Global change and marine geology: Introduction     

Gerold Wefer  Wolfgang H. Berger 《International Journal of Earth Sciences》1996,85(3):399-400

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Activity-composition relationship in Tschermak's substituted Fe biotites at 700°C, 2 kbar     

Artur Benisek  E. Dachs  Günther Redhammer  Gerold Tippelt  Georg Amthauer 《Contributions to Mineralogy and Petrology》1996,125(1):85-99

The reaction-displacement technique was applied to the end-member reaction annite = sanidine + magnetite + H₂ in order to determine the activity of the annite component (a _Ann) in iron biotites with variable degrees of the Tschermak's substitution (^[6]Fe + ^[4]Si = ^[6]Al + ^[4]Al). Based on the simplified relation a _Ann = f _{H 2}/foH₂ (foH₂ = hydrogen fugacity of the end-member reaction at P, T), two types of experiments were performed at 700°C / 2 kbar: Type I used Fe-Al biotites of known starting composition together with sanidine + magnetite + H₂O. This assemblage was exposed to various f _{H 2} conditions (f _{H 2} < foH₂) produced in the pressure vessel either by using different ratios of water/oil as pressure medium (f _{H 2} in this case was measured by the hydrogen sensor technique), or by the Ni′NiO buffer. The composition of the Fe-Al biotites changed through incorporation or release of the annite component in response to the externally imposed f _{H 2}. By using opposite biotite starting compositions, the equilibrium composition as a function of f _H2 was bracketed. For type II, f _{H 2} in equilibrium with a specific combination of fine-grained Fe-Al biotite (+ sanidine + magnetite + H₂O) was measured internally by application of the hydrogen sensor technique. Both type I and type II experiments yield consistent results demonstrating that a fine-grained assemblage of Fe-Al biotite (+ sanidine + magnetite + H₂O) is able to act as a sliding-scale buffer. The final chemical composition of the Fe-Al biotite after the experiments was determined by electron microprobe and Mössbauer spectroscopy. The ^[4]Al and ^[6]Al in the biotites are coupled according to the Tschermak's substitution. In the tetrahedral sheet 0.1 Al-atoms per formula unit are present in excess to the amount required to balance ^[6]Al, and all Fe-Al biotites contain 8–10% Fe³⁺. Therefore, they are not members of the pure annite - siderophyllite join, but have an almost constant amount (15 Mol%) of two additional Fe³⁺-bearing components (ferri-siderophyllite and a vacancy end-member). The volume - composition relationship obtained does not indicate excess molar volumes of mixing for the annite (Ann) - siderophyllite (Sid) binary. The data are consistent with a molar volume of annite of 15.46 ± 0.02 Jbar^–1 and of 15.06 ± 0.02 Jbar^–1 for siderophyllite. The experimentally determined activity - composition relation shows that biotites on the join annite - siderophyllite deviate negatively from ideality. A symmetric interaction parameter W_AnnSid is sufficient to represent the data within error. This was constrained as: W _AnnSid = –29 ± 4 kJmol^–1. This is in contradiction to empirical interaction parameters derived from natural assemblages for this binary that predict positive deviation from ideality. Reasons for this discrepancy are discussed.  相似文献   

Characterizing rainfall‐runoff signatures from micro‐catchments with contrasting land cover characteristics in southern Amazonia          下载免费PDF全文

Alphonce C. Guzha  Rodolfo L. B. Nobrega  Kristof Kovacs  Jessica Rebola‐Lichtenberg  Ricardo S. S. Amorim  Gerhard Gerold 《水文研究》2015,29(4):508-521

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The (Na,Li)FeGe2O6 clinopyroxene-type series: a temperature-dependent single-crystal X-ray diffraction and 57Fe Mössbauer spectroscopic study     

Günther J. Redhammer  Gerold Tippelt 《Physics and Chemistry of Minerals》2016,43(1):1-22

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Evidence for a warm interstellar medium in the Fornax dwarf ellipticals FCC046 and FCC207     

S. De Rijcke  †  W. W. Zeilinger  H. Dejonghe  G. K. T. Hau 《Monthly notices of the Royal Astronomical Society》2003,339(1):225-234

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UV and optical spectral properties in early-type galaxies     

Stefan J. Kautsch  Werner W. Zeilinger 《Astrophysics and Space Science》2003,284(2):929-932

We investigate UV and optical spectra of a sample of nearby early-type galaxies with evidence of nuclear line emission. The spectral signatures of various contributors to the UV, such as the interstellar medium and various stellar populations are analyzed and compared with the optical spectral properties. We discuss the impact of these effects on the observational properties of galaxy evolution. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Evidence for a warm interstellar medium in Fornax dwarf elliptical galaxies – II. FCC032, FCC206 and FCCB729     

D. Michielsen  S. De Rijcke †  W. W. Zeilinger  P. Prugniel  H. Dejonghe  S. Roberts 《Monthly notices of the Royal Astronomical Society》2004,353(4):1293-1303

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Tracing the evolution of nearby early-type galaxies in low density environments. The ultraviolet view from <Emphasis Type="Italic">GALEX</Emphasis>     

R. Rampazzo  F. Annibali  A. Marino  L. Bianchi  A. Bressan  L. M. Buson  M. Clemens  P. Panuzzo  W. W. Zeilinger 《Astrophysics and Space Science》2011,335(1):201-206

We detected recent star formation in nearby early-type galaxies located in low density environments, with GALEX Ultraviolet (UV) imaging. Signatures of star formation may be present in the nucleus and in outer rings/arm like structures. Our study suggests that such star formation may be induced by different triggering mechanisms, such as the inner secular evolution driven by bars, and minor accretion phenomena. We investigate the nature of the (FUV-NUV) color vs. Mg₂ correlation, and suggest that it relates to “downsizing” in galaxy formation.  相似文献   

<Superscript>57</Superscript>Fe Mössbauer spectroscopy,X-ray single-crystal diffractometry,and electronic structure calculations on natural sinhalites     

Sven-Ulf Weber  Michael Grodzicki  Werner Lottermoser  Günther J. Redhammer  Dan Topa  Gerold Tippelt  Georg Amthauer 《Physics and Chemistry of Minerals》2009,36(5):259-269

Natural sinhalites, MgAlBO_4, from the Ratnapura District, Sri Lanka, and from Bodnar Quarry near Hamburg, Sussex Co., New Jersey, USA, have been characterized by ⁵⁷Fe Mössbauer spectroscopy, electron microprobe, X-ray single-crystal diffractometry and by electronic structure calculations in order to determine the oxidation state and site occupancy of iron in the sinhalite structure. The samples contain about 3.35 and 1.46 wt% of total iron oxide, respectively. The structure refinement is successful and reproduces the total iron content provided that the substitution of Mg²⁺ by Fe²⁺ on the M2 position only is assumed. The ⁵⁷Fe Mössbauer spectra at 77, 293, 573 and 773 K can be resolved into two doublets with hyperfine parameters common for octahedrally coordinated high-spin Fe²⁺. There is no evidence for iron in the tetrahedral site. Electronic structure calculations in local spin density approximation yield hyperfine parameters for Fe²⁺ on the M2-site at 0, 293, 573 and 773 K in quantitative agreement with experiments. Calculated spectroscopic properties for Fe²⁺ on the M1-site are at variance with the experimental data and, thus, indicate that substitution of Al³⁺ by Fe²⁺, if occurring at all, must be accompanied by considerable local expansion and distortion of the M1-octahedron.  相似文献   

Invasion of anthropogenic CO<Subscript>2</Subscript> recorded in planktonic foraminifera from the northern Gulf of Aqaba     

Saber?Al-RousanEmail author  Jürgen?P?tzold  Salim?Al-Moghrabi  Gerold?Wefer 《International Journal of Earth Sciences》2004,93(6):1066-1076

The stable carbon isotopic composition of the planktonic foraminifera Globigerinoides sacculifer and G. ruber (white) and sedimentary organic matter from the northern Gulf of Aqaba have been investigated to estimate changes in ¹³C_DIC in surface waters during the last 1,000 years. The high sedimentation rates at the core sites (about 54 cm/Kyear) provide high temporal resolution (~10 years). Recent sediments at the top of the cores reflect conditions younger than 1950. The ¹³C records of the planktonic foraminifera from three multicores display similar trends, showing a uniform and consistent pattern before the 1750s, and a gradual decrease of approximately 0.63 over the last two centuries. This decrease seems to track the decrease of ¹³C_DIC in surface waters, which is mainly caused by the increase of anthropogenic input of ¹³C-depleted CO₂ into the atmosphere. Similarly, a trend towards lighter values of the carbon isotopic composition of sedimentary organic matter (¹³C_org) during the last 200 years supports the interpretation obtained from the planktonic foraminiferal ¹³C. Furthermore, direct measurements of seawater show that ¹³C of the dissolved inorganic carbon (DIC) in the northern Gulf of Aqaba has decreased by about 0.44 during the period 1979–2000. The average annual decrease is 0.021, which is similar to that observed globally. The ¹³C values of planktonic foraminifera combined with organic matter ¹³C from marine sediments are good indicators for reconstructing past changes in atmospheric CO₂ concentrations from the northern Gulf of Aqaba.  相似文献