@misc{Braun2020,
author = {Braun, Jean},
title = {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"},
series = {Gondwana research : international geoscience journal ; official journal of the International Association for Gondwana Research},
volume = {65},
journal = {Gondwana research : international geoscience journal ; official journal of the International Association for Gondwana Research},
publisher = {Elsevier},
address = {Amsterdam},
issn = {1342-937X},
doi = {10.1016/j.gr.2018.10.003},
pages = {174 -- 176},
year = {2020},
language = {en}
}
@article{BrillPassuniPinedaEspichanCuyaetal.2020,
author = {Brill, Fabio Alexander and Passuni Pineda, Silvia and Espichan Cuya, Bruno and Kreibich, Heidi},
title = {A data-mining approach towards damage modelling for El Nino events in Peru},
series = {Geomatics, natural hazards and risk},
volume = {11},
journal = {Geomatics, natural hazards and risk},
number = {1},
publisher = {Routledge, Taylor \& Francis Group},
address = {Abingdon},
issn = {1947-5705},
doi = {10.1080/19475705.2020.1818636},
pages = {1966 -- 1990},
year = {2020},
abstract = {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.},
language = {en}
}
@article{BrunelloAndermannMarcetal.2020,
author = {Brunello, Camilla Francesca and Andermann, Christoff and Marc, Odin and Schneider, Katharina A. and Comiti, Francesco and Achleitner, Stefan and Hovius, Niels},
title = {Annually resolved monsoon onset and withdrawal dates across the Himalayas derived from local precipitation statistics},
series = {Geophysical research letters},
volume = {47},
journal = {Geophysical research letters},
number = {23},
publisher = {American Geophysical Union},
address = {Washington},
issn = {0094-8276},
doi = {10.1029/2020GL088420},
pages = {12},
year = {2020},
abstract = {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.
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.},
language = {en}
}
@article{CalitriSommervanderMeijetal.2020,
author = {Calitri, Francesca and Sommer, Michael and van der Meij, Marijn W. and Egli, Markus},
title = {Soil erosion along a transect in a forested catchment: recent or ancient processes?},
series = {Catena : an interdisciplinary journal of soil science, hydrology, geomorphology focusing on geoecology and landscape evolution},
volume = {194},
journal = {Catena : an interdisciplinary journal of soil science, hydrology, geomorphology focusing on geoecology and landscape evolution},
publisher = {Elsevier},
address = {Amsterdam},
issn = {0341-8162},
doi = {10.1016/j.catena.2020.104683},
pages = {11},
year = {2020},
abstract = {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.
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.},
language = {en}
}
@article{CastinoBookhagenDelaTorre2020,
author = {Castino, Fabiana and Bookhagen, Bodo and De la Torre, Alejandro},
title = {Atmospheric dynamics of extreme discharge events from 1979 to 2016 in the southern Central Andes},
series = {Climate dynamics : observational, theoretical and computational research on the climate system},
volume = {55},
journal = {Climate dynamics : observational, theoretical and computational research on the climate system},
number = {11-12},
publisher = {Springer},
address = {Berlin ; Heidelberg [u.a.]},
issn = {0930-7575},
doi = {10.1007/s00382-020-05458-1},
pages = {3485 -- 3505},
year = {2020},
abstract = {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.},
language = {en}
}
@article{ChengMilsch2020,
author = {Cheng, Chaojie and Milsch, Harald},
title = {Permeability variations in illite-bearing sandstone},
series = {Journal of geophysical research : Solid earth},
volume = {125},
journal = {Journal of geophysical research : Solid earth},
number = {9},
publisher = {American Geophysical Union},
address = {Washington},
issn = {2169-9313},
doi = {10.1029/2020JB020122},
pages = {21},
year = {2020},
abstract = {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.},
language = {en}
}
@article{ChengMilsch2020,
author = {Cheng, Chaojie and Milsch, Harald},
title = {Evolution of fracture aperture in quartz sandstone under hydrothermal conditions},
series = {Minerals},
volume = {10},
journal = {Minerals},
number = {8},
publisher = {MDPI},
address = {Basel},
issn = {2075-163X},
doi = {10.3390/min10080657},
pages = {18},
year = {2020},
abstract = {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.},
language = {en}
}
@article{CoesfeldKuesterKuechlyetal.2020,
author = {Coesfeld, Jacqueline and Kuester, Theres and Kuechly, Helga U. and Kyba, Christopher C. M.},
title = {Reducing variability and removing natural light from nighttime satellite imagery: A case study using the VIIRS DNB},
series = {Sensors},
volume = {20},
journal = {Sensors},
publisher = {MDPI},
address = {Basel},
pages = {13},
year = {2020},
abstract = {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.},
language = {en}
}
@misc{CoesfeldKuesterKuechlyetal.2020,
author = {Coesfeld, Jacqueline and Kuester, Theres and Kuechly, Helga U. and Kyba, Christopher C. M.},
title = {Reducing variability and removing natural light from nighttime satellite imagery: A case study using the VIIRS DNB},
series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
number = {11},
issn = {1866-8372},
doi = {10.25932/publishup-52439},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-524397},
pages = {15},
year = {2020},
abstract = {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.},
language = {en}
}
@article{CookTurowskiHovius2020,
author = {Cook, Kristen L. and Turowski, Jens M. and Hovius, Niels},
title = {Width control on event-scale deposition and evacuation of sediment in bedrock-confined channels},
series = {Earth surface processes and landforms : the journal of the British Geomorphological Research Group},
volume = {45},
journal = {Earth surface processes and landforms : the journal of the British Geomorphological Research Group},
number = {14},
publisher = {Wiley},
address = {Hoboken},
issn = {0197-9337},
doi = {10.1002/esp.4993},
pages = {3702 -- 3713},
year = {2020},
abstract = {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.},
language = {en}
}
@misc{CrisologoHeistermann2020,
author = {Crisologo, Irene and Heistermann, Maik},
title = {Using ground radar overlaps to verify the retrieval of calibration bias estimates from spaceborne platforms},
series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
number = {863},
issn = {1866-8372},
doi = {10.25932/publishup-45963},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-459630},
pages = {17},
year = {2020},
abstract = {Many institutions struggle to tap into the potential of their large archives of radar reflectivity: these data are often affected by miscalibration, yet the bias is typically unknown and temporally volatile. Still, relative calibration techniques can be used to correct the measurements a posteriori. For that purpose, the usage of spaceborne reflectivity observations from the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) platforms has become increasingly popular: the calibration bias of a ground radar (GR) is estimated from its average reflectivity difference to the spaceborne radar (SR). Recently, Crisologo et al. (2018) introduced a formal procedure to enhance the reliability of such estimates: each match between SR and GR observations is assigned a quality index, and the calibration bias is inferred as a quality-weighted average of the differences between SR and GR. The relevance of quality was exemplified for the Subic S-band radar in the Philippines, which is greatly affected by partial beam blockage. The present study extends the concept of quality-weighted averaging by accounting for path-integrated attenuation (PIA) in addition to beam blockage. This extension becomes vital for radars that operate at the C or X band. Correspondingly, the study setup includes a C-band radar that substantially overlaps with the S-band radar. Based on the extended quality-weighting approach, we retrieve, for each of the two ground radars, a time series of calibration bias estimates from suitable SR overpasses. As a result of applying these estimates to correct the ground radar observations, the consistency between the ground radars in the region of overlap increased substantially. Furthermore, we investigated if the bias estimates can be interpolated in time, so that ground radar observations can be corrected even in the absence of prompt SR overpasses. We found that a moving average approach was most suitable for that purpose, although limited by the absence of explicit records of radar maintenance operations.},
language = {en}
}
@article{CrisologoHeistermann2020,
author = {Crisologo, Irene and Heistermann, Maik},
title = {Using ground radar overlaps to verify the retrieval of calibration bias estimates from spaceborne platforms},
series = {Atmospheric measurement techniques : an interactive open access journal of the European Geosciences Union},
volume = {13},
journal = {Atmospheric measurement techniques : an interactive open access journal of the European Geosciences Union},
number = {2},
publisher = {Copernicus},
address = {G{\"o}ttingen},
issn = {1867-1381},
doi = {10.5194/amt-13-645-2020},
pages = {645 -- 659},
year = {2020},
abstract = {Many institutions struggle to tap into the potential of their large archives of radar reflectivity: these data are often affected by miscalibration, yet the bias is typically unknown and temporally volatile. Still, relative calibration techniques can be used to correct the measurements a posteriori. For that purpose, the usage of spaceborne reflectivity observations from the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) platforms has become increasingly popular: the calibration bias of a ground radar (GR) is estimated from its average reflectivity difference to the spaceborne radar (SR). Recently, Crisologo et al. (2018) introduced a formal procedure to enhance the reliability of such estimates: each match between SR and GR observations is assigned a quality index, and the calibration bias is inferred as a quality-weighted average of the differences between SR and GR. The relevance of quality was exemplified for the Subic S-band radar in the Philippines, which is greatly affected by partial beam blockage. The present study extends the concept of quality-weighted averaging by accounting for path-integrated attenuation (PIA) in addition to beam blockage. This extension becomes vital for radars that operate at the C or X band. Correspondingly, the study setup includes a C-band radar that substantially overlaps with the S-band radar. Based on the extended quality-weighting approach, we retrieve, for each of the two ground radars, a time series of calibration bias estimates from suitable SR overpasses. As a result of applying these estimates to correct the ground radar observations, the consistency between the ground radars in the region of overlap increased substantially. Furthermore, we investigated if the bias estimates can be interpolated in time, so that ground radar observations can be corrected even in the absence of prompt SR overpasses. We found that a moving average approach was most suitable for that purpose, although limited by the absence of explicit records of radar maintenance operations.},
language = {en}
}
@article{CrisologoHeistermann2020,
author = {Crisologo, Irene and Heistermann, Maik},
title = {Using ground radar overlaps to verify the retrieval of calibration bias estimates from spaceborne platforms},
series = {Atmospheric Measurement Techniques},
volume = {13},
journal = {Atmospheric Measurement Techniques},
number = {2},
publisher = {Copernicus Publications},
address = {G{\"o}ttingen},
issn = {1867-1381},
doi = {10.5194/amt-13-645-2020},
pages = {645 -- 659},
year = {2020},
abstract = {Many institutions struggle to tap into the potential of their large archives of radar reflectivity: these data are often affected by miscalibration, yet the bias is typically unknown and temporally volatile. Still, relative calibration techniques can be used to correct the measurements a posteriori. For that purpose, the usage of spaceborne reflectivity observations from the Tropical Rainfall Measuring Mission (TRMM) and Global Precipitation Measurement (GPM) platforms has become increasingly popular: the calibration bias of a ground radar (GR) is estimated from its average reflectivity difference to the spaceborne radar (SR). Recently, Crisologo et al. (2018) introduced a formal procedure to enhance the reliability of such estimates: each match between SR and GR observations is assigned a quality index, and the calibration bias is inferred as a quality-weighted average of the differences between SR and GR. The relevance of quality was exemplified for the Subic S-band radar in the Philippines, which is greatly affected by partial beam blockage. The present study extends the concept of quality-weighted averaging by accounting for path-integrated attenuation (PIA) in addition to beam blockage. This extension becomes vital for radars that operate at the C or X band. Correspondingly, the study setup includes a C-band radar that substantially overlaps with the S-band radar. Based on the extended quality-weighting approach, we retrieve, for each of the two ground radars, a time series of calibration bias estimates from suitable SR overpasses. As a result of applying these estimates to correct the ground radar observations, the consistency between the ground radars in the region of overlap increased substantially. Furthermore, we investigated if the bias estimates can be interpolated in time, so that ground radar observations can be corrected even in the absence of prompt SR overpasses. We found that a moving average approach was most suitable for that purpose, although limited by the absence of explicit records of radar maintenance operations.},
language = {en}
}
@article{DahmStillerMechieetal.2020,
author = {Dahm, Torsten and Stiller, Manfred and Mechie, James and Heimann, Sebastian and Hensch, Martin and Woith, Heiko and Schmidt, Bernd and Gabriel, Gerald and Weber, Michael},
title = {Seismological and geophysical signatures of the deep crustal magma systems of the cenozoic volcanic fields Beneath the Eifel, Germany},
series = {Geochemistry, geophysics, geosystems},
volume = {21},
journal = {Geochemistry, geophysics, geosystems},
number = {9},
publisher = {American Geophysical Union},
address = {Washington},
issn = {1525-2027},
doi = {10.1029/2020GC009062},
pages = {21},
year = {2020},
abstract = {The Quaternary volcanic fields of the Eifel (Rhineland-Palatinate, Germany) had their last eruptions less than 13,000 years ago. Recently, deep low-frequency (DLF) earthquakes were detected beneath one of the volcanic fields showing evidence of ongoing magmatic activity in the lower crust and upper mantle. In this work, seismic wide- and steep-angle experiments from 1978/1979 and 1987/1988 are compiled, partially reprocessed and interpreted, together with other data to better determine the location, size, shape, and state of magmatic reservoirs in the Eifel region near the crust-mantle boundary. We discuss seismic evidence for a low-velocity gradient layer from 30-36 km depth, which has developed over a large region under all Quaternary volcanic fields of the Rhenish Massif and can be explained by the presence of partial melts. We show that the DLF earthquakes connect the postulated upper mantle reservoir with the upper crust at a depth of about 8 km, directly below one of the youngest phonolitic volcanic centers in the Eifel, where CO(2)originating from the mantle is massively outgassing. A bright spot in the West Eifel between 6 and 10 km depth represents a Tertiary magma reservoir and is seen as a model for a differentiated reservoir beneath the young phonolitic center today. We find that the distribution of volcanic fields is controlled by the Variscan lithospheric structures and terrane boundaries as a whole, which is reflected by an offset of the Moho depth, a wedge-shaped transparent zone in the lower crust and the system of thrusts over about 120 km length.},
language = {en}
}
@misc{DommainAndamaMcDonoughetal.2020,
author = {Dommain, Ren{\´e} and Andama, Morgan and McDonough, Molly M. and Prado, Natalia A. and Goldhammer, Tobias and Potts, Richard and Maldonado, Jes{\´u}s E. and Nkurunungi, John Bosco and Campana, Michael G.},
title = {The Challenges of Reconstructing Tropical Biodiversity With Sedimentary Ancient DNA},
series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
number = {970},
issn = {1866-8372},
doi = {10.25932/publishup-47430},
url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-474305},
pages = {28},
year = {2020},
abstract = {Sedimentary ancient DNA has been proposed as a key methodology for reconstructing biodiversity over time. Yet, despite the concentration of Earth's biodiversity in the tropics, this method has rarely been applied in this region. Moreover, the taphonomy of sedimentary DNA, especially in tropical environments, is poorly understood. This study elucidates challenges and opportunities of sedimentary ancient DNA approaches for reconstructing tropical biodiversity. We present shotgun-sequenced metagenomic profiles and DNA degradation patterns from multiple sediment cores from Mubwindi Swamp, located in Bwindi Impenetrable Forest (Uganda), one of the most diverse forests in Africa. We describe the taxonomic composition of the sediments covering the past 2200 years and compare the sedimentary DNA data with a comprehensive set of environmental and sedimentological parameters to unravel the conditions of DNA degradation. Consistent with the preservation of authentic ancient DNA in tropical swamp sediments, DNA concentration and mean fragment length declined exponentially with age and depth, while terminal deamination increased with age. DNA preservation patterns cannot be explained by any environmental parameter alone, but age seems to be the primary driver of DNA degradation in the swamp. Besides degradation, the presence of living microbial communities in the sediment also affects DNA quantity. Critically, 92.3\% of our metagenomic data of a total 81.8 million unique, merged reads cannot be taxonomically identified due to the absence of genomic references in public databases. Of the remaining 7.7\%, most of the data (93.0\%) derive from Bacteria and Archaea, whereas only 0-5.8\% are from Metazoa and 0-6.9\% from Viridiplantae, in part due to unbalanced taxa representation in the reference data. The plant DNA record at ordinal level agrees well with local pollen data but resolves less diversity. Our animal DNA record reveals the presence of 41 native taxa (16 orders) including Afrotheria, Carnivora, and Ruminantia at Bwindi during the past 2200 years. Overall, we observe no decline in taxonomic richness with increasing age suggesting that several-thousand-year-old information on past biodiversity can be retrieved from tropical sediments. However, comprehensive genomic surveys of tropical biota need prioritization for sedimentary DNA to be a viable methodology for future tropical biodiversity studies.},
language = {en}
}
@article{DommainAndamaMcDonoughetal.2020,
author = {Dommain, Ren{\´e} and Andama, Morgan and McDonough, Molly M. and Prado, Natalia A. and Goldhammer, Tobias and Potts, Richard and Maldonado, Jes{\´u}s E. and Nkurunungi, John Bosco and Campana, Michael G.},
title = {The Challenges of Reconstructing Tropical Biodiversity With Sedimentary Ancient DNA},
series = {Frontiers in Ecology and Evolution},
volume = {8},
journal = {Frontiers in Ecology and Evolution},
publisher = {Frontiers Media},
address = {Lausanne},
issn = {2296-701X},
doi = {10.3389/fevo.2020.00218},
pages = {26},
year = {2020},
abstract = {Sedimentary ancient DNA has been proposed as a key methodology for reconstructing biodiversity over time. Yet, despite the concentration of Earth's biodiversity in the tropics, this method has rarely been applied in this region. Moreover, the taphonomy of sedimentary DNA, especially in tropical environments, is poorly understood. This study elucidates challenges and opportunities of sedimentary ancient DNA approaches for reconstructing tropical biodiversity. We present shotgun-sequenced metagenomic profiles and DNA degradation patterns from multiple sediment cores from Mubwindi Swamp, located in Bwindi Impenetrable Forest (Uganda), one of the most diverse forests in Africa. We describe the taxonomic composition of the sediments covering the past 2200 years and compare the sedimentary DNA data with a comprehensive set of environmental and sedimentological parameters to unravel the conditions of DNA degradation. Consistent with the preservation of authentic ancient DNA in tropical swamp sediments, DNA concentration and mean fragment length declined exponentially with age and depth, while terminal deamination increased with age. DNA preservation patterns cannot be explained by any environmental parameter alone, but age seems to be the primary driver of DNA degradation in the swamp. Besides degradation, the presence of living microbial communities in the sediment also affects DNA quantity. Critically, 92.3\% of our metagenomic data of a total 81.8 million unique, merged reads cannot be taxonomically identified due to the absence of genomic references in public databases. Of the remaining 7.7\%, most of the data (93.0\%) derive from Bacteria and Archaea, whereas only 0-5.8\% are from Metazoa and 0-6.9\% from Viridiplantae, in part due to unbalanced taxa representation in the reference data. The plant DNA record at ordinal level agrees well with local pollen data but resolves less diversity. Our animal DNA record reveals the presence of 41 native taxa (16 orders) including Afrotheria, Carnivora, and Ruminantia at Bwindi during the past 2200 years. Overall, we observe no decline in taxonomic richness with increasing age suggesting that several-thousand-year-old information on past biodiversity can be retrieved from tropical sediments. However, comprehensive genomic surveys of tropical biota need prioritization for sedimentary DNA to be a viable methodology for future tropical biodiversity studies.},
language = {en}
}
@article{DurandBentzKwiateketal.2020,
author = {Durand, Virginie and Bentz, Stephan and Kwiatek, Grzegorz and Dresen, Georg and Wollin, Christopher and Heidbach, Oliver and Martinez-Garzon, Patricia and Cotton, Fabrice and Nurlu, Murat and Bohnhoff, Marco},
title = {A two-scale preparation phase preceded an M-w 5.8 earthquake in the sea of marmara offshore Istanbul, Turkey},
series = {Seismological research letters},
volume = {91},
journal = {Seismological research letters},
number = {6},
address = {Boulder},
issn = {0895-0695},
doi = {10.1785/0220200110},
pages = {3139 -- 3147},
year = {2020},
abstract = {We analyze the spatiotemporal evolution of seismicity during a sequence of moderate (an M-w 4.7 foreshock and M-w 5.8 mainshock) earthquakes occurring in September 2019 at the transition between a creeping and a locked segment of the North Anatolian fault in the central Sea of Marmara, northwest Turkey. To investigate in detail the seismicity evolution, we apply a matched-filter technique to continuous waveforms, thus reducing the magnitude threshold for detection. Sequences of foreshocks preceding the two largest events are clearly seen, exhibiting two different behaviors: a long-term activation of the seismicity along the entire fault segment and a short-term concentration around the epicenters of the large events. We suggest a two-scale preparation phase, with aseismic slip preparing the mainshock final rupture a few days before, and a cascade mechanism leading to the nucleation of the mainshock. Thus, our study shows a combination of seismic and aseismic slip during the foreshock sequence changing the strength of the fault, bringing it closer to failure.},
language = {en}
}
@article{EngelsMedeirosAxfordetal.2020,
author = {Engels, Stefan and Medeiros, Andrew S. and Axford, Yarrow and Brooks, Steve and Heiri, Oliver and Luoto, Tomi P. and Nazarova, Larisa B. and Porinchu, David F. and Quinlan, Roberto and Self, Angela E.},
title = {Temperature change as a driver of spatial patterns and long-term trends in chironomid (Insecta: Diptera) diversity},
series = {Global change biology},
volume = {26},
journal = {Global change biology},
number = {3},
publisher = {Wiley},
address = {Hoboken},
issn = {1354-1013},
doi = {10.1111/gcb.14862},
pages = {1155 -- 1169},
year = {2020},
abstract = {Anthropogenic activities have led to a global decline in biodiversity, and monitoring studies indicate that both insect communities and wetland ecosystems are particularly affected. However, there is a need for long-term data (over centennial or millennial timescales) to better understand natural community dynamics and the processes that govern the observed trends. Chironomids (Insecta: Diptera: Chironomidae) are often the most abundant insects in lake ecosystems, sensitive to environmental change, and, because their larval exoskeleton head capsules preserve well in lake sediments, they provide a unique record of insect community dynamics through time. Here, we provide the results of a metadata analysis of chironomid diversity across a range of spatial and temporal scales. First, we analyse spatial trends in chironomid diversity using Northern Hemispheric data sets overall consisting of 837 lakes. Our results indicate that in most of our data sets, summer temperature (T-jul) is strongly associated with spatial trends in modern-day chironomid diversity. We observe a strong increase in chironomid alpha diversity with increasing T-jul in regions with present-day T-jul between 2.5 and 14 degrees C. In some areas with T-jul > 14 degrees C, chironomid diversity stabilizes or declines. Second, we demonstrate that the direction and amplitude of change in alpha diversity in a compilation of subfossil chironomid records spanning the last glacial-interglacial transition (similar to 15,000-11,000 years ago) are similar to those observed in our modern data. A compilation of Holocene records shows that during phases when the amplitude of temperature change was small, site-specific factors had a greater influence on the chironomid fauna obscuring the chironomid diversity-temperature relationship. Our results imply expected overall chironomid diversity increases in colder regions such as the Arctic under sustained global warming, but with complex and not necessarily predictable responses for individual sites.},
language = {en}
}
@article{EsfahaniGholamiOhrnberger2020,
author = {Esfahani, Reza Dokht Dolatabadi and Gholami, Ali and Ohrnberger, Matthias},
title = {An inexact augmented Lagrangian method for nonlinear dispersion-curve inversion using Dix-type global linear approximation},
series = {Geophysics : a journal of general and applied geophysics},
volume = {85},
journal = {Geophysics : a journal of general and applied geophysics},
number = {3},
publisher = {GeoScienceWorld},
address = {Tulsa, Okla.},
issn = {0016-8033},
doi = {10.1190/geo2019-0717.1},
pages = {EN77 -- EN85},
year = {2020},
abstract = {Dispersion-curve inversion of Rayleigh waves to infer subsurface shear-wave velocity is a long-standing problem in seismology. Due to nonlinearity and ill-posedness, sophisticated regularization techniques are required to solve the problem for a stable velocity model. We have formulated the problem as a minimization problem with nonlinear operator constraint and then solve it by using an inexact augmented Lagrangian method, taking advantage of the Haney-Tsai Dix-type relation (a global linear approximation of the nonlinear forward operator). This replaces the original regularized nonlinear problem with iterative minimization of a more tractable regularized linear problem followed by a nonlinear update of the phase velocity (data) in which the update can be performed accurately with any forward modeling engine, for example, the finite-element method. The algorithm allows discretizing the medium with thin layers (for the finite-element method) and thus omitting the layer thicknesses from the unknowns and also allows incorporating arbitrary regularizations to shape the desired velocity model. In this research, we use total variation regularization to retrieve the shear-wave velocity model. We use two synthetic and two real data examples to illustrate the performance of the inversion algorithm with total variation regularization. We find that the method is fast and stable, and it converges to the solution of the original nonlinear problem.},
language = {en}
}
@article{FigueroaVillegasWeissHongnetal.2020,
author = {Figueroa Villegas, Sara and Weiss, Jonathan R. and Hongn, Fernando D. and Pingel, Heiko and Escalante, Leonardo and El{\´i}as, Leonardo and Aranda-Viana, R. Germ{\´a}n and Strecker, Manfred},
title = {Late pleistocene to recent deformation in the thick-skinned fold-and-thrust belt of Northwestern Argentina (Central Calchaqui Valley, 26 degrees S)},
series = {Tectonics / American Geophysical Union, AGU ; European Geophysical Society, EGS},
volume = {40},
journal = {Tectonics / American Geophysical Union, AGU ; European Geophysical Society, EGS},
number = {1},
publisher = {American Geophysical Union},
address = {Washington, DC},
issn = {0278-7407},
doi = {10.1029/2020TC006394},
pages = {20},
year = {2020},
abstract = {The thick-skinned fold-and-thrust belt on the eastern flank of the Andean Plateau in northwestern Argentina (NWA) is a zone of active contractional deformation characterized by fault-bounded mountain ranges with no systematic spatiotemporal pattern of tectonic activity. In contrast, the thin-skinned Subandean fold-and-thrust belt of northern Argentina and southern Bolivia is characterized primarily by in-sequence (i.e., west to east) fault progression, with a narrow zone of Quaternary deformation focused at the front of the orogenic wedge. To better understand how recent deformation is accommodated across these mountain ranges and the Argentinian portion of the orogen in particular, estimating and comparing deformation rates and patterns across different timescales is essential. We present Late Pleistocene shortening rates for the central Calchaqui intermontane valley in NWA associated with at least three episodes of deformation. Global Positioning System data for the same region reveal a gradual decrease in horizontal surface velocities from the Eastern Cordillera toward the foreland, which contrasts with the rapid velocity gradient associated with a locked decollement in the Subandean Ranges of southern Bolivia. Our new results represent a small view of regional deformation that, when considered in combination with the shallow crustal seismicity and decadal-scale surface velocities, support the notion that strain release in NWA is associated with numerous slowly deforming structures that are distributed throughout the orogen.},
language = {en}
}