bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of landfast ice simulations with basal stress parameterization using the Regional Arctic System Model
Authors: Niciejewski Jan , Osinski Robert , Maslowski Wieslaw , Craig Anthony
Published: March 2020

The landfast ice (LFI) is an important component of the Arctic environment, especially in regions of shallow shelfs North of Alaska and Siberia. Its presence affects the transfer of energy between the atmosphere and the ocean. Its outer edge continuously interacts with the moving pack ice. One of the mechanisms of LFI formation – grounded ice keels, acting as anchor points – was parametrized in the version 6 of Los Alamos sea ice model (CICE) Consortium.  The parametrization is based on the bathymetry data, ice concentration and the mean ice thickness in a grid cell. It enables determination of the critical thickness, required for large ice keels to reach the bottom and calculation of the basal stress. A series of experiments using the Regional Arctic System Model (RASM) with CICEv6 has been conducted. In addition to sea ice model, RASM includes the atmosphere (WRF), ocean (POP), land hydrology (VIC), and river routing scheme (RVIC) components controlled by a flux coupler (CPL). LFI simulations using two different rheologies: elastic-visous-plast (EVP) and elastic-anisotropic-plastic (EAP) have been evaluated in the fully coupled and forced sea ice - ocean configurations.  Also, sensitivity studies with varying values of the LFI free parameters have been performed. Results are compared against landfast ice extent data from the National Snow & Ice Data Center. In the optimal configuration, including the basal stress parameterization, the model reproduces observed landfast ice in East Siberian, Laptev Sea, and along the coast of Alaska. However, some areas continue to be problematic – like the Kara Sea where LFI is underestimated and the area around the New Siberian Islands, where landfast ice growth is too high. In the former case, the ice arching might be the major landfast ice formation mechanism there, whereas in the latter case the model internal stress distribution might not be adequate to allow realistic sea ice drift between the islands.
Glacier surges initiated in the ablation zone of Hagen Brae, Greenland: observations and theory
Authors: Benn Douglas , Hewitt Ian , Karlsson Nanna , Solgaard Anne
Published: March 2020

Enthalpy balance theory predicts that dynamic oscillations (surge cycles) occur when glaciers cannot achieve stable steady states with regard to their mass and basal enthalpy (heat and water) budgets. That is, if the enthalpy produced by geothermal and frictional heat cannot be removed by conduction or water flux from the bed, sliding-heating feedbacks will lead to surging behaviour. To date, model simulations have focused on 'classic' surges, in which snow accumulation causes ice thickening in a reservoir zone during quiescence, and transition to surge occurs in response to a locally-driven sliding-heating feedbacks. However, many surges are initiated in glacier ablation zones, where surface mass balance is negative. Here, we show that such surges can be explained if the local mass and enthalpy budget is supplemented by non-local sources. Ice thickening during quiescence can occur if ice flux from upglacier exceeds losses by surface melt, and transition to surge occurs if accumulation of water from both local and non-local sources triggers the sliding-heating feedback. We illustrate these processes using data from Hagen Bræ, a major marine terminating glacier in North Greenland. The dataset, which covers the past 35 years at high temporal resolution, shows elevation changes, ice velocities and basal enthalpy budgets over recent surge cycles that are consistent with theory. The average surge cycle lasts 20-30 years while the duration of the active phase is approximately a decade based on the recent cycle. The theory has potentially wide applicability to surges in a range of climatic and topographic contexts.
Slates: a potential rock type to extract geothermal energy from the underground?
Authors: Herrmann Johannes , Rybacki Erik , Wang Wenxia , Milsch Harald , Wagner Bianca , Leiss Bernd
Published: March 2020

Commonly used host rock reservoirs for Enhanced Geothermal Systems (EGS) are composed of granite, as they display highly conductive and sustainable fracture networks after stimulation. However, considering the large amount of metamorphic rocks in Europe’s underground, these rock types may also show a large potential to extract geothermal energy from the subsurface. Within the framework of the European Union’s Horizon 2020 initiative ‘MEET (Multi-Sites EGS Demonstration)’, we are conducting fracture permeability experiments at elevated confining pressures, pc, temperatures, T, and differential stresses,
Rock magnetic signature as a result of gas hydrate dissociation off southwestern Taiwan
Authors: Huang Yin-Sheng , Horng Chorng-Shern , Su Chih-Chieh , Hsu Shu-Kun , Lin Jing-Yi
Published: March 2020

Marginal areas off southwestern Taiwan have been widely considered a high potential reservoir of gas hydrates based on several geophysical, geological, and geochemical investigations since the past decades. First gas hydrate sample has been collected on 21 June 2018 during the cruise MD214 at the core site MD18-3542 on the South Yung-An East Ridge. In the study, we focus on magnetic properties of this MD core. The most attractive feature in the magnetic susceptibility is an abrupt drop recorded at about 4 meters core depth. To clarify and identify the dominant magnetic mineral in the core, hysteresis loop parameters were first measured and then presented on the Day Plot, and further the X-ray diffraction analysis was applied to the selected core samples. Based on the magnetic results, the clear drop in the magnetic susceptibility is related to the change of dominant magnetic minerals in core sediments. Before about 4 meters core depth, the dominant magnetic mineral remains detrital magnetite. Below the depth, however, core sediments should have been infected by methane released by gas hydrate dissociation. Authigenic greigite and pyrite have become dominant, and therefore low magnetic susceptibility appears below 4 meters core depth.
Present-day crustal deformation of Georgia (Caucasus)
Authors: Sokhadze Giorgi , Hahubia Galaktion , Kachakhidze Manana , Khazaradze Giorgi
Published: March 2020

The republic of Georgia is located in the Caucasus, between the Black and Caspian seas from the west and the east, and Greater and Lesser Caucasus mountains from the north and the south. Tectonically, the region belongs to the Alpine-Himalayan collisional zone, formed during the late Cenozoic period as a result of a collision between the Arabian and Eurasian plates. The deformation zone due to this collision is broad and extends from Zagros mountains in southern Iran to the Greater Caucasus in the north. The GPS studies conducted during the last decade suggest a convergence rate of 18 mm/yr between the Arabia and Eurasia plates. Although majority of this convergence occurs in the southern part of the deformation zone, important part of this convergence takes place in Georgia, implying an elevated seismic risk in the region. This is corroborated by a presence of significant historical and instrumental earthquakes in the country.

As part of the project dealing with the detection of possible low frequency electromagnetic emissions proceeding earthquakes, in summer of 2016 we have installed a continuous GNSS station MTSK between Mtskheta and Tbilisi. The station consists of Leica GRX1200 GNSS receiver with an AS10 antenna. It is mounted on top of the building, anchored to the existing brick wall. In contrast, principal convergence between the Lesser and Greater Caucasus across the Tbilisi segment, occurs along the northern boundary of the Lesser Caucasus. To constrain the velocity gradient to the northern boundary of the lesser Caucasus, in 2019 an additional continuous GNSS station MKRN was installed in this deformation zone by the GTDI near the settlement of Mukhrani. It consists of Trimble 5700 receiver with a Zephyr Geodetic antenna.

The analysis of the data is performed using the Gamit/Globk software package from MIT and it is processed in conjunction with 26 continuous GNSS stations of the GEO-CORS network operated by National Agency of Public Registry of Georgia (geocors.napr.gov.ge). In addition, we analyze data form the stations located on Eurasia, Arabia and Africa plates. The principle objective of the given work is to monitor millimeter level deformation of the crust due to the collision of Arabia and Eurasia tectonic plates and identify the regions of higher deformation and relate them to individual faults.

This work has been partially supported by Shota Rustaveli National Science Foundation of Georgia (grant DI/21/9-140/13) and PROMONTEC (CGL2017-84720-R AEI/FEDER, UE) project, financed by the Spanish MINEICO. We are grateful to the Andronikashvili Institute of Physics (www.aiphysics.tsu.ge) for letting us use their facility for the installation of the GNSS station.
Assessing responses to climate stressors in two contrasting pine species
Authors: Nadal-Sala Daniel , Birami Benjamin , Rehschuh Romy , Gattmann Marielle , Grote Ruediger , Grünzweig Jose , Preisler Yakir , Salmon Yann , Tatarinov Fedor , Yakir Dan , Ruehr Nadine
Published: March 2020

Climate conditions in which tree species are able to grow are determined by their ecophysiological traits. The genus Pinus spp. is widespread across Eurasia, so that the different Pinus species have evolved to live within diverse climate envelops, from the boreal Scots pine (Pinus sylvestris L.) to the Mediterranean Aleppo pine (Pinus halepensis Mill.). Therefore, the different pine species are expected to present contrasting responses to environmental stressors, depending on the ones that populations had faced in the past.

Here we analyze the impact of climate on stand carbon fluxes in two contrasting stands -i.e. a boreal Finnish Scots pine stand and a Mediterranean Israeli Aleppo pine stand. We use a machine learning approach -i.e. Random Forest algorithm- to evaluate seasonal changes in the most limiting environmental driver (MLED) for forest productivity. Then, we use data from controlled experiments with Aleppo and Scots pine saplings, in which we evaluated their response to drought and heat stresses, in order to assess if differences in their ecophysiological traits may explain their ability to grow in such contrasting climate conditions.

Our results suggest that the MLED of forest productivity during all year in the boreal stand are low temperatures. Conversely but not surprisingly, the MLED in the Mediterranean stand is soil water availability, especially during summer. Therefore, we expect P. halepensis to be better adapted to heat and drought stresses, whereas we expect P. sylvestris to present higher photosynthetic rates at lower temperatures. Controlled experiments confirm these expectations, with a remarkable isohydric behavior of P. halepensis during drought, and different species responses of photosynthesis thermal optimum to heat and drought stress. Our results highlight the need to understand how traits determine tree species’ responses to different environmental stressors, in order to anticipate their performance in a warmer world.
Stochastic modelling of hydropower generation from small hydropower plants under limited data availability: from post-assessment to forecasting
Authors: Sakki Georgia Konstantina , Papalamprou Vassiliki Maria , Tsoukalas Ioannis , Mamassis Nikos , Efstratiadis Andreas
Published: March 2020

Due to their negligible storage capacity, small hydroelectric plants cannot offer regulation of flows, thus making the prediction of energy production a very difficult task, even for small time horizons. Further uncertainties arise due to the limited hydrological information, in terms of upstream inflow data, since usually the sole available measurements refer to the power production, which is a nonlinear transformation of the river discharge. In this context, we develop a stochastic modelling framework comprising two steps. Initially, we extract past inflows on the basis of energy data, which may be referred to as the inverse problem of hydropower. Key issue of this approach is that the model error is expressed in stochastic terms, which allows for embedding uncertainties within calculations. Next, we generate stochastic forecasting ensembles of future inflows and associated hydropower production, spanning from small (daily to weekly) to meso-scale (monthly to seasonal) time horizons. The methodology is tested in the oldest (est. 1926) small hydroelectric plant of Greece, located at Glafkos river, in Northern Peloponnese. Among other complexities, this comprises a mixing of Pelton and Francis turbines, which makes the overall modelling procedure even more challenging.
Facility-specific environmental footprints of wind and solar power at a global scale
Authors: Bosmans Joyce , Dammeier Tine , Huijbregts Mark
Published: March 2020

Wind and solar power are vital for climate change mitigation, producing electricity at much lower greenhouse gas (GHG) emissions than conventional fossil-based technologies. Here, we obtain facility-specific environmental footprints of utility-scale wind and solar power across the globe. We investigate how the GHG footprint of wind and solar power varies across space and across technological characteristics. We will furthermore investigate other environmental footprints such as mineral resource scarcity to assess whether there is a trade-off between low GHG footprints and possibly higher other footprints.

We use facility-specific technological characteristics of ~30,000 wind parks and ~10,000 photovoltaic solar parks across the globe, such as capacity, hub height, rotor diameter or type of panel, to determine the life-cycle environmental impacts per wind or solar park. The produced power per facility over its lifetime is computed based on technological characteristics as well as location-specific hourly climate input from the ERA5 reanalysis dataset. The environmental footprint is then defined as impact divided by power produced, e.g. g CO2-eq/kWh, to allow for comparison between facilities and across energy sources.

The facility-specific footprints will be shown on maps to indicate spatial variability and range of footprints of both wind and solar power. We will furthermore investigate the variability in footprints using analysis of variance, in order to indicate whether climate (i.e. location-specific wind or radiation) or technological characteristics (i.e. hub height, rotor diameter or type of panel) is the main cause of variability in footprints.
Using a neural network approach to correct for systematic biases in seasonal wind power electricity generation forecasting
Authors: Baumgartner Johann , Schmidt Johannes , Gruber Katharina
Published: March 2020

Neural networks are widely applicable for different modelling purposes in the energy sector such as predictions of electricity generation from wind and solar resources as well as electricity demand and prices. However, neural network approaches heavily rely on the availability of sound climate and actual generation data for model training. Sufficiently long and accurate time series of climate data needed for model training and seasonal climate forecasts for the prediction process are often not available from a data source based on the same climate model for the corresponding study area. Most likely data sources based on different climate models also feature different bias and consequently using one data source for model training and using another one for model prediction will produce systematically biased results that need correction.

Therefore, we assess here if a neural network approach can be successfully applied as a means to correct for systematic biases when a neural network is trained on wind power electricity generation while using a different climate data source for the prediction process.

We apply neural networks on climate assimilation data from climate modelling and train the neural network on actual generation from wind power. The trained neural networks are then used with an ensemble of climate input variables from seasonal forecasts to seasonally predict electricity generation from wind power. As the neural network is trained on a different data source, the modelled generation values are systematically biased. A subsequent neural network is applied to reduce this bias and to gain insight into how the bias between the two data sources differs via an analysis of the networks weights as well as a sensitivity analysis.

The neural network’s ability to correct for systematic biases is assessed based on whether the quality of the modelled distributions in terms of their seasonal characteristics and extreme event frequencies is improved compared to not using this bias correcting neural network. Initial model results show that a neural network can in fact be used to correct for systematic biases introduced by using different data sources in model training and prediction to help generate results of improved quality versus not using a bias correcting neural network.
Interpreting Vegetation Optical Depth (VOD) using detailed destructive vegetation sampling of a corn canopy
Authors: Khabbazan Saeed , Gao Ge , Vermunt Paul , Steele-Dunne Susan , Judge Jasmeet , Vreugdenhil Mariette
Published: March 2020

Vegetation Optical Depth (VOD) is directly related to Vegetation Water Content (VWC), which can be used in different applications including crop health monitoring, water resources management and drought detection. Moreover, VOD is used to account for the attenuating effect of vegetation in soil moisture retrieval using microwave remote sensing.

Commonly, to retrieve soil moisture and VOD from microwave remote sensing, VWC is considered to be vertically homogeneous and relatively static.  However, nonuniform vertical distribution of water inside the vegetation may lead to unrealistic retrievals in agricultural areas. Therefore, it is important to improve the understanding of the relation between vegetation optical depth and distribution of bulk vegetation water content during the entire growing season.

The goal of this study is to investigate the effect of different factors such as phenological stage, different crop elements and nonuniform distribution of internal vegetation water content on VOD. Backscatter data were collected every 15 minutes using a tower-based, fully polarimetric, L-band radar. The methodology of Vreugdenhil et al. [1] was adapted to estimate VOD from single-incidence angle backscatter data in each polarization.

In order to characterize the vertical distribution of VWC, pre-dawn destructive sampling was conducted three times a week for a full growing season. VWC could therefore be analyzed by constituent (leaf, stem, ear) or by height.

A temporal correlation analysis showed that the relation between VOD and VWC during the growing season is not constant. The assumed linear relationship is only valid during the vegetative growth stages for corn.  Furthermore, the sensitivity of VOD to various plant components (leaf, stem and ear) varies between phenological stages and depends on polarization.

Improved understanding of VOD can contribute to improved consideration of vegetation in soil moisture retrieval algorithms. More importantly, it is essential for the interpretation of VOD data in a wide range of vegetation monitoring applications.

[1] M. Vreugdenhil,W. A. Dorigo,W.Wagner, R. A. De Jeu, S. Hahn, andM. J. VanMarle, “Analyzing the vegetation parameterization in the TU-Wien ASCAT soil moisture retrieval,” IEEE Transactions on Geoscience and Remote Sensing, vol. 54, no. 6, pp. 3513–3531, 2016.
Emerging effects of selected rhizosphere properties on transpiration and leaf water potential of two Zea mays L. genotypes in semi-arid environments
Authors: Köhler Tina , Moser Daniel-Sebastian , Botezatu Ákos , Kholova Jana , Carminati Andrea , Ahmed Mutez
Published: March 2020

Understanding the mechanisms that control water use of plants exposed to soil drying and increasing vapour pressure deficit (VPD) has important implications for crop growth in semi-arid regions with low-input agriculture. In particular, the effect of belowground processes on transpiration and stomatal regulation remains controversial. Objective of this study was to understand the role of soil properties and root hairs (as an example of rhizosphere traits) on transpiration and leaf water potential. We hypothesize that root hairs facilitate the water extraction from drying soils, particularly at high VPD, and that this impacts the relation between transpiration rate and leaf water potential. We further hypothesize that stomatal regulation attenuates the drop in leaf water potential when the soil water flow cannot match the transpiration demand and thus emphasizes the importance of root hairs on transpiration rates during soil drying.

We compared maize (Zea mays L.) with (wild-type) and without (mutant) root hairs in three different soil substrates (Alfisol, Vertisol and Sandy Soil). Transpiration and leaf water potential were monitored at varying VPD and soil moistures during soil drying. The hairless mutant showed a higher transpiration in wet soils but declined transpiration at greater water contents as compared to the wild-type. Under well-watered conditions, both genotypes had the highest transpiration rates in Vertisol. In Vertisol, both genotypes closed their stomata at relatively higher water content levels. The relation between transpiration and soil moisture strongly varied between soils. No obvious differences between the genotypes were visible in the relationship between leaf water potential and transpiration. This is explained by the prompt closure of stomata. This study provides experimental evidence of the strong link between stomatal regulation and soil-root hydraulic properties.
Mesoscale eddy characteristics in the Labrador Sea from observations and a 1/60° numerical model
Authors: Bendinger Arne , Karstensen Johannes , Le Sommer Julien , Albert Aurélie , Dilmahamod Fehmi
Published: March 2020

Mesoscale eddies play an important role in lateral property fluxes. Observational studies often use sea level anomaly maps from satellite altimetry to estimate eddy statistics (incl. eddy kinetic energy). Recent findings suggest that altimetry derived eddy characteristics may suffer from the low spatial resolution of past and current satellite-tracks in high-latitude oceans associated with small Rossby radii. Here we present results of an eddy reconstruction based on a nonlinear damping Gauss-Newton optimisation algorithm using ship based current profiler observations from two research expeditions in the Labrador Sea in 2014 and 2016. Overall we detect 14 eddies with radii ranging from 7 to 35 km.

In order to verify the skill of the reconstruction we used the submesoscale permitting NATL60 model (1/60°) as a reference data set. Spectral analysis of the horizontal velocity implies that the mesoscale regime is well represented in NATL60 compared with the observations. The submesoscale regime in the model spectra shows deviations to the observations at scales smaller than 10km near the ocean surface. The representation of the submesoscale flow further decreases in the model with increasing depth.

By subsampling the NATL60 model velocities along artificial ship tracks, applying our eddy reconstruction algorithm, and comparing the results with the full model field, a skill assessment of the reconstruction is done. We show that the reconstruction of the eddy characteristics can be affected by the location of the ship track through the velocity field.

In comparison with the observed eddies the NATL60 eddies have smaller radii and higher azimuthal velocities and thus are more nonlinear. The inner core velocity structure for observations and NATL60 suggests solid body rotation for 2/3 of the radius. The maximum azimuthal velocity may deviate by up to 50% from solid body rotation.

The seasonality of the submesoscale regime can be seen in the data as the power spectrum is reduced from spring to summer in both the ship-based measurements and model.
Chemical variations in time in a context of climate variability: examples in different hydrogeological settings
Authors: Lasagna Manuela , Ducci Daniela , Sellerino Mariangela , Mancini Susanna , De Luca Domenico
Published: March 2020

Increased variability in precipitation and more extreme weather events caused by climate change can lead to more extended periods of droughts and floods, which directly affects the availability of groundwater. The consequent fluctuation of the water table can also affect groundwater quality. Particularly, a higher recharge, and the resultant increase of the piezometric level, can have, as a positive result, the dilution of the contaminants in aquifers and a decrease of the concentrations. On the other side, water that infiltrates can leach pollutants that are present in the unsaturated zone, with an increase of groundwater pollution. Even, the rise of the piezometric level can have negative consequences on groundwater quality, also due to groundwater that leach the capillary fringe and the previously unsaturated zone; if a contaminant is present in these sectors, it can lead to an increase of the aquifer pollution.

The increase or decrease in contaminants levels depend on a complex balance between all the described phenomena, and contaminant behaviour. This study wants to analyse the hydrogeochemical variations in time due to climate variability to define the role of different processes.

Two different hydrogeological environments were chosen as test fields: an alluvial aquifer in the Piedmont Po Plain (NW Italy) and an alluvial-pyroclastic aquifer in the Campanian plain (S Italy).

Piedmont Po plain shows a diffuse nitrate contamination, due to intensive agricultural and livestock activities. A nickel contamination is locally present, due to natural causes, namely the presence of basic and ultrabasic rocks debris in the supply basins, containing high amount of nickel-bearing femic minerals. Consequently, nitrate and nickel fluctuation were analysed and compared with precipitation and piezometric levels.

The hydrogeochemistry of the Campanian plain is influenced by the closeness of volcanic active areas (Phlegrean Fields and Vesuvius), bringing high As and F values, and by the presence of reducing conditions, bringing high Fe and Mn values. Moreover, there is a widespread nitrate contamination, prevalently due to intensive agricultural and livestock activities. The fluctuations of these 5 ions (As, F, Fe, Mn and NO3) have been observed during almost twenty years and compared with the differences in recharge, sometimes significant due to the climate change.

The monitoring and analyses of the chemical concentrations of ions of anthropogenic and natural origin in a context of climate variability represent a key element to offer a new and different research perspective in the field of groundwater chemistry.
Global flood hazard map and exposed GDP inter-comparison for China
Authors: Ward Philip , Aerts Jerom , Uhlemann-Elmer Steffi , Eilander Dirk
Published: March 2020

In this contribution we carried out a comprehensive comparison of flood hazard maps of 8 global flood models for the country of China based on a collective effort of the flood modelling community to participate in this study. In doing so, we assessed how differences in the simulated flood extent between the models lead to differences in simulated exposed GDP and expected annual exposed GDP. This is carried out by addressing the variation in different model structures and the variability between flood hazard maps. Our comparison uses both publicly available GFMs (GLOFRIS, ECMWF, CAMA-UT, JRC, and CIMA-UNEP) as well as industry models (Fathom, KatRisk, and JBA Risk Management) that are applied within the wider re-insurance industry. We expand upon the existing work of global flood model inter-comparison studies (e.g. Trigg et al., 2016; Bernhoffen et al., 2018) by including industry models, the pluvial flood component, and the effects of standards of protection on the flood hazard and exposure.

China is selected as our case study area because it poses many challenges to flood modelling: data scarcity; a variety of flood mechanisms spanning many climatic zones; complex topography; strong anthropogenic influence on the flood regimes, for example through river training; and a very high concentration of exposure. Moreover, China is prone to severe flood events. For example, in June 2016 alone more than 60 million people were affected by floods, resulting in an estimated damage of $22 bn (CRED 2016).

This abstract is an adaptation of “Global flood hazard map and exposed GDP comparison: a China case study” (Aerts et al., under review) and parts of this work have been presented at EGU 2019.
Evaluation of a dendroclimatic process-based model (MAIDEN) over the last century using the PAGES2k tree-ring width database
Authors: Rezsöhazy Jeanne , Goosse Hugues , Guiot Joël
Published: March 2020

Trees are one of the main archives to reconstruct the climate of the last millennium at high resolution. The links between tree-ring proxies and climate have usually been estimated on the basis of statistical approaches, assuming linear and stationary relationships. Both assumptions can be inadequate and this issue can be overcome by ecophysiological models such as MAIDEN (Modeling and Analysis In DENdroecology), which simulates tree-ring growth starting from temperature and precipitation daily inputs. A protocol for the application of MAIDEN to potentially any site with tree-ring width data in the extratropical region has been developed in Rezsöhazy et al. (2019) (in review). In this study, the applicability of the model has been tested over the twentieth century using as a test case tree-ring observations from twenty-one Eastern Canadian taiga sites and three European sites. The paper highlights the potential of MAIDEN as a complex mechanistic proxy system model to analyse the links between tree growth and climatic conditions in paleoclimatic applications. Following on from this recent work, MAIDEN is here applied to the PAGES2k tree-ring width database over the last century using the protocol developed in Rezsöhazy et al. (2019) (in review). We show how this larger network allows refining our protocol. We identify the regions and sites where MAIDEN can be successfully applied, as well as estimate the uncertainty associated with the use of MAIDEN for a wide range of sites.

 

Rezsöhazy, J., Goosse, H., Guiot, J., Gennaretti, F., Boucher, E., André, F., and Jonard, M.: Application and evaluation of the dendroclimatic process-based model MAIDEN during the last century in Canada and Europe, Clim. Past Discuss., https://doi.org/10.5194/cp-2019-140, in review, 2019.
The role of alpha and beta diversity in buffering the effects of intensifying natural disturbance regimes
Authors: Sebald Julius , Thrippleton Timothy , Rammer Werner , Bugmann Harald , Seidl Rupert
Published: March 2020

Forests are strongly affected by climatic changes, but impacts vary between tree species and prevailing site conditions. A number of studies suggest that increasing tree species diversity is a potent management strategy to decrease climate change impacts in general, and increase the resilience of forest ecosystems to changing disturbance regimes. However, most studies to date have focused on stand-level diversity in tree species (alpha diversity), which is often difficult to implement in operational forest management. Inter-species competition requires frequent management interventions to maintain species mixture and complicates the production of high-quality stemwood. An alternative option to increasing alpha diversity is to increase tree species diversity between forest stands (beta diversity). Here we quantify the effects of alpha and beta diversity on the impact of forest disturbances under climate change. We conducted a simulation experiment applying two forest landscape models (i.e. iLand and LandClim) in two landscapes with strongly contrasting environmental conditions in Central Europe. Simulations investigate different levels of tree species diversity (no diversity, low diversity and high diversity) in different spatial arrangements (alpha diversity, beta diversity). Subsequently a standard forest management regime and a series of prescribed disturbances are applied over 200 years. By analyzing biomass values relative to a no-disturbance run, variation in biomass over time and the number of trees > 30 cm dbh per hectare, we isolate the effect of tree species diversity on the resistance of forests to disturbances.
Permeability evolution of pseudotachylytes during hydrothermal alteration experiments
Authors: Rempe Marieke , Renner Jörg
Published: March 2020

The apparently low abundance of pseudotachylytes in field outcrops of fault zones may be due to their alteration and hence destruction of characteristic microstructures. The potential for alteration of rocks is largely controlled by the availability of water that in turn depends on the rocks’ permeability. The permeability of pseudotachylytes, which generally exhibit a fine-grained matrix, is expected to be low relative to their host rock, such that infiltration by fluids should be minimal. We are therefore conducting flow-through experiments at elevated temperatures on pseudotachylyte samples from the Gole Larghe fault zone, Italian Southern Alps. We are monitoring the permeability and its evolution with time due to hydrothermal alteration processes using the pore-pressure oscillation technique. Microstructural analyses of naturally and experimentally altered pseudotachylytes will help to constrain the alteration processes and associated kinetics. Our results contribute to answer the question how pseudotachylytes are lost from the rock record.
2015 Nepal Earthquake: A Comparison between Landslide Inventories
Authors: Valagussa Andrea , Frattini Paolo , Valbuzzi Elena , Billinge-Jones Malcolm , Crosta Giovanni Battista
Published: March 2020

Three landslide inventories were prepared for the area affected by the 7.8 Mw Nepal earthquake (April 25, 2015). The first inventory contains 21,151 earthquake-induced landslides (EQL), directly associated to the 7.8Mw earthquake, mapped by using Google Earth’s pre and post-earthquake images, helicopter footage and Google Crisis data. Landslides were classified as debris flows, shallow translational landslides and rotational landslides. This last class included a relatively small number of events.  The second inventory includes only pre-event shallow landslides (PESL) to evidence those landslides which were already active before the 2015 earthquake. This inventory includes more than 2,500 landslides. The third inventory includes almost 20,000 large landslides (LL), consisting mostly of rock avalanches, slumps, rockslides, and deep-seated gravitational slope deformations (DSGSD). The spatial distribution of the three inventories was analysed with respect to land surface parameters. The EQL inventory shows in general a different spatial distribution with respect to the other two inventories. This is probably related to the seismic triggering and to the characteristics of the geographic area. A joint analysis of the LL and the EQL inventories shows that only a few earthquake-induced landslides (about 15 %) are directly associated to reactivation of LL.

A Principal Component Analysis (PCA) and a Discriminant Analysis were performed to analyse the controlling parameters on EQL and PESL. The analyses were based on: 1) land surface parameters, 2) hydrological parameters, 3) seismic parameters, 4) lithological parameters, 5) land cover, and 6) meteorological parameters. The statistical analyses show that the most critical variables for landslide triggering during an earthquake are associated to the land surface parameters, in association with the cosesimic displacement and the PGA,  that show an effect on the landslide size and density respectively. PESL seem to be mainly controlled by land surface parameters, with some of them (e.g. elevation) showing a slightly inverse relationship with landslide density. Agricultural land use, slope gradient and rainfall (reference period 1980-2000) show a high correlation with the PESL landslide triggering in absence of earthquakes.
Fate of Carbon During the Formation of Earth’s Core
Authors: Blanchard Ingrid , Jennings Eleanor , Franchi Ian , Zhao Zuchao , Petitgirard Sylvain , Miyajima Nobuyoshi , Jacobson Seth , Rubie David
Published: March 2020

Carbon is an element of great importance in the Earth, because it is intimately linked to the presence of life at the surface, and, as a light element, it may contribute to the density deficit of the Earth’s iron-rich core. Carbon is strongly siderophile at low pressures and temperatures (1), hence it should be stored mainly in the Earth’s core. Nevertheless, we still observe the existence of carbon at the surface, stored in crustal rocks, and in the mantle, as shown by the exhumation of diamonds. The presence of carbon in the crust and mantle could be the result of the arrival of carbon during late accretion, after the process of core formation ceased, or because of a change in its metal–silicate partitioning behavior at the conditions of core formation (P >40 GPa – T >3500 K). Previous studies reported metal–silicate partitioning of carbon based on experiments using large volume presses up to 8 GPa and 2200°C (2). Here, we performed laser-heated diamond anvil cell experiments in order to determine carbon partitioning between liquid metal and silicate at the extreme conditions of Earth’s core–mantle differentiation. We recovered our samples using the Focused Ion Beam technique and welded a 3 μm thick slice of each sample onto a TEM grid. Major elements were analyzed by electron microprobe, whereas the concentrations of carbon in the silicate were analyzed by nanoSIMS. We thus have obtained metal–silicate partitioning results for carbon at PT conditions relevant to planetary core formation, where C remains siderophile in all experiments, but partition coefficients are up to two orders of magnitude lower than in low PTexperiments. We derive a new parameterization of the pressure–temperature dependence of the metal–silicate partitioning of carbon and apply this in a state-of-the-art model of planet formation and differentiation (3,4) that is based on astrophysical N-body accretion simulations. Results show that BSE carbon concentrations increase strongly starting at a very early stage of Earth’s accretion and, depending on the concentration of carbon in accreting bodies, can easily reach or exceed estimated BSE values.

 

(1) Dasgupta et al., 2013. Geochimica et Cosmochimica Acta 102, 191-212

(2) Li et al., 2016. Nature Geoscience 9, 781–785

(3) Rubie et al., 2015. Icarus 248, 89–108

(4) Rubie et al., 2016. Science 353, 1141–1144

 
Empirical acquisition of bidirectional reflectance of tropical forest ecosystems using unmanned aerial vehicles
Authors: Maes Wouter , Bovend'aerde Lisa , Lauwers Marlies , Steppe Kathy , Huete Alfredo
Published: March 2020

Both the sensor viewing angle and the solar angle influence the remote sensing signal of terrestrial ecosystems. This influence is characterized by the bidirectional reflectance distribution function (BRDF). Knowledge of this BRDF is needed to correctly interpret the signal, but can also provide information on vegetation characteristics and structure. Obtaining the BRDF is far from straightforward: at leaf scale, laboratory goniometers can measure reflected radiation over a range of sensor-solar angle; for very homogeneous ecosystems, such as grassland or agricultural cropland, unmanned aerial vehicles (UAVs) can be programmed as giant goniometer, scanning the BRDF of an area of up to a few m². For heterogeneous ecosystems such as forests, this is not feasible. In this case, BRDF could so far only be derived from theoretical radiation transfer models or semi-empirical models; yet these models do not always agree.

We here propose a new method for measuring BRDF of forest ecosystems with UAVs, by measuring a star-shaped area of the ecosystem, covering in total about 3600m² and capturing 6 different sensor-solar azimuth angle and three different zenith angles. This approach was applied over two sites of tropical rainforests in Queensland, Australia, with measurements with a RGB camera and a spectrometer. By repeating the flights several times during the day, we were able to test the Helmholtz reciprocity principle – that states the BRDF function of ecosystems remains the same, regardless of the solar angle – and are able to increase the range of sensor-solar angles. Our results present the first strictly empirical BRDF of tropical rainforests and confirm the importance of accurate BRDF correction of remote sensing products from forest ecosystems. 
A synthesis of worldwide sediment source tracing research including fallout radiocesium (Cs-137)
Authors: Evrard Olivier , Chaboche Pierre-Alexis , Ramon Rafael , Foucher Anthony , Laceby J. Patrick
Published: March 2020

Quantifying the main sources delivering harmful sediment loads to river systems is required to improve our knowledge of soil erosion processes. Among these potential sources, quantifying the contributions of surface (e.g. cultivated topsoil) and subsurface (e.g. channel bank, gully, landslide) material to sediment transiting river systems is of particular interest. Radiocesium (137Cs) that was emitted during the atmospheric bomb tests that took mainly place in the 1960s and nuclear accidents provides an effective tracer to distinguish between topsoil material exposed to the fallout and subsoil sheltered from this fallout. A global synthesis of research articles (n=123) that used radiocesium to fingerprint sediment sources indicated that the largest number of publications (~55% of the total) were found in the United Kingdom, Australia and the United States. On the contrary, very few studies (~9% of the total) were published for catchments located in Africa or South America. Given the low proportion of fallout recorded in regions located between 0-20°N and 0-20°S, the potential of this technique for quantifying sediment source contributions may be limited in this part of the world. A similar conclusion may be drawn for applying this method in agricultural areas exposed to several soil erosion during the last several decades, such as Chinese Loess Plateau and South Africa. Overall, 94% of studies incorporating 137Cs as a potential tracer included this property in mixing models. In the future, given the continuous decay of the initial radiocesium fallout that peaked in the 1960s, the access to ultra-low background gamma-ray spectrometry facilities will be increasingly necessary to measure this important sediment tracing property. In addition, more research should be devoted to develop surrogate tracers providing discrimination between surface and subsurface material. Based on this extensive study review, researchers are also recommended to systematically include basic catchment information, details on the soil/sediment sampling design and access to raw data to facilitate the dissemination of this information among the communities of scientists and catchment managers.
Observations of low energy ions around the diamagnetic cavity at comet 67P
Authors: Stenberg Wieser Gabriella , Wieser Martin , Bergman Sofia , Odelstad Elias , Johansson Fredrik , Nilsson Hans
Published: March 2020

We investigate the variations in low energy cometary ions around comet 67P. Detailed measurements of these ions were made possible by implementing a new instrumental mode of the ion mass spectrometer on the Rosetta spacecraft. The nominal time resolution was increased from 192 s to 4 s at the expense of the energy range and the field-of-view.

In this study we focus on ion observations made outside of, but in the vicinity of, the diamagnetic cavity. The ion dynamics here is clearly linked to variations of the magnetic field strength and properties of the electron velocity distribution, manifested by the spacecraft potential. Preliminary results show that the ion flux correlates with the changes of the spacecraft potential. The maximum ion flux is, however, observed about 20 seconds after a sudden decrease of the potential (corresponding to an increase in electron density if electron temperature is constant). We also find evidence of small ion temperature increases both when the spacecraft potential changes fast and at the time of maximum ion flux.
Effects of topography and lithology variation on in situ stress at shallow depths in South Korea: results from statistical characterization of stress data
Authors: Kang Minzy , Chang Chandong
Published: March 2020

In situ stress state at shallow depths (<1 km) is important for designing underground systems for various projects such as nuclear waste disposal, carbon dioxide geological sequestration, and geo-resource development. Stress characterization for such projects rely largely on stress measurement data (such as hydraulic fracturing test data). We compile a large number of hydraulic fracturing test data measured in a total of 226 boreholes in South Korea, and attempt to characterize shallow crustal stress over the country. These data are measurements at depths down to 850 m, and classified mostly low-quality based on World Stress Map quality ranking scheme (B-quality: 7%, C: 42%, and D: 51%). We grid the country by 0.25°×0.25°, and find a circular bin size at each grid point using two statistical methods (weighted standard deviation and quasi interquartile range), by which the uniformity of stress orientation can be estimated. As many data are low-quality, we apply this process to two subsets of data (B-C and B-D) to find an optimal stress characterization. Our most optimal characterization results show that bin diameter in most of the country vary between 100 and 200 km, except for southeastern Korea. Bin diameters in southeastern Korea range between 0 and 60 km, which means that stress heterogeneity is especially significant in the region, where lithology varies markedly and several active faults are clustered. The stress orientations in the northeastern part of the country are characterized as intermediate stress uniformity (bin size of ~120 km in diameter) but a systematic horizontal stress rotation (up to ~60°) from that of the deep-seated regional stress. This region is mountainous with altitude as high as 1.4 km. To verify whether the stress rotation is a result of topographic effect, we model stress perturbation using the digital elevation model (DEM) data of the region, which yields stress rotation comparable to measurements. We find that lithology is a particularly important factor that affects stress magnitudes over the country, as the stress magnitudes at the same depth tend to be markedly smaller in sedimentary rocks than in crystalline rocks. Our study, although given data are of fairly low-quality, can provide a basis for shallow stress map of South Korea.