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  • 1
    ISSN: 1432-1130
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Mercury (Hg) pyrolysis techniques allow the differentation of Hg-binding forms in contaminated soils and sediments. However, data about reproducibility and accuracy of the results concerning quantification of single Hg-compounds and total Hg-concentrations are rare. Therefore the total mercury concentration of different contaminated soils and sediments determined by using a pyrolysis technique were compared to those obtained after aqua regia digestion and cold vapor atomic absorption spectroscopy Hg detection. Twenty replicates of four soil and two sediment samples containing different Hg-compounds were investigated by both methods. All samples were analyzed without any pretreatment. For most of the samples total Hg-concentrations determined by pyrolysis show lower values, and up to threefold higher relative standard deviation(s) (RSD) than those obtained after wet digestion. Soil samples containing specified Hg-compounds like metallic Hg (Hg0) or cinnabar (α-HgS) show by far higher RSD by means of both methods than samples containing only matrix-bound Hg-compounds. Single peak integration indicate that the distribution of Hg0 and cinnabar is usually heterogeneous resulting in RSD of up to 85%, whereas RSD of matrix-bound Hg-compounds were always distinctly lower. Besides the higher standard deviation the pyrolysis technique has been found to be reliable for screening contaminated soils and sediments due to the important additional information about occurring Hg-binding forms.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2018-11-07
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 3
    Publication Date: 2015-01-05
    Description: Specimens of the patellogastropod limpet Patella caerulea were collected within (pHlow-shells) and outside (pHn-shells) a CO2 vent site at Ischia, Italy. Four pHlow-shells and four pHn-shells were sectioned transversally and scanned for polymorph distribution by means of confocal Raman microscopy. The pHlow-shells displayed a twofold increase in aragonite area fraction and size-normalised aragonite area. Size-normalised calcite area was halved in pHlow-shells. Taken together with the increased apical and the decreased flank size-normalised thickness of the pHlow-shells, these data led us to conclude that low-pH-exposed P. caerulea specimens counteract shell dissolution by enhanced shell production. This is different from normal elongation growth and proceeds through addition of aragonitic parts only, while the production of calcitic parts is confined to elongation growth. Therefore, aragonite cannot be regarded as a disadvantageous polymorph per se under ocean acidification conditions.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2019-03-26
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 5
    Publication Date: 2012-11-12
    Description: Marine biogenic carbonates formed by invertebrates (e.g. corals and mollusks) represent complex composites of one or more mineral phases and organic molecules. This complexity ranges from the macroscopic structures observed with the naked eye down to sub micrometric structures only revealed by micro analytical techniques. Understanding to what extent and how organisms can control the formation of these structures requires that the mineral and organic phases can be identified and their spatial distribution related. Here we demonstrate the capability of confocal Raman microscopy applied to cross sections of a shell of Nerita undata to describe the distribution of calcite and aragonite including their crystallographic orientation with high lateral resolution (~300 nm). Moreover, spatial distribution of functional groups of organic compounds can be simultaneously acquired, allowing to specifically relate them to the observed microstructures. The data presented in this case study highlights the possible new contributions of this method to the description of modalities of Nerita undata shell formation, and what could be expected of its application to other marine biogenic carbonates. Localization of areas of interest would also allow further investigations using more localized methods, such as TEM that would provide complementary information on the relation between organic molecules and crystal lattice.
    Type: Article , PeerReviewed
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  • 6
    Publication Date: 2018-03-01
    Description: [1] Recently, calcium isotope fractionation in the coccolithophore Emiliania huxleyi was shown to exhibit a significant temperature dependency. An important subsequent question in this context is whether the observed fractionation patterns are caused by temperature itself or related growth rate changes. In order to separate growth and calcification rate effects from direct temperature effects, batch culture experiments with the coccolithophore E. huxleyi were conducted under varying light intensities. Despite large changes in cellular growth and calcification rates, calcium isotope fractionation remained constant. Independence of calcium isotope fractionation on growth and calcification was also obtained in two additional sets of experiments in which growth rates changed in response to varying calcium concentration and seawater salinity. These experiments also showed no direct effects of calcium concentration and salinity on calcium isotope fractionation. Values for calcium isotope fractionation of E. huxleyi coccoliths fell within a range of −1.0 to −1.6 (1000 lnα), confirming earlier results. This range is similar to that observed in several foraminiferal species and coccolith oozes, suggesting a rather homogeneous calcium isotopic composition in marine biogenic calcite. Our data further show that the calcium isotope fractionation does not change with changing isotopic composition of seawater. This is a basic requirement for reconstructing the calcium isotopic composition of the ocean over time.
    Type: Article , PeerReviewed
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  • 7
    Publication Date: 2016-01-08
    Description: [1] We report measurements of pH, total alkalinity, air-ice CO2 fluxes (chamber method), and CaCO3 content of frost flowers (FF) and thin landfast sea ice. As the temperature decreases, concentration of solutes in the brine skim increases. Along this gradual concentration process, some salts reach their solubility threshold and start precipitating. The precipitation of ikaite (CaCO3.6H2O) was confirmed in the FF and throughout the ice by Raman spectroscopy and X-ray analysis. The amount of ikaite precipitated was estimated to be 25 µmol kg−1 melted FF, in the FF and is shown to decrease from 19 to 15 µmol kg−1 melted ice in the upper part and at the bottom of the ice, respectively. CO2 release due to precipitation of CaCO3 is estimated to be 50 µmol kg−1 melted samples. The dissolved inorganic carbon (DIC) normalized to a salinity of 10 exhibits significant depletion in the upper layer of the ice and in the FF. This DIC loss is estimated to be 2069 µmol kg−1 melted sample and corresponds to a CO2 release from the ice to the atmosphere ranging from 20 to 40 mmol m−2 d−1. This estimate is consistent with flux measurements of air-ice CO2 exchange. Our measurements confirm previous laboratory findings that growing young sea ice acts as a source of CO2 to the atmosphere. CaCO3 precipitation during early ice growth appears to promote the release of CO2 to the atmosphere; however, its contribution to the overall release by newly formed ice is most likely minor.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
    Publication Date: 2015-04-13
    Description: Abstract. Mg= Ca ratios in foraminiferal tests are routinely used as paleotemperature proxies, but on long timescales, they also hold the potential to reconstruct past seawater Mg= Ca. The impact of both temperature and seawater Mg= Ca on Mg incorporation in Foraminifera has been quantified by a number of studies. The underlying mechanism responsible for Mg incorporation in foraminiferal calcite and its sensitivity to environmental conditions, however, has not been fully identified. A recently published biomineralization model (Nehrke et al., 2013) proposes a combination of transmembrane transport and seawater leakage or vacuolization to link calcite Mg= Ca to seawater Mg= Ca and explains interspecies variability in Mg= Ca ratios. To test the assumptions of this model, we conducted a culture study in which seawater Mg= Ca was manipulated by varying [Ca2C] and keeping [Mg2C] constant. Foraminiferal growth rates, test thickness and calcite Mg= Ca of newly formed chambers were analyzed. Results showed optimum growth rates and test thickness at Mg= Ca closest to that of ambient seawater. Calcite Mg= Ca is positively correlated to seawater Mg= Ca, indicating that it is not absolute seawater [Ca2C] and [Mg2C] but their ratio that controls Mg= Ca in tests. These results demonstrate that the calcification process cannot be based only on seawater vacuolization, supporting the mixing model proposed by Nehrke et al. (2013). Here, however, we suggest transmembrane transport fractionation that is not as strong as suggested by Nehrke et al. (2013).
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 9
    Publication Date: 2015-03-18
    Description: A number of studies have shown that the boron isotopic composition (δ11B) and the B / Ca ratio of biogenic carbonates (mostly foraminifers) can serve as proxies for two parameters of the ocean's carbonate chemistry, rendering it possible to calculate the entire carbonate system. However, the B incorporation mechanism into marine carbonates is still not fully understood and analyses of field samples show species-specific and hydrographic effects on the B proxies complicating their application. Identifying the carbonate system parameter influencing boron incorporation is difficult due to the co-variation of pH, CO32- and B(OH)4-. To shed light on the question which parameter of the carbonate system is related to the boron incorporation, we performed culture experiments with the benthic symbiont-bearing foraminifer Amphistegina lessonii using a decoupled pH–CO32- chemistry. The determination of the δ11B and B / Ca ratios was performed simultaneously by means of a new in situ technique combining optical emission spectroscopy and laser ablation MC-ICP-MS. The boron isotopic composition in the tests gets heavier with increasing pH and B / Ca increases with increasing B(OH)4- / HCO3- of the culture media. The latter indicates that boron uptake of A. lessonii features a competition between B(OH)4- and HCO3-. Furthermore, the simultaneous determination of B / Ca and δ11B on single specimens allows for assessing the relative variability of these parameters. Among different treatments the B / Ca shows an increasing variability with increasing boron concentration in the test whereas the variability in the isotope distribution is constant.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 10
    Publication Date: 2019-07-09
    Description: Confocal Raman microscopy (CRM) mapping was used to investigate the microstructural arrangement and organic matrix distribution within the skeleton of the coral Porites lutea. Relative changes in the crystallographic orientation of crystals within the fibrous fan-system could be mapped, without the need to prepare thin sections, as required if this information is obtained by polarized light microscopy. Simultaneously, incremental growth lines can be visualized without the necessity of etching and hence alteration of sample surface. Using these methods two types of growth lines could be identified: one corresponds to the well-known incremental growth layers, whereas the second type of growth lines resemble denticle finger-like structures (most likely traces of former spines or skeletal surfaces). We hypothesize that these lines represent the outer skeletal surface before another growth cycle of elongation, infilling and thickening of skeletal areas continues. We show that CRM mapping with high spatial resolution can significantly improve our understanding of the micro-structural arrangement and growth patterns in coral skeletons.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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