ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

feed icon rss

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Other Sources  (10)
  • 2015-2019  (8)
  • 1960-1964  (2)
  • 1930-1934
Collection
Years
Year
  • 1
    Publication Date: 2019-03-04
    Description: The boron isotope (δ11B) composition of marine calcifiers is considered to be one of the most reliable pH proxies, enabling us to reconstruct past ocean pH and infer on the associated changes in carbon budget involved (e.g. Gut- jahr et al. 2017). The application of the commonly used δ 11 B archives such as foraminifera or corals is however mostly limited to the Cenozoic due to insufficient preservation or incomplete geological records. Brachiopods have a promising potential for extending our knowledge on seawater pH evolution throughout the entire Phanerozoic considering their high abundance in the fossil record and its origin dating back to the early Cambrian. Moreover, their shell is composed of low-magnesium calcite, rendering brachiopods more resistant to post-depositional di-magenetic alteration of its primary chemical signal (e.g. Brand et al. 2012). Additionally, even today they present an extant and widespread taxa, allowing for an assessment of the controls on boron isotope incorporation into brachiopod calcite and possible distortions of the signal due to vital effects or other processes. We present a detailed exploration of boron isotope systematics in three different brachiopod species (Magellania venosa, Terebratella dorsata, Pajaudina atlantica) cultured under controlled laboratory settings for over a year. Our experimental setup includes a control (pH = 8.15) and two pH treatments (pH = 7.6 and 7.35), and we provide both bulk MC-ICP-MS as well as high spatial resolution SIMS data of the shell material. Our results indicate that boron incorporation is primarily driven by vital effects related to their ability to regulate calcifying fluid pH in response to ambient changes, which we further validate by in vivo microelectrode measurements (e.g. Stumpp et al. 2012). Despite internal buffering, the local pH at calcification sites systematically decreases with seawater pH, and hence is impacted by ocean acidification. This not only suggests that brachiopod shells serve as useful and conservative recorders of past ocean pH trends, but also provides new insights into mechanisms that may have enabled brachiopod survival throughout several major environmental crises in the past. Our findings have implications for past climate studies, as well as research on calcification processes and physio- logical adaptations to environmental change (e.g. the actual global ocean acidification). Brand, U., Posenato, R., Came, R., Affek, H., Angiolini, L., Azmy, K. and Farabegoli, E., 2012. The end-Permian mass extinction: A rapid volcanic CO2 and CH4-climatic catastrophe, Chem. Geol. 323, 121-144. Gutjahr M., Ridgewell A., Sexton P.F., Anagnostou E., Pearson P.N., Pälike H., Norris R.D., Thomas E., and Foster G.L., 2017. Very large release of mostly volcanic carbon during the Palaeocene-Eocene Thermal Maximum, Nature 548, 573-577. Stumpp M., Hu M.Y., Melzner F., Gutowska M., Dorey N., Himmerkus N., Holtmann W.C., Dupont S.T., Thorndyke M.C., and Bleich M. Acidified seawater impacts sea urchin larvae pH regulatory systems relevant for calcification, PNAS 44: 18192-18197.
    Type: Conference or Workshop Item , NonPeerReviewed
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    facet.materialart.
    Unknown
    In:  Other Sources
    Publication Date: 2019-01-01
    Description: Optical spectra and properties of radio galaxies
    Keywords: SPACE SCIENCES
    Format: text
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2019-05-11
    Description: Two-stage temperature stabilized circuit using two transistors is described. Increase in temperature causes the base-to-emitter voltage of n-p-n transistor to become less positive whereas the base-to-emitter voltage of p-n-p transistor becomes less negative, so the temperature-induced variation in V sub 1 and V sub 2 cancel out.
    Keywords: ELECTRONIC COMPONENTS AND CIRCUITS
    Type: MSC-20
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2019-07-13
    Description: The Mars rover Curiosity has encountered silica-enriched bedrock (as strata and as veins and associated halos of alteration) in the largely basaltic Murray Fm. of Mt. Sharp in Gale Crater. Alpha Particle X-ray Spectrometer (APXS) investigations of the Murray Fm. revealed decreasing Mg, Ca, Mn, Fe, and Al, and higher S, as silica increased (Fig. 1). A positive correlation between SiO2 and TiO2 (up to 74.4 and 1.7 wt %, respectively) suggests that these two insoluble elements were retained while acidic fluids leached more soluble elements. Other evidence also supports a silica-retaining, acidic alteration model for the Murray Fm., including low trace element abundances consistent with leaching, and the presence of opaline silica and jarosite determined by CheMin. Phosphate stability is a key component of this model because PO4 3- is typically soluble in acidic water and is likely a mobile ion in diagenetic fluids (pH less than 5). However, the Murray rocks are not leached of P; they have variable P2O5 (Fig. 1) ranging from average Mars (0.9 wt%) up to the highest values in Gale Crater (2.5 wt%). Here we evaluate APXS measurements of Murray Fm. bedrock and veins with respect to phosphate stability in acidic fluids as a test of the acidic alteration model for the Lower Mt. Sharp rocks.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-35224 , Lunar and Planetary Science Conference; 21-25 Mar. 2016; The Woodlands, TX; United States
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2019-07-13
    Description: Rocks enriched in Ge have been discovered in Gale Crater, Mars, by the Alpha-particle X-ray spectrometer (APXS) on the Mars Science Lab (MSL) rover, Curiosity. The Ge concentrations in Gale Crater (commonly 〉50 ppm) are remarkably high in comparison to Earth, where Ge ranges from 0.5-4.0 ppm in igneous rocks and 0.2-3.3 ppm in siliciclastic sediment. Primary meteoritic input is not likely the source of high Ge because Ge/Ni in chondrites (approx.0.003) and irons (〈0.04) is lower than in Gale rocks (0.08-0.2). Earth studies show Ge is a useful geochemical tracer because it is coherent with Si during magmatic processes and Ge/Si varies less than 20% in basalts. Ge and Si fractionate during soil/regolith weathering, with Ge preferentially sequestered in clays. Ge is also concentrated in Cu- and Zn-rich hydrothermal sulfide deposits and Fe- and Mnrich oxide deposits. Other fluid-mobile elements (K, Zn, Cl, Br, S) are also enriched at Gale and further constrain aqueous alteration processes. Here, we interpret the sediment alteration history and present a possible model for Ge enrichments at Gale involving fluid alteration of the protolith.
    Keywords: Geophysics
    Type: JSC-CN-32857 , Lunar and Planetary Science Conference; 16-20 Mar. 2015; The Woodlands, TX; United States
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2019-07-13
    Description: MSL Curiosity investigated the Windjana sandstone outcrop, in the Kimberley area of Gale Crater, and obtained mineralogical analyses with the CheMin XRD instrument. Windjana is remarkable in containing an abundance of potassium feldspar (and thus K in its bulk chemistry) combined with a low abundance of plagioclase (and low Na/K in its chemistry). The source of this enrichment in K is not clear, but has significant implications for the geology of Gale Crater and of Mars. The high K could be intrinsic to the sediment and imply that the sediment source area (Gale Crater rim) includes K-rich basalts and possibly more evolved rocks derived from alkaline magmas. Alternatively, the high K could be diagenetic and imply that the Gale Crater sediments were altered by K-rich aqueous fluids after deposition.
    Keywords: Geophysics
    Type: JSC-CN-32824 , Lunar and Planetary Science Conference; 16-20 Mar. 2015; The Woodlands, TX; United States
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2019-07-13
    Description: The Curiosity Rover landed in a lithologically and geochemically diverse region of Mars. We present a recommended rock classification framework based on terrestrial schemes, and adapted for the imaging and analytical capabilities of MSL as well as for rock types distinctive to Mars (e.g., high Fe sediments). After interpreting rock origin from textures, i.e., sedimentary (clastic, bedded), igneous (porphyritic, glassy), or unknown, the overall classification procedure (Fig 1) involves: (1) the characterization of rock type according to grain size and texture; (2) the assignment of geochemical modifiers according to Figs 3 and 4; and if applicable, in depth study of (3) mineralogy and (4) geologic/stratigraphic context. Sedimentary rock types are assigned by measuring grains in the best available resolution image (Table 1) and classifying according to the coarsest resolvable grains as conglomerate/breccia, (coarse, medium, or fine) sandstone, silt-stone, or mudstone. If grains are not resolvable in MAHLI images, grains in the rock are assumed to be silt sized or smaller than surface dust particles. Rocks with low color contrast contrast between grains (e.g., Dismal Lakes, sol 304) are classified according to minimum size of apparent grains from surface roughness or shadows outlining apparent grains. Igneous rocks are described as intrusive or extrusive depending on crystal size and fabric. Igneous textures may be described as granular, porphyritic, phaneritic, aphyric, or glassy depending on crystal size. Further descriptors may include terms such as vesicular or cumulate textures.
    Keywords: Geophysics
    Type: JSC-CN-32866 , Lunar and Planetary Science Conference; 16-20 Mar. 2015; The Woodlands, TX; United States
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2019-07-13
    Description: Sedimentary rocks in Gale Crater on Mars indicate a varied provenance with a range of alteration and weathering [1, 2]. Geochemical trends identified in basaltic and alkalic sedimentary rocks by the Alpha Particle X-ray Spectrometer (APXS) on the Mars rover Curiosity represent a complex interplay of igneous, sedimentary, weathering, and alteration processes. Assessing the relative importance of these processes is challenging with unknown compositions for parent sediment sources and with the constraints provided by Curiosity's instruments. We therefore look to Mars analogues on Earth where higher-resolution analyses and geologic context can constrain interpretations of Gale Crater geochemical observations. We selected Maunakea (AKA Mauna Kea) and Kohala volcanoes, Hawai'i, for an analogue study because they are capped by post-shield transitional basalts and alkalic lavas (hawaiites, mugearites) with compositions similar to Gale Crater [1, 3]. Our aim was to characterize Hawaiian geochemical trends associated with igneous processes, sediment transport, weathering, and alteration. Here, we present initial results and discuss implications for selected trends observed by APXS in Gale Crater.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-38843 , Lunar and Planetary Science Conference; 20-24 Mar. 2017; The Woodlands, TX; United States
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Publication Date: 2019-07-19
    Description: The Mars Science Laboratory rover Curiosity has traversed up section through approximately 100 m of sedimentary rocks deposited in fluvial, deltaic, lacustrine, and eolian environments (Bradbury group and overlying Mount Sharp group). The Stimson formation unconformably overlies a lacustrine mudstone at the base of the Mount Sharp group and has been interpreted to be a cross-bedded sandstone of lithified eolian dunes. Unaltered Stimson sandstone has a basaltic composition similar to the average Mars crustal composition, but is more variable and ranges to lower K and higher Al. Fluids passing through alteration "halos" adjacent to fractures have altered the chemistry and mineralogy of the sandstone. Elemental mass gains and losses in the alteration halos were quantified using immobile element concentrations, i.e., Ti (taus). Alteration halos have elemental gains in Si, Ca, S, and P and large losses in Al, Fe, Mn, Mg, Na, K, Ni, and Zn. Mineralogy of the altered Stimson is dominated by Ca-sulfates, Si-rich X-ray amorphous materials along with plagioclase feldspar, magnetite, and pyroxenes. The igneous phases were less abundant in the altered sandstone with a lower pyroxene/plagioclase feldspar. Large elemental losses suggest acidic fluids initially removed these elements (Al mobile under acid conditions). Enrichments in Si, Ca, and S suggest secondary fluids (possibly alkaline) passed through these fractures leaving behind X-ray amorphous Si and Ca-sulfates. The mechanism for the large elemental gains in P is unclear. The geochemistry and mineralogy of the altered sandstone suggests a complicated diagenetic history with multiple episodes of aqueous alteration under a variety of environmental conditions (e.g., acidic, alkaline).
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-CN-37384 , AGU Fall Meeting 2016; 12-16 Dec. 2016; San Francisco, CA; United States
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2019-07-30
    Description: Characterizing the history of aqueous activity at the martian surface has been an objective of the Mars Exploration Rovers (MER) and the Mars Science Laboratory (MSL). Although the geologic context of the three landing sites are different, comparisons across the datasets can provide greater insight than using data from one mission alone. The Alpha Particle X-ray Spectrometer (APXS) is common to all three rovers (Spirit at Gusev crater, Opportunity at Meridiani Planum, and Curiosity at Gale crater) and provides a consistent basis for these comparisons. Soil and Dust: Fine grained basaltic soils and dust are remarkably uniform in chemical composition across multiple landing sites. These similarities in the concentrations of major, minor, and a few trace elements (Fig. 1) are indicative of planet-wide consistency in the composition of source materials for the soils. S and Cl vary by a factor of two in the soil and dust, but there is no clear association with any bulk cation (e.g., no correlation between S and total Ca, Mg, or Fe in soils). These volatile elements, however, are clearly associated with the nanophase-ferric iron component in the soil established by Mssbauer spectroscopy [1,2]. S and Cl likely originated as acidic species from volcanic out-gassing and subsequently coalesced on dust and sand grain surfaces, possibly with an affinity towards Fe3+ sites. Importantly, given the mobility of S and Cl in aqueous exposures, soil samples maintaining the typical molar S/Cl ratio of ~3.7:1 indicate minimal interactions with liquid water after the addition of S and Cl. In contrast to this well-established baseline, soil samples have been discovered at all three landing sites with atypical S/Cl ratios (e.g., subsurface soils), indicative of a more complex aqueous history.
    Keywords: Lunar and Planetary Science and Exploration
    Type: JSC-E-DAA-TN70395 , International Conference on Mars; Jul 22, 2019 - Jul 25, 2019; Pasadena, CA; United States
    Format: application/pdf
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...