bluuebunny/crossref_metadata_2025 huggingface dataset:
Exploring the mechanism behind successive droughts: Intensification of continental droughts due to positive feedbacks between subsurface water storage anomalies and atmospheric process
Authors: Hartick Carl , Furusho-Percot Carina , Goergen Klaus , Kollet Stefan
Published: March 2021

In the year 2018, Central Europe experienced a meteorological drought and a heatwave, which led to a subsequent evolution of a hydrological drought that is still detectable in subsurface water storage anomalies today. Most likely, the drought also led to significant changes in the energy balance between solar radiation, latent and sensible heat fluxes. In conjunction with water scarcity in the subsurface, these changes may lead to feedbacks that mitigate or enforce drought conditions in the context of land-atmosphere coupling. Understanding these feedbacks is of great interest, especially under various large-scale weather patterns that strongly influence the water and energy budgets over Europe at the interannual time scale. We improve our understanding by applying the Terrestrial Systems Modeling Platform (TSMP) over the 12km resolution pan-European CORDEX model domain simulating the water and energy cycles from the groundwater to the top of the atmosphere. TSMP couples a hydrological, land-surface and atmospheric model, facilitating studies of feedbacks between total water storage anomalies, the energy budget and atmospheric processes. To investigate the feedbacks, we performed TSMP ensemble simulations of three anomalously dry water years (September to August) over Central Europe. The ensembles were initialized with the surface and subsurface states of the end of August of the drought years 2011, 2018 and 2019 from an ERA-Interim driven climatology simulated continuously with TSMP from 1989 to 2019. Every ensemble consists of 22 members, each representing a full subsequent water year, sampled from ERA-Interim reanalysis meteorological boundary conditions from 1996 to 2019, thereby simulating the influence of drought conditions over a wide range of large-scale weather patterns that occurred in Europe since 1996. In addition, to illustrate the potential range of feedbacks we also ran idealized experiments with a completely dry or wet subsurface. The results show that drought conditions may have a significant impact on cloud water and solar radiation at interannual timescales. Effects in winter are negligible, while in summer, an impact of the drought conditions of the previous year on cloud water and solar radiation is detectable in all three ensembles. The results suggest that positive feedbacks between dry subsurface water storage anomalies and atmosphere processes are not negligible and may intensify drought conditions also at the interannual time scale.
Holocene landscape instability in the context of a loessic early Upper Palaeolithic open-air site in the Middle Danube Basin
Authors: Pötter Stephan , Chu Wei , Nett Janina J. , Schulte Philipp
Published: March 2021

The palaeoanthropological record of Western Romania is a prime archive of the early modern human presence in Southeastern Europe. Regional stratified early Upper Palaeolithic open-air and karstic sites enable us to infer temporal and spatial patterns of early modern human behaviour in various geomorphological settings. However, open-air sites are often prone to reworking processes caused by local landscape instabilities. The pristine archaeological and palaeoenvironmental stratigraphic evidence is often overprinted by fluvial and slope processes. Therefore, heavily reworked sites are often neglected by researchers. Nevertheless, reworked archaeological and sediment sequences are crucial archives of landscape evolution because they record fluctuations in subsequent erosional and depositional phases. Here, we present the results of a multi-proxy geoarchaeological investigation of the Upper Palaeolithic site of Temereşti Dealu Vinii. This site is located in the Bega Valley, a well-known area for early Upper Palaeolithic open-air localities. Despite the identification of various Upper Palaeolithic cultural units, the artefacts show no discernible horizontal or vertical distribution patterns and stratigraphic inconsistencies. Geochemical and granulometric data aided by luminescence and radiocarbon dating as well as stratigraphic evidence suggest a sub-continuous hydrological sorting over short transport distances during the Holocene. Consistent luminescence ages and characteristics suggest that erosion and deposition occurred sub-continuously during this period. This record of landscape dynamics is consistent with other archives from the area that show evidence for anthropogenically induced phases of soil erosion during the Holocene. This study highlights the importance of reworked archaeological sites such as Temereşti Dealu Vinii not only as viable archives of human presence during the Late Pleistocene – but also as valuable records of subsequent landscape evolution. Detailed analyses of post-depositional disturbances of archaeological sites enable us to improve the accuracy of early modern human behavioural interpretations, and to better contextualise sites such as Temereşti Dealu Vinii within the assemblage of both “in-situ” and reworked loessic Upper Palaeolithic localities in the Danube Basin to evaluate the importance of palaeogeography for human occupation
Observing the timescales of aerosol-cloud interactions in snapshot satellite images
Authors: Gryspeerdt Edward , Smith Tristan , Goren Tom
Published: March 2021

Cloud processes and their response to perturbations happens at a variety of timescales. These timescales are related to processes such as updrafts and mixing, the formation of precipitation and changes in the background meteorology.

 

Satellites often give a static picture of the world. A single snapshot from an overpass gives a wide view of the cloud field, but not motion within it. Previous studies have used multiple overpass or geostationary satellites to build up a picture of cloud development. Here we use the aerosol perturbation itself as the time axis.

Ships emit large amounts of aerosol into the boundary layer, often in comparatively clean locations. This aerosol can modify the properties of these clouds, creating linear cloud formations known as shiptracks. Using ship SOx emission information derived from ship transponder data, we link the aerosol perturbation to the properties of the shiptrack. By coupling the ship location to reanalysis wind fields, we determine the time since emission for positions along a shiptrack, providing a time axis in a single snapshot image.

We use this combined satellite/aerosol perturbation dataset to investigate the timescales for clouds responses to the aerosol perturbation from ships, linking it to the cloud and meteorological states as well as the properties of the aerosol perturbation.
Metabolic alkalinity release from the Elbe estuary to the North Sea
Authors: Norbisrath Mona , Hansen Jeannette , Dähnke Kirstin , Sanders Tina , van Beusekom Justus E. E. , Thomas Helmuth
Published: March 2021

The Elbe is the largest river entering the German Bight. Its estuary is a heavily used waterway connecting the sea to Germany’s biggest port in Hamburg. The Elbe navigation channel is continuously dredged, and agricultural fertilizer input from the catchment ensuing large phytoplankton blooms in the river Elbe exerts additional anthropogenic pressure. Biogeochemistry in the estuary is additionally governed by the North Sea and its strong tidal cycles, which ensure an exchange of fresh and marine waters.

The aims were to quantify the release of the carbon species total alkalinity (TA) and dissolved inorganic carbon (DIC) along the Elbe estuary, and to estimate the contribution of aerobe and anaerobe metabolic processes. Therefore, we used water samples collected continuously during a cruise in June 2019, to measure TA and DIC, and the stable isotopes of nitrate. We applied mass balances, to characterize the metabolic activity and detect their effect on the carbon species

The Elbe estuary could be subdivided into two parts: 1) an outer marine driven part, which is dominated by conservative mixing, also visible in higher TA than DIC values, and 2) an inner fresh water part in which metabolic processes play an important role.

We found a strong increase in TA and DIC (several hundred µmol kg-1) in the Hamburg port area, with higher DIC than TA values. We unraveled the water column impacts of nitrification and denitrification on TA and DIC by analyzing the stable isotopes δ15N-NO3- and δ18O-NO3-, and identified water column nitrification as a dominant pelagic process in the port of Hamburg and in the fresh water part further downstream. Because nitrification cannot explain the significant increase of TA and DIC in the port region, anaerobic processes such as denitrification in the sediment also appear to play an important role.

 
Different ice sheets – different AMOC? Revisiting the ice-sheet effect on the LGM AMOC
Authors: Klockmann Marlene , Kapsch Marie-Luise , Mikolajewicz Uwe
Published: March 2021

Coupled climate models have produced very different states of the Atlantic Meridional Overturning Circulation (AMOC) in simulations of the Last Glacial Maximum (LGM). In particular, many of them failed to capture the shoaling of the upper AMOC cell, which was indicated by reconstructions. In sensitivity simulations with the Max-Planck-Institute Earth System Model (MPI-ESM) we found that the glacial AMOC response is the sum of two large opposing effects: a strengthening and deepening of the upper cell in response to the glacial ice sheets and a weakening and shoaling of the upper cell in response to the low glacial greenhouse gas concentrations. The magnitude of the respective effects likely depends on the background climate, the ice sheet reconstruction used, and model specifics such as the representation of brine release in the Southern Ocean.

Transient simulations of the deglaciation with two differently tuned versions of MPI-ESM and two different ice-sheet reconstructions differ strongly in their respective AMOC states during the LGM. These simulations, together with selected PMIP3 and PMIP4 LGM simulations, provide a good opportunity to compare the effect of different ice sheet reconstructions on the glacial AMOC. We compare key variables such as water mass properties, salt transport and Southern Ocean sea-ice formation across this ensemble of opportunity with the aim of increasing our understanding of the role of ice sheets in the glacial AMOC response.
Regional groundwater flow conditions and preliminary geothermal potential in asymmetric basins
Authors: Tóth Ádám , Galsa Attila , Mádl-Szőnyi Judit
Published: March 2021

Fluid, as an elemental component of a geothermal system, transports and distributes underground heat according to the topographic driving force within a groundwater basin. As the water table configuration has diverse and distinct forms in real-life basins, asymmetric hydraulic head variation may occur from basin to basin in accordance with real physiographic characteristics. Therefore, the effects of an asymmetric water table distribution in groundwater basins were investigated in several model sets with special emphasis on the temperature field and with the help of five response parameters: maximum temperature of outflowing water, average temperature, the portion of the thermal water reservoir, Péclet number and location and extent of thermal water discharge.

Our simulation results showed that in the absence of thermal springs, the extent of the thermal water reservoir might be larger and the temperatures might be higher. Sedimentary basin fill fosters the formation of heat accumulation under and within this unit. As a new “parameter” in the basin-scale groundwater and geothermal studies, basin asymmetry was introduced which has a critical role in discharge and accumulation patterns, thus it controls the location of basin parts bearing the highest geothermal potential. So if thermal water can reach the ground surface, the discharge might not take place exactly above the thermal water reservoir due to the asymmetric driving forces of groundwater flow. Furthermore, the extent and temperature of thermal water reservoirs are also influenced by local-scale anisotropy, heterogeneities, i.e. faults, fault zones and fractures, and, of course, basal heat flux.

Therefore, the application of asymmetric basin-scale models in preliminary geothermal potential assessment would be beneficial for understanding heat distribution. The results also have further implications on the identification of prospective areas and planning of shallow and deep geothermal energy utilization, the interplay between basin-parts and rejuvenation of geothermal resources.

This research is part of the ENeRAG project that has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No 810980.
Combining distributed glacier mass balance and ice flow models to improve projections of mass change for debris-covered Khumbu Glacier, Nepal
Authors: Schlich-Davies Anya , Rowan Ann , Quincey Duncan , Ross Andrew , Egholm David
Published: March 2021

Debris-covered glaciers in the Himalaya are losing mass more rapidly than expected. Quantifying and understanding the behaviour of these glaciers under climate change requires the use of numerical glacier models that represent the important feedbacks between debris transport, ice flow, and mass balance. However, these approaches have, so far, lacked a robust representation of the distributed mass balance forcing that is critical for making accurate simulations of ice volume change. This study forces a 3D higher-order ice flow model, with the outputs from an ensemble of distributed models of present day and future mass balance of Khumbu Glacier, Nepal. Distributed mass balance modelling, using the open access COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY) model (Sauter et al., 2020), was forced by three statistically downscaled climate models from the Coordinated Regional Climate Downscaling Experiment (CORDEX) project.

Climate models were selected based on their ability to reproduce observed present-day seasonality and to account for several future climate and monsoon scenarios, the latter being of particular importance for these summer-accumulation type glaciers. Two emission scenarios, RCP4.5 and RCP8.5, were also chosen to simulate glacier change to 2100. Statistical downscaling involved Quantile Mapping and Generalized Analog Regression Downscaling, and the efficacy of these approaches was informed by present day mass balance sensitivity studies. Downscaled daily climate data were trained with data from two weather stations to aid disaggregation to an hourly resolution.

The integration of the mass balance and ice flow models posed some interesting challenges. The COSIPY model was run as if Khumbu Glacier were a clean-ice glacier (with no supraglacial debris) with sub-debris ablation resolved in the ice flow model. The value of using distributed mass balance forcing is seen in the simulated present-day velocities in the Khumbu icefall, which give a better fit to remote-sensing observations than previous simulations using a simple elevation-dependent mass balance forcing. The simulated present-day glacier extent is considerably smaller than the existing glacier outline. The debris-covered tongue, known to be losing mass at an accelerating rate, is virtually absent from these results, and is indicative of a stagnant tongue that is now or very soon to be dynamically disconnected from the active upper reaches of Khumbu Glacier.
Scavenging of radionuclides in multicomponent medium with first-order reaction kinetics: Lagrangian and Eulerian modeling
Authors: Brovchenko Igor , Maderich Vladimir , Kivva Sergiy , Kim Kyeong Ok , Kim Hanna , Kovalets Kateryna
Published: March 2021

A process of the removal of dissolved elements in the ocean by adsorption onto sinking particulate matters (scavenging) is studied analytically and using Lagrangian and Eulerian numerical methods. The generalized model of scavenging in a multicomponent reactive medium with first-order kinetics consisting of water and multi-fraction suspended particular matter has developed. Two novel numerical schemes were used to solve advection-diffusion-reaction equations for advection-dominated flows. The particle tracking algorithm based on the method of moments was developed. It is free on time step limitation necessary for an application of a standard method to the equations with reaction kinetics. The modified flux-corrected transport method for the Eulerian equations is a flux-limiter method based on a convex combination of low-order and high-order schemes. The similarity solutions of the model equations for an idealized case of instantaneous release of reactive radionuclide on the ocean surface were obtained. It was found that the dispersion of reactive contamination caused by reversible phase transition can be much greater than caused by diffusion. The solutions using both numerical methods are consistent with the analytical similarity solution even at zero diffusivity. The scavenging of the 239,240Pu that was introduced to the ocean surface due to the fallout from past nuclear weapon testing was simulated. The results of the simulation agreed with observation data in the north-western Pacific Ocean. The importance of the scavenging by both the large fast-sinking particles and small particles slowly sinking and dissolving with depth due to the biochemical processes was shown.
Dilation and compaction accompanying changes in slip velocity in clay-bearing fault gouges
Authors: Ashman Isabel , Faulkner Daniel
Published: March 2021

Many natural fault cores comprise volumes of extremely fine, low permeability, clay-bearing fault rocks. Should these fault rocks undergo transient volume changes in response to changes in fault slip velocity, the subsequent pore pressure transients would produce significant fault weakening or strengthening, strongly affecting earthquake nucleation and possibly leading to episodic slow slip events. Dilatancy at slow slip velocity has previously been measured in quartz-rich gouges but little is known about gouge containing clay. In this work, the mechanical behaviour of synthetic quartz-kaolinite fault gouges and their volume response to velocity step changes were investigated in a suite of triaxial deformation experiments at effective normal stresses of 60MPa, 25MPa and 10MPa. Kaolinite content was varied from 0 to 100wt% and slip velocity was varied between 0.3 and 3 microns/s.

Upon a 10-fold velocity increase or decrease, gouges of all kaolinite-quartz contents displayed measurable volume change transients. The results show the volume change transients are independent of effective normal stress but are sensitive to gouge kaolinite content. Peak dilation values did not occur in the pure quartz gouges, but rather in gouges containing 10wt% to 20wt% kaolinite. Above a kaolinite content of 10wt% to 20wt%, both dilation and compaction decreased with increasing gouge kaolinite content. At 25MPa effective normal stress, the normalised volume changes decreased from 0.1% to 0.06% at 10wt% to 100wt% kaolinite.  The gouge mechanical behaviour shows that increasing the gouge kaolinite content decreases the gouge frictional strength and promotes more stable sliding, rather than earthquake slip. Increasing the effective normal stress slightly decreases the frictional strength, enhances the chance of earthquake nucleation, and has no discernible effect on the magnitude of the pore volume changes during slip velocity changes.

Low permeabilities of clay-rich fault gouges, coupled with the observed volume change transients, could produce pore pressure fluctuations up to 10MPa in response to fault slip. This assumes no fluid escape from an isolated fault core. Where the permeability is finite, any pore pressure changes will be mediated by fluid influx into the gouge. Volume change transients could therefore be a significant factor in determining whether fault slip leads to earthquake nucleation or a dampened response, possibly resulting in episodic slow slip in low permeability fault rock volumes.
Effects of varying injection rate on dynamic slip nucleation along a frictional weakening fault
Authors: Ciardo Federico , Rinaldi Antonio Pio , Wiemer Stefan
Published: March 2021

Anthropogenic injection of fluid into tight fractured reservoirs is known to alter the stress state of the Earth`s crust,  inducing micro-seismicity and eventually significant earthquakes. The injection scenario, in terms of injection pressure or injection rate, is one of the key controlling parameters for injection-induced seismicity. Although a number of studies have been carried out on understanding the effects of injection strategy on seismicity rates, less is known about its effect on the nucleation of dynamic slip on a pressurized fault, especially for non-stationary injection protocols.

In this contribution we study the effects of injection rate variation on the transition between aseismic and seismic slip along a frictional weakenig fault. Notably, we parametrize the injection strategy by assuming an initial linear increase of injection rate in time, up to a value after which it remains constant. We perform a scalying analysis and identify the governing parameters that control the fault response. We solve numerically the coupled hydro-mechanical problem using a fast boundary element solver for localized inelastic deformations [1]. Upon benchmarking the numerical results with the semi-analytical ones of Garagash and Germanovich [2] for the specific case of constant injection rate, we investigate the effect of injection rate variation on critically stressed and marginally pressurized faults. We derive analytical expressions for nucleation time and we confirm them via numerical results. Furthermore, we present a small scale yielding solution for marginallly pressurized faults and investigate the influence of injection scenario on shear crack run-out distances (when occuring).

 

References   

[1] Ciardo, F., Lecampion, B., Fayard, F., and Chaillat, S. (2020), A fast boundary element based solver for localized inelastic deformations, Int J Numer Methods Eng. 2020; 1–23.

[2] Garagash, D., and L. N. Germanovich (2012), Nucleation and arrest of dynamic slip on a pressurized fault, J. Geophys. Res., 117, B10310.
Analysis of anomalies in seismic ambient noise above fluid reservoirs
Authors: El Khoury Christine
Published: March 2021

Anomalies in seismic ambient noise, defined as strong spectral amplification of the vertical components at frequencies of several Hertz, are currently observed on sites located above hydrocarbon reservoirs. If properly understood, these anomalies could have a potential for applications such as geothermal reservoir exploration or underground gas storage monitoring. Under purely elastic modeling, the nature of these anomalies was mainly explained by the geological structure more than the fluid reservoir itself.  The main objective of the present work is to explain the exact origin of the anomalies by numerical simulations of the 3D wave propagation using specfem3D code. The simulated spectral anomalies are essentially static and determined by the typical geological reservoir environments. The effect of an anticline structure, which is a common characteristic of hydrocarbon reservoirs, is investigated using different types of sources. Results show that the spectral anomalies caused by the presence of the anticline structure have similarities with the anomalies observed in real data. More work is needed to extract laws linking geometrical characteristics of the anticline to spectral properties. Future works will also include analysis on real gas storage sites, followed by a transposition to the geothermal field applications, for which more complicated parameters appear to participate to the phenomenon.
The eastern Mediterranean pre-MSC brine pool as an analogue for future subtropical hydroclimate
Authors: Kontakiotis George , Butiseaca Geanina , Antonarakou Assimina , Karakitsios Vasileios , Zarkogiannis Stergios D. , Besiou Evangelia , Agiadi Konstantina , Koskeridou Efterpi , Thivaiou Danae , Mulch Andreas , Vasiliev Iuliana
Published: March 2021

During the Late Miocene the Mediterranean Sea experienced severe disruption of its connectivity to the Atlantic Ocean, highlighted by a rapid sea-level drop, culminating to the Messinian Salinity Crisis (MSC; 5.97-5.33 Ma). Such a paleoceanographic change, triggered by the cumulative effect of climate and tectonics, caused high-amplitude fluctuations in the hydrology of the entire basin, and further influenced the geological history of the Mediterranean Sea. Although a consistent pattern of the paleoclimate has started to emerge, we currently lack a continuous sea surface salinity (SSS) record linking the timing of sea surface temperature (SST) variations, sea-level fluctuations, and the overall environmental change, particularly for the pre-evaporitic period. Initial viewpoints of a linear and gradual salinity increase prior to the onset of the MSC have been recently revised and replaced by highly variable salinity-related patterns representative of the stepwise restriction of the Mediterranean Sea. Here we use the combined Tetra Ether (TEX86-) and/or alkenone unsaturation ratio (UK′37) based SSTs and oxygen isotopes (δ18O) from the cyclic marl-sapropel sedimentary succession of Agios Myron section (north-central Crete, Greece) to assess hydroclimate changes during that time, and we finally present the first record of SSS in the eastern Mediterranean Sea for the earliest Messinian (7.2–6.5 Ma). The relatively stable marine conditions after the Tortonian/Messinian boundary, expressed through a cool and fresh upper water column, significantly changed at ∼6.9 Ma, when an important reversal in the heart of the Messinian cooling trend supplemented by a coherent hypersaline water column took place. The observed SST and SSS patterns provide context for a two-fold evolution of this event (centered at 6.9–6.8 and 6.72 Ma), which finally led to the onset of a brine pool into the eastern Mediterranean basin. The transitional character of the following time interval (6.7–6.5 Ma) marks another important step in the basin restriction with a wider range of salinity fluctuations from highly saline to diluted conditions and enhanced water column stratification prior to the deposition of evaporites. Overall, this evolution supports the concept of a stepwise restriction of the Mediterranean Sea associated with substantial hydroclimate variability and increasing environmental (thermal and salinity) stress, and further confirms its position as a preferred laboratory for developing new conceptual models in paleoceanography, allowing the investigation and scale assessment of a phenomenon with high chances of representing a future analogue scenario.
Direct and indirect photochemical aging of organic aerosol components as a function of temperature
Authors: Vallon Magdalena , Gao Linyu , Song Junwei , Jiang Feng , Saathoff Harald
Published: March 2021

The chemical composition of aerosols, in both gas and particle phase, is an important factor regarding their properties influencing air quality, weather, climate, and human health. Organic compounds are a major fraction of atmospheric aerosols and their composition depends on chemical processing by atmospheric oxidants and photochemical reactions. These processes are complex due to the abundance of potential reactions and rarely studied over a wider range of atmospheric temperatures. To achieve a better understanding of three different photochemical processes relevant for the atmosphere as well as the capabilities to investigate such processes in our simulation chamber we studied three different organic aerosol systems between 213 K and 293 K in the AIDA simulation chamber at the Karlsruhe Institute of Technology.  With the first system we studied the direct photolysis of 2,3-pentanedion which is a typical carbonyl compound emitted by the food industry but also by trees. In the second system we studied the depletion of pinic and pinonic acid by radicals formed through photolysis of an iron oxalate complex, which acts as the photosensitizer in this system, all present in aqueous aerosol particles. Furthermore, we studied the photolysis of a nitrogen heterocycle in aerosol particles, which can form in the atmosphere by the reaction of dicarbonyls and shows strong absorption in the visible [1].

Photochemical reactions were studied using a new LED light-source simulating solar radiation in the UV and visible. The organic aerosols were generated by nebulizing aqueous solutions containing the aerosol components.  The aerosols were analysed by a high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS), a proton transfer mass spectrometer (CHARON-PTRMS) and a high–resolution time-of-flight chemical ionization mass spectrometer (FIGAERO-HR-ToF-CIMS).  The latter two allow to study the composition of gas phase and particle phase separately.

In this presentation, we will discuss the changes that these organic compounds undergo in gas and particle phase, during photochemical aging at temperatures between 213 and 293 K.

 

[1] C. J. Kampf, A. Filippi, C. Zuth, T. Hoffmann and T. Opatz, Secondary brown carbon formation via the dicarbonyl imine pathway: nitrogen heterocycle formation and synergistic effects, Phys. Chem. Chem. Phys, 2016, 18, 18353
Multiple drivers of extreme sea levels in the northern Adriatic Sea
Authors: Ferrarin Christian , Lionello Piero , Orlic Mirko , Raicich Fabio , Salvadori Gianfausto
Published: March 2021

Extreme sea levels at the coast result from the combination of astronomical tides with atmospherically forced fluctuations at multiple time scales. Seiches, river floods, waves, inter-annual and inter-decadal dynamics and relative sea-level rise can also contribute to the total sea level. While tides are usually well described and predicted, the effect of the different atmospheric contributions to the sea level and their trends are still not well understood. Meso-scale atmospheric disturbances, synoptic-scale phenomena and planetary atmospheric waves (PAW) act at different temporal and spatial scales and thus generate sea-level disturbances at different frequencies. In this study, we analyze the 1872-2019 sea-level time series in Venice (northern Adriatic Sea, Italy) to investigate the relative role of the different driving factors in the extreme sea levels distribution. The adopted approach consists in 1) isolating the different contributions to the sea level by applying least-squares fitting and Fourier decomposition; 2) performing a multivariate statistical analysis which enables the dependencies among driving factors and their joint probability of occurrence to be described; 3) analyzing temporal changes in extreme sea levels and extrapolating possible future tendencies. The results highlight the fact that the most extreme sea levels are mainly dominated by the non-tidal residual, while the tide plays a secondary role. The non-tidal residual of the extreme sea levels is attributed mostly to PAW surge and storm surge, with the latter component becoming dominant for the most extreme events. The results of temporal evolution analysis confirm previous studies according to which the relative sea-level rise is the major driver of the increase in the frequency of floods in Venice over the last century. However, also long term variability in the storm activity impacted the frequency and intensity of extreme sea levels and have contributed to an increase of floods in Venice during the fall and winter months of the last three decades.
Remote Sensing of Surface Water Dynamics Between 2015 and 2020 in the Prairie Pothole Region 
Authors: Schlaffer Stefan , Chini Marco , Dorigo Wouter
Published: March 2021

The North American Prairie Pothole Region (PPR) consists of millions of wetlands and holds great importance for biodiversity, water storage and flood management. The wetlands cover a wide range of sizes from a few square metres to several square kilometres. Prairie hydrology is greatly influenced by the threshold behaviour of potholes leading to spilling as well as merging of adjacent wetlands. The knowledge of seasonal and inter-annual surface water dynamics in the PPR is critical for understanding this behaviour of connected and isolated wetlands. Synthetic aperture radar (SAR) sensors, e.g. used by the Copernicus Sentinel-1 mission, have great potential to provide high-accuracy wetland extent maps even when cloud cover is present. We derived water extent during the ice-free months May to October from 2015 to 2020 by fusing dual-polarised Sentinel-1 backscatter data with topographical information. The approach was applied to a prairie catchment in North Dakota. Total water area, number of water bodies and median area per water body were computed from the time series of water extent maps. Surface water dynamics showed strong seasonal dynamics especially in the case of small water bodies (< 1 ha) with a decrease in water area and number of small water bodies from spring throughout summer when evaporation rates in the PPR are typically high. Larger water bodies showed a more stable behaviour during most years. Inter-annual dynamics were strongly related to drought indices based on climate data, such as the Palmer Drought Severity Index. During the extremely wet period of late 2019 to 2020, the dynamics of both small and large water bodies changed markedly. While a larger number of small water bodies was encountered, which remained stable throughout the wet period, also the area of larger water bodies increased, partly due to merging of smaller adjacent water bodies. The results demonstrate the potential of Sentinel-1 data for long-term monitoring of prairie wetlands while limitations exist due to the rather low temporal resolution of 12 days over the PPR.
Beta effect of eCO2 can cause as much rainfall decrease as large-scale deforestation in the Amazon
Authors: Lapola David , Sampaio Gilvan , Shimizu Marília , Guimarães-Júnior Carlos , Alexandre Felipe , Cardoso Manoel , Domingues Tomas , Rammig Anja , von Randow Celso , Rezende Luiz
Published: March 2021

Amazon region’s climate is particularly sensitive to surface processes and properties such as heat fluxes and vegetation coverage. Rainfall is a key expression of such land surface-atmosphere interactions in the region due to its strong dependence on forest transpiration. While a large number of past studies have shown the impacts of large-scale deforestation on annual rainfall, studies on the isolated effects of elevated atmospheric CO2 concentration (eCO2) on plant physiology (i.e. the β effect), for example on canopy transpiration and rainfall, are scarcer. Here we make a systematic comparison of the plant physiological effects of eCO2 and deforestation on Amazon rainfall. We use the CPTEC-Brazilian Atmospheric Model (BAM) with dynamic vegetation under a 1.5xCO2 and a 100% substitution of the forest by pasture grassland, with all other conditions held similar between the two scenarios. We find that both scenarios result in equivalent average annual rainfall reductions (Physiology: -252 mm,-12%; Deforestation: -292 mm, -13%) that are well above observed Amazon rainfall interannual variability of 5.1%. Rainfall decrease in the two scenarios are caused by a reduction of approximately 20% of canopy transpiration, but for different reasons: eCO2-driven reduction of stomatal conductance in the Physiology run; decreased leaf area index of pasture (-66%) and its dry-season lower surface vegetation coverage in the Deforestation run. Walker circulation is strengthened in the two scenarios (with enhanced convection over the Andes and a weak subsidence branch over east Amazon) but, again, through different mechanisms: enhanced west winds from the Pacific and reduced easterlies entering the basin in Physiology, and strongly increased easterlies in Deforestation. Although our results for the Deforestation scenario are in agreement with previous observational and modelling studies, the lack of direct field-based ecosystem-level experimental evidence on the effect of eCO2 in moisture fluxes of tropical forests confers a substantial level of uncertainty to this and any other projections on the physiological effect of eCO2 on Amazon rainfall. Furthermore, our results denote the incurred responsibilities of both Amazonian and non- Amazonian countries to mitigate potential future climatic change and its impacts in the region driven either by local deforestation (to be tackled by Amazonian countries) or global CO2 emissions (to be handled by all countries).
Strong long-lived anticyclonic mesoscale eddies in the Balearic Sea: formation and intensification mechanisms
Authors: Aguiar Eva , Mourre Baptiste , Revélard Adèle , Juza Mélanie , Alvera-Azcárate Aida , Pascual Ananda , Mason Evan , Tintoré Joaquín
Published: March 2021

Anticyclonic mesoscale eddies are often formed in the Balearic Sea towards the end of summer and autumn. In some years, these eddies become strong and persistent, modifying the ocean currents and water mass properties in the area. The generation and intensification mechanisms of two long-lived events observed in 2010 and 2017 were studied by means of the energy conversion terms associated with eddy-mean flow interactions and through complementary model sensitivity tests.

Results show that these eddies were formed through mixed barotropic and baroclinic instabilities. The former was associated with weak meandering of the shelf current near the coast produced by northwesterly wind events, and the latter with the existence of the northward intrusions of relatively warm waters through the intense Pyrenees thermal front. The intensification mechanism varied between the two events. While in 2010 it was driven by intense salinity gradients in the Balearic Sea, in 2017 it resulted from an extra barotropic energy term fed by northwesterly winds.

These eddies lasted more than two months with a radius varying between 30km and 90km and a vertical structure that reached 1500 m depth. Their presence resulted in a 3ºC anomaly between the warm core waters and the outer parts of the eddies.
Mineralogy of the far-side lunar surface explored by Chang’E-4 with visible and near-infrared reflectance spectra
Authors: Ito Gen , Flahaut Jessica , Huang Jun
Published: March 2021

The far side of the Moon, which has generally been less frequently targeted by robotic and human missions in the past, has become more available for compositional analyses with measurements made by the Chang’E-4 mission that landed in South Pole-Aitken Basin in 2019. The rover of the mission, Yutu-2, has traversed over 500 m now and acquired more than 100 measurements of visible and near-infrared (VNIR) reflectance spectra. In this study, we analyze the full set of VNIR reflectance spectra collected so far in order to better understand the geology of the Von Karman mare. We compute spectral parameters to quantize major features of spectra and infer mineralogy, e.g., pyroxene composition analysis using the relationship between spectral band depths at 1 µm and 2 µm. Many of Chang’E-4 spectra do not have a detectable spectral band at 2 µm in which case we use spectral parameters for the band at 1 µm to make classifications and infer the presence of other minerals. Pyroxene composition inferred from Chang’E-4 spectra are midway between orthopyroxene and clinopyroxene, showing noticeably unique grouping when compared with 1 µm and 2 µm band depth data available from past studies. For spectra without detectable band at 2 µm, initial classification efforts based solely on spectral parameters of the 1 µm band seem to indicate that at least two distinct groups exist. We are further investigating these preliminary findings, such as through comparisons to data from Moon Mineralogy Mapper, to better understand the mineralogy of the measured materials and the geology of the region explored by Yutu-2 rover. 
Structuring the water quality policy problem: Applying Q-methodology to explore perspectives in hydrology, government, and community
Authors: Houser Schuyler , Pramana Reza , Ertsen Maurits
Published: March 2021

Recognizing the interrelatedness of water management and conceptual value of IWRM, many water resource governance systems are shifting from hierarchical arrangements towards more collaborative and participative networks. Increasing calls for participation recognize the value of drawing on social, political-administrative, and other kinds of knowledge in addition to technical water expertise. Participatory mandates, coordination bodies, and science-policy networks have emerged to facilitate knowledge integration, promote adaptive capacity, and align organizations in poly-centric systems.

Since the maintenance and effectiveness of such arrangements are contingent on trust and alignment rather than command and control, and since diverse stakeholders are engaged to co-produce knowledge, collaborators must grapple with identifying shared goals, developing knowledge management strategies to organize inputs, and attaining early progress to promote ongoing cooperation. But guidance is limited with respect to how such integrative aims are to be accomplished.

This research explores how systematic (but not necessarily convergent) problem structuring can support the forming, reordering, and cohering of water resource networks, especially when a complex issue – in this case, water quality management – rises to prominence on the policy agenda. In the early stages of a water quality project in the Brantas River Basin, Indonesia, stakeholder discussions suggested divergent conceptualizations of water quality and ideas about what conditions ‘matter’. Thus, instead of taking hydrological data as the starting point, this research first asks: What Brantas River(s) are we talking about, and why? Q-methodology is used to identify alternative perspectives on water quality held by a diverse set of stakeholders, including hydrologists. The analysis explores which aspects of the policy problem are consistent, which are contested, and whether problems indicated by hydrological science overlap, conflict, or cohere with those perceived by other stakeholders.

The research posits that, if scientists, engineers, decision-makers, community leaders, and other participants can appreciate areas of convergence and divergence regarding the water quality problem itself, they can lay groundwork for knowledge co-production; recognize opportunities for cooperation; better locate science in the problem space; and identify potential early wins to secure commitment. The research also asks to what extent consensus in problem structuring is necessary, or whether it is sufficient to identify strategies that are acceptable to different ontological viewpoints.
Reducing leaching using the threshold nitrate root-uptake phenomena
Authors: Kurtzman Daniel , Kanner Beeri , Levy Yehuda , Nitsan Ido , Bar-Tal Asher
Published: March 2021

Reducing nitrate leaching from agricultural land to aquifers is a high priority concern for more than a half a century. Theory and observations of a threshold concentration of nitrate in the root-zone (Cmax), from which the leachate concentration increases at higher rates with increasing root-zone nitrate concentration, are presented. Cmax is derived both by direct results from container experiments with varying nitrogen (N) fertigation, and as calibration parameter in N-transport models beneath commercial agricultural plots. For five different crops, Cmax ranged between 20-45 mg/l of NO3-N derived from experiments and models. However, for lettuce, which was irrigated with a large leaching fraction, a Cmax could not be defined. For the crops irrigated and fertilized in the warm/dry season (corn and citrus) experiments show a dramatic change in leachate concentrations and simulations reveal a wide range of sensitivity of leachate NO3-N concentration to Cmax. Annual crops that are irrigated and fertilized in the cool/wet season (e.g. potato in Mediterranean climate) showed a distinct Cmax yet less dramatic than the summer-irrigated crops in the container experiment, and smaller impact of Cmax in models. Simulations showed that for summer-irrigated crops maintaining fertigation at C<Cmax has a significant effect on deep leachate concentrations, whereas for the winter annual crops the simulations revealed no threshold. It is suggested that for summer-irrigated crops fertigation below Cmax robustly serves the co-sustainability of intensive agriculture and aquifer water quality, for the winter crops it is suggested but benefits are not robust. For short season, small root-system crops (lettuce) efforts should be made to detach the crop from the soil.
Thermodynamicsof giant planetary impacts from ab initiosimulations
Authors: Caracas Razvan , Stewart Sarah T.
Published: March 2021

Impacts are highly energetic phenomena. They abound in the early stages of formation of the solar system, when they actively participated to the formation of large bodies in the protoplanetary disk. Later on, when planetesimals and embryo planets formed, impacts merged smaller bodies into the large planets that we know today. Giant impacts dominated the last phase of the planetary accretion, with some of these impacts leaving traces observable even today (planets tilts, moon, missing mantle, etc). The Earth was not spared, and its most cataclysmic event also contributed to the formation of the Moon.Here we present the theoretical tools used to explore the thermodynamics of the formation of the protolunar disk and the subsequent condensation of this disk. We show how ab initio-based molecular dynamics simulations contribute to the determination of the stability field of melts, to the equilibrium between melts and vapor and the positioning of the critical points. Together all this information helps building the liquid-vapor stability dome. Next we investigate the supercritical regime, typical of the post-impact state. We take a focused look to the transport properties, the formation of the first atmosphere, and compare the properties of the liquid state typical of magma oceans, to the super-critical state, typical of protolunar disks.We apply this theoretical approach on pyrolite melts, as best approximants for the bulk silicate Earth. These simulations help us retrace the thermodynamic state of the protolunar disk and infer possible condensation paths for both the Earth and the moon. 
RC acknowledges support from the European Research Council under EU Horizon 2020 research and innovation program (grant agreement 681818 – IMPACT) and access to supercomputing facilities via the eDARI gen6368 grants, the PRACE RA4947 grant, and the Uninet2 NN9697K grant. STS was supported by NASA grants NNX15AH54G and 80NSSC18K0828; DOE-NNSA grants DE-NA0003842 and DE-NA0003904.