bluuebunny/crossref_metadata_2025 huggingface dataset:
Using plant trait data to extend a theory of global ecosystem function
Authors: Peng Yunke , Bloomfield Keith , Cernusak Lucas , Domingues Thomas , Lloyd Jon , Prentice Iain Colin
Published: March 2020

There remains large uncertainty about the global exchanges of carbon between the atmosphere and the terrestrial biosphere under different environmental change scenarios. Ecosystem and Earth system models rely on photosynthetic capacity (maximum rates of carboxylation (Vcmax) and electron transport (Jmax)) to simulate carbon assimilation. Photosynthetic capacity has been related to environmental and climatic constraints, but also to leaf and soil nutrients. Views differ on which are more important.

We assembled and analysed a large dataset of global observations of photosynthetic and other leaf traits. Photosynthetic capacity was best predicted based on optimality hypotheses. Vcmax standardized to 25°C (Vcmax25) was proportional to light availability, and increased towards colder and drier environments – as expected due to the greater biochemical investment required at lower temperatures, or when stomata are more closed. The ratio Jmax25/ Vcmax25 declined with growth temperature (also predicted). However, theoretical predictions slightly underestimated Vcmax at high growth temperatures, and overestimated it at low growth temperatures. This bias might be due to the difference between leaf and air temperatures.

Statistical models for photosynthetic capacity (all species, and site means) overestimated Vcmax in low-P leaves. Analysis of a subset of the data showed that leaf P tends to increase with measured soil P. A relationship of model bias to leaf N appears in the all-species analysis – perhaps reflecting a correlation of Vcmax, leaf N and light levels within communities. But site-mean analysis showed no such bias, and leaf N showed no relationship to the soil C:N ratio. These results support a previously noted dependency of Vcmax on P availability; but not the control of Vcmax by N availability that has been assumed in many models.
Relating changes in seabed properties and retreating glacier fronts in West-Antarctic fjords.
Authors: Van Landeghem Katrien , Retallick Kate , Howard Floyd , Barnes Dave , Jenkins Stuart , Sands Chester , Muñoz-Ramirez Carlos , Scourse James
Published: March 2020

Retreating marine terminating glaciers influence the rate at which larger ice mass is lost, and thus the rate at which global sea levels rise. About 90% of the circa 240 glaciers terminating in fjords along the West-Antarctic Peninsula coastline are retreating. This happens at variable rates as these fjords have internal feedback mechanisms with e.g. the oceanographic make-up of the bay and the geology / geomorphology of the local hinterland. The NERC-CONICYT funded “ICEBERGS” project is a UK-Chile research collaboration to assess the effects of ice loss and deglaciation on benthic marine ecosystems in Antarctica. Three West-Antarctic fjords where glaciers have been consistently retreating in the last few decades were investigated: Marian Cove (King George Island), Börgen Bay (Anvers Island) and Ryder Bay (Adelaide Island). As part of this project, we monitored the changes in seabed bathymetry and backscatter intensity as a signature of past and on-going ice flow and ice retreat. Together with sediment analyses, the data provide insights in glacial landscape development and on sediment accumulation / seabed erosion rates. We also managed to insonify parts of the changing glacier ice fronts, detailing the grounding zones at the seabed. At the time of abstract submission, the third of three surveys was just underway. In this presentation we will explore the preliminary search for spatial and temporal relationships between grounded ice advance and retreat, undercutting of the grounded glacier terminus, sediment discharge, ice berg scouring, glacial landscape development and mass waste deposits. Our direct time-lapse observations of the seabed and glacier fronts of different fjord systems will help us understand how the local fjord environments define the dynamics of the retreating glaciers they host, whilst the results help elucidate the impact of that deglaciation on the newly emerged seabed and the fast-growing ecosystem it supports. Understanding the ice-filled fjord dynamics in the present-day and in the recent past will also help interpretations made from data representing these environments in the distant past.
Using Phase Annealing to generate surrogate discharge time series
Authors: Anwar Faizan , Bárdossy András
Published: March 2020

Phase randomization and its variants such as the Amplitude-adjusted (AAFT) and the Iterative amplitude adjusted (IAAFT) Fourier transform are used to check statistical significance of a given hypothesis and/or to generate time series that are similar to a reference in some statistical sense. These methods have the drawback of producing incorrect dependence structures e.g. empirical copula density, asymmetries and entropies. Recently, another form of such methods, “Phase Annealing”, was introduced, giving a possibility to generate n-dimensional realizations of a process under given constraint(s). The main concern using this method is the selection of correct objective function(s).

Here we show discharge time series generation using Phase Annealing with new objective functions. This allowed us to generate time series that are much longer than the reference, which in turn was helpful in establishing better distributions of floods.

We also show the generation of discharge time series at multiple locations that have the correct spatio-temporal dependences among all the series. Using the results, we generated full distributions of simultaneous extremes at observation locations.

Further uses may include clustering catchments that are likely to bring floods together and reliability analysis i.e. simulating distributions of failures for a system with many dependent/independent components. Drawbacks using this method are also shown.
Laboratory study of hydraulic refracturing possibility
Authors: Turuntaev Sergey , Zenchenko Evgeny , Zenchenko Petr , Trimonova Maria , Baryshnikov Nikolai
Published: March 2020

The results of laboratory experiments will be considered, that are carried out in a laboratory setup that differs from the standard ones in the shape and size of the test samples. The setup consists from two disks and wide ring between them, which form a high-pressure chamber, and it is capable to produce true 3D stresses in the samples. Laboratory experiments are performed on saturated artificial porous samples created according to similarity criteria using gypsum with Portland cement added as a model material. The samples are created directly in the high-pressure chamber and have the forms of disks with diameters of 430 mm and heights of 70 mm. This sample is saturated with water gypsum solution and loaded with vertical and two horizontal stresses using special chambers. In the upper, lower and lateral parts of the installation there are pressure sensors, ultrasonic transducers and generators. The first fracture was created by viscous fluid (mineral oil) injection through a cased borehole preliminary created in the center of the sample. After the first fracturing, the principal maximal and minimal stress axis orientations were changed, and refracturing was carried out. We failed to create two fractures oriented along the borehole, but we succeeded in creation one fracture perpendicular to the borehole and the second fracture along the borehole. Comparison of the ultrasonic wave amplitude changes during the fracturing with the fracturing pressure variations allowed us to distinct the fracture propagation and the fracture fill-up by the fracturing fluid. It was also found that for an adequate calculation of the minimum compressive stresses from the characteristic parameters ​​of the pressure change in the well, it is necessary to take into account the plastic properties of the rock, the diffusion of the fluid pore pressure in the vicinity of the well and the hydraulic fracture, the lag of the filling of the fracture with the fluid.
Rayleigh wave ellipticity measurements in the North Tanzanian Divergence (Eastern African Rift)
Authors: Parisi Laura , Berbellini Andrea , Mai P. Martin
Published: March 2020

Rayleigh wave ellipticity depends, in theory, only on the Earth structure below a seismic station, offering the advantage of a “single-station” method to infer crustal properties. Therefore, ellipticity measurements can be used to construct pseudo 3-D shear velocity models of the earth structure using even seismic stations that did not record simultaneously.  

Based on that, we carried-out ellipticity measurements by using teleseismic waveforms recorded by the OPS seismic network we deployed at the western flank of the North Tanzanian Divergence between June 2016 and May 2018, covering 17 sites. We then expanded our measurements on the waveforms recorded by the adjacent CRAFTI seismic network from January 2013 and December 2014, available on IRIS, which comprised more than 30 sites. 

While the OPS network covers the transition between the Tanzania Craton and North Tanzanian Divergence, the CRAFTI network is entirely contained in the North Tanzanian Divergence. Therefore, the imaging that can be obtained by integrating the two asynchronous passive seismology experiments will help to better understand the dynamics of this segment of the eastern branch of the Eastern African Rift.

Preliminary results show heterogeneity structure that are in agreement with previous tomographic studies based on ambient noise cross-correlation and body-waves arrival-times. In regions where previous seismological studies are not available, results match the known geological structure of the transition between the Tanzanian Craton and the North Tanzanian Divergence. This demonstrates that measurements of ellipticity can be a useful and integrative tool for earth structure imaging, especially at the edges of the active rifts where the seismicity is scarce.
Optimization of SIMS-based stable isotope measurements with regression diagnostics
Authors: Schobben Martin , Polerecky Lubos
Published: March 2020

Stable isotope measurements with secondary ion mass spectrometry (SIMS) have become an increasingly popular tool for Earth scientists to investigate natural phenomena such as biomineralization and sediment diagenesis, or to track the fate of labelled tracers in stable isotope probing experiments. The random nature of secondary ions emitted from a sample is described by Poisson statistics, which can be used to predict the precision of SIMS measurements under ideal circumstances (e.g., the predicted standard error can be deduced from the total counts of secondary ions). However, besides this fundamental source of imprecision, real SIMS measurements are additionally affected by other factors such as sample heterogeneity, instrument instability, the development and geometry of the sputter pit, and sample charging. Although some of these biases can be avoided by proper instrument tuning and sample documentation (e.g. T/SEM to characterise the textural properties of a rock sample) prior to SIMS measurement, factors such as instrument instability or sample heterogeneity can never be fully eliminated. Here we propose a data treatment procedure capable of identifying the underlying cause of the loss of precision due to instrument instability and sample heterogeneity. The reduced chi-squared statistic, which compares the predicted precision with the precision derived from descriptive statistics, is traditionally used to flag problematic measurements but without pinpointing the cause of precision-loss. We constructed a more sensitive method by the application of regression diagnostics, which calculates the influence of outliers on the regression model, and thus allows for augmentation of the raw count data. Simulations show that the recalculated descriptive and predictive statistics deviate from the original precision along trajectories specific to sample heterogeneity and instrument instability. Thus the proposed diagnostic procedure increases information yield of SIMS isotope measurements.
Potential impacts of anthropogenic forcing on the consecutive 2018-19 droughts in the central Europe
Authors: Hari Vittal , Rakovec Oldrich , Hanel Martin , Markonis Yannis , Kumar Rohini
Published: March 2020

The damages caused by climate extremes to socio-economy and environment is unprecedented during the recent decades, and it causes even more damage when the climate extremes occur in consecutive years. Since the starting of this Century, Europe has witnessed a series of extreme droughts (2003, 2010, 2015, 2018-19) with substantial socioeconomic and ecological losses. This study, with the help of long term data inventory starting from 1766-present, evaluates the occurrence of consecutive two-year droughts using Standardized Precipitation Index (SPI) and Standard Precipitation-Evaporation Index (SPEI) during the vegetation period. Although, the 2018 drought is reported in many of the recent studies, 2019 also suffered a huge rainfall deficit together with rising atmospheric temperature. This indicates an increasing evapotranspiration rates, which may intensify the existing drought conditions that originally developed from rainfall deficits. These effects are further noticed in terms of widespread reduction in the overall vegetative development during 2018-2019.

Considering this impact, we evaluate 2018-19 droughts in terms of both SPI and SPEI and compare its extent with the extreme hot drought of 2003 to place these ongoing droughts within a climatological context. The average severity of the combined two-year drought event (2018-19) is comparable to that of the 2003 drought. However, for the 2003 event, the drought recovered during the proceeding year, which was not the case for the year 2018-19, which is evident from decline in vegetation development dynamics. Furthermore, the analysis with consecutive droughts during 2018-19 in Central Europe shows that it is a very rare event with a return period of over 200 years; and therefore can be considered as one of the most severe droughts in Europe since 1766. 

Using a suite of climate model simulations from CMIP-5 (N=12), we detected an important and potential role of human-induced climate change in increasing the risk of occurrence of the consecutive droughts over central Europe. Here, with the implementation of the fraction of attributable risk (FAR), we show the signifying role of human influence (or anthropogenic forcing) in modulating the consecutive year droughts. Furthermore, these events in the future projection of climate models suggest an increasing frequency in the latter part of 21st century.
Empirical metric for uncertainty assessment of wind forecasting models in terms of power production and economic efficiency
Authors: Pettas Antonios-Gennaios , Mavritsakis Panagiotis , Tsoukalas Ioannis , Mamassis Nikos , Efstratiadis Andreas
Published: March 2020

As made for most of renewable energy sources, wind energy is driven by highly uncertain and thus unpredictable meteorological processes. In the context of wind power scheduling and control, reliable wind predictions across scales is a challenging problem. However, since the generation of wind energy is, in fact, a nonlinear transformation of wind velocity through the power curve of each specific turbine, the errors in meteorological predictions have different impacts on wind power forecasts. It is well-known that for quite a large range of wind velocity values, the wind power production is either zero or constant, thus independent of the individual wind velocity value. This interesting feature allows for ensuring better predictions of the output, i.e. the energy production, with respect to input, i.e. wind velocity. Taking advantage of this, we present a hybrid stochastic framework for multi-step ahead wind velocity predictions and their evaluation by means of power production and economic efficiency. The methodology is tested for different wind regimes and different layouts of wind turbine systems, emphasizing to mixing of different turbine types, which allows for minimizing uncertainties. Finally, we investigate the use of this index in the technical and operational optimization of wind energy systems.
Severe perturbations of the marine biosphere following the Chicxulub impact
Authors: Feulner Georg , Brugger Julia , Hofmann Matthias , Petri Stefan
Published: March 2020

Among the "big five" mass-extinction events during the Phanerozoic, the end-Cretaceous extinction 66 million years ago is particularly well known because it marks the demise of the non-avian dinosaurs. Evidence for the Chicxulub impact as the primary cause of this mass extinction has been accumulating over the past four decades, but there are still many open questions regarding the detailed course of events.

Building on our earlier modelling results demonstrating strong global cooling due to sulfate aerosols formed in the wake of the Chicxulub impact (Brugger, Feulner & Petri 2017, Geophys. Res. Lett., 44:419-427), we here explore the response of the ocean in more detail. Specifically, we added a marine biogeochemistry module to a coupled atmosphere-ocean model to investigate the effects of the impact on ocean geochemistry and primary productivity.

We find that the formation of stratospheric sulfate aerosols leads to a marked decrease in annual global mean surface air temperatures by at least 26°C in the coldest year after the impact, returning to pre-impact temperatures after about one century. The strong surface cooling induces vigorous ocean mixing that leads to changes in oxygen distributions and nutrient availability. Due to the darkness, marine net primary productivity essentially shuts down in the first years after the impact. Once the light returns, however, we find a significant increase in primary productivity caused by a surge in nutrient availability, both due to upwelling in the ocean and delivery by the impactor. These strong perturbations of the marine biosphere further support the notion that the impact played a decisive role in the end-Cretaceous mass extinction.
Quest for Fluid Flow along the Gloria Fault – First results of R/V Meteor expedition 162
Authors: Hensen Christian , Terrinha Pedro , Duarte Joāo , Kaul Norbert , Schmidt Mark , Schmidt Christopher , Batista Luis , Magalhāes Vitor , Liebetrau Volker , Kipfer Rolf , Hübscher Christian , Lever Mark
Published: March 2020

Vast areas of the deep ocean floor are still insufficiently explored with respect to tectonic processes, exchange processes between the lithosphere and the ocean, and potential deep chemosynthetic energy sources for life. Transform faults and fracture zones, which are dominant seafloor morphological features in the abyssal ocean, deserve specific attention in this regard as they provide potential pathways for fluid recycling. One of them is the Gloria Fault, a unique feature in the Central North Atlantic. It has been the source of large magnitude earthquakes (namely the 1941, M8.4, the second largest instrumental earthquake on a fracture zone) and is a special case of a plate boundary, corresponding to the transform reactivation of an old oceanic fracture zone. Seismic refraction has shown an anomalous layer between normal lower crust and uppermost mantle, possibly a 4 km thick layer of hydrated mantle. We present first results of RV Meteor cruise M162 (March-April 2020) dedicated to the groundtruthing of potential fluid emanation sites.
Probabilistic Tsunami Hazard Analysis: High Performance Computing for Massive Scale Monte Carlo type Inundation Simulations
Authors: Gibbons Steven J. , Díaz Manuel J. Castro , Glimsdal Sylfest , Harbitz Carl Bonnevie , Lorenzino Maria Concetta , Lorito Stefano , Løvholt Finn , Nazaria Massimo , Romano Fabrizio , Sánchez Jorge Macías , Selva Jacopo , Tonini Roberto , Vida José Manuel González , Volpe Manuela , Vöge Malte
Published: March 2020

Probabilistic Tsunami Hazard Analysis (PTHA) is an approach to quantifying the likelihood of exceeding a specified metric of tsunami inundation at a given location within a given time interval. It provides scientific guidance for decision making regarding coastal engineering and evacuation planning. PTHA requires a discretization of many potential tsunami source scenarios and an evaluation of the probability of each scenario. The classical approach of PTHA has been the quantification of the tsunami hazard offshore, while estimates of the inundation at a given coastal site have been limited to a few scenarios. PTHA, with an adequate discretization of source scenarios, combined with high-resolution inundation modelling, has been out of reach with existing models and computing capabilities with tens to hundreds of thousands of moderately intensive numerical simulations being required. In recent years, more efficient GPU-based High Performance Computing (HPC) facilities, together with efficient GPU-optimized shallow water type models for simulating tsunami inundation, have made a regional and local long-term hazard assessment feasible. PTHA is one of the so-called Pilot Demonstrators of the EC-funded ChEESE project (Center of Excellence for Exascale Computing in the Solid Earth) where a workflow has been developed with three main stages: source specification and discretization, efficient numerical inundation simulation for each scenario using the HySEA numerical tsunami propagation model, and hazard aggregation. HySEA calculates tsunami offshore propagation and inundation using a system of telescopic topo-bathymetric grids. In this presentation, we illustrate the workflows of the PTHA as implemented for HPC applications, including preliminary simulations carried out on intermediate scale GPU clusters. Finally, we delineate how planned upscaling to exascale applications can significantly increase the accuracy of local tsunami hazard analysis.

This work is partially funded by the European Union’s Horizon 2020 Research and Innovation Program under grant agreement No 823844 (ChEESE Center of Excellence, www.cheese-coe.eu).
Groundwater-borne phosphorus import to eutrophic Lake Arendsee (Germany)
Authors: Lewandowski Jörg , Meinikmann Karin , Hupfer Michael
Published: March 2020

Until recently lake eutrophication was generally associated with phosphorus loads of surface inflows, surface runoff, direct sewage discharge, atmospheric deposition, bathers, waterfowls or other well visible nutrient sources. On the contrary, phosphorus (P) imports by groundwater were systematically disregarded because P was considered immobile in aquifers. This applies also to Lake Arendsee where we started our research about the relevance of lacustrine groundwater discharge (LGD) a decade ago. Lake Arendsee is a 50 m deep, monomictic lake in north-eastern Germany; the lake suffers intense eutrophication problems. We quantified P loads of groundwater to Lake Arendsee using volume fluxes of LGD and near-shore measurements of groundwater P concentrations at a high spatial resolution. Results have shown that LGD accounts for about 50% of the overall external P load, thus fueling the eutrophication of the lake. We assume that both, ancient sewage pits and leaking sewer pipes are major sources of the extremely high P concentrations in the aquifer (above 4000 µg/L). Now, after the renewal of many sewer pipes we present a long-term data set (last decade) of P concentrations close to the groundwater-lake interface. Groundwater is still the major source of the high P concentrations of 180 µg/L in the lake.
Simultaneous retrieval of the lunar solid body tide and topography from laser altimetry
Authors: Thor Robin , Kallenbach Reinald , Christensen Ulrich , Gläser Philipp , Stark Alexander , Steinbrügge Gregor , Oberst Jürgen
Published: March 2020

The Moon is periodically deformed by the tidal forces exerted on it by the Earth and the Sun. The tidal Love number h2 describes the magnitude of the radial component of these deformations at the monthly frequency, which have an amplitude of up to ∼10 cm. Like the potential Love number k2, h2 depends on the density and rheological properties of the materials in the lunar interior and their distribution. We analyze > 3.6 · 109 measurements of the Lunar Orbiter Laser Altimeter (LOLA) obtained during the 27-month circular orbit phase of the Lunar Reconnaissance Orbiter (LRO) at 50 km altitude, when LOLA reached global coverage. We simultaneously invert these observations for the Love number h2 and a global topographic model. The topography is parametrized as an expansion in 2D cubic B-spline basis functions, which are defined on a global equirectangular grid. This parametrization is more computationally efficient than an expansion in spherical harmonics, but still allows for a high smoothness. To deal with data gaps, we constrain the solution by minimizing the second derivative of the topography. We find that the h2 solution depends on the choice of resolution of the equirectangular grid. We determine the accuracy for each investigated resolution (from 6 km to 1 km at the equator) from a Monte Carlo simulation using 100 synthetically generated sets of observations. The topographic signal in the synthetic data follows a power law extrapolated from the real lunar topography. At large scales, the topography is generated using a spherical harmonic expansion, at smaller scales it is generated using Gaussian process regression. Finally, we use the inverse of the root-mean-square h2 obtained from the Monte Carlo simulation as weights for determining a weighted mean of the h2 results for different grid resolutions. The final result of h2 = 0.0386 ± 0.0022 agrees within one standard deviation with a previous result obtained from the same data, but utilizing crossover points of LOLA profiles. This validates the method of simultaneous inversion for tides and topography, especially with regard to future laser altimeter experiments at other planetary bodies, such as Mercury and Ganymede. However, our result also confirms a discrepancy between laser altimeter measurements of h2 and the k2 result of the Gravity Recovery and Interior Laboratory (GRAIL) mission, which needs to be resolved through better modelling of the lunar tidal response.
The role of precipitation in hydrological model uncertainty
Authors: Bárdossy András , Kilsby Chris , Anwar Faizan , Wang Ning
Published: March 2020

Rainfall-runoff models produce outputs which differ from observations due to uncertainties in process description, process parametrization, uncertainties in observations and changing spatio-temporal variability of input and state variables. Traditionally, attention has been focused mostly on process parameters to quantify runoff uncertainty using e.g. GLUE.

Here we have focused on the role of precipitation uncertainty relating to discharge. For this purpose, we used an inverse model approach. We generated time series of daily precipitation with high spatial resolution  using a modified version of Random Mixing and the Shannon-Whittaker interpolation to improve simulated runoff using the SHETRAN (physically-based) and HBV (conceptual) models, both spatially distributed for various sub-catchments of the Neckar River in Germany.  HBV was initially calibrated using interpolated precipitation, while SHETRAN uses pre-defined parameters. The modelling goal was to find a spatio-temporal series of precipitation which improved the predicted runoff,  under the constraints that the precipitation values be the same at the measurement locations and share their spatial variability with the observations at a given step. Care was taken to select subsequent days for improvement such that the previously improved step considered the effect of the previous steps.

We asked the questions: i) does improving precipitation inputs for one sub-catchment bring runoff improvement for the others? ii) Can the improved precipitation using SHETRAN be used for HBV and still get runoff improvements as compared to the interpolated precipitation and vice versa?

Results showed that overall runoff errors were reduced by 40 to 50% for all sub-catchments. For the peaks, a reduction of 70 to 90% was observed. As compared with the interpolated fields, new fields showed similar overall distribution but different details at finer spatial scales. Swapping improved precipitations between SHETRAN and HBV showed improvement as compared with the discharge from interpolated precipitation.
Remote sensing of water storage variation in Dinaric karst
Authors: Vidmar Ines , Brenčič Mihael
Published: March 2020

Having shown potential for long-term monitoring of terrestrial water variation, satellite data from GRACE (Gravity Recovery and Climate Experiment) and its successor GRACE-FO (Follow-on) operating from 2002 could provide a cost-effective approach to water resource management in regions with scarce ground monitoring networks or in regions where representative in-situ monitoring is difficult to ensure, such as karstic areas. One such example is Dinaric karst, a large karstic aquifer system extending from Italy through Slovenia, Croatia, Bosnia-Herzegovina, Montenegro, Serbia to Albania. There, groundwater storage variation on a regional scale is difficult to infer from existing locally scattered data.

For that purpose, GRACE Level-3 gridded mass concentration terrestrial water storage (TWS) anomaly data was used. Gridded scale factors provided at 0.5° resolution based on land-hydrology models were considered as well. Spatial variability was analysed for the area of Dinaric karst and adjacent areas in Austria and Hungary owing to the resolution of the data. For preliminary validation, GRACE derived liquid water equivalent (LWE) thickness data was compared to data from available ground measurement points.

Based on the 2004-2009 average, the temporal data variability analysed for the period of March 2002 until September 2019 (containing 163 monthly data aggregates) showed variability of 17 cm to 83 cm with the average range amounting to 47 cm in the native GRACE resolution. According to the unscaled data, the variability is 29 cm to 54 cm with a mean of 43 cm. In both cases, higher amplitudes were observed at the southern parts of Dinaric karst. Weak negative temporal trend of water storage anomalies is present in all analysed land grid cells showing the difference of less than 10 cm during the entire measurement period, while the average monthly change in total water storage is around 4 cm.
Anisotropy and Mantle Kinematics in the Eastern Mediterranean Region based on Shear Wave Splitting Measurements, Numerical Models and P-wave Tomography
Authors: Confal Judith , Eken Tuna , Bezada Max , Faccenda Manuele , Saygin Erdinc , Taymaz Tuncay
Published: March 2020

Upper mantle dynamics (e.g. subduction processes, slab roll-back, slab tearing and mantle upwelling) impact eastern Mediterranean region tectonics but a detailed understanding of the acting forces has remained elusive. Further progress requires more accurate measurements not just of the surface kinematics (from GPS) but also of indirect indicators of kinematics throughout the lithosphere and convecting upper mantle from seismology. A robust quantification of the magnitude, location and orientation of seismic anisotropy is a primary source of information to provide constraints on tectonic processes of the formation and evolution of the Anatolian Peninsula and the surrounding regions. Direct shear-wave splitting measurements in the Aegean to revealed mostly NNE-SSW oriented fast polarization directions, perpendicular to the trench and parallel to the mantle flow induced by the roll-back and large time delays (1.15-1.62 s) in the upper mantle. In southwestern Turkey the FPDs are more confusing and probably related to the tearing of the slab in the upper mantle underneath this region. With complex non-steady state 3D geodynamic modelling, the plate movement, mantle flow, anisotropy and SKS splitting parameters for the last 20-30 Ma in the regional subduction system of the eastern Mediterranean and Anatolia were calculated. The model shows that tearing underneath southwestern Turkey, a break-off in the collitional regime of eastern Anatolia as well as the retreat of the slab in the Aegean influence on the strength and direction of the mantle flow and anisotropy. At last a P-wave tomography study of the Eastern Mediterranean region, focusing on the upper mantle with a large data set was done. Since anisotropy is present in the region especially due to the active subduction system, travel times were corrected by including anisotropy as an aprori constraint, from the numerical model and SKS splitting parameters. In isotropic inversions as well as the ones corrected for anisotropy, tears in the northern Hellenic slab, underneath southwestern Turkey and in the Cyprian slab can be seen. Spatially large first order velocity perturbations are stable and similar in isotropic and anisotropy corrected models. But differences up to 2% and small geometrical discrepancies beween the models show the importance of including anisotropy to P-wave tomographies.
Benthic Fe-cycling in fjord sediments enhances the reactivity of glacially derived Fe in Arctic fjords of Svalbard
Authors: Laufer Katja , Michaud Alexander , Røy Hans , Jørgensen Bo Barker
Published: March 2020

Glacial runoff is a significant source of Fe to high-latitude marine environments. The amount and characteristics of glacially derived Fe depends on bedrock lithology, glacial comminution as well as glacier type. Because much of the Fe that comes from glaciers is in the particulate phase or will become particulate once in contact with saline and oxic fjord water, much of the glacial Fe ends up in fjord sediments in close proximity to the glaciers. Within these sediments, the glacially derived Fe undergoes redox-cycling driven by indirect (abiotic reaction with metabolic products, such as hydrogen sulfide) and direct interactions with microorganisms. This redox-cycling has the potential to alter the characteristics of the glacially derived Fe and thereby also its fate, for example if it is buried in the sediment or exported to the water column.

We investigated the amount and reactivity of Fe(III) minerals from the meltwater plume, meltwater streams, icebergs, and sediments at stations with increasing distance from the glacier in three different fjords on the west coast of Spitsbergen, Svalbard. Two of the fjords have large tidewater- glaciers at their head and possess differing bedrock lithology (Kongsfjorden and Lilliehöökfjorden). The third fjord, Dicksonfjorden, has land-terminating glaciers with a bedrock lithology similar to the glaciers at the head of Kongsfjorden, thus providing insight into the impact of glacial retreat on benthic biogeochemical processes. Results from sequential and time-course extractions showed that Fe(III)-mineral reactivity increased with distance from the glacier fronts and decreased with sediment depth at each station in all three fjords. Fe(III)-oxide reactivity from different glacial sources (meltwater plume and iceberg material from tidewater glaciers and meltwater stream material from land-terminating glaciers) differed based on source type and Fe(III) from all glacial sources was generally less reactive compared to surficial sediments distal to the glacier front. While the general trends were the same for all three fjords, based on pore water profiles of dissolved Fe, we found a lower potential for Fe-export to the water column when only land-terminating glaciers were present. This difference highlights that glacial retreat potentially impacts the function of fjord sediments as a source of Fe to the water column. We conclude that glacial runoff supplies large quantities of Fe minerals to fjord sediments, but benthic recycling of Fe by microorganisms transforms the relatively unreactive glacially-derived Fe(III)-oxides to a more reactive form. Microbially driven recycling of reactive Fe(III)-oxides in fjord sediments may play a role in liberating Fe to the water column, predominantly at the mouth of the fjord, and might represent an unquantified source of Fe to Fe-limited marine phytoplankton.
Stochastic comparison of climate model outputs to observed relative humidity fields
Authors: Koumakis Apostolos , Dimitriadis Panayiotis , Iliopoulou Theano , Koutsoyiannis Demetris
Published: March 2020

Stochastic comparison of climate model outputs to observed relative humidity fields

We compare the stochastic behaviour of relative humidity outputs of climate models for the 20th century to the historical data (stations and reanalysis fields) at several temporal and spatial scales. In particular we examine the marginal distributions and the dependence structure with emphasis on the Hurst-Kolmogorov behaviour. The comparison aims to contribute to the quantification of reliability and predictive uncertainty of relative humidity climate model outputs over different scales in a framework of assessing their relevance for engineering planning and design.

 

(Acknowledgement: This research is conducted within the frame of the course "Stochastic Methods" of the National Technical University of Athens (NTUA). The School of Civil Engineering of NTUA provided moral support for the participation of the students in the Assembly.)
PRE-SALT CARBONATES DEFINE A NEW STRATIGRAPHIC MODEL FOR THE MESSINIAN SALINITY CRISIS IN THE CENTRAL MEDITERRANEAN (CALCARE DI BASE Fm, SOUTHERN ITALY)
Authors: Borrelli Mario , Perri Edoardo
Published: March 2020

The Calcare di Base Formation (CdB) mostly (but not exclusively) represents a microbial-mediated carbonate body formed during Messinian and extending for more than 500 km across the Southern Italy, along the accretionary wedges of Calabria and Sicily Apennine chain. In these areas, the microbial carbonates, frequently associated with evaporites, are stratigraphically positioned at the onset of the Messinian Salinity Crisis, pre-dating the massive basinal sulphates and halite deposition in the Mediterranean Circum.

The CdB highlights a wide spectrum of different facies positioned along a prograding carbonate platform to slope system. The inner platform environments are characterized by sabkhas, flood-influenced salinas and peritidal mudflats, rich of planar to domal laminated microbial boundstones associated with evaporites, solution breccias and local cross-laminated detrital carbonates. Megabreccias with plarform-derived clasts and a local siliciclastic input prevail in the upper slope, whereas debris flows and high-density turbidity currents occurred in the lower slope. Basinward, thinly laminated clay and marlstones associated to low-density turbidites characterize the outer-platform.

In a newly-proposed general sequential stratigraphic model of the Messinian Salinity Crisis, the carbonate platform systems represent a high-stand phase of at least two depositional cycles that follow one another. Each cycle begins with a relative sea-level fall responsible for the emplacement of prograding wedges composed of terrigenous and evaporitic deposits that, subsequently, evolve in the deposition of huge deposits of primary basin-fill evaporites. This latter phase is followed by open marine transgression due to relative sea-level rise that predates the development of another carbonate platform.

Despite the intense syn-sedimentary tectonic activity, responsible for huge basinward sediments exportation and fast decreasing in the accommodation space, the defined systems tracts succession has been mainly controlled by eustatic sea-level variations.
The effect of sludge from the wastewater treatment plant of TIARET (ALGERIA) on the growth of turnip "Brassica rapa"; Morphological responses and potential efficacy of phytoremediation
Authors: Soudani Leila , Maamar Benchohra , Chafaa Meriem , Nouar Belgacem , Wiche Oliver
Published: March 2020

Wastewater treatment always produces a large amount of sludge. The different uses of sludge disposal have negative consequences for the environment. Agricultural use may appear in some situations as an alternative to current solutions, both to optimize the degradation and recycling of organic and mineral elements. During this work, on the one hand, we investigated  the effect of sludge on the growth of turnip (Brassica rapa), a plant that tolerates metallic trace elements, especially lead (Liu et al., 2000) and which is considered a model plant in eco-toxicology (Sun et al., 2010), and on the other hand to determine if it has the potential to be included in phytoremediation systems.

The seeds were put in different substrates that contained three sludge doses: 20%, 40% and 60%, mixed with agricultural soil  which contained high levels  of metallic trace elements  exceeding the standard eligible concentration  by AFNOR. compared to  the soil, concentrations of potentiall toxic trace elements in sludge were lower than in soil. Morphological measurements were carried out during two months of planting, showing the positive effect of the sludge on the growth of the plant. The recorded biometric values (height, number of leaves, weight, rotation and height of the bulb) for all doses, far exceed those of control plants (100% soil), with high values recorded in the mixture of soil with  60% sludge.

The concentration of metallic trace elements in the different substrates and also in the leaves and the turnip bulb after two months of planting shows that the plant  accumulates and tolerates hight concentrations of elements  and can therefore be used as a phytoremediator for polluted soils. The highest levels of metal accumulation were observed on the substrate in the  soil mixture  with  60% sludge.

 
Evaluation of global ocean model on simulating deep western boundary current in the Pacific
Authors: Jiang Huichang , Xu Hongzhou
Published: March 2020

As an important branch of the global overturning circulation, the deep western boundary current (DWBC) in the Pacific was poorly understood due to sparse observations. Six state-of-the-art global ocean model outputs were used herein to evaluate their performance for simulating the DWBC in the Melanesian Basin (MB) and Central Pacific Basin (CPB). These model outputs were compared to the historical observations, in aspects of water-mass characteristics, spatial structure and meridional volume transport of the DWBC, and seasonal variation. The results showed that most of the models reproduced the DWBC in the two basins well. Besides OFES with obvious cold and salty biases, the other models had minor deviations of the temperature and salinity in the deep layer. These models can reconstruct the spatial structure of the DWBC in detail and simulate appropriate transports of the eastern branch DWBC, ranging from 6.36 Sv to 8.55 Sv. But the western branch DWBC was underestimated in the models except HYCOM (4.48 Sv). HYCOM performed best for the DWBC with a whole transport of 12.84 Sv. Analysis of the temperature and salinity from Levitus data demonstrates the existence of annual and semi-annual cycles in the deep water of the MB and CPB, respectively, with warmer and saltier water mass in summer and autumn. Overall, the six models have good abilities to simulate the seasonal variations of temperature and volume transport of the DWBC in the Pacific. The seasonal signals probably originated from the DWBC upstream and propagated along its pathway.
How strong will be the following earthquake?
Authors: Gentili Stefania , Di Giovambattista Rita
Published: March 2020

In this study, we have applied to northeastern Italy and western Slovenia medium-low seismicity an algorithm for strong aftershock forecasting we originally developed for medium-high seismicity in Italy (Gentili and Di Giovambattista, 2017). The method, called NESTORE (Next STrOng Related Earthquake), analyzes the seismicity after medium and strong earthquakes, in order to forecast if a subsequent large earthquake (SLE) will follow. A SLE following a main shock can cause significant damages to already weakened buildings and infrastructures, therefore a timely advisory information to the civil protection is of great interest for effective decision-making. We performed the analysis on different time-spans after the mainshock, in order to simulate the increase of information available as time passes during the seismic clusters. NESTORE subdivides the clusters of seismicity into two classes: “A” if the difference in magnitude between the mainshock and the strongest aftershock is lower than 1, and B otherwise. Several statistical features based on time-space and energy evolution of seismicity are analyzed separately and, if they are sufficiently informative for SLE forecasting, they are used for independent decision trees training. The results are merged together by a Bayesian approach, obtaining a time-dependent probability Prob(A) to have an A cluster, i.e. to have at least one SLE. This study is possible thanks to the OGS bulletins, an accurate local catalogue, characterized by low completeness magnitude, compiled by the National Institute of Oceanography and Experimental Geophysics. We tested the method on 1976 highly destructive Friuli cluster (mainshock magnitude 6.5 — the strongest in the last 80 years in the region) and on two small clusters of seismicity in NE Italy in 2019, obtaining encouraging results: 6 hours after the mainshock, for two A clusters NESTORE supplies Prob(A)=98% while for the B one Prob(A)=2%.
Interaction of a mantle plume and a moving plate: insights from numerical modeling
Authors: Brune Sascha , Baes Marzieh , Gerya Taras , Sobolev Stephan
Published: March 2020

The impingement of a hot buoyant mantle plume onto the lithosphere can result in either breaking of the lithosphere, which might results in subduction initiation or in under-plating of the plume beneath the lithosphere. Key natural examples of the former and latter are formation of subduction along the southern margin of Caribbean and northwestern South America in the late Cretaceous as well as the hotspot chains of Hawaii, respectively. In previous studies the interaction of a buoyant mantle plume with lithosphere was investigated either for the case of stationary lithosphere or for moving lithosphere but ignoring the effect of magmatic weakening of the lithosphere above the plume head. In this study we aim to investigate the response of a moving lithosphere to the arrival of a stationary mantle plume including the effect of magmatic lithospheric weakening. To do so we use 3d thermo-mechanical models employing the finite difference code I3ELVIS. Our setup consists of an oceanic lithosphere, mantle plume and asthenosphere till depth of 400 km. The moving plate is simulated by imposing a kinematic boundary condition on the lithospheric part of the side boundaries. The mantle plume in our models has a mushroom shape. The experiments differ in the age of the lithosphere, rate of the plate motion and size of the mantle plume. For different combinations of these parameters model results show either (1) breaking of the lithosphere and initiation of subduction above the plume head or (2) asymmetric spreading of the plume material below the lithosphere without large deformation of the lithosphere. We find that the critical radius of the plume that breaks the lithosphere and initiates subduction depends on plume buoyancy and the lithospheric age, but not on the plate speed. In general, the modeling results for the moving plate are similar to the results for a stationary plate, but the shapes of the region of the deformed lithosphere differ.