bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a system for monitoring and assessment of underwater sound
Authors: Marinova Veselka , Stefanov Asen
Published: March 2020

The Bulgarian Black Sea coast is an area with intense human activity, but also there is a complex ecosystem. Several anthropogenic sources generate loud sound levels in this area. The two most wide spread are maritime transport and hydrocarbon exploration and exploitation in the Bulgarian offshore sector. Underwater sound may have negative impact on animals in the Bulgarian waters that are sensitive to sound, such as marine mammals and certain fish species. 

The knowledge of ambient noise levels is very important for the characterization of the environmental status with regard to the European Marine Strategy Framework Directive (MSFD). The directive is aiming at a more effective protection of the marine environment including the protection of marine life exposed to noise, and the improvement of the health of the marine environment as a whole.

To estimate this impact the ocean technologies department of Bulgarian Institute of Oceanology developed a system to monitor the sound generated by marine activities following the TSG Noise guidance. The aim was to provide an integrated solution to monitor and asses the noise impact of ship traffic or other marine activities. The development was funded by program BG02 "Integrated management of marine and inland waters" financed by the financial mechanism of the European economic Area (EEA FM) 2009-2014.

The system consists of monitoring and simulation components. The combination of numerical modelling and noise measurements at selected locations offers a credible solution to the problem of underwater noise monitoring. The monitoring component comprises an array of passive sound recorders, equipped with hydrophones, self-contained power supplies, data acquisition and storage electronics. The simulation tool is in development. Suitable modelling approaches, modelling scenarios, and acoustic model input values are being selected and applied for the most important sources of sound and for underwater sound propagation in the Bulgarian waters. The tool computes sound maps produced by multiple noise point sources, as input for assessment of the environmental status. For optimum results, the simulation tool will be validated using acoustic measurements provided by the monitoring tool.

Future work includes development of a post-processing tool of the sound maps to obtain indicators relevant to both the noise anthropogenic pressure and biological effect of underwater noise impact on marine life.
Detailed monitoring of groundwater quality near municipal solid waste landfills. Case study in Valencia region (Spain)
Authors: Rodrigo-Ilarri Javier , Rodrigo-Clavero María-Elena
Published: March 2020

Municipal solid waste landfills are one of the most relevant soil and groundwater pollution sources. Monitoring networks should be designed on the preliminary phases to guarantee that groundwater quality control is performed periodically over both the operation and post-closure phase of the landfill.

This work shows the results of a groundwater quality detailed monitoring campaign developed on a municipal solid waste landfill in Valencia Region (Spain). The sampling campaign included the continuous analysis over 11 boreholes of the following parameters: mineral oil, As, B, Ba, Cd, Chlorine, electric conductivity, TOC, total Cr, Cr VI, Cu, COD, phenols, fluorine, total P, Hg, hydrocarbons, Mo, total N, Ni, Pb, pH, Sb, Se, suspended solids, sulphates and Zn. Besides, the piezometric levels around the landfill were also controlled.

Despite there is no clear Spanish legislation concerning groundwater quality, results show that the evolution of groundwater quality over time is satisfactory, fulfilling the requirements of the American (USEPA) and European (Dutch) legislation standards.
Characterising and assimilating surface soil moisture drydowns in the ORCHIDEE land-surface model
Authors: Raoult Nina , Ottle Catherine , Peylin Philippe , Bastrikov Vladislav
Published: March 2020

The rate at which land surface soils are drying following rain events is an important feature of terrestrial models since it determines, for example, the water availability for vegetation, the occurrences of droughts, and the surface heat exchanges. As such, soil moisture (SM) “drydowns”, i.e. the SM temporal dynamic following a significant rainfall event, are of particular interest when evaluating and calibrating land-surface models. By investigating drydowns, characterized by an exponential decay time scale metric τ, we aim to improve the representation of soil moisture in the ORCHIDEE global land-surface model. In this presentation, we consider τ calculated over a number of ISMN (International Soil Moisture Network) sites found within the footprint of FLUXNET towers. These in-situ sites cover a range of vegetation types and climates. Using the ORCHIDEE land-surface model, we first compare τ from the modelled SM timeseries to the same values computed from the in-situ SM measurements. We then assess the potential of using τ as a data assimilation metric to constrain some parameters of the ORCHIDEE model through a standard Bayesian optimisation procedure; we first select a number of key of water, carbon, and energy parameters through a sensitivity analysis. The optimised soil moisture timeseries are evaluated using the FLUXNET evapotranspiration and GPP data. We conclude by considering the potential of  global satellite products like SMOS or the ESA-CCI surface SM satellite data in order to scale up the experiment to a global scale optimisation.
Geochemical and mineralogical characteristics of beach sand sediments in southwestern Black Sea: An approach to heavy mineral placers
Authors: Bayram Hatice Nur , Uslu Asli Nur , Bakkalbasi Ali Erdem , Kiran Yildirim Demet , Doner Zeynep , Unluer Ali Tugcan
Published: March 2020

Geochemical and mineralogical characteristics of beach sand sediments in southwestern Black Sea: An approach to heavy mineral placers  

 Hatice Nur Bayram (1*), Aslı Nur Uslu (1), Ali Erdem Bakkalbaşı (1), Demet Kiran Yildirim (1), Zeynep Doner (1), Ali Tugcan Unluer (1)

 (1) Istanbul Technical University, Faculty of Mines, Department of Geological Engineering, Istanbul, Turkey (*hnnurbayram@gmail.com)

Abstract:  

Coastal or beach placer deposits are enrichments of heavy minerals with significant metal content that have been mechanically formed. This work studies the geochemical and mineralogical characteristics of beach sand sediments of southwestern Black Sea, Turkey which cover approximately 20 km2 area. The study area has 4 main geological units: Upper Cretaceous moderately-K kalkalkaline Istanbul volcanics, Oligocene Danismen Formation which is dominated by flood plain, marshy and lake environments, Upper Miocene-Pliocene Belgrad Formation which is dominated by terrestrial deposits, mostly gravel, sand and clay dominated and Quaternary formations which include sandy beaches, sand dunes and river alluvials.

A total of 8 beach sand samples were analyzed by X-ray Diffraction (XRD) and X-ray Fluorecance (XRF). Mineralogical compositions are mainly dominated by quartz, siderite, albite, calcite and minor amount of magnetite. Siderite-rich beach sands are observed in western part of the study area and mostly derived from Danismen Formation. Fe2O3 contents of this area are determined up to 40%.  On the other hand, in eastern part of the study area REE-Th-U content of beach sands are relatively higher than source rocks which is defined as a high-Al moderately-K kalkalkaline felsic rocks. The highest HFSE concentration were determined in -250+125µm fraction which consists of 16.5% of eastern beach sand. In this fraction LREE-Zr-U content rise drastically. It can be considered that REE-LREE contents is related with monazite minerals and U contents is related with zircon minerals, considering the monazite and zircon minerals are resistant to weathering and likely to occur in the orthomagmatic phase in the source volcanics.

Key words: Beach sand sediments; REE-Th-U; heavy minerals; southwestern of Black Sea; Turkey
Orbitally-paced South American Summer Monsoon variability during the mid- to late-Pleistocene
Authors: Hou Alicia Meng Xiao , Bahr André , Raddatz Jacek , Voigt Silke , Albuquerque Ana Luiza , Chiessi Cristiano M. , Friedrich Oliver
Published: March 2020

Hydrological extremes related to the South American Summer Monsoon (SASM) are expected to become more frequent in the near future and might have devastating socioeconomic consequences for the densely populated region of eastern Brazil. Given the complexity in SASM behaviour in space and time, a dense coverage of monsoonal precipitation records, particular those spanning multiple glacial-interglacial cycles, are urgently needed to constrain this high spatial-temporal variability. This information is necessary to reduce the uncertainty associated with projections of SASM precipitation in response to rising anthropogenic greenhouse gas (GHG) emissions. Here we use elemental ratios from X-ray fluorescence scanning of two sediment cores retrieved off the eastern Brazil margin to reconstruct long-term rainfall changes in the hinterland. Our findings from core M125-55-7 (offshore the Doce River, 20°S) reveal that during the past ~320 kyr, precession-paced insolation forcing is the primary pacemaker of variations in SASM precipitation over the Doce basin. We also determined an anomalous interval of weak monsoonal response to insolation forcing during Marine Isotope Stage 6, which we attribute to enhanced wintertime precipitation due to exceptionally strong southeast trade winds created by a steep South Atlantic latitudinal temperature gradient. Moreover, our results suggest that albeit predominantly driven by insolation forcing, the intensity of SASM rainfall responds negatively to GHG forcing, most likely through indirect feedbacks. We propose that GHG forcing directly influences the magnitude of both the inter- and intrahemispheric latitudinal temperature gradients, which in turn modify the strength of atmospheric circulation and precipitation in the tropics. Thus, we suggest that SASM rainfall intensity over tropical eastern Brazil will likely be suppressed by rising CO2 emissions in the future. Our preliminary analysis of core M125-73-3 (off the Contas River; 12°S) reveals regional differences in monsoonal precipitation between the more northerly Contas basin and the more southerly Doce basin. Most notably, unlike the insolation-paced continental rainfall variability recorded at site M125-55-7, SASM rainfall intensity over the Contas basin appears to be more sensitive to glacial-interglacial scale pacing over the past ~800 kyr. Taken together, our records reveal both the high spatial variability in SASM precipitation over eastern Brazil and the dominant influence of orbital forcing on monsoonal rainfall intensity.
From depth to surface: how deep-earth processes and active tectonics shape the landscape in Pamir and Hindu Kush
Authors: Crosetto Silvia , Metzger Sabrina , Scherler Dirk , Oncken Onno
Published: March 2020

The Pamir and Hindu Kush are located at the western tip of the India-Asia collision zone. Approximately a third of the northward motion of India’s western syntax is mostly accommodated by continental-scale underthrusting of the Indian plate beneath Asia. On its way northwards the arcuate, convex Pamir mountain range acts as a rigid indenter penetrating the weaker Eurasian plate, while lateral extrusion occurs to the west in the Tajik Depression.

Intense present-day shallow seismicity indicates active deformation along the northern and north-western semi-arid margin of the Pamir, where over the last century several M>6 and three M>7 crustal earthquakes, including a recent M6.4 event in 2016, were recorded. Earthquakes are distributed in the proximity of three main fault systems: the Pamir thrust system to the north, and the Darvaz fault and Vakhsh thrust system to the north-west. The pronounced topographic expression of these lithospheric faults is associated to a deeply incised landscape, which was profoundly shaped by past widespread glaciations. The transient evolution of the landscape following deglaciation is observed in the dynamic river network, characterised by intense fluvial incision and changes in the fluvial connectivity of the drainage system.

At depth, recent seismic tomography studies suggest delamination, stretching and tearing of the Asian slab beneath SW Pamir, and slab break-off underneath Hindu Kush. Slab break-off episodes are known to result in stress surges in the overlying lithosphere, potentially causing deformation and uplift.

In this complex system characterised by an important interplay between tectonics, climate and surface processes, we use qualitative and quantitative analyses of the topography and of the drainage systems evolution, inclusive of numerical tools, in order to define what is –and has been- the role played by the main lithospheric active faults of this area. In addition, we aim at identifying how landscape and surface dynamics respond, temporally and spatially, to processes, such as slab tearing/break-off, occurring at depth.
High-resolution assessment of the Valgu event: conodont diversity and δ18Ophos during the early Telychian (Silurian) in the Baltic Basin
Authors: Gomez Correa Monica Alejandra , Jarochowska Emilia , Männik Peep , Munnecke Axel , Joachimski Michael
Published: March 2020

The influence of global climate and oceanographic system dynamics over biological patterns throughout Earth’s history is one of the main concerns in paleobiology. Periods that record changes in biodiversity of various magnitude are of particular interest in this field. Previous studies of major Silurian bioevents (e.g. Ireviken, Mulde and Lau) suggest that these events affected different faunas and have been correlated with positive carbon isotope (δ13Ccarb) excursions and positive shifts in oxygen isotopes (δ18Ophos) ratios, suggesting there was a disturbance in the carbon cycle, a drop in temperature, and potential glaciations. However, the impact of the biological events has not been fully assessed, and the influence of climate change remains unclear.

Here, we focus on the Valgu event, a minor episode of proposed environmental and faunistic changes in the early Telychian, which has been recognized in Baltica and Laurentia paleocontinents by changes in conodont succession and a positive excursion in δ13Ccarb. In this study, we assess a limestone-marl alternation core section in Estonia deposited below the storm wave base during the Valgu event. We test for a substantial decrease in the biodiversity of conodont communities, for extent perturbation in the carbon cycle, manifest in a positive δ13Ccarb excursion, and an abrupt positive δ18Ophos shift, which might be indicative of rapid cooling and a rapid sea-level fall typical for glacio-eustatic cycles. To this aim, we measured bulk-rock δ13Ccarb as well as δ18Ophos in monogeneric conodont samples and analyzed the conodont diversity from the event interval.

The lower part of the investigated section is characterized by shallow-water bioclastic limestones containing green algae. On top of this facies, a pronounced hardground indicates a gap in deposition and marks the boundary between the bioclastic limestones and the overlying sediments composed of nodular limestones and marls, which were deposited below the storm wave base. They show a positive carbon shift of ca. 1.4 ‰ during the Valgu interval, but no indication of an extreme change in the conodont biodiversity is evident. Likewise, the δ18Ophos in conodonts remains constant in the section, arguing against cooling or glacially-driven sea-level fluctuations as drivers for the observed changes.
Extreme melt season traction variations recorded on the western Greenland Ice Sheet
Authors: Maier Nathan , Humphrey Neil , Harper Joel , Meierbachtol Toby
Published: March 2020

Basal traction is fundamental to the dynamics of glaciers and ice sheets. On the Greenland Ice Sheet meltwater delivery to the bed and evolving drainage efficiency and connectivity modulate traction producing a characteristic seasonal velocity response. While numerical modelling and basal pressure observations have linked these velocity variations to evolving subglacial drainage, a high-fidelity record of basal traction is needed to constrain the timing and magnitude of traction changes that modulate summer ice flow.  We present a continuous summertime record of basal traction, basal ice deformation, and surface velocity measured at a densely instrumented field site in western Greenland. We use a five-station GPS network and englacial measurements of shearing and ice temperature to directly estimate the basal traction using the force balance method at the site-scale (100s of meters). Localized traction variations (10s of meters) are inferred via variations in the near-basal deformation field recorded by inclinometers installed directly above the basal interface. Combined, the data give a multi-scale perspective on how the basal traction changes during summer and relates to the conceptual model of melt season flow. Our results show the basal traction migrates between extremes during the melt season, with magnitudes greater than three times the average winter traction and near zero. The basal traction extremes correspond with the spring event, the inferred transition to efficient drainage, and the late summer velocity decline. The rapid strengthening and weakening of the basal interface show the complicated interaction of local and regional forcing that modulate melt season sliding. The near-basal deformation variations allow us to constrain the stress configuration and drainage state during each extreme traction period. Overall, the results allow us to refine the conceptual model for melt season traction changes and provide measured estimates of traction variations which can be used as quantitative targets for coupled drainage – ice dynamic models.
LZER0: GNSS cost-effective real-time positioning applied to landslide monitoring
Authors: Tunini Lavinia , Zuliani David , Fabris Paolo , Severin Marco
Published: March 2020

The Global Navigation Satellite Systems (GNSS) provide a globally extended dataset of primordial importance for a wide range of applications, such as crustal deformation, topographic measurements, or near surface processes studies. However, the high costs of GNSS receivers and the supporting software can represent a strong limitation for the applicability to landslide monitoring. Low-cost tools and techniques are strongly required to face the plausible risk of losing the equipment during a landslide event.

Centro di Ricerche Sismologiche (CRS) of Istituto Nazionale di Oceanografia e di Geofisica Sperimentale OGS in collaboration with SoluTOP, in the last years, has developed a cost-effective GNSS device, called LZER0, both for post-processing and real-time applications. The aim is to satisfy the needs of both scientific and professional communities which require low-cost equipment to increase and improve the measurements on structures at risk, such as landslides or buildings, without losing precision.

The landslide monitoring system implements single-frequency GNSS devices and open source software packages for GNSS positioning, dialoguing through Linux shell scripts. Furthermore a front-end web page has been developed to show real-time tracks. The system allows measuring real-time surface displacements with a centimetre precision and with a cost ten times minor than a standard RTK GPS operational system.

This monitoring system has been tested and now applied to two landslides in NE- Italy: one near Tolmezzo municipality and one near Brugnera village. Part of the device development has been included inside the project CLARA 'CLoud plAtform and smart underground imaging for natural Risk Assessment' funded by the Italian Ministry of Education, University and Research (MIUR).
Long-term mass balance, runoff and area change in Stok group of glaciers, Ladakh, India, between 1969 to 2019.
Authors: Soheb Mohd , Ramanathan Alagappan , Lotus Sonam
Published: March 2020

An analysis of mass balance (MB), runoff and area of a group of small glaciers (< 1 km2) in Stok region, Ladakh, India, was conducted to investigate their behaviour in past few decades. These glaciers are essential to the downstream village of ~300 households as they are entirely dependent on the ice and snow meltwater for domestic and agricultural use. The study presents an in-situ (2014-2019) and historical modelled MB (1978-2019) of Stok glacier, which is first of its kind in Ladakh region. The observed MB was found to be negative since 2014 with an average MB of -0.4 m w. e. a-1. However, modelled MB showed a balanced condition during 1980s, followed by a severe retreat in the first decade of 21st century. MB sensitivity analysis suggests that the winter precipitation and summer temperature are almost equally significant in driving mass balance of the glacier and water resources. Around 27% increase in precipitation is required to compensate the melt due to 1°C rise in temperature. Net changes of glacier extent were determined from a detailed manual comparison of remotely sensed imagery acquired between 1969 to 2019 by the high-resolution declassified Corona mission, Landsat ETM+/OLI and PlanetScope satellites. All the glaciers in this region retreated with different rates during different periods. Overall, the reduction in glacier extent was found to be around -0.73 km2 (-0.016 km2 a-1) equivalent to ~15% of the total glacier extent, in the past five decades. Runoff from the catchment was also modelled with the help of available temperature, precipitation and remote sensing data. The runoff model was calibrated and validated using daily in-situ discharge data of two summers (2018 and 2019). It was found that the runoff was highest during July and August months due to both increased snow and ice melt. Winter precipitation in this region is essential not only for glacier health but for early spring sowing season when the demand for the water is highest, and snowmelt water is the only source of early streamflow. Thus, this study assumes greater significance in light of an perceptible shift in precipitation from winter to summer in past two decades, which needs further investigation.
Experimental investigation on turbulent rotating thermal convection at large Rayleigh numbers
Authors: Wedi Marcel , van Gils Dennis , Ahlers Guenter , Bodenschatz Eberhard , Weiss Stephan
Published: March 2020

Thermal convection is of major importance in various astro- and geophysical systems, exemplary are buoyancy driven ﬂows in the atmosphere or in the stellar interior. It has been studied for decades in an idealized model system - the Rayleigh-Bénard convection (RBC) - which consists of a horizontal ﬂuid layer heated at the bottom and cooled at the top. Within the Oberbeck-Boussinesq approximation this system is controlled by two parameters only. These are the Rayleigh number (Ra), which represents the thermal driving and the Prandtl number (Pr) that relates the momentum and thermal diffusivities of the ﬂuid. Convection ﬂows in geo- and astrophysics are often inﬂuenced by Coriolis forces due to the rotation of the planet or the star. In RBC-system, Coriolis forces are introduced by rotating the convection cell around its vertical axis. The rotation is expressed by an additional dimensionless control parameter, i.e., the inverse Rossby number 1/Ro. We study experimentally the inﬂuence of rotation on the heat transport and the temperature ﬁeld at very large Ra in the High Pressure Convection Facility (HPCF) in Göttingen. The facility consists of a cylindrical cell of 1.10m diameter and 2.20m height that is ﬁlled with pressurized sulfur hexaﬂuoride (SF6) at up to 19bar. The height of the cell and the large density of SF6 enable us to reach very large Ra (up to 8×1014) at 0.74<Pr<0.96. The cell is mounted on a rotating table and connected to the non-rotating world via water feed-throughs and slip rings. With these, the signals of more than 100 thermistors close to the sidewalls are collected.
We ﬁnd a monotonic decrease of the heat transport with increasing rotation rate. Furthermore, we measure quantities of the ﬂow close to the lateral side walls of the convection cylinder. For large rotation rates we analyze this as part of the recently proposed “Boundary Zonal Flow” (BZF), where the vertical heat transport is enhanced and warm (cold) up (down) ﬂow self-organizes in a periodic manner. In the experiment we observe the BZF most notably in the probability density function of the temperature, which develops a bimodal Gaussian distribution. We also ﬁnd that the periodic warm-cold structure drifts in anti-cyclonic direction and thus form traveling waves of the temperature ﬁeld.
Understanding basaltic Plinian activity at Masaya caldera, Nicaragua
Authors: Bamber Emily C , Arzilli Fabio , Polacci Margherita , La Spina Giuseppe , Petrelli Maurizio , Hartley Margaret E , Di Genova Danilo , Fellowes Jonathan , Chavarría David , Saballos Jose Armando , De' Michieli Vitturi Mattia , Burton Mike
Published: March 2020

Plinian eruptions are the most hazardous yet enigmatic style of volcanism at basaltic systems. The low viscosity of basaltic magma should preclude its fragmentation; however, there are several recognised examples of basaltic Plinian activity. Historical eruptions of Masaya caldera, Nicaragua; Etna, Italy (122 BC); and Tarawera, New Zealand (1886) have ejected > 1 km3 of material. The Las Sierras-Masaya volcanic complex (Masaya caldera) has produced several basaltic Plinian eruptions, yet currently exhibits low explosive-effusive activity. This volcano has erupted chemically homogeneous magmas over at least the past 6000 years, which suggests that this significant difference in eruptive style is not attributable to a compositional change. Therefore, the cause of increased explosivity at Masaya caldera remains uncertain. 

We present new measurements of major, trace and volatile elements in basaltic Plinian eruption products from the Fontana Lapilli (60 ka) and Masaya Triple Layer (2.1 ka) eruptions of the Las Sierras- Masaya volcanic complex. We use our data in rheological and thermometric models to define the pre- and syn-eruptive conditions that favour highly explosive activity. We then combine our petrological data with a numerical conduit model to constrain the pre-eruptive condition of the magma reservoir and simulate the conduit processes, to understand the magmatic conditions that promote fragmentation during magma ascent. The common physico-chemical magmatic conditions that promote basaltic Plinian activity at Masaya are high microlite crystallinity, moderate storage temperatures and a low initial H2O concentration. Our combined approach greatly improves our general understanding of explosive basaltic activity and provides new insight into the effusive-explosive transition of the highly hazardous Las Sierras-Masaya system.
Modeling the effect of flood and drip irrigation on groundwater recharge
Authors: Pool Sandra , Francés Félix , Garcia-Prats Alberto , Puertes Cristina , Pulido-Velázquez Manuel , Sanchis-Ibor Carles , Schirmer Mario , Yang Hong , Jiménez-Martínez Joaquín
Published: March 2020

Irrigation modernization, here defined as the replacement of traditional flood irrigation systems by pressurized drip-irrigation technology, has been widely promoted with the aim to move towards a more sustainable use of freshwater resources in irrigated agriculture. However, the scale sensitivity of irrigation efficiency challenged the predominantly positive value attributed to irrigation modernization and asked for an integrated evaluation of the technological change at various scales. The aim of this study is therefore to contribute to an improved understanding of the hydrological functioning in a landscape under irrigation modernization. We used local field observations to propose a regional scale modeling approach that allowed to specifically simulate the difference in water balance as a function of irrigation method and crop type. The approach focused on the modification of the spatial input data and had therefore the benefit of being relatively independent of the final choice of the hydrological model. We applied the proposed approach to the semi-arid agricultural area of Valencia (Spain), where regional information about the use of irrigation technologies and irrigation volumes at farm level were available. The distributed hydrological model Tetis was chosen to simulate the daily water balance from 1994 to 2015 for an area of 913 km2 at a spatial resolution of 200 m. Model simulations were based on a random selection of parameter values that were subsequently evaluated in a multi-objective calibration framework. Multiple process scales were addressed within the framework by considering the annual evaporative index, monthly groundwater level dynamics, and daily soil moisture dynamics for evaluation. Simulation results were finally analyzed with a focus on groundwater recharge, which is of particular interest for environmental challenges faced within the study area. Simulation results of groundwater recharge for the entire agricultural area indicated a considerable variability in annual recharge (values from 112 mm up to 337 mm), whereby recharge was strongly controlled by annual rainfall volumes. Annual recharge in flood-irrigated areas tended to exceed annual recharge in drip irrigated-areas except for years with above average rainfall volumes. The observed rainfall dependency could be explained by the fact that recharge in drip-irrigated areas almost exclusively occurred during rainy days, whereby a few heavy rainfall events could produce the majority of annual recharge. Our results indicated interesting differences but also commonalities in groundwater recharge for flood and drip irrigation, and therefore emphasized the importance of explicitly considering irrigation technology when modelling irrigated agricultural areas.
New insights into nutrients dynamics and the carbonate system using a neural network approach in the Mediterranean Sea
Authors: Fourrier Marine , Coppola Laurent , D'Ortenzio Fabrizio
Published: March 2020

The semi-enclosed nature of the Mediterranean Sea, together with its small inertia which is due to the relatively short residence time of its water masses, make it highly reactive to external forcings and anthropogenic pressure. In this context, several rapid changes have been observed in physical and biogeochemical processes in recent decades, partly masked by episodic events and high regional variability. To better understand the underlying processes driving the Mediterranean evolution and, anticipate changes, the measurement, and integration of many biogeochemical variables are mandatory.

The development of new BGC sensors implemented on in situ autonomous platforms allows to increase the acquisition of essential biogeochemical variables. However, the measurements carried out by in situ autonomous platforms (e.g. profiling floats, gliders, moorings) are not exhaustive.

Recently, deep learning techniques and in particular neural networks have been developed. The CANYON-MED (for Carbonate system and Nutrients concentration from hYdrological properties and Oxygen using a Neural-network in the MEDiterranean Sea) neural network-based method provides estimations of nutrients (i.e. nitrates, phosphates, and silicates) and carbonate system variables (i.e. total alkalinity, dissolved inorganic carbon, pHT) from systematically measured oceanographic variables such as in situ measurements of pressure, temperature, salinity, and oxygen together with geolocation and date of sampling.

This regional approach, therefore, using quality-controlled in situ measurements from more than 35 cruises. CANYON-MED obtains satisfactory results: accuracies of 0.73, 0.045, and 0.70 µmol.kg-1 for the nitrates, phosphates and silicates concentrations respectively, and 0.016, 11 µmol.kg-1 and 10 µmol.kg-1 for pHT, total alkalinity and dissolved organic carbon respectively. CANYON-MED thus generates “virtual” data of parameters not yet measured by autonomous platforms, while ably reproducing the data already sampled, emphasizing its ability to fill the gaps in time-series.

Hence, by applying it to the large and growing network of autonomous platforms in the Mediterranean Sea, this method allows us to gain new insights into nutrients and carbonate system dynamics in targeted areas. In particular, in the northwestern Mediterranean Sea, the impact of deep convection on biogeochemistry (e.g., nutrient replenishment and pHT variability) is highly variable over time and poorly covered by observing networks. In this case, CANYON-MED would improve our observations and understanding of the dynamic and coupled system.
Geophysical insights on the internal dynamics of lahars from Lumbre channel, Volcán de Colima, Mexico
Authors: Walsh Braden , Coviello Velio , Capra Lucia , Procter Jonathan , Márquez-Ramirez Victor
Published: March 2020

Here, we present data from lahars through the use of a 3-component broadband seismometer, accelerometer, and a video camera installed 3 m from the Lumbre channel on Volcán de Colima, Mexico to understand rheology differences within multiple events, which occurred in late 2016. We used a combination of peak frequency content, directionality, and video analysis to determine rheology changes amongst the multiple events. Our findings show that different peak frequency patterns in each seismic component correspond to differing rheologies and flow processes. For instance, in the vertical and flow parallel directions the transition from streamflow to lahar coincides with a narrow frequency distribution to wide. Conversely, the cross-channel frequency content is opposite with streamflow portraying a wide frequency distribution transitioning to a narrow distribution with the lahars. Furthermore, there is a drop in overall peak frequencies when transitioning from streamflow to lahar. The directionality ratios computed further yielded evidence for a rheologic change between streamflow and lahar. Directionality ratios >1 were calculated for each lahar, and <1 for streamflow. We go on to show that componential analyses yielded channelization or freedom of movement in the cross-channel, bedload transport in the flow parallel, and channel geology in the vertical direction are possibly the main drivers in the peak frequency output of debris flows.
Why rock glacier deformation velocities correlate with both ground temperatures and water supply at multiple temporal scales
Authors: Kenner Robert , Pruessner Luisa , Beutel Jan , Limpach Philippe , Phillips Marcia
Published: March 2020

Recent studies have highlighted water supply as a driving factor for rock glacier deformation velocities. In parallel, numerous observations of correlating mean annual air- or ground temperatures and rock glacier velocities have been reported. We investigated the connection between rock glacier temperatures and –hydrology and found that there is no contradiction between both hypotheses. We observed that water supply to the shear horizon of rock glaciers is highly correlated to their mean annual temperatures and – even more pronounced – to their temperatures during early winter. The rock glacier temperatures influence the amount of water supplied to the shear horizon to a lesser extent, but strongly determine the duration of the water supply. The main external influencing factor on rock glacier dynamics found next to atmospheric warming was early winter snow cover. Our results are based on deformation- and borehole temperature measurements of four Swiss rock glaciers.
Recent progress and new methods for detecting causal relations in large nonlinear time series datasets
Authors: Runge Jakob
Published: March 2020

Detecting causal relationships from observational time series datasets is a key problem in better understanding the complex dynamical system Earth. Recent methodological advances have addressed major challenges such as high-dimensionality and nonlinearity, e.g., PCMCI (Runge et al. Sci. Adv. 2019), but many more remain. In this talk I will give an overview of challenges and methods and present a novel algorithm to identify causal directions among contemporaneous (or instantaneous) relationships. Such contemporaneous relations frequently appear when time series are aggregated (e.g., at a monthly resolution). Then approaches such as Granger Causality and PCMCI fail because they currently only address time-lagged causal relations.
We present extensive numerical examples and results on the causal relations among major climate modes of variability. The work overcomes a major drawback of current causal discovery methods and opens up entirely new possibilities to discover causal relations from time series in climate research and other fields in geosciences.

Runge et al., Detecting and quantifying causal associations in large nonlinear time series datasets, Science Advances eeaau4996 (2019).
Observations and modeling of the rupture development based on the analysis of Source Time Functions
Authors: Renou Julien , Vallée Martin , Aochi Hideo
Published: March 2020

Our knowledge of earthquake source physics, giving rise to events of very different magnitudes, requires observations of a large population of earthquakes. The development of systematic analysis tools for the global seismicity meets these expectations, and allows us to extract the generic properties of earthquakes, which can then be integrated into models of the rupture process. Following this approach, the SCARDEC method is able to retrieve source time functions of events over a large range of magnitude (Mw > 5.7). The source time function (which describes the temporal evolution of the moment rate) is suitable for the analysis of transient rupture properties which provide insights into the generation of earthquakes of various sizes. Our study aims at observing the rupture development of such earthquakes in order to add better constraints on dynamic source models. We first focus on the development of earthquakes through the analysis of the SCARDEC catalog. The phase leading to the peak of the source time function ("development phase'') is extracted to characterize its evolution. From the computation of moment accelerations at prescribed moment rates, we observe that the evolution of the moment rate during the developement phase is independent of the final magnitude. A quantitative analysis of the moment rate increase as a function of time further indicates that this phase does not respect the steady t² self-similar growth. These observations are then compared with dynamic source models. We develop heterogeneous dynamic models which take into consideration rupture physics. Heterogeneous distributions of the friction parameter and the initial stress contribute to generate highly realistic rupture scenarios. Rupture propagation is strongly influenced by these two dynamic parameters which induce a clear preferential direction of propagation together with a local variability of the rupture velocity. Variability of the kinematic parameters also tends to correlate rupture velocity and slip velocity, which is a key feature for the transient behavior of the development phase previously observed. These findings are expected to put further constraints on future realistic dynamic rupture scenarios.
The use of different spherical radial basis functions to combine terrestrial and airborne measurements for regional gravity field refinement
Authors: Liu Qing , Schmidt Michael , Sánchez Laura
Published: March 2020

The objective of this study is the combination of different types of basis functions applied separately to different kinds of gravity observations. We use two types of regional data sets: terrestrial gravity data and airborne gravity data, covering an area of about 500 km × 800 km in Colorado, USA. These data are available within the “1 cm geoid experiment” (also known as the “Colorado Experiment”). We apply an approach for regional gravity modeling based on series expansions in terms of spherical radial basis functions (SRBF). Two types of basis functions covering the same spectral domain are used, one for the terrestrial data and another one for the airborne measurements. To be more specific, the non-smoothing Shannon function is applied to the terrestrial data to avoid the loss of spectral information. The Cubic Polynomial (CuP) function is applied to the airborne data as a low-pass filter, and the smoothing features of this type of SRBF are used for filtering the high-frequency noise in the airborne data. In the parameter estimation procedure, these two modeling parts are combined to calculate the quasi-geoid.

The performance of our regional quasi-geoid model is validated by comparing the results with the mean solution of independent computations delivered by fourteen institutions from all over the world. The comparison shows that the low-pass filtering of the airborne gravity data by the CuP function improves the model accuracy by 5% compared to that using the Shannon function. This result also makes evident the advantage of combining different SRBFs covering the same spectral domain for different types of observations.
The role of heterogeneity in fault zone weakening and stability
Authors: Bedford John , Faulkner Daniel , Lapusta Nadia
Published: March 2020

Heterogeneity is abundant in crustal fault zones from the micron-scale to the plate interface scale. Despite this, it is still uncertain how different scales of heterogeneity interact and influence the mechanical properties of natural faults. Here we present experimental results where heterogeneous faults are simulated in the laboratory by placing patches of different fault gouge materials next to each other in a direct shear arrangement. These laterally heterogeneous experimental faults (50 mm in total length) are then sheared and the frictional strength evolution is measured with increasing displacement. Two types of fault gouge are used: (1) a fine-grained quartz gouge which obeys Byerlee friction (coefficient of friction = 0.6-0.7) and is rate weakening, and (2) a clay gouge comprised predominantly of kaolinite which has a low friction coefficient (approx. 0.25) and is rate strengthening. We find that with the addition of only a small amount of clay gouge the bulk fault strength weakens considerably after only a few millimetres of slip. Although clay is preferentially smeared along localized Y-shear bands, the observed weakening cannot be explained by clay smear as the total displacement on the fault is far too small for the clay to be smeared through the entire length of the quartz patches. Instead we propose stress concentrations at the boundary between clay and quartz patches, driven by slip on the weaker clay patch, produce enhanced weakening and shear at an overall low stress within the quartz patches.

The scale of heterogeneity also controls the frictional stability of the experimental fault. When clay patches are small and comprise <20% of the total fault area, instabilities occur within the unstable quartz gouge leading to stick-slip behaviour. However when patches of clay comprise >20% of the total sliding area, instabilities within the quartz are supressed leading to stable sliding. In this case, the bulk fault also becomes increasingly rate-strengthening with slip, tending towards the behaviour of a fault comprised of 100% clay. These results demonstrate how natural geological heterogeneity and the interplay between different geologic materials can help explain fault weakness and also control the seismogenic potential of tectonic faults.
A new tracking algorithm for cyclones with tropical characteristics in the Mediterranean basin
Authors: Pravia-Sarabia Enrique , Gómez-Navarro Juan José , Montávez Juan Pedro , Jiménez-Guerrero Pedro
Published: March 2020

Given their potential to damage coastal zones, cyclones with tropical characteristics have been profoundly studied, although their genesis and development mechanisms are not fully established yet. Being less severe and shorter than their tropical counterparts, the so-called medicanes are storms within the mediterranean basin with certain tropical characteristics. One of the most important factors that determine the impacts of these tropical-like storms is their trajectory. Thus, the detection and tracking algorithms have been object of numerous studies since the origins of numerical weather prediction.

 

Due to their similarities with tropical cyclones, the same algorithms should in principle be suitable for these Mediterranean storms, even if some minor changes become necessary considering that they differ in size, duration and intensity. Despite these similarities, there seems to be no consensus on the best algorithm for medicanes tracking. Although some of the existing specific algorithms for tropical cyclones are of a very high spatial accuracy, there are some difficulties that need further assessment and discussion when applying them to medicanes, such as the existence of more intense non-tropical systems within the domain of study, the coexistence of multiple medicanes or interferences due to large orographic barriers. The development of specific medicanes detection and tracking algorithms is not an unspoiled matter and some methods have been developed for this purpose. Nevertheless, their applicability is limited when the aforementioned adversities come into play.

 

Our aim is to propose and evaluate a new algorithm specifically suited for medicanes tracking, flexible, robust and able to detect and track them even in the mentioned adverse conditions. This algorithm consists in the implementation of a time independent methodology allowing the automated detection of simultaneous tropical-like cyclones within the same domain. It also provides the possibility of an easy modification of the cyclone definition parameters to make it useful for the detection of different cyclone types. The computational efficiency and time-saving performance are key factors to take into account for the development of this algorithm. Consequently, it should also be suitable for medicanes climatological studies.
Changes to glacier friction law due to solid friction
Authors: Roldan Blasco Juan Pedro , Gagliardini Olivier , Gimbert Florent , Gilbert Adrien , Vincent Christian
Published: March 2020

Theoretical laws for glacier friction over hard bedrocks rely on several assumptions. One fundamental assumption is that perfect sliding (no resistance to slip) occurs at the local scale between ice and bedrock, in which case friction only occurs at a mesoscale from ice flowing past bed irregularities - here called viscous friction. This assumption is however challenged by the numerous observations that glaciers carry debris at their basal layers, which can exert frictional resistance locally through solid-type friction between debris and rock. This is to be translated at a mesoscale as an additive frictional term to the law.
We study how the action of solid friction modifies the overall glacier basal friction by applying a simple effective-pressure dependant Coulomb friction law into a steady-state finite element model of a glacier over sinusoidal bedrock. We find that the viscous drag reaches the same maximum value regardless of whether there is local solid friction or not. However, we find that in the no-cavitation regime (low water pressures) the deformation-slip ratio near the bed is enhanced when solid friction occurs, although total slip is lower. As a result, the sliding parameter - ratio between viscous drag and slip - is no longer constant, as opposed to expected in a pure-sliding scenario. For high water pressures, the influence of solid friction becomes smaller and the law tends to the pure-sliding case. We propose a simple update to pure-sliding derived laws (Weertman, 1957; Fowler, 1981; Schoof, 2005; Gagliardini et al., 2007) to take into account this effect.