bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of the fault-block structure of the continental margin in the generation of the strongest subduction earthquakes
Authors: Vladimirova Irina , Gabsatarov Yury , Alekseev Dmitry , Lobkovsky Leopold
Published: March 2020

Modern seismotectonic studies are aimed at obtaining a self-consistent explanation of fault zone heterogeneity, the rupture process, recurrence times and rupture mode of large earthquake sequences. In subduction regions large earthquakes are often characterized by very long source zones and complex long-term postseismic processes following the coseismic release of accumulated elastic stresses. A set of mechanical models was proposed to describe the generation of strongest earthquakes based on the idea of the synchronous failure of several adjacent asperities.

In this study we propose a model which is based on verified numerical schemes, which allows us to quantitatively characterize the process of generation of strong earthquakes. The model takes into account the fault-block structure of the continental margin and combined the ideas of a possible synchronous destruction of several adjacent asperities, mutual sliding along a fault plane with a variable coefficient of friction and subsequent healing of medium defects under high pressure conditions.

The applicability of the proposed model is shown by the example of the recent seismic history of the Kuril subduction zone. Kuril island arc is one of the most tectonically active regions of the world due to very high plate convergence rate. Heterogeneities in the mechanical coupling of the interplate interface in this region lead to the formation of the block structure of the continental margin, which is confirmed by various geological and seismological studies.

GPS observations recorded at different stages of seismic cycle related to the 2006–2007 Simushir earthquakes allow us to model geodynamic processes of slow strain accumulation and its rapid release during the earthquake and the subsequent posteseismic process. We use parameters describing the regional tectonic structure and rheology obtained from the inversion of geodetic data to construct a 2D model of generation of large earthquakes in central Kurils. Analysis of paleoseismic data on dates and rupture characteristics of previous major earthquakes shows a good agreement between the modeled and observed seismic cycle features. The predicted horizontal displacements of the seismogenic block at the coseismic stage are consistent with satellite geodetic data recorded during the 2006 Simushir earthquake.

The proposed model provides new insights into the geodynamic processes controlling the occurrence of strong subduction earthquakes.
Complex development of a 300-million-year old subglacial unconformity in southern Namibia
Authors: Le Heron Daniel Paul , Kettler Christoph , Griffis Neil , Dietrich Pierre , Montañez Isabel
Published: March 2020

The expansion of ice masses across southern Africa during the Late Palaeozoic Ice Age (LPIA) at about 300 Ma has been recognised in the literature for over a century, including the distribution of upland areas in controlling the configuration of ice masses (Davis, 1908). In Namibia, increasing attention has focussed on long and deep palaeovalley networks in the north, but comparatively little work has been attempted in the topographically subdued plains of the south. The desert terrain of the Mariental area exposes diamictites of the Dwyka Formation discontinuously over about 300 km, extending further south to the Noordoewer area at the Namibian-South African border along the Orange River. Whilst examined at a stratigraphic level, the nature of the contact between the Dwyka glacial rocks and underlying lithologies has not been systematically investigated. This paper presents some preliminary results from fieldwork in austral winter 2019, in which we describe a highly varying basal contact that records the processes of growth, flow and expansion of ice masses across this part of Gondwana. Subglacially-produced unconformities may exhibit classic glacially-striated pavements at basin margins, which substitute for soft-sediment striated surfaces in comparatively more “basinal” areas. Where these features are absent, additional criteria may be sought. In Mariental, spectacular soft-sediment shear zones exhibit a combination of brittle and ductile end products are recognised, overprinted by shear bands. This type of subglacial unconformity developed over well differentiated, unconsolidated, siliciclastic materials. Where ice advanced over more poorly sorted material or cannibalised pre-existing diamictites, “boulder-pavements” formed in which in single clast-thick boulder-dominated intervals were facetted and striated in situ by overriding ice. By integrating measurements of striation orientations, fold vergence and palaeocurrent information, former ice flow pathways can potentially be reconstructed over a wide area, which is suspected to have been dominated by Piedmont glaciers.
Winter is coming – ecosystem-scale COS exchange during senescence of a deciduous forest
Authors: Spielmann Felix M. , Hammerle Albin , Knohl Alexander , Deventer Malte Julian , Wohlfahrt Georg
Published: March 2020

The gross uptake of CO2 on ecosystem level (GPP) can’t be measured directly, but has to be inferred from models or proxies. One of the newly emerged constrains on GPP is the trace gas carbonyl sulfide (COS). COS enters the plant leaf through the stomata and diffuses through the intercellular space, the cell wall, the plasma membrane and the cytosol like CO2. Within the cytosol, it is then catalyzed by the enzyme carbonic anhydrase (CA) in a one-way reaction to H2S and CO2. Basically, this one way flux would make COS a very promising tracer for GPP on ecosystem level, but there is growing evidence that plants are also capable of emitting COS. Mosses and even vascular plants that are under high stress like drought and fungal infection, have been reported to emit COS. Furthermore, a winter wheat field, that showed a good correlation between the CO2 and COS ecosystem fluxes during the peak growing phase turned into a source for COS after going into senescence. This indicates that yet unknown COS emission processes likely related to plant degradation, could complicate the use of COS as a tracer for GPP.

Since the majority of studies have focused on measuring COS ecosystem fluxes during peak growing times or on evergreen forests, we seek to quantify the relationship between the ecosystem-scale exchange of CO2 and COS of an ecosystem going into senescence.

Between September and November 2019 we deployed our quantum cascade laser (Aerodyne Research Inc., MA, USA) at a beech forest in Leinefelde, Germany to conduct eddy covariance measurements for COS, CO2 and H2O. Our observations started when the beech forest was still green and in full leaf and ended when most of the trees had already shed their leaves. The ecosystem fluxes of COS and CO2 concurrently decreased over the course of our campaign up to the point when we could not observe a net uptake of CO2 anymore. We will further compare the GPP estimates resulting from classical flux partitioning and flux partitioning with the additional use of COS to determine if the model differences increase towards the end of the season.
Improvement of a low-cost CO2 commercial NDIR sensor for UAV atmospheric profiling applications
Authors: Liu Yunsong , Paris Jean-Daniel , Vrekoussis Mihalis , Antoniou Panayiota , Argyrides Marios , Constantinides Christos , Desbree Dylan , Hadjigeorgiou Neoclis , Keleshis Christos , Laurent Olivier , Leonidou Andreas , Philippon Carole , Vouterakos Panagiotis , Quehe Pierre-Yves , Bousquet Philippe , Sciare Jean
Published: March 2020

Unmanned Aerial Vehicles (UAVs) have the potential to fill in gaps in greenhouse gases (GHG) observations by providing high-resolution vertical profiling, horizontal mapping of fluxes and 3D measurements close to the ground. UAVs can ultimately allow better characterizing the spatial distribution of various GHG sources and sinks. To achieve these goals, important efforts are currently put towards the development of compact, lightweight, low powered and highly accurate GHG sensors on UAVs.

This study aims to develop and validate a UAV-CO2 sensor system to map specific source emissions close to the ground. The CO2 sensor used here is the High-Performance Platform (HPP 3.2, SenseAir AB) of a total weight 1058g including battery. Prior to its integration in the UAV, the CO2 sensor accuracy and linearity tests were performed in the laboratory. Allan Deviation showed the sensor precision to be within ±1ppm at 1 Hz. Corrections due to temperature and pressure changes were performed using specific formulas obtained from chamber experiments. Field (manned aircraft) tests were performed, where the P/T correction equations were evaluated for two CO2 sensors which were compared against an airborne reference instrument (Picarro G2401-m). After laboratory tests and field deployment, the HPP CO2 sensor was integrated into a small fixed-wing UAV with a wingspan of 1.83m and customized avionics and payload developed by the Unmanned Systems Research Laboratory of the Cyprus Institute performed successful atmospheric profiling below/above the boundary layer, at an agricultural site in Cyprus. This HPP CO2 sensor is also to be integrated in a quad-copter for vertical take-off ＆ landing (VTOL) in urban environments to execute intensive (every 20-min) atmospheric profiling (0-1km altitude) over the city of Nicosia (Cyprus). These flights provide us with useful insights into the CO2 vertical distribution within the planetary boundary layer (and above) for different (remote/urban) regions in Cyprus.
3D climate simulations of Earth-like planets with a range of atmospheric composition, radiative transfer, ocean, and resolution configurations, using the new version of ROCKE-3D
Authors: Tsigaridis Kostas , Del Genio Anthony D. , Aleinov Igor , Wolf Eric T. , Kelley Maxwell , Way Michael J. , Sohl Linda E. , Ruedy Reto A.
Published: March 2020

Understanding the climate of terrestrial planetary atmospheres has been increasingly the focus of research worldwide, in light of the increasing amount of rocky planet discoveries orbiting other stars in or near their habitable zone. Here we present simulations with the new version of the 3D climate model ROCKE-3D, whose version 2.0 will soon become publicly available. A wide range of configurations will be supported, compared to a handful ones in its predecessor, version 1.0 (Way et al., 2017). These include two model resolutions (4x5 and 2x2.5), two radiation schemes (GISS and SOCRATES), three atmospheric configurations (Earth-like, Earth-like without O3 and aerosols, and N2-dominated), and three ocean setups (prescribed sea-surface temperatures and ice cover, q-flux, and dynamic). Simulations of all different configuration combinations have been performed and will become available for use by the community. Key results will be presented across those configurations, together of the role of the structural uncertainty in model setup in the resulting climate calculated by the model.
Transfer of organic matter through a peatland system – from terrestrial to aquatic systems
Authors: Boothroyd Ian , Worrall Fred , Abbott Geoff , Moody Catherine , Clay Gareth , Rose Rob
Published: March 2020

Peatlands are important terrestrial carbon stores and it is important to understand the processes involved in carbon cycling. At Moor House, an upland blanket bog in the United Kingdom (UK), stoichiometric approaches have been adopted to understand carbon cycling through the peatland and this has been used to understand the production, transport and transformation of organic matter from terrestrial to aquatic systems.

Previous results analysing vegetation, peat cores, soil pore water from shallow and deep sample depths, and stream water from Moor House assessed how the composition of organic matter changes through the peatland system, to its export in the stream network. Results showed that there was an increase in the nominal carbon oxidation state (Cox) of dissolved organic matter (DOM) transferred from soil pore water to stream water. The composition of DOM in soil pore water evolved from near-surface peat layers but stream water DOM was quite distinct in composition. This study assessed the role of DOM in the degradation of peat organic matter by examining the composition of DOM through the peat profile and in separate flow pathways. Sampling was undertaken at Moor House, with sampling from surface, shallow and deep soil water; surface runoff and stream water. Samples were analysed for their elemental content (C, H, N and O), and differential scanning calorimetry and bomb calorimetry.

 
A Method for Estimating the Evolution of Brewer-Dobson Circulation Upwelling
Authors: Charlesworth Edward , Ploeger Felix , Diallo Mohamadu , Birner Thomas , Joeckel Patrick
Published: March 2020

Both theory and climate model results suggest that the Brewer-Dobson circulation should strengthen in the stratosphere with increasing greenhouse gas concentrations. Directly measuring the circulation strength is not possible, so verification of this sensitivity has been limited to indirect inferences from observed tracer fields of long-lived species. These methods, however, are complex and accumulation of the data required for them is difficult. When limiting discussion to the tropical lower stratosphere, ozone concentrations have shown to be consistent with an accelerating circulation. These measurements are particularly useful because of the long timeseries available from multiple datasets, but they have only been used for indirect investigations of the circulation strength, up until now.

In this work, we invert the ozone balance equation to solve for upwelling. By limiting the investigation to 70 hPa in the southern tropics and estimating upwelling anomalies from the long-term mean (and not the absolute value of upwelling) most chemical terms and both horizontal and vertical mixing can be neglected, and calculation of the remaining terms is straight-forward. To verify the validity of the method, a calculation of upwelling is performed using climate model data, from which a comparison of actual upwelling and upwelling from the inverse method can be made. The seasonal cycle of upwelling anomalies is compared to upwelling anomalies from reanalyses and model results, and trends and variability are discussed.
The stratigraphic and magmatic tape recorder of crustal thinning and lithospheric breakup: insights from the NW South China Sea
Authors: Chao Peng , Manatschal Gianreto , Kusznir Nick , Chenin Pauline , Ren Jianye , Pang Xiong
Published: March 2020

In the last two decades, knowledge of the South China Sea (SCS) rifted margins has significantly evolved. However, there are still many open questions related to when, how, and under what conditions major crustal thinning (necking) and lithospheric breakup occurred and how these processes are recorded in the stratigraphic and magmatic tape recorder. In this study, we aim to explore the tectono-sedimentary-magmatic evolution of rift systems during crustal thinning and lithospheric breakup. Our study is based on observation of conjugate margins architecture along high resolution long offset reflection seismic sections through the Northwest SCS. We focus on crustal thinning and lithospheric breakup, and the transition to first oceanic crust and the birth of an oceanic spreading centre. We describe the Northwest SCS crustal architecture, define extensional domains (proximal, necking, hyper-extended, OCT, oceanic domain) and margin architecture (upper and lower plate). We determine the tectono-sedimentary evolution and discuss the evolution of deformation modes through time and space by linking the tectono-stratigraphic-magma evolution with the observed crustal thinning. These results have important implications for understanding the deformation history and processes in time and space, and enable the analysis and linkage of the tectono-stratigraphic evolution of rift systems with the observed crustal thinning and breakup processes.
Vertical distribution of solute input shapes concentration-discharge relations
Authors: Burlando Paolo , Botter Martina , Li Li , Hartmann Jens , Fatichi Simone
Published: March 2020

Understanding the influence of solute inputs on their export dynamics at the catchment scale is an open challenge hampered by the general lack of distributed and time varying input data. The export dynamics is thus often investigated by analyzing concentration and discharge data at catchment outlets. These data together with knowledge of typical solute source location can provide insights about the export dynamics. We collected concentration and discharge data across 492 catchments in 9 countries and analyzed the solute concentration magnitude and dependence on discharge at the catchment outlet. The observations indicate that solutes with typically higher abundancy in the deeper subsurface have a quite different temporal dynamics and concentration-discharge (C-Q) relation than solutes produced near the surface. We further interpret results from observations by running synthetic experiments with a tracer-aided distributed model. The results clearly show that the depth at which the solute is produced is indeed the key-player in shaping the C-Q relation, especially on solutes exhibiting consistent diluting (Ca, Mg, K, Na, Cl) or weakly enriching (DOC) behavior. Such a generalization is not straightforward when moving to nutrients (NO3 and PO4), mostly injected sporadically through point or distributed sources. Their temporal variability is enhanced compared to the other solutes, and it adds uncertainties in the determination of the exponent of the C-Q relation.
The influence of gravel mixed with sand on the formation and development of ripples.
Authors: Van Landeghem Katrien , Yiannoukos Irinios , McCarron Connor , Morgan Jacob , Clayton-Smith Barney
Published: March 2020

Coarse and bimodal sediment mixtures like sand and gravel are common in palaeo-glaciated shelf seas and in coastal environments. Their presence leads to more complex sediment transport and morphodynamic processes, depending on the ratio of sand to gravel in the bed. With increased pressure on our near-and offshore sea beds, there is a growing need to more accurately model sediment transport and bedform dynamics with an increasing focus on bimodal sand-gravel sediment mixtures. Revisiting the quantification of the hiding-exposure (HE) effect highlighted how differently sized grains in a bimodal mixture modify each other’s threshold of motion. The critical shear stress needed to mobilise the sand and gravel fractions increased by up to 75% and decreased by up to 64% respectively, compared to that needed to mobilise well-sorted sediment of similar size. Implementation of this newly quantified HE correction in current-and wave-driven models illustrated that its influence on bedload transport rates and bed morphodynamics was greatest for mixtures where gravel percentage ranges between 10 and 20 %. Laboratory experiments were therefore conducted to investigate ripple formation and bed dynamics in mixtures with gravel percentage between 0 and 25%. The development of initial bedforms was quicker in sand-gravel mixtures compared to those developed in pure sand, whilst final heights and migration rates of the developed ripples decreased with increasing fraction of gravel in the bed. During this presentation, a full comparison will be made of the morphology and “down-core” sedimentary properties of ripples formed at different flow speeds. If we want to use our seabeds cost-effectively and sustainably, we need a better understanding on the influence of a decreased mobilisation of the finer fractions and an increased mobilisation of the coarser fraction on the dynamics of beds with a bimodal sediment composition.
Transformation of Amorphous Calcium Carbonate in Air - The Role of Additives and Humidity
Authors: Goetschl Katja , Spirk Tina , Purgstaller Bettina , Dietzel Martin
Published: March 2020

Amorphous calcium carbonate (ACC) is one of the six well-known CaCO3.nH2O (0 ≤ n ≤ 6) solids and is of vast interest in the development of advanced materials. ACC offers enhanced performance compared to its crystalline equivalents due to its high solubility, specific surface and porosity. A large body of studies has been devoted to the applicability of ACC in pharmaceutical and industrial domains, pointing out material porosity to be a key property for its application. However, less is known about the material porosity evolution during ACC transformation into crystalline calcium carbonate (e.g. calcite or vaterite).

In this study we investigate the transformation of ACC in air and the effect of three additives (magnesium chloride, activated carbon and xanthan) at distinct humidities on the properties of the final crystalline product. ACC standard material was synthesized in either pure form or together with one of the above additives, stamped into a pellet, and exposed to 40 or 75 % RH. Mineralogical characterization of the crystalline products exhibits individual quantitative polymorph distribution induced by different additives and humidities. The most prominent result of the present study is the highly dissimilar pore size distribution when the ACC pellets were exposed to different humidities. Scanning electron microscopy combined with an image analysis software revealed 75 % RH to cause an increase of pore size of the final product by a factor of 10. These findings have significant implications to tailor and improve ACC nanomaterial designs and syntheses for pharmaceutical and industrial applications.
Depth-dependent analysis of fracture patterns inferred from image logs and cores in crystalline rocks
Authors: Afshari Moein Mohammad Javad
Published: March 2020

Enhanced Geothermal System (EGS) development requires an accurate fracture network characterization. The knowledge on the fracture network is fundamental for setting up numerical models to simulate the activated processes in hydraulic stimulation experiments. However, direct measurement of fracture network properties at great depth is limited to the data from exploration wells. Geophysical logging techniques and continuous coring, if available, provide the location and orientation of fractures that intersect the wellbore. The statistical parameters derived from borehole datasets (either from image logs or cores) constrain stochastic realizations of the rock mass, known as Discrete Fracture Network (DFN) models. However, accurate parametrization of DFN models requires sufficient knowledge on the depth-dependent spatial distribution of fractures in the earth’s crust.

This analysis includes a unique collection of fracture datasets from six deep (i.e. 2-5 km depth) boreholes drilled into crystalline basement rocks at the same tectonic settings. All the wells were drilled in the Upper Rhine Graben in Soultz-sous-Forêts Enhanced Geothermal System, France, except the well that was drilled in Basel geothermal project, Switzerland. The datasets included both borehole image logs and core samples, which have a higher resolution. Two-point correlation function was selected to characterize the power-law scaling of fracture patterns. The correlation dimension of spatial patterns showed no systematic variations with depth at one standard deviation level of uncertainty in moving windows of sufficient number of fractures along any of the boreholes. This implies that a single correlation dimension is sufficient to address the global scaling properties of the fractures in crystalline rocks. One could also anticipate the spatial distribution of deeper reservoir conditions from shallower datasets. On the contrary, the fracture density showed some variations with depth that are sometimes consistent with changes in lithology and geological settings at the time of fracture formation.
Research and Education Mine Reiche Zeche in Freiberg, Germany
Authors: Mueller Toni , Mischo Helmut , Lay Vera , Buske Stefan
Published: March 2020

The Reiche Zeche mine is a unique location for research and education. Since 1919, the former ore mine is used for educating and training of miners, engineers and mine surveyors by the TU Bergakademie Freiberg. Drifts and tunnels of the mine stretch over several kilometres at depths down to 230 m. Today, the Reiche Zeche mine plays a major role in mining research and related activities including various research institutes and industrial partners. Several underground test facilities and laboratories are in use and important in university education. A variety of local (15 institutes of TU Bergakademie Freiberg) and external partners (30 from 26 countries) are actively shaping research and education in the mine. Within the framework of the Baltic Sea Underground Innovation Network (BSUIN http://bsuin.eu), we aim at forming an efficient platform for future, innovative research and business activities in underground laboratories.
Using seasonal forecast information to strengthen resilience and improve food security in Niger River Basin
Authors: Minoungou Bernard , Andersson Jafet , Ali Abdou , Hamatan Mohamed
Published: March 2020

The rainy season occupies a central place in socio-economic activities in the Sahelian regions, as more than 80% of the population lives on agriculture and livestock. However, extreme hydroclimatic events such as droughts and floods affect these activities. Efforts made in recent years in the production of hydroclimatic information to enhance the resilience of populations have become insufficient, given the variability and climate change.

In this context, we have conducted a study on improving the quality of seasonal forecast information to strengthen the resilience and improve the food security in West Africa, especially on the Niger River Basin. We used seasonal climate forecasts and the HYPE hydrological model to predict some characteristics of the rainy season in West Africa. The ECMWF seasonal forecast ensemble (system 5) from 1993 to 2015 (hindcast) and 2018 (forecast), available in the Climate Data Store (CDS) catalogue were used. The climatic variables considered are daily precipitation, mean and extreme temperatures (minimum and maximum) at the seasonal scale. The main objective was to assess the ability of the HYPE hydrological model, developed by Swedish Meteorological and Hydrological Institue, to predict runoff over the historical period and to produce hydrological seasonal forecasts for next years.

The main season’s characteristics produced are: (i) cumulative rainfall map for the rainy season (May to November), (ii) the rainfall situation of the season (above, near or below normal considering 1993-2015 as reference period), (iii) hydrological situation of the season (above, near or below normal considering 1993-2015 as reference period), (v) graph of the mean seasonal streamflow over the Niger Basin compared to the reference period (1993-2015).

The predictability of 2018 hydrological seasonal products were assessed and the results are promising. The main challenges we faced were the initialisation of the model, the bias correction (the reference data to be considered and the appropriate method). Further research on these topics should continue to improve the quality of results.
Impacts of Global River Delta Modification on Ecosystem Services
Authors: Reader Martin O. , Santos Maria J. , Damm Alexander , Petchey Owen , de Boer Hugo
Published: March 2020

Human modification of natural systems has typically enhanced provisioning ecosystem services (ES), such as agriculture, at the expense of biodiversity and other types of services. Long-term sustainability requires a balance of ES flows to both maintain human wellbeing, while preserving biodiversity. In river deltas this balance is critical – fertile flat land, well stocked fisheries, and water for use and navigation have promoted rapid population growth and development. Yet the same development degrades the key ES protecting these deltas from hazards and pollution. Many deltas face a critical juncture, at risk or already ‘locked-in’ to the need for engineered solutions to global change problems, unsustainable globally and in the long-term.

We created a global dataset of 237 deltas and collected indicators of the extent each was modified from its natural state, and its ES supply. Several types of modification to the most important aspects of delta systems were considered – overall human impact (human footprint), pressure and demand on ES (population density), modification of water systems (flow disruption) and modification of natural productivity (human appropriation of net primary productivity); grouping deltas by modification state. The impacts of this human modification on over 50 robust biodiversity and ES indicators were then analysed.

Firstly, we attempted to create bundles of commonly associated ES in delta areas. Hierarchical clustering highlighted several logical clusters related to crops, fisheries, water, species richness, biodiversity intactness and NPP. Secondly, we examined synergies and trade-offs between different ES. Provisioning services all showed clear correlations with one another, but clear trade-offs with supporting services or biodiversity. There were weaker synergies within and between regulating and supporting ES. Finally, the relationship between each type of modification and the ES was classified using six typologies fitted by applying a decision tree to their LOESS regression curves. Crop indicators typically had an inverted-U relationship, increasing in moderately modified deltas, but decreasing in the most modified, presumably pushed out by other land uses. While many other ES declined with modification, interestingly, species richness and intactness both began to increase again in the most modified deltas. In summary, this global analysis is the first to illustrate how ES vary along a gradient of development in deltas, and highlights the need to balance further modification against these critical services.
Evolution of Caribbean subduction from P-wave tomography and plate reconstruction
Authors: Allen Robert , Braszus Benedikt , Goes Saskia , Rietbrock Andreas , Collier Jenny ,   The VoiLA Team
Published: March 2020

The Caribbean plate has a complex tectonic history, which makes it  particularly challenging to establish the evolution of the subduction zones at its margins. Here we present a new teleseismic P-wave tomographic model under the Antillean arc that benefits from ocean-bottom seismometer data collected in our recent VoiLA (Volatile Recycling in the Lesser Antilles) project. We combine this imagery with a new plate reconstruction that we use to predict possible slab positions in the mantle today. We find that upper mantle anomalies below the eastern Caribbean correspond to a stack of material that was subducted at different trenches at different times, but ended up in a similar part of the mantle due to the large northwestward motion of the Americas. This stack comprises: in the mantle transition zone, slab fragments that were subducted between 70 and 55 Ma below the Cuban and Aves segments of the Greater Arc of the Caribbean; at 450-250 km depth, material subducted between 55 and 35 Ma below the older Lesser Antilles (including the Limestone Caribees and Virgin Islands);  and above 250 km, slab from subduction between 30 and 0 Ma below the present Lesser Antilles to Hispaniola Arc. Subdued high velocity anomalies in the slab above 200 km depth coincide with where the boundary between the equatorial Atlantic and proto-Caribbean subducted, rather than as previously proposed, with the North-South American plate boundary. The different phases of subduction can be linked to changes in the age, and hence buoyancy structure, of the subducting plate.
Feedbacks between magmatic intrusions, faulting, and surface processes at continental rifts
Authors: Morrow Thomas , Olive Jean-Arthur , Behn Mark , Smalls Paris
Published: March 2020

During continental rifting, faulting, magmatic injection, and surface processes collectively shape the landscape. Although feedbacks between surface processes and faulting at rifts have been explored, the relationship between shallow magmatic intrusions, topography, and surface processes is poorly understood. Magmatic injection is controlled in part by lithospheric stress, and should therefore respond to rift-associated perturbations to the stress field. Along with normal fault formation and evolution, surficial mass redistribution via erosion, sediment transport, and deposition alters lithospheric stresses and has the potential to influence dike emplacement and long-term rift structure. Here we present a series of two-dimensional (2-D) numerical model runs utilizing the particle-in-cell, finite difference code SiStER to quantify the feedbacks between tectonic, magmatic, and surface processes that shape continental rifts. In our models, extension is accommodated through a combination of magmatic intrusion and tectonic stretching. Magmatic intrusion occurs within a narrow region when and where the sum of horizontal deviatoric stress and magmatic overpressure exceeds the tensile strength of the lithosphere. Magmatic overpressure is thus a key parameter that strongly modulates the sensitivity of dike emplacement to faulting, bending, and topographically-induced variations in lithosphere stress. Our results first probe the relationships between fault-related stresses and the timing and depth-distribution of magmatic intrusions at a rift with no active surface processes. In these cases, the locus of magmatic spreading migrates vertically in response to the evolving stress field. The 2-D tectonic model is then coupled to a 1-D landscape evolution model, which modifies topography concurrent with extension. In the simplest case, topographic diffusion effectively redistributes the topographic load, contributing to variations in injection-controlling lithospheric stresses. We compare our tectonic-responsive results with models that incorporate active surface processes to constrain the conditions under which surface processes modulate magmatic injection. Our simulations suggest that the development and redistribution of topography exerts an important control on the partitioning of tectonic and magmatic strain at extensional plate boundaries.
Spatio-temporal variation in NPP and correlation analysis with aerosol loading and PAR in China during 2001-2017
Authors: Li Xin , Cheng Weiming
Published: March 2020

The net primary productivity (NPP) reflects the growth or production of terrestrial vegetation and plays an important role in the carbon cycle on the earth. It quantifies the difference between the organic matter produced by photosynthesis and the loss of maintenance and growth respiration. The investigation of the spatio-temporal variation in NPP is significant for monitoring plant photosynthesis and carbon uptake in terrestrial ecosystems. In this study, the variability and trend of NPP in China during 2001-2017 are analysed using level 4 MODIS product (MOD17A2H). Additionally, to explore whether the NPP change in recent decades are related with the photosynthetically active radiation (PAR) variation caused by increasing aerosol loading, the correlation between NPP, PAR and aerosol optical depth (AOD) are analysed at national, regional, and pixel scales. The results show that the annual mean NPP shows higher values in the southeast than in the northwest. The highest NPP level above 2.5 gCm-2day-1 is mainly distributed in tropical humid regions, including Zhejiang, Fujian, Guangdong and western Yunnan. The NPP increases with an amplitude of 0.131 gCm-2day-1 during the study period. The forests have higher mean levels of NPP (1.808 gCm-2day-1) and larger increasing magnitudes (0.35 gCm-2day-1) than those of croplands and grasslands. The NPP and AOD show a negative correlation (-0.6<R<-0.2) at a significance level of 0.05 over the middle area of China. The PAR direct and diffuse components generally have positive (0<RPARdir_NPP<0.6) and negative correlations (-0.6<RPARdif_NPP<0) with NPP, respectively, in most of China except the northeast and Tibetan Plateau. The NPP have stronger correlations (0.215 and -0.218) with the direct and diffuse PAR in forests than in croplands and grasslands, implying that NPP is more sensitive to the change in PAR in forests than in other vegetation cover types.
Arctic atmospheric surface layer in spring during expedition “Transarctica-2019”
Authors: Makhotina Irina , Makshtas Alexander , Kustov Vasilii
Published: March 2020

Polar expedition “Transarctica-2019” worked in the northern part of the Barents Sea in April 2019. One of the main goals was to study the interaction processes in the system “atmosphere – sea ice – ocean upper layer”. Complex synchronous observations in atmosphere, snow-ice cover and ocean were performed. Present study describes characteristics of atmospheric surface layer and heat balance of snow-ice cover during drift of RV “Akademik Treshnikov” to the north of the Archipelagos Franz Josef Land and Svalbard, in the area 80 – 82N, 30 – 45E, in comparison with observations at drifting station “North Pole-35”, worked in the same area in April 2008, and Research station “Ice Base Cape Baranova” in April 2019.

The characteristics of the near-ice atmospheric layer and energy exchange processes during the drift of the expedition Transarctica-2019 were significantly affected by the presence of clouds and the state of the ice cover. The influence of these factors led to decrease of radiative cooling of the surface, formation of warmer and wetter atmospheric boundary layer and to a weakening of the turbulent exchange between the atmosphere and the snow-ice cover.

Comparison of energy exchange characteristics calculated for the Bolshevik Island (79° N) and area, where expedition “Transarctica 2019” worked, showed good agreement between the monthly averaged values and trends in heat fluxes, despite the fact that in the first case the underlying surface was land surface, and in the second - sea ice cover.

Significantly different conditions were observed in the area of the drifting station “North Pole-35”, drifted in April 2008 about 300 km to the north of the “Transarctica 2019” area. The older and thicker sea ice cover and frequent occurrence of cloudless days, characterized by negative long-wave balance, caused here cooling of the surface, formation of a stable boundary layer, and large values of the sensible heat flux compared to observed during the expedition 2019. Position of “Transarctica-2019” to the south of the massifs of old and thick ice, in an area, characterized by medium-thick ice and, as consequence, more intense heat flux through sea ice cover, as well as the presence of leads, determined higher air and surface temperatures and relative humidity.

The work supported by the Ministry of Science and Higher Education of the Russian Federation (project no. RFMEFI61619X0108).
Modelling ice rise englacial temperature profiles to constrain past ice-sheet dynamics
Authors: Montelli Aleksandr , Kingslake Jonathan
Published: March 2020

Present-day englacial temperatures are the product of the millennial-scale histories of ice flow and thermal boundary conditions experienced by an ice sheet. Vertical englacial temperature profiles extracted from boreholes drilled at ice divides record past ice dynamics and changing external forcings. Bindschadler (1990) estimated the timing of grounding of Crary Ice Rise, Ross Sea, by minimizing the mismatch between modelled and measured temperature profiles. This approach has huge potential if future boreholes are drilled at Antarctic ice rises in locations suspected of undergoing significant dynamics change. Yet, the uncertainties inherent in this approach must be carefully assessed to target and maximize the utility of borehole drilling. Here, using a 1D vertical heat flux model, we simulate the evolution of temperature as a function of depth in six locations with slow-flowing, cold-based ice in the Weddell and Ross Sea sectors of the West Antarctic Ice Sheet. The locations were chosen using output from the Parallel Ice Sheet Model (PISM) as which are most likely to have ungrounded and regrounded during the last deglaciation (i.e., through last 20 k.y.). We use the shallow ice approximation assuming horizontally isothermal ice and no basal sliding. Several parameters, accounting for timing and duration of grounding/ungrounding events, surface temperature evolution, accumulation rate, ice-thickness change, geothermal heat flux and vertical velocity, are varied to generate a range of different temperature profile outputs. Uncertainties associated with each parameter are then evaluated using a Monte-Carlo approach, yielding a statistical account of model sensitivity to key variables. We highlight that the precision needed to infer timing of grounding increases with the duration of grounded ice flow. Results presented here can help in choosing future ice drilling sites, and provide useful constraints on inferring past forcings and changing boundary conditions from in-situ temperature-depth measurements.
Oscillatory and stepwise compositional zoning in high pressure–low temperature garnets: records of transient and spatially-variable fluid-fluxing during subduction?
Authors: George Freya R. , Viete Daniel R. , Ávila Janaína , Seward Gareth G.E.
Published: March 2020

During subduction, devolatization reactions within the downgoing slab release significant volumes of fluid. Once released, the fate of such fluids remains unclear; they may either stagnate such that local rock systems remain undrained, or fluids may be mobilized over large length scales, draining the dehydrating rock volume. The fact that there is evidence from the metamorphic rock record to support both open- and closed-system fluid behavior demonstrates that permeability in deep crystalline metamorphic rock is both spatially and temporally heterogeneous. Prograde eclogitic veins greater than cm-scale are volumetrically scarce in the high pressure–low temperature (HP–LT) rock record, suggesting that either transient channelized flow is incredibly efficient and thus necessitates negligible grain boundary transfer and a low intact rock permeability, or that a large proportion of fluid migration to the subduction interface may be via more elusive grain boundary mechanisms.

Major element electron microprobe maps of HP–LT garnets from metabasic rocks of the Urals, Russia, As Sifa, Oman, and Syros, Greece, variably reveal short-wavelength and concentric oscillatory zoning in the outer rim region. Oscillatory zoning in most garnets is accompanied by homogeneous core-to-rim aluminum content. However, in samples from As Sifa and Syros, the onset of near-rim major element oscillatory zoning is concomitant with a rimwards step increase in Al content. Secondary ion mass spectrometry (SIMS) O-isotope analyses across rhythmic zoning in samples from each setting are used to assess the hypothesis that this sharp, stepwise change in garnet chemistry reflects a period of localized open system fluid-fluxing behavior, superimposed on a history of an otherwise stagnant fluid within an impermeable grain boundary network. In such a case, coupled oscillatory zoning in major and trace elements—as revealed by laser ablation–inductively coupled plasma­–mass spectrometry (LA–ICP–MS) mapping—may point to pulsed P–T fluctuations, variable partitioning behavior, local kinetic effects associated with metamorphic reaction/dehydration, or changes in redox state serving as a driver for the development of this characteristic HP–LT geochemical garnet zoning.
Patterns in time-dependent parameters reveal deficits of a catchment-scale herbicide transport model
Authors: Ammann Lorenz , Fenicia Fabrizio , Doppler Tobias , Stamm Christian , Reichert Peter
Published: March 2020

Many hydrological systems have a stochastic behavior at the spatiotemporal scales we observe them. The reasons are insufficient quantity or quality of input observations, and model structural errors, the effects of which vary over time. Assuming model parameters as time-dependent, stochastic processes can account for such effects. This approach differs from using deterministic models in combination with a stochastic error term on output and or input. We start from an existing deterministic conceptual bucket model, which was developed and calibrated to jointly predict streamflow and herbicide pollution observed in a small stream with an agricultural catchment in the Swiss midlands. The model considers sorption and degradation of herbicides, as well as fast transport processes such as overland flow to shortcuts and macropore flow to tile drains. Subsequently, the model is made stochastic by replacing selected constant parameter values by time-varying stochastic processes. We perform parameter inference according to the Bayesian approach using a Gibbs-sampler to combine Metropolis sampling of the remaining constant parameters with sampling from an Ornstein-Uhlenbeck process for the time-dependent parameter. A preliminary analysis of the resulting time series of the parameters reveals, for example, model deficits w.r.t. baseflow, in particular during dry conditions. We show that the resulting patterns can inspire model improvements by providing information that can be interpreted by the modeler. These findings indicate that stochastic models with time-dependent parameters are a promising tool for uncertainty quantification of water quality models and for facilitating the scientific learning process, which may ultimately lead to better predictions.
Full-waveform inversion for signal enhancement of weak amplitude phases using beamforming and adjoint methods
Authors: Koroni Maria , Fichtner Andreas
Published: March 2020

In this study, we develop a new adjoint- and full-waveform inversion approach for low-amplitude seismic phases that are typically below noise in individual recordings. The methodology aims at enhancing weak signals from body wave phases, which can be used in full-waveform inversion for inferring structural and boundary parameters in the earth. The new approach is based on the formulation of misfit functionals and corresponding adjoint sources for stacks of suitably time-shifted recordings. 

To tackle this problem, we compute synthetic waveforms using spectral-elements for models with and without topographic variations along mantle discontinuities. We focus on global underside reflections which are reportedly almost always undetectable in real seismograms due to their low amplitudes and are considerably affected by topography. We enforce phase alignment on a chosen reference seismogram recorded at an average distance among the selected stations. A time shift towards the reference is applied to all seismograms according to their epicentral distance calculated by 1-D ray tracing. A set of time shifts is calculated by cross-correlation in time windows around predicted traveltimes of the desired phase. Using this set of time shifts, we sum the waveforms creating the main stack for each model.

We use the two linear stacks as observed and synthetic (with and without topography, respectively) and develop a least-squares misfit measurement which gives rise to an adjoint source determined by the time shift between stacks. The expectation is that computing the traveltime Fréchet kernel with respect to volumetric and boundary model parameters will show the exact sensitivity of the enhanced signal and save time from computing each station kernel separately. Upon achieving signal enhancement of the desired phases, we can ensure that these can be used for better informing updates of the initial model given the higher quality measurement of the observable.

This method once fully developed will allow us to leverage information of many recordings by reducing incoherent signal and enhancing weak seismic phases. The computation of sensitivity kernels in our study has a twofold importance. Firstly, it helps us realise whether the stacking technique indeed enhances the desired signal and whether it is ideal for precursor waves. Secondly, the exact sensitivity kernels show us the way of incorporating finite-frequency effects of weak but informative phases and introducing non-linear inversion for improving imaging while reducing some computational cost. 

 