bluuebunny/crossref_metadata_2025 huggingface dataset:
How much of GPS noise refers to hydrology loading? An insight from GRACE-assimilating hydrological modeling
Authors: Klos Anna , A. Karegar Makan , Kusche Jürgen , Springer Anne
Published: March 2020

Global Positioning System (GPS) observations are able to resolve Earth’s surface vertical deformation which originates among others from continental hydrological mass changes. Although long-term signals and seasonal changes of hydrology loading are well-captured by GPS observations, it is still unanswered whether GPS detects also the short-term hydrology-related deformations or not. In this presentation, we use predictions of vertical deformations from a GRACE (Gravity Recovery and Climate Experiment)-assimilating land surface model to separate deterministic and stochastic parts of GPS height changes observed by a set of 221 European EPN (EUREF Permanent GNSS Network) stations. This approach is compared to conventional harmonic functions approach, in which deterministic and stochastic parts are separated by pre-defined annual and semi-annual periods. For the stochastic parts associated with two methods, the noise parameters (spectral indices and amplitudes of power-law noise) are estimated using the Maximum Likelihood Estimation (MLE). Comparing original GPS displacements to displacements reduced for hydrological loading, we notice that annual and semi-annual frequencies are significantly explained by the hydrological model, resulting 60% reduction on average in amplitudes. This means that large part of seasonal crustal deformation arises from hydrological loading or unloading of the lithosphere. We find that the annual and semi-annual peaks are greatly reduced (72% on average) once conventional harmonic functions approach is used instead of GRACE-assimilating hydrological model, but no physical interpretation can be made here since it is difficult to identify the magnitude of each individual processes contributing to seasonal changes. The GRACE-assimilated model can remove the effect of high-frequency hydrological deformations, producing residuals with spectrum closer to the white noise process. Many oscillations present in GPS displacements at periods between 15 and 90 days are well-explained by GRACE-assimilating deformation model. We find the greatest improvement in noise parameters for stations located in the eastern and central regions of Europe, encompassing the Rhine, Elbe, Danube and Oder drainage basins where hydrological mass changes are relatively larger comparing to western Europe. Using GRACE-assimilated model as a deterministic part of GPS displacement time series, we provide a totally new estimates of noise parameters for European sites, which has never been presented before. Our results show that GRACE-assimilating water storage re-analyses can provide essential information for obtaining improved unbiased estimates of GPS vertical velocity, including their uncertainty, which are essential for a range of applications such as upcoming reference frame realizations.
The effect of atmospheric temperature on the calculations of the intensity of oxygen emissions in the framework of the Barth mechanism: sensitivity study
Authors: Yankovsky Valentine
Published: March 2020

In the nightglow of the atmosphere in the altitude range of 90-105 km, the Barth’ mechanism is the dominant mechanism of excitation of oxygen emissions [1].

The source of oxygen emissions in this altitude range is the three-body reaction of the association of oxygen atoms. The rate coefficient of this reaction, as well as the collision quenching rate coefficients of the excited oxygen components O(1S), O2(b1Σ+g), O2(a1Δg) depend on the kinetic temperature of the gas. The method of sensitivity analysis for complex photochemical systems developed in [2] allows one to comprehensively consider the temperature dependence of the processes of excitation and quenching for each excited component. Analytical expressions will be obtained for the sensitivity coefficients of the intensities of these emissions depending on temperature and altitude. The formulas obtained are also suitable for estimation of the effect of temperature on the contribution of the Barth’ mechanism to atmospheric dayglow. This work was supported by the Russian Foundation for Basic Research (grant RFBR No. 20-05-00450 A).

1. Krasnopolsky V. A. (2011), Excitation of the oxygen nightglow on the terrestrial planets, Planetary and Space Science, 59, 754-766, doi: 10.1016/j.pss.2011.02.015.

2. Yankovsky V. A., Martyshenko K. V., Manuilova R. O., Feofilov A. G. (2016), Oxygen dayglow emissions as proxies for atomic oxygen and ozone in the mesosphere and lower thermosphere, Journal of Molecular Spectroscopy, 327, 209-231, doi: 10.1016/j.jms.2016.
Visualising large-scale geodynamic simulations: How to Dive into Earth's Mantle with Virtual Reality
Authors: Wiedemann Markus , Schuberth Bernhard S.A. , Colli Lorenzo , Bunge Hans-Peter , Kranzlmüller Dieter
Published: March 2020

Precise knowledge of the forces acting at the base of tectonic plates is of fundamental importance, but models of mantle dynamics are still often qualitative in nature to date. One particular problem is that we cannot access the deep interior of our planet and can therefore not make direct in situ measurements of the relevant physical parameters. Fortunately, modern software and powerful high-performance computing infrastructures allow us to generate complex three-dimensional models of the time evolution of mantle flow through large-scale numerical simulations.

In this project, we aim at visualizing the resulting convective patterns that occur thousands of kilometres below our feet and to make them "accessible" using high-end virtual reality techniques.

Models with several hundred million grid cells are nowadays possible using the modern supercomputing facilities, such as those available at the Leibniz Supercomputing Centre. These models provide quantitative estimates on the inaccessible parameters, such as buoyancy and temperature, as well as predictions of the associated gravity field and seismic wavefield that can be tested against Earth observations.

3-D visualizations of the computed physical parameters allow us to inspect the models such as if one were actually travelling down into the Earth. This way, convective processes that occur thousands of kilometres below our feet are virtually accessible by combining the simulations with high-end VR techniques.

The large data set used here poses severe challenges for real time visualization, because it cannot fit into graphics memory, while requiring rendering with strict deadlines. This raises the necessity to balance the amount of displayed data versus the time needed for rendering it.

As a solution, we introduce a rendering framework and describe our workflow that allows us to visualize this geoscientific dataset. Our example exceeds 16 TByte in size, which is beyond the capabilities of most visualization tools. To display this dataset in real-time, we reduce and declutter the dataset through isosurfacing and mesh optimization techniques.

Our rendering framework relies on multithreading and data decoupling mechanisms that allow to upload data to graphics memory while maintaining high frame rates. The final visualization application can be executed in a CAVE installation as well as on head mounted displays such as the HTC Vive or Oculus Rift. The latter devices will allow for viewing our example on-site at the EGU conference.
The Absorption Spectrum and Absolute Absorption Cross Sections of Acetylperoxy Radicals, CH3C(O)O2 in the near IR
Authors: Rolletter Michael , Assaf Emmanuel , Assali Mohamed , Fuchs Hendrik , Fittschen Christa
Published: March 2020

Acetylperoxy radicals (CH3C(O)O2) play an important role in the tropospheric chemistry. They are produced by the photooxidation of most emitted biogenic non-methane hydrocarbons. Recent studies show that the CH3C(O)O2 + HO2 reaction, which is the most important tropospheric loss reaction of acetylperoxy radicals in regions that are dominated by biogenic emissions (low NO emissions), does not only lead to radical chain terminating products but can also regenerate OH. The competing secondary chemistry, e. g., the CH3C(O)O2 self-reaction, complicate kinetic measurements. The detection of acetylperoxy radicals in previous kinetic laboratory studies was mainly done in the UV region. However, the spectral overlap of different peroxy species in this region is prone to systematic errors in the quantitative detection. These complications can be avoided, if acetylperoxy radicals are detected by absorption in the near IR.

In our work, the near infrared CH3C(O)O2 spectrum was measured in the spectral ranges from 6094 cm-1 to 6180 cm-1 and 6420 cm-1 to 6600 cm-1. CH3C(O)O2 radicals were generated by pulsed photolysis of a acetaldehyde/Cl2/O2 mixture at 351 nm and were subsequently detected by time-resolved continuous-wave cavity ring-down spectroscopy (cw-CRDS). Experiments were done at 67 hPa in synthetic air and helium. The absorption cross sections of eight discrete absorption lines were determined relative to the absorption cross section of HO2, which has previously been reported.
High temperature in the upper mantle beneath Cape Verde as a possible cause for the oceanic lithosphere rejuvenation inferred from Rayleigh-wave phase-velocity measurements.
Authors: Carvalho Joana , Bonadio Raffaele , Silveira Graça , Lebedev Sergei , Custódio Susana , Mata João , Arroucau Pierre , Meier Thomas , Celli Nicolas
Published: March 2020

Cape Verde is an intraplate archipelago located in the Atlantic Ocean about 560 km west of Senegal, on top of a ~130 Ma sector of the African oceanic lithosphere. Until recently, due to the lack of broadband seismic stations, the upper-mantle structure beneath the islands was poorly known. In this study we used data from two temporary deployments across the archipelago, measuring the phase velocities of Rayleigh-waves fundamental-modes in a broad period range (8–250 s), by cross-correlating teleseismic earthquake data between pairs of stations. Deriving a robust average, phase-velocity curve for the Cape Verde region, we inverted it for a shear-wave velocity profile using non-linear gradient search.

Our results show anomalously low velocities of ∼4.2 km/s in the asthenosphere, indicating the presence of high temperatures and, eventually, partial melting. This temperature anomaly is probably responsible for the thermal rejuvenation of the oceanic lithosphere to an age as young as about 30 Ma, which we inferred from the comparison of seismic velocities beneath Cape Verde and the ones representing different ages in the Central Atlantic.

The present results, together with previously detected low-velocity anomalies in the lower mantle and relatively He-unradiogenic isotopic ratios, also suggest a hot plume deeply rooted in the lower mantle, as the origin of the Cape Verde hotspot.

The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL and FIRE project Ref. PTDC/GEO- GEO/1123/2014.
TOSST Research Expeditions in the North Atlantic Ocean
Authors: Arruda Ricardo , Raimondi Lorenza , Duplessis Patrick , Lehmann Nadine , Schulten Irena , Aali Masoud , Wang Yuan , McCain Scott
Published: March 2020

Over the 6 years of the Transatlantic Ocean System Science and Technology program (TOSST - 2014 – 2019), graduate students participated in a variety of first class research expeditions in the North Atlantic Ocean, contributing to high quality datasets for this region and reaching a total of 380 days at-sea. These research cruises expanded from the Arctic Ocean, Labrador Sea and sub-Polar North Atlantic to the Equatorial North Atlantic, and along the African and Cabo Verdean coasts. A total of 12 long term cruises with collaboration between 18 research institutes, were conducted on board of 10 research vessels of various nationalities (Canada, Germany, Bermuda, Sweden, Ireland and USA). The range of measurements performed during these cruises, which highlights the interdisciplinary nature of the TOSST program, includes: chemical oceanography; biological oceanography; physical oceanography; marine biogeochemistry; microbiology; paleoceanography; geology; marine geophysics; and atmospheric chemistry. In this work, we will showcase the breath of research covered by TOSST graduates in the North Atlantic Ocean and provide details on the overall goals/objectives of each cruise, the teams and research vessels involved, the diverse scientific instrumentation deployed and sampling schemes. We highlight the importance of multi-disciplinary expeditions and at-sea experiences for professional as well as for personal development of early career scientists. Logistic and economic efforts are required to collect samples and to deploy instruments, therefore collaboration between disciplines, research institutes and countries (of which TOSST graduates’ research is an example) are fundamental in order to increase the quality, quantity and variety of observations in the North Atlantic Ocean.
SFM-Forest-Benchmark project: The benchmarking of image-based point cloud for forest inventory
Authors: Mokros Martin , Hollaus Markus , Wang Yunsheng , Liang Xinlian
Published: March 2020

The benchmarking project of image-based point cloud for forest inventory (SFM-Forest-Benchmark) was initiated in 2019 and supported by ISPRS Scientific Initiative 2019. The main goal of the project was the evaluation of the applicability of terrestrial image-based point clouds for forest inventories, the clarification of the potential and limitations of the state-of-the-art techniques, and the exploration of the best practices in practical field inventories. In the project, related tree parameter (i.e. tree position diameter at breast height - DBH) were derived from 14 algorithms and evaluated using field inventory data as a reference. In order to clarify the potential of terrestrial image-based point clouds, the results from the image-based point clouds were also compared to results derived from the best available point clouds obtained by terrestrial laser scanning (TLS).

The project is consisted of two phases. In the first phase, we established two research plots in each country (Austria, China, Czech, Finland and Slovakia), ten plots in total. The stem density ranged from 272 to 875 stems/ha and plot size ranged approximately from 700 to 2500 m2. Dominant tree species across research plots were Norway spruce, European beech, bald cypress, Chinese tulip poplar, Scots pine, European silver fir and sessile oak. TLS, images and reference data acquisition were performed on each study site, where TLS data were acquired through multi-scan approach, images were taken in the stop-and-go mode, and tree positions and the DBHs were measured with a tachymeter and a calliper as field references. Images were processed with structure from motion algorithm within Agisoft Metashape software to final point clouds. The TLS data was pre-processed with RiProcess software. And, the co-registration of all three data sources (TLS, SFM, and reference data) was done with OPALS software.

In the benchmarking phase, we distributed point clouds to participants of the benchmark. Altogether 14 different research groups processed the data with own algorithms. The individual results are evaluated through the reference to clarify the applicability of the image-point clouds in deriving tree parameters, were compared to each other to reveal the state-of-the-art of technologies, and were benchmarked to the up-to-data the most accurate data from TLS to explore the strength and weakness of the image-based point cloud. In this presentation the first benchmark results will be presented and discussed.

All images and point clouds collected for this project will be available as open access data for non-commercial uses.
3D surface velocity variations of the Argentière glacier (French Alps) monitored with a high resolution continuous GNSS network
Authors: Walpersdorf Andrea , Vincent Christian , Gimbert Florent , Helmstetter Agnès , Moreau Luc , Six Delphine , Garambois Stéphane , Ott Laurent , Mercier Stéphane , Laarman Olivier , Piard Luc , Nanni Ugo , Mathey Marguerite , Urruty Benoit , Sue Christian , Bouvier Jean-Noël , Champon Martin , Romeyer Olivier , Mugnier Jean-Louis , Radiguet Mathilde ,   SAUSSURE GNSS team
Published: March 2020

Five continuous GNSS stations monitor the Argentière glacier surface motion on a longitudinal profile at 2400 m altitude over a full melt season, from April to November 2019. High precision data analysis is enabled by a close-by reference station on the bedrock. This GNSS survey is part of the SAUSSURE project 2019-2022 that aims at increasing our knowledge on the physics of glacier basal sliding, by improving friction laws and validating them in a natural environment. The Argentière glacier is particularly interesting due to its long-term subglacial observatory measuring basal sliding velocity and subglacial discharge. The SAUSSURE project furthermore includes seismic, tiltmeter and piezometer measurements. The bedrock topography is obtained from a Ground Penetrating Radar.

The dense GNSS station setup permits to validate individual antenna movements. We then retrieve horizontal and vertical surface velocities on daily and sub-daily time scales. We can deduce strain rates in between the stations and their evolution in time, and relate this observable with the vertical surface motions. The confrontation of the GNSS data with independent observations allows analyzing the surface motions searching for glacier surges that combine horizontal speed-ups combined with uplift due to bed separation of the ice sheet. These events could give indications about cavity growth in spring. We will also try to investigate sub-daily motions that seem to occur in daily cycles in summer, as hinted at by the basal sliding measurements. These daily cycles are usually also seen in the seismic activity. The phase of the different features varies with respect to the daily cycles of temperature and sub-glacial water pressure. These phase offsets can give us indices on eventual mechanisms of sliding at the bedrock interface. The GNSS measurements represent a rare in situ data set that can contribute to better apprehend mechanisms of basal sliding and to provide high-resolution 3D constraints on physical models of glacier flow.
Evaluation of the effect of depth to bedrock on seismic amplification phenomena
Authors: falcone gaetano , naso giuseppe , fabozzi stefania , mori federico , moscatelli massimiliano , peronace edoardo , romagnoli gino
Published: March 2020

When an earthquake occurs, the propagation of the seismic waves is conditioned by local conditions, e.g., depth to seismic bedrock and impedance ratio between soft soil and seismic bedrock. Bearing in mind that the maximum depth of site prospections generally does not extend up to seismic bedrock depth, a parametric study was carried out with reference to ideal case studies in order to investigate the effect on local seismic amplification of the depth to bedrock.

The results are presented in terms of charts of amplification factors (i.e., ratio of integral quantities referred to free-field and reference response spectra) and minimum depth to investigate vs building type. These charts will allow defining the thickness of the cover deposit that should be characterised in terms of geophysical and geotechnical parameters in order to perform seismic site response analysis according to a precautionary approach, in areas where depth to seismic bedrock is higher than conventional maximum depth of site surveys.
Large-scale integrated subglacial drainage around the former Keewatin Ice Divide, Canada reveals interaction between distributed and channelised systems
Authors: Lewington Emma , Livingstone Stephen , Clark Chris , Sole Andrew , Storrar Robert
Published: March 2020

Despite being widely studied, subglacial meltwater landforms are typically mapped and investigated individually, thus the drainage system as a whole remains poorly understood. Here, we identify and map all visible traces of subglacial meltwater flow across the Keewatin sector of the former Laurentide Ice Sheet from the ArcticDEM, generating significant new insights into the connectedness of the drainage system.

Due to similarities in spacing, morphometry and spatial location, we suggest that the 100s-1000s m wide features often flanking and connecting sections of eskers (i.e. tunnel valleys, meltwater tracks and esker splays) are varying expressions of the same phenomena and collectively term these features ‘meltwater corridors’. Based on observations from contemporary ice masses, we propose a new formation model based on the pressure fluctuations surrounding a central conduit, in which the esker records the imprint of the central conduit and the wider meltwater corridors the interactions with the surrounding distributed drainage system, or variable pressure axis (VPA).

We suggest that the widespread aerial coverage of meltwater corridors across the Keewatin sector provides constraints on the extent of basal uncoupling induced by basal water pressure fluctuation and variations in spatial distribution and evolution of the subglacial drainage system, which have important implications for ice sheet dynamics. 
Review, mathematical representation and classification of preventive drought management measures
Authors: paez ana , Corzo Gerald , Solomatine Dimitri
Published: March 2020

In the context of proactive drought management plans, a key element consists of analyzing, selecting and allocating measures aimed at increasing resistance to droughts and reducing its potential impacts on the society, environment and economy. Currently, these measures, known as preventive drought management measures (Fatulová et al., 2015), are embedded within measures for flood management, catchment management plans, rural development plans, among others. This situation raises two issues. Firstly, information about potential preventive drought management measures (PDMM) is commonly fragmented and it is not a trivial task find or select measures that could be implemented as PDDM. Secondly, even though the same measure can be implemented from different management perspectives (Flood management, land degradation management, catchment management, rural development plans,) its applicability, advantages and limitations, may change according to the management perspective.

Considering the above, this study attempts to provide a review of PDMM that includes: measure description, applicability, limitations, mathematical representation (For further implementation in modelling systems) and classification, from a drought management perspective. It is worth to mention that this study is focused on hydrologically based measures, applicable for agricultural and hydrological drought management.

The research methodology is divided in three phases. The first phase consists of identifying drivers that trigger and/or enhance agricultural and hydrological droughts. This analysis is carried out from a hydrological angle, where land surface processes and human activities are potential drivers agricultural and hydrological droughts (Van Loon et al., 2016). The second phase examines an extensive list of technical documents, books, books sections, journal articles and case studies in order to identify those measures that could manage or mitigate the impact of potential drivers of agricultural and hydrological droughts. In this phase, PDMM are described in terms of applicability, advantages, limitations and mathematical representation for further implementation in modelling systems. Based on the analysis of the PDMM, the third phase of the study focusses on their classification, into three categories: nature-based solutions, grey infrastructure and changes in human water consumption
Demand-side Management of Peak Water Demands using Advanced Metering Infrastructure and Persuasive Games
Authors: Pesantez Jorge , Zechman Berglund Emily
Published: March 2020

Residential water demands vary with a diurnal pattern, and peak hour demands lead to inefficiencies in the operation and management of urban water distribution systems. Peak demands generate immediate costs due to the energy requirements of pumping large volumes of water. If peak demands are not mitigated, large investments in infrastructure expansion are needed to support urban growth and economic development. Through data collection and communication approaches available through advanced metering infrastructure (AMI), demand-side management approaches could reduce peak demands. AMI data can be disaggregated to identify end uses that contribute to peak demands, and feedback about hourly use can be used to encourage demand shifting behaviors. Demand-side management implements technical approaches, such as retrofitting households with smart and water-efficient devices, and social approaches, such as dynamic water pricing, mandatory restrictions, and persuasive games that encourage voluntary participation. A community of households that shift demands can distribute the volume of water provision evenly over the hours of a day and reduce peak demands. While demand-side management strategies can reduce energy requirements associated with water supply and the need for new infrastructure development, demand management relies on the behaviors and decision-making of individuals, creating uncertainty in the emergent cost savings and infrastructure impacts. This research develops an agent-based modeling methodology to simulate the performance of demand-management approaches to reduce peak water demands. A persuasive game is simulated that implements a leaderboard to encourage cooperation and competition within and among neighborhoods of water users. Household agents receive points for shifting end-uses, based on the difficulty and water savings associated with end-user behaviors. Opinion dynamics simulate agents’ information exchange using a leaderboard, which provides motivation for agents to increase individual and team scores. The methodology is applied for AMI data to test the effects of persuasive games on reducing peak demands.
Cyclone activities as inferred from the Twentieth Century Reanalysis version 3 (20CRv3) for 1836-2015
Authors: Wang Xiaolan , Feng Yang , Chan Rodney , Compo Gilbert P. , Slivinski Laura C. , Yu Bin , Wehner Michael , Yang Xiao-Yi
Published: March 2020

Preliminary results obtained from tracking cyclones in the ensemble-average and individual members of the NOAA-CIRES-DOE Twentieth Century Reanalysis version 3 (20CRv3) ensemble for the period 1836-2015 will be presented. Comparison with tracking in the 20CRv2c ensemble-average series will also be shown.

The results indicate that the 20CRv3 is an improvement in representing cyclone climate and variability compared to previous versions (20CRv2c or 20CRv2). However, as in previous versions, the 20CRv3 ensemble-average fields are too smooth to use for tracking cyclones and studying cyclone climate, especially for the period before 1960 for the NH and for the entire reanalysis period for the SH, and that there are still temporal inhomogeneity issues in the 20CRv3, especially in the SH and in the early period for the NH, due to the increases over time of observations available for assimilation. The improvements arise from the use of a higher model resolution and the assimilation of more observations. They include that the 20CRv3 ensemble shows cyclones of higher intensities and a higher number of deep cyclones (center pressure ≤ 960 hPa) in the Northern Hemisphere than the 20CRv2c counterpart. Historical trends of cyclone activity and their uncertainties will be discussed based on the results of tracking the individual members of the 20CRv3 ensemble, with the temporal inhomogeneity issues being taken into account.  
The growth of snow bedforms
Authors: Kochanski Kelly , Anderson Robert , Tucker Gregory
Published: March 2020

Wind-blown snow does not lie flat. It self-organizes into dunes, waves, ripples, and anvil-shaped sastrugi. These features, called snow bedforms, are high-speed analogues of sand features barchans, ripples, and yardangs. Snow bedforms appear within hours or days after a blizzard, and may migrate as fast as several meters per hour. They are widespread, and affect the albedo and thermal properties of snow across the polar regions, but thus far they have attracted little attention within aeolian geomorphology.

For the past three winters, I have documented the growth of snow bedforms in Colorado Front Range. I present time-lapse footage showing the movement of snow dunes, ripples and sastrugi (see tinyurl.com/bedform-videos). These observations show that (1) snow is only flat when winds are slower than 6.4 m/s (2) snow dunes adjust minute-by-minute to changes in wind speed, (3) the most widespread bedform, sastrugi, evolve by migrating and eroding downwind, and (4) snow waves and dunes deposit layers of cohesive snow in their wakes, and thus aid snow deposition in windy conditions. These observations provide the basis for new conceptual models of bedform evolution based on the rates of snowfall, aeolian transport, erosion, and snow sintering across the snowscape.
2D Numerical Simulation of Intraoceanic Subduction during the Upper Jurassic Closure of the Vardar Tethys
Authors: Stanković Nikola , Cvetkov Vesna , Cvetković Vladica
Published: March 2020

In this study we report interim results of our ongoing research that involves the application of numerical modeling for constraining the geodynamic conditions associated with the closure of the Vardar branch of the Tethys Ocean. The study is aimed at better understanding the ultimate fate of the Balkan ophiolites, namely at addressing the question whether these ophiolites represent relicts of an ocean that completely closed during Upper Jurassic/lowermost Cretaceous time (Vardar Tethys) or they also contain remnants of the ocean floor of a Late Cretaceous oceanic realm (Sava – Vardar) [Schmid et al., 2008].

In our numerical models we try to simulate a single intraoceanic subduction that commences in the Lower/Mid Jurassic and ends in the Lower Cretaceous, transitioning into oceanic closure processes and subsequent collision between Adria and Eurasia plates. These convergent-collision events should have led to the formation of ophiolite-like igneous rocks of the so-called Sava - Vardar zone.

A series of numerical simulations were performed with varying parameters. In the scope of our numerical simulations, the set of equations is solved: the continuity equation, the Navier-Stokes equations and the temperature equation. Marker in cell method was incorporated in solving this system with finite difference discretization of the equations on a staggered grid. To utilize this numerical method a thermo-mechanical code I2VIS [Gerya et al., 2000; Gerya & Yuen, 2003] was used for obtaining the final results. 

Our actual 2D thermo-mechanical models cover the crust and the upper portion of the mantle with varying starting widths of the Vardar Ocean in the Lower Jurassic. The ocean is modeled with two segments: the western subducting slab and the eastern overriding slab. Slabs with different ages and thicknesses were used and the convergence rate is varied. The intraoceanic subduction is assumed to have been initiated along the mid oceanic ridge. Two continents (i.e. Adria and Eurasia) with different thicknesses of the continental lithosphere and crust are also modeled adjacent to a single oceanic realm between them.

The parameter study is in function of defining conditions under which the hypothesized scenario occurs. So far, we have succeeded in reproducing westward obduction onto the Adriatic margin, which is in accordance with the geological observations, i.e., with the top-west emplaced West Vardar ophiolites [see Schmid et al., 2008 for references]. However, our model is yet to produce sufficient amounts of back-arc extension along the Eurasian active margin and that is crucial for explaining the formation of the igneous provinces occurring within the Late Cretaceous Sava – Vardar zone and the Timok Magmatic Complex.
Onshore-offshore hydrological characterisation of the Canterbury margin (New Zealand) based on geophysical and modelling techniques
Authors: Micallef Aaron , Person Mark , Haroon Amir , Weymer Bradley , Jegen Marion , Schwalenberg Katrin , Faghih Zahra , Duan Shuangmin , Cohen Denis , Mountjoy Joshu , Woelz Susanne , Gable Carl , Averes Tanita , Tiwari Ashwani
Published: March 2020

Offshore freshened groundwater (OFG) is an important component of the global water cycle. Bodies of fresh and moderately brackish groundwater have been documented up to 100 km from modern shorelines. Their global volumetric estimates are on the order of 500,000 cubic kilometres, which is two orders of magnitude greater than the volume of groundwater extracted globally from continental aquifers since 1900. The potential use of OFG systems as a source of potable water is a main driving force for their improved understanding. OFG systems also play a fundamental role in biogeochemical fluxes to the ocean and in benthic and sub-seafloor ecology.

The majority of OFG systems were emplaced by groundwater migration across topographic gradients via permeable connections between offshore and onshore aquifers. The characteristics and dynamics of the offshore aquifers remain poorly constrained, however. There are many first order questions waiting to be addressed, mainly related to the geometry, distribution and dimensions of these aquifers, as well as their flow and emplacement dynamics.

In this study we integrate hydrological modelling with borehole data and offshore geophysical observations from the Canterbury margin (New Zealand) to quantitatively characterise an onshore-offshore groundwater system. Onshore, the main aquifers are hosted in gravels down to at least 150 m depth, with unconnected sand and silt/clay layers forming aquitards. The regional flow of groundwater in the Canterbury aquifers is from the foothills of the Southern Alps towards the sea. Offshore, the groundwater system consists of one main, and two smaller, low salinity groundwater bodies. The main OFG body extends up to a distance of 60 km from the coast to a water depth of 110 m, has a maximum thickness of at least 250 m, and an estimated volume that ranges between 56 and 213 cubic kilometres. It exhibits along-shelf variability in salinity, which we attribute to permeability heterogeneity due to permeable conduits and normal faults, and recharge from rivers during sea level lowstands. A meteoric origin of the OFG and active groundwater migration from onshore are inferred. However, the majority of the OFG was emplaced via topographically-driven flow during sea level lowstands in the last 300 ka.

This study demonstrates that the integration of hydrological modelling, borehole and geophysical data is a powerful approach to quantitatively characterise groundwater systems across continental margins. Applying this approach globally is likely to result in a significant revision of global volumetric estimates of OFG.
Impact of deposition borehole geometry on mechanical spalling in nuclear waste repositories
Authors: Saceanu Maria Cristina , Paluszny Adriana , Zimmerman Robert , Mas Ivars Diego
Published: March 2020

Predictions of rock spalling around deep-drilled boreholes and tunnels in underground geologic repositories in crystalline rocks remain a significant challenge, due to the heterogeneities present in the rock mass, uncertain stress fields, and the complex thermo-mechanical behaviour of the rock mass at elevated temperatures.

This study presents a three-dimensional numerical analysis of multiple fracture growth leading to spalling around a deposition borehole. The mechanical spalling due to stress amplification after drilling is simulated using a finite element-based discrete fracture growth simulator. Fractures are grown by computing stress intensity factors at each fracture tip, and the mesh is adapted to accommodate the changing fracture geometries at every growth step. The model is validated using the Äspö Pillar Stability Experiment (APSE), calibrated to simulate the drilling of a borehole in the Forsmark granite, and subjected to a far-field anisotropic triaxial stress, corresponding to the in situ stress model from Forsmark. The deposition tunnel is implicitly simulated by attaching the deposition borehole to a free domain boundary.

The effect of borehole geometry on the predicted spalling around a typical deposition borehole is studied. The cylindrical borehole is modified at the top to provide an access ramp for the spent fuel canisters, which can effectively improve the repository design by reducing the height of the deposition tunnel. Three cases are investigated, in which the borehole top is cylindrical, conical, and wedge-shaped, respectively. Numerical results show that spalling occurs in all cases, but the borehole geometry affects fracture nucleation and growth patterns. The enlargement of the borehole top induces higher stress concentrations at the borehole-tunnel junction, increasing the severity of spalling at the top of the borehole. The final spalled zone and the fractures-borehole interaction are illustrated for each stress and geometry scenario.
Backtracing of marine litter and microplastic from OSPAR beaches in the North Atlantic
Authors: Röhrs Johannes , Dagestad Knut-Frode , Mauritzen Cecilie , Opstad Strand Kjersti , Grøsvik Bjørn Einar , Antunes Nogueira Leticia
Published: March 2020

Marine litter has been systematically registered at selected beaching sites within a framework of the OSPAR commission. We select a number of sites in the North Sea, Norwegian Sea and the Barents Sea to investigate where marine litter at these site could come from. Using results from hydrodynamic ocean models, wave models and atmospheric forecasts we backtrace litter from the beaching sites to possible origins within a limited time frame at the order of years. While the identified sources are hypothetical at first, we compare the types of registered plastic litter with reasonable sources in the regions identified as possible origins from the model. Thereby we distinguish between fishery related litter, industrial litter and litter from personal consumption, as the composition between these types differ between the OSPAR sites. Our modeling experiments are designed in co-production with  stakeholders for planning strategies to address and reduce marine litter.
“Hot spots” in high-latitude moss-associated N fixation: What drives locally high fixation rates?
Authors: Stuart Julia , Mack Michelle
Published: March 2020

Moss-associated nitrogen (N) fixation provides a substantial but heterogeneous input of new N to nutrient limited ecosystems at high latitudes. The presence of “hot spots”, defined as a rate of N fixation greater than three standard errors over the mean rate, can further increase the difficulty of scaling N inputs to plant communities or ecosystems. We used 15N2 incubations to quantify the fixation rates associated with 34 moss species from 24 sites ranging from 60 to 68 degrees N in Alaska, USA. The total moss-associated fixation rates ranged from 0.08 to 4.4 kg N ha-1yr-1, with an average of 1.1 kg N ha-1yr-1, based on abundance-weighted averages of all mosses summed for each site. Five of the 24 sampled sites were hot spots of N fixation. We hypothesized that host moss diversity would be correlated with higher N fixation rates, since different mosses often have distinct microbial assemblages and higher microbial diversity has been linked with higher N fixation rates in other ecosystems. However, we found no significant correlation between either moss taxonomic richness or Simpson’s D and N fixation rates (p=0.102, R2=0.01 and p=0.522, R2=0.02, respectively). What we found instead was that certain high-fixing species, most importantly Tomentypnum nitens, were present in almost all hot spots. The relevance of moss taxonomic identity in driving N fixation rates was repeatedly observed in our survey, where both machine learning and mixed model approaches found that moss family was a significant predictor of associated fixation rates across ecosystems in Alaska. Taken together, these results indicate the importance of moss identity in driving hot spots and illustrate that host taxonomy may be a useful tool in generating more accurate large-scale assessments of associated N inputs in these vulnerable and valuable ecosystems.
Mapping the abyssal Mediterranean's Messinian Evaporite Giant: Salt volumetrics from all deep basins
Authors: Haq Bilal , Gorini Christian
Published: March 2020

The thick saline series deposited in the deep Mediterranean during the latest Messinian (between 5.97 and 5.3 Ma) is among the youngest of salt giants in Earth history. During this Messinian Salinity Crisis (MSC) voluminous evaporites precipitated in the abyssal basins when the main inflow of saline water from the Atlantic through the Gibraltar Straits was severely restricted. Considerable volumes of sediments were also interbedded with evaporites, eroded from the shelves or mass-transported downslope during the oceanic drawdowns and thus this event was also a major erosional crisis.  Geochronologic advances and better understanding of the geodynamic history of various basins have led to insights about the timing of the salinity crisis and the tectonics and role of Gibraltar passage and other western narrows from the Atlantic to the Mediterranean. However, much of the new understanding comes from the Mediterranean’s shallow peripheral basins whereas knowledge of the nature of evaporites from the deep basins remains sketchy due to lack of deep drilling through the salt, and many controversies remain unresolved. An invaluable collaboration between academia and industry permitted access to most of the available seismic and core data from the Mediterranean allowing the total amount of salt (thicknesses and volumes) and associated interbedded sediment from all abyssal basins to be calculated. These new estimates are based on seismic facies analysis, which reveal that there is between 821 ± 50 and 927 ± 50 thousand cubic km of late Messinian salt, and a total of up to 1.2 ± 0.1 million cubic km of salt plus associated sediment tied up in the deep Mediterranean basins. First isochron maps of the MSC deposits (evaporites + sediment) in all the basins have been produced. These volumetrics suggests that after the initial restriction, the Mediterranean had to be either continuously supplied with brine, or partially to completely refilled several times to produce the total salt edifice. The amount of Atlantic saline water needed to amass this evaporite giant is between 7 and 8 times the modern-day Mediterranean's equivalent of saline water. The volumetric data have implications for the MSC sequestration and desiccation scenarios and should lead to more meaningful geodynamic models and provide constraints for many of the controversies that still surround this major event in geological history. Maps of salt distribution in various basins also have important implications for sub-salt exploration geoscience.

 
Geospatial modeling approaches for mapping topsoil organic carbon stock in northern part of Mongolia
Authors: Manaljav Samdandorj , Tserengunsen Purevdorj
Published: March 2020

Soil organic carbon (SOC) is one of the most important indicators of soil quality and agricultural productivity. This paper presents the application of Regression Kriging (RK), Geographically Weighted Regression (GWR) and Geographically Weighted Regression Kriging (GWRK) for prediction of topsoil organic carbon stock in Tarialan. A total of 25 topsoil (0-30 cm) samples were collected from Tarialan soum of Khuvsgul aimag in Mongolia. In this study, seven independent variables were used including normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), normalized difference moisture index (NDMI), land surface temperature (LST) and terrain factors (DEM, Slope, Aspect). We used root mean square error (RMSE), mean error (ME) and determination coefficient (R2) to evaluate the performance of these methods. Validation results showed that performance of the GWRK, GWR, and RK approaches were good with not only low values of root-mean-square error (1.38 kg m-2, 1.48 kg m-2, 0.69 kg m-2), mean error (0.28 kg m-2, -0.22 kg m-2, 0.17 kg m-2) but also high values of R2 (0.76, 0.72, 0.94). The estimated SOC stock values ranged from 0.28-16.26 kg m-2, 0.72–15.24 kg m-2, 0.16–15.83 kg m-2 using GWRK, GWR, RK approaches in the study area. The highest average SOC stock value was in the wetland (6.47 kg m-2, 6.08 kg m-2, 6.44 kg m-2) and the lowest was in cropland (1.63 kg m-2, 1.48 kg m-2, 1.80 kg m-2) using these approaches. According to the validation, GWRK, GWR, and RK approaches produced satisfactory results for estimating and mapping SOC stock. However, Regression Kriging was the best model, followed by GWRK and GWR to predict topsoil organic carbon stock in Tarialan.
Contemporary uplift of the Kunlun Shan, Northern Tibetan Plateau
Authors: Liu Shaozhuo , Nocquet jean-Mathieu , Klinger Yann , Xu Xiwei , Chen Guihua , Yu Guihua , Jónsson Sigurjón
Published: March 2020

GPS observations across active mountain ranges provide essential constraints on uplift rates, which sheds light on the underlying physical processes contributing to the development of topography. The Kunlun Shan (KLS) mountain range bounds the topographic high of the northern Tibetan Plateau. The elevation across the range sharply decreases from >4000 m in the interior of the plateau to ~2700 m in the Qaidam Basin. The mechanism responsible for its formation is debated with several models proposed on the basis of seismological and geological data. Here we consider data constraints from a cGPS profile that runs across the KLS and was installed in 2007. Our GPS time series reveal direct mechanical response to the crustal thickening across the KLS and therefore provide a promising dataset against which some geodynamical models can be tested.  Based on the GPS time series, we estimate rates of tectonic uplift and evaluate the impacts originating from reference frame drifts, common mode errors, some non-tectonic signals (e.g., hydrological loading), time-correlated noise, and postseismic transients of recent large earthquake. The GPS-derived uplift rate is ~1 mm/yr at the KLS. We find that ~2 mm/yr deep slip on a low- or intermediate-angle south-dipping thrust fault can explain the GPS-derived uplift rate. The possibility of a high-angle thrust fault, as has been proposed for the Longmen Shan (southeastern Tibetan Plateau), does not appear to be likely in the KLS case.