Earth, F. Press, R. Siever (Eds.), Freeman, San Francisco,Calif. (1974), p. 945, £6.60     

E. Clausen 《Engineering Geology》1975,9(3):269-270

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Oxygen isotope and palaeotemperature records from six Greenland ice‐core stations: Camp Century,Dye‐3, GRIP,GISP2, Renland and NorthGRIP     

Sigfus J. Johnsen  Dorthe Dahl‐Jensen  Niels Gundestrup  Jrgen P. Steffensen  Henrik B. Clausen  Heinz Miller  Valerie Masson‐Delmotte  Arny E. Sveinbjrnsdottir  James White 《第四纪科学杂志》2001,16(4):299-307

Oxygen isotope variations spanning the last glacial cycle and the Holocene derived from ice‐core records for six sites in Greenland (Camp Century, Dye‐3, GRIP, GISP2, Renland and NorthGRIP) show strong similarities. This suggests that the dominant influence on oxygen isotope variations reflected in the ice‐sheet records was regional climatic change. Differences in detail between the records probably reflect the effects of basal deformation in the ice as well as geographical gradients in atmospheric isotope ratios. Palaeotemperature estimates have been obtained from the records using three approaches: (i) inferences based on the measured relationship between mean annual δ¹⁸O of snow and of mean annual surface temperature over Greenland; (ii) modelled inversion of the borehole temperature profile constrained either by the dated isotopic profile, or (iii) by using Monte Carlo simulation techniques. The third of these approaches was adopted to reconstruct Holocene temperature variations for the Dye 3 and GRIP temperature profiles, which yields remarkably compatible results. A new record of Holocene isotope variations obtained from the NorthGRIP ice‐core matches the GRIP short‐term isotope record, and also shows similar long‐term trends to the Dye‐3 and GRIP inverted temperature data. The NorthGRIP isotope record reflects: (i) a generally stronger isotopic signal than is found in the GRIP record; (ii) several short‐lived temperature fluctuations during the first 1500 yr of the Holocene; (iii) a marked cold event at ca. 8.2 ka (the ‘8.2 ka event’); (iv) optimum temperatures for the Holocene between ca. 8.6 and 4.3 ka, a signal that is 0.6‰ stronger than for the GRIP profile; (v) a clear signal for the Little Ice Age; and (vi) a clear signal of climate warming during the last century. These data suggest that the NorthGRIP stable isotope record responded in a sensitive manner to temperature fluctuations during the Holocene. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Amino acid biogeo- and stereochemistry in coastal Chilean sediments   总被引：1，自引：0，他引：1  

Bente Aa. Lomstein  Bo B. Jørgensen  Jutta Niggemann 《Geochimica et cosmochimica acta》2006,70(12):2970-2989

The spatial distribution of total hydrolysable amino acids (THAA) and amino acid enantiomers (d- and l-forms) was investigated in sediments underlying two contrasting Chilean upwelling regions: at ∼23 °S off Antofagasta and at ∼36 °S off Concepción. The contribution of amino acids to total organic carbon (%T_AAC: 7-14%) and total nitrogen (%T_AAN: 23-38%) in surface sediments decreased with increasing water depth (from 126 to 1350 m) indicating that organic matter becomes increasingly decomposed in surface sediments at greater water depth. Changes in the ratio between the protein amino acid aspartate and its non-protein degradation product β-alanine confirmed this observation. Furthermore, estimates of THAA mineralization showed that sedimentary amino acid reactivity decreased with both increasing water depth as well as progressive degradation status of the organic matter that was incorporated into the sediment. Reactivity of organic matter in the sediment was also assessed using the Degradation Index (DI) developed by [Dauwe, B., Middelburg, J.J., 1998. Amino acids and hexosamines as indicators of organic matter degradation state in North Sea sediments. Limnol. Oceanogr.43, pp. 782-798.]. Off Concepción, DI was successfully applied to examine the degradation status of sedimentary organic matter at different water depths. However, unexpected results were obtained at the Antofagasta stations as DI increased with sediment depth, suggesting more degraded organic matter at the surface than deeper in the cores. The contribution of peptidoglycan amino acids to THAA was estimated from the concentrations of d-aspartate, d-glutamic acid, d-serine, and d-alanine. Peptidoglycan amino acids accounted for >18% of THAA in all investigated samples. In surface sediments peptidoglycan amino acids accounted for a progressively larger fraction of THAA at increasing water depths (up to >26%). Further, the contribution of peptidoglycan amino acids to THAA increased with increased sediment depth and age (up to 288-year-old) reaching up to 59%. Independent estimates based on d-amino acid concentrations in selected laboratory strains, bacterial counts and the sedimentary concentrations of d-amino acids indicate that a large fraction of the measured d-amino acids (>47 to >97%) originated from cell wall residues rather than from enumerated cells.  相似文献   

Characterization of synthetic hedenbergite (CaFeSi<Subscript>2</Subscript>O<Subscript>6</Subscript>)–petedunnite (CaZnSi<Subscript>2</Subscript>O<Subscript>6</Subscript>) solid solution series by X-ray powder diffraction and <Superscript>57</Superscript>Fe Mössbauer spectroscopy     

A. L.?Huber  M.?Heuer  K. T.?FehrEmail author  K.?Bente  E.?Schmidbauer  G. D.?Bromiley 《Physics and Chemistry of Minerals》2004,31(2):67-79

Clinopyroxenes along the solid solution series hedenbergite (CaFeSi₂O₆)–petedunnite (CaZnSi₂O₆) were synthesized under hydrothermal conditions and different oxygen fugacities at temperatures of 700 to 1200 °C and pressures of 0.2 to 2.5 GPa. Properties were determined by means of X-ray diffraction, electron microprobe analysis and ⁵⁷Fe Mössbauer spectroscopy at 298 K. Unit-cell parameters display a linear dependency with changing composition. Parameters a₀ and b₀ exhibit a linear decrease with increasing Zn content while the monoclinic angle increases linearly. Parameter c₀ is not affected by composition and remains constant at a value of 5.248 Å. The molar volume can be described according to the equation V_mol (ccm mol^–1)=33.963(16)–0.544(31)*Zn pfu. The isomer shifts of ferrous iron on the octahedral M1 site in hedenbergite are not affected by composition along the hedenbergite–petedunnite solid solution series and remain constant at an average value of 1.18 mm s^–1. Quadrupole splittings of Fe²⁺ on the M1 are, however, strongly affected by composition, and they decrease linearly with increasing petedunnite component in hedenbergite, ranging from 2.25 mm s^–1 for pure hedenbergite end member to 1.99 mm s^–1 for a solid solution containing 84 mole% petedunnite. The half-widths of intermediate solid solutions vary between 0.26 and 0.33 mm s^–1, indicating, in accordance with the microprobe analyses and X-ray diffraction, that samples are homogeneous and well-crystallized. The data from this study demonstrate that the crystallinity of hedenbergitic clinopyroxenes can be improved by using oxide mixtures as starting materials. Crystal sizes for intermediate compositions range up to 70 m, suitable for standard single-crystal X-ray analysis.This paper is dedicated to Prof. Dr. Georg Amthauer, Salzburg, on occasion of his 60th birthday  相似文献   

Groundwater-dependent ecology of the shoreline of the subtropical Lake St Lucia estuary   总被引：1，自引：0，他引：1  

Ricky Taylor  Bruce Kelbe  Sylvi Haldorsen  Greg A. Botha  Bente Wejden  Lars Været  Marianne B. Simonsen 《Environmental Geology》2006,49(4):586-600

The ecology of the St Lucia estuary in South Africa is of unique international importance. During droughts the estuary experiences high salinities, with values above that of seawater. Ion-poor groundwater flowing into the estuary from prominent sand aquifers along its eastern shoreline forms low-salinity habitats for salt-sensitive biota. During droughts, plants and animals can take refuge in the groundwater discharge zone until the condition in the estuary regains tolerable salinity. Simulations of the groundwater discharge indicate that the flow can persist during droughts over at least a decade, and be of great important for the resilience of the estuary. Anthropogenic activities have reduced the river inflow and made the St Lucia estuary more sensitive to droughts. The groundwater has thereby become increasingly important for the estuary’s ecology. Protection of the groundwater discharge along the shoreline itself and actions to increase the groundwater recharge are therefore important management tasks.  相似文献   

Tertiary tectonic evolution along the Arne-Elin Trend in the Danish Central Trough     

Ole Rn Clausen  John A. Korstgrd 《地学学报》1993,5(3):233-243

Tertiary sequence boundaries are mapped on reflection seismic sections in the northern part of the Danish Central Trough, North Sea. The geometry of the sequence boundaries and the isopach maps of the sequences are used as indicators of differential subsidence. The Tertiary tectonic evolution is subdivided into: (i) Late Palaeocene and Early Oligocene episodes of inversion along the NNW–SSE striking Arne–Elin Trend (ii) Early Oligocene to Pliocene episodes of differential subsidence across pre-Tertiary fault trends. The observed differential subsidence and inversion is related to pre-Tertiary faults and fault trends, and dating of the sequences shows that the tectonic phases were contemporaneous with tectonic events in NW Europe. It is suggested that the differential subsidence-inversion is controlled by reactivation of pre-Tertiary faults/fault-trends by block movements due to an interaction of the Alpine collision and the opening of the Atlantic.  相似文献   

Morphology and origin of major Cenozoic sequence boundaries in the eastern North Sea Basin: top Eocene,near‐top Oligocene and the mid‐Miocene unconformity     

M. Huuse  O. R. Clausen 《Basin Research》2001,13(1):17-41

Unconformities in sedimentary successions (i.e. sequence boundaries) form in response to the interplay between a variety of factors such as eustasy, climate, tectonics and basin physiography. Unravelling the origin of sequence boundaries is thus one of the most pertinent questions in the analysis of sedimentary basins. We address this question by focusing on three of the most marked physical discontinuities (sequence boundaries) in the Cenozoic North Sea Basin: top Eocene, near‐top Oligocene and the mid‐Miocene unconformity. The Eocene/Oligocene transition is characterized by an abrupt increase in sediment supply from southern Norway and by minor erosion of the basin floor. The near‐top Oligocene and the mid‐Miocene unconformity are characterized by major changes in sediment input directions and by widespread erosion along their clinoform breakpoints. The mid‐Miocene shift in input direction was followed by a marked increase in sediment supply to the southern and central North Sea Basin. Correlation with global δ¹⁸O records suggests that top Eocene correlates with a major long‐term δ¹⁸O increase (inferred climatic cooling and eustatic fall). Near‐top Oligocene does not correlate with any major δ¹⁸O events, while the mid‐Miocene unconformity correlates with a gradual decrease followed by a major long‐term increase in δ¹⁸O values The abrupt increases in sediment supply in post‐Eocene and post‐middle Miocene time correlate with similar changes worldwide and with major δ¹⁸O increases, suggesting a global control (i.e. climate and eustasy) of the post‐Eocene sedimentation in the North Sea Basin. Erosional features observed at near‐top Oligocene and at the mid‐Miocene unconformity are parallel to the clinoform breakpoints and resemble scarps formed by mass wasting. Incised valleys have not been observed, indicating that sea level never fell significantly below the clinoform breakpoint during the Oligocene to middle Miocene.  相似文献   

50,000 YEARS OF RECORDED GLOBAL VOLCANISM     

C. U. Hammer  H. B. Clausen  C. C. Langway Jr. 《Climatic change》1997,35(1):1-15

The 2191 m long ice core recovered at Byrd Station Antarctica in 1968 (BS68) was measured continuously by an electrical conductivity method (ECM). The ECM curve inferes the acidity of seasonal ice layers and major peaks, which identify clearly intermediate and prominent past volcanic activity over the last 50,000 years. We here also present recent data for a suite of the most striking volcanic events that occurred around 17.5 ka ± 0.5 BP. These events emitted enormous amounts of HCl and HF into the atmosphere.  相似文献   

Stabilization of Cu-Fe-Bi-Pb-Sn-sulfides     

Prof. Dr. K. Bente 《Mineralogy and Petrology》1987,36(3-4):205-217

Summary Three stabilization phenomena, 1: special e.g. hydrothermal conditions, 2: stabilization by replacements of ions, as e.g. Cu and Fe and 3: heterogeneous nucleation as, e.g., by epitaxy are tested for phases in the system Cu₂S-CuS₂-Bi₂S₃-FeS-FeS₂. Hydrothermal solution and precipitation conditions can metastabilize or stabilize phases, which are not existent under dry conditions as Cu₄Bi₅S₁₀ or CuS₂-FeS₂ mixed crystals, but are stable at high pressures. Stabilization by Cu-Fe substitution leads to the assumption that stabilization basically depends on the ionic radii similarity, but necessarily electronic interactions have to be involved. Stabilization by heterogeneous nucleation is tested for Pb-Bi sulfosalts, e.g. for the epitaxial growth of Bi₂S₃ on NaCl. In contrast to the normal orthorhombic Bi2S3, the epitaxial Bi₂S₃ shows a pseudotetragonal subcell correlated to NaCl. Satellite reflections indicate a modulation probably caused by a modulation of the metal vacancies.

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Stabilisterung von Cu-Fe-Bi-Pb-Sn-Sulfiden

Zusammenfassung Im System Cu₂S-CuS₂-Bi₂S₃-FeS-FeS₂ werden drei Stabilisierungsphänomene 1: spezielle Stabilisierungsbedingungen z. B. in hydrothermalen Lösungen, 2: Stabilisierungen durch Elemente- bzw. Ionenersatz am Beispiel von Cu und Fe und 3: heterogene Keimbildung anhand von Epitaxieversuchen verifiziert.Hydrothermale Ausscheidungsbedingungen können metastabile oder stabile Phasen bedingen, die z. B. unter trockenen Bedingungen nicht oder nur bei hohen Drucken stabil sind. Dies gilt z. B. für den Cu-Fe-Ersatz in Cu₄Bi₅S₁₀ bzw. für CUS₂-FeS₂ Mischkristalle. Die Stabilisierung durch Cu-Fe-Substitution führt zu der Annahme, daß hierfür als notwendige Voraussetzung die Ähnlichkeit der Ionenradien gilt, jedoch als hinreichende Bedingung die elektronische Wechselwirkung zwischen den sich ersetzenden Ionen anzusehen ist.Die Stabilisierung durch heterogene Keimbildung wird für Pb-Bi-Sulfosalze am Beispiel der Epitaxie von Bi₂S₃ auf NaCI getestet. Im Gegensatz zum normalen orthorhombischen Bi₂S₃ zeigt die epitaktische Phase eine mit NaCl korrelierte tetragonale Subzelle. Satellitenreflexe deuten auf eine Modulation der Leerstellen der Metallionen hin.

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With 10 Figures

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Contribution to the Ore Mineralogy Symposium (IMA/COM) at the 14th General Meeting of the International Mineralogical Association, at Stanford, California, in July, 1986.  相似文献   

Past volcanism and climate revealed by Greenland ice cores     

C. U. Hammer  H. B. Clausen  W. Dansgaard 《Journal of Volcanology and Geothermal Research》1981,11(1):3-10

A new method is outlined for estimating the annual injection of volcanic acids (mainly sulphuric) into the upper troposphere and the stratosphere. The potentiality of the method is demonstrated by data on a number of historically well-known eruptions. Analyses of annual layers in a mid-Greenland ice core reveal a continuous year-by-year record of the volcanic activity north of 20°S back to A.D. 553. Comparison with various climatic records suggests that periods of frequent and violent eruptions usually coincide with cold climatic conditions. For example, the highest volcanic activities since A.D. 553 occurred in A.D. 1250–1500 and A.D. 1550–1700, i.e. in the initial and the culminating phases of “the Little Ice Age”.  相似文献