bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alternatives to Liquid Water Beneath the South Polar Ice Cap of Mars
Authors: Schroeder Dustin M. , Steinbrügge Gregor 
Published: September 2021

AbstractRadar sounding of Mars’ south polar ice cap has revealed portions of its base with stronger radar returns than its surface. These have been used to estimate high real permittivity values consistent with liquid water. However, the thermal, chemical, and geological conditions required to sustain such water bodies are challenging to achieve in the contemporary Martian environment. Three recent papers address this conflict. Khuller and Plaut (2021, https://doi.org/10.1029/2021GL093631) find similar radar signatures across the ice cap, expanding the range conditions associated with water candidates. Bierson et al. (2021, https://doi.org/10.1029/2021GL093880) show that, for non‐zero conductivity, a wider range of materials could produce the observed echoes. Similarly, Smith et al., (2021, https://doi.org/10.1029/2021GL093618) use modeling, laboratory tests, and remote sensing data to propose smectite deposits as their specific source. While not incompatible with bodies of liquid brines, these papers provide potential alternative sources for the bright radar observations.
Scale Dependence of Earthquake Rupture Prestress in Models With Enhanced Weakening: Implications for Event Statistics and Inferences of Fault Stress
Authors: Lambert Valère , Lapusta Nadia , Faulkner Daniel 
Published: September 2021

AbstractDetermining conditions for earthquake slip on faults is a key goal of fault mechanics highly relevant to seismic hazard. Previous studies have demonstrated that enhanced dynamic weakening (EDW) can lead to dynamic rupture of faults with much lower shear stress than required for rupture nucleation. We study the stress conditions before earthquake ruptures of different sizes that spontaneously evolve in numerical simulations of earthquake sequences on rate‐and‐state faults with EDW due to thermal pressurization of pore fluids. We find that average shear stress right before dynamic rupture (aka shear prestress) systematically varies with the rupture size. The smallest ruptures have prestress comparable to the local shear stress required for nucleation. Larger ruptures weaken the fault more, propagate over increasingly under‐stressed areas due to dynamic stress concentration, and result in progressively lower average prestress over the entire rupture. The effect is more significant in fault models with more efficient EDW. We find that, as a result, fault models with more efficient weakening produce fewer small events and result in systematically lower b‐values of the frequency‐magnitude event distributions. The findings (a) illustrate that large earthquakes can occur on faults that appear not to be critically stressed compared to stresses required for slip nucleation; (b) highlight the importance of finite‐fault modeling in relating the local friction behavior determined in the lab to the field scale; and (c) suggest that paucity of small events or seismic quiescence may be the observational indication of mature faults that operate under low shear stress due to EDW.
Adjoint‐State Traveltime Tomography for Azimuthally Anisotropic Media and Insight Into the Crustal Structure of Central California Near Parkfield
Authors: Tong Ping 
Published: September 2021

AbstractSeismic anisotropy provides crucial information on the stress state and geodynamic processes inside the Earth. We develop a novel adjoint‐state traveltime tomography method using P‐wave traveltime data to simultaneously determine velocity heterogeneity and azimuthal anisotropy of the subsurface. First, an anisotropic eikonal equation is derived to model first‐arrival traveltimes in azimuthally anisotropic media. Traveltime tomography is then formulated as an optimization problem constrained by the anisotropic eikonal equation, which is subsequently solved by the adjoint‐state method. Ray tracing is not required. Its high accuracy is achieved by solving the anisotropic eikonal equation and the associated adjoint equation with efficient numerical solvers. In addition, an eikonal equation‐based earthquake location method for azimuthally anisotropic media is developed to solve the coupled hypocenter‐velocity problem. The tomography and earthquake location methods are applied to central California near Parkfield to test their performance in practice. A total of 1,068,850 first P‐wave traveltimes clearly maps the velocity heterogeneity and azimuthal anisotropy in the upper and middle crust. The average P‐wave velocity model shows a striking velocity contrast across the San Andreas Fault (SAF). In the upper crust, we find structural anisotropy in the SAF zone and stress‐induced anisotropy off the SAF zone. In the middle crust, the fast P‐wave velocity directions are generally fault‐parallel due to the decreased effect of the maximum horizontal compressive stress. In all, the real‐data application suggests that the new adjoint‐state traveltime tomography method can be reliably used to investigate anisotropic seismic structures.
Deciphering Fine Electrical Conductivity Structures in the Crust From MT Data Using the Equivalent Conductivity Formula
Authors: Liu Shuyu , Xu Yixian , Yang Bo , Guo Zeqiu , Shi Yuan , Liu Ying 
Published: September 2021

AbstractFine structures in the lower crust sounded by seismic reflection can be formed in various geological processes and their electrical resistivity properties can provide significant insights into the geodynamic processes of the lithosphere. The magnetotelluric (MT) method is popular for imaging the electrical resistivity structure of the lithosphere; however, it lacks high resolution to resolve the small heterogeneities in deep crust. To recover the fine electrical resistivity structures, we propose a strategy based on their equivalent resistivity that defines the relationship between the fine structures and the inverted bulk resistivities. Thus, we first formulated the equivalent resistivity for a 3‐D laminated structure with >95% accuracy. In this strategy, the bulk resistivity inverted from MT data is used to retrieve the fine resistivity structures, for which the corresponding equivalent resistivities should match with the inverted resistivities. The strategy was tested to demonstrate its feasibility for analyzing the electrical property and the cause of lamellae in the lower crust of the Basin and Range Province. From the bulk resistivities of 1‐D anisotropic inversion, we retrieved the resistivity of lamellae that was in the range of 0.15–0.3 and coincident with the resistivity of silicate melts, implying that the lamellae are probably magma chambers with >50% melt fraction, which is also supported by seismic and geological evidences. Our case study demonstrated that this strategy based on equivalence can be successfully used to recover the fine resistivity structures from MT data.
A Driftwood‐Based Record of Arctic Sea Ice During the Last 500 Years From Northern Svalbard Reveals Sea Ice Dynamics in the Arctic Ocean and Arctic Peripheral Seas
Authors: Hole Georgia M. , Rawson Thomas , Farnsworth Wesley R. , Schomacker Anders , Ingólfsson Ólafur , Macias‐Fauria Marc 
Published: September 2021

AbstractWe present a 500‐year history of naturally felled driftwood incursion to northern Svalbard, directly reflecting regional sea ice conditions and Arctic Ocean circulation. Provenance and age determinations by dendrochronology and wood anatomy provide insights into Arctic Ocean currents and climatic conditions at a fine spatial resolution, as crossdating with reference chronologies from the circum‐Arctic boreal forests enables determination of the watershed the driftwood originated from. Sample crossdating may result in a wide range of matches across the pan‐boreal region, which may be biased toward regions covered by the reference chronologies. Our study considers alternate approaches to selecting probable origin sites, by weighting scores via reference chronology span and visualizing results through spatiotemporal density plots, as opposed to more basic ranking systems. As our samples come from naturally felled trees (not logged or both), the relative proportions of different provenances are used to infer past ocean current dominance. Our record indicates centennial‐to decadal‐scale shifts in source regions for driftwood incursion to Svalbard, aligning with Late Holocene high variability and high frequency shifts in the Transpolar Drift and Beaufort Gyre strengths and associated ﬂuctuating climate conditions. Driftwood occurrence and provenance also track the northward ice formation shift in peripheral Arctic seas in the past century. A distinct decrease in driftwood incursion during the last 30 years matches the observed decline in pan‐Arctic sea ice extent in recent decades. Our new approach successfully employs driftwood as a proxy for Arctic Ocean surface circulation and sea ice dynamics.
Is the Relationship Between Stratospheric Arctic Vortex and Arctic Oscillation Steady?
Authors: Hu Dingzhu , Guan Zhaoyong , Liu Meichen , Wang Tao 
Published: September 2021

AbstractThe connections between the stratosphere and troposphere, for example, the stratospheric Arctic vortex (SAV) and Arctic Oscillation (AO), have been paid attention by scientists and the public in recent years. Previous studies suggested that the coupling between the stratosphere and troposphere is the strongest in winter. However, whether the link between SAV and AO during boreal winter on interannual timescales is steady is still unknown. Our results show that the interannual relationship between the SAV in early winter and AO in late winter during 1958–2018 is unsteady and has experienced a remarkable interdecadal change around the 2000s, with large and statistically significant positive correlations before the 2000s but small and insignificant correlations after the 2000s. The weakened linkage between the SAV and AO after the 2000s is possibly caused by (a) the weakened downward effect of SAV on the North Atlantic and polar sectors of AO, and (b) the opposite signs of sea level pressure (SLP) in the North Pacific and North Atlantic. The links of SAV‐AO are enforced (weakened) when AO‐related SLP anomalies over the North Pacific are the same (opposite) signs of those over the North Atlantic before (after) the 2000s. Differences in the tropospheric state over the North Pacific during two periods might be jointly contributed by the SAV and the SAV‐related significant (insignificant) sea surface temperature anomalies over central North Pacific in the earlier (latter) period. Our results may provide evidences to improve the predictability in seasonal or interannual timescales forecasts of weather and climate at mid‐latitudes.
Effects of the June 2018 Global Dust Storm on the Atmospheric Composition of the Martian Upper Atmosphere as Observed by MAVEN
Authors: Farahat Ashraf , Mayyasi Majd , Withers Paul , Dayeh Maher A. , Abuelgasim Abdelgadir 
Published: September 2021

AbstractThe densities of six neutral species in the Martian upper atmosphere were analyzed before and during the 2018 Martian global dust storm (GDS 2018) using data from the Neutral Gas and Ion Mass Spectrometer of the Mars Atmosphere and Volatile EvolutioN mission. The trends of the dayside densities of the neutral species and their relative abundances were investigated between May 27 and June 17, 2018, at altitudes of 160–210 km. GDS 2018 caused variations in the neutral species abundance of the upper atmosphere at its onset in June 5–8, 2018, with the CO2, Ar, CO, O, N2, and He densities decreasing relative to prestorm conditions. The densities of the examined neutral species increased during the storm, except those of O and He. During the storm, the relative abundances of CO2 and Ar increased, while those of CO and O decreased and those of N2 and He remained the same. The variation in the neutral species with altitude was consistent with the regular atmospheric conditions and unrelated to the GDS 2018 drivers. The higher thermospheric temperature observed during the storm onset suggested that changes in the composition of the neutral species were caused by storm‐induced thermal enhancements.
From Sugar to Flowers: A Transition of Shallow Cumulus Organization During ATOMIC
Authors: Narenpitak Pornampai , Kazil Jan , Yamaguchi Takanobu , Quinn Patricia , Feingold Graham 
Published: September 2021

AbstractThe Atlantic Tradewind Ocean‐Atmosphere Mesoscale Interaction Campaign (ATOMIC) took place in January–February, 2020. It was designed to understand the relationship between shallow convection and the large‐scale environment in the trade‐wind regime. A Lagrangian large eddy simulation, following the trajectory of a boundary‐layer airmass, can reproduce a transition of trade cumulus organization from “sugar” to “flower” clouds with cold pools, observed on February 2–3. The simulation is driven with reanalysis large‐scale meteorology, and in‐situ aerosol data from ATOMIC and its joint field study EUREC4A. During the transition, large‐scale upward motion deepens the cloud layer. The total water path and optical depth increase, especially in the moist regions where flowers aggregate. This is due to mesoscale circulation that renders a net convergence of total water in the already moist and cloudy regions, strengthening the organization. An additional simulation shows that stronger large scale upward motion reinforces the mesoscale circulation and accelerates the organization process by strengthening the cloud‐layer mesoscale buoyant turbulence kinetic energy production.
Operational Multi‐GNSS Global Ionosphere Maps at GFZ Derived From Uncombined Code and Phase Observations
Authors: Brack Andreas , Männel Benjamin , Wickert Jens , Schuh Harald 
Published: September 2021

AbstractGlobal navigation satellite system (GNSS) networks with multi‐frequency data can be used to monitor the activity of the Earth's ionosphere and to generate global maps of the vertical total electron content (VTEC). This article introduces and evaluates operational GFZ VTEC maps. The processing is based on a rigorous least squares approach using uncombined code and phase observations, and does not entail leveling techniques. A single‐layer model with a spherical harmonic VTEC representation is used. The solutions are generated in a daily post‐processing mode with GPS, GLONASS, and Galileo data, and are provided for the period since the beginning of 2000. A comparison of the GFZ VTEC maps with the final combined International GNSS Service (IGS) product shows a high consistency with the solutions of the IGS analysis centers. A validation with about four years of Jason‐3 altimetry‐derived VTEC data is provided, in which the GFZ solution has the smallest bias of 1.2 TEC units compared to the solutions of the IGS analysis centers, and with 3.0 TEC units one of the smallest standard deviations.
Experimental and Numerical Study of the Effect of Model Geometric Distortion on Laboratory Modeling of Urban Flooding
Authors: Li Xuefang , Kitsikoudis Vasileios , Mignot Emmanuel , Archambeau Pierre , Pirotton Michel , Dewals Benjamin , Erpicum Sébastien 
Published: September 2021

AbstractLaboratory studies of urban flooding often use geometrically distorted scale models due to the multi‐scale nature of these specific flows. The possible bias induced by geometric distortion has never been thoroughly investigated with dedicated laboratory experiments. In this study, we combine experimental and computational modeling to systematically assess the influence of the distortion ratio, that is, the ratio of horizontal to vertical scale factors, on upscaled flow depths and discharge partition between streets. Three flow configurations were considered: a street junction, a street bifurcation, and a small synthetic urban district. When the distortion ratio is varied up to a value of about 5, the upscaled flow depths at the model inlets decrease monotonously and the flow discharge in the branch that conveys the largest portion of the flow is greatly enhanced. For equal flow depths at the model outlets and depending on the configuration, the distortion effect induces a variation of the upstream flow depth approximately from ∼4% to ∼17% and a change in outlet discharge partition up to 24 percentage points. For a distortion ratio above 5, both upscaled upstream flow depths and outlet discharge partition tend to stabilize asymptotically. Our study indicates the direction and magnitude of the bias induced by geometric distortion for a broad range of flow cases, which is valuable for offsetting these effects in practical laboratory studies of urban flooding.
Field‐Scale Subsurface Flow Processes Inferred From Continuous Gravity Monitoring During a Sprinkling Experiment
Authors: Reich Marvin , Mikolaj Michal , Blume Theresa , Güntner Andreas 
Published: September 2021

AbstractField‐scale subsurface flow processes are difficult to observe and monitor. We investigated the value of gravity time series to identify subsurface flow processes by carrying out a sprinkling experiment in the direct vicinity of a superconducting gravimeter. We demonstrate how different water mass distributions in the subsoil affect the gravity signal and show the benefit of using the shape of the gravity response curve to identify different subsurface flow processes. For this purpose, a simple hydro‐gravimetric model was set up to test different scenarios in an optimization approach, including the processes macropore flow, preferential flow, wetting front advancement (WFA), bypass flow and perched water table rise. Besides the gravity observations, electrical resistivity and soil moisture data were used for evaluation. For the study site, the process combination of preferential flow and WFA led to the best correspondence to the observations in a multi‐criteria assessment. We argue that the approach of combining field‐scale sprinkling experiments in combination with gravity monitoring can be transferred to other sites for process identification, and discuss related uncertainties including limitations of the simple model used here. The study stresses the value of advancing terrestrial gravimetry as an integrative and non‐invasive monitoring technique for assessing hydrological states and dynamics.
MicroRNA-338-3p as a novel therapeutic target for intervertebral disc degeneration
Authors: Jiang Hua , Moro Abu , Wang Jiaqi , Meng Dihua , Zhan Xinli , Wei Qingjun 
Published: September 2021

AbstractRecent studies have demonstrated the pivotal role played by microRNAs (miRNAs) in the etiopathogenesis of intervertebral disc degeneration (IDD). The study of miRNA intervention in IDD models may promote the advancement of miRNA-based therapeutic strategies. The aim of the current study was to investigate whether intradiscal delivery of miRNA can attenuate IDD development. Our results showed that miR-338-3p expression was significantly increased in the nucleus pulposus (NP) of patients with IDD. Moreover, there was a statistically significant positive correlation between the expression level of miR-338-3p and the severity of IDD. Our functional studies showed that miR-338-3p significantly influenced the expression of extracellular matrix synthesis genes, as well as the proliferation and apoptosis of NP cells. Mechanistically, miR-338-3p aggravated IDD progression by directly targeting SIRT6, a negative regulator of the MAPK/ERK pathway. Intradiscal injection of antagomir-338-3p significantly decelerated IDD development in mouse models. Our study is the first to identify miR-338-3p as a mediator of IDD and thus may be a promising target for rescuing IDD.
Gene expression profiling on effect of aspirin on osteogenic differentiation of periodontal ligament stem cells
Authors: Abd Rahman Fazliny 
Published: September 2021

AbstractPeriodontal ligament (PDL) contains a unique population of mesenchymal stem cells (MSCs), also known as PDL stem cells (PDLSCs). The regenerative properties of PDLSCs hold great potential for its use in stem cells based therapy, particularly for periodontal or bone regeneration. The present study investigated the global gene expression profile in PDLSCs during osteogenic differentiation. MSCs from PDL were isolated from normal permanent human teeth (n = 3). Microarray analysis was used to study the effects of ASA (200, 500, and 1000 μM) on the gene expression profiles in PDLSCs during osteogenic differentiation. Microarray study revealed that ASA was able to modulate PDLSCs gene expression profile. At 200 µM, 315 genes were dysregulated genes (DE), involving 151 upregulated and 164 downregulated genes. At 500 µM, 794 genes were DE, involving of 364 upregulated and 430 downregulated genes. At 1000 µM, the number of DE genes increased to 2035, of which 735 were upregulated and 1300 were downregulated. Bioinformatics analyses of the gene expression data revealed that the majority of DE genes (for 500 and 1000 µM ASA treatment) are involved in osteogenic differentiation. The gene network analysis was carried out using Ingenuity Pathway Analysis (IPA) software, and this revealed that the number of gene groups involved in cell adhesion and extracellular matrix components were increased. This study indicated that ASA could enhance PDLSCs functions and provide evidence for the potential use of ASA with PDLSCs for regenerative dentistry applications, particularly in the areas of periodontal health and regeneration. Periodontal ligament stem cells (PDLSCs) Aspirin (ASA) Microarray Osteogenic
The biogeographic differentiation of algal microbiomes in the upper ocean from pole to pole
Authors: Martin Kara , Schmidt Katrin , Toseland Andrew , Boulton Chris A. , Barry Kerrie , Beszteri Bánk , Brussaard Corina P. D. , Clum Alicia , Daum Chris G. , Eloe-Fadrosh Emiley , Fong Allison , Foster Brian , Foster Bryce , Ginzburg Michael , Huntemann Marcel , Ivanova Natalia N. , Kyrpides Nikos C. , Lindquist Erika , Mukherjee Supratim , Palaniappan Krishnaveni , Reddy T. B. K. , Rizkallah Mariam R. , Roux Simon , Timmermans Klaas , Tringe Susannah G. , van de Poll Willem H. , Varghese Neha , Valentin Klaus U. , Lenton Timothy M. , Grigoriev Igor V. , Leggett Richard M. , Moulton Vincent , Mock Thomas 
Published: September 2021

AbstractEukaryotic phytoplankton are responsible for at least 20% of annual global carbon fixation. Their diversity and activity are shaped by interactions with prokaryotes as part of complex microbiomes. Although differences in their local species diversity have been estimated, we still have a limited understanding of environmental conditions responsible for compositional differences between local species communities on a large scale from pole to pole. Here, we show, based on pole-to-pole phytoplankton metatranscriptomes and microbial rDNA sequencing, that environmental differences between polar and non-polar upper oceans most strongly impact the large-scale spatial pattern of biodiversity and gene activity in algal microbiomes. The geographic differentiation of co-occurring microbes in algal microbiomes can be well explained by the latitudinal temperature gradient and associated break points in their beta diversity, with an average breakpoint at 14 °C ± 4.3, separating cold and warm upper oceans. As global warming impacts upper ocean temperatures, we project that break points of beta diversity move markedly pole-wards. Hence, abrupt regime shifts in algal microbiomes could be caused by anthropogenic climate change.