bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrating intensity and context for improved supervised river ice classification from dual-pol Sentinel-1 SAR data 
Authors: de Roda Husman Sophie , van der Sanden Joost J. , Lhermitte Stef , Eleveld Marieke A.
Published: March 2021

River ice is a major contributor to flood risk in cold regions due to the physical impediment of flow caused by ice jamming. Although a variety of classifiers have been developed to distinguish ice types using HH or VV intensity of SAR data, mostly based on data from RADARSAT-1 and -2, these classifiers still experience problems with breakup classification, because meltwater development causes overlap in co-polarization backscatter intensities of open water and sheet ice pixels.

In this study, we develop a Random Forest classifier based on multiple features of Sentinel-1 data for three main classes generally present during breakup: rubble ice, sheet ice and open water, in a case study over the Athabasca River in Canada. For each ice stage, intensity of the VV and VH backscatter, pseudo-polarimetric decomposition parameters and Grey Level Co-occurrence Matrix texture features were computed for 70 verified sample areas. Several classifiers were developed, based on i) solely intensity features or on ii) a combination of intensity, pseudo-polarimetric and texture features and each classifier was evaluated based on Recursive Feature Elimination with Cross-Validation and pair-wise correlation of the studied features.

Results show improved classifier performance when including GLCM mean of VV intensity, and VH intensity features instead of the conventional classifier based solely on intensity. This highlights the importance of texture and intensity features when classifying river ice. GLCM mean incorporates spatial patterns of the co-polarized intensity and sensitivity to context, while VH intensity introduces cross-polarized surface and volume scattering signals, in contrast to the commonly used co-polarized intensity.

We conclude that the proposed method based on the combination of texture and intensity features is suitable for and performs well in physically complex situations such as breakup, which are hard to classify otherwise. This method has a high potential for classifying river ice operationally, also for data from other SAR missions. Since it is a generic approach, it also has potential to classify river ice along other rivers globally.  
Flood-prone areas delineation in coastal regions using the Geomorphic Flood Index
Authors: Albertini Cinzia , Miglino Domenico , Iacobellis Vito , De Paola Francesco , Manfreda Salvatore
Published: March 2021

Detecting areas exposed to flood inundation in coastal zones is of paramount importance for reducing damages and preventing human and economic losses. In general, the Geomorphic Flood Index (GFI) method, based on a Digital Elevation Model (DEM) and mostly applied to riverine flood, provides a good representation of flood-prone areas with low requirements in terms of data, time and costs. However, the method does not account for inter-basin floodwater transfers and, therefore, performs poorly on coastal basins. The present work addresses this shortcoming by explicitly taking into account these potential inter-basin water transfers. We applied the GFI method with this new feature to a coastal basin located in southern Italy and the outcome was compared with a flood inundation map obtained by a two-dimensional hydraulic simulation for a return period of 300 years. Its transferability was tested in a second adjacent coastal basin using a threshold binary classification and the sensitivity of the methodology to the return period was investigated. Results show that coastal flood-prone areas are successfully delineated with performance metrics above 93%. This achievement represents a step further in the application of the GFI method, that can help stakeholders in flood risk management to rapidly and inexpensively characterize hazard-prone areas.
Uncovering the contribution of permafrost thaw to the enhanced terrestrial organic matter input into the Bay of Biscay during the last deglaciation
Authors: Queiroz Alves Eduardo , Wang Yunyi , Hefter Jens , Grotheer Hendrik , A. F. Zonneveld Karin , Mollenhauer Gesine
Published: March 2021

The thawing of permafrost in the polar regions has important implications for climate on Earth. Indeed, permafrost degradation results in a positive climate feedback which is currently aggravated by human action. The dynamic character of Earth’s climate means that past trends and variability can be examined to improve future projections of this effect. Notably, the permafrost zone that covered parts of Europe during the Last Glacial Maximum (LGM) is currently absent, indicating that this region is a crucial area for the study of permafrost carbon remobilization during the last deglacial warming. Here, we investigate the mobilization of permafrost material to the Bay of Biscay, off the English Channel. Although this location has been shown to have experienced an enhanced deposition of terrigenous material during the last deglaciation, the contribution of permafrost thaw is unknown. We have established an accurate and robust chronological framework for this deposition, showing enhanced rates of sediment accumulation from approximately 20.2 to 15.8 kcal BP. Biomarker analysis has revealed periods of marked increases in terrigenous input, namely from approximately 20.5 to 19 and from 19 to 16.5 kcal BP. Moreover, by performing compound specific radiocarbon dating on n-alkanoic acids isolated from the sedimentary archive, we have been able to determine the origin of organic matter deposited at the core location. Our results will help researchers to assess to what extent permafrost thaw contributed to the peak of organic matter deposition present in the marine sediment, allowing us to sharpen our understanding of the mechanisms of permafrost carbon mobilization.
Detecting land deformation due to groundwater changes with InSAR observations - the case of the island of Gotland, Sweden
Authors: Darvishi Mehdi , Jaramillo Fernando
Published: March 2021

In the recent years, southern Sweden has experienced drought conditions during the summer with potential risks of groundwater shortages. One of the main physical effects of groundwater depletion is land subsidence, a geohazard that potentially damages urban infrastructure, natural resources and can generate casualties. We here investigate land subsidence induced by groundwater depletion and/or seasonal variations in Gotland, an agricultural island in the Baltic Sea experiencing recent hydrological droughts in the summer. Taking advantage of the multiple monitoring groundwater wells active on the island, we explore the existence of a relationship between groundwater fluctuations and ground deformation, as obtained from Interferometric Synthetic Aperture Radar (InSAR). The aim in the long-term is to develop a high-accuracy map of land subsidence with an appropriate temporal and spatial resolution to understand groundwater changes in the area are recognize hydroclimatic and anthropogenic drivers of change.

We processed Sentinel-1 (S1) data, covering the time span of 2016-2019, by using the Small BAseline Subset (SBAS) to process 119 S1-A/B data (descending mode). The groundwater level of Nineteen wells distributed over the Gotland island were used to assess the relationship between groundwater depletion and the detected InSAR displacement. In addition to that, the roles of other geological key factors such as soil depth, ground capacity in bed rock, karstification, structure of bedrock and soil type in occurring land subsidence also investigated. The findings showed that the groundwater level in thirteen wells with soil depths of less than 5 meters correlated well with InSAR displacements. The closeness of bedrock to ground surface (small soil depth) was responsible for high coherence values near the wells, and enabled the detection land subsidence. The results demonstrated that InSAR could use as an effective monitoring system for groundwater management and can assist in predicting or estimating low groundwater levels during summer conditions.
Investigating the drivers of Helheim Glacier’s variability from 2007 to 2020
Authors: Cheng Gong , Morlighem Mathieu
Published: March 2021

At least half of today’s mass loss of the Greenland ice sheet is due to the retreat of tidewater glaciers. For example, Helheim Glacier, in southwest Greenland, has one of the largest ice discharge records in the Greenland ice sheet during the previous decade. While there is broad agreement that the intrusion of warmer current in the Sermilik Fjord triggers the acceleration and retreat of this marine terminating glacier, other processes such as changes in basal conditions, surface mass balance or calving dynamics may have also played important roles in controlling the retreat of these glaciers. However, our understanding of these processes and their contributions to the retreat and acceleration of the glaciers remains still limited. The individual contributions of these processes have not been quantified, which makes it difficult to determine which of these processes should be included in ice sheet models to correctly capture the present and future retreat and associated mass loss of the ice sheet. Here, we simulate the dynamics of Helheim Glacier from 2007 to 2020 using the Ice-sheet and Sea-level System Model (ISSM) to investigate the model response to changes in external forcings and boundary conditions, such as basal friction, surface mass balance, ice rheology, and ice-ocean interactions at the calving front. The relative importance of each mechanism to the model is quantified within a series of perturbation experiments. We evaluate the ability of the model to match surface speed and terminus position from the observations collected during the simulation period. Preliminary results suggest that Helheim’s dynamics is relatively insensitive to the choice of friction law or the surface mass balance, but that the position of the calving front and changes in basal sliding conditions are critical to explain the high variability of Helheim’s surface speed. This study, as a result, can be used as a guide for model development of similar glaciers.
Comprehensive palaeomagnetic study of San Borja and Jaraguay monogenetic volcanic fields, Baja California (28–30°N): considerations on latitudinal corrections
Authors: Mahgoub Ahmed Nasser , García-Amador Bernardo Ignacio , Alva-Valdivia Luis Manuel
Published: March 2021

We report 24 palaeomagnetic directions and 10 high-quality Thellier-derived palaeointensity (PI) values, obtained from 27 sites located in Baja California Peninsula, northwestern Mexico. Sampling was done in four rock units (magnesian andesites, calc-alkaline lavas, ignimbrites, adakites) belonging to San Borja and Jaraguay monogenetic volcanic fields. These units were erupted between ~ 15 and 2.6 Ma (previous K-Ar and 40Ar/39Ar data), hence results are presented in two consecutive periods: middle-late Miocene and Pliocene. Based on previous geological and geophysical records, the kinematic evolution of the region was carefully considered, allowing for the independent restoration of the palaeoposition of each sampled site. The identified main magnetic minerals are titanomagnetite, magnetite, and minor hematite, of variable grain size, present as intergrowths, which reflect varying oxidation/reduction conditions during emplacement of high-temperature magmas. We did not observe a clear relationship between the magnetic properties of the different sites and their success rate for PI experiments. This is with the exception of the FORC analysis which showed a fairly good correlation with PI success. Pliocene (Dec=359.2°; Inc= 47.4°; α95=7.6°; and k= 41.43) and Middle-late Miocene (Dec=353.9°; Inc= 38.5°; α95=9.2°; and k= 28.56) mean directions were calculated from 20 sites (10 sites per period), and PI mean values of 29.2 ± 9.1 μT and 23.2 ± 6.3 μT were determined for the two periods, respectively. Compiling global filtered PI data, together with our results, indicates that the strength of the geomagnetic field during middle-late Miocene was weak (virtual dipole moment = 5.0±2.2×1022 Am2) compared to Pliocene (6.4±2.8× 1022 Am2), and also relative to the present-day value (7.6 × 1022 Am2). This indicates the global nature of the low dipole moment during the middle-late Miocene, which is consistent with what was previously concluded that from the past 30 Ma to the present time the magnetic field strength has increased. However, issues related to the Spatio-temporal distribution of PI data still present an obstacle to validating these suggestions; therefore, more reliable data are still needed.
The western termination of the South Pyrenean Triangle Zone; a structural and geophysical characterization.
Authors: Santolaria Pablo , Ayala Concepción , Pueyo Emilio L. , Rubio Félix M. , Soto Ruth , Calvín Pablo , Luzón Aranzazu , Rodríguez-Pintó Adriana , Oliván Carlota , Casas-Sainz Antonio M.
Published: March 2021

The presence of multiple evaporite levels strongly influence the structural style and kinematics of fold-and-thrust belts. Particularly (but not exclusively) in their fronts, it is common for these décollements to favor the formation of triangle zones. In the central portion of the Pyrenees, the South Pyrenean Triangle Zone represents the frontal part of this chain, that involves the Oligocene-Miocene Ebro Basin foreland deposits. We have focused on its western termination, characterized by a salt-cored anticline that laterally passes to a backthrust which dies out to the west. These structures are detached on the Upper Eocene-Lower Oligocene syntectonic evaporite Barbastro Formation (and lateral equivalents) that acted as a multidetachment unit. To the north, the south-directed Pyrenean thrust unit detached on Middle-Upper Triassic evaporites to finally glide along the Upper Eocene-Lower Oligocene décollement horizons.

In this contribution, we present a detailed structural and stratigraphic model of this triangle zone termination, constructed accordingly to two major approaches (1) constraining the geometry and structural architecture based on surface geology, interpretation of seismic lines (>900 km) and wells and, (2) obtaining the 3D density distribution of the detachment level (Barbastro Fm. and lateral equivalents as well as deeper, Triassic evaporites) using gravity stochastic inversion by means of more than 7000 gravity stations and 1500 actual density data from surface rocks. All in all, this multidisciplinary approach allows us to characterize the western termination of the South Pyrenean Triangle zone as the transition from a ramp-dominated and multiple triangle zone to a detachment-dominated one whose geometry, kinematics, and location were controlled by the distribution and heterogeneity of the Upper Eocene-Lower Oligocene syntectonic décollements and the southern pinch-out of the basal detachment of this unit.
Storm Anatol over Europe in December 1999: impacts on societal and energy infrastructure
Authors: Kettle Anthony
Published: March 2021

Storm Anatol impacted the North Sea and northern Europe on 3-4 December 1999. It brought hurricane force winds to Denmark and northern Germany, and high winds also in Sweden and the Baltic states.  For many meteorological stations in Denmark, the wind speeds were the highest on record, and the storm was ranked as a century event.  The storm impacts included extensive forest damage, fatalities, hundreds of injuries, power outages, transportation interruptions, as well as storm surge flooding on the west coast of Denmark.  At the time of the storm, Denmark was strongly committed to wind energy, and approximately 10 onshore wind turbines were destroyed during the storm.  An important industry insurer noted that this was a remarkably low number considering the storm intensity and the large number of turbines (>3500) installed in Denmark.  In 1999, offshore wind energy was just getting started in Europe.  Denmark had just started an environmental monitoring program at Horns Rev off the Danish North Sea coast in advance of an offshore wind farm that would be installed in 2002.  The offshore meteorological mast at Horns Rev survived the storm, but the wave field was significant, and it partially disabled the measurement system.
 
This contribution takes a closer look at the regional met-ocean conditions during the storm.  A brief overview is made of the wind field and available wave measurements from the North Sea.  A closer examination is made of water level meaurements from around the North Sea to characterize the storm surge and identify possible meteotsunamis and infragravity waves.  Offshore accidents are briefly discussed to assess if there had been unusual wave strikes on shipping or platforms.  At the time of the storm in 1999, there was a growing awareness in the scientific community of possible changes in sea state conditions in the North Atlantic area and the increasing threat of rogue waves.  The offshore wind energy research platform FINO1 near Borkum in the southern North Sea experienced large wave damage during Storm Britta on 1 November 2006.  There was a repetition of the wave damage during storms in 2007 and 2013.  Storm Anatol in 1999 was a major North Sea storm, and this contribution presents a survey to assess if there was unusual wave phenomena during the event. 
The potential of small mountain river systems for paleoenvironmental reconstructions in drylands - An example from the Binaloud Mountains in northeastern Iran
Authors: Khosravichenar Azra , Fattahi Morteza , Amini Hamideh , von Suchodoletz Hans
Published: March 2021

Fluvial sediments are valuable paleoenvironmental archives of the Quaternary. Since besides environmental factors they are also affected by local tectonics or intrinsic processes, large instead of small catchments should be studied. In drylands covering ca. 45% of the global terrestrial surface large river systems are generally missing, and most river systems are small rivers originating from mountain ranges. Their sediments are potentially interesting paleoenvironmental archives, but are often affected by intensive tectonics. During this study, to obtain a robust regional paleoenvironmental signal a small river system in the southwestern Binaloud Mountains in semi-arid NE Iran was exemplarily studied with a combined approach that encompassed both alluvial fan and catchment. By using geomorphological mapping and numerical dating, fluvial aggradation followed by incision was independently identified in larger areas or in different parts of the river system ca. 95–88 ka, 40 ka, 20 ka, around/after the Pleistocene/Holocene transition and possibly ca. 2.6 ka. These could be linked with regional and over-regional paleoenvironmental data. Furthermore, large boulders on the alluvial fan suggest anthropogenic destabilisation of the catchment during the last decades. Despite strong local tectonics the fluvial dynamics was mostly controlled by paleoenvironmental changes and human activity. This indicates that despite their small size, such river systems form valuable paleoenvironmental archives in drylands where other archive types are largely missing. 
Mountain freshwater ecosystems and protected areas in the tropical Andes: insights and gaps for climate change adaptation
Authors: Quenta Estefania , Crespo-Pérez Verónica , Mark Bryan , Gonzales Ana Lía , Kulonen Aino
Published: March 2021

Protected areas play an important role in ecosystem conservation and climate change adaptation. However, no systematic information is available on the protection of high elevation freshwater ecosystems (e.g.  lakes, glacierized catchments and streams), their biodiversity and ecosystem services. Here we addressed this issue by reviewing literature and analyzing maps of protected areas and freshwater ecosystems in the tropical Andes. Overall, our revision and inventory indicate: 1) seven national parks were created with the objective of water resources protection, but they were not designed for freshwater conservation (i.e., larger watersheds), and mainly protect small ecosystems. Furthermore, the creation of new local protected areas was needed for water resources conservation; 2) we quantified 12% and 31% of lakes and glacial lakes are protected, respectively. Around 12% of the total stream length is protected. First-order streams predominate in the study area, of which 14% are protected. Furthermore, 29% of glacierized catchments (average surface of 677 km2)are protected, and 46% of the total glacier area is protected. We quantified 31 Ramsar sites; 3) high-value biodiversity sites have not been protected, and ecosystems services information is limited. This review highlights the need for future research to fill knowledge gaps for effective freshwater conservation actions.
Improving earthquake doublet rate predictions in ETAS by using modified spatial trigger distributions
Authors: Grimm Christian , Käser Martin , Hainzl Sebastian , Pagani Marco , Küchenhoff Helmut
Published: March 2021

Earthquake sequences add significant hazard beyond the solely declustered perspective of common probabilistic seismic hazard analysis (PSHA). A particularly strong driver for both social and economic losses are so-called earthquake doublets (more generally multiplets), i.e. sequences of two (or more) comparatively large events in spatial and temporal proximity. Not differentiating between foreshocks and aftershocks, we hypothesize three main drivers of doublet occurrence: (1) the number of direct aftershocks triggered by an earthquake; (2) the underlying, independent background seismicity in the same time-space window; and (3) the magnitude size distribution of triggered events (in contrast to independent events). We tested synthetic catalogs simulated by a common, isotropic epidemic type aftershock sequence (ETAS) model for both Japan and Southern California. Our findings show that the standard ETAS approach dramatically underestimates doublet frequencies compared to observations in historical catalogs. Among others, the results partially smooth out pronounced peaks of temporal and spatial event clustering. Focusing on the impact on direct aftershock productivity, we propose two modifications of the ETAS spatial kernel in order to improve doublet rate predictions: (a) a restriction of the spatial function to a maximum distance of 2.5 estimated rupture lengths; (b) an anisotropic function with contour lines constructed by a box with two semicircular ends around the estimated rupture line. The restriction of the spatial extent shifts triggering potential from weaker to stronger events and in consequence improves doublet rate predictions for larger events. However, this improvement goes at the cost of a weaker overall model fit according to AIC. The anisotropic models improve the overall model fit, but have minor impact on doublet occurrence rate predictions.
PMTools – a new program for paleomagnetic data analysis and visualization
Authors: Efremov Ivan , Veselovskiy Roman
Published: March 2021

There are many programs for the analysis and visualization of paleomagnetic data, but each of them is good only in a certain use case and does not allow to perform a full cycle of paleomagnetic operations. Therefore, one has to resort to using a number of programs to complete the full path of processing paleomagnetic data. You often have to convert data from one format to another, manually vectorize charts, and generally spend more time and effort than could theoretically be spent. Thus, there is a long overdue need for a universal program capable of fast, convenient and high-quality performance of a full cycle of paleomagnetic operations. A set of programs written by Randy Enkin (Enkin, 1996) for DOS was taken as a time-tested example of such a program. The choice fell on them, since these programs (although they are very outdated) allow performing a full cycle of paleomagnetic operations and do it as conveniently and efficiently as possible for that time.

Our goal is to create a program devoid of all of the above disadvantages and capable of developing indefinitely as modular opensource software by the efforts of all people interested in this.

The result of our work is PMTools – a cross-platform software for statistical analysis and visualization of paleomagnetic data. PMTools supports all widely used paleomagnetic data formats and allows you to work with them simultaneously. All charts created in PMTools are vector, adapted for direct using in publications and presentations, and can be exported in both vector and raster formats. At the same time, PMTools implements a full cycle of routine paleomagnetic operations: from finding the best-fit directions to calculating the mean paleomagnetic poles. Moreover, all operations can be performed both with a mouse through a graphical user interface and with hotkeys, which significantly speeds up the data analysis process. 

In the near future, PMTools will become a modular open source application, so that each user will be able to add its own modules, thereby expanding the program's functionality.

References

Enkin, R.J., 1996. A Computer Program Package for Analysis and Presentation of Paleomagnetic Data, Pacific Geoscience Center, Geological Survey of Canada, http://www.pgc.nrcan.gc.ca/tectonic/enkin.htm.
Optimizing ATES performance by increasing warm well temperature and harvesting waste/solar heat
Authors: Bloemendal Martin , Beernink Stijn , Hockin Alex , van Bel Nikki , Hartog Niels
Published: March 2021

Aquifer Thermal Energy Storage (ATES) systems combined with a heat pump stores and thereby reduces energy use for space heating and cooling of buildings. In most countries, the temperature of the stored heat is limited to maximum 25-30°C for such systems. However, when heat is available at higher temperatures (e.g. waste heat, solar heat), it is more efficient to store higher temperatures because that improves heat pump performance or may even makes it abundant. As a result there is a large potential for additional energy savings by transforming ‘regular’ low-temperature ATES systems to a HT-ATES. Such a transformation is tested for a greenhouse in the Netherlands. This greenhouse has a LT-ATES system operational since 2012. From 2015 onwards the storage temperature increased and currently heat is stored in the warm well at temperatures up to 40°C. In this HT-ATES transformation pilot, water quality parameters are closely monitored as well as temperature distribution in the subsurface (using DTS). Together with the operators, the results from the ATES monitoring are used to continuously improve system performance. Numerical groundwater and heat flow simulations of actual and expected well pumping data are used to evaluate how well operation can be optimized. Results show that due to the extra heat harvested and higher warm well temperature CO2 emissions are reduced by 70%, due to larger contribution of heat delivery by the ATES and a more efficient heat pump due to the higher warm well temperature. Groundwater infiltration temperature peaks are up to 40°C during the hottest summer days, while the average warm well temperatures increased mildly by 6°C to about 21°C. Groundwater monitoring results therefore only showed limited water quality changes. The changes that were identified are predominantly contributed to mixing processes, as the ATES system is installed in 2 different aquifers. 
Role of the density structure and air-sea fluxes on subpolar transformation
Authors: Petit Tillys , Lozier M. Susan , Josey Simon A. , Cunningham Stuart A.
Published: March 2021

Convection in the North Atlantic Ocean is a key component of the global overturning circulation (MOC) as it produces dense water at high latitudes. Recent work has highlighted the dominant role of the Irminger and Iceland basins in the production of the North Atlantic deep waters. Dense water formation in these basins is mainly explained by buoyancy forcing that transforms surface waters to the deep waters of the MOC lower limb. Air-sea fluxes and the surface density field are both key determinants of the buoyancy-driven transformation. To better understand the connection between atmospheric forcing and the Atlantic overturning circulation, we analyze the contributions of the air-sea fluxes and of the density structure to the transformation of surface water over the eastern subpolar gyre. More precisely, we consider the densification of subpolar mode water (SPMW) in the Iceland Basin that ‘pre-conditions’ the dense water formation downstream. Analyses using 40 years of observations (1980–2019) reveal that variability in transformation is only weakly sensitive to changes in the heat and freshwater fluxes. Instead, changes in SPMW transformation are largely driven by the variance in the surface density structure, as expressed by the outcropping area for those isopycnals that define SPMW.This large influence of the surface density on the SPMW transformation partly explains the unusually large SPMW transformation in winter 2014–15 over the Iceland Basin.  
A directed percolation model for the permeability of young sea ice
Authors: Maus Sönke
Published: March 2021

The permeability of sea ice is an important property with regard to the role of sea ice in the earth system. It controls fluid flow within sea ice, and thus affects processes like desalination and melt pond drainage. It also impacts the role of sea ice in hosting sea ice algae and organisms, and the uptake and release of nutrients and pollutants from Arctic surface waters. However, as sea ice permeability is difficult to measure in the field, observations are sparse and vary, even for similar porosity, over orders of magnitude. This range is related to the evolution of the sea ice pore space during aging from young ice to thick first year ice. In young ice, the pore network is dominated by primary pores constrained by brine layers and the near-interface microstructure. In older sea ice, the ongoing desalination and thermal fluctuations have created wider secondary brine channels, implying a several orders of magnitude higher permeability. It is a challenge to understand and model these changes in pore space and permeability. Here a directed percolation model for the permeability of young sea ice is proposed. The model describes the dependence of sea ice permeability and electrical conductivity on brine porosity, and its critical behaviour and percolation transition due to necking of pores, and related disconnection of pore networks. Its parameters are based on 3D X-ray micro-tomographic imaging of young sea ice and direct numerical simulation of its transport properties, that strongly support the application of directed percolation theory to young sea ice, with a threshold porosity (impermeable ice) of 2 to 3 percent. Combined to an approach to predict the crystal structure at the ice-ocean interface, the model also the growth-velocity dependence and evolution of permeability near the ice-ocean interface. As the model is strictly valid for growing and cooling sea ice, without present of wider secondary brine channels, it is mostly relevant for sea ice desalination processes during winter. Modelling permeability of older and summer ice (and melt pond drainage) will require more observations of the pore space evolution in warming sea ice, for which the present results can be considered as a starting point.
Assessing the impact of climate change on groundwater in an area in New Zealand
Authors: Yang Jing , Rajanayaka Channa , Kees Lawrence , Zammit Christian
Published: March 2021

Climate and its variability have a considerable impact on seasonal water resources availability. Understanding the impact of climate change and the time lagged  response in areas where groundwater is the main water resource supporting human activity (water supply, agriculture and industry), is necessary to manage potentially damaging consequences for hydrologically-driven ecological functions, ecosystem services, economic response and adaptation, cultural values and recreation.  

In this study, we assess the impact of climate change on groundwater in Edendale area, South New Zealand, which has been experiencing increasing water abstraction pressure and declining groundwater level. We use downscaled CMIP5 IPCC climate predictions to drive a hydrologic model (TopNet) to simulate changes in land surface recharge (LSR) under different climate models and future climate scenarios (i.e. RCPs – Representative Concentration Pathways) , and then the ensemble of LSR simulations further drive the Edendale groundwater model (MODFLOW) to simulate groundwater system.

Our initial result show: in spite of differences in simulations of different climate models and future climate scenarios, to the end of this century, there will be a slight annual increasing trend both for precipitation and LSR, significantly in Autumn and less significantly in other seasons; generally groundwater level and groundwater discharge (to rivers) will be increasing, following seasonal and annual patterns of changes in precipitation and LSR; differences are large for both climate models and future scenarios, largest for RCP8.5 and smallest for RCP2.6. We hope the results will support the long-term water management planning in the Edendale area.
A comprehensive review of algal biochar for soil improvement: bottlenecks and opportunities
Authors: Sun Jiacheng , Masek Ondrej
Published: March 2021

In recent years, the rapid increase of CO2 emission in the atmosphere and the resulting issues such as global warming and climate change have now become significant barriers to environmental sustainability. Although fossil CO2 emissions have decreased in some of the world's largest emitters, including 11% in the EU, 12% in the US and 1.7% in China annually, the estimated global CO2 emission amount still reached 40 G tonnes in 2020. The purpose of studying biochar produced by pyrolysis is essential to develop the knowledge of carbon cycles and nutrient components in soil. Among all types of feedstocks, algae grow incredibly rapidly compared to other biological materials, about 500-1500 times higher, which will boot the carbon sequestration rate. Therefore, the study of algal biochar production through pyrolysis has great significance for migrating climate change and developing carbon capture and storage.

This study focuses on a comprehensive review of previous literature on conventional and advanced macroalgae and microalgae pyrolysis for producing biochar and related valuable by-products like bio-oil and bio-syngas, aiming to establish a state-of-the-art of algal biochar for different soil-related applications and demonstrate the bottlenecks and opportunities. Specifically, a thorough comparison of algae species (20 microalgae and 20 macroalgae) is developed to benefit future researchers, involving chemical compositions, proximate analysis, solid-product fraction, physical properties and chemical properties. Redox conditions, surface functional groups and pH conditions are determined in lab-scale. Moreover, different algal biochar applications on soil and plant are analysed to optimise the commercial value of algal biochar, including soil conditioner, compositing additives, carrier for fertilisers, manure treatment and stable blending. Due to the abundant mineral contents (0.23-1.21% Na, 0.03-2.92% K, 0.75-7.17% Al, 0.19-1.24% Mg, 6.5-7% Ca and 0.04-0.69% Fe) of algal biochar, this study not only reviews the positive effects on soil improvement but also negative effects such as phytotoxic effect and heavy-metal pollution. A laboratory-based chemical oxidation approach (Edinburgh Stability Tool) is used to assess relatively long-term biochar stability and the influence of nutrient cycling. The optimal pyrolysis conditions (temperature, retention time and heating rate) and potential future commercial applications are obtained through the comprehensive review of algal biochar for soil improvement.    
Free radical-related mechanisms in soil and their relevance  to the cycling, stabilization, and storage of carbon
Authors: Yu Guanghui
Published: March 2021

Plant residues in soil create temporal and spatial hotspots of extremely high microbial activities leading to very intensive greenhouse gas (GHG) fluxes that challenge our mechanistic understanding and predictive power. Using a series of well-controlled soil microcosm experiments, we examine how abiotic processes (e.g., iron reduction-oxidation cycling) at residue/soil interfaces contribute to hotspot dynamics. We quantify for the first time the contributions of microbially-initiated Fenton reactions, which produce strongly oxidizing hydroxyl radicals (HO•), to organic matter solubilization and mineralization in hotspots 0–3 mm from the litter surface. The concentrations of ferrous iron (Fe2+), hydrogen peroxide (H2O2) and HO• were 2.1–3.0, 3.0–9.0 and 2.6–2.8 times higher, respectively, at the straw-soil interface than in the bulk soil. Thus, iron minerals, especially in concert with microorganisms, produce a burst of hydroxyl radicals that explain extremely high GHG fluxes from soil hotspots. Our findings highlight how Fe minerals and microorganisms synergistically influence global carbon cycling and stability. Our findings highlight the relevance of free radical-related mechanisms in soil to the cycling, stabilization, and storage of carbon and also extend our mechanistic understanding of processes occurring within hotspots.
Improved estimation method for dynamic bulk moduli of sandstones subjected to hydrostatic stress.
Authors: Nourifard Nazanin , Pasternak Elena , Lebedev Maxim
Published: March 2021

We designed and modified an experimental method to simultaneously measure the stress-strain (static moduli) and stress dependence of S and P-wave velocities of rocks (sandstone) under hydrostatic pressure by a Hoek’s cell. Dynamic moduli were calculated from the direct measurement of ultrasonic P- and S-wave velocities at a central dominant frequency of 1 MHz, while static moduli was recorded by strain gauges. The hydrostatic pressure was applied with a fixed rate at 1MPa/minute. We observed that the dynamic bulk moduli can be up to 44% higher than the static moduli in sandstones with porosity ranging from 8% to 24%. The results are in agreement with the existing empirical equations for soft rocks. Our experimental results demonstrate that the dynamic bulk’s modulus ranges from 4-13GPa, while the static bulk modulus ranges from 2-11GPa. We measured dynamic Young’s modulus and Poisson’s ratio at four different time periods (before applying the stress, right after the unloading, 20 days, and 60 days after the experiment) to investigate the effect of time on stress relaxation and eventually on the properties of the sandstones. All the samples showed an increase of Young’s modulus right after the stress application and then a gradual decrease of this value over time because of this relaxation; however, most of the samples could not reach the original state due to irreversible deformation at micro-level. Dynamic moduli show greater sensitivity to the irreversible deformations as compared to static moduli (even within the elastic limits). Dynamic moduli of porous material are also more sensitive to the microstructure than the static ones. Independent P and S-wave measurement for this study showed that the estimation of the S-wave velocity from the recorded P-wave velocity is not an accurate procedure and introduces a big error in the final calculation of the dynamic moduli. It also confirmed that by registering an accurate P-wave velocity the UCS (Unconfined Compressive Strength) value can be accurately estimated for sandstones. This demonstrates the great potential of dynamic studies as a non-destructive method to estimate this value for porous materials.
A hybrid model coupling extreme gradient boosting model with Gaussian mixture model for streamflow forecasting
Authors: Ni Lingling , Wang Dong , Wu Jianfeng , Wang Yuankun
Published: March 2021

With the increasing water requirements and weather extremes, effective planning and management for water issues has been of great concern over the past decades. Accurate and reliable streamflow forecasting is a critical step for water resources supply and prevention of natural disasters. In this study, we developed a hybrid model (namely GMM-XGBoost), coupling extreme gradient boosting (XGBoost) with Gaussian mixture model (GMM), for monthly streamflow forecasting. The proposed model is based on the principle of modular model, where a complex problem is divided into several simple ones. GMM was applied to cluster streamflow into several groups, using the features selected by a tree-based method. Then, each group was used to fit several single XGBoosts. And the prediction is a weighted average of the single models. Two streamflow datasets were used to evaluate the performance of the proposed model. The prediction accuracy of GMM-XGBoost was compared with that of support vector machine (SVM) and standalone XGBoost. The results indicated that although all three models yielded quite good performance on one-month ahead forecasting with high Nash-Sutclitte efficiency coefficient (NSE) and low root mean squared error (RMSE), GMM-XGBoost provided the best accuracy with significant improvement of forecasting accuracy. It can be inferred from the results that (1) XGBoost is applicable for streamflow forecasting, and in general, performs better than SVM; (2) the cluster analysis-based modular model is helpful in improving accuracy; (3) the proposed GMM-XGBoost model is a superior alternative, which can provide accurate and reliable predictions for optimal water resources management.

Note: This study has been published in Journal of Hydrology (Ni, L., Wang, D., Wu, J., Wang, Y., Tao, Y., Zhang, J. and Liu, J., 2020. Streamflow forecasting using extreme gradient boosting model coupled with Gaussian mixture model. Journal of Hydrology, 586.).
What is driving India-Asia convergence?
Authors: Bose Santanu , Schellart Wouter P , Strak Vincent , Duarte João C. , Chen Zhihao
Published: March 2021

The Himalaya and the Tibetan plateau, the highest mountain range on Earth, have been growing continuously for the last 55 Myrs since India collided with Eurasia. The forces driving this protracted mountain building process are still not fully understood, and continue to puzzle Earth Scientists. Although it is now well accepted that subduction zones are the main driver for plate motion, plate boundary migration, and mantle flow in the asthenosphere, their role in driving Indian indentation into the Asian landmass has never been tested with geodynamic models. This study uses four-dimensional geodynamic physical models to test the role of lateral subduction zones in driving the India-Asia collision. The objective of our study is to investigate if the slab pull force of the Sunda and Makran slabs have any role to play in the dynamics of the ongoing India-Asia convergence, particularly after the complete disappearance of the Tethyan slab, which was primarily steering the northward travel of the Indian plate since late Jurassic. To address this issue, we performed three experiments by varying the size and configuration of the subducting plate in the initial model setup.  Our experimental results show that active subduction of the Indo-Australian plate along the Sunda subduction zone is the main driver of the India-Asia convergence, Indian indentation, the growth of the Himalaya-Tibet mountains, and the eastward extrusion of southeast Asia. Our work further suggests that the protracted growth of collisional mountains on Earth requires nearby active subduction zones and, therefore, Himalayan-type orogens may have been rare in the Earth’s history.
Forces between reactive surfaces
Authors: Dziadkowiec Joanna , Zareeipolgardani Bahareh , Cheng Hsiu-Wei , Dysthe Dag Kristian , Røyne Anja , Valtiner Markus
Published: March 2021

Adhesive and repulsive, nm-range surface forces acting between mineral grains control colloidal stability and mineral aggregation but less is known about how these forces are affected by surface reactivity and to what extent these grain-scale forces can influence various deformation processes in rocks. In this experimental work, we explore and quantify the surface forces acting between dynamic mineral surfaces that undergo recrystallization or are chemically reactive in contact with water or aqueous salt solutions. Our experimental setup consists of the surface forces apparatus (SFA) coupled with the multiple beam interferometry (MBI). This setup can excellently reproduce a typical grain contact geometry with nanometer-thin water films confined between contacting mineral grains over relatively large, micron-sized contact areas. Owing to the use of MBI, both surface growth or dissolution processes can be monitored during force measurements in real-time. As such, SFA can provide information about the links between surface reactivity and adhesive or repulsive surface forces. Using the examples of force measurements between recrystallizing or chemically reactive mineral surfaces such as carbonates, hydroxides, and silicates, we comment on the relationship between the measured surface forces and surface reactivity. We link our findings with the observed changes in mineral phases, surface topographies, or surface roughness. We also comment on how the micron-scale confinement in the SFA affects the growth and dissolution processes in contrast to less confined regions. The magnitude of the forces associated with dynamic mineral surfaces and the potential significance of these forces to macroscopic deformation processes and cohesion in rocks are discussed.
Assessing the representation of the Australian carbon cycle in global vegetation models
Authors: Teckentrup Lina , De Kauwe Martin , Pitman Andy , Bastrikov Vladislav , Goll Daniel , Haverd Vanessa , Jain Atul , Joetzjer Emilie , Kato Etsushi , Lienert Sebastian , Lombardozzi Danica , McGuire12 Patrick , Melton Joe , Nabel Julia , Pongratz Julia , Sitch Stephen , Walker Anthony , Wiltshire Andrew , Zaehle Sönke
Published: March 2021

Australia plays an important role in the global terrestrial carbon cycle on inter-annual timescales. While the Australian continent is included in global assessments of the carbon cycle, the performance of dynamic global vegetation models (DGVMs) over Australia has rarely been evaluated. We assessed simulations of net biome productivity (NBP) and the carbon stored in vegetation between 1901 to 2018 from 13 DGVMs (TRENDY v8 ensemble). The TRENDY models simulated differing magnitudes of NBP on inter-annual timescales, leading to marked differences in carbon accumulation in the vegetation on decadal to centennial timescales. We showed that the spread in carbon storage resulted from differences in simulated carbon residence time rather than differences in net carbon uptake. Differences in simulated long-term accumulated NBP between models were mostly due to model responses to land-use change. The DGVMs also simulated different sensitivities to atmospheric CO2 concentration. Notably, models with nutrient cycles did not simulate the smallest response. While our results suggested that changes in the climate forcing do not have a large impact on the carbon cycle on long timescales, the inter-annual variability in precipitation drives the year-to-year variability in NBP. We analysed the impact of key modes of climate variability, including the El Niño Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). While the DGVMs agreed on sign of the response of NBP to El Niño and La Niña, and to positive and negative IOD events, the magnitude of inter-annual variability in NBP differs strongly between models. In addition, we identified simulated phenology and fire as associated with high model uncertainty, indicating differences in simulated vegetation composition and process representation. Model disagreement in simulated vegetation carbon, phenology and carbon residence time imply different types of vegetation cover across Australia between models, whether prescribed or resulting from model assumptions. Our study highlights the need to evaluate parameter assumptions and key processes that drive vegetation dynamics, such as phenology, mortality and fire, in an Australian context to reduce uncertainty across models.