bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxygenation of the Ox Bel Ha karst subterranean estuary during Tropical Storm Hanna: Mechanisms and implications for methane turnover
Authors: Brankovits David , Pohlman John , Lapham Laura
Published: March 2022

Seasonal precipitation affects methane accumulation and turnover in tropical karst subterranean estuaries, the region of the coastal aquifer where hydrological and biogeochemical processes regulate material exchange between the terrestrial and marine environments. However, the impact of extreme weather events (e.g., tropical storms and hurricanes) on subsurface carbon cycling linked to coastal karst landscapes is unknown. In this study, we present a 5-month long hydrologic and chemical record from inland and coastal portions of the extensive Ox Bel Ha cave system in the northeastern Yucatan Peninsula. The record encompasses wet and dry seasons and includes effects from Tropical Storm Hanna during October 2014. Intense rainfall coincides with an episodic increase in water level and sudden shifts in salinity, indicating a spatially widespread hydrologic response. The most profound effect of the storm was a vanishing pulse of dissolved oxygen to ~0.7 mg l-1 that declined to zero along with the disappearance of methane that had built up during the wet season. A positive shift in methane’s stable carbon isotope content from −62.6 ± 0.6‰ before the storm to −44.0 ± 2.4‰ after the storm indicates microbial methane oxidation was the primary mechanism for the loss of methane from the groundwater. Post-storm methane concentrations, which never reached pre-storm levels, suggest the tropical storm had long-lasting (months) effects on carbon cycling. These findings demonstrate that mixing and oxygen delivered during storm-induced hydrologic forcing has an outsized biogeochemical effect within typically stratified karst subterranean estuaries.
Introducing CLM-FruitTree to model carbon allocation in fruit orchards with the Community Land Model
Authors: Dombrowski Olga , Brogi Cosimo , Hendricks Franssen Harrie-Jan , Zanotelli Damiano , Bogena Heye
Published: March 2022

Carbon allocation is a major driver of plant growth and plays a key role in shaping ecosystem processes and the global carbon (C) cycle. In contrast to annual crops, fruit trees store and remobilize C in their perennial plant components, have long canopy durations, relatively low respiratory costs, and remain productive for decades. To predict C dynamics in fruit tree orchards under global change, it is essential to expand the understanding of carbon allocation in fruit trees and to improve its representation in comprehensive modelling environments such as land surface models (LSMs). LSMs simulate the exchanges of matter and energy between the terrestrial biosphere and the atmosphere. They are widely used in C cycle and climate change studies, and typically include representations of various types of natural vegetation and annual crops. Despite the importance of fruit orchards in regions that are strongly affected by climate change, such as the Mediterranean, they are rarely considered in LSMs, thus leaving an important gap in the representation of C allocation and related biogeophysical and biogeochemical processes of these agro-ecosystems. In this work, we present the new fruit tree sub-model CLM-FruitTree within the Community Land Model version 5 (CLM5). Herein, a fruit tree is described by a perennial deciduous phenology with C allocation to standing woody biomass components and annual organs such as leaves, fine roots, and fruits that are either shed or harvested within the yearly cycle. Two different pools, the storage and the photosynthetic pool, contribute to tree growth while C allocation to the individual plant components is based on allocation coefficients that vary depending on the specific phenological phase. CLM-FruitTree was tested using multiple years of field measurements of above- and belowground biomass components, leaf area index (LAI), yield, soil respiration, and eddy covariance (EC) data from an apple orchard in South Tyrol, Italy. We found that biomass allocation was captured within 1-5 % of the measured values, with about half of the assimilated C allocated to fruits. Growth from C storage thereby played a significant role in shaping initial leaf development and growth of fine roots. Simulated ecosystem C fluxes showed a high correlation (r > 0.84) with the EC measurements and the seasonal dynamics were well represented. Average annual gross primary productivity was predicted within 1.5 % of the measured values while net carbon uptake was overestimated by on average 21 % mostly due to an underestimation of soil respiration in the orchard caused by necessary simplifications in the microbial respiration, orchard structure, and management practices. Overall, the new sub-model CLM-FruitTree allows the exploration of the dynamics of C allocation and fluxes in fruit orchards, and may advance C cycle and climate change studies of such agro-ecosystems at larger scale.
Bifurcation diagram for vegetation patterns model: old ways for new insight
Authors: Vanderveken Lilian , Crucifix Michel
Published: March 2022

Spatial organization is a well-known feature of vegetation in semi-arid regions. This phenomenon appears in various parts of the world where water is the limiting factor for plants growing. Those patterns can be reproduced by using reaction-diffusion equations. Rietkerk developed a vegetation patterns model where the joint effects of a local reaction and diffusion create heterogeneous solutions.

The existence of those solutions expands the range of precipitation conditions under which vegetation can prevail. The complete region in the bifurcation diagram where such stable patterns exist is called the Busse balloon.

To our knowledge, no full investigation of the Busse balloon in Rietkerk’s model is available. Here we address this gap and dissect this Busse balloon by analysing the patterned solution branches of the bifurcation diagram.

For a given domain length, those branches can be computed starting from the different zero modes at the edge of the Turing zone around the branch of homogeneous solutions. Then, we use a Newton-Raphson method to track each branch for precipitation changes. Two types of branches appear. What we call the main branches have a roughly constant wavenumber along the branch. What we call the “mixed state branches” originate at the transition between stability and instability along one main branch. The corresponding solutions appear as mixing the solutions of two main branches, which is why we call them that way. However, we show that the latter plays a minor role in the dynamics of the system.

The awareness of the various patterned branch sheds new light on the dynamics of wavenumber switching or R-tipping for patterned systems. More generally, this work gives new insights into the behaviour of patterned systems under changing environment.
Parametrization and Characterization of Multiple ELVES at the Pierre Auger Observatory 
Authors: Mussa Roberto ,   Pierre Auger Collaboration
Published: March 2022

ELVES are being studied since 2013 with the twenty-four FD Telescopes of the Pierre Auger Observatory, the world’s largest facility for the study of ultra-high energy cosmic rays, in the province of Mendoza (Argentina) exploiting a dedicated trigger and extended readout. Since December 2020, this trigger has been extended to the three High Elevation Auger Telescopes (HEAT), which observe the night sky at elevation angles between 30 and 60 degrees, allowing to study ELVES from closer lightning. The high time resolution of the Auger telescopes allows to do detailed studies on multi-ELVES. The origin of multi-ELVES is not yet fully understood, and can be studied by analysing the time difference(s) and the amplitude ratio(s)  between flashes as a function of the radial distance of lightning emission from the causative lightning. At least two, if not three, distinct models are needed to explain the geometry of multi-ELVES events. This contribution will review the frequency of each class of multi-ELVES and correlate them to data from ENTLN, WWLLN, and GOES databases.
Response of Water-Table Depth to Fallow Duration and Hydro-Meteorological Factors: A Case Study in the Sigang District of Tainan, Taiwan.
Authors: Hsieh Karen
Published: March 2022

The Chia-nan Plain is one of the major grain-growing areas in Taiwan where groundwater over-exploitation for irrigation has long been an unsolvable problem because of uneven temporal /spatial rainfall distribution. Based on past studies, it reveals that paddy field plays an important role in groundwater conservation; however, paddy field also requires a large amount of water for irrigation simultaneously. Furthermore, due to the impacts of climate change, the issue of uneven temporal/spatial rainfall distribution in Southern Taiwan has aggravated, which also affects plenty of hydro-meteorological variables, including the water level of Zheng-wun River, precipitation, temperature, and relative humidity (RH).

This study aims to unravel the nexus between specific agriculture acts, hydro-meteorological variables, and groundwater levels. As a result, the Multi-dimensional Ensemble Empirical Mode Decomposition (MEEMD) method and Time Dependence Intrinsic Correlation (TDIC) method are implemented to analyze the NDVI time series and hydro-meteorological variables. With the analysis of MEEMD, we can establish the most influential time scales of hydro-meteorological variables and fallow duration associated with the groundwater level. Besides, the time lag effect of fallow to water-table depth can be determined by applying time-dependent intrinsic correlation (TDIC) approaches.

Groundwater is one of the valuable water resources worldwide; therefore, this study provides insights into the response of water-table depth to the non-linear, non-stationary hydro-meteorological variables. Additionally, we also formulate a new strategy for groundwater conservation by regulating the fallow duration.

Keywords: Fallow duration; Water-table depth; Hydro-meteorology; Time-frequency analysis (TFA); MEEMD; TDIC
Poro-mechanical modelling of in-situ loading experiments on Venice Lagoon marshes 
Authors: Baldan Selena , Andrea Franceschini , Claudia Zoccarato , Philip S. J. Minderhoud , Veronica Girardi , Massimiliano Ferronato , Pietro Teatini
Published: March 2022

Tidal marshes are coastal landforms daily flooded by sea water. Their fate is strongly conditioned by the future relative sea level rise, intrinsically linked to climate change. The significant ecological and socioeconomic value of these ecosystems is a compelling reason to improve our understanding of marsh platform dynamics relative to the mean sea level. Among various factors influencing the elevation of these depositional landforms, sedimentation and compaction of the marsh body itself play a major role. In particular, it has been observed that marsh soils undergo large autocompaction due to high porosity and compressibility. Hence, characterization of marsh geomechanical properties is of paramount importance to develop reliable long-term predictions. With the aim of characterizing the geomechanical features of tidal marshes in the Venice Lagoon (Italy), a campaign of in-situ loading experiments has been recently carried out. In each experiment, eight 500-l tanks were cyclically filled and emptied with lagoon water, applying loads of various duration and entities on marsh platform. A monitoring system, based on pressure and displacement transducers, tracks the marsh response to the applied loads. This work describes the modeling activities developed to interpret these measurements from the in-situ experiments. The simulations have been carried out using a 3D poro-mechanical model solving Biot’s equations by a mixed finite-element formulation. A power law is used to describe the soil compressibility vs effective stress relationship, and main parameters are initially defined based on oedometric tests carried out on a few samples cored from the marshes. Mechanical hysteresis is also accounted for. The model calibration allows to satisfactory match the available pressure and deformations records. In particular, the numerical simulation accurately accounts for the behavior of (vertically) heterogenous marsh deposits as revealed by core interpretation. Based on these promising results, we are looking towards using the calibrated constitutive relationships in long-term biomorpho-geomechanical analyses, to forecast the fate of the marshes in the Lagoon of Venice.
Assessment of ESA CryoSat-2 radar altimetry data using GNSSdata at three sites on the Greenland Ice Sheet
Authors: Hansen Karina , Larson Kristine M. , Willis Michael J. , Colgan William , Helm Veit , Khan Shfaqat Abbas
Published: March 2022

Ten-year records of ice surface elevation changes derived from three GNSS stations placed on the interior of the Greenland ice sheet are used to assess the ability of CryoSat-2 radar altimetry to capture surface elevation changes during 2010-2021. We use GNSS interferometric reflectometry (GNSS-IR) to derive time series of continuous daily surface elevations. The footprint of GNSS-IR is about 1000 m2 and the accuracy is ±2cm, making it an excellent tool to validate ice surface height from satellite altimetry. We compare GNSS-IR derived ice surface elevations with CryoSat-2 derived surface elevations and find Cryosat-2 performs best at the GNSS site furthest north (GLS3) with a maximum difference of 12cm. The other GNSS sites have a higher residual range because of poorer data availability and local surface variations. The number of Cryosat-2 data points are roughly doubled from GLS1 and GLS2 to GLS3. GLS3 Is located in a very flat area of the ice sheet only moving 55m during 2011-2020. In contrast GLS1 moved 292m in the same period, clearly indicating a steeper slope to the ice sheet at this location, which we have difficulty correcting for because digital elevation models are associated with high uncertainty on the interior of the ice sheet. The strength of this assessment method lies in the continuous daily time series of surface elevation change derived from GNSS, as they clearly capture extreme short-term changes, which otherwise might have been perceived as errors in the radar altimetry measurements.
Investigation of Different Trench Geometries for Optimized Bedding of Buried Power Cables
Authors: Schmid Maximilian , Pham Hung , Schedel Markus , Sass Ingo
Published: March 2022

For an efficient integration of renewable energies, many transmission lines of the electrical power grid have to be extended or newly built. Besides the common overhead transmission lines, an increasing proportion of these grid expansions is conducted using underground power cables.

During the operation of buried cable systems, the mechanical and thermal properties of the cable’s surroundings need to meet certain requirements. To avoid insulation faults in the cables due to overheating, the ampacity is limited by specific conductor temperatures and the thermal energy resulting from the electric losses during transmission needs to be reliably dissipated. Thus, the actual performance of a buried power cable system depends strongly on the thermal properties of the cable bedding materials and soil.

In practice, buried power cable lines typically require the use of cable trenches. The pre-existing soil from the cable trench is usually replaced by sand or artificial fluidized backfill materials with well-known material properties, which may differ from the properties of the surrounding soil. Thus, heterogeneous structures are created in the shallow subsurface, which affect the heat and water transport around the power cables. With an installation depth of 0.5 - 2.5 m, the cables are typically located in the vadose zone, where the thermal properties of the bedding are affected by the varying water content by up to one order of magnitude. Therefore, precise knowledge of the influence of size and geometry of the cable trench on the water distribution around the cable is crucial for an adequate assessment of the cable’s ampacity ratings.

Within the scope of our research, the influence of cable trench geometry and size on heat and mass transfer around buried power cables were investigated with a coupled approach of laboratory experiments and numerical modeling.
PESTIPOND: A fate model of pesticides in ponds
Authors: Bahi Aya , Sauvage Sabine , Payraudeau Sylvain , Imfeld Gwenaël , Tournebize Julien
Published: March 2022

Non-point pollution by pesticides affects the quality of drinking water supplies and aquatic environments. Ponds collecting runoff and erosion fluxes offer a complementary tool to mitigate pesticide transfer to aquatic ecosystems. Pesticides mitigation results from various physicochemical processes operating in the water column, the sediment layer, the vegetation, and the suspended particles of ponds. Many studies on ponds dissipation potential focus on nitrates and suspended sediments, but very little is known about the behavior of pesticides. In order to predict and enhance the dissipation of pesticides in ponds, a new 0D time-dependent model was designed, “PESTIPOND.” The dissipation function of ponds is due to a combination of transport, transfer, and transformation processes of pesticides in an interplay between pond compartments. A previous review helped us identify the main processes of pesticides dissipation in ponds and their controlling factors. A time-dependent environmental fate model is currently developed to describe the behavior of dissolved and particulate pesticides at the pond scale. We tested the performance of this process-based model by simulating the behavior of four molecules with contrasted physicochemical properties (i.e., Aclonifen, chlorotoluron, s-metolachlor, and tebuconazole) in a synthetic scenario representing an experimental pond study. PESTIPOND enabled to compute the outlet concentration of pesticides in ponds based on their inlet concentration. The model simulated the behavior of pesticides in water, sediments, vegetation, and suspended particles of a pond due to sorption, settling/resuspension, volatilization, and degradation processes. The conceptual model is based on pesticide mass-budget equations in pond compartments depending of climate and hydraulic conditions. Sensitivity analysis provides a framework to recognize important variables in the computational model. We adopted the Morris and Sobol methods for the sensitivity analysis of PESTIPOND to identify dominant parameters influencing the model outputs. A preliminary result showed that the prevailing processes determining pesticide fate were sorption and biodegradation for dissolved pesticides and settling for particulate pesticides. The identification of effective mechanisms can be helpful to hierarchize processes based on their contribution to the dissipation function of ponds. This hierarchization may improve the estimation of ponds efficiency with respect to pesticide dissipation. In the future, implementing the PESTIPOND model in SWAT is expected to extend the prediction of ponds dissipation to the catchment scale. PESTIPOND will be particularly helpful to set up dimensioning criteria to design performant and efficient ponds to mitigate pesticides transfer into the environment.
Energy exchanges between two-dimensional front and internal waves.
Authors: Kar Subhajit , Barkan Roy
Published: March 2022

Fronts and near-inertial waves (NIWs) are energetic motions in the upper ocean that are thought to interact and provide a possible route for kinetic energy dissipation of mesoscale balanced flows. To date, the theoretical explanations for such interactions rely on the fronts being geostrophic, with a weak ageostrophic secondary circulation (ASC) and a small Rossby number. We develop a quasilinear model to study the interactions between NIW vertical modes and a 2D front undergoing semigeostrophic frontogenesis. In our model, frontal sharpening is divided into two stages: an exponential stage, that is characterized by a low Rossby number and is driven by geostrophic strain; and a super-exponential stage, that is characterized by an O(1) Rossby number and is driven by the convergence of the ASC. We identify a new mechanism, the convergence production, through which NIWs can efficiently extract energy from the front during the super-exponential stage. It is shown that the convergence production can dominate the known mechanism of energy extraction during the exponential stage, the deformation shear production, for a relatively strong geostrophic strain field.
High resolution vertical information of halogenated trace gas abundances in the polar stratosphere: First flight of the „MegaAirCore“ in summer 2021
Authors: Laube Johannes , Richter Anne , Sitnikow Andreas , Keber Timo , Popa Elena , Schuck Tanja , Wagenhäuser Thomas , Engel Andreas
Published: March 2022

Measurements of halogenated trace gases such as CFCs, halons, HCFCs, HFCs, and PFCs are highly relevant due to their impact on the stratospheric ozone layer as well as their high Global Warming Potentials. Yet in situ profiles of the abundances of many of these species in the stratosphere have been increasingly rare in the last two decades, especially above the altitude range accessible by aircraft (i.e. up to 20 km). More recently, the AirCore technique, which was initially utilized for measurements of more abundant trace gases such as carbon dioxide and methane (Karion et al., 2010), has been demonstrated to also enable stratospheric mixing ratio determination for six halogenated species (Laube et al., 2020). However, a direct measurement comparison of AirCore-based air samples with those collected via a more established technique has been missing so far for such low-abundant species. We here present results from a large balloon flight in Esrange, Sweden (67.8877°N, 21.0838°E) in August 2021. An established cryogenic whole-air sampler (Engel et al., 2009) was flown on the same gondola as a so-called “MegaAirCore”, which has, at ~15 liters, a much larger internal volume than common AirCores (~1-1.5 liters). The air collected between ~32 km and ~5 km by this “MegaAirCore”  was transferred into 51 sub-samples immediately after the flight, and these were subsequently analysed for their content of >30 halogenated trace gases. The 13 larger air samples collected by the cryosampler were also measured on the same mass spectrometry-based instrument.Results compare well for many species, which represents an independent verification of AirCore-based measurements of halogenated trace gases at mixing ratios of parts per trillion levels or below – while at the same time demonstrating the viability of stratospheric air sampling at a much higher vertical resolution than previously possible. This opens up new possibilities for studying stratospheric chemistry and dynamics as well as for improvements of the independent validation of remote sensing-based observations. 

 

References

Engel et al., Nat. Geosci., 2, 28–31, 2009

Karion et al., J. Atmos. Ocean. Technol., 27(11), 1839–1853, 2010

Laube, et al., Atmos. Chem. Phys., 20, 9771–9782, 2020, https://doi.org/10.5194/acp-20-9771-2020
Narrow, fast, and "cold" mantle plumes on Earth explained by strain-weakening rheology in the lower mantle 
Authors: Gülcher Anna , Golabek Gregor , Thielmann Marcel , Ballmer Maxim , Tackley Paul
Published: March 2022

The rheological properties of­­­ Earth’s lower mantle materials are key for mantle dynamics and  planetary evolution. The main rock-forming minerals in the lower mantle are bridgmanite (Br) and smaller amounts of ferropericlase (Fp). Bridgmanite minerals are intrinsically much stronger than ferropericlase minerals, resulting in significant variations in lower-mantle rheological behavior depending on the quantity and degree of interconnectivity of the weak phase. The resulting effective bulk rock viscosity decreases with accumulating strain when the weaker Fp minerals become elongated and eventually interconnected. This implies that strain localization may occur in Earth’s lower mantle, which would in turn influence the pattern of mantle flow and could potentially aid the preservation of compositionally distinct, “hidden” reservoirs. So far, there have been no studies on global-scale mantle convection in the presence of such strain-weakening (SW) rheology.

Here, we present 2D numerical models of thermo-chemical convection in spherical annulus geometry including a new strain-weakening (SW) rheology formulation for lower-mantle materials. This macro-scale SW rheology is based on micro-scale rheological behavior found in prior studies, and combining rheological weakening and healing terms. We determine the effects of SW rheology on the planform of mantle flow, the mixing of chemical reservoirs, and the dynamics of mantle plumes.

We find that, in particular, plume conduits are weakened and act as lubrication channels which allow for the rapid ascent of mantle material. Their thermal anomalies and geometries are significantly different than those of mantle plumes which are not rheologically weakened. Moreover, larger thermochemical piles at the base of the mantle are stabilized by SW rheology, with implications for preservation of chemically-distinct materials over long timescales. Finally, we put our results into context with observations and existing hypotheses on the style of Earth's mantle convection and mixing. Most importantly, we suggest that the new kind of plume dynamics may explain the discrepancy between expected and observed thermal anomalies of deep-seated mantle plumes on Earth.
Deglaciation of the Antarctic Ice Sheet modeled with the coupled solid Earth – ice sheet model system PISM-VILMA
Authors: Albrecht Torsten , Winkelmann Ricarda , Bagge Meike , Klemann Volker
Published: March 2022

The Antarctic Ice Sheet is the largest and most uncertain potential contributor to future sea level rise. Understanding involved feedback mechanisms require physically-based models. Confidence in future projections can be improved by models that can reproduce past ice sheet changes, in particular over the last deglaciation. The complex interaction between ice, bedrock and sea level plays an important role in ice sheet instability with a large variety of characteristic response time scales dependent on the heterogeneous Earth structure underneath Antarctica and the ice sheet dynamics.

We have coupled the VIscoelastic Lithosphere and MAntle model (VILMA) to the Parallel Ice Sheet Model (PISM v2.0, www.pism.io) and ran simulations over the last two glacial cycles. In this framework, VILMA considers both viscoelastic deformations of the solid Earth by considering a three-dimensional rheology and a gravitationally self-consistent mass redistribution in the ocean by solving for the sea-level equation. PISM solves for the stress balance for a changing bed topography, which is updated in 100 years coupling intervals and which can directly affect ice sheet flow and grounding line dynamics.

Here, we show first results of coupled PISM-VILMA simulations scored against a database of geological constraints including sea level index points. We discuss sensitivities of model parameters and climatic forcing in preparation for a larger parameter ensemble study. This project is part of the German Climate Modeling Initiative PalMod.

 
The role of ionospheric convection in shaping the auroral oval
Authors: Gasparini Sara , Laundal Karl M. , Reistad Jone P. , Ohma Anders , Hatch Spencer , Elhawary Reham
Published: March 2022

The solar wind’s embedded interplanetary magnetic field (IMF) impinging on the Earth’s magnetosphere has an impact on the terrestrial environment. The primary mechanism which allows for direct interaction between the solar wind and the terrestrial environment is magnetic reconnection on the Earth’s dayside between the IMF and the Earth’s magnetic field. Changes in the IMF result in a change of magnetic reconnection rates at the Earth’s dayside leading to changes in the auroral oval morphology/topology. The auroral oval is rather dynamic, and its variability is currently not well understood. We hypothesise that much of this variability is due to variations in ionospheric convection. We interpret its temporal and morphological variability in terms of ionospheric convection and dayside and nightside reconnection rates, (i.e., the "expanding/contracting polar cap" paradigm). Dayside reconnection is responsible for opening magnetic flux on the dayside and initiating ionospheric flows whereas nightside reconnection is ensuring closure of open magnetic field lines. In this study we infer convection patterns with SuperDARN (Super Dual Auroral Radar Network) measurements and ground-based magnetometers data (SuperMAG) using a new data assimilation technique. We combine convection flows with auroral precipitation patterns and solar wind parameters to understand the behavior of the auroral oval and the physical mechanisms that drive its dynamical changes. By examining both the dynamic evolution of the ionospheric convection and the corresponding dynamics of the colocated auroral forms seen in global UV images, we investigate to what extent convection can be associated with the changes observed in the large scale auroral boundaries in selected events. 
Video-Imagery Analysis of Aeolian Sand Transport over a Beach
Authors: Baas Andreas
Published: March 2022

Sand transport by wind displays dynamic structure and organisation in the form of streamers (aka ‘sand snakes’) that appear, meander and intertwine, and then dissipate as they are advected downwind. These patterns of saltating grain populations are thought to be initiated and controlled by eddies in the turbulent boundary layer airflow that scrape over the bed surface raking up sand into entrainment. Streamer behaviour is thus fundamental to understanding sand transport dynamics, in particular its strong spatio-temporal variability, and is equally relevant to granular transport in other geophysical flows (fluvial, submarine).

This paper presents findings on sand transport rates and streamer dynamics observed in a field experiment on a beach, by analysing imagery from 30Hz video footage, combined with 50Hz sand transport data from laser particle counters (‘Wenglors’), all taking place over an area of ~10 m2 and over periods of several minutes.

Mapping of streamers and saltation cloud density is compared with fluctuations in sand transport rate measured at the Wenglors. Large-Scale Particle Image Velocimetry (LSPIV) is applied to determine advection vectors that can be matched against in-situ measurements of airflow and sand transport. Analysing video-imagery of aeolian sand transport faces several challenges, however, most notably the difficulties of background subtraction to differentiate the moving streamers from the underlying beach surface.
Experimental investigation of microwave signal scattered by the breaking waves
Authors: Rusakov Nikita , Baidakov Georgy , Kandaurov Alexander , Troitskaya Yuliya , Poplavsky Evgeny , Ermakova Olga
Published: March 2022

The work is concerned with the study of the breaking surface wave impact on the scattered radar signal in laboratory conditions using optical methods for analyzing the state of the water surface.

The experiments were carried out on the reconstructed TSWiWaT wind wave flume of the IAP RAS. The channel is 12 m long, the channel cross-section varies from 0.7 x 0.7 m at the entrance to 0.7 x 0.9 m in the working section at a distance of 9 m. The airflow speed on the axis is 3-35 m/s, which corresponds to the values of the wind speed U10 of 11-50 m/s.

At the beginning of the channel, a wavemaker was installed, operating in a pulsed mode and generating a train of three long waves every 15 seconds. In front of the area under study, an inclined plate was installed under the water, simulating shallow water and stimulating the breaking of waves in the zone of optical and radar measurements. In parallel, wind waves were generated. Due to the design features of the experimental setup, the distance from the beginning of the channel to the inclined plate in the case of optical measurements was 884 cm, and for radar measurements - 781 cm.

Radar measurements were carried out using a Doppler scatterometer operating at a wavelength of 3.2 cm, with the ability to simultaneously receive two direct and two cross-polarizations (VV, HH, VH, HV). The dimensions of the observation window on the water surface varied depending on the selected incidence angles (30, 40, 50 degrees). Optical measurements were carried out independently of radar measurements using three cameras with a shooting frequency of 50 Hz. Using a specially developed algorithm based on threshold processing of the image brightness, the time dependences of the fraction of breakers on the area of the investigated water surface during the passage of a train of three waves were calculated.  Due to the different configuration of the experiments, the data of radar and optical measurements are separated in time, their synchronization was performed using correlation analysis.  Comparison of the data made it possible to find that, on cross-polarization, the received power monotonically increases with an increase in the fraction of breakers, while on direct polarization, the change in power remains within the values observed during collapses of wind waves. Further comparison of the values of the radar cross-section of the water surface and the relative area of the wave breaking will make it possible to determine the influence of the breaking on the formation of the scattered signal.

This work was supported by the Russian Science Foundation (RSF) project No. 21-17-00214.
GNSS Satellite Force Modeling: Unveiling the Origins of the Galileo Y-bias
Authors: Dilssner Florian , Gonzalez Francisco , Schönemann Erik , Springer Tim , Enderle Werner
Published: March 2022

The Y-bias as present on most global navigation satellite system (GNSS) spacecraft plays an important role in precise orbit determination and prediction. Accurate knowledge about the Y-bias and its temporal variability is particularly relevant for the Galileo system in order to fulfil its once-in-a-lifetime station-keeping maneuver requirements. Despite the widely recognized importance, however, no consensus has been reached on the physical mechanism that is responsible for the Y-bias. In this presentation, we shed light on the origins of the Galileo Y-bias using temperature and attitude data series from spacecraft telemetry to analytically determine Y-bias time histories for different Galileo satellites. We start by calculating the thermal radiation pressure forces generated by the two surface radiators at the main body's +Y and -Y sides of satellite GSAT0204 over a period of five years, from the activation of the spacecraft's search and rescue payload in early 2016 to the deactivation of its navigation payload in December 2017 and beyond. The net force from both radiators yields the Y-bias as it evolves over time, with some striking discontinuities due to abrupt changes in the amount of dissipated heat after the payload units have been turned on or off. Comparison against empirical Y-bias estimates from satellite laser ranging long arc analyses proves the correctness of our Y-bias model. In addition, we report on yearly variations in the Y-bias acceleration of GSAT0101 between -0.10 nm/s² and +0.05 nm/s², leading to a secular increase in the satellite orbit's semi-major axis since January 2016. Yaw error measurements from the spacecraft's fine sun sensor (FSS) spanning 2016-2019 provide compelling evidence that these Y-bias variations originate from an attitude-related mispointing of the satellite's solar panels by a few tenths of a degree. Least square fitting of the FSS measurements led to the development of a refined yaw model for GSAT0101. As a result of this new model, estimates of the Y-bias parameter are significantly reduced in magnitude and less dependent upon the position of the sun relative to the orbit plane. Overall, our analyses provide the first hard evidence that the Galileo Y-bias is primarily of thermal origin and, contrary to popular belief, that solar panel orientation errors only play a secondary role. The implications for precise orbit determination will be discussed. In addition, our results confirm the long-standing hypothesis that Y-bias and solar panel orientation error are linearly related.
Correlating Contamination Levels of Potentially Toxic Elements with Foraminiferal Distribution Patterns in Lagos Lagoon (Nigeria)
Authors: Sariaslan Nisan , Martínez-Colón Michael , Council Ivory S. , Kolawole Tesleem O. , Langer Martin R. , Fajemila Olugbenga T.
Published: March 2022

Sediments across Lagos Lagoon have been sampled and analyzed to investigate the extent and distribution of Potentially Toxic Elements (PTEs). The bioavailable fraction of PTEs have been evaluated to explore the relationship between PTE concentration and the spatial distribution, composition, abundance, and species richness of benthic foraminifera biotas. The sediments have been found to show a wide range reflecting a diffuse contamination, where Contamination and Enrichment Factor suggest low to extremely polluted sediments. Our survey of the benthic foraminifera inhabiting Lagos Lagoon revealed diverse assemblages of benthic taxa, species-specific distribution patterns, gradients of species richness and abundance, and a disjunct distribution of agglutinated and hyaline-perforate/porcelaneous taxa along a pronounced salinity gradient. All PTE total concentrations have been shown to positively correlate with mud and Total Organic Carbon (TOC) and two of the most abundant agglutinated taxa, Ammotium salsum, and Trochammina sp. 1, according to our correlation matrix analysis. Moreover, both species display significant positive correlations with CrF4-CoF2-F3-F4-total-CuF4-total-NiF3-F4-total-AlF4-total-FeF3-F4-total-ZnF3-F4-total. On the other hand, both foraminifers correlate negatively with PbF4-SeF3-Setotal. The overall significant positive correlation of these PTEs suggests that they behave as micronutrients when complexed with organic matter. No significant positive correlation with none of the PTEs in any fraction was found for neither species richness nor for the most abundant hyaline perforate species (Ammonia aoteana). Some PTE fractions were found to correlate either positively or negatively with individual foraminifera species, suggesting that they function as either micronutrients and/or stressors. The resulting Contamination Factor of the PTE total concentrations shows that only a few sample sites can be classified as “moderately” polluted for Cr, Zn, and Cu, and that all sampled sites are classified as “highly polluted” for Se. The highest concentrations for Cr, Cu, Ni, and Zn were found towards the industrialized western part, an area that is characterized by moderate to high diversity but low abundances of benthic foraminifera.

 
Quantitative comparison of seismoelectric laboratory data with numerical modelling based on electrokinetic theory
Authors: Martins Gomes Victor , Brito Daniel , Garambois Stephane , Bordes Clarisse , Barucq Helene
Published: March 2022

When a seismic wave propagates in a wet porous medium, the transient movement of ions inside the pores will give rise to an electromagnetic (EM) wavefield that accompanies the seismic field. This coseismic field, due to electrokinetic phenomena, carries valuable information about the fluid content and the petrophysical properties. Additionally, when the seismic disturbance reaches an interface, where either the petrophysical, the fluid, or both properties change, another EM wave will be generated, due to the electric charge imbalance across the interface. This second wave propagates independently and carries information about the discontinuity where it was generated. While the first contains mainly information about the physical properties around the receivers, the second is a noteworthy alternative to near surface exploration since it can be detected away from the interface generating it. Moreover, it can detect layers thinner than what the seismic resolution allows, being specially sensitive to fluid changes. Seeking to extend the understanding of seismoelectric phenomena we developed a experimental setup able to detect both seismo-EM effects. To record seismic displacement we use a laser vibrometer and for the EM signals we measure (approximate) absolute potentials using stainless steel electrodes. We study two cases, the first is a saturated homogeneous sand, and the second includes a thin sandstone layer buried inside the sand. The experimental dataset confirms that measuring absolute potentials allows the interface-generated EM wave to be detected by receivers ten wavelengths away from its origin, whereas it is hardly detected when using dipolar arrays (which are common practice) located near the layer. Using a benchmarked numerical code we quantitatively compare theoretical predictions and experimental data, finding that seismo-EM amplitudes agree within a factor of 2. While this result validates the seismoelectric theory that the code is based on, it also opens the path for future upscaling of the experimental workflow used in the comparison and show that absolute potentials should be systematically measured. Finally, our study supports that thin layers can be detected by this method.
Late Holocene climate changes in the southern Yemen region based on a high-resolution biomarkers and ostracods record from the paleo-lake Gayal el Bazal
Authors: Parth Shah , Yadav Ankit , Mazzini Ilaria , Russell James , Waldmann Nicolas
Published: March 2022

Gayal el Bazal is a karstic paleo-lake situated on the southern margin of the Arabian Desert, a climatic sensitive zone that responds to small-scale hydrological changes modulated by the Indian Ocean monsoon system. High-resolution biomarker and ostracods assemblages obtained from a 3.25 m composite core from the lake provides insight into past environmental changes for the last 1200 years. Moreover, variations in the sediment lithology and geochemical proxies from the lake core suggests fluctuations related to the dominating precipitation regime. Through data amalgamation, we identified two globally recognized events: the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). The study shows that the n-alkane homologues exhibited different distribution modes during these different climatic stages, indicative of variation in the sources of organic matter in response to changes in the regional hydrological conditions. The climate reconstruction based on the n-alkane proxies (Paq, TAR) suggests a higher abundance of longer chain length carbons (C27-C35) derived from higher plants of the watershed during the MCA, indicating wetter conditions in the region. Furthermore, ostracods assemblage data also revealed Paracypretta amati abundance increases during the MCA and decreases during the LIA. The arid phase of LIA is also marked by gypsum formation and dust deposition and is consistent with evidence and theory for weakened summer monsoons during intervals of northern hemisphere cooling. Overall, this study aims to provide a better insight of the monsoon variability and to help to understand the role of northwards migrations of the Intertropical Convergence Zone (ITCZ) vis-à-vis monsoonal dynamics in the region.
Using VIS-NIR reflectance spectroscopy and magnetic susceptibility to assess soil redistribution due to erosion
Authors: Klement Aleš , Fér Miroslav , Kodešová Radka , Nikodem Antonín , Zádorová Tereza , Penížek Vít
Published: March 2022

Soil degradation due to water erosion is one of the greatest problems of agricultural soils worldwide. To be able to map the extent of soil degradation and consequently propose actions for soil improvement, an effective approach is needed. Soil organic carbon (SOC) content and its time fluctuations is one of the key features characterizing the given site and occurring processes. It is widely accepted as the main soil quality indicator and therefore can be used for soil degradation assessment. Traditional laboratory techniques (dry combustion, wet oxidization) of soil organic carbon determination are usually labor intensive and time consuming, which means they are not suitable for large sample collections (e.g., large areas or continual monitoring). Therefore, there is a need for fast, reliable, and cost-effective techniques. Our previous study documented that the VIS-NIR reflectance spectroscopy and magnetic susceptibility can be a very efficient tool for SOC mapping with the Chernozem (a loess region of South Moravia, Czech Republic) areas heavily affected by water erosion. Within this area colluvial soils with up to an about 4 m deep humus enriched horizon were developed. Distribution of soil properties within the colluvial soil profiles at several positions were evaluated using standard and novel methods to distinguishing the different sedimentation phases and understanding colluvial soil formation. The same study was also performed in another two locations (Cambisol and Luvisol areas). Results showed that while both methods could be used for estimation of SOC distribution within the soil profiles in the Chernozem area, in the other two areas the VIS-NIR reflectance spectroscopy method was less accurate and magnetic susceptibility was inaccurate because there was no correlation between SOC and content of ferrimagnetic particles.

 

Acknowledgement: Study was supported by the Czech Science Foundation, project "Pedogenesis of colluvial soils: a multidisciplinary approach in modeling the dynamics of development in the soil-landscape environment" (No. 21-11879S) and also by the European Structural and Investment Funds, projects NutRisk (No. CZ.02.1.01/0.0/0.0/16_019/0000845).