bluuebunny/crossref_metadata_2025 huggingface dataset:
Upper-ocean stratification of the NE South China Sea during the last 35 ka: Implications from oxygen isotope records from planktonic foraminifera
Authors: Wang Tzu-Chun , Lin Andrew Tien-Shun , Mii Horng-Sheng , Horng Chorng-Shern , Colin Christophe
Published: March 2020

The sedimentation rate in the northeastern South China Sea (SCS) is high and it therefore offers an opportunity for a high-resolution paleoceanographic study. This study is based on high-resolution AMS 14C dating on forams and oxygen isotope data of two planktonic foraminifera species (Globigerinoides ruber and Neogloboquadrina dutertrei) from the sediment core, MD18-3568, collected from the northeastern SCS, to reconstruct upper-ocean stratification since 35 ka.

The marine sediment core MD18-3568 is located on the accretionary wedge off SW Taiwan at a water depth of 1,315 m, the whole core is dominated by hemipelagic sediments and is of 20.7 m in length. Samples for AMS 14C dating were selected at roughly 2 ka interval with a total of 16 samples. The ages show a continuously younging-upward trend with bottom of this core around 35,000 years BP. Samples for high-resolution oxygen isotope measurements were selected at a nominal 500-year age interval. The difference in δ18O between G. ruber (mixed layer dwelling species) and N. dutertrei (thermocline dwelling species) is used to reconstruct the upper ocean stratification with large difference indicating significant ocean stratification and vice versa. The results show moderate upper ocean stratification during 35-24 ka, and it became less stratified during the Last Glacial Maximum (LGM, 23-19 ka). During the deglacial stage, the stratification gradually became stronger until the early Holocene (12-9 ka), and it has kept strong upper-ocean stratification since 9 ka. Literature has documented less rainfall intensity during the LGM and heavy rainfall during the Holocene in southern Taiwan. We interpret the upper-ocean stratification in the NE South China Sea near Taiwan is linked to the amount of freshwater inputs from Taiwan. Less Taiwan freshwater input during the LGM led to a weak stratified upper ocean and a large amount of freshwater input from Taiwan led to a strong upper-ocean stratification during the Holocene.
Flows in the Magnetotail
Authors: Walker Raymond , Lapenta Giovanni , El-Alaoui Mostafa , Berchem Jean , Richard Robert , Schriver David
Published: March 2020

Magnetic reconnection leads to fast streaming of electrons and ions away from the reconnection site. We have used an implicit particle-in-cell simulation (iPic3D) embedded within a global MHD simulation of the solar wind and magnetosphere interaction to investigate the evolution of electrons and ion flows in the magnetotail. We first ran the MHD simulation driven by solar wind observations and then used the MHD results to set the initial and boundary conditions for the PIC simulation. Then we let the PIC state evolve and investigated the electron and ion motion. Within a few seconds of the onset of reconnection, electrons near the reconnection site stream earthward at 500-700km/s while the ions move at less than 100 km/s. For electrons, magnetic trapping occurs very close to the reconnection site and they move mostly in the XGSM direction at the E×B/B2 velocity.  Ion trapping occurs several Earth radii from the reconnection site about 100 s after the start of reconnection where both the electrons and ions move together at ~E×B/B2 velocity. Although the particles are moving at the E × B/B2 velocity, they are in a state defined by the kinetic physics not the state that exists in the MHD simulation.
Assessing soil aggregate stability with mobile phones
Authors: Fajardo Mario , Jones Edward , Wittig Rèmi
Published: March 2020

A new methodology for the assessment of soil slaking using a mobile app named SLAKES was developed. The app uses an image recognition algorithm that measures the increasing area of soil aggregates immersed in water at regular intervals over a 10 minutes period. This method measures the kinetics of the slaking process and returns a continuous stability index from 0 (very stable) to higher numbers (higher than 7 as very unstable with 14 as a commonly observed maxima).

The methodology was originally presented in  Fajardo et al. (2016) using a dataset covering a great part of the agro-ecological variability of New South Wales (NSW), Australia. By 2020 the app is already present in 36 countries from 6 continents in its Android version (released in 2017) and the iPhone version is gradually reaching an increasing audience (released in December 2019).

This work presents a study made in a medium sized farm in New South Wales, Australia. Top-soil (0-10 cm) samples were surveyed and analysed by undergraduate students using the app. Different maps of soil aggregate stability were created showing evident aggregate stability geographical patterns at medium scale. The use of SLAKES has shown reliability compared with traditional methods as shown in third party scientific publications. The simplicity of SLAKES makes this app a simple yet powerful way to assess aggregate stability and shows great potential to be included in both citizen and open science educational programs.

Fajardo, M., McBratney, A.B., Field, D.J., Minasny, B., 2016. Soil slaking assessment using image recognition. Soil and Tillage Research 163, 119-129.
MMS-Cluster conjugate observation of disturbance in the current sheet associated with localized fast flow in the near-Earth magnetotail
Authors: Nakamura Rumi , Baumjohann Wolfgang , Birn Joachim , Burch Jim , Carr Chris , Dandouras Iannis , Escoubet Philippe , Fazakerley Andrew , Giles Barbara , Kubyshkina Marina , Le Contel Olivier , Nagai Tsugunobu , Nakamura Takuma , Panov Evgeny , Russell Chris , Sergeev Victor , Torbert Roy
Published: March 2020

We report the evolution of the current sheet associated with a localized flow burst in the near-Earth magnetotail on Sep. 8, 2018 around 14 UT when MMS (Magnetospheric Multiscale) and Cluster at about X=17 RE, separated mainly in the dawn-dusk direction at a distance of about 4 RE, encountered at duskside and dawnside part of a dipolarization front, respectively.  We analyzed the mesoscale current sheet disturbances based on multi-point data analysis between Cluster and MMS. It is shown that the current sheet thickens associated with the passage of the dipolarization front confirming results from previous statistical studies. The thickness of the current sheet, however, decreased subsequently, before recovering toward the original configuration. MMS observed enhanced field aligned currents exclusively during this thinning of the current sheet at the off-equatorial region. Multiple layers of small-scale, intense field-aligned currents accompanied by enhanced Hall-currents were detected at this region.  Based on these mesoscale and microscale multipoint observations, we infer the current structures around the localized flow and discuss the role of these mesoscale flow processes in the larger-scale magnetotail dynamics.

 

 
Experimental technique for visualization of aquitard compaction over aquifer caused by excess pumping
Authors: Tabe Kazunori , Aichi Masaatsu
Published: March 2020

 Transparent soils are developed as a physical modelling of macroscopic soil behaviors in geotechnical engineering aspect. Transparent surrogates with its index-matching fluid, called as transparent porous media or transparent soils, have been used for simulating geotechnical properties of natural soils. Visualization technique itself have been applied to microscopic level of soil deformation and soil flow problems such as X-ray, Computerized Tomography (CT), and Magnetic Resonance Imaging (MRI) cameras by very expensive apparatuses with highly operating skills. Geotechnical researches need rather understanding of macroscopic scale of larger test models with inexpensive experimental industrial substances. Transparent soils have been developed to achieve these needs with easy handling performance. 
 The authors demonstrated a pumping test in a glass tank of 30mm width by 80mm length by 70mm height filled with transparent hydrated superabsorbent polymer to represent aquitard (clay layer) over aquifer (saturated silica sand). The subsidence within the synthetic clay layer due to pumping of pore water from silica sand was constantly monitored by target racking method using four 8mm-diameter particles immersed in the synthetic clay layer. The test successfully visualized deformation due to vertical propagation of pore water pressure during subsidence event within the transparent synthetic clay layer. It was also found that this experiment result and the results from three-dimensional numerical simulation of poroelastic deformation were consistent with each other.
The Effect of Multiple Baseline Evalution with Commercial Software on GPS Position Accuracy
Authors: Tas Baris , Erol Tuna , Turen Yener
Published: March 2020

The evaluation of the observation data obtained from the GPS system is performed with software. The software used today is divided into academic, web-based and commercial software. Researches generally focus on academic software and web-based services that have become widespread in recent years.Commercial software is often used by daily users, mostly in classical geodesy. These softwares differ from each other; users, their purpose of use, processing methods, accuracy, users knowledge level etc. In this study, we focused commercial software’s (Topcon Magnet version 4.0.1) accuracy of GPS positioning in single and multiple base solutions.

10 stations included in IGS network in California, USA, one base and 2, 3 and 4 network solution results in different session times (1h to 24h) positioning accuracy was achieved. In our study, it has been found that the accuracy obtained for the horizontal components North and East varies between 2 mm and 8 mm and vertical component Up varies between 3 mm and 54 mm.

In evaluations with a reference station distance of up to 100km, increasing the number of more than 2 reference stations (3 or 4) for horizontal compenents (North and East) did not make a significant contribution to accuracy. In the case of vertical component (Up) accuracy, it is determined that accuracy is affected by interstation distance and observation time more than the number of reference stations(1, 2, 3 or 4). it was found that it was meaningful to increase the accuracy of the vertical component to be observation time for as long as possible and reference base stations to be selected from the closest possible stations. Avoidance of short observation time (1 hour and less) for all three components was found to be important in terms of accuracy to be achieved.

Keywords: Commercial software, GPS, Multiple base solution.
Absolute Beam Monitor: a device to measure the absolute particle flux of a neutral atom beam – prototype development and testing
Authors: Gasser Jonathan , Wurz Peter , Galli André
Published: March 2020

The Interstellar Mapping and Acceleration Probe (IMAP) mission by NASA, to be launched in 2024, aims at deepening the understanding of the solar heliosphere by verifying and extending the results obtained from the Interstellar Boundary Explorer (IBEX). IMAP-Lo is a neutral atom imaging and analysis instrument to be used to measure heliospheric Energetic Neutral Atoms (ENAs), mainly H, He, O, Ne in the energy range from 10 eV to 1 keV. One key point of improvement of IMAP-Lo compared to IBEX-Lo is having more accurate calibration methods for ENAs at hand. The IMAP-Lo calibration will be carried out in MEFISTO, a calibration facility for ion and neutral particle instruments at the University of Bern. MEFISTO consists of an ion beam source with energies 10 eV/q - 100 keV/q, a removeable beam neutralization stage for neutral atoms from 10 eV to 3 keV, and a large vacuum test chamber.

The beam neutralization process relies on a charge conversion surface and thus results in an energy loss of about 15%, and energy-dependent transmission. It is therefore essential to be able to measure the effective neutral particle flux and beam energies provided at the exit of the neutraliser to improve the calibration process for an ENA instrument, such as IMAP-Lo.

The Absolute Beam Monitor (ABM) is a new laboratory device dedicated to measure the absolute neutral particle flux and coarse energy distribution of a neutral atom beam. The present prototype consists of a tungsten start surface [GJ(1] and two electron multipliers contained in a box of about 1 dm3 volume. By counting the start, stop and coincidence signal rates we infer the effective number of neutral atoms. In addition, the particle energy is determined by a time-of flight measurement.

We present the measurement principle and demonstrate the validity of the concept with the ABM prototype. Neutral H, He, and O beams at different energies and fluxes have been evaluated in MEFISTO with the ABM prototype. The results are compared with IBEX-Lo calibration measurements.
Molecular properties of dissolved organic matter (DOM) in the subterranean estuary of a high-energy beach: Finding proxies for reactive transport
Authors: Waska Hannelore , Simon Heike , Ahrens Janis , Beck Melanie , Schwalfenberg Kai , Zielinski Oliver , Dittmar Thorsten
Published: March 2020

Advective flows of sea- and fresh groundwater through coastal aquifers form a unique ecohydrological interface, the subterranean estuary. Here, freshly produced marine organic matter and oxygen mix with groundwater, which is low in oxygen and contains aged organic carbon from terrestrial sources. Along the underground flow paths, dissolved organic matter (DOM) is degraded and inorganic electron acceptors are successively used up. Because of the different DOM sources and ages, exact degradation pathways are often difficult to delineate, especially in high-energy environments with dynamic changes in beach morphology, source composition, and hydraulic gradients. From a case study site on a barrier island in the German North Sea, we present detailed biogeochemical data from pore water samples collected in the shallow layer of the subterranean estuary. The samples were taken along the major flow paths of recirculating sea water and discharging fresh, meteoric groundwater, and analyzed for physico-chemistry, electron acceptors, and dissolved organic carbon (DOC). DOM was isolated and measured with soft-ionization ultra-high-resolution mass spectrometry, and chemical DOM characteristics were derived by assigning exact molecular formulae to the thousands of intact masses found in each sample. Using geographic and physico-(geo)chemical parameters (longitude, salinity, dissolved silicate, dissolved iron) as indicators of water origin and residence time, we evaluated the behavior of chemical DOM characteristics (H/C and O/C ratios, aromaticity) along the underground flow paths. Overall, DOC concentrations and an H/C-based molecular lability boundary index (MLB) decreased with decreasing oxygen concentrations and parallel increases of dissolved (reduced) iron and dissolved silicate concentrations, in line with the assumption that high H/C ratios are a trait of labile DOM which is continuously degraded. On the other hand, aromaticity indices and relative abundances of a “humic-like” fluorescent DOM fraction increased along the flow paths, likely through accumulation of compounds less susceptible to microbial attack. Our data indicates that even in a highly complex advective flow system like the subterranean estuary, molecular properties of DOM can be harnessed to identify key, perhaps even site- and season-specific biogeochemical processes.
3D structure and kinematics of salt walls and megaflaps driven by differential loading: lessons from analogue modeling and field examples
Authors: Roca Eduard , Ferrer Oriol , Rowan Mark , Escosa Frederic , Muñoz Josep Anton , Giles Katherine
Published: March 2020

The two dimensional geometry and evolution of salt walls driven by differential loading could be considered well established from previous studies. However, little is known about the internal deformation at the flanking edges and the 3D architecture at their terminations. This induces risk in hydrocarbon exploration of poorly imaged areas that could be significantly reduced with a better understanding of near-salt deformation and salt-sediment interaction in three dimensions. Using an experimental approach based on sandbox models and comparing their results with the southeastern termination of the Gypsum Valley salt wall in the Paradox Basin, we investigate both the internal deformation and the 3D structure of rectilinear salt walls emphasizing the development of faults and folds, including megaflaps, around their terminations. The experimental program includes 5 experiments simulating the salt, pre-kinematic overburden and syn-kinematic detrital deposits with a pure polymer, a sand/clay mixture and silica sand, respectively. It includes experiments with different salt/pre-kinematic overburden thickness ratios and salt wall edge geometries.

The experimental results document that in rectilinear salt walls driven by differential loading the plan-view geometry of the salt walls depends (amongst other factors) on the salt thickness. Hence, salt wall terminations developed over a constant-thickness salt layer are abrupt with a rectangular form; and those developed over a progressively decreasing salt layer thickness are gradual with a plan-view triangular shape. They also show that:

At the salt walls edges, the pre-kinematic overburden is folded by limb rotation in the younger minibasin side and by limb lengthening with vertical shearing in the older minibasin side.

The prekinematic overburden is internally almost underformed in the younger minibasin side where megaflaps developed. Instead, it is much strongly deformed (faulted) and broken by extensional faults in the opposite older minibasin side. This could have strong implications for hydrocarbon exploration since: 1) the megaflaps lack any significant secondary porosity and have lateral continuity of bedding; and 2) the prekinematic package of the older minibasin is compartmentalized and affected by internal deformation that can significantly increase its porosity and permeability.

At the ends of the salt walls, faults are mainly parallel or perpendicular to the diapir trend, being predominantly transversal in the abrupt terminations and longitudinal in the gradual ones.

Radial faults are rare and only present at the corners of abrupt salt wall terminations.
Cross-scale insights into flow and nutrient dynamics through coupled tracer-aided ecohydrological and biogeochemical modeling
Authors: Yang Xiaoqiang , Tetzlaff Doerthe , Soulsby Chris , Borchardt Dietrich
Published: March 2020

Stable isotope tracers in water (e.g., 2H and 18O) have recently been widely used in soil-plant-atmosphere-continuum studies to quantify storage-flux-age interactions, mixing processes and the partitioning of precipitation into evaporation and plant transpiration, as well as groundwater recharge and runoff generation. Tracer-aided ecohydrological modeling can explicitly capture the role of vegetation dynamics in these processes, and constraining models using tracers can provide more realistic representation of water flow paths and ages. Such constraints are of particular importance in the context of catchment nutrient modeling, which integrates conservative hydrological mixing and reactive ecological and biogeochemical processes. Therefore, coupled tracer-aided modeling of ecohydrology and water quality has the potential to improve our understanding of catchment functioning and provide an evidence base for managing environmental trends under changing anthropogenic pressures. Moreover, in the domain of process-based modeling, fully distributed models have been shown to be advantageous in terms of efficiently capturing the high heterogeneity of natural and anthropogenic controls, and linking the modeling efforts with multiple data sources at different scales.

In this project, we apply advanced isotope-based modeling concepts to the intensively monitored TERENO - Bode catchment (ca. 3300 km2), which exhibits high gradients of hydroclimate, geology and landscape characteristics, and has associated anthropogenic impact gradients. We firstly focused on a well-studied, agricultural sub-catchment (Schäfertal, 1.44 km2). Rich data sets of long-term, high-frequency hydrometeorological conditions, vegetation dynamics, isotopes and agricultural management practices were integrated into the new tracer-aided ecohydrological model EcH2O-iso, which here is further coupled with the nitrate turnover and transport routines from the new mHM-Nitrate model. The flexible, fully distributed structure of the coupled model allows in-deep, extensive investigation of flow, tracer and nitrate dynamics across scales. Measurements at different spatial scales and under contrasting flow conditions (from lysimeter plots to the catchment monitoring network) were integrated for multi-criteria calibration in order to test and improve the model. The initial modeling in the small headwater catchment opens new opportunities for future upscaling investigations based on the hierarchical monitoring settings in the Bode catchment (from plots to headwaters, and to nested catchments (from ca. 100 to 3000 km2)).
A 20-year reforecast study combining high-resolution hydrological modelling, ensemble forecasting and data assimilation for the 12 largest tributaries of the Rhine
Authors: van Osnabrugge Bart , Smoorenburg Maarten , Uijlenhoet Remko , Weerts Albrecht
Published: March 2020

There is an ongoing trend in hydrological forecasting towards both spatially distributed (gridded) models, ensemble forecasting and data assimilation techniques to improve forecasts’ initial states. While in the last years those different aspects have been investigated separately, there are only few studies where the three techniques are combined: ensemble forecasts with state updating of a gridded hydrological model. Additionally, the studies that have addressed this combination of techniques either focus on a small area, a short study period, or both. We here aim to fill this knowledge gap with a 20-year data assimilation and ensemble reforecast experiment with a high resolution gridded hydrological model (wflow_hbv, 1200x1200m) of the full Rhine basin (160 000 km2). To put the impact of state updating in an operational forecasting context, the data assimilation results were compared with AR post-processing as used by the Dutch Forecasting Centre (WMCN).

This data assimilation and reforecast experiment was conducted for the twelve main tributaries of the river Rhine. The effect on forecast skill of state updating with the Asynchronous Ensemble Kalman Filter (AEnKF) and AR error correction are compared for medium-term (15-day) forecasts over a period of 20 years (1996 to 2016). State updating improved the initial state for all subbasins and resulted in lasting skill score increase. AR also improved the forecast skill, but the forecast skill with AR did not always converge towards the uncorrected model skill, and instead can deteriorate for longer lead times. AR correction outperformed the AEnKF state updating for the first two days, after which state updating became more effective and outperformed AR. We conclude that state updating has more potential for medium-term hydrological forecasts than the operational AR procedure.

Further research is underway to investigate the importance, or added value, of long-term reforecasts as opposed to studies covering a short time span which are often more feasible and therefore more often found in literature.
Relating CME density derived from remote sensing data to CME sheath solar wind plasma pile up as measured in-situ
Authors: Temmer Manuela , Holzknecht Lukas , Dumbovic Mateja , Vrsnak Bojan , Sachdeva Nishtha , Heinemann Stephan , Dissauer Karin , Scolini Camilla , Asvestari Eleanna , Veronig Astrid , Hofmeister Stefan
Published: March 2020

For better estimating the drag force acting on coronal mass ejections (CMEs) in interplanetary space and ram-pressure at planets, improved knowledge of the evolution of CME density/mass is highly valuable. We investigate a sample of 29 well observed CME-ICME events, for which we determine the de-projected 3D mass (STEREO-A and -B data), and the CME volume using GCS modeling (STEREO, SoHO). Expanding the volume to 1AU distance, we derive the density and compare the results to in-situ proton density measurements separately for the ICME sheath and magnetic structure. A fair agreement between calculated and measured density is derived for the magnetic structure as well for the sheath if taking into account mass pile up of solar wind plasma. We give evidence and observational assessment that during the interplanetary propagation of a CME 1) the magnetic structure has rather constant mass and 2) the sheath region at the front of the driver is formed from piled-up mass that is rather depending on the solar wind density ahead of the CME, than on the CME speed. 
Bias in CMIP6 models compared to observed regional dimming and brightening trends (1961-2014)
Authors: Moseid Kine Onsum , Schulz Michael , Storelvmo Trude , Julsrud Ingeborg Rian , Olivié Dirk , Nabat Pierre , Wild Martin , Cole Jason N. S. , Takemura Toshihiko
Published: March 2020

Anthropogenic aerosol emissions have increased considerably over the last century, but climate effects and quantification of the emissions are highly uncertain as one goes back in time. This uncertainty is partly due to a lack of observations in the pre-satellite era, and previous studies show that Earth system models (ESMs) do not adequately represent surface energy fluxes over the historical era. We investigated global and regional aerosol effects over the time period 1961-2014 by looking at surface downwelling shortwave radiation (SDSR).
We used observations from ground stations as well as multiple experiments from five ESMs participating in the Coupled Model Intercomparison Project Version 6 (CMIP6). Our results show that this subset of models reproduces the observed transient SDSR well in Europe, but poorly in China. 
The models do not reproduce the observed trend reversal in SDSR in China in the late 1980s, which is attributed to a change in the emission of SO2 in this region. The emissions of SO2 show no sign of a trend reversal that could explain the observed SDSR evolution over China, and neither do other aerosols relevant to SDSR. The results from various aerosol emission perturbation experiments from DAMIP, RFMIP and AerChemMIP suggest that its likely, that aerosol effects are responsible for the dimming signal, although not its full amplitude. Simulated cloud cover changes in the different models are not correlated with observed changes over China.  Therefore we suggest that the discrepancy between modeled and observed SDSR evolution is partly caused by erroneous aerosol and aerosol precursor emission inventories. This is an important finding as it may help interpreting whether ESMs reproduce the historical climate evolution for the right or wrong reason.
Explicit IMF By-dependence in geomagnetic activity
Authors: Holappa Lauri , Asikainen Timo , Mursula Kalevi
Published: March 2020

The interaction of the solar wind with the Earth’s magnetic field produces geomagnetic activity, which is critically dependent on the orientation of the interplanetary magnetic field (IMF). Most solar wind coupling functions quantify this dependence on the IMF orientation with the so-called IMF clock angle in a way, which is symmetric with respect to the sign of the By component. However, recent studies have shown that IMF By is an additional, independent driver of high-latitude geomagnetic activity, leading to higher (weaker) geomagnetic activity in Northern Hemisphere (NH) winter for By > 0 (By < 0). For NH summer the dependence on the By sign is reversed. We quantify the size of this explicit By-effect with respect to the solar wind coupling function, both for northern and southern high-latitude geomagnetic activity. We show that for a given value of solar wind coupling function, geomagnetic activity is about 40% stronger for By > 0 than for By < 0 in NH winter. The physical mechanism of the By-effect is not yet fully understood. Here we show that IMF By modulates the flux of energetic electrons precipitating into the ionosphere which likely modulates the ionospheric conductivity and, thus, geomagnetic activity. Our results highlight the importance of the IMF By-component for space weather and must be taken into account in future space weather modeling.
Imprints of evaporation and vegetation type in diurnal temperature variations
Authors: Panwar Annu , Kleidon Axel , Renner Maik
Published: March 2020

Diurnal temperature variations are strongly shaped by the absorption of solar radiation, but evaporation, or the latent heat flux, also plays an important role. Generally, evaporation cools, but its relation to diurnal temperature variations is unclear. This study investigates the diurnal response of surface and air temperatures to solar radiation and how evaporation and vegetation modify their response. We used the warming rate of temperature to absorbed solar radiation in the morning under clear-sky conditions and evaluated how the warming rates change for different evaporative fractions. Results for 51 FLUXNET sites show that air temperature carries very weak imprints of evaporation across all vegetation types. However, surface temperature warming rates of short vegetation decrease significantly by ~23 x 10-3 K/W m-2 from dry to wet conditions. Contrarily, warming rates of surface and air temperatures are similar at forest sites and carry literally no imprints of evaporation. We explain these contrasting patterns with a surface energy balance model. The model reveals a strong sensitivity of the warming rates to evaporative fraction and aerodynamic conductance. However, for the large aerodynamic conductance, the sensitivity to the evaporative fraction is strongly reduced. We then show that in addition to the higher aerodynamic conductance of forests, imprints of evaporation in the warming rate of surface temperature are reduced by 50% through an enhanced aerodynamic conductance under dry conditions. This contribution is comparatively weak (28%) for short vegetation. These findings have implications for the interpretation of land-atmosphere interactions and the roles of moisture limitation and vegetation on diurnal maximum temperatures, which is of key importance for ecological functioning. We conclude that surface temperature warming rate is a promising predictor of evaporation for short vegetation. These findings are in agreement with our previous study (Panwar et al., 2019) where the weaker response of air temperature to the evaporative fraction is explained by the larger growth of the boundary layer on drier days. In forests, however, the diurnal variation in temperatures is governed by their aerodynamic properties resulting in no imprint of evaporation in diurnal temperature variations.

Reference: Panwar, A., Kleidon, A. and Renner, M.: Do Surface and Air Temperatures Contain Similar Imprints of Evaporative Conditions?, Geophysical Research Letters, 46(7), 3802–3809, doi:10.1029/2019GL082248, 2019.
Historial thallium deposition trends as recorded in peat bogs - examples from Czech sites with contrasting pollution histories
Authors: Mihaljevic Martin , Ettler Vojtech , Vanek Ales
Published: March 2020

The purpose of this study is to investigate the Tl distribution and accumulation rates in Czech peatbogs with contrasting anthropogenic loads. Nine peat cores were sampled in the mountain areas of the Czech Republic (6 cores in the northern part affected by emissions from coal-burning power plants and 3 in the pristine southern part). In addition, 3 cores were collected close to the Pb mining and smelting area of Pribram. Cores were 210-Pb dated and trace metals/metalloids were measured in the digests by ICP-MS. Maximum Tl concentrations in peat were significantly higher in the polluted northern areas (1.16 mg/kg) and close to the Pb smelter (0.83 mg/kg) than in the pristine area (0.45 mg/kg). Thallium distribution well correlated with other metals (Pb, Hg) and metalloids (As, Sb). Thallium enrichment factors (EFs) calculated against Sc reached the maximum value of 17 indicating significant input of anthropogenic Tl. Thallium accumulation rates in peat varied between 20 and 50 µg/m2/y until 1930s, followed by a significant increase related to industrial activities in the northern part of the Czech Republic (up to 290 µg/m2/y in 1980s). In contrast, maximum Tl accumulation rate at the pristine site was 88 µg/m2/y. Data from the vicinity of Pb mines/smelter indicated higher accumulation rates even in the second half of the 19th century (between 50 and 200 µg/m2/y) followed by a significant decrease in late 1970s as a result of more efficient flue gas cleaning technology installed in the smelter during this period. 
Do alter post-wildfire straw mulching application and salvage logging pine natural regeneration after wildfires?
Authors: Lucas-Borja Manuel Esteban , Fernández Cristina , Plaza- Alvárez Pedro Antonio , González-Romero Javier , Peña-Mollina Esther , Moya Daniel , De las Heras Jorge
Published: March 2020

Mulching application and salvage logging are often performed in forests after fire to recover timber values and avoid soil erosion. These post-fire practices are believed to positively and negatively impact soil properties and initial seedling recruitment or seedling growth in pine stands. Mulch may increase soil moisture and lower soil temperature, which thus promotes seedling recruitment, whereas logging operations may generate soil compaction and destroy seedlings. As Mediterranean forests are delicate ecosystems, and different pine species or contrasting microclimate conditions (semiarid vs. subhumid Mediterranean climates) can display several natural regeneration trends, we investigated whether mulching combined with logging significantly alters soil properties, initial seedling recruitment and seedling growth in burned Pinus halepensis (Lietor) and Pinus pinaster (A Gudiña) stands in the short term. Our results demonstrated that soil organic matter and total nitrogen were the only soil parameters affected by treatments at site Liétor. Monitoring activity confirmed that regardless of tree felling or not, mulch treatment improved seedling density in the short term with a semiarid Mediterranean climate. At Liétor, seedling density was over 40% higher when mulching was applied, whereas aerial seedling length was the only seedling variable affected by this treatment. Conversely, the mulching+logging combination showed the highest seedling density, which could be related with more light availability after tree felling and the almost null effect of employed logging machinery. The harsh conditions at Liétor due to the limited water and light demands of pine species when water resources were ensured at site A Gudiña could be decisive for understanding the effect of mulching and logging operations for initial seedling recruitment. Our results generally suggest short-term soil changes and contrasting initial seedling recruitments after mulch and logging in burned semiarid and subhumid Mediterranean pine forests. 

 
Power usage in the transport sector – potential, costs and greenhouse gas abatement of different well-to-wheel pathways
Authors: Millinger Markus , Tafarte Philip , Jordan Matthias , Hahn Alena , Meisel Kathleen , Thrän Daniela
Published: March 2020

The increase of variable renewable energy sources (VRE), i.e. wind and solar power, may lead to a certain mismatch between power demand and supply. At the same time, in order to decarbonise the heat and transport sectors, power-based solutions are often seen as promising option, through so-called sector coupling. At times when VRE power supply exceeds demand, the surplus power could be used for producing liquid and gaseous electrofuels. The power is used for electrolysis, producing hydrogen, which can in turn be used either directly or combined with a carbon source to produce hydrocarbon fuels.

Here, we analyse the potential development of surplus power for the case of Germany, at an ambitious VRE expansion until 2050 and perform a cost analysis of electrofuels at different production levels using sorted residual load curves. These are then compared to biofuels and electric vehicles with the aid of an optimisation model, considering both cost- and greenhouse gas (GHG)-optimal options for the main transport sectors in Germany.

We find that, although hydrocarbon electrofuels are more expensive than their main renewable competitors, i.e. biofuels, they are most likely indispensable in addition for reaching climate targets in transport. However, the electrofuel potential is constrained by the availability of both surplus power and carbon. In fact, the surplus power potential is projected to remain limited even at currently ambitious VRE targets for Germany and carbon availability is lower in an increasingly renewable energy system unless direct air capture is deployed. In addition, as the power mix is likely to contain fossil fuels for decades to come, electrofuels based on power directly from the mix with associated conversion losses would cause higher GHG-emissions than the fossil transport fuel reference until a very high share of renewables in the power source is achieved. In contrast, electric vehicles are a more climate competitive option under the projected power mix with remaining fossil fuel fractions, due to a superior fuel economy and thereby lower costs and emissions.

As part of the assessment, we quantify the greenhouse gas abatement costs for different well-to-wheel pathways and provide an analysis and recommendations for a transition to sustainable transport.
Viewing soil systems from the top-down can make microbial ecology predictive for ecosystem functions
Authors: Rousk Johannes , Hicks Lettice
Published: March 2020

Understanding the role of ecological communities in maintaining multiple ecosystem processes is a central challenge in ecology. Soil microbial communities perform vital ecosystem functions, such as the decomposition of organic matter to provide plant nutrition. However, despite the functional importance of soil microorganisms, attribution of ecosystem function to particular constituents of the microbial community has been impeded by a lack of information linking microbial processes to community structure.

Here, we propose a new conceptual framework to determine how microbial communities influence ecosystem processes, by applying a “top-down” approach. Looking from the “top”, we first view the microbial community associated with a specific function as a whole, and describe the dependence of microbial community processes on environmental factors (e.g. the intrinsic temperature dependence of bacterial growth rates), allowing us to define the aggregate functional response curve of the community. We then demonstrate that the whole community contribution to ecosystem function can be predicted, by parameterising the functional response curve with current environmental conditions. In a final step, we show how this functional information can be linked to the taxonomic community composition (amplicon assessments of microbial community composition) in order to identify “biomarker” taxa that capture microbial communities’ regulation of ecosystem processes and the susceptibility of microbial community structure and function to environmental change. Ultimately, these biomarkers may be used as a diagnostic tool, enabling predictions of ecosystem function from community composition information combined with environmental metadata.
Using explicit mechanisms of Secondary Organic Aerosol (SOA) formation and evolution to extrapolate chamber studies to the atmosphere
Authors: Thornton Joel A , Shilling John , Pye Havala , D'Ambro Emma , Zawadowicz Maria , Liu Jiumeng
Published: March 2020

 

The applicability of chamber-derived Secondary Organic Aerosol (SOA) yields to the atmosphere remains a key uncertainty in modeling SOA. The chemical and environmental conditions achieved in chambers are narrower than and often significantly biased from those experienced in the atmosphere. We present results from applying explicit chemical mechanisms in a dynamic gas-particle partitioning model (FOAM-WAM) to simulate SOA formation and evolution from a range of chamber experiments involving isoprene and monoterpenes. We focus on how such comparisons can highlight the applicability, or the lack thereof, of derived SOA yields, extrapolate measured SOA yields to more complex chemical or environmental conditions, and identify key gaps in chemical or physical mechanisms and thus feedback on chamber experiment design and earth system model parameterizations. In particular, we show that current mechanisms of low-NOx isoprene and a-pinene oxidation that incorporate RO2 H-shift reactions can adequately explain corresponding fresh SOA without the need for substantial vapor-pressure lowering accretion chemistry, while substantial particle-phase photo-chemistry is required to explain the dynamic evolution of SOA characteristics (volatility, O/C ratios, etc)observed in chambers at longer aging times. We find that chemical conditions, such as absolute concentrations, are as important as vapor wall loss, or even more so, at perturbing SOA yields from realistic values. Consistent with recent field studies but in contrast to previous chamber studies, our modeling predicts that low-NOx isoprene oxidation is unlikely to produce significant SOA in warm boundary layers, except through isoprene epoxy-diol multi-phase chemistry. Current mechanisms are unable to reproduce the non-linear response of isoprene-derived photochemical SOA with NOx observed in multiple chambers, suggesting a potentially important missing mechanism of volatility reduction at intermediate NOx concentrations in that system. 
Concentration affects significantly the capacity of biochar to adsorb nitrogen from forest runoff water
Authors: Palviainen Marjo , Kakaei Lafdani Elham , Cvetkovic Jovana , Saarela Taija , Pumpanen Jukka , Laurén Ari
Published: March 2020

In boreal peatland forests, drainage and harvesting increase nitrogen (N) export to watercourses and the highest N concentration in runoff water occurs outside the growing season when traditional water protection methods based on biological activity are inefficient. In these conditions, water purification based on adsorption could offer a solution. Biochar can be an effective sorbent material for removal of nutrients from water due to its high specific surface area, porous structure and high cation and anion exchange capacity. We tested adsorption capacity for total N (TN) of spruce and birch biochar using water collected from ditch drains of boreal harvested peatland. The water was collected outside the growing season when TN concentration was 4.6 mg L-1. During the growing season, TN concentration varies from 0.5 to 2 mg L-1. To study the effect of TN concentration on adsorption capacity, we diluted water samples to concentrations 1, 2, 3 and 4 mg L-1. We added 5 g of biochar to 1 L of water and shook the samples for 180 h. TN adsorption capacity increased monotonously from the smallest to the highest concentration. Adsorption capacity was 2.6 and 3.7 times greater in the highest concentration compared to the lowest concentration in spruce and birch, respectively. This indicates that concentration affects significantly the capacity of biochar to adsorb N from forest runoff water. Therefore, biochar can be an effective water protection tool in areas, which have high TN concentration, and it can be a complementary method supporting water purification outside the growing season.
Quantification of the organic carbon pool of a large Indonesian peatland using an airborne geophysical method and comparison to an empirical topographic approach
Authors: Silvestri Sonia , Knight Rosemary , Viezzoli Andrea , Richardson Curtis J. , Anshari Gusti Z. , Dewar Noah , Flanagan Neal , Comas Xavier
Published: March 2020

The precise quantification of peat deposits at local to global scale is of key importance for the implementation of adequate conservation policies of peatlands. To this end, new remote sensing applications are needed, that provide high resolution data sets at regional scale. In this presentation, we present the results obtained using Airborne Electromagnetics (AEM) to estimate peat thickness and carbon content of a large peatland site located in Indonesia. The effectiveness of the AEM method for assessing peat thickness and volumes, and in turn carbon stocks, is tested by comparing the results to ground-truth measurements. Our results show that the AEM method can detect both the top and the bottom of a peatland profile over a clay substrate at high spatial resolution, allowing for an accurate three-dimensional morphological description of the peat body. The AEM method performs extremely well along the flight lines, where the instrument clearly detects the peat layer and differentiates it from the underlying mineral substrate. Moving away from the flight lines, the accuracy slightly decreases because the interpolation of the AEM data does not fully capture the highly variable morphology of the peat bottom. We conclude that in varying dome conditions, a high flight line density is preferable to describe the spatial distribution of the peat layer. Once the volume of the peatland is determined, the average organic carbon content by soil volume retrieved from field campaigns and laboratory analyses is used to estimate the total organic carbon stored in the peatland.

The results obtained with the AEM method are compared to those obtained with an empirical method that uses the soil topography to predict the thickness of the peatland. This empirical approach is based on the analyses of several previous studies available from the literature that show how it is common for some dome-shaped peatlands to present a linear correlation between peat thickness and soil topography. In this study, we show that the linear correlation is site-specific, and when used for prediction purposes, it provides incorrect peat volume estimates when it is extended to other sites or over large territories. When compared to the AEM method, our results show that the AEM method is superior in detecting the peat morphology and volume.