The geomorphological features and continuity of the Kyushu-Palau Ridge (KPR)

The Philippine Basin,surrounded by a series of oceanic trenches,is an independent deep ocean basin in the West Pacific Ocean.Its middle part is divided into three marginal sea sub-basins by the Kyushu-Palau and West Mariana Ridges,namely,the West Philippine Basin,the Shikoku and Parece Vela Basins and the Mariana Trough.This paper,through the analysis of the geomorphologic features and gravity and magnetic characteristics of the basin and identification of striped magnetic anomalies,suggests that the entire Philippine Basin developed magnetic lineation of oceanic nature,and therefore,the entire basin is of the nature of oceanic crust.The basin has developed a series of special geomorphic units with different shapes.The KPR runs through the entire Philippine Basin.From the view of geomorphologic features,the KPR is a discontinuous seamount chain （chain-shaped seamounts） and subduction beneath the Japanese Island arc at the Nankai Trough which is the natural boundary between the basin and the Japanese Island arc.At the positions of 25 N,24 N,23 N and 18 N,obvious discontinuity is shown,which belongs to natural topographic discontinuity.Therefore,the KPR is topographically discontinuous.

Topographic and geomorphological features and tectogenesis of the southern section of the Kyushu-Palau Ridge(KPR)and its adjacent areas

The Philippine Sea is the largest marginal sea in the Western Pacific Ocean and is divided into two parts by the Kyushu-Palau Ridge(KPR).The western part is the West Philippine Basin,and the eastern part consists of the Shikoku and Parece Vela basins.Based on surveyed data of massive high-resolution multibeam bathymetric data and sub-bottom profiles data collected from the southern section of the KPR from 2018 to 2021,this paper analyzes the topographic and geomorphological features,shallow sedimentary features,and tectonic genesis of the southern section of the KPR,obtaining the following conclusions.The southern section of the KPR has complex and rugged topography,with positive and negative topography alternatingly distributed and a maximum height difference of 4086 m.The slope of seamounts in this section generally exceeds 10°and is up to a maximum of 59°.All these contribute noticeably discontinuous topography.There are primarily nine geomorphological types in the southern section of the KPR,including seamounts,ridges,and intermontane valleys,etc.Among them,seven independent seamount groups are divided by five large troughs,forming an overall geomorphological pattern of seven abyssal seamount groups and five troughs.This reflects the geomorphological features of a deep oceanic ridge.Intramontane basins and intermontane valleys in the southern section of the KPR are covered by evenly thick sediments.In contrast,sediments in ridges and seamounts in this section are thin or even missing,with slumps developing locally.Therefore,the sediments are discontinuous and unevenly developed.The KPR formed under the control of tectonism such as volcanic activities and plate movements.In addition,exogenic forces such as underflow scouring and sedimentation also play a certain role in shaping seafloor landforms in the KPR.

Oceanic crustal structure and tectonic origin of the southern Kyushu-Palau Ridge in the Philippine Sea

A new high-resolution velocity model of the southern Kyushu-Palau Ridge(KPR) was derived from an activesource wide-angle seismic reflection/refraction profile. The result shows that the KPR crust can be divided into the upper crust with the P-wave velocity less than 6.1 m/s, and lower crust with P-wave velocity between 6.1 km/s and 7.2 km/s. The crustal thickness of the KPR reaches 12.0 km in the center, which gradually decreases to 5.0–6.0 km at sides. The velocity structure of the KPR is similar to the structures of the adjacent West Philippine Basin and Parece Vela Basin(PVB), indicating a typical oceanic crust. Isostatic analysis shows that some regional compensation occurs during the loading of the KPR, which implies that the KPR was built mainly by magmatism during the splitting of the Izu-Bonin-Mariana arc and the following back-arc seafloor spreading of the PVB during30–28 Ma BP. The absence of the thick middle crust(6.0–6.5 km/s) and high velocity lower-crustal layers(7.2–7.6 km/s) suggest that arc magmatism plays a less important role in the KPR formation.

Tectonic implications of the subduction of the Kyushu-Palau Ridge beneath the Kyushu,southwest Japan

The Kyushu-Palau Ridge(KPR),a remnant arc on the Philippine Sea Plate(PSP),is subducting beneath the Kyushu,southwest Japan.Influenced by the subducting KPR,the Kyushu subduction zone corresponding to the KPR is significantly different from Shikoku subduction zone in terms of gravity anomalies,seismicity,the stress state,and the subducting slab morphology.Significant negative free-air and Bouguer gravity anomalies are observed in a prolonged area of KPR,southeast of the Miyazaki Plain,indicating that this is where KPR overlaps the overriding plate.The gravity anomaly in this area is much lower than that in other areas where the inferred KPR extends,suggesting that the subduction of the buoyant KPR may cause the lower mantle density to decrease.More earthquakes have occurred in Hyuga-nada region where the KPR subducts than in Shikoku forearc and other areas in the Kyushu forearc,indicating that the subduction of the KPR enhances the local coupling between the subducting and overriding plates.The centroid moment tensor(CMT)mechanism of earthquakes shows that stress is concentrated in the accumulated crust beneath the Kyushu forearc corresponding to the KPR,and the shallow thrusting events in the obducting plate are caused by the KPR subduction.The buoyant KPR,with a large volume of low-density sediments,was responsible for the differences of the subduction depth and dip angle of the subducting Philippine Sea(PS)slab between northern Kyushu and Shikoku.The seismic gaps and the sudden change of the dipping angle of the subducting PS slab indicate that slab tear may have occurred along the west side of the KPR beneath southwest Kyushu.A two-tear model was proposed,and the subduction of the buoyant KPR was believed to play an important role in the slab tear.

Characteristics of gravity and magnetic fields and deep structural responses in the southern part of the Kyushu-Palau Ridge

The southern part of the Kyushu-Palau Ridge(KPR)is located at the conjunction of the West Philippine Basin,the Parece Vela Basin,the Palau Basin,and the Caroline Basin.This area has extremely complex structures and is critical for the research on the tectonic evolution of marginal seas in the Western Pacific Ocean.However,only few studies have been completed on the southern part,and the geophysical fields and deep structures in this part are not well understood.Given this,this study finely depicts the characteristics of the gravity and magnetic anomalies and extracts information on deep structures in the southern part of the KPR based on the gravity and magnetic data obtained from the 11th expedition of the deep-sea geological survey of the Western Pacific Ocean conducted by the Guangzhou Marine Geological Survey,China Geological Survey using the R/V Haiyangdizhi 6.Furthermore,with the data collected on the water depth,sediment thickness,and multichannel seismic transects as constraints,a 3D density model and Moho depths of the study area were obtained using 3D density inversion.The results are as follows.(1)The gravity and magnetic anomalies in the study area show distinct zoning and segmentation.In detail,the gravity and magnetic anomalies to the south of 11°N of the KPR transition from high-amplitude continuous linear positive anomalies into low-amplitude intermittent linear positive anomalies.In contrast,the gravity and magnetic anomalies to the north of 11°N of the KPR are discontinuous and show alternating positive and negative anomalies.These anomalies can be divided into four sections,of which the separation points correspond well to the locations of deep faults,thus,revealing different field-source attributes and tectonic genesis of the KPR.(2)The Moho depth in the basins in the study area is 6-12 km.The Moho depth in the southern part of KPR show segmentation.Specifically,the depth is 10‒12 km to the north of 11°N,12‒14 km from 9.5°N to 11°N,14-16 km from 8.5°N to 9.5°N,and 16‒25 km in the Palau Islands.(3)The KPR is a remnant intra-oceanic arc with the oceanic-crust basement.which shows noticeably discontinuous from north to south in geological structure and is intersected by NEE-trending lithospheric-scale deep faults.With large and deep faults F3 and F1(the Mindanao fault)as boundaries overall,the southern part of the KPR can be divided into three zones.In detail,the portion to the south of 8.5°N(F3)is a tectonically active zone,the KPR portion between 8.5°N and 11°N is a tectonically active transition zone,and the portion to the north of 11°N is a tectonically inactive zone.(4)The oceanic crust in the KPR is slightly thicker than that in the basins on both sides of the ridge,and it is inferred that the KPR formed from the thickening of the oceanic crust induced by the upwelling of deep magma in the process of rifting of remnant arcs during the Middle Oligocene.In addition,it is inferred that the thick oceanic crust under the Palau Islands is related to the constant upwelling of deep magma induced by the continuous northwestward subduction of the Caroline Plate toward the Palau Trench since the Late Oligocene.This study provides a scientific basis for systematically understanding the crustal attributes,deep structures,and evolution of the KPR.

Crustal structure and variation along the southern part of the Kyushu-Palau Ridge

As an interoceanic arc,the Kyushu-Palau Ridge(KPR)is an exceptional place to study the subduction process and related magmatism through its interior velocity structure.However,the crustal structure and its nature of the KPR,especially the southern part with limited seismic data,are still in mystery.In order to unveil the crustal structure of the southern part of the KPR,this study uses deep reflection/refraction seismic data recorded by 24 ocean bottom seismometers to reconstruct a detailed P-wave velocity model along the ridge.Results show strong alongridge variations either on the crustal velocity or the thickness of the KPR.P-wave velocity model is featured with(1)a crustal thickness between 6–12 km,with velocity increases from 4.0 km/s to 7.0 km/s from top to bottom;(2)high gradient(~1 s^(-1))in the upper crust but low one(<0.2 s^(-1))in the lower crust;(3)a slow mantle velocity between 7.2 km/s and 7.6 km/s in the uppermost mantle;and(4)inhomogenous velocity anomalies in the lower crust beneath seamounts.By comparing with the mature arc in the Izu-Bonin-Mariana arc in the east,this study suggests the southern part of KPR is a thicken oceanic crust rather than a typical arc crust.The origin of low velocities in the lower crust and upper mantle may be related with crustal differentiation,which implies advanced crustal evolution from normal oceanic crust to partly thicken oceanic crust.High velocities in the lower crust are related to the difference in magmatism.

Structural features in the mid-southern section of the Kyushu–Palau Ridge based on satellite altimetry gravity anomaly

The Kyushu–Palau Ridge(KPR),an anti-S-shaped submarine highland at the center of the Philippine Sea Plate(PSP),is considered the residual arc of the Izu–Bonin–Mariana Island Arc,which retains key information about the cessation of the Western Philippine Basin(WPB)expansion and the Parece Vela Basin(PVB)breakup.Herein,using the new generation of satellite altimetry gravity data,high-precision seafloor topography data,and newly acquired ship-borne gravity data,the topographic and gravity characteristics of the KPR mid-southern section and adjacent region are depicted.The distribution characteristics of the faults were delineated using the normalized vertical derivative–total horizontal derivative method(NVDR-THDR)and the minimum curvature potential field separation method.The Moho depth and crustal thickness were inverted using the rapid inversion method for a double-interface model with depth constraints.Based on these results,the crust structure features in the KPR mid-southern section,and the“triangular”structure geological significance where the KPR and Central Basin Rift(CBR)of the WPB intersect are interpreted.The KPR crustal thickness is approximately 6–16 km,with a distinct discontinuity that is slightly thicker than the normal oceanic crust.The KPR mid-southern section crust structure was divided into four segments(S1–S4)from north to south,formed by the CBR eastward extension joint action and clockwise rotation of the PVB expansion axis and the Mindanao fault zone blocking effect.

Cu-Zn isotope compositions of hydrothermal sediments from the southern Mid-Atlantic Ridge:implications to the sediment formation and mineral exploration

Six hydrothermal sediment samples were collected from the Xunmei and Tongguan hydrothermal fields along the southern Mid-Atlantic Ridge during the China Ocean Cruise DY46 in 2017.Sulfides and oxides in the samples were separated,and Cu and Zn isotope compositions were analyzed.Results show that the ranges ofδ^(65)Cu values of the bulk sediments,sulfides,and oxides were 0.36‰-2.46‰,-0.21‰-1.10‰,and 0.68‰-1.52‰,respectively.Theδ^(65)Cu values of sulfides in four samples(46II-14,46II-30,46III-06,and 46II-09)were relatively low(-0.21‰-0.50‰),corresponding to theδ^(65)Cu values of sulfides from inactive old hydrothermal chimneys in northern Mid-Atlantic Ridge(n MAR),suggesting that the sulfides in the sediments were originated from collapsed dead chimney mainly.While theδ^(65)Cu values of the other two samples(46III-02 and 46III-08)were relatively high(1.10‰-0.96‰),corresponding to theδ^(65)Cu values for active hydrothermal chimneys sulfides in n MAR,which indicated that the sulfides in these two samples might mainly come from sulfide particles settled from active hydrothermal plume.Because of the high density of sulfide particles,they tended to settle near the hydrothermal vents first.Therefore,highδ^(65)Cu values of sulfides in 46III-02 and 46III-08 implied that undiscovered active hydrothermal vents near the sampling positions of 46III-02 in the Xunmei hydrothermal field and 46III-08 in the Tongguan hydrothermal field.Theδ^(66)Zn values of hydrothermal sediments and sulfides ranged 0.11‰-0.43‰and 0.29‰-0.67‰,respectively.In the four samples from the Xunmei hydrothermal field,a positive correlation was found between the distance of the sampling position from sulfide mineralized spot and the Zn isotopic ratio,showing that the greater the distance from the mineralized spot,the heavier the Zn isotope composition as seen in two samples(46II-30 and 46II-14)of the Xunmei-3 spot.This result aligned with the findings of Wilkinson et al.(2005)and Baumgartner et al.(2023),suggesting that the lower the Zn isotope composition,the closer it is to the hydrothermal vent.However,in the Xunmei hydrothermal field,the Zn isotope composition in the other two samples(46III-02and 46III-06)showed the opposite trend.This indicated that there might be an active hydrothermal vent near the sampling location of sample 46III-02.This observation aligned with the Cu isotope analysis results.This study showed that Cu-Zn isotopes are good indicators for understanding the formation mechanisms of hydrothermal sediments and for locating active hydrothermal vents.

Discovery and characterization of a new hydrothermal field at 2°N on the slow-spreading Carlsberg Ridge

A new hydrothermal field(Tianshi)was discovered on the rift valley wall through plume anomaly surveys and geological work conducted in 2012 and 2018 between 2°35′N and 2°43′N of the slow-spreading Carlsberg Ridge(CR).Here,the results of two expeditions conducted to detect and characterize the new hydrothermal field are reported.Mineralogical and geochemical data,as well as 14 C ages of a sediment core collected near the field are presented to reveal the hydrothermal history.Results show that the Tianshi field is a basalt-hosted hydrothermal system.Geochemical data of the sediments collected near the field indicate a strong hydrothermal contribution,and hydrothermal Fe and Cu fluxes range from 30 to 155 mg/(cm^(2)·ka)and 0.59 to 11.49 mg/(cm^(2)·ka),respectively.Temporal variations in the fluxes of hydrothermal Fe indicate that there have been at least three amplified hydrothermal venting events(H 1,H 2,and H 3)in the Tianshi field over the last 35.2 ka,in 28.6-35.2 ka BP,22.0-27.6 ka BP,and 1.2-11.4 ka BP,respectively.Hydrothermal event H 2 was driven by an increased magmatic production associated with sea level fall during the Last Glacial Maximum,while event H 3 was promoted by tectonic activity associated with a rapid sea level rise.This study further verified the role of sea level change in modulating hydrothermal activity on mid-ocean ridges.

Hydrographic Characteristics and Oceanic Heat Flux in the Upper Arctic Ocean over the Alpha Ridge Observed by the DTOP Platform in 2018 and 2021

In 2018 and 2021,the Drift-Towing Ocean Profilers(DTOP)provided extensive temperature and salinity data on the upper 120m ocean through their drifts over the Alpha Ridge north of the Canada Basin.The thickness and temperature maximum of Alaska Coastal Water(ACW)ranged from 20m to 40m and-1.5℃to-0.8℃,respectively,and the salinity generally maintained from 30.2 to 32.5.Comparison with World Ocean Atlas 2018’s climatology manifested a 40m-thick and warm ACW roughly ex-ceeding the temperature maximum by 0.4–0.5℃in June–August 2021.This anomalously warm ACW was highly related to the ex-pansion of the Beaufort Gyre in the negative Arctic Oscillation phase.During summer,the under-ice oceanic heat flux F_(w)^(OHF)was elevated,with a maximum value of above 25Wm^(-2).F_(w)^(OHF)was typically low in the freezing season,with an average value of 1.2Wm^(-2).The estimates of upward heat flux contributed by ACW to the sea ice bottom F_(w)^(OHF)were in the range of 3–4Wm^(-2)in June–August 2021,when ACW contained a heat content of more than 80MJm^(-2).The heat loss over this period was driven by a weak stratification upon the ACW layer associated with a surface mixed layer(SML)approaching the ACW core.After autumn,F_(w)^(OHF)was reduced(<2 Wm^(-2))except during rare events when it elevated F_(w)^(OHF)slightly.In addition,the intensive and widespread Ekman suction,which created a violent upwelling north of the Canada Basin,was largely responsible for the substantial cooling and thinning of the ACW layer in the summer of 2021.

Characteristics of the Deep Crustal Structure of the Greenland–Iceland–Faroe Ridge in the North Atlantic

The Greenland–Iceland–Faroe Ridge,located between the central eastern part of Greenland and the northwestern edge of Europe,spans across the North Atlantic.As the core component of the Greenland–Iceland–Faroe Ridge,the Iceland is an alkaline basalt area,which belongs to the periodic submarine magmatism and submarine volcano eruption resulting from mantle plume upwelling(Jiang et al.,2020).For the oceanic plateaus,the characteristics of the Iceland are closest to the continental crust,so the Iceland is considered the most suitable for simulating the earliest continental crust on the Earth(Reimink et al.,2014).

Nuclear charge radius predictions by kernel ridge regression with odd-even effects

The extended kernel ridge regression(EKRR)method with odd-even effects was adopted to improve the description of the nuclear charge radius using five commonly used nuclear models.These are:(i)the isospin-dependent A^(1∕3) formula,(ii)relativistic continuum Hartree-Bogoliubov(RCHB)theory,(iii)Hartree-Fock-Bogoliubov(HFB)model HFB25,(iv)the Weizsacker-Skyrme(WS)model WS*,and(v)HFB25*model.In the last two models,the charge radii were calculated using a five-parameter formula with the nuclear shell corrections and deformations obtained from the WS and HFB25 models,respectively.For each model,the resultant root-mean-square deviation for the 1014 nuclei with proton number Z≥8 can be significantly reduced to 0.009-0.013 fm after considering the modification with the EKRR method.The best among them was the RCHB model,with a root-mean-square deviation of 0.0092 fm.The extrapolation abilities of the KRR and EKRR methods for the neutron-rich region were examined,and it was found that after considering the odd-even effects,the extrapolation power was improved compared with that of the original KRR method.The strong odd-even staggering of nuclear charge radii of Ca and Cu isotopes and the abrupt kinks across the neutron N=126 and 82 shell closures were also calculated and could be reproduced quite well by calculations using the EKRR method.

Environmental characteristics of trace metals in seawater from the Ninety East Ridge in the Indian Ocean

The Ninety East Ridge in the Indian Ocean has complex and unique characteristics.The concentrations and distribution characteristics of 10 trace metals(V,Cr,Mn,Fe,Co,Ni,Cu,Cd,Pb,and U)in seawater from the Ninety East Ridge in the Indian Ocean were investigated.Results show that the average concentrations of different trace metals in all the collected seawater samples were 1.134μg/L for V,0.158μg/L for Cr,0.489μg/L for Mn,0.427μg/L for Fe,0.011μg/L for Co,0.395μg/L for Ni,0.403μg/L for Cu,0.097μg/L for Cd,0.139μg/L for Pb,and 3.470μg/L for U.Differences in the horizontal and vertical distributions of all measured trace metals were revealed,and the occurrence of high concentrations was nonuniform.In addition,the significant differences in the concentration distribution of different trace metals in seawater on both sides of the Ninety East Ridge present regional segmentation in the area for various trace metals in deep sea water.This study provided basic data for future investigations on the environmental and ecological impact of trace metals in the Indian Ocean and the potential water mass transport mechanism.

Microearthquake reveals the lithospheric structure at midocean ridges and oceanic transform faults

Mid-ocean ridge and oceanic transforms are among the most prominent features on the seafloor surface and are crucial for understanding seafloor spreading and plate tectonic dynamics,but the deep structure of the oceanic lithosphere remains poorly understood.The large number of microearthquakes occurring along ridges and transforms provide valuable information for gaining an indepth view of the underlying detailed seismic structures,contributing to understanding geodynamic processes within the oceanic lithosphere.Previous studies have indicated that the maximum depth of microseismicity is controlled by the 600-℃isotherm.However,this perspective is being challenged due to increasing observations of deep earthquakes that far exceed this suggested isotherm along mid-ocean ridges and oceanic transform faults.Several mechanisms have been proposed to explain these deep events,and we suggest that local geodynamic processes(e.g.,magma supply,mylonite shear zone,longlived faults,hydrothermal vents,etc.)likely play a more important role than previously thought.

Molybdenum isotope composition of the upper mantle and its origin:insight from mid-ocean ridge basalt

The molybdenum(Mo)isotope system is pivotal in reconstructing marine redox changes throughout Earth’s history and has emerged as a promising tracer for igneous and metamorphic processes.Understanding its composition and variation across major geochemical reservoirs is essential for its application in investigating high-temperature processes.However,there is debate regarding theδ^(98/95)Mo value of the Earth’s mantle,with estimates ranging from sub-chondritic to super-chondritic values.Recent analyses of global mid-ocean ridge basalt(MORB)glasses revealed significantδ^(98/95)Mo variations attributed to mantle heterogeneity,proposing a two-component mixing model to explain the observed variation.Complementary studies confirmed the sub-chondriticδ^(98/95)Mo of the depleted upper mantle,suggesting remixing of subduction-modified oceanic crust as a plausible mechanism.These findings underscore the role of Mo isotopes as effective tracers for understanding dynamic processes associated with mantle-crustal recycling.

Gravity Fault Subsidence and Beach Ridges Progradation in Quinta-Cassino (RS) Coastal Plain, Brazil

Ground penetrating radar (GPR) surveys have being applied to investigate very near-surface stratification of sedimentary units in coastal plains and to define their depositional conditions. This paper presents, however, low-frequency GPR survey to investigate fault-related depositional systems at greater depths. The Quinta-Cassino area in the Rio Grande do Sul Coastal Plain (RGSCP, Brazil) shows a wide strandplain that is made off by very long, continuous, and linear geomorphic features (beach ridges). This strandplain extends for ~70 km southward. The beach ridges show low-angle truncations against the Quinta escarpment, and also truncations in the strandplain. The traditional approach points that RGSCP was developed by juxtaposition of four lagoons/barrier systems as consequence of sea level changes;previous model assumes that no deformational episode occurred in RGSCP. The geophysical and geological surveys carried out in this area showed the existence of listric fault controlling the beach ridges in the escarpments and hanging-wall blocks. The radargrams could distinguish Pleistocene basement unit anticlockwise rotation, thickening of beach ridges radarfacies close to listric normal faults, and horst structures. These deformational features indicate that the extensional zone of a large-scale gravity-driven structure controlled the mechanical subsidence, the Holocene sedimentation and its stratigraphic and geomorphic features in the Quinta-Cassino area to build up an asymmetric delta. The results point to a new approach in dealing with RGSCP Holocene evolution.

基于Bayesian-Ridge模型的煤炭企业净资产收益率影响因素

为评估各因素对净资产收益的影响程度,以2002—2022年我国上市煤炭企业的相关数据为研究样本,基于机器学习中的Bayesian-Ridge模型进行训练,分析各自变量对因变量的影响程度,并与传统OLS模型进行对比。实验结果表明:在影响因素权重大小方面,Bayesian-Ridge模型与OLS模型均显示经营负债比率对净资产收益率影响最大,其次是国有持股比例和营业利润率;在方法层面,随样本点数据增加,Bayesian-Ridge模型可降低先验分布的影响;Bayesian-Ridge模型决定系数R~2为0.002 3,高于OLS模型的0.001 8,在该问题研究中Bayesian-Ridge模型优于OLS模型。

Review on the fully mulched ridge–furrow system for sustainable maize production on the semi-arid Loess Plateau

The fully mulched ridge–furrow(FMRF) system has been widely used on the semi-arid Loess Plateau of China due to its high maize(Zea mays L.) productivity and rainfall use efficiency. However, high outputs under this system led to a depletion of soil moisture and soil nutrients, which reduces its sustainability in the long run. Therefore, it is necessary to optimize the system for the sustainable development of agriculture. The development, yield-increasing mechanisms,negative impacts, optimization, and their relations in the FMRF system are reviewed in this paper. We suggest using grain and forage maize varieties instead of regular maize;mulching plastic film in autumn or leaving the mulch after maize harvesting until the next spring, and then removing the old film and mulching new film;combining reduced/notillage with straw return;utilizing crop rotation or intercropping with winter canola(Brassica campestris L.), millet(Setaria italica), or oilseed flax(Linum usitatissimum L.);reducing nitrogen fertilizer and partially replacing chemical fertilizer with organic fertilizer;using biodegradable or weather-resistant film;and implementing mechanized production. These integrations help to establish an environmentally friendly, high quality, and sustainable agricultural system, promote highquality development of dryland farming, and create new opportunities for agricultural development in the semi-arid Loess Plateau.

Aseismic ridge subduction and flat subduction:Insights from three-dimensional numerical models

Flat subduction can significantly influence the distribution of volcanism,stress state,and surface topography of the overriding plate.However,the mechanisms for inducing flat subduction remain controversial.Previous two-dimensional(2-D)numerical models and laboratory analogue models suggested that a buoyant impactor(aseismic ridge,oceanic plateau,or the like)may induce flat subduction.However,three-dimensional(3-D)systematic studies on the relationship between flat subduction and buoyant blocks are still lacking.Here,we use a 3-D numerical model to investigate the influence of the aseismic ridge,especially its width(which is difficult to consider in 2-D numerical models),on the formation of flat subduction.Our model results suggest that the aseismic ridge needs to be wide and thick enough to induce flat subduction,a condition that is difficult to satisfy on the Earth.We also find that the subduction of an aseismic ridge parallel to the trench or a double aseismic ridge normal to the trench has a similar effect on super-wide aseismic ridge subduction in terms of causing flat subduction,which can explain the flat subduction observed beneath regions such as Chile and Peru.

Mulching broad ridges with a woven polypropylene fabric increases the growth and yield of young pear trees ‘Yuluxiang' in the North China Plain

Unlike traditional ridging, mulching broad ridges with a woven polypropylene fabric (WPF) can reduce soil evaporation during the drought season and avoid long saturation time in the root zone of pear trees during the rainy season. In this study, field experiments were conducted from 2017 to 2020 in a pear orchard in the North China Plain to investigate the effects of mulching broad ridges (0.3 m in height and 2 m in width) with WPF on soil temperature and moisture, nitrogen leaching, vegetative and reproductive growth of young pear trees(Pyrus bretschneideri Rehd.‘Yuluxiang’). The experiments involved two treatments, namely, control (traditional no-ridge planting without mulching) and mulching broad ridges with WPF (RM treatment). The results showed that the RM treatment increased soil moisture and temperature and decreased nitrogen leaching, resulting in vigorous growth of the young pear trees. Moreover, the RM treatment increased the tree trunk cross-sectional area and height of the young pear trees by 37%and 8%in 2020, respectively. The nitrate nitrogen content at the soil layer depth of 0-30 cm was significantly higher in the RM than that in control. Furthermore, the RM treatment significantly increased the fruit yield due to larger tree size. In addition, compared with control, significantly higher fruit soluble solid content of RM treatment was detected in 2020. High precipitation (423 mm) occurred during fruit enlargement stage in 2020, RM treatment decreased the rainfall infiltration in the ridge and the soil moisture in root region, resulting in the improvement of fruit quality, compared with control.Therefore, mulching broad ridges with WPF can be implemented to increase soil moisture during drought season, soil temperature, and nitrate nitrogen content, thereby improving the growth and fruit yield of young pear trees. Additionally, it can reduce soil moisture in the root zone during the rainy season and improve the fruit quality of the trees. Finally, it can reduce nitrate nitrogen leaching, thereby reducing environmental pollution.