Hydrothermal Systems.

    NASA Astrophysics Data System (ADS)

    Simoneit, B. R.; Rushdi, A. I.

    2004-12-01

    Abiotic organic chemistry in hydrothermal systems is of interest to biologists, geochemists and oceanographers. This chemistry consists of thermal alteration of organic matter and minor prebiotic synthesis of organic compounds. Thermal alteration has been extensively documented to yield petroleum and heavy bitumen products from contemporary organic detritus. Carbon dioxide, carbon monoxide, ammonia and sulfur species have been used as precursors in prebiotic synthesis experiments to organic compounds. These inorganic species are common components of hot spring gases and marine hydrothermal systems. It is of interest to further test their reactivities in reductive aqueous thermolysis. We have synthesized organic compounds (lipids) in aqueous solutions of oxalic acid, and with carbon disulfide or ammonium bicarbonate at temperatures from 175-400° C. The synthetic lipids from oxalic acid solutions consisted of n-alkanols, n-alkanoic acids, n-alkyl formates, n-alkanones, n-alkenes and n-alkanes, typically to C30 with no carbon number preferences. The products from CS2 in acidic aqueous solutions yielded cyclic thioalkanes, alkyl polysulfides, and thioesters with other numerous minor compounds. The synthesis products from oxalic acid and ammonium bicarbonate solutions were homologous series of n-alkyl amides, n-alkyl amines, n-alkanes and n-alkanoic acids, also to C30 with no carbon number predominance. Condensation (dehydration) reactions also occur under elevated temperatures in aqueous medium as tested by model reactions to form amide, ester and nitrile bonds. It is concluded that the abiotic formation of aliphatic lipids, condensation products (amides, esters, nitriles, and CS2 derivatives (alkyl polysulfides, cyclic polysulfides) is possible under hydrothermal conditions and warrants further studies.

  5. Calcite-accumulating large sulfur bacteria of the genus Achromatium in Sippewissett Salt Marsh.

    PubMed

    Salman, Verena; Yang, Tingting; Berben, Tom; Klein, Frieder; Angert, Esther; Teske, Andreas

    2015-11-01

    Large sulfur bacteria of the genus Achromatium are exceptional among Bacteria and Archaea as they can accumulate high amounts of internal calcite. Although known for more than 100 years, they remain uncultured, and only freshwater populations have been studied so far. Here we investigate a marine population of calcite-accumulating bacteria that is primarily found at the sediment surface of tide pools in a salt marsh, where high sulfide concentrations meet oversaturated oxygen concentrations during the day. Dynamic sulfur cycling by phototrophic sulfide-oxidizing and heterotrophic sulfate-reducing bacteria co-occurring in these sediments creates a highly sulfidic environment that we propose induces behavioral differences in the Achromatium population compared with reported migration patterns in a low-sulfide environment. Fluctuating intracellular calcium/sulfur ratios at different depths and times of day indicate a biochemical reaction of the salt marsh Achromatium to diurnal changes in sedimentary redox conditions. We correlate this calcite dynamic with new evidence regarding its formation/mobilization and suggest general implications as well as a possible biological function of calcite accumulation in large bacteria in the sediment environment that is governed by gradients. Finally, we propose a new taxonomic classification of the salt marsh Achromatium based on their adaptation to a significantly different habitat than their freshwater relatives, as indicated by their differential behavior as well as phylogenetic distance on 16S ribosomal RNA gene level. In future studies, whole-genome characterization and additional ecophysiological factors could further support the distinctive position of salt marsh Achromatium.

  6. Dissolution Kinetics of Biogenic Magnesian Calcites

    NASA Astrophysics Data System (ADS)

    Thompson, R.; Guidry, M.; Mackenzie, F. T.; De Carlo, E. H.

    2014-12-01

    Ocean acidification (OA) is a serious concern for the health of calcifying ecosystems in the near future. During the past century, surface ocean pH has decreased by ~0.1 pH units, and is expected to decrease further by 0.3-0.4 pH units by the end of this century. The process of OA will likely result in both decreased calcification rates and increased rates of carbonate mineral dissolution, particularly involving the magnesian calcite (Mg-calcite) calcifiers found in shallow-water reef and other carbonate environments. Many Mg-calcite compositions are the most soluble of the carbonate phases commonly found in reef environments (often comprising much of the cementation and structure within a reef), and are therefore potentially the most susceptible to dissolution processes associated with OA. However, the dissolution kinetics of these phases is poorly known, limiting our ability to understand their behavior in nature. Laboratory experiments designed to investigate the mechanisms and dissolution rates of biogenic Mg-calcite mineral phases in distilled water and seawater over a range of CO2 and T conditions were conducted employing both batch and fluidized-bed reactor systems and using a variety of cleaned and annealed biogenic Mg-calcite phases. Our initial results have shown that the dissolution rate at 298 K and a pCO2 of ~350 ppm of the crustose coralline alga Amphiroa rigida (~20 mol% MgCO3) in seawater undersaturated with respect to this phase is 3.6 μmol g-1 hr-1, nearly 50% greater than that under similar conditions for aragonite. This rate and the derived experimental rate law are consistent with the preliminary findings of Walter and Morse (1985). Additional kinetic (and also solubility) data will be presented for the following species: Chiton tuberculatus (~0-4 mol% MgCO3); Echinometra mathei and/or Lytechinus variegatus (~8-12 mol% MgCO3); Homotrema rubrum (12-16 mol% MgCO3); and Lithothamnion sp. (~18-24 mol% MgCO3). Quantification of the rates of

  7. Alkaline flocculation of Phaeodactylum tricornutum induced by brucite and calcite

    DOE PAGES

    Vandamme, Dries; Pohl, Philip I.; Beuckels, Annelies; ...

    2015-08-20

    Alkaline flocculation holds great potential as a low-cost harvesting method for marine microalgae biomass production. Alkaline flocculation is induced by an increase in pH and is related to precipitation of calcium and magnesium salts. In this study, we used the diatom Phaeodactylum tricornutum as model organism to study alkaline flocculation of marine microalgae cultured in seawater medium. Flocculation started when pH was increased to 10 and flocculation efficiency reached 90% when pH was 10.5, which was consistent with precipitation modeling for brucite or Mg(OH)2. Compared to freshwater species, more magnesium is needed to achieve flocculation (>7.5 mM). Zeta potential measurementsmore » suggest that brucite precipitation caused flocculation by charge neutralization. When calcium concentration was 12.5 mM, flocculation was also observed at a pH of 10. Furthermore, zeta potential remained negative up to pH 11.5, suggesting that precipitated calcite caused flocculation by a sweeping coagulation mechanism.« less

  8. Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation

    NASA Astrophysics Data System (ADS)

    Reddy, Michael M.

    2012-08-01

    Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (Ωc). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and Ωc=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10-4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10-4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

  9. Calcite growth-rate inhibition by fulvic acid and magnesium ion—Possible influence on biogenic calcite formation

    USGS Publications Warehouse

    Reddy, Michael M.

    2012-01-01

    Increases in ocean surface water dissolved carbon dioxide (CO2) concentrations retard biocalcification by reducing calcite supersaturation (Ωc). Reduced calcification rates may influence growth-rate dependent magnesium ion (Mg) incorporation into biogenic calcite modifying the use of calcifying organisms as paleoclimate proxies. Fulvic acid (FA) at biocalcification sites may further reduce calcification rates. Calcite growth-rate inhibition by FA and Mg, two common constituents of seawater and soil water involved in the formation of biogenic calcite, was measured separately and in combination under identical, highly reproducible experimental conditions. Calcite growth rates (pH=8.5 and Ωc=4.5) are reduced by FA (0.5 mg/L) to 47% and by Mg (10−4 M) to 38%, compared to control experiments containing no added growth-rate inhibitor. Humic acid (HA) is twice as effective a calcite growth-rate inhibitor as FA. Calcite growth rate in the presence of both FA (0.5 mg/L) and Mg (10−4 M) is reduced to 5% of the control rate. Mg inhibits calcite growth rates by substitution for calcium ion at the growth site. In contrast, FA inhibits calcite growth rates by binding multiple carboxylate groups on the calcite surface. FA and Mg together have an increased affinity for the calcite growth sites reducing calcite growth rates.

  10. Fabrication of interconnected porous calcite by bridging calcite granules with dicalcium phosphate dihydrate and their histological evaluation.

    PubMed

    Ishikawa, Kunio; Koga, Noriko; Tsuru, Kanji; Takahashi, Ichiro

    2015-10-28

    Interconnected porous calcite has attracted attention as an artificial bone replacement material and as a precursor for the fabrication of carbonate apatite, which is also an artificial bone replacement material. In this study, calcite granules were exposed to acidic calcium phosphate solution, and the feasibility of fabricating interconnected porous calcite using this process was evaluated. No setting reaction was observed under the non-loading condition. In contrast, under loading conditions, calcite granules were bridged with dicalcium phosphate dihydrate crystals, and the calcite granules set into interconnected porous calcite foam. When applied 0.4 MPa of loading pressure during sample preparation, compressive strength of the obtained interconnected porous calcite was approximately 1.5 MPa. The exposure of the calcite granules to acidic calcium phosphate solution under loading conditions was the key for the setting reaction to occur. This is because calcite granules cannot contact one another under the non-loading condition because of bubble formation on the surfaces of the calcite granules. The interconnected porous calcite revealed excellent tissue response, and new bone was able to penetrate into the porous calcite two weeks after implantation. This article is protected by copyright. All rights reserved.

  11. Magnesian calcite sorbent for carbon dioxide capture.

    PubMed

    Mabry, James C; Mondal, Kanchan

    2011-01-01

    Magnesian calcite with controlled properties was synthesized for the removal of carbon dioxide. The results from characterization, reactivity and CO2 capture capacity for different synthesis conditions are reported. The magnesian calcite samples (CaCO3:MgCO3) were synthesized by the coprecipitation of specific amounts of commercially available CaO and MgO by carbon dioxide. Characterization was done with BET, SEM/EDS, particle size analysis and XRD. The capacity was measured using TGA cycles at 800 degrees C and compared for different preparation conditions. The effects of CaO, MgO and surfactant loading on the physical properties and carbonation activity were studied to determine the optimal synthesis condition. A long-term carbonation-calcination cycling test was conducted on the optimal sample. It was observed that the sample maintained its capacity to 86% of its original uptake even after 50 cycles.

  12. Frictional behavior of talc-calcite mixtures

    NASA Astrophysics Data System (ADS)

    Giorgetti, C.; Carpenter, B. M.; Collettini, C.

    2015-09-01

    Faults involving phyllosilicates appear weak when compared to the laboratory-derived strength of most crustal rocks. Among phyllosilicates, talc, with very low friction, is one of the weakest minerals involved in various tectonic settings. As the presence of talc has been recently documented in carbonate faults, we performed laboratory friction experiments to better constrain how various amounts of talc could alter these fault's frictional properties. We used a biaxial apparatus to systematically shear different mixtures of talc and calcite as powdered gouge at room temperature, normal stresses up to 50 MPa and under different pore fluid saturated conditions, i.e., CaCO3-equilibrated water and silicone oil. We performed slide-hold-slide tests, 1-3000 s, to measure the amount of frictional healing and velocity-stepping tests, 0.1-1000 µm/s, to evaluate frictional stability. We then analyzed microstructures developed during our experiments. Our results show that with the addition of 20% talc the calcite gouge undergoes a 70% reduction in steady state frictional strength, a complete reduction of frictional healing and a transition from velocity-weakening to velocity-strengthening behavior. Microstructural analysis shows that with increasing talc content, deformation mechanisms evolve from distributed cataclastic flow of the granular calcite to localized sliding along talc-rich shear planes, resulting in a fully interconnected network of talc lamellae from 20% talc onward. Our observations indicate that in faults where talc and calcite are present, a low concentration of talc is enough to strongly modify the gouge's frictional properties and specifically to weaken the fault, reduce its ability to sustain future stress drops, and stabilize slip.

  13. Neptunium(V) coprecipitation with calcite.

    PubMed

    Heberling, Frank; Denecke, Melissa A; Bosbach, Dirk

    2008-01-15

    Coprecipitation experiments of Np(V) and U(VI) with calcite were performed in mixed-flow reactors under steady state conditions at room temperature for up to 400 h at precipitation rates of 1.0 x 10(-8) to 6.8 x 10(-8) mol/(m2 s). The saturation index with respect to calcite varied between 0.04 and 0.95. Initial Np(V) or U(VI) concentrations were 1 micromol/L, 0.01 mol/L NaCl was used as background electrolyte, and pH ranged from 7.8 to 12.8. Partition coefficients for Np(V) were in the range of 0.5-10.3, compared to 0.02 for U(VI). Np L(III) and U L(III) EXAFS were used to characterize the local structural environment of the incorporated actinides. In the case of U(VI), the structural environment is not unambiguously characterized. Our data suggest that Np(V) ions occupy calcium lattice sites. The two axial oxygen atoms of the linear neptunyl moiety substitute two calcite carbonate groups in the first coordination sphere. Thus, four carbonate groups coordinate the neptunyl-ion in a monodentate fashion with four equatorial oxygen atoms (Oeq) at 2.4 A and associated carbon atoms (C) at 3.2 A. The interatomic distances indicate slight structural relaxation of the carbonate groups from their ideal sites. A similar structural model has been reported for U(VI) incorporated into natural calcite.

  14. Origin of micro-rhombic calcite matrix within Cretaceous reservoir rock, West Stuart City Trend, Texas

    NASA Astrophysics Data System (ADS)

    Perkins, Ronald D.

    1989-07-01

    Cores from four wells from the West Stuart City Trend in La Salle and Webb Counties, Texas, were analyzed to define depositional and diagenetic facies and to determine factors controlling porosity distribution. In all, 1187 ft (362 m) of core and 220 thin sections were examined in detail and supplemented by SEM analyses of fractured surfaces and plastic casts of pore systems. A comparison of lithofacies and ecologic facies to permeability and porosity values compiled from core data revealed that zones with permeabilities greater than 0.1 md and porosities of at least 6% were associated with rudistid grainstones cemented by isopachous, submarine cement and packstones with a finely crystalline rhombic calcite matrix. Isotopic and trace element analyses of both isopachous submarine cements and micro-rhombic matrix suggest a common origin. The precursor to the micro-rhombic calcite is believed to have been peloidal, high-magnesian calcite. This internal marine sediment may be analogous to the peloidal fabrics that have been reported from Holocene and Pleistocene carbonates. Diagenetic equilibration of both submarine cements and peloidal infill is believed to have occurred during burial either in marine pore waters at elevated temperatures or in restricted flow, phreatic freshwaters.

  15. Origin of epigenetic calcite in coal from Antarctica and Ohio based on isotope compositions of oxygen, carbon and strontium

    USGS Publications Warehouse

    Faure, G.; Botoman, G.

    1984-01-01

    Isotopic compositions of oxygen, carbon and strontium of calcite cleats in coal seams of southern Victoria Land, Antarctica, and Tuscarawas County, Ohio, contain a record of the conditions a the time of their formation. The Antarctic calcites (?? 18O(SMOW) = +9.14 to +11.82%0) were deposited from waters enriched in 16O whose isotopic composition was consistent with that of meteoric precipitation at low temperature and high latitude. The carbon of the calcite cleats (?? 13C(PDB) = -15.6 to -16.9%0) was derived in part from the coal (?? 13C(PDB) = -23.5 to -26.7%0) as carbon dioxide and by oxidation of methane or other hydrocarbon gases. The strontium ( 87Sr 86Sr = 0.71318-0.72392) originated primarily from altered feldspar grains in the sandstones of the Beacon Supergroup. Calcite cleats in the Kittaning No. 6 coal seam of Ohio (?? 18O(SMOW) = +26.04 to +27.79%0) were deposited from waters that had previously exchanged oxygen, possibly with marine carbonate at depth. The carbon (?? 13C(PDB) = 0.9 to +2.4%0) is enriched in 13C even though that cleats were deposited in coal that is highly enriched in 12C and apparently originated from marine carbonates. Strontium in the cleats ( Sr 87 0.71182-0.71260) is not of marine origin but contains varying amounts of radiogenic 87Sr presumably derived from detrital Rb-bearing minerals in the adjacent sedimentary rocks. The results of this study suggest that calcite cleats in coal of southern Victoria Land, Antarctica, were deposited after the start of glaciation in Cenozoic time and that those in Ohio precipitated from formation waters derived from the underlying marine carbonate rocks, probably in the recent geologic past. ?? 1984.

  16. Atomistic simulations of calcium uranyl(VI) carbonate adsorption on calcite and stepped-calcite surfaces.

    PubMed

    Doudou, Slimane; Vaughan, David J; Livens, Francis R; Burton, Neil A

    2012-07-17

    Adsorption of actinyl ions onto mineral surfaces is one of the main mechanisms that control the migration of these ions in environmental systems. Here, we present computational classical molecular dynamics (MD) simulations to investigate the behavior of U(VI) in contact with different calcite surfaces. The calcium-uranyl-carbonate [Ca(2)UO(2)(CO(3))(3)] species is shown to display both inner- and outer-sphere adsorption to the flat {101̅4} and the stepped {314̅8} and {31̅2̅16} planes of calcite. Free energy calculations, using the umbrella sampling method, are employed to simulate adsorption paths of the same uranyl species on the different calcite surfaces under aqueous condition. Outer-sphere adsorption is found to dominate over inner-sphere adsorption because of the high free energy barrier of removing a uranyl-carbonate interaction and replacing it with a new uranyl-surface interaction. An important binding mode is proposed involving a single vicinal water monolayer between the surface and the sorbed complex. From the free energy profiles of the different calcite surfaces, the uranyl complex was also found to adsorb preferentially on the acute-stepped {314̅8} face of calcite, in agreement with experiment.

  17. Observations and Experiments on Carbonate Secretion in "Calcite Seas": Why Massive Chalk Deposits Formed in Late Cretaceous Time

    NASA Astrophysics Data System (ADS)

    Stanley, S. M.; Ries, J. B.; Hardie, L. A.

    2003-12-01

    It is now well-established that oscillations in the Mg/Ca ratio of seawater, driven by changes in spreading rates along mid-ocean ridges, have determined the mineralogy of nonskeletal marine carbonate precipitation throughout earth history. Low-Mg calcite has formed at Mg/Ca ratios < 2 ("calcite seas"), and aragonite has formed at ratios > 2 ("aragonite seas"). High-Mg calcite (mole % Mg > 4) has formed by itself at Mg/Ca ratios of 1-2, and along with aragonite at ratios above 2. We report here on experiments rooted in the paleontological observation that the carbonate mineralogy of major reef-building and sediment-producing organisms has tended to correspond to that of nonskeletal precipitates throughout Phanerozoic time. Earlier experiments showed that, with changes in the Mg/Ca ratio of ambient seawater, the Mg content of calcite in coralline algae varies like that of nonskeletal calcite precipitates. New experiments reveal that many kinds of calcite-secreting marine animals exhibit similar mineralogical trends, but with varying partition coefficients. Other experiments address the effects of seawater chemistry on productivity. One can predict that secretion of calcium carbonate will facilitate growth of algae because it releases carbon dioxide that can be used in photosynthesis. Indeed, we found that Halimeda, a major producer of aragonite sediment in present-day aragonite seas, grows less rapidly when living at ambient Mg/Ca ratios below the modern marine level of 5.2. Conversely, calcareous nannoplankton, which secrete calcite, become much more productive when ambient Mg/Ca ratios are below unity and associated concentrations of Ca are high. Such conditons characterized the extreme calcite seas of Late Cretaceous time, when nannoplankton formed massive chalk deposits throughout the world. Thus, we attribute the formation of these deposits, which gave the Cretaceous Period its name, to seawater chemistry. Calcareous nannoplankton in modern seas are adapted to

  18. Environmental controls for the precipitation of different fibrous calcite cement fabrics

    NASA Astrophysics Data System (ADS)

    Ritter, Ann-Christine; Wiethoff, Felix; Neuser, Rolf D.; Richter, Detlev K.; Immenhauser, Adrian

    2016-04-01

    Abiogenic calcite cements are widely used as climate archives. They can yield information on environmental change and climate dynamics at the time when the sediment was lithified in a (marine) diagenetic environment. Radiaxial-fibrous (RFC) and fascicular-optic fibrous (FOFC) calcite cements are two very common and similar pore-filling cement fabrics in Palaeozoic and Mesozoic carbonate rocks (Richter et al., 2011) and in Holocene Mg-calcitic speleothems (Richter et al., 2015). Both fabrics are characterised by distinct crystallographic properties. Current research has shown that these fabrics are often underexplored and that a careful combination of conservative and innovative proxies allows for a better applicability of these carbonate archives to paleoenvironmental reconstructions (Ritter et al., 2015). A main uncertainty in this context is that it is still poorly understood which parameters lead to the formation of either RFC or FOFC and if differential crystallographic parameters affect proxy data from these fabrics. This study aims at a better understanding of the environmental factors that may control either RFC or FOFC precipitation. Therefore, suitable samples (a stalagmite and a Triassic marine cement succession), each with clearly differentiable layers of RFC and FOFC, were identified and analysed in high detail using a multi-proxy approach. Detailed thin section and cathodoluminescence analysis of the samples allowed for a precise identification of layers consisting solely of either RFC or FOFC. Isotopic (δ13C, δ18O) as well as trace elemental compositions have been determined and the comparison of data obtained from these different carbonate archives sheds light on changes in environmental parameters during RFC or FOFC precipitation. References: Richter, D.K., et al., 2011. Radiaxial-fibrous calcites: A new look at an old problem. Sedimentary Geology, 239, 26-36 Richter, D.K., et al., 2015. Radiaxial-fibrous and fascicular-optic Mg-calcitic cave

  19. Stable isotope variations in the Quaternary epithermal calcite-fluorite deposit at Monte delle Fate near Cerveteri (Latium, central Italy)

    USGS Publications Warehouse

    Masi, U.; O'Neil, J.R.

    1980-01-01

    Carbon, oxygen and hydrogen isotope variations have been measured in samples from the epithermal fluorite vein deposit at Monte delle Fate, Latium. The ranges in ?? 13C and ??18O of calcite are -1.3 to 3.4 and 9.5 to 17.3, respectively. ??D values of water extracted from fluid inclusions are -49 to -39 for calcite and -41 to -34 for fluorite. Fluid inclusion filling temperatures (225??-240??C) and salinites (3.75) are nearly the same for both fluorite and sparry calcite. An elongated form of calcite, of minor abundance, precipitated at lower temperatures. The data indicate that (1) the CO2 involved in the mineralization was provided by the local marine limestones, (2) the waters were meteoric in origin and underwent an 18O shift of ??? 10 permil by exchange with marine country rocks, and (3) all geochemical features can be explained by the action of two hydrothermal fluids. Hot brines recently discovered in the Cesano geothermal area, 30 km to the east, have temperatures and some chemical characteristics similar to the hydrothermal fluids at Monte delle Fate. ?? 1980 Springer-Verlag.

  20. Cloud Condensation Nucleus Activity of calcite and calcite coated with model humic and fulvic acids

    NASA Astrophysics Data System (ADS)

    Hatch, C. D.; Gierlus, K. M.; Schuttlefield, J. D.; Grassian, V. H.

    2007-12-01

    Many recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of common inactive cloud nuclei, such as mineral aerosol. As many studies have shown that a large fraction of unidentified organic material in aerosol particles is composed of polycarboxylic acids resembling humic substances, the presence of these large molecular weight Humic-Like Substances (HULIS) may also alter the water adsorption and CCN activity of mineral aerosol. Thus, we have measured the water adsorption and CCN activity of model humic and fulvic acids. Additionally, the water adsorption and CCN activity of mineral aerosol particles coated with humic and fulvic acids have been studied. We find that humic and fulvic acids show continual multilayer water adsorption as the relative humidity is raised. Additionally, we find that calcite particles mixed with humic and fulvic acids take up more water by mass, by a factor of two, compared to the uncoated calcite particles at approximately 70% RH. CCN measurements also indicate that internally mixed calcite-humic or fulvic acid aerosols are more CCN active than the otherwise inactive, uncoated calcite particles. Our results suggest that mineral aerosol particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the Earth's atmosphere than single-component mineral aerosol.

  1. Spectroscopic characterization of natural calcite minerals

    NASA Astrophysics Data System (ADS)

    Gunasekaran, S.; Anbalagan, G.

    2007-11-01

    The FT-IR, FT-Raman, NMR spectral data of ten different limestone samples have been compared. FT-IR and FT-Raman spectral data show that calcium carbonate in limestone, principally in the form of calcite, as identified by its main absorption bands at 1426, 1092, 876 and 712 cm -1. The sharp diffractions at the d-spacings, 3.0348, 1.9166 and 1.8796 confirm the presence of calcite structure and the calculated lattice parameters are: a = 4.9781 Å, c = 17.1188 Å. The range of 13C chemical shifts for different limestone samples is very small, varying from 198.38 to 198.42 ppm. The observed chemical shifts are consistent with the identical C-O bonding in different limestone samples. 27Al MAS NMR spectra of the samples exhibit a central line at 1 ppm and another line at 60 ppm corresponding to octahedral and tetrahedral Al ions, respectively. The five component resonances were observed in 29Si MAS NMR spectrum of limestone and these resonances were assigned to Si (4 Al), Si (3 Al), Si (2 Al), Si (1 Al) and Si (0 Al) from low field to high field.

  2. Neptunium(V) adsorption to calcite.

    PubMed

    Heberling, Frank; Brendebach, Boris; Bosbach, Dirk

    2008-12-12

    The migration behavior of the actinyl ions U(VI)O2(2+), Np(V)O2+ and Pu(V,VI)O2(+,2+) in the geosphere is to a large extend controlled by sorption reactions (inner- or outer-sphere adsorption, ion-exchange, coprecipitation/structural incorporation) with minerals. Here NpO2+ adsorption onto calcite is studied in batch type experiments over a wide range of pH (6.0-9.4) and concentration (0.4 microM-40 microM) conditions. pH is adjusted by variation of CO2 partial pressure. Adsorption is found to be pH dependent with maximal adsorption at pH 8.3 decreasing with increasing and decreasing pH. pH dependence of adsorption decreases with increasing Np(V) concentration. EXAFS data of neptunyl adsorbed to calcite and neptunyl in the supernatant shows differences in the Np(V)-O-yl distance, 1.85+/-0.01 angstroms for the adsorbed and 1.82+/-0.01 angstroms for the solution species. The equatorial environment of the neptunyl in solution shows about 5 oxygen neighbours at 2.45+/-0.02 angstroms. For adsorbed neptunyl there are also about 5 oxygen neighbours at 2.46+/-0.01 angstroms. An additional feature in the adsorbed species' R-space spectrum can be related to carbonate neighbours, 3 to 6 carbon backscatterers (C-eq) at 3.05+/-0.03 angstroms and 3 to 6 oxygen backscatterers (O-eq2) at 3.31+/-0.02 angstroms. The differences in the Np(V)-O-yl distance and the C-eq and O-eq2 backscatterers which are only present for the adsorbed species indicate inner-sphere bonding of the adsorbed neptunyl species to the calcite surface. Experiments on adsorption kinetics indicate that after a fast surface adsorption process a continuous slow uptake occurs which may be explained by incorporation via surface dissolution and reprecipitation processes. This is also indicated by the part irreversibility of the adsorption as shown by increased KD values after desorption compared to adsorption.

  3. Uranium isotope fractionation during coprecipitation with aragonite and calcite

    NASA Astrophysics Data System (ADS)

    Chen, Xinming; Romaniello, Stephen J.; Herrmann, Achim D.; Wasylenki, Laura E.; Anbar, Ariel D.

    2016-09-01

    Natural variations in 238U/235U of marine calcium carbonates might provide a useful way of constraining redox conditions of ancient environments. In order to evaluate the reliability of this proxy, we conducted aragonite and calcite coprecipitation experiments at pH ∼7.5 and ∼8.5 to study possible U isotope fractionation during incorporation into these minerals. Small but significant U isotope fractionation was observed in aragonite experiments at pH ∼8.5, with heavier U isotopes preferentially enriched in the solid phase. 238U/235U of dissolved U in these experiments can be fit by Rayleigh fractionation curves with fractionation factors of 1.00007 + 0.00002/-0.00003, 1.00005 ± 0.00001, and 1.00003 ± 0.00001. In contrast, no resolvable U isotope fractionation was observed in an aragonite experiment at pH ∼7.5 or in calcite experiments at either pH. Equilibrium isotope fractionation among different aqueous U species is the most likely explanation for these findings. Certain charged U species are preferentially incorporated into calcium carbonate relative to the uncharged U species Ca2UO2(CO3)3(aq), which we hypothesize has a lighter equilibrium U isotope composition than most of the charged species. According to this hypothesis, the magnitude of U isotope fractionation should scale with the fraction of dissolved U that is present as Ca2UO2(CO3)3(aq). This expectation is confirmed by equilibrium speciation modeling of our experiments. Theoretical calculation of the U isotope fractionation factors between different U species could further test this hypothesis and our proposed fractionation mechanism. These findings suggest that U isotope variations in ancient carbonates could be controlled by changes in the aqueous speciation of seawater U, particularly changes in seawater pH, PCO2 , Ca2+, or Mg2+ concentrations. In general, these effects are likely to be small (<0.13‰), but are nevertheless potentially significant because of the small natural range of

  4. U-Th dating of calcite corals from the Gulf of Aqaba

    NASA Astrophysics Data System (ADS)

    Yehudai, Maayan; Lazar, Boaz; Bar, Neta; Kiro, Yael; Agnon, Amotz; Shaked, Yonathan; Stein, Mordechai

    2017-02-01

    Most of the fossil corals in the elevated reef terraces along the Gulf of Aqaba (GOA) were extensively altered to calcite. This observation indicates extensive interaction with freshwater, possibly when the terraces passed through a coastal aquifer that existed along the shores of the GOA, implying a wetter climate during the time of recrystallization from aragonite to calcite. Thus, dating of the recrystallization events should yield the timing of past wetter conditions in the current hyper-arid area of the GOA. In the present study, 18 aragonite and calcite corals were collected from several elevated coral reef terraces off the coast, south of the city of Aqaba. While aragonite corals were dated with the conventional closed system age equation (assuming zero initial Th), the dating of the calcite corals required the development of adequate equations to allow the calculation of both the initial formation age of the aragonite corals and the time of recrystallization to calcite. The two age calculations were based on the assumptions that each reef terrace went through a single and rapid recrystallization event and that the pristine aragonite corals were characterized by a rather uniform initial U concentration, typical for pristine modern corals. Two recrystallization events were identified at 104 ± 6 ka and 124 ± 8 ka. The ages coincide with the timing of sapropel events S4 and S5, respectively, when the African monsoon induced enhanced wetness in the desert area. Considering the age uncertainties, the times of formation of the two major reef terraces are estimated to be ∼124 ka (reef terrace R2) and ∼130 ka (reef terrace R3), matching the peaks in the global sea level during the last interglacial MIS 5e stage. Apparently, sea level of the GOA did not fluctuate a lot during the period between ∼130 ka and ∼104 ka and remained close to the Marine Isotopic stage (MIS) 5e highstand. The availability of freshwater (during the sapropel periods) and limited sea

  5. Urease activity in microbiologically-induced calcite precipitation.

    PubMed

    Bachmeier, Keri L; Williams, Amy E; Warmington, John R; Bang, Sookie S

    2002-02-14

    The role of microbial urease in calcite precipitation was studied utilizing a recombinant Escherichia coli HB101 containing a plasmid, pBU11, that encodes Bacillus pasteurii urease. The calcite precipitation by E. coli HB101 (pBU11) was significant although its precipitation level was not as high as that by B. pasteurii. Addition of low concentrations (5-100 microM) of nickel, the cofactor of urease, to the medium further enhanced calcite precipitation by E. coli (pBU11). Calcite precipitation induced by both B. pasteurii and E. coli (pBU11) was inhibited in the presence of a urease inhibitor, acetohydroxamic acid (AHA). These observations on the recombinant urease have confirmed that urease activity is essential for microbiologically-induced calcite precipitation. Partially purified B. pasteurii urease was immobilized in polyurethane (PU) foam to compare the efficacy of calcite precipitation between the free and immobilized enzymes. The immobilized urease showed higher K(m) and lower V(max) values, which were reflected by a slower overall calcite precipitation. However, scanning electron micrographs (SEM) identified that the calcite precipitation occurred throughout the matrices of polyurethane. Furthermore, PU-immobilized urease retained higher enzymatic activities at high temperatures and in the presence of a high concentration of pronase, indicating that immobilization protects the enzyme activity from environmental changes.

  6. Emission polarization study on quartz and calcite.

    NASA Technical Reports Server (NTRS)

    Vincent, R. K.

    1972-01-01

    Calculation of the spectral emission polarization of quartz and calcite polished plates for observation angles of 20 and 70 deg by the substitution of complex index of refraction values for each mineral into Fresnel's equations. The emission polarization is shown to be quite wavelength-dependent, demonstrating that selected narrow or medium-width spectral bands exhibit a significantly higher percentage of polarization than a broad spectral band for these two minerals. Field measurements with a broadband infrared radiometer yield polarizations on the order of 2% for a coarse-grained granite rock and beach sand (both quartz-rich). This implies that a more sensitive detector with a selected medium-width filter may be capable of measuring emission polarization accurately enough to make this parameter useful as a remote sensing tool for discrimination among rocks on the basis of texture.

  7. Comparison of garnet-biotite, calcite-graphite, and calcite-dolomite thermometry in the Grenville Orogen; Ontario, Canada

    NASA Astrophysics Data System (ADS)

    Rathmell, Mark A.; Streepey, Margaret M.; Essene, Eric J.; van der Pluijm, Ben A.

    The Elzevir Terrane of the Grenville Orogen in southern Ontario contains metapelites and abundant graphitic marbles that were regionally metamorphosed from the upper greenschist to upper amphibolite facies. Comparative thermometry was undertaken with widely used calibrations for the systems garnet-biotite, calcite-dolomite, and calcite-graphite. Temperatures that are obtained from matrix biotites paired with prograde garnet near-rim analyses are usually consistent with those determined using calcite-graphite thermometry. However, calcite-graphite thermometry occasionally yields low temperatures due to lack of equilibration of anomalously light graphite. Application of calcite-graphite and garnet-biotite systems may yield temperatures up to 70°C higher than calcite-dolomite in amphibolite facies rocks. Calcite-dolomite temperatures most closely approach those from calcite-graphite and garnet-biotite when the samples contain a single generation of dolomite and calcite grains contain no visible dolomite exsolution lamellae. However, some of these samples yield temperatures considerably lower than temperatures calculated from calcite-graphite and garnet-biotite thermometry, indicating that the calcite-dolomite thermometer may have been partially reset during retrogression. Estimated peak metamorphic temperatures of regional metamorphism between Madoc (upper greenschist facies) and Bancroft (upper amphibolite facies) range from 500 to 650°C. These results place the chlorite-staurolite isograd at 540°C, the kyanite-sillimanite isograd at 590°C, and the sillimanite-K-feldspar isograd at 650°C. Although each thermometer may have an absolute uncertainty of as much as +/-50°C, the 50 to 60°C temperature differences between the isograds are probably accurate to 10 to 20°C. An incomplete picture of the thermal gradients can result from the application of only one thermometer in a given area. Simultaneous application of several systems allows one to recognize and

  8. No extreme bipolar glaciation during the main Eocene calcite compensation shift.

    PubMed

    Edgar, Kirsty M; Wilson, Paul A; Sexton, Philip F; Suganuma, Yusuke

    2007-08-23

    Major ice sheets were permanently established on Antarctica approximately 34 million years ago, close to the Eocene/Oligocene boundary, at the same time as a permanent deepening of the calcite compensation depth in the world's oceans. Until recently, it was thought that Northern Hemisphere glaciation began much later, between 11 and 5 million years ago. This view has been challenged, however, by records of ice rafting at high northern latitudes during the Eocene epoch and by estimates of global ice volume that exceed the storage capacity of Antarctica at the same time as a temporary deepening of the calcite compensation depth approximately 41.6 million years ago. Here we test the hypothesis that large ice sheets were present in both hemispheres approximately 41.6 million years ago using marine sediment records of oxygen and carbon isotope values and of calcium carbonate content from the equatorial Atlantic Ocean. These records allow, at most, an ice budget that can easily be accommodated on Antarctica, indicating that large ice sheets were not present in the Northern Hemisphere. The records also reveal a brief interval shortly before the temporary deepening of the calcite compensation depth during which the calcite compensation depth shoaled, ocean temperatures increased and carbon isotope values decreased in the equatorial Atlantic. The nature of these changes around 41.6 million years ago implies common links, in terms of carbon cycling, with events at the Eocene/Oligocene boundary and with the 'hyperthermals' of the Early Eocene climate optimum. Our findings help to resolve the apparent discrepancy between the geological records of Northern Hemisphere glaciation and model results that indicate that the threshold for continental glaciation was crossed earlier in the Southern Hemisphere than in the Northern Hemisphere.

  9. Calcite-accumulating large sulfur bacteria of the genus Achromatium in Sippewissett Salt Marsh

    PubMed Central

    Salman, Verena; Yang, Tingting; Berben, Tom; Klein, Frieder; Angert, Esther; Teske, Andreas

    2015-01-01

    Large sulfur bacteria of the genus Achromatium are exceptional among Bacteria and Archaea as they can accumulate high amounts of internal calcite. Although known for more than 100 years, they remain uncultured, and only freshwater populations have been studied so far. Here we investigate a marine population of calcite-accumulating bacteria that is primarily found at the sediment surface of tide pools in a salt marsh, where high sulfide concentrations meet oversaturated oxygen concentrations during the day. Dynamic sulfur cycling by phototrophic sulfide-oxidizing and heterotrophic sulfate-reducing bacteria co-occurring in these sediments creates a highly sulfidic environment that we propose induces behavioral differences in the Achromatium population compared with reported migration patterns in a low-sulfide environment. Fluctuating intracellular calcium/sulfur ratios at different depths and times of day indicate a biochemical reaction of the salt marsh Achromatium to diurnal changes in sedimentary redox conditions. We correlate this calcite dynamic with new evidence regarding its formation/mobilization and suggest general implications as well as a possible biological function of calcite accumulation in large bacteria in the sediment environment that is governed by gradients. Finally, we propose a new taxonomic classification of the salt marsh Achromatium based on their adaptation to a significantly different habitat than their freshwater relatives, as indicated by their differential behavior as well as phylogenetic distance on 16S ribosomal RNA gene level. In future studies, whole-genome characterization and additional ecophysiological factors could further support the distinctive position of salt marsh Achromatium. PMID:25909974

  10. Control of carbonate alkalinity on Mg incorporation in calcite: Insights on the occurrence of high Mg calcites in diagenetic environments

    NASA Astrophysics Data System (ADS)

    Purgstaller, Bettina; Mavromatis, Vasileios; Dietzel, Martin

    2015-04-01

    High Mg calcites (HMC), with up to 25 mol % of Mg, are common features in early diagenetic environments and are frequently associated with bio-induced anaerobic oxidation of methane (AOM). Such archives hold valuable information about the biogeochemical processes occurring in sedimentary environments in the geological past. Despite the frequency AOM-induced HMC observed in marine diagenetic settings and their potential role in dolomitization, only a minor number of experimental studies has been devoted on deciphering their formation conditions. Thus, in order to improve our understanding on the formation mechanism of HMC induced by elevated carbonate ion concentrations, we precipitated HMC by computer controlled titration of a (Mg,Ca)Cl2 solution at different Mg/Ca ratios into a NaHCO3 solution under precisely defined physicochemical conditions (T = 25.00 ±0.03°C; pH = 8.3 ±0.1). The formation of carbonates was monitored at a high temporal resolution using in situ Raman spectroscopy as well as by continuous sampling and analyzing of precipitates and reactive solutions. We identified two distinct mechanisms of HMC formation. In solutions with molar Mg/Ca ratios ≤ 1/8 calcium carbonate was precipitated as crystalline phases directly from homogeneous solution. In contrast, higher Mg/Ca ratios induced the formation of Mg-rich ACC (up to 10 mol % of Mg), which was subsequently transformed to HMC with up 20 mol % of Mg. Our experimental results highlight that the finally formed HMC has a higher Mg content than the ACC precursor phase. Considering experimental data for Mg containing ACC transformation to crystalline calcium carbonate from literature, the continuous enrichment of Mg in the precipitate throughout transformation of amorphous to crystalline CaCO3 most likely occurs due to the high carbonate alkalinity (DIC about 0.1 M) of our reactive solutions. The Mg incorporation into calcite lattice seems to be favored by intensive supply of carbonate ions as

  11. Differences in the immobilization of arsenite and arsenate by calcite

    NASA Astrophysics Data System (ADS)

    Yokoyama, Yuka; Tanaka, Kazuya; Takahashi, Yoshio

    2012-08-01

    The sorption and coprecipitation experiments of arsenic (As) with calcite coupled with determinations of the chemical state of As both in the reaction fluid and in calcite were conducted to investigate the influence of the As oxidation state on its immobilization into calcite. The oxidation states of As in calcite and water were determined via As K-edge XANES and HPLC-ICP-MS analysis, respectively. The results of the sorption experiments at pH 8.2 show that only As(V) is distributed to calcite regardless of the As oxidation state in the solution. In coprecipitation experiments, As(V) is preferentially incorporated into calcite over a wide range of pH (7-12). On the other hand, the incorporation of As(III) into calcite is not observed at circumneutral pH. This difference between As(III) and As(V) is attributed to the fact that their dissolved species are neutral vs. negatively charged, respectively, at circumneutral pH (arsenite as H3AsO3; arsenate as H2AsO4- or HAsO42-). As the pH increases (>9), up to 33% of As(III)/Astotal ratio is partitioned into calcite or a precursor of calcite (metastable vaterite formed during the early stage of precipitation). The higher interaction of As with calcite at an alkaline pH compared with circumneutral pH is due to the negative charge of As(III) at alkaline pH. However, the As(III)/Astotal ratio decreases as time progresses and only As(V) can be found finally in calcite. The ratio of distribution coefficients of As(III) and As(V) into calcite (KAs(V)/KAs(III)) at pH ˜7 is larger than 2.1 × 103, suggesting that the oxidation state of As is a significant issue in considering the interaction between As and calcite in groundwater. Moreover, low KAs(III) shows that the sequestration of As via coprecipitation with calcite is not an important chemical process under reducing conditions, such as in the groundwaters in Bangladesh and other As-contaminated areas where As(III) is the dominant dissolved species of As. In the system spiked

  12. Abiotic degradation of plastic films

    NASA Astrophysics Data System (ADS)

    Ángeles-López, Y. G.; Gutiérrez-Mayen, A. M.; Velasco-Pérez, M.; Beltrán-Villavicencio, M.; Vázquez-Morillas, A.; Cano-Blanco, M.

    2017-01-01

    Degradable plastics have been promoted as an option to mitigate the environmental impacts of plastic waste. However, there is no certainty about its degradability under different environmental conditions. The effect of accelerated weathering (AW), natural weathering (NW) and thermal oxidation (TO) on different plastics (high density polyethylene, HDPE; oxodegradable high density polyethylene, HDPE-oxo; compostable plastic, Ecovio ® metalized polypropylene, PP; and oxodegradable metalized polypropylene, PP-oxo) was studied. Plastics films were exposed to AW per 110 hours; to NW per 90 days; and to TO per 30 days. Plastic films exposed to AW and NW showed a general loss on mechanical properties. The highest reduction in elongation at break on AW occurred to HDPE-oxo (from 400.4% to 20.9%) and was higher than 90% for HDPE, HDPE-oxo, Ecovio ® and PP-oxo in NW. No substantial evidence of degradation was found on plastics exposed to TO. Oxo-plastics showed higher degradation rates than their conventional counterparts, and the compostable plastic was resistant to degradation in the studied abiotic conditions. This study shows that degradation of plastics in real life conditions will vary depending in both, their composition and the environment.

  13. Production Engineering for Growth of Synthetic Calcite Polarizer Material

    DTIC Science & Technology

    1974-08-01

    AD-A008 043 PRODUCTION ENGINEERING FOR GROWTH OF SYNTHETIC CALCITE POLARIZER MATERIAL Roger F. Belt, et al Litton Systems...Production Bngin««ring for Growth of Synthetic Calcit « Polarizer Material I. RCCIPItNT’tCATALOO NUMMN i. T.vpc or ncpoMT • rtmoo covtnto Final Report...VOKOt (CanlliMit en »xift •id« II ntffrt Kid Idtnlllr br block iwmbmr) Crystal Growth Hydrothermal Growth Calcite Polarizers 30. AtSTHACT

  14. Magnesium inhibition of calcite dissolution kinetics

    SciTech Connect

    Arvidson, Rolf S.; Collier, Martin; Davis, Kevin J.; Vinson, Michael D.; Amonette, James E.; Luttge, Andreas

    2006-02-01

    We present evidence of inhibition of calcite dissolution by dissolved magnesium through direct observations of the (104) surface using atomic force microscopy (AFM) and vertical scanning interferometry (VSI). Far from equilibrium, the pattern of magnesium inhibition is dependent on solution composition and specific to surface step geometry. In CO2-free solutions (pH 8.8), dissolved magnesium brings about little inhibition even at concentrations of 0.8 x 10-3 molal. At the same pH, magnesium concentrations of less than 0.05 x 10-3 molal in carbonate-buffered solutions generate significant inhibition, although no changes in surface and etch pit morphology are observed. As concentrations exceed magnesite saturation, the dissolution rate shows little additional decrease; however, selective pinning of step edges results in unique etch-pit profiles, seen in both AFM and VSI datasets. Despite the decreases in step velocity, magnesium addition in carbonated solutions also appears to activate the surface by increasing the nucleation rate of new defects. These relationships suggest that the modest depression of the bulk rate measured by VSI reflects a balance between competing reaction mechanisms that simultaneously depress the rate through selective inhibition of step movement, but also enhance reactivity on terraces by lowering the energy barrier to new etch-pit formation.

  15. Reconstructing Cambro-Ordovician Seawater Composition using Clumped Isotope Paleothermometry on Calcitic and Phosphatic Brachiopods

    NASA Astrophysics Data System (ADS)

    Bergmann, K.; Robles, M.; Finnegan, S.; Hughes, N. C.; Eiler, J. M.; Fischer, W. W.

    2012-12-01

    A secular increase in δ18O values of marine fossils through early Phanerozoic time raises questions about the evolution of climate and the water cycle. This pattern suggests two end-member hypotheses 1) surface temperatures during early Paleozoic time were very warm, in excess of 40°C (tropical MAT), or 2) the isotopic composition of seawater increased by up to 7-8‰. It has been difficult to evaluate these hypotheses because the δ18O composition of fossils depends on both temperature and the δ18O of water. Furthermore, primary isotopic signatures can be overprinted by diagenetic processes that modify geological materials. This too could explain the decrease in δ18O values of marine fossils with age. Carbonate clumped isotope thermometry can constrain this problem by providing an independent measure of crystallization temperature and, when paired with classical δ18O paleothermometry, can determine the isotopic composition of the fluid the mineral last equilibrated with. Combined with traditional tools, this method has the potential to untangle primary isotopic signatures from diagenetic signals. We measured the isotopic ordering of CO3 groups (Δ47) substituted into the phosphate lattice of phosphatic brachiopods in Cambrian strata. Phosphatic fossils are generally less soluble than carbonates in surface and diagenetic environments, and so are hypothesized to provide a more robust record of primary growth conditions. They also provide an archive prior to the rise of thick shelled calcitic fossils during the Ordovician Radiation. Additionally, measurements of the δ18O of the CO3 groups can be compared with the δ18O of PO4 groups to test whether their mutual fractionation is consistent with primary growth and the apparent temperature recorded by carbonate clumped isotope measurements. We are constructing a phosphatic brachiopod calibration for carbonate clumped isotope thermometry, and Δ47 values of CO2 extracted from modern phosphatic brachiopods suggest

  16. A simplified methodology to approach the complexity of foraminiferal calcite oxygen-isotope data - model comparison

    NASA Astrophysics Data System (ADS)

    Roche, Didier; Waelbroeck, Claire

    2016-04-01

    Since the pioneering work of Epstein (Epstein et al., 1953), numerous calcite isotopic records from the ocean have been used to attempt reconstructing paleoclimatic information. Additional to the well known complexity brought by the fact that foraminiferal calcite records both temperature and isotopic composition of the surrounding oceanic waters, an additional effect for surface - dwelling foraminifers is the fact that two different species do not have the same habitat and may thus record different signals. This is obvious when comparing paleoclimatic records where different species have been measured for the isotopic composition of the calcite. The difference in habitat produces a three dimensional spatial complexity (a foraminifera living in preferred climatic conditions at a specific location, but also at a specific depth, sometimes far from the surface) but also a temporal uncertainty (foraminifers generally live for only a few weeks and their growth season may be evolving through time with climate change). While the different species habitats potentially contain a wealth of information that could be used to better understand the sequences of climate change, this has seldom been used in modeling studies, most models deriving calcite isotopic signal from surface and annual mean conditions (e.g. Roche et al., 2014). In the present work, we propose a reduced complexity approach to compute the calcite for several planktonic foraminifers from climate model simulations under pre-industrial conditions. We base our approach on simple functions describing the temperature dependence of the different species growth rates (Lombard et al., 2009) and on probability of presence based on the physical variables computed in the climate model. We present a comparison to available sediment traps and core tops data as a validation of the methodology, focusing on the possibility for future applicability towards inversion of the signal measured in oceanic sediment cores. References

  17. Paleoclimatic and paleohydrologic records from secondary calcite: Yucca Mountain, Nevada

    SciTech Connect

    Whelan, J.F.; Stuckless, J.S.; Moscati, R.J.; Vaniman, D.T.

    1994-12-31

    Stable isotope analyses of calcite and opal, fluid inclusion formation conditions and gas compositions, Sr isotope ratios, and REE compositions all support formation of secondary calcite in the unsaturated zone of Yucca Mountain from infiltration of surface-derived (and soil zone buffered) waters of meteoric origin. Detailed sampling of growth-banding preserved by the secondary calcite should provide a record of past variations in the stable isotope chemistry of these infiltrating waters, and, hence, of precipitation at Yucca Mountain, i.e., a proxy of past climate at Yucca Mountain. The precision of this record depends on how well it can be dated. The distribution and texture of secondary calcite occurrences, if mapped in careful detail from existing bore hole samples and underground workings (as exposures become accessible), could provide a time/space map of fracture and fault unsaturated-zone ground water flow-paths during past wetter climates which might prevail in the future with change in climate.

  18. Calcite crystal growth rate inhibition by polycarboxylic acids

    USGS Publications Warehouse

    Reddy, M.M.; Hoch, A.R.

    2001-01-01

    Calcite crystal growth rates measured in the presence of several polycarboxyclic acids show that tetrahydrofurantetracarboxylic acid (THFTCA) and cyclopentanetetracarboxylic acid (CPTCA) are effective growth rate inhibitors at low solution concentrations (0.01 to 1 mg/L). In contrast, linear polycarbocylic acids (citric acid and tricarballylic acid) had no inhibiting effect on calcite growth rates at concentrations up to 10 mg/L. Calcite crystal growth rate inhibition by cyclic polycarboxyclic acids appears to involve blockage of crystal growth sites on the mineral surface by several carboxylate groups. Growth morphology varied for growth in the absence and in the presence of both THFTCA and CPTCA. More effective growth rate reduction by CPTCA relative to THFTCA suggests that inhibitor carboxylate stereochemical orientation controls calcite surface interaction with carboxylate inhibitors. ?? 20O1 Academic Press.

  19. An AFM study of calcite dissolution in concentrated electrolyte solutions

    NASA Astrophysics Data System (ADS)

    Ruiz Agudo, E.; Putnis, C. V.; Putnis, A.; Rodriguez-Navarro, C.

    2009-04-01

    Calcite-solution interactions are of a paramount importance in a range of processes such as the removal of heavy metals, carbon dioxide sequestration, landscape modeling, weathering of building stone and biomineralization. Water in contact with minerals often carries significant amounts of solutes; additionally, their concentration may vary due to evaporation and condensation. It is well known that calcite dissolution is affected dramatically by the presence of such solutes. Here we present investigations on the dissolution of calcite in the presence of different electrolytes. Both bulk (batch reactors) experiments and nanoscale (in situ AFM) techniques are used to study the dissolution of calcite in a range of solutions containing alkaly cations balanced by halide anions. Previous works have indicated that the ionic strength has little influence in calcite dissolution rates measured from bulk experiments (Pokrovsky et al. 2005; Glendhill and Morse, 2004). Contrary to these results, our quantitative analyses of AFM observations show an enhancement of the calcite dissolution rate with increasing electrolyte concentration. Such an effect is concentration-dependent and it is most evident in concentrated solutions. AFM experiments have been carried out in a fluid cell using calcite cleavage surfaces in contact with solutions of simple salts of the alkaly metals and halides at different undersaturations with respect to calcite to try to specify the effect of the ionic strength on etch pit spreading rate and calcite dissolution rate. These results show that the presence of soluble salts may critically affect the weathering of carbonate rocks in nature as well as the decay of carbonate stone in built cultural heritage. References: Pokrosky, O.S.; Golubev, S.V.; Schott, J. Dissolution kinetics of calcite, dolomite and magnesite at 25°C and 0 to 50 atm pCO2. Chemical Geology, 2005, 217 (3-4) 239-255. Glendhill, D.K.; Morse, J.W. Dissolution kinetics of calcite in Na

  20. Kinetics and Mechanisms of Calcite Reactions with Saline Waters

    SciTech Connect

    Chapman, Piers; *Morse, John W.

    2010-11-15

    1. Objective The general objective of this research was to determine the kinetics and mechanisms of calcite reactions with saline waters over a wide range of saline water composition, carbon dioxide partial pressure (pCO2), and modest ranges of T and P. This would be done by studying both reaction rates and solubility from changes in solution chemistry. Also, nanoscale observations of calcite surface morphology and composition would be made to provide an understanding of rate controlling mechanisms.

  1. The differnces between bond lengths in biogenic and geologocal calcite.

    SciTech Connect

    Zlotoyabko, E.; Caspi, E. N.; Fieramosca, J. S.; Von Dreele, R. B.; Marin, F.; Mor, G.; Politi, Y.; Addadi, L.; Weiner, S.

    2010-01-01

    We used high-resolution neutron powder diffraction to accurately measure the atomic positions and bond lengths in biogenic and geological calcite. A special procedure for data analysis was developed in order to take into account the considerable amounts of magnesium present in all the investigated samples. As a result, in biogenic calcite we found some atomic bonds to have significantly different lengths as compared to those in geological calcite, after the contribution of magnesium is accounted for. The maximum effect (elongation up to 0.7%) was found for the C-O bonds. We also analyzed changes in frequencies and spectral widths of normal vibrations of carbonate groups in biogenic calcite (as compared to geological calcite) measured by Raman and Fourier transform IR techniques. Surprisingly, the frequency shifts after subtracting the magnesium contribution are close to zero. At the same time, substantial spectral broadening (up to 1.2%) in biogenic calcite as compared to geological samples was detected. Possible explanations for the experimental findings are discussed.

  2. Methanogenic calcite, 13C-depleted bivalve shells, and gas hydrate from a mud volcano offshore southern California

    USGS Publications Warehouse

    Hein, J.R.; Normark, W.R.; McIntyre, B.R.; Lorenson, T.D.; Powell, C.L.

    2006-01-01

    Methane and hydrogen sulfide vent from a cold seep above a shallowly buried methane hydrate in a mud volcano located 24 km offshore southern California in?? 800 m of water. Bivalves, authigenic calcite, and methane hydrate were recovered in a 2.1 m piston core. Aragonite shells of two bivalve species are unusually depleted in 13C (to -91??? ??13C), the most 13C-depleted shells of marine macrofauna yet discovered. Carbon isotopes for both living and dead specimens indicate that they used, in part, carbon derived from anaerobically oxidized methane to construct their shells. The ??13C values are highly variable, but most are within the range -12??? to -91???. This variability may be diagnostic for identifying cold-seep-hydrate systems in the geologic record. Authigenic calcite is abundant in the cores down to ???1.5 m subbottom, the top of the methane hydrate. The calcite is depleted in 13C (??13C = -46??? to -58???), indicating that carbon produced by anaerobically oxidized methane is the main source of the calcite. Methane sources include a geologic hydrocarbon reservoir from Miocene source rocks, and biogenic and thermogenic degradation of organic matter in basin sediments. Oxygen isotopes indicate that most calcite formed out of isotopic equilibrium with ambient bottom water, under the influence of gas hydrate dissociation and strong methane flux. High metal content in the mud volcano sediment indicates leaching of basement rocks by fluid circulating along an underlying fault, which also allows for a high flux of fossil methane. ?? 2006 Geological Society of America.

  3. A 250,000-year climatic record from great basin vein calcite: implications for milankovitch theory.

    PubMed

    Winograd, I J; Coplen, T B; Szabo, B J; Riggs, A C

    1988-12-02

    A continuous record of oxygen-18 (delta(18)O) variations in the continental hydrosphere during the middle-to-late Pleistocene has been obtained from a uranium-series dated calcitic vein in the southern Great Basin. The vein was deposited from ground water that moved through Devils Hole-an open fault zone at Ash Meadows, Nevada-between 50 and 310 ka (thousand years ago). The configuration of the delta(18)O versus time curve closely resembles the marine and Antarctic ice core (Vostok) delta(18)O curves; however, the U-Th dates indicate that the last interglacial stage (marine oxygen isotope stage 5) began before 147 +/- 3 ka, at least 17,000 years earlier than indicated by the marine delta(18)O record and 7,000 years earlier than indicated by the less well dated Antarctic delta(18)O record. This discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine delta(18)O chronology may need revision and that orbital forcing may not be the principal cause of the Pleistocene ice ages.

  4. A 250,000-year climatic record from great basin vein calcite: Implications for Milankovitch theory

    USGS Publications Warehouse

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

    1988-01-01

    A continuous record of oxygen-18 (??18O) variations in the continental hydrosphere during the middle-to-late Pleistocene has been obtained from a uranium-series dated calcitic vein in the southern Great Basin. The vein was deposited from ground water that moved through Devils Hole - an open fault zone at Ash Meadows, Nevada - between 50 and 310 ka (thousand years ago). The configuration of the ??18O versus time curve closely resembles the marine and Antarctic ice core (Vostok) ??18O curves; however, the U-Th dates indicate that the last interglacial stage (marine oxygen isotope stage 5) began before 147 ?? 3 ka, at least 17,000 years earlier than indicated by the marine ??18O record and 7,000 years earlier than indicated by the less well dated Antarctic ??18O record. This discrepancy and other differences in the timing of key climatic events suggest that the indirectly dated marine ??18O chronology may need revision and that orbital forcing may not be the principal cause of the Pleistocene ice ages.

  5. Oxygen isotope fractionation between bird eggshell calcite and body water: application to fossil eggs from Lanzarote (Canary Islands).

    PubMed

    Lazzerini, Nicolas; Lécuyer, Christophe; Amiot, Romain; Angst, Delphine; Buffetaut, Eric; Fourel, François; Daux, Valérie; Betancort, Juan Francisco; Flandrois, Jean-Pierre; Marco, Antonio Sánchez; Lomoschitz, Alejandro

    2016-10-01

    Oxygen and carbon isotope compositions of fossil bird eggshell calcite (δ(18)Ocalc and δ(13)Ccalc) are regularly used to reconstruct paleoenvironmental conditions. However, the interpretation of δ(18)Ocalc values of fossil eggshells has been limited to qualitative variations in local climatic conditions as oxygen isotope fractionations between calcite, body fluids, and drinking water have not been determined yet. For this purpose, eggshell, albumen water, and drinking water of extant birds have been analyzed for their oxygen and carbon isotope compositions. Relative enrichments in (18)O relative to (16)O between body fluids and drinking water of +1.6 ± 0.9 ‰ for semi-aquatic birds and of +4.4 ± 1.9 ‰ for terrestrial birds are observed. Surprisingly, no significant dependence to body temperature on the oxygen isotope fractionation between eggshell calcite and body fluids is observed, suggesting that bird eggshells precipitate out of equilibrium. Two empirical equations relating the δ(18)Ocalc value of eggshell calcite to the δ(18)Ow value of ingested water have been established for terrestrial and semi-aquatic birds. These equations have been applied to fossil eggshells from Lanzarote in order to infer the ecologies of the Pleistocene marine bird Puffinus sp. and of the enigmatic giant birds from the Pliocene. Both δ(13)Ccalc and δ(18)Ocalc values of Puffinus eggshells point to a semi-aquatic marine bird ingesting mostly seawater, whereas low δ(13)Ccalc and high δ(18)Ocalc values of eggshells from the Pliocene giant bird suggest a terrestrial lifestyle. This set of equations can help to quantitatively estimate the origin of waters ingested by extinct birds as well as to infer either local environmental or climatic conditions.

  6. Oxygen isotope fractionation between bird eggshell calcite and body water: application to fossil eggs from Lanzarote (Canary Islands)

    NASA Astrophysics Data System (ADS)

    Lazzerini, Nicolas; Lécuyer, Christophe; Amiot, Romain; Angst, Delphine; Buffetaut, Eric; Fourel, François; Daux, Valérie; Betancort, Juan Francisco; Flandrois, Jean-Pierre; Marco, Antonio Sánchez; Lomoschitz, Alejandro

    2016-10-01

    Oxygen and carbon isotope compositions of fossil bird eggshell calcite (δ18Ocalc and δ13Ccalc) are regularly used to reconstruct paleoenvironmental conditions. However, the interpretation of δ18Ocalc values of fossil eggshells has been limited to qualitative variations in local climatic conditions as oxygen isotope fractionations between calcite, body fluids, and drinking water have not been determined yet. For this purpose, eggshell, albumen water, and drinking water of extant birds have been analyzed for their oxygen and carbon isotope compositions. Relative enrichments in 18O relative to 16O between body fluids and drinking water of +1.6 ± 0.9 ‰ for semi-aquatic birds and of +4.4 ± 1.9 ‰ for terrestrial birds are observed. Surprisingly, no significant dependence to body temperature on the oxygen isotope fractionation between eggshell calcite and body fluids is observed, suggesting that bird eggshells precipitate out of equilibrium. Two empirical equations relating the δ18Ocalc value of eggshell calcite to the δ18Ow value of ingested water have been established for terrestrial and semi-aquatic birds. These equations have been applied to fossil eggshells from Lanzarote in order to infer the ecologies of the Pleistocene marine bird Puffinus sp. and of the enigmatic giant birds from the Pliocene. Both δ13Ccalc and δ18Ocalc values of Puffinus eggshells point to a semi-aquatic marine bird ingesting mostly seawater, whereas low δ13Ccalc and high δ18Ocalc values of eggshells from the Pliocene giant bird suggest a terrestrial lifestyle. This set of equations can help to quantitatively estimate the origin of waters ingested by extinct birds as well as to infer either local environmental or climatic conditions.

  7. Controls on Calcite Solubility in Metamorphic and Magmatic Fluids

    NASA Astrophysics Data System (ADS)

    Manning, C. E.; Eguchi, J.; Galvez, M.

    2015-12-01

    Calcite is an important hydrothermal alteration product in a wide range of environments. The role of calcite in hydrothermal alteration depends on its solubility in geologic fluids, especially H2O. At ambient T and P, calcite solubility is low and it exhibits well-known declining, or "reverse", solubility with rising T. However, experimental and theoretical studies show that increasing P yields higher solubility and restricts the region of reverse solubility behavior to higher temperature. At 0.2 GPa the reverse solubility region lies at T>600°C; at 0.5 GPa, >800°C. Thus, whereas calcite possesses relatively low solubility in pure H2O in shallow hydrothermal systems (typically <10 ppm C), it is substantially more soluble at conditions of middle and lower crustal metamorphism and magmatism, reaching concentrations ≥1000 ppm. At the higher P of subduction zones, aragonite solubility in H2O is even greater. Thus, neglecting other solubility controls, calcite precipitation is favored as crustal fluids cool and/or decompress. However, the solubility of calcite in H2O also depends strongly on other solutes, pH, and fO2. Sources of alkalinity decrease calcite solubility. In contrast, sources of acidity such as CO2 and Cl increase solubility. Crustal fluids can be enriched in alkali halides such as NaCl. Calcite solubility increases with increasing salt content at a given P and T. From approximately seawater salinity to salt saturation, the fluid behaves as a dilute molten salt and calcite solubility increases as the square of the salt mole fraction regardless of the alkali (Li, Na, K, Cs) or halogen (F, Cl, Br, I) considered. Similar behavior is seen in mixed salt solutions. At lower salinities, solubility behavior is as expected in dilute electrolyte solutions. The transition from dilute electrolyte to molten salt is fundamental to the properties of crustal fluids. Reduction of carbonate species or CO2 in the fluid to CH4, which is common during serpentinization of

  8. An explanation for the 18O excess in Noelaerhabdaceae coccolith calcite

    NASA Astrophysics Data System (ADS)

    Hermoso, M.; Minoletti, F.; Aloisi, G.; Bonifacie, M.; McClelland, H. L. O.; Labourdette, N.; Renforth, P.; Chaduteau, C.; Rickaby, R. E. M.

    2016-09-01

    Coccoliths have dominated the sedimentary archive in the pelagic environment since the Jurassic. The biominerals produced by the coccolithophores are ideally placed to infer sea surface temperatures from their oxygen isotopic composition, as calcification in this photosynthetic algal group only occurs in the sunlit surface waters. In the present study, we dissect the isotopic mechanisms contributing to the "vital effect", which overprints the oceanic temperatures recorded in coccolith calcite. Applying the passive diffusion model of carbon acquisition by the marine phytoplankton widely used in biogeochemical and palaeoceanographic studies, our results suggest that the oxygen isotope offsets from inorganic calcite in fast dividing species Emiliania huxleyi and Gephyrocapsa oceanica originates from the legacy of assimilated 18O-rich CO2 that induces transient isotopic disequilibrium to the internal dissolved inorganic carbon (DIC) pool. The extent to which this intracellular isotopic disequilibrium is recorded in coccolith calcite (1.5 to +3‰ over a 10 to 25 °C temperature range) is set by the degree of isotopic re-equilibration between CO2 and water molecules before intracellular mineralisation. We show that the extent of re-equilibration is, in turn, set by temperature through both physiological (dynamics of the utilisation of the DIC pool) and thermodynamic (completeness of the re-equilibration of the relative 18O-rich CO2 influx) processes. At the highest temperature, less ambient aqueous CO2 is present for algal growth, and the consequence of carbon limitation is exacerbation of the oxygen isotope vital effect, obliterating the temperature signal. This culture dataset further demonstrates that the vital effect is variable for a given species/morphotype, and depends on the intricate relationship between the environment and the physiology of biomineralising algae.

  9. Defluoridation of drinking water by boiling with brushite and calcite.

    PubMed

    Larsen, M J; Pearce, E I F

    2002-01-01

    Existing methods for defluoridating drinking water involve expensive high technology or are slow, inefficient and/or unhygienic. A new method is now suggested, encompassing brushite and calcite suspension followed by boiling. Our aim was to examine the efficiency of the method and the chemical reactions involved. Brushite, 0.3-0.5 g, and an equal weight of calcite were suspended in 1 litre water containing 5-20 ppm fluoride. The suspensions were boiled in an electric kettle, left to cool and the calcium salts to sediment. Solution ion concentrations were determined and sediments were examined by X-ray diffraction. In distilled water initially containing 5, 10 and 20 ppm fluoride the concentration was reduced to 0.06, 0.4 and 5.9 ppm, respectively. Using Aarhus tap water which contained 2.6 mmol/l calcium the final concentrations were 1.2, 2.5 and 7.7 ppm, respectively, and runs without calcite gave results similar to those with calcite. Without boiling the fluoride concentration remained unaltered, as did the brushite and calcite salts, despite occasional agitation by hand. All solutions were supersaturated with respect to fluorapatite and hydroxyapatite and close to saturation with respect to brushite. Boiling produced well-crystallised apatite and traces of calcite, while boiling of brushite alone left a poorly crystallised apatite. We conclude that boiling a brushite/calcite suspension rapidly converts the two salts to apatite which incorporates fluoride if present in solution, and that this process may be exploited to defluoridate drinking water.

  10. Polygenetic Karsted Hardground Omission Surfaces in Lower Silurian Neritic Limestones: a Signature of Early Paleozoic Calcite Seas

    NASA Astrophysics Data System (ADS)

    James, Noel P.; Desrochers, André; Kyser, Kurt T.

    2015-04-01

    Exquisitely preserved and well-exposed rocky paleoshoreline omission surfaces in Lower Silurian Chicotte Formation limestones on Anticosti Island, Quebec, are interpreted to be the product of combined marine and meteoric diagenesis. The different omission features include; 1) planar erosional bedding tops, 2) scalloped erosional surfaces, 3) knobs, ridges, and swales at bedding contacts, and 4) paleoscarps. An interpretation is proposed that relates specific omission surface styles to different diagenetic-depositional processes that took place in separate terrestrial-peritidal-shallow neritic zones. Such processes were linked to fluctuations in relative sea level with specific zones of diagenesis such as; 1) karst corrosion, 2) peritidal erosion, 3) subtidal seawater flushing and cementation, and 4) shallow subtidal deposition. Most surfaces are interpreted to have been the result of initial extensive shallow-water synsedimentary lithification that were, as sea level fell, altered by exposure and subaerial corrosion, only to be buried by sediments as sea level rose again. This succession was repeated several times resulting in a suite of recurring polyphase omission surfaces through many meters of stratigraphic section. Synsedimentary cloudy marine cements are well preserved and are thus interpreted to have been calcitic originally. Aragonite components are rare and thought to have to have been dissolved just below the Silurian seafloor. Large molluscs that survived such seafloor removal were nonetheless leached and the resultant megamoulds were filled with synsedimentary calcite cement. These Silurian inner neritic-strandline omission surfaces are temporally unique. They are part of a suite of marine omission surfaces that are mostly found in early Paleozoic neritic carbonate sedimentary rocks. These karsted hardgrounds formed during a calcite-sea time of elevated marine carbonate saturation and extensive marine cement precipitation. The contemporaneous greenhouse

  11. Modeling the evolution of complex conductivity during calcite precipitation on glass beads

    NASA Astrophysics Data System (ADS)

    Leroy, Philippe; Li, Shuai; Jougnot, Damien; Revil, André; Wu, Yuxin

    2017-01-01

    SUMMARYWhen pH and alkalinity increase, <span class="hlt">calcite</span> frequently precipitates and hence modifies the petrophysical properties of porous media. The complex conductivity method can be used to directly monitor <span class="hlt">calcite</span> precipitation in porous media because it is sensitive to the evolution of the mineralogy, pore structure and its connectivity. We have developed a mechanistic grain polarization model considering the electrochemical polarization of the Stern and diffuse layer surrounding <span class="hlt">calcite</span> particles. Our complex conductivity model depends on the surface charge density of the Stern layer and on the electrical potential at the onset of the diffuse layer, which are computed using a basic Stern model of the <span class="hlt">calcite</span>/water interface. The complex conductivity measurements of Wu et al. (2010) on a column packed with glass beads where <span class="hlt">calcite</span> precipitation occurs are reproduced by our surface complexation and complex conductivity models. The evolution of the size and shape of <span class="hlt">calcite</span> particles during the <span class="hlt">calcite</span> precipitation experiment is estimated by our complex conductivity model. At the early stage of the <span class="hlt">calcite</span> precipitation experiment, modeled particles sizes increase and <span class="hlt">calcite</span> particles flatten with time because <span class="hlt">calcite</span> crystals nucleate at the surface of glass beads and grow into larger <span class="hlt">calcite</span> grains around glass beads. At the later stage of the <span class="hlt">calcite</span> precipitation experiment, modeled sizes and cementation exponents of <span class="hlt">calcite</span> particles decrease with time because large <span class="hlt">calcite</span> grains aggregate over multiple glass beads, a percolation threshold is achieved, and small and discrete <span class="hlt">calcite</span> crystals polarize.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.B21G..08D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.B21G..08D"><span><span class="hlt">Calcite</span> and Picocyanobacteria in Lakes: Factors Affecting Their Interaction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dittrich, M.; Obst, M.; Mavrocordatos, D.</p> <p>2003-12-01</p> <p><span class="hlt">Calcites</span> build large deposits which have been observed in the rock record throughout geological time at various localities around the globe. Carbonate deposits have affected atmospheric carbon dioxide concentration. As it has been generally accepted, inorganic precipitation represents a source of carbon dioxide on short geological time scales and a sink of inorganic carbon at long time scales from millions to thousands of millions years. However, recent research indicates that <span class="hlt">calcite</span> deposits may result from microbial calcification instead of inorganic precipitation. In this case the process may reduce atmospheric carbon dioxide on geologically short time scales. Thus the effect of carbonate sediment deposition on global carbon cycling depends on the origin of carbonate. Thus it is essential to understand the cause and the key parameters affecting <span class="hlt">calcite</span> precipitation. The role of algae and bacteria in <span class="hlt">calcite</span> formation in lakes has not been evaluated in detail. Some evidence, however, exists supporting precipitation of calcium carbonate by microbes as the origin of whiting. Several field studies on lakes have also produced puzzling results: The peaks of algal blooms were often not found at the same time as precipitation events of <span class="hlt">calcite</span>. We suspect that parts of the discrepancies in the interpretation of field observations are due to the activity of autotrophic picoplankton. The unicellular autotrophic picoplankton (APP) is a ubiquitous component of pelagic ecosystems. But it has often been overlooked due to its small cell size of 0.2 - 2 μ m in diameter. Coccoid picocyanobacteria of the Synechococcus-type dominate the picoplankton community in most oligotrophic systems. Recently, laboratory experiments and field observations suggested that APP may play an important role in <span class="hlt">calcite</span> precipitation. The aim of this study was to examine the influence of environmental factors such as saturation state, concentration of different dissolved ions and characteristics of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70028056','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70028056"><span><span class="hlt">Calcite</span>-graphite thermometry of the Franklin Marble, New Jersey Highlands</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Peck, W.H.; Volkert, R.A.; Meredith, M.T.; Rader, E.L.</p> <p>2006-01-01</p> <p>We present new stable-isotope data for the Mesoproterozoic Franklin Marble from outcrops along an 80-km traverse parallel to and across strike of the structural grain of the western New Jersey Highlands. <span class="hlt">Calcite</span> and dolomite from marble have an average ??13C of 0.35??? ?? 0.73??? PDB (n = 46) and a more limited range than other Mesoproterozoic marbles from the Adirondacks and the Canadian Grenville Province. The small range of ??13C values from the New Jersey samples is consistent with the preservation of a primary <span class="hlt">marine</span> isotopic signature and limited postdepositional isotopic modification, except proximal to Zn or Fe ore deposits and fault zones. Fractionations between <span class="hlt">calcite</span> and well-formed graphite (??13C[Cal-Gr]) for analyzed Franklin Marble samples average 3.31???. ?? 0.25??? (n = 34), and dolomite-graphite fractionations average 3.07??? ?? 0.30??? (n = 6). Taken together, these indicate an average temperature of 769?? ?? 43??C during metamorphism associated with the Ottawan Orogeny in the New Jersey Highlands. Thus, carbon isotope fractionations demonstrate that the Franklin Marble was metamorphosed at granulite facies conditions. Metamorphic temperatures are relatively constant for the area sampled and overprint the metamorphosed carbonatehosted Zn-Fe-Mn ore deposits. The results of this study support recent work proposing that pressure and temperature conditions during Ottawan orogenesis did not vary greatly across faults that partition the Highlands into structural blocks. ?? 2006 by The University of Chicago. All rights reserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17835123','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17835123"><span>Continuous 500,000-year climate record from vein <span class="hlt">calcite</span> in devils hole, nevada.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Winograd, I J; Coplen, T B; Landwehr, J M; Riggs, A C; Ludwig, K R; Szabo, B J; Kolesar, P T; Revesz, K M</p> <p>1992-10-09</p> <p>Oxygen-18 (delta(18)O) variations in a 36-centimeter-long core (DH-11) of vein <span class="hlt">calcite</span> from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and <span class="hlt">marine</span> delta(18)O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of the last four glacial cycles recorded in the <span class="hlt">calcite</span> increased from 80,000 to 130,000 years; this variation suggests that major climate changes were aperiodic. The timing of specific climatic events indicates that orbitally controlled variations in solar insolation were not a major factor in triggering deglaciations. Interglacial climates lasted about 20,000 years. Collectively, these observations are inconsistent with the Milankovitch hypothesis for the origin of the Pleistocene glacial cycles but they are consistent with the thesis that these cycles originated from internal nonlinear feedbacks within the atmosphere-ice sheet-ocean system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016979','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016979"><span>Continuous 500,000-year climate record from vein <span class="hlt">calcite</span> in Devils Hole, Nevada</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Winograd, I.J.; Coplen, T.B.; Landwehr, J.M.; Riggs, A.C.; Ludwig, K. R.; Szabo, B. J.; Kolesar, Peter T.; Revesz, K.M.</p> <p>1992-01-01</p> <p>Oxygen-18 (??18O) variations in a 36-centimeter-long core (DH-11) of vein <span class="hlt">calcite</span> from Devils Hole, Nevada, yield an uninterrupted 500,000-year paleotemperature record that closely mimics all major features in the Vostok (Antarctica) paleotemperature and <span class="hlt">marine</span> ??18O ice-volume records. The chronology for this continental record is based on 21 replicated mass-spectrometric uranium-series dates. Between the middle and latest Pleistocene, the duration of the last four glacial cycles recorded in the <span class="hlt">calcite</span> increased from 80,000 to 130,000 years; this variation suggests that major climate changes were aperiodic. The timing of specific climatic events indicates that orbitally controlled variations in solar insolation were not a major factor in triggering deglaciations. Interglacial climates lasted about 20,000 years. Collectively, these observations are inconsistent with the Milankovitch hypothesis for the origin of the Pleistocene glacial cycles but they are consistent with the thesis that these cycles originated from internal nonlinear feedbacks within the atmosphere-ice sheet-ocean system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.192...70R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.192...70R"><span>Hydrochemical controls on aragonite versus <span class="hlt">calcite</span> precipitation in cave dripwaters</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rossi, Carlos; Lozano, Rafael P.</p> <p>2016-11-01</p> <p>Despite the paleoclimatic relevance of primary <span class="hlt">calcite</span> to aragonite transitions in stalagmites, the relative role of fluid Mg/Ca ratio, supersaturation and CO32- concentration in controlling such transitions is still incompletely understood. Accordingly, we have monitored the hydrochemistry of 50 drips and 8 pools that are currently precipitating <span class="hlt">calcite</span> and/or aragonite in El Soplao and Torca Ancha Caves (N. Spain), investigating the mineralogy and geochemistry of the CaCO3 precipitates on the corresponding natural speleothem surfaces. The data reveal that, apart from possible substrate effects, dripwater Mg/Ca is the only obvious control on CaCO3 polymorphism in the studied stalagmites and pools, where <span class="hlt">calcite</span>- and aragonite-precipitating dripwaters are separated by an initial (i.e. at stalactite tips) Mg/Ca threshold at ≈1.1 mol/mol. Within the analyzed ranges of pH (8.2-8.6), CO32- concentration (1-6 mg/L), supersaturation (SIaragonite: 0.08-1.08; SIcalcite: 0.23-1.24), drip rate (0.2-81 drops/min) and dissolved Zn (6-90 μg/L), we observe no unequivocal influence of these parameters on CaCO3 mineralogy. Despite the almost complete overlapping supersaturations of <span class="hlt">calcite</span>- and aragonite-precipitating waters, the latter are on average less supersaturated because the waters having Mg/Ca above ∼1.1 have mostly achieved such high ratios by previously precipitating <span class="hlt">calcite</span>. Both <span class="hlt">calcite</span> and aragonite precipitated at or near oxygen isotopic equilibrium, and Mg incorporation into <span class="hlt">calcite</span> was consistent with literature-based predictions, indicating that in the studied cases CaCO3 precipitation was not significantly influenced by strong kinetic effects. In the studied cases, the <span class="hlt">calcites</span> that precipitate at ∼11 °C from dripwaters with initial Mg/Ca approaching ∼1.1 incorporate ∼5 mol% MgCO3, close to the published value above which <span class="hlt">calcite</span> solubility exceeds aragonite solubility, suggesting that aragonite precipitation in high-relative-humidity caves is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AcSpA.117..158S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AcSpA.117..158S"><span>A Raman spectroscopic comparison of <span class="hlt">calcite</span> and dolomite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L.</p> <p>2014-01-01</p> <p>Raman spectroscopy was used to characterize and differentiate the two minerals <span class="hlt">calcite</span> and dolomite and the bands related to the mineral structure. The (CO3)2- group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the <span class="hlt">calcite</span> and dolomite were observed at 1440, 1088, 715 and 278 cm-1. The significant differences between the minerals <span class="hlt">calcite</span> and dolomite are observed by Raman spectroscopy. <span class="hlt">Calcite</span> shows the typical bands observed at 1361, 1047, 715 and 157 cm-1, and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm-1 for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. <span class="hlt">Calcite</span> has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.6903M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.6903M"><span>Microstructures and elastic properties of sheared <span class="hlt">calcite</span> flowstone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mitrovic, Ivanka; Grasemann, Bernhard; Plan, Lukas; Tesei, Telemaco; Baron, Ivo</p> <p>2016-04-01</p> <p>Flowstone is a monomineralic rock precipitated along cave walls and floors, composed of columnar centimeter-scale <span class="hlt">calcite</span> crystals with strong growth orientation perpendicular to the growth surface. Broken and scratched flowstone can serve as evidence for active faulting and has been found in several alpine caves in Austria. In order to understand the fault mechanics, and associated potential earthquake hazard, experimentally deformed flowstone is studied using microstructural analysis and EBSD-measured physical properties of <span class="hlt">calcite</span> crystals. For that purpose, we have performed sliding experiments using a rock deformation biaxial apparatus on rectangular blocks of flowstone that were sheared perpendicular to the <span class="hlt">calcite</span> growth direction. The experiments were performed under room conditions, with sub-seismic sliding velocity (0.001-0.01 mm/s) and constant effective normal stress (3-10 MPa). The deformed samples show diverse brittle features, including high fracture density, the development of <span class="hlt">calcite</span>-rich fault gouge with Riedel shears within a foliated cataclasite, and drastic grain size reduction down to nm-scale grains. The dominant plastic microstructure is mechanical twinning. Due to the strong growth orientation of <span class="hlt">calcite</span> in flowstone, crystals can be bent due to shearing. We examine the bending by applying orientation distribution, Schmid factor and elasticity tensor calculations using MTEX Toolbox from EBSD data. In this unique case the flowstone deformation experiments bridge the gap between single crystal and rock powder experiments. This study is supported by the Austrian Science Foundation: SPELEOTECT project (P25884-N29).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23988531','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23988531"><span>A Raman spectroscopic comparison of <span class="hlt">calcite</span> and dolomite.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sun, Junmin; Wu, Zeguang; Cheng, Hongfei; Zhang, Zhanjun; Frost, Ray L</p> <p>2014-01-03</p> <p>Raman spectroscopy was used to characterize and differentiate the two minerals <span class="hlt">calcite</span> and dolomite and the bands related to the mineral structure. The (CO3)(2-) group is characterized by four prominent Raman vibrational modes: (a) the symmetric stretching, (b) the asymmetric deformation, (c) asymmetric stretching and (d) symmetric deformation. These vibrational modes of the <span class="hlt">calcite</span> and dolomite were observed at 1440, 1088, 715 and 278 cm(-1). The significant differences between the minerals <span class="hlt">calcite</span> and dolomite are observed by Raman spectroscopy. <span class="hlt">Calcite</span> shows the typical bands observed at 1361, 1047, 715 and 157 cm(-1), and the special bands at 1393, 1098, 1069, 1019, 299, 258 and 176 cm(-1) for dolomite are observed. The difference is explained on the basis of the structure variation of the two minerals. <span class="hlt">Calcite</span> has a trigonal structure with two molecules per unit cell, and dolomite has a hexagonal structure. This is more likely to cause the splitting and distorting of the carbonate groups. Another cause for the difference is the cation substituting for Mg in the dolomite mineral.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1339818','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1339818"><span>Nanometer-Scale Chemistry of a <span class="hlt">Calcite</span> Biomineralization Template: Implications for Skeletal Composition and Nucleation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Branson, Oscar; Bonnin, Elisa A.; Perea, Daniel E.; Spero, Howard J.; Zhu, Zihua; Winters, Maria; Hönisch, Bärbel; Russell, Ann D.; Fehrenbacher, Jennifer S.; Gagnon, Alexander C.</p> <p>2016-10-28</p> <p>Biomineralizing organisms exhibit exquisite control over skeletal morphology and composition. The promise of understanding and harnessing this feat of natural engineering has motivated an intense search for the mechanisms that direct in vivo mineral self-assembly. We used atom probe tomography, a sub-nanometer 3D chemical mapping technique, to examine the chemistry of a buried organic-mineral interface in biomineral <span class="hlt">calcite</span> from a <span class="hlt">marine</span> foraminifer. The chemical patterns at this interface capture the processes of early biomineralization, when the shape, mineralogy, and orientation of skeletal growth are initially established. Sodium is enriched by a factor of nine on the organic side of the interface. Based on this pattern, we suggest that sodium plays an integral role in early biomineralization, potentially altering interfacial energy to promote crystal nucleation, and that interactions between organic surfaces and electrolytes other than calcium or carbonate could be a crucial aspect of CaCO3 biomineralization.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70017028','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70017028"><span>Time and metamorphic petrology: <span class="hlt">Calcite</span> to aragonite experiments</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hacker, B.R.; Kirby, S.H.; Bohlen, S.R.</p> <p>1992-01-01</p> <p>Although the equilibrium phase relations of many mineral systems are generally well established, the rates of transformations, particularly in polycrystalline rocks, are not. The results of experiments on the <span class="hlt">calcite</span> to aragonite transformation in polycrystalline marble are different from those for earlier experiments on powdered and single-crystal <span class="hlt">calcite</span>. The transformation in the polycrystalline samples occurs by different mechanisms, with a different temperature dependence, and at a markedly slower rate. This work demonstrates the importance of kinetic studies on fully dense polycrystalline aggregates for understanding mineralogic phase changes in nature. Extrapolation of these results to geological time scales suggests that transformation of <span class="hlt">calcite</span> to aragonite does not occur in the absence of volatiles at temperatures below 200??C. Kinetic hindrance is likely to extend to higher temperatures in more complex transformations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20026848','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20026848"><span>Chemistry and kinetics of <span class="hlt">calcite</span> dissolution in passive treatment systems</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Rose, A.W.</p> <p>1999-07-01</p> <p>Reaction of <span class="hlt">calcite</span> with AMD is a key remediation process in anoxic limestone drains, (ALD), SAPS, and many wetlands, but predictions of effluent quality are currently based mainly on rules of thumb and prior experience. The PHREEQC computer program can be used to calculate the progress of this and similar reactions, and aid in understanding, design and evaluation of these systems. At pH values less than 5, <span class="hlt">calcite</span> dissolution rates are strongly influenced by transport parameters such as flow velocity. Estimated <span class="hlt">calcite</span> dissolution rates from ALD's and column experiments indicate little change in rate with pH, in contrast to published data for well stirred lab experiments. The dissolution rate is affected by concentration of SO{sub 4}, Fe, Al, Ca, P, and other trace solutes. The optimum contact time and sizing of ALD's will be dependent on these and possibly other parameters. Additional experiments are needed to evaluate these dependencies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26468620','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26468620"><span><span class="hlt">Abiotic</span> Bromination of Soil Organic Matter.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Leri, Alessandra C; Ravel, Bruce</p> <p>2015-11-17</p> <p>Biogeochemical transformations of plant-derived soil organic matter (SOM) involve complex <span class="hlt">abiotic</span> and microbially mediated reactions. One such reaction is halogenation, which occurs naturally in the soil environment and has been associated with enzymatic activity of decomposer organisms. Building on a recent finding that naturally produced organobromine is ubiquitous in SOM, we hypothesized that inorganic bromide could be subject to <span class="hlt">abiotic</span> oxidations resulting in bromination of SOM. Through lab-based degradation treatments of plant material and soil humus, we have shown that <span class="hlt">abiotic</span> bromination of particulate organic matter occurs in the presence of a range of inorganic oxidants, including hydrogen peroxide and assorted forms of ferric iron, producing both aliphatic and aromatic forms of organobromine. Bromination of oak and pine litter is limited primarily by bromide concentration. Fresh plant material is more susceptible to bromination than decayed litter and soil humus, due to a labile pool of mainly aliphatic compounds that break down during early stages of SOM formation. As the first evidence of <span class="hlt">abiotic</span> bromination of particulate SOM, this study identifies a mechanistic source of the natural organobromine in humic substances and the soil organic horizon. Formation of organobromine through oxidative treatments of plant material also provides insights into the relative stability of aromatic and aliphatic components of SOM.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5344909','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5344909"><span>RBM25 Mediates <span class="hlt">Abiotic</span> Responses in Plants</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Cheng, Chunhong; Wang, Zhijuan; Yuan, Bingjian; Li, Xia</p> <p>2017-01-01</p> <p>Alternative splicing (AS) of pre-mRNAs is one of the most important post-transcriptional regulations that enable a single gene to code for multiple proteins resulting in the biodiversity of proteins in eukaryotes. Recently, we have shown that an Arabidopsis thaliana RNA recognition motif-containing protein RBM25 is a novel splicing factor to modulate plant response to ABA during seed germination and post-germination through regulating HAB1 pre-mRNA AS. Here, we show that RBM25 is preferentially expressed in stomata and vascular tissues in Arabidopsis and is induced by ABA and <span class="hlt">abiotic</span> stresses. Loss-of-function mutant is highly tolerant to drought and sensitive to salt stress. Bioinformatic analysis and expression assays reveal that Arabidopsis RBM25 is induced by multiple <span class="hlt">abiotic</span> stresses, suggesting a crucial role of RBM25 in Arabidopsis responses to adverse environmental conditions. Furthermore, we provide a comprehensive characterization of the homologous genes of Arabidopsis RBM25 based on the latest plant genome sequences and public microarray databases. Fourteen homologous genes are identified in different plant species which show similar structure in gene and protein. Notably, the promoter analysis reveals that RBM25 homologs are likely controlled by the regulators involved in multiple plant growth and <span class="hlt">abiotic</span> stresses, such as drought and unfavorable temperature. The comparative analysis of general and unique cis regulatory elements of the RBM25 homologs highlights the conserved and unique molecular processes that modulate plant response to <span class="hlt">abiotic</span> stresses through RBM25-mediated alternative splicing. PMID:28344583</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28344583','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28344583"><span>RBM25 Mediates <span class="hlt">Abiotic</span> Responses in Plants.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cheng, Chunhong; Wang, Zhijuan; Yuan, Bingjian; Li, Xia</p> <p>2017-01-01</p> <p>Alternative splicing (AS) of pre-mRNAs is one of the most important post-transcriptional regulations that enable a single gene to code for multiple proteins resulting in the biodiversity of proteins in eukaryotes. Recently, we have shown that an Arabidopsis thaliana RNA recognition motif-containing protein RBM25 is a novel splicing factor to modulate plant response to ABA during seed germination and post-germination through regulating HAB1 pre-mRNA AS. Here, we show that RBM25 is preferentially expressed in stomata and vascular tissues in Arabidopsis and is induced by ABA and <span class="hlt">abiotic</span> stresses. Loss-of-function mutant is highly tolerant to drought and sensitive to salt stress. Bioinformatic analysis and expression assays reveal that Arabidopsis RBM25 is induced by multiple <span class="hlt">abiotic</span> stresses, suggesting a crucial role of RBM25 in Arabidopsis responses to adverse environmental conditions. Furthermore, we provide a comprehensive characterization of the homologous genes of Arabidopsis RBM25 based on the latest plant genome sequences and public microarray databases. Fourteen homologous genes are identified in different plant species which show similar structure in gene and protein. Notably, the promoter analysis reveals that RBM25 homologs are likely controlled by the regulators involved in multiple plant growth and <span class="hlt">abiotic</span> stresses, such as drought and unfavorable temperature. The comparative analysis of general and unique cis regulatory elements of the RBM25 homologs highlights the conserved and unique molecular processes that modulate plant response to <span class="hlt">abiotic</span> stresses through RBM25-mediated alternative splicing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1817255R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1817255R"><span>Small scale shear zone in <span class="hlt">calcite</span>: AMS and microstructure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roxerová, Zuzana; Machek, Matěj; Kusbach, Vladimír; Racek, Martin; Silva, Pedro F.</p> <p>2016-04-01</p> <p>Two structural profiles across thin shear zone in <span class="hlt">calcite</span> from quarry in Estremoz (Portugal) were studied to find a relationship between AMS and strain in natural rocks. The mesoscopic fabric is characterized by the change from the subhorizontal coarse-grained foliation towards the ~2cm-wide shear zone center with subvertical fine-grained foliation. In microstructure, the shear zone records dynamic recrystallization of <span class="hlt">calcite</span> aggregate which resulted in development of porphyroclastic microstructure with increasing proportion of fine-grained recrystallized matrix towards the shear zone center. Two distinct crystallographic preferred orientations of <span class="hlt">calcite</span> were recorded. One related with porphyroclasts, characterized by subvertical orientation of <span class="hlt">calcite</span> <c> axes and another associated with recrystallized matrix showing subhorizontal <span class="hlt">calcite</span> <c> axes orientation. The magnetic susceptibility ranges from -8e-6SI to 9e-6SI, with the average -4e-6SI. The majority of the rock mass is diamagnetic, corresponding well with the thermomagnetic curves, with local paramagnetic accumulations in form of thin bands. The AMS of the both profiles exhibits stable subvertical foliation bearing vertical lineation which is locally alternated by the medium-angle foliation. We interpret the AMS fabric pattern which is perpendicular to the mineral one as a type of inverse AMS fabric, due to high iron content in major part of <span class="hlt">calcite</span> grains The magnetic and microstructural description of the shear zone is accompanied by numerical modeling of AMS based on CPO and different proportion of porphyroclasts, matrix and mica for purposes of deciphering the influence of present microstructural features on AMS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.H21A1051S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.H21A1051S"><span>Microbially Induced <span class="hlt">Calcite</span> Precipitation for Subsurface Immobilization of Contaminants</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, R. W.; Fujita, Y.; Ginn, T. R.; Hubbard, S. S.; Dafflon, B.; Delwiche, M.; Gebrehiwet, T.; Henriksen, J. R.; Peterson, J.; Taylor, J. L.</p> <p>2011-12-01</p> <p>Subsurface radionuclide and metal contaminants throughout the U.S. Department of Energy (DOE) complex pose one of the greatest challenges for long-term stewardship. One promising stabilization mechanism for divalent trace ions, such as the short-lived radionuclide 90Sr, is co-precipitation in <span class="hlt">calcite</span>. We have found that <span class="hlt">calcite</span> precipitation and co-precipitation of Sr can be accelerated by the activity of urea hydrolyzing microorganisms, that higher <span class="hlt">calcite</span> precipitation rates can result in increased Sr partitioning, and that nutrient additions can stimulate ureolytic activity. To extend our understanding of microbially induced <span class="hlt">calcite</span> precipitation (MICP) in an aquifer setting a continuous recirculation field experiment evaluating MICP was conducted at the Integrated Field Research Challenge (IFRC) site located at Rifle, CO. In this experiment, groundwater extracted from an onsite well was amended with urea (total mass of 42.5 kg) and molasses (a carbon and electron donor) and re-injected into a well approximately 4 meters up-gradient for a period of 12 days followed by 10 months of groundwater sampling and monitoring. Crosshole radar and electrical tomographic data were collected prior, during, and after the MICP treatment. The urea and molasses treatment resulted in an enhanced population of sediment associated urea hydrolyzing organisms as evidenced by increases in the number of ureC gene copies, increases in 14C urea hydrolysis rates, and long-term observations of ammonium (a urea hydrolysis product) in the injection, extraction and down gradient monitoring wells. Permeability changes and increases in the <span class="hlt">calcite</span> saturation indexes in the well field suggest that mineral precipitation has occurred; ongoing analysis of field samples seeks to confirm this. Changes in dielectric constant and electrical conductivity were used to interpret the spatiotemporal distribution of the injectate and subsequent <span class="hlt">calcite</span> precipitation. Modeling activities are underway to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.176..198A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.176..198A"><span>Is bicarbonate stable in and on the <span class="hlt">calcite</span> surface?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andersson, M. P.; Rodriguez-Blanco, J. D.; Stipp, S. L. S.</p> <p>2016-03-01</p> <p>We have used density functional theory with the COSMO-RS implicit solvent model to predict the pKa for the deprotonation of bicarbonate to carbonate, i.e. HCO3- <=> CO32- + H+, when HCO3- is included in, and adsorbed on, a <span class="hlt">calcite</span> surface. We have used cluster models (80-100 atoms) to represent the flat {10.4} surface, acute steps, obtuse steps, two types of kinks on the acute step and two types of kinks on the obtuse steps. Based on the predicted pKa values, which range from -6.0 to 2.4 depending on the surface site, we conclude that bicarbonate deprotonates to carbonate when it is in <span class="hlt">calcite</span> even when pH in solution is very low. This is true for all surface sites, even for solutions where 2.4 < pH < 6.35, where H2CO30 is the dominant dissolved species. When bicarbonate is adsorbed on <span class="hlt">calcite</span>, the predicted pKa for deprotonation is 7.5, which is ∼3 pH units lower than in aqueous solution, 10.35. This means that adsorbed carbonate is stable even when the concentration of dissolved CO32- is several orders of magnitude lower. This has a significant effect on surface charge and thus the behaviour of the <span class="hlt">calcite</span> surface. Our results help explain the potential determining behaviour of the carbonate species in <span class="hlt">calcite</span>-water systems, particularly in the pH range where the bicarbonate species dominates in water and where the carbonate species dominates at the surface, i.e. when 7.5 < pH < 10.35. Our atomic scale data for the various <span class="hlt">calcite</span> surface sites provide the needed input to improve and constrain surface complexation modelling and are especially useful for predicting behaviour in systems where experiments are difficult or impossible, such as at high temperature and pressure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.B12C0787D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.B12C0787D"><span>Sulfated Macromolecules as Templates for <span class="hlt">Calcite</span> Nucleation and Growth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>David, M.; Passalacqua, K.; Neira, A. C.; Fernandez, M. S.</p> <p>2003-12-01</p> <p>Mineralization of egg and seashells is controlled by an intimate association of inorganic materials with organic macromolecules. Among them, particular polyanionic sulfated macromolecules referred to as proteoglycans have been described to be involved in the calcification of these biominerals. The sulfated moieties of the proteoglycans are part of polymer chains constituted of building-blocks of disaccharide units, referred to as sulfated glycosaminoglycans (GAGs), which are covalently attached to a protein core. By using a sitting drop crystallization assay under controlled conditions of time, pH and reactants concentration, we have tested several sulfated and non-sulfated GAGs (i.e.: dermatan and keratan sulfate, hyaluronic acid and heparin), differing in their sulfonate and carboxylate degree and pattern, in their ability to modify calcium carbonate crystal morphology as observed under scanning electron microscopy. Without the addition of GAGs, regular \\{104\\} rhombohedral <span class="hlt">calcite</span> crystals were obtained. When hyaluronic acid (HA), a non-sulfated but carboxylated GAG, was added, 20 mm long piles of unmodified <span class="hlt">calcite</span> crystals were observed. When desulfated dermatan, which is an epimeric form of HA but shorter polymer, having their carboxylate groups in an inverted configuration, was added, isolated rhombohedral \\{104\\} <span class="hlt">calcite</span> crystals showing rounded corners with planes oriented parallel to the c axis were observed. When dermatan sulfated was added, isolated <span class="hlt">calcite</span> crystals exhibit a columnar morphology as a \\{hk0\\} cylinder with three \\{104\\} faces forming a cap at both ends. Heparin activity depends on the fraction added. Fast-moving heparin fraction (FM), is an undersulfated, low-molecular-weight heterogeneous polymer, while slow-moving heparin fraction (SM) is an high-molecular-weight homogeneous polymer rich in trisulfated-disaccharide units. When FM was added, isolated <span class="hlt">calcite</span> crystals displayed rhombohedrical \\{104\\} faces but flat corners of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PNAS..11014540R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PNAS..11014540R"><span>Surface chemistry allows for <span class="hlt">abiotic</span> precipitation of dolomite at low temperature</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roberts, Jennifer A.; Kenward, Paul A.; Fowle, David A.; Goldstein, Robert H.; González, Luis A.; Moore, David S.</p> <p>2013-09-01</p> <p>Although the mineral dolomite is abundant in ancient low-temperature sedimentary systems, it is scarce in modern systems below 50 °C. Chemical mechanism(s) enhancing its formation remain an enigma because <span class="hlt">abiotic</span> dolomite has been challenging to synthesize at low temperature in laboratory settings. Microbial enhancement of dolomite precipitation at low temperature has been reported; however, it is still unclear exactly how microorganisms influence reaction kinetics. Here we document the <span class="hlt">abiotic</span> synthesis of low-temperature dolomite in laboratory experiments and constrain possible mechanisms for dolomite formation. Ancient and modern seawater solution compositions, with identical pH and pCO2, were used to precipitate an ordered, stoichiometric dolomite phase at 30 °C in as few as 20 d. Mg-rich phases nucleate exclusively on carboxylated polystyrene spheres along with <span class="hlt">calcite</span>, whereas aragonite forms in solution via homogeneous nucleation. We infer that Mg ions are complexed and dewatered by surface-bound carboxyl groups, thus decreasing the energy required for carbonation. These results indicate that natural surfaces, including organic matter and microbial biomass, possessing a high density of carboxyl groups may be a mechanism by which ordered dolomite nuclei form. Although environments rich in organic matter may be of interest, our data suggest that sharp biogeochemical interfaces that promote microbial death, as well as those with high salinity may, in part, control carboxyl-group density on organic carbon surfaces, consistent with origin of dolomites from microbial biofilms, as well as hypersaline and mixing zone environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23964124','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23964124"><span>Surface chemistry allows for <span class="hlt">abiotic</span> precipitation of dolomite at low temperature.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Roberts, Jennifer A; Kenward, Paul A; Fowle, David A; Goldstein, Robert H; González, Luis A; Moore, David S</p> <p>2013-09-03</p> <p>Although the mineral dolomite is abundant in ancient low-temperature sedimentary systems, it is scarce in modern systems below 50 °C. Chemical mechanism(s) enhancing its formation remain an enigma because <span class="hlt">abiotic</span> dolomite has been challenging to synthesize at low temperature in laboratory settings. Microbial enhancement of dolomite precipitation at low temperature has been reported; however, it is still unclear exactly how microorganisms influence reaction kinetics. Here we document the <span class="hlt">abiotic</span> synthesis of low-temperature dolomite in laboratory experiments and constrain possible mechanisms for dolomite formation. Ancient and modern seawater solution compositions, with identical pH and pCO2, were used to precipitate an ordered, stoichiometric dolomite phase at 30 °C in as few as 20 d. Mg-rich phases nucleate exclusively on carboxylated polystyrene spheres along with <span class="hlt">calcite</span>, whereas aragonite forms in solution via homogeneous nucleation. We infer that Mg ions are complexed and dewatered by surface-bound carboxyl groups, thus decreasing the energy required for carbonation. These results indicate that natural surfaces, including organic matter and microbial biomass, possessing a high density of carboxyl groups may be a mechanism by which ordered dolomite nuclei form. Although environments rich in organic matter may be of interest, our data suggest that sharp biogeochemical interfaces that promote microbial death, as well as those with high salinity may, in part, control carboxyl-group density on organic carbon surfaces, consistent with origin of dolomites from microbial biofilms, as well as hypersaline and mixing zone environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5676977','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5676977"><span>Shallow burial dolomitization of Mid-Cenozoic, cool-water, <span class="hlt">calcitic</span> deep-shelf limestones, southern Australia</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>James. N.P. ); Bone, Y. ); Kyser, T.K. )</p> <p>1991-03-01</p> <p>Oligocene to middle Miocene, deep-shelf, bryozoan-rich limestones across southern Australia are variably replaced by green to orange, Ca-rich, zoned, medium-crystalline, sucrosic dolomite. The degree of replacement varies from scattered rhombs in limestone to complete dolostones a few tens of meters in thickness and a few kilometers in lateral extent. Dolostone texture ranges from dense and well lithified to completely unlithified, resembling a loose sand of dolomite rhombs. Dolomitization is fabric specific; <span class="hlt">calcite</span> and Mg-<span class="hlt">calcite</span> bryozoans are either the last components to be replaced or are molds. The timing and locale of dolomitization are tightly constrained; Sr isotopes indicate a middle to late Miocene age while clasts of dolostone in overlying Pliocene limestones above a regional unconformity confirm a shallow-burial, pre-Pliocene origin. {delta}{sup 13}C and {delta}{sup 18}O values support a <span class="hlt">marine</span> source for the carbonate; the influence of meteoric fluids appears to have been negligible. Quaternary exposure has resulted in local dedolomitization and/or subaerial erosion, especially in the Murray basin. These rocks are excellent analogues for localized, lenticular dolostone bodies in <span class="hlt">calcite</span>-rich Paleozoic platform carbonates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFMPP33A..04B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFMPP33A..04B"><span>Interrogating coccolith <span class="hlt">calcite</span>: paleoceanographic proxy data from nannofractions, foraminifera and single coccolith specimens</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bown, P. R.; Lees, J. A.; Young, J.; Robinson, S. A.; MacLeod, K. G.; Grocke, D. R.; Schmidt, D. N.; Hinton, R.</p> <p>2009-12-01</p> <p>Nannofossils are the calcareous cell-wall coverings of oceanic phytoplankton and the most abundant but smallest routinely studied fossil group. Small size (typically <8 microns and <400 pg of <span class="hlt">calcite</span> per lith) has limited their use as geochemical proxies because it is difficult to separate them by mechanical picking or using centrifuge or filtration techniques. However, the <63µm fraction of <span class="hlt">marine</span> sediments is often implied to represent the bulk nannofossil signal in geochemical studies, but actually represents a spectrum of oceanic carbonate, from parts of larger organisms (potentially benthic, nektonic and planktonic) to micarb (of unknown, possibly non-biological, origin), consequently obfuscating the true nannofossil signal. Additionally, it is known that certain nannofossil taxa are more responsive to paleoenvironmental change than others, and so a bulk nannofossil signal is potentially misleading. Consequently, there has been a strong incentive to develop techniques that overcome these difficulties, as coccoliths represent a potentially invaluable and inexhaustible geochemical archive of paleoenvironmental information. Most importantly, coccoliths are hugely abundant in <span class="hlt">marine</span> sediments deposited above the <span class="hlt">calcite</span> compensation depth (billions of specimens per gram) and their chemical composition is resistant to the modifying effects of diagenesis since they are relatively non-porous structures formed from a small number of solid <span class="hlt">calcite</span> crystals. Here we compare a range of paleoceanographic geochemical proxies (element ratios, stable isotopes) measured from (a) bulk sediment, single foraminifers and sieved near-monotaxic nannofossil fractions using wet chemistry and (b) single coccolith specimens using an ion microprobe SIMS. The data come from the PETM interval of ODP Leg 207 Site 1259 (Demerara Rise, western equatorial Atlantic) and enable comparisons between paleontological, assemblage-based productivity proxies and geochemical proxies based on</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.2122B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.2122B"><span>Stable carbon isotopes and lipid biomarkers provide new insight into the formation of <span class="hlt">calcite</span> and siderite concretions in organic-matter rich deposits</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Baumann, Lydia; Birgel, Daniel; Wagreich, Michael; Peckmann, Jörn</p> <p>2015-04-01</p> <p>Carbonate concretions from two distinct settings have been studied for their petrography, stable carbon and oxygen isotopes, and lipid biomarker content. Carbonate concretions are in large part products of microbial degradation of organic matter, as for example by sulfate-reducing bacteria, iron-reducing bacteria, and methanogenic archaea. For these prokaryotes certain lipid biomarkers such as hopanoids, terminally-branched fatty acids (bacteria) and isoprenoids (archaea) are characteristic. Two different types of concretions were studied: a) Upper Miocene septarian <span class="hlt">calcite</span> concretions of the southern Vienna Basin embedded in brackish sediments represented by partly bituminous calcareous sands, silts and clays; b) Paleocene-Eocene siderite concretions enclosed in <span class="hlt">marine</span>, sandy to silty turbidites with varying carbonate contents and marl layers from the Upper Gosau Subgroup in northern Styria. <span class="hlt">Calcite</span> concretions consist of abundant <span class="hlt">calcite</span> microspar (80-90 vol.%), as well as detrital minerals and iron oxyhydroxides. The septarian cracks show beginning cementation with dog-tooth <span class="hlt">calcite</span> to varying degrees. Framboidal pyrite occurs in some of the <span class="hlt">calcite</span> concretions, pointing to bacterial sulfate reduction. Siderite concretions consist of even finer carbonate crystals, mainly siderite (40-70 vol.%) but also abundant ferroan <span class="hlt">calcite</span>, accompanied by iron oxyhydroxides and detrital minerals. The δ13C values of the <span class="hlt">calcite</span> concretions (-6.8 to -4.1o ) most likely reflect a combination of bacterial organic matter oxidation and input of <span class="hlt">marine</span> biodetrital carbonate. The δ18O values range from -8.9 to -7.8o agreeing with a formation within a meteoric environment. The surrounding host sediment shows about 1-2o higher δ13C and δ18O values. The siderite δ13C values (-11.1 to -7.5o ) point to microbial respiration of organic carbon and the δ18O values (-3.5 to +2.2o ) agree with a <span class="hlt">marine</span> depositional environment. In contrast to the <span class="hlt">calcite</span> concretions, the stable isotope</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/675514','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/675514"><span><span class="hlt">Marine</span> botany. Second edition</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dawes, C.J.</p> <p>1998-12-01</p> <p><span class="hlt">Marine</span> plants are a diverse group that include unicellular algae, seaweeds, seagrasses, salt marshes, and mangrove forests. They carry out a variety of ecological functions and serve as the primary producers in coastal wetlands and oceanic waters. The theme that connects such a wide variety of plants is their ecology, which was also emphasized in the 1981 edition. The goal of this revision is to present taxonomic, physiological, chemical, and ecological aspects of <span class="hlt">marine</span> plants, their adaptations, and how <span class="hlt">abiotic</span> and biotic factors interact in their communities. The data are presented in a concise, comparative manner in order to identify similarities and differences between communities such as salt marsh and mangroves or subtidal seaweeds and seagrasses. To accomplish this, the text is organized into five chapters that introduce the <span class="hlt">marine</span> habitats, consider <span class="hlt">abiotic</span> and biotic factors, and anthropogenic influences on the communities followed by seven chapters that deal with microalgae, seaweeds, salt marshes, mangroves, seagrasses, and coral reefs. Two appendixes are included; one presents simple field techniques and the other is a summary of seaweed uses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27618958','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27618958"><span>Incorporation of Eu(III) into <span class="hlt">Calcite</span> under Recrystallization conditions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hellebrandt, S E; Hofmann, S; Jordan, N; Barkleit, A; Schmidt, M</p> <p>2016-09-13</p> <p>The interaction of <span class="hlt">calcite</span> with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three <span class="hlt">calcite</span> powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu(3+) occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk crystal. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different <span class="hlt">calcites</span>. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na(+). These findings emphasize the different retention potential of <span class="hlt">calcite</span> as a primary and secondary mineral e.g. in a nuclear waste disposal site.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20050000477&hterms=Amphibians&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DAmphibians','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20050000477&hterms=Amphibians&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DAmphibians"><span>Utricular otoconia of some amphibians have <span class="hlt">calcitic</span> morphology</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Pote, K. G.; Ross, M. D.</p> <p>1993-01-01</p> <p>This report concerns the morphological features of otoconia removed from the inner ear of four amphibian species. Results from scanning electron microscopic examination are compared based on the site of origin. These results show that utricular otoconia have a mineral structure that mimics <span class="hlt">calcite</span>, rather than the widely accepted idea that they are mineralized by calcium carbonate of the aragonite polymorph.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5020613','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5020613"><span>Incorporation of Eu(III) into <span class="hlt">Calcite</span> under Recrystallization conditions</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hellebrandt, S. E.; Hofmann, S.; Jordan, N.; Barkleit, A.; Schmidt, M.</p> <p>2016-01-01</p> <p>The interaction of <span class="hlt">calcite</span> with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three <span class="hlt">calcite</span> powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu3+ occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk crystal. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different <span class="hlt">calcites</span>. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na+. These findings emphasize the different retention potential of <span class="hlt">calcite</span> as a primary and secondary mineral e.g. in a nuclear waste disposal site. PMID:27618958</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...633137H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...633137H"><span>Incorporation of Eu(III) into <span class="hlt">Calcite</span> under Recrystallization conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hellebrandt, S. E.; Hofmann, S.; Jordan, N.; Barkleit, A.; Schmidt, M.</p> <p>2016-09-01</p> <p>The interaction of <span class="hlt">calcite</span> with trivalent europium under recrystallization conditions was studied on the molecular level using site-selective time-resolved laser fluorescence spectroscopy (TRLFS). We conducted batch studies with a reaction time from seven days up to three years with three <span class="hlt">calcite</span> powders, which differed in their specific surface area, recrystallization rates and impurities content. With increase of the recrystallization rate incorporation of Eu3+ occurs faster and its speciation comes to be dominated by one species with its excitation maximum at 578.8 nm, so far not identified during previous investigations of this process under growth and phase transformation conditions. A long lifetime of 3750 μs demonstrates complete loss of hydration, consequently Eu must have been incorporated into the bulk crystal. The results show a strong dependence of the incorporation kinetics on the recrystallization rate of the different <span class="hlt">calcites</span>. Furthermore the investigation of the effect of different background electrolytes (NaCl and KCl) demonstrate that the incorporation process under recrystallization conditions strongly depends on the availability of Na+. These findings emphasize the different retention potential of <span class="hlt">calcite</span> as a primary and secondary mineral e.g. in a nuclear waste disposal site.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/289451','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/289451"><span>Atomistic simulation of the differences between <span class="hlt">calcite</span> and dolomite surfaces</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Titiloye, J.O.; Leeuw, N.H. de; Parker, S.C.</p> <p>1998-08-01</p> <p>Atomistic simulation methods have been used to calculate and compare the surface structures and energies of the {l_brace}10{bar 1}4{r_brace}, {l_brace}0001{r_brace}, {l_brace}10{bar 1}0{r_brace}, {l_brace}11{bar 2}0{r_brace} and {l_brace}10{bar 1}1{r_brace} surfaces of <span class="hlt">calcite</span> and dolomite and to evaluate their equilibrium morphologies. The <span class="hlt">calcite</span> {l_brace}10{bar 1}4{r_brace} and the dolomite {l_brace}10{bar 1}0{r_brace} and {l_brace}11{bar 2}0{r_brace} surfaces are the most stable crystal planes. Investigation of the segregation of Mg and Ca ions in the dolomite crystal shows a clear preference for Ca{sup 2+} ions at the surface sites and for Mg{sup 2+} ions in the bulk sites and hence growth onto dolomite results in calcium carbonate or high magnesian <span class="hlt">calcite</span> crystals which helps explain the difficulty in crystallizing dolomite vs. <span class="hlt">calcite</span> under laboratory conditions.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20449036','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20449036"><span>Proton/calcium ion exchange behavior of <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Villegas-Jiménez, Adrián; Mucci, Alfonso; Paquette, Jeanne</p> <p>2009-10-21</p> <p>The characterization of the proton sorptive properties of <span class="hlt">calcite</span> in aqueous solutions at 25 +/- 1 degrees C over a relatively wide range of chemical conditions (7.16 <or= pH <or= 9.7; 3 x 10(-5) M <or=SigmaCa <or= 5 x 10(-3) M; 10(-4) M <or=SigmaCO(2)<or= 1.7 x 10(-3) M) and solid : solution ratios (0.4 to 12.3 g L(-1)) was performed using a novel surface titration technique. A large net proton uptake, coupled with a significant release of Ca(2+) ions is consistently observed, greatly exceeding the theoretical number of reactive surface sites. These observations are interpreted as a fast proton/calcium exchange equilibrium between the solution and "exchangeable cation sites" (e.g., lattice positions) at and/or beneath the <span class="hlt">calcite</span> surface (species identified by "(exc)"), , that leads to a transient, "apparent" incongruent dissolution regime and the formation of a stable calcium-deficient, proton-enriched layer within the <span class="hlt">calcite</span> lattice under circum-neutral and alkaline regimes at standard conditions. The 2H(+)/Ca(2+) ion exchange is quantitatively described by the Langmuir-power exchange function under the Vanselow convention: where n = 1 and log(10)K(ex) = 13.0 +/- 0.3. This <span class="hlt">calcite</span> behavior, never reported before, masks surface equilibria and directly impacts the aqueous speciation of carbonate-rock systems with poor CO(2)(g) ventilation (e.g., aquifers, pore and deep sea waters, industrial reactors) via the buffering of pH and <span class="hlt">calcite</span> dissolution. In contrast, at fixed pCO(2) conditions, aqueous speciation remains unaffected upon CO(2)(g) sequestration resulting from ion exchange-induced <span class="hlt">calcite</span> precipitation: ([triple bond]CaCO3)2(exc) + CO2(g) + H2O <==> [triple bond]Ca(HCO3)2(exc) + CaCO3(s). Accordingly, reliable predictions of aqueous speciation in natural or engineered <span class="hlt">calcite</span>-containing systems at variable pCO(2) conditions must consider this exchange reaction and the associated K(ex). The postulated proton/calcium exchange may have far</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.183...46P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.183...46P"><span>NMR spectroscopic study of organic phosphate esters coprecipitated with <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Phillips, Brian L.; Zhang, Zelong; Kubista, Laura; Frisia, Silvia; Borsato, Andrea</p> <p>2016-06-01</p> <p>Organic phosphorus incorporated in <span class="hlt">calcite</span> during laboratory precipitation experiments and in natural cave deposits was investigated by solid-state NMR spectroscopy. For <span class="hlt">calcite</span> precipitated in the presence of organic phosphoesters of varying size and functionality, solid-state 31P{1H} CP/MAS NMR shows that the phosphoesters were incorporated intact into the solid. Systematic changes in the 31P NMR chemical shift of the phosphate group were observed between the solid phosphoester and that incorporated in the solid precipitate, yielding 31P NMR chemical shifts of the coprecipitates in the range of +1.8 to -2.2 ppm. These chemical shifts are distinct from that of similarly prepared <span class="hlt">calcite</span> coprecipitated with inorganic phosphate, 3.5 ppm. Only minor changes were noted in the phosphoester 31P chemical shift anisotropy (CSA) which suggests no significant change in the local structure of the phosphate group, which is dominated by C-O-P bonding. Close spatial proximity of the organic phosphate group to <span class="hlt">calcite</span> structural components was revealed by 31P/13C rotational echo double resonance (REDOR) experiments for coprecipitates prepared with 13C-labeled carbonate. All coprecipitates showed significant 31P dephasing effects upon 13C-irradiation, signaling atomic-scale proximity to carbonate carbon. The dephasing rate for smaller organophosphate molecules is similar to that observed for inorganic phosphate, whereas much slower dephasing was observed for larger molecules having long and/or bulky side-chains. This result suggests that small organic molecules can be tightly enclosed within the <span class="hlt">calcite</span> structure, whereas significant structural disruption required to accommodate the larger organic molecules leads to longer phosphate-carbonate distances. Comparison of 31P NMR spectroscopic data from the synthetic coprecipitates with those from <span class="hlt">calcite</span> moonmilk speleothems indicates that phosphorus occurs mainly as inorganic orthophosphate in the natural deposits, although small</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001GeCoA..65.4131H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001GeCoA..65.4131H"><span>The behavior of Ni 2+ on <span class="hlt">calcite</span> surfaces</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hoffmann, U.; Stipp, S. L. S.</p> <p>2001-11-01</p> <p>Transport of Ni 2+ in the geosphere plays a role in the formation of ore deposits as well as in the dispersion of contaminants in the environment. Some elements (Cd 2+, Zn 2+, Na +, K +, and Cl -) are known to diffuse in <span class="hlt">calcite</span> at the rate of nanometers in months, so questions arose about the ability of Ni 2+ to move away from adsorption sites at the surface into the bulk. Nickel incorporation into <span class="hlt">calcite</span> is limited by its high dehydration enthalpy and by its ligand field hindrance to entering the distorted octahedra of <span class="hlt">calcite</span>, but evidence exists that <span class="hlt">calcite</span> can tolerate several percent Ni 2+ in the structure. Cleaved samples of Iceland spar were exposed for 1 minute to solutions of 10 -3 M and 10 -2 M Ni(ClO 4) 2, the solution was physically removed and the samples were examined using the surface sensitive techniques: X-ray Photoelectron Spectroscopy (XPS), Time-of-Flight Secondary Ion Mass Spectroscopy (TOF-SIMS) and Atomic Force Microscopy (AFM). XPS and TOF-SIMS showed that Ni 2+ was adsorbed while AFM confirmed that dissolution was taking place. The sample was stored in air and relative surface concentration and physical morphology were monitored for 2 years. Trends in the chemical data suggested statistically significant loss of surface Ni 2+ with time, but the decrease was very close to the limits for significance. AFM images demonstrated that surface topography of the Ni-exposed samples is modified by spontaneous recrystalization in the water layer adsorbed from air in exactly the same way that clean <span class="hlt">calcite</span> surfaces typically rearrange. This process could bury a small amount of Ni 2+ in the bulk, explaining the very weak loss. Limited burial of Ni 2+ within the near-surface could renew <span class="hlt">calcite</span> adsorption sites, thus increasing uptake capacity. Evidence indicates that surface recrystalization occurs even in very dry environments (<5% humidity). This means that burial could play a role in Ni 2+ mobility in unsaturated groundwater regimes or in fractures</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.156...75R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.156...75R"><span>Experimental study of the replacement of <span class="hlt">calcite</span> by calcium sulphates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ruiz-Agudo, E.; Putnis, C. V.; Hövelmann, J.; Álvarez-Lloret, P.; Ibáñez-Velasco, A.; Putnis, A.</p> <p>2015-05-01</p> <p>Among the most relevant mineral replacement reactions are those involving sulphates and carbonates, which have important geological and technological implications. Here it is shown experimentally that during the interaction of <span class="hlt">calcite</span> (CaCO3) cleavage surfaces with sulphate-bearing acidic solutions, <span class="hlt">calcite</span> is ultimately replaced by gypsum (CaSO4 2H2O) and anhydrite (CaSO4), depending on the reaction temperature. Observations suggest that this occurs most likely via an interface-coupled dissolution-precipitation reaction, in which the substrate is replaced pseudomorphically by the product. At 120 and 200 °C gypsum and/or bassanite (CaSO4·0.5H2O) form as precursor phases for the thermodynamically stable anhydrite. Salinity promotes the formation of less hydrated precursor phases during the replacement of <span class="hlt">calcite</span> by anhydrite. The reaction stops before equilibrium with respect to <span class="hlt">calcite</span> is reached and during the course of the reaction most of the bulk solutions are undersaturated with respect to the precipitating phase(s). A mechanism consisting of the dissolution of small amounts of solid in a thin layer of fluid at the mineral-fluid interface and the subsequent precipitation of the product phase from this layer is in agreement with these observations. PHREEQC simulations performed in the framework of this mechanism highlight the relevance of transport and surface reaction kinetics on the volume change associated with the CaCO3-CaSO4 replacement. Under our experimental conditions, this reaction occurs with a positive volume change, which ultimately results in passivation of the unreacted substrate before <span class="hlt">calcite</span> attains equilibrium with respect to the bulk solution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AtmEn..42.5672H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AtmEn..42.5672H"><span>Water adsorption and cloud condensation nuclei activity of <span class="hlt">calcite</span> and <span class="hlt">calcite</span> coated with model humic and fulvic acids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hatch, Courtney D.; Gierlus, Kelly M.; Schuttlefield, Jennifer D.; Grassian, Vicki H.</p> <p></p> <p>Recent studies have shown that organics can alter the water adsorption and cloud condensation nuclei (CCN) activity of common deliquescent species in the Earth's atmosphere. However, very little is known about the effect of organics on water adsorption and CCN activity of insoluble nuclei, such as mineral dust aerosol. A large fraction of unidentified organic material in aerosol particles is composed of poly-acidic compounds resembling humic substances. The presence of these humic-like substances (HULIS) can alter the water adsorption and CCN activity of mineral dust aerosol. We have measured the CCN activity of model humic and fulvic acids and of mineral dust particles coated with these substances in the laboratory. We find that coatings of humic and fulvic acids on <span class="hlt">calcite</span> particles significantly increases water adsorption compared to uncoated particles. CCN measurements indicate that humic- or fulvic acid-coated <span class="hlt">calcite</span> particles are more CCN active than uncoated <span class="hlt">calcite</span> particles. Additionally, thicker coatings of humic or fulvic acids appear to result in more efficient CCN activity. Thus, mineral dust particles coated with high molecular weight organic materials will take up more water and become more efficient CCN in the atmosphere than uncoated mineral dust particles, potentially altering the effect of mineral dust on the Earth's climate. In addition to the experimental results, we have explored a newly modified Köhler theory for predicting the CCN activity of insoluble, wettable particles based on multi layer water adsorption measurements of <span class="hlt">calcite</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998GeCoA..62..433S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998GeCoA..62..433S"><span>Cosmogenic Chlorine-36 Production in <span class="hlt">Calcite</span> by Muons</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stone, J. O. H.; Evans, J. M.; Fifield, L. K.; Allan, G. L.; Cresswell, R. G.</p> <p>1998-02-01</p> <p>At depths below a few metres, 36Cl production in <span class="hlt">calcite</span> is initiated almost entirely by cosmic ray muons. The principal reactions are (1) direct negative muon capture by Ca; 40Ca(μ -,α) 36Cl, and (2) capture by 35Cl of secondary neutrons produced in muon capture and muon-induced photodisintegration reactions. We have determined rates for 36Cl and neutron production due to muon capture in <span class="hlt">calcite</span> from a 20 m (5360 g cm -2) depth profile in limestone. The 36Cl yield from muon capture by Ca in pure <span class="hlt">calcite</span> is 0.012 ± 0.002 atom per stopped negative muon. The surface production rate of 36Cl by muon capture on Ca in <span class="hlt">calcite</span> is, therefore, 2.1 ± 0.4 atom g -1a -1 at sea level and high latitude, approximately 11% of the production rate by Ca spallation. If it is assumed that 34% of the negative muons are captured by the Ca atom in <span class="hlt">calcite</span>, the α-yield from 40Ca following muon capture is 0.043 ± 0.008, somewhat lower than the result of a recent muon irradiation experiment (0.062 ± 0.020), but well within the extremes of existing theoretical predictions (0.0033-0.15). The average neutron yield following muon capture in pure <span class="hlt">calcite</span> is 0.44 ± 0.15 secondary neutrons per stopped negative muon, in good agreement with existing theoretical predictions. Cosmogenic isotope production by muons must be taken into account when dating young geomorphic surfaces, especially those created by excavation of only a few metres of overlying rock. Attention to isotope production by muons is also crucial to determining surface erosion rates accurately. Due to the deep penetration of muons compared to cosmic ray hadrons, the accumulation of muon-produced 36Cl is less sensitive to erosion than that of spallogenic 36Cl. Although production by muons at the surface is only a small fraction of production by spallation, the fraction of muon-produced 36Cl in rapidly eroding limestone surfaces can approach 50%. In such cases, erosion rates estimated using conventional models which attribute</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.H31D1214J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.H31D1214J"><span>Fracture-aperture alteration induced by <span class="hlt">calcite</span> precipitation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jones, T.; Detwiler, R. L.</p> <p>2013-12-01</p> <p>Mineral precipitation significantly alters the transport properties of fractured rock. Chemical solubility gradients that favor precipitation induce mineral growth, which decreases the local aperture and alters preferential flow paths. Understanding the resulting development of spatial heterogeneities is necessary to predict the evolution of transport properties in the subsurface. We present experimental results that quantify the relationship between mineral precipitation and aperture alteration in a transparent analog fracture, 7.62cm x 7.62cm, with a uniform aperture of ~200 μm. Prior to flow experiments, a pump circulated a super-saturated <span class="hlt">calcite</span> solution over the bottom glass, coating the glass surface with <span class="hlt">calcite</span>. This method of seeding resulted in clusters of <span class="hlt">calcite</span> crystals with large reactive surface area and provided micro-scale variability in the aperture field. A continuous flow syringe pump injected a reactive fluid into the fracture at 0.5 ml/min. The fluid was a mixture of sodium bicarbonate (NaHCO3, 0.02M) and calcium chloride (CaCl2 0.0004M) with a saturation index, Ω, of 8.51 with respect to <span class="hlt">calcite</span>. A strobed LED panel backlit the fracture and a high-resolution CCD camera monitored changes in transmitted light intensity. Light transmission techniques provided a quantitative measurement of fracture aperture over the flow field. Results from these preliminary experiments showed growth near the inlet of the fracture, with decreasing precipitation rates in the flow direction. Over a period of two weeks, the fracture aperture decreased by 17% within the first 4mm of the inlet. Newly precipitated <span class="hlt">calcite</span> bridged individual crystal clusters and smoothed the reacting surface. This observation is an interesting contradiction to the expectation of surface roughening induced by mineral growth. Additionally, the aperture decreased uniformly across the width of the fracture due to the initial aperture distribution. Future experiments of precipitation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1236222','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1236222"><span>Alkaline flocculation of <i>Phaeodactylum tricornutum</i> induced by brucite and <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Vandamme, Dries; Pohl, Philip I.; Beuckels, Annelies; Foubert, Imogen; Brady, Patrick Vane; Muylaert, Koenraad; Hewson, John C.</p> <p>2015-08-20</p> <p>Alkaline flocculation holds great potential as a low-cost harvesting method for <span class="hlt">marine</span> microalgae biomass production. Alkaline flocculation is induced by an increase in pH and is related to precipitation of calcium and magnesium salts. In this study, we used the diatom <i>Phaeodactylum tricornutum</i> as model organism to study alkaline flocculation of <span class="hlt">marine</span> microalgae cultured in seawater medium. Flocculation started when pH was increased to 10 and flocculation efficiency reached 90% when pH was 10.5, which was consistent with precipitation modeling for brucite or Mg(OH)<sub>2</sub>. Compared to freshwater species, more magnesium is needed to achieve flocculation (>7.5 mM). Zeta potential measurements suggest that brucite precipitation caused flocculation by charge neutralization. When calcium concentration was 12.5 mM, flocculation was also observed at a pH of 10. Furthermore, zeta potential remained negative up to pH 11.5, suggesting that precipitated <span class="hlt">calcite</span> caused flocculation by a sweeping coagulation mechanism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP51D..06F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP51D..06F"><span>Outside the pH box: Boron isotopes in synthetic <span class="hlt">calcite</span> precipitated under varying solution chemistry</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Farmer, J. R.; Uchikawa, J.; Penman, D. E.; Hoenisch, B.; Zeebe, R. E.</p> <p>2015-12-01</p> <p>Boron isotopic measurements (δ11B) in <span class="hlt">marine</span> carbonates are a powerful tool for reconstructing past ocean carbon chemistry and the carbon cycle. Boron systematics in <span class="hlt">marine</span> carbonates are rooted in the equilibrium dissociation of dissolved boron in seawater, but existing evidence from biogenic carbonates (corals, planktic and benthic foraminifers) suggests somewhat variable controls on boron concentration and δ11B. Synthetic precipitation experiments provide an opportunity to study boron systematics without biological interference, and recent studies (e.g., Uchikawa et al., 2015, GCA v150, 171-191) suggest that boron incorporation (measured as B/Ca ratios) into synthetic carbonates varies both with the elemental composition of experimental seawater and precipitation rate. Here we extend the geochemical characterization of synthetic <span class="hlt">calcite</span> by investigating the influences of changing solution chemistry (pH, [Ca2+], [DIC] and [B]) and precipitation rate on their boron isotopic composition. Our results will be evaluated in the context of carbonate precipitation rates, modes of boron incorporation, and changing seawater chemistry through geologic time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JCrGr.338..147F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JCrGr.338..147F"><span>The effect of sulfated polysaccharides on the crystallization of <span class="hlt">calcite</span> superstructures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fried, Ruth; Mastai, Yitzhak</p> <p>2012-01-01</p> <p><span class="hlt">Calcite</span> with unique morphology and uniform size has been successfully synthesized in the presence of classes of polysaccharides based on carrageenans. In the crystallization of <span class="hlt">calcite</span>, the choice of different carrageenans, (iota, lambda and kappa), as additives concedes systematic study of the influence of different chemical structures and particularly molecular charge on the formation of CaCO 3 crystals. The uniform <span class="hlt">calcite</span> superstructures are formed by assemblies and aggregation of <span class="hlt">calcite</span> crystals. The mechanism for the formation of <span class="hlt">calcite</span> superstructures was studied by a variety of techniques, SEM, TEM, XRD, time-resolved conductivity and light scattering measurements, focusing on the early stages of crystals' nucleation and aggregation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatMa..15..903K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatMa..15..903K"><span>Tuning hardness in <span class="hlt">calcite</span> by incorporation of amino acids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kim, Yi-Yeoun; Carloni, Joseph D.; Demarchi, Beatrice; Sparks, David; Reid, David G.; Kunitake, Miki E.; Tang, Chiu C.; Duer, Melinda J.; Freeman, Colin L.; Pokroy, Boaz; Penkman, Kirsty; Harding, John H.; Estroff, Lara A.; Baker, Shefford P.; Meldrum, Fiona C.</p> <p>2016-08-01</p> <p>Structural biominerals are inorganic/organic composites that exhibit remarkable mechanical properties. However, the structure-property relationships of even the simplest building unit--mineral single crystals containing embedded macromolecules--remain poorly understood. Here, by means of a model biomineral made from <span class="hlt">calcite</span> single crystals containing glycine (0-7 mol%) or aspartic acid (0-4 mol%), we elucidate the origin of the superior hardness of biogenic <span class="hlt">calcite</span>. We analysed lattice distortions in these model crystals by using X-ray diffraction and molecular dynamics simulations, and by means of solid-state nuclear magnetic resonance show that the amino acids are incorporated as individual molecules. We also demonstrate that nanoindentation hardness increased with amino acid content, reaching values equivalent to their biogenic counterparts. A dislocation pinning model reveals that the enhanced hardness is determined by the force required to cut covalent bonds in the molecules.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.148..343S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.148..343S"><span>U(VI) behaviour in hyperalkaline <span class="hlt">calcite</span> systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, Kurt F.; Bryan, Nicholas D.; Swinburne, Adam N.; Bots, Pieter; Shaw, Samuel; Natrajan, Louise S.; Mosselmans, J. Frederick W.; Livens, Francis R.; Morris, Katherine</p> <p>2015-01-01</p> <p>The behaviour of U(VI) in hyperalkaline fluid/<span class="hlt">calcite</span> systems was studied over a range of U(VI) concentrations (5.27 × 10-5 μM to 42.0 μM) and in two high pH systems, young and old synthetic cement leachate in batch sorption experiments. These systems were selected to be representative of young- (pH 13.3) and old-stage (pH 10.5) leachate evolution within a cementitious geological disposal facility. Batch sorption experiments, modelling, extended X-ray absorption fine structure spectroscopy, electron microscopy, small angle X-ray scattering and luminescence spectroscopy were used to define the speciation of U(VI) across the systems of study. At the lowest concentrations (5.27 × 10-5 μM 232U(VI)) significant U removal was observed for both old and young cement leachates, and this was successfully modelled using a first order kinetic adsorption modelling approach. At higher concentrations (>4.20 μM) in the young cement leachate, U(VI) showed no interaction with the <span class="hlt">calcite</span> surface over an 18 month period. Small angle X-ray scattering techniques indicated that at high U concentrations (42.0 μM) and after 18 months, the U(VI) was present in a colloidal form which had little interaction with the <span class="hlt">calcite</span> surface and consisted of both primary and aggregated particles with a radius of 7.6 ± 1.1 and 217 ± 24 Å, respectively. In the old cement leachate, luminescence spectroscopy identified two surface binding sites for U(VI) on <span class="hlt">calcite</span>: in the system with 0.21 μM U(VI), a liebigite-like Ca2UO2(CO3)3 surface complex was identified; at higher U(VI) concentrations (0.42 μM), a second binding site of undetermined coordination was identified. At elevated U(VI) concentrations (>2.10 μM) in old cement leachate, both geochemical data and luminescence spectroscopy suggested that surface mediated precipitation was controlling U(VI) behaviour. A focused ion beam mill was used to create a section across the U(VI) precipitate-<span class="hlt">calcite</span> interface. Transmission electron</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5438497','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5438497"><span>Interaction of copper with the surface of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Franklin, M.L.; Morse, J.W.</p> <p>1981-05-01</p> <p>The interaction of Cu ions in solution with the surface of <span class="hlt">calcite</span> has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto <span class="hlt">calcite</span> indicates that the process is rapid and strong in both distilled water and seawater. In distilled water, Cu uptake is directly proportional to the concentration of Cu in solution; Cu/sub s/ = K/sub s/Cu/sub 1/. This Cu/sub s/ dependence on Cu/sub 1/ is linear over the entire Cu concentration range studied (0.1 to 200 ..mu..M). Results do not indicate the formation of a precipitate of either malachite or copper carbonate. In seawater, the uptake of Cu is also directly proportional to the concentration of Cu/sub 1/ up to a limiting value of approximately 13 ..mu..M. The average value for K/sub s/ in seawater, 0.24 +- 0.06 (Cu/sub 1/ less than or equal to 13 ..mu..M), is approximately an order of magnitude less than in distilled water. This is probably the result of smaller Cu/sub 1/ activity coefficients and increased site competition by other ions in seawater. Attempts to increase the Cu/sub 1/ concentration above 13 ..mu..M resulted in the additional Cu being deposited on the surface of the <span class="hlt">calcite</span>. A possible explanation for this behavior is the formation of a precipitate of malachite on the <span class="hlt">calcite</span> surface. The value of K/sub s/ decreased slightly with increasing solid to solution ratios in seawater.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/15010163','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/15010163"><span>Variation in <span class="hlt">Calcite</span> Dissolution Rates: A Fundamental Problem?</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Arvidson, Rolf S.; Ertan, Inci E.; Amonette, James E.; Luttge, Andreas</p> <p>2003-05-01</p> <p>A comparison of published <span class="hlt">calcite</span> dissolution rates measured far from equilibrium at a pH of {approx} 6 and above shows well over an order of magnitude in variation. Recently published AFM step velocities extend this range further still. In an effort to understand the source of this variation, and to provide additional constraint from a new analytical approach, we have measured dissolution rates by vertical scanning interferometry. In areas of the <span class="hlt">calcite</span> cleavage surface dominated by etch pits, our measured dissolution rate is 10{sup 10.95} mol/cm{sup 2}/s (PCO{sub 2} 10{sup 3.41} atm, pH 8.82), 5 to {approx}100 times slower than rates published in bulk powder experiments, although similar to rates derived from AFM step velocities. On cleavage surfaces free of local etch pit development, dissolution is limited by a slow, ''global'' rate (10{sup 11.68} mol/cm{sup 2}/s). Although these differences confirm the importance of etch pit (defect) distribution as a controlling mechanism in <span class="hlt">calcite</span> dissolution, they also suggest that ''bulk'' <span class="hlt">calcite</span> dissolution rates observed in powder experiments may derive substantial enhancement from grain boundaries having high step and kink density. We also observed significant rate inhibition by introduction of dissolved manganese. At 2.0 {micro}M Mn, the rate diminished to 10{sup 12.4} mol/cm{sup 2}/s, and the well formed rhombic etch pits that characterized dissolution in pure solution were absent. These results are in good agreement with the pattern of manganese inhibition in published AFM step velocities, assuming a step density on smooth terraces of {approx} 9 {micro}m{sup -1}.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27502176','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27502176"><span>Magnesium-<span class="hlt">Calcite</span> Crystal Formation Mediated by the Thermophilic Bacterium Geobacillus thermoglucosidasius Requires Calcium and Endospores.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Murai, Rie; Yoshida, Naoto</p> <p>2016-11-01</p> <p>Fresh Geobacillus thermoglucosidasius cells grown on soybean-casein digest nutrient agar were inoculated as a parent colony 1 cm in diameter on the surface of an agar gel containing acetate and calcium ions (<span class="hlt">calcite</span>-promoting hydrogel) and incubated at 60 °C for 4 days, after which magnesium-<span class="hlt">calcite</span> single crystals of 50-130 µm in size formed within the parent colony. Addition of EDTA, polyacrylic acid or N,N-dicyclohexylcarbodiimide to the <span class="hlt">calcite</span>-forming hydrogel inhibited the parent colony from forming magnesium-<span class="hlt">calcite</span> crystals. Inoculation of G. thermoglucosidasius on <span class="hlt">calcite</span>-forming hydrogel containing 5 µM cadmium and 20 µM zinc resulted in a decrease in the sporulation rate from 55 to 7-8 %. Magnesium-<span class="hlt">calcite</span> synthesis decreased relative to the sporulation rate. G. thermoglucosidasius exhibited higher adsorption/absorbance of calcium than other Geobacillus sp. that do not mediate <span class="hlt">calcite</span> formation and higher levels of magnesium accumulation. Calcium ions contained in the <span class="hlt">calcite</span>-promoting hydrogel and magnesium ions concentrated in G. thermoglucosidasius cells serve as the elements for magnesium-<span class="hlt">calcite</span> synthesis. The observed decreases in sporulation rate and magnesium-<span class="hlt">calcite</span> formation support the hypothesis that endospores act as nuclei for the synthesis of magnesium-<span class="hlt">calcite</span> single crystals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018861','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018861"><span>Chemistry and petrography of <span class="hlt">calcite</span> in the KTB pilot borehole, Bavarian Oberpfalz, Germany</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Komor, S.C.</p> <p>1995-01-01</p> <p>The KTB pilot borehole in northeast Bavaria, Germany, penetrates 4000 m of gneiss, amphibolite, and subordinate calc-silicate, lamprophyre and metagabbro. There are three types of <span class="hlt">calcite</span> in the drilled section: 1) metamorphic <span class="hlt">calcite</span> in calc-silicate and marble; 2) crack-filling <span class="hlt">calcite</span> in all lithologies; and 3) replacement <span class="hlt">calcite</span> in altered minerals. Crack-filling and replacement <span class="hlt">calcite</span> postdate metamorphic <span class="hlt">calcite</span>. Multiple <span class="hlt">calcite</span> generations in individual cracks suggest that different generations of water repeatedly flowed through the same cracks. Crack-filling mineral assemblages that include <span class="hlt">calcite</span> originally formed at temperatures of 150-350??C. Presently, crack-filling <span class="hlt">calcite</span> is in chemical and isotopic equilibrium with saline to brackish water in the borehole at temperatures of ???120??C. The saline to brackish water contains a significant proportion of meteoric water. Re-equilibration of crack-filling <span class="hlt">calcite</span> to lower temperatures means that <span class="hlt">calcite</span> chemistry tells us little about water-rock interactions in the crystal section of temperatures higher than ~120??C. -from Author</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3623123','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3623123"><span>Geobacillus thermoglucosidasius Endospores Function as Nuclei for the Formation of Single <span class="hlt">Calcite</span> Crystals</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Murai, Rie</p> <p>2013-01-01</p> <p>Geobacillus thermoglucosidasius colonies were placed on an agar hydrogel containing acetate, calcium ions, and magnesium ions, resulting in the formation of single <span class="hlt">calcite</span> crystals (<span class="hlt">calcites</span>) within and peripheral to the plating area or parent colony. Microscopic observation of purified <span class="hlt">calcites</span> placed on the surface of soybean casein digest (SCD) nutrient medium revealed interior crevices from which bacterial colonies originated. <span class="hlt">Calcites</span> formed on the gel contained [1-13C]- and [2-13C]acetate, demonstrating that G. thermoglucosidasius utilizes carbon derived from acetate for <span class="hlt">calcite</span> formation. During <span class="hlt">calcite</span> formation, vegetative cells swam away from the parent colony in the hydrogel. Hard-agar hydrogel inhibited the formation of <span class="hlt">calcites</span> peripheral to the parent colony. The <span class="hlt">calcite</span> dissolved completely in 1 M HCl, with production of bubbles, and the remaining endospore-like particles were easily stained with Brilliant green dye. The presence of DNA and protein in <span class="hlt">calcites</span> was demonstrated by electrophoresis. We propose that endospores initiate the nucleation of <span class="hlt">calcites</span>. Endospores of G. thermoglucosidasius remain alive and encapsulated in <span class="hlt">calcites</span>. PMID:23455343</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24910209','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24910209"><span>Oxylipins and plant <span class="hlt">abiotic</span> stress resistance.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Savchenko, T V; Zastrijnaja, O M; Klimov, V V</p> <p>2014-04-01</p> <p>Oxylipins are signaling molecules formed enzymatically or spontaneously from unsaturated fatty acids in all aerobic organisms. Oxylipins regulate growth, development, and responses to environmental stimuli of organisms. The oxylipin biosynthesis pathway in plants includes a few parallel branches named after first enzyme of the corresponding branch as allene oxide synthase, hydroperoxide lyase, divinyl ether synthase, peroxygenase, epoxy alcohol synthase, and others in which various biologically active metabolites are produced. Oxylipins can be formed non-enzymatically as a result of oxygenation of fatty acids by free radicals and reactive oxygen species. Spontaneously formed oxylipins are called phytoprostanes. The role of oxylipins in biotic stress responses has been described in many published works. The role of oxylipins in plant adaptation to <span class="hlt">abiotic</span> stress conditions is less studied; there is also obvious lack of available data compilation and analysis in this area of research. In this work we analyze data on oxylipins functions in plant adaptation to <span class="hlt">abiotic</span> stress conditions, such as wounding, suboptimal light and temperature, dehydration and osmotic stress, and effects of ozone and heavy metals. Modern research articles elucidating the molecular mechanisms of oxylipins action by the methods of biochemistry, molecular biology, and genetics are reviewed here. Data on the role of oxylipins in stress signal transduction, stress-inducible gene expression regulation, and interaction of these metabolites with other signal transduction pathways in cells are described. In this review the general oxylipin-mediated mechanisms that help plants to adjust to a broad spectrum of stress factors are considered, followed by analysis of more specific responses regulated by oxylipins only under certain stress conditions. New approaches to improvement of plant resistance to <span class="hlt">abiotic</span> stresses based on the induction of oxylipin-mediated processes are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23036948','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23036948"><span>Evaluation of strengthening mechanisms in <span class="hlt">calcite</span> single crystals from mollusk shells.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kunitake, Miki E; Mangano, Lauren M; Peloquin, John M; Baker, Shefford P; Estroff, Lara A</p> <p>2013-02-01</p> <p>Biogenic single-crystal <span class="hlt">calcite</span> is often reported to be harder and tougher than geologic <span class="hlt">calcite</span> in the form of Iceland spar. However, the mechanistic origins of the superior mechanical properties of the biogenic materials are still debated. We investigate the hardness and modulus of biogenic <span class="hlt">calcite</span> from the prismatic layer of the mollusk Atrina rigida compared with a pure geologic <span class="hlt">calcite</span>, Iceland spar. On the {001} face, biogenic <span class="hlt">calcite</span> is found to be 50-70% harder than geologic <span class="hlt">calcite</span>. This range is due to the fact that changes in azimuthal angle of the indenter tip lead to a hardness variation of ∼20% in A. rigida but only ∼7% in Iceland spar. The higher hardness and increased anisotropy of biogenic <span class="hlt">calcite</span> could be accounted for by hardening mechanisms based on hindered dislocation motion rather than crack deflection.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21963207','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21963207"><span>Interactions of salicylic acid derivatives with <span class="hlt">calcite</span> crystals.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ukrainczyk, Marko; Gredičak, Matija; Jerić, Ivanka; Kralj, Damir</p> <p>2012-01-01</p> <p>Investigation of basic interactions between the active pharmaceutical compounds and calcium carbonates is of great importance because of the possibility to use the carbonates as a mineral carrier in drug delivery systems. In this study the mode and extent of interactions of salicylic acid and its amino acid derivates, chosen as pharmaceutically relevant model compounds, with <span class="hlt">calcite</span> crystals are described. Therefore, the crystal growth kinetics of well defined rhombohedral <span class="hlt">calcite</span> seed crystals in the systems containing salicylic acid (SA), 5-amino salicylic acid (5-ASA), N-salicyloil-l-aspartic acid (N-Sal-Asp) or N-salicyloil-l-glutamic acid (N-Sal-Glu), were investigated. The precipitation systems were of relatively low initial supersaturation and of apparently neutral pH. The data on the crystal growth rate reductions in the presence of the applied salicylate molecules were analyzed by means of Cabrera & Vermileya's, and Kubota & Mullin's models of interactions of the dissolved additives and crystal surfaces. The crystal growth kinetic experiments were additionally supported with the appropriate electrokinetic, spectroscopic and adsorption measurements. The Langmuir adsorption constants were determined and they were found to be in a good correlation with values obtained from crystal growth kinetic analyses. The results indicated that salicylate molecules preferentially adsorb along the steps on the growing <span class="hlt">calcite</span> surfaces. The values of average spacing between the adjacent salicylate adsorption active sites and the average distance between the neighboring adsorbed salicylate molecules were also estimated.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5322967','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5322967"><span><span class="hlt">Calcite</span> deposition at Miravalles geothermal field, Costa Rica</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Vaca, L.; Alvarado, A.; Corrales, R. )</p> <p>1989-01-01</p> <p>The <span class="hlt">calcite</span> deposition problem at Miravalles has been studied since it was observed in the first three wells drilled on the slopes of the Miravalles Volcano. Long-term tests have been carried out to study reservoir characteristics. The change in the production behavior of the wells with the restriction imposed by the deposited <span class="hlt">calcite</span> has been studied trying to evaluate and quantify the scaling problem. Work is being done on predictions of the deposition rate, location and distribution of the deposited mineral inside the wells. This work was compared with real data obtained from caliper logs of the wells before and after production. The feasibility of the first 55 MW power plant has been demonstrated. It was considered that the solution for the <span class="hlt">calcite</span> problem is the reaming during discharge of the wells trying at the same time to minimize the cleaning interventions with a new well design. It is believed, due to the thermodynamics and chemical characteristics of the extracted fluids, that it is possible to find a non-deposition zone which will permit the drilling of wells without a scaling problem.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17242744','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17242744"><span>Heterogeneous conversion of <span class="hlt">calcite</span> aerosol by nitric acid.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Preszler Prince, A; Grassian, V H; Kleiber, P; Young, M A</p> <p>2007-02-07</p> <p>The reaction of nitric acid with <span class="hlt">calcite</span> aerosol at varying relative humidities has been studied under suspended particle conditions in an atmospheric reaction chamber using infrared absorption spectroscopy. The reactant concentration in the chamber, as well as the appearance of gas phase products and surface adsorbed species, was spectroscopically monitored before and after mixing with CaCO(3) (<span class="hlt">calcite</span>) particles. The interaction with HNO(3) was found to lead to gas phase CO(2) evolution and increased water uptake due to heterogeneous conversion of the carbonate to particulate nitrate. The reaction was enhanced as the relative humidity of the system was increased, especially at relative humidities above the reported deliquescence point of particulate Ca(NO(3))(2). The measured reaction extent demonstrates that the total <span class="hlt">calcite</span> particulate mass is available for reaction with HNO(3) and the conversion process is not limited to the particle surface. The spectroscopy of the surface formed nitrate suggests a highly concentrated solution environment with a significant degree of ion pairing. The implications of the HNO(3) loss and the formation of the particulate nitrate product for atmospheric chemistry are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999Geo....27..347K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999Geo....27..347K"><span>Alternative origins for nannobacteria-like objects in <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kirkland, Brenda L.; Lynch, F. Leo; Rahnis, Michael A.; Folk, Robert L.; Molineux, Ian J.; McLean, Robert J. C.</p> <p>1999-04-01</p> <p>More than 40 <span class="hlt">calcite</span>-precipitation experiments were performed under sterile conditions in order to investigate the origins of 25 300 nm spherical-, rod-, and ovoid-shaped objects that have been widely interpreted as evidence of nanometer-scale life (i.e., nannobacteria). Individual experiments included the addition of soluble organic compounds, common species of eubacteria, or phage-induced eubacterial lysates. These experiments indicate that many of the nanometer-scale objects have inorganic or nonnannobacterial origins. In the precipitation experiments, <span class="hlt">calcite</span> formed euhedral crystals 50 800 nm in diameter and smaller (<50 nm) anhedral or rounded particles or protocrystals. The small anhedral or rounded solids resembled nannobacteria. The relative amount of anhedral or rounded <span class="hlt">calcite</span> was greatest in experiments with a dissolved organic component. These controlled experiments are in accord with observations that rounded nanometer-scale objects are more common in minerals formed in organic-rich environments. Bacterial fragments occur as rounded to irregularly shaped particles that included cell-wall fragments, expulsed cytoplasm, and relict capsules that also closely resembled nannobacteria. Acid etching of the large euhedral crystals produced in the precipitation experiments also resulted in the formation of nanometer-scale features that resembled nannobacteria in natural carbonates. The shapes of the etching artifacts vary as a function of the strength of the acid and the duration of etching. Much caution is advisable in interpreting the origin of rounded features <50 nm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeCoA.123..351V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeCoA.123..351V"><span>Earthworm-produced <span class="hlt">calcite</span> granules: A new terrestrial palaeothermometer?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Versteegh, Emma A. A.; Black, Stuart; Canti, Matthew G.; Hodson, Mark E.</p> <p>2013-12-01</p> <p>In this paper we show for the first time that <span class="hlt">calcite</span> granules, produced by the earthworm Lumbricus terrestris, and commonly recorded at sites of archaeological interest, accurately reflect temperature and soil water δ18O values. Earthworms were cultivated in an orthogonal combination of two different (granule-free) soils moistened by three types of mineral water and kept at three temperatures (10, 16 and 20 °C) for an acclimatisation period of three weeks followed by transfer to identical treatments and cultivation for a further four weeks. Earthworm-secreted <span class="hlt">calcite</span> granules were collected from the second set of soils. δ18O values were determined on individual <span class="hlt">calcite</span> granules (δ18Oc) and the soil solution (δ18Ow). The δ18Oc values reflect soil solution δ18Ow values and temperature, but are consistently enriched by 1.51 (± 0.12)‰ in comparison to equilibrium in synthetic carbonates. The data fit the equation 1000 ln α = [20.21 ± 0.92] (103 T-1) - [38.58 ± 3.18] (R2 = 0.95; n = 96; p < 0.0005). As the granules are abundant in modern soils, buried soils and archaeological contexts, and can be dated using U-Th disequilibria, the developed palaeotemperature relationship has enormous potential for application to Holocene and Pleistocene time intervals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25233226','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25233226"><span>Nucleation, growth and evolution of calcium phosphate films on <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Naidu, Sonia; Scherer, George W</p> <p>2014-12-01</p> <p>Marble, a stone composed of the mineral <span class="hlt">calcite</span>, is subject to chemically induced weathering in nature due to its relatively high dissolution rate in acid rain. To protect monuments and sculpture from corrosion, we are investigating the application of thin layers of hydroxyapatite (HAP) onto marble. The motivation for using HAP is its low dissolution rate and crystal and lattice compatibility with <span class="hlt">calcite</span>. A mild, wet chemical synthesis route, in which diammonium hydrogen phosphate salt was reacted with marble, alone and with cationic and anionic precursors under different reaction conditions, was used to produce inorganic HAP layers on marble. Nucleation and growth on the <span class="hlt">calcite</span> substrate was studied, as well as metastable phase evolution, using scanning electron microscopy, grazing incidence X-ray diffraction, and atomic force microscopy. Film nucleation was enhanced by surface roughness. The rate of nucleation and the growth rate of the film increased with cationic (calcium) and anionic (carbonate) precursor additions. Calcium additions also influenced phase formation, introducing a metastable phase (octacalcium phosphate) and a different phase evolution sequence.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20579928','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20579928"><span>Visualization of acoustic cavitation effects on suspended <span class="hlt">calcite</span> crystals.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wagterveld, R M; Boels, L; Mayer, M J; Witkamp, G J</p> <p>2011-01-01</p> <p>The acoustic cavitation (42,080 Hz, 7.1 W cm(-2) or 17 W) effects on suspended <span class="hlt">calcite</span> crystals, sized between 5 and 50 μm, have been visualized for the first time using high speed photography. High speed recordings with a duration of 1 s containing up to 300,000 frames per second, revealed the effect of cluster and streamer cavitation on several <span class="hlt">calcite</span> crystals. Cavitation clusters, evolved from cavitation inception and collapse, caused attrition, disruption of aggregates and deagglomeration, whereas streamer cavitation was observed to cause deagglomeration only. Cavitation on the surface gave the crystals momentum. However, it is shown that breakage of accelerated crystals by interparticle collisions is unrealistic because of their small sizes and low velocities. Crystals that were accelerated by bubble expansion, subsequently experienced a deceleration much stronger than expected from drag forces, upon bubble collapse. Experiments with pre-dried crystals seemed to support the current theory on bubble nucleation through the presence of pre-existing gas pockets. However, experiments with fully wetted crystals also showed the nucleation of bubbles on the crystal surface. Although microjet impingement on the crystal surface could not be directly visualized with high speed photography, scanning electron microscopy (SEM) analysis of irradiated <span class="hlt">calcite</span> seeds showed deep circular indentations. It was suggested that these indentations might be caused by shockwave induced jet impingement. Furthermore, the appearance of voluminous fragments with large planes of fracture indicated that acoustic cavitation can also cause the breakage of single crystal structures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5532821','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5532821"><span>Interaction of copper with the surface of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Franklin, M.L.; Morse, J.W.</p> <p>1981-12-01</p> <p>The interaction of Cu ions in solution with the surface of <span class="hlt">calcite</span> has been studied in a range of solutions from pure water to seawater. Observations of the uptake of Cu from solution onto <span class="hlt">calcite</span> indicates that the process is rapid and strong in both distilled water and seawater. In distilled water, Cu uptake is directly proportional to the concentration of Cu in solution; Cu/sub s/ = K/sub s/Cu/sub 1/. The average value for K/sub s/ is 3.5 +- 1.7. The Cu/sub s/ dependence on Cu/sub 1/ is linear over the entire Cu concentration range studied (0.1 to 200 ..mu..M). Results do not indicate the formation of a precipitate of either malachite or copper carbonate. A precipitate of the form Cu/sub x/Ca/sub 1-x/CO/sub 3/ may be deposited onto the <span class="hlt">calcite</span> surface in distilled water. The value of K/sub s/ in distilled water decreased sharply over the solid to solution ratio range of 0.1 to 2 g CaCO/sub 3/ 1/sup -1/. This was followed by a small change in K/sub s/ for solid to solution ratios in the range of 2 to 10 g CaCO/sub 3/ 1/sup -1/. In seawater, the uptake of Cu is also directly proportional to the concentration of Cu/sub 1/ up to a limiting value of approximately 13 ..mu..M. The average value for K/sub s/ in seawater, 0.24 +- 0.06 (Cu/sub 1/ less than or equal to 13 ..mu..M), is approximately an order of magnitude less than in distilled water. This is probably the result of smaller Cu/sub 1/ activity coefficients and increased site competition by other ions in seawater. Attempts to increase the Cu/sub 1/ concentration above 13 ..mu..M resulted in the additional Cu being deposited on the surface of the <span class="hlt">calcite</span>. A possible explanation for this behavior is the formation of a precipitate of malachite on the <span class="hlt">calcite</span> surface. The value of K/sub s/ decreased slightly with increasing solid to solution ratios in seawater.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28063520','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28063520"><span>Zeta potential of artificial and natural <span class="hlt">calcite</span> in aqueous solution.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Al Mahrouqi, Dawoud; Vinogradov, Jan; Jackson, Matthew D</p> <p>2017-02-01</p> <p>Despite the broad range of interest and applications, controls on <span class="hlt">calcite</span> surface charge in aqueous solution, especially at conditions relevant to natural systems, remain poorly understood. The primary data source to understand <span class="hlt">calcite</span> surface charge comprises measurements of zeta potential. Here we collate and review previous measurements of zeta potential on natural and artificial <span class="hlt">calcite</span> and carbonate as a resource for future studies, compare and contrast the results of these studies to determine key controls on zeta potential and where uncertainties remain, and report new measurements of zeta potential relevant to natural subsurface systems. The results show that the potential determining ions (PDIs) for the carbonate mineral surface are the lattice ions Ca(2+), Mg(2+) and CO3(2-). The zeta potential is controlled by the concentration-dependent adsorption of these ions within the Stern layer, primarily at the Outer Helmholtz Plane (OHP). Given this, the Iso-Electric Point (IEP) at which the zeta potential is zero should be expressed as pCa (or pMg). It should not be reported as pH, similar to most metal oxides. The pH does not directly control the zeta potential. Varying the pH whilst holding pCa constant yields constant zeta potential. The pH affects the zeta potential only by moderating the equilibrium pCa for a given CO2 partial pressure (pCO2). Experimental studies that appear to yield a systematic relationship between pH and zeta potential are most likely observing the relationship between pCa and zeta potential, with pCa responding to the change in pH. New data presented here show a consistent linear relationship between equilibrium pH and equilibrium pCa or pMg irrespective of sample used or solution ionic strength. The surface charge of <span class="hlt">calcite</span> is weakly dependent on pH, through protonation and deprotonation reactions that occur within a hydrolysis layer immediately adjacent to the mineral surface. The Point of Zero Charge (PZC) at which the surface</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3767548','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3767548"><span>Surface chemistry allows for <span class="hlt">abiotic</span> precipitation of dolomite at low temperature</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Roberts, Jennifer A.; Kenward, Paul A.; Fowle, David A.; Goldstein, Robert H.; González, Luis A.; Moore, David S.</p> <p>2013-01-01</p> <p>Although the mineral dolomite is abundant in ancient low-temperature sedimentary systems, it is scarce in modern systems below 50 °C. Chemical mechanism(s) enhancing its formation remain an enigma because <span class="hlt">abiotic</span> dolomite has been challenging to synthesize at low temperature in laboratory settings. Microbial enhancement of dolomite precipitation at low temperature has been reported; however, it is still unclear exactly how microorganisms influence reaction kinetics. Here we document the <span class="hlt">abiotic</span> synthesis of low-temperature dolomite in laboratory experiments and constrain possible mechanisms for dolomite formation. Ancient and modern seawater solution compositions, with identical pH and pCO2, were used to precipitate an ordered, stoichiometric dolomite phase at 30 °C in as few as 20 d. Mg-rich phases nucleate exclusively on carboxylated polystyrene spheres along with <span class="hlt">calcite</span>, whereas aragonite forms in solution via homogeneous nucleation. We infer that Mg ions are complexed and dewatered by surface-bound carboxyl groups, thus decreasing the energy required for carbonation. These results indicate that natural surfaces, including organic matter and microbial biomass, possessing a high density of carboxyl groups may be a mechanism by which ordered dolomite nuclei form. Although environments rich in organic matter may be of interest, our data suggest that sharp biogeochemical interfaces that promote microbial death, as well as those with high salinity may, in part, control carboxyl-group density on organic carbon surfaces, consistent with origin of dolomites from microbial biofilms, as well as hypersaline and mixing zone environments. PMID:23964124</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.B23D..06Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.B23D..06Z"><span><span class="hlt">Abiotic</span> Methane Synthesis: Caveats and New Results</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zou, R.; Sharma, A.</p> <p>2005-12-01</p> <p>The role of mineral interaction with geochemical fluids under hydrothermal conditions has invoked models of geochemical synthesis of organic molecules at deep crustal conditions. Since Thomas Gold's (1992) hypothesis of the possibility of an <span class="hlt">abiotic</span> organic synthesis, there have been several reports of hydrocarbon formation under high pressure and temperature conditions. Several previous experimental studies have recognized that small amounts of methane (and other light HC compounds) can be synthesized via catalysis by transition metals: Fe, Ni (Horita and Berndt, 1999 Science) and Cr (Foustavous and Seyfried, 2004 Science). In light of these pioneering experiments, an investigation of the feasibility of <span class="hlt">abiotic</span> methane synthesis at higher pressure conditions in deep geological setting and the possible role of catalysis warrants a closer look. We conducted three sets of experiments in hydrothermal diamond anvil cell using FeO nanopowder, CaCO 3 and water at 300° - 600° C and 0.5 - 5 GPa : (a) with stainless steel gasket, (b) gold-lined gasket, and (c) gold-lined gasket with added Fe and Ni nanopowder. The reactions were monitored in-situ using micro-Raman spectroscopy with 532nm and 632nm lasers. The solids phases were characterized in-situ using synchrotron X-ray diffraction at CHESS-Cornell and quenched products with an electron microprobe. Interestingly, a variable amount of hydrocarbon was observed only in runs with stainless steel gasket and with Fe, Ni nanoparticles. Experiments with gold-lined reactors did not show any hydrocarbon formation. Added high resolution microscopy of the products and their textural relationship within the diamond cell with Raman spectroscopy data show that the hydrocarbon (methane and other light fractions) synthesis is a direct result of transition metal catalysis, rather than wustite - calcium carbonate reaction as recently reported by Scott et al (2004, PNAS). The author will further present new results highlighting <span class="hlt">abiotic</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010cosp...38.3251D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010cosp...38.3251D"><span>Generation of RNA in <span class="hlt">abiotic</span> conditions.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>di Mauro, Ernesto</p> <p></p> <p>Generation of RNA in <span class="hlt">abiotic</span> conditions. Ernesto Di Mauro Dipartimento di Genetica Bi-ologia Molecolare, Universit` "Sapienza" Roma, Italy. a At least four conditions must be satisfied for the spontaneous generation of (pre)-genetic poly-mers: 1) availability of precursors that are activated enough to spontaneously polymerize. Preliminary studies showed that (a) nucleic bases and acyclonucleosides can be synthesized from formamide H2NCOH by simply heating with prebiotically available mineral catalysts [last reviewed in (1)], and that b) nucleic bases can be phosphorylated in every possible posi-tion [2'; 3'; 5'; cyclic 2',3'; cyclic 3',5' (2)]. The higher stability of the cyclic forms allows their accumulation. 2) A polymerization mechanism. A reaction showing the formation of RNA polymers starting from prebiotically plausible precursors (3',5' cyclic GMP and 3', 5'cyclic AMP) was recently reported (3). Polymerization in these conditions is thermodynamically up-hill and an equilibrium is attained that limits the maximum length of the polymer produced to about 40 nucleotides for polyG and 100 nucleotides for polyA. 3) Ligation of the synthesized oligomers. If this type of reaction could occur according to a terminal-joining mechanism and could generate canonical 3',5' phosphodiester bonds, exponential growth would be obtained of the generated oligomers. This type of reaction has been reported (4) , limited to homogeneous polyA sequences and leading to the production of polyA dimers and tetramers. What is still missing are: 4) mechanisms that provide the proof of principle for the generation of sequence complexity. We will show evidence for two mechanisms providing this proof of principle for simple complementary sequences. Namely: <span class="hlt">abiotic</span> sequence complementary-driven terminal ligation and sequence-complementary terminal growth. In conclusion: all the steps leading to the generation of RNA in <span class="hlt">abiotic</span> conditions are satisfied. (1) R Saladino, C Crestini, F</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011GeCoA..75.3956D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011GeCoA..75.3956D"><span>Oxygen isotopes in <span class="hlt">calcite</span> grown under cave-analogue conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Day, C. C.; Henderson, G. M.</p> <p>2011-07-01</p> <p>Speleothem oxygen isotopes and growth rates are valuable proxies for reconstructing climate history. There is debate, however, about the conditions that allow speleothems to grow in oxygen isotope equilibrium, and about the correct equilibrium fractionation factors. We report results from a series of carbonate growth experiments in karst-analogue conditions in the laboratory. The setup closely mimics natural processes (e.g. precipitation driven by CO 2-degassing, low ionic strength solution, thin solution film) but with a tight control on growth conditions (temperature, pCO 2, drip rate, <span class="hlt">calcite</span> saturation index and the composition of the initial solution). <span class="hlt">Calcite</span> is dissolved in water in a 20,000 ppmV pCO 2 environment. This solution is dripped onto glass plates (coated with seed-carbonate) in a lower pCO 2 environment (<2500 ppmV), where degassing leads to <span class="hlt">calcite</span> growth. Experiments were performed at 7, 15, 25 and 35 °C. At each temperature, <span class="hlt">calcite</span> was grown at three drip rates (2, 6 and 10 drips per minute) on separate plates. The mass of <span class="hlt">calcite</span> grown in these experiments varies with temperature ( T in K) and drip rate ( d_ r in drips min -1) according to the relationship daily growth mass = 1.254 + 1.478 ∗ 10 -9 ∗ e0.0679 T + ( e0.00248 T - 2) ∗ (-0.779 d_ r2 + 10.05 d_ r + 11.69). This relationship indicates a substantial increase of growth mass with temperature, a smaller influence of drip rate on growth mass at low temperature and a non-linear relationship between drip rate and growth mass at higher temperatures. Low temperature, fast dripping conditions are found to be the most favourable for reducing effects associated with evaporation and rapid depletion of the dissolved inorganic carbon reservoir (rapid DIC-depletion). The impact of evaporation can be large so caves with high relative humidity are also preferable for palaeoclimate reconstruction. Even allowing for the maximum offsets that may have been induced by evaporation and rapid DIC</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010877','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010877"><span>The sensitized luminescence of manganese-activated <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Schulman, J.H.; Evans, L.W.; Ginther, R.J.; Murata, K.J.</p> <p>1947-01-01</p> <p>Synthetic manganese-activated <span class="hlt">calcites</span> are shown to be practically inert to ultraviolet excitation in the range 2000-3500A, while they are luminescent under cathode-ray excitation. The incorporation of small amounts of an auxiliary impurity along with the manganese produces the strong response to ultraviolet radiation hitherto ascribed to CaCO3:Mn itself. Three such impurities have been studied: lead, thallium, and cerium. The first two induce excitation in the neighborhood of the mercury resonance line, while the cerium introduces a response principally to longer wave ultraviolet. The strong response to 2537A excitation shown by some natural <span class="hlt">calcites</span> is likewise found to be due to the presence of lead along with the manganese, rather than to the manganese alone. The data do not warrant ascribing the longer wave-length ultraviolet-excited luminescence of all natural <span class="hlt">calcites</span> to the action of an auxiliary impurity. The essential identity of the cathode-ray excited luminescence spectra of CaCO 3:Mn, CaCO3: (Pb+Mn), CaCO3:(Tl+Mn), and CaCO3:(Ce+Mn) with the 2537A-excited spectra of the latter three is evidence that the luminescent center in all cases is the manganese ion or the MnO6 group. It is shown that a "cascade" mechanism for the action of the auxiliary impurities, lead, thallium, and cerium, is incorrect; and that the phenomenon must be considered as a case of sensitized luminescence. Owing to the nature of cathode-ray excitation, the manganese activator can be excited by this agent even in the absence of a second impurity. For optical excitation, however, an absorption band for the ultraviolet must be established by building into the CaCO3:Mn a second impurity or "sensitizer.".</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4105460','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4105460"><span>Principles of <span class="hlt">Calcite</span> Dissolution in Human and Artificial Otoconia</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Walther, Leif Erik; Blödow, Alexander; Buder, Jana; Kniep, Rüdiger</p> <p>2014-01-01</p> <p>Human otoconia provide mechanical stimuli to deflect hair cells of the vestibular sensory epithelium for purposes of detecting linear acceleration and head tilts. During lifetime, the volume and number of otoconia are gradually reduced. In a process of degeneration morphological changes occur. Structural changes in human otoconia are assumed to cause vertigo and balance disorders such as benign paroxysmal positional vertigo (BPPV). The aim of this study was to investigate the main principles of morphological changes in human otoconia in dissolution experiments by exposure to hydrochloric acid, EDTA, demineralized water and completely purified water respectively. For comparison reasons artificial (biomimetic) otoconia (<span class="hlt">calcite</span> gelatin nanocomposits) and natural <span class="hlt">calcite</span> were used. Morphological changes were detected in time steps by the use of environmental scanning electron microscopy (ESEM). Under in vitro conditions three main dissolution mechanisms were identified as causing characteristic morphological changes of the specimen under consideration: pH drops in the acidic range, complex formation with calcium ions and changes of ion concentrations in the vicinity of otoconia. Shifts in pH cause a more uniform reduction of otoconia size (isotropic dissolution) whereas complexation reactions and changes of the ionic concentrations within the surrounding medium bring about preferred attacks at specific areas (anisotropic dissolution) of human and artificial otoconia. Owing to successive reduction of material, all the dissolution mechanisms finally produce fragments and remnants of otoconia. It can be assumed that the organic component of otoconia is not significantly attacked under the given conditions. Artificial otoconia serve as a suitable model system mimicking chemical attacks on biogenic specimens. The underlying principles of <span class="hlt">calcite</span> dissolution under in vitro conditions may play a role in otoconia degeneration processes such as BPPV. PMID:25048115</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4285730','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4285730"><span>Cell wall remodeling under <span class="hlt">abiotic</span> stress</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tenhaken, Raimund</p> <p>2015-01-01</p> <p>Plants exposed to <span class="hlt">abiotic</span> stress respond to unfavorable conditions on multiple levels. One challenge under drought stress is to reduce shoot growth while maintaining root growth, a process requiring differential cell wall synthesis and remodeling. Key players in this process are the formation of reactive oxygen species (ROS) and peroxidases, which initially cross-link phenolic compounds and glycoproteins of the cell walls causing stiffening. The function of ROS shifts after having converted all the peroxidase substrates in the cell wall. If ROS-levels remain high during prolonged stress, OH°-radicals are formed which lead to polymer cleavage. In concert with xyloglucan modifying enzymes and expansins, the resulting cell wall loosening allows further growth of stressed organs. PMID:25709610</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1985OrLi...15..115O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1985OrLi...15..115O"><span><span class="hlt">Abiotic</span> formation of oligonucleotides on basalt surfaces</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Otroshchenko, V. A.; Vasilyeva, N. V.; Kopilov, A. M.</p> <p>1985-06-01</p> <p>The complication and further evolution of <span class="hlt">abiotic</span> syntheses products occurred under environmental influences at the prebiological stage. From this point of view, the influence of some types of irradiation on the organic molecules adsorbed on the surfaces of volcanic rocks, appeared to be of great importance. In this connection, the effect of gamma rays on the AMP molecules adsorbed on mineral surfaces such as cinders and ashes has been studied. It has been shown that they can polymerize with the formation of oligonucleotides. The treatment of oligomers obtained by venom phosphodiesterase has shown that a polymeric product has mainly 3' 5' and 2' 5' bonds between nucleotides. The results obtained have been discussed from the evolutionary aspect.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6568348','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6568348"><span><span class="hlt">Calcite</span> dissolution: an in situ study in the Panama Basin</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Thunell, R.C.; Keir, R.S.; Honjo, S.</p> <p>1981-05-08</p> <p>The results of an in situ study of <span class="hlt">calcite</span> dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17739398','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17739398"><span><span class="hlt">Calcite</span> Dissolution: An in situ Study in the Panama Basin.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Thunell, R C; Keir, R S; Honjo, S</p> <p>1981-05-08</p> <p>The results of an in situ study of <span class="hlt">calcite</span> dissolution in the Panama Basin indicate that the rate of dissolution in the water column increases suddenly below a water depth of about 2800 meters. This coincides with the depth at which the calcium carbonate content of surface sediments begins to decrease rapidly or the sedimentary lysocline. Since this level of increased dissolution both in the water column and on the sea floor does not appear to be related to the transition from supersaturation to undersaturation with respect to carbonate, there may be a kinetic origin for the lysocline in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=64057&keyword=time+AND+management+AND+students&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=84846782&CFTOKEN=39205604','EPA-EIMS'); return false;" href="http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=64057&keyword=time+AND+management+AND+students&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=84846782&CFTOKEN=39205604"><span><span class="hlt">ABIOTIC</span> IN SITU TECHNOLOGIES FOR GROUNDWATER REMEDIATION CONFERENCE: PROCEEDINGS</span></a></p> <p><a target="_blank" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p></p> <p></p> <p>The USEPA conference on <span class="hlt">Abiotic</span> In Situ Technologies for Groundwater Remediation was held in Dallas, TX, 8/31-9/2/99. The goal of the meeting was to disseminate current information on <span class="hlt">abiotic</span> in situ groundwater treatment echnologies. Although much information is being provided a...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25757363','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25757363"><span>Improved <span class="hlt">abiotic</span> stress tolerance of bermudagrass by exogenous small molecules.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chan, Zhulong; Shi, Haitao</p> <p>2015-01-01</p> <p>As a widely used warm-season turfgrass in landscapes and golf courses, bermudagrass encounters multiple <span class="hlt">abiotic</span> stresses during the growth and development. Physiology analysis indicated that <span class="hlt">abiotic</span> stresses induced the accumulation of ROS and decline of photosynthesis, resulting in increased cell damage and inhibited growth. Proteomic and metabolomic approaches showed that antioxidant enzymes and osmoprotectant contents (sugar, sucrose, dehydrin, proline) were extensively changed under <span class="hlt">abiotic</span> stress conditions. Exogenous application of small molecules, such as ABA, NO, CaCl2, H2S, polyamine and melatonin, could effectively alleviate damages caused by multiple <span class="hlt">abiotic</span> stresses, including drought, salt, heat and cold. Based on high through-put RNA seq analysis, genes involved in ROS, transcription factors, hormones, and carbohydrate metabolisms were largely enriched. The data indicated that small molecules induced the accumulation of osmoprotectants and antioxidants, kept cell membrane integrity, increased photosynthesis and kept ion homeostasis, which protected bermudagrass from damages caused by <span class="hlt">abiotic</span> stresses.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4622623','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4622623"><span><span class="hlt">Abiotic</span> stresses induce different localizations of anthocyanins in Arabidopsis</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kovinich, Nik; Kayanja, Gilbert; Chanoca, Alexandra; Otegui, Marisa S; Grotewold, Erich</p> <p>2015-01-01</p> <p>Anthocyanins are induced in plants in response to <span class="hlt">abiotic</span> stresses such as drought, high salinity, excess light, and cold, where they often correlate with enhanced stress tolerance. Numerous roles have been proposed for anthocyanins induced during <span class="hlt">abiotic</span> stresses including functioning as ROS scavengers, photoprotectants, and stress signals. We have recently found different profiles of anthocyanins in Arabidopsis (Arabidopsis thaliana) plants exposed to different <span class="hlt">abiotic</span> stresses, suggesting that not all anthocyanins have the same function. Here, we discuss these findings in the context of other studies and show that anthocyanins induced in Arabidopsis in response to various <span class="hlt">abiotic</span> stresses have different localizations at the organ and tissue levels. These studies provide a basis to clarify the role of particular anthocyanin species during <span class="hlt">abiotic</span> stress. PMID:26179363</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70029040','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70029040"><span>The ubiquitous nature of accessory <span class="hlt">calcite</span> in granitoid rocks: Implications for weathering, solute evolution, and petrogenesis</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>White, A.F.; Schulz, M.S.; Lowenstern, J. B.; Vivit, D.V.; Bullen, T.D.</p> <p>2005-01-01</p> <p><span class="hlt">Calcite</span> is frequently cited as a source of excess Ca, Sr and alkalinity in solutes discharging from silicate terrains yet, no previous effort has been made to assess systematically the overall abundance, composition and petrogenesis of accessory <span class="hlt">calcite</span> in granitoid rocks. This study addresses this issue by analyzing a worldwide distribution of more than 100 granitoid rocks. <span class="hlt">Calcite</span> is found to be universally present in a concentration range between 0.028 to 18.8 g kg-1 (mean = 2.52 g kg-1). <span class="hlt">Calcite</span> occurrences include small to large isolated anhedral grains, fracture and cavity infillings, and sericitized cores of plagioclase. No correlation exists between the amount of <span class="hlt">calcite</span> present and major rock oxide compositions, including CaO. Ion microprobe analyses of in situ <span class="hlt">calcite</span> grains indicate relatively low Sr (120 to 660 ppm), negligible Rb and 87Sr/86Sr ratios equal to or higher than those of coexisting plagioclase. Solutes, including Ca and alkalinity produced by batch leaching of the granitoid rocks (5% CO2 in DI water for 75 d at 25??C), are dominated by the dissolution of <span class="hlt">calcite</span> relative to silicate minerals. The correlation of these parameters with higher <span class="hlt">calcite</span> concentrations decreases as leachates approach thermodynamic saturation. In longer term column experiments (1.5 yr), reactive <span class="hlt">calcite</span> becomes exhausted, solute Ca and Sr become controlled by feldspar dissolution and 87Sr/ 86Sr by biotite oxidation. Some accessory <span class="hlt">calcite</span> in granitoid rocks is related to intrusion into carbonate wall rock or produced by later hydrothermal alteration. However, the ubiquitous occurrence of <span class="hlt">calcite</span> also suggests formation during late stage (subsolidus) magmatic processes. This conclusion is supported by petrographic observations and 87Sr/86Sr analyses. A review of thermodynamic data indicates that at moderate pressures and reasonable CO2 fugacities, <span class="hlt">calcite</span> is a stable phase at temperatures of 400 to 700??C. Copyright ?? 2005 Elsevier Ltd.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA452109','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA452109"><span>A Laboratory Study Investigating the Feasibility of Applying <span class="hlt">Calcite</span>-Type Coatings to Segregated Ballast Tanks</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1981-08-01</p> <p>A LABORATORY STUDY INVESTIGATIING THE FEASIBILITY OF APPLYING <span class="hlt">CALCITE</span> -TYPE COATINGS TO SEGREGATED BALLAST TANKS AUGUST, 1981 Prepared by: Ocean City...Laboratory Study Investigating The Feasibility of Applying <span class="hlt">Calcite</span> -Type Coatings to Segregated Ballast Tanks 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c...Executive Summary List of Figures I. Conclusions II. Introduction III. Background-The Development and Use of <span class="hlt">Calcite</span> -Type Coatings IV. Experimental</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA451914','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA451914"><span>An Investigation of Possible Ways to Enhance the Deposition of <span class="hlt">Calcite</span>-Type Coatings</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>1984-01-01</p> <p>AN INVESTIGATION OF POSSIBLE WAYS TO ENHANCE THE DEPOSITION OF <span class="hlt">CALCITE</span> -TYPE COATINGS JANUARY 1984 Prepared by: OCEAN CITY RESEARCH CORP. in...Enhance The Deposition of <span class="hlt">Calcite</span> -Type Coatings 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e...City, New Jersey under the direction of Mr. The research study continued of applying <span class="hlt">calcite</span> -type coatings George A. Gehring, Jr. an to investigation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17807291','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17807291"><span><span class="hlt">Calcite</span>: rates of dissolution in a vertical profile in the central pacific.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Peterson, M N</p> <p>1966-12-23</p> <p>Rate of dissoluton of calcium carbonate (<span class="hlt">calcite</span>) was determined for a vertical profile 5000 mizeters deep in the central Pacific by measuring the loss of weight of optical <span class="hlt">calcite</span> spheres arrayed on a mooring. Waters of the Pacific are undersaturated in all but the upper several hundred meters. A sharp increase in the rate of dissolution occurs at a depth of about 3700 meters, which corresponds closely to the depth below which <span class="hlt">calcite</span> hias been dissolved from the sediments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21794973','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21794973"><span>Utilization of <span class="hlt">calcite</span> and waste glass for preparing construction materials with a low environmental load.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Maeda, Hirotaka; Imaizumi, Haruki; Ishida, Emile Hideki</p> <p>2011-11-01</p> <p>In this study, porous <span class="hlt">calcite</span> materials are hydrothermally treated at 200 °C using powder compacts consisting of <span class="hlt">calcite</span> and glasses composed of silica-rich soda-lime. After treatment, the glasses are converted into calcium aluminosilicate hydrates, such as zeolite phases, which increase their strength. The porosity and morphology of new deposits of hydrothermally solidified materials depend up on the chemical composition of glass. The use of <span class="hlt">calcite</span> and glass in the hydrothermal treatment plays an important role in the solidification of <span class="hlt">calcite</span> without thermal decomposition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JVGR..323...38M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JVGR..323...38M"><span><span class="hlt">Calcite</span> sealing in a fractured geothermal reservoir: Insights from combined EBSD and chemistry mapping</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McNamara, David D.; Lister, Aaron; Prior, Dave J.</p> <p>2016-09-01</p> <p>Fractures play an important role as fluid flow pathways in geothermal resources hosted in indurated greywacke basement of the Taupo Volcanic Zone, New Zealand, including the Kawerau Geothermal Field. Over time, the permeability of such geothermal reservoirs can be degraded by fracture sealing as minerals deposit out of transported geothermal fluids. <span class="hlt">Calcite</span> is one such fracture sealing mineral. This study, for the first time, utilises combined data from electron backscatter diffraction and chemical mapping to characterise <span class="hlt">calcite</span> vein fill morphologies, and gain insight into the mechanisms of <span class="hlt">calcite</span> fracture sealing in the Kawerau Geothermal Field. Two <span class="hlt">calcite</span> sealing mechanisms are identified 1) asymmetrical syntaxial growth of <span class="hlt">calcite</span>, inferred by the presence of single, twinned, <span class="hlt">calcite</span> crystals spanning the entire fracture width, and 2) 3D, interlocking growth of bladed vein <span class="hlt">calcite</span> into free space as determined from chemical and crystallographic orientation mapping. This study also identifies other potential uses of combined EBSD and chemical mapping to understand geothermal field evolution including, potentially informing on levels of fluid supersaturation from the study of <span class="hlt">calcite</span> lattice distortion, and providing information on a reservoir's history of stress, strain, and deformation through investigation of <span class="hlt">calcite</span> crystal deformation and twinning patterns.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JChPh.145h4702F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JChPh.145h4702F"><span>Anisotropic parallel self-diffusion coefficients near the <span class="hlt">calcite</span> surface: A molecular dynamics study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Franco, Luís F. M.; Castier, Marcelo; Economou, Ioannis G.</p> <p>2016-08-01</p> <p>Applying classical molecular dynamics simulations, we calculate the parallel self-diffusion coefficients of different fluids (methane, nitrogen, and carbon dioxide) confined between two { 10 1 ¯ 4 } <span class="hlt">calcite</span> crystal planes. We have observed that the molecules close to the <span class="hlt">calcite</span> surface diffuse differently in distinct directions. This anisotropic behavior of the self-diffusion coefficient is investigated for different temperatures and pore sizes. The ion arrangement in the <span class="hlt">calcite</span> crystal and the strong interactions between the fluid particles and the <span class="hlt">calcite</span> surface may explain the anisotropy in this transport property.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27586936','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27586936"><span>Anisotropic parallel self-diffusion coefficients near the <span class="hlt">calcite</span> surface: A molecular dynamics study.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Franco, Luís F M; Castier, Marcelo; Economou, Ioannis G</p> <p>2016-08-28</p> <p>Applying classical molecular dynamics simulations, we calculate the parallel self-diffusion coefficients of different fluids (methane, nitrogen, and carbon dioxide) confined between two {101̄4} <span class="hlt">calcite</span> crystal planes. We have observed that the molecules close to the <span class="hlt">calcite</span> surface diffuse differently in distinct directions. This anisotropic behavior of the self-diffusion coefficient is investigated for different temperatures and pore sizes. The ion arrangement in the <span class="hlt">calcite</span> crystal and the strong interactions between the fluid particles and the <span class="hlt">calcite</span> surface may explain the anisotropy in this transport property.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15562998','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15562998"><span>Modeling intrinsic bioremediation for interpret observable biogeochemical footprints of BTEX biodegradation: the need for fermentation and <span class="hlt">abiotic</span> chemical processes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Maurer, Max; Rittmann, Bruce E</p> <p>2004-12-01</p> <p>The intrinsic bioremediation of BTEX must be documented by the stoichiometric consumption and production of several other compounds, called 'footprints' of the biodegradation reaction. Although footprints of BTEX biodegradation are easy to identify from reaction stoichiometry, they can be confounded by the stepwise nature of the biodegradation reactions and by several <span class="hlt">abiotic</span> chemical reactions that also produce or consume the footprints. In order to track the footprints for BTEX biodegradation, the following reactions need to be considered explicitly: (1) fermentation and methanogenesis as separate processes, (2) precipitation and dissolution of <span class="hlt">calcite</span>, (3) precipitation and dissolution of amorphous iron monosulfide (FeS), (4) conversion of FeS into the thermodynamically stable pyrite (FeS2) with loss of sulfide and <span class="hlt">abiotic</span> formation of H2, and (5) reductive dissolution of solid iron(III) by oxidation of sulfide. We critically review the research that underlies why these mechanisms must be included and how to describe them quantitatively. A companion manuscript develops and applies a mathematical model that includes these reactions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/884762','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/884762"><span>Acceleration of <span class="hlt">calcite</span> kinetics by abalone nacre proteins</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Fu, G; Qiu, S R; Orme, C A; Morse, D E; De Yoreo, J J</p> <p>2005-06-09</p> <p>The fascinating shapes and hierarchical designs of biomineralized structures have long been an inspiration to materials scientists because of the potential they suggest for biomolecular control over synthesis of crystalline materials. One prevailing view is that mineral-associated macromolecules are responsible for initiating and stabilizing non-equilibrium crystal polymorphs and morphologies through interactions between anionic moieties and cations in solution or at mineral surfaces. Indeed, numerous studies have demonstrated that bio-organic additives can dramatically alter crystal shapes and growth-rates in vitro. However, previous molecular-scale studies revealing mechanisms of growth modification focused on small molecules such as amino acids or peptides and always observed growth inhibition. In contrast, studies using full proteins were non-quantitative and underlying sources of growth modification were ill-defined. Here we investigate interactions between proteins isolated from abalone shell nacre and growing surfaces of <span class="hlt">calcite</span>. We find that these proteins significantly accelerate the molecular-scale kinetics and, though much larger than atomic steps, alter growth morphology through step-specific interactions that lower their free energies. We propose that these proteins act as surfactants to promote ion attachment at <span class="hlt">calcite</span> surfaces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1087499','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1087499"><span>Upscaling <span class="hlt">Calcite</span> Growth Rates from the Mesoscale to the Macroscale</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bracco, Jacquelyn N.; Stack, Andrew G.; Steefel, Carl I.</p> <p>2013-07-02</p> <p>Quantitative prediction of mineral reaction rates in the subsurface remains a daunting task partly because a key parameter for macroscopic models, the reactive site density, is poorly constrained. Here we report atomic force microscopy (AFM) measurements on the <span class="hlt">calcite</span> surface of monomolecular step densities, treated as equivalent to the reactive site density, as a function of aqueous calcium-to-carbonate ratio and saturation index. Data for the obtuse step orientation are combined with existing step velocity measurements to generate a model that predicts overall macroscopic <span class="hlt">calcite</span> growth rates. The model is quantitatively consistent with several published macroscopic rates under a range of alkaline solution conditions, particularly for two of the most comprehensive data sets without the need for additional fit parameters. The model reproduces peak growth rates and its functional form is simple enough to be incorporated into reactive transport or other macroscopic models designed for predictions in porous media. However, it currently cannot model equilibrium, pH effects, and may overestimate rates at high aqueous calcium-to-carbonate ratios. The discrepancies in rates at high calcium-to-carbonate ratios may be due to differences in pre-treatment, such as exposing the seed material to SI 1.0 to generate/develop growth hillocks, or other factors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015APS..SHK.U2001T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015APS..SHK.U2001T"><span>Anisotropic Transverse Stress in <span class="hlt">Calcite</span> and Sapphire Measured Using Birefringence</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tear, Gareth R.; Chapman, David J.; Eakins, Daniel E.; Proud, William G.</p> <p>2015-06-01</p> <p>Many significant geological minerals have anisotropic crystal structures leading to material properties that are anisotropic, including compressive elastic behaviour. A non-invasive approach to investigate the directional dependence of transverse stress in these materials during shock compression would supplement current understanding. As many geological minerals are transparent and hence optically anisotropic, measuring the change in birefringence induced by transverse stress in the material offers the possibility of a fast, non-invasive approach to probe transverse behaviour. Shock compression experiments have been performed on a-cut <span class="hlt">calcite</span> and a-cut sapphire for strain rates of order 105 s-1 and up to longitudinal stresses of 2 GPa for <span class="hlt">calcite</span> and 12 GPa for sapphire. We present measured changes in birefringence for these materials under shock compression, comparing with current and past literature as well as an in house optical model. The authors would like to thank Mr Steve Johnson and Mr David Pittman for technical support. The Institute of Shock Physics acknowledges the continued support of AWE and Imperial College London.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3730695','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3730695"><span>Crystallographic orientation inhomogeneity and crystal splitting in biogenic <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Checa, Antonio G.; Bonarski, Jan T.; Willinger, Marc G.; Faryna, Marek; Berent, Katarzyna; Kania, Bogusz; González-Segura, Alicia; Pina, Carlos M.; Pospiech, Jan; Morawiec, Adam</p> <p>2013-01-01</p> <p>The <span class="hlt">calcitic</span> prismatic units forming the outer shell of the bivalve Pinctada margaritifera have been analysed using scanning electron microscopy–electron back-scatter diffraction, transmission electron microscopy and atomic force microscopy. In the initial stages of growth, the individual prismatic units are single crystals. Their crystalline orientation is not consistent but rather changes gradually during growth. The gradients in crystallographic orientation occur mainly in a direction parallel to the long axis of the prism, i.e. perpendicular to the shell surface and do not show preferential tilting along any of the <span class="hlt">calcite</span> lattice axes. At a certain growth stage, gradients begin to spread and diverge, implying that the prismatic units split into several crystalline domains. In this way, a branched crystal, in which the ends of the branches are independent crystalline domains, is formed. At the nanometre scale, the material is composed of slightly misoriented domains, which are separated by planes approximately perpendicular to the c-axis. Orientational gradients and splitting processes are described in biocrystals for the first time and are undoubtedly related to the high content of intracrystalline organic molecules, although the way in which these act to induce the observed crystalline patterns is a matter of future research. PMID:23804442</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70011987','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70011987"><span>Crystal growth of <span class="hlt">calcite</span> from calcium bicarbonate solutions at constant PCO2 and 25°C: a test of a <span class="hlt">calcite</span> dissolution model</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Reddy, Michael M.; Plummer, L. Neil; Busenberg, E.</p> <p>1981-01-01</p> <p>A highly reproducible seeded growth technique was used to study <span class="hlt">calcite</span> crystallization from calcium bicarbonate solutions at 25°C and fixed carbon dioxide partial pressures between 0.03 and 0.3 atm. The results are not consistent with empirical crystallization models that have successfully described <span class="hlt">calcite</span> growth at low PCO2 (< 10−3 atm). Good agreement was found between observed crystallization rates and those calculated from the <span class="hlt">calcite</span> dissolution rate law and mechanism proposed by Plummer et al. (1978).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1815535S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1815535S"><span>Bony fish and their contribution to <span class="hlt">marine</span> inorganic carbon cycling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Salter, Michael; Perry, Chris; Wilson, Rod; Harborne, Alistair</p> <p>2016-04-01</p> <p>Conventional understanding of the <span class="hlt">marine</span> inorganic carbon cycle holds that CaCO3 (mostly as low Mg-<span class="hlt">calcite</span> and aragonite) precipitates in the upper reaches of the ocean and sinks to a point where it either dissolves or is deposited as sediment. Thus, it plays a key role controlling the distribution of DIC in the oceans and in regulating their capacity to absorb atmospheric CO2. However, several aspects of this cycle remain poorly understood and have long perplexed oceanographers, such as the positive alkalinity anomaly observed in the upper water column of many of the world's oceans, above the aragonite and <span class="hlt">calcite</span> saturation horizons. This anomaly would be explained by extensive dissolution of a carbonate phase more soluble than low Mg-<span class="hlt">calcite</span> or aragonite, but major sources for such phases remain elusive. Here we highlight <span class="hlt">marine</span> bony fish as a potentially important primary source of this 'missing' high-solubility CaCO3. Precipitation of CaCO3 takes place within the intestines of all <span class="hlt">marine</span> bony fish as part of their normal physiological functioning, and global production models suggest it could account for up to 45 % of total new <span class="hlt">marine</span> CaCO3 production. Moreover, high Mg-<span class="hlt">calcite</span> containing >25 % mol% MgCO3 - a more soluble phase than aragonite - is a major component of these precipitates. Thus, fish CaCO3 may at least partially explain the alkalinity anomaly in the upper water column. However, the issue is complicated by the fact that carbonate mineralogy actually varies among fish species, with high Mg-<span class="hlt">calcite</span> (HMC), low Mg-<span class="hlt">calcite</span> (LMC), aragonite, and amorphous calcium carbonate (ACC) all being common products. Using data from 22 Caribbean fish species, we have generated a novel production model that resolves phase proportions. We evaluate the preservation/dissolution potential of these phases and consider potential implications for <span class="hlt">marine</span> inorganic carbon cycling. In addition, we consider the dramatic changes in fish biomass structure that have resulted</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009IJAsB...8..193P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009IJAsB...8..193P"><span>Experimental evidence for the global acidification of surface ocean at the Cretaceous-Palaeogene boundary: the biogenic <span class="hlt">calcite</span>-poor spherule layers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Premović, Pavle I.</p> <p>2009-07-01</p> <p>The massive amount of impact-generated atmospheric CO2 at the Cretaceous-Palaeogene boundary (KPB) would have accumulated globally in the surface ocean, leading to acidification and CaCO3 undersaturation. These chemical changes would have caused a crisis of biocalcification of calcareous plankton and enhanced dissolution of their shells; these factors together may have played a crucial role in forming the biogenic <span class="hlt">calcite</span>-poor KPB spherule layers observed at numerous oceanic sites and <span class="hlt">marine</span> (now on land) sites in Europe and Africa. Experimental data and observations indicate that the deposition spherule layer probably lasted only a few decades at most.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.3783R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.3783R"><span>Interactions of arsenic with <span class="hlt">calcite</span> surfaces revealed by in-situ nanoscale imaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Renard, Francois; Putnis, Christine; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion; Hövelmann, Jörn; Sarret, Géraldine</p> <p>2015-04-01</p> <p>Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments <span class="hlt">calcite</span> may play an important role in arsenic solubility and transfer in water. Arsenic-<span class="hlt">calcite</span> interactions remain controversial, especially for As(III) which was proposed to be either incorporated as such, or as As(V) after oxidation. Here, we provide the first time-lapse in-situ study of <span class="hlt">calcite</span> dissolution and growth in the presence of solutions with various amounts of As(III) or As(V). This was performed at room temperature and pH range 6-9 using a flow through cell connected to an atomic force microscope (AFM), to study the evolution of the (10-14) <span class="hlt">calcite</span> cleavage surface morphology. Reaction products were then characterized by Raman spectroscopy. In parallel, co-precipitation experiments with either As(III) or As(V) were performed in batch reactors, and the speciation of arsenic in the resulting solids was studied by X-ray absorption spectroscopy (XAS). For As(V), AFM results showed that it interacts strongly with the <span class="hlt">calcite</span> surface, and XAS results showed that As(V) was mostly incorporated in the <span class="hlt">calcite</span> structure. For As(III), AFM results showed much less impact on <span class="hlt">calcite</span> growth and dissolution and less incorporation was observed. This was confirmed by XAS results that indicate that As(III) was partly oxidized into As(V) before being incorporated into <span class="hlt">calcite</span> and the resulting <span class="hlt">calcite</span> contained 36% As(III) and 64% As(V). All these experimental results confirm that As(V) has a much stronger interaction with <span class="hlt">calcite</span> than As(III) and that <span class="hlt">calcite</span> may represent an important reservoir for arsenic in various geological environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996GeCoA..60.4417V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996GeCoA..60.4417V"><span>Paleotransport of lanthanides and strontium recorded in <span class="hlt">calcite</span> compositions from tuffs at Yucca Mountain, Nevada, USA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vaniman, David T.; Chipera, Steve J.</p> <p>1996-11-01</p> <p>Secondary <span class="hlt">calcite</span> occurs in both saturated and unsaturated hydrologic zones (SZ and UZ, respectively) in the tuffs at Yucca Mountain, Nevada, USA. In the upper UZ, the major constituents of the <span class="hlt">calcite</span> crystal structure (C, O) have surface origins. At greater depth there is a “barren zone,” straddling the water table, where <span class="hlt">calcite</span> is rare and mixing of surface and subsurface sources may occur. Deep in the SZ, distinctive Mn <span class="hlt">calcites</span> reflect deep sources, including Ca released as analcime or albite formed and carbonates derived from underlying Paleozoic rocks. In the UZ and in the barren zone, above the deep Mn <span class="hlt">calcites</span>, variations in <span class="hlt">calcite</span> lanthanide chemistry can be used to distinguish rhyolitic from quartz-latitic sources. Lanthanide ratios and Sr contents of <span class="hlt">calcites</span> record the chemical evolution of waters flowing through the UZ and upper SZ. Variations in <span class="hlt">calcite</span> chemistry in the UZ and in the barren zone show that (1) Sr, which is readily exchanged with clays or zeolites, is essentially removed from some flowpaths that are in contact with these minerals and (2) traces of Mn oxides found in the tuffs have a significant effect on groundwater chemistry in the UZ and in the barren zone by removing almost all Ce from solution (evidenced by characteristic Ce depletions in <span class="hlt">calcite</span> throughout this zone). Extreme Ce removal may be a result of Ce oxidation (Ce 3+→ Ce 4+) at the surfaces of some Mn oxides, particularly rancieite. Higher Sr contents and lack of Ce depletions in the deeper Mn <span class="hlt">calcites</span> reflect different ages, origins, and transport systems. The <span class="hlt">calcite</span> record of lanthanide and Sr transport in the UZ shows that minor minerals (clays and zeolites) and even trace minerals (Mn oxides) will affect the compositions of groundwaters that flow over distances greater than a few tens of meters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1213531','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1213531"><span>Kinetics and Mechanisms of <span class="hlt">Calcite</span> Reactions with Saline Waters</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gorman, Brian P</p> <p>2015-09-02</p> <p>Project Description: The general objective of the proposed research is to determine the kinetics and mechanisms of <span class="hlt">calcite</span> reactions with saline waters over a wide range of saline water composition, pCO<sub>2</sub>, and modest ranges in T and P. This will be accomplished by studying both reaction rates and solubility from changes in solution chemistry, and making nanoscale observations of <span class="hlt">calcite</span> precipitate surface morphology and composition at the micro-to-nano-scale to provide an understanding of controlling reaction mechanisms and pathways. The specific objectives necessary to reach the general objective are: a) determination of how pCO<sub>2</sub>, Ca<sup>2+</sup>, ionic strength and “foreign” ions influence reaction rates; and b) investigate the influence of these parameters on apparent kinetic solubility from dissolution and precipitation reactions. This information will clearly be central to the construction of reliable reaction-transport models to predict reservoir and formation response to increased CO<sub>2</sub> in saline waters. This program was initially collaborative with John Morse at Texas A&M, however his passing shortly after the beginning of this program resulted in abbreviated research time and effort. Summary of Results: Early studies using electron microscopy and spectroscopy indicated that carbonate precipitation from natural seawater (NSW) conditions onto aragonite substrates was mediated by a surface amorphous calcium carbonate layer. It was hypothesized that this ACC layer (observed after < 5days reaction time) was responsible for the abnormal reaction kinetics and also served as a metastable seed layer for growth of epitaxial aragonite. Further studies of the ACC formation mechanism indicated a strong dependence on the Mg concentration in solution. Subsequent studies at shorter times (10 hrs) on <span class="hlt">calcite</span> substrates and in a wide range of supersaturation conditions did not indicate any ACC layer. Instead, an epitaxial layer by layer</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3430256','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3430256"><span>Recent Molecular Advances on Downstream Plant Responses to <span class="hlt">Abiotic</span> Stress</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>dos Reis, Sávio Pinho; Lima, Aline Medeiros; de Souza, Cláudia Regina Batista</p> <p>2012-01-01</p> <p><span class="hlt">Abiotic</span> stresses such as extremes of temperature and pH, high salinity and drought, comprise some of the major factors causing extensive losses to crop production worldwide. Understanding how plants respond and adapt at cellular and molecular levels to continuous environmental changes is a pre-requisite for the generation of resistant or tolerant plants to <span class="hlt">abiotic</span> stresses. In this review we aimed to present the recent advances on mechanisms of downstream plant responses to <span class="hlt">abiotic</span> stresses and the use of stress-related genes in the development of genetically engineered crops. PMID:22942725</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=pr+AND+today&pg=2&id=ED055793','ERIC'); return false;" href="http://eric.ed.gov/?q=pr+AND+today&pg=2&id=ED055793"><span><span class="hlt">Marine</span> Careers.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Gordon, Bernard L.</p> <p></p> <p>The five papers in this publication on <span class="hlt">marine</span> careers were selected so that science teachers, guidance councilors, and students could benefit from the experience and knowledge of individuals active in <span class="hlt">marine</span> science. The areas considered are indicated by the titles: Professional Careers in <span class="hlt">Marine</span> Science with the Federal Government, <span class="hlt">Marine</span> Science…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2835953','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2835953"><span>Polyamines and <span class="hlt">abiotic</span> stress tolerance in plants</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Gill, Sarvajeet Singh</p> <p>2010-01-01</p> <p>Environmental stresses including climate change, especially global warming, are severely affecting plant growth and productivity worldwide. It has been estimated that two-thirds of the yield potential of major crops are routinely lost due to the unfavorable environmental factors. On the other hand, the world population is estimated to reach about 10 billion by 2050, which will witness serious food shortages. Therefore, crops with enhanced vigour and high tolerance to various environmental factors should be developed to feed the increasing world population. Maintaining crop yields under adverse environmental stresses is probably the major challenge facing modern agriculture where polyamines can play important role. Polyamines (PAs)(putrescine, spermidine and spermine) are group of phytohormone-like aliphatic amine natural compounds with aliphatic nitrogen structure and present in almost all living organisms including plants. Evidences showed that polyamines are involved in many physiological processes, such as cell growth and development and respond to stress tolerance to various environmental factors. In many cases the relationship of plant stress tolerance was noted with the production of conjugated and bound polyamines as well as stimulation of polyamine oxidation. Therefore, genetic manipulation of crop plants with genes encoding enzymes of polyamine biosynthetic pathways may provide better stress tolerance to crop plants. Furthermore, the exogenous application of PAs is also another option for increasing the stress tolerance potential in plants. Here, we have described the synthesis and role of various polyamines in <span class="hlt">abiotic</span> stress tolerance in plants. PMID:20592804</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3121982','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3121982"><span><span class="hlt">Abiotic</span> stress and the plant circadian clock</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Sanchez, Alfredo; Shin, Jieun</p> <p>2011-01-01</p> <p>In this review, we focus on the interaction between the circadian clock of higher plants to that of metabolic and physiological processes that coordinate growth and performance under a predictable, albeit changing environment. In this, the phytochrome and cryptochrome photoreceptors have shown to be important, but not essential for oscillator control under diurnal cycles of light and dark. From this foundation, we will examine how emerging findings have firmly linked the circadian clock, as a central mediator in the coordination of metabolism, to maintain homeostasis. This occurs by oscillator synchronization of global transcription, which leads to a dynamic control of a host of physiological processes. These include the determination of the levels of primary and secondary metabolites, and the anticipation of future environmental stresses, such as mid-day drought and midnight coldness. Interestingly, metabolic and stress cues themselves appear to feedback on oscillator function. In such a way, the circadian clock of plants and <span class="hlt">abiotic</span>-stress tolerance appear to be firmly interconnected processes. PMID:21325898</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996JCrGr.163..434G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996JCrGr.163..434G"><span>Struvite and <span class="hlt">calcite</span> crystallization induced by cellular membranes of Myxococcus xanthus</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>González-Muñoz, Ma Teresa; Omar, Nabil Ben; Martínez-Cañamero, Magdalena; Rodríguez-Gallego, Manuel; Galindo, Alberto López; Arias, JoséMa</p> <p>1996-06-01</p> <p>In this work we have proved that struvite and <span class="hlt">calcite</span> crystals can be obtained in the presence of the cellular membrane fraction of Myxococcus xanthus, when appropriate supersaturated solutions are used. Probably, the negative charged points of the external side of the cellular structures could reduce the metastability field of struvite and <span class="hlt">calcite</span>, acting as heterogeneous nuclei of crystallization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6458514','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6458514"><span>Carbon and oxygen isotopes in apatite CO/sub 2/ and co-existing <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kolodny, Y.; Kaplan, I. R.</p> <p>1981-04-01</p> <p>Carbon and oxygen isotopes were analyzed in carbonate apatite CO/sub 2/ and in co-existing <span class="hlt">calcite</span>. Both C and O in apatite CO/sub 2/ are enriched in the respective light isotopes relative to <span class="hlt">calcite</span>. These results confirm the proposition that carbonate is part of the apatite structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3946587','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3946587"><span>Biotic Control of Skeletal Growth by Scleractinian Corals in Aragonite–<span class="hlt">Calcite</span> Seas</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Higuchi, Tomihiko; Fujimura, Hiroyuki; Yuyama, Ikuko; Harii, Saki; Agostini, Sylvain; Oomori, Tamotsu</p> <p>2014-01-01</p> <p>Modern scleractinian coral skeletons are commonly composed of aragonite, the orthorhombic form of CaCO3. Under certain conditions, modern corals produce <span class="hlt">calcite</span> as a secondary precipitate to fill pore space. However, coral construction of primary skeletons from <span class="hlt">calcite</span> has yet to be demonstrated. We report a <span class="hlt">calcitic</span> primary skeleton produced by the modern scleractinian coral Acropora tenuis. When uncalcified juveniles were incubated from the larval stage in seawater with low mMg/Ca levels, the juveniles constructed <span class="hlt">calcitic</span> crystals in parts of the primary skeleton such as the septa; the deposits were observable under Raman microscopy. Using scanning electron microscopy, we observed different crystal morphologies of aragonite and <span class="hlt">calcite</span> in a single juvenile skeleton. Quantitative analysis using X-ray diffraction showed that the majority of the skeleton was composed of aragonite even though we had exposed the juveniles to manipulated seawater before their initial crystal nucleation and growth processes. Our results indicate that the modern scleractinian coral Acropora mainly produces aragonite skeletons in both aragonite and <span class="hlt">calcite</span> seas, but also has the ability to use <span class="hlt">calcite</span> for part of its skeletal growth when incubated in <span class="hlt">calcite</span> seas. PMID:24609012</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19800060500&hterms=Cactus&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DCactus','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19800060500&hterms=Cactus&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DCactus"><span>Shock-induced effects in <span class="hlt">calcite</span> from Cactus Crater</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Vizgirda, J.; Ahrens, T. J.; Tsay, F.-D.</p> <p>1980-01-01</p> <p>The paper discusses shock metamorphism of <span class="hlt">calcite</span> from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16240102','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16240102"><span>On the origin of fiber <span class="hlt">calcite</span> crystals in moonmilk deposits.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Cañaveras, Juan Carlos; Cuezva, Soledad; Sanchez-Moral, Sergio; Lario, Javier; Laiz, Leonila; Gonzalez, Juan Miguel; Saiz-Jimenez, Cesareo</p> <p>2006-01-01</p> <p>In this study, we show that moonmilk subaerial speleothems in Altamira Cave (Spain) consist of a network of fiber <span class="hlt">calcite</span> crystals and active microbial structures. In Altamira moonmilks, the study of the typology and distribution of fiber crystals, extracellular polymeric substances, and microorganisms allowed us to define the initial stages of fiber crystal formation in recent samples as well as the variations in the microstructural arrangement in more evolved stages. Thus, we have been able to show the existence of a relationship among the different types of fiber crystals and their origins. This allowed us to outline a model that illustrates the different stages of formation of the moonmilk, developed on different substrata, concluding that microbes influence physicochemical precipitation, resulting in a variety of fiber crystal morphologies and sizes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4759641','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4759641"><span><span class="hlt">Calcite</span> orientations and composition ranges within teeth across Echinoidea</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Stock, Stuart R.; Ignatiev, Konstantin; Lee, Peter L.; Almer, Jonathan D.</p> <p>2016-01-01</p> <p>Sea urchin’s teeth from four families of order Echinoida and from orders Temnopleuroida, Arbacioida and Cidaroida were studied with synchrotron x-ray diffraction. The high and very high Mg <span class="hlt">calcite</span> phases of the teeth, i.e. the first and second stage mineral constituents, respectively, have the same crystallographic orientations. The co-orientation of first and second stage mineral, which the authors attribute to epitaxy, extends across the phylogenic width of the extant regular sea urchins and demonstrates that this is a primitive character of this group. The range of compositions Δx for the two phases of Ca1−xMgxCO3 is about 0.20 or greater and is consistent with a common biomineralization process. PMID:25158180</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3788374','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3788374"><span>Structural evolution of <span class="hlt">calcite</span> at high temperatures: Phase V unveiled</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ishizawa, Nobuo; Setoguchi, Hayato; Yanagisawa, Kazumichi</p> <p>2013-01-01</p> <p>The <span class="hlt">calcite</span> form of calcium carbonate CaCO3 undergoes a reversible phase transition between Rc and Rm at ~1240 K under a CO2 atmosphere of ~0.4 MPa. The joint probability density function obtained from the single-crystal X-ray diffraction data revealed that the oxygen triangles of the CO3 group in the high temperature form (Phase V) do not sit still at specified positions in the space group Rm, but migrate along the undulated circular orbital about carbon. The present study also shows how the room temperature form (Phase I) develops into Phase V through an intermediate form (Phase IV) in the temperature range between ~985 K and ~1240 K. PMID:24084871</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP22B..02B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP22B..02B"><span>A global deglacial negative carbon isotope excursion in speleothem <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Breecker, D.</p> <p>2015-12-01</p> <p>δ13C values of speleothem <span class="hlt">calcite</span> decreased globally during the last deglaciation defining a carbon isotope excursion (CIE) despite relatively constant δ13C values of carbon in the ocean-atmosphere system. The magnitude of the CIE varied with latitude, increasing poleward from ~2‰ in the tropics to as much as 7‰ at high latitudes. This recent CIE provides an interesting comparison with CIEs observed in deep time. A substantial portion of this CIE can be explained by the increase in atmospheric pCO2 that accompanied deglaciation. The dependence of C3 plant δ13C values on atmospheric pCO2 predicts a 2‰ δ13C decrease driven by the deglacial pCO2 increase. I propose that this signal was transferred to caves and thus explains nearly 100% of the CIE magnitude observed in the tropics and no less than 30% at the highest latitudes in the compilation. An atmospheric pCO2 control on speleothem δ13C values, if real, will need to be corrected for using ice core data before δ13C records can be interpreted in a paleoclimate context. The decrease in the magnitude of the equilibrium <span class="hlt">calcite</span>-CO2 carbon isotope fractionation factor explains a maximum of 1‰ of the CIE at the highest northern latitude in the compilation, which experienced the largest deglacial warming. Much of the residual extratropical CIE was likely driven by increasing belowground respiration rates, which were presumably pronounced at high latitudes as glacial retreat exposed fresh surfaces and/or vegetation density increased. The largest increases in belowground respiration would have therefore occurred at the highest latitudes, explaining the meridional trend. This work supports the notion that increases in atmospheric pCO2 and belowground respiration rates can result in large CIEs recorded in terrestrial carbonates, which, as previously suggested, may explain the magnitude of the PETM CIE as recorded by paleosol carbonates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1811382B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1811382B"><span>Nanoscale observations of the effect of citrate on calcium oxalate precipitation on <span class="hlt">calcite</span> surfaces.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Burgos-Cara, Alejandro; Ruiz-Agudo, Encarnacion; Putnis, Christine V.</p> <p>2016-04-01</p> <p>Calcium oxalate (CaC2O4ṡxH2O) minerals are naturally occurring minerals found in fossils, plants, kidney stones and is a by-product in some processes such as paper, food and beverage production [1,2]. In particular, calcium oxalate monohydrate phase (COM) also known as whewellite (CaC2O4ṡH2O), is the most frequently reported mineral phase found in urinary and kidney stones together with phosphates. Organic additives are well known to play a key role in the formation of minerals in both biotic and <span class="hlt">abiotic</span> systems, either facilitating their precipitation or hindering it. In this regard, recent studies have provided direct evidence demonstrating that citrate species could enhance dissolution of COM and inhibit their precipitation. [3,4] The present work aims at evauate the influence of pH, citrate and oxalic acid concentrations in calcium oxalate precipitation on <span class="hlt">calcite</span> surfaces (Island Spar, Chihuahua, Mexico) through in-situ nanoscale observation using in situ atomic force microscopy (AFM, Multimode, Bruker) in flow-through experiments. Changes in calcium oxalate morphologies and precipitated phases were observed, as well as the inhibitory effect of citrate on calcium oxalate precipitation, which also lead to stabilization an the amorphous calcium oxalate phase. [1] K.D. Demadis, M. Öner, Inhibitory effects of "green"additives on the crystal growth of sparingly soluble salts, in: J.T. Pearlman (Ed.), Green Chemistry Research Trends, Nova Science Publishers Inc., New York, 2009, pp. 265-287. [2] M. Masár, M. Zuborová, D. Kaniansky, B. Stanislawski, Determination of oxalate in beer by zone electrophoresis on a chip with conductivity detection, J. Sep. Sci. 26 (2003) 647-652. [3] Chutipongtanate S, Chaiyarit S, Thongboonkerd V. Citrate, not phosphate, can dissolve calcium oxalate monohydrate crystals and detach these crystals from renal tubular cells. Eur J Pharmacol 2012;689:219-25. [4] Weaver ML, Qiu SR, Hoyer JR, Casey WH, Nancollas GH, De Yoreo JJ</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/tei/0118/report.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/tei/0118/report.pdf"><span>The quantitative determination of <span class="hlt">calcite</span> associated with the carbonate-bearing apatites</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Silverman, Sol R.; Fuyat, Ruth K.; Weiser, Jeanne D.</p> <p>1951-01-01</p> <p>The CO2 combined as <span class="hlt">calcite</span> in carbonate-bearing apatites as been distinguished from that combined as carbonate-apatite, or present in some form other than <span class="hlt">calcite</span>, by use of X-ray powder patterns, differential thermal analyses, and differential solubility tests. These methods were applied to several pure apatite minerals, to one fossil bone, and to a group of phosphorites from the Phosphoria formation of Permian age from Trail Canyon and the Conda mine, Idaho, and the Laketown district, Utah. With the exceptions of pure fluorapatite, pure carbonate-flueorapatite, and one phosphorite from Trail Canyon, these substances contain varying amounts of <span class="hlt">calcite</span>, but in all the samples an appreciable part of the carbonite content is not present as <span class="hlt">calcite</span>. The results of solubility tests, in which the particle size of sample and the length of solution time were varied, imply that the carbonate content is not due to shielded <span class="hlt">calcite</span> entrapped along an internal network of surfaces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1130649','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1130649"><span>Influence of <span class="hlt">calcite</span> on uranium(VI) reactive transport in the groundwater–river mixing zone</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ma, Rui; Liu, Chongxuan; Greskowiak, Janek; Prommer, Henning; Zachara, John M.; Zheng, Chunmiao</p> <p>2014-01-23</p> <p><span class="hlt">Calcite</span> is an important mineral that can affect uranyl reactive transport in subsurface sediments. This study investigated the distribution of <span class="hlt">calcite</span> and its influence on uranyl adsorption and reactive transport in the groundwater-river mixing zone at US Hanford 300A, Washington State. Simulations using a 2D reactive transport model under field-relevant hydrogeochemical conditions revealed a complex distribution of <span class="hlt">calcite</span> concentration as a result of dynamic groundwater-river interactions. The <span class="hlt">calcite</span> concentration distribution in turn affected the spatial and temporal changes in aqueous carbonate, calcium, and pH, which subsequently influenced U(VI) mobility and discharge rates into the river. The results implied that <span class="hlt">calcite</span> distribution and its concentration dynamics is an important consideration for field characterization, monitoring, and reactive transport prediction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998SedG..116...13H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998SedG..116...13H"><span>Low limit of Mn 2+-activated cathodoluminescence of <span class="hlt">calcite</span>: state of the art</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Habermann, Dirk; Neuser, Rolf D.; Richter, Detlev K.</p> <p>1998-02-01</p> <p>In the literature, the lower limit for Mn 2+-activated cathodoluminescence (CL) of <span class="hlt">calcite</span> is variously reputed to over a very wide range of values above 10 ppm Mn. Our spectroscopic investigations of the CL response in natural <span class="hlt">calcite</span> reveal that below 10 ppm manganese content Mn 2+-activation is also present. Using the Quantitative High Resolution Spectral analysis of CL (QHRS-CL) an activation by Mn 2+ in the range of 700 ppb is proved, which cannot be determined visually. So, if not quenched, the minimum Mn 2+ content for Mn 2+-activation is one atom in the irradiated <span class="hlt">calcite</span> crystal lattice volume. As the intrinsic (background blue) luminescence is used to determine non-altered biogenic <span class="hlt">calcite</span>, the limit of Mn 2+-activation plays an important role in the interpretation of diagenetic processes. Our results of spectroscopic analyses require a revision of current opinions about the diagenesis of <span class="hlt">calcite</span> as revealed by CL investigation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24188740','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24188740"><span>Unusual micrometric <span class="hlt">calcite</span>-aragonite interface in the abalone shell Haliotis (Mollusca, Gastropoda).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dauphin, Yannicke; Cuif, Jean-Pierre; Castillo-Michel, Hiram; Chevallard, Corinne; Farre, Bastien; Meibom, Anders</p> <p>2014-02-01</p> <p>Species of Haliotis (abalone) show high variety in structure and mineralogy of the shell. One of the European species (Haliotis tuberculata) in particular has an unusual shell structure in which <span class="hlt">calcite</span> and aragonite coexist at a microscale with small patches of aragonite embedded in larger <span class="hlt">calcitic</span> zones. A detailed examination of the boundary between <span class="hlt">calcite</span> and aragonite using analytical microscopies shows that the organic contents of <span class="hlt">calcite</span> and aragonite differ. Moreover, changes in the chemical composition of the two minerals seem to be gradual and define a micrometric zone of transition between the two main layers. A similar transition zone has been observed between the layers in more classical and regularly structured mollusk shells. The imbrication of microscopic patches of aragonite within a <span class="hlt">calcitic</span> zone suggests the occurrence of very fast physiological changes in these taxa.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994JCrGr.142..156A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994JCrGr.142..156A"><span>Crystal-protein interactions studied by overgrowth of <span class="hlt">calcite</span> on biogenic skeletal elements</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Aizenberg, J.; Albeck, S.; Weiner, S.; Addadi, L.</p> <p>1994-09-01</p> <p>A key parameter in the biological control of crystal formation is the interaction of a group of acidic macromolecules with the mineral phase. Here we study protein-<span class="hlt">calcite</span> interactions using epitaxial overgrowth of synthetic <span class="hlt">calcite</span> crystals under conditions in which local release of occluded macromolecules from the biogenic substrate occurs. The macromolecules subsequently interact with the newly formed overgrown crystals, resulting in modified <span class="hlt">calcite</span> morphology. This novel method provides a means of mapping crystal-protein interactions under conditions that minimally affect the conformational states of the acidic macromolecules. We show that proteins released from <span class="hlt">calcitic</span> sponge spicules and mollusc prisms specifically interact with {001} and {01 l} faces of <span class="hlt">calcite</span>, whereas proteins released from echinoderm skeletal elements only interact with {01 l} faces. The extent to which the overgrown crystals are affected by the proteins varies even in the same organism and within the same element, depending on the site and crystallographic orientation of the skeletal elements.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25063580','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25063580"><span>Aragonite shells are more ancient than <span class="hlt">calcite</span> ones in bivalves: new evidence based on omics.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Xiaotong; Li, Li; Zhu, Yabing; Song, Xiaorui; Fang, Xiaodong; Huang, Ronglian; Que, Huayong; Zhang, Guofan</p> <p>2014-11-01</p> <p>Two calcium carbonate crystal polymorphs, aragonite and <span class="hlt">calcite</span>, are the main inorganic components of mollusk shells. Some fossil evidences suggest that aragonite shell is more ancient than <span class="hlt">calcite</span> shell for the Bivalvia. But, the molecular biology evidence for the above deduction is absent. In this study, we searched for homologs of bivalve aragonite-related and <span class="hlt">calcite</span>-related shell proteins in the oyster genome, and found that no homologs of <span class="hlt">calcite</span>-related shell protein but some homologs of aragonite-related shell proteins in the oyster genome. We explained the results as the new evidence to support that aragonite shells are more ancient than <span class="hlt">calcite</span> shells in bivalves combined the published biogeological and seawater chemistry data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4550785','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4550785"><span>Circadian regulation of <span class="hlt">abiotic</span> stress tolerance in plants</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Grundy, Jack; Stoker, Claire; Carré, Isabelle A.</p> <p>2015-01-01</p> <p>Extremes of temperatures, drought and salinity cause widespread crop losses throughout the world and impose severe limitations on the amount of land that can be used for agricultural purposes. Hence, there is an urgent need to develop crops that perform better under such <span class="hlt">abiotic</span> stress conditions. Here, we discuss intriguing, recent evidence that circadian clock contributes to plants’ ability to tolerate different types of environmental stress, and to acclimate to them. The clock controls expression of a large fraction of <span class="hlt">abiotic</span> stress-responsive genes, as well as biosynthesis and signaling downstream of stress response hormones. Conversely, <span class="hlt">abiotic</span> stress results in altered expression and differential splicing of the clock genes, leading to altered oscillations of downstream stress-response pathways. We propose a range of mechanisms by which this intimate coupling between the circadian clock and environmental stress-response pathways may contribute to plant growth and survival under <span class="hlt">abiotic</span> stress. PMID:26379680</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3900766','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3900766"><span><span class="hlt">Abiotic</span> stress responses in plant roots: a proteomics perspective</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ghosh, Dipanjana; Xu, Jian</p> <p>2014-01-01</p> <p><span class="hlt">Abiotic</span> stress conditions adversely affect plant growth, resulting in significant decline in crop productivity. To mitigate and recover from the damaging effects of such adverse environmental conditions, plants have evolved various adaptive strategies at cellular and metabolic levels. Most of these strategies involve dynamic changes in protein abundance that can be best explored through proteomics. This review summarizes comparative proteomic studies conducted with roots of various plant species subjected to different <span class="hlt">abiotic</span> stresses especially drought, salinity, flood, and cold. The main purpose of this article is to highlight and classify the protein level changes in <span class="hlt">abiotic</span> stress response pathways specifically in plant roots. Shared as well as stressor-specific proteome signatures and adaptive mechanism(s) are simultaneously described. Such a comprehensive account will facilitate the design of genetic engineering strategies that enable the development of broad-spectrum <span class="hlt">abiotic</span> stress-tolerant crops. PMID:24478786</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeCoA.159...61R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeCoA.159...61R"><span>Interactions of arsenic with <span class="hlt">calcite</span> surfaces revealed by in situ nanoscale imaging</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Renard, François; Putnis, Christine V.; Montes-Hernandez, German; Ruiz-Agudo, Encarnacion; Hovelmann, Jörn; Sarret, Géraldine</p> <p>2015-06-01</p> <p>Arsenic dissolved in water represents a key environmental and health challenge because several million people are under the threat of contamination. In calcareous environments <span class="hlt">calcite</span> may play an important role in arsenic solubility and transfer in water. Arsenic-<span class="hlt">calcite</span> interactions remain controversial, especially for As(III) which was proposed to be either incorporated as such, or as As(V) after oxidation. Here, we provide the first time-lapse in situ study of the evolution of the (10-14) <span class="hlt">calcite</span> cleavage surface morphology during dissolution and growth in the presence of solutions with various amounts of As(III) or As(V) at room temperature and pH range 6-11 using a flow-through cell connected to an atomic force microscope (AFM). Reaction products were then characterized by Raman spectroscopy. In parallel, co-precipitation experiments with either As(III) or As(V) were performed in batch reactors, and the speciation of arsenic in the resulting solids was studied by X-ray absorption spectroscopy (XAS). For As(V), AFM results showed that it interacts strongly with the <span class="hlt">calcite</span> surface, and XAS results showed that As(V) was mostly incorporated in the <span class="hlt">calcite</span> structure. For As(III), AFM results showed much less impact on <span class="hlt">calcite</span> growth and dissolution and less incorporation was observed. This was confirmed by XAS results that indicate that As(III) was partly oxidized into As(V) before being incorporated into <span class="hlt">calcite</span> and the resulting <span class="hlt">calcite</span> contained 36% As(III) and 64% As(V). All these experimental results confirm that As(V) has a much stronger interaction with <span class="hlt">calcite</span> than As(III) and that <span class="hlt">calcite</span> may represent an important reservoir for arsenic in various geological environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/20006591','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/20006591"><span>Diel cycles in <span class="hlt">calcite</span> production and dissolution in a eutrophic basin</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cicerone, D.S.; Stewart, A.J.; Roh, Y.</p> <p>1999-10-01</p> <p><span class="hlt">Calcite</span> production is understood largely as a longer-term phenomenon (e.g., seasonal whitings) that can occur in hardwater lakes, and is significant ecologically because it can slow the rate of eutrophication by reducing, through adsorption, the availability of nutrients to primary producers. In this study the authors show that rapid changes in concentration of dissolved CO{sub 2} by photosynthesis and respiration within a eutrophic basin generated strong day-to-night cycles in <span class="hlt">calcite</span> production and dissolution. Diel cycles in <span class="hlt">calcite</span> production and dissolution were large enough that they could drive secondary diel cycles in the availability of metals that strongly sorb to the surfaces of <span class="hlt">calcite</span> particles. They explored the possibility of the secondary diel cycling of metals by intensive 7-d in situ monitoring of water-quality conditions in a shallow, eutrophic spill-control basin near an industrial facility in eastern Tennessee; inspecting data from a 7-year record of water-quality parameters for this basin; analyzing physicochemical characteristics and mineralogic composition of sediments in the basin; and conducting laboratory experiments to characterize the interaction of <span class="hlt">calcite</span> with Cd, under solid-liquid nonequilibrium conditions. The authors found that the basin accumulated and stored <span class="hlt">calcite</span>. In situ monitoring showed that <span class="hlt">calcite</span> was produced during daylight, and tended to dissolve again at night; the <span class="hlt">calcite</span> production and dissolution processes seemed to be modulated by dissolved-phase CO{sub 2} dynamics, in concert with large diel fluctuations in pCa, pH, and Po{sub 2}. Laboratory experiments showed a rapid interaction ({lt}6 h) of Cd with <span class="hlt">calcite</span>, in response to dissolved CO{sub 2} changes. Thus, concentrations of dissolved Cd can vary over daily cycles, mediated by diel changes in <span class="hlt">calcite</span> production and dissolution. Thermodynamic considerations suggest that other metals, such as Zn, Sr, Ni, and Ba, may demonstrate this behavior as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSG....70..200K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSG....70..200K"><span>The mechanical and microstructural behaviour of <span class="hlt">calcite</span>-dolomite composites: An experimental investigation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kushnir, Alexandra R. L.; Kennedy, L. A.; Misra, Santanu; Benson, Philip; White, J. C.</p> <p>2015-01-01</p> <p>The styles and mechanisms of deformation associated with many variably dolomitized limestone shear systems are strongly controlled by strain partitioning between dolomite and <span class="hlt">calcite</span>. Here, we present experimental results from the deformation of four composite materials designed to address the role of dolomite on the strength of limestone. Composites were synthesized by hot isostatic pressing mixtures of dolomite (Dm) and <span class="hlt">calcite</span> powders (% Dm: 25%-Dm, 35%-Dm, 51%-Dm, and 75%-Dm). In all composites, <span class="hlt">calcite</span> is finer grained than dolomite. The synthesized materials were deformed in torsion at constant strain rate (3 × 10-4 and 1 × 10-4 s-1), high effective pressure (262 MPa), and high temperature (750 °C) to variable finite shear strains. Mechanical data show an increase in yield strength with increasing dolomite content. Composites with <75% dolomite (the remaining being <span class="hlt">calcite</span>), accommodate significant shear strain at much lower shear stresses than pure dolomite but have significantly higher yield strengths than anticipated for 100% <span class="hlt">calcite</span>. The microstructure of the fine-grained <span class="hlt">calcite</span> suggests grain boundary sliding, accommodated by diffusion creep and dislocation glide. At low dolomite concentrations (i.e. 25%), the presence of coarse-grained dolomite in a micritic <span class="hlt">calcite</span> matrix has a profound effect on the strength of composite materials as dolomite grains inhibit the superplastic flow of <span class="hlt">calcite</span> aggregates. In high (>50%) dolomite content samples, the addition of 25% fine-grained <span class="hlt">calcite</span> significantly weakens dolomite, such that strain can be partially localized along narrow ribbons of fine-grained <span class="hlt">calcite</span>. Deformation of dolomite grains by shear fracture is observed; there is no intracrystalline deformation in dolomite irrespective of its relative abundance and finite shear strain.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/277592','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/277592"><span>Significance of aragonite cements around Cretaceous <span class="hlt">marine</span> methane seeps</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Savard, M.M.; Beauchamp, B.; Veizer, J.</p> <p>1996-05-01</p> <p>Detailed petrography and geochemistry of carbonate precipitates in Cretaceous cold seep mounds from the Canadian Arctic show spectacular early diagenetic products: some still-preserved splays and isopachous layers of fine, acicular aragonite, and large botryoids and crusts of low-magnesium <span class="hlt">calcite</span> showing unusual entanglement of former fibrous <span class="hlt">calcite</span> and aragonite. The latter mineralogy is suggested by clear, flat-terminated cathodoluminescence patterns interpreted as ancient crystal growth steps, and the former by rhombohedral terminations. The early cement phases very likely precipitated in cold Arctic water dominated by bicarbonates derived from bacterially oxidized methane: these cements have {delta}{sup 13}C values around {minus}44.0% and {delta}{sup 18}O values of 1.8 to 0.1% PDB. Coexistence of <span class="hlt">calcite</span> and aragonite early cements in the Cretaceous seep mounds is unusual, because precipitation occurred in high-latitude, cold-water settings, and during a so-called <span class="hlt">calcite</span> sea mode. As in modern <span class="hlt">marine</span> hydrocarbon seeps, the chemistry of the Cretaceous system was apparently controlled by chemosynthetic bacterial activity, resulting in high a{sub HCO{sub 3}{sup {minus}}} that promoted precipitation of carbonates. The authors suggest that, locally, fluctuations in a{sub HCO{sub 3}{sup {minus}}}/a{sub SO{sub 4}{sup 2{minus}}} resulted in oscillating aragonite or <span class="hlt">calcite</span> supersaturation, and hence, controlled the mineralogy of the early precipitates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28160163','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28160163"><span>Nucleotide Selectivity in <span class="hlt">Abiotic</span> RNA Polymerization Reactions.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Coari, Kristin M; Martin, Rebecca C; Jain, Kopal; McGown, Linda B</p> <p>2017-02-03</p> <p>In order to establish an RNA world on early Earth, the nucleotides must form polymers through chemical rather than biochemical reactions. The polymerization products must be long enough to perform catalytic functions, including self-replication, and to preserve genetic information. These functions depend not only on the length of the polymers, but also on their sequences. To date, studies of <span class="hlt">abiotic</span> RNA polymerization generally have focused on routes to polymerization of a single nucleotide and lengths of the homopolymer products. Less work has been done the selectivity of the reaction toward incorporation of some nucleotides over others in nucleotide mixtures. Such information is an essential step toward understanding the chemical evolution of RNA. To address this question, in the present work RNA polymerization reactions were performed in the presence of montmorillonite clay catalyst. The nucleotides included the monophosphates of adenosine, cytosine, guanosine, uridine and inosine. Experiments included reactions of mixtures of an imidazole-activated nucleotide (ImpX) with one or more unactivated nucleotides (XMP), of two or more ImpX, and of XMP that were activated in situ in the polymerization reaction itself. The reaction products were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify the lengths and nucleotide compositions of the polymerization products. The results show that the extent of polymerization, the degree of heteropolymerization vs. homopolymerization, and the composition of the polymeric products all vary among the different nucleotides and depend upon which nucleotides and how many different nucleotides are present in the mixture.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017OLEB..tmp....2C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017OLEB..tmp....2C"><span>Nucleotide Selectivity in <span class="hlt">Abiotic</span> RNA Polymerization Reactions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Coari, Kristin M.; Martin, Rebecca C.; Jain, Kopal; McGown, Linda B.</p> <p>2017-02-01</p> <p>In order to establish an RNA world on early Earth, the nucleotides must form polymers through chemical rather than biochemical reactions. The polymerization products must be long enough to perform catalytic functions, including self-replication, and to preserve genetic information. These functions depend not only on the length of the polymers, but also on their sequences. To date, studies of <span class="hlt">abiotic</span> RNA polymerization generally have focused on routes to polymerization of a single nucleotide and lengths of the homopolymer products. Less work has been done the selectivity of the reaction toward incorporation of some nucleotides over others in nucleotide mixtures. Such information is an essential step toward understanding the chemical evolution of RNA. To address this question, in the present work RNA polymerization reactions were performed in the presence of montmorillonite clay catalyst. The nucleotides included the monophosphates of adenosine, cytosine, guanosine, uridine and inosine. Experiments included reactions of mixtures of an imidazole-activated nucleotide (ImpX) with one or more unactivated nucleotides (XMP), of two or more ImpX, and of XMP that were activated in situ in the polymerization reaction itself. The reaction products were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to identify the lengths and nucleotide compositions of the polymerization products. The results show that the extent of polymerization, the degree of heteropolymerization vs. homopolymerization, and the composition of the polymeric products all vary among the different nucleotides and depend upon which nucleotides and how many different nucleotides are present in the mixture.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22122668','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22122668"><span>An omics approach to understand the plant <span class="hlt">abiotic</span> stress.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Debnath, Mousumi; Pandey, Mukeshwar; Bisen, P S</p> <p>2011-11-01</p> <p><span class="hlt">Abiotic</span> stress can lead to changes in development, productivity, and severe stress and may even threaten survival of plants. Several environmental stresses cause drastic changes in the growth, physiology, and metabolism of plants leading to the increased accumulation of secondary metabolites. As medicinal plants are important sources of drugs, steps are taken to understand the effect of stress on the physiology, biochemistry, genomic, proteomic, and metabolic levels. The molecular responses of plants to <span class="hlt">abiotic</span> stress are often considered as a complex process. They are mainly based on the modulation of transcriptional activity of stress-related genes. Many genes have been induced under stress conditions. The products of stress-inducible genes protecting against these stresses includes the enzymes responsible for the synthesis of various osmoprotectants. Genetic engineering of tolerance to <span class="hlt">abiotic</span> stresses help in molecular understanding of pathways induced in response to one or more of the <span class="hlt">abiotic</span> stresses. Systems biology and virtual experiments allow visualizing and understanding how plants work to overcome <span class="hlt">abiotic</span> stress. This review discusses the omic approach to understand the plant response to <span class="hlt">abiotic</span> stress with special emphasis on medicinal plant.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeCoA.114..188M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeCoA.114..188M"><span>Kinetics of Mg partition and Mg stable isotope fractionation during its incorporation in <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mavromatis, Vasileios; Gautier, Quentin; Bosc, Olivier; Schott, Jacques</p> <p>2013-08-01</p> <p><span class="hlt">Calcite</span> growth experiments have been performed in the presence of aqueous Mg at 25 °C and 1 bar pCO2 to quantify magnesium partition coefficient D={(Mg/Ca)}/{(Mg/Ca)} and Mg isotope fractionation between <span class="hlt">calcite</span> and reactive fluid (Δ26Mgcalcite-fluid) as a function of <span class="hlt">calcite</span> precipitation rate rp (mol m-2 s-1). Mg partition coefficient, DMg, increases with <span class="hlt">calcite</span> growth rate according to: LogD=0.2517(±0.0150)×Logrp+0.0944(±0.0182); R2=0.93,(10-8.3⩽rp⩽10-6.6molms) Δ26Mgcalcite-fluid was found to depend heavily on <span class="hlt">calcite</span> growth rate with preferential incorporation of 24Mg in <span class="hlt">calcite</span> and the extent of isotope fractionation decreasing with increasing <span class="hlt">calcite</span> growth rate in accord with: Δ26Mg=0.7918(±0.0452)×Logrp+3.2366(±0.3360); R2=0.97(10-8.3⩽rp⩽10-6.6molms) The negative Δ26Mgcalcite-fluid values found in this study, with <span class="hlt">calcite</span> overgrowths enriched in light Mg, are consistent with (i) recent experimental data on Mg isotope fractionation during low-Mg <span class="hlt">calcite</span> homogeneous precipitation (Immenhauser et al., 2010) and magnesite growth (Pearce et al., 2012) and (ii) with theoretical values calculated for Mg-<span class="hlt">calcite</span> by density-functional electronic structure models (Rustad et al., 2010). The deviation of the isotopic composition of precipitated Mg-<span class="hlt">calcite</span> from the equilibrium mass fractionation line in a three isotope diagram is a linear function of <span class="hlt">calcite</span> growth rate. The equilibrium Δ26Mgcalcite-fluid value at 25 °C derived from this linear extrapolation, Δ26Mgcalcite-fluid = -3.5 ± 0.2‰ (2σ), is in good agreement with the theoretical value calculated by Rustad et al. (2010) for Mg-<span class="hlt">calcite</span> (Δ26Mgcalcite-fluid = -3.6‰; BP86 functional). A striking feature of the results of this study is the decrease of the extent of Mg isotope fractionation (from -3.16‰ to -1.88‰) with the increase of <span class="hlt">calcite</span> precipitation rate (from 10-8.3 to 10-6.6 mol m-2 s-1) which is opposite to the variation of Ca, Ba and Sr isotope fractionation with <span class="hlt">calcite</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/860281','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/860281"><span>STRONTIUM ISOTOPE EVOLUTION OF PORE WATER AND <span class="hlt">CALCITE</span> IN THE TOPOPAH SPRING TUFF, YUCCA MOUNTAIN , NEVADA</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>B.D. Marshall; K. Futa</p> <p>2001-02-07</p> <p>Yucca Mountain, a ridge of Miocene volcanic rocks in southwest Nevada, is being characterized as a site for a potential high-level radioactive waste repository. One issue of concern for the future performance of the potential repository is the movement of water in and around the potential repository horizon. Past water movement in this unsaturated zone is indicated by fluid inclusions trapped in <span class="hlt">calcite</span> coatings on fracture footwall surfaces and in some lithophysal cavities. Some of the fluid inclusions have homogenization temperatures above the present-day geotherm (J.F. Whelan, written communication), so determining the ages of the <span class="hlt">calcite</span> associated with those fluid inclusions is important in understanding the thermal history of the potential repository site. <span class="hlt">Calcite</span> ages have been constrained by uranium-lead dating of silica polymorphs (opal and chalcedony) that are present in most coatings. The opal and chalcedony ages indicate that deposition of the <span class="hlt">calcite</span> and opal coatings in the welded part of the Topopah Spring Tuff (TSw hydrogeologic unit) spanned nearly the entire history of the 12.8-million-year-old rock mass at fairly uniform overall long-term rates of deposition (within a factor of five). Constraining the age of a layer of <span class="hlt">calcite</span> associated with specific fluid inclusions is complicated. <span class="hlt">Calcite</span> is commonly bladed with complex textural relations, and datable opal or chalcedony may be millions of years older or younger than the <span class="hlt">calcite</span> layer or may be absent from the coating entirely. Therefore, a more direct method of dating the <span class="hlt">calcite</span> is presented in this paper by developing a model for strontium evolution in pore water in the TSw as recorded by the strontium coprecipitated with calcium in the <span class="hlt">calcite</span>. Although the water that precipitated the <span class="hlt">calcite</span> in fractures and cavities may not have been in local isotopic equilibrium with the pore water, the strontium isotope composition of all water in the TSw is primarily controlled by water</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6863258','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6863258"><span>Controls of carbonate mineralogy and solid-solution of Mg in <span class="hlt">calcite</span>: evidence from spelean systems</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Gonzalez, L.A.; Lohmann, K.C.</p> <p>1985-01-01</p> <p>Precipitation of carbonate minerals in spelean systems occurs under a wide range of fluid chemistry, Mg-Ca ratios, alkalinities, pH and temperatures; thus, spelean systems provide ideal settings to determine factors controlling the mineralogy of precipitated carbonates and solid-solution of Mg in <span class="hlt">calcite</span>. Cave waters and actively-precipitating carbonate speleothems were collected from Carlsbad Caverns National Park, New Mexico and the Mammoth-Flint Cave System, Kentucky. Carbonate mineralogy of precipitated phases was determined by x-ray diffraction, and major and minor element composition of waters and accompanying minerals were determined by Atomic Absorption Spectrophotometry. Results demonstrate that at a constant CO3 concentration the precipitation threshold for <span class="hlt">calcite</span> to aragonite is controlled dominantly by the Mg/Ca ratio of the ambient fluid. Aragonite precipitation is favored by high Mg/Ca ratios. Conversely, with increasing CO3 concentration at constant fluid Mg/Ca ratios, <span class="hlt">calcite</span> is preferentially precipitated. Solid-solution of Mg in <span class="hlt">calcite</span> is positively correlated with both increased Mg/Ca ratios and CO3 concentrations. These data suggest that Mg contents of <span class="hlt">calcite</span> can not be defined solely in terms of a homogeneous distribution coefficient. Rather, Mg concentrations can be also be affected by the CO3 concentration and degree of <span class="hlt">calcite</span> saturation, suggesting that the rate of crystal growth also plays and important role in Mg solid-solution in <span class="hlt">calcites</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26852350','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26852350"><span>Influence of surface conductivity on the apparent zeta potential of <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Li, Shuai; Leroy, Philippe; Heberling, Frank; Devau, Nicolas; Jougnot, Damien; Chiaberge, Christophe</p> <p>2016-04-15</p> <p>Zeta potential is a physicochemical parameter of particular importance in describing the surface electrical properties of charged porous media. However, the zeta potential of <span class="hlt">calcite</span> is still poorly known because of the difficulty to interpret streaming potential experiments. The Helmholtz-Smoluchowski (HS) equation is widely used to estimate the apparent zeta potential from these experiments. However, this equation neglects the influence of surface conductivity on streaming potential. We present streaming potential and electrical conductivity measurements on a <span class="hlt">calcite</span> powder in contact with an aqueous NaCl electrolyte. Our streaming potential model corrects the apparent zeta potential of <span class="hlt">calcite</span> by accounting for the influence of surface conductivity and flow regime. We show that the HS equation seriously underestimates the zeta potential of <span class="hlt">calcite</span>, particularly when the electrolyte is diluted (ionic strength ⩽ 0.01 M) because of <span class="hlt">calcite</span> surface conductivity. The basic Stern model successfully predicted the corrected zeta potential by assuming that the zeta potential is located at the outer Helmholtz plane, i.e. without considering a stagnant diffuse layer at the <span class="hlt">calcite</span>-water interface. The surface conductivity of <span class="hlt">calcite</span> crystals was inferred from electrical conductivity measurements and computed using our basic Stern model. Surface conductivity was also successfully predicted by our surface complexation model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4142853','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4142853"><span>Direct nanoscale observations of the coupled dissolution of <span class="hlt">calcite</span> and dolomite and the precipitation of gypsum</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Cama, Jordi; Soler, Josep Maria; Putnis, Christine V</p> <p>2014-01-01</p> <p>Summary In-situ atomic force microscopy (AFM) experiments were performed to study the overall process of dissolution of common carbonate minerals (<span class="hlt">calcite</span> and dolomite) and precipitation of gypsum in Na2SO4 and CaSO4 solutions with pH values ranging from 2 to 6 at room temperature (23 ± 1 °C). The dissolution of the carbonate minerals took place at the (104) cleavage surfaces in sulfate-rich solutions undersaturated with respect to gypsum, by the formation of characteristic rhombohedral-shaped etch pits. Rounding of the etch pit corners was observed as solutions approached close-to-equilibrium conditions with respect to <span class="hlt">calcite</span>. The calculated dissolution rates of <span class="hlt">calcite</span> at pH 4.8 and 5.6 agreed with the values reported in the literature. When using solutions previously equilibrated with respect to gypsum, gypsum precipitation coupled with <span class="hlt">calcite</span> dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the <span class="hlt">calcite</span> surface, forming arrow-like forms parallel to the crystallographic orientations of the <span class="hlt">calcite</span> etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of <span class="hlt">calcite</span>, indicating the dissolution rate to be the rate-controlling step. The resulting gypsum coating partially covered the surface during the experimental duration of a few hours. PMID:25161860</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25649514','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25649514"><span>Fabrication of porous <span class="hlt">calcite</span> using chopped nylon fiber and its evaluation using rats.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ishikawa, Kunio; Tram, Nguyen Xuan Thanh; Tsuru, Kanji; Toita, Riki</p> <p>2015-02-01</p> <p>Although porous <span class="hlt">calcite</span> has attracted attention as bone substitutes, limited studies have been made so far. In the present study, porous <span class="hlt">calcite</span> block was fabricated by introducing chopped nylon fiber as porogen. Ca(OH)2 powder containing 10 wt% chopped nylon fiber was compacted at 150 MPa, and sintered to burn out the fiber and to carbonate the Ca(OH)2 under stream of 1:2 O2-CO2. Sintering of Ca(OH)2 at 750 °C or lower temperature resulted in incomplete burning out of the fiber whereas sintering at 800 °C or higher temperature resulted in the formation of CaO due to the thermal decomposition of Ca(OH)2. However, sintering at 770 °C resulted in complete burning out of the fiber and complete carbonation of Ca(OH)2 to <span class="hlt">calcite</span> without forming CaO. Macro- and micro-porosities of the porous <span class="hlt">calcite</span> were approximately 23 and 16%, respectively. Diameter of the macropores was approximately 100 μm which is suitable for bone tissue penetration. Porous <span class="hlt">calcite</span> block fabricated by this method exhibited good tissue response when implanted in the bone defect in femur of 12-weeks-old rat. Four weeks after implantation, bone bonded on the surface of <span class="hlt">calcite</span>. Furthermore, bone tissue penetrated interior to the macropore at 8 weeks. These results demonstrated the good potential value of porous <span class="hlt">calcite</span> as artificial bone substitutes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25161860','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25161860"><span>Direct nanoscale observations of the coupled dissolution of <span class="hlt">calcite</span> and dolomite and the precipitation of gypsum.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Offeddu, Francesco Giancarlo; Cama, Jordi; Soler, Josep Maria; Putnis, Christine V</p> <p>2014-01-01</p> <p>In-situ atomic force microscopy (AFM) experiments were performed to study the overall process of dissolution of common carbonate minerals (<span class="hlt">calcite</span> and dolomite) and precipitation of gypsum in Na2SO4 and CaSO4 solutions with pH values ranging from 2 to 6 at room temperature (23 ± 1 °C). The dissolution of the carbonate minerals took place at the (104) cleavage surfaces in sulfate-rich solutions undersaturated with respect to gypsum, by the formation of characteristic rhombohedral-shaped etch pits. Rounding of the etch pit corners was observed as solutions approached close-to-equilibrium conditions with respect to <span class="hlt">calcite</span>. The calculated dissolution rates of <span class="hlt">calcite</span> at pH 4.8 and 5.6 agreed with the values reported in the literature. When using solutions previously equilibrated with respect to gypsum, gypsum precipitation coupled with <span class="hlt">calcite</span> dissolution showed short gypsum nucleation induction times. The gypsum precipitate quickly coated the <span class="hlt">calcite</span> surface, forming arrow-like forms parallel to the crystallographic orientations of the <span class="hlt">calcite</span> etch pits. Gypsum precipitation coupled with dolomite dissolution was slower than that of <span class="hlt">calcite</span>, indicating the dissolution rate to be the rate-controlling step. The resulting gypsum coating partially covered the surface during the experimental duration of a few hours.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002A%26A...395L..29C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002A%26A...395L..29C"><span>Discovery of <span class="hlt">calcite</span> in the solar type protostar NGC 1333-IRAS 4</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ceccarelli, C.; Caux, E.; Tielens, A. G. G. M.; Kemper, F.; Waters, L. B. F. M.; Phillips, T.</p> <p>2002-11-01</p> <p>We present observations, obtained with ISO-LWS, of the continuum between 50-200 mu m of the solar type protostar IRAS 4, in the NGC 1333 complex. The continuum presents an excess, around 95 mu m, that we demonstrate must be a dust feature. We compared the 95 mu m excess with the <span class="hlt">calcite</span> feature at 92 mu m and find that it fits the observations reasonably well. There may be a further contribution from hydrous silicates at ~ 100 mu m, but this seems a less robust result. The detected <span class="hlt">calcite</span> mass is ~ 8 x 10-5 Msun and represents about 1% of the warm ( ~ 23 K) dust mass surrounding IRAS 4. This is only the second observation indicating the presence of carbonates outside the solar system, and the first revealing <span class="hlt">calcite</span> in a young protostar. It is remarkable and intriguing that in all the objects where <span class="hlt">calcite</span> has been detected so far, namely meteorites, planetary nebulae and IRAS 4, it represents from 0.3 to 1% of the dust mass. This new detection of <span class="hlt">calcite</span> strengthens the claim by Kemper et al. (2002a) that <span class="hlt">calcite</span> formation does not necessarely requires liquid water. We suggest that <span class="hlt">calcite</span> forms at the surface of the grains, where water ice layers may locally have an enhanced mobility caused by heating due to hard X-rays emitted by the central object.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4017135','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4017135"><span>Polyamines and <span class="hlt">abiotic</span> stress in plants: a complex relationship1</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Minocha, Rakesh; Majumdar, Rajtilak; Minocha, Subhash C.</p> <p>2014-01-01</p> <p>The physiological relationship between <span class="hlt">abiotic</span> stress in plants and polyamines was reported more than 40 years ago. Ever since there has been a debate as to whether increased polyamines protect plants against <span class="hlt">abiotic</span> stress (e.g., due to their ability to deal with oxidative radicals) or cause damage to them (perhaps due to hydrogen peroxide produced by their catabolism). The observation that cellular polyamines are typically elevated in plants under both short-term as well as long-term <span class="hlt">abiotic</span> stress conditions is consistent with the possibility of their dual effects, i.e., being protectors from as well as perpetrators of stress damage to the cells. The observed increase in tolerance of plants to <span class="hlt">abiotic</span> stress when their cellular contents are elevated by either exogenous treatment with polyamines or through genetic engineering with genes encoding polyamine biosynthetic enzymes is indicative of a protective role for them. However, through their catabolic production of hydrogen peroxide and acrolein, both strong oxidizers, they can potentially be the cause of cellular harm during stress. In fact, somewhat enigmatic but strong positive relationship between <span class="hlt">abiotic</span> stress and foliar polyamines has been proposed as a potential biochemical marker of persistent environmental stress in forest trees in which phenotypic symptoms of stress are not yet visible. Such markers may help forewarn forest managers to undertake amelioration strategies before the appearance of visual symptoms of stress and damage at which stage it is often too late for implementing strategies for stress remediation and reversal of damage. This review provides a comprehensive and critical evaluation of the published literature on interactions between <span class="hlt">abiotic</span> stress and polyamines in plants, and examines the experimental strategies used to understand the functional significance of this relationship with the aim of improving plant productivity, especially under conditions of <span class="hlt">abiotic</span> stress. PMID:24847338</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/18453407','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/18453407"><span>Contribution of hydrolysis in the <span class="hlt">abiotic</span> attenuation of RDX and HMX in coastal waters.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Monteil-Rivera, Fanny; Paquet, Louise; Giroux, Romain; Hawari, Jalal</p> <p>2008-01-01</p> <p>Sinking of military ships, dumping of munitions during the two World Wars, and military training have resulted in the undersea deposition of numerous unexploded ordnances (UXOs). Leaching of energetic compounds such as hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) from these UXOs may cause adverse ecological effects so that the long-term fate of these chemicals in the sea should be known. The present study assesses the contribution of alkaline hydrolysis into the natural attenuation of RDX and HMX in coastal waters. Alkaline hydrolysis rates were shown to be unaffected by the presence of sodium chloride, the most common component in <span class="hlt">marine</span> waters. Kinetic parameters (E(a), ln A, k(2)) quantified for the alkaline hydrolysis of RDX and HMX in deionized water (30-50 degrees C, pH 10-12) agreed relatively well with <span class="hlt">abiotic</span> degradation rates determined in sterilized natural coastal waters (50 and 60 degrees C, variable salinity) even if the latter were generally slightly faster than the former. Furthermore, similar products (HCHO, NO(2)(-), O(2)NNHCH(2)NHCHO) were obtained on alkaline hydrolysis in deionized water and <span class="hlt">abiotic</span> degradation in coastal waters. These two findings suggested that degradation of nitramines in sterilized natural coastal waters, away from light, was mainly governed by alkaline hydrolysis. Kinetic calculations using the present parameters showed that alkaline hydrolysis of RDX and HMX in <span class="hlt">marine</span> waters at 10 degrees C would respectively take 112 +/- 10 and 2408 +/- 217 yr to be completed (99.0%). We concluded that under natural conditions hydrolysis should not contribute significantly to the natural attenuation of HMX in coastal waters whereas it could play an active role in the natural attenuation of RDX.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5561175','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5561175"><span><span class="hlt">Marine</span> pollution</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Albaiges, J. )</p> <p>1989-01-01</p> <p>This book covers the following topics: Transport of <span class="hlt">marine</span> pollutants; Transformation of pollutants in the <span class="hlt">marine</span> environment; Biological effects of <span class="hlt">marine</span> pollutants; Sources and transport of oil pollutants in the Persian Gulf; Trace metals and hydrocarbons in Syrian coastal waters; and Techniques for analysis of trace pollutants.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016049','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016049"><span>Activators of photoluminescence in <span class="hlt">calcite</span>: evidence from high-resolution, laser-excited luminescence spectroscopy</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pedone, V.A.; Cercone, K.R.; Burruss, R.C.</p> <p>1990-01-01</p> <p>Laser-excited luminescence spectroscopy of a red-algal, biogenic <span class="hlt">calcite</span> and a synthetic Mn-<span class="hlt">calcite</span> can make the distinction between organic and trace-element activators of photoluminescence. Organic-activated photoluminescence in biogenic <span class="hlt">calcite</span> is characterized by significant peak shifts and increasing intensity with shorter-wavelength excitation and by significant decreases in intensity after heating to ??? 400??C. In contrast, Mn-activated photoluminescence shows no peak shift, greatest intensity under green excitation and limited changes after heating. Examination of samples with a high-sensitivity spectrometer using several wavelengths of exciting light is necessary for identification of photoluminescence activators. ?? 1990.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_13 --> <div id="page_14" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="261"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4996599','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4996599"><span>Recurrent Pure <span class="hlt">Calcite</span> Urolithiasis Confirmed by Endoscopic Removal and Infrared Spectroscopy in a Malnourished Anorectic Female</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Andreassen, Kim Hovgaard; Sloth Osther, Palle Jörn</p> <p>2016-01-01</p> <p>Abstract Often when <span class="hlt">calcite</span> is found as a component of urinary calculi, they are considered false calculi or artifacts. We present a case of true <span class="hlt">calcite</span> urolithiasis. The stone material was removed percutaneously from a severely malnourished anorectic woman and analyzed by infrared spectroscopy (IRS). In addition, <span class="hlt">calcite</span> urolithiasis was confirmed in several recurrent stone events by IRS. Laxative abuse with magnesium oxide was believed to be the underlying cause of stone formation, and ammonium chloride given as one weekly dose turned out to be effective for stone prevention. PMID:27579419</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984JCrGr..66..639M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984JCrGr..66..639M"><span>The influence of impurities on the growth rate of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Meyer, H. J.</p> <p>1984-05-01</p> <p>The effects of 34 different additives on the growth rate of <span class="hlt">calcite</span> were investigated. An initial growth rate of about one crystal monolayer (3 × 10 -8 cm) per minute was adjusted at a constant supersaturation which was maintained by a control circuit. Then the impurity was added step by step and the reduction of the growth rate was measured. The impurity concentration necessary to reduce the initial growth rate by a certain percentage increased in the order Fe 2+, ATP, P 3O 5-10, P 2O 4-7, (PO 3) 6-6, Zn 2+, ADP, Ce 3+, Pb 2+, carbamyl phosphate, Fe 3+, PO 3-4, Co 2+, Mn 2+, Be 2+, β-glycerophosphate, Ni 2+, Cd 2+, "Tris", phenylphosphate, chondroitine sulphate, Ba 2+, citrate, AMP, Sr 2+, tricarballylate, taurine, SO 2-4, Mg 2+ by 4 orders of magnitude. The most effective additives halved the initial growth rate in concentrations of 2 × 10 -8 mol/1. For Fe 2+ the halving concentration was nearly proportional to the initial rate. The mechanism of inhibition by adsorption of the impurities at growth sites (kinks) is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4991261','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4991261"><span>Thin-film-induced morphological instabilities over <span class="hlt">calcite</span> surfaces</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Vesipa, R.; Camporeale, C.; Ridolfi, L.</p> <p>2015-01-01</p> <p>Precipitation of calcium carbonate from water films generates fascinating <span class="hlt">calcite</span> morphologies that have attracted scientific interest over past centuries. Nowadays, speleothems are no longer known only for their beauty but they are also recognized to be precious records of past climatic conditions, and research aims to unveil and understand the mechanisms responsible for their morphological evolution. In this paper, we focus on crenulations, a widely observed ripple-like instability of the the calcite–water interface that develops orthogonally to the film flow. We expand a previous work providing new insights about the chemical and physical mechanisms that drive the formation of crenulations. In particular, we demonstrate the marginal role played by carbon dioxide transport in generating crenulation patterns, which are indeed induced by the hydrodynamic response of the free surface of the water film. Furthermore, we investigate the role of different environmental parameters, such as temperature, concentration of dissolved ions and wall slope. We also assess the convective/absolute nature of the crenulation instability. Finally, the possibility of using crenulation wavelength as a proxy of past flows is briefly discussed from a theoretical point of view. PMID:27547086</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001GeoJI.144...96R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001GeoJI.144...96R"><span>Stress remagnetization in pyrrhotite-<span class="hlt">calcite</span> synthetic aggregates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Robion, Philippe; Borradaile, Graham J.</p> <p>2001-01-01</p> <p>Stress-induced remagnetization has been applied to multidomain pyrrhotite-<span class="hlt">calcite</span> synthetic aggregates in a triaxial rig. Experimental deformation used 150MPa confining pressure, a constant strain rate of 10-5 s-1 and applied differential stresses of up to 70MPa. New components of magnetization, parallel to the direction of the pressure vessel field, were added to the pre-deformational magnetization. The intensity of remagnetization (M'-M0) increases with the intensity of the applied differential stress and affects the coercivity fraction below 15mT. Bulk shortening is less than 8 per cent, thus grain rotation cannot explain selective remagnetization of the low-coercivity fraction. Remagnetization is thus attributed to deformational viscous remanent magnetization (DVRM). It is observed that high-coercivity (>15mT) grains do not remagnetize. There is, however, slight progressive rotation of pre-deformational magnetization with increasing strain up to 8 per cent of bulk shortening. The lack of piezoremanent magnetization in the high-coercivity range may be due to defects introduced in pyrrhotite during sample preparation. Experiments using synthetic pyrrhotite, expected to show low dislocation densities, would be necessary to test this effect.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19630003648&hterms=calcite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcalcite','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19630003648&hterms=calcite&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcalcite"><span>Ultrasonic Observation of the <span class="hlt">Calcite</span>-Aragonite Transition</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ahrens, T. J.; Katz, S.</p> <p>1963-01-01</p> <p>Elastic-wave velocities were measured as a function of pressure by ultrasonic pulse Interferometry in Solenhofen and Manilus limestone specimens to pressures of 27 and 38 kb. Longitudinal velocities decrease sharply from 5.3 km/sec at a mean pressure of 4 kb to a minimum of 4.8 km/sec at 8 kb. Transverse velocities decrease from 3.1 to 2.9 km/sec. At the minimum bulk and rigidity moduli are 25 and 20 per cent below their 4-kb values. A density increase of 1.7 per cent is associated with this minimum. The observed effects are attributed to the <span class="hlt">calcite</span>-aragonite transition, and they may be due to an inherent property of the material, a component of which undergoes a polymorphic transition, the low- and high-pressure phases coexisting over a considerable pressure range. This may be an additional mechanism to account for low-velocity zones in the earth?s interior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26697045','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26697045"><span>ROS Regulation During <span class="hlt">Abiotic</span> Stress Responses in Crop Plants.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>You, Jun; Chan, Zhulong</p> <p>2015-01-01</p> <p><span class="hlt">Abiotic</span> stresses such as drought, cold, salt and heat cause reduction of plant growth and loss of crop yield worldwide. Reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide anions (O2 (•-)), hydroxyl radical (OH•) and singlet oxygen ((1)O2) are by-products of physiological metabolisms, and are precisely controlled by enzymatic and non-enzymatic antioxidant defense systems. ROS are significantly accumulated under <span class="hlt">abiotic</span> stress conditions, which cause oxidative damage and eventually resulting in cell death. Recently, ROS have been also recognized as key players in the complex signaling network of plants stress responses. The involvement of ROS in signal transduction implies that there must be coordinated function of regulation networks to maintain ROS at non-toxic levels in a delicate balancing act between ROS production, involving ROS generating enzymes and the unavoidable production of ROS during basic cellular metabolism, and ROS-scavenging pathways. Increasing evidence showed that ROS play crucial roles in <span class="hlt">abiotic</span> stress responses of crop plants for the activation of stress-response and defense pathways. More importantly, manipulating ROS levels provides an opportunity to enhance stress tolerances of crop plants under a variety of unfavorable environmental conditions. This review presents an overview of current knowledge about homeostasis regulation of ROS in crop plants. In particular, we summarize the essential proteins that are involved in <span class="hlt">abiotic</span> stress tolerance of crop plants through ROS regulation. Finally, the challenges toward the improvement of <span class="hlt">abiotic</span> stress tolerance through ROS regulation in crops are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22029473','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22029473"><span>Plant cell organelle proteomics in response to <span class="hlt">abiotic</span> stress.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hossain, Zahed; Nouri, Mohammad-Zaman; Komatsu, Setsuko</p> <p>2012-01-01</p> <p>Proteomics is one of the finest molecular techniques extensively being used for the study of protein profiling of a given plant species experiencing stressed conditions. Plants respond to a stress by alteration in the pattern of protein expression, either by up-regulating of the existing protein pool or by the synthesizing novel proteins primarily associated with plants antioxidative defense mechanism. Improved protein extraction protocols and advance techniques for identification of novel proteins have been standardized in different plant species at both cellular and whole plant level for better understanding of <span class="hlt">abiotic</span> stress sensing and intracellular stress signal transduction mechanisms. In contrast, an in-depth proteome study of subcellular organelles could generate much detail information about the intrinsic mechanism of stress response as it correlates the possible relationship between the protein abundance and plant stress tolerance. Although a wealth of reviews devoted to plant proteomics are available, review articles dedicated to plant cell organelle proteins response under <span class="hlt">abiotic</span> stress are very scanty. In the present review, an attempt has been made to summarize all significant contributions related to <span class="hlt">abiotic</span> stresses and their impacts on organelle proteomes for better understanding of plants <span class="hlt">abiotic</span> stress tolerance mechanism at protein level. This review will not only provide new insights into the plants stress response mechanisms, which are necessary for future development of genetically engineered stress tolerant crop plants for the benefit of humankind, but will also highlight the importance of studying changes in protein abundance within the cell organelles in response to <span class="hlt">abiotic</span> stress.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4672674','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4672674"><span>ROS Regulation During <span class="hlt">Abiotic</span> Stress Responses in Crop Plants</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>You, Jun; Chan, Zhulong</p> <p>2015-01-01</p> <p><span class="hlt">Abiotic</span> stresses such as drought, cold, salt and heat cause reduction of plant growth and loss of crop yield worldwide. Reactive oxygen species (ROS) including hydrogen peroxide (H2O2), superoxide anions (O2•-), hydroxyl radical (OH•) and singlet oxygen (1O2) are by-products of physiological metabolisms, and are precisely controlled by enzymatic and non-enzymatic antioxidant defense systems. ROS are significantly accumulated under <span class="hlt">abiotic</span> stress conditions, which cause oxidative damage and eventually resulting in cell death. Recently, ROS have been also recognized as key players in the complex signaling network of plants stress responses. The involvement of ROS in signal transduction implies that there must be coordinated function of regulation networks to maintain ROS at non-toxic levels in a delicate balancing act between ROS production, involving ROS generating enzymes and the unavoidable production of ROS during basic cellular metabolism, and ROS-scavenging pathways. Increasing evidence showed that ROS play crucial roles in <span class="hlt">abiotic</span> stress responses of crop plants for the activation of stress-response and defense pathways. More importantly, manipulating ROS levels provides an opportunity to enhance stress tolerances of crop plants under a variety of unfavorable environmental conditions. This review presents an overview of current knowledge about homeostasis regulation of ROS in crop plants. In particular, we summarize the essential proteins that are involved in <span class="hlt">abiotic</span> stress tolerance of crop plants through ROS regulation. Finally, the challenges toward the improvement of <span class="hlt">abiotic</span> stress tolerance through ROS regulation in crops are discussed. PMID:26697045</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010GeCoA..74..252R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010GeCoA..74..252R"><span>Formation of pristane from α-tocopherol under simulated anoxic sedimentary conditions: A combination of biotic and <span class="hlt">abiotic</span> degradative processes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rontani, Jean-François; Nassiry, Mina; Michotey, Valérie; Guasco, Sophie; Bonin, Patricia</p> <p>2010-01-01</p> <p>Incubation of intact and oxidized α-tocopherol (vitamin E) in anaerobic sediment slurries allowed us to demonstrate that, as previously suggested by Goossens et al. (1984), the degradation of α-tocopherol in anoxic sediments results in the formation of pristane. The conversion of α-tocopherol to this isoprenoid alkane involves a combination of biotic and <span class="hlt">abiotic</span> degradative processes, i.e. the anaerobic biodegradation (which seems to be mainly induced by denitrifying bacteria) of trimeric structures resulting from the <span class="hlt">abiotic</span> oxidation of α-tocopherol. On the basis of the results obtained, it is proposed that in the <span class="hlt">marine</span> environment most of the α-tocopherol present in phytoplanktonic cells should be quickly degraded within the water column and the oxic zone of sediments by way of aerobic biodegradation, photo- and autoxidation processes. <span class="hlt">Abiotic</span> transformation of this compound mainly results in the production of trimeric oxidation products, sufficiently stable to be incorporated into anoxic sediments and whose subsequent anaerobic bacterial degradation affords pristane. These results confirm that the ratio pristane to phytane cannot be used as an indicator of the oxicity of the environment of deposition; in contrast, they support the use of PFI (Pristane Formation Index) as a proxy for the state of diagenesis of sedimentary organic matter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993SedG...87..139P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993SedG...87..139P"><span>Geochemistry and diagenesis of stratabound <span class="hlt">calcite</span> cement layers within the Rannoch Formation of the Brent Group, Murchison Field, North Viking Graben (northern North Sea)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Prosser, D. J.; Daws, J. A.; Fallick, A. E.; Williams, B. P. J.</p> <p>1993-11-01</p> <p>Up to four <span class="hlt">calcite</span>-cemented horizons (doggers) form impermeable barriers to fluid flow within the Middle Jurassic Rannoch Formation and are correlatable across the Murchison Field. <span class="hlt">Calcite</span> precipitated during early diagenesis, within high porosity/permeability sandstones at the top of coarsening (shoaling) upward shoreface cycles. <span class="hlt">Calcite</span> δ 13C and δ 18O compositions range from -4.1 to -13.4‰ PDB, and -6.6 to -16.7‰ PDB, respectively. Sr concentrations of up to 1334 ppm are consistent with <span class="hlt">marine</span> carbonate sources (probably shell fragments), but no viable intraformational carbonate source has been identified in the Murchison Field area. Initial 87Sr/ 86Sr compositions (0.71109-0.71266) are higher than Middle Jurassic seawater (0.7073), and consistent with precipitation from modified porewaters containing significant proportions of continentally derived "meteoric" fluids enriched in 87Sr as a result of basement weathering, or percolation through hinterland soils/unconsolidated detritus. An internal source of 87Sr is not considered viable in view of the high proportion (up to 25‰ clastic constituents) of unaltered detrital alkali feldspar and mica within the Rannoch Formation. Geochemical and isotope data indicate correlations between increasing δ 18O composition and increasing iron and magnesium content within <span class="hlt">calcite</span>. Calcium concentrations decrease with increasing δ 18O for <span class="hlt">calcites</span>. Geochemical data trends can be interpreted differently in terms of either "static" or "evolving" δ 18O porewater models. Static δ 18O porewater models using Jurassic/Early Cretaceous "meteoric" water ( δ 18O = -6‰; SMOW) predict cement precipitation temperatures of 17-77°C. However, δ 13C compositions are more depleted than those typical of carbon derived from shell debris, and correlation between decreasing δ 18O and decreasing δ 13C suggests modification of a meteoric-derived porewater system during burial via contribution of low δ 13C carbon derived from a deep</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.B11A0064J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.B11A0064J"><span><span class="hlt">Abiotic</span> Dissolved Organic Matter-Mineral Interaction in the Karstic Floridan Aquifer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jin, J.; Zimmerman, A.</p> <p>2007-12-01</p> <p>Dissolved organic matter (DOM)-mineral interaction (e.g. adsorption, desorption, mineral dissolution) in groundwater is a significant factor controlling geochemical, environmental and microbial processes and may be helpful in efforts to track groundwater sources or contaminant fate. Despite its importance, the dynamics and consequences of these <span class="hlt">abiotic</span> interactions remain poorly understood, largely due to the inaccessibility and heterogeneity of the subsurface, as well as the chemical complexity of DOM. This study models the OM-mineral interactions that takes place in the Floridan aquifer through laboratory adsorption-desorption experiments using DOM (groundwater, river water, soil extracts) and carbonate minerals (<span class="hlt">calcite</span>, dolomite) collected in north Florida. High performance liquid chromatography-size exclusion chromatography (HPLC-SEC) and UV-fluorescence excitation-emission matrix (EEM) spectrophotometry was used to examine the organic compound types exhibiting preferential affinity for carbonate minerals. Our results show that the DOM-carbonate adsorption/desorption isotherms are well described by the Freundlich model. Freundlich exponents (average value: 0.6488) less than one indicated a filling of adsorption sites. Minerals from Ocala tend to have higher adsorption affinity as well as adsorption capacity than those from Suwannee River Basin; however, both were found to have mineral dissolution. Two fluorescent signals, indicative of a fulvic-like (at excitation wavelength 295-310 nm, emission 400-420 nm) and a protein-like (275/345nm) moiety, were detected in DOM. A reduction in the fulvic-like peak intensity occurred following carbonate adsorption while the protein-like peaks remain almost unchanged indicating the preferential adsorption of fulvic acids. HPLC-SEC results (DOM properties as a function of molecular weight) will be discussed. The chemical properties of DOM in environmental groundwater samples will also be presented and evaluated in light of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22395925','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22395925"><span>Calcium sulfoaluminate (Ye'elimite) hydration in the presence of gypsum, <span class="hlt">calcite</span>, and vaterite</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hargis, Craig W.; Telesca, Antonio; Monteiro, Paulo J.M.</p> <p>2014-11-15</p> <p>Six calcium sulfoaluminate-based cementitious systems composed of calcium sulfoaluminate, <span class="hlt">calcite</span>, vaterite, and gypsum were cured as pastes and mortars for 1, 7, 28 and 84 days. Pastes were analyzed with X-ray diffraction, thermogravimetric and differential thermal analyses. Mortars were tested for compressive strength, dimensional stability and setting time. Furthermore, pastes with a water/cementitious material mass ratio of 0.80 were tested for heat evolution during the first 48 h by means of isothermal conduction calorimetry. It has been found that: (1) both <span class="hlt">calcite</span> and vaterite reacted with monosulfoaluminate to give monocarboaluminate and ettringite, with vaterite being more reactive; (2) gypsum lowered the reactivity of both carbonates; (3) expansion was reduced by <span class="hlt">calcite</span> and vaterite, irrespective of the presence of gypsum; and (4) both carbonates increased compressive strength in the absence of gypsum and decreased compressive strength less in the presence of gypsum, with vaterite's action more effective than that of <span class="hlt">calcite</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011APS..MARD39015E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011APS..MARD39015E"><span>Enhancing mechanical properties of <span class="hlt">calcite</span> by Mg substitutions: An ab initio study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Elstnerova, Pavlina; Friak, Martin; Hickel, Tilmann; Fabritius, Helge Otto; Lymperakis, Liverios; Petrov, Michal; Raabe, Dierk; Neugebauer, Joerg; Nikolov, Svetoslav; Zigler, Andreas; Hild, Sabine</p> <p>2011-03-01</p> <p>Arthropoda representing a majority of all known animal species are protected by an exoskeleton formed by their cuticle. The cuticle represents a hierarchically structured multifunctional bio-composite based on chitin and proteins. Some groups like Crustacea reinforce the load-bearing parts of their cuticle with <span class="hlt">calcite</span>. As the <span class="hlt">calcite</span> sometimes contains Mg it was speculated that Mg may have a stiffening impact on the mechanical properties of the cuticle. We present a theoretical parameter-free quantum-mechanical study of thermodynamic, structural and elastic properties of Mg-substituted <span class="hlt">calcite</span>. Our results show that substituting Ca by Mg causes an almost linear decrease in the crystal volume with Mg concentration and of substituted crystals. As a consequence the <span class="hlt">calcite</span> crystals become stiffer giving rise e.g. to substantially increased bulk moduli.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23493708','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23493708"><span>Flexible minerals: self-assembled <span class="hlt">calcite</span> spicules with extreme bending strength.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Natalio, Filipe; Corrales, Tomas P; Panthöfer, Martin; Schollmeyer, Dieter; Lieberwirth, Ingo; Müller, Werner E G; Kappl, Michael; Butt, Hans-Jürgen; Tremel, Wolfgang</p> <p>2013-03-15</p> <p>Silicatein-α is responsible for the biomineralization of silicates in sponges. We used silicatein-α to guide the self-assembly of <span class="hlt">calcite</span> "spicules" similar to the spicules of the calcareous sponge Sycon sp. The self-assembled spicules, 10 to 300 micrometers (μm) in length and 5 to 10 μm in diameter, are composed of aligned <span class="hlt">calcite</span> nanocrystals. The spicules are initially amorphous but transform into <span class="hlt">calcite</span> within months, exhibiting unusual growth along [100]. They scatter x-rays like twinned <span class="hlt">calcite</span> crystals. Whereas natural spicules evidence brittle failure, the synthetic spicules show an elastic response, which greatly enhances bending strength. This remarkable feature is linked to a high protein content. With nano-thermogravimetric analysis, we measured the organic content of a single spicule to be 10 to 16%. In addition, the spicules exhibit waveguiding properties even when they are bent.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70015615','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70015615"><span>Simulation of <span class="hlt">calcite</span> dissolution and porosity changes in saltwater mixing zones in coastal aquifers</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Sanford, W.E.; Konikow, L.F.</p> <p>1989-01-01</p> <p>Thermodynamic models of aqueous solutions have indicated that the mixing of seawater and <span class="hlt">calcite</span>-saturated fresh groundwater can produce a water that is undersaturated with respect to <span class="hlt">calcite</span>. Mixing of such waters in coastal carbonate aquifers could lead to significant amounts of limestone dissolution. The potential for such dissolution in coastal saltwater mixing zones is analyzed by coupling the results from a reaction simulation model (PHREEQE) with a variable density groundwater flow and solute transport model. Idealized cross sections of coastal carbonate aquifers are simulated to estimate the potential for <span class="hlt">calcite</span> dissolution under a variety of hydrologic and geochemical conditions. Results show that limestone dissolution in mixing zones is strongly dependent on groundwater flux and nearly independent of the dissolution kinetics of <span class="hlt">calcite</span>. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=calcite+OR+montmorillonite+OR+kaolinite+OR+gibbsite&id=EJ213146','ERIC'); return false;" href="http://eric.ed.gov/?q=calcite+OR+montmorillonite+OR+kaolinite+OR+gibbsite&id=EJ213146"><span>High School Forum: "Invitations to Enquiry": The <span class="hlt">Calcite</span>/Acid Reaction.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Herron, J. Dudley, Ed.; Driscoll, D. R.</p> <p>1979-01-01</p> <p>Describes a high school chemistry experiment which involves the reaction between <span class="hlt">calcite</span> and hydrochloric and sulfuric acids. This reaction can be carried out as a projected demonstration and on an individual basis. (HM)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MinPe.109..453G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MinPe.109..453G"><span>Phase transformation of Mg-<span class="hlt">calcite</span> to aragonite in active-forming hot spring travertines</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Greer, Heather F.; Zhou, Wuzong; Guo, Li</p> <p>2015-08-01</p> <p>A travertine specimen collected from the western part of Yunnan Province of China was subjected to microstructural analysis by powder X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. A new formation mechanism was proposed whereby polycrystalline rhombohedral particles of magnesium-containing <span class="hlt">calcite</span> underwent a phase transformation into sheaf-like clusters of aragonite microrods. It is proposed that a high concentration of magnesium ions and embedded biological matter poisoned the growth of <span class="hlt">calcite</span> and therefore instigated the phase transformation of the core of the rhombohedral <span class="hlt">calcite</span> particles to an aragonite phase with a higher crystallinity. The single crystalline aragonite microrods with a higher density than the Mg-<span class="hlt">calcite</span> nanocrystallites grew at the expense of the latter to generate sheaf-like clusters. This newly discovered formation mechanism is expected to enhance previous knowledge on this geologically important phase transformation from a morphology point of view.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12742051','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12742051"><span>Polymer coatings to passivate <span class="hlt">calcite</span> from acid attack: polyacrylic acid and polyacrylonitrile.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Thompson, Mary; Wilkins, Shelley J; Compton, Richard G; Viles, Heather A</p> <p>2003-04-01</p> <p>The extent of passivation of <span class="hlt">calcite</span> toward dissolution by aqueous acids arising from polymeric coatings based on polyacrylic acid or polyacrylonitrile is evaluated using a channel flow cell technique with microdisc electrode detection. In situ passivation with polyacrylic acid leads to a reduction in the reactivity of <span class="hlt">calcite</span> toward acid attack with a reduction in the rate constant by up to an order of magnitude compared with untreated <span class="hlt">calcite</span>. Ex situ passivation with polyacrylic acid for 24 h results in good coverage of the <span class="hlt">calcite</span> by the polymer but it is shown to erode from the surface when exposed to an aqueous acid solution. In contrast, polyacrylonitrile is demonstrated to form a regular coating after exposure for just 1 h and offers robust potent protection from aqueous acid attack.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JCrGr.457..356C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JCrGr.457..356C"><span>Morphological changes of <span class="hlt">calcite</span> single crystals induced by graphene-biomolecule adducts</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Calvaresi, Matteo; Di Giosia, Matteo; Ianiro, Alessandro; Valle, Francesco; Fermani, Simona; Polishchuk, Iryna; Pokroy, Boaz; Falini, Giuseppe</p> <p>2017-01-01</p> <p><span class="hlt">Calcite</span> has the capability to interact with a wide variety of molecules. This usually induces changes in shape and morphology of crystals. Here, this process was investigated using sheets of graphene-biomolecule adducts. They were prepared and made dispersible in water through the exfoliation of graphite by tip sonication in the presence tryptophan or N-acetyl-D-glucosamine. The crystallization of calcium carbonate in the presence of these additives was obtained by the vapor diffusion method and only <span class="hlt">calcite</span> formed. The analysis of the microscopic observations showed that the graphene-biomolecule adducts affected shape and morphology of rhombohedral {10.4} faced <span class="hlt">calcite</span> crystals, due to their stabilization of additional {hk.0} faces. The only presence of the biomolecule affected minimally shape and morphology of <span class="hlt">calcite</span> crystals, highlighting the key role of the graphene sheets as 2D support for the adsorption of the biomolecules.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26552883','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26552883"><span>The impact of <span class="hlt">abiotic</span> factors on cellulose synthesis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Ting; McFarlane, Heather E; Persson, Staffan</p> <p>2016-01-01</p> <p>As sessile organisms, plants require mechanisms to sense and respond to changes in their environment, including both biotic and <span class="hlt">abiotic</span> factors. One of the most common plant adaptations to environmental changes is differential regulation of growth, which results in growth either away from adverse conditions or towards more favorable conditions. As cell walls shape plant growth, this differential growth response must be accompanied by alterations to the plant cell wall. Here, we review the impact of four <span class="hlt">abiotic</span> factors (osmotic conditions, ionic stress, light, and temperature) on the synthesis of cellulose, an important component of the plant cell wall. Understanding how different <span class="hlt">abiotic</span> factors influence cellulose production and addressing key questions that remain in this field can provide crucial information to cope with the need for increased crop production under the mounting pressures of a growing world population and global climate change.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25618839','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25618839"><span>Integrated metabolomics for <span class="hlt">abiotic</span> stress responses in plants.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Nakabayashi, Ryo; Saito, Kazuki</p> <p>2015-04-01</p> <p>Plants are considered to biosynthesize specialized (traditionally called secondary) metabolites to adapt to environmental stresses such as biotic and <span class="hlt">abiotic</span> stresses. The majority of specialized metabolites induced by <span class="hlt">abiotic</span> stress characteristically exhibit antioxidative activity in vitro, but their function in vivo is largely yet to be experimentally confirmed. In this review, we highlight recent advances in the identification of the role of <span class="hlt">abiotic</span> stress-responsive specialized metabolites with an emphasis on flavonoids. Integrated 'omics' analysis, centered on metabolomics with a series of plant resources differing in their flavonoid accumulation, showed experimentally that flavonoids play a major role in antioxidation in vivo. In addition, the results also suggest the role of flavonoids in the vacuole. To obtain more in-depth insights, chemical and biological challenges need to be addressed for the identification of unknown specialized metabolites and their in vivo functions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..1711145C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..1711145C"><span>The Influence of <span class="hlt">Calcite</span> on The Mechanical Behavior of Quartz-Bearing Gouge</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carpenter, Brett; Di Stefano, Giuseppe; Collettini, Cristiano</p> <p>2015-04-01</p> <p>Mechanical heterogeneities along faults can result in diverse and complex fault slip. These heterogeneities can vary spatially and temporally and may result from changes in fault structure or frictional properties. The accumulation of <span class="hlt">calcite</span> in non-carbonate faults, via cementation or entrainment, is likely to alter the frictional properties of that fault gouge. Furthermore, widespread observations of <span class="hlt">calcite</span> as cement, veins, or cataclasites in non-carbonate hosted faults indicates that <span class="hlt">calcite</span> is readily available and could play an important role during fault reactivation at shallow- and mid-crustal earthquakes. We report on laboratory experiments designed to explore the mechanical behavior of quartz/<span class="hlt">calcite</span> mixtures as a means to better understand the evolution in behavior of quartz-bearing gouge in the presence of exotic <span class="hlt">calcite</span>. We sheared mixtures of powdered Carrara marble (>98% CaCO3) and disaggregated Ottawa sand (99.8% SiO2) at constant normal stresses of 5 and 50 MPa under saturated conditions at room temperature. We performed slide-hold-slide tests, 1-3,000 seconds, and velocity stepping tests, 0.1-1000 µm/s, to measure the amount of frictional healing and velocity dependence of friction respectively. At low normal stress, the addition of <span class="hlt">calcite</span> to quartz-based synthetic fault gouge results in increases in the steady-state frictional strength, and rates of frictional healing and creep relaxation of the gouge. In particular, with the addition of as little as 2.5 wt% <span class="hlt">calcite</span>, the frictional healing rate increases by 30%. Microstructural observations indicate that shear is accommodated by distributed deformation throughout the gouge layer and that <span class="hlt">calcite</span> undergoes significantly more comminution compared to quartz. Large quartz grains frequently show minor rounding of angular edges with fine-grained <span class="hlt">calcite</span> often penetrating fractures. The in-situ addition of <span class="hlt">calcite</span> to fault gouge, by either the circulation of fluids or the involvement of carbonate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T22C..01C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T22C..01C"><span>The Influence of Exotic <span class="hlt">Calcite</span> on the Mechanical Behavior of Quartz Bearing Fault Gouge</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carpenter, B. M.; Di Stefano, G.; Collettini, C.</p> <p>2014-12-01</p> <p>The interseismic recovery of frictional strength is a fundamental part of the seismic cycle. This restrengthening, and related phenomena, plays a key role in determining the stability and mode of tectonic faulting. Recent experimental data has shown that gouge mineralogy has a strong influence on the rate of frictional healing, with <span class="hlt">calcite</span>-dominated gouges showing the highest rates. Combining these data with widespread observations of <span class="hlt">calcite</span> as cement or veins in non-carbonate hosted faults, indicates that the presence of <span class="hlt">calcite</span> within a fault gouge could play an important role in shallow- and mid-crustal earthquakes. We report on laboratory experiments designed to explore the mechanical behavior of quartz/<span class="hlt">calcite</span> mixtures as a means to better understand the evolution of fault behavior in faults where carbonate materials are present. We sheared mixtures of powdered Carrara marble (>98% CaCO3) and disaggregated Ottawa sand (99.8% SiO2) at constant normal stress of 5 MPa under saturated conditions at room temperature. We performed slide-hold-slide tests, 1-3,000 seconds, and velocity stepping tests, 0.1-1000 μm/s, to measure the amount of frictional healing and velocity dependence of friction respectively. Small subsets of experiments were conducted at different boundary conditions. Preliminary results show that the presence of <span class="hlt">calcite</span> in quartz-based fault gouge has a hardening effect, both in overall frictional strength, where the strength of our mixtures increases with increasing <span class="hlt">calcite</span> content, and in single experiments, where mixtures with low percentages of <span class="hlt">calcite</span> show a consistent strain-hardening trend. We also observe that the rates of frictional healing and creep relaxation increase with increasing <span class="hlt">calcite</span> content. Finally, our results show that the addition of as little as 2.5% <span class="hlt">calcite</span> within a fault gouge results in a 30% increase in the rate of frictional healing, with further increases in <span class="hlt">calcite</span> content resulting in larger increases in the rate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6641100','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6641100"><span><span class="hlt">Calcite</span> genesis in the Upper Freeport coal bed as indicated by stable isotope geochemistry</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dulong, F.T.; Spiker, E.C.; Cecil, C.B.; Stanton, R.W.</p> <p>1985-01-01</p> <p>The grinding and sizing in float-sink testing of the Upper Freeport coal bed physically separates <span class="hlt">calcite</span> of different origins. The different origins are distinguished by different isotopic compositions. The isotopic compositions of <span class="hlt">calcite</span> indicates at least two, possibly three, stages of <span class="hlt">calcite</span> formation in the Upper Freeport coal bed. <span class="hlt">Calcite</span> samples obtained from cleat, and isolated from 8x100 mesh-1.8 specific gravity sink fraction and -100 mesh size fraction, are enriched in /sup 13/C. The dispersion in /sup 18/O values for all three sample types, as measured by the standard deviation, is 2.7 per mil relative to SMOW, which may indicate similar temperature of formation. In contrast, <span class="hlt">calcite</span> from the 1.275 specific gravity float fraction is depleted in /sup 13/C (mean = -4.6 per mil), indicative of CO/sub 2/ generated from the oxidation of organic matter. The standard deviation of /sup 18/O values for these samples is 9.2 per mil, probably indicating variation in the temperature of formation. Limestone samples associated with the Upper Freeport coal bed are slightly depleted in /sup 13/C (mean = -3.1 per mil). Genesis of <span class="hlt">calcite</span> in the coal apparently resulted from biotic, as well as, thermogenic processes. A second stage of <span class="hlt">calcite</span> formation, resulting from fermentation and methanogenesis is in cleat, and in the 8x100 mesh-1.8 specific gravity sink and -100 mesh size fractions. Part of the <span class="hlt">calcite</span> in the 1.275 specific gravity float fraction may have formed from thermally generated CO/sub 2/ released during coalification.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeCoA.197..226P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeCoA.197..226P"><span>The coordination of sulfur in synthetic and biogenic Mg <span class="hlt">calcites</span>: The red coral case</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Perrin, J.; Rivard, C.; Vielzeuf, D.; Laporte, D.; Fonquernie, C.; Ricolleau, A.; Cotte, M.; Floquet, N.</p> <p>2017-01-01</p> <p>Sulfur has been recognized in biogenic <span class="hlt">calcites</span> for a long time. However, its structural position is matter of debate. For some authors, sulfur is a marker of the organic matrix while it is part of the <span class="hlt">calcite</span> structure itself for others. To better understand the place of sulfur in <span class="hlt">calcite</span>, sulfated magnesian <span class="hlt">calcites</span> (S-Mg<span class="hlt">Calcite</span>) have been synthetized at high pressure and temperature and studied by μ-XANES spectroscopy. S-Mg<span class="hlt">Calcite</span> XANES spectra show two different types of sulfur: sulfate (SO42-) as a predominant species and a small contribution of sulfite (SO32-), both substituting for carbonate ions in the <span class="hlt">calcite</span> structure. To address the question of the position of sulfur in biogenic <span class="hlt">calcites</span>, the oxidation states of sulfur in the skeleton and organic tissues of Corallium rubrum have been investigated by micro X-ray fluorescence (μ-XRF) and sulfur K-edge micro X-ray absorption near edge structure (μ-XANES) spectroscopy at the European Synchrotron Radiation Facility (ESRF, Grenoble, France) on beamline ID21. In the skeleton, sulfur is mainly present as oxidized sulfur SO42- (+VI), plus a weak sulfite contribution. XANES spectra indicate that sulfur is inorganically incorporated as sulfur structurally substituted to carbonate ions (SSS). Although an organic matrix is present in the red coral skeleton, reduced organic sulfur could not be detected by μ-XANES spectroscopy in the skeleton probably due to low organic/inorganic sulfur ratio. In the organic tissues surrounding the skeleton, several sulfur oxidation states have been detected including disulfide (S-S), thioether (R-S-CH3), sulfoxide (SO2), sulfonate (SO2O-) and sulfate (SO42-). The unexpected occurrence of inorganic sulfate within the organic tissues suggests the presence of pre-organized organic/inorganic complexes in the circulatory system of the red coral, precursors to biomineralization ahead of the growth front.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70029387','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70029387"><span>The <span class="hlt">calcite</span> → aragonite transformation in low-Mg marble: Equilibrium relations, transformations mechanisms, and rates</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hacker, Bradley R.; Rubie, David C.; Kirby, Stephen H.; Bohlen, Steven R.</p> <p>2005-01-01</p> <p>Experimental transformation of a rather pure natural <span class="hlt">calcite</span> marble to aragonite marble did not proceed via the expected straightforward polymorphic replacement. Instead, the small amount of Mg in the starting material (0.36 wt %) was excluded from the growing aragonite and diffused preferentially into the remaining <span class="hlt">calcite</span> grains, producing Mg-rich <span class="hlt">calcite</span> rods that persisted as relicts. Nucleation of aragonite occurred exclusively on grain boundaries, with aragonite [001] oriented subparallel to <span class="hlt">calcite</span> [0001]. The aragonite crystals preferentially consumed the <span class="hlt">calcite</span> crystal on which they nucleated, and the reaction fronts developed preferentially along the {010} and {110} planes of aragonite. Each aragonite neoblast that grew was nearly free of Mg (typically <0.1 wt %). The excess Mg was taken up by the <span class="hlt">calcite</span> grains in between, stabilizing them and causing a few volume percent rodlike relicts of Mg-enriched <span class="hlt">calcite</span> (up to 10 wt % MgO) to be left behind by the advancing reaction front. The aragonite growth rates are approximately linear and range from ∼3 × 10−11 m s−1 at 600°C to ∼9 × 10−9 m s−1 at 850°C, with an apparent activation enthalpy of 166 ± 91 kJ mol−1. This reaction mechanism and the resultant texture are akin to cellular precipitation reactions in metals. Similar transformation textures have been reported from high-Mg marbles in Japan and China that disproportionated to low-Mg <span class="hlt">calcite</span> and dolomite.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1005573','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1005573"><span>Effects of chitosan on the alignment, morphology and shape of <span class="hlt">calcite</span> crystals nucleating under Langmuir monolayers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kim, Kyungil; Uysal, Ahmet; Kewalramani, Sumit; Stripe, Benjamin; Dutta, Pulak</p> <p>2009-04-22</p> <p>The growth of calcium carbonate crystals under Langmuir monolayers was investigated in the presence of chitosan, a soluble derivative of chitin added to the subphase to better simulate the polyelectrolyte-containing in vivo environment. Chitosan causes distinct concentration-dependent changes in the orientation, shape and morphology of the <span class="hlt">calcite</span> crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic <span class="hlt">calcite</span> crystals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/980170','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/980170"><span>Effects of Chitosan on the Morphology and Alignment of <span class="hlt">Calcite</span> Crystals Nucleating Under Langmuir Monolayers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kim, K.; Uysal, A; Kewalramani, S; Stripe, B; Dutta, P</p> <p>2009-01-01</p> <p>The growth of calcium carbonate crystals under Langmuir monolayers was investigated in the presence of chitosan, a soluble derivative of chitin added to the subphase to better simulate the polyelectrolyte-containing in vivo environment. Chitosan causes distinct concentration-dependent changes in the orientation, shape and morphology of the <span class="hlt">calcite</span> crystals nucleating under acid and sulfate monolayers. Our results suggest that polyelectrolytes may play essential roles in controlling the growth of biogenic <span class="hlt">calcite</span> crystals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27821742','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27821742"><span><span class="hlt">Abiotic</span> methane formation during experimental serpentinization of olivine.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>McCollom, Thomas M</p> <p>2016-12-06</p> <p>Fluids circulating through actively serpentinizing systems are often highly enriched in methane (CH4). In many cases, the CH4 in these fluids is thought to derive from <span class="hlt">abiotic</span> reduction of inorganic carbon, but the conditions under which this process can occur in natural systems remain unclear. In recent years, several studies have reported <span class="hlt">abiotic</span> formation of CH4 during experimental serpentinization of olivine at temperatures at or below 200 °C. However, these results seem to contradict studies conducted at higher temperatures (300 °C to 400 °C), where substantial kinetic barriers to CH4 synthesis have been observed. Here, the potential for <span class="hlt">abiotic</span> formation of CH4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200 °C to 320 °C. A (13)C-labeled inorganic carbon source was used to unambiguously determine the origin of CH4 generated in the experiments. Consistent with previous high-temperature studies, the results indicate that <span class="hlt">abiotic</span> formation of CH4 from reduction of dissolved inorganic carbon during the experiments is extremely limited, with nearly all of the observed CH4 derived from background sources. The results indicate that the potential for <span class="hlt">abiotic</span> synthesis of CH4 in low-temperature serpentinizing environments may be much more limited than some recent studies have suggested. However, more extensive production of CH4 was observed in one experiment performed under conditions that allowed an H2-rich vapor phase to form, suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for <span class="hlt">abiotic</span> synthesis of CH4.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23595200','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23595200"><span>Strategies to ameliorate <span class="hlt">abiotic</span> stress-induced plant senescence.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gepstein, Shimon; Glick, Bernard R</p> <p>2013-08-01</p> <p>The plant senescence syndrome resembles, in many molecular and phenotypic aspects, plant responses to <span class="hlt">abiotic</span> stresses. Both processes have an enormous negative global agro-economic impact and endanger food security worldwide. Premature plant senescence is the main cause of losses in grain filling and biomass yield due to leaf yellowing and deteriorated photosynthesis, and is also responsible for the losses resulting from the short shelf life of many vegetables and fruits. Under <span class="hlt">abiotic</span> stress conditions the yield losses are often even greater. The primary challenge in agricultural sciences today is to develop technologies that will increase food production and sustainability of agriculture especially under environmentally limiting conditions. In this chapter, some of the mechanisms involved in <span class="hlt">abiotic</span> stress-induced plant senescence are discussed. Recent studies have shown that crop yield and nutritional values can be altered as well as plant stress tolerance through manipulating the timing of senescence. It is often difficult to separate the effects of age-dependent senescence from stress-induced senescence since both share many biochemical processes and ultimately result in plant death. The focus of this review is on <span class="hlt">abiotic</span> stress-induced senescence. Here, a number of the major approaches that have been developed to ameliorate some of the effects of <span class="hlt">abiotic</span> stress-induced plant senescence are considered and discussed. Some approaches mimic the mechanisms already used by some plants and soil bacteria whereas others are based on development of new improved transgenic plants. While there may not be one simple strategy that can effectively decrease all losses of crop yield that accrue as a consequence of <span class="hlt">abiotic</span> stress-induced plant senescence, some of the strategies that are discussed already show great promise.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PNAS..11313965M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PNAS..11313965M"><span><span class="hlt">Abiotic</span> methane formation during experimental serpentinization of olivine</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McCollom, Thomas M.</p> <p>2016-12-01</p> <p>Fluids circulating through actively serpentinizing systems are often highly enriched in methane (CH4). In many cases, the CH4 in these fluids is thought to derive from <span class="hlt">abiotic</span> reduction of inorganic carbon, but the conditions under which this process can occur in natural systems remain unclear. In recent years, several studies have reported <span class="hlt">abiotic</span> formation of CH4 during experimental serpentinization of olivine at temperatures at or below 200 °C. However, these results seem to contradict studies conducted at higher temperatures (300 °C to 400 °C), where substantial kinetic barriers to CH4 synthesis have been observed. Here, the potential for <span class="hlt">abiotic</span> formation of CH4 from dissolved inorganic carbon during olivine serpentinization is reevaluated in a series of laboratory experiments conducted at 200 °C to 320 °C. A 13C-labeled inorganic carbon source was used to unambiguously determine the origin of CH4 generated in the experiments. Consistent with previous high-temperature studies, the results indicate that <span class="hlt">abiotic</span> formation of CH4 from reduction of dissolved inorganic carbon during the experiments is extremely limited, with nearly all of the observed CH4 derived from background sources. The results indicate that the potential for <span class="hlt">abiotic</span> synthesis of CH4 in low-temperature serpentinizing environments may be much more limited than some recent studies have suggested. However, more extensive production of CH4 was observed in one experiment performed under conditions that allowed an H2-rich vapor phase to form, suggesting that shallow serpentinization environments where a separate gas phase is present may be more favorable for <span class="hlt">abiotic</span> synthesis of CH4.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28389176','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28389176"><span>Identification of the <span class="hlt">abiotic</span> stress-related transcription in little Neptune grass Cymodocea nodosa with RNA-seq.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Malandrakis, E E; Dadali, O; Kavouras, M; Danis, T; Panagiotaki, P; Miliou, H; Kuepper, F C; Exadactylos, A</p> <p>2017-04-04</p> <p>Seagrasses exhibit vital ecological roles in the <span class="hlt">marine</span> environment. Nevertheless, the genomic resources available for seagrasses are still scarce. In the present study, the transcriptome of Cymodocea nodosa was sequenced with a view to study the molecular mechanisms underlying <span class="hlt">abiotic</span> stress responses. The sequenced transcriptome for the species was near-complete and a high percentage of the transcripts was computationally annotated. An experimental simulation of <span class="hlt">marine</span> plant exposure to extreme temperature (34°C), salinity (50psu) and their combination was conducted. A dynamic transcriptome 24h response (short-term) from stress initialization was recorded. The most noteworthy alteration in gene expression was observed in heat-stressed plants. Transcripts associated with development, photosynthesis, osmotic balance and stress-response were differentially expressed, under the set experimental conditions. Results indicate a potential negative interaction of heat and osmotic stress on seagrasses transcriptome.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5695970','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5695970"><span>Geochemistry of metastable carbonate minerals from the Brush Creek <span class="hlt">marine</span> interval (Missourian), Indiana County, Pennsylvania</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cercone, K.R.; Kime, A.; Mutchler, S.; Rittle, K. )</p> <p>1991-08-01</p> <p>Many <span class="hlt">marine</span> fossils from the Missourian Brush Creek interval of western Pennsylvania display partial preservation of metastable aragonite and high-magnesium <span class="hlt">calcite</span> shell material. Bivalve mollusks have been shown by x-ray diffraction to contain as much as 96% aragonite, with lesser amounts of both high-magnesium and low-magnesium <span class="hlt">calcite</span>. Stable carbon and oxygen isotopic ratios from these bivalves suggest they precipitated in equilibrium with Pennsylvanian ocean water. The bellerophontid Pharkidonotus, which exhibits partial recrystallization textures under scanning electron microscopy, consists of 45% aragonite and 55% low-magnesium <span class="hlt">calcite</span>, and has slightly more depleted isotopic values than bivalves. Crinoids also appear to have been partially recrystallized, resulting in a mixture of primary high-magnesium <span class="hlt">calcite</span> and secondary low-magnesium <span class="hlt">calcite</span> and microdolomite, with much of the original shell structure still preserved. The degree of preservation of metastable carbonate minerals varies both stratigraphically and spatially within the Brush Creek interval. Maximum preservation occurs in organic-rich shales deposited in low-lying areas of the Brush Creek sea floor. The preservation of aragonite and high-magnesium <span class="hlt">calcite</span> in such units may have resulted from a lack of circulating porewater during early diagenesis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19017111','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19017111"><span>Nitric oxide signaling in plant responses to <span class="hlt">abiotic</span> stresses.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Qiao, Weihua; Fan, Liu-Min</p> <p>2008-10-01</p> <p>Nitric oxide (NO) plays important roles in diverse physiological processes in plants. NO can provoke both beneficial and harmful effects, which depend on the concentration and location of NO in plant cells. This review is focused on NO synthesis and the functions of NO in plant responses to <span class="hlt">abiotic</span> environmental stresses. <span class="hlt">Abiotic</span> stresses mostly induce NO production in plants. NO alleviates the harmfulness of reactive oxygen species, and reacts with other target molecules, and regulates the expression of stress responsive genes under various stress conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28277621','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28277621"><span>Starch as a determinant of plant fitness under <span class="hlt">abiotic</span> stress.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Thalmann, Matthias; Santelia, Diana</p> <p>2017-03-09</p> <p>I. II. III. IV. V. VI. References SUMMARY: <span class="hlt">Abiotic</span> stresses, such as drought, high salinity and extreme temperatures, pose one of the most important constraints to plant growth and productivity in many regions of the world. A number of investigations have shown that plants, including several important crops, remobilize their starch reserve to release energy, sugars and derived metabolites to help mitigate the stress. This is an essential process for plant fitness with important implications for plant productivity under challenging environmental conditions. In this Tansley insight, we evaluate the current literature on starch metabolism in response to <span class="hlt">abiotic</span> stresses, and discuss the key enzymes involved and how they are regulated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70025674','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70025674"><span>Estimation of past seepage volumes from <span class="hlt">calcite</span> distribution in the Topopah Spring Tuff, Yucca Mountain, Nevada</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Marshall, B.D.; Neymark, L.A.; Peterman, Z.E.</p> <p>2003-01-01</p> <p>Low-temperature <span class="hlt">calcite</span> and opal record the past seepage of water into open fractures and lithophysal cavities in the unsaturated zone at Yucca Mountain, Nevada, site of a proposed high-level radioactive waste repository. Systematic measurements of <span class="hlt">calcite</span> and opal coatings in the Exploratory Studies Facility (ESF) tunnel at the proposed repository horizon are used to estimate the volume of <span class="hlt">calcite</span> at each site of <span class="hlt">calcite</span> and/or opal deposition. By estimating the volume of water required to precipitate the measured volumes of <span class="hlt">calcite</span> in the unsaturated zone, seepage rates of 0.005 to 5 liters/year (l/year) are calculated at the median and 95th percentile of the measured volumes, respectively. These seepage rates are at the low end of the range of seepage rates from recent performance assessment (PA) calculations, confirming the conservative nature of the performance assessment. However, the distribution of the <span class="hlt">calcite</span> and opal coatings indicate that a much larger fraction of the potential waste packages would be contacted by this seepage than is calculated in the performance assessment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22413251','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22413251"><span>NMR characterization of hydrocarbon adsorption on <span class="hlt">calcite</span> surfaces: A first principles study</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bevilaqua, Rochele C. A.; Miranda, Caetano R.; Rigo, Vagner A.; Veríssimo-Alves, Marcos</p> <p>2014-11-28</p> <p>The electronic and coordination environment of minerals surfaces, as <span class="hlt">calcite</span>, are very difficult to characterize experimentally. This is mainly due to the fact that there are relatively few spectroscopic techniques able to detect Ca{sup 2+}. Since <span class="hlt">calcite</span> is a major constituent of sedimentary rocks in oil reservoir, a more detailed characterization of the interaction between hydrocarbon molecules and mineral surfaces is highly desirable. Here we perform a first principles study on the adsorption of hydrocarbon molecules on <span class="hlt">calcite</span> surface (CaCO{sub 3} (101{sup ¯}4)). The simulations were based on Density Functional Theory with Solid State Nuclear Magnetic Resonance (SS-NMR) calculations. The Gauge-Including Projector Augmented Wave method was used to compute mainly SS-NMR parameters for {sup 43}Ca, {sup 13}C, and {sup 17}O in <span class="hlt">calcite</span> surface. It was possible to assign the peaks in the theoretical NMR spectra for all structures studied. Besides showing different chemical shifts for atoms located on different environments (bulk and surface) for <span class="hlt">calcite</span>, the results also display changes on the chemical shift, mainly for Ca sites, when the hydrocarbon molecules are present. Even though the interaction of the benzene molecule with the <span class="hlt">calcite</span> surface is weak, there is a clearly distinguishable displacement of the signal of the Ca sites over which the hydrocarbon molecule is located. A similar effect is also observed for hexane adsorption. Through NMR spectroscopy, we show that aromatic and alkane hydrocarbon molecules adsorbed on carbonate surfaces can be differentiated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5677360','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5677360"><span>Multiple origins for zoned cathodoluminescent and noncathodoluminescent <span class="hlt">calcite</span> cements in Pennsylvanian limestones</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Goldstein, R.H.; Anderson, J.E.; Phares, R.A. )</p> <p>1991-03-01</p> <p>Noncathodoluminescent <span class="hlt">calcite</span> containing brightly to moderately luminescent zones is a common early cement in limestones. Three such cements in Upper Pennsylvanian limestones from different areas were studied. All three units are overlain up-section by Permian evaporites and consist of carbonate-siliciclastic 'cyclothems' in which individual cycles were subject to subaerial exposure. With such similar settings, one might predict that petrographically similar <span class="hlt">calcite</span> cements would have similar origins. In the Holder Formation (New Mexico), the zoned <span class="hlt">calcite</span> predates compaction, and cross-cutting relationships with cycle-capping paleosols show that zoned cements precipitated during 15 events of subaerial exposure. Therefore, cements precipitated from freshwater during early and repeated subaerial exposure. For the Lansing-Kansas City groups in northwestern Kansas, the zoned <span class="hlt">calcite</span> cements commonly are among the first precipitated but may postdate some compaction. All-liquid fluid inclusions indicated precipitation below about 50C, from brines of approximately 23 weight %. NaCl equivalent. The brines may have refluxed downward during deposition of Permian evaporites. A limestone of the Lansing-Kansas City groups of west-central Kansas contains early zoned <span class="hlt">calcite</span> cement that predates compaction. The cement contains all-liquid fluid inclusions indicating precipitation below about 50C. The presence of nonluminescent <span class="hlt">calcite</span> containing bright subzones is not indicative of a single diagenetic environment. Petrographically similar cements from similar settings may originate in markedly different diagenetic environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23176816','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23176816"><span>Initial formation of <span class="hlt">calcite</span> crystals in the thin prismatic layer with the periostracum of Pinctada fucata.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Suzuki, Michio; Nakayama, Seiji; Nagasawa, Hiromichi; Kogure, Toshihiro</p> <p>2013-02-01</p> <p>Although the formation mechanism of <span class="hlt">calcite</span> crystals in the prismatic layer has been studied well in many previous works, the initial state of <span class="hlt">calcite</span> formation has not been observed in detail using electron microscopes. In this study, we report that the soft prismatic layer with transparent color (the thin prismatic layer) in the tip of the fresh shell of Pinctada fucata was picked up to observe the early calcification phase. A scanning electron microscope (SEM) image showed that the growth tip of the thin prismatic layer was covered by the periostracum, which was also where the initial formation of <span class="hlt">calcite</span> crystals began. A cross-section containing the thin <span class="hlt">calcite</span> crystals in the thin prismatic layer with the periostracum was made using a focused ion beam (FIB) system. In a transmission electron microscope (TEM) observation, the thin <span class="hlt">calcite</span> crystal (thickness is about 1μm) on the periostracum was found to be a single crystal with the c-axis oriented perpendicular to the shell surface. On the other hand, many aggregated small particles consisting of bassanite crystals were observed in the periostracum suggesting the possibility that not only organic sulfate but also inorganic sulfates exist in the prismatic layer. These discoveries in the early calcification phase of the thin prismatic layer may help to clarify the mechanism of regulating the nucleation and orientation of the <span class="hlt">calcite</span> crystal in the shell.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3483407','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3483407"><span>Sea urchin tooth mineralization: <span class="hlt">Calcite</span> present early in the aboral plumula</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Stock, Stuart R.; Veis, Arthur; Xiao, Xianghui; Almer, Jonathan D.; Dorvee, Jason R.</p> <p>2012-01-01</p> <p>In both vertebrate bone, containing carbonated hydroxyapatite as the mineral phase, and in invertebrate hard tissue comprised of calcium carbonate, a popular view is that the mineral phase develops from a long-lived amorphous precursor which later transforms into crystal form. Important questions linked to this popular view are: When and where is the crystallized material formed, and is amorphous solid added subsequently to the crystalline substrate? Sea urchin teeth, in which the earliest mineral forms within isolated compartments, in a time and position dependent manner, allow direct investigation of the timing of crystallization of the <span class="hlt">calcite</span> primary plates. Living teeth of the sea urchin Lytechinus variegatus, in their native coelomic fluid, were examined by high-energy synchrotron x-ray diffraction. The diffraction data show that <span class="hlt">calcite</span> is present in the most aboral portions of the plumula, representing the very earliest stages of mineralization, and that this <span class="hlt">calcite</span> has the same crystal orientation as in the more mature adoral portions of the same tooth. Raman spectroscopy of the aboral plumula confirms the initial primary plate mineral material is <span class="hlt">calcite</span> and does not detect amorphous calcium carbonate; in the more mature adoral incisal flange, it does detect a broader <span class="hlt">calcite</span> peak, consistent with two or more magnesium compositions. We hypothesize that some portion of each syncytial membrane in the plumula provides the information for nucleation of identically oriented <span class="hlt">calcite</span> crystals that subsequently develop to form the complex geometry of the single crystal sea urchin tooth. PMID:22940703</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22864212','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22864212"><span>Fabrication of microporous <span class="hlt">calcite</span> block from calcium hydroxide compact under carbon dioxide atmosphere at high temperature.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Otsu, Akihiro; Tsuru, Kanji; Maruta, Michito; Munar, Melvin L; Matsuya, Shigeki; Ishikawa, Kunio</p> <p>2012-01-01</p> <p>Effects of carbonation temperature and compacting pressure on basic properties of <span class="hlt">calcite</span> block were studied using Ca(OH)2 compact made with 0.2-2.0 MPa and their carbonation at 200-800ºC for 1 h. Microporous <span class="hlt">calcite</span> was obtained only when carbonated at 600ºC using Ca(OH)2 compact made with 0.2 MPa even though thermogravimetry analysis showed that <span class="hlt">calcite</span> powder was stable up to 920ºC under CO2 atmosphere. CaO formed by carbonation at 700ºC and 800ºC is thought to be caused by the limited CO2 diffusion interior to the Ca(OH)2 compact. Also, unreacted Ca(OH)2 was found for Ca(OH)2 compact prepared with 0.5 MPa or higher pressure even when carbonated at 600ºC. As a result of high temperature carbonation, crystallite size of the <span class="hlt">calcite</span>, 58.0 nm, was significantly larger when compared to that of <span class="hlt">calcite</span> prepared at room temperature, 35.5 nm. Porosity and diametral tensile strength of the microporous <span class="hlt">calcite</span> were 39.5% and 6.4 MPa.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1038168','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1038168"><span>Mixing-induced <span class="hlt">calcite</span> precipitation and dissolution kinetics in micromodel experiments.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Valocchi, Albert J.; Dewers, Thomas A.; Dehoff, Karl; Yoon, Hongkyu; Werth, Charles J.</p> <p>2010-12-01</p> <p>Dissolved CO2 from geological CO2 sequestration may react with dissolved minerals in fractured rocks or confined aquifers and cause mineral precipitation. The overall rate of reaction can be limited by diffusive or dispersive mixing, and mineral precipitation can block pores and further hinder these processes. Mixing-induced <span class="hlt">calcite</span> precipitation experiments were performed by injecting solutions containing CaCl2 and Na2CO3 through two separate inlets of a micromodel (1-cm x 2-cm x 40-microns); transverse dispersion caused the two solutions to mix along the center of the micromodel, resulting in <span class="hlt">calcite</span> precipitation. The amount of <span class="hlt">calcite</span> precipitation initially increased to a maximum and then decreased to a steady state value. Fluorescent microscopy and imaging techniques were used to visualize <span class="hlt">calcite</span> precipitation, and the corresponding effects on the flow field. Experimental micromodel results were evaluated with pore-scale simulations using a 2-D Lattice-Boltzmann code for water flow and a finite volume code for reactive transport. The reactive transport model included the impact of pH upon carbonate speciation and <span class="hlt">calcite</span> dissolution. We found that proper estimation of the effective diffusion coefficient and the reaction surface area is necessary to adequately simulate precipitation and dissolution rates. The effective diffusion coefficient was decreased in grid cells where <span class="hlt">calcite</span> precipitated, and keeping track of reactive surface over time played a significant role in predicting reaction patterns. Our results may improve understanding of the fundamental physicochemical processes during CO2 sequestration in geologic formations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JSG....94..116K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JSG....94..116K"><span>Reaction-induced fracturing in a hot pressed <span class="hlt">calcite</span>-periclase aggregate</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kuleci, H.; Ulven, O. I.; Rybacki, E.; Wunder, B.; Abart, R.</p> <p>2017-01-01</p> <p>The chemo-mechanical feedbacks associated with hydration of periclase immersed in a <span class="hlt">calcite</span> matrix were investigated experimentally. Dense <span class="hlt">calcite</span>-periclase aggregates with <5% porosity and with a <span class="hlt">calcite</span> to periclase ratio of 90/10 and 95/5 by volume were prepared by hot isostatic pressing. Subsequent hydration experiments were performed in a hydrothermal apparatus at temperatures of 580-610 °C and a pressure of 200 MPa for run durations of 5-60 min. The rate of the periclase to brucite transformation was primarily controlled by the access of fluid. Where fluid was present, the reaction was too fast for the associated positive volume increase of the solids of about 100% to be accommodated by creep of the <span class="hlt">calcite</span> matrix, and fracturing was induced. The newly formed cracks greatly enhanced the access of fluid leading to a positive feedback between hydration and fracturing. Mostly the newly formed cracks follow pre-existing grain boundaries in the <span class="hlt">calcite</span> matrix. Comparison of experimental results with numerical 2D discrete element modelling (DEM) of crack formation revealed that the geometry of the crack pattern around a reacting particle depends on the shape of the original periclase particle, on the mechanical strength of the particle-matrix interface and on the mechanical strength and arrangement of grain boundaries in the <span class="hlt">calcite</span> matrix in the immediate vicinity of the swelling particle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..1112182V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..1112182V"><span>Static Grain Growth in Contact Metamorphic <span class="hlt">Calcite</span>: A Cathodoluminescence Study.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vogt, B.; Heilbronner, R.; Herwegh, M.; Ramseyer, K.</p> <p>2009-04-01</p> <p>In the Adamello contact aureole, monomineralic mesozoic limestones were investigated in terms of grain size evolution and compared to results on numerical modeling performed by Elle. The sampled area shows no deformation and therefore represents an appropriate natural laboratory for the study of static grain growth (Herwegh & Berger, 2003). For this purpose, samples were collected at different distances to the contact to the pluton, covering a temperature range between 270 to 630°C. In these marbles, the grain sizes increase with temperature from 5 µm to about 1 cm as one approaches the contact (Herwegh & Berger, 2003). In some samples, photomicrographs show domains of variable cathodoluminescence (CL) intensities, which are interpreted to represent growth zonations. Microstructures show grains that contain cores and in some samples even several growth stages. The cores are usually not centered and the zones not concentric. They may be in touch with grain boundaries. These zonation patterns are consistent within a given aggregate but differ among the samples even if they come from the same location. Relative CL intensities depend on the Mn/Fe ratio. We assume that changes in trace amounts of Mn/Fe must have occurred during the grain size evolution, preserving local geochemical trends and their variations with time. Changes in Mn/Fe ratios can either be explained by (a) locally derived fluids (e.g. hydration reactions of sheet silicate rich marbles in the vicinity) or (b) by the infiltration of the <span class="hlt">calcite</span> aggregates by externally derived (magmatic?) fluids. At the present stage, we prefer a regional change in fluid composition (b) because the growth zonations only occur at distances of 750-1250 m from the pluton contact (350-450°C). Closer to the contact, neither zonations nor cores were found. At larger distances, CL intensities differ from grain to grain, revealing diagenetic CL patterns that were incompletely recrystallized by grain growth. The role of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1987JSG.....9..747S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1987JSG.....9..747S"><span>Simple shear experiments on <span class="hlt">calcite</span> rocks: rheology and microfabric</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmid, S. M.; Panozzo, R.; Bauer, S.</p> <p></p> <p>Ideal simple shearing of Carrara marble and Solnhofen limestone was achieved by inserting <span class="hlt">calcite</span> rock slices into sandstone cylinders precut at 35°. The experiments covered a wide range in temperatures (25-900°C) at confining pressures of 200 and 250 MPa and at strain rates between 10 -3 and 10 -5 s -1. Shear strains of up γ = 2.7 were achieved. The stress-strain data for simple shear favourably compare with predictions on the basis of existing flow laws established in coaxial testing. This comparison demonstrates that the simple shear experiments covered most of the previously established flow regimes for <span class="hlt">calcite</span> rocks. At the highest temperatures Carrara marble exhibited substantial work softening after high shear strains. A complete texture analysis was carried out with the U-stage and a texture goniometer. The following four distinct microfabric regimes were found. (1) Twinning regime: an oblique c-axis maximum deflected from the pole to the flattening plane towards σ1 and against the imposed sense of shear results directly from e-twinning. Extensive twinning (some grains are completely twinned) rapidly rotates the c-axes into near parallelism with σ1. This regime was observed for Carrara marble deformed at temperatures below 700°C and for Solnhofen limestone at room temperature. (2) Intracrystalline slip regime: three c-axis maxima were observed in both rock types at more elevated temperatures and in the absence of twinning. These c-axis orientations result from an alignment of slip planes and slip directions into parallelism with the shear-zone boundary and the shear direction, respectively. This finding supports the idea of an 'orientation for easy slip' resulting from simple shearing. In addition to r- and f-glide, basal glide is inferred to have been operative. (3) Grain-boundary sliding regime: a great circle distribution of c-axes approximately perpendicular to the direction of finite shortening is observed. This texture is weaker compared to the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17812283','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17812283"><span><span class="hlt">Marine</span> Diagenesis of Shallow <span class="hlt">Marine</span> Lime-Mud Sediments: Insights from dgrO18 and dgrC13 Data.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Choquette, P W</p> <p>1968-09-13</p> <p>Shallow <span class="hlt">marine</span> lime-mud sediments of the Ste. Genevieve Formation (Mississippian), in part of the Illinois Basin, underwent at least three diagenetic changes: (i) local dolomitization in seawater or a brine, producing dolostone having average deltaC(13) of +2.5 per mille and deltaO(18) of +1.9 per mille (versus PDB-1); (ii) more usually cementation of unreplaced CaCO(3), in intrasediment seawater, yielding isotopically <span class="hlt">marine</span> lime mudstone mainly composed of <span class="hlt">calcite</span>, 4-micron or finer, with deltaO(18) of from -1 to +1 per mille; (iii) later partial alteration of CaCO(3), in permeable dolomitic rocks, by isotopically "lighter" waters, to <span class="hlt">calcite</span> with an estimated deltaO(18) of -10 per mille or less. Isotope data appraised by petrographic analysis thus suggest "submarine" cementation of these carbonates in shallow <span class="hlt">marine</span> conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T43F2715G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T43F2715G"><span>(U-Th)/He dating and He diffusion in <span class="hlt">calcite</span> from veins and breccia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gautheron, C.; Cros, A.; Pagel, M.; Berthet, P.; Tassan-Got, L.; Douville, E.; Pinna-Jamme, R.; Sarda, P.</p> <p>2013-12-01</p> <p>Knowledge of He retention in crystalline <span class="hlt">calcite</span> is mandatory to estimate the possibility of (U-Th)/He dating of <span class="hlt">calcite</span>. To this aim, fault-filling <span class="hlt">calcite</span> crystals from the Eocene/Oligocene Gondrecourt graben, Paris Basin, Eastern France, have been sampled, based on their relatively old, Eocene-Oligocene, precipitation age and cold thermal history (<40°C since precipitation). The samples were sorted into three main tectonic and morphological groups, including successively (1) micro-fracture <span class="hlt">calcites</span>, (2) breccia and associated geodic <span class="hlt">calcites</span>, and (3) vein and associated geodic <span class="hlt">calcites</span>. (U-Th)/He dating of 63 <span class="hlt">calcite</span> fragments yields ages dispersed from 0.2×0.02 to 35.8×2.7 Ma, as well as two older dates of 117×10 and 205×28 Ma (1s). These He ages correlate to grain chemistry, such as to Sr and ΣREE concentrations or (La/Yb)N ratios, and these correlations probably reflect the evolution of parent fluid. Only the oldest He ages are in agreement with the He-retentive character of <span class="hlt">calcite</span> as determined by Copeland et al. (2007), and these ages were obtained for the most recently precipitated crystals. To better understand the large He-age scatter and why <span class="hlt">calcites</span> precipitated earlier show younger ages, He diffusion experiments have been conducted on 10 Gondrecourt <span class="hlt">calcite</span> fragments from 3 samples with He ages of 0.2 to 6 Ma. In addition, a crystallographic investigation by X-Ray Diffraction (XRD) performed on similar samples reveals that the crystal structure evolves with increasing temperature, showing with micro-cracks and cleavage opening. These XRD results indicate that, in fault-filling <span class="hlt">calcite</span>, He retention is controlled by multiple diffusion domains (MDD, Lovera et al., 1991) with various sizes, and therefore, evolves through time with strong consequences on (U-Th)/He age. We thus interpret the Gondrecourt <span class="hlt">calcite</span> (U-Th)/He age scatter of older samples as a consequence of cleavage opening due to a succession of <span class="hlt">calcite</span> crystallization phases related to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012OLEB...42..519F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012OLEB...42..519F"><span><span class="hlt">Abiotic</span> Formation of Valine Peptides Under Conditions of High Temperature and High Pressure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Furukawa, Yoshihiro; Otake, Tsubasa; Ishiguro, Takato; Nakazawa, Hiromoto; Kakegawa, Takeshi</p> <p>2012-12-01</p> <p>We investigated the oligomerization of solid valine and the stabilities of valine and valine peptides under conditions of high temperature (150-200 °C) and high pressure (50-150 MPa). Experiments were performed under non-aqueous condition in order to promote dehydration reaction. After prolonged exposure of monomeric valine to elevated temperatures and pressures, the products were analyzed by liquid chromatography mass spectrometry comparing their retention times and masses. We identified linear peptides that ranged in size from dimer to hexamer, as well as a cyclic dimer. Previous studies that attempted <span class="hlt">abiotic</span> oligomerization of valine in the absence of a catalyst have never reported valine peptides larger than a dimer. Increased reaction temperature increased the dissociative decomposition of valine and valine peptides to products such as glycine, β-alanine, ammonia, and amines by processes such as deamination, decarboxylation, and cracking. The amount of residual valine and peptide yields was greater at higher pressures at a given temperature, pressure, and reaction time. This suggests that dissociative decomposition of valine and valine peptides is reduced by pressure. Our findings are relevant to the investigation of diagenetic processes in prebiotic <span class="hlt">marine</span> sediments where similar pressures occur under water-poor conditions. These findings also suggest that amino acids, such as valine, could have been polymerized to peptides in deep prebiotic <span class="hlt">marine</span> sediments within a few hundred million years.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70021504','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70021504"><span>The role of disseminated <span class="hlt">calcite</span> in the chemical weathering of granitoid rocks</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>White, A.F.; Bullen, T.D.; Vivit, D.V.; Schulz, M.S.; Clow, D.W.</p> <p>1999-01-01</p> <p>Accessory <span class="hlt">calcite</span>, present at concentrations between 300 and 3000 mg kg-1, occurs in fresh granitoid rocks sampled from the Merced watershed in Yosemite National Park, CA, USA; Loch Vale in Rocky Mountain National Park CO USA; the Panola watershed, GA USA; and the Rio Icacos, Puerto Rico. <span class="hlt">Calcite</span> occurs as fillings in microfractures, as disseminated grains within the silicate matrix, and as replacement of calcic cores in plagioclase. Flow-through column experiments, using de-ionized water saturated with 0.05 atm. CO2, produced effluents from the fresh granitoid rocks that were dominated by Ca and bicarbonate and thermodynamically saturated with <span class="hlt">calcite</span>. During reactions up to 1.7 yr, <span class="hlt">calcite</span> dissolution progressively decreased and was superceded by steady state dissolution of silicates, principally biotite. Mass balance calculations indicate that most <span class="hlt">calcite</span> had been removed during this time and accounted for 57-98% of the total Ca released from these rocks. Experimental effluents from surfically weathered granitoids from the same watersheds were consistently dominated by silicate dissolution. The lack of excess Ca and alkalinity indicated that <span class="hlt">calcite</span> had been previously removed by natural weathering. The extent of Ca enrichment in watershed discharge fluxes corresponds to the amounts of <span class="hlt">calcite</span> exposed in granitoid rocks. High Ca/Na ratios relative to plagioclase stoichiometries indicate excess Ca in the Yosemite, Loch Vale, and other alpine watersheds in the Sierra Nevada and Rocky Mountains of the western United States. This Ca enrichment correlates with strong preferential weathering of <span class="hlt">calcite</span> relative to plagioclase in exfoliated granitoids in glaciated terrains. In contrast, Ca/Na flux ratios are comparable to or less than the Ca/Na ratios for plagioclase in the subtropical Panola and tropical Rio Icacos watersheds, in which deeply weathered regoliths exhibit concurrent losses of <span class="hlt">calcite</span> and much larger masses of plagioclase during transport</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/840694','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/840694"><span><span class="hlt">Calcite</span> Fluid Inclusion, Paragenetic, and Oxygen Isotopic Records of Thermal Event(s) at Yucca Mountain, Nevada</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>B. Peterman; R. Moscati</p> <p>2000-08-10</p> <p>Yucca Mountain, Nevada, is under consideration as a potential high-level radioactive waste repository situated above the water table in 12.7 Ma tuffs. A wealth of textural and geochemical evidence from low-temperature deposits of <span class="hlt">calcite</span> and silica, indicates that their genesis is related to unsaturated zone (UZ) percolation and that the level of the potential repository has never been saturated. Nonetheless, some scientists contend that thermal waters have periodically risen to the surface depositing <span class="hlt">calcite</span> and opal in the tuffs and at the surface. This hypothesis received some support in 1996 when two-phase fluid inclusions (FIs) with homogenization temperatures (Th) between 35 and 75 C were reported from UZ <span class="hlt">calcite</span>. <span class="hlt">Calcite</span> deposition likely followed closely on the cooling of the tuffs and continues into the present. The paragenetic sequence of <span class="hlt">calcite</span> and silica in the UZ is early stage <span class="hlt">calcite</span> followed by chalcedony and quartz, then <span class="hlt">calcite</span> with local opal during middle and late stages. Four types of FIs are found in <span class="hlt">calcite</span> assemblages: (1) all-liquid (L); (2) all-vapor (V); (3) 2-phase with large and variable V:L ratios; and (4) a few 2-phase with small and consistent V:L ratios. Late <span class="hlt">calcite</span> contains no FI assemblages indicating elevated depositional temperatures. In early <span class="hlt">calcite</span>, the Th of type 4 FIs ranges from {approx} 40 to {approx} 85 C. Such temperatures (sub-boiling) and the assemblage of FIs are consistent with deposition in the UZ. Some delta 18O values < 10 permil in early <span class="hlt">calcite</span> support such temperatures. Type 4 FIs, however, seem to be restricted to the early <span class="hlt">calcite</span> stage, during which either cooling of the tuffs or regional volcanism were possible heat sources. Nonetheless, at present there is no compelling evidence of upwelling water as a source for the <span class="hlt">calcite</span>/opal deposits.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5630888','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5630888"><span><span class="hlt">Marine</span> biology</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Thurman, H.V.; Webber, H.H.</p> <p>1984-01-01</p> <p>This book discusses both taxonomic and ecological topics on <span class="hlt">marine</span> biology. Full coverage of <span class="hlt">marine</span> organisms of all five kingdoms is provided, along with interesting and thorough discussion of all major <span class="hlt">marine</span> habitats. Organization into six major parts allows flexibility. It also provides insight into important topics such as disposal of nuclear waste at sea, the idea that life began on the ocean floor, and how whales, krill, and people interact. A full-color photo chapter reviews questions, and exercises. The contents are: an overview <span class="hlt">marine</span> biology: fundamental concepts/investigating life in the ocean; the physical ocean, the ocean floor, the nature of water, the nature and motion of ocean water; general ecology, conditions for life in the sea, biological productivity and energy transfer; <span class="hlt">marine</span> organisms; monera, protista, mycota and metaphyta; the smaller <span class="hlt">marine</span> animals, the large animals <span class="hlt">marine</span> habitats, the intertidal zone/benthos of the continental shelf, the photic zone, the deep ocean, the ocean under stress, <span class="hlt">marine</span> pollution, appendix a: the metric system and conversion factors/ appendix b: prefixes and suffixes/ appendix c: taxonomic classification of common <span class="hlt">marine</span> organisms, and glossary, and index.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ars.usda.gov/research/publications/publication/?seqNo115=304748','TEKTRAN'); return false;" href="http://www.ars.usda.gov/research/publications/publication/?seqNo115=304748"><span>Genetic mapping of <span class="hlt">abiotic</span> stress responses in sorghum</span></a></p> <p><a target="_blank" href="http://www.ars.usda.gov/services/TekTran.htm">Technology Transfer Automated Retrieval System (TEKTRAN)</a></p> <p></p> <p></p> <p>Due to rich genetic diversity for tolerance to various <span class="hlt">abiotic</span> stress conditions, sorghum is an ideal system for genetic mapping and elucidation of genome regions that confer such response among cereal crops. Coupled with the development of DNA marker technologies and most recently the sequencing o...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=131589&keyword=explosive&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=90470151&CFTOKEN=42594265','EPA-EIMS'); return false;" href="http://cfpub.epa.gov/si/si_public_record_report.cfm?dirEntryId=131589&keyword=explosive&actType=&TIMSType=+&TIMSSubTypeID=&DEID=&epaNumber=&ntisID=&archiveStatus=Both&ombCat=Any&dateBeginCreated=&dateEndCreated=&dateBeginPublishedPresented=&dateEndPublishedPresented=&dateBeginUpdated=&dateEndUpdated=&dateBeginCompleted=&dateEndCompleted=&personID=&role=Any&journalID=&publisherID=&sortBy=revisionDate&count=50&CFID=90470151&CFTOKEN=42594265"><span><span class="hlt">ABIOTIC</span> DEGRADATION OF TRICHLOROETHYLENE UNDER THERMAL REMEDIATION CONDITIONS</span></a></p> <p><a target="_blank" href="http://oaspub.epa.gov/eims/query.page">EPA Science Inventory</a></p> <p></p> <p></p> <p>The degradation of TCE (C<SUB>2</SUB>HCl<SUB>3</SUB>) to carbon dioxide (CO<SUB>2</SUB>) and chloride (Cl<SUP>-</SUP>) has been reported to occur during thermal remediation of subsurface environments. The overall goal of this study was to evaluate <span class="hlt">abiotic</span> degradation of TCE at el...</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/wri/2001/wri01-4049/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/wri/2001/wri01-4049/"><span>Ages and Origins of <span class="hlt">Calcite</span> and Opal in the Exploratory Studies Facility Tunnel, Yucca Mountain, Nevada</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Paces, James B.; Neymark, Leonid A.; Marshall, Brian D.; Whelan, Joseph F.; Peterman, Zell E.</p> <p>2001-01-01</p> <p>Deposits of <span class="hlt">calcite</span> and opal are present as coatings on open fractures and lithophysal cavities in unsaturated-zone tuffs at Yucca Mountain, Nevada, site of a potential high-level radioactive waste repository. Outermost layers of <span class="hlt">calcite</span> and opal have radiocarbon ages of 16,000 to 44,000 years before present and thorium-230/uranium ages of 28,000 to more than 500,000 years before present. These ages are young relative to the 13-million-year age of the host rocks. Multiple subsamples from the same outer layer typically show a range of ages with youngest ages from the thinnest subsamples. Initial uranium-234/uranium-238 activity ratios between 1 and 9.5 show a distinct negative correlation with thorium-230/uranium age and are greater than 4 for all but one sample younger than 100,000 years before present. These data, along with micrometer-scale layering and distinctive crystal morphologies, are interpreted to indicate that deposits formed very slowly from water films migrating through open cavities. Exchanges of carbon dioxide and water vapor probably took place between downward-migrating liquids and upward-migrating gases at low rates, resulting in oversaturation of mineral constituents at crystal extremities and more or less continuous deposition of very thin layers. Therefore, subsamples represent mixtures of older and younger layers on a scale finer than sampling techniques can resolve. Slow, long-term rates of deposition (less than about 5 millimeters of mineral per million years) are inferred from subsamples of outermost <span class="hlt">calcite</span> and opal. These growth rates are similar to those calculated assuming that total coating thicknesses of 10 to 40 millimeters accumulated over 12 million years. <span class="hlt">Calcite</span> has a wide range of delta carbon-13 values from about -8.2 to 8.5 per mil and delta oxygen-18 values from about 10 to 21 per mil. Systematic microsampling across individual mineral coatings indicates basal (older) <span class="hlt">calcite</span> tends to have the largest delta carbon-13 values</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006GeCoA..70.2253L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006GeCoA..70.2253L"><span>The role of citrate and phthalate during Co(II) coprecipitation with <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lee, Young J.; Reeder, Richard J.</p> <p>2006-05-01</p> <p>The influence of citrate and phthalate on Co coprecipitation with <span class="hlt">calcite</span> was investigated using a combination of batch experiments, Fourier-transform infra-red (FT-IR) spectroscopy, and thermogravimetric analysis (TGA) over a wide range of precipitation rates. Steady-state growth conditions (at constant [Ca], [Co], DIC, and pH) were generally achieved within 3-5 h, after which Co(II) partitioning into <span class="hlt">calcite</span> was evaluated. Only minor differences are observed in the partition coefficient ( Kd) trends with and without citrate and phthalate as a function of <span class="hlt">calcite</span> precipitation rate except at very low rates. Slight inhibition of <span class="hlt">calcite</span> growth is observed in the presence of citrate or phthalate, which can be attributed to adsorption at surface sites. TGA curves for samples coprecipitated with citrate show a significant mass loss between 375 and 550 °C, whereas the weight-loss curves for the Co-phthalate coprecipitates are indistinguishable from those of the organic-free Co coprecipitates. This indicates that citrate is incorporated into <span class="hlt">calcite</span> during <span class="hlt">calcite</span> crystallization, whereas phthalate is excluded. FT-IR spectra for the sample with citrate show a broad absorption in the range 3700-3100 cm -1, which is attributable to water molecules coordinated to citrate coprecipitated with <span class="hlt">calcite</span>. The preferential incorporation of citrate over phthalate likely reflects differences in both aqueous speciation and conformation of the carboxylate groups. This new finding may provide new insight to the factors that control the behavior of macromolecules and their incorporation into the structure of calcium carbonate during biomineralization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090011851','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090011851"><span>Thermal and Evolved Gas Behavior of <span class="hlt">Calcite</span> Under Mars Phoenix TEGA Operating Conditions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ming, D.W.; Niles, P.B.; Morris, R.V.; Boynton, W.V.; Golden, D.C.; Lauer, H.V.; Sutter, B.</p> <p>2009-01-01</p> <p>The Mars Phoenix Scout Mission with its diverse instrument suite successfully examined several soils on the Northern plains of Mars. The Thermal and Evolved Gas Analyzer (TEGA) was employed to detect organic and inorganic materials by coupling a differential scanning calorimeter (DSC) with a magnetic-sector mass spectrometer (MS). Martian soil was heated up to 1000 C in the DSC ovens and evolved gases from mineral decomposition products were examined with the MS. TEGA s DSC has the capability to detect endothermic and exothermic reactions during heating that are characteristic of minerals present in the Martian soil. Initial TEGA results indicated the presence of endothermic peaks with onset temperatures that ranged from 675 C to 750 C with corresponding CO2 release. This result suggests the presence of <span class="hlt">calcite</span> (CaCO3. CaO + CO2). Organic combustion to CO2 is not likely since this mostly occurs at temperatures below 550 C. Fe-carbonate and Mg-carbonate are not likely because their decomposition temperatures are less than 600 C. TEGA enthalpy determinations suggest that <span class="hlt">calcite</span>, may occur in the Martian soil in concentrations of approx.1 to 5 wt. %. The detection of <span class="hlt">calcite</span> could be questioned based on previous results that suggest Mars soils are mostly acidic. However, the Phoenix landing site soil pH was measured at pH 8.3 0.5, which is typical of terrestrial soils where pH is controlled by <span class="hlt">calcite</span> solubility. The range of onset temperatures and <span class="hlt">calcite</span> concentration as calculated by TEGA is poorly con-strained in part because of limited thermal data of <span class="hlt">cal-cite</span> at reduced pressures. TEGA operates at <30 mbar while most <span class="hlt">calcite</span> literature thermal data was obtained at 1000 mbar or higher pressures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/930338','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/930338"><span>Coprecipitation of Chromate with <span class="hlt">Calcite</span>: Batch Experiments and X-ray Absorption Spectroscopy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tang,Y.; Elzinga, E.; Lee, Y.; Reeder, R.</p> <p>2007-01-01</p> <p>Batch experiments, combined with in situ spectroscopic methods, are used to examine the coprecipitation of Cr(VI) with <span class="hlt">calcite</span>, including partitioning behavior, site-specific distribution of Cr on the surface of <span class="hlt">calcite</span> single crystals, and local coordination of Cr(VI) in the <span class="hlt">calcite</span> structure. It is found that the concentration of Cr incorporated in <span class="hlt">calcite</span> increases with increasing Cr concentration in solution. The calculated apparent partition coefficient, K{sub d}*, is highest at low Cr solution concentration, and decreases to a constant value with increasing Cr solution concentration. DIC images of the (1 0 {bar 1} 4) surface of <span class="hlt">calcite</span> single crystals grown in the presence of CrO{sub 4}{sup 2-}exhibit well-defined growth hillocks composed of two pairs of symmetrically nonequivalent vicinal faces, denoted as + and -, which reflect the orientation of structurally nonequivalent growth steps. Micro-XRF mapping of the Cr distribution over a growth hillock shows preferential incorporation of Cr into the -- steps, which is considered to result from differences in surface structure geometry. XANES spectra confirm that incorporated Cr is hexavalent, and no reduction of Cr(VI) in the X-ray beam was observed up to 2 days at room temperature. EXAFS fit results show the incorporated Cr(VI) has the expected first shell of 4 O at {approx}1.64 {+-} 0.01 {angstrom}, consistent with CrO{sub 4}{sup 2-}. Best fit results show that the second shell is split with {approx}2.5 Ca at {approx}3.33 {+-} 0.05 and {approx}2.2 Ca at 3.55 {+-} 0.05 {angstrom}, which confirms the incorporation of chromate into <span class="hlt">calcite</span>. Consideration of possible local coordination indicates that significant distortion or disruption is required to accommodate CrO{sub 4}{sup 2-}in the <span class="hlt">calcite</span> structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70030200','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70030200"><span>Seasonal variations in modern speleothem <span class="hlt">calcite</span> growth in Central Texas, U.S.A</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Banner, J.L.; Guilfoyle, A.; James, E.W.; Stern, L.A.; Musgrove, M.</p> <p>2007-01-01</p> <p>Variations in growth rates of speleothem <span class="hlt">calcite</span> have been hypothesized to reflect changes in a range of paleoenvironmental variables, including atmospheric temperature and precipitation, drip-water composition, and the rate of soil CO2 delivery to the subsurface. To test these hypotheses, we quantified growth rates of modern speleothem <span class="hlt">calcite</span> on artificial substrates and monitored concurrent environmental conditions in three caves across the Edwards Plateau in central Texas. Within each of two caves, different drip sites exhibit similar annual cycles in <span class="hlt">calcite</span> growth rates, even though there are large differences between the mean growth rates at the sites. The growth-rate cycles inversely correlate to seasonal changes in regional air temperature outside the caves, with near-zero growth rates during the warmest summer months, and peak growth rates in fall through spring. Drip sites from caves 130 km apart exhibit similar temporal patterns in <span class="hlt">calcite</span> growth rate, indicating a controlling mechanism on at least this distance. The seasonal variations in <span class="hlt">calcite</span> growth rate can be accounted for by a primary control by regional temperature effects on ventilation of cave-air CO2 concentrations and/or drip-water CO2 contents. In contrast, site-to-site differences in the magnitude of <span class="hlt">calcite</span> growth rates within an individual cave appear to be controlled principally by differences in drip rate. A secondary control by drip rate on the growth rate temporal variations is suggested by interannual variations. No <span class="hlt">calcite</span> growth was observed in the third cave, which has relatively high values of and small seasonal changes in cave-air CO2. These results indicate that growth-rate variations in ancient speleothems may serve as a paleoenvironmental proxy with seasonal resolution. By applying this approach of monitoring the modern system, speleothem growth rate and geochemical proxies for paleoenviromnental change may be evaluated and calibrated. Copyright ?? 2007, SEPM (Society for</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4042060','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4042060"><span>Integrating omic approaches for <span class="hlt">abiotic</span> stress tolerance in soybean</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Deshmukh, Rupesh; Sonah, Humira; Patil, Gunvant; Chen, Wei; Prince, Silvas; Mutava, Raymond; Vuong, Tri; Valliyodan, Babu; Nguyen, Henry T.</p> <p>2014-01-01</p> <p>Soybean production is greatly influenced by <span class="hlt">abiotic</span> stresses imposed by environmental factors such as drought, water submergence, salt, and heavy metals. A thorough understanding of plant response to <span class="hlt">abiotic</span> stress at the molecular level is a prerequisite for its effective management. The molecular mechanism of stress tolerance is complex and requires information at the omic level to understand it effectively. In this regard, enormous progress has been made in the omics field in the areas of genomics, transcriptomics, and proteomics. The emerging field of ionomics is also being employed for investigating <span class="hlt">abiotic</span> stress tolerance in soybean. Omic approaches generate a huge amount of data, and adequate advancements in computational tools have been achieved for effective analysis. However, the integration of omic-scale information to address complex genetics and physiological questions is still a challenge. In this review, we have described advances in omic tools in the view of conventional and modern approaches being used to dissect <span class="hlt">abiotic</span> stress tolerance in soybean. Emphasis was given to approaches such as quantitative trait loci (QTL) mapping, genome-wide association studies (GWAS), and genomic selection (GS). Comparative genomics and candidate gene approaches are also discussed considering identification of potential genomic loci, genes, and biochemical pathways involved in stress tolerance mechanism in soybean. This review also provides a comprehensive catalog of available online omic resources for soybean and its effective utilization. We have also addressed the significance of phenomics in the integrated approaches and recognized high-throughput multi-dimensional phenotyping as a major limiting factor for the improvement of <span class="hlt">abiotic</span> stress tolerance in soybean. PMID:24917870</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23425848','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23425848"><span>Reactive oxygen species signaling in plants under <span class="hlt">abiotic</span> stress.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Choudhury, Shuvasish; Panda, Piyalee; Sahoo, Lingaraj; Panda, Sanjib Kumar</p> <p>2013-04-01</p> <p><span class="hlt">Abiotic</span> stresses like heavy metals, drought, salt, low temperature, etc. are the major factors that limit crop productivity and yield. These stresses are associated with production of certain deleterious chemical entities called reactive oxygen species (ROS), which include hydrogen peroxide (H₂O₂), superoxide radical (O₂(-)), hydroxyl radical (OH(-)), etc. ROS are capable of inducing cellular damage by degradation of proteins, inactivation of enzymes, alterations in the gene and interfere in various pathways of metabolic importance. Our understanding on ROS in response to <span class="hlt">abiotic</span> stress is revolutionized with the advancements in plant molecular biology, where the basic understanding on chemical behavior of ROS is better understood. Understanding the molecular mechanisms involved in ROS generation and its potential role during <span class="hlt">abiotic</span> stress is important to identify means by which plant growth and metabolism can be regulated under acute stress conditions. ROS mediated oxidative stress, which is the key to understand stress related toxicity have been widely studied in many plants and the results in those studies clearly revealed that oxidative stress is the main symptom of toxicity. Plants have their own antioxidant defense mechanisms to encounter ROS that is of enzymic and non-enzymic nature . Coordinated activities of these antioxidants regulate ROS detoxification and reduces oxidative load in plants. Though ROS are always regarded to impart negative impact on plants, some reports consider them to be important in regulating key cellular functions; however, such reports in plant are limited. Molecular approaches to understand ROS metabolism and signaling have opened new avenues to comprehend its critical role in <span class="hlt">abiotic</span> stress. ROS also acts as secondary messenger that signals key cellular functions like cell proliferation, apoptosis and necrosis. In higher eukaryotes, ROS signaling is not fully understood. In this review we summarize our understanding on ROS</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/22365135','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/22365135"><span><span class="hlt">Abiotic</span> ozone and oxygen in atmospheres similar to prebiotic Earth</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Domagal-Goldman, Shawn D.; Segura, Antígona; Claire, Mark W.; Robinson, Tyler D.; Meadows, Victoria S.</p> <p>2014-09-10</p> <p>The search for life on planets outside our solar system will use spectroscopic identification of atmospheric biosignatures. The most robust remotely detectable potential biosignature is considered to be the detection of oxygen (O{sub 2}) or ozone (O{sub 3}) simultaneous to methane (CH{sub 4}) at levels indicating fluxes from the planetary surface in excess of those that could be produced <span class="hlt">abiotically</span>. Here we use an altitude-dependent photochemical model with the enhanced lower boundary conditions necessary to carefully explore <span class="hlt">abiotic</span> O{sub 2} and O{sub 3} production on lifeless planets with a wide variety of volcanic gas fluxes and stellar energy distributions. On some of these worlds, we predict limited O{sub 2} and O{sub 3} buildup, caused by fast chemical production of these gases. This results in detectable <span class="hlt">abiotic</span> O{sub 3} and CH{sub 4} features in the UV-visible, but no detectable <span class="hlt">abiotic</span> O{sub 2} features. Thus, simultaneous detection of O{sub 3} and CH{sub 4} by a UV-visible mission is not a strong biosignature without proper contextual information. Discrimination between biological and <span class="hlt">abiotic</span> sources of O{sub 2} and O{sub 3} is possible through analysis of the stellar and atmospheric context—particularly redox state and O atom inventory—of the planet in question. Specifically, understanding the spectral characteristics of the star and obtaining a broad wavelength range for planetary spectra should allow more robust identification of false positives for life. This highlights the importance of wide spectral coverage for future exoplanet characterization missions. Specifically, discrimination between true and false positives may require spectral observations that extend into infrared wavelengths and provide contextual information on the planet's atmospheric chemistry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SMaS...25h4008P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SMaS...25h4008P"><span>A bacteria-based bead for possible self-healing <span class="hlt">marine</span> concrete applications</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Palin, D.; Wiktor, V.; Jonkers, H. M.</p> <p>2016-08-01</p> <p>This work presents a bacteria-based bead for potential self-healing concrete applications in low-temperature <span class="hlt">marine</span> environments. The bead consisting of calcium alginate encapsulated bacterial spores and mineral precursor compounds was assessed for: oxygen consumption, swelling, and its ability to form a biocomposite in a simulative <span class="hlt">marine</span> concrete crack solution (SMCCS) at 8 °C. After six days immersion in the SMCCS the bacteria-based beads formed a <span class="hlt">calcite</span> crust on their surface and <span class="hlt">calcite</span> inclusions in their network, resulting in a <span class="hlt">calcite</span>-alginate biocomposite. Beads swelled by 300% to a maximum diameter of 3 mm, while theoretical calculations estimate that 0.112 g of the beads were able to produce ˜1 mm3 of <span class="hlt">calcite</span> after 14 days immersion; providing the bead with considerable crack healing potential. The bacteria-based bead shows great potential for the development of self-healing concrete in low-temperature <span class="hlt">marine</span> environments, while the formation of a biocomposite healing material represents an exciting avenue for self-healing concrete research.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://files.eric.ed.gov/fulltext/EJ151850.pdf','ERIC'); return false;" href="http://files.eric.ed.gov/fulltext/EJ151850.pdf"><span><span class="hlt">Marine</span> Biology</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Dewees, Christopher M.; Hooper, Jon K.</p> <p>1976-01-01</p> <p>A variety of informational material for a course in <span class="hlt">marine</span> biology or oceanology at the secondary level is presented. Among the topics discussed are: food webs and pyramids, planktonic blooms, <span class="hlt">marine</span> life, plankton nets, food chains, phytoplankton, zooplankton, larval plankton and filter feeders. (BT)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=BIomedicine&pg=4&id=EJ161057','ERIC'); return false;" href="http://eric.ed.gov/?q=BIomedicine&pg=4&id=EJ161057"><span><span class="hlt">Marine</span> Biomedicine</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Bang, Frederik B.</p> <p>1977-01-01</p> <p>Describes early scientific research involving <span class="hlt">marine</span> invertebrate pathologic processes that may have led to new insights into human disease. Discussed are inquiries of Metchnikoff, Loeb, and Cantacuzene (immunolgic responses in sea stars, horseshoe crabs, and <span class="hlt">marine</span> worms, respectively). Describes current research stemming from these early…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMPP51A1108H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMPP51A1108H"><span>The Influence of Kinetic Growth Factors on the Clumped Isotope Composition of <span class="hlt">Calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hunt, J. D.; Watkins, J. M.; Tripati, A.; Ryerson, F. J.; DePaolo, D. J.</p> <p>2014-12-01</p> <p>Clumped isotope paleothermometry is based on the association of 13C and 18O within carbonate minerals. Although the influence of temperature on equilibrium 13C-18O bond ordering has been studied, recent oxygen isotope studies of inorganic <span class="hlt">calcite</span> demonstrate that <span class="hlt">calcite</span> grown in laboratory experiments and in many natural settings does not form in equilibrium with water. It is therefore likely that the carbon and clumped isotope composition of these <span class="hlt">calcite</span> crystals are not representative of true thermodynamic equilibrium. To isolate kinetic clumped isotope effects that arise at the mineral-solution interface, clumped isotopic equilibrium of DIC species must be maintained. This can be accomplished by dissolving the enzyme carbonic anhydrase (CA) into the solution, thereby reducing the time required for isotopic equilibration of DIC species by approximately two orders of magnitude between pH 7.7 and 9.3. We conduct <span class="hlt">calcite</span> growth experiments aimed specifically at measuring the pH-dependence of kinetic clumped isotope effects during non-equilibrium precipitation of <span class="hlt">calcite</span>. We precipitated <span class="hlt">calcite</span> from aqueous solution at a constant pH and controlled supersaturation over the pH range 7.7-9.3 in the presence of CA. For each experiment, a gas mixture of N2 and CO2 is bubbled through a beaker of solution without seed crystals. As CO2 from the gas dissolves into solution, <span class="hlt">calcite</span> crystals grow on the beaker walls. The pH of the solution is maintained by use of an autotitrator with NaOH as the titrant. We control the temperature, pH, the pCO2 of the gas inflow, and the gas inflow rate, and monitor the total alkalinity, the pCO2 of the gas outflow, and the amount of NaOH added. A constant crystal growth rate of ~1.6 mmol/m2/hr is maintained over all experiments. Results from these experiments are compared to predictions from a recently-developed isotopic ion-by-ion growth model of <span class="hlt">calcite</span>. The model describes the rate, temperature and pH dependence of oxygen isotope uptake</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/12831020','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/12831020"><span>Influence of Bacillus subtilis cell walls and EDTA on <span class="hlt">calcite</span> dissolution rates and crystal surface features.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Friis, A K; Davis, T A; Figueira, M M; Paquette, J; Mucci, A</p> <p>2003-06-01</p> <p>This study investigates the influence of EDTA and the Gram-positive cell walls of Bacillus subtilis on the dissolution rates and development of morphological features on the <span class="hlt">calcite</span> [1014] surface. The <span class="hlt">calcite</span> dissolution rates are compared at equivalent saturation indicies (SI) and relative to its dissolution behavior in distilled water (DW). Results indicate that the presence of metabolically inactive B. subtilis does not affect the dissolution rates significantly. Apparent increases in dissolution rates in the presence of the dead bacterial cells can be accounted for by a decrease of the saturation state of the solution with respect to <span class="hlt">calcite</span> resulting from bonding of dissolved Ca2+ by functional groups on the cell walls. In contrast, the addition of EDTA to the experimental solutions results in a distinct increase in dissolution rates relative to those measured in DW and the bacterial cell suspensions. These results are partly explained by the 6.5-8 orders of magnitude greater stability of the Ca-EDTA complex relative to the Ca-B. subtilis complexes as well as its free diffusion to and direct attack of the <span class="hlt">calcite</span> surface. Atomic force microscopy images of the [1014] surface of <span class="hlt">calcite</span> crystals exposed to our experimental solutions reveal the development of dissolution pits with different morphologies according to the nature and concentration of the ligand. Highly anisotropic dissolution pits develop in the early stages of the dissolution reaction at low B. subtilis concentrations (0.004 mM functional group sites) and in DW. In contrast, at high functional group concentrations (4.0 mM EDTA or equivalent B. subtilis functional group sites), dissolution pits are more isotropic. These results suggest that the mechanism of <span class="hlt">calcite</span> dissolution is modified by the presence of high concentrations of organic ligands. Since all the pits that developed on the <span class="hlt">calcite</span> surfaces display some degree of anisotropy and dissolution rates are strongly SI dependent, the rate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010748','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010748"><span>Dolomite-magnesian <span class="hlt">calcite</span> relations at elevated temperatures and CO2 pressures</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Graf, D.L.; Goldsmith, J.R.</p> <p>1955-01-01</p> <p>The equilibrium thermal decomposition curve of dolomite has been determined up to a CO2 pressure of 20,000 lb/in.2, at which pressure dolomite decomposes at 857??C. Equilibrium was approached from both directions, by the breakdown and by the solid-state synthesis of dolomite. At elevated temperatures and pressures, <span class="hlt">calcites</span> in equilibrium with periclase as well as those in equilibrium with dolomite contain Mg in solid solution. In the former, the Mg content increases with increasing CO2 pressure, and decreases with increasing temperature. In the latter, it is a function of temperature only. The exsolution curve of dolomite and magnesian <span class="hlt">calcite</span> has been determined between 500?? and 800??C; at 500?? dolomite is in equilibrium with a magnesian <span class="hlt">calcite</span> containing ~6 mol per cent MgCO2; at 800??, ~22 mol per cent. There appears to be a small but real deviation from the ideal 1 : 1 Ca : Mg ratio of dolomite, in the direction of excess Ca, for material in equilibrium with magnesian <span class="hlt">calcite</span> at high temperature. The experimental findings indicate that very little Mg is stable in the <span class="hlt">calcites</span> of sedimentary environments, but that an appreciable amount is stable under higher-temperature metamorphic conditions, if sufficient CO2 pressure is maintained. ?? 1955.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.125..528H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.125..528H"><span>Trace concentration - Huge impact: Nitrate in the <span class="hlt">calcite</span>/Eu(III) system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hofmann, Sascha; Voïtchovsky, Kislon; Schmidt, Moritz; Stumpf, Thorsten</p> <p>2014-01-01</p> <p>The interactions of trivalent lanthanides and actinides with secondary mineral phases such as <span class="hlt">calcite</span> is of high importance for the safety assessment of deep geological repositories for high level nuclear waste (HLW). Due to similar ionic radii, calcium-bearing mineral phases are suitable host minerals for Ln(III) and An(III) ions. Especially <span class="hlt">calcite</span> has been proven to retain these metal ions effectively by both surface complexation and bulk incorporation. Since anionic ligands (e.g., nitrate) are omnipresent in the geological environment and due to their coordinating properties, their influence on retentive processes should not be underestimated. Nitrate is a common contaminant in most HLW forms as a result of using nitric acid in fuel reprocessing. It is also formed by microbial activity under aerobic conditions. In this study, atomic force microscopy investigations revealed a major influence of nitrate upon the surface of <span class="hlt">calcite</span> crystals. NaNO3 causes serious modifications even in trace amounts (<10-7 M) and forms a soft surface layer of low crystallinity on top of the <span class="hlt">calcite</span> crystal. Time-resolved laser fluorescence spectroscopy of Eu(III) showed that, within this layer, Eu(III) ions are incorporated, while losing most of their hydration shell. The results show that solid solution modelling for actinides in <span class="hlt">calcite</span> must take into account the presence of nitrate in pore and ground waters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26087312','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26087312"><span>Growth and Dissolution of <span class="hlt">Calcite</span> in the Presence of Adsorbed Stearic Acid.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ricci, Maria; Segura, Juan José; Erickson, Blake W; Fantner, Georg; Stellacci, Francesco; Voïtchovsky, Kislon</p> <p>2015-07-14</p> <p>The interaction of organic molecules with the surface of <span class="hlt">calcite</span> plays a central role in many geochemical, petrochemical, and industrial processes and in biomineralization. Adsorbed organics, typically fatty acids, can interfere with the evolution of <span class="hlt">calcite</span> when immersed in aqueous solutions. Here we use atomic force microscopy in liquid to explore in real-time the evolution of the (1014) surface of <span class="hlt">calcite</span> covered with various densities of stearic acid and exposed to different saline solutions. Our results show that the stearic acid molecules tend to act as "pinning points" on the <span class="hlt">calcite</span>'s surface and slow down the crystal's restructuring kinetics. Depending on the amount of material adsorbed, the organic molecules can form monolayers or bilayer islands that become embedded into the growing crystal. The growth process can also displaces the organic molecules and actively concentrate them into stacked multilayers. Our results provide molecular-level insights into the interplay between the adsorbed fatty acid molecules and the evolving <span class="hlt">calcite</span> crystal, highlighting mechanisms that could have important implications for several biochemical and geochemical processes and for the oil industry.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15589541','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15589541"><span>Crystal growth of aragonite and <span class="hlt">calcite</span> in presence of citric acid, DTPA, EDTA and pyromellitic acid.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Westin, K-J; Rasmuson, A C</p> <p>2005-02-15</p> <p>The influence of four calcium complexing substances, i.e., citric acid (CIT), diethylenetriaminepentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA) and pyromellitic acid (PMA), on the crystal growth rate of the calcium carbonate polymorphs aragonite and <span class="hlt">calcite</span> has been studied. Using a seeded constant supersaturation method supersaturation was maintained at 4 by keeping a constant pH of 8.5 through addition of sodium carbonate and calcium chloride solutions. The unique composition of each solution was calculated using chemical speciation. The growth rate was interpreted in terms of an overall growth rate. For both <span class="hlt">calcite</span> and aragonite, the crystal growth rate is significantly reduced in the presence of the calcium complexing substances. The growth retarding effect depends on both the concentration and the polymorph. The relative crystal growth rate was correlated to the total complexing agent concentration using a Langmuir adsorption approach. Aragonite appeared fully covered for lower total concentrations than <span class="hlt">calcite</span>. Furthermore, CIT very efficiently blocked aragonite growth contrary to what was observed for <span class="hlt">calcite</span>. This is thought to be related to certain distinct features of the dominant aragonite crystal faces compared to the dominant <span class="hlt">calcite</span> faces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23872026','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23872026"><span>Monitoring bacterially induced <span class="hlt">calcite</span> precipitation in porous media using magnetic resonance imaging and flow measurements.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sham, E; Mantle, M D; Mitchell, J; Tobler, D J; Phoenix, V R; Johns, M L</p> <p>2013-09-01</p> <p>A range of nuclear magnetic resonance (NMR) techniques are employed to provide novel, non-invasive measurements of both the structure and transport properties of porous media following a biologically mediated <span class="hlt">calcite</span> precipitation reaction. Both a model glass bead pack and a sandstone rock core were considered. Structure was probed using magnetic resonance imaging (MRI) via a combination of quantitative one-dimensional profiles and three-dimensional images, applied before and after the formation of <span class="hlt">calcite</span> in order to characterise the spatial distribution of the precipitate. It was shown through modification and variations of the <span class="hlt">calcite</span> precipitation treatment that differences in the <span class="hlt">calcite</span> fill would occur but all methods were successful in partially blocking the different porous media. Precipitation was seen to occur predominantly at the inlet of the bead pack, whereas precipitation occurred almost uniformly along the sandstone core. Transport properties are quantified using pulse field gradient (PFG) NMR measurements which provide probability distributions of molecular displacement over a set observation time (propagators), supplementing conventional permeability measurements. Propagators quantify the local effect of <span class="hlt">calcite</span> formation on system hydrodynamics and the extent of stagnant region formation. Collectively, the combination of NMR measurements utilised here provides a toolkit for determining the efficacy of a biological-precipitation reaction for partially blocking porous materials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/983508','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/983508"><span>Mechanism of <span class="hlt">Calcite</span> Co-Orientation in the Sea Urchin Tooth</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Killian, Christopher; Metzler, Rebecca; Gong, Y. U. T.; Olson, Ian; Aizenberg, Joanna; Politi, Yael; Wilt, Fred; Scholl, Andreas; Young, Anthony; Doran, Andrew; Kunz, Martin; Tamura, Nobumichi; Coppersmith, Susan; Gilbert, P. U. P. A.</p> <p>2009-12-01</p> <p>Sea urchin teeth are remarkable and complex <span class="hlt">calcite</span> structures, continuously growing at the forming end and self-sharpening at the mature grinding tip. The <span class="hlt">calcite</span> (CaCO{sub 3}) crystals of tooth components, plates, fibers, and a high-Mg polycrystalline matrix, have highly co-oriented crystallographic axes. This ability to co-orient <span class="hlt">calcite</span> in a mineralized structure is shared by all echinoderms. However, the physico-chemical mechanism by which <span class="hlt">calcite</span> crystals become co-oriented in echinoderms remains enigmatic. Here, we show differences in <span class="hlt">calcite</span> c-axis orientations in the tooth of the purple sea urchin (Strongylocentrotus purpuratus), using high-resolution X-ray photoelectron emission spectromicroscopy (X-PEEM) and microbeam X-ray diffraction ({mu}XRD). All plates share one crystal orientation, propagated through pillar bridges, while fibers and polycrystalline matrix share another orientation. Furthermore, in the forming end of the tooth, we observe that CaCO{sub 3} is present as amorphous calcium carbonate (ACC). We demonstrate that co-orientation of the nanoparticles in the polycrystalline matrix occurs via solid-state secondary nucleation, propagating out from the previously formed fibers and plates, into the amorphous precursor nanoparticles. Because amorphous precursors were observed in diverse biominerals, solid-state secondary nucleation is likely to be a general mechanism for the co-orientation of biomineral components in organisms from different phyla.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017Ocgy...57..174K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017Ocgy...57..174K"><span>Authigenic Mg-<span class="hlt">calcite</span> at a cold methane seep site in the Laptev Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kravchishina, M. D.; Lein, A. Yu.; Savvichev, A. S.; Reykhard, L. E.; Dara, O. M.; Flint, M. V.</p> <p>2017-01-01</p> <p>Authigenic minerals were studied in Holocene shelf sediments of the Laptev Sea (cold methane seep site, water depth 71 m). The study presents the first finds of large hard carbonate concretions with Mg-<span class="hlt">calcite</span> cement in recent sediments of the Arctic shelf seas. These concretions differ from previously reported glendonites and concretions from bottom sediments of the White Sea, Kara Sea, Sea of Okhotsk, etc. A study of the morphology, microstructure, and composition of these newly reported concretions revealed the multistage formation of carbonates (structural varieties of Mg-<span class="hlt">calcite</span> and aragonite). It was shown that organic matter played an important role in the formation of authigenic carbonates, i.e., in the formation of sedimentary-diagenetic Mg-<span class="hlt">calcite</span>. The role of methane as a possible source for authigenic carbonate formation was estimated. It was found that methane-derived Mg-<span class="hlt">calcite</span> accounts for 17-35% of concretion materials. Mg-<span class="hlt">calcite</span> had δ13C-Ccarb values between-24 and-23‰ and δ13C-Corg values between-44.5 and-88.5‰.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21069231','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21069231"><span>The kinetics and mechanisms of amorphous calcium carbonate (ACC) crystallization to <span class="hlt">calcite</span>, via vaterite.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Rodriguez-Blanco, Juan Diego; Shaw, Samuel; Benning, Liane G</p> <p>2011-01-01</p> <p>The kinetics and mechanisms of nanoparticulate amorphous calcium carbonate (ACC) crystallization to <span class="hlt">calcite</span>, via vaterite, were studied at a range of environmentally relevant temperatures (7.5-25 °C) using synchrotron-based in situ time-resolved Energy Dispersive X-ray Diffraction (ED-XRD) in conjunction with high-resolution electron microscopy, ex situ X-ray diffraction and infrared spectroscopy. The crystallization process occurs in two stages; firstly, the particles of ACC rapidly dehydrate and crystallize to form individual particles of vaterite; secondly, the vaterite transforms to <span class="hlt">calcite</span> via a dissolution and reprecipitation mechanism with the reaction rate controlled by the surface area of <span class="hlt">calcite</span>. The second stage of the reaction is approximately 10 times slower than the first. Activation energies of <span class="hlt">calcite</span> nucleation and crystallization are 73±10 and 66±2 kJ mol(-1), respectively. A model to calculate the degree of <span class="hlt">calcite</span> crystallization from ACC at environmentally relevant temperatures (7.5-40 °C) is also presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16352327','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16352327"><span>Arsenic removal from high-arsenic water by enhanced coagulation with ferric ions and coarse <span class="hlt">calcite</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Song, S; Lopez-Valdivieso, A; Hernandez-Campos, D J; Peng, C; Monroy-Fernandez, M G; Razo-Soto, I</p> <p>2006-01-01</p> <p>Arsenic removal from high-arsenic water in a mine drainage system has been studied through an enhanced coagulation process with ferric ions and coarse <span class="hlt">calcite</span> (38-74 microm) in this work. The experimental results have shown that arsenic-borne coagulates produced by coagulation with ferric ions alone were very fine, so micro-filtration (membrane as filter medium) was needed to remove the coagulates from water. In the presence of coarse <span class="hlt">calcite</span>, small arsenic-borne coagulates coated on coarse <span class="hlt">calcite</span> surfaces, leading the settling rate of the coagulates to considerably increase. The enhanced coagulation followed by conventional filtration (filter paper as filter medium) achieved a very high arsenic removal (over 99%) from high-arsenic water (5mg/l arsenic concentration), producing a cleaned water with the residual arsenic concentration of 13 microg/l. It has been found that the mechanism by which coarse <span class="hlt">calcite</span> enhanced the coagulation of high-arsenic water might be due to attractive electrical double layer interaction between small arsenic-borne coagulates and <span class="hlt">calcite</span> particles, which leads to non-existence of a potential energy barrier between the heterogeneous particles.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8314N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8314N"><span>Exploring biotic vs. <span class="hlt">abiotic</span> controls on syngenetic carbonate and clay mineral precipitation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nascimento, Gabriela S.; McKenzie, Judith A.; Martinez Ruiz, Francisca; Bontognali, Tomaso R. R.; Vasconcelos, Crisogono</p> <p>2016-04-01</p> <p>A possible syngenetic relationship between carbonate and clay mineral precipitation has been reported for sedimentary rocks deposited in both lacustrine and <span class="hlt">marine</span> sedimentary environments throughout the geological record. In particular, the mineral dolomite is often found associated with Mg-rich clays, such as stevensite. It is notable that this carbonate/clay association has been recorded in numerous samples taken from modern dolomite precipitating environments; for example, the Coorong lakes, South Australia, coastal sabkhas, Abu Dhabi, UAE and coastal hypersaline lagoons (Lagoa Vermelha and Brejo do Espinho) east of Rio de Janeiro, Brazil. An HRTEM study of samples from these three locations indicates a possible physical/chemical association between the Ca-dolomite and Mg-rich clays, demonstrating a probable co-precipitation. To test this hypothesis, we have conducted a series of biotic and <span class="hlt">abiotic</span> laboratory experiments. If this syngenesis actually occurs in nature, what, if any, are the biogeochemical processes controlling these precipitation reactions? Our experiments were designed to determine the extent of the biotic versus <span class="hlt">abiotic</span> component influencing the mineral precipitation and, in the case of a biotic influence, to understand the mechanism through which microorganisms might mediate the formation of clay minerals. The experiments were carried out in the Geomicrobiology Laboratory of ETH Zürich using cultures of living microbes and artificial organic compounds that simulate functional groups present in natural biofilms formed under both aerobic and anaerobic conditions. In addition, pure inorganic experiments were designed to understand possible physico-chemical conditions for diagenetic processes that could induce dissolution of Mg-carbonates and precipitation of Mg-rich clays. Our results show a remarkable biotic influence during the formation of clay minerals. Specifically, extracellular polymeric substances (EPS), released by microbes in their</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002GMS...131..205D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002GMS...131..205D"><span>Trace elements in <span class="hlt">marine</span> ostracodes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dwyer, Gary S.; Cronin, Thomas M.; Baker, Paul A.</p> <p></p> <p>Extending the work of Cadot, Kaesler, De Deckker, Chivas, and Corrège, we have measured the elemental chemistry of shells of <span class="hlt">marine</span> ostracodes to evaluate the usefulness of ostracode shell chemistry as a paleoenvironmental proxy. Our work has focused primarily on Mg/Ca, Sr/Ca, and Na/Ca ratios of two common genera: deep-sea genus Krithe and shallow <span class="hlt">marine</span>/estuarine genus Loxoconcha. We evaluated in vivo effects including genus, species, gender, ontogeny, shell size, intra-shell heterogeneity (Mg), water temperature, and salinity, and postmortem diagenetic effects including partial dissolution, recrystallization, and shell surface contamination. Analysis of modern (core-top), fossil, and laboratory-raised specimens across a wide range of temperature and salinity conditions confirms earlier work indicating that Krithe and Loxoconcha Mg/Ca ratios are dominantly controlled by water temperature. Sr/Ca and Na/Ca ratios co-vary with temperature in core-top Krithe, but not in cultured Loxoconcha suggesting that the Krithe Sr/Ca and Na/Ca correlation with temperature may be related to another variable that broadly co-varies with temperature. Phylogenetic and ontogenetic effects are also indicated, including different Mg-thermodependence and intra-shell Mg distribution between Krithe and Loxoconcha. Inter-specific effects are suggested for two species of Krithe. Magnesium uptake in eldest juvenile shells seems to be identical to that of adult shells, thus greatly increasing the amount of shell material available for paleoenvironmental studies. No salinity effects were observed. Shell Na/Ca ratios showed a dramatic decrease with increasing dissolution (natural and artificial) in waters that are undersaturated with respect to <span class="hlt">calcite</span>, whereas Mg/Ca ratios displayed a minor decrease and Sr/Ca ratios showed no change. Of the ratios studied, Mg/Ca offers the most promise for Quaternary <span class="hlt">marine</span> studies as a paleothermometer. Further calibration studies are needed to better</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/980374','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/980374"><span>Observation of an Organic-Inorganic Lattice Match during Biomimetic Growth of (001)-Oriented <span class="hlt">Calcite</span> Crystals under Floating Sulfate Monolayers</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kewalramani, S.; Kim, K; Stripe, B; Evmenenko, G; Dommett, G; Dutta, P</p> <p>2008-01-01</p> <p>Macromolecular layers rich in amino acids and with some sulfated polysaccharides appear to control oriented <span class="hlt">calcite</span> growth in living organisms. <span class="hlt">Calcite</span> crystals nucleating under floating acid monolayers have been found to be unoriented on average. We have now observed directly, using in situ grazing incidence X-ray diffraction, that there is a 1:1 match between the monolayer unit cell and the unit cell of the (001) plane of <span class="hlt">calcite</span>. Thus, sulfate head groups appear to act as templates for the growth of (001)-oriented <span class="hlt">calcite</span> crystals, which is the orientation commonly found in biominerals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25318063','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25318063"><span>Infrared spectroscopy and density functional theory investigation of <span class="hlt">calcite</span>, chalk, and coccoliths--do we observe the mineral surface?</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Andersson, M P; Hem, C P; Schultz, L N; Nielsen, J W; Pedersen, C S; Sand, K K; Okhrimenko, D V; Johnsson, A; Stipp, S L S</p> <p>2014-11-13</p> <p>We have measured infrared spectra from several types of <span class="hlt">calcite</span>: chalk, freshly cultured coccoliths produced by three species of algae, natural <span class="hlt">calcite</span> (Iceland Spar), and two types of synthetic <span class="hlt">calcite</span>. The most intense infrared band, the asymmetric carbonate stretch vibration, is clearly asymmetric for the coccoliths and the synthetic <span class="hlt">calcite</span> prepared using the carbonation method. It can be very well fitted by two peaks: a narrow Lorenzian at lower frequency and a broader Gaussian at higher frequency. These two samples both have a high specific surface area. Density functional theory for bulk <span class="hlt">calcite</span> and several <span class="hlt">calcite</span> surface systems allows for assignment of the infrared bands. The two peaks that make up the asymmetric carbonate stretch band come from the bulk (narrow Lorenzian) and from a combination of two effects (broad Gaussian): the surface or near surface of <span class="hlt">calcite</span> and line broadening from macroscopic dielectric effects. We detect water adsorbed on the high surface area synthetic <span class="hlt">calcite</span>, which permits observation of the chemistry of thin liquid films on <span class="hlt">calcite</span> using transmission infrared spectroscopy. The combination of infrared spectroscopy and density functional theory also allowed us to quantify the amount of polysaccharides associated with the coccoliths. The amount of polysaccharides left in chalk, demonstrated to be present in other work, is below the IR detection limit, which is 0.5% by mass.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA04594&hterms=celsius&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dcelsius','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA04594&hterms=celsius&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dcelsius"><span><span class="hlt">Mariner</span> 2</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2003-01-01</p> <p><span class="hlt">Mariner</span> 2 was the world's first successful interplanetary spacecraft. Launched August 27, 1962, on an Atlas-Agena rocket, <span class="hlt">Mariner</span> 2 passed within about 34,000 kilometers (21,000 miles) of Venus, sending back valuable new information about interplanetary space and the Venusian atmosphere. <span class="hlt">Mariner</span> 2 recorded the temperature at Venus for the first time, revealing the planet's very hot atmosphere of about 500 degrees Celsius (900 degrees Fahrenheit). The spacecraft's solar wind experiment measured for the first time the density, velocity, composition and variation over time of the solar wind.<p/></p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27645701','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27645701"><span>Lattice distortions in coccolith <span class="hlt">calcite</span> crystals originate from occlusion of biomacromolecules.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hood, Matthew A; Leemreize, Hanna; Scheffel, André; Faivre, Damien</p> <p>2016-11-01</p> <p>During biomineralization, organisms control the formation and morphology of a mineral using biomacromolecules. The biomacromolecules that most strongly interact with the growing crystals frequently get occluded within. Such an observation has been recently obtained for the calcium carbonate producing coccolithophore species Pleurochrysis carterae. Coccolithophores are unicellular algae that produce calcified scales built from complex-shaped <span class="hlt">calcite</span> crystals, termed coccoliths. It is unclear how widespread the phenomenon of biomacromolecular occlusion within <span class="hlt">calcite</span> crystals is in calcifying haptophytes such as coccolithophores. Here, the coccoliths of biological replicates of the bloom forming Emiliania huxleyi are compared with that of Pleurochrysis carterae, two species with different coccolith morphologies and crystal growth mechanisms. From high-resolution synchrotron X-ray diffraction, changes in the lattice parameters of coccolith <span class="hlt">calcite</span>, after heating to 450°C, are observed and associated with macrostrain originating from occluded biomacromolecules. We propose a mechanism governing the biomacromolecules' interaction with the growing coccolith crystals and their likely origin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17664967','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17664967"><span>Heterogeneous interactions of <span class="hlt">calcite</span> aerosol with sulfur dioxide and sulfur dioxide-nitric acid mixtures.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Prince, A Preszler; Kleiber, P; Grassian, V H; Young, M A</p> <p>2007-07-14</p> <p>The heterogeneous chemistry of sulfur dioxide with CaCO(3) (<span class="hlt">calcite</span>) aerosol as a function of relative humidity (RH) has been studied under isolated particle conditions in an atmospheric reaction chamber using infrared absorption spectroscopy. The reaction of SO(2) with <span class="hlt">calcite</span> produced gas phase CO(2) as a product in addition to the conversion of the particulate carbonate to sulfite. The reaction extent was found to increase with elevated RH, as has been observed for the similar reaction with HNO(3), but much higher relative humidities were needed to significantly enhance the reaction. Mixed experiments in which <span class="hlt">calcite</span> aerosol was exposed to both HNO(3) and SO(2) were also performed. The overall reaction extent at a given relative humidity did not appear to be increased by having both reactant gases present. The role of carbonate aerosol as an atmospheric sink for sulfur dioxide and particulate nitrogen and sulfur correlations are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26675363','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26675363"><span>Heterogeneous distribution of dye-labelled biomineralizaiton proteins in <span class="hlt">calcite</span> crystals.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Chuang; Xie, Liping; Zhang, Rongqing</p> <p>2015-12-17</p> <p>Biominerals are highly ordered crystals mediated by organic matters especially proteins in organisms. However, how specific proteins are distributed inside biominerals are not well understood. In the present study, we use fluorescein isothiocyanate (FITC) to label extracted proteins from the shells of bivalve Pinctada fucata. By confocal laser scanning microscopy (CLSM), we observe a heterogeneous distribution of dye-labelled proteins inside synthetic <span class="hlt">calcite</span> at the microscale. Proteins from the prismatic <span class="hlt">calcite</span> layers accumulate at the edge of crystals while proteins from the nacreous aragonite layers accumulate at the center of crystals. Raman and X-ray powder diffraction show that both the proteins cannot alter the crystal phase. Scanning electron microscope demonstrates both proteins are able to affect the crystal morphology. This study may provide a direct approach for the visualization of protein distributions in crystals by small-molecule dye-labelled proteins as the additives in the crystallization process and improve our understanding of intracrystalline proteins distribution in biogenic <span class="hlt">calcites</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009SSCom.149.1905N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009SSCom.149.1905N"><span>Swift heavy ion irradiation induced phase transformation in <span class="hlt">calcite</span> single crystals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nagabhushana, H.; Nagabhushana, B. M.; Lakshminarasappa, B. N.; Singh, Fouran; Chakradhar, R. P. S.</p> <p>2009-11-01</p> <p>Ion irradiation induced phase transformation in <span class="hlt">calcite</span> single crystals have been studied by means of Raman and infrared spectroscopy using 120 MeV Au 9+ ions. The observed bands have been assigned according to group theory analysis. For higher fluence of 5×10 12 ion/cm 2, an extra peak on either side of the 713 cm -1 peak and an increase in the intensity of 1085 cm -1 peak were observed in Raman studies. FTIR spectra exhibit extra absorption bands at 674, 1589 cm -1 and enhancement in bands at 2340 and 2374 cm -1 was observed. This might be due to the phase transformation from <span class="hlt">calcite</span> to vaterite. The damage cross section ( σ) for all the Raman and FTIR active modes was determined. The increase of FWHM, shift in peak positions and appearance of new peaks indicated that <span class="hlt">calcite</span> phase is converted into vaterite.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JCrGr.338..244Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JCrGr.338..244Y"><span>Effects of L-Aspartic acid on the step retreat kinetics of <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yoshino, Toru; Kagi, Hiroyuki</p> <p>2012-01-01</p> <p>Effects of L-Aspartic acid (L-Asp) on step retreat kinetics in the dissolution of <span class="hlt">calcite</span> were investigated. The step retreat velocities under surface-controlled kinetics were determined from in-situ atomic force microscopic observations using an improved flow-through system. Comparison of the present results with those obtained under a mixed kinetics condition revealed that the addition of L-Asp promotes the transport process in the <span class="hlt">calcite</span> dissolution through acid-base and/or complex forming reactions in the diffusion boundary layer. Additionally, promotion of the acute and obtuse step retreats by the L-Asp additive was observed under surface-controlled kinetics. This report is the first to clarify that L-Asp promotes surface processes in the dissolution of <span class="hlt">calcite</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/759850','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/759850"><span>Structure of the (1014) Surfaces of <span class="hlt">Calcite</span>, Dolomite, and Magnesite under Wet and Dry Conditions</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>WRIGHT,KATE; CYGAN,RANDALL T.; SLATER,BEN</p> <p>2000-06-12</p> <p>Atomistic computer simulation methods have been employed to model the structure of the (10{bar 1}4) surfaces of <span class="hlt">calcite</span>, dolomite and magnesite. The authors calculations show that under vacuum conditions, <span class="hlt">calcite</span> undergoes the greatest degree of surface relaxation with rotation and distortion of the carbonate group accompanied by movement of the calcium ion. The magnesite surface is the least distorted of the three carbonates, with dolomite being intermediate to the two end members. When water molecules are placed on the surface to produce complete monolayer coverage, the <span class="hlt">calcite</span> surface is stabilized and the amount of relaxation is substantially reduced. In contrast, the dolomite and magnesite surfaces are destabilized by hydration as indicated by a significant increase in the surface energies relative to the dry surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21377404','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21377404"><span>Hormone balance and <span class="hlt">abiotic</span> stress tolerance in crop plants.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Peleg, Zvi; Blumwald, Eduardo</p> <p>2011-06-01</p> <p>Plant hormones play central roles in the ability of plants to adapt to changing environments, by mediating growth, development, nutrient allocation, and source/sink transitions. Although ABA is the most studied stress-responsive hormone, the role of cytokinins, brassinosteroids, and auxins during environmental stress is emerging. Recent evidence indicated that plant hormones are involved in multiple processes. Cross-talk between the different plant hormones results in synergetic or antagonic interactions that play crucial roles in response of plants to <span class="hlt">abiotic</span> stress. The characterization of the molecular mechanisms regulating hormone synthesis, signaling, and action are facilitating the modification of hormone biosynthetic pathways for the generation of transgenic crop plants with enhanced <span class="hlt">abiotic</span> stress tolerance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21853987','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21853987"><span>An <span class="hlt">abiotic</span> analogue of the nuclear pore complex hydrogel.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bird, Sean P; Baker, Lane A</p> <p>2011-09-12</p> <p>We describe an <span class="hlt">abiotic</span> hydrogel that mimics selectivity of the nuclear pore complex. Copolymerization of peptide tetramers (phenylalanine-serine-phenylalanine-glycine, FSFG) with acrylamide results in hydrophobic interactions significant enough to allow the formation of freestanding hydrogel structures. Incorporation of FSFG motifs also renders the hydrogels selective. Selective binding of importins and nuclear transport receptor-cargo complexes is qualitatively demonstrated and compared with polyacrylamide, hydrogels prepared from a control peptide, and hydrogels prepared from the nuclear pore complex protein Nsp1. These <span class="hlt">abiotic</span> hydrogels will enable further studies of the unique transport mechanisms of the nuclear pore complex and provide an interesting paradigm for the future development of synthetic platforms for separations and selective interfaces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26563752','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26563752"><span><span class="hlt">Abiotic</span> mediation of a mutualism drives herbivore abundance.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Mooney, Emily H; Phillips, Joseph S; Tillberg, Chadwick V; Sandrow, Cheryl; Nelson, Annika S; Mooney, Kailen A</p> <p>2016-01-01</p> <p>Species abundance is typically determined by the <span class="hlt">abiotic</span> environment, but the extent to which such effects occur through the mediation of biotic interactions, including mutualisms, is unknown. We explored how light environment (open meadow vs. shaded understory) mediates the abundance and ant tending of the aphid Aphis helianthi feeding on the herb Ligusticum porteri. Yearly surveys consistently found aphids to be more than 17-fold more abundant on open meadow plants than on shaded understory plants. Manipulations demonstrated that this abundance pattern was not due to the direct effects of light environment on aphid performance, or indirectly through host plant quality or the effects of predators. Instead, open meadows had higher ant abundance and per capita rates of aphid tending and, accordingly, ants increased aphid population growth in meadow but not understory environments. The <span class="hlt">abiotic</span> environment thus drives the abundance of this herbivore exclusively through the mediation of a protection mutualism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21700871','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21700871"><span><span class="hlt">Abiotic</span> pyrite formation produces a large Fe isotope fractionation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Guilbaud, Romain; Butler, Ian B; Ellam, Rob M</p> <p>2011-06-24</p> <p>The iron isotope composition of sedimentary pyrite has been proposed as a potential proxy to trace microbial metabolism and the redox evolution of the oceans. We demonstrate that Fe isotope fractionation accompanies <span class="hlt">abiotic</span> pyrite formation in the absence of Fe(II) redox change. Combined fractionation factors between Fe(II)(aq), mackinawite, and pyrite permit the generation of pyrite with Fe isotope signatures that nearly encapsulate the full range of sedimentary δ(56)Fe(pyrite) recorded in Archean to modern sediments. We propose that Archean negative Fe isotope excursions reflect partial Fe(II)(aq) utilization during <span class="hlt">abiotic</span> pyrite formation rather than microbial dissimilatory Fe(III) reduction. Late Proterozoic to modern sediments may reflect greater Fe(II)(aq) utilization and variations in source composition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810047658&hterms=Leucine&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3DLeucine','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810047658&hterms=Leucine&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3DLeucine"><span>Experiments on the <span class="hlt">abiotic</span> amplification of optical activity</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bonner, W. A.; Blair, N. E.; Dirbas, F. M.</p> <p>1981-01-01</p> <p>Experiments concerning the physical mechanisms for the <span class="hlt">abiotic</span> generation and chemical mechanisms for the amplification of optical activity in biological compounds are reviewed. Attention is given to experiments involving the determination of the differential adsorption of racemic amino acids on d- and l-quartz, the asymmetric photolysis of racemic amino acids by circularly polarized light, and the asymmetric radiolysis of solid amino acids by longitudinally polarized electrons, and the enantiomeric enrichments thus obtained are noted. Further experiments on the amplification of the chirality in the polymerization of D, L-amino acid mixtures and the hydrolysis of D-, L-, and D, L-polypeptides are discussed. It is suggested that a repetitive cycle of partial polymerization-hydrolyses may account for the <span class="hlt">abiotic</span> genesis of optically enriched polypeptides on the primitive earth.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25646668','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25646668"><span>Transcriptional networks-crops, clocks, and <span class="hlt">abiotic</span> stress.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gehan, Malia A; Greenham, Kathleen; Mockler, Todd C; McClung, C Robertson</p> <p>2015-04-01</p> <p>Several factors affect the yield potential and geographical range of crops including the circadian clock, water availability, and seasonal temperature changes. In order to sustain and increase plant productivity on marginal land in the face of both biotic and <span class="hlt">abiotic</span> stresses, we need to more efficiently generate stress-resistant crops through marker-assisted breeding, genetic modification, and new genome-editing technologies. To leverage these strategies for producing the next generation of crops, future transcriptomic data acquisition should be pursued with an appropriate temporal design and analyzed with a network-centric approach. The following review focuses on recent developments in <span class="hlt">abiotic</span> stress transcriptional networks in economically important crops and will highlight the utility of correlation-based network analysis and applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22903295','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22903295"><span>SUMO, a heavyweight player in plant <span class="hlt">abiotic</span> stress responses.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Castro, Pedro Humberto; Tavares, Rui Manuel; Bejarano, Eduardo R; Azevedo, Herlânder</p> <p>2012-10-01</p> <p>Protein post-translational modifications diversify the proteome and install new regulatory levels that are crucial for the maintenance of cellular homeostasis. Over the last decade, the ubiquitin-like modifying peptide small ubiquitin-like modifier (SUMO) has been shown to regulate various nuclear processes, including transcriptional control. In plants, the sumoylation pathway has been significantly implicated in the response to environmental stimuli, including heat, cold, drought, and salt stresses, modulation of abscisic acid and other hormones, and nutrient homeostasis. This review focuses on the emerging importance of SUMO in the <span class="hlt">abiotic</span> stress response, summarizing the molecular implications of sumoylation and emphasizing how high-throughput approaches aimed at identifying the full set of SUMO targets will greatly enhance our understanding of the SUMO-<span class="hlt">abiotic</span> stress association.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26803396','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26803396"><span>Arbuscular mycorrhizal fungal responses to <span class="hlt">abiotic</span> stresses: A review.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lenoir, Ingrid; Fontaine, Joël; Lounès-Hadj Sahraoui, Anissa</p> <p>2016-03-01</p> <p>The majority of plants live in close collaboration with a diversity of soil organisms among which arbuscular mycorrhizal fungi (AMF) play an essential role. Mycorrhizal symbioses contribute to plant growth and plant protection against various environmental stresses. Whereas the resistance mechanisms induced in mycorrhizal plants after exposure to <span class="hlt">abiotic</span> stresses, such as drought, salinity and pollution, are well documented, the knowledge about the stress tolerance mechanisms implemented by the AMF themselves is limited. This review provides an overview of the impacts of various <span class="hlt">abiotic</span> stresses (pollution, salinity, drought, extreme temperatures, CO2, calcareous, acidity) on biodiversity, abundance and development of AMF and examines the morphological, biochemical and molecular mechanisms implemented by AMF to survive in the presence of these stresses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1184974','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1184974"><span>Heterogeneous growth of cadmium and cobalt carbonate phases at the (101¯4) <span class="hlt">calcite</span> surface</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Xu, Man; Ilton, Eugene S.; Engelhard, Mark H.; Qafoku, Odeta; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.</p> <p>2015-03-01</p> <p>The ability of surface precipitates to form heteroepitaxially is an important factor that controls the extent of heterogeneous growth. In this work, the growth of cadmium and cobalt carbonate phases on (10-14) <span class="hlt">calcite</span> surfaces is compared for a range of initial saturation states with respect to otavite (CdCO3) and sphaerocobaltite (CoCO3), two isostructural metal carbonates that exhibit different lattice misfits with respect to <span class="hlt">calcite</span>. <span class="hlt">Calcite</span> single crystals were reacted in static conditions for 16 hours with CdCl2 and CoCl2 aqueous solutions with initial concentrations 0.3 ≤ [Cd2+]0 ≤ 100 μM and 25 ≤ [Co2+]0 ≤ 200 μM. The reacted crystals were imaged in situ with atomic force microscopy (AFM) and analyzed ex situ with X-ray photoelectron spectroscopy (XPS). AFM images of Cd-reacted crystals showed the formation of large islands elongated along the direction, clear evidence of heteroepitaxial growth, whereas surface precipitates on Co-reacted crystals were small round islands. Deformation of <span class="hlt">calcite</span> etch pits in both cases indicated the incorporation of Cd and Co at step edges. XPS analysis pointed to the formation of a Cd-rich (Ca,Cd)CO3 solid solution coating atop the <span class="hlt">calcite</span> substrate. In contrast, XPS measurements of the Co-reacted crystals provided evidence for the formation of a mixed hydroxy-carbonate cobalt phase. The combined AFM and XPS results suggest that the lattice misfit between CoCO3 and CaCO3 ( 15% based on surface areas) is too large to allow for heteroepitaxial growth of a pure cobalt carbonate phase on <span class="hlt">calcite</span> surfaces in aqueous solutions and at ambient conditions. The use of the satellite structure of the Co 2p3/2 photoelectron line as a tool for determining the nature of cobalt surface precipitates is also discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/289447','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/289447"><span>Origin of platy <span class="hlt">calcite</span> crystals in hot-spring deposits in the Kenya Rift Valley</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jones, B.; Renault, R.W.</p> <p>1998-09-01</p> <p>Platy <span class="hlt">calcite</span> crystals, which have their c axis parallel to their shortest length axis, are common components of travertine deposits found around some hot springs in the Kenya Rift Valley. They are composite crystals formed of numerous paper-thin subcrystals. Individual plates allowed to grow without obstruction develop a hexagonal motif. The Kenyan crystals typically form in hot (>75 C) waters that have a low Ca content (<10 mg/l), a high CO{sub 2} content, and a high rate of CO{sub 2} degassing. At Chemurkeu, aggregates of numerous small platy crystals collectively form lattice crystals that superficially resemble ray crystals. The walls of the lattice crystals are formed of large platy crystals that have their long and intermediate length axes aligned parallel to the plane of the long axis of the lattice crystal. Internally, the lattice crystals are formed of small platy <span class="hlt">calcite</span> crystals arranged in a boxlike pattern that creates the appearance of a lattice when viewed in thin section. Lattice crystals are highly porous, with each pore being enclosed by platy crystals. At Lorusio, travertines are mainly formed of pseudodentrites that are constructed by numerous small platy crystals attached to a main stem which is a large platy crystal that commonly curves along its long axis. The pseudodentrites are the main construction blocks in ledges and lilypads that form in the vent pool and spring outflow channels, where the water is too hot for microbes other than hyperthermophiles. The platy <span class="hlt">calcite</span> crystals in the Kenyan travertines are morphologically similar to platy <span class="hlt">calcite</span> crystals that form as scale in pipes in the geothermal fields of New Zealand and hydrothermal angel wing <span class="hlt">calcite</span> from the La Fe mine in Mexico. Comparison of the Kenyan and New Zealand crystals indicates that platy <span class="hlt">calcite</span> crystals form from waters with a low Ca{sup 2+} content and a high CO{sub 3}/Ca ratio due to rapid rates of CO{sub 2} degassing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRB..121.1631B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRB..121.1631B"><span>The effect of fluid composition, salinity, and acidity on subcritical crack growth in <span class="hlt">calcite</span> crystals</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bergsaker, Anne Schad; Røyne, Anja; Ougier-Simonin, Audrey; Aubry, Jérôme; Renard, François</p> <p>2016-03-01</p> <p>Chemically activated processes of subcritical cracking in <span class="hlt">calcite</span> control the time-dependent strength of this mineral, which is a major constituent of the Earth's brittle upper crust. Here experimental data on subcritical crack growth are acquired with a double torsion apparatus to characterize the influence of fluid pH (range 5-7.5) and ionic strength and species (Na2SO4, NaCl, MgSO4, and MgCl2) on the propagation of microcracks in <span class="hlt">calcite</span> single crystals. The effect of different ions on crack healing has also been investigated by decreasing the load on the crack for durations up to 30 min and allowing it to relax and close. All solutions were saturated with CaCO3. The crack velocities reached during the experiments are in the range 10-9-10-2 m/s and cover the range of subcritical to close to dynamic rupture propagation velocities. Results show that for <span class="hlt">calcite</span> saturated solutions, the energy necessary to fracture <span class="hlt">calcite</span> is independent of pH. As a consequence, the effects of fluid salinity, measured through its ionic strength, or the variation of water activity have stronger effects on subcritical crack propagation in <span class="hlt">calcite</span> than pH. Consequently, when considering the geological sequestration of CO2 into carbonate reservoirs, the decrease of pH within the range of 5-7.5 due to CO2 dissolution into water should not significantly alter the rate of fracturing of <span class="hlt">calcite</span>. Increase in salinity caused by drying may lead to further reduction in cracking and consequently a decrease in brittle creep. The healing of cracks is found to vary with the specific ions present.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1815569W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1815569W"><span>Determination of aragonite trace element partition coefficients from speleothem <span class="hlt">calcite</span>-aragonite transitions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wassenburg, Jasper A.; Scholz, Denis; Jochum, Klaus Peter; Cheng, Hai; Oster, Jessica; Immenhauser, Adrian; Richter, Detlev K.; Haeger, Tobias; Hoffmann, Dirk; Breitenbach, Sebastian F. M.</p> <p>2016-04-01</p> <p>Speleothem trace element variability has often been linked to environmental changes. While research has focused on element incorporation into speleothem <span class="hlt">calcite</span>, our current knowledge of trace element variability in speleothem aragonite is limited to a few studies only. Here we present, to our knowledge, for the first time quantitative estimates of distribution coefficients for speleothem aragonite (DMg, DBa, DSr, and DU). These were derived from ten <span class="hlt">calcite</span>-to-aragonite transitions from seven speleothems from Morocco, Germany, Spain, France and India. Our calculations indicate the following distribution coefficients: DMg = 1.01E-04 ± 9.0E-05, DBa(Ar) = 0.91 ± 0.53, DSr(Ar) = 1.38 ± 0.53, and DU(Ar) = 6.26 ± 4.53. These results are discussed in the context of speleothem growth rates, Rayleigh distillation effects, temperature, drip water elemental composition and drip water pH. We conclude that speleothem aragonite DMg(Ar) is below one, DSr(Ar) is close to unity, and DU(Ar) is above one. For DBa(Ar), such a conclusion is difficult. Speleothem growth rate may affect aragonite DSr in samples forming at a growth rate lower than 20 μm/a. Our results also indicate that <span class="hlt">calcite</span> DSr and <span class="hlt">calcite</span> DBa are affected by the Mg content of <span class="hlt">calcite</span>. This has important implications for studies attempting to quantify processes like prior <span class="hlt">calcite</span> precipitation. In particular, DSr and DBa cannot be transferred from caves developed within a limestone host rock to caves developed within a dolostone host rock.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA476323','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA476323"><span>Sustainability of Long-Term <span class="hlt">Abiotic</span> Attenuation of Chlorinated Ethenes</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2007-09-28</p> <p>that contribute to <span class="hlt">abiotic</span> transformations is critical to assess the feasibility of natural attenuation and promote the rationale design of...anaerobic glovebox. The resulting slurry was mixed for three days and then decanted into polypropylene centrifuge bottles. These bottles were...tightly sealed and centrifuged at 8000 rpm for 10 minutes. The supernatant in the bottles was discarded, and fresh nitrogen-purged deionized water was</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA602346','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA602346"><span>Biotic-<span class="hlt">Abiotic</span> Nanoscale Interactions in Biological Fuel Cells</span></a></p> <p><a target="_blank" href="https://publicaccess.dtic.mil/psm/api/service/search/search">DTIC Science & Technology</a></p> <p></p> <p>2014-03-28</p> <p>Force Office of Scientific Research 875 North Randolph Street 4027 Arlington VA 22203 email: Patrick.Bradshaw@afosr.af.mil phone : 703-588-8492...Science Center 215C Los Angeles, CA 90089-0484 email: mnaggar@usc.edu phone : 213-740-2394 2 Biotic-<span class="hlt">Abiotic</span> Nanoscale Interactions in...aggregation – collaboration with Naval Research Lab. 2.4 As part of an international collaboration, we reported on filamentous bacteria mediating centimeter</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008ECSS...80..555G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008ECSS...80..555G"><span>Changes in biotic and <span class="hlt">abiotic</span> processes following mangrove clearing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Granek, Elise; Ruttenberg, Benjamin I.</p> <p>2008-12-01</p> <p>Mangrove forests, important tropical coastal habitats, are in decline worldwide primarily due to removal by humans. Changes to mangrove systems can alter ecosystem properties through direct effects on <span class="hlt">abiotic</span> factors such as temperature, light and nutrient supply or through changes in biotic factors such as primary productivity or species composition. Despite the importance of mangroves as transitional habitats between land and sea, little research has examined changes that occur when they are cleared. We examined changes in a number of biotic and <span class="hlt">abiotic</span> factors following the anthropogenic removal of red mangroves ( Rhizophora mangle) in the Panamanian Caribbean, including algal biomass, algal diversity, algal grazing rates, light penetration, temperature, sedimentation rates and sediment organic content. In this first study examining multiple ecosystem-level effects of mangrove disturbance, we found that areas cleared of mangroves had higher algal biomass and richness than intact mangrove areas. This increase in algal biomass and richness was likely due to changes in <span class="hlt">abiotic</span> factors (e.g. light intensity, temperature), but not biotic factors (fish herbivory). Additionally the algal and cyanobacterial genera dominating mangrove-cleared areas were rare in intact mangroves and included a number of genera that compete with coral for space on reefs. Interestingly, sedimentation rates did not differ between intact and cleared areas, but the sediments that accumulated in intact mangroves had higher organic content. These findings are the first to demonstrate that anthropogenic clearing of mangroves changes multiple biotic and <span class="hlt">abiotic</span> processes in mangrove forests and that some of these changes may influence adjacent habitats such as coral reefs and seagrass beds. Additional research is needed to further explore the community and ecosystem-level effects of mangrove clearing and their influence on adjacent habitats, but it is clear that mangrove conservation is an</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1539019','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1539019"><span>Wheat EST resources for functional genomics of <span class="hlt">abiotic</span> stress</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Houde, Mario; Belcaid, Mahdi; Ouellet, François; Danyluk, Jean; Monroy, Antonio F; Dryanova, Ani; Gulick, Patrick; Bergeron, Anne; Laroche, André; Links, Matthew G; MacCarthy, Luke; Crosby, William L; Sarhan, Fathey</p> <p>2006-01-01</p> <p>Background Wheat is an excellent species to study freezing tolerance and other <span class="hlt">abiotic</span> stresses. However, the sequence of the wheat genome has not been completely characterized due to its complexity and large size. To circumvent this obstacle and identify genes involved in cold acclimation and associated stresses, a large scale EST sequencing approach was undertaken by the Functional Genomics of <span class="hlt">Abiotic</span> Stress (FGAS) project. Results We generated 73,521 quality-filtered ESTs from eleven cDNA libraries constructed from wheat plants exposed to various <span class="hlt">abiotic</span> stresses and at different developmental stages. In addition, 196,041 ESTs for which tracefiles were available from the National Science Foundation wheat EST sequencing program and DuPont were also quality-filtered and used in the analysis. Clustering of the combined ESTs with d2_cluster and TGICL yielded a few large clusters containing several thousand ESTs that were refractory to routine clustering techniques. To resolve this problem, the sequence proximity and "bridges" were identified by an e-value distance graph to manually break clusters into smaller groups. Assembly of the resolved ESTs generated a 75,488 unique sequence set (31,580 contigs and 43,908 singletons/singlets). Digital expression analyses indicated that the FGAS dataset is enriched in stress-regulated genes compared to the other public datasets. Over 43% of the unique sequence set was annotated and classified into functional categories according to Gene Ontology. Conclusion We have annotated 29,556 different sequences, an almost 5-fold increase in annotated sequences compared to the available wheat public databases. Digital expression analysis combined with gene annotation helped in the identification of several pathways associated with <span class="hlt">abiotic</span> stress. The genomic resources and knowledge developed by this project will contribute to a better understanding of the different mechanisms that govern stress tolerance in wheat and other cereals. PMID</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.B42E..07F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.B42E..07F"><span>Field Experiment to Stimulate Microbial Urease Activity in Groundwater for in situ <span class="hlt">Calcite</span> Precipitation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fujita, Y.; Taylor, J. L.; Tyler, T. L.; Banta, A. B.; Reysenbach, A. L.; Delwiche, M. E.; McLing, T. L.; Colwell, F. S.; Smith, R. W.</p> <p>2003-12-01</p> <p>Groundwater contamination by radionuclides and metals from past weapons processing activities is a significant problem for the United States Department of Energy. Removal of these pollutants from the subsurface can be prohibitively expensive and result in worker exposure, and therefore in situ containment and stabilization is an attractive remediation alternative. One potential approach for the immobilization of certain radionuclides and metals (e.g., 90Sr, 60Co, Pb, Cd) is to induce geochemical conditions that promote co-precipitation in <span class="hlt">calcite</span>. Many aquifers in the arid western US are <span class="hlt">calcite</span>-saturated, and <span class="hlt">calcite</span> precipitated under an engineered remediation scheme in such aquifers should remain stable even after return to ambient conditions. We have proposed that an effective way to promote <span class="hlt">calcite</span> precipitation is to utilize native microorganisms that hydrolyze urea. Urea hydrolysis results in carbonate and ammonium production, and an increase in pH. The increased carbonate alkalinity favors <span class="hlt">calcite</span> precipitation, and the ammonium serves the additional role of promoting desorption of sorbed metal ions from the aquifer matrix by ion exchange. The desorbed metals are then accessible to co-precipitation in <span class="hlt">calcite</span>, which can be a longer-term immobilization mechanism than sorption. The ability to hydrolyze urea is common among environmental microorganisms, and we have shown in the laboratory that microbial urea hydrolysis can be linked to <span class="hlt">calcite</span> precipitation and co-precipitation of the trace metal strontium. As a next step in the development of our remediation approach, we aimed to demonstrate that we can stimulate the native microbial community to express urease in the field. In 2002 we conducted a preliminary field trial of our approach, using a well in the Eastern Snake River Plain Aquifer in Idaho Falls, Idaho, USA. A dilute molasses solution (0.00075%) was injected to promote overall biological growth, and then urea (50 mM) was added to the aquifer</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/929930','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/929930"><span>Arsenate Uptake by <span class="hlt">Calcite</span>: Macroscopic and Spectroscopic Characterization of Adsorption and Incorporation Mechanisms</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Alexandratos,V.; Elzinga, E.; Reeder, R.</p> <p>2007-01-01</p> <p>Batch uptake experiments and X-ray element mapping and spectroscopic techniques were used to investigate As(V) (arsenate) uptake mechanisms by <span class="hlt">calcite</span>, including adsorption and coprecipitation. Batch sorption experiments in <span class="hlt">calcite</span>-equilibrated suspensions (pH 8.3; PCO{sub 2} = 10{sup -3.5} atm) reveal rapid initial sorption to <span class="hlt">calcite</span>, with sorption rate gradually decreasing with time as available sorption sites decrease. An As(V)-<span class="hlt">calcite</span> sorption isotherm determined after 24 h equilibration exhibits Langmuir-like behavior up to As concentrations of 300 {mu}M. Maximum distribution coefficient values (K{sub d}), derived from a best fit to a Langmuir model, are {approx}190 L kg{sup -1}. <span class="hlt">Calcite</span> single crystals grown in the presence of As(V) show well-developed rhombohedral morphology with characteristic growth hillocks on (10{bar 1}4) surfaces at low As(V) concentrations ({<=}5 {mu}M), but habit modification is evident at As(V) concentrations {>=}30 {mu}M in the form of macrostep development preferentially on the - vicinal surfaces of growth hillocks. Micro-X-ray fluorescence element mapping of (10{bar 1}4) surfaces shows preferential incorporation of As in the - vicinal faces relative to + vicinals. EXAFS fit results for both adsorption and coprecipitation samples confirm that As occurs in the 5+ oxidation state in tetrahedral coordination with oxygen, i.e., as arsenate. For adsorption samples, As(V) forms inner-sphere surface complexes via corner-sharing with Ca octahedra. As(V) coprecipitated with <span class="hlt">calcite</span> substitutes in carbonate sites but with As off-centered, as indicated by two Ca shells, and with likely disruption of local structure. The results indicate that As(V) interacts strongly with the <span class="hlt">calcite</span> surface, similar to often-cited analog phosphate, and uptake can occur via both adsorption and coprecipitation reactions. Therefore, <span class="hlt">calcite</span> may be effective for partial removal of dissolved arsenate from aquatic and soil systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1995Metic..30R.550M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1995Metic..30R.550M"><span>New Shocked <span class="hlt">Calcite</span> and Fe Grains from Noerdlingen Ries Impact Crater</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miura, Y.</p> <p>1995-09-01</p> <p>Shocked minerals with simple chemical composition of silica, carbon or iron material reveal high-pressure phase during compression process [1]. As <span class="hlt">calcite</span> mineral shows high-pressure phase of aragonite it should have the "shocked phase" formed from high-pressure phase mixed with quenched materials of gas-melt reaction [2,3,4]. The main purposes of this paper are (1) to discuss new shocked materials of <span class="hlt">calcite</span> found in the Noerdlingen Ries impact crater. Germany and artificial impact phases. and (2) to show new findings of fine Fe-grains and anomalous plagioclase in suevite. Single grains of anomalous <span class="hlt">calcite</span> for X-ray analysis were selected from limestone with wormy or bubble-included texture in Buschelberg Ries impact crater (sample R8) [3 4]. Powdered and single grain samples of anomalous <span class="hlt">calcites</span> show low X-ray intensity and high Bragg angle shift. compared with standard <span class="hlt">calcite</span> of Akiyoshi limestone as listed in Table 1 [2.3.4]. The unit-cell dimensions of the single grain measured with the four-axes X-ray diffractometer in Yamaguchi University were determined by the least square calculation from the "highest X-ray intensity peak" of each crystal plane which is the same data of the powdered X-ray diffraction sample as an average structure . Both powdered and single grain data reveal high density of 2.76 g/cm^3 (between aragonite of density: rho=2.8g/cm^3, and normal <span class="hlt">calcite</span>: rho=2.71g/cm^3) of the <span class="hlt">calcite</span> cell which is the same characters of shocked phases of quartz or graphite [1,2,3,4] (Table 1). Anomalous <span class="hlt">calcite</span> contains minor amount of Si Fe Ti, though major cation is Ca of 99.4% in cation content. These foreign elements are mixed with during the formation in vapor plume [5]. Table 1, showing the x-ray density and unit-cell parameters of anomalous shocked <span class="hlt">calcite</span> with high density from Ries and artificial impact craters, appears here in the hard copy. Two types of shocked <span class="hlt">calcites</span> are found in artificial impact experiments of railgun of the ISAS. Japan. (a</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040088053&hterms=golgi&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dgolgi','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040088053&hterms=golgi&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dgolgi"><span>Galacturonomannan and Golgi-derived membrane linked to growth and shaping of biogenic <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Marsh, M. E.; Ridall, A. L.; Azadi, P.; Duke, P. J.</p> <p>2002-01-01</p> <p>The coccolithophores are valuable models for the design and synthesis of composite materials, because the cellular machinery controlling the nucleation, growth, and patterning of their <span class="hlt">calcitic</span> scales (coccoliths) can be examined genetically. The coccoliths are formed within the Golgi complex and are the major CaCO(3) component in limestone sediments-particularly those of the Cretaceous period. In this study, we describe mutants lacking a sulfated galacturonomannan and show that this polysaccharide in conjunction with the Golgi-derived membrane is directly linked to the growth and shaping of coccolith <span class="hlt">calcite</span> but not to the initial orientated nucleation of the mineral phase.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990JSG....12..351B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990JSG....12..351B"><span>Experimental <span class="hlt">calcite</span> fabrics in a synthetic weaker aggregate by coaxial and non-coaxial deformation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Borradaile, G. J.; McArthur, J.</p> <p></p> <p><span class="hlt">Calcite</span> grain aggregates, supported by a weaker, macroscopically ductile, matrix of set Portland cement, were deformed triaxially at room temperature with a confining pressure of 150 MPa and at rates corresponding to a pure shear, natural strain rate of 10 -5 s -1. Extensive grain rotation accompanied the twinning of <span class="hlt">calcite</span>. Stress orientations inside the specimens, determined from <span class="hlt">calcite</span> twins, agree well with the stresses imposed upon the specimens. Thus <span class="hlt">calcite</span> twins are sound kinematic indicators in this study. Various sample configurations were used to simulate pure shear, transpression and simple shear. In pure shear or coaxial strain, preferred dimensional orientations ( PDO) of <span class="hlt">calcite</span> are produced more efficiently in the presence of high pore fluid pressure. Those grain alignments are stronger than the bulk strain would predict assuming homogeneous strain. Strain is overestimated by methods assuming continuum behaviour because they fail to take into account the extensive interparticle motions that occur in the presence of high pore fluid pressure. Fluid pressure suppresses the twinning of <span class="hlt">calcite</span> by reducing the intergranular stresses. During deformation, small rapid variations in pore fluid pressure are believed to represent ephemeral dilatations accompanying particulate flow as groups of grains slide past one another. In dry specimens, pure shear is more effective than simple shear in producing a PDO of the <span class="hlt">calcite</span> grains. <span class="hlt">Calcite</span> grains are rotated rigidly and somewhat strained to produce L < S alignment fabrics in pure shear but give S-fabrics in transpression and perhaps also in simple shear. Thus grain-shape fabrics do not conform to the symmetry of bulk deformation in this study. Mean grain alignment is perpendicular to shortening in pure shear, initially inclined and later parallel to shear zone walls in transpression, and weak but statistically inclined to shear zone walls in simple shear. The mean orientation of grain-alignment fabrics is</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AIPC.1793f0005T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AIPC.1793f0005T"><span>Birefringence measurements in single crystal sapphire and <span class="hlt">calcite</span> shocked along the a axis</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tear, Gareth R.; Chapman, David J.; Eakins, Daniel E.; Proud, William G.</p> <p>2017-01-01</p> <p><span class="hlt">Calcite</span> and sapphire were shock compressed along the <10 1 ¯0 > direction (a axis) in a plate impact configuration. Polarimetery and Photonic Doppler Velocimetery (PDV) were used to measure the change in birefringence with particle velocity in the shock direction. Results for sapphire agree well with linear photoelastic theory and current literature showing a linear relationship between birefringence and particle velocity up to 310 m s-1. A maximum change in birefringence of 5% was observed. <span class="hlt">Calcite</span> however showed anomolous behaviour with no detectable change in birefringence (less than 0.1%) over the range of particle velocities studied (up to 75 m s-1).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/1571024','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/1571024"><span><span class="hlt">Marine</span> stings.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gurry, D</p> <p>1992-01-01</p> <p>Our superb coastline attracts local tourists and overseas visitors seeking recreation. There is increasing contact with <span class="hlt">marine</span> life. The unwary and unprepared holiday-maker can be at risk of serious injury from a number of common sea creatures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.176..279L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.176..279L"><span>Intra-skeletal <span class="hlt">calcite</span> in a live-collected Porites sp.: Impact on environmental proxies and potential formation process</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lazareth, Claire E.; Soares-Pereira, Caroline; Douville, Eric; Brahmi, Chloé; Dissard, Delphine; Le Cornec, Florence; Thil, François; Gonzalez-Roubaud, Cécile; Caquineau, Sandrine; Cabioch, Guy</p> <p>2016-03-01</p> <p>Geochemical proxies measured in the carbonate skeleton of tropical coral Porites sp. have commonly been used to reconstruct sea surface temperature (SST) and more recently seawater pH. Nevertheless, both reconstructed SST and pH depend on the preservation state of the skeleton, here made of aragonite; i.e., diagenetic processes and its related effects should be limited. In this study, we report on the impact of the presence of intra-skeletal <span class="hlt">calcite</span> on the skeleton geochemistry of a live-collected Porites sp. The Porites skeleton preservation state was analyzed using X-ray diffraction and scanning electron microscopy. Sr/Ca, Mg/Ca, U/Ca, Ba/Ca, Li/Mg, and B/Ca ratios were measured at a monthly and yearly resolution using quadrupole ICP-MS and multi-collector ICP-MS. The δ11B signatures and the <span class="hlt">calcite</span> percentages were acquired at a yearly timescale. The coral colony presents two parts, one with less than 3% <span class="hlt">calcite</span> (referred to as "no-<span class="hlt">calcite</span>" skeleton), the other one, corresponding to the skeleton formed during the last 4 years of growth, with <span class="hlt">calcite</span> percentages varying from 13% to 32% (referred to as "with <span class="hlt">calcite</span>" skeleton). This intra-skeletal <span class="hlt">calcite</span> replaces partly or completely numerous centers of calcification (COCs). All investigated geochemical tracers are significantly impacted by the presence of <span class="hlt">calcite</span>. The reconstructed SST decreases by about 0.1 °C per <span class="hlt">calcite</span>-percent as inferred from the Sr/Ca ratio. Such impact reaches up to 0.26 °C per <span class="hlt">calcite</span>-percent for temperature deduced from the Li/Mg ratio. So, less than 5% of such intra-skeletal <span class="hlt">calcite</span> does not prevent SST reconstructions using Sr/Ca ratio, but the percentage and type of <span class="hlt">calcite</span> have to be determined before fine SST interpretation. Seawater pH reconstruction inferred from boron isotopes drop by about -0.011 pH-unit per <span class="hlt">calcite</span>-percent. Such sensitivity to <span class="hlt">calcite</span> presence is particularly dramatic for fine paleo-pH reconstructions. Here we suggest that after being brought to shallow</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1068646','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1068646"><span><span class="hlt">Abiotic</span> Reductive Immobilization of U(VI) by Biogenic Mackinawite</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Veeramani, Harish; Scheinost, Andreas; Monsegue, Niven; Qafoku, Nikolla; Kukkadapu, Ravi K.; Newville, Mathew; Lanzirotti, Anthony; Pruden, Amy; Murayama, Mitsuhiro; Hochella, Michael F.</p> <p>2013-03-01</p> <p>During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in-situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze <span class="hlt">abiotic</span> U6+ reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe1+xS, x = 0 to 0.11) to reduce U6+ <span class="hlt">abiotically</span> was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U6+ indicate the formation of nanoparticulate UO2. This study suggests the relevance of Fe(II) and sulfide bearing biogenic minerals in mediating <span class="hlt">abiotic</span> U6+ reduction, an alternative pathway in addition to direct enzymatic U6+ reduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015ESS.....310703N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015ESS.....310703N"><span>Titania may produce <span class="hlt">abiotic</span> oxygen atmospheres on habitable exoplanets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Narita, Norio; Enomoto, Takafumi; Masaoka, Shigeyuki; Kusakabe, Nobuhiko</p> <p>2015-12-01</p> <p>The search for habitable exoplanets in the Universe is actively ongoing in the field of astronomy. The biggest future milestone is to determine whether life exists on such habitable exoplanets. In that context, oxygen in the atmosphere has been considered strong evidence for the presence of photosynthetic organisms. In this paper, we show that a previously unconsidered photochemical mechanism by titanium (IV) oxide (titania) can produce <span class="hlt">abiotic</span> oxygen from liquid water under near ultraviolet (NUV) lights on the surface of exoplanets. Titania works as a photocatalyst to dissociate liquid water in this process. This mechanism offers a different source of a possibility of <span class="hlt">abiotic</span> oxygen in atmospheres of exoplanets from previously considered photodissociation of water vapor in upper atmospheres by extreme ultraviolet (XUV) light. Our order-of-magnitude estimation shows that possible amounts of oxygen produced by this <span class="hlt">abiotic</span> mechanism can be comparable with or even more than that in the atmosphere of the current Earth, depending on the amount of active surface area for this mechanism. We conclude that titania may act as a potential source of false signs of life on habitable exoplanets.Reference:Narita N. et al.,Scientific Reports 5, Article number: 13977 (2015)http://www.nature.com/articles/srep13977</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26354078','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26354078"><span>Titania may produce <span class="hlt">abiotic</span> oxygen atmospheres on habitable exoplanets.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Narita, Norio; Enomoto, Takafumi; Masaoka, Shigeyuki; Kusakabe, Nobuhiko</p> <p>2015-09-10</p> <p>The search for habitable exoplanets in the Universe is actively ongoing in the field of astronomy. The biggest future milestone is to determine whether life exists on such habitable exoplanets. In that context, oxygen in the atmosphere has been considered strong evidence for the presence of photosynthetic organisms. In this paper, we show that a previously unconsidered photochemical mechanism by titanium (IV) oxide (titania) can produce <span class="hlt">abiotic</span> oxygen from liquid water under near ultraviolet (NUV) lights on the surface of exoplanets. Titania works as a photocatalyst to dissociate liquid water in this process. This mechanism offers a different source of a possibility of <span class="hlt">abiotic</span> oxygen in atmospheres of exoplanets from previously considered photodissociation of water vapor in upper atmospheres by extreme ultraviolet (XUV) light. Our order-of-magnitude estimation shows that possible amounts of oxygen produced by this <span class="hlt">abiotic</span> mechanism can be comparable with or even more than that in the atmosphere of the current Earth, depending on the amount of active surface area for this mechanism. We conclude that titania may act as a potential source of false signs of life on habitable exoplanets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27271677','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27271677"><span><span class="hlt">Abiotic</span> Deposition of Fe Complexes onto Leptothrix Sheaths.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kunoh, Tatsuki; Hashimoto, Hideki; McFarlane, Ian R; Hayashi, Naoaki; Suzuki, Tomoko; Taketa, Eisuke; Tamura, Katsunori; Takano, Mikio; El-Naggar, Mohamed Y; Kunoh, Hitoshi; Takada, Jun</p> <p>2016-06-03</p> <p>Bacteria classified in species of the genus Leptothrix produce extracellular, microtubular, Fe-encrusted sheaths. The encrustation has been previously linked to bacterial Fe oxidases, which oxidize Fe(II) to Fe(III) and/or active groups of bacterial exopolymers within sheaths to attract and bind aqueous-phase inorganics. When L. cholodnii SP-6 cells were cultured in media amended with high Fe(II) concentrations, Fe(III) precipitates visibly formed immediately after addition of Fe(II) to the medium, suggesting prompt <span class="hlt">abiotic</span> oxidation of Fe(II) to Fe(III). Intriguingly, these precipitates were deposited onto the sheath surface of bacterial cells as the population was actively growing. When Fe(III) was added to the medium, similar precipitates formed in the medium first and were <span class="hlt">abiotically</span> deposited onto the sheath surfaces. The precipitates in the Fe(II) medium were composed of assemblies of globular, amorphous particles (ca. 50 nm diameter), while those in the Fe(III) medium were composed of large, aggregated particles (≥3 µm diameter) with a similar amorphous structure. These precipitates also adhered to cell-free sheaths. We thus concluded that direct <span class="hlt">abiotic</span> deposition of Fe complexes onto the sheath surface occurs independently of cellular activity in liquid media containing Fe salts, although it remains unclear how this deposition is associated with the previously proposed mechanisms (oxidation enzyme- and/or active group of organic components-involved) of Fe encrustation of the Leptothrix sheaths.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4810371','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4810371"><span><span class="hlt">Abiotic</span> carbonate dissolution traps carbon in a semiarid desert</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Fa, Keyu; Liu, Zhen; Zhang, Yuqing; Qin, Shugao; Wu, Bin; Liu, Jiabin</p> <p>2016-01-01</p> <p>It is generally considered that desert ecosystems release CO2 to the atmosphere, but recent studies in drylands have shown that the soil can absorb CO2 <span class="hlt">abiotically</span>. However, the mechanisms and exact location of <span class="hlt">abiotic</span> carbon absorption remain unclear. Here, we used soil sterilization, 13CO2 addition, and detection methods to trace 13C in the soil of the Mu Us Desert, northern China. After 13CO2 addition, a large amount of 13CO2 was absorbed by the sterilised soil, and 13C was found enriched both in the soil gaseous phase and dissolved inorganic carbon (DIC). Further analysis indicated that about 79.45% of the total 13C absorbed by the soil was trapped in DIC, while the amount of 13C in the soil gaseous phase accounted for only 0.22% of the total absorbed 13C. However, about 20.33% of the total absorbed 13C remained undetected. Our results suggest that carbonate dissolution might occur predominately, and the soil liquid phase might trap the majority of <span class="hlt">abiotically</span> absorbed carbon. It is possible that the trapped carbon in the soil liquid phase leaches into the groundwater; however, further studies are required to support this hypothesis. PMID:27020762</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4564821','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4564821"><span>Titania may produce <span class="hlt">abiotic</span> oxygen atmospheres on habitable exoplanets</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Narita, Norio; Enomoto, Takafumi; Masaoka, Shigeyuki; Kusakabe, Nobuhiko</p> <p>2015-01-01</p> <p>The search for habitable exoplanets in the Universe is actively ongoing in the field of astronomy. The biggest future milestone is to determine whether life exists on such habitable exoplanets. In that context, oxygen in the atmosphere has been considered strong evidence for the presence of photosynthetic organisms. In this paper, we show that a previously unconsidered photochemical mechanism by titanium (IV) oxide (titania) can produce <span class="hlt">abiotic</span> oxygen from liquid water under near ultraviolet (NUV) lights on the surface of exoplanets. Titania works as a photocatalyst to dissociate liquid water in this process. This mechanism offers a different source of a possibility of <span class="hlt">abiotic</span> oxygen in atmospheres of exoplanets from previously considered photodissociation of water vapor in upper atmospheres by extreme ultraviolet (XUV) light. Our order-of-magnitude estimation shows that possible amounts of oxygen produced by this <span class="hlt">abiotic</span> mechanism can be comparable with or even more than that in the atmosphere of the current Earth, depending on the amount of active surface area for this mechanism. We conclude that titania may act as a potential source of false signs of life on habitable exoplanets. PMID:26354078</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27135320','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27135320"><span>Cell Wall Metabolism in Response to <span class="hlt">Abiotic</span> Stress.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Le Gall, Hyacinthe; Philippe, Florian; Domon, Jean-Marc; Gillet, Françoise; Pelloux, Jérôme; Rayon, Catherine</p> <p>2015-02-16</p> <p>This review focuses on the responses of the plant cell wall to several <span class="hlt">abiotic</span> stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most <span class="hlt">abiotic</span> stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to <span class="hlt">abiotic</span> stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23373896','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23373896"><span><span class="hlt">Abiotic</span> reductive immobilization of U(VI) by biogenic mackinawite.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Veeramani, Harish; Scheinost, Andreas C; Monsegue, Niven; Qafoku, Nikolla P; Kukkadapu, Ravi; Newville, Matt; Lanzirotti, Antonio; Pruden, Amy; Murayama, Mitsuhiro; Hochella, Michael F</p> <p>2013-03-05</p> <p>During subsurface bioremediation of uranium-contaminated sites, indigenous metal and sulfate-reducing bacteria may utilize a variety of electron acceptors, including ferric iron and sulfate that could lead to the formation of various biogenic minerals in situ. Sulfides, as well as structural and adsorbed Fe(II) associated with biogenic Fe(II)-sulfide phases, can potentially catalyze <span class="hlt">abiotic</span> U(VI) reduction via direct electron transfer processes. In the present work, the propensity of biogenic mackinawite (Fe 1+x S, x = 0 to 0.11) to reduce U(VI) <span class="hlt">abiotically</span> was investigated. The biogenic mackinawite produced by Shewanella putrefaciens strain CN32 was characterized by employing a suite of analytical techniques including TEM, SEM, XAS, and Mössbauer analyses. Nanoscale and bulk analyses (microscopic and spectroscopic techniques, respectively) of biogenic mackinawite after exposure to U(VI) indicate the formation of nanoparticulate UO2. This study suggests the relevance of sulfide-bearing biogenic minerals in mediating <span class="hlt">abiotic</span> U(VI) reduction, an alternative pathway in addition to direct enzymatic U(VI) reduction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4929540','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4929540"><span><span class="hlt">Abiotic</span> Deposition of Fe Complexes onto Leptothrix Sheaths</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Kunoh, Tatsuki; Hashimoto, Hideki; McFarlane, Ian R.; Hayashi, Naoaki; Suzuki, Tomoko; Taketa, Eisuke; Tamura, Katsunori; Takano, Mikio; El-Naggar, Mohamed Y.; Kunoh, Hitoshi; Takada, Jun</p> <p>2016-01-01</p> <p>Bacteria classified in species of the genus Leptothrix produce extracellular, microtubular, Fe-encrusted sheaths. The encrustation has been previously linked to bacterial Fe oxidases, which oxidize Fe(II) to Fe(III) and/or active groups of bacterial exopolymers within sheaths to attract and bind aqueous-phase inorganics. When L. cholodnii SP-6 cells were cultured in media amended with high Fe(II) concentrations, Fe(III) precipitates visibly formed immediately after addition of Fe(II) to the medium, suggesting prompt <span class="hlt">abiotic</span> oxidation of Fe(II) to Fe(III). Intriguingly, these precipitates were deposited onto the sheath surface of bacterial cells as the population was actively growing. When Fe(III) was added to the medium, similar precipitates formed in the medium first and were <span class="hlt">abiotically</span> deposited onto the sheath surfaces. The precipitates in the Fe(II) medium were composed of assemblies of globular, amorphous particles (ca. 50 nm diameter), while those in the Fe(III) medium were composed of large, aggregated particles (≥3 µm diameter) with a similar amorphous structure. These precipitates also adhered to cell-free sheaths. We thus concluded that direct <span class="hlt">abiotic</span> deposition of Fe complexes onto the sheath surface occurs independently of cellular activity in liquid media containing Fe salts, although it remains unclear how this deposition is associated with the previously proposed mechanisms (oxidation enzyme- and/or active group of organic components-involved) of Fe encrustation of the Leptothrix sheaths. PMID:27271677</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4855980','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4855980"><span>Abscisic Acid and <span class="hlt">Abiotic</span> Stress Tolerance in Crop Plants</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Sah, Saroj K.; Reddy, Kambham R.; Li, Jiaxu</p> <p>2016-01-01</p> <p><span class="hlt">Abiotic</span> stress is a primary threat to fulfill the demand of agricultural production to feed the world in coming decades. Plants reduce growth and development process during stress conditions, which ultimately affect the yield. In stress conditions, plants develop various stress mechanism to face the magnitude of stress challenges, although that is not enough to protect them. Therefore, many strategies have been used to produce <span class="hlt">abiotic</span> stress tolerance crop plants, among them, abscisic acid (ABA) phytohormone engineering could be one of the methods of choice. ABA is an isoprenoid phytohormone, which regulates various physiological processes ranging from stomatal opening to protein storage and provides adaptation to many stresses like drought, salt, and cold stresses. ABA is also called an important messenger that acts as the signaling mediator for regulating the adaptive response of plants to different environmental stress conditions. In this review, we will discuss the role of ABA in response to <span class="hlt">abiotic</span> stress at the molecular level and ABA signaling. The review also deals with the effect of ABA in respect to gene expression. PMID:27200044</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4844334','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4844334"><span>Cell Wall Metabolism in Response to <span class="hlt">Abiotic</span> Stress</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Gall, Hyacinthe Le; Philippe, Florian; Domon, Jean-Marc; Gillet, Françoise; Pelloux, Jérôme; Rayon, Catherine</p> <p>2015-01-01</p> <p>This review focuses on the responses of the plant cell wall to several <span class="hlt">abiotic</span> stresses including drought, flooding, heat, cold, salt, heavy metals, light, and air pollutants. The effects of stress on cell wall metabolism are discussed at the physiological (morphogenic), transcriptomic, proteomic and biochemical levels. The analysis of a large set of data shows that the plant response is highly complex. The overall effects of most <span class="hlt">abiotic</span> stress are often dependent on the plant species, the genotype, the age of the plant, the timing of the stress application, and the intensity of this stress. This shows the difficulty of identifying a common pattern of stress response in cell wall architecture that could enable adaptation and/or resistance to <span class="hlt">abiotic</span> stress. However, in most cases, two main mechanisms can be highlighted: (i) an increased level in xyloglucan endotransglucosylase/hydrolase (XTH) and expansin proteins, associated with an increase in the degree of rhamnogalacturonan I branching that maintains cell wall plasticity and (ii) an increased cell wall thickening by reinforcement of the secondary wall with hemicellulose and lignin deposition. Taken together, these results show the need to undertake large-scale analyses, using multidisciplinary approaches, to unravel the consequences of stress on the cell wall. This will help identify the key components that could be targeted to improve biomass production under stress conditions. PMID:27135320</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014BGeo...11..135S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014BGeo...11..135S"><span>Not all <span class="hlt">calcite</span> ballast is created equal: differing effects of foraminiferan and coccolith <span class="hlt">calcite</span> on the formation and sinking of aggregates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmidt, K.; De La Rocha, C. L.; Gallinari, M.; Cortese, G.</p> <p>2014-01-01</p> <p>Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking <span class="hlt">calcite</span> particles like coccoliths and large, rapidly sinking <span class="hlt">calcite</span> like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added <span class="hlt">calcite</span> ballast. The foraminiferan tests, which sank as fast as 700 m d-1, became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foram-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the rolling tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast - different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013BGD....1014861S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013BGD....1014861S"><span>Not all <span class="hlt">calcite</span> ballast is created equal: differing effects of foraminiferan and coccolith <span class="hlt">calcite</span> on the formation and sinking of aggregates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmidt, K.; De La Rocha, C. L.; Gallinari, M.; Cortese, G.</p> <p>2013-09-01</p> <p>Correlation between particulate organic carbon (POC) and calcium carbonate sinking through the deep ocean has led to the idea that ballast provided by calcium carbonate is important for the export of POC from the surface ocean. While this idea is certainly to some extent true, it is worth considering in more nuance, for example, examining the different effects on the aggregation and sinking of POC of small, non-sinking <span class="hlt">calcite</span> particles like coccoliths and large, rapidly sinking <span class="hlt">calcite</span> like planktonic foraminiferan tests. We have done that here in a simple experiment carried out in roller tanks that allow particles to sink continuously without being impeded by container walls. Coccoliths were efficiently incorporated into aggregates that formed during the experiment, increasing their sinking speed compared to similarly sized aggregates lacking added <span class="hlt">calcite</span> ballast. The foraminiferan tests, which sank as fast as 700 m d-1, became associated with only very minor amounts of POC. In addition, when they collided with other, larger, foraminferan-less aggregates, they fragmented them into two smaller, more slowly sinking aggregates. While these effects were certainly exaggerated within the confines of the roller tanks, they clearly demonstrate that calcium carbonate ballast is not just calcium carbonate ballast- different forms of calcium carbonate ballast have notably different effects on POC aggregation, sinking, and export.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/pages/biblio/1324076-sturgeon-paddlefish-acipenseridae-saggital-otoliths-composed-calcium-carbonate-polymorphs-vaterite-calcite-acipenseridae-otoliths-vaterite-calcite','SCIGOV-DOEP'); return false;" href="https://www.osti.gov/pages/biblio/1324076-sturgeon-paddlefish-acipenseridae-saggital-otoliths-composed-calcium-carbonate-polymorphs-vaterite-calcite-acipenseridae-otoliths-vaterite-calcite"><span>Sturgeon and paddlefish (Acipenseridae) saggital otoliths are composed of the calcium carbonate polymorphs vaterite and <span class="hlt">calcite</span>: acipenseridae otoliths are vaterite and <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGES</a></p> <p>Pracheil, Brenda M.; Chakoumakos, Bryan C.; Feygenson, Mikhail; ...</p> <p>2016-07-27</p> <p>The otoliths of modern fishes are most commonly comprised of the metastable aragonite polymorph of calcium carbonate (CaCO3); however, sturgeons have otoliths reportedly comprised of the least stable of the three most-common polymorphs, vaterite. In this study, we used neutron diffraction to characterize CaCO3 polymorph composition of lake sturgeon and paddlefish otoliths. Based on previous summaries of CaCO3 composition over fish evolutionary history, we hypothesized that sturgeon and paddlefish otoliths would have similar polymorph composition. We found that despite previous reports of sturgeon otoliths being comprised entirely of vaterite, that all otoliths we examined in this study also had amore » <span class="hlt">calcite</span> fraction that ranged from 17.9+ 6.0 wt. % to 35.9 + 2.9 wt. %. We also conducted a grinding experiment that demonstrated that <span class="hlt">calcite</span> fractions were due to biological variation and not an artifact of polymorph transformation during preparation. Our study provides the initial characterization of the polymorph composition of the otoliths of lake sturgeon, and paddlefish and also provides the first-ever report of otoliths of Acipenserids as having a <span class="hlt">calcite</span> fraction.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1324076','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1324076"><span>Sturgeon and paddlefish (Acipenseridae) saggital otoliths are composed of the calcium carbonate polymorphs vaterite and <span class="hlt">calcite</span>: acipenseridae otoliths are vaterite and <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Pracheil, Brenda M.; Chakoumakos, Bryan C.; Feygenson, Mikhail; Whitledge, Gregory W.; Koenigs, Ryan P.; Bruch, Ronald M.</p> <p>2016-07-27</p> <p>The otoliths of modern fishes are most commonly comprised of the metastable aragonite polymorph of calcium carbonate (CaCO3); however, sturgeons have otoliths reportedly comprised of the least stable of the three most-common polymorphs, vaterite. In this study, we used neutron diffraction to characterize CaCO3 polymorph composition of lake sturgeon and paddlefish otoliths. Based on previous summaries of CaCO3 composition over fish evolutionary history, we hypothesized that sturgeon and paddlefish otoliths would have similar polymorph composition. We found that despite previous reports of sturgeon otoliths being comprised entirely of vaterite, that all otoliths we examined in this study also had a <span class="hlt">calcite</span> fraction that ranged from 17.9+ 6.0 wt. % to 35.9 + 2.9 wt. %. We also conducted a grinding experiment that demonstrated that <span class="hlt">calcite</span> fractions were due to biological variation and not an artifact of polymorph transformation during preparation. Our study provides the initial characterization of the polymorph composition of the otoliths of lake sturgeon, and paddlefish and also provides the first-ever report of otoliths of Acipenserids as having a <span class="hlt">calcite</span> fraction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26116411','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26116411"><span>Quantified biotic and <span class="hlt">abiotic</span> responses to multiple stress in freshwater, <span class="hlt">marine</span> and ground waters.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Nõges, Peeter; Argillier, Christine; Borja, Ángel; Garmendia, Joxe Mikel; Hanganu, Jenică; Kodeš, Vit; Pletterbauer, Florian; Sagouis, Alban; Birk, Sebastian</p> <p>2016-01-01</p> <p>We reviewed 219 papers and built an inventory of 532 items of ecological evidence on multiple stressor impacts in rivers, lakes, transitional and coastal waters, as well as groundwaters. Our review revealed that, despite the existence of a huge conceptual knowledge base in aquatic ecology, few studies actually provide quantitative evidence on multi-stress effects. Nutrient stress was involved in 71% to 98% of multi-stress situations in the three types of surface water environments, and in 42% of those in groundwaters. However, their impact manifested differently along the groundwater-river-lake-transitional-coastal continuum, mainly determined by the different hydro-morphological features of these ecosystems. The reviewed papers addressed two-stressor combinations most frequently (42%), corresponding with the actual status-quo of pressures acting on European surface waters as reported by the Member States in the WISE WFD Database (EEA, 2015). Across all biological groups analysed, higher explanatory power of the stress-effect models was discernible for lakes under multi-stressor compared to single stressor conditions, but generally lower for coastal and transitional waters. Across all aquatic environments, the explanatory power of stress-effect models for fish increased when multi-stressor conditions were taken into account in the analysis, qualifying this organism group as a useful indicator of multi-stress effects. In contrast, the explanatory power of models using benthic flora decreased under conditions of multiple stress.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16566092','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16566092"><span><span class="hlt">Marine</span> enzymes.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Debashish, Ghosh; Malay, Saha; Barindra, Sana; Joydeep, Mukherjee</p> <p>2005-01-01</p> <p><span class="hlt">Marine</span> enzyme biotechnology can offer novel biocatalysts with properties like high salt tolerance, hyperthermostability, barophilicity, cold adaptivity, and ease in large-scale cultivation. This review deals with the research and development work done on the occurrence, molecular biology, and bioprocessing of <span class="hlt">marine</span> enzymes during the last decade. Exotic locations have been accessed for the search of novel enzymes. Scientists have isolated proteases and carbohydrases from deep sea hydrothermal vents. Cold active metabolic enzymes from psychrophilic <span class="hlt">marine</span> microorganisms have received considerable research attention. <span class="hlt">Marine</span> symbiont microorganisms growing in association with animals and plants were shown to produce enzymes of commercial interest. Microorganisms isolated from sediment and seawater have been the most widely studied, proteases, carbohydrases, and peroxidases being noteworthy. Enzymes from <span class="hlt">marine</span> animals and plants were primarily studied for their metabolic roles, though proteases and peroxidases have found industrial applications. Novel techniques in molecular biology applied to assess the diversity of chitinases, nitrate, nitrite, ammonia-metabolizing, and pollutant-degrading enzymes are discussed. Genes encoding chitinases, proteases, and carbohydrases from microbial and animal sources have been cloned and characterized. Research on the bioprocessing of <span class="hlt">marine</span>-derived enzymes, however, has been scanty, focusing mainly on the application of solid-state fermentation to the production of enzymes from microbial sources.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..1413658M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..1413658M"><span>Experimental fractionation of stable carbon isotopes during degassing of carbon dioxide and precipitation of <span class="hlt">calcite</span> from aqueous solutions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Müller, K.; Winde, V.; Escher, P.; von Geldern, R.; Böttcher, M. E.</p> <p>2012-04-01</p> <p>Processes in the carbonate system of surface waters are in particular sensitive to variations of boundary conditions as, for instance, the partial pressure of carbon dioxide in the atmosphere and the aqueous solution. Examples range from streams, rivers, to coastal <span class="hlt">marine</span> waters. The flux of carbon dioxide from continental flowing waters was recently included into calculations of the global carbon budget (Butman & Raymond, 2011, Nature Geo.). These solutions, are often supersaturated in carbon dioxide with respect to the atmosphere. The degassing of carbon dioxide is associated with a kinetically controlled fractionation of the stable carbon isotopes, which has to be considered in balancing water-air carbon dioxide fluxes. The degassing process additionally leads to the super-saturation of the aqueous solution with respect to calcium carbonate. Stable isotope fractionation is of particular value to identify and quantify processes at the water-gas phase interface and link these non-equilibrium processes to the formation mechanisms of <span class="hlt">calcite</span> and the hydrodynamics of surface waters. Experiments were carried out with or without inert N2 gas flow to degas carbon dioxide from initially supersaturated solutions. Natural solutions used are from different stations of the Elbe estuary, the Jade Bay, the backbarrier tidal area of Spiekeroog Island, carbonate springs of Rügen Island, and the Baltic Sea coastline. Results are compared experiments using bottled mineral waters. By following the (physico) chemical changes in the solutions (pH, TA, Ca PHREEQC modeling) it was found, that two evolutionary stages can be differentiated. Reaction progress led to the preferential liberation of carbon dioxide containing the light carbon isotope, following a Rayleigh-type process. After an induction period, where only degassing of carbon dioxide took place, a second stage was observed where <span class="hlt">calcite</span> began to form from the highly supersaturated solutions. In this stage the carbonate</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..DFDH13010W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..DFDH13010W"><span>Ocean acidification: Towards a better understanding of <span class="hlt">calcite</span> dissolution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wilhelmus, Monica M.; Adkins, Jess; Menemenlis, Dimitris</p> <p>2016-11-01</p> <p>The drastic increase of anthropogenic CO2 emissions over the past two centuries has altered the chemical structure of the ocean, acidifying upper ocean waters. The net impact of this pH decrease on <span class="hlt">marine</span> ecosystems is still unclear, given the unprecedented rate at which CO2 is being released into the atmosphere. As part of the carbon cycle, calcium carbonate dissolution in sediments neutralizes CO2: phytoplankton at the surface produce carbonate minerals, which sink and reach the seafloor after the organisms die. On time scales of thousands of years, the calcium carbonate in these shells ultimately reacts with CO2 in seawater. Research in this field has been extensive; nevertheless, the dissolution rate law, the impact of boundary layer transport, and the feedback with the global ocean carbon cycle remain controversial. Here, we (i) develop a comprehensive numerical framework via 1D modeling of carbonate dissolution in sediments, (ii) approximate its impact on water column properties by implementing a polynomial approximation to the system's response into a global ocean biogeochemistry general circulation model (OBGCM), and (iii) examine the OBGCM sensitivity response to different formulations of sediment boundary layer properties. We find that, even though the burial equilibration time scales of calcium carbonate are in the order of thousands of years, the formulation of a bottom sediment model along with an improved description of the dissolution rate law can have consequences on multi-year to decadal time scales.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20020002122&hterms=biofilm&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dc%252B%252B%2Bbiofilm','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20020002122&hterms=biofilm&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dc%252B%252B%2Bbiofilm"><span><span class="hlt">Abiotic</span> Versus Biotic Weathering Of Olivine As Possible Biosignatures</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Longazo, Teresa G.; Wentworth, Susan J.; Clemett, Simon J.; Southam, Gordon; McKay, David S.</p> <p>2001-01-01</p> <p>We are investigating the weathering of silicate minerals by both purely inorganic, and biologically mediated processes using field-emission scanning electron microscopy (FESEM) and energy dispersive x-ray spectroscopy (EDS). By resolving surface textures and chemical compositions of weathered surfaces at the sub-micron scale we hope to be able to distinguish <span class="hlt">abiotic</span> from biotic weathering processes and so establish a new biosignature applicable to the study of astromaterials including but not limited to the Martian meteorites. Sterilized olivine grains (San Carlos, Arizona) no more than 1-2 mm in their longest dimension were optically assayed to be uniform in color and free of inclusions were selected as weathering subjects. Prior to all experiments surface morphologies and Fe/Mg ratios were determined for each grain using FE-SEM and EDS. Experiments were divided into two categories <span class="hlt">abiotic</span> and biotic and were compared with "naturally" weathered samples. For the preliminary experiments, two trials (open and closed to the ambient laboratory environment) were performed under <span class="hlt">abiotic</span> conditions, and three trials under biotic conditions (control, day 1 and day 2). The open system <span class="hlt">abiotic</span> trials used sterile grains heated at 98 C and 200 C for both 24 and 48 hours in 1L double distilled de-ionized water. The closed system <span class="hlt">abiotic</span> trials were conducted under the same conditions but in a sealed two layer steel/Teflon "bomb" apparatus. The biotic trials used sterile grains mounted in a flow-through device attached to a wellhead on the Columbia River aquifer. Several discolored, altered, grains were selected to document "natural" weathering surface textures for comparison with the experimental samples. Preliminary results indicate there are qualitative differences in weathered surface textures among all the designed experiments. The olivine grains in <span class="hlt">abiotic</span> trials displayed etching, pitting, denticulate margins, dissolution and clay formation. The scale of the features</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992GeCoA..56.4095K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992GeCoA..56.4095K"><span>Solid-solute phase equilibria in aqueous solution: VII. A re-interpretation of magnesian <span class="hlt">calcite</span> stabilities</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Königsberger, Erich; Gamsjäger, Heinz</p> <p>1992-11-01</p> <p>It is proposed to model magnesian <span class="hlt">calcites</span> thermodynamically as dilute solid solutions of MgCO 3 in CaCO 3 according to the Unified Interaction Parameter Formalism ( BALE and PELTON, Met. Trans. A21A, 1997-2002, 1990). In this case both stoichiometric saturation and precipitation data of synthetic magnesian <span class="hlt">calcites</span> taken from literature can consistently be explained.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/15635407','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/15635407"><span>Rapid stepwise onset of Antarctic glaciation and deeper <span class="hlt">calcite</span> compensation in the Pacific Ocean.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Coxall, Helen K; Wilson, Paul A; Pälike, Heiko; Lear, Caroline H; Backman, Jan</p> <p>2005-01-06</p> <p>The ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution is termed the <span class="hlt">calcite</span> compensation depth. At present, this depth is approximately 4,500 m, with some variation between and within ocean basins. The <span class="hlt">calcite</span> compensation depth is linked to ocean acidity, which is in turn linked to atmospheric carbon dioxide concentrations and hence global climate. Geological records of changes in the <span class="hlt">calcite</span> compensation depth show a prominent deepening of more than 1 km near the Eocene/Oligocene boundary (approximately 34 million years ago) when significant permanent ice sheets first appeared on Antarctica, but the relationship between these two events is poorly understood. Here we present ocean sediment records of calcium carbonate content as well as carbon and oxygen isotopic compositions from the tropical Pacific Ocean that cover the Eocene/Oligocene boundary. We find that the deepening of the <span class="hlt">calcite</span> compensation depth was more rapid than previously documented and occurred in two jumps of about 40,000 years each, synchronous with the stepwise onset of Antarctic ice-sheet growth. The glaciation was initiated, after climatic preconditioning, by an interval when the Earth's orbit of the Sun favoured cool summers. The changes in oxygen-isotope composition across the Eocene/Oligocene boundary are too large to be explained by Antarctic ice-sheet growth alone and must therefore also indicate contemporaneous global cooling and/or Northern Hemisphere glaciation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016BGeo...13..535E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016BGeo...13..535E"><span>Unusual biogenic <span class="hlt">calcite</span> structures in two shallow lakes, James Ross Island, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Elster, J.; Nedbalová, L.; Vodrážka, R.; Láska, K.; Haloda, J.; Komárek, J.</p> <p>2016-01-01</p> <p>The floors of two shallow endorheic lakes, located on volcanic surfaces on James Ross Island, are covered with calcareous organosedimentary structures. Their biological and chemical composition, lake water characteristics, and seasonal variability of the thermal regime are introduced. The lakes are frozen down to the bottom for 8-9 months a year and their water chemistry is characterised by low conductivity and neutral to slightly alkaline pH. The photosynthetic microbial mat is composed of filamentous cyanobacteria and microalgae that are considered to be Antarctic endemic species. The mucilaginous black biofilm is covered by green spots formed by a green microalga and the macroscopic structures are packed together with fine material. Thin sections consist of rock substrate, soft biofilm, <span class="hlt">calcite</span> spicules and mineral grains originating from different sources. The morphology of the spicules is typical of calcium carbonate monocrystals having a layered structure and specific surface texture, which reflect growth and degradation processes. The spicules' chemical composition and structure correspond to pure <span class="hlt">calcite</span>. The lakes' age, altitude, morphometry, geomorphological and hydrological stability, including low sedimentation rates, together with thermal regime predispose the existence of this community. We hypothesise that the precipitation of <span class="hlt">calcite</span> is connected with the photosynthetic activity of the green microalgae that were not recorded in any other lake in the region. This study has shown that the unique community producing biogenic <span class="hlt">calcite</span> spicules is quite different to any yet described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17394362','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17394362"><span>Crystalline order of a water/glycine film coadsorbed on the (104) <span class="hlt">calcite</span> surface.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Magdans, Uta; Torrelles, Xavier; Angermund, Klaus; Gies, Hermann; Rius, Jordi</p> <p>2007-04-24</p> <p>For biomineralization processes, the interaction of the surface of <span class="hlt">calcite</span> crystals with organic molecules is of particular importance. Especially, biologically controlled biomineralization as in exoskeletons of mollusks and echinoderms, e.g., sea urchin with single-crystal-like spines and shells,1-3 requires molecular control of seed formation and growth process. So far, experiments showing the obvious influence of organic molecules on the morphology and habit of <span class="hlt">calcite</span> crystals have demonstrated the molecular dimension of the interaction.4-7 Details of the kinetics of growth and dissolution of mineral surfaces influenced by additives are available,8,9 but other experimental data about the structure of the organic/inorganic interface on the atomic scale are rare. On the other hand, complicated organic macromolecules which are involved in biomineralization are numerous, with only a small fraction solved in structure and function so far.10-13 Therefore, model systems have to be designed to provide a basic understanding for the interaction process.14 Using grazing incidence X-ray diffraction combined with molecular modeling techniques, we show that glycine molecules order periodically on the <span class="hlt">calcite</span> (104) face in competition with the solvent water when exposed to an aqueous solution of the most simple amino acid. In contrast to the general concept of the charge-matching fit of organic molecules on mineral surfaces,4,14 glycine is not attached to the <span class="hlt">calcite</span> surface directly but substitutes for water molecules in the second hydration layer.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016NatSR...628854A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016NatSR...628854A"><span>Modelling how incorporation of divalent cations affects <span class="hlt">calcite</span> wettability–implications for biomineralisation and oil recovery</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andersson, M. P.; Dideriksen, K.; Sakuma, H.; Stipp, S. L. S.</p> <p>2016-06-01</p> <p>Using density functional theory and geochemical speciation modelling, we predicted how solid-fluid interfacial energy is changed, when divalent cations substitute into a <span class="hlt">calcite</span> surface. The effect on wettability can be dramatic. Trace metal uptake can impact organic compound adsorption, with effects for example, on the ability of organisms to control crystal growth and our ability to predict the wettability of pore surfaces. Wettability influences how easily an organic phase can be removed from a surface, either organic compounds from contaminated soil or crude oil from a reservoir. In our simulations, transition metals substituted exothermically into <span class="hlt">calcite</span> and more favourably into sites at the surface than in the bulk, meaning that surface properties are more strongly affected than results from bulk experiments imply. As a result of divalent cation substitution, <span class="hlt">calcite</span>-fluid interfacial energy is significantly altered, enough to change macroscopic contact angle by tens of degrees. Substitution of Sr, Ba and Pb makes surfaces more hydrophobic. With substitution of Mg and the transition metals, <span class="hlt">calcite</span> becomes more hydrophilic, weakening organic compound adsorption. For biomineralisation, this provides a switch for turning on and off the activity of organic crystal growth inhibitors, thereby controlling the shape of the associated mineral phase.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23787771','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23787771"><span>Morphological and mechanical characterization of composite <span class="hlt">calcite</span>/SWCNT-COOH single crystals.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Calvaresi, Matteo; Falini, Giuseppe; Pasquini, Luca; Reggi, Michela; Fermani, Simona; Gazzadi, Gian Carlo; Frabboni, Stefano; Zerbetto, Francesco</p> <p>2013-08-07</p> <p>A growing number of classes of organic (macro)molecular materials have been trapped into inorganic crystalline hosts, such as <span class="hlt">calcite</span> single crystals, without significantly disrupting their crystalline lattices. Inclusion of an organic phase plays a key role in enhancing the mechanical properties of the crystals, which are believed to share structural features with biogenic minerals. Here we report the synthesis and mechanical characterization of composite <span class="hlt">calcite</span>/SWCNT-COOH single crystals. Once entrapped into the crystals SWCNT-COOH appeared both as aggregates of entangled bundles and nanoropes. Their observation was possible only after crystal etching, fracture or FIB (focused ion beam) cross-sectioning. SWCNT-COOHs occupied a small volume fraction and were randomly distributed into the host crystal. They did not strongly affect the crystal morphology. However, although the Young's modulus of composite <span class="hlt">calcite</span>/SWCNT-COOH single crystals was similar to that of pure <span class="hlt">calcite</span> their hardness increased by about 20%. Thus, SWCNT-COOHs provide an obstacle against the dislocation-mediated propagation of plastic deformation in the crystalline slip systems, in analogy with the well-known hardness increase in fiber-reinforced composites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SPIE.9922E..2DH','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SPIE.9922E..2DH"><span>Rotation rate measurement and calculation for <span class="hlt">calcite</span> crystals in a C-point mode</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Herne, Catherine M.; O'Brien, Ann E.</p> <p>2016-09-01</p> <p>A polarization singularity mode offers a unique tool for actuating an array of birefringent <span class="hlt">calcite</span> crystals, and measurement of the rotation rates of these crystals is in turn a way to image modes with varying polarization. In this work, we show the calculated and measured rotation rates of individual <span class="hlt">calcite</span> crystals in a C-point mode and their dependence on three key factors: polarization, mode intensity profile, and crystal size. The C-point is a polarization singularity mode in which the mode has a circularly polarized center surrounded by elliptically polarized regions, with the orientation of the ellipse varying azimuthally and the degree of ellipticity changing radially. The beam is focused into an optical trapping region, and micron-sized birefringent <span class="hlt">calcite</span> crystals in solution are positioned at key points in the mode. The crystals experience different torques at each location. The spin angular momentum of the light is proportional to the degree of ellipticity and to the intensity at each point in the mode. Our technique for generating C-point modes results in an intensity profile with a nonlinear radial dependence. Our crystal growth process generates crystals of varying width and thickness; the crystal size and shape affect the drag forces and light torque acting on them. We explain the crystal growth process and estimations of torque, demonstrate the rate and direction of rotation of <span class="hlt">calcite</span> crystals placed at different points in the laser mode, and discuss the difference between the estimated and measured rotation rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4418924','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4418924"><span>Probing the energetics of organic–nanoparticle interactions of ethanol on <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wu, Di; Navrotsky, Alexandra</p> <p>2015-01-01</p> <p>Knowing the nature of interactions between small organic molecules and surfaces of nanoparticles (NP) is crucial for fundamental understanding of natural phenomena and engineering processes. Herein, we report direct adsorption enthalpy measurement of ethanol on a series of <span class="hlt">calcite</span> nanocrystals, with the aim of mimicking organic–NP interactions in various environments. The energetics suggests a spectrum of adsorption events as a function of coverage: strongest initial chemisorption on active sites on fresh <span class="hlt">calcite</span> surfaces, followed by major chemical binding to form an ethanol monolayer and, subsequently, very weak, near-zero energy, physisorption. These thermochemical observations directly support a structure where the ethanol monolayer is bonded to the <span class="hlt">calcite</span> surface through its polar hydroxyl group, leaving the hydrophobic ends of the ethanol molecules to interact only weakly with the next layer of adsorbing ethanol and resulting in a spatial gap with low ethanol density between the monolayer and subsequent added ethanol molecules, as predicted by molecular dynamics and density functional calculations. Such an ordered assembly of ethanol on <span class="hlt">calcite</span> NP is analogous to, although less strongly bonded than, a capping layer of organics intentionally introduced during NP synthesis, and suggests a continuous variation of surface structure depending on molecular chemistry, ranging from largely disordered surface layers to ordered layers that nevertheless are mobile and can rearrange or be displaced by other molecules to strongly bonded immobile organic capping layers. These differences in surface structure will affect chemical reactions, including the further nucleation and growth of nanocrystals on organic ligand-capped surfaces. PMID:25870281</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5859811','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5859811"><span>Intercalation of sea urchin proteins in <span class="hlt">calcite</span>: Study of a crystalline composite material</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Berman, A.; Addadi, L.; Leiserowitz, L.; Weiner, S. ); Kvick, A.; Nelson, M. )</p> <p>1990-11-02</p> <p>Sea urchin skeletal elements are composed of single crystals of <span class="hlt">calcite</span>. Unlike their synthetic counterparts, these crystals do not have well-developed cleavage and are consequently much more resistant to fracture. This phenomenon is due in part to the presence of acidic glycoproteins occluded within the crystals. By means of x-ray diffraction with synchrotron radiation, it is shown that the presence of the protein in synthetic <span class="hlt">calcite</span> only slightly decreases the coherence length but significantly increases the angular spread of perfect domains of the crystals. In biogenic <span class="hlt">calcite</span>, the coherence length is 1/3 to 1/4 as much as that in synthetic <span class="hlt">calcite</span> and the angular spread is 20 to 50 times as wide. It is proposed that the presence of macromolecules concentrated at mosaic boundaries that are oblique to cleavage planes is responsible for the change in fracture properties. These results may be important in the material sciences, because of the unusual nature of this material, namely, a composite based on the controlled intercalation of macromolecules inside single-crystal lattices. 20 refs., 3 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/460050','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/460050"><span>Control of macromolecule distribution within synthetic and biogenic single <span class="hlt">calcite</span> crystals</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Aizenberg, J.; Weiner, S.; Addadi, L.; Hanson, J.; Koetzle, T.F.</p> <p>1997-02-05</p> <p>The ability of organisms to exercise control over crystal growth is wonderfully exemplified by skeleton formation in echinoderms. A sea urchin spine is a unique composite of a single crystal of <span class="hlt">calcite</span> and glycoproteins intercalated inside the crystal during its growth. Here we performed a detailed morphological and high-resolution synchrotron X-ray diffraction study of the textures of synthetic and biogenic <span class="hlt">calcite</span> crystals. We show that the intracrystalline macromolecules from sea urchin spines, when allowed to interact with growing <span class="hlt">calcite</span> crystals in vitro, selectively reduce the coherence lengths and degrees of alignment of the perfect domains in specific crystallographic directions. These directions also correspond to the newly-developed stable faces. In contrast, the defect distribution of young sea urchin spines composed entirely of spongy stereomic structure is much more isotropic. In mature spines containing secondarily filled-in wedges of <span class="hlt">calcite</span>, the degree of anisotropy is intermediate between that of the synthetic crystals and the young spines. The macromolecules extracted from young and mature spines are, however, very similar. These observations demonstrate the inherent capability of occluded matrix macromolecules to finely differentiate between crystal planes by stereochemical recognition processes. 20 refs., 5 figs., 2 tabs.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996GeCoA..60.1053T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996GeCoA..60.1053T"><span>Solid solution partitioning of Sr 2+, Ba 2+, and Cd 2+ to <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tesoriero, Anthony J.; Pankow, James F.</p> <p>1996-03-01</p> <p>Although solid solutions play important roles in controlling the concentrations of minor metal ions in natural waters, uncertainties regarding their compositions, thermodynamics, and kinetics usually prevent them from being considered. A range of precipitation rates was used here to study the nonequilibrium and equilibrium partitioning behaviors of Sr 2+, Ba 2+, and Cd 2+ to <span class="hlt">calcite</span> (CaCO 3(s)). The distribution coefficient of a divalent metal ion Me 2+ for partitioning from an aqueous solution into <span class="hlt">calcite</span> is given by DMe = ( XMeCO 3(s)/[Me 2+])/( XCaCO 3(s)/[Ca 2+]). The X values are solid-phase mole fractions; the bracketed values are the aqueous molal concentrations. In agreement with prior work, at intermediate to high precipitation rates R (nmol/mg-min), DSr, DBa, and DCd were found to depend strongly on R. At low R, the values of DSr, DBa, and DCd became constant with R. At 25 °C, the equilibrium values for DSr, DBa, and DCd for dilute solid solutions were estimated to be 0.021 ± 0.003, 0.012 ± 0.005, and 1240 ± 300, respectively. Calculations using these values were made to illustrate the likely importance of partitioning of these ions to <span class="hlt">calcite</span> in groundwater systems. Due to its large equilibrium DMe value, movement of Cd 2+ will be strongly retarded in aquifers containing <span class="hlt">calcite</span>; Sr 2+ and Ba 2+ will not be retarded nearly as much.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JSG....68..142R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JSG....68..142R"><span>Clast-cortex aggregates in experimental and natural <span class="hlt">calcite</span>-bearing fault zones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rempe, Marieke; Smith, Steven A. F.; Ferri, Fabio; Mitchell, Thomas M.; Di Toro, Giulio</p> <p>2014-11-01</p> <p>We investigated the formation mechanisms of rounded clast-cortex aggregates, a composite grain found in the slipping zones of faults hosted in <span class="hlt">calcite</span>- and clay-rich rocks. The natural aggregates contain a central clast commonly made of host-rock fragments or reworked cataclasite from the slipping zone. The central clasts are surrounded by an outer cortex of <span class="hlt">calcite</span> or clay grains a few μm or less in size. In laboratory experiments on <span class="hlt">calcite</span> gouges using two rotary-shear apparatus we investigated the dependence of clast-cortex aggregate formation on the applied slip rate, normal stress, total displacement and ambient humidity. Clast-cortex aggregates formed at all investigated slip rates (100 μm/s to 1 m/s) but only at relatively low normal stresses (≤5 MPa). The aggregates were better developed with increasing displacement (up to 5 m) and did not form in experiments with water-dampened gouges. In the experiments, aggregates formed in low-strain regions within the gouge layers, adjacent to the highest-strain slip zones. We propose that clast-cortex aggregates in <span class="hlt">calcite</span>-bearing slip zones form in the shallow portions of faults during shearing in relatively dry conditions, but our experiments suggest that they cannot be used as indicators of seismic slip. Formation involves clast rotation due to granular flow accompanied by accretion of fine matrix material possibly facilitated by electrostatic forces.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/932245','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/932245"><span>STIMULATION OF MICROBIAL UREA HYDROLYSIS IN GROUNDWATER TO ENHANCE <span class="hlt">CALCITE</span> PRECIPITATION</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yoshiko Fujita; Joanna L. Taylor; Tina L. Gresham; Mark E. Delwiche; Frederick S. Colwell; Travis McLing; Lynn Petzke; Robert W. Smith</p> <p>2008-04-01</p> <p>Sequential addition of molasses and urea was tested as a means of stimulating microbial urea hydrolysis in the Eastern Snake River Plain Aquifer in Idaho. Ureolysis is an integral component of a novel remediation approach for divalent trace metal and radionuclide contaminants in groundwater and associated geomedia, where the contaminants are immobilized by coprecipitation in <span class="hlt">calcite</span>. The generation of carbonate alkalinity from ureolysis promotes <span class="hlt">calcite</span> precipitation. In <span class="hlt">calcite</span>-saturated aquifers, this represents a potential long-term contaminant sequestration mechanism. In a single well experiment, dilute molasses was injected three times over two weeks to promote overall microbial growth, followed by one urea injection. With molasses addition, total cell numbers in the groundwater increased one to two orders of magnitude. Estimated ureolysis rates in recovered groundwater samples increased from <0.1 nmol L-1 hr-1 to >25 nmol L-1 hr-1. A quantitative PCR assay for the bacterial ureC gene indicated that urease gene numbers increased up to 170 times above pre-injection levels. Following urea injection, <span class="hlt">calcite</span> precipitates were recovered. Estimated values for an in situ first order ureolysis rate constant ranged from 0.016 to 0.057 day-1. The results are promising with respect to the potential to manipulate in situ biogeochemical processes to promote contaminant sequestration.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28198900','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28198900"><span>Elasticity and yielding of a <span class="hlt">calcite</span> paste: scaling laws in a dense colloidal suspension.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liberto, Teresa; Le Merrer, Marie; Barentin, Catherine; Bellotto, Maurizio; Colombani, Jean</p> <p>2017-03-08</p> <p>We address the mechanical characterization of a <span class="hlt">calcite</span> paste as a model system to investigate the relation between the microstructure and macroscopic behavior of colloidal suspensions. The ultimate goal is to achieve control of the elastic and yielding properties of <span class="hlt">calcite</span> which will prove valuable in several domains, from paper coating to paint manufacture and eventually in the comprehension and control of the mechanical properties of carbonate rocks. Rheological measurements have been performed on <span class="hlt">calcite</span> suspensions over a wide range of particle concentrations. The <span class="hlt">calcite</span> paste exhibits a typical colloidal gel behavior, with an elastic regime and a clear yield strain above which it enters a plastic regime. The yield strain shows a minimum when increasing the solid concentration, connected to a change in the power law scaling of the storage modulus. In the framework of the classical fractal elasticity model for colloidal suspensions proposed by Shih et al. [Phys. Rev. A, 1990, 42, 4772], we interpret this behavior as a switch with the concentration from the strong-link regime to the weak-link regime, which had never been observed so far in one well-defined system without external or chemical forcing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/16190195','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/16190195"><span>Inhibition of <span class="hlt">calcite</span> precipitation by natural organic material: kinetics, mechanism, and thermodynamics.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Lin, Yi-Pin; Singer, Philip C; Aiken, George R</p> <p>2005-09-01</p> <p>The inhibition of <span class="hlt">calcite</span> precipitation by natural organic material (NOM) in solutions seeded with <span class="hlt">calcite</span> was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25 degrees C and 1 atm suggest that the interaction between NOM molecules and the <span class="hlt">calcite</span> surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of <span class="hlt">calcite</span> precipitation was dictated bythe balance between the enthalpy change and the entropy change of the adsorption reaction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70027810','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70027810"><span>Inhibition of <span class="hlt">calcite</span> precipitation by natural organic material: Kinetics, mechanism, and thermodynamics</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lin, Y.-P.; Singer, P.C.; Aiken, G.R.</p> <p>2005-01-01</p> <p>The inhibition of <span class="hlt">calcite</span> precipitation by natural organic material (NOM) in solutions seeded with <span class="hlt">calcite</span> was investigated using a pH-stat system. Experiments were carried out using three NOMs with different physical/chemical properties. For each of the materials, inhibition was found to be more effective at lower carbonate/calcium ratios and lower pH values. The reduction in the precipitation rate could be explained by a Langmuir adsorption model using a conditional equilibrium constant. By identification of the type of site on the NOM molecules that is involved in the adsorption reaction, the "conditional" equilibrium constants obtained at different solution compositions converged to a single "nonconditional" value. The thermodynamic data determined at 25??C and 1 atm suggest that the interaction between NOM molecules and the <span class="hlt">calcite</span> surface is chemisorptive in nature and that adsorption is an endothermic reaction driven by the entropy change. The greatest degree of inhibition was observed for the NOM with the highest molecular weight and aromatic carbon content. For a given type of NOM, the degree of inhibition of <span class="hlt">calcite</span> precipitation was dictated by the balance between the enthalpy change and the entropy change of the adsorption reaction. ?? 2005 American Chemical Society.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018436','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018436"><span>Solid solution partitioning of Sr2+, Ba2+, and Cd2+ to <span class="hlt">calcite</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Tesoriero, A.J.; Pankow, J.F.</p> <p>1996-01-01</p> <p>Although solid solutions play important roles in controlling the concentrations of minor metal ions in natural waters, uncertainties regarding their compositions, thermodynamics, and kinetics usually prevent them from being considered. A range of precipitation rates was used here to study the nonequilibrium and equilibrium partitioning behaviors of Sr2+, Ba2+, and Cd2+ to <span class="hlt">calcite</span> (CaCO3(s)). The distribution coefficient of a divalent metal ion Me2+ for partitioning from an aqueous solution into <span class="hlt">calcite</span> is given by DMe = (XMeCO3(s)/[Me2+])/(XCaCO3(s)/[Ca 2+]). The X values are solid-phase mole fractions; the bracketed values are the aqueous molal concentrations. In agreement with prior work, at intermediate to high precipitation rates R (nmol/mg-min), DSr, DBa, and DCd were found to depend strongly on R. At low R, the values of DSr, DBa, and DCd became constant with R. At 25??C, the equilibrium values for DSr, DBa, and DCd for dilute solid solutions were estimated to be 0.021 ?? 0.003, 0.012 ?? 0.005, and 1240 ?? 300, respectively. Calculations using these values were made to illustrate the likely importance of partitioning of these ions to <span class="hlt">calcite</span> in groundwater systems. Due to its large equilibrium DMe value, movement of Cd2+ will be strongly retarded in aquifers containing <span class="hlt">calcite</span>; Sr2+ and Ba2+ will not be retarded nearly as much.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3513936','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3513936"><span>Amelogenin processing by MMP-20 prevents protein occlusion inside <span class="hlt">calcite</span> crystals</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Bromley, Keith M.; Lakshminarayanan, Rajamani; Thompson, Mitchell; Lokappa, Sowmya B.; Gallon, Victoria A.; Cho, Kang R.; Qiu, S. Roger; Moradian-Oldak, Janet</p> <p>2012-01-01</p> <p><span class="hlt">Calcite</span> crystals were grown in the presence of full-length amelogenin and during its proteolysis by recombinant human matrix metalloproteinase 20 (rhMMP-20). Recombinant porcine amelogenin (rP172) altered the shape of <span class="hlt">calcite</span> crystals by inhibiting the growth of steps on the {104} faces and became occluded inside the crystals. Upon co-addition of rhMMP-20, the majority of the protein was digested resulting in a truncated amelogenin lacking the C-terminal segment. In rP172-rhMMP-20 samples, the occlusion of amelogenin into the <span class="hlt">calcite</span> crystals was drastically decreased. Truncated amelogenin (rP147) and the 25-residue C-terminal domain produced crystals with regular shape and less occluded organic material. Removal of the C-terminal diminished the affinity of amelogenin to the crystals and therefore prevented occlusion. We hypothesize that HAP and <span class="hlt">calcite</span> interact with amelogenin in a similar manner. In the case of each material, full-length amelogenin binds most strongly, truncated amelogenin binds weakly and the C-terminus alone has the weakest interaction. Regarding enamel crystal growth, the prevention of occlusion into maturing enamel crystals might be a major benefit resulting from the selective cleavage of amelogenin at the C-terminus by MMP-20. Our data have important implications for understanding the hypomineralized enamel phenotype in cases of amelogenesis imperfecta resulting from MMP-20 mutations and will contribute to the design of enamel inspired biomaterials. PMID:23226976</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/28198353','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/28198353"><span>Adsorption and migration of single metal atoms on the <span class="hlt">calcite</span> (10.4) surface.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pinto, H; Haapasilta, V; Lokhandwala, M; Öberg, S; Foster, Adam S</p> <p>2017-04-05</p> <p>Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating <span class="hlt">calcite</span> (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca-Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the <span class="hlt">calcite</span> surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the <span class="hlt">calcite</span> surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the <span class="hlt">calcite</span> surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4926276','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4926276"><span>Modelling how incorporation of divalent cations affects <span class="hlt">calcite</span> wettability–implications for biomineralisation and oil recovery</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Andersson, M. P.; Dideriksen, K.; Sakuma, H.; Stipp, S. L. S.</p> <p>2016-01-01</p> <p>Using density functional theory and geochemical speciation modelling, we predicted how solid-fluid interfacial energy is changed, when divalent cations substitute into a <span class="hlt">calcite</span> surface. The effect on wettability can be dramatic. Trace metal uptake can impact organic compound adsorption, with effects for example, on the ability of organisms to control crystal growth and our ability to predict the wettability of pore surfaces. Wettability influences how easily an organic phase can be removed from a surface, either organic compounds from contaminated soil or crude oil from a reservoir. In our simulations, transition metals substituted exothermically into <span class="hlt">calcite</span> and more favourably into sites at the surface than in the bulk, meaning that surface properties are more strongly affected than results from bulk experiments imply. As a result of divalent cation substitution, <span class="hlt">calcite</span>-fluid interfacial energy is significantly altered, enough to change macroscopic contact angle by tens of degrees. Substitution of Sr, Ba and Pb makes surfaces more hydrophobic. With substitution of Mg and the transition metals, <span class="hlt">calcite</span> becomes more hydrophilic, weakening organic compound adsorption. For biomineralisation, this provides a switch for turning on and off the activity of organic crystal growth inhibitors, thereby controlling the shape of the associated mineral phase. PMID:27352933</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22713885','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22713885"><span>Atomic modifications by synchrotron radiation at the <span class="hlt">calcite</span>-ethanol interface.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pasarín, I S; Bovet, N; Glyvradal, M; Nielsen, M M; Bohr, J; Feidenhans'l, R; Stipp, S L S</p> <p>2012-07-01</p> <p>This article reports on studies of the chemical alterations induced by synchrotron radiation at the <span class="hlt">calcite</span>-ethanol interface, a simple model system for interfaces between minerals and more complex organic molecules containing OH groups. A combination of X-ray reflectivity and X-ray photoelectron spectroscopy of natural <span class="hlt">calcite</span>, cleaved in distilled ethanol to obtain new clean interfaces, indicated that, during a 5 h period, the two top atomic layers of <span class="hlt">calcite</span>, CaCO(3), transform into calcium oxide, CaO, by releasing CO(2). Also, the occupation of the first ordered layer of ethanol attached to <span class="hlt">calcite</span> by hydrogen bonds almost doubles. Comparison between radiated and non-radiated areas of the same samples demonstrate that these effects are induced only by radiation and not caused by aging. These observations contribute to establishing a time limit for synchrotron experiments involving fluid-mineral interfaces where the polar OH group, as present in ethanol, plays a key role in their molecular structure and bonding. Also, the chemical evolution observed in the interface provides new insight into the behavior of some complex organic molecules involved in biomineralization processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JPCM...29m5001P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JPCM...29m5001P"><span>Adsorption and migration of single metal atoms on the <span class="hlt">calcite</span> (10.4) surface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pinto, H.; Haapasilta, V.; Lokhandwala, M.; Öberg, S.; Foster, Adam S.</p> <p>2017-04-01</p> <p>Transition metal atoms are one of the key ingredients in the formation of functional 2D metal organic coordination networks. Additionally, the co-deposition of metal atoms can play an important role in anchoring the molecular structures to the surface at room temperature. To gain control of such processes requires the understanding of adsorption and diffusion properties of the different transition metals on the target surface. Here, we used density functional theory to investigate the adsorption of 3d (Ti, Cr, Fe, Ni, Cu), 4d (Zr, Nb, Mo, Pd, Ag) and 5d (Hf, W, Ir, Pt, Au) transition metal adatoms on the insulating <span class="hlt">calcite</span> (10.4) surface. We identified the most stable adsorption sites and calculated binding energies and corresponding ground state structures. We find that the preferential adsorption sites are the Ca–Ca bridge sites. Apart from the Cr, Mo, Cu, Ag and Au all the studied metals bind strongly to the <span class="hlt">calcite</span> surface. The calculated migration barriers for the representative Ag and Fe atoms indicates that the metal adatoms are mobile on the <span class="hlt">calcite</span> surface at room temperature. Bader analysis suggests that there is no significant charge transfer between the metal adatoms and the <span class="hlt">calcite</span> surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/37117','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/37117"><span>Noncrystallographic <span class="hlt">calcite</span> dendrites from hot-spring deposits at Lake Bogoria, Kenya</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jones, B.; Renaut, R.W.</p> <p>1995-01-02</p> <p>Complex <span class="hlt">calcite</span> crystals are an integral component of precipitates that form around the orifices of the Loburu and Mawe Moto hot springs on the shores of Lake bogoria, Kenya. Two types of large (up to 4 cm long) noncrystallographic dendrites are important components of these deposits. Feather dendrites are characterized by multiple levels of branching with individual branches developed through crystal splitting and spherulitic growth. Scandulitic (from Latin meaning shingle) dendrites are formed of stacked <span class="hlt">calcite</span> crystals and are generally more compact than feather dendrites. These developed through the incremental stacking of rectangular-shaped <span class="hlt">calcite</span> crystals that initially grew as skeletal crystals. Feather and scandulitic dendrites precipitated from the same waters in the same springs. The difference in morphology is therefore related to microenvironments in which they grew. Feather dendrites grew in any direction in pools of free-standing water provided that they were in constant contact with the solute. Conversely, scandulitic dendrites grew on rims of dams where water flowed over the surface in concert with the pulses of spring water. Thus, each <span class="hlt">calcite</span> crystal in these dendrites represents one episode of crystal growth. The orientation of the component crystals in scandulitic dendrites is controlled by the topography of the dam or surface, not crystallographic criteria. The noncrystallographic dendrites formed from spring waters with initial temperatures of 90--99 C. Surficial water cooling, loss of CO{sub 2}, and presence of other elements that can interfere with crystal growth contributed to the formation of these unusual crystals.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.134..221X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.134..221X"><span>Kinetics and mechanisms of cadmium carbonate heteroepitaxial growth at the <span class="hlt">calcite</span> (10 1bar 4) surface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien</p> <p>2014-06-01</p> <p>Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at <span class="hlt">calcite</span>-water interfaces was investigated by exposing <span class="hlt">calcite</span> (10 1bar 4) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the <span class="hlt">calcite</span> substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and <span class="hlt">calcite</span> shows perfect, dislocation-free epitaxy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/9665783','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/9665783"><span>The Influence of Chelating Agents on the Kinetics of <span class="hlt">Calcite</span> Dissolution.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Fredd; Fogler</p> <p>1998-08-01</p> <p>The kinetics of <span class="hlt">calcite</span> dissolution in the presence of calcium chelating agents was investigated over the pH range of 3.3-12 using a rotating disk apparatus. The results show that the rate of dissolution is increased significantly by the presence of chelating agents such as CDTA, DTPA, and EDTA. The rate of dissolution is influenced by the kinetics of the chelation reactions and varies considerably with pH and type of chelating agent. A surface chelation mechanism was introduced to describe the dissolution. The mechanism involves the adsorption of the chelating agent onto the <span class="hlt">calcite</span> surface and follows Langmuir-Hinshelwood kinetics. The dissolution is different from conventional hydrogen ion attack in that the chelating agent attacks the calcium component of the lattice rather than the carbonate component. Therefore, the rate of dissolution is enhanced by the influence of hydrogen ion attack at low pH. In addition, the various ionic forms of the chelating agents react with the <span class="hlt">calcite</span> surface at different rates depending on the number of hydrogen ions associated with the species. In general, the rate of dissolution increases with increasing protonation. The surface complexation mechanism was shown to describe the rate of <span class="hlt">calcite</span> dissolution in the presence of chelating agents over the pH range of 4-12. Copyright 1998 Academic Press.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1015293','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1015293"><span>Manganese at <span class="hlt">Calcite</span> Surfaces: Molecular-Scale Studies of Dissolution and Heteroepitaxy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Lea, Alan S.; Amonette, James E.; El-Azab, Anter Aa; Baer, Donald R.; Heald, Steve M.; Colton, Nancy G.</p> <p>2002-06-01</p> <p>We studied the impact of aqueous Mn(II) on the (1014) surface of <span class="hlt">calcite</span> using AFM and a flow-through cell. These experiments show equivalent interactions of Mn with the obtuse and acute steps on <span class="hlt">calcite</span>, similar to results with Ca ions and in marked contrast to results with carbonate and Sr ions. Little impact on dissolution rate is seen until a threshold level is reached, whereupon near complete frustration of dissolution occurs for a further four-fold increase in Mn concentration. These nonlinear results can be explained using a simple terrace-ledge-kink model that incorporates site-blocking and works equally well with metal ion or carbonate ion pair concentrations. With even higher concentrations of Mn, a new lath-shaped phase forms on the <span class="hlt">calcite</span> surface oriented along the [221] direction, having a uniform width of 150-220 nm, variable length, and a height of only 2.5 nm. Spectroscopic evidence (EPR, XPS, XANES) suggests that Mn(II) is present, but the exact composition is unknown. Assuming a Mn-substituted carbonate forms, the direction of growth is along the direction of greatest lattice mismatch to <span class="hlt">calcite</span>. This barrier to growth is apparently overcome by a decrease in lattice stiffness. The cross-sectional morphology of the heteroepitaxial layer is described well by a glued wetting layer model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015BGD....1213593E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015BGD....1213593E"><span>Unusual biogenic <span class="hlt">calcite</span> structures in two shallow lakes, James Ross Island, Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Elster, J.; Nedbalová, L.; Vodrážka, R.; Láska, K.; Haloda, J.; Komárek, J.</p> <p>2015-08-01</p> <p>The floors of two shallow endorheic lakes, located on volcanic surfaces on James Ross Island, are covered with calcareous organosedimentary structures. Their biological and chemical composition, lake water characteristics, and seasonal variability of the thermal regime are introduced. The lakes are frozen down to the bottom eight-nine months per year and their water chemistry is characterized by low conductivity and neutral to slightly alkaline pH. The photosynthetic microbial mat is composed of filamentous cyanobacteria and microalgae that are considered to be Antarctic endemic species. The mucilaginous black biofilm is covered by green spots formed by a green microalga and the macroscopic structures are packed together with fine material. Thin sections consist of rock substrate, soft biofilm, <span class="hlt">calcite</span> spicules and mineral grains originating from different sources. The morphology of the spicules is typical of calcium carbonate monocrystals having a layered structure and worn surface, which reflect growth and degradation processes. The spicules chemical composition and structure correspond to pure <span class="hlt">calcite</span>. Lakes age, altitude, morphometry, geomorphological and hydrological stability, including low sedimentation rates, together with thermal regime predispose the existence of this community. We hypothesize that the precipitation of <span class="hlt">calcite</span> is connected with the photosynthetic activity of the green microalgae that were not recorded in any other lake in the region. This study has shown that the unique community producing biogenic <span class="hlt">calcite</span> spicules is quite different to any yet described.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/1130243','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/1130243"><span>Kinetics and Mechanisms of Cadmium Carbonate Heteroepitaxial Growth at the <span class="hlt">Calcite</span> (101¯4) Surface</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Xu, Man; Kovarik, Libor; Arey, Bruce W.; Felmy, Andrew R.; Rosso, Kevin M.; Kerisit, Sebastien N.</p> <p>2014-06-01</p> <p>Elucidating the kinetics and mechanisms of heteroepitaxial nucleation and growth at mineral-water interfaces is essential to understanding surface reactivity in geochemical systems. In the present work, the formation of heteroepitaxial cadmium carbonate coatings at <span class="hlt">calcite</span>-water interfaces was investigated by exposing <span class="hlt">calcite</span> (10-14) surfaces to Cd-bearing aqueous solutions. In situ atomic force microscopy (AFM) was employed as the primary technique. The AFM results indicate that the heteroepitaxial growth of cadmium carbonate proceeds via three different mechanisms depending on the initial supersaturation of the aqueous solution: advancement of existing steps, nucleation and growth of three-dimensional (3D) islands, and nucleation and spread of two-dimensional (2D) nuclei. The 3D islands and 2D nuclei exhibit different morphologies and growth kinetics. The effects of supersaturation on heteroepitaxial growth mechanisms can be interpreted in terms of the free energy barrier for nucleation. At low initial supersaturation, where 3D nucleation dominates, it is hypothesized, from the growth rate and morphology of the 3D islands observed with AFM, that the crystallization of the overgrowth follows a non-classical pathway involving the formation of a surface precursor that is not fully crystalline, whereas high supersaturation favors the formation of crystalline 2D nuclei whose morphology is based on the atomic structure of the <span class="hlt">calcite</span> substrate. Cross-sectional transmission electron microscopy (TEM) images reveal that the atomic structure of the interface between the cadmium carbonate coating and <span class="hlt">calcite</span> shows perfect, dislocation-free epitaxy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25760891','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25760891"><span>Tracing formation and durability of <span class="hlt">calcite</span> in a Punic-Roman cistern mortar (Pantelleria Island, Italy).</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dietzel, Martin; Schön, Frerich; Heinrichs, Jens; Deditius, Artur P; Leis, Albrecht</p> <p>2016-01-01</p> <p>Ancient hydraulic lime mortar preserves chemical and isotopic signatures that provide important information about historical processing and its durability. The distribution and isotopic composition of <span class="hlt">calcite</span> in a mortar of a well-preserved Punic-Roman cistern at Pantelleria Island (Italy) was used to trace the formation conditions, durability, and individual processing periods of the cistern mortar. The analyses of stable carbon and oxygen isotopes of <span class="hlt">calcite</span> revealed four individual horizons, D, E, B-1 and B-2, of mortar from the top to the bottom of the cistern floor. Volcanic and ceramic aggregates were used for the production of the mortar of horizons E/D and B-1/B-2, respectively. All horizons comprise hydraulic lime mortar characterized by a mean cementation index of 1.5 ± 1, and a constant binder to aggregate ratio of 0.31 ± 0.01. This suggests standardized and highly effective processing of the cistern. The high durability of <span class="hlt">calcite</span> formed during carbonation of slaked lime within the matrix of the ancient mortar, and thus the excellent resistance of the hydraulic lime mortar against water, was documented by (i) a distinct positive correlation of δ(18)Ocalcite and δ(13)Ccalcite; typical for carbonation through a mortar horizon, (ii) a characteristic evolution of δ(18)Ocalcite and δ(13)Ccalcite through each of the four mortar horizons; lighter follow heavier isotopic values from upper to lower part of the cistern floor, and (iii) δ(18)Ocalcite varying from -10 to -5 ‰ Vienna Pee Dee belemnite (VPDB). The range of δ(18)Ocalcite values rule out recrystallization and/or neoformation of <span class="hlt">calcite</span> through chemical attack of water stored in cistern. The combined studies of the chemical composition of the binder and the isotopic composition of the <span class="hlt">calcite</span> in an ancient mortar provide powerful tools for elucidating the ancient techniques and processing periods. This approach helps to evaluate the durability of primary <span class="hlt">calcite</span> and demonstrates the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.H53C0867L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.H53C0867L"><span>Permeability of <span class="hlt">calcite</span>-cemented fractures in mudrocks: Flow highway or hindrance?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Landry, C. J.; Eichhubl, P.; Prodanovic, M.; Tokan-Lawal, A.</p> <p>2014-12-01</p> <p>Among natural fractures observed in core of Eagle Ford Shale, Texas, tall sub-vertical <span class="hlt">calcite</span>-cemented fractures are the most spatially extensive. Similar sub-vertical opening-mode fractures are found in many mudrocks, and far more often than not they are completely cemented. Currently there is very little evidence that these <span class="hlt">calcite</span> cements are anything but impermeable, and thus would hinder flow across the fractures while having an insignificant effect on flow parallel to the fractures. This suggests that natural fractures in mudrocks are barriers to flow, which goes against the general consensus that natural fractures in mudrocks enhance flow. We used scanning-electron microscopy (SEM) on broad-beam argon-ion milled samples of a <span class="hlt">calcite</span>-cemented fracture with a kinematic aperture (width) of 200 μm to study the pore space of the <span class="hlt">calcite</span> for any indication that completely cemented fractures are permeable. In the fracture <span class="hlt">calcite</span> cement, we observed primary porosity between <span class="hlt">calcite</span> grains that is generally well-connected with an average aperture between 25 and 100 nm. The permeability of these flow-paths was determined by lattice Boltzmann methods to be between 50 to 200 μD. These flow-paths have a spacing between 50 and 300 μm, therefore a square centimeter (length*height) of fracture cement will contain on average more than 100 flow-paths. Thus for flow across the fracture cement (orthogonal to the fracture) the overall cross-fracture permeability of the cement can be approximated using simple effective medium upscaling. The fracture cement studied here is found to have a cross-fracture permeability in the range of 25 to 100 nD. Although this is a very low permeability, it is within the range of the permeability of the host rock, and thus these <span class="hlt">calcite</span> cements would have almost no effect on flow orthogonal to the plane of the fracture. These flow-paths are also connected within the cement creating the equivalent of a single tortuous flow-path along the plane</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012EGUGA..14..582K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012EGUGA..14..582K"><span>Carbonates in thrust faults: High temperature investigations into deformation processes in <span class="hlt">calcite</span>-dolomite systems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kushnir, A.; Kennedy, L.; Misra, S.; Benson, P.</p> <p>2012-04-01</p> <p>The role of dolomite on the strength and evolution of <span class="hlt">calcite</span>-dolomite fold and thrust belts and nappes (as observed in the Canadian Rockies, the Swiss Alps, the Italian Apennines, and the Naukluft Nappe Complex) is largely unknown. Field investigations indicate that strain in natural systems is localized in <span class="hlt">calcite</span>, resulting in a ductile response, while dolomite deforms in a dominantly brittle manner. To date, experimental studies on polymineralic carbonate systems are limited to homogeneous, fine-grained, <span class="hlt">calcite</span>-dolomite composites of relatively low dolomite content. The effect of dolomite on limestone rheology, the onset of crystal-plastic deformation in dolomite in composites, and the potential for strain localization in composites have not yet been fully quantified. Constant displacement rate (3x10-4 s-1and 10-4 s-1), high confining pressure (300 MPa) and high temperature (750° C and 800° C) torsion experiments were conducted to address the role of dolomite on the strength of <span class="hlt">calcite</span>-dolomite composites. Experiments were performed on samples produced by hot isostatic pressing (HIP) amalgams of a natural, pure dolomite and a reagent, pure <span class="hlt">calcite</span>. We performed experiments on the following mixtures (given as dolomite%): 25%, 35%, 50%, and 75%. These synthetic HIP products eliminated concerns of mineralogical impurities and textural anomalies due to porosity, structural fabrics (e.g., foliation) and fossil content. The samples were deformed up to a maximum finite shear strain of 5.0 and the experimental set up was unvented to inhibit sample decarbonation. Mechanical data shows a considerable increase in sample yield strength with increasing dolomite content. Experimental products with low starting dolomite content (dol%: 25% and 35%) display macroscopic strain localization along compositionally defined foliation. Experimental products with high dolomite content (dol%: 50% and 75%) demonstrate no macroscopic foliation. Post-deformation microstructure analysis</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JAESc.119..167P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JAESc.119..167P"><span>Factors controlling the growth rate, carbon and oxygen isotope variation in modern <span class="hlt">calcite</span> precipitation in a subtropical cave, Southwest China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pu, Junbing; Wang, Aoyu; Shen, Licheng; Yin, Jianjun; Yuan, Daoxian; Zhao, Heping</p> <p>2016-04-01</p> <p>A prerequisite for using cave speleothems to reconstruct palaeoenvironmental conditions is an accurate understanding of specific factors controlling <span class="hlt">calcite</span> growth, in particular the isotopic partitioning of oxygen (δ18O) and carbon (δ13C) which are the most commonly used proxies. An in situ monitoring study from April 2008 to September 2009 at Xueyu Cave, Chongqing, SW China, provides insight into the controls on <span class="hlt">calcite</span> growth rates, drip water composition, cave air parameters and δ18O and δ13C isotopic values of modern <span class="hlt">calcite</span> precipitation. Both cave air PCO2 and drip water hydrochemical characteristics show obvious seasonality driven by seasonal changes in the external environment. <span class="hlt">Calcite</span> growth rates also display clear intra-annual variation, with the lowest values occurring during wet season and peak values during the dry season. Seasonal variations of <span class="hlt">calcite</span> growth rate are primarily controlled by variations of cave air PCO2 and drip water rate. Seasonal δ18O-VPDB and δ13C-VPDB in modern <span class="hlt">calcite</span> precipitates vary, with more negative values in the wet season than in the dry season. Strong positive correlation of δ18O-VPDB vs. δ13C-VPDB is due to simultaneous enrichment of both isotopes in the <span class="hlt">calcite</span>. This correlation indicates that kinetic fractionation occurs between parent drip water and depositing <span class="hlt">calcite</span>, likely caused by the variations of cave air PCO2 and drip rate influenced by seasonal cave ventilation. Kinetic fractionation amplifies the equilibrium fractionation value of <span class="hlt">calcite</span> δ18O (by ∼1.5‰) and δ13C (by ∼1.7‰), which quantitatively reflects surface conditions during the cave ventilation season. These results indicate that the cave monitoring of growth rate and δ18O and δ13C of modern <span class="hlt">calcite</span> precipitation are necessary in order to use a speleothem to reconstruct palaeoenvironment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997GeCoA..61.1783N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997GeCoA..61.1783N"><span>A model for microbially induced precipitation of vadose-zone <span class="hlt">calcites</span> in fractures at LOS Alamos, New Mexico, USA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Newman, Brent D.; Campbell, Andrew R.; Norman, David I.; Ringelberg, David B.</p> <p>1997-05-01</p> <p>Fractures are unique environments that can concentrate the flow of water, nutrients, and contaminants. As such, fractures play an important role in controlling the flux of various substances into and through the vadose zone. <span class="hlt">Calcite</span> fracture fillings are present in the near surface in the Bandelier Tuff Formation at Los Alamos, New Mexico, and provide a record of the geochemical and hydrologic processes that have occurred in fractures. The objective of this study was to examine <span class="hlt">calcite</span> fracture fills in order to improve understanding of processes within fractures, and in particular those that lead to precipitation of <span class="hlt">calcite</span>. Samples of <span class="hlt">calcite</span> fillings were collected from vertical and horizontal fractures exposed in a shallow waste-burial pit. Scanning electron microscopy show morphologies which suggest that plants, fungi, and bacteria were important in the precipitation process. Quadrupole mass spectrometric analyses of fluid inclusion gases show predominantly methane (17-99%) and little to no oxygen (0-8%), suggesting the development of anaerobic conditions in the fractures. Ester-linked phospholipid biomarkers are evidence for a diverse microbial community in the fractures, and the presence of di-ether lipids indicate that the methane was generated by anaerobic bacteria. The <span class="hlt">calcite</span> fillings apparently resulted from multiple biological and chemical processes in which plant roots in the fractures were converted to <span class="hlt">calcite</span>. Roots grew into the fractures, eventually died, and were decomposed by bacteria and fungi. Anaerobic gases were generated from encapsulated organic material within the <span class="hlt">calcite</span> via microbial decomposition, or were generated by microbes simultaneously with <span class="hlt">calcite</span> precipitation. It is likely that the biological controls on <span class="hlt">calcite</span> formation that occurred in the Los Alamos fractures also occurs in soils, and may explain the occurrence of other types of pedogenic <span class="hlt">calcites</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22834863','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22834863"><span>Ion exchange model for reversible sorption of divalent metals on <span class="hlt">calcite</span>: implications for natural environments.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tertre, Emmanuel; Page, Jacques; Beaucaire, Catherine</p> <p>2012-09-18</p> <p>Most of the thermodynamic models available in the literature describing the speciation of the <span class="hlt">calcite</span> surface do not predict a significant concentration of sorbed Ca(II), whereas previous electrokinetics studies clearly show that Ca(2+) is the main cation determining the potential of the <span class="hlt">calcite</span> surface. This study proposes a new thermodynamic model based on ion-exchange theory that is able to describe the reversible sorption of Ca(2+) on <span class="hlt">calcite</span>. To constrain the model, concentrations of Ca(II) sorbed reversibly on the mineral surface were obtained as a function of pH. Such experimental data were obtained using solutions in equilibrium with both <span class="hlt">calcite</span> and fixed p(CO2(g)) values (from 10(-5) to 10(-2) atm). The concentration of (de)sorbed Ca(II) is almost constant in the [7-9.5] pH range, having a value of approximately 1.2 × 10(-6) ± 0.4 × 10(-7) eq·g(-1). Such a value agrees with total sorption site densities that were previously calculated by crystallography and is used to obtain a selectivity coefficient between H(+) and Ca(2+) species by fitting the experimental data. Then, selectivity coefficients between H(+) and different metallic cations (Zn(2+), Cd(2+), Pb(2+)) that are able to accurately describe previously published data are proposed. Finally, the model is used to predict the contribution of <span class="hlt">calcite</span> in the overall sorption of Cd(II) on a natural and complex solid (calcareous aquifer sand).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27010399','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27010399"><span>Atomistic Molecular Dynamics Simulations of Crude Oil/Brine Displacement in <span class="hlt">Calcite</span> Mesopores.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sedghi, Mohammad; Piri, Mohammad; Goual, Lamia</p> <p>2016-04-12</p> <p>Unconventional reservoirs such as hydrocarbon-bearing shale formations and ultratight carbonates generate a large fraction of oil and gas production in North America. The characteristic feature of these reservoirs is their nanoscale porosity that provides significant surface areas between the pore walls and the occupying fluids. To better assess hydrocarbon recovery from these formations, it is crucial to develop an improved insight into the effects of wall-fluid interactions on the interfacial phenomena in these nanoscale confinements. One of the important properties that controls the displacement of fluids inside the pores is the threshold capillary pressure. In this study, we present the results of an integrated series of large-scale molecular dynamics (MD) simulations performed to investigate the effects of wall-fluid interactions on the threshold capillary pressures of oil-water/brine displacements in a <span class="hlt">calcite</span> nanopore with a square cross section. Fully atomistic models are utilized to represent crude oil, brine, and <span class="hlt">calcite</span> in order to accommodate electrostatic interactions and H-bonding between the polar molecules and the <span class="hlt">calcite</span> surface. To this end, we create mixtures of various polar and nonpolar organic molecules to better represent the crude oil. The interfacial tension between oil and water/brine and their contact angle on <span class="hlt">calcite</span> surface are simulated. We study the effects of oil composition, water salinity, and temperature and pressure conditions on these properties. The threshold capillary pressure values are also obtained from the MD simulations for the <span class="hlt">calcite</span> nanopore. We then compare the MD results against those generated using the Mayer-Stowe-Princen (MSP) method and explain the differences.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.175..271S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.175..271S"><span>Crystallization of ikaite and its pseudomorphic transformation into <span class="hlt">calcite</span>: Raman spectroscopy evidence</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sánchez-Pastor, N.; Oehlerich, Markus; Astilleros, José Manuel; Kaliwoda, Melanie; Mayr, Christoph C.; Fernández-Díaz, Lurdes; Schmahl, Wolfgang W.</p> <p>2016-02-01</p> <p>Ikaite (CaCO3·6H2O) is a metastable phase that crystallizes in nature from alkaline waters with high phosphate concentrations at temperatures close to 0 °C. This mineral transforms into anhydrous calcium carbonate polymorphs when temperatures rise or when exposed to atmospheric conditions. During the transformation in some cases the shape of the original ikaite crystal is preserved as a pseudomorph. Pseudomorphs after ikaite are considered as a valuable paleoclimatic indicator. In this work we conducted ikaite crystal growth experiments at near-freezing temperatures using the single diffusion silica gel technique, prepared with a natural aqueous solution from the polymictic lake Laguna Potrok Aike (51°57‧S, 70°23‧W) in Patagonia, Argentina. The ikaite crystals were recovered from the gels and the transformation reactions were monitored by in situ Raman spectroscopy at two different temperatures. The first spectra collected showed the characteristic features of ikaite. In successive spectra new bands at 1072, 1081 and 1086 cm-1 and changes in the intensity of bands corresponding to the OH modes were observed. These changes in the Raman spectra were interpreted as corresponding to intermediate stages of the transformation of ikaite into <span class="hlt">calcite</span> and/or vaterite. After a few hours, the characteristics of the Raman spectrum were consistent with those of <span class="hlt">calcite</span>. While ikaite directly transforms into <span class="hlt">calcite</span> at 10 °C in contact with air, at 20 °C this transformation involves the formation of intermediate, metastable vaterite. During the whole process the external shape of ikaite crystals was preserved. Therefore, this transformation showed the typical characteristics of a pseudomorphic mineral replacement, involving the generation of a large amount of porosity to account for the large difference in molar volumes between ikaite and <span class="hlt">calcite</span>. A mechanism involving the coupled dissolution of ikaite and crystallization of <span class="hlt">calcite</span>/vaterite is proposed for this</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.458..203P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.458..203P"><span>Diagenetic Mg-<span class="hlt">calcite</span> overgrowths on foraminiferal tests in the vicinity of methane seeps</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Panieri, Giuliana; Lepland, Aivo; Whitehouse, Martin J.; Wirth, Richard; Raanes, Morten P.; James, Rachael H.; Graves, Carolyn A.; Crémière, Antoine; Schneider, Andrea</p> <p>2017-01-01</p> <p>Methane is a potent greenhouse gas and some episodes of past global warming appear to coincide with its massive release from seafloor sediments as suggested by carbon isotope records of foraminifera. Here, we present structural, geochemical, and stable carbon isotope data from single foraminiferal <span class="hlt">calcite</span> tests and authigenic Mg-<span class="hlt">calcite</span> overgrowths in a sediment core recovered from an area of active methane seepage in western Svalbard at ca. 340 m water depth. The foraminifera are from intervals in the core where conventional bulk foraminiferal δ13 C values are as low as -11.3 ‰. Mg/Ca analyses of the foraminiferal tests reveal that even tests for which there is no morphological evidence for secondary authigenic carbonate can contain Mg-rich interlayers with Mg/Ca up to 220 mmol/mol. Transmission electron microscopy (TEM) of the contact point between the biogenic <span class="hlt">calcite</span> and authigenic Mg-<span class="hlt">calcite</span> layers shows that the two phases are structurally indistinguishable and they have the same crystallographic orientation. Secondary ion mass spectrometry (SIMS) analyses reveal that the Mg-rich layers are strongly depleted in 13C (δ13 C as low as -34.1 ‰). These very low δ13 C values indicate that the authigenic Mg-<span class="hlt">calcite</span> precipitated from pore waters containing methane-derived dissolved inorganic carbon at the depth of the sulfate-methane transition zone (SMTZ). As the depth of the SMTZ can be located several meters below the sediment-seawater interface, interpretation of low foraminiferal δ13 C values in ancient sediments in terms of the history of methane seepage at the seafloor must be undertaken with care.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1616010W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1616010W"><span>Impact of trace metals on the water structure at the <span class="hlt">calcite</span> surface</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wolthers, Mariette; Di Tommaso, Devis; De Leeuw, Nora</p> <p>2014-05-01</p> <p>Carbonate minerals play an important role in regulating the chemistry of aquatic environments, including the oceans, aquifers, hydrothermal systems, soils and sediments. Through mineral surface processes such as dissolution, precipitation and sorption, carbonate minerals affect the biogeochemical cycles of not only the constituent elements of carbonates, such as Ca, Mg, Fe and C, but also H, P and trace elements. Surface charging of the <span class="hlt">calcite</span> mineral-water interface, and its reactivity towards foreign ions can be quantified using a surface structural model that includes, among others, the water structure at the interface (i.e. hydrogen bridging) [1,2] in accordance with the CD-MUSIC formalism [3]. Here we will show the impact of foreign metals such as Mg and Sr on the water structure around different surface sites present in etch pits and on growth terraces at the <span class="hlt">calcite</span> (10-14) surface. We have performed Molecular Dynamics simulations of metal-doped <span class="hlt">calcite</span> surfaces, using different interatomic water potentials. Results show that the local environment around the structurally distinct sites differs depending on metal presence, suggesting that metal substitutions in <span class="hlt">calcite</span> affect its reactivity. The information obtained in this study will help in improving existing macroscopic surface model for the reactivity of <span class="hlt">calcite</span> [2] and give more general insight in mineral surface reactivity in relation to crystal composition. [1] Wolthers, Charlet, & Van Cappellen (2008). Am. J. Sci., 308, 905-941. [2] Wolthers, Di Tommaso, Du, & de Leeuw (2012). Phys. Chem. Chem. Phys. 14, 15145-15157. [3] Hiemstra and Van Riemsdijk (1996) J. Colloid Interf. Sci. 179, 488-508.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/15001334','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/15001334"><span>Microscopic Effects of Carbonate, Manganese, and Strontium ions on <span class="hlt">Calcite</span> Dissolution</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Lea, Alan S.; Amonette, James E.; Baer, Donald R.; Liang, Yong; Colton, Nancy G.</p> <p>2001-02-01</p> <p>Aqueous dissolution of the (1014) surface of <span class="hlt">calcite</span> was observed at pH near 9 using an atomic force microscope equipped with a fluid cell. The influence of carbonate, Sr, and Mn ion concentrations were observed. Carbonste ions were shown to have a step-specific effect on <span class="hlt">calcite</span> dissolution. At ow levels (5 mu-M) of carbonate, the retreat rate of the more structually open [441]+steps was than the retreat rate of the structurally confined [441]-steps, leading to anisotropic dissolution. Increasing the carbonate level to 200 mu-M decreased the rate of retreat of both steps, but the [411]+step was slowed to a much greater extent making the dissolution nearly isotropic. At high levels (800 mu-M) of carbonate, the rate of retreat of the [441]+step was slower than that of the [441]-step making dissolution anisotropic in the opposite sense to that observed at low levels of carbonate. This decrease in step velocity at high carbonate levels was attributed to a corresponding increase in the reaction (i.e., precipitation) as the solution approached saturation with respect to <span class="hlt">calcite</span>, and thus is related to the rate of incorporation of calcium cations into the structure. In addition to changing the rate, this back reaction also altered the shape of etch pits formed by dissolution. Strontium cations were also shown to have a step-specific effect on <span class="hlt">calcite</span> dissolution similar to that of carbonate, suggesting that strontium is preferentially incorporated into the [441]-step to a greater extent than strontium. When the solution exceeded saturation with respect to rhodochrosite, <span class="hlt">calcite</span> dissolution was nearly isotropic. These results suggest that the small manganese ion (r = 83 pm), is readily incorporated into both [441]+ and [441]-steps, in contrast to the larger Ca (r = 100 pm) and Sr (r = 131 pm) cations, which are preferentially incorporated into the [441]+step.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/17272244','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/17272244"><span><span class="hlt">Marine</span> energy.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kerr, David</p> <p>2007-04-15</p> <p><span class="hlt">Marine</span> energy is renewable and carbon free and has the potential to make a significant contribution to energy supplies in the future. In the UK, tidal power barrages and wave energy could make the largest contribution, and tidal stream energy could make a smaller but still a useful contribution. This paper provides an overview of the current status and prospects for electrical generation from <span class="hlt">marine</span> energy. It concludes that a realistic potential contribution to UK electricity supplies is approximately 80 TWh per year but that many years of development and investment will be required if this potential is to be realized.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUSM.V43C..04B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUSM.V43C..04B"><span>Distinguishing Biotic from <span class="hlt">Abiotic</span> Phosphate Oxygen Isotopic Signatures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blake, R.; Moyer, C.; Colman, A.; Liang, Y.; Dogru, D.</p> <p>2006-05-01</p> <p>On earth, phosphate has a strong biological oxygen isotope signature due to its concentration and intense cycling by living organisms as an essential nutrient. Phosphate does not undergo oxygen isotope exchange with water at low temperature without enzymatic catalysis, making the oxygen isotope ratio (18O/16O) of phosphate, δ18OP, an attractive biosignature in the search for early and extraterrestrial life. Recent laboratory and field studies have demonstrated that the δ18OP value of dissolved inorganic phosphate (PO4) records specific microbial activity and enzymatic reaction pathways in both laboratory cultures and natural waters/sediments (Blake et al., 2005; Colman et al 2005; Liang and Blake, 2005). Phosphate oxygen isotope biosignatures may be distinguished from <span class="hlt">abiotic</span> signatures by: (1) evaluating the degree of temperature-dependent PO4-water oxygen isotope exchange in aqueous systems and deviation from equilibrium; and (2) evolution from an <span class="hlt">abiotic</span> P reservoir signature towards a biotic P reservoir signature. Important <span class="hlt">abiotic</span> processes potentially affecting phosphate δ18OP values include dissolution/precipitation, adsorption/desorption, recrystallization of PO4 mineral phases, diagenesis and metamorphism. For most of these processes, the recording, retention and alteration of δ18OP biosignatures have not been evaluated. Deep-sea hydrothermal vent fields are an ideal system in which to study the preservation and alteration of δ18OP biosignatures, as well as potential look-alikes produced by heat-promoted PO4 -water oxygen isotope exchange. Results from recent studies of δ18OP biosignatures in hydrothermal deposits near 9 and 21 degrees N. EPR and at Loihi seamount will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4485091','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4485091"><span>Pathways for <span class="hlt">abiotic</span> organic synthesis at submarine hydrothermal fields</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>McDermott, Jill M.; Seewald, Jeffrey S.; German, Christopher R.; Sylva, Sean P.</p> <p>2015-01-01</p> <p>Arguments for an <span class="hlt">abiotic</span> origin of low-molecular weight organic compounds in deep-sea hot springs are compelling owing to implications for the sustenance of deep biosphere microbial communities and their potential role in the origin of life. Theory predicts that warm H2-rich fluids, like those emanating from serpentinizing hydrothermal systems, create a favorable thermodynamic drive for the <span class="hlt">abiotic</span> generation of organic compounds from inorganic precursors. Here, we constrain two distinct reaction pathways for <span class="hlt">abiotic</span> organic synthesis in the natural environment at the Von Damm hydrothermal field and delineate spatially where inorganic carbon is converted into bioavailable reduced carbon. We reveal that carbon transformation reactions in a single system can progress over hours, days, and up to thousands of years. Previous studies have suggested that CH4 and higher hydrocarbons in ultramafic hydrothermal systems were dependent on H2 generation during active serpentinization. Rather, our results indicate that CH4 found in vent fluids is formed in H2-rich fluid inclusions, and higher n-alkanes may likely be derived from the same source. This finding implies that, in contrast with current paradigms, these compounds may form independently of actively circulating serpentinizing fluids in ultramafic-influenced systems. Conversely, widespread production of formate by ΣCO2 reduction at Von Damm occurs rapidly during shallow subsurface mixing of the same fluids, which may support anaerobic methanogenesis. Our finding of abiogenic formate in deep-sea hot springs has significant implications for microbial life strategies in the present-day deep biosphere as well as early life on Earth and beyond. PMID:26056279</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26056279','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26056279"><span>Pathways for <span class="hlt">abiotic</span> organic synthesis at submarine hydrothermal fields.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>McDermott, Jill M; Seewald, Jeffrey S; German, Christopher R; Sylva, Sean P</p> <p>2015-06-23</p> <p>Arguments for an <span class="hlt">abiotic</span> origin of low-molecular weight organic compounds in deep-sea hot springs are compelling owing to implications for the sustenance of deep biosphere microbial communities and their potential role in the origin of life. Theory predicts that warm H2-rich fluids, like those emanating from serpentinizing hydrothermal systems, create a favorable thermodynamic drive for the <span class="hlt">abiotic</span> generation of organic compounds from inorganic precursors. Here, we constrain two distinct reaction pathways for <span class="hlt">abiotic</span> organic synthesis in the natural environment at the Von Damm hydrothermal field and delineate spatially where inorganic carbon is converted into bioavailable reduced carbon. We reveal that carbon transformation reactions in a single system can progress over hours, days, and up to thousands of years. Previous studies have suggested that CH4 and higher hydrocarbons in ultramafic hydrothermal systems were dependent on H2 generation during active serpentinization. Rather, our results indicate that CH4 found in vent fluids is formed in H2-rich fluid inclusions, and higher n-alkanes may likely be derived from the same source. This finding implies that, in contrast with current paradigms, these compounds may form independently of actively circulating serpentinizing fluids in ultramafic-influenced systems. Conversely, widespread production of formate by ΣCO2 reduction at Von Damm occurs rapidly during shallow subsurface mixing of the same fluids, which may support anaerobic methanogenesis. Our finding of abiogenic formate in deep-sea hot springs has significant implications for microbial life strategies in the present-day deep biosphere as well as early life on Earth and beyond.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.B21B0050I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.B21B0050I"><span>Coupled <span class="hlt">Abiotic</span>-Biotic Degradation of Bisphenol A</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Im, J.; Prevatte, C.; Campagna, S. R.; Loeffler, F.</p> <p>2014-12-01</p> <p>Bisphenol A (BPA) is a ubiquitous environmental contaminant with weak estrogenic activity. BPA is readily biodegradable with oxygen available, but is recalcitrant to microbial degradation under anoxic conditions. However, BPA is susceptible to <span class="hlt">abiotic</span> transformation under anoxic conditions. To better understand the fate of BPA in anoxic environments, the kinetics of BPA transformation by manganese oxide (d-MnO2) were investigated. BPA was rapidly transformed by MnO2 with a pseudo-first-order rate constant of 0.413 min-1. NMR and LC-MS analyses identified 4-hydroxycumyl alcohol (HCA) as a major intermediate. Up to 64% of the initial amount of BPA was recovered as HCA within 5 min, but the conversion efficiency decreased with time, suggesting that HCA was further degraded by MnO2. Further experiments confirmed that HCA was also susceptible to transformation by MnO2, albeit at 5-fold lower rates than BPA transformation. Mass balance approaches suggested that HCA was the major BPA transformation intermediate, but other compounds may also be formed. The <span class="hlt">abiotic</span> transformation of BPA by MnO2 was affected by pH, and 10-fold higher transformation rates were observed at pH 4.5 than at pH 10. Compared to BPA, HCA has a lower octanol-water partitioning coefficient (Log Kow) of 0.76 vs 2.76 for BPA and a higher aqueous solubility of 2.65 g L-1 vs 0.31 g L-1 for BPA, suggesting higher mobility of HCA in the environment. Microcosms established with freshwater sediment materials collected from four geographically distinct locations and amended with HCA demonstrated rapid HCA biodegradation under oxic, but not under anoxic conditions. These findings suggest that BPA is not inert under anoxic conditions and <span class="hlt">abiotic</span> reactions with MnO2 generate HCA, which has increased mobility and is susceptible to aerobic degradation. Therefore, coupled <span class="hlt">abiotic</span>-biotic processes can affect the fate and longevity of BPA in terrestrial environments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19892980','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19892980"><span><span class="hlt">Abiotic</span> gas formation drives nitrogen loss from a desert ecosystem.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>McCalley, Carmody K; Sparks, Jed P</p> <p>2009-11-06</p> <p>In arid environments such as deserts, nitrogen is often the most limiting nutrient for biological activity. The majority of the ecosystem nitrogen flux is typically thought to be driven by production and loss of reactive nitrogen species by microorganisms in the soil. We found that high soil-surface temperatures (greater than 50 degrees C), driven by solar radiation, are the primary cause of nitrogen loss in Mojave Desert soils. This <span class="hlt">abiotic</span> pathway not only enables the balancing of arid ecosystem nitrogen budgets, but also changes our view of global nitrogen cycling and the predicted impact of climate change and increased temperatures on nitrogen bioavailability.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24275176','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24275176"><span><span class="hlt">Marine</span> envenomations.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Balhara, Kamna S; Stolbach, Andrew</p> <p>2014-02-01</p> <p>This article describes the epidemiology and presentation of human envenomation from <span class="hlt">marine</span> organisms. Venom pathophysiology, envenomation presentation, and treatment options are discussed for sea snake, stingray, spiny fish, jellyfish, octopus, cone snail, sea urchin, and sponge envenomation. The authors describe the management of common exposures that cause morbidity as well as the keys to recognition and treatment of life-threatening exposures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=arctic+AND+ocean&id=ED265031','ERIC'); return false;" href="http://eric.ed.gov/?q=arctic+AND+ocean&id=ED265031"><span><span class="hlt">Marine</span> Mammals.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Meith, Nikki</p> <p></p> <p><span class="hlt">Marine</span> mammals have not only fascinated and inspired human beings for thousands of years, but they also support a big business by providing flesh for sea-borne factories, sustaining Arctic lifestyles and traditions, and attracting tourists to ocean aquaria. While they are being harpooned, bludgeoned, shot, netted, and trained to jump through…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://eric.ed.gov/?q=fiberglass+OR+fibreglass+OR+%22glass+fiber%22+OR+%22glass+fibre%22&pg=4&id=ED287065','ERIC'); return false;" href="http://eric.ed.gov/?q=fiberglass+OR+fibreglass+OR+%22glass+fiber%22+OR+%22glass+fibre%22&pg=4&id=ED287065"><span><span class="hlt">Marine</span> Trades.</span></a></p> <p><a target="_blank" href="http://www.eric.ed.gov/ERICWebPortal/search/extended.jsp?_pageLabel=advanced">ERIC Educational Resources Information Center</a></p> <p>Abbott, Alan</p> <p></p> <p>This curriculum guide provides materials for a competency-based course in <span class="hlt">marine</span> trades at the secondary level. The curriculum design uses the curriculum infused model for the teaching of basic skills as part of vocational education and demonstrates the relationship of vocationally related skills to communication, mathematics, and science…</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2000eaa..bookE2176S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2000eaa..bookE2176S"><span><span class="hlt">Mariner</span> Missions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Snyder, C.; Murdin, P.</p> <p>2000-11-01</p> <p><span class="hlt">Mariner</span> was the name given to the earliest set of American space missions to explore the planets and to the spacecraft developed to carry them out. The missions were planned and executed by the JET PROPULSION LABORATORY (JPL) of the California Institute of Technology, which had been designated by the National Aeronautics and Space Administration (NASA) as its lead center for planetary missions....</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19760010532','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19760010532"><span><span class="hlt">Marine</span> Resources</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sherman, J. W., III</p> <p>1975-01-01</p> <p>The papers presented in the <span class="hlt">marine</span> session may be broadly grouped into several classes: microwave region instruments compared to infrared and visible region sensors, satellite techniques compared to aircraft techniques, open ocean applications compared to coastal region applications, and basic research and understanding of ocean phenomena compared to research techniques that offer immediate applications.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4632763','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4632763"><span>Small RNAs in Plant Responses to <span class="hlt">Abiotic</span> Stresses: Regulatory Roles and Study Methods</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ku, Yee-Shan; Wong, Johanna Wing-Hang; Mui, Zeta; Liu, Xuan; Hui, Jerome Ho-Lam; Chan, Ting-Fung; Lam, Hon-Ming</p> <p>2015-01-01</p> <p>To survive under <span class="hlt">abiotic</span> stresses in the environment, plants trigger a reprogramming of gene expression, by transcriptional regulation or translational regulation, to turn on protective mechanisms. The current focus of research on how plants cope with <span class="hlt">abiotic</span> stresses has transitioned from transcriptomic analyses to small RNA investigations. In this review, we have summarized and evaluated the current methodologies used in the identification and validation of small RNAs and their targets, in the context of plant responses to <span class="hlt">abiotic</span> stresses. PMID:26501263</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5143345','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5143345"><span><span class="hlt">Calcite</span> Dissolution by Brevibacterium sp. SOTI06: A Futuristic Approach for the Reclamation of Calcareous Sodic Soils</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Tamilselvi, S. M.; Thiyagarajan, Chitdeshwari; Uthandi, Sivakumar</p> <p>2016-01-01</p> <p>Assessing the ability of soil microorganisms to dissolute poorly soluble native <span class="hlt">calcite</span> to supply Ca2+ is a new area to be explored in reclaiming sodic soils by supplying adequate Ca2+ and reducing the recurrent sodicity. Hence, the present study aimed to isolate a <span class="hlt">calcite</span> dissolving bacteria (CDB) from calcareous sodic soils and to understand the mechanism of <span class="hlt">calcite</span> dissolution. Of the 33 CDB isolates recovered from the calcareous sodic soils of Tamil Nadu (Coimbatore, Ramnad, and Trichy), 11 isolates were screened for <span class="hlt">calcite</span> dissolution based on titratable acidity. 16S rRNA gene sequence analysis of the three best isolates viz., SORI09, SOTI05, and SOTI06 revealed 99% similarity to Bacillus aryabhattai, 100% to B. megaterium, and 93% to Brevibacterium sp., respectively. Among them, Brevibacterium sp. SOTI06 released more Ca2+ (3.6 g.l−1) by dissolving 18.6% of the native <span class="hlt">calcite</span>. The spectral data of FTIR also showed reduction in the intensity of <span class="hlt">calcite</span> (55.36–41.27) by the isolate at a wave number of 1636 cm−1 which confirmed the dissolution. Besides producing organic acids (gluconic acid and acetic acid), Brevibacterium sp. SOTI06 also produced siderophore (91.6%) and extracellular polysaccharides (EPS, 13.3 μg. ml−1) which might have enhanced the <span class="hlt">calcite</span> dissolution. PMID:28008333</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUSMNB31F..03C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUSMNB31F..03C"><span>Linking Species Traits to the <span class="hlt">Abiotic</span> Template of Flowing Waters: Contrasting Eco physiologies Underlie Displacement of Zebra Mussels by Quagga Mussels in a Large River-Estuary</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Casper, A. F.</p> <p>2005-05-01</p> <p>The St. Lawrence River-Estuary was the gateway of entry for dreissenids to North America and holds some of the oldest populations. The St. Lawrence also has four distinct physical-chemical water masses (a regional scale <span class="hlt">abiotic</span> template) that both species inhabit. Despite their ecological similarities, quagga mussels are supplanting zebra mussels in much of their shared range. In order to try to better understand the changing distributions of these two species we compared glycogen, shell mass and tissue biomass in each of the water masses. This comparative physiological combined with experimental approaches (estuarine salinity experiments and reciprocal transplants) showed that while quagga mussels should dominate in most habitats, that <span class="hlt">abiotic</span>/bioenergetic constraints in two regions (the Ottawa River plume and the freshwater-<span class="hlt">marine</span> transition zone) might prevent them from dominating these locations. These findings are an example of how the interaction of landscape scale <span class="hlt">abiotic</span> heterogeneity and a species-specific physiology can have strong impacts of distribution of biota large rivers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25880454','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25880454"><span>Expression of the tetrahydrofolate-dependent nitric oxide synthase from the green alga Ostreococcus tauri increases tolerance to <span class="hlt">abiotic</span> stresses and influences stomatal development in Arabidopsis.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Foresi, Noelia; Mayta, Martín L; Lodeyro, Anabella F; Scuffi, Denise; Correa-Aragunde, Natalia; García-Mata, Carlos; Casalongué, Claudia; Carrillo, Néstor; Lamattina, Lorenzo</p> <p>2015-06-01</p> <p>Nitric oxide (NO) is a signaling molecule with diverse biological functions in plants. NO plays a crucial role in growth and development, from germination to senescence, and is also involved in plant responses to biotic and <span class="hlt">abiotic</span> stresses. In animals, NO is synthesized by well-described nitric oxide synthase (NOS) enzymes. NOS activity has also been detected in higher plants, but no gene encoding an NOS protein, or the enzymes required for synthesis of tetrahydrobiopterin, an essential cofactor of mammalian NOS activity, have been identified so far. Recently, an NOS gene from the unicellular <span class="hlt">marine</span> alga Ostreococcus tauri (OtNOS) has been discovered and characterized. Arabidopsis thaliana plants were transformed with OtNOS under the control of the inducible short promoter fragment (SPF) of the sunflower (Helianthus annuus) Hahb-4 gene, which responds to <span class="hlt">abiotic</span> stresses and abscisic acid. Transgenic plants expressing OtNOS accumulated higher NO concentrations compared with siblings transformed with the empty vector, and displayed enhanced salt, drought and oxidative stress tolerance. Moreover, transgenic OtNOS lines exhibited increased stomatal development compared with plants transformed with the empty vector. Both in vitro and in vivo experiments indicate that OtNOS, unlike mammalian NOS, efficiently uses tetrahydrofolate as a cofactor in Arabidopsis plants. The modulation of NO production to alleviate <span class="hlt">abiotic</span> stress disturbances in higher plants highlights the potential of genetic manipulation to influence NO metabolism as a tool to improve plant fitness under adverse growth conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004AGUFMPP43A0597Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004AGUFMPP43A0597Y"><span>A Modified Method for Saline Lake <span class="hlt">Calcite</span> Isotope Analysis: Application to a Study of Climate Change over 200,000 Years in Death Valley, California.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yang, W.; Lowenstein, T. K.; Krouse, R. H.; Spencer, R. J.; Ku, T.</p> <p>2004-12-01</p> <p> sediments. For a continuous 200,000-year δ 18O record of lacustrine <span class="hlt">calcite</span> from a 186-meter sediment core from Badwater Basin, Death Valley, California, a two-level climatic fluctuation model is suggested.. This record provides new insight to the debate on the timing and driving forces of late Quaternary paleoclimatic changes. Excursions in <span class="hlt">calcite</span> δ 18O are similar to those of δ 18O in sulfate in the Death Valley core, as well as to those in <span class="hlt">marine</span> carbonate (SPECMAP) and polar ice in the Summit ice core (GRIP), Greenland. The Death Valley record shows periodicities of 96000, 39000, 21000, 14000 and 8000 years. The longer-term (96000, 39000 & 21000 years) fluctuations match Milankovitch orbital forcing, and are thus likely to be global in origin; the shorter-term (14000 and 8000 years) fluctuations probably reflect regional climatic and/or hydrologic forcing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24330167','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24330167"><span>Influence of <span class="hlt">abiotic</span> factors on the antimicrobial activity of chitosan.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Tavaria, Freni K; Costa, Eduardo M; Gens, Eduardo J; Malcata, Francisco Xavier; Pintado, Manuela E</p> <p>2013-12-01</p> <p>In an effort to bypass the adverse secondary effects attributed to the traditional therapeutic approaches used to treat skin disorders (such as atopic dermatitis), alternative antimicrobials have recently been suggested. One such antimicrobial is chitosan, owing to the already proved biological properties associated with its use. However, the influence of <span class="hlt">abiotic</span> factors on such activities warrants evaluation. This research effort assessed the antimicrobial activity of chitosan upon skin microorganisms (Staphylococcus aureus, Staphylococcus epidermidis and Escherichia coli) in vitro when subject to a combination of different <span class="hlt">abiotic</span> factors such as pH, ionic strength, organic acids and free fatty acids. Free fatty acids, ionic strength and pH significantly affected chitosan's capability of reducing the viable numbers of S. aureus. This antimicrobial action was potentiated in the presence of palmitic acid and a lower ionic strength (0.2% NaCl), while a higher ionic strength (0.4% NaCl) favored chitosan's action upon the reduction of viable numbers of S. epidermidis and E. coli. Although further studies are needed, these preliminary results advocate that chitosan can in the future be potentially considered as an antimicrobial of choice when handling symptoms associated with atopic dermatitis.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5002411','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5002411"><span>Calcium-Mediated <span class="hlt">Abiotic</span> Stress Signaling in Roots</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Wilkins, Katie A.; Matthus, Elsa; Swarbreck, Stéphanie M.; Davies, Julia M.</p> <p>2016-01-01</p> <p>Roots are subjected to a range of <span class="hlt">abiotic</span> stresses as they forage for water and nutrients. Cytosolic free calcium is a common second messenger in the signaling of <span class="hlt">abiotic</span> stress. In addition, roots take up calcium both as a nutrient and to stimulate exocytosis in growth. For calcium to fulfill its multiple roles must require strict spatio-temporal regulation of its uptake and efflux across the plasma membrane, its buffering in the cytosol and its sequestration or release from internal stores. This prompts the question of how specificity of signaling output can be achieved against the background of calcium’s other uses. Threats to agriculture such as salinity, water availability and hypoxia are signaled through calcium. Nutrient deficiency is also emerging as a stress that is signaled through cytosolic free calcium, with progress in potassium, nitrate and boron deficiency signaling now being made. Heavy metals have the capacity to trigger or modulate root calcium signaling depending on their dose and their capacity to catalyze production of hydroxyl radicals. Mechanical stress and cold stress can both trigger an increase in root cytosolic free calcium, with the possibility of membrane deformation playing a part in initiating the calcium signal. This review addresses progress in identifying the calcium transporting proteins (particularly channels such as annexins and cyclic nucleotide-gated channels) that effect stress-induced calcium increases in roots and explores links to reactive oxygen species, lipid signaling, and the unfolded protein response. PMID:27621742</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26795146','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26795146"><span><span class="hlt">Abiotic</span> factors influence plant storage lipid accumulation and composition.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Singer, Stacy D; Zou, Jitao; Weselake, Randall J</p> <p>2016-02-01</p> <p>The demand for plant-derived oils has increased substantially over the last decade, and is sure to keep growing. While there has been a surge in research efforts to produce plants with improved oil content and quality, in most cases the enhancements have been small. To add further complexity to this situation, substantial differences in seed oil traits among years and field locations have indicated that plant lipid biosynthesis is also influenced to a large extent by multiple environmental factors such as temperature, drought, light availability and soil nutrients. On the molecular and biochemical levels, the expression and/or activities of fatty acid desaturases, as well as diacylglycerol acyltransferase 1, have been found to be affected by <span class="hlt">abiotic</span> factors, suggesting that they play a role in the lipid content and compositional changes seen under <span class="hlt">abiotic</span> stress conditions. Unfortunately, while only a very small number of strategies have been developed as of yet to minimize these environmental effects on the production of storage lipids, it is clear that this feat will be of the utmost importance for developing superior oil crops with the capability to perform in a consistent manner in field conditions in the future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23093803','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23093803"><span>RNA helicases: diverse roles in prokaryotic response to <span class="hlt">abiotic</span> stress.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Owttrim, George W</p> <p>2013-01-01</p> <p>Similar to proteins, RNA molecules must fold into the correct conformation and associate with protein complexes in order to be functional within a cell. RNA helicases rearrange RNA secondary structure and RNA-protein interactions in an ATP-dependent reaction, performing crucial functions in all aspects of RNA metabolism. In prokaryotes, RNA helicase activity is associated with roles in housekeeping functions including RNA turnover, ribosome biogenesis, translation and small RNA metabolism. In addition, RNA helicase expression and/or activity are frequently altered during cellular response to <span class="hlt">abiotic</span> stress, implying they perform defined roles during cellular adaptation to changes in the growth environment. Specifically, RNA helicases contribute to the formation of cold-adapted ribosomes and RNA degradosomes, implying a role in alleviation of RNA secondary structure stabilization at low temperature. A common emerging theme involves RNA helicases acting as scaffolds for protein-protein interaction and functioning as molecular clamps, holding RNA-protein complexes in specific conformations. This review highlights recent advances in DEAD-box RNA helicase association with cellular response to <span class="hlt">abiotic</span> stress in prokaryotes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3329344','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3329344"><span>Influence of <span class="hlt">abiotic</span> stress signals on secondary metabolites in plants</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Ramakrishna, Akula; Ravishankar, Gokare Aswathanarayana</p> <p>2011-01-01</p> <p>Plant secondary metabolites are unique sources for pharmaceuticals, food additives, flavors, and industrially important biochemicals. Accumulation of such metabolites often occurs in plants subjected to stresses including various elicitors or signal molecules. Secondary metabolites play a major role in the adaptation of plants to the environment and in overcoming stress conditions. Environmental factors viz. temperature, humidity, light intensity, the supply of water, minerals, and CO2 influence the growth of a plant and secondary metabolite production. Drought, high salinity, and freezing temperatures are environmental conditions that cause adverse effects on the growth of plants and the productivity of crops. Plant cell culture technologies have been effective tools for both studying and producing plant secondary metabolites under in vitro conditions and for plant improvement. This brief review summarizes the influence of different <span class="hlt">abiotic</span> factors include salt, drought, light, heavy metals, frost etc. on secondary metabolites in plants. The focus of the present review is the influence of <span class="hlt">abiotic</span> factors on secondary metabolite production and some of important plant pharmaceuticals. Also, we describe the results of in vitro cultures and production of some important secondary metabolites obtained in our laboratory. PMID:22041989</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21889038','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21889038"><span><span class="hlt">Abiotic</span> stress and control of grain number in cereals.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Dolferus, Rudy; Ji, Xuemei; Richards, Richard A</p> <p>2011-10-01</p> <p>Grain number is the only yield component that is directly associated with increased grain yield in important cereal crops like wheat. Historical yield studies show that increases in grain yield are always accompanied by an increase in grain number. Adverse weather conditions can cause severe fluctuations in grain yield and substantial yield losses in cereal crops. The problem is global and despite its impact on world food production breeding and selection approaches have only met with limited success. A specific period during early reproductive development, the young microspore stage of pollen development, is extremely vulnerable to <span class="hlt">abiotic</span> stress in self-fertilising cereals (wheat, rice, barley, sorghum). A better understanding of the physiological and molecular processes that lead to stress-induced pollen abortion may provide us with the key to finding solutions for maintaining grain number under <span class="hlt">abiotic</span> stress conditions. Due to the complexity of the problem, stress-proofing our main cereal crops will be a challenging task and will require joint input from different research disciplines.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2948668','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2948668"><span><span class="hlt">Marine</span> microbial genomics in Europe: current status and perspectives</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Glöckner, Frank Oliver; Joint, Ian</p> <p>2010-01-01</p> <p>Summary The oceans are the Earth's largest ecosystem, covering 70% of our planet and providing goods and services for the majority of the world's population. Understanding the complex <span class="hlt">abiotic</span> and biotic processes on the micro‐ to macroscale is the key to protect and sustain the <span class="hlt">marine</span> ecosystem. <span class="hlt">Marine</span> microorganisms are the ‘gatekeepers’ of the biotic processes that control the global cycles of energy and organic matter. A multinational, multidisciplinary approach, bringing together research on oceanography, biodiversity and genomics, is now needed to understand and finally predict the complex responses of the <span class="hlt">marine</span> ecosystem to ongoing global changes. Such an integrative approach will not only bring better understanding of the complex interplay of the organisms with their environment, but will reveal a wealth of new metabolic processes and functions, which have a high potential for biotechnological applications. This potential has already been recognized by the European commission which funded a series of workshops and projects on <span class="hlt">marine</span> genomics in the sixth and seventh framework programme. Nevertheless, there remain many obstacles to achieving the goal – such as a lack of bioinformatics tailored for the <span class="hlt">marine</span> field, consistent data acquisition and exchange, as well as continuous monitoring programmes and a lack of relevant <span class="hlt">marine</span> bacterial models. <span class="hlt">Marine</span> ecosystems research is complex and challenging, but it also harbours the opportunity to cross the borders between disciplines and countries to finally create a rewarding <span class="hlt">marine</span> research era that is more than the sum of its parts. PMID:20953416</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AdWR...95..246E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AdWR...95..246E"><span>3D Mapping of <span class="hlt">calcite</span> and a demonstration of its relevance to permeability evolution in reactive fractures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ellis, Brian R.; Peters, Catherine A.</p> <p>2016-09-01</p> <p>There is a need to better understand reaction-induced changes in fluid transport in fractured shales, caprocks and reservoirs, especially in the context of emerging energy technologies, including geologic carbon sequestration, unconventional natural gas, and enhanced geothermal systems. We developed a method for 3D <span class="hlt">calcite</span> mapping in rock specimens. Such information is critical in reactive transport modeling, which relies on information about the locations and accessible surface area of reactive minerals. We focused on <span class="hlt">calcite</span> because it is a mineral whose dissolution could lead to substantial pathway alteration because of its high solubility, fast reactivity, and abundance in sedimentary rocks. Our approach combines X-ray computed tomography (XCT) and scanning electron microscopy. The method was developed and demonstrated for a fractured limestone core containing about 50% <span class="hlt">calcite</span>, which was 2.5 cm in diameter and 3.5 cm in length and had been scanned using XCT. The core was subsequently sectioned and energy dispersive X-ray spectroscopy was used to determine elemental signatures for mineral identification and mapping. Back-scattered electron microscopy was used to identify features for co-location. Finally, image analysis resulted in characteristic grayscale intensities of X-ray attenuation that identify <span class="hlt">calcite</span>. This attenuation mapping ultimately produced a binary segmented 3D image of the spatial distribution of <span class="hlt">calcite</span> in the entire core. To demonstrate the value of this information, permeability changes were investigated for hypothetical fractures created by eroding <span class="hlt">calcite</span> from 2D rock surfaces. Fluid flow was simulated using a 2D steady state model. The resulting increases in permeability were profoundly influenced by the degree to which <span class="hlt">calcite</span> is contiguous along the flow path. If there are bands of less reactive minerals perpendicular to the direction of flow, fracture permeability may be an order of magnitude smaller than when <span class="hlt">calcite</span> is contiguous</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.V23B3170H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.V23B3170H"><span>A preliminary study of the <span class="hlt">calcite</span> beef found in the Cretaceous Jinju Formation, Gyeongsang Basin, South Korea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ha, S.; Chae, Y. U.; Son, M.; Jeong, G. Y.; Paik, I. S.; Lim, H. S.</p> <p>2015-12-01</p> <p>The term "beef" refers to fibrous minerals in bedding-parallel veins, where the fibers are approximately perpendicular to the vein margins (Cobbold et al., 2013). It mostly appears within organic-rich black shale layers in sedimentary basin. Although the veins can consist of white gangue minerals, such as <span class="hlt">calcite</span>, gypsum, or quartz, the commonest mineral in the fibers is <span class="hlt">calcite</span>. According to the worldwide localities of <span class="hlt">calcite</span> beef compiled by Cobbold et al (2012), they concentrated in some areas, especially around the Atlantic Ocean. However, they have been rarely reported in the western Pacific margin, except Australia and New Zealand. Recently, <span class="hlt">calcite</span> beefs have been found in the Cretaceous Jinju Formation, Gyeongsang Basin, Korea. As far as we know, this is the first report of <span class="hlt">calcite</span> beef in Korea. The lacustrine Jinju Formation is about 1,200 m thick, and made up mainly of lacustrine dark grey to black mudstones. In the study area, <span class="hlt">calcite</span> beefs were commonly found in the organic-rich black shale layers. The vein thickness is anywhere between a few millimeters to maximum 3 centimeters, and their length ranges from a few centimeters to several tens of meters. The interval between successive veins is from a few centimeters to about 1 meter. Most of them occur parallel to the bedding planes, although some of them are developed along fault planes or within deformed layers. In case of relatively thick beefs, the center of veins often shows a dark grey to black central median line, defined by fine-grained <span class="hlt">calcite</span> grains, fluid inclusion lines, or wall rock particles. Based on the orientation of fibrous <span class="hlt">calcite</span>, they can be divided into two types: straight and sigmoidal types. The fibrous <span class="hlt">calcites</span> are thought to have been symmetrically grown from the median lines to top and bottom of wall rock. The formation mechanism of horizontal fractures, and the formation temperature of beefs in the study area remain as a matter to be studied further.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/22512172','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/22512172"><span>[In situ experimental study of phase transition of <span class="hlt">calcite</span> by Raman spectroscopy at high temperature and high pressure].</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Liu, Chuan-jiang; Zheng, Hai-fei</p> <p>2012-02-01</p> <p>The phase transitions of <span class="hlt">calcite</span> at high temperature and high pressure were investigated by using hydrothermal diamond anvil cell combined with Raman spectroscopy. The result showed that the Raman peak of 155 cm(-1) disappeared, the peak of 1 087 cm(-1) splited into 1083 and 1 090 cm(-1) peaks and the peak of 282 cm(-1) abruptly reduced to 231 cm(-1) at ambient temperature when the system pressure increased to 1 666 and 2 127 MPa respectively, which proved that <span class="hlt">calcite</span> transformed to <span class="hlt">calcite</span>-II and <span class="hlt">calcite</span>-III. In the heating process at the initial pressure of 2 761 MPa and below 171 degrees C, there was no change in Raman characteristic peaks of <span class="hlt">calcite</span>-III. As the temperature increased to 171 degrees C, the color of <span class="hlt">calcite</span> crystal became opaque completely and the symmetric stretching vibration peak of 1 087 cm(-1), in-plane bending vibration peak of 713 cm(-1) and lattice vibration peaks of 155 and 282 cm(-1) began to mutate, showing that the <span class="hlt">calcite</span>-III transformed to a new phase of calcium carbonate at the moment. When the temperature dropped to room temperature, this new phase remained stable all along. It also indicated that the process of phase transformation from <span class="hlt">calcite</span> to the new phase of calcium carbonate was irreversible. The equation of phase transition between <span class="hlt">calcite</span>-III and new phase of calcium carbonate can be determined by P(MPa) = 9.09T x (degrees C) +1 880. The slopes of the Raman peak (v1 087) of symmetrical stretching vibration depending on pressure and temperature are dv/dP = 5.1 (cm(-1) x GPa(-1)) and dv/dT = -0.055 3(cm(-1) x degrees C(-1)), respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T23C2069R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T23C2069R"><span>Stress and Temperature Dependence of <span class="hlt">Calcite</span> Twinning: New Experimental and Field Constraints</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rybacki, E.; Janssen, C.; Dresen, G.</p> <p>2008-12-01</p> <p>In low-grade metamorphic terrains at temperatures < 300° C e-twinning of <span class="hlt">calcite</span> is common. The width and density of e-twins have been suggested to indicate stress and temperature representing robust paleopiezometers and geothermometers. To evaluate the stress- and temperature dependence of e-twins in <span class="hlt">calcite</span> we have performed a series of deformation experiments on specimens of Carrara marble. 14 experiments were performed at 100-400 MPa confining pressure and T < 350° C in a Paterson-type gas deformation apparatus. Seven samples were deformed in axial compression test at strain rates from 10-4 -10-6s-1. Seven samples were deformed in torsion tests to shear strains γ < 1.8. After testing, thin sections of all samples were prepared for optical inspection of twin density and twin width. Twin density varied between 10 and 500 [twins/mm] at stresses up to 280 MPa. At given conditions and with increasing strain twin density increased significantly. No clear dependence of twin density on temperatures up to 300° C was found in experiments. The experimentally deformed samples were compared to naturally-deformed low-grade <span class="hlt">calcite</span> rocks from different fault zones. From optical thin sections of 20 samples deformation temperatures were estimated based on twin width and fluid inclusion data. These samples were subsequently used for optical measurements of twin density. Twin density varied between 10 and 100 [twins/mm] up to temperatures of 300° C. Using published <span class="hlt">calcite</span> piezometers (Rowe and Rutter 1990) we estimated paleostresses. From our experiments and field data we did not observe a clear relation between twin width and temperature up to 250° C. Above 250° C, temperatures estimated from <span class="hlt">calcite</span> twin widths in naturally deformed <span class="hlt">calcite</span> samples do correspond to temperatures estimated using other methods (e.g. fluid inclusion analysis, vitrinite reflection, conodont colour alteration index). Using the existing paleopiezometres, differential stresses inferred from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.B31D0624S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.B31D0624S"><span>New Origins of the Vital Effect in <span class="hlt">Calcites</span>: Mg-Enhancing Influence of Biomolecules</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stephenson, A. E.; Wu, L.; Wu, K. J.; Deyoreo, J. J.; Dove, P. M.</p> <p>2007-12-01</p> <p>Owing to the intense interest in the compositional signatures of biominerals, the mechanistic basis for vital effects and their roles in modifying or masking impurity contents are receiving increasing scrutiny. To date, much of the effort has been focused on the influence of physical environment and inorganic chemical factors. In a recent study that investigated the effects of acidic proteins on <span class="hlt">calcite</span> growth, our research group found that nanomolar concentratios of acidic amino acids, peptides, and full proteins accelerate the rate of mineral formation by a relationship that correlates with the acidity (hydrophilicity) of the biomolecule (Elhadj et al., 2006, PNAS). Experimental and theoretical evidence suggest that the measured rate-enhancing effect (up to 25X) arises from weak interactions of the biomolecule with the <span class="hlt">calcite</span> surface to alter the local solvation environment. This relation suggests that the acidic macromolecules that have been isolated from diverse calcifying taxa may have yet unrecognized effects on mineralization. Because Mg has a strong hydration shell relative to Ca, we hypothesized that the presence of these rate-modifying peptides in growt