@article{AichnerHiltPerillonetal.2017,
author = {Aichner, Bernhard and Hilt, Sabine and Perillon, Cecile and Gillefalk, Mikael and Sachse, Dirk},
title = {Biosynthetic hydrogen isotopic fractionation factors during lipid synthesis in submerged aquatic macrophytes: Effect of groundwater discharge and salinity},
series = {Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry},
volume = {113},
journal = {Organic geochemistry : the international journal for rapid publication of current research in organic geochemistry and biochemistry},
publisher = {Elsevier},
address = {Oxford},
issn = {0146-6380},
doi = {10.1016/j.orggeochem.2017.07.021},
pages = {10 -- 16},
year = {2017},
abstract = {Sedimentary lipid biomarkers have become widely used tools for reconstructing past climatic and ecological changes due to their ubiquitous occurrence in lake sediments. In particular, the hydrogen isotopic composition (expressed as delta D values) of leaf wax lipids derived from terrestrial plants has been a focus of research during the last two decades and the understanding of competing environmental and plant physiological factors influencing the delta D values has greatly improved. Comparatively less attention has been paid to lipid biomarkers derived from aquatic plants, although these compounds are abundant in many lacustrine sediments. We therefore conducted a field and laboratory experiment to study the effect of salinity and groundwater discharge on the isotopic composition of aquatic plant biomarkers. We analyzed samples of the common submerged plant species, Potamogeton pectinatus (sago pondweed), which has a wide geographic distribution and can tolerate high salinity. We tested the effect of groundwater discharge (characterized by more negative delta D values relative to lake water) and salinity on the delta D values of n-alkanes from P. pectinatus by comparing plants (i) collected from the oligotrophic freshwater Lake Stechlin (Germany) at shallow littoral depth from locations with and without groundwater discharge, and (ii) plants grown from tubers collected from the eutrophic Lake Muggelsee in nutrient solution at four salinity levels. Isotopically depleted groundwater did not have a significant influence on the delta D values of n-alkanes in Lake Stechlin P. pectinatus and calculated isotopic fractionation factors epsilon(l/w) between lake water and n-alkanes averaged -137 +/- 9\%(n-C-23), -136 +/- 7\%(n-C-25) and -131 +/- 6\%(n-C-27), respectively. Similar epsilon values were calculated for plants from Lake Muggelsee grown in freshwater nutrient solution (-134 +/- 11\% for n-C-23), while greater fractionation was observed at increased salinity values of 10 (163 +/- 12\%) and 15(-172 +/- 15\%). We therefore suggest an average e value of -136 +/- 9\% between source water and the major n-alkanes in P. pectinatus grown under freshwater conditions. Our results demonstrate that isotopic fractionation can increase by 30-40\% at salinity values 10 and 15. These results could be explained either by inhibited plant growth at higher salinity, or by metabolic adaptation to salt stress that remain to be elucidated. A potential salinity effect on dD values of aquatic lipids requires further examination, since this would impact on the interpretation of downcore isotopic data in paleohydrologic studies. (C) 2017 Elsevier Ltd. All rights reserved.},
language = {en}
}
@article{AichnerMakhmudovRajabovetal.2019,
author = {Aichner, Bernhard and Makhmudov, Zafar and Rajabov, Iljomjon and Zhang, Qiong and Pausata, Francesco Salvatore R. and Werner, Martin and Heinecke, Liv and Kuessner, Marie L. and Feakins, Sarah J. and Sachse, Dirk and Mischke, Steffen},
title = {Hydroclimate in the Pamirs Was Driven by Changes in Precipitation-Evaporation Seasonality Since theLast Glacial Period},
series = {Geophysical research letters},
volume = {46},
journal = {Geophysical research letters},
number = {23},
publisher = {American Geophysical Union},
address = {Washington},
issn = {0094-8276},
doi = {10.1029/2019GL085202},
pages = {13972 -- 13983},
year = {2019},
abstract = {The Central Asian Pamir Mountains (Pamirs) are a high-altitude region sensitive to climatic change, with only few paleoclimatic records available. To examine the glacial-interglacial hydrological changes in the region, we analyzed the geochemical parameters of a 31-kyr record from Lake Karakul and performed a set of experiments with climate models to interpret the results. delta D values of terrestrial biomarkers showed insolation-driven trends reflecting major shifts of water vapor sources. For aquatic biomarkers, positive delta D shifts driven by changes in precipitation seasonality were observed at ca. 31-30, 28-26, and 17-14 kyr BP. Multiproxy paleoecological data and modelling results suggest that increased water availability, induced by decreased summer evaporation, triggered higher lake levels during those episodes, possibly synchronous to northern hemispheric rapid climate events. We conclude that seasonal changes in precipitation-evaporation balance significantly influenced the hydrological state of a large waterbody such as Lake Karakul, while annual precipitation amount and inflows remained fairly constant.},
language = {en}
}
@article{AikenAikenCotton2018,
author = {Aiken, John M. and Aiken, Chastity and Cotton, Fabrice},
title = {A python library for teaching computation to seismology students},
series = {Seismological research letters},
volume = {89},
journal = {Seismological research letters},
number = {3},
publisher = {Seismological Society of America},
address = {Albany},
issn = {0895-0695},
doi = {10.1785/0220170246},
pages = {1165 -- 1171},
year = {2018},
abstract = {Python is at the forefront of scientific computation for seismologists and therefore should be introduced to students interested in becoming seismologists. On its own, Python is open source and well designed with extensive libraries. However, Python code can also be executed, visualized, and communicated to others with "Jupyter Notebooks". Thus, Jupyter Notebooks are ideal for teaching students Python and scientific computation. In this article, we designed an openly available Python library and collection of Jupyter Notebooks based on defined scientific computation learning goals for seismology students. The Notebooks cover topics from an introduction to Python to organizing data, earthquake catalog statistics, linear regression, and making maps. Our Python library and collection of Jupyter Notebooks are meant to be used as course materials for an upper-division data analysis course in an Earth Science Department, and the materials were tested in a Probabilistic Seismic Hazard course. However, seismologists or anyone else who is interested in Python for data analysis and map making can use these materials.},
language = {en}
}
@article{AkalKoralayCandanetal.2011,
author = {Akal, Cuneyt and Koralay, O. Ersin and Candan, Osman and Oberh{\"a}nsli, Roland and Chen, Fukun},
title = {Geodynamic significance of the early triassic karaburun granitoid (Western Turkey) for the opening history of Neo-Tethys},
series = {Turkish journal of earth sciences = T{\"u}rk yerbilimleri dergisi},
volume = {20},
journal = {Turkish journal of earth sciences = T{\"u}rk yerbilimleri dergisi},
number = {3},
publisher = {T{\"u}bitak},
address = {Ankara},
issn = {1300-0985},
doi = {10.3906/yer-1008-1},
pages = {255 -- 271},
year = {2011},
abstract = {The Karaburun Peninsula, which is considered part of the Anatolide-Tauride Block of Turkey, contains clastic and carbonate sequences deposited on the northern margin of Gondwana. The Palaeozoic clastic sequence, which is intruded by the Early Triassic granitoid and tectonically overlies a Mesozoic melange sequence, can be divided into three subunits: a lower clastic subunit consisting of a sandstone-shale alternation, an upper clastic subunit consisting of black chert-bearing shales, sandstone and conglomerate, and a Permo-Carboniferous carbonate subunit. The lower Triassic Karaburun I-type granitoid has a high initial Sr-87/Sr-86 ratio (0.709021-0.709168), and low Nd-143/Nd-144 ratio (0.512004-0.512023) and epsilon Nd (-5.34 to -5.70) isotopic values. Geochronological data indicate a crystallization (intrusion) age of 247.1 +/- 2.0 Ma (Scythian). Geochemically, the acidic magmatism reflects a subduction-related continental-arc basin tectonic setting, which can be linked to the opening of the northern branch of Neo-Tethys as a continental back-arc rifting basin on the northern margin of Gondwana. This can be related to the closure through southward subduction of the Palaeotethys Ocean beneath Gondwana.},
language = {en}
}
@article{AkalCandanKoralayetal.2012,
author = {Akal, C{\"u}neyt and Candan, Osman and Koralay, O. Ersin and Oberh{\"a}nsli, Roland and Chen, Fukun and Prelevic, Dejan},
title = {Early Triassic potassic volcanism in the Afyon Zone of the Anatolides/Turkey - implications for the rifting of the Neo-Tethys},
series = {International journal of earth sciences},
volume = {101},
journal = {International journal of earth sciences},
number = {1},
publisher = {Springer},
address = {New York},
issn = {1437-3254},
doi = {10.1007/s00531-011-0654-2},
pages = {177 -- 194},
year = {2012},
abstract = {Afyon Zone, which was derived from the Anatolide-Tauride platform during closure of the Neo-Tethys, is made up of pre-Mesozoic basement and unconformably overlying Triassic-Early Tertiary cover series. The Afyon Zone contains widespread metavolcanic rocks, which are dominated by rhyolite, dacite, and trachyandesite. They form a distinct volcanic succession, which is separated from the underlying Silurian-Lower Carboniferous metacarbonates and meta-siliciclastics by a regional unconformity. Trachyandesitic metavolcanics are made up of massive lava flows, pyroclastics and epiclastics, less frequently, domes and dikes, which were developed on a deeply eroded subaerial landmass. U/Pb and Pb/Pb zircon geochronology yielded Lower Triassic (similar to 250 Ma) ages, which are interpreted as extrusion age of trachyandesitic volcanics. Based on the stratigraphic, geochronological, and geochemical data, we suggest that these Lower Triassic magmatic rocks represent an extensional tectonic setting on the northern active margin of the Gondwana, which led to the development of the northern branch of the Neo-Tethys.},
language = {en}
}
@article{AlAtikAbrahamsonBommeretal.2010,
author = {Al Atik, Linda and Abrahamson, Norman A. and Bommer, Julian J. and Scherbaum, Frank and Cotton, Fabrice and Kuehn, Nicolas},
title = {The variability of ground-motion prediction models and its components},
issn = {0895-0695},
doi = {10.1785/gssrl.81.5.794},
year = {2010},
language = {en}
}
@phdthesis{AlHalbouni2019,
author = {Al-Halbouni, Djamil},
title = {Photogrammetry and distinct element geomechanical modelling of sinkholes and large-scale karstic depressions},
doi = {10.25932/publishup-43215},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-432159},
school = {Universit{\"a}t Potsdam},
pages = {137},
year = {2019},
abstract = {Sinkholes and depressions are typical landforms of karst regions. They pose a considerable natural hazard to infrastructure, agriculture, economy and human life in affected areas worldwide. The physio-chemical processes of sinkholes and depression formation are manifold, ranging from dissolution and material erosion in the subsurface to mechanical subsidence/failure of the overburden. This thesis addresses the mechanisms leading to the development of sinkholes and depressions by using complementary methods: remote sensing, distinct element modelling and near-surface geophysics. In the first part, detailed information about the (hydro)-geological background, ground structures, morphologies and spatio-temporal development of sinkholes and depressions at a very active karst area at the Dead Sea are derived from satellite image analysis, photogrammetry and geologic field surveys. There, clusters of an increasing number of sinkholes have been developing since the 1980s within large-scale depressions and are distributed over different kinds of surface materials: clayey mud, sandy-gravel alluvium and lacustrine evaporites (salt). The morphology of sinkholes differs depending in which material they form: Sinkholes in sandy-gravel alluvium and salt are generally deeper and narrower than sinkholes in the interbedded evaporite and mud deposits. From repeated aerial surveys, collapse precursory features like small-scale subsidence, individual holes and cracks are identified in all materials. The analysis sheds light on the ongoing hazardous subsidence process, which is driven by the base-level fall of the Dead Sea and by the dynamic formation of subsurface water channels. In the second part of this thesis, a novel, 2D distinct element geomechanical modelling approach with the software PFC2D-V5 to simulating individual and multiple cavity growth and sinkhole and large-scale depression development is presented. The approach involves a stepwise material removal technique in void spaces of arbitrarily shaped geometries and is benchmarked by analytical and boundary element method solutions for circular cavities. Simulated compression and tension tests are used to calibrate model parameters with bulk rock properties for the materials of the field site. The simulations show that cavity and sinkhole evolution is controlled by material strength of both overburden and cavity host material, the depth and relative speed of the cavity growth and the developed stress pattern in the subsurface. Major findings are: (1) A progressively deepening differential subrosion with variable growth speed yields a more fragmented stress pattern with stress interaction between the cavities. It favours multiple sinkhole collapses and nesting within large-scale depressions. (2) Low-strength materials do not support large cavities in the material removal zone, and subsidence is mainly characterised by gradual sagging into the material removal zone with synclinal bending. (3) High-strength materials support large cavity formation, leading to sinkhole formation by sudden collapse of the overburden. (4) Large-scale depression formation happens either by coalescence of collapsing holes, block-wise brittle failure, or gradual sagging and lateral widening. The distinct element based approach is compared to results from remote sensing and geophysics at the field site. The numerical simulation outcomes are generally in good agreement with derived morphometrics, documented surface and subsurface structures as well as seismic velocities. Complementary findings on the subrosion process are provided from electric and seismic measurements in the area. Based on the novel combination of methods in this thesis, a generic model of karst landform evolution with focus on sinkhole and depression formation is developed. A deepening subrosion system related to preferential flow paths evolves and creates void spaces and subsurface conduits. This subsequently leads to hazardous subsidence, and the formation of sinkholes within large-scale depressions. Finally, a monitoring system for shallow natural hazard phenomena consisting of geodetic and geophysical observations is proposed for similarly affected areas.},
language = {en}
}
@misc{AlHalbouniHolohanTaherietal.2018,
author = {Al-Halbouni, Djamil and Holohan, Eoghan P. and Taheri, Abbas and Sch{\"o}pfer, Martin P. J. and Emam, Sacha and Dahm, Torsten},
title = {Geomechanical modelling of sinkhole development using distinct elements},
series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
number = {1061},
issn = {1866-8372},
doi = {10.25932/publishup-46843},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-468435},
pages = {35},
year = {2018},
abstract = {Mechanical and/or chemical removal of material from the subsurface may generate large subsurface cavities, the destabilisation of which can lead to ground collapse and the formation of sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and overburden collapse is desirable to better understand the sinkhole hazard but is a challenging task due to the involved high strains and material discontinuities. Here, we present 2-D distinct element method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, stepwise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and boundary element method models of a deep void space in a linear elastic material. Secondly, we explore the effects of properties of different uniform materials on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geotechnical parameters of three model materials representative of those in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion-style subsidence. Strong materials support quasi-stable to stable cavities, the overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly, we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the overburden but also due to an inhibition of stabilising stress arching. Finally, we compare our model sinkhole geometries to observations at the Ghor Al-Haditha sinkhole site in Jordan. Sinkhole depth ∕ diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth ∕ diameter values in each material type may partly reflect sinkhole growth trends.},
language = {en}
}
@article{AlHalbouniHolohanTaherietal.2018,
author = {Al-Halbouni, Djamil and Holohan, Eoghan P. and Taheri, Abbas and Sch{\"o}pfer, Martin P. J. and Emam, Sacha and Dahm, Torsten},
title = {Geomechanical modelling of sinkhole development using distinct elements},
series = {Solid earth},
volume = {9},
journal = {Solid earth},
number = {6},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1869-9510},
doi = {10.5194/se-9-1341-2018},
pages = {1341 -- 1373},
year = {2018},
abstract = {Mechanical and/or chemical removal of material from the subsurface may generate large subsurface cavities, the destabilisation of which can lead to ground collapse and the formation of sinkholes. Numerical simulation of the interaction of cavity growth, host material deformation and overburden collapse is desirable to better understand the sinkhole hazard but is a challenging task due to the involved high strains and material discontinuities. Here, we present 2-D distinct element method numerical simulations of cavity growth and sinkhole development. Firstly, we simulate cavity formation by quasi-static, stepwise removal of material in a single growing zone of an arbitrary geometry and depth. We benchmark this approach against analytical and boundary element method models of a deep void space in a linear elastic material. Secondly, we explore the effects of properties of different uniform materials on cavity stability and sinkhole development. We perform simulated biaxial tests to calibrate macroscopic geotechnical parameters of three model materials representative of those in which sinkholes develop at the Dead Sea shoreline: mud, alluvium and salt. We show that weak materials do not support large cavities, leading to gradual sagging or suffusion-style subsidence. Strong materials support quasi-stable to stable cavities, the overburdens of which may fail suddenly in a caprock or bedrock collapse style. Thirdly, we examine the consequences of layered arrangements of weak and strong materials. We find that these are more susceptible to sinkhole collapse than uniform materials not only due to a lower integrated strength of the overburden but also due to an inhibition of stabilising stress arching. Finally, we compare our model sinkhole geometries to observations at the Ghor Al-Haditha sinkhole site in Jordan. Sinkhole depth / diameter ratios of 0.15 in mud, 0.37 in alluvium and 0.33 in salt are reproduced successfully in the calibrated model materials. The model results suggest that the observed distribution of sinkhole depth / diameter values in each material type may partly reflect sinkhole growth trends.},
language = {en}
}
@article{AlHalbouniHolohanTaherietal.2019,
author = {Al-Halbouni, Djamil and Holohan, Eoghan P. and Taheri, Abbas and Watson, Robert A. and Polom, Ulrich and Schoepfer, Martin P. J. and Emam, Sacha and Dahm, Torsten},
title = {Distinct element geomechanical modelling of the formation of sinkhole clusters within large-scale karstic depressions},
series = {Solid earth},
volume = {10},
journal = {Solid earth},
number = {4},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1869-9510},
doi = {10.5194/se-10-1219-2019},
pages = {1219 -- 1241},
year = {2019},
abstract = {The 2-D distinct element method (DEM) code (PFC2D_V5) is used here to simulate the evolution of subsidence-related karst landforms, such as single and clustered sinkholes, and associated larger-scale depressions. Subsurface material in the DEM model is removed progressively to produce an array of cavities; this simulates a network of subsurface groundwater conduits growing by chemical/mechanical erosion. The growth of the cavity array is coupled mechanically to the gravitationally loaded surroundings, such that cavities can grow also in part by material failure at their margins, which in the limit can produce individual collapse sinkholes. Two end-member growth scenarios of the cavity array and their impact on surface subsidence were examined in the models: (1) cavity growth at the same depth level and growth rate; (2) cavity growth at progressively deepening levels with varying growth rates. These growth scenarios are characterised by differing stress patterns across the cavity array and its overburden, which are in turn an important factor for the formation of sinkholes and uvalalike depressions. For growth scenario (1), a stable compression arch is established around the entire cavity array, hindering sinkhole collapse into individual cavities and favouring block-wise, relatively even subsidence across the whole cavity array. In contrast, for growth scenario (2), the stress system is more heterogeneous, such that local stress concentrations exist around individual cavities, leading to stress interactions and local wall/overburden fractures. Consequently, sinkhole collapses occur in individual cavities, which results in uneven, differential subsidence within a larger-scale depression. Depending on material properties of the cavity-hosting material and the overburden, the larger-scale depression forms either by sinkhole coalescence or by widespread subsidence linked geometrically to the entire cavity array. The results from models with growth scenario (2) are in close agreement with surface morphological and subsurface geophysical observations from an evaporite karst area on the eastern shore of the Dead Sea.},
language = {en}
}
@article{AlMashaikhiOswaldAttingeretal.2012,
author = {Al-Mashaikhi, K. and Oswald, Sascha and Attinger, Sabine and B{\"u}chel, G. and Kn{\"o}ller, K. and Strauch, G.},
title = {Evaluation of groundwater dynamics and quality in the Najd aquifers located in the Sultanate of Oman},
series = {Environmental earth sciences},
volume = {66},
journal = {Environmental earth sciences},
number = {4},
publisher = {Springer},
address = {New York},
issn = {1866-6280},
doi = {10.1007/s12665-011-1331-2},
pages = {1195 -- 1211},
year = {2012},
abstract = {The Najd, Oman, is located in one of the most arid environments in the world. The groundwater in this region is occurring in four different aquifers A to D of the Hadhramaut Group consisting mainly of different types of limestone and dolomite. The quality of the groundwater is dominated by the major ions sodium, calcium, magnesium, sulphate, and chloride, but the hydrochemical character is varying among the four aquifers. Mineralization within the separate aquifers increases along the groundwater flow direction from south to north-northeast up to high saline sodium-chloride water in aquifer D in the northeast area of the Najd. Environmental isotope analyses of hydrogen and oxygen were conducted to monitor the groundwater dynamics and to evaluate the recharge conditions of groundwater into the Najd aquifers. Results suggest an earlier recharge into these aquifers as well as ongoing recharge takes place in the region down to present day. Mixing of modern and submodern waters was detected by water isotopes in aquifer D in the mountain chain (Jabal) area and along the northern side of the mountain range. In addition, delta H-2 and delta O-18 variations suggest that aquifers A, B, and C are assumed to be connected by faults and fractures, and interaction between the aquifers may occur. Low tritium concentrations support the mixing assumption in the recharge area. The knowledge about the groundwater development is an important factor for the sustainable use of water resources in the Dhofar region.},
language = {en}
}
@article{AlawiSchneiderKallmeyer2014,
author = {Alawi, Mashal and Schneider, Beate and Kallmeyer, Jens},
title = {A procedure for separate recovery of extra- and intracellular DNA from a single marine sediment sample},
series = {Journal of microbiological methods},
volume = {104},
journal = {Journal of microbiological methods},
publisher = {Elsevier},
address = {Amsterdam},
issn = {0167-7012},
doi = {10.1016/j.mimet.2014.06.009},
pages = {36 -- 42},
year = {2014},
abstract = {Extracellular DNA (eDNA) is a ubiquitous biological compound in aquatic sediment and soil. Previous studies suggested that eDNA plays an important role in biogeochemical element cycling, horizontal gene transfer and stabilization of biofilm structures. Previous methods for eDNA extraction were either not suitable for oligotrophic sediments or only allowed quantification but no genetic analyses. Our procedure is based on cell detachment and eDNA liberation from sediment particles by sequential washing with an alkaline sodium phosphate buffer followed by a separation of cells and eDNA. The separated eDNA is then bound onto silica particles and purified, whereas the intracellular DNA from the separated cells is extracted using a commercial kit. The method provides extra- and intracellular DNA of high purity that is suitable for downstream applications like PCR. Extracellular DNA was extracted from organic-rich shallow sediment of the Baltic Sea, glacially influenced sediment of the Barents Sea and from the oligotrophic South Pacific Gyre. The eDNA concentration in these samples varied from 23 to 626 ng g(-1) wet weight sediment. A number of experiments were performed to verify each processing step. Although extraction efficiency is higher than other published methods, it is not fully quantitative. (C) 2014 Elsevier B.V. All rights reserved.},
language = {en}
}
@article{AlbrechtMartinHaseloffetal.2011,
author = {Albrecht, Tanja and Martin, M. and Haseloff, M. and Winkelmann, Ricarda and Levermann, Anders},
title = {Parameterization for subgrid-scale motion of ice-shelf calving fronts},
series = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
volume = {5},
journal = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
number = {1},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1994-0416},
doi = {10.5194/tc-5-35-2011},
pages = {35 -- 44},
year = {2011},
abstract = {A parameterization for the motion of ice-shelf fronts on a Cartesian grid in finite-difference land-ice models is presented. The scheme prevents artificial thinning of the ice shelf at its edge, which occurs due to the finite resolution of the model. The intuitive numerical implementation diminishes numerical dispersion at the ice front and enables the application of physical boundary conditions to improve the calculation of stress and velocity fields throughout the ice-sheet-shelf system. Numerical properties of this subgrid modification are assessed in the Potsdam Parallel Ice Sheet Model (PISM-PIK) for different geometries in one and two horizontal dimensions and are verified against an analytical solution in a flow-line setup.},
language = {en}
}
@article{AlbrechtWinkelmannLevermann2020,
author = {Albrecht, Torsten and Winkelmann, Ricarda and Levermann, Anders},
title = {Glacial-cycle simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model (PISM)},
series = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
volume = {14},
journal = {The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union},
number = {2},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1994-0416},
doi = {10.5194/tc-14-599-2020},
pages = {599 -- 632},
year = {2020},
abstract = {Simulations of the glacial-interglacial history of the Antarctic Ice Sheet provide insights into dynamic threshold behavior and estimates of the ice sheet's contributions to global sea-level changes for the past, present and future. However, boundary conditions are weakly constrained, in particular at the interface of the ice sheet and the bedrock. Also climatic forcing covering the last glacial cycles is uncertain, as it is based on sparse proxy data.
We use the Parallel Ice Sheet Model (PISM) to investigate the dynamic effects of different choices of input data, e.g., for modern basal heat flux or reconstructions of past changes of sea level and surface temperature. As computational resources are limited, glacial-cycle simulations are performed using a comparably coarse model grid of 16 km and various parameterizations, e.g., for basal sliding, iceberg calving, or for past variations in precipitation and ocean temperatures. In this study we evaluate the model's transient sensitivity to corresponding parameter choices and to different boundary conditions over the last two glacial cycles and provide estimates of involved uncertainties. We also discuss isolated and combined effects of climate and sea-level forcing. Hence, this study serves as a "cookbook" for the growing community of PISM users and paleo-ice sheet modelers in general.
For each of the different model uncertainties with regard to climatic forcing, ice and Earth dynamics, and basal processes, we select one representative model parameter that captures relevant uncertainties and motivates corresponding parameter ranges that bound the observed ice volume at present. The four selected parameters are systematically varied in a parameter ensemble analysis, which is described in a companion paper.},
language = {en}
}
@article{AlbrichFrijiaParenteetal.2014,
author = {Albrich, Sergi and Frijia, Gianluca and Parente, Mariano and Caus, Esmeralda},
title = {The evolution of the earliest representatives of the genus Orbitoides: Implications for Upper Cretaceous biostratigraphy},
series = {Cretaceous research},
volume = {51},
journal = {Cretaceous research},
publisher = {Elsevier},
address = {London},
issn = {0195-6671},
doi = {10.1016/j.cretres.2014.04.013},
pages = {22 -- 34},
year = {2014},
abstract = {The biostratigraphy of Campanian-Maastrichtian carbonate platforms is largely based on the larger foraminiferal genus Orbitoides. However, while the taxonomy and the chronostratigraphic age of the younger species of this genus are well established, there are still many controversies on the earliest species. We have restudied their morphological characters using a large collection of samples from the type-localities and from continuous sections in the southern Pyrenees. Based on these new observations, the long forgotten species O. sanctae-pelagiae is reinstated, while O. dordoniensis is considered a junior synonym. Successive populations of O. hottingeri, O. sanctae-pelagiae and O. douvillei show gradual morphological changes in time marked by an increase in the size and complexity of the macrospheric embryonal apparatus, an increase of the size of the adult specimens of both generations and the progressive appearance and development of true lateral chamberlets. The Font de les Bagasses Unit in the southern Pyrenees preserves a high-resolution archive of the evolution of the earliest Orbitoides. Strontium isotope stratigraphy indicates that the oldest species, O. hottingeri, made its first appearance in the earliest Campanian, close to the Santonian-Campanian boundary, and was replaced by O. sanctae-pelagiae at a level closely corresponding to the boundary between the Placenticeras bidorsatum and Menabites delawarensis ammonite zones. (C) 2014 Elsevier Ltd. All rights reserved.},
language = {en}
}
@article{AliGiurcoArndtetal.2017,
author = {Ali, Saleem H. and Giurco, Damien and Arndt, Nicholas and Nickless, Edmund and Brown, Graham and Demetriades, Alecos and Durrheim, Ray and Enriquez, Maria Amelia and Kinnaird, Judith and Littleboy, Anna and Meinert, Lawrence D. and Oberh{\"a}nsli, Roland and Salem, Janet and Schodde, Richard and Schneider, Gabi and Vidal, Olivier and Yakovleva, Natalia},
title = {Mineral supply for sustainable development requires resource governance},
series = {Nature : the international weekly journal of science},
volume = {543},
journal = {Nature : the international weekly journal of science},
publisher = {Nature Publ. Group},
address = {London},
issn = {0028-0836},
doi = {10.1038/nature21359},
pages = {367 -- 372},
year = {2017},
abstract = {Successful delivery of the United Nations sustainable development goals and implementation of the Paris Agreement requires technologies that utilize a wide range of minerals in vast quantities. Metal recycling and technological change will contribute to sustaining supply, but mining must continue and grow for the foreseeable future to ensure that such minerals remain available to industry. New links are needed between existing institutional frameworks to oversee responsible sourcing of minerals, trajectories for mineral exploration, environmental practices, and consumer awareness of the effects of consumption. Here we present, through analysis of a comprehensive set of data and demand forecasts, an interdisciplinary perspective on how best to ensure ecologically viable continuity of global mineral supply over the coming decades.},
language = {en}
}
@article{AlinaghiKruger2014,
author = {Alinaghi, Alireza and Kruger, Frank},
title = {Seismic array analysis and redetermination of depths of earthquakes in Tien-Shan: implications for strength of the crust and lithosphere},
series = {Geophysical journal international},
volume = {198},
journal = {Geophysical journal international},
number = {2},
publisher = {Oxford Univ. Press},
address = {Oxford},
issn = {0956-540X},
doi = {10.1093/gji/ggu141},
pages = {1111 -- 1129},
year = {2014},
abstract = {We have redetermined focal depths of moderate and major earthquakes with reported lower-crust and upper-mantle depths that have occurred in Tien-Shan, since the availability of broad-band array data. Records of earthquakes at global arrays have been used for identification and modelling of depth phases in order to make accurate estimation of focal depths. Our results show that half of the purportedly deep earthquakes are indeed originating from depths attributable to middle-crust and lower-crust regions. Also one exceptional event in the northern foreland of Tien-Shan in Junggar Basin is located in the upper mantle at the depth of 64 km. Such unusually deep earthquakes for intraplate continental tectonic domain are all located at the margin of Tien-Shan with its adjacent stable blocks and at least some of them have occurred where the brittle behaviour of continental rocks is not highly expected. The reverse mechanisms of all these earthquakes and their proximity to formerly subducting and later colliding and underplating stable blocks and their interactions with overlying Tien-Shan are clues to explain this extremity.},
language = {en}
}
@phdthesis{Allroggen2015,
author = {Allroggen, Niklas},
title = {Observation of subsurface flow from the surface : applications of ground-penetrating radar},
school = {Universit{\"a}t Potsdam},
pages = {67},
year = {2015},
language = {en}
}
@article{AllroggenBeiterTronicke2020,
author = {Allroggen, Niklas and Beiter, Daniel and Tronicke, Jens},
title = {Ground-penetrating radar monitoring of fast subsurface processes},
series = {Geophysics},
volume = {85},
journal = {Geophysics},
number = {3},
publisher = {Society of Exploration Geophysicists},
address = {Tulsa},
issn = {0016-8033},
doi = {10.1190/GEO2019-0737.1},
pages = {A19 -- A23},
year = {2020},
abstract = {Earth and environmental sciences rely on detailed information about subsurface processes. Whereas geophysical techniques typically provide highly resolved spatial images, monitoring subsurface processes is often associated with enormous effort and, therefore, is usually limited to point information in time or space. Thus, the development of spatial and temporal continuous field monitoring methods is a major challenge for the understanding of subsurface processes. We have developed a novel method for ground-penetrating-radar (GPR) reflection monitoring of subsurface flow processes under unsaturated conditions and applied it to a hydrological infiltration experiment performed across a periglacial slope deposit in northwest Luxembourg. Our approach relies on a spatial and temporal quasicontinuous data recording and processing, followed by an attribute analysis based on analyzing differences between individual time steps. The results demonstrate the ability of time-lapse GPR monitoring to visualize the spatial and temporal dynamics of preferential flow processes with a spatial resolution in the order of a few decimeters and temporal resolution in the order of a few minutes. We observe excellent agreement with water table information originating from different boreholes. This demonstrates the potential of surface-based GPR reflection monitoring to observe the spatiotemporal dynamics of water movements in the subsurface. It provides valuable, and so far not accessible, information for example in the field of hydrology and pedology that allows studying the actual subsurface processes rather than deducing them from point information.},
language = {en}
}
@article{AllroggenHeinckeKoyanetal.2022,
author = {Allroggen, Niklas and Heincke, Bjorn H. and Koyan, Philipp and Wheeler, Walter and Ronning, Jan S.},
title = {3D ground-penetrating radar attribute classification},
series = {Geophysics},
volume = {87},
journal = {Geophysics},
number = {4},
publisher = {Society of Exploration Geophysicists},
address = {Tulsa},
issn = {0016-8033},
doi = {10.1190/GEO2021-0651.1},
pages = {WB19 -- WB30},
year = {2022},
abstract = {Ground-penetrating radar (GPR) is a method that can provide detailed information about the near subsurface in sedimentary and carbonate environments. The classical interpretation of GPR data (e.g., based on manual feature selection) often is labor-intensive and limited by the experience of the intercally used for seismic interpretation, can provide faster, more repeatable, and less biased interpretations. We have recorded a 3D GPD data set collected across a paleokarst breccia pipe in the Billefjorden area on Spitsbergen, Svalbard. After performing advanced processing, we compare the results of a classical GPR interpretation to the results of an attribute-based classification. Our attribute classification incorporates a selection of dip and textural attributes as the input for a k-means clustering approach. Similar to the results of the classical interpretation, the resulting classes differentiate between undisturbed strata and breccias or fault zones. The classes also reveal details inside the breccia pipe that are not discerned in the classical fer that the intrapipe GPR facies result from subtle differences, such as breccia lithology, clast size, or pore-space filling.},
language = {en}
}