bluuebunny/crossref_metadata_2025 huggingface dataset:
Convective transport of enzymes through soil columns
Authors: Guber Andrey , Blagodatskaya Evgenia , Kravchenko Alexandra
Published: March 2021

Plant roots and soil microorganisms produce hydrolytic extracellular enzymes to acquire nutrients via transformation of organic matter. Microorganisms inhabit hydraulically active pores, being attached to their surfaces or to organic and mineral colloids in soil solution. Therefore, diffusion of enzymes due to Brownian motion is constrained by their interactions with the surfaces of soil particles dispersed in the solution. It is generally unknown to which extent the extracellular enzymes are associated with solid and liquid soil phases and whether enzyme motility is affected by the movement of colloids occurring in soil solution. Therefore, the goal of our study was to quantify enzyme transport in soils with contrasting properties. Transport of ß-glucosidase, acid-phosphatase, xylosidase and cellobiohydrolase was studied in undisturbed non-sterile columns of soils with three contrasting textures: sandy, sandy loam and loam. The colloids, microorganisms, and enzymes inherent for each soil were applied via soil suspensions to the tops of the undisturbed columns. The suspensions were prepared by dispersing 1 g of each soil in 100 ml of de-ionized water, followed by 30 min sedimentation. Approximately 2.5 pore volumes of the applied suspensions were passed through the columns with continuous collection of the effluent from the bottom of the columns. The effluent was analyzed for colloid contents and enzyme activities before and after removal of soil particles of size 1-10 μm by centrifugation. From 7 to 49% of applied colloids recovered from the columns with higher colloid retention capacity in finer textured soils. The enzyme activity and colloid content were the highest in the first portions of the effluent and decreased as more suspension passed the columns, suggesting presence of enzymes and colloids in soil pores readily available for convective transport. Removal of soil particles of size 1-10 μm from the effluents by centrifugation reduced enzyme activity by factors 2-5, which was much larger than reduction in the enzyme solutions free of colloids centrifuged at the same settings (24- 30%). Our results indicated that most enzymes are present and transported through soil pores convectively while attached to soil colloids. Support for this research was provided by the USDA NIFA Program (Award # 2019-67019-29361), by the NSF LTER Program (DEB 1027253) at the Kellogg Biological Station, by USDA NC1187 project, by the Great Lakes Bioenergy Research Center, U.S. Department of Energy, Office of Science, Office of Biological and Environmental Research under Award Number DE-SC0018409.
Long-term water quality monitoring in Lake Simcoe based on the empirical method and machine learning
Authors: Wang Bo , Huang Jinhui , Guo Hongwei
Published: March 2021

Abstract: The traditional water quality monitoring methods are time-consuming and laborious, which can only reflect the water quality status of single point scale, and have some problems such as irregular sampling time and limited sample size. Remote sensing technology provides a new idea for water quality monitoring, and the temporal resolution of MODIS is one day, which is suitable for long-term, continuous real-time large-scale monitoring of lakes. In this study, Lake Simcoe (located in Ontario, Canada) was selected as the research area. The long-term spatiotemporal changes of chlorophyll-a, transparency, total phosphorus and dissolved oxygen were analyzed by comparing the empirical method, multiple linear regression, random forest and neural network with MODIS data. Finally, the water quality condition of Lake Simcoe is evaluated. The results show that the overall retrieval results of two machine learning models are better than that of the empirical method. The optimal retrieval accuracy R² for four water quality parameters are 0.976, 0.988, 0.943, 0.995, and RMSE are 0.13μg/L, 0.3m, 0.002mg/L and 0.14mg/L, respectively. On the annual scale, the annual mean values of the four water quality parameters during the 10-year period from 2009 to 2018 were 1.37μg/L, 6.9m, 0.0112mg/L and 10.17mg/L, respectively. On the monthly scale, chlorophyll a, total phosphorus and dissolved oxygen first decreased and then increased at the time of year. The higher concentrations of chlorophyll a and total phosphorus in the south and east of Lake Simcoe are related to the input of nutrients from the surrounding residents and farmland.

Key words: water quality monitoring; MODIS; empirical method; machine learning
Characterization of the in-flight spectral response function of Geostationary Environment Monitoring Spectrometer (GEMS) retrieved using observed solar irradiance
Authors: Kang Mina , Ahn Myoung-Hwan , Ko Dai Ho , Kim Jhoon , Nicks Dennis , Eo Mijin , Lee Yeeun , Moon Kyung-Jung , Lee Dong-Won
Published: March 2021

The successful launch of Geostationary Environment Monitoring Spectrometer (GEMS) onboard the Geostationary Korea Multipurpose Satellite 2B (GK-2B) opens up a new possibility to provide daily air quality information for trace gases and aerosols over East Asia with high spatiotemporal resolution. As a part of major efforts to calibrate and validate the performance of the GEMS, accurate characterization of the spectral response functions (SRFs) is critical. The characteristics of preflight SRFs examined in terms of shape, width, skewness, and kurtosis vary smoothly along both the spectral and spatial direction thanks to highly symmetrical optic system of GEMS. While the preflight SRFs are determined with high accuracy, there is possibility of changes of in-flight SRFs during the harsh launch processes and/or operations over the mission lifetime. Thus, it is important to verify the in-flight SRFs after launch and to continue monitoring of their variability over time to assure the reliable trace gases retrievals. Here, we retrieve the in-flight SRFs for all spectral and spatial domain of the GEMS using spectral fitting of observed daily solar measurement and high-resolution solar reference spectrum. A variety of analytic model functions including hybrid form of Gaussian and flat-topped function, asymmetric super Gaussian, Voigt function are tested to determine the best representative function for GEMS SRF. The SRFs retrieved from early solar irradiances measured during the in-orbit tests agree well with the preflight SRFs indicating that no significant change occurred during the launch process. Continuous monitoring of the in-flight SRF is planned, using daily solar irradiances to investigate the temporal variation along with spectral and spatial directions. The detailed results of the in-flight SRF retrieval are to be presented.
ADATools for Persistent Scatterer Interferometry based displacement maps analysis: an example in Granada Province (Spain)
Authors: Monserrat Oriol , Barra Anna , Reyes Cristina , Tomas Roberto , Navarro Jose , Galve Jorge Pedro , Solari Lorenzo , Sarro Roberto , Azañon Jose Miguel , Luque Juan Antonio , Mateos Rosa María
Published: March 2021

The Persistent Scatterer Interferometry (PSI) technique is being more and more used at all scale’s applications. Several regional and national Ground Motions Services based on PSI are nowadays active and operational. The European Ground Motion Service project is going to generate a displacement map over the whole Europe once per year. This context makes indispensable tools and methodologies that facilitate the management and analysis of huge amount of data and information. The ADATools are a set of tools that can be considered a first step in this direction, they are simple and fast tools to firstly extract and make a preliminary interpretation of the main detected Active Deformation Areas (ADA). The ADATools includes: i. the ADAFinder, detecting the main ADA and giving information for each polygon as well as a Quality Index (representing the noise of time series of deformation); ii. the LOS2hv, that is used in case we have datasets from both ascending and descending geometries to derive the horizontal (east-west) and vertical components of the movement; and iii. the ADAClassifier, that makes a preliminary classification of the ADA between landslide, subsidence, settlement, and sinkholes, based on available external data (i.e., DEM, geology, inventories, infrastructures). In this presentation, the algorithm, and performances of the ADATools are presented and some results of their application are showed. Specifically, some results over an area of the Granada Province (S Spain), achieved in the framework of the Project RISKCOAST (funded by the IV Interreg Sudoe Programme through the European Regional Development Fund), will be used to illustrate ADATools performance.
Numerical Modelling of Injection-induced Seismicity at Campi Flegrei Caldera, Southern Italy
Authors: Akande Waheed Gbenga , Gan Quan , Cornwell David G. , De Siena Luca
Published: March 2021

Modelling volcanic processes at active volcanoes often requires a multidisciplinary approach, which adequately describes the complex and ever-dynamic nature of volcanic unrests. Campi Flegrei caldera (southern Italy) is an ideal laboratory where numerical modelling of injection-induced seismicity could be tested to match the observed seismicity. In the current study, thermal-hydraulic-mechanical (THM) effects of hot-water (fluid) injections were investigated to ascertain whether the observed seismicity (past and ongoing seismic swarms) could be quantitatively reproduced and modelled in isothermal or non-isothermal approximations. Fluid-flow modelling was carried out using a coupled TOUGHREACT-FLAC3D approach to simulate THM effects of fluid injections in a capped reservoir, where the sealing formation serves as a geological interface between supercritical reservoir and fractured shallow layers of the caldera. Results from previous seismic, deformation, tomographic and rock physics studies were used to constrain the model for realistic volcano modelling. The results indicated that fluid injections generated overpressure beneath the caprock and subjected it to different stress regimes at its top and bottom, and this prompted deformation. Thus, caprock deformation, triggered by injection-induced basal compressional forces and top extensional fractures, is a critical factor determining the required timing for pressure build-up and fault reactivation, and magnitudes of seismicity. Higher fluid injection rates and temperature contrasts, heterogeneity due to fault and its contrast with the host rock, and caprock hydraulic properties were among the identified secondary factors modulating fault reactivation and seismicity. Simulation results revealed that seismicity can be better modelled in isothermal (HM) approximations. A comparative study of the THM-modelled seismicity and 4-month-long (August 5th to December 5th, 2019) seismic monitoring data recorded at the Osservatorio Vesuviano showed that our model reproduced the magnitudes and depths (~2.5 Ms within 2 km) at the onset of the ongoing unrests on October 5th, 2019. However, the model could not adequately reproduce the highest magnitude (3.3 Ms at 2.57 km) seismicity on April 26th, 2020 observed since 1984 major unrests.

 
Neogene rift tectonic activity in the West Somali Basin, offshore Tanzania: example of a segmented oblique rift structure.
Authors: Ruocco Salvatore , Iacopini David , Tavani Stefano , Ebinger Cynthia , Dottore Stagna Marina , Reynolds Dave , Maselli Vittorio
Published: March 2021

Little is still known about the structural fabric of a potential continuation of the East African Rift System (EARS) offshore Tanzania in the West Somali Basin. This continuation has been established mostly through sparse GPS measurements, earthquake slip vector data, spatial distribution of teleseismically detected earthquake focal mechanisms, and some recent seismic reflection data. West of the Davie Ridge (which part of a larger structure named the Davie Fracture Zone) and across its northern extension, regional seismic reflection profiles indicate the occurrence of continental - oceanic crust transition, which is characterized by early Cretaceous reverse faulting localized along deformation corridors. After the Aptian, the seafloor spreading ceased and the Tanzania margin evolved into a passive margin dominated by clastic deep-water deposition. In this contribution, we describe some results obtained from structural mapping of a 3D seismic dataset, calibrated by few explorations well, covering an area located between the Davie Ridge and the continent, south of Mafia Island.  The seismic data maps suggest a major structural style change across the Neogene that is still active today. The recent structures are represented by two main interacting fault trends: some NS boundary faults corridors and a NW-SE internal arcuate segmented fault, both depicting a widely and diffused distribution of normal fault (with an overall cumulative amount of horizontal brittle extension ranging between 5 to 10 km). Some of the largest faults appear to reactivate older extensional structures but the general absence of growth faults cutting across the Paleo-Neogene depositional units suggest very recent rift re-activation. The recent rift system appears to show a component of obliquity with respect to the orientation of the Davie Ridge, and to the onshore structure related to the EARS tectonics.
Scale-dependent impacts of natural and anthropogenic drivers on groundwater level dynamics – analysis of shallow coastal aquifers using deep learning
Authors: Nolte Annika , Bender Steffen , Hartmann Jens , Baltruschat Stefan
Published: March 2021

Groundwater level dynamics are very sensitive to groundwater withdrawal, but their effects and magnitude – especially in combination with natural fluctuations – must be often estimated due to missing or inaccurate information of all local pumping activities in an area. This study examines the potential of deep learning applications at large spatial scales to estimate the parts of local withdrawal activities and natural impacts – meteorological and environmental – on groundwater level dynamics. We will use big data elements from a newly constructed global groundwater database in a single long-term short-term memory (LSTM) model to examine scale-dependent impacts. The data used in the model consists of continuous groundwater level observations and catchment attributes – spatially heterogeneous but temporally static catchment attributes (e.g. topography) and continuous observations of the meteorological forcing (e.g. precipitation) – from several hundred catchments of shallow coastal aquifers of different continents. Our approach is to use only freely accessible data sources covering the global scale as catchment attributes. We will test how relationships between groundwater level dynamics and catchment attributes, at different scales, can improve interpretability of groundwater level simulations using deep learning techniques.
GPU-based pseudo-transient finite difference solution for power-law viscous flow in cartesian, polar and spherical coordinates
Authors: Macherel Emilie , Podladchikov Yuri , Räss Ludovic , Schmalholz Stefan M.
Published: March 2021

Power-law viscous flow describes well the first-order features of long-term lithosphere deformation. Due to the ellipticity of the Earth, the lithosphere is mechanically analogous to a shell, characterized by a double curvature. The mechanical characteristics of a shell are fundamentally different to the characteristics of plates, having no curvature in their undeformed state. The systematic quantification of the magnitude and the spatiotemporal distribution of strain, strain-rate and stress inside a deforming lithospheric shell is thus of major importance: stress is for example a key physical quantity that controls geodynamic processes such as metamorphic reactions, decompression melting, lithospheric flexure, subduction initiation or earthquakes.

Stress calculations in a geometrically and mechanically heterogeneous 3-D lithospheric shell require high-resolution and high-performance computing. The pseudo-transient finite difference (PTFD) method recently enabled efficient simulations of high-resolution 3-D deformation processes, implementing an iterative implicit solution strategy of the governing equations for power-law viscous flow. Main challenges for the PTFD method is to guarantee convergence, minimize the required iteration count and speed-up the iterations.

Here, we present PTFD simulations for simple mechanically heterogeneous (weak circular inclusion) incompressible 2-D power-law viscous flow in cartesian and cylindrical coordinates. The flow laws employ a pseudo-viscoelastic behavior to optimize the iterative solution by exploiting the fundamental characteristics of viscoelastic wave propagation.

The developed PTFD algorithm executes in parallel on CPUs and GPUs. The development was done in Matlab (mathworks.com), then translated into the Julia language (julialang.org), and finally made compatible for parallel GPU architectures using the ParallelStencil.jl package (https://github.com/omlins/ParallelStencil.jl). We may unveil preliminary results for 3-D spherical configurations including gravity-controlled lithospheric stress distributions around continental plateaus.
Accounting for Non-detects in Satellite Retrievals: Application Using CrIS Ammonia Observations
Authors: White Evan , Shephard Mark , Cady-Periera Karen , Kharol Shailesh , Dammers Enrico , Chow Evan , Tobin Dave , Quinn Greg , O'Brien Jason , Bash Jesse
Published: March 2021

For measurements from any instrument there is a minimum detection limit below which the sensor cannot measure (i.e., non-detects). Measurements of trace gases from satellite instruments can also suffer from a significant number of non-detects, especially for species with very low atmospheric concentrations  and that have a very weak or absent signals (signal-to-noise<1) in the spectral region used to detect the species (e.g., ammonia).  For ammonia, these non-signal conditions generally occur when thick clouds obscure the ammonia signal, or atmospheric conditions generates too weak of a radiometric signal to detect (e.g., very low concentrations). Presented is a robust approach to explicitly identify and account for cloud-free satellite observations that are below the detection limit of the sensor (which occur principally in  non-source regions) for the Cross-Track Infrared Sounder (CrIS) Fast Physical Retrieval (CFPR) ammonia (NH3) product. This approach uses the newly developed CrIS Ammonia Cloud Detection Algorithm (CACDA) to compute a cloud flag based on the CrIS IMG (CIMG) product . The CIMG product uses coincident Visible Infrared Imaging Radiometer Suite (VIIRS) brightness temperatures and cloud fractions mapped onto CrIS Field of Views (FOV). This cloud flag is used to separate CrIS FOVs without signal due to clouds from FOVs that are below the detection limit due to the atmospheric state (referred to as non-detects).  Survival data is generated from in-situ surface observations from non-emission source regions to produce ammonia concentration values under CrIS non-detect conditions. Accounting for these non-detects can be significant in reducing bias of averaged values (i.e., Level 3 products) in regions or conditions with low concentration amounts (e.g. wintertime, non-agriculture regions, etc.), with little impact on concentrations in emission regions. This presentation will provide examples and evaluations of the CACDA and the inclusion of non-detects in the CFPR generated ammonia product. This will include comparisons of annual and seasonal averages of surface level ammonia concentrations with and without survival data to demonstrate the reduction in bias.
Rainfall Thresholds for Shallow Landslides by coupled Physically-Based Models and Machine Learning methods in Colombian Andes Basins
Authors: Jaramillo-González Ricardo , Aristizábal Edier , García-Aristizábal Edwin F.
Published: March 2021

Landslides have taken thousands of lives worldwide in the last decades, especially in developing countries. In the Colombian Andes, tropical rainfall conditions and steep terrains are the most common triggering factors of landslides. According to DESINVENTAR in Colombia between 1921-2020, 10.438 landslides have been registered and left almost 7.313 fatalities and destructive outcomes to the economic system. Rainfall thresholds have been used to forecast the occurrence of landslides. Physically-based rainfall thresholds take into account the effects of rainfall coupling hydrological and geotechnical models providing a wide understanding of the physical behavior of the rainfall throw the hillslope and infiltration processes. On the other hand, Machine Learning methods have been implemented to evaluate the correlation between the spatial distribution of the landslide hazard and the morphometric parameters of the basin (e.g. average slope, area, and Melton ratio).

This work was performed implementing the physically-based model TRIGRS to analyze the distribution of the safety factor under different combinations of intensity and duration from gauge-based IDF curves. And, morphometric parameters were calculated to 14 basins distributed along the Colombian Andes; all them were processed by machine learning methods to correlate the influence of each parameter with the rainfall threshold.  The results of coupling physically-based models and machine learning methods could provide criteria that allow setting up a procedure that defines a condition of instability based on the distribution of the safety factor in a basin.

Keywords: Rainfall thresholds, Shallow Landslides, Morphometric Parameters, IDF Curves, TRIGRS
Literature review: Possible implications of introducing new technologies in artisanal and small scale mining activities on climate literacy in regional population
Authors: Comaniciu Alexandra-Cosmina
Published: March 2021

The evolution of new technology and the progressive integration of automated processes in mining had been encouraged by reformed policies around the world. Initiatives were adopted in the hope that they will bring a more sustainable approach to mineral exploitation and help reduce CO2 emissions and put a stop in the temperature rises. Remote control machines and fully autonomous vehicles, as well as new applications in machine learning and big data management, used to analyse data collected from automated machines, are continuously innovated and introduced to mine sites across the globe by medium and large companies in the industry. Overall, they reduce the carbon footprint of companies and create a safer work environment. 

But what about artisanal and small-scale mining? How can new technology improve safety conditions? And how does that translate into a change in public opinion about the effects of mining on climate change? Also, could the introduction of new technologies be a way to push for climate literacy in regions where the most basic needs are generally the only concerns of the population?  

A ponderable part of the reasons why the sector is still vastly lagging in formalization and sustainable exploitation conditions is stemming from the lack of proper education and training, including climate literacy. This paper aims to show an overview of the changes automation would impose on a sector that is characterized by informal work in dangerous environments, limited use of mechanical tools, low capital and productivity, and limited access to markets - be it positive or negative- and highlight the main challenges that such a technological disruption would have to overcome. 
Model Uncertainty in Deep Learning Simulation of Daily Streamflow with Monte Carlo Dropout
Authors: Sadeghi Tabas Sadegh , Samadi Vidya
Published: March 2021

Deep Learning (DL) is becoming an increasingly important tool to produce accurate streamflow prediction across a wide range of spatial and temporal scales. However, classical DL networks do not incorporate uncertainty information but only return a point prediction. Monte-Carlo Dropout (MC-Dropout) approach offers a mathematically grounded framework to reason about DL uncertainty which was used here as random diagonal matrices to introduce randomness to the streamflow prediction process. This study employed Recurrent Neural Networks (RNNs) to simulate daily streamflow records across a coastal plain drainage system, i.e., the Northeast Cape Fear River Basin, North Carolina, USA. We employed MC-Dropout approach with the DL algorithm to make streamflow simulation more robust to potential overfitting by introducing random perturbation during training period. Daily streamflow was calibrated during 2000-2010 and validated during 2010-2014 periods. Our results provide a unique and strong evidence that variational sampling via MC-Dropout acts as a dissimilarity detector. The MC-Dropout method successfully captured the predictive error after tuning a hyperparameter on a representative training dataset. This approach was able to mitigate the problem of representing model uncertainty in DL simulations without sacrificing computational complexity or accuracy metrics and can be used for all kind of DL-based streamflow (time-series) model training with dropout.
Zirconium-based metal organic framework as novel adsorbent for Indigo Carmine
Authors: Kekes Tryfon , Kolliopoulos Georgios , Tzia Constantina
Published: March 2021

Drinking water is a vital component for sustaining life on our planet. Unfortunately, the presence of numerous recalcitrant organic and inorganic contaminants in the aquatic environment cause adverse health effects in humans, rendering water consumption dangerous. Therefore, it has become urgent to develop and establish treatment methods to decontaminate waters from persistent chemicals. Adsorption is such a promising method, mainly due to its low-cost, high performance, easiness of operation, and effectiveness in a wide pH range. The current research work focuses on the effectiveness of a novel Zirconium-based metal organic framework (MOF) solvothermally synthesized in our laboratory to remove Indigo Carmine from water. Indigo Carmine is a water-soluble organic salt used as colorant in pharmaceuticals, foods, and cosmetics; however, its presence in water has been associated with hypertension, cardiovascular and respiratory effects, carcinogenesis, and neurotoxicity. MOFs are novel compounds consisting of metals ions coordinated to organic ligands. They possess high surface areas and porosity, which classify them as ideal for the adsorption of various water contaminants. This work aims to develop comprehensive insights that will lead to more advanced efficient adsorption processes.
How HERI (Human Evolution Research Institute) is disrupting, transforming and decolonising long held patriarchal narratives of human evolution in South Africa.
Authors: Pickering Robyn , Ackermann Rebecca , Black Wendy , Sahle Yonatan , Wilkins Jayne
Published: March 2021

South Africa has an extraordinary record of human evolution spanning from our early hominin ancestors in the Cradle of Humankind World Heritage site, through to more recent evidence for the emergence of modern humans.  Human evolution research in South Africa has received international attention for nearly a hundred years and has been vast and broad in terms of research foci, as well as researcher participation. However, the leading researchers in South Africa have been almost entirely men, with women and people of colour under-represented, and black women largely absent. Since its inception in 2016, the Human Evolution Research Institute (HERI) at the University of Cape Town (UCT) has developed a tangible plan to change this: to disrupting, transform and decolonise the long held patriarchal narrative of human evolution in South Africa. Our intervention has a three-tiered design, focusing on the institutional (UCT), the current undergraduate and postgraduate student body, and the public. Using HERI, we are creating more inclusive and diverse spaces for the production and dissemination of high-quality research into human origins, through both physical changes and interactive programmes (e.g. seminars, workshops). We bring young, black women into this space, facilitate cohort-building, and give them knowledge, skills and courage to be the future of scholarship into human evolution in South Africa. We have programmes in place to support and graduate a new cohort of young, black woman PhD students, as well as postdoctoral support that will provide a stepping-stone for these young women to continue in their scientific careers. Field camps are used to demystify the fieldwork experience and encourage interaction between undergraduate and postgraduate women – as well as academics – and help younger women receive the skills they need, as well as the experiences necessary to spark their interest and imagine themselves entering the discipline. Finally, in order to reach beyond the bounds of higher education institutes and out into the public domain, we are developing a new, permanent museum exhibition on human evolution at the Iziko Museum of South Africa, in Cape Town. The exhibition reframes the human origins narrative to centre on the diversity of all people in South Africa, exploring how evolution produced that diversity through a lens of inclusivity and aiming to demystify the topic in an environment that is not alienating but welcoming.
Lithosphere velocity structure of the Khibiny and Lovozero plutons (Eastern part of the Baltic shield) from receiver functions
Authors: Goev Andrey
Published: March 2021

The Kola region of the Russian Arctic is located in the northeast of the Baltic Shield and is widely known for its unique geology in regards to the presence of massive Paleozoic intrusions. Multidisciplinary researches have been carried out to provide a comprehensive reconstruction of Khibiny and Lovozero plutons’ formation and their structure models The main source of geochronological data comes from isotope analysis of the arrays’ rocks. The amount of research focuses on the deep structure beneath the Khibiny pluton is scarce. To investigate velocity structure of the investigated region we used receiver function technique. Essence of the method is to analyze P-S (PRF) and S-P (SRF) converted waves form seismic boundaries along with their multiples. For the given research we used seismograms of the teleseismic events recorded by the Apatity (APA) and Lovozero (LVZ) broadband seismic stations since 2000. We selected 220 and 232 individual PRF;147 and 122 individual SRF for LVZ and APA station respectively. As both LVZ and APA are located relatively close to each other, we combined all 452 PRF to get a robust estimation of delay times of P410s and P660s phases. Our estimations of P410s and P660s phases are 43.6 and 67.6 sec respectively. Delay time between these phases is 24 sec that is close to “standard” according to the IASP91 model. The individual times of each phase are slightly less than predicted by IASP91 (by 0.4 sec) and could indicate an increase of velocities in the upper mantle, but it is not unusual for cratonic regions. Joint inversion of PRF and SRF was used to restore velocity sections for the depth up to 300 km. All models have shown a gradient increase in velocities in the earth's crust and sharp crust-mantle boundary at depth of 40 ± 1 km with a velocity jump from 3.9 to 4.4 km/s. The most prominent feature of the upper mantle structure is the presence of the low-velocity zone at a depth from 90 to 140 km. One of the possible explanation of this discontinuity could be the presence of deep fluids and the high porosity of this zone. This study was partially supported by the RFBR grant 18-05-70082 and the SRW theme No. АААА-А19-119022090015-6.
Assessing Arctic Ground Surface Temperatures from Borehole Temperatures and Paleoclimatic Model Simulations
Authors: Beltrami Hugo , Cuesta-Valero Fracisco José , García-García Almudena , Gruber Stephan , Jaume-Santero Fernando
Published: March 2021

The surface temperature response to changes in our planet’s external forcing is larger at higher latitudes, a phenomenon known as polar amplification. The Arctic amplification has been particularly intense during the last century, with arctic-wide paleoclimatic reconstructions and state-of-the-art model simulations revealing a twofold arctic warming in comparison with the average global temperature increase. As a consequence, Arctic ground temperatures respond with rapid warming, but this response varies with snow cover and permafrost processes. Thus, changes in arctic ground temperatures are difficult to reconstruct from data, and to simulate in climate models.

Here, we reconstruct the ground surface temperature histories of 120 borehole temperature profiles above 60ºN for the last 400 years. Past surface temperature evolution from each profile was estimated using a Perturbed Parameter Inversion approach based on a singular value decomposition method. Long-term surface temperature climatologies (circa 1300 and 1700 CE) and quasi-steady state heat flow are also estimated from linear regression through the depth range 200 to 300 m of each borehole temperature profile. The retrieved temperatures are assessed against simulated ground surface temperatures from five Past Millennium and five Historical experiments from the Paleoclimate Modelling Intercomparison Project Phase III (PMIP3), and the fifth phase of the Coupled Model Intercomparison Project (CMIP5) archives, respectively.

Preliminary results from borehole estimates and PMIP3/CMIP5 simulations reveal that changes in recent Arctic ground temperatures vary spatially and are related to each site’s earlier thermal state of the surface. The magnitudes of ground warming from data and simulations differ with large discrepancies among models. As a consequence, a better understanding of freezing processes at and below the air-ground interface is necessary to interpret subsurface temperature records and global climate model simulations in the Arctic.
Laboratory experiments of water injection coupled with ultrasonic monitoring reveal wave-induced fluid flow in microporous carbonate rock
Authors: Geremia Davide , David Christian , Barnes Christophe , Menéndez Beatriz , Dautriat Jérémie , Esteban Lionel , Sarout Joel , Vandycke Sara , Descamps Fanny
Published: March 2021

Monitoring of fluid movements in the crust is one of the most discussed topics in oil & gas industry as well as in geothermal systems and CO2 storage, but still remains a challenge. The seismic method is one of the most common ways to detect the fluid migration. However, the use of ultrasonic monitoring at the sample scale in laboratory experiments persists as the most effective way to highlight large scale observations in which the boundary conditions are not well constrained.

To unravel the fluid effect on P-wave and S-wave velocity, we performed mechanical experiments coupled with ultrasonic monitoring on Obourg chalk from Mons basin (Belgium). Water injection tests under critical loading, imbibition tests and evaporation tests provided a full spectrum of observations of fluid-induced wave alteration in term of propagation time and attenuation.

The analysis of these experimental results showed that significant velocity dispersion and attenuation developed through variations in water saturation, and that these processes are linked to the presence of patches of water and air in the pore space.

We used the White’s formulation to model the relaxation effects due to spherical pockets of air homogeneously distributed in a water-saturated medium. In this framework, the pressure induced by the passing wave, produces a fluid flow across the water-air boundary with consequent energy loss.

This model reproduces both qualitatively and quantitatively the experimental results observed on the water injection tests. Indeed, it is shown that the progressive water saturation or desaturation of this chalk, generates a shift of the critical frequency (from the undrained relaxed towards unrelaxed regimes) which at some point matches the resonance frequency of the piezoelectric transducers used in the experimental setup (0.5 MHz). This phenomenon allowed us to get a continuous recording of the relaxation processes induced by saturation variations.

The outcomes of this work can significantly improve the actual knowledge on coupled effects of waves and fluids which is a crucial aspect of fluid monitoring in the context of reservoir evaluation and production.
Making sense of irreversible soil salinization and sodification
Authors: Mau Yair , Kramer Isaac , Adeyemo Taiwo , Bayer Yuval
Published: March 2021

Soil salinity and sodicity present serious risks to agriculture, in the face of dwindling freshwater resources and changing rainfall patterns. As a finite resource of crucial importance, soils must be protected from irreversible degradation. However, very little is known about how soils respond to adverse conditions in the long run, in particular regarding salinity and sodicity. As a proxy for soil stability and health, we will discuss what (little) is known about the irreversible deterioration of saturated hydraulic conductivity (Ks), subjected to water of varying levels of salinity and sodicity. We present novel soil column experiments measuring Ks hysteresis, for three soils of varying clay content. We then present a mathematical framework that allows us to make sense of the hysteresis in Ks, and that helps us understand the pivotal role of a soil's history of salinization and sodification in determining future Ks behavior. Most importantly, our model gives specific guidelines of what to measure in order to best characterize a soil's partial decline in Ks. We will focus on the role of reversal curves as the key to unlock a full characterization of the Ks hysteresis. With the help of weighting functions, we will show that our modeling framework is able to describe soils of any texture and clay mineralogy, making it both versatile and useful.
H/V spectral ratios at the InSight landing site using ambient noise and Marsquake records
Authors: Carrasco Sebastián , Knapmeyer-Endrun Brigitte , Margerin Ludovic , Schmelzbach Cédric , Clinton John , Stähler Simon , Giardini Domenico , Kedar Sharon , Grott Matthias , Golombek Matthew , Lognonné Philippe , Banfield Don
Published: March 2021

The InSight mission landed on Mars on November 26th, 2018 and its seismometer, the Seismic Experiment for Interior Structure (SEIS), has recorded continuous Martian seismic data since February 2019, consisting of mainly ambient seismic noise but also hundreds of seismic events.

We used the SEIS data to study the horizontal-to-vertical spectral ratios from both the ambient seismic noise (nHV) and the seismic events (eHV), for frequencies above 0.6 Hz, in order to get further constraints on the first tens of meters at the Insight landing site. The nHV curve was obtained by using data segments of 50 s over more than 400 Sols. The preferred nHV curve is observed during the northern spring and summer at low wind levels and it is a mostly flat curve with a prominent trough around ~2.4 Hz. Outside of these time periods, the nHV curve is contaminated with artificial peaks likely related to lander modes. On the other hand, the eHV curve was created using 336 seismic events with quality either A, B or C, as defined by the Marsquake Service. For each seismic event, we computed the signal-to-noise ratio (SNR) at each frequency and only frequencies with SNR>3 were used to obtain the final eHV curve. In addition to the 2.4 Hz trough, the final eHV curve shows a strong peak around 8 Hz, which is not observed from the ambient noise data possibly due to a lack of seismic energy in this frequency band able to excite it.

A preliminary inversion of the eHV curve, considering the fundamental mode of the Rayleigh wave only, shows that the 2.4 Hz trough and the 8 Hz peak can be explained by a shear-wave velocity model increasing from the surface to a depth of 5-8 m (likely the boundary between the regolith and coarse ejecta), in good agreement with previous analysis based on compliance observations, hammering measurements and satellite images. At this depth, a discontinuity leading to a higher velocity layer is observed, which is followed by a deeper low-velocity layer about 20 m thick. The modeling assuming body waves only or a full diffuse seismic wavefield is currently under investigation.
Removal of a dense bottom layer by a gravity current
Authors: Zhu Rui , He Zhiguo , Meiburg Eckart
Published: March 2021

We investigate the removal of a dense bottom layer by a gravity current, via Navier-Stokes Boussinesq simulations. The problem is governed by a dimensionless thickness parameter for the bottom layer, and by the ratio of two density differences. A quasisteady gravity current propagates along the interface and displaces some of the dense bottom fluid, which accumulates ahead of the gravity current and forms an undular bore or a series of internal gravity waves. Depending on the ratio of the gravity current front velocity to the linear shallow-water wave velocity, we observe small-amplitude waves or a train of steep, nonlinear internal waves. We develop a self-contained model based on the conservation principles for mass and vorticity that does not require empirical closure assumptions. This model is able to predict the gravity current height and the internal wave or bore velocity, generally to within about 10% accuracy. An energy budget analysis provides information on the rates at which potential energy is converted into kinetic energy and then dissipated, and on the processes by which energy is transferred from the gravity current fluid to the dense and ambient fluids. We observe that the energy content of thicker and denser bottom layers grows more rapidly.
The sheath region of April 2020 magnetic cloud and the associated energetic ions 
Authors: Kilpua Emilia , Good Simon , Dresing Nina , Vainio Rami , Davies Emma , Forsyth Robert , Lavraud Benoit , Heyner Daniel , Horbury Tim , Angeli Virginia , O'Brien Helen , Evans Vincent , Wimmer Bob , Rodriguez-Pacheco Javier , Gomez-Herrero Raul , Ho George
Published: March 2021

Acceleration of energetic particles is a fundamental and ubiquitous mechanism in space and astrophysical plasmas. One of the open questions is the role of the sheath region behind the shock in the acceleration process. We analyze observations by Solar Orbiter, BepiColombo and the L1 spacecraft to explore the structure of a coronal mass ejection (CME)-driven sheath and its relation to enhancements of energetic ions that occurred on April 19-20, 2020. Our detailed analysis of the magnetic field, plasma and particle observations show that the enhancements were related to the Heliospheric Current Sheet crossings related to the reconnecting current sheets in the vicinity of the shock and a mini flux rope that was compressed at the leading edge of the CME ejecta. This study highlights the importance of smaller-scale sheath structures for the energization process. These structures likely formed already closer to the Sun and were swept and compressed from the upstream wind past the shock into the sheath. The upcoming observations by the recent missions (Solar Orbiter, Parker Solar Probe and BepiColombo) provide an excellent opportunity to explore further their role.  
Capillary effect on the tidal response of buried aquifers – an interaction between shallow and deep groundwater systems
Authors: Zhu Aiyu , Wang Chi-Yuen
Published: March 2021

The interaction between the shallow and deep groundwater systems is important for a number of issues on water resources and the environment but is difficult to evaluate directly. Here we use two-dimensional numerical simulations to show that the tidal response of deep aquifers may be significantly affected by capillary force on the water table. We propose a criterion to evaluate the capillary effect and apply the model to interpret the tidal response of the Arbuckle aquifer in a USGS deep monitoring well in Oklahoma. Our study suggests that the shallow and deep groundwater systems may interact across thick layers of intervening aquitards and that the analysis of the tidal response of deep aquifers may be an effective means to evaluate such interaction.
Convection permitting simulation of summer precipitation over the Tibetan Plateau
Authors: Liu Zhaoyang , Gao Yanhong
Published: March 2021

The Tibetan Plateau (TP), known as the "Third Pole" and "Water Tower of Asia", plays an essential role in the regional water cycle and global climate change through its unique topography and abundant water resources. Precipitation is an important part of the hydrological process, but realistically simulating precipitation over the TP is still a major challenge for most models, which hinders our understanding of the strength of the land-atmosphere interaction and its influences on regional, or even global climate and water cycle. In order to better depict precipitation spatial and temporal distributions over the TP, a 4-km convection permitting modelling (CPM) and a 28-km dynamical downscale modelling (DDM) using the weather Research and Forecasting model (WRF) were conducted for a summer (from June to August 2014). WRF simulations are evaluated against CMA in-situ observations, the Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation of water resources (APHRODITE), the Global Precipitation Measurement (GPM), as well as two reanalysis datasets ERA-Interim and ERA5. We focus on the added values of the CPM in summer precipitation simulations, in terms of the spatial seasonal mean precipitation amounts, spatial distributions, and diurnal cycles. We found the six datasets (CPM, DDM, APHRODITE, GPM, ERA-Interim and ERA5) showed great differences in summer precipitation over the TP. The great advantages of CPM and DDM over reanalyses are observed. Slight improvements are found in CPM over DDM as well. Mechanisms for these differences will be explored.
Lateral and vertical pulsed-photon portable luminescence (PPSL) profiling of anthropogenically-altered sediments in rescue excavations of different landscapes 
Authors: Roskin Joel , Ackermann Oren , Asscher Yotam
Published: March 2021

Growing infrastructure development in Israel has increased the number of rescue excavations involving multi-layer archaeological sites and "megasites" in landscapes ranging from dunes to clay-rich soils and yielding prehistoric to early modern finds. The limited time and resources allocated for the excavations requires rapid on-site scientific data, which are used for research during and after excavation, prioritizing artefact treatment, sediment analysis, and absolute and relative dating.

Lateral and vertical pulsed-photon (portable) OSL (PPSL) profiling of sections of anthropogenically-altered sediments containing feldspar or quartz, provide rapid and partial answers for interpreting depositional processes. These answers allow researchers to discriminate between natural and human-intervened sedimentation, identify relative age and laterally synchronize between similar sediment units, which, in turn, often help to orient the excavation goals. The potential for inhomogeneity of archaeological sediments in some cases constrain the comparability of results and call for complementary analysis of the measured sediments in order to define their inter-compatibility. Independent mineralogical and chemical and textural properties of the sediments affect the inherent luminescence signals and should therefore be analyzed.

Here we present a PPSL profiling approach combining tailored sedimentological analyses to validate sample comparability in different sedimentological and archaeological settings. The analyses include gamma and FTIR spectroscopy, portable XRF geochemistry, carbon content, particle-size distribution and colorimetry. The complementary data are intended to improve PPSL protocols by characterizing the context inhomogeneity and helping to prioritize samples for OSL dating