Salt transport on islands in the Okavango Delta: Numerical investigations     

S. Zimmermann  P. Bauer  R. Held  W. Kinzelbach  J.H. Walther 《Advances in water resources》2006

This study uses a numerical model to investigate the groundwater flow and salt transport mechanisms below islands in the Okavango Delta. Continuous evapotranspiration on the islands results in accumulation of solutes and the formation of a saline boundary layer, which may eventually become unstable. A novel Lagrangian method is employed in this study and compared to other numerical methods. The numerical results support the geophysical observations of density fingering on Thata Island. However, the process is slow and it takes some hundreds of years until density fingering is triggered. The results are sensitive to changes of the hydraulic gradient and the evapotranspiration rate. Small changes may lead to different plume developments. Results further demonstrate that density effects may be entirely overridden by lateral flow on islands embedded in a sufficiently high regional hydraulic gradient.  相似文献   

Buchbesprechungen     

F. Klötzli  Rudolf Koblet  Chr Zimmermann 《Aquatic Sciences - Research Across Boundaries》1978,40(2):384-386

Ohne Zusammenfassung  相似文献   

Solar and meteoritic abundance of silicon     

U. Becker  P. Zimmermann  H. Holweger 《Geochimica et cosmochimica acta》1980,44(12):2145-2149

Recent lifetime measurements on excited electronic states of neutral silicon (Beckeret al., Phys. Lett. In press, 1980) lead to a reassessment of widely used experimental transition probabilities Garz, Astron. Astrophys., 26, 471–477, 1973 of Si I lines. This translates into a 25% downward revision of the Si abundance determined from the solar spectrum.A solar atomic ratio, Si/Ca = 15.5 is inferred. This value coincides with that found in carbonaceous chondrites, but contrasts with ordinary and enstatite chondrites.  相似文献   

Isotopic age and metamorphic history of the banded gneiss at Danmarkshavn,East Greenland     

Rudolf H. Steiger  Gorica Harnik-Šoptrajanova  Emil Zimmermann  Niels Henriksen 《Contributions to Mineralogy and Petrology》1976,57(1):1-24

Along the northern part of the East Greenland coast the Caledonian structures are superimposed on an older fold system called the Carolinidian. Traces of this Carolinidian belt are preserved in a few isolated fragments within the Caledonian fold belt. According to Haller (1970) one of these fragments exhibiting the typical Carolinidian NNW to NW-trending infrastructural folds is the peninsula of Germania Land which is accessible near the Danish weather station Danmarkshavn. The rock sampled there is a banded gneiss of granodioritic composition with steeply inclined, NNW-trending layers. Isotopic age determinations yielded essentially two groups of ages: 1) 3,000±150 m.y. (zircon suite and Rb/Sr whole rock analyses of layers) and 2) 320–380 m.y. (Rb/Sr mineral isochrons, U-Th-Pb on sphene, K/Ar on hornblende and biotite). The egg-shaped zircons support a sedimentary origin of the banded gneiss and in conjunction with the Rb/Sr whole rock ages determine the age of formation of the banded gneiss (or its last high grade metamorphism) some 3,000 m.y. ago. No other Precambrian metamorphism or orogeny is recorded in the rock. The ages between 320–380 m.y. date a thermal event of lower amphibolite facies grade related to a late Caledonian spasm.The new isotopic data reveal the existence of very old rocks in the hinterland — away from the direction of thrusting—of the East Greenland Caledonian belt. With respect to the age of the Carolinidian fold system three geological interpretations are compatible with the results of this study:

1.	the Carolinidian fold system formed approximately 3,000 m.y. ago;
2.	the banded gneiss represents part of an old basement: the Carolinidian orogeny is younger than 3,000 m.y. Its marked structural imprint on the Danmarkshavn area was accompanied by very low grade metamorphism not recognised in the isotopic record;
3.	the fold structures observed in the Danmarkshavn area are not of Carolinidian age but belong to an earlier fold system preserved in the basement.

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Über die Vertikalverteilung und jahreszeitliche Entwicklung der Larvendichte vonDreissena polymorpha Pallas im Pelagial des unteren Zürichseebeckens im Jahre 1974     

Peter Suter-Weider  Dr. Ulrich Zimmermann 《Aquatic Sciences - Research Across Boundaries》1976,38(2):159-170

The freshwater musselDreissena polymorpha Pallas was sighted for the first time in Lake Zürich about 1969. This meant a real problem for the water treatment of lake water. By means of a pump and vertical net hauls it was tried to add more information to the scarce results on Lake Zürich. Additional dates about temperature, depth of Secchi disk visibility and beam transmittance were collected. There was a first appearance of the larvae ofD. polymorpha at the beginning of June. Following the mean temperature of the epilimnion the number of individuals/m² reached max. 210,000. The greatest concentration measured in 1974 of larvae/m³ was 54,375 at a depth of 4 m. The last appearance ofD. polymorpha was observed at the end of October.

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Nitrogen isotopes in the recent solar wind from the analysis of Genesis targets: Evidence for large scale isotope heterogeneity in the early solar system     

Bernard Marty  Laurent Zimmermann  Rainer Wieler  Donald L. Burnett  Peter Bochsler 《Geochimica et cosmochimica acta》2010,74(1):340-19141

We have analyzed nitrogen, neon and argon abundances and isotopic ratios in target material exposed in space for 27 months to solar wind (SW) irradiation during the Genesis mission. SW ions were extracted by sequential UV (193 nm) laser ablation of gold-plated material, purified separately in a dedicated line, and analyzed by gas source static mass spectrometry. We analyzed gold-covered stainless steel pieces from the Concentrator, a device that concentrated SW ions by a factor of up to 50. Despite extensive terrestrial N contamination, we could identify a non-terrestrial, ¹⁵N-depleted nitrogen end-member that points to a 40% depletion of ¹⁵N in solar-wind N relative to inner planets and meteorites, and define a composition for the present-day Sun (¹⁵N/¹⁴N = [2.26 ± 0.67] × 10⁻³, 2σ), which is indistinguishable from that of Jupiter’s atmosphere. These results indicate that the isotopic composition of nitrogen in the outer convective zone of the Sun has not changed through time, and is representative of the protosolar nebula. Large ¹⁵N enrichments due to e.g., irradiation, low temperature isotopic exchange, or contributions from ¹⁵N-rich presolar components, are therefore required to account for inner planet values.  相似文献   

Origin and age of ultramafic rocks and gabbros in the southern Puna of Argentina: an alleged Ordovician suture revisited     

Udo Zimmermann  Heinrich Bahlburg  Klaus Mezger  Jasper Berndt  Suzanne Mahlburg Kay 《International Journal of Earth Sciences》2014,103(4):1023-1036

Ultramafic rocks and gabbros are exposed in the southern Puna (NW Argentina) in tectonic association with continental arc-related Ordovician (volcano) sedimentary successions and granitoids. The origin of this mafic rock suite has been debated for three decades as either representing an Ordovician terrane suture, primitive Ordovician arc-related rocks or relics of the pre-Ordovician basement in tectonic contact with the Ordovician retro-arc basin successions. We present the first U–Pb ages of primary and inherited zircon from gabbros of this mafic–ultramafic assemblage. LA-ICP-MS analyses on cores and rims of these zircon grains yielded a concordia age of 543.4 ± 7.2 Ma for the gabbroic rocks. Other analysed zircons have Mesoproterozoic, and Early Ediacaran core and rim ages indicating that the magmas also assimilated Meso- and Neoproterozoic crustal material prior to final crystallization. The mafic rocks witnessed higher metamorphic grade than associated Ordovician rocks, which are unmetamorphosed or only affected by anchimetamorphism. The gabbros are mostly tholeiitic and enriched in Zr, Th, as well as other incompatible elements and have εNd _t=540Ma ranging from 1.3 to 7.4 with most of the values between 5 and 7. ¹⁴⁷Sm/¹⁴⁴Nd ratios show evidence of weak crustal contamination. The mafic rocks do not reveal any affinity to mid-ocean ridge basalts in their geochemistry but point instead to an emplacement in an active plate margin arc environment. Chromites from ultramafic rocks show typical Ti, Al, Cr#, Fe³⁺ abundances found in magmatic arc rocks. The formation of the gabbros and the associated ultramafic rocks in the southern Argentine Puna is related to the evolution of the margin of the Pampia terrane, including the Puncoviscana basin, during the Late Neoproterozoic and earliest Cambrian. In contrast to previous interpretations, the rocks predate the Ordovician evolution of the Central proto-Andean active margin. Consequently, interpretations assuming these rocks to represent an oceanic terrane suture of Ordovician age have to be dismissed as much as all palaeotectonic models that define Ordovician terranes in the Central Andes based on assumption that the ultramafic rocks and gabbros exposed in the southern Puna mark plate boundaries.  相似文献   

Chemische und bakteriologische Untersuchungen im unteren Zürichsee während der Jahre 1948–1957     

Peter Zimmermann 《Aquatic Sciences - Research Across Boundaries》1961,23(2):342-397

Ohne Zusammenfassung  相似文献   

Static and Dynamic Moduli of Malm Carbonate: A Poroelastic Correlation     

Alireza Hassanzadegan  Romain Guérizec  Thomas Reinsch  Guido Blöcher  Günter Zimmermann  Harald Milsch 《Pure and Applied Geophysics》2016,173(8):2841-2855

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Analysing Debris-Flow Impact Models, Based on a Small Scale Modelling Approach   总被引：4，自引：0，他引：4  

Christian Scheidl  Michael Chiari  Roland Kaitna  Matthias Müllegger  Alexander Krawtschuk  Thomas Zimmermann  Dirk Proske 《Surveys in Geophysics》2013,34(1):121-140

The objective of this study is to analyse adaptable debris-flow impact models, which are very important for mitigation measurements and buildings using their sphere of influence. For this reason, 16 debris-flow experiments, on a small-scale modelling approach, were performed. Impact forces were measured with a force plate panel, consisting of 24 aluminium devices, coaxially mounted with resistance strain gauges. Flow velocities, flow heights as well as horizontal impact forces were sampled with a frequency of 2.4 kHz. Sub datasets of sampled raw force data were defined by applying an average median filter, a low-pass filter routine. Further, estimated peak pressure values as well as empirical coefficients of hydraulic impact models were compared, and the influence of signal processing is discussed.  相似文献