bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the sensitivity of open source DEM vs. local high resolution DEM data in tsunami hazard assessment
Authors: Tufekci-Enginar Duygu , Suzen M. Lutfi , Dogan G. Guney , Yalciner Ahmet Cevdet
Published: March 2020

Tsunami simulations using high resolution datasets would always resemble the results that are closer to the reality. However, high resolution airborne or spaceborne local datasets have not yet been available for many regions and acquisition of this data is costly or might not even be possible for some locations. This hard-to-reach situation of high resolution datasets obliged researchers to work with open source datasets in their studies, which forces them to cope with the uncertainties of low spatial resolution.

Tsunami numerical models require both bathymetric and topographic data in order to calculate wave propagation in the water and inundation on the land. Leaving aside the availability of reliable bathymetric data, there are different open source global Digital Elevation Model (DEM) datasets, which are freely available. ASTER GDEM, SRTM and ALOS World 3D are present global open source DEMs that have highest spatial resolution of 30 meters. These three different sources of DEMs are generated using different technologies during data acquisition and different methodologies while processing. Even if they are the best available open source datasets, they all include variable sources of differences and errors.

This study aims evaluation of the sensitivity of open source DEM datasets against high resolution DEM datasets for tsunami hazard assessment and examination of accuracy of the simulations’ results. A small area in Silivri district of Istanbul is selected as study area, where 1m resolution of topographic data is available. Tsunami simulations are performed using NAMI DANCE GPU with topography data of 1m resolution based on LiDAR measurements and topography data of 30m resolution based on ASTER GDEM, SRTM and ALOS World 3D datasets. The resulted inundation on land and flow depth distributions are plotted and discussed with comparisons.

 

Acknowledgement: MSc. Bora Yalciner and Assoc. Prof. Dr. Andrey Zaytsev are acknowledged for their contributions in developing tsunami numerical model NAMI DANCE GPU used in this study. The authors also thank Istanbul Metropolitan Municipality, Directorate of Earthquake and Ground Investigation for providing high quality data and close cooperation.

Keywords: tsunami, hazard assessment, numerical modeling, open source DEM, high-resolution DEM
Archaeomagnetic directions and intensities from New Zealand: evidence for a fifteenth century AD archaeomagnetic “spike” in the SW Pacific?
Authors: Turner Gillian M. , Kinger Rimpy , McFadgen Bruce , Gevers Monique
Published: March 2020

The arrival of the great Maori waka and the settlement of New Zealand some seven or eight hundred years ago are described in oral history, but details of exactly when and how colonisation occurred are undocumented. Radiocarbon dating of early archaeological sites is particularly problematic, due to the inbuilt age of datable materials, and non-linearity and ambiguity in the calibration of measurements to calendar dates. Hangi stones, used as heat retainers in traditional Maori earth ovens, hold thermoremanent records of Earth’s magnetic field at the time of their last cooling. Matching the directions of these magnetizations to established reference curves provides alternative, archaeomagnetic, estimates of age. Our results cover the past 700 years, with a cluster of dates between 1500 and 1600 AD, from both North and South Islands, but none earlier than 1300 AD, thus supporting a model of rapid coordinated migration around that time. Archaeointensity data have been obtained from sixteen distinct archaeological features, including twelve hangi from eight sites, and from them the first archaeointensity record for New Zealand has been constructed. To this has been added other archaeointensity and palaeointensity data from the SW Pacific region and virtual axial dipole moments (VADMs) have been plotted. This plot outlines steady VADM values of about 8 x1022 Am2 from 1000-1300 AD, and 9.5 x1022 Am2 from 1500 AD to the present, with an intervening sharp peak in the early 15th century when the VADM reached about 13 x1022 Am2. This peak bears many similarities to archaeomagnetic “jerks” and “spikes” in northern hemisphere records from the first millennia BC and AD. However, it is the first such feature to be found in the southern hemisphere at this date, suggesting, in accordance with recent modelling, that it may be a feature of the non-dipole field, associated with rapid growth and decay of an intense flux patch on the core-mantle boundary.
Dynamics of foreshocks and pre-slip during the nucleation of laboratory earthquakes
Authors: Schubnel Alexandre , Marty Samson , Gardonio Blandine , Bhat Harsha , Fukuyama Eiichi , Madariaga Raùl
Published: March 2020

Over the past decades, an increasing number of seismological observations and improvement in data quality have allowed to better detect foreshock sequences prior to earthquakes. However, due to strong spatial and temporal variations of foreshock occurrence, their underlying physical processes and their links to earthquake nucleation are still under debate. Here we address these issues by looking at precursory acoustic activity during laboratory earthquakes (stick-slip instabilities).

Here, laboratory earthquake experiments were performed on saw-cut Indian metagabbro under upper crustal stress conditions ranging from 30 to 60 MPa confining pressure. Using a high-frequency monitoring system and calibrated piezoelectric acoustic sensors we continuously record particle velocity field at 10 MHz sampling rate during the experiments. Based on a trigger logic we identify acoustic emissions (AE) within continuous data. From P-wave arrival-time data and from spectral analysis we are able to estimate the following seismological parameters for each AE: location, absolute magnitude, stress-drop and size.

First, we show that the source parameters of AE (Mw -9.0 to Mw -7.0) follow the same scaling relationship as natural earthquakes justifying the use of acoustic precursors as proxy to foreshocks. We observe that foreshock triggering is systematically related to aseismic slip and that the dynamics of foreshocks mirrors the acceleration of slip-rate preceding failure. Experimental scalings demonstrate that : i- the nucleation evolves  from an aseismic process into a cascading one, and ii) the duration and magnitude of the pre-seismic moment correlates with the magnitude of the mainshock, at least at the scale of the laboratory. Finally, using Hertz contact theory, we find a scaling law between the seismic energy released by foreshocks, the fault roughness  and the normal stress acting on the fault interface.
Comparison of the elastic properties of reservoir rocks in the field and the laboratory: link between seismic, sonic and ultrasonic measurements
Authors: Gallagher Ariel
Published: March 2020

Elastic waves are commonly studied in geophysics. They are used for example for prospecting, to follow the exploitation of hydrocarbon reservoirs, to study the effect of fluid injection (CO2 storage)… However, the wave frequencies used in the field (sonic – seismic measurements) are not the same as the ones commonly used in the laboratory (ultrasonic measurements), and fluid-saturated rocks are known to be dispersive, i.e the P- and S- wave velocity in fluid-saturated rock change with frequency. The comparison between field and laboratory measurements is therefore not straightforward.

In the ENS facilities, it is possible to subject samples, under pressure (1 to 30 MPa) to forced - oscillations varying from 0.01 Hz to 1 kHz (field frequencies) and 1 MHz (ultrasonic frequencies) using a triaxial cell. Axial and radial strain gauges are installed to record the resulting strains on the sample. Forced-oscillation can be done on 1) confining pressure to get the bulk modulus as function of frequency or on 2) axial stress to get the Young modulus and Poisson ratio as function of frequency.  With this information, it is thus possible to deduce the P- and S- wave velocities with frequency.

The elastic properties were measured on different samples from the Libra oil field, for which logging measurements are available. Thus, the measurements obtained in the laboratory can be compared to the measurements in the field at the same frequency. In addition, the evolution of the velocity with frequency measured in the laboratory allows us to discuss the mechanisms at the origin of the dispersion.  
The modern assemblages of benthic foraminifers of the East Siberian Sea initial and active methane seeps zones of the Laptev Sea
Authors: Tikhonova Anna , Merenkova Sofia
Published: March 2020

We present the initial data on the distribution of benthic foraminifera (BF) on East Siberian Sea shelf. Previous researchers analyzed BF in the sediment cores from the continental slope and basin areas of the East Siberian Sea (Wollenburg et al., 2000; Mackensen et al, 2014; Barrientos et al, 2018) but not from central shelf. Last year we received boxcorer samples of bottom sediments from the shelf of the East Siberian Sea and the Laptev Sea during the 78th cruise of research vessel Akademik Mstislav Keldysh (September-October 2019). We examined the species composition of BF assemblages of Rose Bengal-stained surface samples from 2 stations in the East Siberian Sea and 7 stations in the Laptev Sea, and compared this data set with an existing data set along the East Siberian Sea and the Laptev Sea.

Recent studies (Shakhova et al, 2007, 2009, 2015; Nicolsky et al, 2009) state that the East Siberian Sea is one of the largest sources of methane emission into the atmosphere due to degradation of permafrost, ice complex retreat and decaying gas hydrates deposits. Perhaps this has an impact on the species composition of the BF assemblages and the morphological changes and defects of their shells, which we have identified. Samples from active methane seeps of the Laptev Sea have been studied to identify the relationship between methane emission and the reaction of benthic foraminifera. This data have been compared with “background” (i.e. non-venting, without any methane seeps activity) stations of the Laptev Sea and the East Siberian Sea.

The identified features require further detailed study.
HER: an information theoretic alternative for geostatistics
Authors: Thiesen Stephanie , Vieira Diego , Mälicke Mirko , Wellmann Florian , Ehret Uwe
Published: March 2020

Interpolation of spatial data has been considered in many different forms. This study proposes a stochastic, non-parametric, geostatistical estimator that combines measures of information theory with probability aggregation method. Histogram via entropy reduction (HER) can be used to analyze the data spatial correlation and for predicting distributions at unobserved locations directly based on empirical probability. The method minimizes estimation uncertainty, relaxes normality assumptions and therefore avoids the risk of adding information not available in data (or losing available information). In particular, the applied probability aggregation method provides a proper framework for uncertainty estimation that reflects both the spatial configuration of the data as well as data values, while allowing to infer (or introduce) physical properties (continuous or discontinuous characteristics) from the field under study. Three different aggregation methods were explored in terms of uncertainty, resulting in predictions ranging from conservative to more confident ones. We investigate the performance of the framework using four synthetically generated datasets from known Gaussian processes and demonstrate the efficacy of the method in ascertaining the underlying true field with varying sample sizes. By comparing the method performance to popular benchmark models, namely nearest neighbors (NN), inverse distance weighting (IDW) and ordinary kriging (OK), we were able to obtain competitive results with respect to OK, with the advantage of presenting generalization properties. The novel method brings a new perspective of spatial and uncertainty analysis to geostatistics and statistical learning, using the lens of information theory.
The effect of multiple splay fault rupture on tsunamis
Authors: van Zelst Iris , Rannabauer Leonhard , Gabriel Alice-Agnes , van Dinther Ylona
Published: March 2020

Earthquake rupture on splay faults in subduction zones could pose a significant tsunami hazard, as they could accommodate more vertical displacement and are situated closer to the coast. To better understand this tsunami hazard, we model splay fault rupture dynamics and tsunami propagation and inundation constrained by a geodynamic seismic cycle (SC) model; building on work presented in Van Zelst et al. (2019). This two-dimensional modelling framework considers geodynamics, seismic cycles, dynamic ruptures, and tsunamis together for the first time. The SC model provides six blind splay fault geometries, self-consistent stress and strength conditions, and heterogeneous material properties in the domain. We find that all six splay faults are activated when the megathrust ruptures. The largest splay fault closest to the nucleation region ruptures immediately when the main rupture front passes the branching point. The other splay faults are activated through dynamic stress transfer from the main megathrust rupture or reflected waves from the surface. Splay fault rupture results in distinct peaks in the vertical surface displacements with a smaller wavelength and larger amplitudes. The effect of the vertical surface displacements also translates into the resulting tsunami, which consists of one large wave for the megathrust-only model and seven waves for the model including splay faults. Here, six of the waves can be attributed to the splay faults and the seventh wave results from the shallow tip of the megathrust. The waves from the rupture including splay faults have larger amplitudes and result in two episodes of coastal flooding. The first episode is due to the large wave caused by rupture on the largest splay fault nearest to the coast. The second flooding episode results from the combination and interference of the waves caused by the rest of the splay faults and the shallow megathrust tip. In contrast, the tsunami caused by rupture on only the megathrust has only one episode of flooding. Our results suggest that larger-than-expected tsunamis could be attributed to rupture on large splay faults. When multiple smaller splay faults rupture their effect on the tsunami might be hard to distinguish from a pure megathrust rupture. Considering the significant effects splay fault rupture can have on a tsunami, it is important to understand splay fault activation and to consider them in hazard assessment.

References:

Van Zelst, I., Wollherr, S., Madden, E. H. , Gabriel, A.-A., and Van Dinther, Y. (2019). Modeling megathrust earthquakes across scales: one-way coupling from geodynamics and seismic cycles to dynamic rupture. Journal of Geophysical Research: Solid Earth, 124, https://doi.org/10.1029/2019JB017539
Comparing a random forest based prediction of winter wheat yield to historical production potential
Authors: Roell Yannik , Beucher Amélie , Møller Per , Greve Mette , Greve Mogens
Published: March 2020

Predicting wheat yield is crucial due to the importance of wheat across the world. When modeling yield, the difference between potential and actual yield consistently changes because of technology. Considering historical yield potential would help determine spatiotemporal trends in agricultural development. Comparing current and historical production in Denmark is possible because production has been documented throughout history. However, the current winter wheat yield model is solely based on soil. The aim of this study was to generate a new Danish winter wheat yield map and compare the results to historical production potential. Utilizing random forest with soil, climate, and topography variables, a winter wheat yield map was generated from 876 field trials carried out from 1992 to 2018. The random forest model performed better than the model based only on soil. The updated national yield map was then compared to production potential maps from 1688 and 1844. While historical time periods are characterized by numerous low production potential areas and few highly productive areas, present-day production is evenly distributed between low and high production. Advances in technology and farm practices have exceeded historical yield predictions. Thus, modeling current yield could be unreliable in future years as technology progresses.
Interannual variations in Lower Stratospheric Ozone during the period 1984-2016
Authors: Lu Jinpeng , Xie Fei , Tian Wenshou , Li Jianping , Feng Wuhu , Chipperfield Martyn , Zhang Jiankai , Ma Xuan
Published: March 2020

In this work we investigate interannual variations in lower stratospheric ozone from 1984 to 2016 based on a satellite-derived dataset and simulations from a chemical transport model. An empirical orthogonal function (EOF) analysis of ozone variations between 2000 and 2016 indicates that the first, second, and third EOF modes are related to the quasi-biennial oscillation (QBO), canonical El Niño–Southern Oscillation (ENSO), and ENSO Modoki events, respectively; these three leading EOFs capture nearly 80% of the variance. However, for the period 1984–2000, the first, second, and third modes are related to the QBO, ENSO Modoki, and canonical ENSO events, respectively. The explained variance of the second mode in relation to ENSO Modoki is nearly twice that of the third mode for canonical ENSO. Since the frequency of ENSO Modoki events was higher from 1984 to 2000 than after 2000, the Brewer–Dobson circulation anomalies related to ENSO Modoki were stronger during 1984–2000, which caused ENSO Modoki events to have a greater effect on lower stratospheric ozone before 2000 than after. Ozone anomalies associated with QBO, ENSO Modoki, and canonical ENSO events are largely caused by dynamic processes, and the effect of chemical processes on ozone anomalies is opposite to that of dynamic processes. Ozone anomalies related to dynamic processes are 3–4 times greater than those related to chemical processes.
Uncertainty in strain-rate from field measurements of the geometry, rates and kinematics of active normal faults: Implications for seismic hazard assessment
Authors: Sgambato Claudia , Faure Walker Joanna P. , Roberts Gerald P.
Published: March 2020

Multiple measurements of the geometry, kinematics and rates of slip across the well-exposed Auletta fault scarp (Campania, Italy) are presented, and we use these in order to investigate: (1) the spatial resolution of field measurements needed to accurately calculate a representative strain-rate for seismic hazard calculations; (2) what aspects of the geometry and kinematics would introduce uncertainty in calculated strain-rate, if those are not measured in the field. Our results show that the magnitude of the post-glacial maximum (15±3 ka) throw gradually decreases towards the tip of the fault, but variations are observed along strike, across areas of structural complexity such as along-strike bends in the fault plane where the fault dip is greater. We find that if such variations are unnoticed, different values of strain-rate would be produced, and hence different values would result in seismic hazard calculations. To demonstrate this, we calculate the strain-rate across the Auletta fault using all our measurements, and subsequently degrade the dataset removing one measurement at a time and recalculating the implied strain-rate at each step. The results show that excluding measurements can alter strain-rate results beyond 1 σ uncertainty, thus we suggest caution when using only one measurement of slip-rate along a fault for calculating hazard, as a full understanding of the potential implied errors needs consideration. Furthermore, we investigate the effect of approximating the throw profile along the fault using boxcar and triangular slip distributions; we show that this can underestimate or overestimate the strain-rate, with results in the range of 72–237% of our most detailed strain-rate calculation. We suggest that improved understanding of the potential implied errors in strain-rate calculations from field structural data should be implemented in seismic hazard calculations.
Evolution of supraglacial lakes on Shackleton Ice Shelf, East Antarctica
Authors: Arthur Jennifer , Stokes Chris , Jamieson Stewart , Carr Rachel , Leeson Amber
Published: March 2020

Supraglacial lakes (SGLs) enhance surface melting and their development and subsequent drainage can flex and fracture ice shelves, leading to their disintegration. However, the seasonal evolution of SGLs and their potential influence on ice shelf stability in East Antarctica remains poorly understood, despite a number of potentially vulnerable ice shelves. Using optical satellite imagery, climate reanalysis data and surface melt predicted by a regional climate model, we provide the first multi-year analysis (1974-2019) of seasonal SGL evolution on Shackleton Ice Shelf in Queen Mary Land, which is Antarctica’s northernmost remaining ice shelf. We mapped >43,000 lakes on the ice shelf and >5,000 lakes on grounded ice over the 45-year analysis period, some of which developed up to 12 km inland from the grounding line. Lakes clustered around the ice shelf grounding zone are strongly linked to the presence of blue ice and exposed rock, associated with an albedo-lowering melt-enhancing feedback. Lakes either drain supraglacially, refreeze at the end of the melt season, or shrink in-situ. Furthermore, we observe some relatively rapid (≤ 7 days) lake drainage events and infer that some lakes may be draining by hydrofracture. Our observations suggest that enhanced surface meltwater could increase the vulnerability of East Antarctic ice shelves already preconditioned for hydrofracture, namely those experiencing high surface melt rates, firn air depletion, and extensional stress regimes with minimum topographic confinement. Our results could be used to constrain simulations of current melt conditions on the ice shelf and to investigate the impact of increased surface melting on future ice shelf stability.
A Two-Dimensional Analytical Solution for Remediation of Salt Affected Site through Ditch Drainage System
Authors: Tiwari Shubham , Yadav Brijesh Kumar
Published: March 2020

Agricultural fields are facing the problem of salinity, which is the key reason behind the decreased productivity of crop plants and reduced fertility of the soils. The ditch drainage system is extensively used for the elimination of salts present in agricultural fields. In this study, an analytical solution is developed for a ponded surface agricultural field with a fully penetrating ditch drainage system in presence of an additional sink in the study domain to improve the efficiency of saline water extraction. The considered study domain is taken of confined finite extent having homogenous and isotropic nature. The obtained analytical solution is compared well with a numerical model for a similar study domain. The analytical model is also validated for an existing analytical solution with no sink.  Results show that the travel time of water molecules containing salt concentration reduced drastically due to the presence of sink in the middle of the porous domain. The path line of saline water started deviating from the original position represents that the sink has a strong impact on discharge from the side drains. Therefore, the efficiency of the ditch drainage system is increased significantly with the influence of sink in the flow domain. The proposed study is expected to help in the understanding of solute transport flow dynamics in the ditch drainage system with the influence of source/sink in real field conditions. The analytical solution may also be useful in testing and comparing the numerical codes generated for such types of flow scenarios in the subsurface.
The influence of solar panel roof on urban thermal environment and cooling energy demand during a heat wave event in 2017
Authors: Wang Yongwei , Chen Fei , Hao Xiaolong , Wang Fan
Published: March 2020

With the rapid development of social economy, China's energy demand has been growing at an alarming rate. The annual cumulative power generation is about  6.8 trillion kilowatts hour in 2017, and 70% of them is provided by fossil fuel resources, so it is important to promote the use of renewable and clean energy, such as solar power generation technology. The advantages of using solar panel roof in urban areas include reduction of the need of land use in the crowed city and less dependence on fossil fuels. However, there is need to understand impacts of solar roof on local climate, on energy supply during heatwaves, and associated economic benefits in China. This study selected a heatwave event in Jiangsu province, China to simulate the impact of solar panel roof on local thermal environment and energy supply. During that time, the cooling energy consumption reached more than half of the total electricity consumption. A new heat transfer scheme of solar panel roof was introduced into WRF/BEP/BEM model, which include layers (glass protective panel, solar panel, bottom plate) and was divided into two types for heat transfer calculation: bracket and non-bracket. The results showed that the urban average 2-m daytime temperature decreased by 0.3℃ in non-bracket case which is better than that of bracket case, while its cooling effect on nighttime temperature was small. For the bracket case, its cooling effect on daytime and nighttime air temperature were equal (0.2oC). Both solar panel roofs can reduce indoor daytime air temperature with the maximum cooling effect around 11:00 local time for non-bracket roof and 14:00 for bracket roof. However, bracket roof increased nighttime indoor air temperature and air-conditioning energy consumption. Solar panel roofs also reduce daytime turbulent kinetic energy and constrain the development of boundary layer. Results also show that with solar photoelectric conversion efficiency being 0.14, the photovoltaic power generation can meet 84.1%, 61.3% and 35.9% of the cooling energy consumption for high-density, low-density residential areas and commercial areas, respectively, during this heatwave event.
Seasonal effects of additional HONO sources and the heterogeneous reactions of N2O5 on nitrate in the North China Plain
Authors: Qu Yu , An Junling
Published: March 2020

We coupled the heterogeneous hydrolysis of N2O5 into the newly updated Weather Research and Forecasting model with Chemistry (WRF-Chem) to reveal the relative importance of the hydrolysis of N2O5 and additional nitrous acid (HONO) sources for the formation of nitrate during high PM2.5 events in the North China Plain (NCP) in four seasons. The results showed that additional HONO sources produced the largest nitrate concentrations in winter and negligible nitrates in summer, leading to a 10% enhancement of a PM2.5 peak in southern Beijing and a 15% enhancement in southeastern Hebei in winter. In contrast, the hydrolysis of N2O5 produced high nitrate in summer and low nitrate in winter, with the largest contribution of nearly 20% for a PM2.5 peak in southeastern Hebei in summer. During PM2.5 explosive growth events, the additional HONO sources played a key role in nitrate increases in southern Beijing and southwestern Hebei in winter, whereas the hydrolysis of N2O5 contributed the most to a rapid increase in nitrate in other seasons. HONO photolysis produced more hydroxyl radicals, which were greater than 1.5 μg m-3 h-1 in the early explosive stage and led to a rapid nitrate increase at the southwestern Hebei sites in winter, while the heterogeneous reaction of N2O5 contributed greatly to a significant increase in nitrate in summer. The above results suggest that the additional HONO sources and the heterogeneous hydrolysis of N2O5 contributed the most to nitrate formation in NCP in winter and summer, respectively.
TraML: separation of seismically-induced ground-motion signals with Autoencoder architecture
Authors: Novoselov Artemii , Hein Gerrit , Bokelmann Goetz , Fuchs Florian
Published: March 2020

Any time series can be represented as a sum of sine waves with the help of the Fourier transform. But such a transformation doesn’t answer whether the signal is coming from one source or several; neither it allows separation of such sources. In this work, we present a technique from the Machine Learning domain, called Auto-encoders that utilizes the ability of the neural network to generate signals from the latent space, which in turn allows us to identify signals from an arbitrary number of sources and can generate them as separate waveforms without any loss. We took ground motion records of passing trains and trams in the vicinity of the University of Vienna and trained the network to produce “clean” individual signals from “mixed” waveforms. This work proves the concept and steers the direction for further research of earthquake-induced source separation. It also benefits interference seismometry, since “noise” used for such research can be separated from the signal, thus reducing manual processing (cutting and clipping signals) of seismic records. 
Continental scientific drilling: A game changer for understanding ecosystem evolution in Africa
Authors: Cohen Andrew S.
Published: March 2020

Over the past 20 years a series of scientific drilling campaigns around Africa have yielded exciting new information about the evolutionary ecological history of that continent. Most of these records have come from highly resolved lacustrine deposits with rapid sedimentation rates, and primarily, though not exclusively, have come from the East African Rift Valley, spanning the last ~3.5Ma. Important insights about both lacustrine and terrestrial ecosystem evolution have emerged, including ones with implications for the ecological context of human evolution. During the transition from the Late Pliocene warm period into the Quaternary, phytoliths, charcoal, pollen and leaf wax records are reshaping our understanding of fine scale structure of landscape vegetation transformation, and the implications these changes had for resources and cover that mammals (including early hominins) relied upon.  Pleistocene drill core paleoecological records from Lake Malawi have provided evidence for transformations of that lake’s ecosystem, including water column mixing, transparency and nutrient recycling, that help explain the explosive phylogenetic radiation of that lake’s extraordinary endemic cichlid fish fauna. And high-resolution records from that same lake spanning the time of the ~75ka Toba super-eruption allow us to test and falsify hypotheses linking volcanic activity to wholesale transformation of the African ecosystem, including purported links to modern human population bottlenecks. These valuable archives will in the future be complemented by even longer records from Africa’s oldest lake, L. Tanganyika, allowing us to build a comprehensive picture of African ecosystem evolution extending back to the late Miocene.
Mitigation of Model Bias Influences on Wave Data Assimilation with Multiple Assimilation Systems
Authors: li jiangyu , zhang shaoqing
Published: March 2020

High-quality wave prediction with a numerical wave model is of societal value. To initialize the wave model, wave data assimilation (WDA) is necessary to combine the model and observations. Due to inaccurate wind forcing, imperfect numerical schemes, and approximated physical processes, a wave model is always biased in relation to the real world. In this study, two assimilation systems are first developed using two nearly independent wave models; then, “perfect” and “biased” assimilation frameworks based on the two assimilation systems are designed to reveal the uncertainties of WDA. A series of “biased” assimilation experiments is conducted to systematically examine the adverse impact of initial condition, boundary forcing, and model bias on WDA, then model bias play a strongest role among them . A statistical approach based on the results from multiple assimilation systems is explored to carry out bias correction, by which the final wave analysis is significantly improved with the merits of individual assimilation systems. The framework with multiple assimilation systems provides an effective platform to improve wave analyses and predictions and help identify model deficits, thereby improving the model.
Investigation of different anaerobic respiratory pathways and their impacts on the release ratio of DIC/alkalinity at selected North Sea regions
Authors: Treblin Nele , Böttcher Michael E. , Zimmermann Tristan , Pröfrock Daniel , Norbisrath Mona , van Dam Bryce , Thomas Helmuth
Published: March 2020

Investigation of different anaerobic respiratory pathways and their impacts on the release ratio of DIC/alkalinity at selected North Sea regions

Tentative authors: Nele Treblin1,2, Michael E. Böttcher3, Tristan Zimmermann1, Daniel Pröfrock1, Mona Norbisrath1, Bryce van Dam1, Helmuth Thomas1

1Institute for Coastal Research, Helmholtz Center Geesthacht

2Alfred-Wegener-Institute Helmholtz Center for Polar and Marine Research

3Leibniz Institute for Baltic Sea Research Warnemünde

 

Coastal sediments play a crucial role in carbon metabolism, which decreases with increasing distance from the shoreline. The North Sea, a NW European shelf sea, represents a relatively shallow, well-ventilated (on annual timescales) system, connected to the Baltic Sea and the North Atlantic. Especially the southern part of the North Sea receives a large amount of organic matter (OM), both from riverine input and internal North Sea sources. After the depletion of oxygen due to aerobic OM respiration, anaerobic metabolic activities become dominant in the sediment. In the absence of oxygen, electron acceptors, such as NO3-, Fe3+, Mn4+ and SO42-, facilitate not only the release of respired CO2, but also of alkalinity, furthermore enhanced by potential dissolution of sedimentary carbonates. Therefore, under these conditions, benthic-pelagic coupling may impact on the potential to absorb CO2 from the atmosphere.

To investigate the described processes, porewater and sediment samples, collected from six different stations in the German Bight (North Sea) during the RV Heincke cruise HE541 in September 2019, have been analyzed for their vertical concentration profiles of nutrients, various trace metals, sulfur, DIC and alkalinity.

Benthic oxic and anoxic zones have been identified based on the vertical concentration gradients. Furthermore, alkalinity and DIC are set in relation to anaerobic metabolic activities. Finally, active reworking and ventilation becomes pivotal in areas such as the North Sea. Thus, the influence of bioturbation on anaerobic respiration is also considered.
Remoteness and austerity: a major driver of vulnerabilities to natural hazards
Authors: Papathoma-Koehle Maria , Maris Fotis , Fuchs Sven
Published: March 2020

To a great extent, literature concerning efforts to assess vulnerability to natural hazards focuses on the vulnerability of mega-cities and urban areas due to the significant concentration of vital assets and high population density in a relatively small area. However, the antipode of this condition, the one of remoteness, insularity and isolation also constitutes a major drive of vulnerability to natural hazards. Remote areas are often dependent on decisions that are taken somewhere else, such as central governments, and they have limited funds for preparedness but also limited material and human resources to respond to natural hazards. Remote areas can be found in many regions across Europe including the European Alps, the Scandinavian tundra and small islands in the North Sea but also in the Mediterranean. However, in the European south, the capacities of remote areas have deteriorated further due to the recent financial crisis and austerity measures.

An integrated approach to vulnerability is attempted for the island of Samothraki, Greece. The specific island is located in the northeast part of the country, and despite the relatively short distance to the coast of Greece and Turkey, it is particularly isolated due to the poor transport connections to the mainland, demographic problems, the effects of the financial crisis and governance particularities. In September 2017 Samothraki was affected by a major torrential event that revealed its vulnerabilities and the vulnerabilities of remote areas in general. The vulnerabilities investigated in this study include physical, social, economic and institutional. A framework for the assessment of these vulnerabilities in remote areas and some preliminary results are presented.
The long-time spatial and temporal development of Triadic Resonance Instability
Authors: Grayson Katherine , Dalziel Stuart , Lawrie Andrew
Published: March 2020

Various mechanisms have been cited as an explanation of how internal waves transfer energy across the wavenumber and frequency spectra and eventually contribute to small scale turbulence and mixing. Triadic Resonance Instability (TRI) has become increasingly recognised as one of these methods. This talk will focus on new experimental investigation into the temporal and spatial evolution of this instability. Experiments have been conducted using a new generation of wave maker, featuring a flexible horizontal boundary condition which is driven by an array of independently controlled actuators. This allows for varying amplitude, frequency and wavelength in both the spatial and temporal domain. We present results utilising this ability to vary the forcing parameters during the course of an experiment and investigate what effects this has on the evolution of TRI. Experimentally, we have found that the approach to a saturated equilibrium state for the three triadic waves is not monotonic, rather their amplitudes continue to oscillate without reaching an equilibrium.  
Optimal 3D Time-Energy Trajectory Planning for AUVs using Ocean General Circulation Models
Authors: Albarakati Sultan , Lima Ricardo , Theussl thomas , Hoteit Ibrahim , Knio Omar
Published: March 2020

We develop a new approach for solving optimal time and energy-trajectory planning problems for Autonomous Underwater Vehicles (AUVs) in transient, 3D ocean currents. Realistic forecasts using an Ocean General Circulation Model (OGCM) are used for this purpose. The approach is based on decomposing the problem into a minimal time problem, followed by minimal energy subproblems. In both cases, a Non-Linear Programming (NLP) formulation is adopted. The methodology is first tested in idealized, steady, 2D settings, to verify the effectiveness of the method in addressing the multi-objective optimization problem. The scheme is then demonstrated for time-energy trajectory planning problems in the Gulf of Aden. In particular, the numerical experiments illustrate the capability of generating Pareto optimal solutions in a broad range of mission durations. In addition, the analysis also highlights how the methodology effectively exploits both the vertical structure of the current field, as well as its unsteadiness, namely, to minimize travel time and energy consumption.
Thermomechanical models with surface processes: Low-Temperature Thermochronology predictions for model calibration
Authors: Beucher Romain , Moresi Louis , Brown Roderick , Mallard Claire
Published: March 2020

State of the art thermo-mechanical models have become very efficient at testing scenarios of tectonic evolution but uncertainties on the rheologies and the complexity of the have so far limited the potential to quantitatively predict uplift and subsidence. Coupling thermo-mechanical models to landscape evolution models remains challenging and require careful validation and better integration of field data to prevent error in interpretation.

 

Low temperature thermochronology has been extensively used to quantitatively constrain the thermal histories of rocks. It can provide important information on tectonic uplift (or subsidence) by measuring the erosional (or burial) response and can also map the spatial and temporal pattern of geomorphic response of a landscape.

 

We use the temperature evolution of our coupled thermo-mechanical models with surface processes to predict Apatite fission track data (Ages and Track lengths distributions). The aim is to provide a direct means of comparison with actual empirical thermochronometric data which will allow different model scenarios and/or model parameter choices to be robustly tested.

We present a series of 3D coupled models (Underworld / Badlands) of Rifts and the associated Apatite Fission Track predicted by the thermal evolution of the rocks exhumed to the surface. We compare models predictions to existing thermochronological transects across passive margins.

 

We discuss the technical challenges in obtaining sufficiently high resolution temperature field and other associated challenges that need to be addressed to satisfactory apply our model to natural examples.
Spatio-temporal patterns of debris-flow erosion and deposition in the Illgraben torrent
Authors: de Haas Tjalling , Nijland Wiebe , McArdell Brian
Published: March 2020

Debris flows can grow greatly in size and hazardous potential by eroding bed material, but effective hazard assessment and mitigation is currently hampered by limited understanding of erosion and deposition dynamics. We have collected high-resolution pre- and post-flow topography with drone-based photogrammetry in the Illgraben channel in the Swiss Alps. We present erosion and deposition patterns as a result of six debris flows and intensive subcatchment activity over a 3.3 km long unconsolidated reach with check dams, and interpret these erosion and deposition patterns with in-situ flow measurements. We show that the spatio-temporal patterns of erosion and deposition in natural debris-flow torrents are highly variable and dynamic. We identify a memory effect where erosion is strong at locations of strong deposition during previous flows and vice versa. Large sediment inputs from subcatchments initially result in new channel erosion through the subcatchments deposits and at the same time upstream deposition as a result of backwater effects. It is generally believed that erosion increases with debris-flow magnitude, but we show that there is a limit to debris-flow bulking set by channel geometry. Large flows that overtop their channel deposit large amount of sediment in levees and on overbanks, leading to net deposition despite strong thalweg erosion, and thus a decrease in flow volume. These findings provide key guidelines for flow volume forecasting, emphasizing the importance of memory effects and the need to resolve both erosion and deposition for accurate flow volume estimation.
Wetlandscape size thresholds for multiple ecosystem service delivery
Authors: Åhlén Imenne , Hambäck Peter , Thorslund Josefin , Frampton Andrew , Destouni Georgia , Jarsjö Jerker
Published: March 2020

Wetlands are increasingly considered as nature based solution as they provide valuable services and functions to the society and environment, such as water quality improvement and biodiversity support. However, while land use and climate change have been affecting the functions and service of these ecosystems, it has become important to study the large-scale behaviour of wetlands in the landscape. Consequently, previous studies have suggested to study wetlands within wetlandscapes, defined as catchments containing networks of several wetlands, in order to understand large-scale functions of wetlands and their response to land-use and climate changes. This emphasizes the ecohydrological interactions of wetlands rather than having focus of individual wetlands. However, as the concept of wetlandscape is new, its governing properties have not yet been systematically quantified.

In this paper, we quantify ecohydrological properties of individual wetlands in multiple wetlandscapes, typical for northern Europe, that may impact biodiversity and modulate nutrient flows (e.g. wetland area, wetland catchment area and wetland type) as well as characteristics of the whole wetlandscape in terms of their large-scale processes and functions. We also investigate possible systematic differences between wetlandscapes of different size. Results show that large wetlandscapes generally contained features to support different ecosystem services compare to smaller wetlandscapes. More specifically, results indicated that small wetlandscapes have a poor ability to route water through their wetlands (i.e. catch flow from the entire wetlandscape) which was in contrast to large wetlandscapes. This implies that large wetlandscapes have a higher potential for large-scale retention of nutrients and contaminants. Present result support the importance of wetlandscape studies and the priority of a wetlandscape focus in future management programs for instance targeting regions with large-scale pollution issues.
Mapping the Friction Coefficient of Asphalt Roads Using Airborne Imaging Spectroscopy
Authors: Ben Dor Eyal , Carmon Nimrod
Published: March 2020

The purpose of this study was to evaluate the realistic feasibility of using hyperspectral remote sensing airborne data for mapping asphalt road conditions. We constructed a real-life operational scenario, where the road's dynamic friction coefficient was modeled against the reflectance information extracted from the image. The asphalt pavement's dynamic friction coefficient was measured by a standardized technique, using a Dynatest friction-measuring system. The hyperspectral data were acquired by both the Specim AisaFENIX 1K and Telops Hyper-Cam airborne sensors at a selected study site, with roads characterized by different aging conditions. The spectral radiance data were processed to provide apparent surface reflectance and emissivity using ground calibration targets. Our final dataset was comprised of thousands of clean asphalt pixels coupled with geo-rectified in situ friction measurement points. We deployed a partial least squares regression model with the PARACUDA-II spectral data-mining engine, which uses an automated outlier-detection procedure and dual validation routines—a full cross-validation and an iterative internal validation based on a Latin hypercube sampling algorithm. Our results show prediction capabilities across the visible–near infrared–shortwave infrared (0.4–2.5 mm) spectral region of R2 = 0.72 for the best available model in internal validation, and across the longwave infrared (7.6–11.4 mm) spectral region of R2=0.62  for the best available model in internal validation. Both spectral regions (optical and thermal) maintained high significant results with p < 0.0001. Using spectral assignment analysis, we located the spectral bands with the highest weight in the model, and discuss their possible physical and chemical assignments. The derived model was applied back on the hyperspectral images to predict and map the friction values of every road's pixels in the scene. We conclude that although a relatively strong prediction model can be achieved, the imaging spectroscopy technique from airborne platforms ) may open a new frontier in road safety and present a new capability for the promising airborne technology.

 