bluuebunny/crossref_metadata_2025 huggingface dataset:
Seasonal variation of nitrogen biogeochemical processes constrained by nitrate dual isotopes in cascade reservoirs, Southwestern China 
Authors: Chen Sainan , Yue Fu-Jun , Liu Xiao-Long , Zhong Jun , Yi Yuan-Bi , Wang Wan-Fa , Qi Yulin , Xiao Hua-Yun , Li Si-Liang
Published: March 2021

The increase of affected river reaches by reservoirs has drastically disturbed the original hydrological conditions, and subsequently influenced the nutrient biogeochemistry in the aquatic system, particularly in the cascade reservoir system. To understand the seasonal variation of nitrogen (N) behaviors in cascade reservoirs, hydrochemistry and nitrate dual isotopes (δ15N-NO3− andδ18O-NO3−) were conducted in a karst watershed (Wujiang River) in southwest China. The results showed that NO3−–N accounted for almost 90% of the total dissolved nitrogen (TDN) concentration with high average concentration 3.8 ± 0.4 mg/L among four cascade reservoirs. Higher N concentration (4.0 ± 0.8 mg/L) and larger longitudinal variation were observed in summer than in other seasons. The relationship between the variation of NO3−–N and dual isotopes in the profiles demonstrated that nitrification was dominated transformation, while assimilation contributed significantly in the epilimnion during spring and summer. The high dissolved oxygen concentration in the present cascade reservoirs system prevented the occurrence of N depletion processes in most of the reservoirs. Denitrification occurred in the oldest reservoir during winter with a rate ranging from 18 % to 28 %. The long-term record of surface water TDN concentration in reservoirs demonstrated an increase from 2.0 to 3.6 mg/L during the past two decades (~ 0.1 mg/L per year). The seasonal nitrate isotopic signature and continuously increased fertilizer application demonstrated that chemical fertilizer contribution significantly influenced NO3−–N concentration in the karst cascade reservoirs. The research highlighted that the notable N increase in karst cascade reservoirs could influence the aquatic health in the region and further investigations were required.
Effects of air quality on the health of Mediterranean forests
Authors: García Bruzón Adrián , Arrogante Funes Patricia , Muñoz Moral Laura
Published: March 2021

The climate change has turned out to be a determining factor in the development of forest in Spain. Production systems have emitted polluting gases and other particles into the atmosphere, for which some plants have not yet developed adaptation systems. Among the most harmful pollutants for the environment are gases such as nitrous oxides, ozone, particulate matter.

However, this condition is not the same in Peninsular Spain, and the Balearic Islands since the plant compositions differ in the territory and the bioclimatic, topographic, and anthropic characteristics. Monitoring the vegetation with sufficient spatial and temporal resolution, studying variables conditioning plant health is a challenge from the nature of the variables and the amount of data to be handled. 

The Mediterranean forest is one of the most ecosystem affected by climate change because of usually experimented long periods of drought that, in combination with increased temperatures, can drastically reduce the photosynthetic activity of trees and therefore the biomass of forests.

That is why the application of environmental technologies based on Remote Sensing (which provide plant health indices from passive sensors on satellite platforms and other variables of interest), Geographic Information Systems (to integrate, process, analyze spatial and temporal data) and machine learning models (which facilitate the extraction of relationships between variables, conditioning factors and predict patterns). 

In this regard, this work's objective is to evaluate the possible effect that different pollutants have on the health of the vegetation, measured from the annual values of the Normalized Difference Vegetation Index (NDVI), in the Mediterranean forests of Peninsular Spain. To achieve this, we are used machine learning techniques using the Random Forest algorithm. The study has also been done with various climatic, topographic, and anthropic variables that characterize the forest to carry it out. 

The results showed that certain variables such as the aridity index had generated the NDVI values and therefore plant development, while others are limiting factors such as the concentration of certain pollutants and the direct relationship between them particulates and NOx. This study can verify how the Random Forest algorithm offers reliable results, even when working with heterogeneous variables. 
Warning and evacuation, case studies from Japan, Philippines and Dominica
Authors: Faure Walker Joanna , Yore Rebekah
Published: March 2021

In order to be effective, warning systems need to both reach those at risk and prompt appropriate action. We study the efficacy of early warning systems in prompting residents to take appropriate action ahead of severe hazards in island countries that experience regular disasters, namely following the Great East Japan Earthquake and Tsunami in Japan, Typhoon Yolanda in The Phillippines, and Hurricane Maria in Dominica. All these events were extreme in their impact and in addition had aspects which surprised residents such as the size of the tsunami, the strom surge and the late change in intensity which provided challenges with warning. We find that multiple forms of warning are needed in order for the whole population to be reached as no one form of warning reaches everyone. The timing of the warning is important for evacuation decisions including who stays and who evacuates. It is important that the whole cycle of a warning system is considered, and that it is viewed as a process, such that we consider the scientific, communications, social and infrastructure aspects of warning systems.
Comparing methods to estimate chloride natural background levels to assess sea water intrusion
Authors: Pulido-Velazquez David , Baena-Ruiz Leticia , Voutchkova Denitza , Hansen Birgitte , Hinsby Klaus , Arnó Georgina , Camps Victor , Fernandes Judite , Retike Inga , Bikse Janis , Oude Essink Gualbet , Kroon Timo , Delsman Joost , Collados-Lara Antonio-Juan , Morel Ignacio , Luque Juan Antonio , Grima Juan
Published: March 2021

In order to assess the anthropogenic impacts on groundwater quality we generally need to identify the natural conditions or Natural background levels (NBLs) within groundwater systems, which are used as references to assess the evolution of the contamination status. This information, in addition to the threshold values (TVs), which are derived from NBLs and based on specific criteria values for legitimate water uses and the environment (terrestrial and aquatic ecosystems), is required to appropriately assess of the chemical status of groundwater in accordance with the European Water Framework Directive and to analyse and propose potential measures where they are required.

In literature, different methodologies are available to assess NBLs and reference TVs for different geochemical substances based on the available measurements of groundwater salinity (e.g. based on probability plots). In this work we analyze and compare three previously proposed methods for derivation of chloride NBLs, which is a conservation solute and is closely related to salt water intrusion in inland and coastal aquifers. We discuss and compare their applicability in pilots located in different settings (southern /northern European / Mediteranean/ North Sea /Baltic Sea) covering different typologies (detrital, karstic, fissured aquifers) and management issues (overexploitation, land use and land cover changes, etc). We perform sensitivity analysis to different constraints applied to remove samples affected by human activity (Nitrate and the brackish saline constraints) in the assessment of NBLs. Finally, based on this analysis, we propose a general approach for derivation of NBLs that could be applied to any of the tested pilots as well as other similar settings in Europe.

 

This research has been partially supported by the SIGLO-AN project (RTI2018-101397-B-I00) from the Spanish Ministry of Science, Innovation and Universities (Programa Estatal de I+D+I orientada a los Retos de la Sociedad).

This work has been partially supported by the GeoE.171.008-TACTIC and GeoE.171.008-HOVER projects from GeoERA organization funded by European Union’s Horizon 2020 research and innovation program.
Complex magmatic-tectonic interactions during the 2020 Makushin Volcano, Alaska, earthquake swarm
Authors: Roman Diana , Lanza Federica , Power John , Thurber Cliff , Hudson Thomas
Published: March 2021

We investigate the processes driving a significant earthquake swarm that occurred between June and December 2020 on Unalaska Island, Alaska, ~12 km southeast of the summit of Makushin Volcano. The swarm was energetic, with two M>4 events that were widely felt by the population in Dutch Harbor, ~ 15 km west of the epicenters. This is the strongest seismic activity ever recorded at Makushin since instrumental monitoring began in 1996. To date, no eruptive activity or other surface changes have been observed at the volcano in satellite views, webcam images, GPS or InSAR. Seismic swarms close to volcanoes are often associated with the onset of unrest that can lead to eruption. However, determining whether they reflect magmatic rather than tectonic stresses is challenging. Here, we integrate information from space-time patterns of the hypocenters of the swarm earthquakes with their double-couple fault-plane solutions (FPS). We relocate swarm events using double-difference relocation techniques and a 3D velocity model. We find that most of the events cluster into two perpendicular lineaments with NW-SE and SW-NE orientations, but no apparent migration in time towards a preferred fault. On the one hand, the lack of temporal migration (with both faults slipping concurrently), and FPS for M3+ events consistent with regional stresses, seem to indicate a tectonic driving process. On the other hand, FPS for the lower-magnitude earthquakes have 90°-rotated P-axes perpendicular to the regional principal stress orientation, providing strong evidence for dike inflation/magma intrusion. Coulomb stress modeling indicates that the rotated FPS are best explained by an inflating dike to the SW of the swarm epicenters, in a zone of long-term elevated seismicity. This complex overlapping of regional and magmatic stresses is also evident in the statistical analysis of the sequence, which started as a main-shock/aftershock sequence with the first event having the largest magnitude, and evolved into a swarm sequence indicative of a more pronounced role of magmatic processes.
High-resolution records of grain-size and depositional environment correlated to the Homo erectus Nariokotome Boy site, West Turkana, Kenya
Authors: O'Reilly Conner , Beck Catherine C. , van der Lubbe Jeroen H. , Feibel Craig S. , Wegter Bruce , Cohen Andrew S.
Published: March 2021

The Turkana Basin in northern Kenya contains a robust record of hominin fossils, including Nariokotome Boy (discovered from the NK3 site), the most complete H. erectus specimen found to date. Understanding the paleoenvironmental context in which hominins such as H. erectus evolved has been an objective of decades of research in eastern Africa. Here, we present a study using grain size analyses to infer the paleoenvironmental conditions responsible for the deposition of the sedimentary sequences directly associated with NK3. We resampled a ~14 m interval at from the West Turkana Kaitio (WTK13) core, collected as part of the Hominin Sites and Paleolakes Drilling Project. This interval ties directly to the outcrop where Nariokotome Boy was recovered. By sampling continuously at 0.5 cm intervals (~7 yrs/sample), we document the paleoenvironment in ultra high-resolution (i.e. a scale relevant to a hominin life) that directly correlates to the NK3 site. Over 350 sediment samples were pre-treated to remove carbonate, biogenic silica, and other organic material from detrital material. Grain size distributions were measured on a Malvern Mastersizer 3000 using wet suspension. Based on these analyses, the interval was dominated by silt, which was further investigated using end-member modeling. A four end-member solution explained on average 99% of the population variability. The bottom of the interval was more coarse-grained, with an abrupt fining transition at 38.83 meter below surface (mbsf), which corresponds with the transition out of a tuffaceous interval (Natoo tuff) and into a pedogenically modified interval. This correlation is significant as the top of this tuff is the surface upon which Nariokotome Boy was recovered. Previous facies and grain size analyses revealed and quantified Turkana’s dynamic lake level history. However, our grain size analysis provides unprecedented resolution for the paleoenvironment during which Nariokotome Boy lived. Our 0.5 cm sampling resolution enables us to quantify depositional changes on a scale comparable with previous descriptive facies analyses and to refine transitions between paleosols, fluvial deposits, and lacustrine deposition at the interface of these three paleoenvironments enabling us to reconstruct a dynamic lakeshore environment during the lifetime of the Nariokotome Boy.
The relative roles of Arctic and Antarctic sea-ice loss in the response to greenhouse warming
Authors: Hay Stephanie , Kusnher Paul
Published: March 2021

Antarctic sea ice has gradually increased in extent over the forty-year-long satellite record, in contrast with the clear decrease in sea-ice extent seen in the Arctic over the same time period. However, state-of-the-art climate models ubiquitously project Antarctic sea-ice to decrease over the coming century, much as they do for Arctic sea-ice. Several recent years have also seen record low Antarctic sea-ice. It is therefore of interest to understand what the climate response to Antarctic sea-ice loss will be. 

We have carried out new fully coupled climate model simulations to assess the response to sea-ice loss in either hemisphere separately or coincidentally under different albedo parameter settings to determine the relative importance of each. By perturbing the albedo of the snow overlying the sea ice and the albedo of the bare sea ice, we obtain a suite of simulations to assess the linearity and additivity of sea-ice loss. We find the response to sea-ice loss in each hemisphere exhibits a high degree of additivity, and can simply be decomposed into responses due to loss in each hemisphere separately. We find that the response to Antarctic sea-ice loss exceeds that of Arctic sea-ice loss in the tropics, and that Antarctic sea-ice loss leads to statistically significant Arctic warming, while the opposite is not true.

With these new simulations and one in which CO2 is instantaneously doubled , we can further characterize the response to sea-ice loss from each hemisphere using an extension to classical pattern scaling that includes three controlling parameters. This allows us to simultaneously compute the sensitivity patterns to Arctic sea-ice loss, Antarctic sea-ice loss, and to tropical warming. The statistically significant response to Antarctic sea-ice loss in the Northern Hemisphere extratropics is found to be mediated by tropical warming and small amounts of Arctic sea-ice loss.
Early humans in East Asia: Insights into climatic influence on human evolution
Authors: Zhu Rixiang
Published: March 2021

East Asia is a key area for probing into the interplay between Quaternary climate change and human adaptations to diverse terrestrial ecosystems. Integrated chronology based mainly on high-resolution magnetostratigraphy in conjunction with detailed biostratigraphy and high-precision isotopic dating of early humans and Paleolithic stone tools in mainland East Asia, western and southeastern Asia has provided insights into our understanding of climatic influence on human evolution in a variety of environments in the eastern Old World. For example, there is a prominent geographic expansion for early humans from low southern latitudes (e.g., tropical SE Asia and subtropical Yuanmou Basin and Bose Basin), through middle latitudes, to high northern latitudes (e.g., the Nihewan Basin). Especially, increased toolmaking skills and technological innovations are evident in temperate Nihewan Basin at the onset of the Mid-Pleistocene Climate Transition. The improved ability to adjust to diverse environments for early humans in East Asia has contributed to better understanding how climate change has shaped early human evolution.
Wet and dry plastic deposition in the western United States
Authors: Brahney Janice , Hallerud Margaret , Heim Eric , Hahnenberger Maura , Sukumaran Suja
Published: March 2021

Eleven billion tons of plastic are projected to accumulate in the environment by 2025. Because plastics are persistent, they fragment into pieces that are susceptible to wind entrainment. Using high resolution spatial and temporal data we tested whether plastics deposited wet versus dry have unique atmospheric life histories. Further, we report on the rates and sources of deposition to remote U.S. conservation areas. We show that urban centers and resuspension from soils or water are important sources for wet deposition. In contrast, plastics deposited dry were smaller in size and rates were related to indices that suggest longer range or global transport. Deposition rates averaged 132 plastics m-2 day-1 amounting to > 1000 tons of plastic deposition to western U.S. protected lands annually.
Geophysical signature of the alpine slab: Field analogues and direct models 
Authors: Sonnet Manon , Labrousse Loïc , Bascou Jérôme , Plunder Alexis
Published: March 2021

Recent geophysical data (receiver functions and body wave tomography) in the Alps show the continuity of the alpine dipping slab with the lower continental crust of the European plate. The eclogitization of the continental crust is often mentioned to explain its signature and its disappearing in the mantle beneath 80 km.

The aim of the present study is to use potential lithological analogues sampled in the outcropping European crust to directly predict the seismic properties of the buried crust. Here, we focus on mafic intercalations, present in the variscan basement series of the external crystalline massifs. We compare them with acknowledged generic chemical compositions for the continental lower crust or regional granulite facies rock units. Using the bulk rock chemistries of these samples and representative rocks, we calculate pressure-temperature on which we represent the seismic velocities (Vp, Vs ot Vp/Vs) assuming that the rocks have completely rebalanced during burial. In these diagrams, the main seismic contrasts seem to match the onset of jadeite formation (mostly Vp/Vs diagram), as well as the boundaries of the garnet and omphacite stability fields.

Considering the selected rocks are relevant analogues, we then compare the evolution of the seismic properties along the top of the alpine dipping slab with the profiles deduced from recent Vp and Vs tomography models (CIFALPS and AlpArray), varying the effective thermal profile of the Alpine slab, its reaction rate and its overall chemistry. Preliminary results suggest the Alpine lower crustal slab inherited most of his properties from its burial stage, with limited impact of subsequent evolution.
Now you see me... : Impact of sample representativity in fracture network characterization.
Authors: Nazari Vanani Fatemeh , Fernandez Oscar
Published: March 2021

Adequately characterizing the properties of a fracture network is the first step in accurately modelling its behavior, be it mechanically or hydraulically. Characterizing fracture networks requires determining fracture frequency, orientation, connectivity, and fracture properties. This becomes particularly challenging in subsurface systems, where hard data on fracture networks comes mainly from boreholes, that are samples of very limited volume in relation to the fracture network. Because of this scale relationship between sample dimension and the dimension of natural fracture networks, boreholes capture a very partial picture of the fracture network. This is particularly relevant when attempting to estimate fracture frequency and network connectivity from borehole data. Corrections are normally used to account for sampling bias related to fracture size and orientation. Whereas these corrections are valid for the sample itself, the topology and heterogeneity of fracture networks means that measurements obtained in any given borehole are not necessarily representative of the broader fracture network.

To determine how “wrong” single-borehole analyses can be, we have conducted experiments on synthetic datasets to quantify how representative borehole samples are of entire fracture networks. Results show that properties that have an impact on the anisotropy of the fracture network (orientation, number of fracture sets) can be accurately resolved even in low data-density scenarios. On the contrary, accurately determining fracture frequency (which also impacts connectivity) for the entire fracture network is strongly dependent on the ratio between fracture frequency and the sampled volume. Measurements of fracture frequency in individual boreholes indicate that it frequency easily be overestimated or underestimated by a factor of 2 relative to the real network’s fracture frequency. The application of sampling bias corrections has a limited impact on reducing this error.

Based on the results from our experiments, we present methods to assess how representative of a fracture network a single borehole is. Representativity can be translated into uncertainty in fracture frequency, a metric that can be used in fracture modelling.
Control of obliquity directions on structural development, from rifting to inversion: Examples from the Tethyan domain
Authors: Fernández Oscar , Ramos Adrià , García-Senz Jesús , Pedrera Antonio
Published: March 2021

Oblique rift systems form when the axis of rifting is not orthogonal to the direction of tectonic extension, normally due to pre-existing zones of weakness that influence the location and orientation of new faults. Irrespective of the regional-scale obliquity, most individual extensional faults will tend to nucleate according to the orientation of the tectonic stress orientations, and therefore normal to the direction of maximum extension. Transfer faults in oblique systems will tend to form parallel to the direction of extension and, in contrast to orthogonal rifting, will play a major role in the architecture and development of the rift and its sedimentary basins.

An intriguing feature in oblique rift systems is the formation of reverse structures evocative of wrench tectonics during the syn-rifting stage. This stems from the orientation of geological structures relative to the direction of tectonic extension. Even slight changes in tectonic transport direction or stress orientations during the development of the rift system can lead to events of transpression or transtension along transfer structures. Because of the relevance of transfer structures in oblique systems, transpression can result in the appearance of discontinuities in the sedimentary record that are often interpreted as, somewhat incongruent, inversion events.

Oblique structures also play a crucial role during the full inversion of the rift system during convergence, particularly so because tectonic shortening will strike at an angle to the orientation of faults. Irrespective of the evolution of oblique rifting and inversion, the initial fault pattern is also normally preserved in fully inverted systems involved in fold-and-thrust systems. In many of cases, when the original rift obliquity is not well understood, the characteristic rhomboidal pattern is interpreted to relate to wrench tectonics.  In this presentation we will review evidence from Iberia, Northwestern Africa and the Eastern Alps to discuss the role that obliquity plays in rift development and its inheritance in fold-and-thrust belts with different degrees of inversion.
Assessing Water Availability for Development in Africa using GRACE Satellites
Authors: Scanlon Bridget R , Rateb Ashraf , Xie Hua
Published: March 2021

Access to water is a critical issue in Sub-Saharan Africa. The objective of our work was to assess spatiotemporal variability in water storage using GRACE satellites in the major aquifers and potential for development. Results show that Total Water Storage (TWS) variability tracked by GRACE satellites is dominated by interannual variability in most aquifer systems driven by dry and wet climate cycles, such as El Nino Southern Oscillation, Indian Ocean Dipole, Pacific Decadal Oscillation and others. Climate cycles result in systems being subjected to droughts or floods, which is challenging for water resources management. Linear trends in TWS were limited to west Africa attributed to land use change and north Africa linked to water use. Variability in storage of some reservoirs and groundwater hydrographs is similar to storage variability from GRACE satellites. Examples of approaches toward sustainable management of water resources include storage of excess flood water for use during droughts in surface reservoirs, conjunctive use of surface water and groundwater, and managed aquifer recharge. Understanding the linkages between climate cycles and water storage should help optimize water management within this framework.
Towards operational use of satellite SO2 measurements in a volcano observatory
Authors: Epiard Matthieu , Carn Simon
Published: March 2021

Along with monitoring of seismic activity and ground deformation, the measurement of volcanic gas emissions and composition plays a key role in the surveillance of active volcanoes and the mitigation of volcanic hazards. Volcanic gas emissions also potentially impact the environment, human health and climate, providing further motivation for study. Currently, volcano observatories typically employ ground-based or airborne techniques to monitor volcanic gas emissions, mainly sulfur dioxide (SO2) fluxes and its ratios over other species (e.g., CO2, H2S). However, in recent years there have been significant breakthroughs in satellite observations of passive volcanic SO2 emissions, including high-resolution ultraviolet (UV) measurements from the Tropospheric Monitoring Instrument (TROPOMI) on the Sentinel-5 Precursor (S5P) satellite, and the development of long-term records of volcanic SO2 degassing from the Ozone Monitoring Instrument (OMI) on NASA’s Aura satellite. Satellite measurements offer some advantages over traditional gas monitoring techniques, e.g., synoptic coverage of large regions, relative immunity to variations in wind direction, and ability to map the spatial extent and dispersion of volcanic SO2 plumes with applications for health hazard mitigation. Although these satellite datasets are potentially valuable for active volcano monitoring and as a supplement to other gas monitoring techniques, significant barriers remain to their use at many volcano observatories, particularly in low-income countries. Notably, the increasing volume of satellite datasets (NASA’s database is bigger than 3 petabytes) and the demands of data processing represent challenges to their operational use at observatories with limited internet connectivity or computational capacity. Here, we present an ongoing effort to develop open-source Python software to access and process SO2 data directly through NASA’s Earthdata portal Application Processing Interface (API), in order to streamline the satellite SO2 data processing workflow for a volcano observatory. By allowing server-side satellite data subsetting around the volcano of interest, this API greatly reduces the processing burden and only requires an internet connection to the NASA server hosting the required datasets (including S5P/TROPOMI, Aura/OMI and many others). We present some examples of software output and potential applications. Our current goal is to deploy and test the software for operational use in a volcano observatory.  
Characterizing solar supergranulation using the bispectrum: Convection or wave turbulence?
Authors: Böning Vincent
Published: March 2021

Turbulent convection is generally believed to occur on the Sun on three different characteristic length scales. These are the smaller granulation scale, the intermediate supergranulation scale, and the potentially existing giant cell scale. While granulation is mostly understood, there are several competing theories for the emergence of supergranules as a characteristic length scale and coherent phenomenon. While the prevailing approaches assume a convective origin of supergranulation, others follow the path of a potential wave-like behaviour of these features, because the power spectrum of supergranulation seemingly follows a dispersion relation. Since supergranulation shows an asymmetry in up and downflows, it is clear that non-linear affects must play a role in its evolution, which create a characteristic observed skewness in the divergence of the horizontal motions at the solar surface. Supergranulation may thus as well be a non-linear wave or an example of wave turbulence. While the power spectrum of supergranulation is reasonably constrained by observations, we here present an observational characterization of the non-linearities involved in creating supergranules. We characterize the spatial pattern of solar supergranulation using a third-order correlation in Fourier space, the bispectrum. We find that the strongest non-linearity is present when the three coupling wave vectors are all at the supergranular scale. These are the same wave vectors that are present in regular hexagons, which have been used in analytical studies of solar convection. At these Fourier components, the bispectrum is positive, consistent with the positive skewness in the data and consistent with supergranules preferentially consisting of outflows surrounded by a network of inflows. We use the bispectral estimates to generate synthetic divergence maps that are very similar to the data. Using this method, we estimate the fraction of the variance in the divergence maps from the nonlinear component to be of the order of 4–6%. We conclude by discussing the implications of our study on the question whether supergranulation is rather a convective feature or an example of wave turbulence.
Virtual Advocacy Days for Science in Times of Crisis: Communications and Engagement Influencing Decision-Making
Authors: Villafranca Michael , Webster Brittany , Landau Elizabeth
Published: March 2021

Communicating the value of science to policymakers has never been more importance, but how do you make a difference while adhering to new norms for physical distancing? Regardless of one’s level of technological aptitude, and no matter if time constraints exist, scientists can still effectively communicate the value of their science to policymakers through virtual means. The Public Affairs team from the American Geophysical Union will share lessons learned from several virtual advocacy events held in 2020 and will cover a few communications strategies for influencing policymakers through virtual science policy engagements—from virtual meetings with policymakers to social media to traditional media.
Feature-based classification of European windstorms
Authors: Passow Christian , Ulbrich Uwe , Rust Henning
Published: March 2021

Scientific work on European windstorms mainly focused on local damages, location (tracks), temporal evolution or the overall severity, often measured by severity indices of di erent de nitions. Each of the aforementioned windstorm properties is directly related to important characteristics within the windstorm itself, such as wind speed, duration, spatial extent or internal variability. Variation or changes within these characteristics are therefore defining aspects in the spatial and temporal evolution of windstorm. As a step towards a better understanding of such variations, we classify windstorms based on these characteristics using Quasi-Supervised K-Means clustering, a novel procedure that was specifically developed by us to cluster windstorm tracks based on a reference windstorm catalog. One of the resulting clusters, containing 300 out of more than 2000 storm tracks over the North Atlantic and Europe, includes the tracks of the 20 most severe storm events according to the XWS catalog. This cluster is further
examined to identify common characteristics of the large scale situations that determine the cluster characteristics.
Thermodynamic-informed machine learning for pressure-sensitive plasticity model
Authors: Sun WaiChing , Vlassis Nikolas
Published: March 2021

This talk will present a machine learning framework that builds interpretable macroscopic surrogate elasto-plasticity models inferred from sub-scale direction numerical simulations (DNS) or experiments with limited data. To circumvent the lack of interpretability of the classical black-box neural network, we introduce a higher-order supervised machine learning technique that generates components of elasto-plastic models such as elasticity functional, yield function, hardening mechanisms, and plastic flow. The geometrical interpretation in the principal stress space allows us to use convexity and smoothness to ensure thermodynamic consistency. The speed function from the Hamilton-Jacobi equation is deduced from the DNS data to formulate hardening and non-associative plastic flow rules governed by the evolution of the low-dimensional descriptors. By incorporating a non-cooperative game that determines the necessary data to calibrate material models, the machine learning generated model is continuously tested, calibrated, and improved as new data guided by the adversarial agents are generated. A graph convolutional neural network is used to deduce low-dimensional descriptors that encodes the evolutional of particle topology under path-dependent deformation and are used to replace internal variables. The resultant constitutive laws can be used in a finite element solver or incorporated as a loss function for the physical-informed neural network run physical simulations.
Flash drought in Australia: deriving a long-term climatology from drought metrics based on precipitation, evapotranspiration, and evaporative demand.
Authors: Hobbins Mike , Parker Tess , Gallant Ailie , Hoffmann David
Published: March 2021

Until the scientific community coalesces around a consensus definition of flash drought, we might usefully distinguish them from “ordinary” droughts by applying a criterion of a rapid intensification from near-normal soil moisture to drought conditions over a period of a few weeks. Here, we use such a definition to generate the first spatially distributed, long-term climatology of flash droughts across Australia, which we derive using a suite of indices that capture both the supply and the demand perspectives of drought: evaporative demand describes the atmospheric demand for moisture from the surface; precipitation, the supply of moisture from the atmosphere to the surface; and evaporative stress, the supply of moisture from the surface relative to evaporative demand.

Regardless of metric-based definition, flash droughts are observed across all seasons. They can terminate as rapidly as they start, but in some cases can eventuate in a seasonal-scale drought. We show that flash-drought variability and its prevalence can be related to ENSO phases, which suggests an opportunity for enhanced seasonal-scale prediction. We examine a case study in the Wimmera Region of southeast Australia (around the South Australia / Victoria border), we show that monitoring precipitation is less useful for capturing the onset of flash drought. Instead, indices that capture the demand perspective of drought--such as the Evaporative Demand Drought Index (EDDI) and Evaporative Stress Index (ESI)--are more useful for monitoring flash-drought development.
Ocean sulfate scarcity as a pre-condition for Large Igneous Province driven mass extinction
Authors: Newton Robert J. , He Tianchen , Dal Corso Jacopo , Wignall Paul , Mills Ben , Dunhill Alex
Published: March 2021

Records of sulfur cycling during mass extinction events increasingly show that they are associated with rapid shifts in the sulfur isotope composition of seawater indicative of low concentrations of ocean sulfate [1-4]. These events are also often associated with the spread of anoxic conditions in the marine realm. We propose a feedback mechanism whereby the production of methane in marine sediments increases in proportion to decreasing sulfate and consumes bottom water oxygen, thus acting as a positive feedback on spread of anoxic waters. This can be further amplified via increased weathering or recycled fluxes of phosphate enhancing productivity [e.g. 5], the effects of increasing temperature on the rate of methanogenesis and the additional suppression of marine sulfate via increased pyrite burial.

We propose that sulfate drawdown occurs prior to climate forcing and other extinction drivers imposed by large igneous province (LIP) eruption. The likely mechanism for the drawdown of sulfate prior to these extinction is the removal of sulfate from the oceans as gypsum in evaporite deposits. Several large mid-Phanerozoic mass extinctions have clear evidence of increased evaporite deposition prior to, or approximately coincidental with LIP eruption and extinction.

If this idea is correct, the biological impact of a LIP will partly depend on the sulfate status of the ocean at the time of its eruption, and may at least partly explain the observation that whilst many mass extinctions are associated temporally with a LIP, not all LIPs seem to cause mass extinctions.

1. Newton, R.J., et al., Geology, 2011. 39(1): p. 7-10.

2. Song, H., et al., Geochimica et Cosmochimica Acta, 2014. 128(0): p. 95-113.

3. Witts, J.D., et al., Geochimica et Cosmochimica Acta, 2018. 230: p. 17-45.

4. He, T., et al., Science Advances, 2020. 6(37): p. eabb6704.

5. Schobben, M., et al., Nature Geoscience, 2020. 
Monitoring changes in carbon pools matched to land use and land-use change based on field sampling measurements
Authors: Petersson Hans , Breidenbach Johannes , Ellison David , Lundblad Mattias , Appiah Mensah Alex
Published: March 2021

Changes in carbon pools, land use and land-use change can be monitored based on field inventoried sampling units without using maps or remote sensing products. One way is to use a sampling framework. The framework can be based on a map, but the map does not necessarily need to be used for improving the estimates. The map can consist of a Member state’s total land and freshwater area. The sampling units can be distributed using a systematic grid with randomized location in the framework. A permanent design (the same sample units are re-inventoried in a periodic cycle) has been proven efficient when estimating change. Stratification into assumed homogenous strata is another way to further improve the accuracy of estimates. The distribution of sampling units can be spatially explicit (geo-referenced) in the sense that their locations are identified using GPS. This, combined with the permanent design, makes it possible to estimate both gross and net land use transfers in order to provide a land use matrix. The area-based sampling combined with the Horvitz and Thompson-estimator, makes a sampling unit representative of a certain area and all sample units together comprise the total land and freshwater area. This design makes it possible to match changes in carbon pools to land use and land-use change and to trace them back in time. 

We present a monitoring design based on the Swedish NFI and adapted to reporting under the UNFCCC/KP frameworks or the EU-regulation. Pros and cons are discussed and we compare with alternative designs (combining ground truth with remote sensing). Finally, we assess the accuracy of estimates of selected variables (sample and model errors).
Collecting geochemical data of deep formation fluids for Geothermal Fluid Atlas for Europe
Authors: Kieling Katrin , Regenspurg Simona , Kovács Károly , Fekete Zsombor , Sánchez Miravalles Alberto , Madarász Tamás , Hartai Éva
Published: March 2021

Most problems in deep geothermal operations are related to the chemistry of the geothermal fluid, which might cause deleterious physical and chemical reactions such as degassing and mineral precipitation or corrosion. However, data related the fluid properties are still scarce, largely as a consequence of the difficulty in determining these properties at in situ geothermal conditions, and the fact that those data are scattered across countries and often the “property” of commercial operators of geothermal power plants.

The EU H2020 project REFLECT aims to collect existing and new data on geothermal fluids across Europe through field measurements, detailed lab experiments simulating in situ conditions, and by calculations. These data will be implemented in case-specific predictive models simulating reactions at geothermal sites, as well as in a European geothermal Fluid Atlas.

To harmonize the metadata information for different fluid samples, REFLECT partners plan to register IGSNs (International Geo Sample Numbers) for fluid and reservoir rock samples collected and analysed within the project. The IGSN is a unique sample identifier, i.e. it is the equivalent to a DOI for publications. It was originally developed for drill cores and extended for various sample types, including fluid samples (seawater, river or lake water, hydrothermal fluids, porewater). Registration of fluid and rock samples with an IGSN will help to allow making the data accessible and re-usable even if the fluid sample itself is destroyed.

All data produced and collected within REFLECT form the base of the European Geothermal Fluid Atlas, which will include query and filtering tools to explore the database with a GIS based map visualization. The Atlas makes the data accessible to the geothermal community and the general public. The aim is to create a database, which can easily be integrated into other databases, such that the Fluid Atlas can be an addition to already existing initiatives of geological data collection.
Using the learnings of machine learning to distill cloud controlling environmental regimes from satellite observations
Authors: Douglas Alyson , Stier Philip
Published: March 2021

Cloud processes are the leading source of uncertainty in our current global climate models. Therefore understanding cloud formation, lifetime, and decay remains pivotal in order to reduce uncertainty in our global climate models future projections. Exploiting over ten years of satellite observations, the relationships between cloud properties and environmental factors, including aerosols, can be better understood and clustered into environmental regimes. We cluster regimes based on the regional strength of the relationships between the environment and cloud properties revealed using a random forest. Numerous processes, such as stratocumulus to cumulus transitions, may be constrained by the environmental regimes revealed by our analysis. Our results show that depending on the region, aerosol and the environment work to determine the baseline cloud properties. These observation based regimes can be compared to regimes derived from global climate models to understand how well model parameterizations capture the cloud controlling factors.
A Novel Method for Correction of Slope-Induced Errors in Radar Altimetry
Authors: Li Weiran , Slobbe Cornelis , Lhermitte Stef
Published: March 2021

Satellite altimetry has been an important tool for observing the cryosphere. Various radar altimetry missions including CryoSat-2, Sentinel-3, and AltiKa have been exploited to measure ice-sheet elevation or to capture ice-sheet anomalies (e.g. the extensive melt in Greenland in 2012). These studies usually serve for understanding the change and status of the ice sheet, thus require highly accurate height measurements. However, multiple error sources exist that significantly lower the accuracy of the radar altimeter-derived heights. A potential multi-meter source of error is the slope-induced error caused by the undulating topography within the kilometre-wide pulse-limited footprint. The topography directs the reflecting point of radar pulse from the nadir to the point on the ground that is closest to the satellite. 

To correct for this error, different methods have been developed to determine the impact point, which all rely on footprint assumptions: e.g. slope-method, which assumes a constant slope within the footprint, or the refined point-based method, which assumes a fixed footprint size and defines the reflecting point as the shortest mean range of points within each assumed footprint. Each of these methods have shortcoming as they either neglect the actual topography or the actual footprint that can be estimated by a combination of the leading edge and topography.

To overcome this shortcoming, we present a novel Leading Edge Point-Based (LEPTA) method that corrects for the slope-induced error by including the leading edge information of the radar waveform to determine the impact point. The principle of the method is that only the points on the ground that are within range determined by the begin and end of the leading edge are used to determine the impact point. This requires the assistance of a high-resolution DEM, e.g. 100m resolution. To assess the performance of the LEPTA method, we adopt it to all CryoSat-2 LRM acquisitions over Greenland in 2019 and benchmark it to the slope- and point-based method. To evaluate the results, we use the newly-launched laser altimeter, ICESat-2. 

Validation results show that heights obtained by LEPTA have good agreements with ICESat-2 height observations, both in the flat, interior regions of Greenland and in regions with more complex topography. The median difference between the slope-corrected CryoSat-2 heights and the ICESat-2 heights is almost negligible, whereas the other methods can have a 0.22m and 0.69m difference, and the Level-2 data provided by ESA have a 0.01m difference. The median absolute deviation, which we use as an indicator of the variation of errors, is also the lowest in LEPTA (0.09m) in comparison to the aforementioned methods (0.22m and 0.13m) and ESA Level-2 data (0.15m). Based on that, we recommend considering LEPTA to obtain accurate height measurements with radar altimetry data, especially in regions with complex topography.