The physical properties of gas hydrate‐bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase. The host sediment grain size and the state of effective stress ...determine the hydrate morphology in sediments; this information can be used to significantly constrain estimates of the physical properties of hydrate‐bearing sediments, including the coarse‐grained sands subjected to high effective stress that are of interest as potential energy resources. Reported data and physical analyses suggest hydrate‐bearing sands contain a heterogeneous, patchy hydrate distribution, whereby zones with 100% pore‐space hydrate saturation are embedded in hydrate‐free sand. Accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate‐bearing sands and captures observed physical‐property dependencies on hydrate saturation. For example, numerical modeling results of sands with patchy saturation agree with experimental observation, showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations. The hydrate‐patch size itself impacts the physical properties of hydrate‐bearing sediments; for example, at constant hydrate saturation, we find that conductivity (electrical, hydraulic and thermal) increases as the number of hydrate‐saturated patches increases. This increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate‐saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross‐section of the specimen.
Key Points
Controls on hydrate morphology in natural sediments
Accounting for patchy hydrate yields tighter estimates of physical properties
Models to characterize stiffness and conductivities of sands with patchy hydrate
Surface effects of sea‐level rise (SLR) in permafrost regions are obvious where increasingly iceless seas erode and inundate coastlines. SLR also drives saltwater intrusion, but subsurface impacts on ...permafrost‐bound coastlines are unseen and unclear due to limited field data and the absence of models that include salinity‐dependent groundwater flow with solute exclusion and freeze‐thaw dynamics. Here, we develop a numerical model with the aforementioned processes to investigate climate change impacts on coastal permafrost. We find that SLR drives lateral permafrost thaw due to depressed freezing temperatures from saltwater intrusion, whereas warming drives top‐down thaw. Under high SLR and low warming scenarios, thaw driven by SLR exceeds warming‐driven thaw when normalized to the influenced surface area. Results highlight an overlooked feedback mechanism between SLR and permafrost thaw with potential implications for coastal infrastructure, ocean‐aquifer interactions, and carbon mobilization.
Plain Language Summary
Along coastlines globally, sea‐level rise is causing saltwater to intrude into terrestrial environments and freshwater reservoirs (i.e., saltwater intrusion). The impact of saltwater intrusion on temperate and tropical environments has been extensively studied, but assessment of saltwater intrusion impacts on high‐latitude permafrost environments is lacking due to limited field data and appropriate models. This knowledge gap limits projections of climate change impacts to coastal Arctic ecosystems and communities. In this study, we develop and use a mathematical model that incorporates multiple, interrelated processes, including how salt content affects the freezing temperature of water, to evaluate the impacts of sea‐level rise and associated saltwater intrusion on coastal permafrost. Results show that sea‐level rise causes saltwater to intrude into the unfrozen pore space of permafrost. With a lower freezing temperature than freshwater, saltwater intrusion triggers permafrost thaw and lateral retreat. The combination of atmospheric and oceanic warming and sea‐level rise has the potential to drive extensive permafrost loss along Arctic coastlines.
Key Points
Newly developed cryohydrogeological model incorporates salinity‐dependent freeze‐thaw processes and solute exclusion
Subsurface saltwater intrusion drives lateral thaw of coastal ice‐saturated permafrost
Combination of sea‐level rise and land surface warming results in extensive ice‐saturated permafrost loss
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Stable isotope composition of speleothems reflects the physicochemical condition of their formation environment such as the local temperature and the isotopic composition of surface precipitation, ...making them one of the best archives of terrestrial climate. However, quantitative reconstruction of paleo-temperature from speleothem isotope records is challenging, because most speleothems do not form in isotope equilibrium with the drip water. These disequilibrium isotope effects, often thought to arise from the rapid degassing of CO2 from a thin water film, vary among different speleothems and over time, and hinder the applications of many isotope thermometers in speleothems, including both the conventional carbonate-water oxygen isotope thermometer and the recently developed carbonate clumped isotope thermometer. Here we present an isotope-enabled reaction-diffusion model of speleothem formation (IsoCave), and use it to systematically examine the patterns and controls of the disequilibrium isotope effects in speleothems (δ13C, δ18O, Δ′17O, Δ47, Δ48 and Δ49) and explore their implications for isotope thermometry in speleothems.
We show that prior calcite precipitation, cave air pCO2 and δ13CCO2exert the strongest controls on the disequilibrium isotope effects in speleothems, followed by cave temperature, water film thickness and water drip rate. Together, changes in these environment parameters explain the variations of disequilibrium isotope effects in natural speleothems. Our model reproduces the apparent temperature dependence of oxygen isotope compositions of speleothems compiled from multiple caves over a large temperature range, but highlights the challenges in the application of speoleothem-specific calibration of isotope thermometers due to the effects of non-temperature factors. Further, we show the disequilibrium effects in different isotope systems are highly correlated. The slopes of these correlations reflect mainly the kinetic isotope fractionations associated with HCO3− dehydration and dehydroxylation reactions, and remain relatively constant despite changes in environmental conditions especially for speleothems formed during the early evolution period of drip water. Based on these correlations, specifically the correlation between disequilibrium Δ47 and Δ48 effects, we propose a novel approach to quantitatively correct for disequilibrium isotope effects in speleothems and derive more accurate estimates of speleothem formation temperatures. Application of this coupled Δ47-Δ48 approach to synthetic speleothem isotope records reproduces the speleothem formation temperatures, suggesting new opportunities for quantitative paleo-temperature reconstruction based on speleothem isotope records.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Based on the electrochemical-thermal coupling model of lithium-ion battery, the electrochemical behavior and parameter sensitivity identification of the numerical model are profoundly studied. Also, ...the internal physico-chimica evolution and design optimization under different working conditions are analyzed. On this basis, summarized is the sensitivity of 23 parameters such as electrode structure parameters, material property parameters and kinetics parameters of the power lithium-ion battery, and the battery design is therefore optimized. The research shows that if the battery voltage is used as the basis for measuring the degree of dispersion of the model output when the parameters are changed, the parameter identification work can be more accurate. The 23 parameters selected in this paper are identified, and the high, medium, low and non-sensitive parameters are respectively 7, 8, 4, 4; changes in design parameters will cause changes in the state of charge, which in turn affect the model output.
•Electrochemical-thermal coupling model analysis performed on battery pole pieces.•The local current density is optimal at the ear side and center.•Identified high, medium, low, and non-sensitive parameters 7,8,4, and 4 respectively.•Electrode structure parameters have a large fluctuation range for the model results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
15.
A Multi‐Phase Mass Flow Model Pudasaini, Shiva P.; Mergili, Martin
Journal of geophysical research. Earth surface,
December 2019, 2019-12-00, 20191201, Volume:
124, Issue:
12
Journal Article
Peer reviewed
Open access
Geomorphic mass flows are often complex in terms of material composition and its evolution in space and time. The simulation of those hazardous phenomena would strongly benefit from a multi‐phase ...model, considering the motion and—importantly—interaction of phases characterized by different physical aspects including densities, frictions, viscosities, fractions, and their mechanical responses. However, such a genuine multi‐phase model is still lacking. Here, we present a first‐ever, multi‐mechanical, multi‐phase mass flow model composed of three different phases: the coarse solid fraction, fine‐solid fraction, and viscous fluid. The coarse solid component, called solid, represents boulders, cobbles, gravels, or blocks of ice. Fine‐solid represents fine particles and sand, whereas water and very fine particles, including colloids, silt, and clay, constitute the viscous fluid component in the mixture. The involved materials display distinct mechanical responses and dynamic behaviors. Therefore, the solid, fine‐solid, and fluid phases are described by Coulomb‐plastic, shear‐ and pressure‐dependent plasticity‐dominated viscoplastic, and viscosity‐dominated viscoplastic rheologies. They are supposed to best represent those materials. The new model is flexible and addresses some long‐standing issues of multi‐phase mass flows on how to reliably describe the flow dynamics, runout, and deposition morphology of such type of phenomena. With reference to some benchmark simulations, the essence of the model and its applicability are discussed.
Key Points
We introduce a new multi‐mechanical, multi‐phase model accounting for the complexity of geomorphic mass flows
Solid, fine‐solid, and fluid fractions can be considered separately, allowing to simulate a broad range of possible material compositions
Benchmark tests on generic landscapes yield plausible results indicating the potential use of the new model for complex real events
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Microseismic activity, recorded everywhere on Earth, is largely due to ocean waves. Recent progress has clearly identified sources of microseisms in the most energetic band, with periods from 3 to ...10s. In contrast, the generation of longer-period microseisms has been strongly debated. Two mechanisms have been proposed to explain seismic wave generation: a primary mechanism, by which ocean waves propagating over bottom slopes generate seismic waves, and a secondary mechanism which relies on the nonlinear interaction of ocean waves. Here we show that the primary mechanism explains the average power, frequency distribution, and most of the variability in signals recorded by vertical seismometers, for seismic periods ranging from 13 to 300s. The secondary mechanism only explains seismic motions with periods shorter than 13s. Our results build on a quantitative numerical model that gives access to time-varying maps of seismic noise sources. Key Points * The "hum" is caused by the interaction of ocean waves with the bottom slope * Our model yields maps of seismic sources at all periods from 3 to 300s * Sources of the hum are strongest along shelf breaks, on the east side of oceans
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•Convective heat transfer plays a vital role in the ignition process.•Ignition time is investigated under critical operating conditions.•The thermal performance of the reactor is comprehensively ...evaluated.
This study numerically investigates a smoldering-driven pyrolysis reactor. The reactor consists of two chambers: the smoldering chamber for the contaminated sand remediation and the pyrolysis chamber for the waste valorization. This study aims to develop a numerical model to verify the feasibility of the reactor and evaluate its thermal performance. The findings reveal that the contaminant (char) in the sand can be destroyed via smoldering and that the process can be self-sustaining after ignition. It is noteworthy that the ignition requires external energy input. Smoldering can produce a heatwave with a stable peak temperature and propagation velocity. The heatwave generated in the smoldering chamber can heat the pyrolysis chamber through the boundary. The results highlight that the reactor’s pivotal operating characteristics (peak temperature, ignition time, and reaction duration) can be regulated by the critical parameters (char concentration, air inlet velocity, and oxygen concentration).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Many orogens, including the Central Andes and Himalayas, are characterized by wide areas that have undergone upper crustal shortening and surface uplift. The behaviour of the deep lithosphere is ...poorly constrained, and in some mountain belts, lower crust and mantle lithosphere appear to have been removed through delamination during orogen development. Thermal–mechanical numerical models demonstrate that as crust thickens during shortening, the lowermost crust may undergo metamorphic eclogitization, which increases its density. Even a small density increase (7% or more) causes shortening to localize above the eclogitic crustal root, promoting the development of thick lithosphere in this area which is then prone to gravitational removal. Complete removal of orogen mantle lithosphere occurs if the eclogitized lower crust is weak enough to allow full detachment of negatively buoyant mantle lithosphere; this can occur even if the lower crust is less dense than the mantle. The onset of delamination may be determined by the hydration state of the lower crust, as the presence of water promotes eclogitization and significantly reduces rock strength. Two distinct styles of delamination are observed: (1) retreating delamination in which weak mantle lithosphere rolls back and peels away from the crust, producing a contemporaneous migration of crustal thickening, surface uplift and magmatism, and (2) stationary delamination in which strong lithosphere separates from the weak lower crust and slides into the deep mantle at a stationary detachment point, followed by widespread crustal deformation and magmatism.
► Many orogens have experienced lithosphere removal during shortening. ► Numerical models examine lower crustal eclogization during orogen evolution. ► A small density increase for eclogitized crust causes localized shortening. ► Delamination of orogen mantle lithosphere occurs if the lower crust is weak. ► Two styles of delamination are observed in the models.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•An integrated physical and index-overlay method helps predict groundwater vulnerability.•The numerical model improves the accuracy of the index-overlay method.•Land use plays an essential role in ...regional variations of groundwater sustainability.•The groundwater system in the Pingtung plain is in a critical condition.
This study presents a new concept that integrates the index-overlay method and a physical-based numerical model for predicting groundwater sustainability under various climate conditions and anthropogenic activities. The index-overlay DRASTIC method was modified with an analytical hierarchy process theory and employed to create groundwater vulnerability maps for the Pingtung plain groundwater basin in southern Taiwan. The physical-based MODFLOW model was used for predicting the dynamics of a basin-scale groundwater system. Solutions and calibrated hydrogeological parameters in the MODFLOW model provide feedback to the factors in the modified DRASTIC method which enables predicting groundwater vulnerability. In this study, different climate conditions were considered in the numerical model to obtain the changes in depth of water and net recharge for predicting future groundwater vulnerability and for evaluating the current state of the sustainability indicators. Results show that the depth of water and net recharge obtained from the groundwater model improve the accuracy of the groundwater vulnerability prediction. The variations of future climate conditions have less influence on the variations of groundwater vulnerability because of the dense river network that controls the shallow groundwater levels in the Pingtung plain groundwater basin. Therefore, the influence of climate conditions on the risk of groundwater contamination is also relatively low. Based on the analysis of the sustainability indicators, we found that the groundwater resource system in the Pingtung plain groundwater basin is in a critical condition of high vulnerability.
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The organic pollutants disposed at the Sardas landfill in Sabiñánigo (Huesca, northeastern Spain) by the INQUINOSA lindane factory have reached the Gállego alluvial aquifer and could affect the ...Sabiñánigo reservoir. The daily oscillations of the reservoir water level produce a tidal effect on the piezometric heads of the aquifer. These oscillations are transmitted in a damped way with a time lag, thus attesting that the silting sediments of the reservoir and the natural silts of the Gállego alluvial are interposed between the reservoir water and the layer of sands and gravels. A 2D finite element groundwater flow and total dissolved hexachlorocyclohexane (HCH) transport model through the Gállego alluvial aquifer is presented here. The flow model was constructed to: (1) Quantify the tidal effect, produced by the daily fluctuations of the reservoir water level on the aquifer; (2) Estimate the hydrodynamic parameters of the layer of sands and gravels; and 3) Estimate the vertical hydraulic conductivity of the silting sediments and silts; and (4) Quantify aquifer/reservoir interactions. The flow model reproduces the dynamics of the tidal effect and attests that groundwater velocity and flow direction changes daily in response to the oscillations of the reservoir level. Model results reproduce the measured well hydrographs and the Darcy velocity derived from tracer tests and confirm the validity of the conceptual model. The transport model of total dissolved HCH simulates the time evolution of the contaminant plume. The computed concentrations of total dissolved HCH and the contaminant mass outflux are very sensitive to changes in the source terms and the distribution coefficient, Kd of HCH. The best fit to the measured HCH plumes in September 2010 and December 2020 is obtained with a Kd ranging from 1 to 3 L/kg. The computed flux of dissolved HCH leaving the Sardas site in 2020 towards the Sabiñánigo reservoir ranges from 0.6 kg/year for Kd = 3 L/kg to 3.1 kg/year for Kd = 1 L/kg. The findings of this study will be most useful for planning and designing remedial and containment actions at the Sardas site and other similar lindane-affected sites.
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•Oscillations of the reservoir level produce a tidal effect in the aquifer.•Groundwater flow changes from E-W to W-E direction when reservoir level is high.•Polluted groundwater does not discharge directly into the reservoir.•Computed concentrations of dissolved HCH are very sensitive to the Kd.•The best fit to measured HCH data is achieved with Kd 1, 3 L/kg.
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