bluuebunny/crossref_metadata_2025 huggingface dataset:
Shear attenuation and anelastic mechanisms in the central Pacific upper mantle
Authors: Ma Zhitu , Dalton Colleen , Russell Joshua , Gaherty James , Hirth Greg , Forsyth Donald
Published: March 2020

We determine the mantle attenuation (1/Q) structure beneath 70 Myr seafloor in the central Pacific. We use long-period (33-100 sec) Rayleigh waves recorded by the NoMelt array of broadband ocean-bottom seismometers. After the removal of tilt and compliance noise, we are able to measure Rayleigh wave phase and amplitude for 125 earthquakes. The compliance correction for ocean wave pressure on the seafloor is particularly important for improving signal-to-noise at periods longer than 55 sec. Attenuation and azimuthally anisotropic phase velocity in the study area are determined by approximating the wavefield as the interference of two plane waves. We find that the amplitude decay of Rayleigh waves across the NoMelt array can be adequately explained using a two-layer model: in the shallow layer, in the deeper layer, and a transition depth at 70 km, although the sharpness of the transition is not well resolved by the Rayleigh wave data. Notably, observed in the NoMelt lithosphere is significantly higher than values in this area from global attenuation models. When compared with lithospheric measured at higher frequency (~3 Hz), the frequency dependence of attenuation is very slight, revising previous interpretations. The effect of anelasticity on shear velocity (VS) is estimated from the ratio of observed velocity to the predicted anharmonic value. We use laboratory-based parameters to predict attenuation and velocity-dispersion spectra that result from the superposition of a weakly frequency dependent high-temperature background and an absorption peak. We test a large range of frequencies for the position of the absorption peak (fe) and determine, at each depth, which values of fe predict and VS that can fit the NoMelt and VS values simultaneously. We show that between depths of 60 and 80 km the seismic models require an increase in fe by at least 3-4 orders of magnitude. Under the assumption that the absorption peak is caused by elastically accommodated grain-boundary sliding, this increase in fe reflects a decrease in grain-boundary viscosity of 3-4 orders of magnitude. A likely explanation is an increase in the water content of the mantle, with the base of the dehydrated lid located at ~70-km depth.   
Seismic Full Waveform Inversion (FWI) to characterise the structure of firn
Authors: Pearce Emma , Booth Adam , Sava Paul , Jones Ian
Published: March 2020

The transformation of snow into ice is a fundamental process in glaciology. The yearly accumulation of fresh snowfall increases the overburden pressure, changing the snow’s properties such that it transitions into firn and pure glacier ice thereafter. Additionally, periods of melt and variations in subsurface and surface conditions can lead to the presence of ice layers and firn aquifers within the firn column. Therefore, firn characteristics provide a tool for evaluating past and present climate conditions relating to the amount of snow accumulation, melt, temperature conditions and the subsequent preservation of the snow.

Due to the importance of relationships between firn and other glaciological processes (e.g., settling, sublimation, recrystallization and other deformation processes) it has not been possible to develop a theoretically-based model which accurately predicts firn properties with depth. Therefore, methods of measuring firn are either intrusive or rely on (potentially unreliable) empirical conversions. Full Waveform Inversion (FWI) may offer a new standard for glaciological seismic modelling, mitigating issues within current seismic modelling techniques and paving the way for the recovery of elastic properties, including density. Constraining firn properties also leads to improved corrections for deeper seismic responses, e.g. glacier bed reflectivity.

 

Using seismic datasets obtained from Norway’s Hardangerjøkulen Ice Cap (60.47°N, 7.49°W) along with varying synthetic firn column scenarios (introducing the presence of ice lenses and firn aquifers), we show how FWI can mitigate the dependence on intrusive techniques and empirical relationships. Furthermore, we compare the robustness of the FWI approaches versus traditional glaciological approaches to velocity model building (Herglotz-Wiechert inversion).

 
Back-propagating super-shear rupture in the 2016 M7.1 Romanche transform fault earthquake
Authors: Hicks Stephen , Okuwaki Ryo , Steinberg Andreas , Rychert Catherine , Harmon Nicholas , Abercrombie Rachel , Bogiaztis Petros , Schlaphorst David , Zahradnik Jiri , Kendall J-Michael , Yagi Yugi , Shimizu Kousuke , Sudhaus Henriette
Published: March 2020

Rupture propagation of an earthquake strongly influences potentially destructive ground shaking. Variable rupture behaviour is often caused by complex fault geometries, masking information on fundamental frictional properties. Geometrically smoother ocean transform fault (OTF) plate boundaries offer a favourable environment to study fault zone dynamics because strain is accommodated along a single, wide zone (up to 20 km width) offsetting homogeneous geology comprising altered mafic or ultramafic rocks. However, fault friction during OTF ruptures is unknown: no large (Mw>7.0) ruptures had been captured and imaged in detail. In 2016, we recorded an Mw 7.1 earthquake on the Romanche OTF in the equatorial Atlantic on nearby seafloor seismometers. We show that this rupture had two phases: (1) up and eastwards propagation towards the weaker ridge-transform intersection (RTI), then (2) unusually, back-propagation westwards at super-shear speed toward the fault’s centre. Deep slip into weak fault segments facilitated larger moment release on shallow locked zones, highlighting that even ruptures along a single distinct fault zone can be highly dynamic. The possibility of reversing ruptures is absent in rupture simulations and unaccounted for in hazard assessments.
An experiment to assess the influence of urban pavements on biocide leaching from facades into urban soil and groundwater
Authors: Linke Felicia , Lange Jens
Published: March 2020

Biocides added to facade renders and paints prevent algae and fungi growing at conventional buildings. During rain events biocides leach from facades into the urban environment and its compartments i.e. soil, surface water and groundwater. In many cases polluted façade runoff reaches partly sealed pavements and a major part infiltrates. Transport and transformation processes of biocides below these pavements are largely unknown. It may be hypothesized that concentrated infiltration in joints surrounding paving stones may enhance water percolation and accelerate solute transport. This would mean that partly sealed pavements beneath building facades are hotspots for the entry of biocides into groundwater. This study aims at testing this hypothesis using an experimental mass balance approach.

Five weighable lysimeters in freestanding boxes represent a small-scale section of an urban environment. Three lysimeter have a sealed or partly sealed plaster surface (concrete stones, granite stones with sand joints, and grass paver). The other two lysimeter represent unsealed surfaces, one of them contains a 10cm soil layer with grass cover. The fifth lysimeter acts as a control and has a 40cm layer of filter gravel. Below all surface layers there is 20cm of crushed sand and 10cm of filter gravel. This setup follows typical guidelines of urban construction.

A hose with holes represents the linear leachate of a façade during a rain event. In pre-tests isotopically depleted (collected snowmelt) and enriched (spiked with a heavy standard) water serves to illustrate differences between areal and linear infiltration. Then Terbutryn dissolved in water acts as the main contaminant. It is a biocidal ingredient of a variety of paints and renders. Additional tracers such as bromide, uranine and sulforhodamine B help to illustrate the solute transport inside the lysimeters. Brilliant blue is used to visualize infiltration patterns.

For the experiment the boxes are saturated to field capacity. Pulses of the Terbutryn and tracer solution are poured on the gutter to represent a series of rainfall events with façade leaching. The entire percolate is collected at the bottom of the lysimeter and water samples are taken at regular intervals. After the experiment, the lysimeter matrices are sampled for Terbutryn, three prominent transformation products and for the different tracers. In parallel, physico-chemical soil properties are assessed. This experiment will provide new insights into processes that promote biocide leaching from building facades into urban groundwater.
Developing performance checks on machine-learning models in an automated system for developing hazard maps
Authors: Massam Ashleigh , Barnes Ashley , Lane Siân , Platt Robert , Wood David
Published: March 2020

JBA Risk Management (JBA) uses JFlow®,  a two-dimensional hydraulic model, to simulate surface water, fluvial, and dam break flood risk. National flood maps are generated on a computer cluster that parallelises up to 20,000 model simulations , covering an area of up to 320,000 km3 and creating up to 10 GB of data per day.

JBA uses machine-learning models to identify artefacts in the flood simulations. The ability of machine-learning models to quickly process and detect these artefacts, combined with the use of an automated control system, means that hydraulic modelling throughput can be maximised with little user intervention. However, continual retraining of the model and application of software updates introduce the risk of a significant decrease in performance. This necessitates the use of a system to monitor the performance of the machine-learning model to ensure that a sufficient level of quality is maintained, and to allow drops in quality to be investigated.

We  present an approach used to develop performance checks on a machine-learning model that identifies artificial depth differences between hydraulic model simulations. Performance checks are centred on the use of control charts, an approach commonly used in manufacturing processes to monitor the proportion of items produced with defects. In order to develop this approach for a geoscientific context, JBA has (i) built a database of randomly-sampled hydraulic model outputs currently totalling 200 GB of data; (ii) developed metrics to summarise key features across a modelled region, including geomorphology and hydrology; (iii) used a random forest regression model to identify feature dominance to determine the most robust relationships that contribute to depth differences in the flood map; and (iv) developed the performance check in an automated system that tests every nth hydraulic modelling output against data sampled  based on common features.

The implementation of the performance checks allows JBA to assess potential changes in the quality of artificial feature identification following a training cycle in a development environment prior to release in a production environment.
The nature and origin of moving solar radio bursts associated with coronal mass ejections
Authors: Morosan Diana , Kilpua Emilia , Palmerio Erika , Lynch Benjamin , Pomoell Jens , Vainio Rami , Palmroth Minna , Räsänen Juska
Published: March 2020

Flares and coronal mass ejections (CMEs) from the Sun are the most powerful and spectacular explosions in the solar system, capable of releasing vast amounts of magnetic energy over relatively short periods of time. These phenomena are often associated with particle acceleration processes that are often observed directly by spacecraft here at Earth. At the Sun, there are no direct methods of measuring these particles, which is necessary to predict their origin and propagation direction through the heliosphere. However, accelerated particles, in particular fast electrons, can generate emission at radio wavelengths through various mechanisms. Here, we exploit radio observations of Type II and Type IV radio bursts that accompany CME eruptions, in particular those radio bursts that show movement with the CME expansion in the low solar corona. Using multi-wavelength analysis, reconstruction of the radio emission and CME in three dimensions, we aim to determine the sources and locations of electron acceleration responsible for the Type II and Type IV emission in relation to the CME location and propagation. Such studies are important to understand CMEs and the sources of electron acceleration to ultimately improve the lead time to these impacts here at Earth.
Variation of uplift pressure of debris flow on the dam bottom
Authors: Chen Xingzhang , Chen Hui
Published: March 2020

Abstract: Uplift pressure is crucial for the stability of debris flow dam because of its reducing the effective pressure on the dam foundation and the anti-slide force of the dam. This study investigates the spatial and temporal variations of the uplift pressures during the debris flow impact processes, through a series of flume experiments. Before the debris flow impacting on the dam, the uplift pressure keeps stable due to the steady water level, and then it decreases slightly at the instant of debris flow impacting on the dam which lasts for no more than 1 s, and then increases sharply within a time lag no more than 2 s, and then decreases sharply soon afterwards. The maximal increasing ratio is 6.4 and the average value is 3, comparing with the uplift pressure before the impacting. The peak pressure occurs before the dam and decreases with the distance from the dam with a nearly linear tendency. The increment of uplift pressure also presents a similar tendency with the distance from the dam. In addition, the uplift pressure is found to be strongly influenced by the permeability of debris flow deposits, especially by the fine content of grain composition, and by the properties of the flow, such as the flow density, runoff volume and hydraulic gradient, and the pressure rises in a nearly linear form with the properties.

Keywords: debris flow, uplift pressure, check dam, flume experiments
Seismicity induced by fluid migration in the Main Ethiopian Rift
Authors: Raggiunti Martina , Keir Derek , Pagli Carolina , Lavayssiere Aude
Published: March 2020

Faults can act as preferential degassing pathways for fluids of deep origin. Their migration and consequently variation of fluid pore pressure can cause a reduction of normal stress on the fault planes and trigger earthquakes. This can generate not only microseismicity but also events with significant magnitude. To understand this phenomenon, we studied the spatial, temporal and waveform characteristics of local seismicity from the northern sector of Main Ethiopian Rift (MER) of East Africa near Fentale and Dofen volcanoes. The seismic database contains events occurred in the MER from October 2001 to January 2003, and acquired by the Ethiopia Afar Geoscientific Experiment (EAGLE Project). The recorded events have been relocated with NLLoc using a new 3D velocity model derived from a wide-angle controlled source experiment. The relocated catalog contains a total of 1543 events with magnitudes between 0 and 4. The seismicity is mainly concentrated in two areas: near the border faults of the Ethiopian plateau and within the rift. On the border faults, events mostly occur down to 20 km depth, with an average depth of ~ 12 km. Within the rift, the events mostly happen down to 15 km depth, with an average depth of ~ 9 km. The seismicity is divided into several clusters aligned parallel to the rift direction, and in profile sections the clusters are mostly dipping steeply sub-vertical and dipping consistent with Andersonian normal faults. The analysis of the temporal-spatial distribution of earthquakes shows that some of the clusters are strongly concentrated in time and in space, and therefore swarm-like. To understand if the different clusters have been conditioned by fluid migration we have also analyzed the frequency content, release of seismic moment, and b-val is cut out. The link between earthquakes and fluid migration has also been explored by interpreting the distribution of seismicity using remote sensing mapping of faults, fumaroles and hydrothermal springs. Understanding where and how the fluid migration occurs will aid geothermal exploration efforts in the region, also improved knowledge of where geothermal activity is linked to seismicity has implications for seismic hazard estimation, which is very important for this densely and economically active areas.
Dislocation Theory in a 3-dimensional Viscoelastic Earth Model
Authors: zhang xinlin
Published: March 2020

This study presents a new method to calculate displacement and potential changes caused by an earthquake in a three-dimensional viscoelastic earth model. It is the first time to compute co- and post-seismic deformation in a spherical earth with lateral heterogeneities. Such a method is useful to investigate the 3-dimensional viscoelastic structure of the earth by interpreting precise satellite gravity and GPS data. Firstly, we concern with Maxwell’s constitutive equation, the linearized equation of momentum conservation and Poisson’s equation, and obtain the solution in the Laplace domain in a spherical symmetric viscoelastic earth model. Furthermore, we employ the perturbed method to deal with the effect of lateral heterogeneities and obtain the relation between the solutions of the spherical symmetric earth model, the three-dimension earth model with lateral inhomogeneity and the auxiliary solutions. Then, using the given surface boundary conditions to determine the auxiliary solutions, we obtain the perturbed solutions of lateral increment in the Laplace domain. Finally, taking the inverse Laplace transforms of solutions in a spherical symmetric viscoelastic earth model and perturbed solutions with respect to lateral hetergeneities, we obtain the solutions of deformation in a three-dimensional viscoelastic earth model. 
Yuli Belt in the eastern Taiwan orogen: a part of suture zone separating Eurasian and Philippine Sea plates
Authors: Zhang Yiqiong , Tsai Chin-Ho , Froitzheim Nikolaus , Ustaszewski Kamil
Published: March 2020

The Taiwan orogen formed as a consequence of the oblique subduction of the Eurasian continental margin below the Luzon volcanic arc of the Philippine Sea Plate since the late Miocene. The Yuli Belt of the eastern Taiwan Central Range, exposed in the retro-wedge of the fold-and-thrust belt, hosts slivers of a heterogeneous unit of blueschist-facies rocks that are among the youngest blueschist units worldwide. However, the palaeogeographic provenance of this unit is still debated. This is due to the fact that numerous structural aspects, including the kinematics of the Yuli Belt’s tectonic contacts with adjacent units, are improperly understood.

Our studies form part of an ongoing reinvestigation of the tectonic evolution of the Yuli Belt. A revised geological map of the Yuli Belt was generated, incorporating own structural data from several river transects. Fieldwork and microstructural analyses suggest that the Yuli Belt was polyphasely deformed. Based on newly constructed cross sections we suspect that the blueschist-facies units were tectonically emplaced along thrusts on top of a mostly greenschist-facies metasedimentary unit that locally exhibits characteristics of a mélange. Later, both blueschist-facies and metasedimentary units were tightly folded, likely during the emplacement of the Yuli Belt onto the westerly adjacent Eurasia-derived Tailuko Belt along the so-called Shoufeng Fault. Lithological and fabric transitions across this fault are gradual, suggesting that the juxtaposition of Yuli and Tailuko Belts occurred during an early W-directed transport direction before becoming refolded during later E-vergent backfolding. Peak metamorphic temperatures in the greenschist-facies metasediments, estimated by Raman spectroscopic analyses of carbonaceous material (RSCM), reveal systematic spatial variations across the Yuli belt, supporting the idea of an allochthonous nature of the blueschist units on top of the lower grade metasedimentary unit.

The incorporation of published geochronological and whole-rock geochemical data and their combination with own paleogeographic reconstructions led us to fundamentally reinterpret the structural position of the Yuli Belt. We suggest that the blueschist-facies unit most likely represents a mid-Miocene fragment of oceanic crust and mantle issued in the South China Sea before having been subducted, exhumed and ‘sandwiched’ between the (Eurasia-derived) Tailuko Belt and the easterly adjacent Coastal Ranges derived from the Philippine Sea plate. The Yuli Belt should hence be considered to contain the suture between the Eurasian and the Philippine Sea plates.
An opposite response of the low-latitude ionosphere at Asian and American sectors during storm recovery phase: drivers from below and above
Authors: Xiong Chao , Luehr Hermann , Yamazaki Yosuke
Published: March 2020

The energy input from the solar wind and magnetosphere is thought to dominate the ionospheric response during geomagnetic storms. However, at the storm recovery phase, the role of forces from lower atmosphere could be as important as that from above. In this study, we focused on the geomagnetic storm happened on 6–11 September 2017. The ground-based total electron content (TEC) data as well as the F region in situ electron density measured by the Swarm satellites reveals that at low and equatorial latitudes the dayside ionosphere shows as prominent positive and negative responses at the Asian and American longitudinal sectors, respectively. The global distribution of thermospheric O/N2 ratio measured by global ultraviolet imager on board the TIMED satellite cannot well explain such longitudinally opposite response of the ionosphere. Comparison between the equatorial electrojet variations from stations at Huancayo in Peru and Davao in the Philippines suggests that the longitudinally opposite ionospheric response should be closely associated with the interplay of E region electrodynamics. By further applying nonmigrating tidal analysis to the ground‐based TEC data, we find that the diurnal tidal components, D0 and DW2, as well as the semidiurnal component SW1, are clearly enhanced over prestorm days and persist into the early recovery phase, indicating the possibility of lower atmospheric forcing contributing to the longitudinally opposite response of the ionosphere on 9–11 September 2017.
Forecasting Model of Short-term PM2.5 Concentration based on Deep Learning
Authors: Tang Wei , Zhao Wen-fang , Lin Runsheng , Zhou Yong
Published: March 2020

In order to improve the accuracy of PM2.5 concentration forecast in Beijing Meteorological Bureau, a deep learning prediction model based on convolutional neural network (CNN) and long short term memory neural network (LSTM) was proposed. Firstly, the feature vectors extraction was carried out by using the correlation analysis technique from meteorological data such as temperature, wind, relative humidity, precipitation, visibility and atmospheric pressure. Secondly, taking into account the fact that PM2.5 concentration was significantly affected by surrounding meteorological impact factors, meteorological grid analysis data was novel involved into the model, as well as the historical PM2.5 concentration data and meteorological observation data of the present station. Spatio-temporal sequence data was generated from these data after integrated processing. High level spatio-temporal features were extracted through the combination of the CNN and LSTM. Finally, future 24-hour prediction of PM2.5 concentration was made by the model. The comparison among the accuracy of this optimized model, support vector machine (SVM) and existing PM2.5 forecast system is performed to evaluate their performance. The results show that the proposed CNN-LSTM model performs better than SVM and current operational models in Beijing Meteorological Bureau, which has effectively improved the prediction accuracy of PM2.5 concentration for different time predictions scales in the next 24 hours.
Photochemical aging of organic aerosols at temperatures between 213 K and 293 K
Authors: Vallon Magdalena , Gao Linyu , Song Junwei , Jiang Feng , Saathoff Harald
Published: March 2020

The chemical composition of aerosols, in both gas and particle phase, is an important factor regarding their properties influencing weather, climate and human health. Organic compounds are a major fraction of atmospheric aerosols and their composition depends on chemical processing by atmospheric oxidants and photochemical reactions. These processes are complex due to the abundance of possible reactions and reaction partners and rarely studied over a wider range of atmospheric temperatures. To get a better understanding of photochemical processes in the atmosphere we studied different organic test aerosols from simple to more complex systems between 213 K and 293 K in the AIDA simulation chamber at the Karlsruhe Institute of Technology.  Photochemical reactions were studied using a new LED light-source simulating solar radiation in the UV and visible. The organic aerosols were either generated in situ by oxidation of VOC with ozone, OH radicals and NO3 radicals or by nebulizing aqueous solutions containing the aerosol components.  The aerosols were analysed by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) and a high–resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-ToF-CIMS).  The latter one offers the possibility to study the composition of gas phase and particle phase separately. First results suggest that secondary organic aerosols from single precursors like toluene or α-pinene show no or only very small changes related to photochemistry even when formed in presence of high NOx concentrations. In contrast, aerosol particles containing molecules with larger mesomeric systems or atmospherically relevant photosensitizers show significant changes upon irradiation.

In this presentation, we will discuss the changes that organic aerosols undergo in gas and particle phase, during photochemical aging at temperatures between 213 and 293 K.
How does dissipation work in the electron diffusion region of asymmetric magnetic reconnection
Authors: Hesse Michael , Norgren Cecilia , Tenfjord Paul , Burch James , Liu Yi-Hsin , Chen Li-Jen , Bessho Naoki , Spinnangr Susanne , Kolstø Håkon
Published: March 2020

At some level, magnetic reconnection functions by means of a balance between current dissipation, and current maintenance due to the reconnection electric field. While this dissipation is well understood process in symmetric magnetic reconnection, the way nonideal electric fields interact with the current density in asymmetric reconnection is still unclear. In symmetric reconnection, the current density maximum, the X point location, and the nonideal electric field determined by the divergence of the electron pressure tensor usually coincide. In asymmetric reconnection, however, the electric field at the X point can be partly provided by bulk inertia terms, implying that the X point cannot be the dominant location of dissipation. On the other hand, we know that the nongyrotropic pressure-based electric field must dominate at the stagnation point of the in-plane electron flow, and that electron distributions here feature crescents. The further fact that the current density peak is shifted off the position of the X point indicates that there may be a relation between this current density enhancement, the location of the stagnation point, and the electron nongyrotropies. In this presentation we report on further progress investigating the physics of the electron diffusion region in asymmetric reconnection with a focus on how to explain the dissipation operating under these conditions. 
Constraining uncertainty in projected gross primary production with machine learning
Authors: Schlund Manuel , Eyring Veronika , Camps-Valls Gustau , Friedlingstein Pierre , Gentine Pierre , Reichstein Markus
Published: March 2020

By absorbing about one quarter of the total anthropogenic CO2 emissions, the terrestrial biosphere is an important carbon sink of Earth’s carbon cycle. A key metric of this process is the terrestrial gross primary production (GPP), which describes the biogeochemical production of energy by photosynthesis. Elevated atmospheric CO2 concentrations will increase GPP in the future (CO2 fertilization effect). However, projections from different Earth system models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) show a large spread in carbon cycle related quantities. In this study, we present a new supervised machine learning approach to constrain multi-model climate projections using observation-driven data. Our method based on Gradient Boosted Regression Trees handles multiple predictor variables of the present-day climate and accounts for non-linear dependencies. Applied to GPP in the representative concentration pathway RCP 8.5 at the end of the 21st century (2081–2100), the new approach reduces the “likely” range (as defined by the Intergovernmental Panel on Climate Change) of the CMIP5 multi-model projection of GPP to 161–203 GtC yr-1. Compared to the unweighted multi-model mean (148–224 GtC yr-1), this is an uncertainty reduction of 45%. Our new method is not limited to projections of the future carbon cycle, but can be applied to any target variable where suitable gridded data is available.
Ancient plant DNA, macro- and microfossil studies of the lake sediments from the High Arctic lake Tenndammen, Svalbard
Authors: Poliakova Anastasia , Håkansson Lena M. , Schomacker Anders , Garces Pastor Sandra , Alsos Inger Greve
Published: March 2020

Ancient DNA metabarcoding applied together with the investigations of the plant macro-remains, pollen, spores and non-pollen palynomorphs (NPP), open new perspectives and give better taxonomical resolution, allowing to obtain more precise and specific data on the local environment conditions and their changes. So far, only three multiproxy studies that involve both molecular and palaeobotanical/palynological methods are available for the high Arctic archipelago Svalbard. We intend to contribute filling this gap. Therefore, a field trip to Svalbard was undertaken in September, 2019, and three sediment cores were retrieved from the Tenndammen lake (N 78°06.118; E 15°02.024, 7 m asl) which is a small and shallow water body (ca 2.5 m depth). The lake is located in the valley of Colesdalen, a well-known Svalbard’s biodiversity hot spots and a home for about seven to ten thermophilic plant species.

To investigate the Holocene to modern vegetation history of this place, the 85cm core Te2019 was chosen, it was described for lithology, X-rayed, µXRF-scanned, line-scan photographed with high resolution and sampled for sedaDNA, pollen, spores and NPP studies as well as for studies on plant macrofossils. Ten 14C AMS dates were taken in order to establish an age-depth model. The DNA record contains around 100 taxa, most findings of those are supported by pollen studies (Asteraceae, Betula, Brassicaceae, Salix, Saxifraga, Vaccinium/Ericaceae) and by spores (Equisetum and Bryophyta). In addition, various fungi spores were identified. Investigations of plant macro-remains well support findings of the aquatic (i.e. Warnstorfia fluitans) and terrestrial mosses (e.g. Aulacomnium conf. turgidum, Bryum spp., Distichium capillaceum, Calliergon richardsonii, Scorpidium cossonii, Sphagnum spp., Rhizomnium spp.). Besides, fragments of Salix and Betula leaves and fruit parts, various leaf, stem tissues and flower fragments of Saxifraga species were found within the samples from the same depths with the correspondence to DNA records. Three DNA zones (SvDNA 1 – SvDNA3) and  one subzone within the earliest zone (SvDNA-1a – SvDNA-1b) were established. Relations between DNA, pollen and macrofossil zones were studied. This study is performed within the “Future ArcTic Ecosystems” (FATE) research program: Initiative for investigation on drivers of diversity and future scenarios from ethnoecology, contemporary ecology and ancient DNA.
Optimal policies with tipping points and uncertainties
Authors: Martinez Montero Marina , Botta Nicola , Brede Nuria , Crucifix Michel
Published: March 2020

Global warming generates the possibility of 'abrupt' or 'irreversible' changes, associated with tipping points. Uncertainties are however sometimes invoked as an argument against political action. The Tipping Points in the Earth System (TIPES) project includes a workpackage whose goal is to rationalise the effects of uncertainty on what should be regarded as an 'optimal policy', given the possibility of tipping points.

To this end, we rely on two disciplinary fields. On the one hand, climate models integrate the dynamical principles, which determine the existence of 'tipping points'. On the other hand, formal decision theory defines the concept of optimal policies and allows us to compute them.

The current contribution outlines the implications and hypotheses needed for combining both frameworks. To exemplify this, we use a simple ice sheet model coupled to both carbon and aerosol models. The coupled system provides us with the formal basis to define the notions of control, irreversibility, and commitment. From this basis, we sketch out the mathematical problem of finding an optimal policy, with emphasis on what needs to be defined to pose the problem properly.

 
Experimenting on simple and flexible top-down approaches for hydrological modelling
Authors: Moustakas Sotirios , Willems Patrick
Published: March 2020

Nowadays, a plethora of modelling software on rainfall-runoff and groundwater dynamics are available. Considering the complexity and heterogeneity of natural processes governing the water cycle, many of those models involve physically-based formulations. Inevitably, a large amount of data is also required. However, the available data are often insufficient, while their quality questionable. At the same time, an increasing model complexity also gives rise to high computational requirements. In order to mitigate some of the aforementioned issues, during the past years a simple and flexible top-down approach for distributed rainfall-runoff modelling has been developed (Tran et al., 2018). Essentially, the distributed rainfall-runoff model is built starting from a simple lumped model, whose parameters are then spatially disaggregated. Disaggregation is carried out using conceptual links between model parameters and natural catchment characteristics.

We now test an extended version of this methodology involving disaggregation relationships for more model parameters. Moreover, we evaluate modelling performance for 2 different configurations. The first starts from the parameters of a lumped conceptual model and is essentially the original approach. The second one starts from the parameters of a uniform distributed conceptual model. The motivation behind the new approach is that it allows a better-integrated routing scheme with less model parameters. In turn, this can further reduce equifinality (denoting the “phenomenon” that largely different parameter-sets can often result to largely similar model outcomes). The two approaches are inter-compared and evaluated against flow observations.

With the disaggregated models as basis, we also experiment on the potential of simple methods for modelling groundwater levels. We approach this challenge by trying to identify links between a) the variations and b) the reference levels of the modelled groundwater storages and observed groundwater levels. For example, we hypothesize that modelled storages can be scaled to the actual level variations via the specific yield, which expresses the amount of interconnected pores in the soil. The modelling methodology is evaluated against groundwater level measurements.

 

Tran, Q.Q., De Niel, J., Willems, P., 2018. Spatially Distributed Conceptual Hydrological Model Building: A Generic Top-Down Approach Starting From Lumped Models. Water Resour. Res. 54, 8064–8085.
Analysis of CTBT IMS Hydroacoustic hydrophone station underwater system electronics calibration sequences
Authors: Zampolli Mario , Haralabus Georgios , Stanley Jerry , Nielsen Peter
Published: March 2020

The end-to-end calibration from the hydrophone ceramic element input to the digitizer output of CTBT IMS Hydroacoustic (HA) hydrophone stations is measured in a laboratory environment before deployment. After the hydrophones are deployed permanently with the Underwater System (UWS) hydrophone triplets, the response of the digitizer component can be measured by activating remotely a relay which excludes the hydrophone ceramic, preamplifier and riser cable, and feeds a pre-stored known waveform into the digitizer circuit via a digital-to-analogue converter. Analysis of these underwater calibration sequences makes it possible to verify the stability of the digitizer response over time and obtain useful information for investigations which require an accurate knowledge of the system response. Results are presented showing the stability of the UWS electronics response over time and one case, pertaining to the H10S triplet of HA10 Ascension Island, where changes in the calibration response appeared after the onset of electronic noise in one hydrophone channel with cross-talk to the other two channels.
2D velocity profiles along south- and northwestern Norway: An approach using receiver function analysis and Markov chains
Authors: Brönner Marco , Pavez Claudia
Published: March 2020

A receiver function analysis was carried out along two profiles located in north- and southwestern Norway. We selected and processed 801 teleseismic events registered by twelve seismic stations belonging to the 2002-2005 Geofon/Aarhus temporary network. The HK (depth vs Vp/Vs) stacking procedure and a Reversible jump Markov chain Monte Carlo (Rj-McMC) inversion were applied independently with the objective to reveal new crustal and crust-mantle transitional contrasts gaining a better understanding of the geology. In the southern profile, the most noticeable feature corresponds to a Moho offset of about ~5 km ca. 85 km to the east of the Norwegian coast: That feature was previously observed in several occasions and is also well-supported from this research. Furthermore, a very deep Moho discontinuity – at between 45 – 50 km depth - was found beneath the northern profile, approximately 70 km inland from the coast, and dipping about 30° to the northwest. Even when this deep structure was previously inferred through other methods, its presence was not certainly confirmed and so far, the origin of this feature is still disputed. We discuss two hypotheses, which are valid to explain the occurrence of the noticeable anomaly. First, a gradual and wide crust-mantle transition zone, which is also reflected in the velocity model or second, the presence of a paleo-slab of Fennoscandian basement subducted and deformed during the Caledonian Orogen (490-390 Ma).
Mercury dynamics in a changing coastal area over industrial and post-industrial phases
Authors: Rosati Ginevra , Solidoro Cosimo , Melaku Canu Donata
Published: March 2020

The Venice Lagoon (Mediterranean Sea) is a shallow coastal lagoon that have been subjected to several anthropogenic pressures, including significant Hg loadings from industrial activities. Inorganic Hg is methylated to neurotoxic MeHg in lagoon water and sediment, posing the ecosystem wealth at risk.

Here, we use a biogeochemical model to investigate the long-term dynamics of Hg species in the Venice Lagoon from the pre-industrial period to the post-industrial period (1900-2100), also taking into account environmental changes occurred in the lagoon such as eutrophication, and the increase of sediment resuspension driven by manila clam harvesting.

Time-variable Hg emissions from industries were estimated from available information about industrial production and technology-dependent emissions factors, while Hg loading species from other sources (river, atmospheric deposition, urban wastes) where estimated through downscaling from global studies, using observations from previous field studies (1970 - 2010) as constraints. The impacts of future trends of Hg atmospheric deposition are explored through scenario analysis. 

Modeled Hg species are in a satisfactory agreement with the available observations. In the current postindustrial phase, HgT in the lagoon waters comes mostly from sediments, while MeHg comes primarily from the watershed.

We estimate in ∼56 kg y-1 the HgT export for 2019 to the Adriatic Sea, which includes ∼0.13 kg y-1 of MeHg. Both Hg and MeHg concentrations are decreasing since outputs slightly exceed inputs. The analysis of Hg and MeHg reservoirs and fluxes reveals the impacts of the changes in environmental conditions on Hg fluxes. On the one hand, eutrophication has enhanced sediment deposition to the seabed, causing a maximum in sediment Hg concentrations when Hg inputs were already declining; on the other hand, the enhanced sediment resuspension due to clam harvesting led to increased Hg fluxes from the sediment to the water, also causing a redistribution of Hg from the central lagoon to the northern and southern areas, as reported by observational studies. These results emphasize the importance of adopting an ecosystem approach when investigating Hg dynamics, considering the different uses of the ecosystem.
One TGF and two elves produced by the same thunderstorm system
Authors: Ostgaard Nikolai , Cummer Steve , Mezentsev Andrey , Neubert Torsten , Reglero Victor , Olivier Olivier Arnaud , Marisaldi Martino , Kochkin Pavlo , Lehtinen Nikolai , Sarria David , Maiorana Carolina , Skeie Chris Alexander , Lindanger Anders , Pu Yunjiao , Christiansen Freddy , Ullaland Kjetil , Genov Georgi
Published: March 2020

On February 8, 2019 the Atmosphere-Space Interaction Monitor (ASIM) passed a thunderstorm system north east of Puerto Rico and observed a TGF and an Elve from the same lightning stroke at the very beginning of a lightning flash. A second Elve was observed 456 ms later but without any signature of a TGF about 300 km south-east of the first Elve.
The strokes associated with the two Elve events were detected by WWLLN and Vaisala, which allows for an absolute timing accuracy of the ASIM measurements of at least 100 us. Images of the lighting strokes support the source locations for the Elves and TGF.  
Both the rise time of the UV pulse by ASIM MMIA photometer and radio measurements from Puerto Rico indicate that the first stroke was an intracloud positive while the latter was a cloud-to-ground stroke.
The UV emissions from the Elves preceded the optical emissions in 777 nm by
50 us and 90 us, respectively. This can partly be explained by the scattering of 777 nm within the cloud.
Current moments derived from radio measurements at Puerto Rico and Duke University  indicate a fast (30 us) and large (200 kA) current pulse emitting an electromagnetic wave that produces an Elve and a slow (1-2 ms) current producing the optical signals.

 
Imaging the Deep Galicia margin using three-dimensional full waveform inversion
Authors: Boddupalli Bhargav , Minshull Tim , Morgan Joanna , Bayrakci Gaye
Published: March 2020

Imaging of hyperextended zone and exhumed continental mantle rocks can improve our understanding of the tectonics of the final stages of rifting. In the Deep Galicia margin, the upper and lower crust are coupled allowing the normal faults to cut through the brittle crust and penetrate to the mantle leading to serpentinization of the mantle. Localized extensional forces caused extreme thinning and elongation of crystalline continental crust causing the continental blocks to slip over a lithospheric-scale detachment fault called the S-reflector.  

A high-resolution velocity model obtained using seismic full waveform inversion gives us deeper insights into the rifting process. In this study, we present results from three dimensional acoustic full waveform inversion performed using wide-angle seismic data acquired in the deep water environments of the Deep Galicia margin using ocean bottom seismometers. We performed full waveform inversion in the time domain, starting with a velocity model obtained using travel-time tomography, of dimensions 78.5 km x 22.1 km and depth 12 km. The high-resolution modelling shows short-wavelength variations in the velocity, adding details to the travel-time model. We superimposed our final model, converted to two-way time, on pre-stack time-migrated three-dimensional reflection data from the same survey. Compared to the starting model, our model shows improved alignment of the velocity variations along the steeply dipping normal faults and a sharp velocity contrast across the S-reflector. We validated our result using checkerboard tests, by tracking changes in phases of the first arrivals during the inversion and by comparing the observed and the synthetic waveforms. We observe a clear evidence for preferential serpentinization (45 %) of the mantle with lower velocities in the mantle correlating with the fault intersections with the S-reflector.
Uncertainty Evaluations of the CRCS In-orbit Field Radiometric Calibration Methods for Thermal Infrared Channels of FENGYUN Meteorological Satellites
Authors: Zhang Yong , Rong Zhiguo , Hao Xiaopeng
Published: March 2020

Meteorological satellites have become an irreplaceable weather and ocean-observing tool in China. These satellites are used to monitor natural disasters and improve the efficiency of many sectors of Chinese national economy. It is impossible to ignore the space-derived data in the fields of meteorology, hydrology, and agriculture, as well as disaster monitoring in China, a large agricultural country. For this reason, China is making a sustained effort to build and enhance its meteorological observing system and application system. The first Chinese polar-orbiting weather satellite was launched in 1988. Since then China has launched 17 meteorological satellites, 8 of which are sun synchronous and 9 of which are geostationary satellites; China will continue its two types of meteorological satellite programs.

In order to achieve the in-orbit absolute radiometric calibration of the operational meteorological satellites’ thermal infrared channels, China radiometric calibration sites (CRCS) established a set of in-orbit field absolute radiometric calibration methods (FCM) for thermal infrared channels (TIR) and the uncertainty of this method was evaluated and analyzed based on TERRA/AQUA MODIS observations. Comparisons between the MODIS at pupil brightness temperatures (BTs) and the simulated BTs at the top of atmosphere using radiative transfer model (RTM) based on field measurements showed that the accuracy of the current in-orbit field absolute radiometric calibration methods was better than 1.00K (@300K, K=1) in thermal infrared channels. Therefore, the current CRCS field calibration method for TIR channels applied to Chinese metrological satellites was with favorable calibration accuracy: for 10.5-11.5µm channel was better than 0.75K (@300K, K=1) and for 11.5-12.5µm channel was better than 0.85K (@300K, K=1).