Evidence of Dry and Cold Climatic Conditions at Glacial Times in Tropical Southeastern Brazil     

Hermann Behling  Martin Lichte 《Quaternary Research》1997,48(3):348-358

Last-glacial paleoenvironments have been reconstructed from a pollen and charcoal record analyzed in organic sediments and dated between ca. 18,000 and >48,000¹⁴C yr B.P. The site is located near the village Catas Altas in the lower highland region of southeastern Brazil. The last-glacial landscape was covered by extensive areas of subtropical grasslands and small areas of gallery forests along the rivers, where tropical semideciduous forests and cerrado ecosystems exist today. The subtropical gallery forests were composed ofAraucariaforest trees such asAraucaria angustifolia, Podocarpus, Drimys, Ilex,andSymplocos.Paleofires were frequent. The record indicates that subtropical grassland vegetation, which today is found in patches on the highlands in southern Brazil (especially in the state of Santa Catarina), expanded from southern Brazil to southeastern Brazil, over a distance of more than 750 km, from latitudes of about 28° S to at least 20° S. The completely different last-glacial environment, in comparison to the present-day environment, reflects a dry and cold climate with strong frosts during the winter months. Temperatures of 5°–7°C below those of the present are inferred for the last glaciation.  相似文献   

Illite mineral synthesis at surface temperatures     

Hermann Harder 《Chemical Geology》1974,14(4):241-253

The synthesis of illite mixed-layer minerals at surface conditions is possible through precipitation of Al hydroxides from Si-, Mg- and K-containing solutions. It has been shown that amorphous hydroxides of Al, Fe, etc. are capable of coprecipitating silica even from very dilute solutions. By aging of these X-ray amorphous hydroxide—silica precipitates under certain conditions, clay minerals can be synthesized at low temperatures. The presence of Mg particularly favors the formation of three-layer clay minerals. Mg-rich Al hydroxide—silica precipitates permit formation of tri- and di-octahedral smectite, illite and chlorite. The formation of three-layer clay minerals is only possible when the precipitates contain at least 6% MgO. The precipitates stay amorphous if the Mg content is lower. The adsorption of Mg and K on the hydroxide—silica precipitate controls the illite or montmorillonite portion in the mixture of the three-layer silicates. There is a competition for K and Mg adsorption on the hydroxide—silica precipitates. Higher K concentration inhibits the three-layer mineral formation through the lowering of the Mg content in the precipitates. Illite mineral formation is favored under certain K/Mg ratios. Higher NaCl contents do not favor the three-layer mineral formation.The enrichment of Mg and K in the precipitates is not as large as the enrichment of Si in the hydroxides. This means that the illite mineral formation is only possible from solutions with a high-salt content like seawater.  相似文献   

Nontronite synthesis at low temperatures     

Hermann Harder 《Chemical Geology》1976,18(3):169-180

The low-temperature synthesis of clay minerals is possible through the aging of freshly prepared hydroxide—silica precipitates. The rapid synthesis of nontronite is only possible at surface temperatures under reducing conditions. Under oxidizing conditions, pure Fe(III)- or pure Al-smectite minerals could not be synthesized at low temperatures. It is only from Fe(II)-containing solutions that nontronite and lembergite, the di-[Fe(III)] and tri-[Fe(II)] octahedral three-layer silicates, are built up in several days at low temperatures. The presence of Fe(II) enables an octahedral layer of the brucite—gibbsite type to be formed. These are necessary for the bidimensional orientation of SiO₄ tetrahedrons, leading to clay-mineral formation. The Fe²⁺ and/or Mg²⁺ ions are necessary for the formation of the Al³⁺- and Fe³⁺-containing three-layer silicate minerals.Under reducing diagenetic conditions, the Fe contents in recent sediments are sufficient to build up Al-rich three-layer minerals under both fresh-water and salt-water conditions.  相似文献   

Applied and theoretical considerations for constructing spatially explicit individual-based models of marine larval fish that include multiple trophic levels   总被引：3，自引：2，他引：3  

Hermann  Albert J.; Hinckley  Sarah; Megrey  Bernard A.; Napp  Jeffrey M. 《ICES Journal of Marine Science》2001,58(5):1030-1041

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Chela-height vs. body-weight relationships for North Sea hermit crabs (Paguridae)     

Reiss  Henning; Neumann  Hermann; Kroncke  Ingrid 《ICES Journal of Marine Science》2005,62(4):723-726

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An energy tax to reduce the greenhouse effect: An all winners concept     

Wilfrid Bach  Hermann Scheer 《Climatic change》1990,16(3):iii-v

This is based on a concept worked out by EUROSOLAR, an Association for the Solar Energy Age, of which Hermann Scheer is chairman and Wilfrid Bach is a member of the board.  相似文献   

OH-bearing planar defects in olivine produced by the breakdown of Ti-rich humite minerals from Dabie Shan (China)   总被引：2，自引：0，他引：2  

Jörg Hermann  John D. Fitz Gerald  Nadia Malaspina  Andrew J. Berry  Marco Scambelluri 《Contributions to Mineralogy and Petrology》2007,153(4):417-428

The partial breakdown of Ti-chondrodite and Ti-clinohumite during exhumation from ultra-high pressure to amphibolite facies conditions in garnet-pyroxenites from Dabie Shan (China) produces coronas of olivine coexisting with ilmenite blebs. Fourier transform infrared (FTIR) spectra of this newly formed olivine exhibit absorption bands in the hydroxyl-stretching region. Two intense peaks were observed at 3,564 and 3,394 cm⁻¹, identical in energy to peaks in Ti-clinohumite. Transmission electron microscopy (TEM) of the same olivine domains revealed the presence of a complex (001) planar intergrowth. These interlayers have a 1.35 nm repeat distance, which is characteristic of clinohumite. Such interlayers are also enriched in Ti with respect to the adjacent olivine as shown by energy dispersive spectrometry. The combined evidence from FTIR spectroscopy and TEM indicates that OH is incorporated along Ti-clinohumite planar defects. This study provides evidence that the nominally anhydrous phase olivine may contain OH as a humite-type defect beyond the breakdown of the hydrous humite minerals and confirms earlier suggestions that Ti plays a key role in OH incorporation in mantle olivine. We suggest that olivine containing Ti-clinohumite defects is an important phase for water transport in subduction zones and for the storage of water in cold subcontinental mantle. However, these defects are unlikely to be stable in hotter parts of the oceanic mantle such as where basaltic magmas are generated.  相似文献   

The potential role of spectral properties in detecting thresholds in the Earth system: application to the thermohaline circulation   总被引：5，自引：0，他引：5  

Thomas Kleinen  Hermann Held  Gerhard Petschel-Held 《Ocean Dynamics》2003,53(2):53-63

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Ellsworth Huntington and his perspective on Central Asia. Great game experiences and their influence on development thought     

Hermann Kreutzmann 《GeoJournal》2004,59(1):27-31

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Simulation Experiments with Cometary Analogous Material     

Kochan  Hermann W.  Huebner  Walter F.  Sears  Derek W. G. 《Earth, Moon, and Planets》1998,80(1-3):369-411

Comet simulation experiments are discussed, in the context of physical models and the results in cometary physics, gathered especially from the GIOTTO space mission to comet P'Halley. The “status of the today knowledge” about comets, the experiments could start from, is briefly reviewed. The setup of the KOSI (German = Kometen Simulation) - experiments and the techniques to produce cometary analogous material, on the basis of that knowledge are described in general, as for the different KOSI experiments. The limitations of the simulation of physical processes at the surface of real comets in an earth-bound laboratory are discussed, and the possibilities to receive common insights in cometary physics are shown. Methods and procedures are described, and the major results reviewed. As with attempting to reproduce any natural phenomenon in the laboratory, there are short-comings to these experiments, but there are possibly major new insights to be gained. Physical laws only have the same consequences under same experimental or environmental conditions. A number of small-scale comet simulation experiments have been performed, since the early 60ties in many laboratories, but the largest and most ambitious series of comet simulation experiments to date were performed between 1987 and 1993 using the German space agency's (DLR) space hardware testing facilities in Cologne. These experiments were triggered by the scientific community after the comet P'Halley's recurrence in 1986 and the many data gathered by the space missions in this year. Simulation experiments have proved valuable in developing methods for making cometary analogues, and for exploring specific properties of such materials in detail. These experiments provided new insights into the morphology and physical behavior of aggregates formed out of silicate- /water-ice -grains likely to exist in comets. The formation of a dust mantle on the surface, and a system of ice layers below the mantle from the different admixed materials, have been detected after the insolation of the artificial comet. The mechanisms for heat transfer between the comet's surface and its interior, compositional, structural, and isotopic changes that occur near the comet's surface, were described by modeling in accordance with the experimental results. The mechanisms of the ejection of dust and ice grains from the surface, and the importance of gas-drag in propelling grains were investigated by close-up video cameras. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献