bluuebunny/crossref_metadata_2025 huggingface dataset:
Are temporary stream observations useful for the calibration of a lumped hydrological model?
Authors: Scheller Mirjam , van Meerveld Ilja , Sauquet Eric , Seibert Jan , Vis Marc
Published: March 2022

Since 2012 the Observatoire National des Étiages (ONDE) has collected observations about the state of headwater streams across France. Streams that occasionally dry up (also called temporary or intermittent streams) are visited at least five times a year by trained staff and the flow state is visually assessed (dry stream, standing water, flowing water). These data have been used to calculate regional probabilities of drying with statistical models. However, the usefulness of this kind of data for the calibration or validation of bucket-type hydrological models has so far not been assessed.

We, therefore, used the ONDE dataset for the calibration of the HBV model to evaluate the potential of temporary stream observations to improve model predictions in data-scarce regions. The model was calibrated for almost 90 catchments throughout France. We used the information on the flow state of temporary streams, either alone or in combination with limited observations of discharge or water level at the outlet of the catchment for model calibration and evaluated the simulations based on the measured discharge. Because the ONDE data set is large, we could do an extensive analysis of the value of temporary stream observations and the way to optimize their use in hydrological models. While the study focuses on catchments in France, visual observations of temporary streams can - with the help of citizen scientists - be collected at any place in the world. Thus, the method has the potential to be applied in truly data scarce regions.
Seismic to aseismic slip scaling during fluid injection experiments
Authors: Passarelli Luigi , De Barros Louis , Rinaldi Antonio Pio , Wiemer Stefan
Published: March 2022

A growing number of direct and indirect measurements and observation indicates that aseismic slip transients are often induced during fluid injection operation alongside with swarm-like seismicity. The detection of fluid-induced aseismic slip has made a paradigm shift on our understanding of the spatio-temporal evolution of earthquake activity during injection operation, classically interpreted as triggered by a diffusive front of high pore pressure. Instead, unclamping of the fault by pressurization induced by fluid injection creates the condition to nucleate synchronous aseismic and seismic slip transients.  In this scenario, the spatio-temporal evolution of the induced seismicity is driven by the stressing rate imparted at the leading edges of the aseismic rupture front. However, the relationship between the magnitude of aseismic slip and the hydraulic energy input in the system remains still elusive. A similar mechanism has been proposed for natural earthquake swarms triggered by shallow (5-10 km depth) slow slip events (SSEs), for which a robust power-law scaling has been demonstrated between seismic and aseismic slip. Notably, the power-law moment scaling of shallow SEEs and associated earthquake swarms has been interpreted with a mechanism of fault pressurization enhanced by intense fracturing in a seismogenic volume with abundance of crustal fluids. Similar fault conditions are at play for fluid-induced seismicity. Here, we collected several case studies of recorded induced aseismic deformation during injection experiments together with the accompanying seismic activity. We investigated the spatial distribution and temporal evolution of the seismicity with respect to the ongoing transient aseismic slip. We focused in particular on the seismic and aseismic slip budget of induced seismicity and compared it with previous scaling of SSEs. The aseismic and seismic moments of induced events are compatible with the power-law scaling of shallow natural earthquakes swarms triggered by SSEs, although a data gap exits for SSEs in 0-4 magnitude range, where no SSEs have never been recorded due to the low resolution of surface geodetic instrumentation. We performed also numerical simulation using a 3D hydro-mechanical model using realistic fault and hydraulic parameters in order to fill in the data gap. Our results serve as a basis to build up empirical models that incorporate aseismic slip together with injected volume and pressure to forecast seismicity during fluid-injection experiments.
Hydrogeological, hydrochemical and isotopic study of the Chibunga river basin (Ecuador)
Authors: Santillan Quiroga Luis Miguel , Marchina Chiara , Lasagna Manuela , Deluca Domenico , Destefanis Enrico
Published: March 2022

This study provides a description of the hydrogeologic, hydrogeochemical and isotopic setting of the Chibunga river basin in the Province of Chimborazo (Ecuador). The basin has an area of approximately 514 km2 and 44 km in length. Its main river, the Chibunga River, originates on the slopes of the Chimborazo Volcano. The study area is located at an altitude comprised between 6268 aslm of Chimborazo volcano and 2598 aslm. This area has suffered for years of social conflicts for the access to water, due to an inadequate water resources management system.  Moreover, there is a deficiency of information about the water quality and groundwater recharge. The aims of this study was to investigate hydrogeochemical features of the Chibunga water resources and to improve information about hydrogeological structure, groundwater recharge processes and water quality.

From a hydrogeological point of view, a multilayer aquifer system is present, consisting in volcanoclastic deposits, and alternating pyroclastic and lava layers. An unconfined shallow aquifer is located in the most superficial part, feeding the plain springs. More in depth, confined and semiconfined aquifers are hosted in the more permeable layers, and are used for drinking water purposes. The plain is bordered by volcanic formations, mainly of andesitic rocks, characterized by a low permeability by fracturing. According to the literature, the aquifer system is mainly recharged by melting glaciers from the Chimborazo volcano. However, glaciers have been affected by a generalize retreat in the last decades that influences the water availability.

In this view, sampling campaigns were carried out to improve the hydrogeochemical characterization of precipitation, surface water and groundwater of the area.

The analyses of major elements highlight that, although Ca-HCO3 hydrochemical facies is the most common, a wide variability can be found in the groundwater of the area. On the whole, excluding the wells nearby urban settlements, chemical analyses show good quality of the water for drinking, irrigation, and agricultural use. Isotopic results, represented in δ18O – δ2H plot, are close to the Global Meteoric Water Line with a d-excess on average 16.3. Water stable isotopes reveal the contribution of precipitation to springs (δ18O ranging between -15.9 and -14.5; and; δ2H ranging between -110.5 and -99.2) at different altitude, while, near-stream groundwater has a similar isotopic signature to that of the river water (δ18O ranging between -14.4 and -13.7; and; δ2H ranging between -96.5 and -92.7) and reveal the interaction between surface and groundwater system.
Can earthworms enhance mineral weathering and thereby increase carbon sequestration?  
Authors: Calogiuri Tullia , Garamszegi Peter , Vidal Alix , van Groenigen Jan Willem , Hagens Mathilde
Published: March 2022

Negative Emission Technologies (NETs) are urgently needed if we want to keep global temperature increase below 1.5 °C. Enhanced Silicate Weathering (ESW) is a NET with as yet unknown potential to mitigate climate change. There are indications that ESW rates can be amplified by biotic activity, including that of earthworms. Earlier studies have suggested various pathways through which earthworms might enhance weathering rates, including the grinding of minerals in their gizzard, the stimulation of microbial communities in their gut, as well as the production of mucus rich in organic acids and digestive enzymes. Within this research, we aim to unravel the mechanisms through which earthworms increase mineral weathering rates, and ultimately to develop a bio-reactor in which these processes are optimized. As a first step, we carried out two experiments to determine the suitability of two earthworm species and to establish the optimal conditions for earthworms and mineral weathering in a small bio-reactor. The first study tested the potential of two endogeic earthworm species, Aporrectodea caliginosa and Allolobophora chlorotica, in a system with two types of rock flours (dunite and basalt) and three organic sources (hay, straw and co-digestate solid). The results showed that both earthworm species can thrive and remain active in the bio-reactor in the presence of basalt mixed with either co-digestate or straw. In the second study we tested the tolerance of the same two earthworm species to two temperatures exceeding earthworms ambient levels (20°C and 25°C) and two flow rates (50 ml/day and 80 ml/day) in a system with basalt and straw. The results showed that both earthworm species can survive and remain active at the highest temperature level and the highest flow rate. Our findings demonstrate that earthworms are suitable for use in a bio-reactor and can tolerate physical conditions which are known to stimulate weathering. Future studies will elucidate to what extent earthworms can enhance weathering.
Natural Flood Management features mitigate sediment and nutrient loading in a lowland agricultural catchment in England
Authors: Robotham John , Old Gareth , Rameshwaran Ponnambalam , Sear David , Trill Emily , Bishop James , Gasca-Tucker David , Old Joanne , McKnight David
Published: March 2022

Natural Flood Management (NFM) is a nature-based solution for reducing flood risk whilst delivering multiple benefits such as water quality improvements through the mitigation of diffuse pollution (e.g. from soil erosion). This study aimed to assess the ability of NFM storage features to trap potential pollutants in run-off from two small (3.4 km2) agricultural catchments. The masses of sediment, total phosphorus and organic carbon trapped by 14 NFM features (since construction 2 to 3 years previously) were quantified through sediment surveying and sampling. Streamflow and suspended sediment monitoring downstream of the features enabled catchment fluxes to be calculated. The features trapped a total of 83 tonnes sediment, 122 kg phosphorus, and 4.3 tonnes organic carbon over 2 to 3 years of functioning. Although the footprint of the features was <1% of the catchment area, they drained 44% of the total land area and were able to capture the equivalent of 25% of the total suspended sediment flux (22% of the fine (silt and clay) sediment flux), 14% of the total phosphorus flux, and 13% of the particulate organic carbon flux during the monitored period. Results show how accumulation rates were influenced by hydrological connectivity, with greater accumulation in features constructed directly on streams (online features), and offline features which filled from streamflow diverted by instream woody dams. Compared with the topsoil in each contributing area, trapped sediment was enriched in phosphorus and carbon in the majority of features, having on average 50% higher phosphorus and 17% higher organic carbon concentrations than surrounding arable soils, highlighting its potential value for redistribution on farmland. The results of this monitoring demonstrate the potential of NFM interventions to provide additional value by mitigating diffuse pollution in lowland catchments.
Changes in Arctic Meridional Overturning (ArMOC) under past abrupt warming 
Authors: Bretones Anais , Nisancioglu Kerim Hestnes , Guo Chuncheng
Published: March 2022

According to the recent generation of global climate models, a weakening of the Atlantic Meridional Overturning Circulation (AMOC) is unequivocal in the context of global warming. However, a recent study (Bretones et al, 2021) showed that the weakening of the AMOC at the reference latitude of 26N is decorrelated from the overturning trend north of the Greenland-Scotland Ridge.

From a paleo perspective, AMOC oscillations are believed to be one of the main drivers of the Dansgaard–Oeschger events, an alternation of cold and warm periods during the last glacial period in Greenland and with global signatures. During a warming phase, the AMOC is believed to be in a strong mode compared to the cold phase, thereby with increased amount of northward heat transport, and hence increased air temperature.

 In this study, we investigate the presence and evolution of the Arctic Meridional Overturning Circulation(ArMOC) during the abrupt warming transition from Heinrich event 4 (H4) to the Greenland interstadial 8 (GI8) in the NorESM climate model (Guo et al, 2019). The simulation is based on a validated GI8 simulation and freshwater hosing experiments to simulate H4 conditions. In the model, the transition of H4 to GI8 presents a warming of around 10°C within 30 years in Greenland, which is similar with what was observed in ice cores.
How dilatancy-induced pore pressure changes control rupture and slip during failure experiments in crystalline rock.
Authors: Aben Franciscus , Brantut Nicolas
Published: March 2022

Failure and fault slip in crystalline rocks is associated with dilation. When pore fluids are present and drainage is insufficient, dilation leads to pore pressure drops, which in turn lead to strengthening of the material. We conducted laboratory rock fracture experiments with direct in-situ fluid pressure measurements which demonstrate that dynamic rupture propagation and fault slip can be stabilised (i.e., become quasi-static) by such a dilatancy strengthening effect. We also observe that, for the same effective pressures but lower pore fluid pressures, the stabilisation process may be arrested when the pore fluid pressure approaches zero and vaporises, resulting in dynamic shear failure.

We use acoustic emission locations and our fluid pressure sensors to further detail dilatancy-induced stable failure by tracking the progression of the rupture front (i.e., creation of the fault) and the active slip patches of the newly formed fault. In doing so, we are able to link local pore pressure records to the position of the rupture front where dilation is strongest. We see minimal slip in the wake of the rupture front. Once the fault is completed, we observe that the entire fault slips for up to a few minutes, driven by pore pressure recharge of the fault zone. Hence, we directly observe decoupling of rupture and “after”-slip that would otherwise – in a dynamic failure – occur simultaneously.

All our observations are quantitatively explained by a spring-slider model combining slip-weakening behaviour, slip-induced dilation, and pore fluid diffusion. Using our data in an inverse problem, we estimate the key parameters controlling rupture stabilization: fault dilation rate and fault zone storage. These estimates are used to make predictions for the pore pressure drop associated with faulting, and where in the crust we may expect dilatancy stabilisation or vaporisation during earthquakes. For intact rock and well consolidated faults, we expect strong dilatancy strengthening between 4 and 6 km depth regardless of ambient pore pressure, and at greater depths when the ambient pore pressure approaches lithostatic pressure. In the uppermost part of the crust (<4 km), we predict vaporisation of pore fluids that limits dilatancy strengthening.
Global lake evaporation responses to climate change
Authors: La Fuente Sofia , Woolway Iestyn , Jennings Eleanor
Published: March 2022

Global lake evaporation is a critical and continuous process that plays an important role in the earth’s water cycle. Accurate quantification of lake evaporation dynamics is crucial to understanding lake energy budgets, land-atmosphere interactions, as well as water availability. However, despite its importance, relatively few studies have investigated the impacts of climate change on global lake evaporation. In this study, we present global lake evaporation projections from 1901-2099 using an ensemble of lake-climate projections from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP). Our results show that global lake evaporation will increase by the end of the 21st century with the largest changes occurring in tropical regions. Furthermore, our analysis suggests that lake evaporation extremes (90th percentile) are projected to occur more frequently, with greater changes detected at low latitudes. We anticipate lake evaporation increases to have severe impacts on the water budget, and therefore, on the availability of surface freshwater this century. 
The Space Weather events those accompany the long-lived macrosynoptic processes
Authors: Stupishina Olga , Golovina Elena
Published: March 2022

The presented work evolves the study of the Space Weather state before and during the macrosynoptic processes movements in North Atlantic and Eurasia extratropical latitudes. The atmosphere circulation types – E-type (east transport), W-type (west transport) and C-type (meridional transport) – were investigated by their periods of the conservation:  (5-7) days which corresponds to the Natural Synoptic Period (NSP) in Europe region and the Long Period (LP) which endured more than 10 days.

The investigation time interval: 1.01.2007 – 1.01.2014. That corresponds to: the Solar Activity (SA) 23-d cycle's fall branch, the SA minimum, the rise branch of the 24-th SA cycle, the maximum of 24-th SA cycle.

Space Weather parameters were: global  variations of SA parameters; daily characteristics of the SA flare component in various bands of the electromagnetic spectrum; variations of daily statistics of Interplanetary Space characteristics in the near-Earth space; variations of daily statistics of Geomagnetic Field characteristics.

Results:

1. LP-E-type occurs 56% of all LP when LP-W-type occurs 36% and LP-C-type occurs 8%.

2. The concrete Space Weather parameters which behavior differences the moments of LP-beginnings from the moments of NSP-beginnings for the E-type circulation (here we are presenting only results for the most frequent macrosynoptic type) are follows:

All daily indexes of SA global variations – the integral solar radioflux on the wavelength of 10.7cm, the solar spot number, the summarized spot area on the solar disk, the number of new Active Regions on the solar disk.

The daily statistics (maximum, mean, range, standard deviation) of α-particle fluxes with the energy of 4-10 MeV. 

The daily statistics (maximum, mean, range, standard deviation) of electron fluxes of energy that is greater than 2 MeV. 

The daily statistics (maximum, mean, range, standard deviation) of the intensity of the whole magnetic field vector in the near-Earth space.

The daily statistics (maximum, mean, range, standard deviation) of the intensity of the geomagnetic field that was measured at different terrestrial latitudes.

3. The most prominent events we can see in the behavior of the α-particle fluxes and in the behavior of the whole magnetic field vector in the near-Earth space those went on the background of the significant changing of global SA-indexes.

We suppose the complex impact the mentioned above Space Weather characteristics on the terrestrial atmosphere.

Results may be useful for the forecast of atmosphere response to the space impact.
Evolution of the Antarctic firn layer until 2100 under two climate change scenarios. 
Authors: Veldhuijsen Sanne , van de Berg Willem Jan , Brils Max , Kuipers Munneke Peter , van den Broeke Michiel
Published: March 2022

Firn covers ~99% of the Antarctic ice sheet, providing pore space in which nearly all of the surface meltwater refreezes or is retained in liquid form. For now, this prevents most of the surface melt to contribute to sea level rise, however as atmospheric warming continues, changes in precipitation, temperature, melt and refreezing will cause the firn layer to evolve. Surface melt and densification rates are expected to increase, which will lead to firn air content depletion and increased firn saturation. Such conditions are extremely important for the Antarctic ice sheet: saturation of firn layers can lead to hydrofracturing induced ice shelf disintegration. On the other hand, snowfall is expected to increase as well, which will add additional pore space to the firn. Firn models can be used to simulate such firn processes and identify future firn conditions.

       In this study, we force the recently improved version of the IMAU Firn Densification model (IMAU-FDM v1.2A) with outputs of the regional atmospheric climate model RACMO2.3p2 at resolution of 27 km covering the period 1950-2100. RACMO2.3p2 is forced with CESM2, which includes the historical period 1950-2015 followed by two climate change scenarios for the period 2015-2100 (SSP126 and SSP585). The historical performance is evaluated by comparing the outputs to a run in which IMAU-FDM v1.2A was forced with RACMO2.3p2, which was forced with ERA-5, a climate model reanalysis nudged towards surface and satellite observations. After evaluation, we present how the firn layer will evolve over the coming century under these scenarios, and identify which areas will potentially become susceptible to ice shelf disintegration.
Ground deformation time series prediction based on machine learning
Authors: Guardiola-Albert Carolina , Aguilera Héctor , Arias Patiño Juliana , Fullea Urchulutegui Javier , Ezquerro Pablo , Bru Guadalupe
Published: March 2022

The problem of predicting terrain deformation time series from radar interferometry (InSAR) data is one of the biggest current challenges for the prevention and mitigation of the impact of geological risks (e.g. earthquakes, volcanoes, subsidence, slope landslides) that affect both urban (e.g. building movement) and non-urban areas. Generating spatio-temporal alert systems on the processes of deformation of the terrain based on predictive models is one of the great current challenges in the face of the prevention and management of geological risks. Within machine learning techniques, deep learning offers the possibility of applying prediction models of deformation time series on images using convolutional neural networks (Ma et al., 2020).

The objective of the present study is to develop a methodology to obtain predictive models of time series of terrain deformation from InSAR images using machine learning algorithms (e.g. deep convolutional neural networks). Data to train the algorithm will be time series of terrain deformation contained in InSAR images processed by the Geological Survey of Spain (IGME-CSIC). Different architectures and parameterizations of machine learning will be tested.

This work is performed within the framework of the SARAI Project PID2020-116540RB-C22 funded by MCIN/ AEI /10.13039/501100011033.

Reference:

Ma, P., Zhang, F., Lin, H. (2020). Prediction of InSAR time-series deformation using deep convolutional neural networks. Remote Sensing Letters, 11:2, 137-145.

 
Lessons learned from the extreme wildfires of early August 2021 in Greece
Authors: Giannaros Theodore , Papavasileiou Georgios , Lagouvardos Konstantinos , Kotroni Vassiliki , Dafis Stavros , Karagiannidis Athanassios , Dragozi Eleni
Published: March 2022

This work focuses on the extreme pyroconvective wildfires that impacted southern Greece in early August 2021. These wildfires were unprecedented in extent, intensity, and impacts. They broke out in Attica, Euboea, Elis, Messenia, and Laconia, on August 03 and 04, 2021, and kept burning for several days. Observational evidence indicates that all wildfires exhibited extreme fire behavior, characterized by erratic fire spread, prolific spotting, and the formation of pyroclouds. The factors that contributed to this outbreak of extreme wildfires are sought in the combination of (1) antecedent meteorological conditions that allowed for the accumulation and extreme dry-out of fuels, and (2) concurrent adverse fire weather that enabled the wildfires to couple with the atmosphere and evolve into extreme pyroconvective events. Both topics serve as the motivation of this work, which presents a preliminary analysis of the extreme early August 2021 wildfires in Greece. The analysis was conducted employing ground-based and spaceborne observations. Results indicate the build-up of large potential for the occurrence of extreme wildfires in the affected regions since at least the beginning of the 2021 fire season. Our overarching goal is to consolidate the need for early detection and warning of elevated potential for extreme pyroconvective events, which are becoming a globally increasing concern due to inter alia climate change. The presented work was conducted in the frame of the CLIMPACT and FLAME (project number: 00559) research projects.
The seismicity of Cyprus
Authors: Merry Thomas , Bastow Ian , Green David , Ugo Freddie , Bell Rebecca , Pilidou Sylvana , Dimitriadis Iordanis
Published: March 2022

The island of Cyprus sits at the boundary between the Anatolian and African plates, at a transition between oceanic subduction and incipient continental collision. Seismicity has been recorded here for millenia, with at least 12 town-destroying earthquakes recorded over the last 2,000 years. However, the instrumental coverage on the island has remained poor until relatively recently, and there is no bespoke velocity model or local magnitude scale, meaning that local seismicity is relatively poorly understood. Larger earthquakes, mainly to the south and west of the island, have revealed a mix of strike-slip and reverse faulting mechanisms. More enigmatic is the onshore seismicity, and questions remain over deformation within the Cyprus slab and uplift mechanisms of the Troodos ophiolite. We investigate seismicity in and around the island, in order to better understand these processes and their associated seismic hazard. We combine records of a temporary deployment of five broadband seismometers with the 13 permanent broadband seismometers on the island, as well as two accelerometers, to create a two-year local earthquake catalogue. We locate earthquakes both within the overriding Cyprus crust and the underthrusting African plate, and identify previously unrecognised seismically active regions on the island, especially around the Troodos ophiolite. We use this earthquake catalogue to constrain a new 1-D velocity model and local magnitude scale for the region. We also constrain new focal mechanisms and interpret these in the context of the regional tectonics.
Deep learning for surrogate modeling of two-dimensional mantle convection
Authors: Agarwal Siddhant , Tosi Nicola , Kessel Pan , Breuer Doris , Montavon Grégoire
Published: March 2022

Mantle convection plays a fundamental role in the long-term thermal evolution of terrestrial planets like Earth, Mars, Mercury and Venus. The buoyancy-driven creeping flow of silicate rocks in the mantle is modeled as a highly viscous fluid over geological time scales and quantified using partial differential equations (PDEs) for conservation of mass, momentum and energy. Yet, key parameters and initial conditions to these PDEs are poorly constrained and often require a large sampling of the parameter space to find constraints from observational data. Since it is not computationally feasible to solve hundreds of thousands of forward models in 2D or 3D, some alternatives have been proposed. 

The traditional alternative to high-fidelity simulations has been to use 1D models based on scaling laws. While computationally efficient, these are limited in the amount of physics they can model (e.g., depth-dependent material properties) and predict only mean quantities such as the mean mantle temperature. Hence, there has been a growing interest in machine learning techniques to come up with more advanced surrogate models. For example, Agarwal et al. (2020) used feedforward neural networks (FNNs) to reliably predict the evolution of entire 1D laterally averaged temperature profile in time from five parameters: reference viscosity, enrichment factor for the crust in heat producing elements, initial mantle temperature, activation energy and activation volume of the diffusion creep. 

We extend that study to predict the full 2D temperature field, which contains more information in the form of convection structures such as hot plumes and cold downwellings. This is achieved by training deep learning algorithms on a data set of 10,525 2D simulations of the thermal evolution of the mantle of a Mars-like planet. First, we use convolutional autoencoders to compress the size of each temperature field by a factor of 142. Second,  we compare the use of two algorithms for predicting the compressed (latent) temperature fields: FNNs and long-short-term memory networks (LSTMs).  On the one hand, the FNN predictions are slightly more accurate with respect to unseen simulations (99.30%  vs. 99.22% for the LSTM). On the other hand, Proper orthogonal decomposition (POD) of the LSTM and FNN predictions shows that despite a lower mean relative accuracy, LSTMs capture the flow dynamics better than FNNs. The POD coefficients from FNN predictions sum up to 96.51% relative to the coefficients of the original simulations, while for LSTMs this metric increases to 97.66%. 

We conclude the talk by stating some strengths and weaknesses of this approach, as well as highlighting some ongoing research in the broader field of fluid dynamics that could help increase the accuracy and efficiency of such parameterized surrogate models.
Long-term trajectories of Nitrogen and Phosphorous point sources to German river systems
Authors: Sarrazin Fanny , Attinger Sabine , Kumar Rohini
Published: March 2022

Concurrent excesses of nitrogen (N) and phosphorous (P) compounds in the environment are causing the eutrophication of water bodies worldwide, including the North Sea and Baltic Sea that border Germany. The N:P ratio is a crucial measure of the nature of nutrient limitation and of the state of aquatic ecosystems. While many studies focus on the diffuse sources of N and P, point sources from urban and industrial wastewater can substantially contribute to in-stream N and P levels. Yet, systematic studies of the co-development of N and P point sources that span different river basins and a long time period are greatly lacking at a national scale like Germany.

To this end, we provide a comprehensive investigation of the long-term trajectories of N and P point sources in German catchments over the last seven decades (1950-2019). We construct a novel gridded dataset of N and P point sources for Germany, adapting the methodology proposed by Morée et al. (2013) and using country-specific datasets on population counts, protein supply, food wastes, and population connection to sewer and wastewater treatment plants. In addition, we estimate the consumption of P detergents combining datasets of household detergent phosphate and phosphonate sales, household ownership of automatic dishwashers, and professional detergent use. Our reconstruction approach accounts for the uncertainty in coefficients (e.g. efficiency of wastewater treatment, N content in proteins). We create an ensemble of plausible combinations of coefficient values that are constrained by the contemporary observed N and P loading from urban wastewater treatment plants (2012-2016 values; Büttner 2020).

From the newly constructed dataset, we analyze the trajectories of N and P loading, the N:P ratio and the relative importance of diffuse and point sources across major German river basins. In particular, N and P loadings show large differences between West and East Germany. In addition, P loading exhibits a stronger decrease in the 1980s and early 1990s than N loading because of the introduction of phosphate-free laundry detergents. Overall, N and P trajectories have large temporal and spatial variations, in particular due to differences in treatment efficiency, in population density, and in regulations that limit the maximum phosphate content in detergents.

Büttner, O.: DE-WWTP - data collection of wastewater treatment plants of Germany (status 2015, metadata), https://doi.org/10.4211/hs.712c1df62aca4ef29688242eeab7940c, 2020.

Morée, A. L., Beusen, A. H. W., Bouwman, A. F., and Willems, W. J.: Exploring global nitrogen and phosphorus flows in urban wastes during the twentieth century, Global Biogeochemical Cycles, 27, 836–846, https://doi.org/10.1002/gbc.20072, 2013.
An innovative and automated vortex identification method based on the estimation of the center of rotation with application to solar simulations
Authors: Canivete Cuissa José Roberto , Steiner Oskar
Published: March 2022

Ubiquitous small-scale vortical motions in the solar atmosphere are thought to play an important role in local heating of the quiet chromosphere and corona. However, an unambiguous method for their detection in observations and numerical simulations has not been found yet.
We aim at developing a robust method for the automated identification of vortices. Local and global rotations in the flow should be considered as both are necessary for the detection of coherent vortical structures. Moreover, the use of a threshold should be avoided to not exclude slow vortices in the identification process.
We present a new method that combines the rigor of mathematical criteria and the global perspective of morphological techniques. The core of the method is the estimation of the center of rotation for every point that presents some degree of local rotation in the flow. For that, we employ the Rortex criterion and the morphology of the neighboring velocity field. We then identify coherent vortical structures by clustering the estimated centers of rotation.
The application of the method to synthetic velocity fields demonstrates its reliability and accuracy. A first statistical study is performed on realistic numerical simulations of the solar atmosphere carried out with the radiative magneto-hydrodynamical code CO5BOLD. We counted on average 0.8 Mm-2 swirls in the photosphere and 1.9 Mm-2 at the bottom of the chromosphere. The average radius varies between 59 km and 72 km. Compared to previous studies, our analysis reveals more and smaller vortical motions in the simulated solar atmosphere. Moreover, we find that 84 % of the swirls in the photosphere show twists in the magnetic field lines compatible with torsional Alfvén waves. 
Reconstruction of intermediate water temperature in the tropical North Atlantic since the Little Ice Age using cold-water corals 
Authors: Liu Qian , Robinson Laura F. , Hendy Erica , Chen Si-Yuan Sean , Stewart Joseph A. , Knowles Timothy , Li Tao , Samperiz Vizcaino Ana
Published: March 2022

Long-lived colonial cold-water corals have the potential to provide robust continuous archives of environmental change. These high-resolution records of the subsurface ocean are particularly valuable, especially at understudied intermediate water depths. Yet, to understand the anthropogenic impacts on the sub-surface ocean and better predict future changes, it is critical to establish the natural variation of temperature and circulation of the ocean system prior to the Industrial Revolution.

Here we combine temperature proxy and radiocarbon data from specimens of two taxa of cold-water coral that grew in intermediate water depths (~1500 m) in the tropical North Atlantic. In 2013, specimens of the bamboo coral Lepidisis spp. and scleractinian coral Enallopsammia rostrata were collected from sites currently situated in the boundary of North Atlantic Deep Water and Antarctic Intermediate Water to reconstruct the temperature and circulation history of the region. We demonstrate that bamboo corals can be used to reconstruct ambient seawater radiocarbon content when independently dated by organic node annual band counting. Radiocarbon was also analysed in Enallopsammia rostrata to develop age models for both the radial section and from discrete corallites (polyps) along a branch. Dating results show that this coral is about 500 years old, allowing us to generate a temperature record as far back as the Little Ice Age. Trace metal ratios were analysed along the growth axis of the coral, and the Li/Mg ratio was used as a temperature proxy. We find that the Li/Mg derived temperature of the most recent polyps is consistent with modern ambient temperature. The overall temperature record shows a general increasing trend since the Little Ice Age, while the radiocarbon record indicates no significant change until the late 20th century. Combining these records allows us to reconstruct potential ocean circulation changes in the central tropical North Atlantic over last 500 years.
On the vertical distribution of microplastics particles in sea ice cores 
Authors: Chubarenko Irina , Lazaryuk Alexander , Saliu Francesco , Lobchuk Olga , Raguso Clarissa , Orlova Tatiana , Lasagni Marina
Published: March 2022

Sea ice is shown to be heavily contaminated by microplastics (MPs, <5 mm), but its vertical distribution is not consistent. Previous investigations suggested that contamination by MPs is size-specific and time variable. To attain the level of contamination and vertical distribution of MPs in the ice of the Novik bay (Peter the Great Bay, Sea of Japan), three ice cores (ca. 100 m apart from one another, thickness ~40 cm) were taken from the one-year sea ice on 8 March 2020. One core was used to obtain the salinity profile within the ice, while two other cores were segmented into 5-cm thick layers and analyzed for MPs content using different methods: µ-FTIR analysis for particles in the size range of 25-300 µm (S-MPs), and visual identification followed by Raman spectroscopy for 300 µm – 5 mm particles (L-MPs).

MPs particles of both size ranges were found in all layers of the cores. Contamination in upper\lower layers was up to 3 times larger than in the middle of the cores (observed in both size ranges). The majority (45%) of L-MPs are 1-2 mm in size. Preliminary, the level of contamination by MPs in the ice of the Novik bay is of the order of 200-300 items per liter of melted water (in each of the size ranges), which confirms a certain deficit of smaller MPs within the ice. In shape, fibers (53%) followed by fragments (44%) are prevalent types of L-MPs, while among S-MPs more than 60% are films. Ice salinity (averaged over 5 cm depth) generally increases with depth (from 4 to 8 psu), however has a minimum (3 psu) in the layer 10-15 cm. Minima of MPs content are in the layers 20-25 cm (for S-MPs) and 5-15 cm (for L-MPs). Environmental conditions are analyzed and physical processes are discussed, which might have led to the observed MPs distribution.

Investigations are supported by RSF via grant No 19-17-0041.
The influence of meteorological parameters on wind speed extreme events:  A causal inference approach
Authors: Hlavackova-Schindler (Schindlerova) Katerina , Fuchs Andreas , Plant Claudia , Schicker Irene , DeWit Rosmarie
Published: March 2022

Based on the ERA5  data of hourly  meteorological parameters [1], we investigate temporal effects of  12 meteorological parameters on  the extreme values occurring in  wind speed.  We approach the problem by using the Granger causal inference, namely by the heterogeneous graphical Granger model (HGGM) [2]. In contrary to the classical Granger model proposed for causal inference among Gaussian processes, the HGGM detects causal relations among time series with distributions from the exponential family, which includes a wider class of common distributions. In previous synthetic experiments, HGGM combined with the genetic algorithm search based on the minimum message length principle has been shown superior in precision over the baseline causal methods [2].  We investigate various experimental settings of all 12 parameters with respect to the wind extremes in various time intervals. Moreover, we compare the influence of various data preprocessing methods and evaluate the interpretability of the discovered causal connections based on meteorological knowledge.

[1] https://cds.climate.copernicus.eu/cdsapp#!/dataset/reanalysis-era5-single-levels?tab=overview

[2] Behzadi, S, Hlaváčková-Schindler, K., Plant, C. (2019) Granger causality for heterogeneous processes, In: Pacific-Asia Conference on Knowledge Discovery and Data Mining. Springer, pp. 463-475.

[3] Hlaváčková-Schindler, K., Plant, C. (2020) Heterogeneous graphical Granger causality by minimum message length, Entropy, 22(1400). pp. 1-21 ISSN 1099-4300 MDPI (2020).
Quantifying Arctic methane emissions from Alaska’s North Slope and Northeast Siberia from 2010-2020 using high-frequency atmospheric measurements
Authors: Ward Rebecca , Ganesan Anita , Sweeney Colm , Miller John , Goeckede Mathias
Published: March 2022

Atmospheric methane mole fractions have been rising globally since 2007, with 2020 exhibiting the largest annual growth since intensive measurements began globally in 1983. Quantifying methane emissions from Arctic regions is crucial as temperatures have been increasing twice as fast over the Arctic as the global mean. Temperature is an important driver of methane emissions from Arctic soils, controlling rates of microbial production and permafrost thaw.

 

We use a range of methods to quantify emissions and assess trends from the North Slope of Alaska and Northeast Siberia using the most recent data from near-coastal Arctic surface sites. Methods include: the analysis of trends in methane mole fraction enhancements over background from the land sector and as the quantification of emissions at monthly resolution through Bayesian inversions using the NAME atmospheric transport model. This study employs data from the surface sites at Barrow, Alaska and Ambarchik.

 

Preliminary analyses at Barrow using data up to 2020 show that emissions from Alaska’s North Slope have increased substantially in recent years, reflecting a change from previous analyses, which showed no significant increase in summertime methane emissions between 1986-2014.  (Sweeney et al., 2016). We show that methane enhancements over background from the land sector increased most prominently from July to September, and that late Autumn enhancements continue to rise at a rate similar to the previous decades. We also find substantial terrestrial emissions from Northeast Siberia occurring both in the Summer as well as in the Autumn months, suggesting important “zero-curtain” emissions. We investigate correlations between surface air temperature and surface inundation with methane enhancements to determine the likely drivers of these enhanced emissions. Our findings can be used to assess whether important changes to the Arctic cryosphere are beginning to be observed.
Insights from the first detailed record of Late Cretaceous seawater lithium isotopic composition
Authors: Huber Sandra J. , Schlidt Vanessa , Lenk Linus , Seitz H.-Michael , Raddatz Jacek , Voigt Silke
Published: March 2022

The late Cretaceous climate is represented by an 8-10 °C decline of global mean temperatures that terminated global warmth of mid-Cretaceous times. Causal mechanisms of the cooling are still not well constrained and discussed in the interplay of reduced volcanic greenhouse gas emission and intensified silicate weathering as a global carbon cycle feedback. The lithium isotopic composition (δ7Li) of marine carbonates is a proxy for the chemical weathering intensity of silicate rocks, and thus provides information about the role of silicate weathering as thermostat and sink for atmospheric CO2.

Here, we present the first detailed chalk-derived Late Cretaceous δ7Li record (91-66 Ma) of the boreal white chalk in Northern Germany (Lägerdorf-Kronsmoor-Hemmoor) and from sections in southern England as archive for the seawater lithium isotopic composition. In the course of this study, we will also analyze the archives of skeletal calcite from brachiopods, belemnites and rudists, which should enable us to identify systematic offsets among different calcifiers related to vital effects by the direct comparison of fossilized shells and their surrounding sediments.

To handle the potential impact of clay contamination in bulk carbonates, we applied a pre-leaching and leaching procedure with 1 M ammonium acetate and 0.05 M nitric acid. The method was tested for a 1.85 Ma old sample of coccolith ooze from the Manihiki Plateau (equatorial West Pacific Ocean), which has consistent δ7Li values and shows a systematic negative 3-4 ‰ offset to modern seawater. In addition, the degree of potentially leached silicates is monitored by the analysis of E/Ca ratios, like Al/Ca.

In total, our late Cretaceous lithium isotope record shows a trend of rising δ7Li values between +16 and +25 ‰. Superimposed, the curve displays a rise in the Santonian, a local maximum in the early Campanian followed by a drop to a local minimum in the late Campanian. Subsequently, the δ7Li values rise again towards elevated values in the Maastrichtian. Overall, the shape of the δ7Li curve strongly resembles the evolution of deep-sea temperatures based on benthic oxygen isotopes suggesting a close link between climate and weathering. Thereby, more positive δ7Li values correspond to cooling periods and the late Campanian lowering of δ7Li values parallels the intermittent deep-sea warming. Such a pattern points towards a strong relationship between the congruency of silicate weathering and climate on a multi-million year time scale.
Variations in the wind-driven response of the Rhine ROFI during a spring-neap cycle
Authors: Keyzer Lennart , Pietrzak Julie , Snellen Mirjam , Katsman Caroline , Zijl Firmijn , Afrasteh Yosra , Guarneri Henrique , Verlaan Martin , Klees Roland , Slobbe Cornelis
Published: March 2022

The position and properties of a river plume strongly depend on the wind conditions. Upwelling-favourable winds force the plume offshore, while the freshwater layer thins. Downwelling-favourable winds confine the plume against the coast, resulting in a thicker freshwater layer. The Rhine Region Of Freshwater Influence (ROFI) along the Dutch coast is not only modulated by winds, but also influenced by tides and bottom friction. The near-field region is dominated by tidal plume fronts, which are formed by the release of freshwater. The mid- to far-field region of the plume switches between stratified conditions on neap tide and well-mixed conditions on spring tide. Furthermore, tidal straining induces a semidiurnal cycle in the stratification. In this study, we investigate how winds influence this shallow frictional river plume. We use an unstructured high-resolution 3D model to perform idealized simulations of a spring-neap cycle, forced with constant upwelling- or downwelling-favourable winds. It is shown that the state of the ROFI depends on the combined effect of tides and winds. In the absence of winds, a multi-frontal system forms on neap tide, which is strongly stratified. On spring tide, however, stronger tidal currents in combination with stronger salinity gradients result in separate, buoyant fronts that propagate northwards. The background plume is well-mixed vertically, due to strong tidal mixing. Under downwelling winds, flood currents are aligned with the wind direction, resulting in faster propagating fronts. As a result, separate freshwater lenses arise on neap tide. In contrast, upwelling winds hinder the alongshore propagation of tidal plume fronts, which results in a multi-frontal system on spring tide. Furthermore, we show that winds change the semidiurnal cycle in the stratification, induced by tidal straining. Under downwelling winds, this cycle is enhanced due to stronger cross-shore salinity gradients. Under upwelling winds, there is less variability in the stratification within the tidal cycle. Understanding the dominant physical processes of this complex system is important for transport of, amongst others, sediments, nutrients and pollutants in coastal systems.