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.
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 - Zhang, Liyu A1 - Chen, Daizhao A1 - Kuang, Guodun A1 - Guo, Zenghui A1 - Zhang, Gongjing A1 - Wang, Xia T1 - Persistent oxic deep ocean conditions and frequent volcanic activities during the Frasnian-Famennian transition recorded in South China JF - Global and planetary change N2 - The Frasnian-Famennian (F-F) transition of Late Devonian was a critical episode in geological history, recording a major mass extinction event. In this study, we focus on an F-F succession from a deep marine context in Bancheng, southern Guangxi, South China, to investigate coeval changes in pelagic environments of the Paleo-Tethys Ocean. The studied succession is exclusively composed of bedded cherts intercalated with multiple siliceous volcanic ash beds. A SIMS zircon U-Pb Concordia age of 367.8 +/- 2.5 Ma is reported for a tuffaceous layer slightly above the F-F boundary. Geochemical ratios of Al/(Al + Fe + Mn), Ce/Ce*, Y/Ho, and Al, Fe contents in bedded cherts indicate that they are of predominantly biogenic/chemical origin with some terrigenous inputs. Negligible enrichment of redox sensitive elements (Mo, U, V) and low V/Cr ratios (<2) suggest persistently oxic conditions existed in the deep pelagic basin at Bancheng, South China during the F-F transition. These findings call into question the widely held hypothesis that marine anoxia was the primary killing mechanism for the F-F crisis. In contrast, multiple tuffaceous layers throughout the F-F boundary succession indicate frequent volcanic activity, which could have released massive amounts of greenhouse gases into the atmosphere, inducing climate warming. This scenario may have increased continental weathering and riverine fluxes into the ocean, reconciling the increases in Al2O3 content and Al/(Al + Fe + Mn) ratio across the F-F boundary. Documentation of persistently oxic conditions and frequent volcanic activitiy provides new perspectives on the inter-relationship between volcanism, climate, and oceanic redox fluctuation during the F-F biotic crisis. KW - Late Devonian KW - Bedded chert KW - Major and trace elements KW - Deep ocean redox condition KW - Volcanic activity KW - Zircon U-Pb dating Y1 - 2020 U6 - https://doi.org/10.1016/j.gloplacha.2020.103350 SN - 0921-8181 VL - 195 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 - Wietzke, Luzie M. A1 - Merz, Bruno A1 - Gerlitz, Lars A1 - Kreibich, Heidi A1 - Guse, Björn A1 - Castellarin, Attilio A1 - Vorogushyn, Sergiy T1 - Comparative analysis of scalar upper tail indicators JF - Hydrological sciences journal = Journal des sciences hydrologiques N2 - Different upper tail indicators exist to characterize heavy tail phenomena, but no comparative study has been carried out so far. We evaluate the shape parameter (GEV), obesity index, Gini index and upper tail ratio (UTR) against a novel benchmark of tail heaviness - the surprise factor. Sensitivity analyses to sample size and changes in scale-to-location ratio are carried out in bootstrap experiments. The UTR replicates the surprise factor best but is most uncertain and only comparable between records of similar length. For samples with symmetric Lorenz curves, shape parameter, obesity and Gini indices provide consistent indications. For asymmetric Lorenz curves, however, the first two tend to overestimate, whereas Gini index tends to underestimate tail heaviness. We suggest the use of a combination of shape parameter, obesity and Gini index to characterize tail heaviness. These indicators should be supported with calculation of the Lorenz asymmetry coefficients and interpreted with caution. KW - upper tail behaviour KW - heavy-tailed distributions KW - extremes KW - diagnostics KW - surprise Y1 - 2020 U6 - https://doi.org/10.1080/02626667.2020.1769104 SN - 0262-6667 SN - 2150-3435 VL - 65 IS - 10 SP - 1625 EP - 1639 PB - Routledge, Taylor & Francis Group CY - Abingdon ER - TY - JOUR A1 - Kruse, Stefan A1 - Kolmogorov, Aleksey I. A1 - Pestryakova, Luidmila Agafyevna A1 - Herzschuh, Ulrike T1 - Long-lived larch clones may conserve adaptations that could restrict treeline migration in northern Siberia JF - Ecology and evolution N2 - The occurrence of refugia beyond the arctic treeline and genetic adaptation therein play a crucial role of largely unknown effect size. While refugia have potential for rapidly colonizing the tundra under global warming, the taxa may be maladapted to the new environmental conditions. Understanding the genetic composition and age of refugia is thus crucial for predicting any migration response. Here, we genotype 194 larch individuals from an similar to 1.8 km(2)area in northcentral Siberia on the southern Taimyr Peninsula by applying an assay of 16 nuclear microsatellite markers. For estimating the age of clonal individuals, we counted tree rings at sections along branches to establish a lateral growth rate that was then combined with geographic distance. Findings reveal that the predominant reproduction type is clonal (58.76%) by short distance spreading of ramets. One outlier of clones 1 km apart could have been dispersed by reindeer. In clonal groups and within individuals, we find that somatic mutations accumulate with geographic distance. Clonal groups of two or more individuals are observed. Clonal age estimates regularly suggest individuals as old as 2,200 years, which coincides with a major environmental change that forced a treeline retreat in the region. We conclude that individuals with clonal growth mode were naturally selected as it lowers the likely risk of extinction under a harsh environment. We discuss this legacy from the past that might now be a maladaptation and hinder expansion under currently strongly increasing temperatures. KW - adaptation KW - clonal growth KW - growth rate KW - Larix KW - leading edge KW - treeline KW - migration Y1 - 2020 U6 - https://doi.org/10.1002/ece3.6660 SN - 2045-7758 VL - 10 IS - 18 SP - 10017 EP - 10030 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Voss, Katalyn A. A1 - Bookhagen, Bodo A1 - Sachse, Dirk A1 - Chadwick, Oliver A. T1 - Variation of deuterium excess in surface waters across a 5000-m elevation gradient in eastern Nepal JF - Journal of hydrology N2 - The strong elevation gradient of the Himalaya allows for investigation of altitude and orographic impacts on surface water delta O-18 and delta D stable isotope values. This study differentiates the time- and altitude-variable contributions of source waters to the Arun River in eastern Nepal. It provides isotope data along a 5000-m gradient collected from tributaries as well as groundwater, snow, and glacial-sourced surface waters and time-series data from April to October 2016. We find nonlinear trends in delta O-18 and delta D lapse rates with high-elevation lapse rates (4000-6000 masl) 5-7 times more negative than low-elevation lapse rates (1000-3000 masl). A distinct seasonal signal in delta O-18 and delta D lapse rates indicates time-variable source-water contributions from glacial and snow meltwater as well as precipitation transitions between the Indian Summer Monsoon and Winter Westerly Disturbances. Deuterium excess correlates with the extent of snowpack and tracks melt events during the Indian Summer Monsoon season. Our analysis identifies the influence of snow and glacial melt waters on river composition during low-flow conditions before the monsoon (April/May 2016) followed by a 5-week transition to the Indian Summer Monsoon-sourced rainfall around mid-June 2016. In the post-monsoon season, we find continued influence from glacial melt waters as well as ISM-sourced groundwater. KW - stable isotopes KW - Himalaya KW - glacier KW - snow KW - precipitation KW - seasonality Y1 - 2020 U6 - https://doi.org/10.1016/j.jhydrol.2020.124802 SN - 0022-1694 SN - 1879-2707 VL - 586 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Ganguli, Poulomi A1 - Paprotny, Dominik A1 - Hasan, Mehedi A1 - Güntner, Andreas A1 - Merz, Bruno T1 - Projected changes in compound flood hazard from riverine and coastal floods in northwestern Europe JF - Earth's future N2 - Compound flooding in coastal regions, that is, the simultaneous or successive occurrence of high sea levels and high river flows, is expected to increase in a warmer world. To date, however, there is no robust evidence on projected changes in compound flooding for northwestern Europe. We combine projected storm surges and river floods with probabilistic, localized relative sea-level rise (SLR) scenarios to assess the future compound flood hazard over northwestern coastal Europe in the high (RCP8.5) emission scenario. We use high-resolution, dynamically downscaled regional climate models (RCM) to drive a storm surge model and a hydrological model, and analyze the joint occurrence of high coastal water levels and associated river peaks in a multivariate copula-based approach. The RCM-forced multimodel mean reasonably represents the observed spatial pattern of the dependence strength between annual maxima surge and peak river discharge, although substantial discrepancies exist between observed and simulated dependence strength. All models overestimate the dependence strength, possibly due to limitations in model parameterizations. This bias affects compound flood hazard estimates and requires further investigation. While our results suggest decreasing compound flood hazard over the majority of sites by 2050s (2040-2069) compared to the reference period (1985-2005), an increase in projected compound flood hazard is limited to around 34% of the sites. Further, we show the substantial role of SLR, a driver of compound floods, which has frequently been neglected. Our findings highlight the need to be aware of the limitations of the current generation of Earth system models in simulating coastal compound floods. KW - compound flood KW - storm surge KW - river floods KW - sea level rise KW - climate KW - change KW - Europe Y1 - 2020 U6 - https://doi.org/10.1029/2020EF001752 SN - 2328-4277 VL - 8 IS - 11 PB - Wiley-Blackwell CY - Hoboken, NJ ER - TY - JOUR A1 - Vogt-Vincent, Noam A1 - Lippold, Jörg A1 - Kaboth-Bahr, Stefanie A1 - Blaser, Patrick T1 - Ice-rafted debris as a source of non-conservative behaviour for the epsilon Nd palaeotracer BT - insights from a simple model JF - Geo-marine letters : an international journal of marine geology N2 - Neodymium isotopic composition (epsilon Nd) has enjoyed widespread use as a palaeotracer, principally because it behaves quasi-conservatively in the modern ocean. However, recent bottom water epsilon Nd reconstructions from the eastern North Atlantic are difficult to interpret under assumptions of conservative behaviour. The observation that this apparent departure from conservative behaviour increases with enhanced ice-rafted debris (IRD) fluxes has resulted in the suggestion that IRD leads to the overprinting of bottom water epsilon Nd through reversible scavenging. In this study, a simple water column model successfully reproduces epsilon Nd reconstructions from the eastern North Atlantic at the Last Glacial Maximum and Heinrich Stadial 1, and demonstrates that the changes in scavenging intensity required for good model-data fit is in good agreement with changes in the observed IRD flux. Although uncertainties in model parameters preclude a more definitive conclusion, the results indicate that the suggestion of IRD as a source of non-conservative behaviour in the epsilon Nd tracer is reasonable and that further research into the fundamental chemistry underlying the marine neodymium cycle is necessary to increase confidence in assumptions of conservative epsilon Nd behaviour in the past. KW - Neodymium isotopes KW - epsilon Nd KW - ice-rafted debris KW - IRD KW - last glacial KW - maximum KW - LGM KW - Heinrich event KW - Palaeoceanography KW - Paleoceanography KW - model KW - reversible scavenging KW - conservative KW - ocean circulation KW - atlantic KW - meridional overturning circulation KW - geochemical cycling Y1 - 2020 U6 - https://doi.org/10.1007/s00367-020-00643-x SN - 0276-0460 SN - 1432-1157 VL - 40 IS - 3 SP - 325 EP - 340 PB - Springer CY - Berlin ER - TY - JOUR A1 - Huang, Sichao A1 - Herzschuh, Ulrike A1 - Pestryakova, Luidmila Agafyevna A1 - Zimmermann, Heike Hildegard A1 - Davydova, Paraskovya A1 - Biskaborn, Boris A1 - Shevtsova, Iuliia A1 - Stoof-Leichsenring, Kathleen Rosemarie T1 - Genetic and morphologic determination of diatom community composition in surface sediments from glacial and thermokarst lakes in the Siberian Arctic JF - Journal of paleolimnolog N2 - Lakes cover large parts of the climatically sensitive Arctic landscape and respond rapidly to environmental change. Arctic lakes have different origins and include the predominant thermokarst lakes, which are small, young and highly dynamic, as well as large, old and stable glacial lakes. Freshwater diatoms dominate the primary producer community in these lakes and can be used to detect biotic responses to climate and environmental change. We used specific diatom metabarcoding on sedimentary DNA, combined with next-generation sequencing and diatom morphology, to assess diatom diversity in five glacial and 15 thermokarst lakes within the easternmost expanse of the Siberian treeline ecotone in Chukotka, Russia. We obtained 163 verified diatom sequence types and identified 176 diatom species morphologically. Although there were large differences in taxonomic assignment using the two approaches, they showed similar high abundances and diversity of Fragilariceae and Aulacoseiraceae. In particular, the genetic approach detected hidden within-lake variations of fragilarioids in glacial lakes and dominance of centric Aulacoseira species, whereas Lindavia ocellata was predominant using morphology. In thermokarst lakes, sequence types and valve counts also detected high diversity of Fragilariaceae, which followed the vegetation gradient along the treeline. Ordination analyses of the genetic data from glacial and thermokarst lakes suggest that concentrations of sulfate (SO42-), an indicator of the activity of sulfate-reducing microbes under anoxic conditions, and bicarbonate (HCO3-), which relates to surrounding vegetation, have a significant influence on diatom community composition. For thermokarst lakes, we also identified lake depth as an important variable, but SO42- best explains diatom diversity derived from genetic data, whereas HCO3- best explains the data from valve counts. Higher diatom diversity was detected in glacial lakes, most likely related to greater lake age and different edaphic settings, which gave rise to diversification and endemism. In contrast, small, dynamic thermokarst lakes are inhabited by stress-tolerant fragilarioids and are related to different vegetation types along the treeline ecotone. Our study demonstrated that genetic investigations of lake sediments can be used to interpret climate and environmental responses of diatoms. It also showed how lake type affects diatom diversity, and that such genetic analyses can be used to track diatom community changes under ongoing warming in the Arctic. KW - diatoms KW - diversity KW - glacial lakes KW - sedimentary DNA KW - Siberian arctic KW - thermokarst Y1 - 2020 U6 - https://doi.org/10.1007/s10933-020-00133-1 SN - 0921-2728 SN - 1573-0417 VL - 64 IS - 3 SP - 225 EP - 242 PB - Springer CY - Dordrecht ER - TY - JOUR A1 - Guzman, Diego A. A1 - Samprogna Mohor, Guilherme A1 - Mendiondo, Eduardo Mario T1 - Multi-year index-based insurance for adapting Water Utility Companies to hydrological drought BT - case study of a water supply system of the Sao Paulo metropolitan region, Brazil JF - Water N2 - The sustainability of water utility companies is threatened by non-stationary drivers, such as climate and anthropogenic changes. To cope with potential economic losses, instruments such as insurance are useful for planning scenarios and mitigating impacts, but data limitations and risk uncertainties affect premium estimation and, consequently, business sustainability. This research estimated the possible economic impacts of business interruption to the Sao Paulo Water Utility Company derived from hydrological drought and how this could be mitigated with an insurance scheme. Multi-year insurance (MYI) was proposed through a set of "change" drivers: the climate driver, through forcing the water evaluation and planning system (WEAP) hydrological tool; the anthropogenic driver, through water demand projections; and the economic driver, associated with recent water price policies adopted by the utility company during water scarcity periods. In our study case, the evaluated indices showed that MYI contracts that cover only longer droughts, regardless of the magnitude, offer better financial performance than contracts that cover all events (in terms of drought duration). Moreover, through MYI contracts, we demonstrate solvency for the insurance fund in the long term and an annual average actuarially fair premium close to the total expected revenue reduction. KW - multi-year insurance KW - climate change KW - hydrological drought KW - water KW - security and economy Y1 - 2020 U6 - https://doi.org/10.3390/w12112954 SN - 2073-4441 VL - 12 IS - 11 PB - MDPI CY - Basel ER - TY - JOUR A1 - Izgi, Gizem A1 - Eken, Tuna A1 - Gaebler, Peter A1 - Eulenfeld, Tom A1 - Taymaz, Tuncay T1 - Crustal seismic attenuation parameters in the western region of the North Anatolian Fault Zone JF - Journal of geodynamics N2 - Detailed knowledge of the crustal structure along the North Anatolian Fault Zone can help in understanding past and present tectonic processes in relation to the deformation history. To estimate the frequency-dependent crustal attenuation parameters beneath the western part of the North Anatolian Fault Zone we apply acoustic radiative transfer theory under the assumption of multiple isotropic scattering to generate synthetic seismogram envelopes. The inversion depends on finding an optimal fit between observed and synthetically computed coda wave envelopes in five frequency bands. 2-D lateral variation of intrinsic and scattering attenuation at various frequencies tends to three crustal blocks (i.e., Armutlu-Almacik, Istanbul-Zonguldak and Sakarya Zones) separated by the southern and northern branches of the western part of the North Anatolian Fault Zone. Overall, scattering attenuation appears to be dominant over intrinsic attenuation in the study area at lower frequencies. Relatively low attenuation properties are observed beneath the older Istanbul Zone whereas higher attenuation properties are found for the younger Sakarya Zone. The Armutlu Almacik Zone exhibits more complex lateral variations. Very high attenuation values towards the west characterize the area of the Kuzuluk Basin, a pull-apart basin formed under west-east extension. Our coda-derived moment magnitudes are similar to the local magnitude estimates that were previously calculated for the same earthquakes. For smaller earthquakes (M-L < 2.5), however, the relation between local and moment magnitudes appears to lose its coherency. This may stem from various reasons including the use of seismic data recorded in finite sampling interval, possible biases in local magnitude estimates of earthquake catalogues as well as biases due to wrong assumptions to consider anelastic attenuation terms. Y1 - 2020 U6 - https://doi.org/10.1016/j.jog.2020.101694 SN - 0264-3707 VL - 134 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Reschke, Maria A1 - Kröner, Igor A1 - Laepple, Thomas T1 - Testing the consistency of Holocene and Last Glacial Maximum spatial correlations in temperature proxy records JF - Journal of quaternary science : JQS N2 - Holocene temperature proxy records are commonly used in quantitative synthesis and model-data comparisons. However, comparing correlations between time series from records collected in proximity to one another with the expected correlations based on climate model simulations indicates either regional or noisy climate signals in Holocene temperature proxy records. In this study, we evaluate the consistency of spatial correlations present in Holocene proxy records with those found in data from the Last Glacial Maximum (LGM). Specifically, we predict correlations expected in LGM proxy records if the only difference to Holocene correlations would be due to more time uncertainty and more climate variability in the LGM. We compare this simple prediction to the actual correlation structure in the LGM proxy records. We found that time series data of ice-core stable isotope records and planktonic foraminifera Mg/Ca ratios were consistent between the Holocene and LGM periods, while time series of Uk'37 proxy records were not as we found no correlation between nearby LGM records. Our results support the finding of highly regional or noisy marine proxy records in the compilation analysed here and suggest the need for further studies on the role of climate proxies and the processes of climate signal recording and preservation. KW - Holocene KW - LGM KW - spatial correlation KW - temperature KW - Uk'37 Y1 - 2020 U6 - https://doi.org/10.1002/jqs.3245 SN - 0267-8179 SN - 1099-1417 VL - 36 IS - 1 SP - 20 EP - 28 PB - Wiley CY - New York ER - TY - JOUR A1 - Zimmermann, Heike Hildegard A1 - Stoof-Leichsenring, Kathleen Rosemarie A1 - Kruse, Stefan A1 - Müller, Juliane A1 - Stein, Ruediger A1 - Tiedemann, Ralf A1 - Herzschuh, Ulrike T1 - Changes in the composition of marine and sea-ice diatoms derived from sedimentary ancient DNA of the eastern Fram Strait over the past 30 000 years JF - Ocean science N2 - The Fram Strait is an area with a relatively low and irregular distribution of diatom microfossils in surface sediments, and thus microfossil records are scarce, rarely exceed the Holocene, and contain sparse information about past richness and taxonomic composition. These attributes make the Fram Strait an ideal study site to test the utility of sedimentary ancient DNA (sedaDNA) metabarcoding. Amplifying a short, partial rbcL marker from samples of sediment core MSM05/5-712-2 resulted in 95.7% of our sequences being assigned to diatoms across 18 different families, with 38.6% of them being resolved to species and 25.8% to genus level. Independent replicates show a high similarity of PCR products, especially in the oldest samples. Diatom sedaDNA richness is highest in the Late Weichselian and lowest in Mid- and Late Holocene samples. Taxonomic composition is dominated by cold-water and sea-ice-associated diatoms and suggests several reorganisations - after the Last Glacial Maximum, after the Younger Dryas, and after the Early and after the Mid-Holocene. Different sequences assigned to, amongst others, Chaetoceros socialis indicate the detectability of intra-specific diversity using sedaDNA. We detect no clear pattern between our diatom sedaDNA record and the previously published IP25 record of this core, although proportions of pennate diatoms increase with higher IP25 concentrations and proportions of Nitzschia cf. frigida exceeding 2% of the assemblage point towards past sea-ice presence. Y1 - 2020 U6 - https://doi.org/10.5194/os-16-1017-2020 SN - 1812-0784 VL - 16 IS - 5 SP - 1017 EP - 1032 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Montero-Lopez, Carolina A1 - Hongn, Fernando D. A1 - Lopez Steinmetz, Romina L. A1 - Aramayo, Alejandro A1 - Pingel, Heiko A1 - Strecker, Manfred A1 - Cottle, John A1 - Bianchi, Carlos T1 - Development of an incipient Paleogene topography between the present-day Eastern Andean Plateau (Puna) and the Eastern Cordillera, southern Central Andes, NW Argentina JF - Basin research / publ. in conjunction with the European Association of Geoscientists & Engineers and the International Association of Sedimentologists N2 - The structural and topographic evolution of orogenic plateaus is an important research topic because of its impact on atmospheric circulation patterns, the amount and distribution of rainfall, and resulting changes in surface processes. The Puna region in the north-western Argentina (between 13 degrees S and 27 degrees S) is part of the Andean Plateau, which is the world's second largest orogenic plateau. In order to investigate the deformational events responsible for the initial growth of this part of the Andean plateau, we carried out structural and stratigraphic investigations within the present-day transition zone between the northern Puna and the adjacent Eastern Cordillera to the east. This transition zone is characterized by ubiquitous exposures of continental middle Eocene redbeds of the Casa Grande Formation. Our structural mapping, together with a sedimentological analysis of these units and their relationships with the adjacent mountain ranges, has revealed growth structures and unconformities that are indicative of syntectonic deposition. These findings support the notion that tectonic shortening in this part of the Central Andes was already active during the middle Paleogene, and that early Cenozoic deformation in the region that now constitutes the Puna occurred in a spatially irregular manner. The patterns of Paleogene deformation and uplift along the eastern margin of the present-day plateau correspond to an approximately north-south oriented swath of reactivated basement heterogeneities (i.e. zones of mechanical weakness) stemming from regional Paleozoic mountain building that may have led to local concentration of deformation belts. KW - Andean Plateau KW - Eastern Cordillera KW - Eocene deformation KW - growth structures KW - northern Puna KW - north-western Argentina KW - southern Central Andes Y1 - 2020 U6 - https://doi.org/10.1111/bre.12510 SN - 0950-091X SN - 1365-2117 VL - 33 IS - 2 SP - 1194 EP - 1217 PB - Wiley-Blackwell CY - Oxford ER - TY - JOUR A1 - Zhou, Renjie A1 - Aitchison, Jonathan C. A1 - Lokho, Kapesa A1 - Sobel, Edward A1 - Feng, Yuexing A1 - Zhao, Jian-xin T1 - Unroofing the Ladakh Batholith: constraints from autochthonous molasse of the Indus Basin, NW Himalaya JF - Journal of the Geological Society N2 - The Indus Molasse records orogenic sedimentation associated with uplift and erosion of the southern margin of Asia in the course of ongoing India-Eurasia collision. Detailed field investigation clarifies the nature and extent of the depositional contact between this molasse and the underlying basement units. We report the first dataset on detrital zircon U-Pb ages, Hf isotopes and apatite U-Pb ages for the autochthonous molasse in the Indus Suture Zone. A latest Oligocene depositional age is proposed on the basis of the youngest detrital zircon U-Pb age peak and is consistent with published biostratigraphic data. Multiple provenance indicators suggest exclusively northerly derivation with no input from India in the lowermost parts of the section. The results provide constraints on the uplift and erosion history of the Ladakh Range following the initial India-Asia collision. Y1 - 2020 U6 - https://doi.org/10.1144/jgs2019-188 SN - 0016-7649 SN - 2041-479X VL - 177 IS - 4 SP - 818 EP - 825 PB - Geological Society (London) CY - London 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 - Glerum, Anne A1 - Brune, Sascha A1 - Stamps, D. Sarah A1 - Strecker, Manfred T1 - Victoria continental microplate dynamics controlled by the lithospheric strength distribution of the East African Rift JF - Nature Communications N2 - The Victoria microplate between the Eastern and Western Branches of the East African Rift System is one of the largest continental microplates on Earth. In striking contrast to its neighboring plates, Victoria rotates counterclockwise with respect to Nubia. The underlying cause of this distinctive rotation has remained elusive so far. Using 3D numerical models, we investigate the role of pre-existing lithospheric heterogeneities in continental microplate rotation. We find that Victoria's rotation is primarily controlled by the distribution of rheologically stronger zones that transmit the drag of the major plates to the microplate and of the mechanically weaker mobile belts surrounding Victoria that facilitate rotation. Our models reproduce Victoria's GPS-derived counterclockwise rotation as well as key complexities of the regional tectonic stress field. These results reconcile competing ideas on the opening of the rift system by highlighting differences in orientation of the far-field divergence, local extension, and the minimum horizontal stress. One of the largest continental microplates on Earth is situated in the center of the East African Rift System, and oddly, the Victoria microplate rotates counterclockwise with respect to the neighboring African tectonic plate. Here, the authors' modelling results suggest that Victoria microplate rotation is caused by edge-driven lithospheric processes related to the specific geometry of rheologically weak and strong regions. Y1 - 2020 U6 - https://doi.org/10.1038/s41467-020-16176-x SN - 2041-1723 VL - 11 IS - 1 PB - Nature Publishing Group CY - London 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 - JOUR A1 - Forbriger, Thomas A1 - Gao, Lingli A1 - Malischewsky, Peter A1 - Ohrnberger, Matthias A1 - Pan, Yudi T1 - A single Rayleigh mode may exist with multiple values of phase-velocity at one frequency JF - Geophysical journal international N2 - Other than commonly assumed in seismology, the phase velocity of Rayleigh waves is not necessarily a single-valued function of frequency. In fact, a single Rayleigh mode can exist with three different values of phase velocity at one frequency. We demonstrate this for the first higher mode on a realistic shallow seismic structure of a homogeneous layer of unconsolidated sediments on top of a half-space of solid rock (LOH). In the case of LOH a significant contrast to the half-space is required to produce the phenomenon. In a simpler structure of a homogeneous layer with fixed (rigid) bottom (LFB) the phenomenon exists for values of Poisson's ratio between 0.19 and 0.5 and is most pronounced for P-wave velocity being three times S-wave velocity (Poisson's ratio of 0.4375). A pavement-like structure (PAV) of two layers on top of a half-space produces the multivaluedness for the fundamental mode. Programs for the computation of synthetic dispersion curves are prone to trouble in such cases. Many of them use mode-follower algorithms which loose track of the dispersion curve and miss the multivalued section. We show results for well established programs. Their inability to properly handle these cases might be one reason why the phenomenon of multivaluedness went unnoticed in seismological Rayleigh wave research for so long. For the very same reason methods of dispersion analysis must fail if they imply wave number k(l)(omega) for the lth Rayleigh mode to be a single-valued function of frequency.. This applies in particular to deconvolution methods like phase-matched filters. We demonstrate that a slant-stack analysis fails in the multivalued section, while a Fourier-Bessel transformation captures the complete Rayleigh-wave signal. Waves of finite bandwidth in the multivalued section propagate with positive group-velocity and negative phase-velocity. Their eigenfunctions appear conventional and contain no conspicuous feature. KW - Surface waves and free oscillations KW - Theoretical seismology KW - Wave KW - propagation Y1 - 2020 U6 - https://doi.org/10.1093/gji/ggaa123 SN - 0956-540X SN - 1365-246X VL - 222 IS - 1 SP - 582 EP - 594 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Menges, Johanna A1 - Hovius, Niels A1 - Andermann, Christoff A1 - Lupker, Maarten A1 - Haghipour, Negar A1 - Märki, Lena A1 - Sachse, Dirk T1 - Variations in organic carbon sourcing along a trans-Himalayan river determined by a Bayesian mixing approach JF - Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society N2 - Rivers transfer particulate organic carbon (POC) from eroding mountains into geological sinks. Organic carbon source composition and selective mobilization have been shown to affect the type and quantity of POC export, but their combined effects across complex mountain ranges remain underexplored. Here, we examine the variation in organic carbon sourcing and transport in the trans-Himalayan Kali Gandaki River catchment, along strong gradients in precipitation, rock type and vegetation. Combining bulk stable nitrogen, and stable and radioactive organic carbon isotopic composition of bedrock, litter, soil and river sediment samples with a Bayesian end-member mixing approach, we differentiate POC sources along the river and quantify their export. Our analysis shows that POC export from the Tibetan segment of the catchment, where carbon bearing shales are partially covered by aged and modern soils, is dominated by petrogenic POC. Based on our data we re-assess the presence of aged biospheric OC in this part of the catchment, and its contribution to the river load. In the High Himalayan segment, we observed low inputs of petrogenic and biospheric POC, likely due to very low organic carbon concentrations in the metamorphic bedrock, combined with erosion dominated by deep-seated landslides. Our findings show that along the Kali Gandaki River, the sourcing of sediment and organic carbon are decoupled, due to differences in rock organic carbon content, soil and above ground carbon stocks, and geomorphic process activity. While the fast eroding High Himalayas are the principal source of river sediment, the Tibetan headwaters, where erosion rates are lower, are the principal source of organic carbon. To robustly estimate organic carbon export from the Himalayas, the mountain range should be divided into tectono-physiographic zones with distinct organic carbon yields due to differences in substrate and erosion processes and rates. KW - particulate organic carbon KW - Himalaya KW - rivers KW - carbon cycle KW - stable KW - isotopes KW - erosion KW - end-member mixing Y1 - 2020 U6 - https://doi.org/10.1016/j.gca.2020.07.003 SN - 0016-7037 VL - 286 SP - 159 EP - 176 PB - Elsevier CY - New York [u.a.] ER - TY - JOUR A1 - Obreht, Igor A1 - Wörmer, Lars A1 - Brauer, Achim A1 - Wendt, Jenny A1 - Alfken, Susanne A1 - De Vleeschouwer, David A1 - Elvert, Marcus A1 - Hinrichs, Kai-Uwe T1 - An annually resolved record of Western European vegetation response to Younger Dryas cooling JF - Quaternary science reviews : the international multidisciplinary research and review journal N2 - The regional patterns and timing of the Younger Dryas cooling in the North Atlantic realm were complex and are mechanistically incompletely understood. To enhance understanding of regional climate patterns, we present molecular biomarker records at subannual to annual resolution by mass spectrometry imaging (MSI) of sediments from the Lake Meerfelder Maar covering the Allerod-Younger Dryas transition. These analyses are supported by conventional extraction-based molecular-isotopic analyses, which both validate the imaging results and constrain the sources of the target compounds. The targeted fatty acid biomarkers serve as a gauge of the response of the local aquatic and terrestrial ecosystem to climate change. Based on the comparison of our data with existing data from Meerfelder Maar, we analyse the short-term environmental evolution in Western Europe during the studied time interval and confirm the previously reported delayed hydrological response to Greenland cooling. However, despite a detected delay of Western European environmental change of similar to 135 years, our biomarker data show statistically significant correlation with deuterium excess in Greenland ice core at - annual resolution during this time-transgressive cooling. This suggests a coherent atmospheric forcing across the North Atlantic realm during this transition. We propose that Western European cooling was postponed due to major reorganization of the westerlies that were intermittently forcing warmer and wetter air masses from lower latitudes to Western Europe and thus resulted in delayed cooling relative to Greenland. KW - lateglacial KW - paleoclimatology KW - Western Europe KW - Meerfelder Maar KW - high-resolution biomarkers KW - fatty acids KW - FT-ICR-MS KW - mass spectrometry KW - imaging Y1 - 2020 U6 - https://doi.org/10.1016/j.quascirev.2020.106198 SN - 0277-3791 VL - 231 PB - Elsevier CY - Amsterdam [u.a.] ER - TY - JOUR A1 - Krmíček, Lukáš A1 - Timmerman, Martin Jan A1 - Ziemann, Martin Andreas A1 - Sudo, Masafumi A1 - Ulrych, Jaromir T1 - 40Ar/39Ar step-heating dating of phlogopite and kaersutite megacrysts from the Železná hůrka (Eisenbühl) Pleistocene scoria cone, Czech Republic JF - Geologica Carpathica N2 - (40)A/Ar-39 step-heating of mica and amphibole megacrysts from hauyne-bearing olivine melilitite scoria/tephra from the Zelezna hurka yielded a 435 +/- 108 ka isotope correlation age for phlogopite and a more imprecise 1.55 Ma total gas age of the kaersutite megacryst. The amphibole megacrysts may constitute the first, and the younger phlogopite megacrysts the later phase of mafic, hydrous melilitic magma crystallization. It cannot be ruled out that the amphibole megacrysts are petrogenetically unrelated to tephra and phlogopite megacrysts and were derived from mantle xenoliths or disaggregated older, deep crustal pegmatites. This is in line both with the rarity of amphibole at Zelezna hurka and with the observed signs of magmatic resorption at the edges of amphibole crystals. KW - Bohemian Massif KW - Zelezna hurka KW - Eisenbuhl KW - argon dating KW - mica KW - amphibole KW - melilitite Y1 - 2020 U6 - https://doi.org/10.31577/GeolCarp.71.4.6 SN - 1335-0552 SN - 1336-8052 VL - 71 IS - 4 SP - 382 EP - 387 PB - Veda CY - Bratislava ER - TY - JOUR A1 - Rybski, Diego A1 - Dawson, Richard J. A1 - Kropp, Jürgen T1 - Comparing generic and case study damage functions BT - London storm-surge example JF - Natural hazards review N2 - Two different approaches are used to assess the impacts associated with natural hazards and climate change in cities. A bottom-up approach uses high resolution data on constituent assets within the urban area. In contrast, a top-down approach uses less detailed information but is consequently more readily transferable. Here, we compare damage curves generated by each approach for coastal flooding in London. To compare them, we fit a log-logistic regression with three parameters to the calculated damage curves. We find that the functions are remarkably similar in their shape, albeit with different inflection points and a maximum damage that differs by 13%-25%. If rescaled, the curves agree almost exactly, which enables damage assessment to be undertaken following the calculation of the three parameters. Y1 - 2020 U6 - https://doi.org/10.1061/(ASCE)NH.1527-6996.0000336 SN - 1527-6988 SN - 1527-6996 VL - 21 IS - 1 PB - American Society of Civil Engineers CY - Reston ER - TY - JOUR A1 - Baes, Marzieh A1 - Sobolev, Stephan A1 - Gerya, Taras V. A1 - Brune, Sascha T1 - Plume-induced subduction initiation BT - single-slab or multi-slab subduction? JF - Geochemistry, geophysics, geosystems 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. KW - subduction zone KW - plume KW - numerical model KW - singleslab KW - multi-slab Y1 - 2020 U6 - https://doi.org/10.1029/2019GC008663 SN - 1525-2027 VL - 21 IS - 2 PB - American Geophysical Union CY - Washington ER - TY - JOUR A1 - Liu, Qi A1 - Adler, Karsten A1 - Lipus, Daniel A1 - Kämpf, Horst A1 - Bussert, Robert A1 - Plessen, Birgit A1 - Schulz, Hans-Martin A1 - Krauze, Patryk A1 - Horn, Fabian A1 - Wagner, Dirk A1 - Mangelsdorf, Kai A1 - Alawi, Mashal T1 - Microbial signatures in deep CO2-saturated miocene sediments of the active Hartousov mofette system (NW Czech Republic) JF - Frontiers in microbiology N2 - The Hartousov mofette system is a natural CO2 degassing site in the central Cheb Basin (Eger Rift, Central Europe). In early 2016 a 108 m deep core was obtained from this system to investigate the impact of ascending mantle-derived CO2 on indigenous deep microbial communities and their surrounding life habitat. During drilling, a CO2 blow out occurred at a depth of 78.5 meter below surface (mbs) suggesting a CO2 reservoir associated with a deep low-permeable CO2-saturated saline aquifer at the transition from Early Miocene terrestrial to lacustrine sediments. Past microbial communities were investigated by hopanoids and glycerol dialkyl glycerol tetraethers (GDGTs) reflecting the environmental conditions during the time of deposition rather than showing a signal of the current deep biosphere. The composition and distribution of the deep microbial community potentially stimulated by the upward migration of CO2 starting during Mid Pleistocene time was investigated by intact polar lipids (IPLs), quantitative polymerase chain reaction (qPCR), and deoxyribonucleic acid (DNA) analysis. The deep biosphere is characterized by microorganisms that are linked to the distribution and migration of the ascending CO2-saturated groundwater and the availability of organic matter instead of being linked to single lithological units of the investigated rock profile. Our findings revealed high relative abundances of common soil and water bacteria, in particular the facultative, anaerobic and potential iron-oxidizing Acidovorax and other members of the family Comamonadaceae across the whole recovered core. The results also highlighted the frequent detection of the putative sulfate-oxidizing and CO2-fixating genus Sulfuricurvum at certain depths. A set of new IPLs are suggested to be indicative for microorganisms associated to CO2 accumulation in the mofette system. KW - geo-bio interaction KW - CO2 KW - mofette systems KW - Eger Rift KW - microbial lipid KW - biomarker KW - microbial diversity KW - deep biosphere KW - saline groundwater Y1 - 2020 U6 - https://doi.org/10.3389/fmicb.2020.543260 SN - 1664-302X VL - 11 PB - Frontiers Media CY - Lausanne ER - TY - JOUR A1 - Mogrovejo Arias, Diana Carolina A1 - Brill, Florian H. H. A1 - Wagner, Dirk T1 - Potentially pathogenic bacteria isolated from diverse habitats in Spitsbergen, Svalbard JF - Environmental earth sciences N2 - The Arctic ecosystem, a reservoir of genetic microbial diversity, represents a virtually unlimited source of microorganisms that could interact with human beings. Despite continuous exploration of Arctic habitats and description of their microbial communities, bacterial phenotypes commonly associated with pathogenicity, such as hemolytic activity, have rarely been reported. In this study, samples of snow, fresh and marine water, soil, and sediment from several habitats in the Arctic archipelago of Svalbard were collected during Summer, 2017. Bacterial isolates were obtained after incubation on oligotrophic media at different temperatures and their hemolytic potential was assessed on sheep blood agar plates. Partial (alpha) or true (beta) hemolysis was observed in 32 out of 78 bacterial species. Genes expressing cytolytic compounds, such as hemolysins, likely increase the general fitness of the producing microorganisms and confer a competitive advantage over the availability of nutrients in natural habitats. In environmental species, the nutrient-acquisition function of these compounds presumably precedes their function as toxins for mammalian erythrocytes. However, in the light of global warming, the presence of hemolytic bacteria in Arctic environments highlights the possible risks associated with these microorganisms in the event of habitat melting/destruction, ecosystem transition, and re-colonization. KW - Arctic KW - Svalbard KW - hemolysins KW - climate change KW - pathogens KW - virulence Y1 - 2020 U6 - https://doi.org/10.1007/s12665-020-8853-4 SN - 1866-6280 SN - 1866-6299 VL - 79 IS - 5 PB - Springer CY - Berlin ; Heidelberg ER - TY - JOUR A1 - Niemz, Peter A1 - Cesca, Simone A1 - Heimann, Sebastian A1 - Grigoli, Francesco A1 - von Specht, Sebastian A1 - Hammer, Conny A1 - Zang, Arno A1 - Dahm, Torsten T1 - Full-waveform-based characterization of acoustic emission activity in a mine-scale experiment BT - a comparison of conventional and advanced hydraulic fracturing schemes JF - Geophysical journal international / the Royal Astronomical Society, the Deutsche Geophysikalische Gesellschaft and the European Geophysical Society N2 - Understanding fracturing processes and the hydromechanical relation to induced seismicity is a key question for enhanced geothermal systems (EGS). Commonly massive fluid injection, predominately causing hydroshearing, are used in large-scale EGS but also hydraulic fracturing approaches were discussed. To evaluate the applicability of hydraulic fracturing techniques in EGS, six in situ, multistage hydraulic fracturing experiments with three different injection schemes were performed under controlled conditions in crystalline rock at the Aspo Hard Rock Laboratory (Sweden). During the experiments the near-field ground motion was continuously recorded by 11 piezoelectric borehole sensors with a sampling rate of 1 MHz. The sensor network covered a volume of 30x30x30 m around a horizontal, 28-m-long injection borehole at a depth of 410 m. To extract and characterize massive, induced, high-frequency acoustic emission (AE) activity from continuous recordings, a semi-automated workflow was developed relying on full waveform based detection, classification and location procedures. The approach extended the AE catalogue from 196 triggered events in previous studies to more than 19600 located AEs. The enhanced catalogue, for the first time, allows a detailed analysis of induced seismicity during single hydraulic fracturing experiments, including the individual fracturing stages and the comparison between injection schemes. Beside the detailed study of the spatio-temporal patterns, event clusters and the growth of seismic clouds, we estimate relative magnitudes and b-values of AEs for conventional, cyclic progressive and dynamic pulse injection schemes, the latter two being fatigue hydraulic fracturing techniques. While the conventional fracturing leads to AE patterns clustered in planar regions, indicating the generation of a single main fracture plane, the cyclic progressive injection scheme results in a more diffuse, cloud-like AE distribution, indicating the activation of a more complex fracture network. For a given amount of hydraulic energy (pressure multiplied by injected volume) pumped into the system, the cyclic progressive scheme is characterized by a lower rate of seismicity, lower maximum magnitudes and significantly larger b-values, implying an increased number of small events relative to the large ones. To our knowledge, this is the first direct comparison of high resolution seismicity in a mine-scale experiment induced by different hydraulic fracturing schemes. KW - Fracture and flow KW - Spatial analysis KW - Statistical methods KW - Time-series analysis KW - Induced seismicity Y1 - 2020 U6 - https://doi.org/10.1093/gji/ggaa127 SN - 0955-419X SN - 1365-246X VL - 222 IS - 1 SP - 189 EP - 206 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Wang, Lei A1 - Dresen, Georg A1 - Rybacki, Erik A1 - Bonnelye, Audrey A1 - Bohnhoff, Marco T1 - Pressure-dependent bulk compressibility of a porous granular material modeled by improved contact mechanics and micromechanical approaches BT - effects of surface roughness of grains JF - Acta materialia N2 - The change of the mechanical properties of granular materials with pressure is an important topic associated with many industrial applications. In this paper we investigate the influence of hydrostatic pressure (P-e) on the effective bulk compressibility (C-eff) of a granular material by applying two modified theoretical approaches that are based on contact mechanics and micromechanics, respectively. For a granular material composed of rough grains, an extended contact model is developed to elucidate the effect of roughness of grain surfaces on bulk compressibility. At relatively low pressures, the model predicts that the decrease of bulk compressibility with pressure may be described by a power law with an exponent of -1/2 (i.e., C-eff proportional to P-e(1/2) ), but deviates at intermediate pressures. At elevated pressures beyond full contact, bulk compressibility remains almost unchanged, which may be roughly evaluated by continuum contact mechanics. As an alternative explanation of pressure-dependent bulk compressibility, we suggest a micromechanical model that accounts for effects of different types of pore space present in granular materials. Narrow and compliant inter-granular cracks are approximated by three-dimensional oblate spheroidal cracks with rough surfaces, whereas the equant and stiff pores surrounded by three and four neighboring grains are modeled as tubular pores with cross sections of three and four cusp-like corners, respectively. In this model, bulk compressibility is strongly reduced with increasing pressure by progressive closure of rough-walled cracks. At pressures exceeding crack closure pressure, deformation of the remaining equant pores is largely insensitive to pressure, with almost no further change in bulk compressibility. To validate these models, we performed hydrostatic compression tests on Bentheim sandstone (a granular rock consisting of quartz with high porosity) under a wide range of pressure. The relation between observed microstructures and measured pressure-dependent bulk compressibility is well explained by both suggested models. KW - Bulk compressibility KW - Granular materials KW - Roughness KW - Micromechanical model KW - Contact model Y1 - 2020 U6 - https://doi.org/10.1016/j.actamat.2020.01.063 SN - 1359-6454 SN - 1873-2453 VL - 188 SP - 259 EP - 272 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Pradhan, Prajal A1 - Kriewald, Steffen A1 - Costa, Luís Fílípe Carvalho da A1 - Rybski, Diego A1 - Benton, Tim G. A1 - Fischer, Günther A1 - Kropp, Jürgen T1 - Urban food systems: how regionalization can contribute to climate change mitigation JF - Environmental science & technology N2 - Cities will play a key role in the grand challenge of nourishing a growing global population, because, due to their population density, they set the demand. To ensure that food systems are sustainable, as well as nourishing, one solution often suggested is to shorten their supply chains toward a regional rather than a global basis. While such regional systems may have a range of costs and benefits, we investigate the mitigation potential of regionalized urban food systems by examining the greenhouse gas emissions associated with food transport. Using data on food consumption for 7108 urban administrative units (UAUs), we simulate total transport emissions for both regionalized and globalized supply chains. In regionalized systems, the UAUs' demands are fulfilled by peripheral food production, whereas to simulate global supply chains, food demand is met from an international pool (where the origin can be any location globally). We estimate that regionalized systems could reduce current emissions from food transport. However, because longer supply chains benefit from maximizing comparative advantage, this emission reduction would require closing yield gaps, reducing food waste, shifting toward diversified farming, and consuming seasonal produce. Regionalization of food systems will be an essential component to limit global warming to well below 2 degrees C in the future. Y1 - 2020 U6 - https://doi.org/10.1021/acs.est.0c02739 SN - 0013-936X SN - 1520-5851 VL - 54 IS - 17 SP - 10551 EP - 10560 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Schönfeldt, Elisabeth A1 - Pánek, Tomáš A1 - Winocur, Diego A1 - Silhan, Karel A1 - Korup, Oliver T1 - Postglacial Patagonian mass movement BT - from rotational slides and spreads to earthflows JF - Geomorphology : an international journal on pure and applied geomorphology N2 - Many of the volcanic plateau margins of the eastern, formerly glaciated, foreland of the Patagonian Andes are undermined by giant landslides (>= 10(8) m(3)). One cluster of such landslides extends along the margin of the Meseta del Lago Buenos Aires (MLBA) plateau that is formed mainly by Neogene-Quaternary basalts. The dry climate is at odds with numerous >2-km long earthflows nested within older and larger compound landslides. We present a hydrological analysis, a detailed geomorphic map, interpretations of exposed landslide interiors, and radiocarbon dating of the El Mirador landslide, which is one of the largest and morphologically most representative landslide. We find that the presence of lakes on top of the plateau, causing low infiltration rates, correlates negatively with the abundance of earthflows on compound landslides along the plateau margins. Field outcrops show that the pattern of compound landslides and earthflows is likely controlled by groundwater seepage at the contact between the basalts and underlying soft Miocene molasse. Numerous peat bogs store water and sediment and are more abundant in earthflow-affected areas than in their contributing catchment areas.
Radiocarbon dates indicate that these earthflows displaced metre-thick layers of peat in the late Holocene (<2.5 ka). We conclude that earthflows of the MLBA plateau might be promising proxies of past hydroclimatic conditions in the Patagonian foreland, if strong earthquakes or gradual crustal stress changes due to glacioisostatic rebound can be ruled out. KW - landslide KW - lateral spread KW - earthflow KW - Patagonia Y1 - 2020 U6 - https://doi.org/10.1016/j.geomorph.2020.107316 SN - 0169-555X SN - 1872-695X VL - 367 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Scherler, Dirk A1 - Schwanghart, Wolfgang T1 - Drainage divide networks BT - Part 2: Response to perturbations JF - Earth surface dynamics N2 - Drainage divides are organized into tree-like networks that may record information about drainage divide mobility. However, views diverge about how to best assess divide mobility. Here, we apply a new approach of automatically extracting and ordering drainage divide networks from digital elevation models to results from landscape evolution model experiments. We compared landscapes perturbed by strike-slip faulting and spatiotemporal variations in erodibility to a reference model to assess which topographic metrics (hillslope relief, flow distance, and chi) are diagnostic of divide mobility. Results show that divide segments that are a minimum distance of similar to 5 km from river confluences strive to attain constant values of hillslope relief and flow distance to the nearest stream. Disruptions of such patterns can be related to mobile divides that are lower than stable divides, closer to streams, and often asymmetric in shape. In general, we observe that drainage divides high up in the network, i.e., at great distances from river confluences, are more susceptible to disruptions than divides closer to these confluences and are thus more likely to record disturbance for a longer time period. We found that across-divide differences in hillslope relief proved more useful for assessing divide migration than other tested metrics. However, even stable drainage divide networks exhibit across-divide differences in any of the studied topographic metrics. Finally, we propose a new metric to quantify the connectivity of divide junctions. KW - dynamics KW - landscape evolution KW - low-relief KW - patterns KW - river KW - scale KW - tectonics Y1 - 2020 U6 - https://doi.org/10.5194/esurf-8-261-2020 SN - 2196-6311 SN - 2196-632X VL - 8 IS - 2 SP - 261 EP - 274 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Sieber, Melanie Jutta A1 - Brink, Frank J. A1 - Leys, Clyde A1 - King, Penelope L. A1 - Henley, Richard W. T1 - Prograde and retrograde metasomatic reactions in mineralised magnesium- silicate skarn in the Cu-Au Ertsberg East Skarn System, Ertsberg, Papua Province, Indonesia JF - Ore geology reviews N2 - The 2.7-2.9 Ma Ertsberg East Skarn System (EESS) is a world-class Cu-Au skarn that formed within and adjacent to an intrusion within a paleodepth of 0.5 km and > 2.5 km. Its economic mineralisation developed by sustained reaction of magmatic fluid with contact metamorphosed siliciclastic and carbonate rocks at the margin of the adjacent Ertsberg quartz monzodiorite intrusion. Based on high-resolution mineral mapping, chemical analysis and thermodynamic calculations, the multistage formation processes of the exoskarn components of the EESS are examined in the context of changing pressure, temperature, fluid composition and fluid phase. We show that contact metamorphism of dolomitic sediments occurred at 51 +/- 5 MPa, between 700 degrees C and 800 degrees C and in the presence of a H2O-CO2-fluid containing similar to 10 to similar to 70 mol% CO2. This prograde metamorphism formed a forsterite + diopside + calcite + phlogopite + spinel assemblage. Such forsterite-dominated skarns account for similar to 55 vol% of the EESS exoskarns. Rare pargasite (previously unrecognized in this deposit) formed locally in the metamorphosed carbonate sequence where the protolith was composed of supratidal evaporites with dolomitic carbonate and interlayered calc-silicate rocks. The subsequent flux of a lower pressure magmatic gas containing SO2(g) caused sulphate metasomatism. This high temperature gas alteration of the metamorphic assemblage also caused skarn Cu-Fe-sulphide mineralisation. The influx of a SO2 gas through fracture permeability occurred at a temperature between similar to 600 and 700 degrees C and caused calcite to be replaced by anhydrite, with the coupled release of H2S(g). This in-situ release of H2S(g) scavenged trace Cu from the gas phase to deposit Cu-Fe-sulphides, which make the economic value of the distinct. We demonstrate that the formation of metal sulphides within forsterite skarns of the Ertsberg East Skarn System required a minimum flux of similar to 1,050 Mt SO2(g) and show that volcanic degassing may have occurred over a time span of similar to 3,900 years. As the system waned, the ambient fluid resulted in partial retrograde serpentinization of olivine and diopside without carbonation, and at temperatures sufficiently high to preserve anhydrite. KW - porphyry Cu-Au deposit KW - magnesium silicate skarn KW - pargasite KW - gas-solid KW - reaction KW - sulphate metasomatism Y1 - 2020 U6 - https://doi.org/10.1016/j.oregeorev.2020.103697 SN - 0169-1368 SN - 1872-7360 VL - 125 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Zhang, Xiaolin A1 - Yang, Xiaoqiang A1 - Jomaa, Seifeddine A1 - Rode, Michael T1 - Analyzing impacts of seasonality and landscape gradient on event-scale nitrate-discharge dynamics based on nested high-frequency monitoring JF - Journal of hydrology N2 - Increasingly available high-frequency data during storm events, when hydrological dynamics most likely activate nitrate storage-flux exchanges, reveal insights into catchment nitrate dynamics. In this study, we explored impacts of seasonality and landscape gradients on nitrate concentration-discharge (C-Q) hysteresis patterns in the Selke catchment, central Germany, which has heterogeneous combinations of meteorological, hydrogeological and land use conditions. Three nested gauging stations established along the main Selke River captured flow and nitrate export dynamics from the uppermost subcatchment (mixed forest and arable land), middle subcatchment (pure steep forest) and lowermost subcatchment (arable and urban land). We collected continuous high-frequency (15-min) discharge and nitrate concentration data from 2012 to 2017 and analyzed the 223 events detected at all three stations. A dominant hysteresis pattern in the uppermost and middle subcatchments was counter-clockwise and combined with an accretion effect, indicating many proximal and mobilized distal nitrate sources. However, 66% of all events at the catchment outlet experienced a dilution effect, possibly due to mechanisms that vary seasonally. During wetting/wet periods (October-March), it was combined mainly with a counter-clockwise pattern due to the dominance of event runoff volume from the uppermost and middle subcatchments. During drying/dry periods (April-September), however, it was combined mainly with a clockwise pattern due to occasional quick surface flows from lowland near-stream urban areas. In addition, the clockwise hysteresis occurred mainly from May-October during mostly drying/dry periods at all three sites, indicating little distal nitrate transport in response to the low terrestrial hydrological connectivity, especially in the lowermost dry and flat sub-catchment. This comprehensive analysis (i.e., clockwise vs. counter-clockwise, accretion vs. dilution) enables in-depth analysis of nitrate export mechanisms during certain periods under different landscape conditions. Specific combination of C-Q relationships could identify target locations for agricultural management actions that decrease nitrate output. Therefore, we strongly encourage long-term multisite and high-frequency monitoring strategies in heterogeneous nested catchment(s), which can help understand process mechanisms, generate data for physical-based water-quality modeling and provide guidance for water and agricultural management. KW - nitrate export dynamic KW - C-Q relationship KW - hysteresis pattern KW - high-frequency data KW - landscape effect KW - seasonality effect Y1 - 2020 U6 - https://doi.org/10.1016/j.jhydrol.2020.125585 SN - 0022-1694 SN - 1879-2707 VL - 591 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Albrecht, Torsten A1 - Winkelmann, Ricarda A1 - Levermann, Anders T1 - Glacial-cycle simulations of the Antarctic Ice Sheet with the Parallel Ice Sheet Model (PISM) BT - Part 1: boundary conditions and climatic forcing JF - The Cryosphere : TC ; an interactive open access journal of the European Geosciences Union N2 - 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. Y1 - 2020 U6 - https://doi.org/10.5194/tc-14-599-2020 SN - 1994-0416 SN - 1994-0424 VL - 14 IS - 2 SP - 599 EP - 632 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Figueroa Villegas, Sara A1 - Weiss, Jonathan R. A1 - Hongn, Fernando D. A1 - Pingel, Heiko A1 - Escalante, Leonardo A1 - Elías, Leonardo A1 - Aranda-Viana, R. Germán A1 - Strecker, Manfred T1 - Late pleistocene to recent deformation in the thick-skinned fold-and-thrust belt of Northwestern Argentina (Central Calchaqui Valley, 26 degrees S) JF - Tectonics / American Geophysical Union, AGU ; European Geophysical Society, EGS N2 - 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. Y1 - 2020 U6 - https://doi.org/10.1029/2020TC006394 SN - 0278-7407 SN - 1944-9194 VL - 40 IS - 1 PB - American Geophysical Union CY - Washington, DC ER - TY - JOUR A1 - Wetzel, Maria A1 - Kempka, Thomas A1 - Kühn, Michael T1 - Hydraulic and mechanical impacts of pore space alterations within a sandstone quantified by a flow velocity-dependent precipitation approach JF - Materials N2 - Geochemical processes change the microstructure of rocks and thereby affect their physical behaviour at the macro scale. A micro-computer tomography (micro-CT) scan of a typical reservoir sandstone is used to numerically examine the impact of three spatial alteration patterns on pore morphology, permeability and elastic moduli by correlating precipitation with the local flow velocity magnitude. The results demonstrate that the location of mineral growth strongly affects the permeability decrease with variations by up to four orders in magnitude. Precipitation in regions of high flow velocities is characterised by a predominant clogging of pore throats and a drastic permeability reduction, which can be roughly described by the power law relation with an exponent of 20. A continuous alteration of the pore structure by uniform mineral growth reduces the permeability comparable to the power law with an exponent of four or the Kozeny-Carman relation. Preferential precipitation in regions of low flow velocities predominantly affects smaller throats and pores with a minor impact on the flow regime, where the permeability decrease is considerably below that calculated by the power law with an exponent of two. Despite their complete distinctive impact on hydraulics, the spatial precipitation patterns only slightly affect the increase in elastic rock properties with differences by up to 6.3% between the investigated scenarios. Hence, an adequate characterisation of the spatial precipitation pattern is crucial to quantify changes in hydraulic rock properties, whereas the present study shows that its impact on elastic rock parameters is limited. The calculated relations between porosity and permeability, as well as elastic moduli can be applied for upscaling micro-scale findings to reservoir-scale models to improve their predictive capabilities, what is of paramount importance for a sustainable utilisation of the geological subsurface. KW - Bentheim sandstone KW - digital rock physics KW - micro-CT KW - elastic properties KW - permeability KW - precipitation Y1 - 2020 U6 - https://doi.org/10.3390/ma13143100 SN - 1996-1944 VL - 13 IS - 14 PB - MDPI CY - Basel 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 - 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 - TY - JOUR A1 - Wieczorek, Mareike A1 - Herzschuh, Ulrike T1 - Compilation of relative pollen productivity (RPP) estimates and taxonomically harmonised RPP datasets for single continents and Northern Hemisphere extratropics JF - Earth system science data : ESSD N2 - Relative pollen productivity (RPP) estimates are fractionate values, often in relation to Poaceae, that allow vegetation cover to be estimated from pollen counts with the help of models. RPP estimates are especially used in the scientific community in Europe and China, with a few studies in North America. Here we present a comprehensive compilation of available northern hemispheric RPP studies and their results arising from 51 publications with 60 sites and 131 taxa. This compilation allows scientists to identify data gaps in need of further RPP analyses but can also aid them in finding an RPP set for their study region. We also present a taxonomically harmonised, unified RPP dataset for the Northern Hemisphere and subsets for North America (including Greenland), Europe (including arctic Russia), and China, which we generated from the available studies. The unified dataset gives the mean RPP for 55 harmonised taxa as well as fall speeds, which are necessary to reconstruct vegetation cover from pollen counts and RPP values. Data are openly available at https://doi.org/10.1594/PANGAEA.922661 (Wieczorek and Herzschuh, 2020). Y1 - 2020 U6 - https://doi.org/10.5194/essd-12-3515-2020 SN - 1866-3508 SN - 1866-3516 VL - 12 IS - 4 SP - 3515 EP - 3528 PB - Copernicus CY - Göttingen ER - TY - JOUR A1 - Heeschen, Katja U. A1 - Janocha, Julian A1 - Spangenberg, Erik A1 - Schicks, Judith Maria A1 - Giese, Ronny T1 - The impact of ice on the tensile strength of unconsolidated sand BT - a model for gas hydrate-bearing sands? JF - Marine and petroleum geology N2 - Tensile strength is an important parameter when it comes to predictions of potential fracturing of sediments by natural processes such as the emplacement of ice or gas hydrate lenses, as well as anthropogenic fracturing or else the stability of engineering constructions such as boreholes. Yet, tensile strength (sigma(tau)) measurements of unconsolidated ice-bearing or gas hydrate-bearing sands are scarce and affected by a large variability.
In the course of the SUGAR project we successfully used ice as a model for pore-filling and "load-bearing" gas hydrate in sand to determine compressional wave velocity. We were thus able to verify comparable formation characteristics and morphologies of ice and gas hydrate within the pore space. As these are important values for the tensile strength of ice/hydrate-bearing sands, ice was also used as a model for hydrate-bearing sands, despite differences in the mechanical behavior and strength of pure ice and gas hydrate. Water-saturated sand cores with ice saturations (S-ice) between 0 and 100% were tested at -6.8 degrees C. The varying S-ice were a result of the freezing point depression caused by saline solutions of different concentrations. The sigma(tau) was directly determined using a sleeve-fracturing test with an internal pressure that was created within the frozen samples. The setup was also adapted to fit a pressure vessel for tests using confining pressure.
The correlation of S-ice - sigma(tau) shows an exponential increase of sigma(tau) with S-ice. Whereas at S-ice < 60% the increase is small, it is large at S-ice > 80%. In conjunction with the change in strength, the viscoelastic behavior changes. A clear peak strength occurs at S-ice > 80%. We conclude that given 60% < S-ice < 80% the pore-filling morphology of the ice converts into a frame-building habitus and at S-ice > 80% the frame gains strength while the amount of residual water decreases. Tensile failure and cracking now exceed grain boundary sliding as the prevailing failure mode. The ice morphology in the sand is non-cementing and comparable to a gas hydrate-sand mixture. KW - tensile strength KW - ice-grain mixture KW - gas hydrate KW - saline permafrost KW - ice KW - frozen soil Y1 - 2020 U6 - https://doi.org/10.1016/j.marpetgeo.2020.104607 SN - 0264-8172 SN - 1873-4073 VL - 122 PB - Elsevier CY - Oxford ER - TY - JOUR A1 - Weatherill, Graeme A1 - Kotha, Sreeram Reddy A1 - Cotton, Fabrice T1 - Re-thinking site amplification in regional seismic risk assessment JF - Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute N2 - Probabilistic assessment of seismic hazard and risk over a geographical region presents the modeler with challenges in the characterization of the site amplification that are not present in site-specific assessment. Using site-to-site residuals from a ground motion model fit to observations from the Japanese KiK-net database, correlations between measured local amplifications and mappable proxies such as topographic slope and geology are explored. These are used subsequently to develop empirical models describing amplification as a direct function of slope, conditional upon geological period. These correlations also demonstrate the limitations of inferring 30-m shearwave velocity from slope and applying them directly into ground motion models. Instead, they illustrate the feasibility of deriving spectral acceleration amplification factors directly from sets of observed records, which are calibrated to parameters that can be mapped uniformly on a regional scale. The result is a geologically calibrated amplification model that can be incorporated into national and regional seismic hazard and risk assessment, ensuring that the corresponding total aleatory variability reflects the predictive capability of the mapped site proxy. KW - earthquake hazard analysis KW - ground motion KW - seismic risk KW - site effects KW - regional mapping Y1 - 2020 U6 - https://doi.org/10.1177/8755293019899956 SN - 8755-2930 SN - 1944-8201 VL - 36 IS - 1_SUPPL SP - 274 EP - 297 PB - Sage Publishing CY - Thousand Oaks, CA ER - TY - JOUR A1 - Putra, Muhammad Panji Islam Fajar A1 - Pradhan, Prajal A1 - Kropp, Jürgen T1 - A systematic analysis of Water-Energy-Food security nexus BT - a South Asian case study JF - The science of the total environment : an international journal for scientific research into the environment and its relationship with man N2 - Most South Asian countries have challenges in ensuring water, energy, and food (WEF) security, which are often interacting positively or negatively. To address these challenges, the nexus approach provides a framework to identify the interactions of the WEF sectors as an integrated system. However, most nexus studies only qualitatively discuss the interactions between these sectors. This study conducts a systematic analysis of the WEF security nexus in South Asia by using open data sources at the country scale. We analyze interactions between the WEF sectors statistically, defining positive and negative correlations between the WEF security indicators as synergies and trade-offs, respectively. By creating networks of the synergies and trade-offs, we further identify most positively and negatively influencing indicators in the WEF security nexus. We observe a larger share of trade-offs than synergies within the water and energy sectors and a larger share of synergies than trade-offs among the WEF sectors for South Asia. However, these observations vary across the South Asian countries. Our analysis highlights that strategies on promoting sustainable energy and discouraging fossil fuel use could have overall positive effects on the WEF security nexus in the countries. This study provides evidence for considering the WEF security nexus as an integrated system rather than just a combination of three different sectors or securities. KW - water security KW - food security KW - energy security KW - network analysis KW - water-energy-food nexus KW - sustainable development Y1 - 2020 U6 - https://doi.org/10.1016/j.scitotenv.2020.138451 SN - 0048-9697 SN - 1879-1026 VL - 728 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Specht, Sebastian von T1 - ICBM Integrated Combined Baseline Modification BT - an algorithm for segmented baseline estimation JF - Seismological research letters N2 - Accelerograms are the primary source for characterizing strong ground motion. It is therefore of paramount interest to have high-quality recordings free from any nonphysical contamination. Frequently, accelerograms are affected by baseline jumps and drifts, either related to the instrument and/or a major earthquake. In this work, I propose a correction method for these undesired baseline drifts based on segmented linear least squares. The algorithm operates on the integrated waveforms and combines all three instrument components to estimate a model that modifies the baseline to be at zero continuously. The procedure consists of two steps: first a suite of models with variable numbers of discontinuities is derived for all three instrument components. During this process, the number of discontinuities is reduced in a parsimonious way, for example, two very close discontinuities are merged into a single one. In the second step, the optimal model is selected on the basis of the Bayesian information criterion. I exemplify the application on synthetic waveforms with known discontinuities and on observed waveforms from a unified strong-motion database of the Japan Meteorological Agency (JMA) and the National Research Institute for Earth Science and Disaster Prevention (NIED, Japan) networks for the major events of the 2016 Kumamoto earthquakes. After the baseline jump correction, the waveforms are furthermore corrected for displacement according to Wang et al.(2011). The resulting displacements are comparable to the Interferometric Synthetic Aperture Radar-derived displacement estimates for the Kumamoto earthquake sequence. Y1 - 2019 U6 - https://doi.org/10.1785/0220190134 SN - 0895-0695 SN - 1938-2057 VL - 91 IS - 1 SP - 475 EP - 487 PB - Seismological Society of America, Eastern Section CY - Boulder, Colo. ER - TY - JOUR A1 - Karamzadeh Toularoud, Nasim A1 - Heimann, Sebastian A1 - Dahm, Torsten A1 - Krüger, Frank T1 - Earthquake source arrays BT - optimal configuration and applications in crustal structure studies JF - Geophysical journal international N2 - A collection of earthquake sources recorded at a single station, under specific conditions, are considered as a source array (SA), that is interpreted as if earthquake sources originate at the station location and are recorded at the source location. Then, array processing methods, that is array beamforming, are applicable to analyse the recorded signals. A possible application is to use source array multiple event techniques to locate and characterize near-source scatterers and structural interfaces. In this work the aim is to facilitate the use of earthquake source arrays by presenting an automatic search algorithm to configure the source array elements. We developed a procedure to search for an optimal source array element distribution given an earthquake catalogue including accurate origin time and hypocentre locations. The objective function of the optimization process can be flexibly defined for each application to ensure the prerequisites (criteria) of making a source array. We formulated four quantitative criteria as subfunctions and used the weighted sum technique to combine them in one single scalar function. The criteria are: (1) to control the accuracy of the slowness vector estimation using the time domain beamforming method, (2) to measure the waveform coherency of the array elements, (3) to select events with lower location error and (4) to select traces with high energy of specific phases, that is, sp- or ps-phases. The proposed procedure is verified using synthetic data as well as real examples for the Vogtland region in Northwest Bohemia. We discussed the possible application of the optimized source arrays to identify the location of scatterers in the velocity model by presenting a synthetic test and an example using real waveforms. KW - location of scatterers KW - optimization KW - source array design Y1 - 2020 U6 - https://doi.org/10.1093/gji/ggaa002 SN - 0956-540X SN - 1365-246X VL - 221 IS - 1 SP - 352 EP - 370 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Morishita, Yu A1 - Lazecky, Milan A1 - Wright, Tim J. A1 - Weiss, Jonathan R. A1 - Elliott, John R. A1 - Hooper, Andy T1 - LiCSBAS BT - an open-source InSAR time series analysis package integrated with the LiCSAR automated Sentinel-1 InSAR processor JF - Remote sensing N2 - For the past five years, the 2-satellite Sentinel-1 constellation has provided abundant and useful Synthetic Aperture Radar (SAR) data, which have the potential to reveal global ground surface deformation at high spatial and temporal resolutions. However, for most users, fully exploiting the large amount of associated data is challenging, especially over wide areas. To help address this challenge, we have developed LiCSBAS, an open-source SAR interferometry (InSAR) time series analysis package that integrates with the automated Sentinel-1 InSAR processor (LiCSAR). LiCSBAS utilizes freely available LiCSAR products, and users can save processing time and disk space while obtaining the results of InSAR time series analysis. In the LiCSBAS processing scheme, interferograms with many unwrapping errors are automatically identified by loop closure and removed. Reliable time series and velocities are derived with the aid of masking using several noise indices. The easy implementation of atmospheric corrections to reduce noise is achieved with the Generic Atmospheric Correction Online Service for InSAR (GACOS). Using case studies in southern Tohoku and the Echigo Plain, Japan, we demonstrate that LiCSBAS applied to LiCSAR products can detect both large-scale (>100 km) and localized (similar to km) relative displacements with an accuracy of <1 cm/epoch and similar to 2 mm/yr. We detect displacements with different temporal characteristics, including linear, periodic, and episodic, in Niigata, Ojiya, and Sanjo City, respectively. LiCSBAS and LiCSAR products facilitate greater exploitation of globally available and abundant SAR datasets and enhance their applications for scientific research and societal benefit. KW - InSAR KW - Sentinel-1 KW - time series analysis KW - deformation monitoring KW - tectonics KW - subsidence KW - automatic processing KW - global Y1 - 2020 U6 - https://doi.org/10.3390/rs12030424 SN - 2072-4292 VL - 12 IS - 3 PB - MDPI CY - Basel ER - TY - JOUR A1 - Zhu, Chuanbin A1 - Cotton, Fabrice A1 - Pilz, Marco T1 - Detecting site resonant frequency using HVSR BT - Fourier versus response spectrum and the first versus the highest peak frequency JF - Bulletin of the Seismological Society of America : BSSA N2 - In this investigation, we examine the uncertainties using the horizontal-to-vertical spectral ratio (HVSR) technique on earthquake recordings to detect site resonant frequencies at 207 KiK-net sites. Our results show that the scenario dependence of response (pseudospectral acceleration) spectral ratio could bias the estimates of resonant frequencies for sites having multiple significant peaks with comparable amplitudes. Thus, the Fourier amplitude spectrum (FAS) should be preferred in computing HVSR. For more than 80% of the investigated sites, the first peak (in the frequency domain) on the average HVSR curve over multiple sites coincides with the highest peak. However, for sites with multiple peaks, the highest peak frequency (f(p)) is less susceptible to the selection criteria of significant peaks and the extent of smoothing to spectrum than the first peak frequency (f(0)). Meanwhile, in comparison to the surface-to-borehole spectral ratio, f(0) tends to underestimate the predominant frequency (at which the largest amplification occurs) more than f(p). In addition, in terms of characterizing linear site response, f(p) shows a better overall performance than f(0). Based on these findings, we thus recommend that seismic network operators provide f(p) on the average HVSRFAS curve as a priority, ideally together with the average HVSRFAS curve in site characterization. Y1 - 2020 U6 - https://doi.org/10.1785/0120190186 SN - 0037-1106 SN - 1943-3573 VL - 110 IS - 2 SP - 427 EP - 440 PB - Seismological Society of America CY - El Cerito, Calif. ER - TY - JOUR A1 - Tronicke, Jens A1 - Allroggen, Niklas A1 - Biermann, Felix A1 - Fanselow, Florian A1 - Guillemoteau, Julien A1 - Krauskopf, Christof A1 - Lück, Erika T1 - Rapid multiscale analysis of near-surface geophysical anomaly maps BT - application to an archaeogeophysical data set JF - Geophysics N2 - In near- surface geophysics, ground-based mapping surveys are routinely used in a variety of applications including those from archaeology, civil engineering, hydrology, and soil science. The resulting geophysical anomaly maps of, for example, magnetic or electrical parameters are usually interpreted to laterally delineate subsurface structures such as those related to the remains of past human activities, subsurface utilities and other installations, hydrological properties, or different soil types. To ease the interpretation of such data sets, we have developed a multiscale processing, analysis, and visualization strategy. Our approach relies on a discrete redundant wavelet transform (RWT) implemented using cubic-spline filters and the a trous algorithm, which allows to efficiently compute a multiscale decomposition of 2D data using a series of 1D convolutions. The basic idea of the approach is presented using a synthetic test image, whereas our archaeogeophysical case study from northeast Germany demonstrates its potential to analyze and process rather typical geophysical anomaly maps including magnetic and topographic data. Our vertical-gradient magnetic data show amplitude variations over several orders of magnitude, complex anomaly patterns at various spatial scales, and typical noise patterns, whereas our topographic data show a distinct hill structure superimposed by a microtopographic stripe pattern and random noise. Our results demonstrate that the RWT approach is capable to successfully separate these components and that selected wavelet planes can be scaled and combined so that the reconstructed images allow for a detailed, multiscale structural interpretation also using integrated visualizations of magnetic and topographic data. Because our analysis approach is straightforward to implement without laborious parameter testing and tuning, computationally efficient, and easily adaptable to other geophysical data sets, we believe that it can help to rapidly analyze and interpret different geophysical mapping data collected to address a variety of near-surface applications from engineering practice and research. KW - archaeology KW - case history KW - near surface KW - magnetics KW - decomposition Y1 - 2020 U6 - https://doi.org/10.1190/GEO2019-0564.1 SN - 0016-8033 SN - 1942-2156 VL - 85 IS - 4 SP - B109 EP - B118 PB - Society of Exploration Geophysicists CY - Tulsa, Okla. ER - TY - JOUR A1 - Wolf, Sabina A1 - Pham, My A1 - Matthews, Nathanial A1 - Bubeck, Philip T1 - Understanding the implementation gap BT - policy-makers’ perceptions of ecosystem-based adaptation in Central Vietnam JF - Climate & development N2 - In recent years, nature-based solutions are receiving increasing attention in the field of disaster risk reduction and climate change adaptation as inclusive, no regret approaches. Ecosystem-based adaptation (EbA) can mitigate the impacts of climate change, build resilience and tackle environmental degradation thereby supporting the targets set by the 2030 Agenda, the Paris Agreement and the Sendai Framework. Despite these benefits, EbA is still rarely implemented in practice. To better understand the barriers to implementation, this research examines policy-makers' perceptions of EbA, using an extended version of Protection Motivation Theory as an analytical framework. Through semi-structured interviews with policy-makers at regional and provincial level in Central Vietnam, it was found that EbA is generally considered a promising response option, mainly due to its multiple ecosystem-service benefits. The demand for EbA measures was largely driven by the perceived consequences of natural hazards and climate change. Insufficient perceived response efficacy and time-lags in effectiveness for disaster risk reduction were identified as key impediments for implementation. Pilot projects and capacity building on EbA are important means to overcome these perceptual barriers. This paper contributes to bridging the knowledge-gap on political decision-making regarding EbA and can, thereby, promote its mainstreaming into policy plans. KW - climate change KW - ecosystem-based adaptation KW - risk perception KW - protection KW - motivation theory KW - decision making Y1 - 2020 U6 - https://doi.org/10.1080/17565529.2020.1724068 SN - 1756-5529 SN - 1756-5537 VL - 13 IS - 1 SP - 81 EP - 94 PB - Taylor & Francis LTD CY - Abingdon ER - TY - JOUR A1 - Rötzler, Jochen A1 - Timmerman, Martin Jan T1 - Geochronological and petrological constraints from the evolution in the Saxon Granulite Massif, Germany, on the Variscan continental collision orogeny JF - Journal of metamorphic geology N2 - Controversy over the plate tectonic affinity and evolution of the Saxon granulites in a two- or multi-plate setting during inter- or intracontinental collision makes the Saxon Granulite Massif a key area for the understanding of the Palaeozoic Variscan orogeny. The massif is a large dome structure in which tectonic slivers of metapelite and metaophiolite units occur along a shear zone separating a diapir-like body of high-Pgranulite below from low-Pmetasedimentary rocks above. Each of the upper structural units records a different metamorphic evolution until its assembly with the exhuming granulite body. New age and petrologic data suggest that the metaophiolites developed from early Cambrian protoliths during high-Pamphibolite facies metamorphism in the mid- to late-Devonian and thermal overprinting by the exhuming hot granulite body in the early Carboniferous. A correlation of new Ar-Ar biotite ages with publishedP-T-tdata for the granulites implies that exhumation and cooling of the granulite body occurred at average rates of similar to 8 mm/year and similar to 80 degrees C/Ma, with a drop in exhumation rate from similar to 20 to similar to 2.5 mm/year and a slight rise in cooling rate between early and late stages of exhumation. A time lag ofc. 2 Ma between cooling through the closure temperatures for argon diffusion in hornblende and biotite indicates a cooling rate of 90 degrees C/Ma when all units had assembled into the massif. A two-plate model of the Variscan orogeny in which the above evolution is related to a short-lived intra-Gondwana subduction zone conflicts with the oceanic affinity of the metaophiolites and the timescale ofc. 50 Ma for the metamorphism. Alternative models focusing on the internal Variscan belt assume distinctly different material paths through the lower or upper crust for strikingly similar granulite massifs. An earlier proposed model of bilateral subduction below the internal Variscan belt may solve this problem. KW - geochronology KW - granulite KW - high-Pmetamorphism KW - metaophiolite KW - Variscan KW - orogeny Y1 - 2020 U6 - https://doi.org/10.1111/jmg.12559 SN - 0263-4929 SN - 1525-1314 VL - 39 IS - 1 SP - 3 EP - 38 PB - Wiley CY - Hoboken ER - TY - JOUR A1 - Scharf, Andreas A1 - Sudo, Masafumi A1 - Pracejus, Bernhard A1 - Mattern, Frank A1 - Callegari, Ivan A1 - Bauer, Wilfried A1 - Scharf, Katharina T1 - Late Lutetian (Eocene) mafic intrusion into shallow marine platform deposits north of the Oman Mountains (Rusayl Embayment) and its tectonic significance JF - Journal of African earth sciences N2 - A silica undersaturated alkali-olivine basanitic magma intruded the late Paleocene/early Eocene Jafnayn Formation near Muscat. Geochemical analyses indicate that a significant amount of host rock (limestone) was assimilated into the magma. We dated the basanite as 42.7 +/- 1.0 Ma (2 sigma error; late Lutetian), using the whole rock Ar-40/Ar-39 step-wise heating technique. Intrusion occurred in the hanging wall of a major regional extensional shear zone (Frontal Range Fault, FRF) bounding the northern margin of two domes within the Oman Mountains (Jabal Akhdar and Saih Hatat domes). Two shear intervals along the FRF have been documented. The first interval lasted immediately after emplacement of the Semail Ophiolite (latest Cretaceous-early Eocene) while the second and poorly constrained interval was assumed to have occurred during the Oligocene. The proximity of the basanite to the FRF suggests that magma used extensional faults for the upper part of its ascent path. Reactivated Permian rift faults of the Pangaea rift or other preexisting faults may have been used for the lower ascent part. We conclude that the basanite intrusion coincided with the onset of the second deformation interval along the FRF, because (1) the position of the basanite is near a dextral releasing bend, associated with the second shear interval, (2) the overlap of our Ar-40/Ar-39 age with the cooling curves for rocks from the nearby Jabal Akhdar Dome, and (3) the basanite postdates the first FRF deformation episode by > 10 Ma. Thus, the second interval along the FRF had started already during the late Lutetian and probably lasted into the Miocene. KW - Ar-40/Ar-39 age KW - Jafnayn formation KW - gravitational collapse KW - Basanite KW - extension KW - Limestone assimilation in basanite Y1 - 2020 U6 - https://doi.org/10.1016/j.jafrearsci.2020.103941 SN - 1464-343X SN - 1879-1956 VL - 170 PB - Elsevier CY - Oxford ER -