Edge Of Plateau Research Articles

Bacterial community structure in geothermal springs on the northern edge of Qinghai-Tibet plateau.

In order to reveal the composition of the subsurface hydrothermal bacterial community in the zones of magmatic tectonics and their response to heat storage environments. In this study, we performed hydrochemical analysis and regional sequencing of the 16S rRNA microbial V4-V5 region in 7 Pleistocene and Lower Neogene hot water samples from the Gonghe basin. Two geothermal hot spring reservoirs in the study area were found to be alkaline reducing environments with a mean temperature of 24.83°C and 69.28°C, respectively, and the major type of hydrochemistry was SO4-Cl·Na. The composition and structure of microorganisms in both types of geologic thermal storage were primarily controlled by temperature, reducing environment intensity, and hydrogeochemical processes. Only 195 ASVs were shared across different temperature environments, and the dominant bacterial genera in recent samples from temperate hot springs were Thermus and Hydrogenobacter, with both genera being typical of thermophiles. The correlation analysis showed that the overall level of relative abundance of the subsurface hot spring relied on a high temperature and a slightly alkaline reducing environment. Nearly all of the top 4 species in the abundance level (53.99% of total abundance) were positively correlated with temperature and pH, whereas they were negatively correlated with ORP (oxidation-reduction potential), nitrate, and bromine ions. In general, the composition of bacteria in the groundwater in the study area was sensitive to the response of the thermal storage environment and also showed a relationship with geochemical processes, such as gypsum dissolution, mineral oxidation, etc.

Quantitative relative humidity reconstruction combining tree-ring with ice core oxygen isotope records

As one of the driest regions in the Asia, the ecological conditions in Northwest China are very fragile. Although relative humidity (RH) plays a vital role in the environment, the lack of long-term RH records hinders the development of reliable scenarios for future extreme environmental conditions in this region. We developed a new method for quantitative regional RH reconstruction; in this method, the signals of precipitation oxygen isotope ratios (δ18O) and temperature in the tree-ring δ18O series are removed to extract the RH signal from the tree-ring δ18O records to the greatest extent. We then combined published millennium tree-ring δ18O, ice core δ18O, and paleo-temperature data to reconstruct a new millennium-long RH record around Delingha, Qinghai, China, on the edge of the northeastern Tibetan Plateau (TP). The reconstructed RH was closely related to both temperature and rainfall, and revealed cycles of approximately 35, 85, 130–160 and 200 years, which are associated with solar insolation variations, Pacific decadal oscillation, and the Atlantic multidecadal variability. With continuous global warming, RH may decrease as the contribution of the temperature increase becomes larger than that of the precipitation over the northeastern TP. This study provides a basis for a new method of RH reconstruction based on different paleoclimate archives.

Moho depth inversion in the Tibetan Plateau from high-precision gravity data

The Tibetan Plateau (TP) is the youngest orogenic belt formed by continental collision on the Earth. It is a natural laboratory for studying continental dynamics such as continental convergence, plate subduction, and plateau uplift. Studying its deep structure has always been a hot issue in geological research. The Moho is the interface between the crust and the mantle and is an important interface in the structure of the Earth's circle. Its depth, lateral variation, and fine structure of the crust-mantle interface are important parameters to reveal the process of lithospheric dynamics in the TP. The study of the Moho surface generally has two methods: seismic and gravity. Seismic detection has the characteristics of high precision, but they are limited along a few cross-sectional lines and have a high cost. It is not suitable and cannot be carried out in a large area of the TP; Gravity inversion can obtain large-area Moho depth, but affected by gravity data and inversion methods, the accuracy is lower than that of seismic. In this paper, a high-precision gravity field model is selected. With the constraint of seismic observation, the Parker-Oldenburg interface inversion method is used, and the Bott iteration method is introduced to improve the inversion efficiency. The high-precision Moho depth in the TP is obtained, consistent with the seismic detection results. The research results show that the shape of the Moho in the TP is complex, and the variation range is large, reaching 60-80 km. In sharp contrast with the adjacent area, there is a clear sharpness zone at the plateau's edge. In the TP's interior, the Moho's buried depth is characterized by "two depressions and two uplifts". The Moho in the south of the Yarlung Zangbo River (YZR) inclines to the north, and the Moho in the north depresses downward, interpreted as the Indian plate subducts to the north below Tibet. The Moho depression on the north side of the Qiangtang block (QTB), up to 72 km deep, may be related to the southward subduction of the lithosphere. The Moho uplift of the QTB has the same strike as the Bangong-Nujiang suture zone (BNS), which may reflect that the area is compensated by a low-density and low-velocity mantle.

Population whole-genome resequencing reveals the phylogenetic relationships and population structure of four Hunan typical tea landraces

Hunan located at the evolutionary transitional zone edge of the Yunnan-Guizhou plateau, tea germplasms are abundant. At present, although morphological, enzymological and molecular markers have been used to study the genetic relationship of these tea germplasms. However, due to the complexity of the genetic background of tea germplasm resources, the evolution history and taxonomy of Hunan tea germplasm is still unclear. In this study, four Hunan tea landraces from the evolutionary transitional zone were collected, including 9 'Chengbu Dongcha' (CBDC), 8 'Jianghua Kucha' (JHKC), 11 'Rucheng Baimao' (RCBM) and 8 'Anhua Yuntai' (AHYT). We used whole-genome re-sequencing to identify genetic variation, phylogenetic placement, and population structure among the four tea landraces and then scanned the genome for regions related to population potential selective. Across the samples, we identified an average of 1.38 million (M) SNPs and 6.82 × 10³ INDELs. Based on the high-quality SNPs, we performed neighbor-joining phylogenetic tree, population structure, and principal component analysis, all of which supported that the 36 tea germplasms could been divided into two groups, CBDC and AHYT were clustered into a group, and RCBM and JHKC were clustered into another group. With CBDC, JHKC, and RCBM as control, 407, 380, and 147 selected genes were identified in AHYT, respectively, were in the top 5% of F_ST and Log₂^Ratioθπ scores. The identified genes are mainly involved in stress tolerance, biosynthesis of important secondary metabolites, adaptability, and yield. These results will be helpful in the classification of tea germplasms and investigating selection–related genes.

Современные сейсмотектонические деформации на вулканическом плато Асхатэ и их роль в структуре вулканического поля Дариганга, Юго-Восточная Монголия

From instrumental measurements in southeastern Mongolia and adjacent China, weak seismicity is determined. However, 7.5-kilometer long system of ditches, probably of seismic nature, was detected in the western part of the Dariganga volcanic field, on the edge of the Ashate Plateau that resulted from erosional dissection of the 4.8–4.3 Ma shield edifice. We propose that the modern seismotectonic reactivation of the Askhate volcano is related to tectonic motions in the Late Cenozoic Tamtsag foredeep of the Nukut-Daban range, spatially associated with neotectonic reactivation of the Solonker suture.

Мангуп-Дорос в фемный период истории

The modern reconstruction of the history of the fortified settlement atop Mangup mountain from the mid-ninth to the mid-eleventh century, when it was a part of the Byzantine theme in the Crimea, was developed by A. G. Gertsen in 1990. This article discusses the new materials obtained by recent years of archaeological research of the site which allow significant corrections to it. The review of archaeological objects and complexes from the mid-ninth to the mid-eleventh centuries uncovered in the ancient town shows that Mangup-Doros continued to be a large, well-fortified Byzantine fortress, with the main defensive line running along the outer edge of the Mangup plateau. Very important are the traces of big repairs and reconstructions of the fortification system discovered by excavations and dated from the mid-ninth and late tenth century. They indicate that maintaining the defensive system of the settlement was one of the main tasks assigned to the Byzantine commanders and the military contingent stationed there. The intra-fortress space was divided into two functional zones, residential and industrial buildings (up to 50% of the total area) and the unbuilt territory, which could be a refuge for the population of the neighbouring area. The excavations of residential areas indicate their ordinary character. As in the previous period, the basilica was topographic, ideological, and administrative centre of the settlement. Specifically, archaeological research has not discovered traces of the fortified centre (citadel) at Mangup, though such centre was typical of many towns and fortresses of the Byzantine Empire from the Middle Byzantine Period on. Throughout the Theme Period, the population of the town in question continued cattle-breeding and agriculture, with viticulture and commercial winemaking oriented to exportation gradually became specialized branches. The Byzantine administration controlled the winemaking, as evidenced by the finds of stationary winepresses in the habitable zone of the fortress.

The China plant trait database version 2

Plant functional traits represent adaptive strategies to the environment, linked to biophysical and biogeochemical processes and ecosystem functioning. Compilations of trait data facilitate research in multiple fields from plant ecology through to land-surface modelling. Here we present version 2 of the China Plant Trait Database, which contains information on morphometric, physical, chemical, photosynthetic and hydraulic traits from 1529 unique species in 140 sites spanning a diversity of vegetation types. Version 2 has five improvements compared to the previous version: (1) new data from a 4-km elevation transect on the edge of Tibetan Plateau, including alpine vegetation types not sampled previously; (2) inclusion of traits related to hydraulic processes, including specific sapwood conductance, the area ratio of sapwood to leaf, wood density and turgor loss point; (3) inclusion of information on soil properties to complement the existing data on climate and vegetation (4) assessments and flagging the reliability of individual trait measurements; and (5) inclusion of standardized templates for systematical field sampling and measurements.

Comprehensive evaluation of soil quality of different land use types on the northeastern margin of the Qinghai-Tibet Plateau, China

Soil quality evaluation is an important prerequisite for the rational soil resource utilization. We collected soil samples from forest (n=9), grassland (n=18) and cropland (n=38) in Tianzhu County, Gansu Province, which is located on the northeastern edge of the Qinghai-Tibet Plateau. Soil quality was evaluated based on thirteen soil physical and chemical indicators, including soil bulk density, field capacity, and organic matter. A minimum data set (MDS) was constructed using principal component analysis and correlation analysis to establish a soil qua-lity evaluation index (SQI) system, which was used in the soil quality evaluation for the three land-use types. The results showed that total porosity, capillary porosity, field capacity, capillary water capacity, saturated water content, organic matter, total nitrogen and available potassium content were significantly higher in forest than those in grassland and cropland. The SQI system of forest was based on field capacity, organic matter, total nitrogen, available nitrogen, and available potassium, and the SQI ranged between 0.329 to 0.678, with a mean value of 0.481. Grassland SQI system was based on field capacity and available nitrogen, with the SQI ranging between 0.302 to 0.703 and a mean value of 0.469. Cropland SQI system was based on capillary water capacity, non-capillary porosity, available nitrogen, available phosphorus, and available potassium, and the SQI ranged from 0.337 to 0.616 with a mean value of 0.462. The most important barriers to soil quality improvement in forest, grassland, and cropland were available potassium, field capacity, and capillary water capacity, respectively. The MDS-based SQI enabled an accurate evaluation of soil quality across different land-use types in the study area, which was best in forest followed by grassland and cropland. The evaluation results would provide important reference for sustainable soil management in the local area.

Response of bacterial communities to shrub encroachment and forage planting in alpine grassland of the Qinghai-Tibetan Plateau

Shrub encroachment and conversion of grazing land to forage cultivation are the main disturbance factors at alpine grasslands in the Qinghai-Tibetan plateau. Yet our understanding of soil bacterial communities impacts of these disturbances is limited. Using shrub (Potentilla fruticose) encroachment systems and forage lands (Medicago sativa lands, and Elymus sibiricus lands) as a model, we investigated the effects of shrub encroachment and land use on bacterial communities in alpine grass soil at the Eastern edge of the Qinghai-Tibetan plateau of China. Soil bacterial communities were examined using high-throughput sequencing of the 16S rRNA gene (V4-V5 region, Illumina MiSeq). Soil properties of TN and SOC were tested using an Elementar Variomax CNS Analyser (Elementar Corp., Germany). WEOC concentrations were determined following Ma's procedures, to answer the following hypotheses: i) shrub encroachment and forage cultivation would reduce soil organic carbon content, ii) the bacterial communities in shrub encroachment and forage lands are less diverse than those of alpine grassland, and iii) the occurrence of extensive mutualism or commensalism in alpine grassland, and competition or mutual exclusion in shrub encroachment and forage land. In this study, we found that SOC and TN decreased on shrub encroached and forage lands, supporting our first hypothesis. In total, 56 bacterial phyla were identified across the sampling sites. The dominant phyla at the four plots, Proteobacteria, Actinobacteria, Acidobacteria, Bacteroidetes and Chloroflexi, accounted for 27–28%, 13–30%, 13–26%, 4–8% and 4–9% of the total population, respectively. Contrary to our expectation, alpha-diversities (phylogenetic diversity, Operational Taxonomic Unit (OTU) richness, Shannon, and Chao1) were consistently higher in disturbed soils than in alpine grassland, and the highest appeared in Medicago sativa lands compared to other sites. Soil texture and soil organic carbon together explained 30% of the total variations of bacterial communities, indicating that bacterial habitat (e.g. soil texture) and substrate (soil organic carbon) were affected in shrub encroachment and forage lands. Copiotrophs (Actinobacteria and Proteobacteria) and Nitrospirae were enriched in alpine grassland, while oligotrophs (Acidobacteria) were concentrated in shrub encroached and forage lands, indicating that shrub encroachment and conversion of alpine grassland to forage land may alter bacterial life history strategies. Through the phylogenetic molecular ecological network approach, we found that the bacterial network of alpine grassland was more complex than that of shrub and forage lands. Furthermore, the bacterial network of alpine grassland was more modular, and the taxa tended to co-occur, with positive associations accounting for 95% of all potential interactions. By contrast, negative interactions appeared more in shrub encroached (34%) and forage land (33%) compared to alpine grassland. This indicated that bacterial species have greater niche-sharing and more collaboration in alpine grassland than in shrub and forage lands. In conclusion, our findings revealed that shrub encroachment and conversion of alpine grassland to forage increased competition of bacterial species for substrates, with potential for serious consequences such as elevating losses of soil carbon.

Topography effect on ambient noise tomography: a case study for the Longmen Shan area, eastern Tibetan Plateau

SUMMARY Ambient noise tomography (ANT) is a widely used method to obtain shear wave velocity structure in the crust and upper mantle. Usually, the topography is assumed to have negligible effect on the resulting models. This, however, might not be proper in regions with large topographic variation, such as plateau edges, submarine slopes and volcanic islands. In this study, we use synthetics from waveform-based numerical simulation to quantify the topography effect on ANT in the Longmen Shan area, eastern Tibetan Plateau margin. Three kinds of models are used in forward simulation to obtain theoretical waveforms, including Case1: the layered model, Case2: the layered model with topographic variation and Case3: the flattened model of Case2. The final inversion results show that the bias of ANT is negligible in the blocks with relatively flat topography, such as the interior regions of the Tibetan Plateau and the Sichuan Basin. However, for the Longmen Shan boundary zone with significant topographic variation (∼4 km), the shear wave velocity image has an obvious negative bias that can reach up to −4 per cent. The maximum depth of bias is ∼5 km, which is mirrored with the maximum topographic elevation difference of the region, and the average bias disappears as the depth decreases to the surface (0 km) or increases to three times of the maximum influence depth (∼15 km). The horizontal distribution of the tomographic bias is almost linearly related to the topographic elevation difference with a slope of −1.04 and a correlation coefficient of 0.90 at maximum influence depth. According to this first-order correction formula and the decreasing trend of average bias with depth, the topography effect on ANT can be suppressed to a certain extent.

Influence of Surface Processes on Strain Localization and Seismic Activity in the Longmen Shan Fold‐and‐Thrust Belt: Insights From Discrete‐Element Modeling

AbstractWe investigated interactions between structural deformation and surface processes in the Longmen Shan fold‐and‐thrust belt and the adjacent western Sichuan foreland basin (WSFB) in the eastern margin of the Tibetan Plateau. The discrete‐element modeling (DEM) method was used to study the influences of the various mechanical properties of the detachments and syn‐tectonic erosion/deposition on the structural evolution of the Longmen Shan and WSFB. DEM simulations demonstrated two stages of surface processes during the Late Cenozoic profoundly influenced thrusting sequences and strain localization in the hinterland and foreland portions of the Longmen Shan. Models indicate that the fold‐and‐thrust belt lacking surface processes propagate in a forward‐breaking manner, whereas those with surface processes develop following an out‐of‐sequence thrusting pattern. We infer that large‐scale erosion propagation from the Sichuan Basin westward to the Tibetan Plateau since Late Cenozoic caused the Longmen Shan hinterland to reach a subcritical wedge state. Tectonic activity retreats to the edge of Plateau, enhancing the rapid uplift of the Longmen Shan and inhibiting the propagation of substantial shortening deformation to the foreland basin. The foreland thrust belt slides stably along the shallow detachment, causing the initiation and growth of the Longquan fault in the leading front. These results explain why both the Longmen Shan hinterland and the western Sichuan foreland thrust belts are currently in a state of simultaneous seismic activity. Our findings offer important implications regarding the seismic potentials of other fold‐and‐thrust belts that interact with dynamic surface processes.

Applicability Assessment of Coherent Doppler Wind LiDAR for Monitoring during Dusty Weather at the Northern Edge of the Tibetan Plateau

Wind profile light detection and ranging (LiDAR) is an important tool for observing features within the atmospheric boundary layer. Observations of the wind field and boundary layer height from coherent Doppler wind LiDARs (CDWLs) under sandy and dusty weather conditions were evaluated using observations from two CDWLs and one GTS radio sounding located at the northern edge of the Tibetan plateau from 1 May to 30 August 2021. The results showed that CDWL has good applicability in reproducing wind fields in dust, precipitation, and in clear-sky conditions, and that it is superior to the v wind field for real measurements of the u wind fields. In terms of the planetary boundary layer height (PBLH), the validity of the inversion of PBLH in dusty weather was higher than that under clear-sky conditions. It was found that the PBLH retrieved by the CDWL at 20:00 (BJT) was better than that at 08:00 (BJT). The diurnal variation amplitude of the PBLH before the occurrence of a sandstorm was larger than the diurnal variation amplitude of the PBLH occurring during a sandstorm.

Controlling factors and palaeoclimatic significance of colour reflectance in the Late Tertiary red clay on the Chinese Loess Plateau

The colour of soil is one of its most striking features, and records the palaeoenvironment conditions when the soil is formed; however, the controlling factors and palaeoclimatic significance of colour reflectance in the Late Tertiary red clay are poorly understood. In this study, the Jiaxian section, on the northern edge of the Chinese Loess Plateau, was selected to explore the aforementioned issue using colour reflectance, diffuse reflectance spectroscopy (DRS), geochemical, and magnetic approaches. In the red clay sequence, (1) the concentration of iron oxides (mainly haematite and goethite) and the intensity of pedogenesis were significantly positively correlated with redness (a*) and yellowness (b*). (2) a*, b*, and a*/b* can be used as proxy indicators of haematite concentration, goethite concentration, and temperature, respectively. (3) The parameters derived from colour reflectance and DRS measurements were proven to be better than magnetic susceptibility (χ) in recording palaeoclimatic evolution, and Ca*b* was better than the chemical weathering index in recording soil development.

Paleoglaciology of the central East Antarctic Ice Sheet as revealed by blue-ice sediment

We present ∼100 cosmogenic surface exposure ages, including 75 new analyses, for a blue-ice moraine complex at Mt. Achernar, head of Law Glacier, in the central Transantarctic Mountains. The 10Be–3He–26Al ages along with previously-published boron concentrations chronicle past behavior of the East Antarctic Ice Sheet (EAIS) along the edge of the polar plateau since the sediments started to accumulate, around 0.5–1 Ma. Samples analyzed for 10Be from the Law Glacier surface record <100 years of exposure, indicating they likely have negligible inheritance when first exposed. The Law Glacier surface experienced relatively minor fluctuations in surface elevation throughout MIS 6 and 5, and likely during prior periods, as geomorphic features are intact and exposure ages are coherent on the moraine, ranging from ∼210 to ∼86 ka; respective means for MIS 5 till in two different areas are 106 ± 9.1 ka [n = 4 ages] and 106 ± 5.1 ka [n = 6]. Although we infer the Law Glacier has been relatively close to its current configuration generally since 0.5–1 Ma, disturbances to Achernar blue-ice moraine architecture seem apparent at times especially prior to the last two glacial cycles. The largest observed disturbance occurred when the nearby Lewis Cliffs Ice Tongue expanded either close to, or earlier than, 500-400 ka. A minimum ice thickness increase of 30 m is associated with the ∼20 ka blue-ice ridges, and a lateral moraine indicates the Law Glacier surface was ∼40–50 m higher at ∼9.2 ± 0.5 ka. Our findings support that lateral accretion over time formed the Mt. Achernar blue-ice moraine sequence, and by implication, other analogue Antarctic deposits. We interpret blue-ice moraines as representing, at times, relatively constant outlet glacier conditions and concur with prior studies that they reflect near-equilibrium forms. Blue-ice sediments are an underutilized and dateable paleoglaciologic and paleoclimate archive in Antarctica, including for former ice surface dynamics and possibly as a repository of old ice during periods such as MIS 5 and prior.

Combining sediment source tracing techniques with traditional monitoring: The “Arvorezinha catchment” experience

AbstractTo truly understand the hydrologic and erosive processes that occur at the catchment scale regarding land use and soil management changes, intensive monitoring is required over a long period. Variables such as precipitation, flow rate and suspended sediment concentration are the fundamentals needed to estimate sediment yield (SY). However, in order to shed more light on the effects of soil management changes on SY, traditional hydrologic monitoring techniques can be paired with sediment tracing to identify sediment sources. In addition, mathematical models that predict erosion and SY can also help understand the dynamics of erosion and deposition between the hillslope and stream channel. Given the above, this article provides an overview of almost 20 years of monitoring (2002–2021) in the Arvorezinha experimental catchment (1.23 km2) located on the edge of the Brazilian meridional plateau in southern Brazil, which is subject to extreme erosion due to a combination of factors related to intensive agriculture and steep slopes. The catchment was selected as a study site to evaluate the effects of land‐use changes and soil conservation management on hydrology and SY. The text reviews the history of the study, synthesizes the main results and describes the evolution of the monitoring techniques used while giving special attention to the fingerprinting approach. In addition, the article discusses the importance of catchment‐scale studies for teaching, generating technical‐scientific knowledge and fostering collaboration between national and international research groups.

Ex vivo assessment of surgically repaired tibial plateau fracture displacement under axial load using large-volume micro-CT

Postoperative weight bearing has the potential to generate fragmental motion of surgically repaired tibial plateau fractures (TPFs), which may contribute to loss of fracture reduction. The effect of loading on the internal distribution of fragmentary displacements is currently unknown. The aim of this study was to determine the internal displacements of surgically repaired split TPFs due to a three-bodyweight load, using large-volume micro-CT imaging and image correlation. Fractures were generated and surgically repaired for two cadaveric specimens. Load was applied to the specimens inside a large-volume micro-CT system and scanned at 0.046 mm isotropic voxel size. Pre- and post-loading images were paired, co-registered, and internal fragmentary displacements quantified. Internal fragmental displacements of the cadaveric bones were compared to in vivo displacements measured in the lateral split fragments of TPFs in a clinical cohort of patients who had similar surgical repair and were prescribed pain tolerated postoperative weight bearing. The split fragments of cadaveric specimens displaced, on average, less than 0.3 mm, consistent with in vivo measurements. Specimen one rotated around the mediolateral axis, while specimen two displaced consistently caudally. Specimen two also had varying displacements along the mediolateral axis where, at the fracture site, the fragment displaced caudally and laterally, while the most lateral edge of the tibial plateau displaced caudally and medially. The methods applied in this study can be used to measure internal fragmental motion within TPFs.

Diversity and distribution of fish in the Qilian Mountain Basin.

The Qilian Mountain Basin, on the north-eastern edge of the Qinghai-Tibet Plateau (QTP), supports a high diversity of native and endemic fish. However, the detailed species inventory and distribution patterns concerning fish in the whole Basin remain unknown, which hinders the conservation of biodiversity and assessment of ecological health. We compiled a comprehensive species richness and distribution database of freshwater fish in the Qilian Mountain Basin, based on field investigations and exhaustive data collection from 50 rivers or lakes. Then, we elucidated a distribution pattern using clustering and ordination analyses based on a βdissim matrix with species presence/absence data. A total of 79 freshwater fish species within eight orders, 17 families and 42 genera were recorded. The Qilian Mountain Basin could be grouped into six systems, which match the six Basins (i.e. Heihe River Basin, HHR; Qaidam Basin, QDM; Qinghai Lake Basin, QHL; Shule River Basin, SLR; Shiyang River Basin, SYR; Yellow River Basin, YR), based on the fish distribution pattern. Additionally, the spatial pattern of species distribution showed the distance decay of taxonomic similarity. Our results demonstrate that riverine connectivity resulting from historical processes plays a vital role in shaping the freshwater ichthyofauna of High Central Asia. These findings will be valuable for future systematic conservation of fish in the Qilian Mountain Basin.

Electron transport properties for a zigzag graphene nanoribbon embedding multiple rectangular quantum dots under a periodically modulated magnetic field

Based on the tight-binding model and recursive Green-function method, the electronic transport properties for a zigzag graphene nanoribbon (ZGNR) embedded with a finite-length superlattice composing of a single or multiple rectangular quantum dot (s) under a periodically modulated magnetic field are investigated. The numerical results of simulation show that the transmittance coefficient T is not only related to the structure of the finite-length superlattice, but also to the addition of a periodically modulated magnetic field. By increasing the height or width of a single rectangular quantum dot (QD), resonant dip of the transmission coefficient T distinctly shifts toward the lower energy region. For a ZGNR embedding n rectangular QDs, the resonant peak splitting is (n-1)-fold in the most energy regions, while the resonant peak splitting is (n-2)-fold in transmission zero (E ≈ 0.37). Nevertheless, three new resonant peaks appear at E ≈ 0.29, E ≈ 0.61 and E ≈ 0.71 under the addition of a periodically modulated magnetic field. Correspondingly, the resonance peak splitting becomes n-fold in the minigap at the edge of transmittance plateau (high energy side). It is determined that the number of quasibound states in the ZGNR can be controlled under a periodically modulated magnetic field. In addition, the conductance and local density of states (LDOS) of ZGNRs are discussed, respectively. With increasing the width of a single rectangular QD, the conductance gradually decreases in the Fermi energy. An uprush peak of the LDOS appears at the position of the conductance peaks or dips under a magnetic field. Therefore, these interesting quantum phenomena are expected to be used as the building blocks of the future nanoelectronics.

Megathrust Heterogeneity, Crustal Accretion, and a Topographic Embayment in the Western Nepal Himalaya: Insights From the Inversion of Thermochronological Data

AbstractBetween 81°30ʹE and 83°E, the Himalayan range's “perfect” arcuate shape is interrupted by an embayment. We hypothesize that thrust geometry and duplexing along the megathrust at midlower‐crustal depths play a leading role in growth of the embayment as well the southern margin of the Tibetan plateau. To test this hypothesis, we conducted thermokinematic modeling of published thermochronologic data from the topographic and structural embayment in the western Nepal Himalaya to investigate the three‐dimensional geometry and kinematics of the megathrust at midlower‐crustal depths. Models that can best reproduce observed cooling ages suggest that the megathrust in the western Nepal Himalaya is best described as two ramps connected by a long flat that extends further north than in segments to the east and west. These models suggest that the high‐slope zone along the embayment lies above the foreland limb of an antiformal crustal accretion zone on the megathrust with lateral and oblique ramps at midlower‐crustal depths. The lateral and oblique ramps may have initiated by ca. 10 Ma. This process may have controlled along‐strike variation in Himalayan‐plateau growth and therefore development of the topographic embayment. Finally, we analyze geological and morphologic features and propose an evolution model in which landscape and drainage systems across the central‐western Himalaya evolve in response to crustal accretion at depth and the three‐dimensional geometry of the megathrust. Our work highlights the importance of crustal accretion at different depths in orogenic‐wedge growth and that the midlower crustal accretion determines the location of plateau edge.

Seamount effects on micronekton at a subtropical central Pacific seamount

Seamounts are globally ubiquitous features with potential for increased biodiversity and biomass, including those of economically important fish. Although their ecological and economical importance is well known, the mechanisms for supporting seamount-associated communities are not well understood. In this study, the effects of an intermediate depth seamount (Cross Seamount) on the micronekton communities, forage for economically important bigeye tuna, are investigated. Relative biomass and composition estimates were calculated from multi-frequency active acoustic data from surveys over 3 years. Mean micronekton biomass was significantly higher than in the ambient environment and its composition differed over the flanks and plateau of Cross Seamount. The effects of the seamount extended ∼3.5 km away from the plateau's edge, possibly further below 400 m depth at the flanks. Micronekton occupied the water column from the surface to the 400 m deep plateau with dense aggregations immediately over the bottom at night. During the day, these micronekton migrated both horizontally and downward, occupying depths of 500–700 m, preferably along the upstream flank of the seamount. Descending micronekton from near-surface waters appeared to be temporarily blocked by the topography before swimming below the plateau at the flanks. Mechanisms supporting the increase in micronekton biomass are uncertain, although hydrographic data support topographic trapping of zooplankton and the existence of transient or semi-permanent Taylor caps.