bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and temporal distributions of clay minerals in mud deposits on the inner shelf of the East China Sea: Implications for paleoenvironmental changes in the Holocene
Authors: Liu Shengfa , Shi Xuefa , Fang Xisheng , Dou Yanguang , Liu Yanguang , Wang Xuchen
Published: March 2020

We present a paleoclimatic reconstruction for the Holocene by clay mineral analyses of sediments from core MZ02 retrieved from the mud area of the inner continental shelf of the East China Sea (ECS). The clay minerals mainly consist of illite (66%-79%) and chlorite (12%-19%), with minor kaolinite (7%-13%) and smectite (0-6%). Provenance analysis suggests that the illite-dominated clay minerals were derived mainly from the detrital outputs of the Changjiang, Minjiang, and small rivers from Taiwan Island. Our study indicates that the sea level rise since the last glacial, the strength of the Taiwan Warm Current (TWC) and Chinese Coastal Current (CCC) have controlled the dispersal and deposition of clay minerals on the ECS, that in turn determined the clay mineral compositions in the core sediments. During 13,000-9500 BP, due to the lower sea level and shorter distance between these three estuaries and core MZ02, fine sediments on the inner shelf of the ECS were primarily supplied by mixed provenances from the Changjiang, Taiwanese, and Minjiang rivers. During the early Holocene (9500-6200 BP), stronger sediment reworking and erosion at the shelf edge was responsible for the increased lateral transport of fine sediments in the ECS, which lead to a dominance of the sediment source from the Changjiang, while the Taiwanese and Minjiang rivers only provided minor components of detrital sediment to the shelf. Increased strength of TWC might have played an important role in the sediment dispersal and deposition on the inner shelf of the ECS during 6200-2400 BP, with a dominance of more than 60% sediments transported from Taiwanese rivers. Furthermore, our study implies that the Asian monsoon and the weakening of TWC were linked to the abrupt increase of Changjiang and Minjiang derived terrigenous detritus materials since 2400 BP.

 

Acknowledgments

This work was supported by National Nature Science Foundation of China (No.41106063), Science and Technology Basic Special Program of China (No.2008FY220300), Marine Public Welfare Research Project of China (No.200805063), China Postdoctoral Science Foundation (No.20100481304) and Coastal Investigation and Research Project of China (No. 908-01-CJ12).
Test of chemistry boundary conditions large-eddy simulations in urban areas
Authors: Forkel Renate , Khan Basit , Werhahn Johannes , Banzhaf Sabine , Chan Edward C. , Kanani-Sühring Farah , Ketelsen Klaus , Maronga Björn , Mauder Matthias , Raasch Siegfried , Sühring Matthias
Published: March 2020

Large-Eddy Simulation (LES) allow to simulate pollutant dispersion at a fine-scale turbulence-resolving scale with explicitly resolved turbulent transport around building structures and in street canyons. The microscale urban climate model with atmospheric chemistry PALM-4U (i.e. PALM for Urban applications; Maronga et al., 2019, Met. Z., https://doi.org/10.1127/metz/2019/0909) has been developed within the collaborative project MOSAIK (Model-based city planning and application in climate change). With such a large-eddy simulation (LES) model, pollutant dispersion around buildings and within street canyons can be simulated, with explicitly resolving the turbulent transport in urban environments.

Cyclic boundaries are frequently applied in LES in order to obtain lateral boundary conditions for the turbulent quantities. In addition to the default cyclic boundary conditions, PALM-4U allows also time-dependent boundary conditions from regional models to account for variable weather conditions and regional scale pollutant transport. Turbulent fluctuations, which are not included in the boundary conditions from the regional simulation but are needed as additional boundary conditions for the LES model are produced by a turbulence generator (Maronga et al, 2019, GMDD, https://doi.org/10.5194/gmd-2019-103).

PALM-4U simulations with and without time dependent boundary conditions from regional simulations with WRF-Chem are performed for different setups in order to test the impact of the domain configuration. The simulations indicate that cyclic boundary conditions can lead to unrealistic accumulation of pollutants over urban areas with strong sources, which is not the case when time-dependent boundary conditions are applied. However, even though a turbulence generator is applied, explicit setting of time-dependent boundary conditions requires large model domains, in order to obtain fully developed turbulence within the domain of interest, increasing the computational demand of the simulation.
A new version of the IBI near real time system for November 2020: what will be changed?
Authors: Reffray Guillaume , Benkiran Mounir , Levier Bruno , Gutknecht Elodie , Aznar Roland , Guihou Karen , Garcia-Sotillo Marcos
Published: March 2020

The IBI (Iberian-Biscay-Ireland) MFC (Monitoring and Forecasting Centre) is in charge of providing ocean forecasts for the IBI region in the framework of the Copernicus Marine Environment Monitoring Service (CMEMS). To do so, a coupled model system is operated daily to monitor and forecast the ocean dynamics and marine ecosystem. The domain of the model is a subset of the ORCA grid at the resolution of 1/36° and covers the North-East Atlantic Ocean from the Canary Islands to Iceland, including the North Sea and the Western Mediterranean.

The IBI system is operated since 2010 and regularly released. The coupled model is based on NEMO-PISCES. A data assimilation method based on SEEK Kalman filter is applied to the physical component. This coupled system with data assimilation has been operational since April 2018, providing 5-day physical forecasts on a daily basis and 7-day ecosystem and carbon forecasts on a weekly basis.

A new release of this system is planned for November 2020, and includes a lot of changes about the physical NEMO model especially on its vertical component (turbulence, solar penetration, bulk formulaes, ...), a new tuning for the data assimilation method and a new CMEMS global biogeochemical system to initialise and force at the open boundaries of the IBI system. The objective is to summarize these changes and to illustrate their impacts by confronting the model results to in-situ data profiles, SST satellites products, BGC-Argo floats ...
Cosmic-ray neutron sensing based monitoring of snowpack dynamics: A comparison of four conversion methods
Authors: Bogena Heye Reemt , Herrmann Frank , Jakobi Jannis , Pisinaras Vassilios , Brogi Cosimo , Huisman Johan Alexander , Panagopoulos Andreas
Published: March 2020

Snow monitoring instruments like snow pillows are influenced by disturbances such as energy transport into the snowpack, influences from wind fields or varying snow properties within the snowpack (e.g. ice layers). The intensity of epithermal neutrons that are produced in the soil by cosmic radiation and measured above the ground surface is sensitive to soil moisture in the upper decimetres of the ground within a radius of hectometres. Recently, it has been shown that aboveground cosmic ray neutron sensors (CRNS) are also a promising technique to monitor snow pack development thanks to the larger support that they provide and to the lower need for maintenance compared to conventional sensor systems. The basic principle is that snow water moderates neutron intensity in the footprint of the CRNS probe. The epithermal neutrons originating from the soil become increasingly attenuated with increasing depth of the snow cover, so that the neutron intensity measured by the CRN probe above the snow cover is directly related to the snow water equivalent.

In this paper, we use long-term CRNS measurements in the Pinios Hydrologic Observatory, Greece, to test different methods for the conversion from neutron count rates to snow pack characteristics, namely: i) linear regression, ii) the standard N0-calibration function, iii) a physically-based calibration approach and iv) the thermal to epithermal neutron ratio. The latter was also tested for its reliability in determining the start and end of snowpack development, respectively. The CRNS-derived snow pack dynamics are compared with snow depth measurements by a sonic sensor located near the CRNS probe. In the presentation, we will discuss the accuracy of the four conversion methods and provide recommendations for the application of CRNS-based snow pack measurements.
Evaluation of the WRF Physics Ensemble using Multivariable Integrated Evaluation Approach over Haihe river basin in north China
Authors: Dai Danqiong
Published: March 2020

  A crucial step of the application of WRF in regional climate research is selection of the proper combinations of physical parameterizations. In this study, we performed experiments in WRF to assess the predict skill of various parametrization schemes sets in simulating precipitation, temperature over the Haihe river basin. The experiments driven by ERA-INTERIM reanalysis data are performed for a period of summer (1 June to 31 August, 2016) in this domain with 13 km grid spacing. Fifty-eight members of physics combinations thoroughly covering five types of physics options are assessed against the available observational data by utilizing the multivariable integrated evaluation (MVIE) method. It is deduced that the best performing setup consists of CAM5.1 microphysics, MRF PBL, BMJ Cumulus, CAM Longwave/Shortwave radiation, and Noah Land Surface schemes. To identify the robustness of the optimal scheme set, the vector field evaluation (VFE) diagram for displaying all simulations reveals that the optimal one is distinguished from others by higher vector field similarity coefficient(Rν), smaller root mean square vector deviation(RMSVD). The model deviations spatially for the precipitation show a promising tendency that a strong overestimation about 5 mm/day for the default configuration evolves small biases of the optimal setup with a range between -1 and 1 mm/day, and the surface temperature forecasts have improved to some extent although not significant as that of precipitation. The temporally analysis of the spatial average of all simulations exhibits that for temperature the optimal setup is more approaching to the observational data, but for precipitation no remarkable difference between all simulation and the observations. Further analysis of the sensitivities of model output to different types of physics option suggests that, microphysics, PBL, and Cumulus schemes have more significant impact on the model performances measured by a multivariable integrated evaluation index (MIEI) than radiation scheme and Land Surface schemes.
Indoor height determination of the new absolute gravimetric station of L'Aquila
Authors: Mazzoni Augusto , Fortunato Marco , Sonnessa Alberico , Berrino Giovanna , Greco Filippo , Riguzzi Federica
Published: March 2020

In 2018 INGV funded a project aimed to detect gravity variations and ground deformations over different time-scale possibly associated with the postseismic relaxation affecting the area where the recent seismic events of L'Aquila (2009 Mw 6.3) and Amatrice-Norcia (2016 Mw 6.1 and 6.5) took place. To this aim a network of five absolute gravity stations was realized (Terni, Popoli, Sant’Angelo Romano, L’Aquila University and L'Aquila Laboratori Nazionali del Gran Sasso). The site of L'Aquila University was chosen since location of the permanent GNSS station (AQUI) managed by the Italian Space Agency and contributing to the EUREF network. AQUI is continuously operating on the roof of the Science Faculty (Coppito, L'Aquila).

In the basement of the same building we realized the absolute gravimetric station (AQUIg), indoor the Geomagnetic laboratory of the Physics Department. This is one of the numerous applications where satellite systems must be integrated with traditional terrestrial surveying techniques. These include the case of underground or indoor gravimetric surveys, where the height of the gravimetric reference point should be determined precisely starting from an outdoor reference point with known coordinates. In this case, the use of classical observation techniques and instruments (e.g., total stations, levels) is crucial to measure the height difference between a reference GNSS station and a gravimetric benchmark. We will draw the steps followed to estimate the height difference between AQUIg and AQUI by a classical topographic survey and therefore the height of AQUIg from estimating first the height of AQUI.
ADCP with onboard GPS for streamflow velocity measurement usable for physical models calibration
Authors: Morlot Thomas , Oustriere Pierre , Leclercq Franck , Scheepers Hélène
Published: March 2020

Human beings always wanted to protect themselves from hazards associated with rivers and streams. Wether we talk about low flow, pollution or flooding, streams very quickly interested scientists and engineers for their wealth and abilities.

EDF (Electricité de France) is a french company dealing with energy production. Dealer or owner operator of electricity production structures, the company is responsible for their operation in safe conditions. Thus, the knowledge of parameters such as streamflow discharge or streamflow velocities is one of its priorities to better respond to three key issues which are plant safety, compliance with reguatory requirements and optimization of the means of production.

The present work consists in showing how to use ADCP (Accoustic Doppler Current Profiler) to accurately measure streamflow volocities in complicated conditions (tide cycle, complex flow, bubbles, factory in operation…). Such device can be coupled with GPS to precisely geolocalize the measured velocities to make them usable for models calibration. By showing a case study, this work aims at underlining how field work using ADCP with onboard GPS can create input data for the adaptation and the calibration of physical models.
Identification and enhancement of the thermal and mechanical properties of two types of plasters successively derived from gypsum: from the Safi basin and the High Atlas of Marrakech, Morocco
Authors: baba imane , Ibnoussina Mounsif , Witam Omar
Published: March 2020

Over the past few decades, the construction industry has focused on sustainable, environmentally friendly and easily recyclable materials. The objective of this work is to characterize and enhance the thermal conductivity, mechanical strength and setting time of a composite material based on plaster and lime. This material is designed for use in plasters.

Two types of gypsum are studied, the first one belongs to the Safi basin, the second one characterizes the High Atlas of Marrakech and precisely Douar Tafza. Geologically speaking, the two sites have many similarities. They are characterized by a Meso-Cenozoic age coverage covering a deformed Paleozoic age basement.

The characterization of the plaster's raw material, gypsum, was necessary to determine its physical and geotechnical properties, mineralogy, thermal behaviour and microscopic structure. Several analyses have been developed such as: pycnometer density measurement, X-ray diffraction, infrared spectroscopy and scanning electron microscopy.

We made samples, of standardized dimensions, of two mixtures based on the two types of plaster reinforced by the addition of two types of lime from different localities. The latter are from Marrakech and the Agadir region. The water/plaster mass ratio was set at 0.75 and the addition of lime was achieved by increasing its percentage in slices by 12.5% and up to 50%.

The reinforcement of plaster with lime has enhanced its thermal and mechanical properties and setting time. The measurements show that the addition of lime has reduced the thermal conductivity and increased the mechanical strength of both types of plaster. In addition, following the addition of lime, the setting time has decreased and the basicity of the material has increased. Noting that the intrinsic properties of the raw material influence the mechanical and thermal properties of the material.

Keywords:   plaster, enhancement, properties, mechanical, thermal, Morocco
Determination of depth to the magnetic sources using spectral analysis with application to Sicily, Southern Italy
Authors: Kelemework Yemane , Fedi Maurizio
Published: March 2020

Spectral analysis is among the most old and common techniques for the processing and interpretation of potential field data. This is related to the decay properties of the field power spectra which allows an easy estimation of the depths to the top and to the bottom of the sources of magnetic and gravity field anomalies. Such analysis can be accomplished however in different theoretical frameworks, assuming either a statistical ensemble of homogeneous sources or random fractal source distribution. Here, we present the many existing spectral analysis techniques to compare them with respect to estimating the depth to the source top and bottom. We evidence practical constraints on the depth estimation and inherent assumptions/limitations of the different approaches. Depth estimation using spectral methods requires a critical evaluation of window size, window location, and wavenumber range. Careful consideration of the merits and of the limitations of these different spectral techniques for different source distribution models may lead to robust and geologically meaningful outcomes. In fact, despite the several different approaches all the methods give quite consistent and often similar estimates of the source depths. However, due to ambiguities on the correction spectral factor, the best estimates are obtained if this factor is constrained by a priori information. Finally, we estimate the depth to the magnetic sources beneath Sicily, which may provide additional constraints to better understand the deep crustal geometry and thermal gradients of the region.
Long-term changes in stratospheric water vapour and its implications for climate
Authors: Hegglin Michaela I.
Published: March 2020

Water vapour is the most important natural greenhouse gas in the atmosphere and provides a positive feedback to the climate forcing from carbon dioxide. Water vapour is also the source of hydroxyl (OH) which controls the lifetime of shorter-lived pollutants and long-lived greenhouse gases. Despite the importance of water vapour to chemistry and the radiative balance of the atmosphere, its observed long-term changes in the stratosphere are not well understood, and may even conflict with the theoretical understanding of its drivers. 

I here present a new climate data record of stratospheric water vapour developed within the ESA Water Vapour Climate Change Initiative and discuss recent changes in stratospheric water vapour concentrations in the light of earlier observational studies, modelling results from the SPARC Chemistry-Climate Model Initiative, and our theoretical understanding of its drivers. In addition, the radiative forcing of surface climate and inferred changes in the Brewer-Dobson Circulation will be highlighted. 
Carbon and nutrient cycling between estuarine and adjacent coastal waters
Authors: Rewrie Louise , Voynova Yoana , Brix Holger , Baschek Burkard
Published: March 2020

Seasonal and annual nitrate and phosphate loads were determined from FerryBox measurements to investigate the high seasonal and inter-annual variability of carbon and nutrient exchange between the Elbe estuary and North Sea. At the inner continental shelf, high biological activity is driven by riverine nutrient inputs, which can contribute to the net carbon dioxide (CO2) uptake. It is possible that in tidal systems this newly formed phytoplankton is transported back into the estuary over the flood tide, and this organic matter can be remineralized in the intertidal region. At present, the influence of this tidally driven mechanism on the nutrient exports and primary production in the coastal zone is not fully characterized, hence carbon sources and sinks at the estuary-coastal boundary may not be well accounted for.

The coupling between nutrient inputs from the Elbe estuary to adjacent coastal waters and the subsequent biological activity are now being investigated with a high-frequency dataset provided by a FerryBox situated at the mouth of the estuary. The FerryBox continuously measures physical and biogeochemical parameters every 10 to 60 minutes. Prelimary seasonal and nutrient (nitrate and phosphate) loads from the Elbe estuary to the coastal waters were calculated with FerryBox data between 2014 and 2017. The nutrient loads exhibited high seasonal and inter-annual variability. For example, in summer 2014 nitrate loads reached 100 x 107 mol yr-1 whereas, in summer 2017 nitrate loads were 50 x 107 mol yr-1, which cannot be explained by river discharge alone. Such changes in nutrient loads are likely to influence primary production rates in the adjacent coastal waters and impact CO2 uptake and therefore carbon cycling.

Time-series analysis is employed to determine patterns in oxygen changes in relation to photosynthesis and respiration, along with nutrient fluctuations, between 2014 and 2017. Salinity is used to differentiate between the coastal and estuarine end members, with low and high salinity representing flood tide (estuarine waters) and ebb tide (coastal waters), respectively. Changes in dissolved oxygen concentrations are used to estimate primary production (P) and community respiration (R) rates in the water column. The P/R ratio provides the ability to classify the community into autotrophic and heterotrophic systems. Results of this analysis will show the role of varying nutrient loads in supporting primary production in the coastal waters, along with estimating net ecosystem metabolism, and therefore give us a better understanding of nutrient and carbon cycling. 
Volatile-rich melts as markers of the asthenospheric influx prior to rifting events: the case of the alkaline-carbonatitic lamprophyres of the Dolomitic Area (Southern Alps, Italy)
Authors: Casetta Federico , Ickert Ryan B. , Mark Darren F. , Bonadiman Costanza , Giacomoni Pier Paolo , Ntaflos Theodoros , Coltorti Massimo
Published: March 2020

The appearance of alkali- and volatile-rich melts often marks the opening of major magmatic cycles, always reflecting the partial melting of heterogeneously enriched mantle domains. In these cases the study of highly alkaline, H2O-CO2-rich magmatic pulses provide important insights on the composition and behavior of the sub-continental lithospheric mantle (SCLM) prior to rift initiation. The camptonitic dykes cropping out at Predazzo (Dolomitic Area, NE Italy) are among the oldest examples of lamprophyric rocks in Italy, and were historically related to the orogenic-like Middle Triassic magmatism of the Southern Alps. A detailed petrological, geochemical and geochronological characterization of these rocks was developed to frame them inside the articulated geodynamic evolution of the Southern Alps domain during Triassic. Whole-rock and mineral phase geochemistry, together with 40Ar/39Ar data showed that Predazzo lamprophyres represent an alkaline-carbonatitic magmatic event temporally isolated (~220 Ma) from the major Ladinian orogenic-like magmatism of the Southern Alps (~238 Ma). Lamprophyres can thus be attributed to the volumetrically limited alkaline magmatic phase that infiltrated several portions of the Southern Alps lithosphere between 225 and 190 Ma. Partial melting models and Sr-Nd isotopes demonstrate that Predazzo lamprophyres were produced by low partial melting degree of a garnet-amphibole-bearing mantle source interacting with a significant asthenospheric contribution. In the light of these new findings, they are interpreted as the geochemical/geochronological bridge between the orogenic-like Ladinian magmatism and the rifting phase related to the opening of the Alpine Tethys. This study highlights the paramount importance of alkaline magmas for tracking the volatiles cycle in the SCLM and the potential lithosphere-asthenosphere interactions during large-scale geodynamic processes.
Astrochronology of the Barremian Stage: implications for the dynamics of the anoxic events in the Early Cretaceous
Authors: Martinez Mathieu , Aguado Roque , Company Miguel , Sandoval Jose , O'Dogherty Luis
Published: March 2020

Large uncertainties exist on the numerical ages of the stages in the Early Cretaceous which hamper from an accurate reconstruction of the past climate. Recent radio-astrochronologic data suggest to move the ages of the Tithonian to the Hauterivian stages by 3 to 5 Myr toward younger ages (Lena et al., 2019; Aguirre-Urreta et al., 2019). As the numerical ages in the Cenomanian are constrained with radio-astrochronology, this means that the duration of the Barremian to the Albian stages is overestimated. The duration of the Barremian Stage was estimated by bed counting on the assumption of a control by precession and eccentricity cycles (e.g., Bodin et al., 2006). The alternations and bundling can vanish leading to uncertainties in the duration estimates. Here, we provide an astrochronology from the eccentricity cycles based on spectral analyses performed on both magnetic susceptibility and calcium carbonate content series. Two sections are studied here in the Subbetic Domain (SE Spain). They are composed of marl-limestone alternations which reflect humid-arid cycles orbitally-driven. Detailed ammonite and calcareous nannofossil controls allow correlations with other sections in the basin and in the Tethyan Realm. The short and long-eccentricity cycles are identified throughout the Late Hauterivian to the earliest Aptian. The interval around the Hauterivian-Barremian boundary was recovered in a section previously studied for astrochronology and shows that the eccentricity cycles can be correlated to the sections studied here, validating the interpretations. From the record of the 405-kyr eccentricity cycle, the duration of the Barremian Stage is proposed at 4.25 ± 0.13 Myr. Anchoring this duration on previously obtained radio-astrochronology at the end of the Hauterivian, the Barremian Stage started at 125.91 ± 0.06 Ma and ended at 121.67 ± 0.11 Ma. The age of the latest Barremian agrees well with the age of the base of magnetochron M0r calculated from a synthesis of radiometric ages (Olierook et al., 2019). The Faraoni, Mid-Barremian and Taxy episodes show a pacing of 2.34 Myr, suggesting a strong orbital control on the expansion of oceanic anoxic conditions in the Tethys.

References:

Aguirre-Urreta, B., et al., 2019. Gondwana Res., 70, 104–132. https://doi.org/10.1016/j.gr.2019.01.006.

Bodin, S., et al., 2006. Palaeo-3, 235, 245–264. https://doi.org/10.1016/j.palaeo.2005.09.030.

Lena, L., et al., 2019. Solid Earth, 10, 1–14. https://doi.org/10.5194/se-10-1-2019.

Olierook, H.K.H., et al., 2019. Earth-Sci. Rev., 197, 102906. https://doi.org/10.1016/j.earscirev.2019.102906.
Aged streams: Time lags of nitrate, chloride and tritium assessed by Dynamic Groundwater Flow Tracking
Authors: Kaandorp Vince , Broers Hans Peter , de Louw Perry
Published: March 2020

Groundwater connects the agricultural fields in a catchment with the drainage network and it therefore plays an important role in the pollution of surface waters. To study this transport mechanism, we derived dynamic groundwater travel time distributions from a distributed, transient 3D groundwater flow model using forward particle tracking. We then calculated in-stream concentrations by coupling the travel time distributions with input time-series of tritium and the agricultural tracers chloride and nitrate, representing the water quality of the groundwater recharge throughout the catchment. We tested this approach for a lowland stream in the Netherlands and found that the variable contribution of different groundwater flow paths to stream water quality reasonably explained most of the long-term and seasonal variation in the measured stream nitrate concentrations. To study the observed lag in the breakthrough of agricultural solutes we performed a sensitivity analysis and found that the main contributors to such a time lag are the unsaturated zone, increased mean travel times and longer distances between agricultural fields and the drainage network. We found that the time between the application and effect of measures aimed to reduce in-stream concentrations depends on the combination of the input reduction rate and the mean travel time of the catchment. Furthermore, the location of agricultural fields in relation to the catchments’ drainage network was found to be an important factor that largely governs the travel times of the agricultural pollutants.
Physiographic controls on pre-event hydrological states and hydrological response to extreme precipitation in the Alzette River Basin, Luxembourg
Authors: Tamez-Melendez Carol , Meyer Judith , Douinot Audrey , Blöschl Günter , Pfister Laurent
Published: March 2020

The hydrological regime of rivers in Luxembourg (Central Western Europe) is characterised by summer low flows and winter high flows. In winter, large-scale floods are typically triggered by long-lasting sequences of precipitation events, related to westerly atmospheric fluxes that carry wet and temperate air masses from the Atlantic Ocean. In recent years, several flash flood events have been observed in Luxembourg. While being a common feature of Mediterranean river basins, this type of flooding events is uncommon at higher latitudes. The design of the hydro-meteorological monitoring and forecasting systems operated in Luxembourg is not adapted to this type of extreme events and there is a pressing need for a better mechanistic understanding of flash flood triggering mechanisms.

Here, we explore two lines of research – focusing on (i) the spatio-temporal variability of flash flood generation across a set of 41 nested catchments covering a wide range of physiographic settings (with mixed land use, soil types and bedrock geology) and (ii) the responsivity (resistance) and elasticity (resilience) of these catchments to global change.

Our area of interest is the Sûre River basin (4,240 km2), characterised by a homogenous climate (temperate oceanic), as well as various bedrock (e.g. sandstone, marls, shale) and land use (e.g. forests, grassland, crops, urban areas) types. Based on 8 years’ worth of daily hydrological data (precipitation, discharge and potential evapotranspiration) we computed the increments of the water balance to determine the maximum storage capacity and pre-event wetness state (expressed as storage deficit). Based on the relationship between storage deficit and discharge we first estimated total storage at nearly zero flow conditions. Second, we compared event runoff ratios (Q/P) to pre-hydrological states (as expressed to storage deficit prior to a rainfall-runoff event) in order to assess each catchment’s sensitivity to antecedent wetness conditions. Third, we assessed the responsivity (resistance) and elasticity (resilience) to climate variations – as expressed through the PET/P and AET/P deviations from the Budyko curve – for each individual catchment. Finally, we investigated potential physiographic controls on catchment responsivity and elasticity across our set of 41 nested catchments.
Silicon Cycling in Greenlandic fjords: Comparison of Marine and Land-Terminating Glaciers
Authors: Hatton Jade , Ng Hong Chin , Beaton Alexander , Meire Lorenz , Hendry Katharine
Published: March 2020

Meltwaters from glaciers and ice sheets in the Arctic region potentially provide significant fluxes of key nutrients to downstream ecosystems, and hence recent acceleration of melting has implications for the high-latitude biogeochemical cycles. Previous work has shown that silicon (Si) exported from glacial environments also has a distinct isotopic signature compared to those in non-glacial rivers. However, the extent to which glacially-derived Si and other bioavailable nutrients reach the open ocean is much debated, due to biological uptake and complex physical processes within heterogeneous fjord environments.

We assess the impact of glacial meltwater from marine and land-terminating glaciers on fjord biogeochemistry, with a focus upon Si cycling, by sampling two fjords (Godthåbsfjord and Ameralik Fjord) in southwest Greenland over two melt seasons. We combine silicon isotope measurements with a range of complementary physical and chemical parameters to evaluate the role of glacially derived nutrients and benthic recycling on biological productivity within the two contrasting fjord environments. Data from two consecutive melt seasons also enables us to begin to assess inter-annual variability. In addition, continuous measurements of silicic acid and nitrate concentrations along Godthåbsfjord during the 2019 melt season, obtained using novel sensor technology, allow us to assess intra-annual variations in nutrient export. Our targeted field campaigns have provided a suite of nutrient, trace element and isotopic data that will improve the current understanding of the complex biogeochemical cycling within fjord environments, and allow a better assessment of the importance of glacial meltwater on nutrient export and primary productivity in downstream ecosystems.
In-situ and imaging spectroscopy for grape disease detection: towards a global surveillance and warning system
Authors: Gold Kaitlin
Published: March 2020

Disease is one of the greatest threats to the environmental, financial, and societal sustainability of wine grape production worldwide, and is expected to become of greater and more dire importance as the negative effects of climate change continue to intensify. Advanced field, aerial, and satellite based methods of disease detection that can identify infection at extremely low intensity or before the onset of visual symptoms would greatly improve management by reducing disease potential and spread. In-vivo foliar and imaging spectroscopic methods have been shown to be effective for rapid, early, real-time disease detection in grape and specialty crops, and for characterizing the underlying physiological differences that enable disease discrimination. Infection on a relatively small part of a plant will trigger the cascade release of defense compounds, regardless of whether or not the individual plant succumbs to disease. This leads to the phenomenon of unaffected plant parts of diseased plants displaying different physiology and biochemistry than seemingly identically unaffected plant parts of non-diseased plants. Early detection and quantification of these differences could lead to earlier management intervention and an increased understanding of the spatial and temporal variability associated with disease and its subsequent impacts on crop health and downstream product quality. In this talk, the opportunities and challenges facing in the use of this approach for grape disease detection, differentiation, and management will be discussed, as well as the use of satellite-based imaging spectroscopy for grape and broader specialty crop disease detection.
More perceived but not faster evolution of heat stress than temperature extremes in the future
Authors: Brouillet Audrey , Joussaume Sylvie
Published: March 2020

Global warming is projected to intensify during the 21st century. This warming will be more readily perceived by human populations if it occurs rapidly and if it induces a thermal heat stress on the human body. Yet, only few studies investigate how climate change could be felt by future populations. Here we assess this possible perceived evolution between 1959 and 2100 only combining thermodynamic and statistical indicators. We analyse extremes of temperature (T99) and simplified Wet-Bulb Globe Temperature (WBGT99), a common heat stress index assessing the combined effect of elevated temperature and humidity on the human body. For each year of the period, we define the speed of change as a difference between two successive 20-year periods (i.e. with a moving baseline), and assess how these running changes emerge from each last 20-y inter-annual variability.

According to a subset of 12 CMIP5 Earth System Models and the RCP8.5 scenario, the change of T99 and WBGT99 will be twice as fast in the future compared to the current speed of change in the mid-latitudes, and by up to four times faster tropical regions such as Amazonia. Warming accelerations are thus similar for both T99 and WBGT99. However, in tropical regions by 2080, the speed is projected to be 2.3 times larger than the recent inter-annual variability for WBGT99, and only 1.5 to 1.8 times larger for T99. Currently, speeds of change are only 0.2 to 0.8 times as large as the recent year-to-year variability for both metrics. We also show that 36% of the total world population will experience an emergent WBGT99 intensification in 2080, but only 15% of the population for T99. According to future projections, the accelerated warming of future heat extremes will be more felt by populations than current changes, and this perceived change will be more severe for WBGT99 than for T99, particularly in the tropics.
Global-to-Cartesian 3-D EM modeling using a nested IE approach with application to long-period responses from island geomagnetic observatories
Authors: Chen Chaojian , Kruglyakov Mikhail , Kuvshinov Alexey
Published: March 2020

There is a significant interest in constraining the mantle conductivity beneath oceans. One of the main sources of data that can be used to reveal the conductivity distribution in the oceanic mantle are time-varying magnetic fields measured at island geomagnetic observatories. From these data local electromagnetic (EM) responses are estimated and then inverted in terms of conductivity. The challenge here is that island responses are strongly distorted by the ocean induction effect (OIE) originating from the lateral conductivity contrasts between the conductive ocean and resistive land. OIE is generally modeled by global simulations using relatively coarse grids (down to 0.25 degree resolution) to represent the bathymetry. Insufficiently accurate accounting for the OIE may lead to the wrong interpretation of the observed responses. We study whether the small-scale bathymetry features influence the island responses. To address this question we developed a global-to-Cartesian 3-D EM modeling framework based on a nested integral equation approach, which allows to efficiently account for the effects of high-resolution bathymetry. Two geomagnetic observatories, located in Indian (Cocos Island) and Pacific (Oahu Island) Oceans, are chosen to study the OIE in long-period responses. Numerical tests demonstrate that accounting of the very local bathymetry (down to 1 km resolution) dramatically change modeling results. Remarkably, the anomalous behavior of the imaginary parts of the responses at Cocos Island, namely, the change of sign at short periods, is reproduced by using highly detailed bathymetry.
Measurements of bromine monoxide over four halogen activation seasons in the Canadian high Arctic
Authors: Bognar Kristof , Zhao Xiaoyi , Strong Kimberly , Chang Rachel Y.-W. , Frieß Udo , Hayes Patrick L. , McClure-Begley Audra , Morris Sara , Tremblay Samantha , Vicente-Luis Andy
Published: March 2020

Bromine explosions and corresponding ozone depletion events (ODEs) are common in the Arctic spring. The snowpack on sea ice and sea salt aerosols (SSA) are both thought to release bromine, but the relative contribution of each source is not yet known. Furthermore, the role of atmospheric conditions is not fully understood. Long-term measurements of bromine monoxide (BrO) provide useful insight into the underlying processes of bromine activation. Here we present a four-year dataset (2016-2019) of springtime BrO partial columns retrieved from Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) measurements in Eureka, Canada (80.1° N, 86.4° W). Due to the altitude of the measurement site (610 m), the measurements often represent BrO above the shallow boundary layer, and the strength of the temperature inversion has limited impact on the BrO partial columns. When the boundary layer is deep, however, the effects of the enhanced vertical mixing manifest as an increase in the minimum BrO values (and reduced ODE frequency) for wind speeds of ~8 m/s or greater. We find that BrO events show two modes differentiated by local wind direction and air mass history. Longer time spent in first-year sea ice areas corresponds to increased BrO for one of these modes only. We argue that snow on multi-year ice (salted and acidified by Arctic haze) might also contribute to bromine release. The MAX-DOAS measurements show that high aerosol optical depth is required to maintain lofted BrO. In situ measurements indicate that accumulation mode aerosols (mostly Arctic haze) have no direct correlation with BrO. The presence of coarse mode aerosols, however, is a necessary and sufficient condition for observing enhanced BrO at Eureka. The measurements of coarse mode aerosols are consistent with SSA generated from blowing snow. The good correlation between BrO and coarse mode aerosols (R2 up to 0.57) supports the view that SSA is a direct source of bromine to the polar troposphere.
Distinct Impacts of Increased Aerosols on Cloud Droplet Number Concentration of Stratus/Stratocumulus and Cumulus
Authors: Jia Hailing , Ma Xiaoyan , Yu Fangqun , Liu Yangang , Yin Yan
Published: March 2020

In situ aircraft measurements obtained during the RACORO field campaign are analyzed to study the aerosol effects on different cloud regimes. The results show that with increasing cloud condensation nuclei (CCN), cloud droplet number concentration (Nd) significantly increases in stratocumulus (Sc) while remains almost unchanged in cumulus (Cu). By using a new approach to strictly constrain the dynamics in Cu, we found that neither simultaneously changing cloud dynamics nor dilution of cloud water induced by entrainment-mixing can explain the observed insensitivity of Nd. The different degree of reduction in cloud supersaturation caused by increasing aerosols might be responsible for the observed different aerosol indirect effect between Sc and Cu.
Contribution of tree stem and canopy fluxes to the CH4 budget of a boreal birch and spruce forest
Authors: Pihlatie Mari , Vainio Elisa , Haikarainen Iikka , Putkinen Anuliina , Santalahti Minna , Koskinen Markku , Machacova Katerina
Published: March 2020

Upland forest soils are typically a net methane (CH4) sink, while trees may act as CH4 sources. Studies on tree CH4 exchange in boreal forests, especially regarding canopies, are rare. We aimed to quantify the contribution of trees to the forest CH4 budget during spring leaf-out period and to reveal the role of microbes in the CH4 exchange of trees. We measured stem and shoot fluxes of two common boreal tree species at a fen and at an upland site at Hyytiälä, southern Finland, together with soil CH4 flux, environmental variables and the abundances methanogens and methanotrophs within the forest. Both birch (Betula pubescens) and spruce (Picea abies) trees emitted CH4 from their aboveground surfaces, with significantly higher stem emissions detected from the birch and higher shoot emissions from the spruce. The shoot CH4 exchange had no clear link to the vertical profile of the canopy or the progress of the leaf-out. The stem CH4 emissions from birches at the fen were high (mean 45 µg h−1 m−2) and decreased drastically with stem height. Their dynamics followed soil temperature, suggesting the emitted CH4 originated from the soil. A lack of similar pattern in the fen spruces and in the upland birch indicates other processes behind the stem CH4 fluxes of these trees. The lack of detection of methanogens or methanotrophs in the aboveground plant tissues suggest that the observed tree-derived CH4 fluxes were not induced by these microbes. The emitted CH4 from the tree stems may, however, be produced microbially in the soil indicating that physiological differences in tree anatomy or adaptation to different belowground conditions might be a key factor explaining the differences between the tree species.

Acknowledgements: This research was supported Academy of Finland (288494, 2884941), National Centre of Excellence (272041), ICOS-FINLAND (281255), Helsinki Institute of Life Science (HiLIFE), Czech Science Foundation (17-18112Y) and National Sustainability Program I (LO1415), and the European Research Council (ERC) under Horizon 2020 research and innovation programme, grant agreement No (757695).
Full 3-D pseudo-transient finite difference modelling of stress distribution around continental plateaus
Authors: Macherel Emilie , Podladchikov Yuri , Spitz Richard , Schmalholz Stefan M.
Published: March 2020

On Earth, different geodynamic features form in response to a tectonic event. Continental plateaus, such as the Tibetan Plateau, are formed in a collisional environment and they are characterized by an unusually large crustal thickness, which generates lateral variations of gravitational potential energy per unit area (GPE). These GPE variations cause the thickened crust to flow apart and thin by gravitational collapse. Due to mass conservation, thinning of the crust implies horizontal spreading of the plateau towards the lower altitude surroundings. This spreading is observed in GPS velocity records. For example, around the Tibetan Plateau, horizontal surface velocities are in the order of 2 cm/yr. Crustal flow also generates differential stresses in and around the plateau. Estimating these stresses and their spatial variation in 3-D is a computational challenge and necessitates new advanced computing methods.

 

Here, we present a new 3-D numerical algorithm to solve the Stokes equations under gravity. The algorithm is based on an Eulerian pseudo-transient finite difference method. To test the algorithm, we consider a simplified plateau geometry and density structure. Two different simulations are performed, one pseudo-2D simulation and one full 3-D simulation considering the corner region of a plateau. The pseudo-transient method allows an explicit solution of the Stokes equations. When the pseudo-transient time derivatives approach zero, a steady-state solution for the velocity field is obtained. In the first simulations, the rheology is linear viscous. The crust-mantle interface and the interface between crust and overlying sticky air are tracked with a Cahn-Hilliard diffuse interface model. To test our results, we compare the results of the pseudo-transient model with 3-D results obtained with the implicit numerical algorithm LAMEM (bitbucket.org/bkaus/lamem) and with 2-D results obtained with a Lagrangian finite element model. We have developed two versions of the algorithm, one in Matlab (mathworks.com) and one in Julia language (julialang.org). The aim of the Julia version is to eventually utilize a parallel GPU computing environment. Furthermore, we also present first results for cylindrical coordinates for the same plateau geometries. The aim of the model with cylindrical coordinates is to quantify the impact of the Earth’s curvature on the stress state.
Large organized structures in stably stratified turbulent shear flows.
Authors: Glazunov Andrey , Mortikov Evgeny , Zasko Grigory , Nechepurenko Yuri , Zilitinkevich Sergej
Published: March 2020

We analyzed the data of the numerical simulation of stably stratified turbulent shear flows. It is shown that, along with chaotic turbulence, the flows contain large organized structures. In the temperature field, these structures appear as inclined layers with weakly stable stratification, separated by very thin layers with large temperature gradients. The existence of such layered structures in nature is indirectly confirmed by the analysis of field measurements. An increase of the turbulent Prandtl number with increasing gradient Richardson number was fixed in simulation data. The hypothesis is proposed that physical mechanism for maintaining of turbulence in supercritically stable stratification is connected with the revealed  structures. It is shown that the spatial scales and the shapes of the identified organized structures can be explained using the calculation of  optimal disturbances for the simplified linear model.

This study was supported by the Russian Foundation for Basic Research (grants nos. 18-05-60126,  20-05-00776) and by Academy of Finland project ClimEco no. 314 798/799 (2018-2020).