TY  - GEN
A1  - Baes, Marzieh
A1  - Sobolev, Stephan Vladimir
A1  - Gerya, Taras V.
A1  - Brune, Sascha
T1  - Plume-induced subduction initiation
BT  - Single-slab or multi-slab subduction?
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Initiation of subduction following the impingement of a hot buoyant mantle plume is one of the few scenarios that allow breaking the lithosphere and recycling a stagnant lid without requiring any preexisting weak zones. Here, we investigate factors controlling the number and shape of retreating subducting slabs formed by plume-lithosphere interaction. Using 3-D thermomechanical models we show that the deformation regime, which defines formation of single-slab or multi-slab subduction, depends on several parameters such as age of oceanic lithosphere, thickness of the crust and large-scale lithospheric extension rate. Our model results indicate that on present-day Earth multi-slab plume-induced subduction is initiated only if the oceanic lithosphere is relatively young (<30-40 Myr, but >10 Myr), and the crust has a typical thickness of 8 km. In turn, development of single-slab subduction is facilitated by older lithosphere and pre-imposed extensional stresses. In early Earth, plume-lithosphere interaction could have led to formation of either episodic short-lived circular subduction when the oceanic lithosphere was young or to multi-slab subduction when the lithosphere was old.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1167 
KW  - subduction zone
KW  - plume
KW  - numerical model
KW  - singleslab
KW  - multi-slab
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-522742
SN  - 1866-8372
IS  - 2
ER  - 
TY  - JOUR
A1  - Bahr, André
A1  - Kolber, Gilles
A1  - Kaboth-Bahr, Stefanie
A1  - Reinhardt, Lutz
A1  - Friedrich, Oliver
A1  - Pross, Jörg
T1  - Mega-monsoon variability during the late Triassic
BT  - re-assessing the role of orbital forcing in the deposition of playa sediments in the Germanic Basin
JF  - Sedimentology : the journal of the International Association of Sedimentologists
N2  - The formation of the supercontinent Pangaea during the Permo-Triassic gave rise to an extreme monsoonal climate (often termed 'mega-monsoon') that has been documented by numerous palaeo-records. However, considerable debate exists about the role of orbital forcing in causing humid intervals in an otherwise arid climate. To shed new light on the forcing of monsoonal variability in subtropical Pangaea, this study focuses on sediment facies and colour variability of playa and alluvial fan deposits in an outcrop from the late Carnian (ca 225 Ma) in the southern Germanic Basin, south-western Germany. The sediments were deposited against a background of increasingly arid conditions following the humid Carnian Pluvial Event (ca 234 to 232 Ma). The ca 2 center dot 4 Myr long sedimentary succession studied shows a tripartite long-term evolution, starting with a distal mud-flat facies deposited under arid conditions. This phase was followed by a highly variable playa-lake environment that documents more humid conditions and finally a regression of the playa-lake due to a return of arid conditions. The red-green (a*) and lightness (L*) records show that this long-term variability was overprinted by alternating wet/dry cycles driven by orbital precession and ca 405 kyr eccentricity, without significant influence of obliquity. The absence of obliquity in this record indicates that high-latitude forcing played only a minor role in the southern Germanic Basin during the late Carnian. This is different from the subsequent Norian when high-latitude signals became more pronounced, potentially related to the northward drift of the Germanic Basin. The recurring pattern of pluvial events during the late Triassic demonstrates that orbital forcing, in particular eccentricity, stimulated the occurrence and intensity of wet phases. It also highlights the possibility that the Carnian Pluvial Event, although most likely triggered by enhanced volcanic activity, may also have been modified by an orbital stimulus.
KW  - Carnian Pluvial Event
KW  - Germanic Basin
KW  - Late Triassic
KW  - mega-monsoon
KW  - orbital forcing
KW  - playa-lake
Y1  - 2019
U6  - https://doi.org/10.1111/sed.12668
SN  - 0037-0746
SN  - 1365-3091
VL  - 67
IS  - 2
SP  - 951
EP  - 970
PB  - Wiley-Blackwell
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Balischewski, Christian
A1  - Behrens, Karsten
A1  - Zehbe, Kerstin
A1  - Günter, Christina
A1  - Mies, Stefan
A1  - Sperlich, Eric
A1  - Kelling, Alexandra
A1  - Taubert, Andreas
T1  - Ionic liquids with more than one metal
BT  - optical and rlectrochemical properties versus d-block metal vombinations
JF  - Chemistry - a European journal
N2  - Thirteen N-butylpyridinium salts, including three monometallic [C4Py](2)[MCl4], nine bimetallic [C4Py](2)[(M1-xMxCl4)-M-a-Cl-b] and one trimetallic compound [C4Py](2)[(M1-y-zMyMz (c) Cl4)-M-a-M-b] (M=Co, Cu, Mn; x=0.25, 0.50 or 0.75 and y=z=0.33), were synthesized and their structure and thermal and electrochemical properties were studied. All compounds are ionic liquids (ILs) with melting points between 69 and 93 degrees C. X-ray diffraction proves that all ILs are isostructural. The conductivity at room temperature is between 10(-4) and 10(-8) S cm(-1). Some Cu-based ILs reach conductivities of 10(-2) S cm(-1), which is, however, probably due to IL dec. This correlates with the optical bandgap measurements indicating the formation of large bandgap semiconductors. At elevated temperatures approaching the melting points, the conductivities reach up to 1.47x10(-1) S cm(-1) at 70 degrees C. The electrochemical stability windows of the ILs are between 2.5 and 3.0 V.
KW  - bandgap
KW  - electrochemistry
KW  - ionic liquids
KW  - metal-containing ionic
KW  - liquids
KW  - tetrahalido metallates
Y1  - 2020
U6  - https://doi.org/10.1002/chem.202003097
SN  - 0947-6539
SN  - 1521-3765
VL  - 26
IS  - 72
SP  - 17504
EP  - 17513
PB  - Wiley-VCH
CY  - Weinheim
ER  - 
TY  - JOUR
A1  - Barbolini, Natasha
A1  - Woutersen, Amber
A1  - Dupont-Nivet, Guillaume
A1  - Silvestro, Daniele
A1  - Tardif-Becquet, Delphine
A1  - Coster, Pauline M. C.
A1  - Meijer, Niels
A1  - Chang, Cun
A1  - Zhang, Hou-Xi
A1  - Licht, Alexis
A1  - Rydin, Catarina
A1  - Koutsodendris, Andreas
A1  - Han, Fang
A1  - Rohrmann, Alexander
A1  - Liu, Xiang-Jun
A1  - Zhang, Y.
A1  - Donnadieu, Yannick
A1  - Fluteau, Frederic
A1  - Ladant, Jean-Baptiste
A1  - Le Hir, Guillaume
A1  - Hoorn, M. Carina
T1  - Cenozoic evolution of the steppe-desert biome in Central Asia
JF  - Science Advances
N2  - The origins and development of the arid and highly seasonal steppe-desert biome in Central Asia, the largest of its kind in the world, remain largely unconstrained by existing records. It is unclear how Cenozoic climatic, geological, and biological forces, acting at diverse spatial and temporal scales, shaped Central Asian ecosystems through time. Our synthesis shows that the Central Asian steppe-desert has existed since at least Eocene times but experienced no less than two regime shifts, one at the Eocene-Oligocene Transition and one in the mid-Miocene. These shifts separated three successive "stable states," each characterized by unique floral and faunal structures. Past responses to disturbance in the Asian steppe-desert imply that modern ecosystems are unlikely to recover their present structures and diversity if forced into a new regime. This is of concern for Asian steppes today, which are being modified for human use and lost to desertification at unprecedented rates.
Y1  - 2020
U6  - https://doi.org/10.1126/sciadv.abb8227
SN  - 2375-2548
VL  - 6
IS  - 41
PB  - American Association for the Advancement of Science
CY  - Washington
ER  - 
TY  - JOUR
A1  - Baroni, Gabriele
A1  - Francke, Till
T1  - An effective strategy for combining variance- and distribution-based global sensitivity analysis
JF  - Environmental modelling & software with environment data news
N2  - We present a new strategy for performing global sensitivity analysis capable to estimate main and interaction effects from a generic sampling design. The new strategy is based on a meaningful combination of varianceand distribution-based approaches. The strategy is tested on four analytic functions and on a hydrological model. Results show that the analysis is consistent with the state-of-the-art Saltelli/Jansen formula but to better quantify the interaction effect between the input factors when the output distribution is skewed. Moreover, the estimation of the sensitivity indices is much more robust requiring a smaller number of simulations runs. Specific settings and alternative methods that can be integrated in the new strategy are also discussed. Overall, the strategy is considered as a new simple and effective tool for performing global sensitivity analysis that can be easily integrated in any environmental modelling framework.
KW  - global sensitivity analysis
KW  - variance
KW  - distribution
KW  - generic sampling
KW  - design
Y1  - 2020
U6  - https://doi.org/10.1016/j.envsoft.2020.104851
SN  - 1364-8152
SN  - 1873-6726
VL  - 134
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - THES
A1  - Barrionuevo, Matías
T1  - The role of the upper plate in the Andean tectonic evolution (33-36°S): insights from structural geology and numerical modeling
T1  - El rol de la placa superior en la evolución tectónica andina (33-36°S): aportes desde la geología estructural y el modelado numérico
T1  - Die Rolle der oberen Platte in der tektonischen Entwicklung der Anden (33-36°S): Erkenntnisse aus der Strukturgeologie und der numerischen Modellierung
N2  - Los Andes Centrales del Sur (33-36°S) son un gran laboratorio para el estudio de los procesos de deformación orogénica, donde las condiciones de borde, como la geometría de la placa subductada, imponen un importante control sobre la deformación andina. Por otro lado, la Placa Sudamericana presenta una serie de heterogeneidades que también imparten un control sobre el modo de deformación. El objetivo de esta tesis es probar el control de este último factor sobre la construcción del sistema orogénico andino. 
A partir de la integración de la información superficial y de subsuelo en el área sur (34°-36°S), se estudió la evolución de la deformación andina sobre el segmento de subducción normal. Se desarrolló un modelo estructural que evalúa el estado de esfuerzos desde el Mioceno hasta la actualidad, el rol de estructuras previas y su influencia en la migración de fluidos. Con estos datos y publicaciones previas de la zona norte del área de estudio (33°-34ºS), se realizó un modelado numérico geodinámico para probar la hipótesis del papel de las heterogeneidades de la placa superior en la evolución andina. Se utilizaron dos códigos (LAPEX-2D y ASPECT) basados en elementos finitos/diferencias finitas, que simulan el comportamiento de materiales con reologías elastoviscoplásticas bajo deformación. Los resultados del modelado sugieren que la deformación contraccional de la placa superior está significativamente controlada por la resistencia de la litósfera, que está definida por la composición de la corteza superior e inferior y por la proporción del manto litosférico, que a su vez está definida por eventos tectónicos previos. Estos eventos previos también definieron la composición de la corteza y su geometría, que es otro factor que controla la localización de la deformación. Con una composición de corteza inferior más félsica, la deformación sigue un modo de cizalla pura mientras que las composiciones más máficas provocan un modo de deformación tipo cizalla simple. Por otro lado, observamos que el espesor inicial de la litósfera controla la localización de la deformación, donde zonas con litósfera más fina es propensa a concentrar la deformación. Un límite litósfera-astenósfera asimétrico, como resultado del flujo de la cuña mantélica tiende a generar despegues vergentes al E.
N2  - The Southern Central Andes (33°-36°S) are an excellent natural laboratory to study orogenic deformation processes, where boundary conditions, such as the geometry of the subducted plate, impose an important control on the evolution of the orogen. On the other hand, the South American plate presents a series of heterogeneities that additionally impart control on the mode of deformation. This thesis aims to test the control of this last factor over the construction of the Cenozoic Andean orogenic system.
From the integration of surface and subsurface information in the southern area (34-36°S), the evolution of Andean deformation over the steeply dipping subduction segment was studied. A structural model was developed evaluating the stress state from the Miocene to the present-day and its influence in the migration of magmatic fluids and hydrocarbons. Based on these data, together with the data generated by other researchers in the northern zone of the study area (33-34°S), geodynamic numerical modeling was performed to test the hypothesis of the decisive role of upper-plate heterogeneities in the Andean evolution. Geodynamic codes (LAPEX-2D and ASPECT) which simulate the behavior of materials with elasto-visco-plastic rheologies under deformation, were used. The model results suggest that upper-plate contractional deformation is significantly controlled by the strength of the lithosphere, which is defined by the composition of the upper and lower crust, and by the proportion of lithospheric mantle, which in turn is determined by previous tectonic events. In addition, the previous regional tectono-magmatic events also defined the composition of the crust and its geometry, which is another factor that controls the localization of deformation. Accordingly, with more felsic lower crustal composition, the deformation follows a pure-shear mode, while more mafic compositions induce a simple-shear deformation mode. On the other hand, it was observed that initial lithospheric thickness may fundamentally control the location of deformation, with zones characterized by thin lithosphere are prone to concentrate it. Finally, it was found that an asymmetric lithosphere-astenosphere boundary resulting from corner flow in the mantle wedge of the eastward-directed subduction zone tends to generate east-vergent detachments.
N2  - Die südlichen Zentralanden (33°-36°S) sind eine ausgezeichnete, natürliche Forschungsumgebung zur Untersuchung gebirgsbildender Deformationsprozesse, in der Randbedingungen, wie die Geometrie der subduzierten Platte, einen starken Einfluss auf die Evolution des Gebirges besitzen. Anderseits sind die Deformationsmechanismen geprägt  von der Heterogenität der Südamerikanischen Platte. In dieser Arbeit wird die Bedeutung dieses Mechanismus  für die Herausbildung der Anden während des Känozoikums untersucht.
Im südlichen Teil (34-36°S), in dem die subduzierte Platte in einem steileren Winkel in den Erdmantel absinkt, wird die Entwicklung der Andendeformation mithilfe von oberflächlich aufgezeichneten und in tiefere Erdschichten reichenden Daten untersucht. Das darauf aufbauende Strukturmodell ermöglicht die Abschätzung der tektonischen Spannungen vom Miozän bis in die Neuzeit und den Einfluss der Bewegungen von magmatischen Fluiden, sowie Kohlenwasserstoffen. Auf Grundlage dieser Daten und solcher, die von Wissenschaftlern im nördlichen Bereich des Untersuchungsgebietes (33-34°S) erfasst wurden, wurde eine geodynamische, numerische Modellierung durchgeführt, um die Hypothese des Einflusses der Heterogenität der oberen Platten auf die Gebirgsbildung der Anden zu überprüfen. Die genutzte geodynamische Softwares (LAPEX-2D und ASPECT) simulieren das Verhalten von elasto-viskoplastischen Materialien, wenn diese unter Spannung stehen. Die Modellierungsergebnisse zeigen, dass die Kontraktionsprozesse hauptsächlich durch die Stärke der Lithosphäre beeinflusst werden. Diese Kenngröße wird aus der Zusammensetzung von Ober- und Unterkruste und dem Anteil des lithosphärischen Mantels, der durch vorhergehende tektonische Vorgänge überprägt ist, bestimmt. Diese räumlich begrenzten tektono-magmatischen Events definieren ebenfalls die Zusammensetzung und die Geometrie der Erdkruste, welche einen großen Einfluss auf das räumliche Auftreten von Deformationsprozessen hat. Eine eher felsische Unterkruste führt vorrangig zu pure-shear, während eine eher mafisch zusammengesetzte Unterkruste primär zu einem Deformationsmechanismus führt, der simple-shear genannt wird. Weiterhing wurde beobachtet, dass die Dicke der Lithosphäre vor der Deformation einen fundamentalen Einfluss auf die räumliche Eingrenzung von Deformation hat, wobei Regionen mit einer dünnen Lithosphärenschicht verstärkt Deformation aufweisen. Eine asymmetrische Grenzschicht zwischen Lithosphäre und Asthenosphäre ist das Resultat von Fließprozessen im Erdmantel, im Keil zwischen der obenliegenden Platte und der sich ostwärts absinkenden Subduktionszone, und verstärkt die Herausbildung von nach Osten gerichteten Abscherungen in der Erdkruste.
KW  - structural geology
KW  - tectonics
KW  - subduction
KW  - geodynamic modeling
KW  - geodynamische Modellierung
KW  - Strukturgeologie
KW  - Subduktion
KW  - Tektonik
Y1  - 2021
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-515909
ER  - 
TY  - GEN
A1  - Ben Dor, Yoav
A1  - Neugebauer, Ina
A1  - Enzel, Yehouda
A1  - Schwab, Markus J.
A1  - Tjallingii, Rik
A1  - Erel, Yigal
A1  - Brauer, Achim
T1  - Reply to comment on: Ben Dor, Yoav et al. : Varves of the Dead Sea sedimentary record. - In: Quaternary science reviews : the international multidisciplinary research and review journal. - 215 (2019), S. 173 - 184. - (ISSN: 0277-3791). - https://doi.org/10.1016/j.quascirev.2019.04.011
T2  - Quaternary science reviews : the international multidisciplinary research and review journal
N2  - In the comment on "Varves of the Dead Sea sedimentary record." Quaternary Science Reviews 215 (Ben Dor et al., 2019): 173-184. by R. Bookman, two recently published papers are suggested to prove that the interpretation of the laminated sedimentary sequence of the Dead Sea, deposited mostly during MIS2 and Holocene pluvials, as annual deposits (i.e., varves) is wrong. In the following response, we delineate several lines of evidence which coalesce to demonstrate that based on the vast majority of evidence, including some of the evidence provided in the comment itself, the interpretation of these sediments as varves is the more likely scientific conclusion. We further discuss the evidence brought up in the comment and its irrelevance and lack of robustness for addressing the question under discussion.
Y1  - 2020
U6  - https://doi.org/10.1016/j.quascirev.2019.106063
SN  - 0277-3791
SN  - 1873-457X
VL  - 231
PB  - Elsevier
CY  - Amsterdam [u.a.]
ER  - 
TY  - JOUR
A1  - Bentz, Stephan
A1  - Kwiatek, Grzegorz
A1  - Martinez-Garzon, Patricia
A1  - Bohnhoff, Marco
A1  - Dresen, Georg
T1  - Seismic moment evolution during hydraulic stimulations
JF  - Geophysical research letters
N2  - Analysis of past and present stimulation projects reveals that the temporal evolution and growth of maximum observed moment magnitudes may be linked directly to the injected fluid volume and hydraulic energy. Overall evolution of seismic moment seems independent of the tectonic stress regime and is most likely governed by reservoir specific parameters, such as the preexisting structural inventory. Data suggest that magnitudes can grow either in a stable way, indicating the constant propagation of self-arrested ruptures, or unbound, for which the maximum magnitude is only limited by the size of tectonic faults and fault connectivity. Transition between the two states may occur at any time during injection or not at all. Monitoring and traffic light systems used during stimulations need to account for the possibility of unstable rupture propagation from the very beginning of injection by observing the entire seismicity evolution in near-real time and at high resolution for an immediate reaction in injection strategy. 

Plain Language Summary Predicting and controlling the size of earthquakes caused by fluid injection is currently the major concern of many projects associated with geothermal energy production. Here, we analyze the magnitude and seismic moment evolution with injection parameters for prominent geothermal and scientific projects to date. Evolution of seismicity seems to be largely independent of the tectonic stress background and seemingly depends on reservoir specific characteristics. We find that the maximum observed magnitudes relate linearly to the injected volume or hydraulic energy. A linear relation suggests stable growth of induced ruptures, as predicted by current models, or rupture growth may no longer depend on the stimulated volume but on tectonics. A system may change between the two states during the course of fluid injection. Close-by and high-resolution monitoring of seismic and hydraulic parameters in near-real time may help identify these fundamental changes in ample time to change injection strategy and manage maximum magnitudes.
Y1  - 2020
U6  - https://doi.org/10.1029/2019GL086185
SN  - 0094-8276
SN  - 1944-8007
VL  - 47
IS  - 5
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - THES
A1  - Biedermann, Nicole
T1  - Carbonate-silicate reactions at conditions of the Earth’s mantle and the role of carbonates as possible trace-element carriers
N2  - Carbonates play a key role in the chemistry and dynamics of our planet. They are directly connected to the CO2 budget of our atmosphere and have a great impact on the deep carbon cycle. Moreover, recent studies have shown that carbonates are stable along the geothermal gradient down to Earth's lower mantle conditions, changing their crystal structure and related properties. Subducted carbonates may also react with silicates to form new phases. These reactions will redistribute elements, such as calcium (Ca), magnesium (Mg), iron (Fe) and carbon in the form of carbon dioxide (CO2), but also trace elements, that are carried by the carbonates. The trace elements of most interest are strontium (Sr) and rare earth elements (REE) which have been found to be important constituents in the composition of the primitive lower mantle and in mineral inclusions found in super-deep diamonds. However, the stability of carbonates in presence of mantle silicates at relevant temperatures is far from being well understood. Related to this, very little is known about distribution processes of trace elements between carbonates and mantle silicates. To shed light on these processes, we studied reactions between Sr- and REE-containing CaCO3 and Mg/Fe-bearing silicates of the system (Mg,Fe)2SiO4 - (Mg,Fe)SiO3 at high pressure and high temperature using synchrotron radiation based μ-X-ray diffraction (μ-XRD) and μ-X-ray fluorescence (μ-XRF) with μm-resolution in a laser-heated diamond anvil cell. X-ray diffraction is used to derive the structural changes of the phase reactions whereas X-ray fluorescence gives information on the chemical changes in the sample. In-situ experiments at high pressure and high temperature were performed at beamline P02.2 at PETRA III (Hamburg, Germany) and at beamline ID27 at ESRF (Grenoble, France). In addition to μ-XRD and μ-XRF, ex-situ measurements were made on the recovered sample material using transmission electron microscopy (TEM) and provided further insights into the reaction kinetics of carbonate-silicate reactions.
Our investigations show that CaCO3 is unstable in presence of mantle silicates above 1700 K and a reaction takes place in which magnesite plus CaSiO3-perovskite are formed. In addition, we observed that a high content of iron in the carbonate-silicate system favours dolomite formation during the reaction. The subduction of natural carbonates with significant amounts of Sr leads to a comprehensive investigation of the stability not only of CaCO3 phases in contact with mantle silicates but also of SrCO3 (and of Sr-bearing CaCO3). We found that SrCO3 reacts with (Mg,Fe)SiO3-perovskite to form magnesite and gained evidence for the formation of SrSiO3-perovskite.
To complement our study on the stability of SrCO3 at conditions of the Earth's lower mantle, we performed powder X-ray diffraction and single crystal X-ray diffraction experiments at ambient temperature and up to 49 GPa. We observed a transformation from SrCO3-I into a new high-pressure phase SrCO3-II at around 26 GPa with Pmmn crystal structure and a bulk modulus of 103(10) GPa. This information is essential to fully understand the phase behaviour and stability of carbonates in the Earth's lower mantle and to elucidate the possibility of introducing Sr into mantle silicates by carbonate-silicate reactions.
Simultaneous recording of μ-XRD and μ-XRF in the μm-range over the heated areas provides spatial information not only about phase reactions but also on the elemental redistribution during the reactions. A comparison of the spatial intensity distribution of the XRF signal before and after heating indicates a change in the elemental distribution of Sr and an increase in Sr-concentration was found around the newly formed SrSiO3-perovskite. With the help of additional TEM analyses on the quenched sample material the elemental redistribution was studied at a sub-micrometer scale. Contrary to expectations from combined μ-XRD and μ-XRF measurements, we found that La and Eu were not incorporated into the silicate phases, instead they tend to form either isolated oxide phases (e.g. Eu2O3, La2O3) or hydroxyl-bastnäsite (La(CO3)(OH)). In addition, we observed the transformation from (Mg,Fe)SiO3-perovskite to low-pressure clinoenstatite during pressure release. The monoclinic structure (P21/c) of this phase allows the incorporation of Ca as shown by additional EDX analyses and, to a minor extent, Sr too.
Based on our experiments, we can conclude that a detection of the trace elements in-situ at high pressure and high temperature remains challenging. However, our first findings imply that silicates may incorporate the trace elements provided by the carbonates and indicate that carbonates may have a major effect on the trace element contents of mantle phases.
N2  - Karbonate spielen eine wesentliche Rolle in der Chemie und Dynamik unseres Planeten. Sie stehen im direkten Zusammenhang mit dem CO2-Haushalt unserer Atmosphäre und dem tiefen, erdinneren Kohlenstoff-Kreislauf. Darüber hinaus haben jüngste Studien gezeigt, dass subduzierte Karbonate entlang des geothermischen Gradienten bis hinunter zu unteren Erdmantelbedingungen stabil sind, wobei sich ihre Kristallstruktur und die damit verbundenen Eigenschaften ändern. Ebenso können subduzierte Karbonate mit Mantelsilikaten reagieren. Diese Reaktionen führen zu einer Umverteilung von Elementen, welche von den subduzierten Karbonaten hinunter in die Tiefen der Erde transportiert werden. Die Elemente, um die es sich hauptsächlich handelt, sind dabei Calcium (Ca), Magnesium (Mg), Eisen (Fe) und Kohlenstoff (C). Aber auch Spurenelemente, wie beispielsweise Strontium (Sr) und Seltene Erdelemente (REE), können über Karbonate in den unteren Erdmantelbereich gelangen. Die Stabilität der Karbonate in Gegenwart von Mantelsilikaten bei relevanten Erdmantelbedingungen ist jedoch bei Weitem nicht bekannt. Ebenso ist nur sehr wenig über die Verteilungsprozesse von Spurenelementen zwischen Karbonaten und Mantelsilikaten bekannt. Um diese Prozesse zu beleuchten, wurden Reaktionen zwischen Sr- und REE-haltigem CaCO3 und Mg/Fe-haltigen Silikaten aus dem System (Mg,Fe)2SiO4 - (Mg,Fe)SiO3 unter hohem Druck und hoher Temperatur mit μm-aufgelöster Röntgenbeugung (μ-XRD) und Röntgenfluoreszenz (μ-XRF) in einer lasergeheizten Diamantstempelzelle durchgeführt. Dabei wird Röntgenbeugung verwendet, um die strukturellen Änderungen der Phasenreaktionen abzuleiten, während Röntgenfluoreszenz Informationen über die chemischen Änderungen in der Probe liefert.
Unsere Untersuchungen zeigen, dass sowohl SrCO3 als auch CaCO3 in Gegenwart von Mantelsilikaten bei über 1700 K instabil sind und eine Reaktion stattfindet, bei der Magnesit und CaSiO3-Perowskit bzw. SrSiO3-Perowskit gebildet werden. Ein Vergleich der räumlichen Intensitätsverteilungen von XRF Signalen vor und nach dem Heizen zeigt eine Änderung in der Elementverteilung von Sr und eine Zunahme der Sr-Konzentration um den neugebildeten SrSiO3-Perowskit. Zusätzliche Aufnahmen am zurückgewonnenen, abgeschreckten Probenmaterial mittels Transmissionselektronenmikroskopie (TEM) lieferten weitere Erkenntnisse zur Reaktionskinetik. Entgegen den Erwartungen eines Einbaus der Seltenen Erdelemente in die neugebildeten Mantelsilikate, haben wir aus kombinierten μ-XRD-, μ-XRF- und TEM-Messungen festgestellt, dass La und Eu entweder isolierte Oxidphasen (Eu2O3, La2O3) oder Hydroxyl-Bastnäsit (La(CO3)(OH)) bilden. Zusätzlich war zu beobachten, dass (Mg,Fe)SiO3-Perowskit sich während der Druckentlastung in Clinoenstatit umgewandelt hat. Die monokline Struktur dieser Phase ermöglicht den Einbau von Ca und, im geringerem Maße, Sr, wie durch zusätzliche EDX-Analysen gezeigt wurde. Ergänzend zu unserer Studie führten wir Pulver-Röntgenbeugung in Kombination mit Einkristall-Röntgenbeugung bei Umgebungstemperatur und bis zu 49 GPa am Endglied Strontianit (SrCO3) durch. Wir beobachteten eine Umwandlung von SrCO3-I in eine neue Hochdruckphase SrCO3-II bei etwa 26 GPa mit Pmmn-Kristallstruktur und einem Kompressionsmodul von 103(10) GPa. Solche Informationen sind sehr wichtig, da sie Aufschlüsse sowohl über das Phasenverhalten als auch über die Stabilität von Karbonaten in Gegenwart von Mantelsilikaten geben und helfen, sie vollständig zu verstehen.
Basierend auf den Erkenntnissen aus unseren Experimenten können wir schließen, dass ein Nachweis von Spurenelementen in-situ unter hohem Druck und hoher Temperatur eine Herausforderung bleibt. Unsere Ergebnisse deuten jedoch darauf hin, dass Silikate die Spurenelemente, welche von den Karbonaten transportiert werden, aufnehmen können und demzufolge Karbonate einen wesentlichen Einfluss auf den Spurenelementgehalt von Mantelphasen haben.
T2  - Karbonat-Silikat-Reaktionen bei Erdmantelbedingungen und die Rolle der Karbonate als mögliche Spurenelementträger
KW  - laser-heated Diamond Anvil Cell
KW  - Carbonate-Silicate reactions
KW  - Earth's mantle
KW  - Karbonat-Silikat-Reaktionen
KW  - Erdmantel
KW  - laser-geheizte Diamantstempelzelle
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-482772
ER  - 
TY  - THES
A1  - Borghini, Alessia
T1  - Melt inclusions in mafic rocks as witnesses of metasomatism in the Bohemian Massif
N2  - Orogenic peridotites represent portions of upper subcontinental mantle now incorporated in mountain belts. They often contain layers, lenses and irregular bodies of pyroxenite and eclogite. The origin of this heterogeneity and the nature of these layers is still debated but it is likely to involve processes such as transient melts coming from the crust or the mantle and segregating in magma conduits, crust-mantle interaction, upwelling of the asthenosphere and metasomatism. All these processes occur in the lithospheric mantle and are often related with the subduction of crustal rocks to mantle depths. In fact, during subduction, fluids and melts are released from the slab and can interact with the overlying mantle, making the study of deep melts in this environment crucial to understand mantle heterogeneity and crust-mantle interaction. The aim of this thesis is precisely to better constrain how such processes take place studying directly the melt trapped as primary inclusions in pyroxenites and eclogites. The Bohemian Massif, crystalline core of the Variscan belt, is targeted for these purposes because it contains orogenic peridotites with layers of pyroxenite and eclogite and other mafic rocks enclosed in felsic high pressure and ultra-high pressure crustal rocks. Within this Massif mafic rocks from two areas have been selected: the garnet clinopyroxenite in orogenic peridotite of the Granulitgebirge and the ultra-high pressure eclogite in the diamond-bearing gneisses of the Erzgebirge. In both areas primary melt inclusions were recognized in the garnet, ranging in size between 2-25 µm and with different degrees of crystallization, from glassy to polycrystalline. They have been investigated with Micro Raman spectroscopy and EDS mapping and the mineral assemblage is kumdykolite, phlogopite, quartz, kokchetavite, phase with a main Raman peak at 430 cm-1, phase with a main Raman peak at 412 cm-1, white mica and calcite with some variability in relative abundance depending on the case study. In the Granulitgebirge osumilite and pyroxene are also present, whereas calcite is one of the main phases in the Erzgebirge. The presence of glass and the mineral assemblage in the nanogranitoids suggest that they were former droplets of melt trapped in the garnet while it was growing. Glassy inclusions and re-homogenized nanogranitoids show a silicate melt that is granitic, hydrous, high in alkalis and weakly peraluminous. The melt is also enriched in both case studies in Cs, Pb, Rb, U, Th, Li and B suggesting the involvement of crustal component, i.e. white mica (main carrier of Cs, Pb, Rb, Li and B), and a fluid (Cs, Th and U) in the melt producing reaction. The whole rock in both cases mainly consists of garnet and clinopyroxene with, in Erzgebirge samples, the additional presence of quartz both in the matrix and as a polycrystalline inclusion in the garnet. The latter is interpreted as a quartz pseudomorph after coesite and occurs in the same microstructural position as the melt inclusions. Both rock types show a crustal and subduction zone signature with garnet and clinopyroxene in equilibrium. Melt was likely present during the metamorphic peak of the rock, as it occurs in garnet. 
Our data suggest that the processes most likely responsible for the formation of the investigated rocks in both areas is a metasomatic reaction between a melt produced in the crust and mafic layers formerly located in the mantle wedge for the Granulitgebirge and in the subducted continental crust itself in the Erzgebirge. Thus metasomatism in the first case took place in the mantle overlying the slab, whereas in the second case metasomatism took place in the continental crust that already contained, before subduction, mafic layers. Moreover, the presence of former coesite in the same microstructural position of the melt inclusions in the Erzgebirge garnets suggest that metasomatism took place at ultra-high pressure conditions.
Summarizing, in this thesis we provide new insights into the geodynamic evolution of the Bohemian Massif based on the study of melt inclusions in garnet in two different mafic rock types, combining the direct microstructural and geochemical investigation of the inclusions with the whole-rock and mineral geochemistry. We report for the first time data, directly extracted from natural rocks, on the metasomatic melt responsible for the metasomatism of several areas of the Bohemian Massif. Besides the two locations here investigated, belonging to the Saxothuringian Zone, a signature similar to the investigated melt is clearly visible in pyroxenite and peridotite of the T-7 borehole (again Saxothuringian Zone) and the durbachite suite located in the Moldanubian Zone.
N2  - Die Präsenz orogener Peridotite - metamorphosierte Bestanteile des Mantels -, die in Gebirgen auftreten, belegt, dass der Erdmantel an Kontinent-Kontinent-Kollisionen beteiligt sein kann. Solche orogenen Peridotite sind häufig heterogen, da sie Pyroxenit- und Eklogitlagen und Linsen enthalten, d.h. Hochdruckgesteine, die aus Granat und Klinopyroxen bestehen. Die meisten Prozesse, die für diese Heterogenität verantwortlich sind, involvieren Schmelzen, die durch den Mantel migrieren und dabei zu dessen Metasomatose oder zu der Anreicherung von Granat und Klinopyroxen in Adern und Kanälen führen. Ein weiterer Prozess kann auch das Recyceln subduzierter ozeanischer Kruste im Erdmantel sein. Im Allgemeinen finden all diese Prozesse während der Subduktion der Kruste in Manteltiefe statt. Unter diesen Bedingungen stehen die Krustengesteine im direkten Kontakt mit den Mantelgesteinen und die dabei freigesetzten Fluide oder Schmelzen können mit den Peridotiten wechselwirken. Letztere können anschließend von den Krustengesteinen aufgenommen und zur Erdoberfläche exhumiert werden, wo sie untersucht werden können. Diese Arbeit fokussiert sich vor allem auf die Untersuchung der Pyroxenit- und Eklogitbildung sowie auf die Wechselwirkung zwischen Schmelze und Gestein während der Subduktion der Kontinentalkruste in Manteltiefe. Dafür ist das Böhmische Massiv die ideale geologische Umgebung, da es erhebliche Mengen an Pyroxeniten und Eklogiten enthält, die sich in einigen Fällen in orogenen Peridotiten befinden, und die alle in einer ehemals tief subduziertern kontinentalern Kruste eingegliedert wurden. Um die Zielstellung zu erreichen, wurde die Schmelze mit einem neuartigen Ansatz untersucht, wobei diese hier direkt in primären Schmelzeinschlüssen, die im Granat eingeschlossenen sind, untersucht wird. Es wurden zwei Gebiete mit Pyroxeniten und Eklogiten, die Schmelzeinschlüsse enthalten, ausgewählt, ein Pyroxenit aus dem Granulitgebirge und ein Ultrahochdruck-Eklogit aus dem Erzgebirge (Sachsen, Deutschland). Die Einschlüsse bestehen aus einer granitischen, wasserhaltigen Schmelze krustaler Herkunft. Das Auftreten der im Granat unregelmäßig verteilten Einschlüsse bestätigt das Vorhandensein von Schmelze während der Peakmetamorphose. Da die Schmelzen in beiden Fällen ähnlich sind, schlussfolgern wir daraus, dass beide Gesteinsarten durch metasomatische Prozesse infolge der Wechselwirkung von silikatreicher Schmelze und mafischen Lagen gebildete wurden. Im Granulitgebirge ging die Schmelze eine Wechselwirkung mit mafischen Lagen im Mantel ein und erst später wurde der Wirtsperidotit einschließlich der neugebildeten Pyroxenit- und Eklogitlagen in die subduzierte Kruste eingebaut. Im Fall der Pyroxenite und Eklogite des Erzgebirges fand die Metasomatose stattdessen in der kontinentalen Kruste statt. Hier ging die Schmelze eine Wechselwirkung mit mafischen Lagen ein, die sich bereits vor der Subduktion in der Kruste befunden hatten. Im letzteren Fall belegt der Hinweis auf ehemaligen Coesit , d. h. auf ein Mineral, das Tiefen >95 km anzeigt, welches anwesend war während der Metasomatose, dass die Prozesse in größeren Tiefen stattfanden als im Granulitgebirge.
T2  - Schmelzeinschlüsse in mafischen Gesteinen als Zeugen von Metasomatose im Böhmischen Massiv
KW  - Petrology
KW  - Petrologie
KW  - Metamorphism
KW  - Melt inclusions
KW  - Metasomatism
KW  - Metamorphose
KW  - Schmelzeinschlüsse
KW  - Metasomatose
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-473639
ER  - 
TY  - GEN
A1  - Braun, Jean
T1  - Response to comment by Japsen et al. on "A review of numerical modeling studies of passive margin escarpments leading to a new analytical expression for the rate of escarpment migration velocity"
T2  - Gondwana research : international geoscience journal ; official journal of the International Association for Gondwana Research
Y1  - 2020
U6  - https://doi.org/10.1016/j.gr.2018.10.003
SN  - 1342-937X
SN  - 1878-0571
VL  - 65
SP  - 174
EP  - 176
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Brill, Fabio Alexander
A1  - Passuni Pineda, Silvia
A1  - Espichan Cuya, Bruno
A1  - Kreibich, Heidi
T1  - A data-mining approach towards damage modelling for El Nino events in Peru
JF  - Geomatics, natural hazards and risk
N2  - Compound natural hazards likeEl Ninoevents cause high damage to society, which to manage requires reliable risk assessments. Damage modelling is a prerequisite for quantitative risk estimations, yet many procedures still rely on expert knowledge, and empirical studies investigating damage from compound natural hazards hardly exist. A nationwide building survey in Peru after theEl Ninoevent 2017 - which caused intense rainfall, ponding water, flash floods and landslides - enables us to apply data-mining methods for statistical groundwork, using explanatory features generated from remote sensing products and open data. We separate regions of different dominant characteristics through unsupervised clustering, and investigate feature importance rankings for classifying damage via supervised machine learning. Besides the expected effect of precipitation, the classification algorithms select the topographic wetness index as most important feature, especially in low elevation areas. The slope length and steepness factor ranks high for mountains and canyons. Partial dependence plots further hint at amplified vulnerability in rural areas. An example of an empirical damage probability map, developed with a random forest model, is provided to demonstrate the technical feasibility.
KW  - Natural hazard
KW  - damage model
KW  - residential buildings
KW  - data-mining
KW  - remote
KW  - sensing
KW  - open data
Y1  - 2020
U6  - https://doi.org/10.1080/19475705.2020.1818636
SN  - 1947-5705
SN  - 1947-5713
VL  - 11
IS  - 1
SP  - 1966
EP  - 1990
PB  - Routledge, Taylor & Francis Group
CY  - Abingdon
ER  - 
TY  - JOUR
A1  - Brunello, Camilla Francesca
A1  - Andermann, Christoff
A1  - Marc, Odin
A1  - Schneider, Katharina A.
A1  - Comiti, Francesco
A1  - Achleitner, Stefan
A1  - Hovius, Niels
T1  - Annually resolved monsoon onset and withdrawal dates across the Himalayas derived from local precipitation statistics
JF  - Geophysical research letters
N2  - A local and flexible definition of the monsoon season based on hydrological evidence is important for the understanding and management of Himalayan water resources. Here, we present an objective statistical method to retrieve seasonal hydrometeorological transitions. Applied to daily rainfall data (1951-2015), this method shows an average longitudinal delay of similar to 15 days, with later monsoon onset and earlier withdrawal in the western Himalaya, consistent with the continental progression of wet air masses. This delay leads to seasons of different length along the Himalaya and biased precipitation amounts when using uniform calendric monsoon boundaries. In the Central Himalaya annual precipitation has increased, due primarily to an increase of premonsoon precipitation. These findings highlight issues associated with a static definition of monsoon boundaries and call for a deeper understanding of nonmonsoonal precipitation over the Himalayan water tower. <br /> Plain Language Summary Precipitation in the Himalayas determines water availability for the Indian foreland with large socioeconomic implications. Despite its importance, spatial and temporal patterns of precipitation are poorly understood. Here, we estimate the long-term average and trends of seasonal precipitation at the scale of individual catchments draining the Himalayas. We apply a statistical method to detect the timing of hydrometeorological seasons from local precipitation measurements, focusing on monsoon onset and withdrawal. We identify longitudinal and latitudinal delays, resulting in seasons of different length along and across the Himalayas. These spatial patterns and the annual variability of the monsoon boundaries mean that oft-used, fixed calendric dates, for example, 1 June to 30 September, may be inadequate for retrieving monsoon rainfall totals. Moreover, we find that, despite its prominent contribution to annual rainfall totals, the Indian summer monsoon cannot explain the increase of the annual precipitation over the Central Himalayas. Instead, this appears to be mostly driven by changes in premonsoon and winter rainfall. So far, little attention has been paid to premonsoon precipitation, but governed by evaporative processes and surface water availability, it may be enhanced by irrigation and changed land use in the Gangetic foreland.
Y1  - 2020
U6  - https://doi.org/10.1029/2020GL088420
SN  - 0094-8276
SN  - 1944-8007
VL  - 47
IS  - 23
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Calitri, Francesca
A1  - Sommer, Michael
A1  - van der Meij, Marijn W.
A1  - Egli, Markus
T1  - Soil erosion along a transect in a forested catchment: recent or ancient processes?
JF  - Catena : an interdisciplinary journal of soil science, hydrology, geomorphology focusing on geoecology and landscape evolution
N2  - Forested areas are assumed not to be influenced by erosion processes. However, forest soils of Northern Germany in a hummocky ground moraine landscape can sometimes exhibit a very shallow thickness on crest positions and buried soils on slope positions. The question consequently is: Are these on-going or ancient erosional and depositional processes? Plutonium isotopes act as soil erosion/deposition tracers for recent (last few decades) processes. Here, we quantified the 239+240PU inventories in a small, forested catchment (ancient forest "Melzower Forst", deciduous trees), which is characterised by a hummocky terrain including a kettle hole. Soil development depths (depth to C horizon) and 239+240PU inventories along a catena of sixteen different profiles were determined and correlated to relief parameters. Moreover, we compared different modelling approaches to derive erosion rates from Pu data. <br /> We find a strong relationship between soil development depths, distance-to-sink and topography along the catena. Fully developed Retisols (thicknesses > 1 m) in the colluvium overlay old land surfaces as documented by fossil Ah horizons. However, we found no relationship of Pu-based erosion rates to any relief parameter. Instead, 239+240PU inventories showed a very high local, spatial variability (36-70 Bq m(-2)). Low annual rainfall, spatially distributed interception and stem flow might explain the high variability of the 239+240PU inventories, giving rise to a patchy input pattern. Different models resulted in quite similar erosion and deposition rates (max: -5 t ha(-1) yr(-1) to +7.3 t ha(-1) yr(-1)). Although some rates are rather high, the magnitude of soil erosion and deposition - in terms of soil thickness change - is negligible during the last 55 years. The partially high values are an effect of the patchy Pu deposition on the forest floor. This forest has been protected for at least 240 years. Therefore rather natural events and anthropogenic activities during medieval times or even earlier must have caused the observed soil pattern, which documents strong erosion and deposition processes.
KW  - Soil erosion
KW  - 239+240 Plutonium
KW  - Forest
KW  - Moraine landscape
KW  - Soil catena
Y1  - 2020
U6  - https://doi.org/10.1016/j.catena.2020.104683
SN  - 0341-8162
SN  - 1872-6887
VL  - 194
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Castino, Fabiana
A1  - Bookhagen, Bodo
A1  - De la Torre, Alejandro
T1  - Atmospheric dynamics of extreme discharge events from 1979 to 2016 in the southern Central Andes
JF  - Climate dynamics : observational, theoretical and computational research on the climate system
N2  - During the South-American Monsoon season, deep convective systems occur at the eastern flank of the Central Andes leading to heavy rainfall and flooding. We investigate the large- and meso-scale atmospheric dynamics associated with extreme discharge events (> 99.9th percentile) observed in two major river catchments meridionally stretching from humid to semi-arid conditions in the southern Central Andes. Based on daily gauge time series and ERA-Interim reanalysis, we made the following three key observations: (1) for the period 1940-2016 daily discharge exhibits more pronounced variability in the southern, semi-arid than in the northern, humid catchments. This is due to a smaller ratio of discharge magnitudes between intermediate (0.2 year return period) and rare events (20 year return period) in the semi-arid compared to the humid areas; (2) The climatological composites of the 40 largest discharge events showed characteristic atmospheric features of cold surges based on 5-day time-lagged sequences of geopotential height at different levels in the troposphere; (3) A subjective classification revealed that 80% of the 40 largest discharge events are mainly associated with the north-northeastward migration of frontal systems and 2/3 of these are cold fronts, i.e. cold surges. This work highlights the importance of cold surges and their related atmospheric processes for the generation of heavy rainfall events and floods in the southern Central Andes.
KW  - South American monsoon system
KW  - cold surges
KW  - orographic barrier
KW  - mesoscale convective systems
KW  - extreme discharge
KW  - daily-discharge time
KW  - series ERA-interim
Y1  - 2019
U6  - https://doi.org/10.1007/s00382-020-05458-1
SN  - 0930-7575
SN  - 1432-0894
VL  - 55
IS  - 11-12
SP  - 3485
EP  - 3505
PB  - Springer
CY  - Berlin ; Heidelberg [u.a.]
ER  - 
TY  - JOUR
A1  - Cheng, Chaojie
A1  - Milsch, Harald
T1  - Permeability variations in illite-bearing sandstone
BT  - effects of temperature and NaCl fluid salinity
JF  - Journal of geophysical research : Solid earth
N2  - Temperature changes and variations in pore fluid salinity may negatively affect the permeability of clay-bearing sandstones with implications for natural fluid flow and geotechnical applications alike. In this study these factors are investigated for a sandstone dominated by illite as the clay phase. Systematic long-term flow-through experiments were conducted and complemented with comprehensive microstructural investigations and the application of Derjaguin-Landau-Verwey-Overbeek (DLVO) theory to explain mechanistically the observed permeability changes. Initially, sample permeability was not affected by low pore fluid salinity indicating strong attraction of the illite particles to the pore walls as supported by electron microprobe analysis (EMPA). Increasing temperature up to 145 degrees C resulted in an irreversible permeability decrease by 1.5 orders of magnitude regardless of the pore fluid composition (i.e., deionized water and 2 M NaCl solution). Subsequently diluting the high salinity pore fluid to below 0.5 M yielded an additional permeability decline by 1.5 orders of magnitude, both at 145 degrees C and after cooling to room temperature. By applying scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) thermo-mechanical pore throat closure and illite particle migration were identified as independently operating mechanisms responsible for observed permeability changes during heating and dilution, respectively. These observations indicate that permeability of illite-bearing sandstones will be impaired by heating and exposure to low salinity pore fluids. In addition, chemically induced permeability variations proved to be path dependent with respect to the applied succession of fluid salinity changes.
Y1  - 2020
U6  - https://doi.org/10.1029/2020JB020122
SN  - 2169-9313
SN  - 2169-9356
VL  - 125
IS  - 9
PB  - American Geophysical Union
CY  - Washington
ER  - 
TY  - JOUR
A1  - Cheng, Chaojie
A1  - Milsch, Harald
T1  - Evolution of fracture aperture in quartz sandstone under hydrothermal conditions
BT  - mechanical and chemical effects
JF  - Minerals
N2  - Fractures efficiently affect fluid flow in geological formations, and thereby determine mass and energy transport in reservoirs, which are not least exploited for economic resources. In this context, their response to mechanical and thermal changes, as well as fluid-rock interactions, is of paramount importance. In this study, a two-stage flow-through experiment was conducted on a pure quartz sandstone core of low matrix permeability, containing one single macroscopic tensile fracture. In the first short-term stage, the effects of mechanical and hydraulic aperture on pressure and temperature cycles were investigated. The purpose of the subsequent intermittent-flow long-term (140 days) stage was to constrain the evolution of the geometrical and hydraulic fracture properties resulting from pressure solution. Deionized water was used as the pore fluid, and permeability, as well as the effluent Si concentrations, were systematically measured. Overall, hydraulic aperture was shown to be significantly less affected by pressure, temperature and time, in comparison to mechanical aperture. During the long-term part of the experiment at 140 degrees C, the effluent Si concentrations likely reached a chemical equilibrium state within less than 8 days of stagnant flow, and exceeded the corresponding hydrostatic quartz solubility at this temperature. This implies that the pressure solution was active at the contacting fracture asperities, both at 140 degrees C and after cooling to 33 degrees C. The higher temperature yielded a higher dissolution rate and, consequently, a faster attainment of chemical equilibrium within the contact fluid. X-ray mu CT observations evidenced a noticeable increase in fracture contact area ratio, which, in combination with theoretical considerations, implies a significant decrease in mechanical aperture. In contrast, the sample permeability, and thus the hydraulic fracture aperture, virtually did not vary. In conclusion, pressure solution-induced fracture aperture changes are affected by the degree of time-dependent variations in pore fluid composition. In contrast to the present case of a quasi-closed system with mostly stagnant flow, in an open system with continuous once-through fluid flow, the activity of the pressure solution may be amplified due to the persistent fluid-chemical nonequilibrium state, thus possibly enhancing aperture and fracture permeability changes.
KW  - flow-through experiment
KW  - fracture aperture
KW  - pressure solution
KW  - mass
KW  - transfer
KW  - silica concentration
KW  - permeability
KW  - quartz sandstone
Y1  - 2020
U6  - https://doi.org/10.3390/min10080657
SN  - 2075-163X
VL  - 10
IS  - 8
PB  - MDPI
CY  - Basel
ER  - 
TY  - JOUR
A1  - Coesfeld, Jacqueline
A1  - Kuester, Theres
A1  - Kuechly, Helga U.
A1  - Kyba, Christopher C. M.
T1  - Reducing variability and removing natural light from nighttime satellite imagery: A case study using the VIIRS DNB
JF  - Sensors
N2  - Temporal variation of natural light sources such as airglow limits the ability of night light sensors to detect changes in small sources of artificial light (such as villages). This study presents a method for correcting for this effect globally, using the satellite radiance detected from regions without artificial light emissions. We developed a routine to define an approximate grid of locations worldwide that do not have regular light emission. We apply this method with a 5 degree equally spaced global grid (total of 2016 individual locations), using data from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB). This code could easily be adapted for other future global sensors. The correction reduces the standard deviation of data in the Earth Observation Group monthly DNB composites by almost a factor of two. The code and datasets presented here are available under an open license by GFZ Data Services, and are implemented in the Radiance Light Trends web application.
KW  - airglow
KW  - artificial light
KW  - calibration
KW  - VIIRS DNB
KW  - nightlights
KW  - remote sensing
Y1  - 2020
VL  - 20
PB  - MDPI
CY  - Basel
ER  - 
TY  - GEN
A1  - Coesfeld, Jacqueline
A1  - Kuester, Theres
A1  - Kuechly, Helga U.
A1  - Kyba, Christopher C. M.
T1  - Reducing variability and removing natural light from nighttime satellite imagery: A case study using the VIIRS DNB
T2  - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe
N2  - Temporal variation of natural light sources such as airglow limits the ability of night light sensors to detect changes in small sources of artificial light (such as villages). This study presents a method for correcting for this effect globally, using the satellite radiance detected from regions without artificial light emissions. We developed a routine to define an approximate grid of locations worldwide that do not have regular light emission. We apply this method with a 5 degree equally spaced global grid (total of 2016 individual locations), using data from the Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB). This code could easily be adapted for other future global sensors. The correction reduces the standard deviation of data in the Earth Observation Group monthly DNB composites by almost a factor of two. The code and datasets presented here are available under an open license by GFZ Data Services, and are implemented in the Radiance Light Trends web application.
T3  - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 1181 
KW  - airglow
KW  - artificial light
KW  - calibration
KW  - VIIRS DNB
KW  - nightlights
KW  - remote sensing
Y1  - 2020
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-524397
SN  - 1866-8372
IS  - 11
ER  - 
TY  - JOUR
A1  - Cook, Kristen L.
A1  - Turowski, Jens M.
A1  - Hovius, Niels
T1  - Width control on event-scale deposition and evacuation of sediment in bedrock-confined channels
JF  - Earth surface processes and landforms : the journal of the British Geomorphological Research Group
N2  - In mixed bedrock-alluvial rivers, the response of the system to a flood event can be affected by a number of factors, including coarse sediment availability in the channel, sediment supply from the hillslopes and upstream, flood sequencing and coarse sediment grain size distribution. However, the impact of along-stream changes in channel width on bedload transport dynamics remains largely unexplored. We combine field data, theory and numerical modelling to address this gap. First, we present observations from the Daan River gorge in western Taiwan, where the river flows through a 1 km long 20-50 m wide bedrock gorge bounded upstream and downstream by wide braidplains. We documented two flood events during which coarse sediment evacuation and redeposition appear to cause changes of up to several metres in channel bed elevation. Motivated by this case study, we examined the relationships between discharge, channel width and bedload transport capacity, and show that for a given slope narrow channels transport bedload more efficiently than wide ones at low discharges, whereas wider channels are more efficient at high discharges. We used the model sedFlow to explore this effect, running a random sequence of floods through a channel with a narrow gorge section bounded upstream and downstream by wider reaches. Channel response to imposed floods is complex, as high and low discharges drive different spatial patterns of erosion and deposition, and the channel may experience both of these regimes during the peak and recession periods of each flood. Our modelling suggests that width differences alone can drive substantial variations in sediment flux and bed response, without the need for variations in sediment supply or mobility. The fluctuations in sediment transport rates that result from width variations can lead to intermittent bed exposure, driving incision in different segments of the channel during different portions of the hydrograph.
KW  - bedload transport
KW  - discharge variability
KW  - bedrock-alluvial channels
KW  - channel width
KW  - hysteresis
Y1  - 2020
U6  - https://doi.org/10.1002/esp.4993
SN  - 0197-9337
SN  - 1096-9837
VL  - 45
IS  - 14
SP  - 3702
EP  - 3713
PB  - Wiley
CY  - Hoboken
ER  -