bluuebunny/crossref_metadata_2025 huggingface dataset:
Dust and pyrogenic iron boost phytoplankton blooms in sub-Antarctic waters of the Tasman Sea
Authors: Llort Joan , Matear Richard J. , Strutton Pete G. , Bowie Andrew R. , Chase Zanna
Published: March 2020

Although it is commonly accepted that atmospheric deposition of Fe particles can fertilise phytoplankton, there is yet no clear evidence on how such a fertilisation effect takes place. Several studies have attempted to link individual dust events with surface chlorophyll responses but generally, they do not find a clear correspondence between dust deposition and its impact on chlorophyll. In this work, we use a biogeochemical model to show that the atmospheric deposition of Fe in high-latitude seas, rather than creating instantaneous phytoplankton responses, replenish the upper mixed layer of the ocean during the pre-bloom period, from winter to early summer. The Fe accumulated at the surface boosts the phytoplankton bloom of the following summer, resulting in surface chlorophyll accumulations of up to 3 times larger than the years without atmospheric deposition. We used this mechanism to explain the strong inter-annual variability of the phytoplankton bloom in sub-Antarctic iron-limited waters east of Australia. Putting together more than a 15-years-long record of ocean colour observations and atmospheric aerosols reanalysis we uncovered a strong correlation (r2>0.6) between the dust that crossed the region during the pre-bloom period and the magnitude of the surface chlorophyll bloom. Interestingly, the correlation increased when taking into account pyrogenic aerosols in addition to dust. Our study presents the first observational link between Climate Change-enhanced droughts and wildfires, atmospheric aerosols and primary production of iron-limited waters.
Origins of variability and predictability in the North Atlantic region
Authors: Domeisen Daniela
Published: March 2020

The atmosphere over the North Atlantic sector exhibits significant interannual and interdecadal variability, as well as long-term trends due to global change. This variability is accompanied by changes in predictability. The origins of North Atlantic variability can to a large extent be traced back to the ocean and the land surface, the upper atmosphere, the tropics, as well as circum-global patterns. In particular, the tropical Pacific and the upper atmosphere have a strong influence on interannual and decadal variability in the North Atlantic region. As an example, the tropical Pacific affects the North Atlantic both through a tropospheric pathway across North America and through an indirect pathway through the stratosphere. Hence, due to the large number of factors influencing the North Atlantic region, their inter-dependence and their non-stationarity, the influence of these different factors is difficult to disentangle. Furthermore, models are often not able to capture the inter-dependence and superposition of these factors, which affects to what extent models are able to predict the North Atlantic region. This submission will explore the contribution to variability and predictability for several of these remote influences.

 
On the multi-technique combination with atmospheric ties
Authors: Balidakis Kyriakos , Glaser Susanne , Zus Florian , Nilsson Tobias , Schuh Harald , Gross Richard
Published: March 2020

We explore a new strategy to combine geodetic observations employing the existing and future systems. Imposing atmospheric ties on the combination at either the observation or normal equation level introduces a physical interpretation to the estimated atmospheric delay parameters, that is, zenith delays and gradients. In essence, besides combining station coordinates via local ties, we combine atmospheric delays via atmospheric ties. The purpose of this work is to assess the advantages and caveats of such a combination approach, on legacy, state-of-the-art, and next generation geodetic systems. We simulate 10 years of observations of all space geodetic techniques that currently contribute to the realization of the international terrestrial reference system; that is, very long baseline interferometry (VLBI), satellite laser ranging (SLR), global navigation satellite systems (GNSS), and Doppler orbitography and radiopositioning integrated by satellite (DORIS). The noise we inject in the simulated observations is technique-specific and - besides a thermal contribution - stems from three-state clock models and ray-traced delays from the latest ECMWF reanalysis, ERA5. To make the simulations more realistic, we estimate the probability of potential observations being successful by utilizing ERA5 fields, for example cloud fields for SLR. To avoid overoptimistic uncertainty estimates, we have accounted for the correlation between observations based on ERA5 fields. In a bias-free setup, we find that the improvement of employing atmospheric ties in addition to local ties to fuse multi-sensor observations, on the combined station coordinates and atmospheric delays is statistically significant for all techniques except for GNSS. We attribute the latter to the relatively good observing geometry. We also find that employing atmospheric ties reveals unaccounted systematic errors stemming from erroneous auxiliary data that are necessary for the reduction of geodetic observations, such as pressure measurements, cable calibrations, and range biases. Performing the observation combination with atmospheric ties improves the combined solution, especially for sparse observing geometry, and facilitates the detection of unaccounted systematic errors.
Behind the scenes of runoff performance
Authors: de Boer-Euser Tanja , Bouaziz Laurène , Thirel Guillaume , Melsen Lieke , Buitink Joost , Brauer Claudia , de Niel Jan , Moustakas Sotirios , Willems Patrick , Grelier Benjamin , Drogues Gilles , Fenicia Fabrizio , Nossent Jiri , Pereira Fernando , Savenije Hubert , Weerts Albrecht , Hrachowitz Markus
Published: March 2020

Hydrological models are valuable tools for short-term forecasting of river flows, long-term predictions for water resources management and to increase our understanding of the complex interactions of water storage and release processes at the catchment scale. Hydrological models provide relatively robust estimates of streamflow dynamics, as shown by the countless applications in many regions across the world. However, various model structures can lead to similar aggregated outputs, i.e. model equifinality. To provide reliable estimates, it is of critical importance that not only the aggregated response but also the internal behaviors are consistent with their real-world equivalents. In a previous international comparison study (de Boer-Euser et al., 2017), eight research groups followed the same protocol to calibrate their twelve models on streamflow for several catchments within the Meuse basin. In the current study, we hypothesize that these twelve process-based models with similar runoff performance have similar representations of internal states and fluxes. We test our hypothesis by comparing internal states and fluxes between models and we assess their plausibility using remotely-sensed products of actual evaporation, snow cover, soil moisture and total storage anomalies. Our results indicate that models with similar runoff performance represent internal states and fluxes differently. The dissimilarities in internal process representation imply that these models cannot all simultaneously be close to reality. Using remotely-sensed products, the plausibility of process representation could only be evaluated to some extent as many variables remain unknown, highlighting the need for more experimental research. The study further emphasizes the value of multi-model, multi-parameter studies to reveal to decision-makers the uncertainty inherent to the lack of evaluation data and the heterogeneous hydrological landscape.

References:
de Boer-Euser, T., Bouaziz, L., De Niel, J., Brauer, C., Dewals, B., Drogue, G., Fenicia, F., Grelier, B., Nossent, J., Pereira, F., Savenije, H., Thirel, G., and Willems, P.: Looking beyond general metrics for model comparison – lessons from an international model intercomparison study, Hydrol. Earth Syst. Sci., 21, 423–440, https://doi.org/10.5194/hess-21-423-2017, 2017.
Coupling historical maps and Lidar data to recognize man-made landforms in urban areas
Authors: Terrone Martino , Paliaga Guido , Piana Pietro , Faccini Francesco
Published: March 2020

In the last years there is growing interest on urban geomorphology both for the links with landscape planning and for its historical, cultural and scientific interest.

The identification of landforms in urban contexts is particularly difficult due to the progressive stratification of urban phases: the foundation of cities in the Mediterranean area dates back to ancient times and their growth in size is generally significant from the Middle Ages. This makes it frequent to find landforms which date back to more than 1000 years ago: they can be new, man-made landforms or modifications of natural ones, particularly coastal or fluvial features. Land modifications are particularly significant in the last 2 centuries, notably in the second half of the C19th and in the second half of the C20th, two periods identified as the potential start of the Anthropocene.

Anthropogenic terrain features are generally due to excavation and fill: unlike natural landforms which are generally identifiable through field surveys, the former require field observations, cartographical comparisons, multitemporal comparison of topographical views and historical photographs, geognostic investigations and geophysical surveys.

This research presents the results of a multitemporal analysis of the city of Genoa carried out by superimposing data from nineteenth-century historical cartography and topographical data from Remote Sensing.  The 1:2.000 scale map of Ignazio Porro, dating back to the first half of the C19th, has been digitalised on Lidar images from 2019 and with 1 m resolution, provided by Genoa Municipality. This methodology, developed with QGIS, has been applied on 5 sample areas particularly significant for their anthropogenic modifications: the area around Sant’Agata bridge in Val Bisagno, the area of Morandi Bridge in Val Polcevera, the road called Circonvallazione a Monte, the Promontory of the Lighthouse and the Via Digione area. Through the overlaying of multitemporal cartographies it was possible to identify and quantify with great precision excavation, landfill and mixed areas, allowing the identification of the most significant anthropogenic landforms. The obtained results have been validated through direct observations and supported by data from the geognostic regional database, revealing the potential of this approach for other urban areas.
Using Forbush decreases at Earth and Mars to measure the radial evolution of ICMEs
Authors: von Forstner Johan , Guo Jingnan , Wimmer-Schweingruber Robert F. , Dumbović Mateja , Janvier Miho , Démoulin Pascal , Veronig Astrid , Temmer Manuela , Papaioannou Athanasios , Dasso Sergio , Hassler Donald M. , Zeitlin Cary J.
Published: March 2020

Interplanetary coronal mass ejections (ICMEs), large clouds of plasma and magnetic field regularly expelled from the Sun, are one of the main drivers of space weather effects in the solar system. While the prediction of their arrival time at Earth and other locations in the heliosphere is still a complex task, it is also necessary to further understand the time evolution of their geometric and magnetic structure, which is even more challenging considering the limited number of available observation points.

Forbush decreases (FDs), short-term drops in the flux of galactic cosmic rays (GCR), can be caused by the shielding from strong and/or turbulent magnetic structures in the solar wind, such as ICMEs and their associated shock/sheath regions. In the past, FD observations have often been used to determine the arrival times of ICMEs at different locations in the solar system, especially where sufficient solar wind plasma and magnetic field measurements are not (or not always) available. One of these locations is Mars, where the Radiation Assessment Detector (RAD) onboard the Mars Science Laboratory (MSL) mission's Curiosity rover has been continuously measuring GCRs and FDs on the surface for more than 7 years.

In this work, we investigate whether FD data can be used to derive additional information about the ICME properties than just the arrival time by performing a statistical study based on catalogs of FDs observed at Earth or Mars. In particular, we find that the linear correlation between the FD amplitude and the maximum steepness, which was already seen at Earth by previous authors (Belov et al., 2008, Abunin et al., 2012), is likewise present at Mars, but with a different proprtionality factor.

By consulting physics-based analytical models of FDs, we find that this quantity is not expected to be influenced by the different energy ranges of GCR particles observed by the instruments at Earth and Mars. Instead, we suggest that the difference in FD characteristics at the two planets is caused by the radial enlargement of the ICMEs, and particularly their sheath regions, as they propagate from Earth (1 AU) to Mars (~ 1.5 AU). This broadening factor derived from our analysis extends observations for the evolution closer to the Sun by Janvier et al. (2019, JGR Space Physics) to larger heliocentric distances and is consistent with these results.
GNSS/IMU/Odometer based Train Positioning
Authors: Li Qing , Weber Robert
Published: March 2020

Usually train positioning is realized via counting wheel rotations (Odometer), and correcting at fixed locations known as balises. A balise is an electronic beacon or transponder placed between the rails of a railway as part of an automatic train protection (ATP) system. Balises constitute an integral part of the European Train Control System, where they serve as “beacons” giving the exact location of a train. Unfortunately, balises are expensive sensors which need to be placed over about 250 000 km of train tracks in Europe.

Therefore, recently tremendous efforts aim on the development of satellite-based techniques in combination with further sensors to ensure precise train positioning. A fusion of GNSS receiver and Inertial Navigation Unit (IMU) observations processed within a Kalman Filter proved to be one of potential optimal solutions for train traction vehicles positioning.

Today several hundreds of trains in Austria are equipped with a single-frequency GPS/GLONASS unit. However, when the GNSS signal fails (e.g. tunnels and urban areas), we expect an outage or at least a limited positioning quality. To yet ensure availability of a reliable trajectory in these areas, the GNSS sensor is complemented by a strapdown IMU platform and a wheel speed sensor (odometer).

In this study a filtering algorithm based on the fusion of three sensors GPS, IMU and odometer is presented, which enables a reliable train positioning performance in post-processing. Odometer data are counts of impulses, which relate the wheel’s circumference to the velocity and the distance traveled by the train. This odometer data provides non-holonomic constraints as one-dimensional velocity updates and complements the basic IMU/GPS navigation system. These updates improve the velocity and attitude estimates of the train at high update rates while GPS data is used to provide accurate determination in position with low rates. In case of GNSS outages, the integrated system can switch to IMU/odometer mode. Using the exponentially weighted moving average method to estimate of measurement noise for odometer velocity helps to construct measurement covariance matrices. In the presented examples an IMU device, a GPS receiver and an Odometer provide the data input for the loosely coupled Kalman Filter integration algorithm. The quality of our solution was tested against trajectories obtained with the software iXCOM-CMD (iMAR) as reference.
Prospects for predicting the type and timing of the surface response after stratospheric events
Authors: Domeisen Daniela , Afargan-Gerstman Hilla , Baehr Johanna , Dobrynin Mikhail , Grams Christian , Hitchcock Peter , Papritz Lukas
Published: March 2020

Extreme events in the stratosphere, so-called sudden stratospheric warming (SSW) events, can have a significant impact on surface weather. However, only about two thirds of SSW events have a surface impact, and the expected response is not always observed at the same time lag after the stratospheric event. In order to achieve skillful long-range predictions it will be necessary to understand the reasons for the presence or absence of a response, and to successfully predict the timing of the surface impact.
This contribution investigates several potential long-range predictors for the tropospheric response: the persistence of the lower stratospheric temperature signal, anomalous eddy driving in the east Pacific, as well as the North Atlantic weather regime present at the onset of the stratospheric event. All of these are found to help determine the type and timing of the tropospheric surface impact, and a strong potential for long-range predictability of several weeks based on these predictors is found over Europe.
Greenland Ice Sheet surface runoff projections to AD2500 using degree-day model
Authors: Yue Chao , Zhao Liyun , Moore John C.
Published: March 2020

      The Greenland ice sheet (GrIS) surface melt-water runoff dominates recent ice mass loss under global warming. We present runoff simulations during 1950-2500 over GrIS under RCP (Representative Concentration Pathways) 4.5, RCP8.5 and their extensions scenarios using three modified degree-day models, forced with five CMIP5 (Coupled Model Intercomparison Project) Earth System Models (CanESM2, BNU-ESM, HadGEM2-ES, MIROC-ESM and MIROC-ESM-CHEM). The degree-day factors are tuned at two sites on Greenland to best match the results by surface energy and mass balance model SEMIC. The modeled SMB over Greenland by modified degree-day models agree well with SEMIC in 21th century, then is applied to do projections for the 2100-2500 period. We also consider equilibrium line altitude evolution, surface topography changes and runoff-elevation feedback in the post-2100 simulations. The ensemble mean projected GrIS runoff is equivalent to sea-level rise of 7 cm (RCP4.5) and 10 cm (RCP8.5) by the end of the 21st century relative to the period 1950-2005, and 25cm (RCP4.5) and 121cm (RCP8.5) by 2500. Runoff-elevation feedback increases extra runoff of 7% (RCP4.5, RCP8.5) by 2100 and 23% (RCP4.5) and 22% (RCP8.5) by 2500. Sensitivity experiments show that 150% and 200% snowfall in post-2100 period would lead to 10% and 20% runoff increase under RCP4.5, 5% and 10% for RCP8.5, respectively.
Response of Hydrological Process to Climate Change of Basins with Different Glacier Ratio in the Tibet Plateau
Authors: Wang Li , Zhang Fan
Published: March 2020

The glacier ratio influences both the contribution of meltwater runoff and the response of the basin's hydrological processes to climate change. In this study, the Karuxung, the Tuotuo and the Babao river basins with glaciers accounting for 20.7%, 2.1% and 0.38% respectively, were selected to study their hydrological processes under the climate change. Based on the daily runoff data of 30 years and MODIS snow cover products, the J2000 model was applied to quantify the contribution of meltwater and rainfall runoff, analyze the temporal and spatial variation characteristics of runoff and clarify the influence of climate change on these three basin. The main findings are as follows: (1) The contribution of glacier and snow melt runoff for the Karuxung, Tuotuo and Babao river basin was 60.7%, 25.3% and 19.9%, respectively. The contribution of rainfall runoff for the three basins was 39.3%, 74.7% and 81.1%, respectively. (2) The peak of glacier and snow melt runoff converted from summer to spring with the glacier ratio decreasing. (3) The runoff supplies in the Karuxung, Tuotuo and Babao river basin were from the 5500m-6500m, 4500m-5500m zone, and 3500m-4500m elevation zone, respectively. (4) The runoff and its components in the Karuxung and Tuotuo river basins showed significant increasing trends while the Babao river basin showed no significant change trends. (5) In the Karuxung river basin with large glacier ratio, the increase in temperature mainly caused the increase of meltwater and runoff, showing a positive impact on runoff. For the Tuotuo and Babao river basin with small glacier ratios, the increase in temperature mainly caused increased evaporation and reduced runoff, showing a negative impact on runoff.
Climatology of heat waves characteristics based on different metrics- Application on a centennial air temperature record of the eastern Mediterranean
Authors: Founda Dimitra , Katavoutas George , Pierros Fragiskos
Published: March 2020

Today, there is a strong scientific consensus that severe weather phenomena and climatic extremes represent an increasing threat in the background of climate change, with profound and unpredictable impacts on the environment, economy and humans.  Heat waves (HWs) in particular, are among the most disastrous phenomena across the globe, imposing significant pressure on human health, with severe heat waves being associated with thousands of excess deaths in the past. Considerable recent research focuses on the study of the main characteristics of HWs (e.g. amplitude, duration or frequency) and their long-term trends, using different approaches and metrics. Such approaches differ with respect to the used climatic index (maximum, minimum, mean air temperature or combination), the use of fixed or dynamic temperature thresholds, the duration and others. The plethora of existing indices in literature and the lack of a universal metric to define HWs is underlined  in most studies.

  This research attempts to investigate how and to what extent are the long-term statistics and trends in HWs characteristics affected by the use of different definitions. The analysis was based on the centennial, uninterrupted records of air temperature of the National Observatory of Athens which constitute a unique material for the study of climatology of HWs in the long-term. Yet, capital cities of the eastern Mediterranean have been assigned as hot spots among other European cities, with respect to future heat-related risk.

The analysis revealed substantial deviations in HWs features among different definitions, as for instance changes in seasonal occurrence of HWs, or an eightfold increase in the number of HWs since the late 19th century, when the six-days minimum duration of HWs was replaced by three-days.

The better understanding of the impact of different HWs indices on their long-term statistics is crucial for better future projections, especially at a vulnerable to heat-related risk area, like the eastern Mediterranean.

 
Biogeochemical signature of elevated methane in water column of the outer East Siberian Arctic Shelf
Authors: Lee DongHun , Kim Ji-Hoon , Lee Yung Mi , Jin Young Keun , Shin Kyung-Hoon
Published: March 2020

The East Siberian Arctic Shelf (ESAS) had high methane concentrations in the seawater of the inner shelf over the decades, which was regarded as significant methane source for global warming. The source information of elevated dissolved methane at the inner ESAS has so far been reported, however, the characterizations (i.e., formation and transport) of enriched ones in the outer ESAS remain to date still unclear. To unravel this, we have reported methane properties along south-north transects of the outer ESAS (73.7°-77.1°N and 164.3°-178.0°E, water depths; 41-370m) performed from 2016, 2018 and 2019 ARAON Expeditions. The dissolved methane concentrations in surface seawater were mostly higher than those of the atmospheric equilibrium concentration and its maximum value in the water column of the outer ESAS hotspots had ca. 204 nM. Based on principal component analysis including CTD profiles (i.e., temperature, salinity, dissolved oxygen and fluorescence) and methane concentrations, elevated methane concentrations (88 to 204 nM) were close to fluorescence concentrations (0.1 to 0.4 mg/m3). Furthermore, the isotopic signatures of dissolved methane (δ13C; -66.6 to -26.6‰ and δD; -218.8 to -34.0‰) and dissolved inorganic carbon (δ13C; -10.1 to -4.4‰) showed large isotopic variations, indicating the methane production in the study area is likely to be complicated using carbon dioxide and methyl substrates. In this regard, organic matter preserved in the submerged permafrost and/or methyl compound produced by phytoplankton might be also potential substrates for elevated methane at some locations. In the near future, mass balance model via end-member approach will be applied for determining the discriminative contributions of possible methane sources in the outer ESAS.
Study on present deep crust deformation in northern and middle of the Red river fault zone by gravity method
Authors: Wang JIan
Published: March 2020

Multidisciplinary research shows the Red river fault zone’s (RRFZ) present movement and deformation state has complex segmentation feature. In order to further reveal its deep deformation mode, firstly, we extract tectonic movement gravity change information from mobile gravity measurement data by remove water storage varation and Vertical movement gravity effect; Secondly, together crust density interfaces model with gravity change information, then we can get the NMRFZ’s deformation mode of deep crust, which causes gravity variation.

The average effect with a 50km radius is calculated for the recent gravity change rate in the Sichuan-Yunnan region, then the background rate field and the residual gravity change rate field are obtained. The trend of -0.66μGal/yr gravity-low-speed change in Sichuan-Yunnan region indicates that there is an inheritance between the gravity field and the uplifting background of the southeastern Tibetan Plateau. The crustal uplift is an important reason for the negative surface gravity changes, but it is mainly related to the deep tectonic environment. There are local positive change zones in the block boundary area, with obvious lateral extrusion and deep mass accumulation. It reflects that under the dynamic environment of the eastward flow of the Tibetan Plateau, the crust of north and middle-south section of the RRFZ are extruded and the underground mass become densification which make the surface gravity raising. The positive gravity changes in up-middle crust are more obvious than lower crust and Moho in Sichuan-Yunnan area. The RRFZ also exhibits a strong demarcation feature as a plate boundary, and the northern segment is the dividing line of gravity positive and negative changes area, while the middle-southern segment and its two sides also showed a wide range of positive change trends, with deep mass continue accumulation.

The results of crustal deep deformation show that both the upper and the lower crust are obviously demarcated along the 101.5°E boundary, with the west side of the southwest Yunnan descending (moho: -0.05m/yr, upper-middle crust: -0.03m/yr) and east side of Sichuan-Yunnan block rising (moho ： 0.05m/yr，upper-middle crust： 0.02m/yr), which shows that the control effects in depth of the Kangdian crustal axis. The deformation rate of the deep crust in the RRFZ is the largest, the middle-south is next and the south the smallest. Gradual zone between the middle-south segment of the RRFZ and the Chuxiong-Jianshui fault zone shows strong activity and difference in the upper middle crust.
Improving hydrological model performance by incorporating dynamic variability of parameters
Authors: Girija Lakshmi , Kulamullaparambathu Sudheer
Published: March 2020

Extensive research is being carried out in developing new calibration procedures for improving the efficacy of hydrologic models. Considering the simulation period into separate wet and dry periods, and performing discrete calibration on each of them has resulted in improvement in model performance, especially during dry periods. In this procedure, it is envisaged that by splitting the time period into wet and dry, the temporal variability of soil moisture, which play a major role in maintaining the water balance of the catchment, is accounted. The discretely calibrated data is then recombined to form the entire time series. However, while recombining the discretely calibrated time periods, the physics of the hydrological processes, at the time of transition from one period to the other, may show abrupt variations. In addition, the short spells of wetness and dryness within this partitioned period, which influences the soil saturation, may not get effectively simulated. This study proposes division of simulation period into wet and dry spells considering the state of saturation of the watershed. This is achieved by clustering the time series of the data using the antecedent precipitation and the soil moisture conditions. A supervised Gustafson-Kessel clustering technique is employed for the same. Subsequently, a relationship between the precipitation, the daily change in soil moisture and a selected model parameter is established for all the cluster transitions and incorporated into the model structure. The proposed methodology is tested using a grid based model with six parameters, on Riesel watershed, Texas, USA. The results indicate that clusters formed are unique, with no fixed duration and no repetitive patterns across the entire simulation period. For preliminary analysis, only one parameter is dynamically varied depending on the incoming rainfall. The performance of the refined model (NSE = 0.85) over the conventional static parameter model (NSE = 0.83), though not significant, indicate that better process representation can aid in improving model simulations. It is noted that this method eliminates the abrupt variation of soil moisture across the wet and dry periods, as the simulation is continuous.
Simulation of electric discharges in unsteady airflow using a 3D fluid model
Authors: Niknezhad Mojtaba , Chanrion Olivier , Köhn Christoph , Holbøll Joachim , Neubert Torsten
Published: March 2020

We have developed a 3D fluid model to simulate streamer discharges in unsteady air flow. The model couples the drift-diffusion equations for the charged particles, the Navier-Stokes equations for the air and the Poisson equation for the electric field. It allows to study electrical discharges at different timescales defined by light and heavy particles and to investigate the effects of unsteady airflow. The model treats the time integration in an implicit manner to allow longer time steps, which makes the simulation of long duration discharges feasible. Moreover, the model uses an unstructured mesh with adaptive refinement allowing the incorporation of solid bodies with complex geometries. The accuracy of the model has been verified by comparing its results with a test case from the literature comparing simulation in steady air from five different streamer codes. Our results were consistent and among the most accurate. We present results from a simulation of long duration discharges, in which a series of successive positive streamers are initiated from a positive polarity electrode in a transverse airflow condition. It shows that the impact of a low speed air flow on the streamer comes essentially from the ions being blown away by the wind.
Long-term multibeam monitoring of natural methane seepage offshore Prins Karls Forland, Svalbard
Authors: Moser Manuel , Bergès Benoît , Hanssen Alfred , Ferré Bénédicte
Published: March 2020

Natural methane seepage from the seafloor to the hydrosphere occurs worldwide in marine environments, from continental shelves to deep-sea basins. Depending on water depth, methane fluxes from the sediment to the water column and mixing rate of the seawater, methane may partially reach the atmosphere where it could contribute to the global greenhouse effect. This can be observed from hydro-acoustic systems during research surveys. However, natural gas emission is not a continuous process and may vary in intensity and frequency. It is therefore necessary to study the temporal variability of methane seeps using long-term observation methods. One sensitive, accurate and reliable way to do this is by hydro-acoustic systems mounted on ocean observatories.

Here we present new long-term hydro-acoustic monitoring data from a known highly active seepage site offshore Prins Karls Forland, Svalbard. The data were acquired by a horizontally looking M3 multibeam echosounder system that was mounted on a benthic ocean observatory from October 2016 to July 2017. Our preliminary results show the presence of several individual seeps in the vicinity (<40 m) of the observatory throughout the observation period. Their activity patterns vary from non-existent to constant phases. We present the frequency of appearance and changes of the observed seeps over time. The first results confirm that methane seepage is not a constant process and emphasize the importance of long-term monitoring of methane seeps with regard to reliable flux rates estimates for a more accurate impact assessment on the climate.

The research is part of the Centre for Arctic Gas Hydrate, Environment and Climate (CAGE) and is supported by the Research Council of Norway through its Centres of Excellence funding scheme grant No. 223259 and UiT.
Emerald Mining in Large Scale Debris and Slumped Blocks from the Eastern Cordillera of Colombia
Authors: Diaz Munoz Juan Ricardo , Rong Song Sheng
Published: March 2020

The Colombian emeralds are  well-known green gems, which are very famous in its unique characteristics and quality of color and sizes in the world. It is dominantly distributed in the Eastern Cordillera of Colombia with underground mining in various locations of about 3km2 and a total extent of 500km2, separated by approximately 130Km are located the Eastern Emerald Belt ( EEB) and the Western Emerald Belts (WEB), in a general context they share chemical and tectonic similarities, but, with a complex tectonic evolution.

The geology of emerald and its tectonic configuration is believed to be composed of a series of disharmonic structures, e.g. thrusted and folded areas. Current and past exploitations created many mines, more than few tens in WEB, which are predominantly distributed in three areas, Muzo, Cunas and Coscuez. Based on field surveys into those mines, we observed paths that suggest the location of mines in debris flow deposits or slumped areas, which are characterized by matrix-supported structures with  block sizes ranging from few cm to  hundreds of meters. Rock types of blocks include black shale, calcite-rich veins with emeralds, stratiform-pyrite shale, hydrothermal hydraulic breccia, albitite. Most of the emeralds occur in calcite veins, but those cannot be traced along the veins in the mines and suddenly crosscut with no common factors involved (faults, discontinuities). The lines of evidence suggest that  the current mining of the emeralds in some places takes place on  slumped blocks or matrix of debris flow deposits. These observations attached with remote sensing techniques ( DEM, DTM, LANDSAT, AERIAL IMAGES) on WEB show slumped areas are well correlated with emerald mines in those three exploited areas. These findings could be of great usefulness for further exploration, ongoing research projects about the Eastern cordillera uplifting and emeralds worldwide tectonostratigraphy.
The LiDAR revolution in glacial geomorphology: its gifts and challenges
Authors: Johnson Mark
Published: March 2020

Science progresses when we are afforded with a ‘better look’ at nature. For geomorphology, the production over the last 100 years of an ever-increasingly resolved view of landscapes with topographic maps, DEMs, remote-sensing images, etc. has always been accompanied by new geomorphologic discoveries. LiDAR images of formerly glaciated landscapes reveal glacial landforms in extraordinary detail, showing previously mapped landforms in exquisite new detail (for example, end moraines, drumlins, eskers, ice-walled-lake plains etc.). Particularly important are a range of ‘mesoscale’ landforms that are better seen with LiDAR: De Geer moraines, crag-and-tail ridges, low-relief lineations, post-glacial faults, glacial hummocks, and raised shorelines to name a few. A spate of research has come out recently on such features. LiDAR images also have the potential of revealing landforms new to glacier science, of which ‘murtoos’ are an example. But LiDAR also raises the challenge of geomorphic classification. For example, glacial hummocks and glacial hummocky topography are a mesoscale landform that is known for its high variability. This variability, made more dramatic with new LiDAR images, along with the polygenetic origin of landforms called ‘hummocks’ reveals a weakness in our terminology that needs to be acknowledged and dealt with.
Effect of conservation agriculture on soil organic carbon sequestration in Mediterranean region. A systematic map.
Authors: Tadiello Tommaso , Acutis Marco
Published: March 2020

Conservation agriculture (CA) is characterized by minimal soil disturbance, permanent soil cover, and diversification of crop species, as stated by FAO in 2017. Many CA experiments, however, have been carried out so far, by taking into account only one or two of the three principles. Therefore, the meta-analyses recently published may fail in giving correct results about the CA effectiveness on agroecosystem variables, mostly on soil organic carbon (SOC) content or stock.

In preparation of conducting a meta-analysis, the present study was carried out to collect published results about the effect of the concurrent adoption of the three CA principles on SOC under Mediterranean climate with a systematic literature search in Scopus and Web of Science. Initially, a single nested query has been applied to both the database, using the Boolean operators, in order to include all the international literature about CA experiments and SOC variable without climate filter at this step. The resulting raw files were downloaded and merged in a unique dataframe using R software with "Bibliometrix" package1, which is an open-source tool developed for bibliometric analysis. The use of merged dataframe has mainly two advantages: it allows an easy duplicate removal (847 records in our case) and a more detailed information research both automatic and manual. Bibliometrix indeed provides tools for bibliometric analysis and data matrices building for co-citation, coupling, and co-word analysis highlighting, for example, that in the European continent both Italy and Spain are the most productive countries on these topics.
With these possibilities, as a further step, a new sub dataframe has been extracted by using the Köppen classification for Mediterranean climate (sub-climates, Csa/Csb/Csc), allowing a reduction of 32% of the records.

1) Aria, M., Cuccurullo, C., 2017. Bibliometrix: An R-tool for comprehensive science mapping analysis, Journal of Informetrics, 11(4).

 
How trustworthy are absolute age data from reprecipitated mineral grains?
Authors: Konrad-Schmolke Matthias , Halama Ralf
Published: March 2020

Absolute dating of rock deformation is often hampered by the observation that the affected minerals are only partly re-equilibrated with respect to their isotopic composition.

Generally, three different processes enable mineral grains to adjust isotopically during the deformation event, i.e. volume diffusion, recrystallisation as well as dissolution and reprecipitation.

The degree to which the crystal structure is affected by these processes is different and thus the extent of isotopic equilibration during these processes generally differs in a way that diffusive element exchange is believed to be the most ineffective and slowest process, whereas re- and neo-crystallization seem to be fast and thorough.

Fluid-induced dissolution and reprecipitation is a very common mineral reaction mechanism in the solid Earth and as the crystal lattice is intensively reworked during this process, elemental and isotopic exchange between matrix and the newly formed crystal should be facilitated.   

Commonly, element and isotopic exchange during such mineral reactions is thought to occur via aqueous solutions, but new experimental as well as natural data show that the element transfer during mineral dissolution and reprecipitation can also occur in an amorphous material that forms directly by depolymerization of the crystal lattice.

Furthermore, precipitation of product minerals occurs directly by repolymerization of the amorphous material at the product surface, hence the entire element and isotopic transfer between reactant and product mineral might not involve equilibration with the intercrystalline transport medium with important consequences for the interpretation of age data from re- and neo-crystallized grains.
Modeling Nitrate Export at the Catchment Scale using StorAge Selection Functions
Authors: Nguyen Tam , Kumar Rohini , Lutz Stefanie R. , Musolff Andreas , Fleckenstein Jan H.
Published: March 2020

Catchments store and release water of different ages. The time of a water parcel remaining in contact with the catchment subsurface affects the solute dynamics in the catchment and ultimately in the stream. Catchment storage can be conceptualized as a collection of different water parcels with different ages, the so-called residence time distribution (RTD). Similarly, the distribution of water ages in streamflow at the catchment outlet, which is sampled from the RTD, is called the travel time distribution (TTD). The selection preferences for discharge can be characterized by StorAge selection (SAS) functions. In recent years, numerical experiments have shown that SAS functions are time-variant and can be approximated, for example, by the beta distribution function. SAS functions have been emerging as a promising tool for modeling catchment-scale solute export.

In this study, we aim to integrate the SAS-based description of nitrate transport with the mHM-Nitrate model (Yang et al., 2018) to simulate solute transport and turnover above and below the soil zone including legacy effects. The mHM-Nitrate is a grid based distributed model with the hydrological concept taken from the mesoscale Hydrologic Model (mHM) and the water quality concept taken from the HYdrological Predictions for the Environment (HYPE) model. Here, we replaced the description of nitrate transport in groundwater from the original mHM-Nitrate with time-variant SAS-based modeling, while we kept the detailed description of turnover of organic and inorganic nitrogen in the near-surface (root zone) from mHM-Nitrate. First-order decay was used to represent biogeochemical (denitrification) processes below the root zone and in the stream. The proposed model was tested in a mixed agricultural-forested headwater catchment in the Harz Mountains, Germany. Results show that the proposed SAS augmented nitrate model (with the time-variant beta function) is able to represent streamflow and catchment nitrate export with satisfactory results (NSE for streamflow = 0.83 and for nitrate = 0.5 at the daily time step). Overall, our combined model provides a new approach for a spatially distributed simulation of nitrogen reaction processes in the soil zone and a spatially implicit simulation of transport pathways of nitrate and denitrification in the entire catchment.

Yang, X., Jomaa, S., Zink, M., Fleckenstein, J. H., Borchardt, D., & Rode, M. ( 2018). A new fully distributed model of nitrate transport and removal at catchment scale. Water Resources Research, 54, 5856– 5877.
Characterization of recent deep-sea debrites in the Eastern Mediterranean based on foraminiferal taphonomy
Authors: Katz Oded , Ashkenazi Leeron , Sultan-Levi Shani , Abramovich Sigal , Almogi-Labin Ahuva , Hyams-Kaphzan Orit
Published: March 2020

It is hypothesized that submarine transport of sediments down a continental slope induce physical disintegration of pristine (non-broken) foraminifera shells, and thus mass transport deposits should include a significant percentage of fragmented shells. To validate this hypothesis, we studied two gravity-cores from the Eastern-Mediterranean continental slope, offshore Israel: AM113 sampled within a landslide lobe at 848 m water depth, and AM015 located away from a landslide at 1080 m. At least one interval, ~0.5 m thick, of massive sediments hosting mud-clasds (i.e. debrite) was identified within each core. The timing of these debrites, based on biostratigraphy, oxygen isotopes and total organic carbon data, predates sapropel S1 in both cores and is contemporaneous (AM113) or slightly predates (AM015) the most recent deglaciation.

We found a noticeable increase in benthic and planktic foraminiferal shells fragmentation through the last deglaciation and up to the base of S1. This strongly-fragmented sequence is located in the debrite of AM113 but it is overlaying the debrite of AM015. Accordingly, we suggest two possible mechanisms for the increased fragmentation of foraminiferal shells in both cores: Sediment transport and turbulence related to submarine mass-transport events, or geochemical changes in the lower water column properties at the transition from MIS-2 to the Holocene.
A new comparative scale between tropopause height and beryllium 7 and the weight of quasi-biennial oscillation (QBO) effect.
Authors: Terzi Lucrezia , Wotawa Gerhard , Staten Paul W. , Luan Lan , Gabriel Axel , Kalinowski Martin
Published: March 2020

Recent studies demonstrated how accurate beryllium 7 can be used as proxy to predict seasonal weather, in particular Indian monsoons, climate change patterns such as tropopause height changes, tropopause breathing and Jet Stream stalling.

Beryllium 7 studies also prove that climate change phenomena are not driven by solar flux or earth magnetic field but are only partially influenced by them.

In this work we will compare recent tropopause height data with Beryllium 7 in order to build a comparative scale between the 2 parameters, including a focus on QBO (quasi-biennual oscillation) to quantify the effect of QBO on the analysed beryllium 7 data.