bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the physical drivers of the decadal variability of the Southern Ocean carbon uptake
Authors: Patara Lavinia , Martin Torge , Frenger Ivy , Rieck Jan Klaus , Chien Chia-Te
Published: March 2021

Observational estimates point to pronounced changes of the Southern Ocean carbon uptake in the past decades, but the mechanisms are still not fully understood. In this study we assess physical drivers of the Southern Ocean carbon uptake variability in a suite of global ocean biogeochemistry models with 0.5º, 0.25º and 0.1º horizontal resolution as well as in a 3-member ensemble performed with an Earth System Model (ESM) sharing the same ocean biogeochemistry model. The ocean models show a positive trend of the Southern Ocean CO2 uptake in the past decades, with a weakening of its rate of increase in the 1990s. The 0.1º model exhibits the strongest trend in the Southern Ocean carbon uptake. Different physical drivers of the carbon uptake variability and of its trends (such as changes in stratification, ventilation, overturning circulation, and SST) are analyzed. A particular focus of this study is to assess the role of open-ocean polynyas in driving Southern Ocean carbon uptake. Open-ocean polynyas in the Southern Ocean have pronounced climate fingerprints, such as reduced sea-ice coverage, heat loss by the ocean and enhanced bottom water formation, but their role for the Southern Ocean carbon uptake has been as yet little studied. To this end we analyze conjunctly ESM simulations and an ocean-only sensitivity experiment where open-ocean polynyas are artificially created by perturbing the Antarctic freshwater runoff. We find that enhanced CO2 outgassing takes place during the polynya opening, because old carbon-rich waters come in contact with the atmosphere. The concomitant increased uptake of anthropogenic CO2 partially compensates the CO2 outgassing. When the polynya closes, the ocean CO2 uptake increases significantly, possibly fueled by abundant nutrients and higher alkalinity brought to the surface during the previous convective phase. Our results suggest that open-ocean polynyas could have a significant impact on the Southern Ocean CO2 uptake and could thus modulate its decadal variability.

 
 Generation of planetary waves by gravity-wave drag in the middle atmosphere
Authors: Chun Hye-Yeong , Song Byeong-Gwon , Song In-Sun
Published: March 2021

Large-scale atmospheric circulation has been represented mostly by interaction between the mean flow and planetary waves (PWs). Although the importance of gravity waves (GWs) has been recognized for long time, contribution of GWs to the large-scale circulation is receiving more attention recently, with conjunction to GW drag (GWD) parameterizations for climate and global weather forecasting models that extend to the middle atmosphere. As magnitude of GWD increases with height significantly, circulations in the middle atmosphere are determined largely by interactions among the mean flow, PWs and GWs. Classical wave theory in the middle atmosphere has been represented mostly by the Transformed Eulerian Mean (TEM) equation, which include PW and GW forcing separately to the mean flow. Recently, increasing number of studies revealed that forcing by combined PWs and GWs is the same, regardless of different PW and GW forcings, implying a compensation between PWs and GWs forcing. There are two ways for GWs to influence on PWs: (i) changing the mean flow that either influences on waveguide of PWs or induces baroclinic/brotropic instabilities to generate in situ PWs, and (ii) generating PWs as a source of potential vorticity (PV) equation when asymmetric components of GWD exist. The fist mechanism has been studies extensively recently associated with stratospheric sudden warmings (SSWs) that are involved large amplitude PWs and GWD. The second mechanism represents more directly the relationship between PWs and GWs, which is essential to understand the dynamics in the middle atmosphere completely (among the mean flow, PWs and GWs). In this talk, a recently reported result of the generation of PWs by GWs associated with the strongest vortex split-type SSW event occurred in January 2009 (Song et al. 2020, JAS) is presented focusing on the second mechanism.  
Trend analysis of extratropical cyclones in long-term ERA5 data series (1950-2019)
Authors: Blender Richard , Karwat Alexia , Franzke Christian
Published: March 2021

Extratropical cyclones are the primary natural hazards affecting Europe. With the release of ERA5 reanalysis data from 1950-1978 by the European Centre for Medium-Range Weather Forecasts (ECMWF), new opportunities have arisen to investigate mid-latitude cyclones in terms of climatic features and trends in longer and higher resolution. We analyze cyclones by nearest neighbor search in 1000 hPa geopotential height minima in different high resolutions for different minimum life-times. We find an intensification of North Atlantic cyclones in 1950-2019. Short-lived cyclones grow in radius and depth. In the Mediterranean, however, long-lived cyclones have weakened; but traveled also further in 1950-2019. Additionally, we illustrate relations between cyclone tracks, radii and correlated weather and climate extremes.
Interaction between Atlantic cyclones and Eurasian atmospheric blocking drives warm extremes in the high Arctic
Authors: Murto Sonja , Caballero Rodrigo , Svensson Gunilla , Papritz Lukas
Published: March 2021

Atmospheric blocking can influence Arctic weather by diverting the mean westerly flow polewards, bringing warm, moist air to high latitudes. Recent studies have shown that diabatic heating processes in the ascending warm conveyor belt branch of extratropical cyclones are relevant to blocking dynamics. This leads to the question of the extent to which diabatic heating associated with mid-latitude cyclones may influence high-latitude blocking and drive Arctic warm events. In this study we investigate the dynamics behind 50 extreme warm events of wintertime high Arctic surface temperature anomalies. We find that 30 of these events are associated with “Ural” blocking, featuring negative upper-level PV anomalies over central Siberia north of the Ural Mountains. Lagrangian back-trajectory calculations show that almost 70% of the air parcels making up these negative PV anomalies experience lifting and diabatic heating (average 14,7 K) in the 9-days prior to blocking. Further, 43,4 % of the heated trajectories undergo maximum heating and lifting in a compact region of the midlatitude North Atlantic, temporally taking place between 6 and 2.5 days before arriving in the blocking region. These trajectories mainly reside in the subtropics before being advected into the lifting region. We also find anomalously high cyclonic activity (on average 3,9 cyclones within a 3,5-day window around the time of maximum lifting) within a sector northwest of the main lifting domain. This study highlights the importance of the interaction between mid-latitude cyclones and Eurasian blocking as driver for Arctic warm extremes.
Assessing the impact of irrigating with saline water on physical properties of a sandy loam soil.
Authors: Mawodza Tinashe , Menon Manoj , Babaei Masoud , Burca Genoveva , Magdysyuk Oxana V.
Published: March 2021

Soil salinisation is one of the most potent forms of land degradation that affects soils of arid and semi-arid regions of the world. Management of soils with potential for salinisation is key to ensuring the sustainability of marginal soils in predominantly dry regions of the world. In this research, to assess the potential impact of irrigation with saline water on the physical properties of a marginal soil. We subjected a sandy loam soil to flood irrigation with water of variable salinity levels (namely 0, 2,  5 and 10 g/L NaCl) for up to 40 days. After every irrigation cycle, each of the soil samples was subjected hydraulic conductivity measurements for the duration of the experiment. At the end of the 40 day experimental irrigation period, soil cores were non-invasively scanned using X-Ray CT scanning to assess for changes in pore distribution as a result of the different irrigation quality water. Furthermore, measurement of other physio-chemical soil properties such as aggregate stability, EC and pH of each soil were also done to get a more complete idea of the changes that occurred during the experiment. 
Testing the validity of different synthetic scenarios for flow and transport simulation in karst systems using a real case study application. 
Authors: Doummar Joanna , Farran Nidal , Fahs Marwan , Belfort Benjamin , Graf Thomas
Published: March 2021

Climate change and pollution are posing additional unprecedented threats to existing water resources, especially to water supply from karst aquifers in Mediterranean and semi-arid regions. A numerical model considering the most important key hydraulic parameters can forecast the impact of any given input on model quality and quantity output. In this work, we propose to model flow and transport using Comsol multiphysics in a synthetic model and to apply it to a simplified real case study (Jeita spring in Lebanon supplying water to 1.5 million inhabitants). The model geometry consists of a 5300 m long variably saturated horizontal conduit portrayed as 1) 2-D continuum and/or 2) a channel draining a porous equivalent matrix (400 m thick). Flow is simulated using the Richards Equation in both saturated and unsaturated medium. Recharge is applied vertically as both diffuse and point source in a shaft linked to the conduit. Percentages of fast infiltration rates are obtained from the analysis of event time series recorded at the spring (electrical conductivity and discharge). Flow rates at the outlet are used for transient model calibration. Mean velocities, dispersivities, and phreatic conduit diameters obtained from tracer experiments under various flow periods are used for transport validation in the channel. The aim is to test the validity of a functional simplified flow model on a complex real case and to identify based on a sensitivity analysis the key parameters that allow an optimal calibration of such a model. 
The Formation of Saturn’s and Jupiter’s Electron Radiation Belts by Magnetospheric Electric Fields
Authors: Hao Yixin , Sun Yixin , Roussos Elias , Liu Ying , Kollmann Peter , Yuan Chongjing , Krupp Norbert , Paranicas Chris , Zhou Xuzhi , Murakami Go , Kita Hajime , Zong Qiugang
Published: March 2021

The existence of planetary radiation belts with relativistic electron components means that powerful acceleration mechanisms are operating within their volume. Mechanisms that bring charged particles planetward toward stronger magnetic fields can cause their heating. On the basis that electron fluxes in Saturn’s radiation belts are enhanced over discrete energy intervals, previous studies have suggested that rapid inward plasma flows may be controlling the production of their most energetic electrons. However, rapid plasma inflows languish in the planet’s inner magnetosphere, and they are not spatially appealing as a mechanism to form the belts. Here we show that slow, global-scale flows resulting from transient noon-to-midnight electric fields successfully explain the discretized flux spectra at quasi- and fully relativistic energies, and that they are ultimately responsible for the bulk of the highest energy electrons trapped at Saturn. This finding is surprising, given that plasma flows at Saturn are dominated by the planetary rotation; these weak electric field perturbations were previously considered impactful only over a very narrow electron energy range where the magnetic drifts of electrons cancel out with corotation. We also find quantitative evidence that ultrarelativistic electrons in Jupiterʼs radiation belts are accelerated by the same mechanism. Given that similar processes at Earth drive a less efficient electron transport compared to Saturn and Jupiter, the conclusion is emerging that global-scale electric fields can provide powerful relativistic electron acceleration, especially at strongly magnetized and fast-rotating astrophysical objects.
Remote Sensing-based Spatiotemporal Analysis of Near-Surface Temperatures for Cities Located in Different Climatic Zones
Authors: Jallu Sriram , Bommineni Poorna Chander Reddy , Srivastav Roshan
Published: March 2021

Urbanization has a major impact on the spatio-temporal variation of near-surface temperature for world cities. Recent studies indicate that the understanding of changes in temperature with urbanization has provided greater insights into the effects of Urban Heat Islands (UHI) on various issues such as excessive energy consumption, health hazard and climate change. In this study, spatio-temporal variations of near-surface temperature for India’s three major cities with different climatic conditions are evaluated. In addition, an attempt is made to establish a quantitative relation between land surface temperature (LST) and various geographical indices indicating vegetation cover (NDVI, Normalized Difference Vegetation Index), water surfaces (NDWI, Normalized Difference Water Index), and impervious land (NDBI, Normalized Difference Built-up Index). The dataset is selected for years 2014 to 2020 for three major cities: (i) Chennai (coastal); (ii) Hyderabad (inland); and (ii) Mumbai (coastal). The study uses Landsat – 8 OLI / TIRS images to derive land use/cover types, land surface temperature datasets, NDVI, NDBI, and NDWI. The preliminary evaluations indicate that the maximum contribution towards the UHI is impervious land, and the effect is more prominent in the areas of rapid urbanization. Urban areas relatively have a high temperature compared to the surrounding rural areas, and the effect is more prominent during night times. The analysis derived from the study will be useful for decision-makers or stakeholders to take necessary actions for reducing the effects of UHI and planning for urban sprawl.
High Water Content Areas Identified In Equatorial Band of Mars by FREND Neutron Telescope Onboard ExoMars TGO
Authors: Malakhov Alexey , Mitrofanov Igor , Litvak Maxim , Sanin Anton , Golovin Dmitry , Djachkova Maya , Nikiforov Sergey , Anikin Artem , Lisov Denis , Lukyanov Nikita , Mokrousov Maxim
Published: March 2021

FREND is a neutron telescope installed onboard Russian-European ExoMars mission Trace Gas Orbiter. Neutron measurements from orbit are a good characteristic of water content in the subsurface of Mars down to 1 meter in depth. The instrument’s major characteristic is its neutron collimator that narrows significantly the field of view allowing for mapping with high spatial resolution of 60-200 km.

Previous missions (e.g. HEND experiment on NASA’s Mars Odyssey) showed that water content is enhanced mainly in Martian polar regions and at Arabia area, however spatial resolution of these instruments only allowed to map the surface with a resolution of several hundreds of kilometers. A study performed on FREND data accumulated during its science mission between May 2018 and January 2021 was targeted on equatorial band of ±40° latitude. We identified several local areas with enhanced mass fraction of water and performed a thorough analysis of each of them to identify the water content and estimate statistical significance of such wet spots.

The locations found are associated with major Martian relief formations, e.g. Olympus Mons, Ascraeus Mons, Xanthe Terra, Valles Marineris and others, each showing water content of tens of weight percent (wt%), with good statistical certainty above 3σ relative to the immediate dry surroundings.

In this talk we will present the areas identified as well as explain the search algorithm and water content estimation techniques.
Phosphate sorption-desorption behavior in volcanic topsoils along a chronosequence (1.5 ka – 1070 ka) in the humid zone, Galápagos Islands
Authors: Rechberger Maria V. , Gerzabek Martin H. , Zehetner Franz
Published: March 2021

Soil phosphorus (P) is one of the main factors affecting ecosystem productivity. With progressing soil weathering, P can be increasingly immobilized and become the limiting nutrient in ecosystems. Volcanic soils are known for their exceptionally high phosphate (PO4) retention capacity. However, the changes in PO4 sorption behavior as their mineralogy evolves during pedogenic development, are still not fully understood. Short-term and longer-term PO4 sorption-desorption behavior was studied in six volcanic topsoils (0 – 10 cm) from four Galápagos Islands along an age gradient (chronosequence, 1.5 – 1070 ka) under humid climate. Labile P (Mehlich-3 P, resin P), PO4 sorption kinetics (4 h – 62 days), PO4 sorption capacity (sorption isotherms, equilibration time = 72 h) and longer-term desorption (resin P after 1 and 6 month incubation, respectively) were analyzed. Soils developed very high PO4 sorption capacity within 4.3 ka of soil weathering (Langmuir Qmax = 18.2 g P kg-1) due to the development of amorphous soil constituents. As the colloidal fraction changed to 2:1-type crystalline clays after 26 ka of soil weathering, PO4 sorption capacity declined rapidly while the labile P fraction reached a maximum. In older soils (≥ 165 ka), acidification and prevalence of Al und Fe (hydr)oxides led to increased P sorption again. Overall, soil PO4 retention capacity was closely related to amorphous Si, Al and Fe phases; however, it did not predict P availability.
Exploiting a paleobiological database to constrain sub-plate support: Examples from western North America, northeast Brazil and northern Africa
Authors: Milanez Fernandes Victoria , Roberts Gareth
Published: March 2021

The shape of the Earth's surface is the result of complex interactions between deep and surface processes operating on a range of spatial and temporal scales. However, generating sufficient geological observations at the spatial and temporal scales relevant to investigating deep-Earth processes (~100–1000 km, ~1–100 Ma) remains a challenge. To address this challenge, I exploit a paleobiological database to generate a new compilation of >24,000 spot measurements of net surface uplift across all continents. The present-day elevation of marine fossil assemblages that crop out at the Earth’s surface provides a direct constraint on the timing and amplitude of net surface uplift on geological timescales. I explore how these surface observations can be used to explore the evolution of sub-plate processes in three key regions: Western North America, Borborema Province in northeast Brazil, and Northern Africa. This new data compilation provides self-consistent, and in places high resolution measurements for Cretaceous to Recent net uplift. Geophysical observations (e.g., free-air gravity, shear-wave topography) and isostatic calculations are combined with net uplift measurements from these regions to explore how mantle thermal anomalies and lithospheric thinning might generate the observed uplift patterns. Uncertainties associated with paleo-bathymetry, post-deposition compaction and glacio-eustasy are assessed. The results emphasise the importance of large inventories of paleobiological data for understanding the history of tectonic and mantle convective processes as expressed at the Earth's surface.
Gibbs-ensemble Monte Carlo simulations for binary mixtures
Authors: Bergermann Armin , French Martin , Redmer Ronald
Published: March 2021

We explore the performance of the Gibbs-ensemble Monte Carlo simulation method by calculating the miscibility gap of H2-He mixtures with analytical exponential-six potentials [1]. We calculate demixing curves for pressures up to 500 kbar and temperatures up to 1800 K. Our results are in good agreement with ab initio simulations in the non-dissociated region of the phase diagram. Next, we determine new parameters for the Stockmayer potential [2] to model the interactions in the H2O-H2O system for temperatures of 1000 K < T < 2000 K. The corresponding miscibility gap of H2-H2O mixtures was determined and we calculated demixing curves for pressures up to 150 kbar and temperatures up to 2000 K. Our results show reasonable agreement with previous experimental data of Bali et al. [3]. These results are important for interior and evolution models for ice giant planets [4].

References
[1] A. Bergermann, M. French, M. Schöttler and R. Redmer, Phys. Rev. E, 103 (2021)
[2] W. Stockmayer, The Journal of Chemical Physics 9, S. 398-402 (1941)
[3] E. Bali, A. Audétat and H. Keppler, Nature, 495, 7440 (2013)
[4] R. Helled, N. Nettelmann and T. Guillot, Space Science Reviews, 216 (2020)
Towards a reproducible snow load map – an example for Austria
Authors: Schellander Harald , Winkler Michael , Hell Tobias
Published: March 2021

The European Committee for Standardization provides coarse rules for the estimation of snow load maps for structural design. European countries can apply their own methodologies, resulting in inconsistencies for the 50-year return level of snow load at national borders. Commonly used approaches base on more or less sophisticated interpolation of snow depths with a subsequent assignment of snow density, or spatial extreme value interpolation of snow load measurements.  

We propose a novel methodology for Austria, where snow load observations are not available. It is based on (1) modeling yearly snow load maxima with the specially developed ∆SNOW model, and (2) a generalized additive model, where explaining covariates and their combinations are represented by penalized regression splines, fitted to such derived snow load series. Results show an RMSE of 0.7 kN/m2, and a BIAS of -0.2 kN/m2 over all altitudes, thereby outperforming a smooth spatial extreme value model and the actual Austrian standard, when compared to locally estimated, “quasi-observed “ 50-year snow load maxima at 870 stations in and tightly around Austria.

The new approach requires no zoning and provides a reproducible and transparent approach. Due to the relatively ease of use and snow depth measurements as single prerequisite, the method is applicable in other countries as well. Negative BIASes, that significantly underestimate 50-year snow loads at a small number of stations, are the only objective problem that has to be solved before the new map can be proposed as a successor of the actual Austrian snow load map.
3D lithological structure in a steady state model drives divide migration
Authors: Graf Emma , Mudd Simon , Kober Florian , Landgraf Angela , Ludwig Andreas
Published: March 2021

Predicting future relief is a longstanding challenge in the field of geomorphology. Past denudation and incision rates can be reconstructed and modelled from field data such as thermochronometers, cosmogenic nuclides or optically stimulated luminescence, whereas future rates are then, by definition, fully unknown. Predicting future landscape evolution is further complicated by the dynamic nature of drainage networks, as well as the necessity of constraining properties such as erodibility in order to make sensible predictions. One of the few constraints available for future landscape properties is the underground stratigraphy imaged by wells or geophysical methods. The 3D rock structure will eventually be exhumed and can be utilised to constrain the future states of model simulations.

In this contribution, we present a landscape evolution model capable of ingesting 3D lithologic information and adapting to alternative channel networks, and demonstrate it using a study area in the Swiss Jura Mountains. The model calculates local relief using steady state solutions of the stream power incision model, and also quantifies hillslope relief using a very simple critical slope gradient where hillslope angles are set to a critical value on pixels that have a small drainage area. Further, drainage divides are allowed to migrate to minimize sharp breaks in relief across drainage divides.

We calibrate the values of erodibility, K, for each lithological unit by extracting ranges of apparent K value from the present-day landscape based on drainage area and gradient along the drainage network. This is then further refined by i) using a Monte Carlo approach to create combinations of K based on these ranges, and ii) comparing the real and model landscape for each combination with the aim to minimise the difference between the two. We then run selected model simulations of future base level fall and potential drainage reorganisation events, highlighting the effects of i.) spatially variable erodibility and ii.) lateral changes of the main channel axis on divide migration.
Climate-induced hysteresis of the tropical forest in the fire-enabled Earth system model CM2Mc-LPJmL
Authors: Drüke Markus , v. Bloh Werner , Sakschewski Boris , Wunderling Nico , Petri Stefan , Cardoso Manoel , Barbosa Henrique , Thonicke Kirsten
Published: March 2021

Tropical rainforests are recognized as one of the terrestrial tipping elements which could have profound impacts on the global climate, once their vegetation has transitioned into savanna or grassland states. While several studies investigated the savannization of, e.g., the Amazon rainforest, few studies considered the influence of fire. Fire is expected to potentially shift the savanna-forest boundary and hence impact the dynamical equilibrium between these two possible vegetation states under changing climate. To investigate the climate-induced hysteresis in pan-tropical forests and the impact of fire under future climate conditions, we coupled the well established and comprehensively validated Dynamic Global Vegetation Model LPJmL5.0-FMS to the coupled climate model CM2Mc, which is based on the atmosphere model AM2 and the ocean model MOM5 (CM2Mc-LPJmL v1.0). In CM2Mc, we replaced the simple land surface model LaD with LPJmL and fully coupled the water and energy cycles. Exchanging LaD by LPJmL, and therefore switching from a static and prescribed vegetation to a dynamic vegetation, allows us to model important biosphere processes, including wildfire, tree mortality, permafrost, hydrological cycling, and the impacts of managed land (crop growth and irrigation).

With CM2Mc-LPJmL we conducted simulation experiments where atmospheric CO2 concentrations increased from a pre-industrial level up to 1280 ppm (impact phase) followed by a recovery phase where CO2 concentrations reach pre-industrial levels again. This experiment is performed with and without allowing for wildfires. We find a hysteresis of the biomass and vegetation cover in tropical forest systems, with a strong regional heterogeneity. After biomass loss along increasing atmospheric CO2 concentrations and accompanied mean surface temperature increase of about 4°C (impact phase), the system does not recover completely into its original state on its return path, even though atmospheric CO2 concentrations return to their original state. While not detecting large-scale tipping points, our results show a climate-induced hysteresis in tropical forest and lagged responses in forest recovery after the climate has returned to its original state. Wildfires slightly widen the climate-induced hysteresis in tropical forests and lead to a lagged response in forest recovery by ca. 30 years.
Environmental drivers of plankton and sediment microbial communities along latitudinal and vertical gradients in the deepest freshwater lake (Baikal, Southern Siberia)
Authors: Lopez-Garcia Purificacion , Reboul Guillaume , David Gwendoline , Jardillier Ludwig , Annenkova Nataliia , Bertolino Paola , Lopez-Archilla Ana I. , Vershinin Konstantin , Moreira David
Published: March 2021

Understanding how abiotic and biotic factors influence microbial community assembly and function is crucial to understand ecological processes and predict how communities will respond to environmental change. Lake Baikal (Russian Federation) is the oldest, deepest and most voluminous freshwater lake on Earth, resembling in several respects sea environments. It thus offers a unique opportunity to test the effect of horizontal versus vertical gradients in community structure. Since climate change is rapidly affecting Siberia and Lake Baikal, this information can be useful both, as a reference for future monitoring of the lake and to help predictions about how local communities change as a function of environmental parameters. In order to address these questions, in 2017, we carried out a comprehensive sampling of Lake Baikal water columns and sediments along a North–South latitudinal gradient (ca. 600 km) across the three major basins of the lake, from coastal to pelagic areas and from surface to the deepest zones (0.5 to 1450 m deep). We then applied metabarcoding approaches based on 16S and 18S rRNA gene amplicon sequencing to characterize the composition of microbial communities, in particular, both prokaryotes and eukaryotes in sediments and microbial eukaryotes (0.2-30 µm cell size) in plankton (65 samples from 17 water columns). As expected, depth had a strong significant effect on protist community stratification in the water column. The effect of the latitudinal gradient was marginal and no significant difference was observed between coastal and surface open water communities. Co-occurrence network analyses showed that epipelagic protist communities were significantly more interconnected than in the dark water column. Surprisingly, Baikal benthic communities (13 sites) displayed remarkable stability across sites and seemed not determined by depth or latitude. Comparative analyses with other freshwater, brackish and marine sediments confirmed the distinctness of Baikal benthic communities, which show some similarity to marine and hydrothermally-influenced systems likely owing to its high oligotrophy, depth and fault-associated seepage. Metagenomic analyses of sediment samples show a wide metabolic potential of Baikal benthos and highlight the relative importance ammonia-oxidizing archaea in upper sediment layers.
Atmospheric circulation and meteorological conditions during dust aerosol episodes over the broader Mediterranean Basin. The case of 16 June 2016
Authors: Gavrouzou Maria , Hatzianastassiou Nikos , Gkikas Antonis , Korras-Carraca Marios-Bruno , Lolis Christos , Mihalopoulos Nikos
Published: March 2021

Mediterranean Basin (MB), due to its position near to the greatest world deserts (the Sahara Desert in North Africa and the deserts of Middle East), is frequently affected by dust transport. This results in dust episodes, associated with high Dust Aerosol (DA) loads reaching the northern parts of MB, taking place every year with different intensity, but with specific seasonal and spatial characteristics. The seasonal and spatial characteristics of Dust Aerosol Episodes (DAEs) in the region are connected to specific atmospheric conditions that favor the injection of DA into the region’s atmosphere, as well as to specific atmospheric circulation characteristics favoring the transport to the MB.

DA not only are affected by, but they also can affect the atmospheric conditions and thus the regional weather and climate regime. Specifically, due to their ability to absorb the shortwave, but also the longwave, radiation, DA can modify the temperature structure of the atmosphere as well as the radiative budget. In addition, DA are effective Ice Nuclei (IN), and also, under mature stages, Cloud Condensation Nuclei (CCN), thus affecting cloud properties. These effects of DA become more important, but also complicated, when high dust loads are associated with other aerosol types, e.g. sea-salt (SS) and biomass burning (BB) over a region with high solar radiation, diverse topography and cloud regimes such as the MB.

In the present study, the atmospheric circulation (geopotential height and mean sea level pressure), as well as the meteorological conditions (cloud fraction, cloud optical thickness, cloud phase, temperature and humidity profiles and vertical velocity) before, during and after an extreme Dust Aerosol Episode Case (DAEC) that took place over the western MB on June 16, 2016 are examined. The studied DAEC is identified using a satellite algorithm, which uses MODIS C6.1 and OMI OMAERUV derived aerosol optical properties.  Emphasis is given to the understanding of the 3-D structure of the episode and its possible effects on the atmospheric temperature and humidity regime, as well as on cloud properties. For this reason, different reanalyses and satellite data, namely from the NCEP/NCAR (National Centers for Environmental Prediction/National Center for Atmospheric Research Reanalysis Project), MERRA-2 (Modern-Era Retrospective analysis for Research and Applications, Version 2) and MODIS databases, are analyzed. In addition, the vertical aerosol profile is obtained from MERRA-2 data.
Contagious Transformations? Inter-City Spreading of Sustainability Innovations.
Authors: Kitzmann Niklas H. , Donges Jonathan F. , Bai Xuemei , Lade Steven , Romanczuk Pawel , Winkelmann Ricarda
Published: March 2021

In the Anthropocene, socio-economic systems are an integral and highly interconnected part of Earth System. The internal dynamics of these systems will decide whether the Earth can remain in, or return to, a resilient state that resembles the Holocene. Understanding these dynamics thus represents an important aspect of Earth System Science.

To prevent the irreversible crossing of Planetary Boundaries, a rapid, global societal shift towards decarbonization and sustainability is imperative. Incremental political measures have thus far proven to be insufficient to adequately address this necessity. Social Contagion and Tipping Processes related to sustainable behavior and innovations represent some of the few promising mechanisms by which the societal and economic transformation may be achieved in the remaining window of opportunity.

Such contagion processes are not limited to individual human beings; in their high political responsiveness and cultural radiance, cities may also be viewed as promising agents in the sustainability transformation. Responsible for a dis-proportionally large part of greenhouse gas emissions, and simultaneously one of the main drivers of sustainable policy innovation and implementation, cities may play a unique role in the global sustainability transformation. Learning from each other to reduce, prepare for and react to the coming environmental changes, they can be conceptualized as nodes in a globe-spanning network. Investigating such a learning network model may yield insights into the social tipping dynamics that are so urgently needed to control the human impacts on the Earth System.

The study presented here aims to identify whether network-based contagion effects are dominant in sustainability policy adoption by cities. An attempt is made to approximate the inter-city innovation spreading network using the global air traffic network, political and trade relations, and other city-to-city connections. These networks are extracted from empirical data, and their prediction power is compared. We analyze the spreading of several municipal policies and innovations related to sustainability transformations as contagion processes on these inter-city networks. Surrogate data methods and a dose-response-contagion approach are used to identify network-spreading-correlations. We then investigate the nature of the spreading process by attempting to reproduce it using statistical models. Examples for investigated spreading innovations are the implementation of Bus Rapid Transit public transport systems, and membership in a sustainability organization.
Effective kinetics and phases saturation impact on surface reactions in porous media
Authors: Jimenez-Martinez Joaquin , Markale Ishaan , Velásquez-Parra Andrés
Published: March 2021

Coupling of unsaturated flows and surface reactions, including sorption and desorption, takes place in environmental contexts such as soils and the unsaturated zone. Lower sorption coefficients than those observed from batch experiments are found in natural soils. However, a deep understanding of this coupling is missing. To achieve this objective, we designed microfluidics experiments and performed direct numerical simulations based on experimental images at the microscale. We explore the effects of fluid flow dynamics and reaction kinetics on the effective kinetics. We have observed that an increase in the air volume within the porous medium promotes more heterogeneous fluid flow velocities, controlling the mixing of the transported reactant and resulting in a non-monotonic effective kinetic of the surface reaction.
Derivating forest structure from Sentinel-1 time series to assist forest fire risk assessments
Authors: Bruggisser Moritz , Dorigo Wouter , Dostálová Alena , Hollaus Markus , Navacchi Claudio , Schlaffer Stefan , Pfeifer Norbert
Published: March 2021

The assessment of forest fire risk has recently gained interest in countries of Central Europe and the alpine region since the occurrence of forest fires is expected to increase with a changing climate. Information on forest fuel structure, which is related to forest structure, is a key component in such assessments. Forest structure information can be derived from airborne laser scanning (ALS) data, whose value for the derivation of respective metrics at a high accuracy level has been demonstrated in numerous studies over the last years.

Yet, the temporal resolution of ALS data is low as flight missions are typically carried out in time intervals of five to ten years in Central Europe. ALS-derived forest structure descriptors for fire risk assessments, therefore, are often outdated. Open access earth observation data offer the potential to fill these information gaps. Data provided by synthetic aperture radar (SAR) sensors, in particular, are of interest in this context since this technology has a known sensitivity to the vegetation structure and acquires data independent of weather or daylight conditions.

In our study, we investigate the potential to derive forest structure descriptors from time series of Sentinel-1 (S-1) SAR data for a deciduous forest site in the Eastern part of Austria. We focus on forest stand height and fractional cover, which is a measure for forest density, as both of these components impact forest fire propagation and ignition. The two structure metrics are estimated using a random forest (RF) model, which takes a total of 36 predictors as input, which we compute from the S-1 time series. The model is trained using ALS-derived structure metrics acquired during the same year as the S-1 data.

We estimated stand height with a root mean square error (RMSE) of 4.76 m and a bias of 0.09 m at 100 m resolution, while the RMSE for the fractional cover estimation is 0.08 with a bias of zero at the same resolution. The spatial comparison of the structure predictions with the ALS reference further shows that the general structure is well reproduced. Yet, fine scale variations cannot be completely reproduced by the S1-derived structure products, and the height of tall stands and very dense canopy parts are underestimated. Due to the high correlation of the predicted values to the reference (Pearson’s R of 0.88 and 0.94 for the stand height and the fractional cover, respectively), we consider S-1 time series in combination with ALS data with low temporal resolution and machine learning techniques to be a reliable data source and workflow for regularly (e.g. < yearly) updating ALS structure information in an operational way.
Fast and localized temperature measurements during simulated earthquakes in carbonate rocks
Authors: Di Toro Giulio , Aretusini Stefano , Núñez-Cascajero Arántzazu , Spagnuolo Elena , Tapetado Alberto , Vasquez Garcia Maria Carmen
Published: March 2021

The understanding of earthquake physics is hindered by the poor knowledge of fault strength and temperature evolution during seismic slip. Experiments reproducing seismic velocity (~1 m/s) allow us to measure both the evolution of fault strength and the associated temperature increase due to frictional heating. However, temperature measurements were performed with techniques having insufficient spatial and temporal resolution. Here we conduct high velocity friction experiments on Carrara marble rock samples sheared at 20 MPa normal stress, velocity of 0.3 and 6 m/s, and 20 m of total displacement. We measure the temperature evolution of the fault surface at the acquisition rate of 1 kHz and over a spatial resolution of ~40 µmwith optical fibers conveying the infrared radiation to a two-color pyrometer. Temperatures up to 1250 °C and low coseismic fault shear strength are compatible with the activation of grain size dependent viscous creep.
Assessing succession stages and community distribution characteristics on mountainous ecosystem hosting coming winter Olympics games
Authors: Zhang Hengshuo , Yu Yang , Zha Tonggang
Published: March 2021

Alpine mountain ecosystem shows strong interactions between abiotic and biotic parameters. They also received high attention from human activities. Considering coming international events such as the Winter Olympic Games (WOG) and its human impacts, foreseeing uncontrolled ecosystem changes is key. In this research, the vegetation communities distribution under different conditions were modeled in the Yin Mountains in Chongli Country (China), the core area of the 2022 Winter Olympic Games. Firstly, we surveyed the key factors limiting the vegetation communities development to guide the vegetation restoration after major events in this region. After that, the vegetation succession stage was assessed using the Two-way indicator species analysis (TWINSPAN) and market basket analysis (MBA) to classify the vegetation communities. Plant community and relationships among environmental variables were investigated through the trend correspondence (DCA) and canonical correspondence analyses (CCA). The results show that soil moisture and organic matter could be considered the main factors limiting the development of shrub and herb communities. The distribution of different forest communities was mainly affected by geomorphological factors such as slope positions, aspect and inclination. In middle and high altitude areas, apart of arbor and shrub communities generally showed the process of transformation from the pioneer community to transitional community in the competition. We conclude that providing the basis to understand the environmental factors that restrict the development of vegetation communities in the northern Yin Mountains was helpful to foresee uncontrolled and coming impacts after the WOG.
Alternating wet-dry cycles rather than sulfate fertilization control pathways of methanogenesis and methane turnover in rice straw-amended paddy soil
Authors: Liu Qiong , Romani Marco , Wang Jiajia , Planer-Friedrich Britta , Pausch Johanna , Dorodnikov Maxim
Published: March 2021

Alternate wet-drying (AWD) and sulfate fertilization have been considered as effective management practices for lowering CH4 emissions from paddy soils. However, the effects of management practices on in situ belowground CH4 turnover (production and oxidation) are not yet fully understood. Here, soil CO2 and CH4 concentrations and their C isotope compositions were measured at three rice growing stages in straw-amended paddy soils with and without sulfate fertilization under continuously flooded conditions and two wet-dry-cycles. CH4 concentration reached 51.0 mg C L-1 at flowering stage under flooded conditions, while it decreased to 0.04 mg C L-1 under AWD. Relative enrichment of δ13C in CH4 and depletion of δ13C in CO2 under AWD indicated CH4 oxidation. Sulfate addition had no significant effect on CH4 concentration. The ample substrate supply might have prevented sulfate-reducing bacteria from out-competing methanogenic archaea and could therefore explain the absence of a fall in CH4 production. The δ13C-CO2 enrichment over time (7 ‰ and 5‰ with and without sulfate fertilizer, respectively) under flooded conditions likely indicates an increasing contribution of hydrogenotrophic methanogenesis to CH4 production with ongoing rice growth. Overall, the results showed that AWD could more efficiently reduce CH4 production than sulfate fertilization in rice-straw-amended paddy soils.

 
The influence of fracture networks on stability and geohazards of the Niagara Escarpment in southern Ontario
Authors: Formenti Serena , Peace Alexander , Waldron John , Eyles Carolyn , Lee Rebecca
Published: March 2021

The Niagara Escarpment is a geological feature comprised of highly fractured Ordovician and Silurian shales and carbonates stretching through southern Ontario and parts of the north-eastern United States. Differential erosion of the shale and carbonate strata has generated a steep cliff face bisecting the city of Hamilton, Ontario. Fractures occur throughout the cliff face and result in the formation of loose blocks of rock that are subject to erosion through rockfalls. This presents structural stability issues and an associated geohazard, which is of particular concern due to the proximity of the escarpment to city infrastructure. Previous work has alluded towards the role of geologic fractures in controlling erosion and stability of the Niagara Escarpment, but the causal mechanisms and extent to which these processes operate remains unclear. As such, the aim of this study is to quantify and analyse fracture networks using a combined field and numerical modelling-based approach to understand the distribution and nature of fractures throughout the escarpment, their connectivity, fluid flow properties, and relationship to structural stability. The location, orientation, and aperture of fractures were systematically quantified and documented around Hamilton. Data were plotted and analysed using the software Orient to identify clusters representative of fracture sets and to calculate average fracture set orientations and the respective confidence intervals. Three primary sets of geological fractures were identified including: 1) a near-vertical bedding confined set oriented north-south, 2) a near-vertical bedding confined set oriented east-west and 3) sedimentary bedding planes which have facilitated fracture migration and controlled resultant fracture geometry. Discrete fracture network modelling of these fracture sets in MOVE highlights their high degree of connectivity and indicates that the distribution and nature of these discontinuities are predominant controls on the locations and sizes of rock fragments generated on the cliff face resulting in rockfalls. Moreover, fracture-controlled porosity is a significant contributor to fluid flow throughout the escarpment. We conclude that geologic fractures present a first-order control on the stability of the Niagara Escarpment near Hamilton.