16 search hits
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Documentation of reference data for the experimental areas of the Bayreuth Centre for Ecology and Environmental Research (BayCEER) at the Waldstein site
(2007)
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Katharina Staudt
Thomas Foken
- no abstract
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COPS experiment - Convective and orographically induced precipitation study, 01 June 2007 – 31 August 2007
(2007)
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Stefan Metzger
Thomas Foken
- no abstract
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The Arctic Turbulence Experiment 2006, Direct measurements of turbulent fluxes in the near surface environment at high latitudes applying the eddy-covariance method, Part 3
(2007)
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Johannes Lüers
Jörg Bareiss
- no abstract
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The Arctic Turbulence Experiment 2006, Direct measurements of turbulent fluxes in the near surface environment at high latitudes applying the eddy-covariance method, Part 2
(2007)
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Johannes Lüers
Jörg Bareiss
- no abstract
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The Arctic Turbulence Experiment 2006, Direct measurements of turbulent fluxes in the near surface environment at high latitudes applying the eddy-covariance method, Part 1
(2007)
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Johannes Lüers
Jörg Bareiss
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Ultraschallanemometer-Überprüfung im Windkanal der TU Dresden
(2007)
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Lukas Siebicke
Andrei Serafimovich
- keine Zusammenfassung
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Investigations of the geomorphologic and pedologic system of sedimentary vega deposits from Lanzarote (Canary Islands) supported by luminescence dating – important steps towards their palaeoclimatic interpretation
(2007)
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Hans von Suchodoletz
- On Lanzarote (Canary Islands/Spain), sequences similar to loess-palaeosol-sequences from other regions developed in dammed volcanic valleys during the Middle and Late Pleistocene. Based on former investigations, we assumed that these sequences could serve as palaeoclimate archives for the NW-African region, an area characterised by a lack of investigations from continuous terrestrial palaeoclimate archives. The material deposited in the valleys consists of Saharan dust as well as of local volcanic material. Due to their location in valley positions and adjacent strongly eroded slopes it is obvious that these sequences do not represent classic loess-palaeosol-archives. Instead, they must consist of a mixture of in situ aeolian fallout as well as of sediments derived from colluvial input from the slopes. Consequently, prior to a correct palaeoclimatic interpretation the geomorphologic character of the archives and the properties of their sediments must be analysed. Thus, in this study we intensively investigate the geomorphologic and pedologic system, combining geomorphologic mapping and quantitative GIS-calculations with sedimentological-pedological methods (grain size, XRD, rock magnetic und pedologic analyses as well as investigation of micromorphologic properties). Furthermore, we built up a chronostratigraphy using different luminescence-methods (quartz coarse- and fine grain-OSL, polymineral fine grain-IRSL). Fundamental investigations on the bleaching-behaviour of recent Saharan dust and colluvial sediments on Lanzarote demonstrate, that in spite of partial insufficient bleaching of the luminescence signal a dating of the valley-bottom sediments is possible. These datings were supported by a correlation of local kaolinite-contents with iron and kaolinite contents from nearby marine cores as well as a stratigraphic correlation between different profiles. Thus, we could establish a chronostratigraphy for the last 180 ka. We demonstrate that outcropped sediments were deposited almost continuously from the Middle Pleistocen until the Holocene, wheras the uppermost sections of the profiles consist of anthropogenic colluvia which can not be interpreted in a palaeoclimatic way. The alternation of reddish-clayey and yellowish-silty layers tracks changes of soil humidity on Lanzarote rather than variations of the composition of Saharan dust. Due to the colluvial dynamics of the valleys, reddish-silty layers in the valley bottoms are no palaeosoils sensu strictu but mainly consist of colluvial soil sediments originating from pedogenesis on the slopes. These soils as well as unweathered material were eroded and deposited with high frequency and low amplitude. Thus, their sedimentation age in the valley bottoms is close to the primary time of aeolian deposition on the slopes and the formation of pedogenetic properties. These findings allow a palaeoclimatic interpretation of the sediment sequences. We could demonstrate that glacials and stadials were characterised by higher soil moisture than interglacials and interstadials. When comparing our results with other palaeoclimatic studies from a broader region, we can show that the causes for periods of enhanced humidity were westerly cyclones using a more southern way than at recent, as well as lowered sea and air temperatures in the area of the Canary Islands. During some periods, soil humidity was possibly occasionally amplified by a northward advance of the African summer monsoon up to the latitude of Lanzarote. Although we are not able to directly derive palaeoprecipitation values from soil moisture, we can show that maximal precipitation values must have been in the the range of ca. 560 mm/a. Our results demonstrate that during most of the investigated period of the Late Quaternary the climate of Lanzarote was influenced by northern high latitude processes. Furthermore, during most of the investigated period the recent aridity of the island was somewhat mitigated.
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Untersuchungen zum Wasserhaushalt eines Fichtenwaldstandorts unter Berücksichtigung der Humusauflage
(2007)
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Tobias Zuber
- Die Humusauflage ist ein wichtiger Bestandteil von Waldböden, der stark durchwurzelt wird und, in Abhängigkeit von der Mächtigkeit, einen bedeutenden Beitrag zur pflanzenverfügbaren Speicherung von Wasser leisten kann. Dennoch wird die Humusauflage in Bodenwasserhaushaltsmodellen nur selten berücksichtigt. In dieser Arbeit soll der Wasserhaushalt der Humusauflage eines Fichtenbestands (Picea abies L.) im Fichtelgebirge (NO-Bayern) für eine Kontroll- und eine Manipulationsfläche, die über sechs Wochen experimentell ausgetrocknet und anschließend wiederbefeuchtet wurde, quantifiziert und modelliert werden. Für die korrekte Abbildung des Bodenwasserhaushalts im Modell wurden die bodenphysikalischen Parameter am Untersuchungsstandort umfassend charakterisiert. Die pF-Kurve wurde für die Mineralbodenhorizonte bis pF 4,2, für die Humusauflage bis pF 5,5 ermittelt. Die Spanne der volumetrischen Wassergehalte zwischen Sättigung und maximaler Austrocknung ist dabei in der Humusauflage sehr viel größer als im Mineralboden. Dies wirkt sich auf die Höhe der nutzbaren Feldkapazität aus, die für die 13 cm mächtige Humusauflage mit 41 mm, für den Mineralboden bis 40 cm Bodentiefe, unter Berücksichtigung des Skelettanteils, mit 71 mm bestimmt wurde. Die experimentelle Austrocknung des Fichtenbestands führte, im Vergleich zur Kontrollfläche, lediglich in der Humusauflage zu signifikant geringeren Wassergehalten, während im Mineralboden keine Manipulationseffekte auftraten. Zwischen Juli und August 2006 wurden für die Humusauflage der Manipulations- und der Kontrollfläche maximale Saugspannungen von pF 6 bzw. pF 5 über die pF-Kurve errechnet. Ein weiteres Ziel war die Weiterentwicklung eines Lindenholzsensors zur horizontgenauen Bestimmung von Matrixpotentialen in Humusauflagen mittels elektrischer Leitfähigkeitsmessung. Im Bereich der Messtechnik und bei der Beachtung des Temperatureinflusses konnten Fortschritte erzielt werden, eine kontinuierliche in situ-Bestimmung von Matrixpotentialen wurde aber nicht erreicht. Die volumetrischen Wassergehalte konnten im trockenen Bereich bis 20 Vol.-% erfasst werden, im feuchteren Bereich sind die Lindenholzsensoren ungeeignet. Neben der Entwicklung von Lindenholzsensoren sollten weitere Sensoren auf ihre Anwendbarkeit in Humusauflagen hin getestet und verglichen werden. ECH2O-Sonden bildeten über eine gute Freilandkalibrierung die volumetrischen Wassergehalte in der Humusauflage von 3 bis 60 Vol.-% kontinuierlich und korrekt ab, bei weitestgehender Wartungsfreiheit der Messtechnik. Auch mit einer mobilen FDR-Sonde konnte im Freiland eine gute Kalibrierung zur Bestimmung von volumetrischen Wassergehalten in der Humusauflage erzielt werden. Die Verwendung von Einstichtensiometern hingegen kann nur unter feuchten Bedingungen zur Ermittlung von Saugspannungen in Humusauflagen empfohlen werden. Mit einem Wasserhaushaltsmodell konnte der Wasserhaushalt der Mineralbodenhorizonte und der Humusauflage für die Austrocknungsperiode abgebildet werden. Nach stärkeren Niederschlagsereignissen wurden die Wassergehalte, insbesondere in der Humusauflage, jedoch teils deutlich überschätzt. Dies wird auf die Ausbildung von Hydrophobizität und dadurch bedingtem präferentiellen Fluss als Folge vorausgegangener Austrocknung zurückgeführt. Die Arbeit hat gezeigt, dass die Humusauflage in der Vegetationsperiode für den Wasserhaushalt des Fichtenbestands von großer Bedeutung ist. Durch den Vergleich unterschiedlicher Sensoren und die Simulation des Wasserhaushalts im Modell hat sich gezeigt, dass die hohe Dynamik der Wassergehalte und Saugspannungen in der Humusauflage relativ zuverlässig beschrieben werden kann.
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Experimental studies on the adsorption of SO2 on volcanic ashes
(2007)
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Deborah Schmauß-Schreiner
- The adsorption of SO2 on synthetic and on natural volcanic glasses was studied. The synthetic glasses were of rhyolitic, dacitic and andesitic composition and were synthesized in a high-temperature furnace at 1600°C. The natural volcanic glasses were Lipari obsidian and Puu Waawaa obsidian. Before the adsorption experiments the glasses were ground up to powder with a planetary mill under dry conditions. The surface area of the powder then was determined with a surface area analyzer. Adsorption experiments were conducted at -80 °C, -20 °C, 0 °C, 25 °C and 150 °C. The experiments covered a pressure range from 0.1 to 984 mbar. The experiments at 0 °C (p = 0.1 to 984 mbar) and at 25 °C (p = 38 to 938 mbar) were performed with andesitic, dacitic and rhyolitic glass. Additional experiments with rhyolitic glass were carried out at 150 °C (p = 118 to 538 mbar), -20 °C (p = 75 mbar) and -80 °C (p = 46 mbar). Two experiments were performed with Lipari obsidian and Puu Waawaa obsidian respectively, each at 0 °C (p = 31 to 949 mbar). During the experiments the amount that adsorbes on the surface of the respective glass powder was determined volumetrically. For this purpose a device was designed, consisting of several glass containers, each of known volume. The glass powder was stored in the device, which then was purged with pure SO2. The amount of adsorbed SO2 then was determined from the pressure drop in the device, that occured due to adsorption. Equilibrium pressure was reached within a few hours (4-5 h). During all experiments SO2 adsorbed readily on the surface of the glasses. The adsorption isotherms from the experiments at room temperature could be classified as type II isotherms, suggesting the formation of multilayers of SO2 on the glass surface. The adsorption-desorption isotherms showed a hysteresis-like behaviour, suggesting that remarkable amounts of SO2 remain on the surface of the glass even after desorption. During the experiments at room temperature about 30 wt% of the originally adsorbed SO2 remained on the surface after desorption. XRF measurements confirmed this. Moreover, the values for the monolayer capacity Vm for SO2, that were derived from the BET isotherms, suggest that the binding of nearly the whole first monolayer was irreversible. The amount of adsorbed gas strongly depended on the temperature. It was shown that low temperatures promote the amount of adsorbed gas. An universal expression of the temperature dependence of adsorption was derived by developing a regression model for each of the synthetic glasses. The regression model is given as ln (c) = A(1/T)+ B ln p + C; where p is the pressure in mbar; c is the amount of adsorbed SO2 in mg/m2 and T is the temperature in Kelvin. According to the regression model, the amount of adsorbed SO2 varies with exp (1/T ). The precoefficients A, B and C depend on the composition of the glass, indicating that the amount of adsorbed SO2 also depends on the glass composition: Andesite: A=1644.28; B=0.29; C=-7.43; Dacite: A=2139.52; B=0.29; C=-9.32; Rhyolite: A=909.75; B=0.21; C=-4.48. The heats of adsorption Delta(Ha) for the synthetic glasses were inferred from the regression model: For rhyolite Delta (Ha) was approx. 7.6 kJ/mol, for dacite Delta (Ha) was approx. 17.8 kJ/mol and for andesite Delta(Ha) was approx. 13.7 kJ/mol. The heats of adsorption Delta(Ha) for the natural glasses were inferred from their BET isotherms: For the Lipari obsidian and for the Puu Waawaa obsidian Delta(Ha) was approx. 15 kJ/mol. The experimental adsorption data fitted both the BET equation, describing multilayeradsorption, and the Freundlich equation, desribing monolayer adsorption, quite well. For adsorption at 0 °C the following BET constants were derived: Rhyolite: C=93.4; Vm=0.32 cm3/m2; Dacite: C=5.86; Vm=0.34cm3/m2; Andesite: C=72.02; Vm=0.29cm2/m2; Lipari obsidian: C=16.00; Vm=0.33cm3/m2; Pu Waawaa obsidian: C=20.10;Vm=0.47cm3/m2. The following Freundlich Constants were derived: 1/a (in ln (mg/m2)/ ln(mbar))/ ln (k) (in ln(mg/m2)). Rhyolite: 0.25/-1.01; Dacite: 0.28/-1.47; Andesite: 0.27/-1.37; Lipari obsidian: 0.62/-3.59; Pu Waawaa obsidian: 0.64/-3.32; Experimental results provided evidence for both chemical (a) and physical (b) adsorption mechanisms: (a) the amount of adsorbed SO2 appears to depend on the glass composition and the adsorption is partially irreversible; (b) adsorption relationships, like the isotherm type and the enthalpies of adsorption are more characteristic for physical adsorption. Geological implications: Adsorption of SO2 on volcanic ash during a natural volcanic eruption mainly occurs in the umbrella region of the volcanic plume. According to the regression model, adsorption is controlled by the partial pressure of SO2 at the maximum ascent height of the plume and by the ambient stratospheric temperature prevailing at the maximum ascent height. The total amount of adsorbed SO2 depends on the total surface area of the ash suspended in the plume, which again results from the starting gas mass-fraction sigma = (mGas/mash) in the eruption column and the grain size distribution of the ejected material. A decrease in sigma = (mGas/mash) results in an increase of ash mass in the plume and thus in an increase of the total surface area of the ash suspended in the plume. The relative amount of adsorbed SO2 (e. g. the adsorbed amount, compared to the total amount in the plume) depends on the initial SO2 content x(SO2) = n(SO2)/n(Gas) in the volcanic gas: The higher the molar fraction of SO2 in the starting gas, the less is the percentage fraction of adsorbed SO2 relative to the totally available amount in the eruption column. Therefore, that if the SO2 is strongly diluted for example by water vapour it will be adsorbed by the volcanic ash very strongly, so that the impact of such eruptions on the environment is likely to be small. On the other hand, if the SO2 concentration in the volcanic gas is high, only part of it will be adsorbed and a much stronger impact of the eruption on climate is expected. For a plume model with a starting gas mass-fraction sigma = 0.03, an initial SO2 content of 1.17 Mole%, an ascent height of the eruption column of 9 km and a grain size distribution typical for Plinian eruptions, the ejected SO2 is completly adsorbed by the volcanic ash. It is likely, that the adsorbed SO2 desorbs again, except for the first monolayer, when the partial pressure of SO2 drops due to dilution. This effect probably accounts for the apparent increase in stratospheric SO2 concentration 1–2 days after an eruption, which is often observed in satellite measurements.
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Physical and chemical constraints on core - mantle differentiation in terrestrial planets.
(2007)
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Ute Mann
- In this study a physical mechanism and geochemical parameters have been examined in high pressure (P) and high temperature (T) experiments in order to place constraints on the conditions and the manner by which core-mantle differentiation occurred on Earth and terrestrial planets. The wetting characteristics of liquid Fe-Si alloys in a matrix of the respective predominating stable silicate mantle mineral (forsterite, silicate perovskite) at pressures of 2-5 and 25 GPa and temperatures of 1600-2000°C have been studied by determining the liquid metal - solid silicate contact angles. The median angle values from texturally-equilibrated samples were found to be independent of P, T, silicate mineralogy and the Si content in the metal fraction and range between 130° and 140° which is far above the critical wetting boundary of 60°. Therefore, within the studied range of conditions dissolved Si does not lower the surface energies between Fe-rich liquids and silicate mantle grains. As a consequence, under reducing conditions the presence of Si in the metal phase of planetary bodies would not have enhanced percolative flow as an effective metal-silicate separation process. The effects of P, T and oxygen fugacity on the liquid metal - liquid silicate partitioning behaviour of the elements Ta, Nb, V, Cr, Si, Mn, Ga, In and Zn have been studied experimentally over a wide range of high-P and high-T conditions of 2-24 GPa, 1750-2600°C and at low oxygen fugacities of -1.3 to -4.2 log units below the iron wüstite buffer. With the derived parameters the respective element depletions in the mantle can be tested under various conditions suggested in core formation models. These data indicate that Nb can serve as an important constraint on oxygen fugacity and P for metal-silicate equilibration. Core formation must have occurred at conditions significantly greater than 20 GPa in order for Nb not to have been massively depleted under conditions necessary to deplete the weakly siderophile element V. Moreover, our study shows that the volatile elements Mn and Ga, would experience strong fractionations in any core-mantle equilibration scenario at pressures below 60 GPa and temperatures at least as high as the peridotite liquidus, while their observed abundances in the mantle is near-chondritic. To a more extreme extent such an observation has been made for the elements Zn and In for which pressures over 80 GPa may be required to explain their near-chondritic ratio in the mantle. Based on these observations we find strong support for the existence of a deep magma ocean during metal-silicate separation, which is an essential component in current polybaric multi-stage core formation models. Although these models succeed in reproducing the observed mantle abundances of many siderophile elements, and can be constrained based on the partitioning behaviour of elements such as Nb, the observed behaviour of the volatile elements Mn, Ga, Zn and In may call for an additional process. Such a process may be the late accretion of volatiles in material that did not undergo core-mantle separation or strong fractionation processes in the condensing nebula that are reflected in the meteorite record. In a third study, the first liquid metal-liquid silicate partitioning data at high pressures up to 18 GPa and high temperatures up to 2500 °C have been obtained for the highly siderophile elements (HSEs) Ru, Rh, Pd, Re, Ir and Pt. This group of elements presents a number of experimental and analytical difficulties, mainly due to their extreme metal-silicate partition coefficients. In addition to refining the experimental technique we have succeeded in producing suitable standards for trace analysis of these elements in quenched silicates using LA-ICP-MS. This study shows that both increasing P and T would decrease the partition coefficients of all HSEs examined in a way similar to the P effect observed for the siderophile elements Ni and Co. This involves two pressure regimes with a strong decrease of the partition coefficients at < 6 GPa, but only a weak P dependence at higher pressures. This difference in P effect can most likely be assigned to structural changes in the silicate melt. In order for the determined partition coefficients to be used quantitatively in models for the Earth, the data have to be corrected from the experimental level of large HSE-concentrations in the metallic phase to infinite dilution. Using Rh as an example for which data exist to perform such a correction, it can be shown that the principal P and T trend does not change significantly once the correction for dilution is performed. From this we can conclude that the P-effect would not be sufficient to decrease the partition coefficients to a degree that the mantle concentrations of the HSEs could be explained. Therefore, a process such as the accretion of an undifferentiated late veneer seems to be necessary.
