Science China Earth Sciences最新文献

Using data from the regional broadband dense temporary array deployed by the ChinArray project, we applied the three-dimensional (3D) Kirchhoff migration method of the teleseismic P-wave receiver function to investigate discontinuity structures of the mantle transition zone (MTZ) in the central and western parts of the North China Craton (NCC) using a high-resolution 3D velocity model of the East Asian region. The results show that the 410-km discontinuity beneath the Datong Volcano is depressed by ∼10 km, indicating the presence of a high-temperature anomaly near the depth of 410 km, which is likely related to small-scale mantle upwelling caused by the dehydration of the stagnant Pacific Plate in the MTZ. The upwelling of hot material provides a heat source for surface magmatic activity. Beneath the Bohai Bay Basin, significant subsidence of the 660-km discontinuity is observed, and the transition zone here is extensively thickened. It’s suggested that the anomalies in this region are related to the stagnation of the Pacific slab in the MTZ. Although the thickness of the transition zone west of the North-South Gravity Lineament appears normal, we propose that the subducting front of the Pacific slab did not cross the gravity lineament in the NCC. In comparison, the small-scale subsidence of the 660-km discontinuity and the thickening of the MTZ observed north of the Hannuoba Volcano likely indicate that the slab crossed the gravity lineament at its turning point and remained in the MTZ. Furthermore, a local thickening of the MTZ is observed in the Dabie orogenic belt of the Qinling Mountains. This is believed to be a combined effect of lithospheric delamination into the transition zone in the lower Yangtze region and the stagnation of the Pacific Plate.

The Eocene-Oligocene transition (EOT) marked a rapid global cooling event, often considered as the beginning of the modern icehouse world. Influenced by various factors, including tectonic activity and paleogeographic settings, the terrestrial records indicate a diverse response of fauna and vegetation to this global event. We examined nine macrofossil assemblages from seven fossil localities on the southeastern margin of the Tibetan Plateau and from the mid-latitudinal Europe ranging from the latest Bartonian and Priabonian (37.71–33.9 Ma) to the Rupelian (33.9–27.82 Ma). Our aims were to trace and compare the vegetation history of both regions in the late Eocene and early Oligocene. The results show that both regions experienced changes in vegetation composition in response to climate change, characterized by a decrease in the percentages of broad-leaved evergreen elements and distinctive changes in general vegetation types. A general change in the overall vegetation type from subtropical broad-leaved evergreen forests in the late Eocene to temperate broad-leaved mixed deciduous evergreen forests, or mixed mesophytic forests, in the early Oligocene is recognized in both regions. The results indicate a clear change in leaf architecture, leaf margin states, and secondary venation types in the mid-latitudinal Europe, while the results from the south-eastern margin of the Tibetan Plateau show a distinct reduction in leaf size. Our data suggest that both global and regional factors played key roles in shaping the vegetation in the two regions.

One of the challenges in global change research is the significant uncertainty in global historical land use and land cover (LUCC) datasets, which are widely used as foundational data. In addition to the regional cropland area reconstructions, improving the grid allocation method is another feasible way to raise the reliability of historical LUCC data. In this study, an integrated reconstruction of the national cropland areas over the past 200 years was developed for 36 European countries. After that, the allocation algorithm was built using physiogeographic variables and historical city sites for accounting for land suitability and cultivation preferences, respectively. Finally, cropland data in Europe with a spatial resolution of 5′×5′ at five time sections from AD 1800 to 2000 were generated using the optimal allocation algorithm in accordance with the stages of the regional history. The results were as follows: (1) The dominant factors governing the distribution of croplands in Europe vary at different agricultural stages, but the results can be merged together. Land suitability was more optimal for allocation during the modern agricultural stage (AD 1950 and 2000); the priority index combined with land suitability and cultivation preference was more reasonable for allocation during the traditional agricultural stage (AD 1800). The average of the allocations by priority index and the land suitability could be adopted as the allocation results during the transitional stage (AD 1850 and 1900) because the grids for absolute differences within ±10 and ±20 percentage points between the results obtained from the above two allocations were above 80% and 95%, respectively, which means the two allocation results could be merged. (2) Over the past 200 years, the total cropland area in Europe first increased to a peak in AD 1900 and then decreased. Spatially, the centre of the higher cropland fraction shifted from the western part of Europe in AD 1800 to the eastern part of the continent after AD 1950. (3) Both the cropland area and the spatial distribution in this study are more reasonable than the global dataset HYDE3.2.

The phenomenon termed “zebra stripes” manifests as regular patterns in the energy-space (L shell) spectrum of energetic electrons (ranging from tens to hundreds keV) within the inner radiation belt. These structures exhibit drift-periodic behavior and commonly arise from large-scale electric field perturbations near the substorm onsets. In this study, we introduce a composite electric field model and replicate the formation, structure, and evolution of zebra stripes using a bounce-averaged test particle code under this electric field model. High-resolution measurements of energetic electrons obtained from the Van Allen Probes and the recently launched Macao Science Satellites-1 are used as initial conditions and served to validate our test particle simulations. Comparative analyses between observed data and simulations demonstrate our test particle method’s efficacy in capturing zebra stripes’ general behavior. Moreover, the composite model proves capable of reproducing realistic variations in the electric field within the inner radiation belt to a certain extent. Nevertheless, subtle differences emerge in the flux strength and the positions of stripes. These disparities primarily stem from limitations inherent in the electric field model and the initial conditions of the simulation. Acknowledging that the model represents an average case, it is conceivable that real-world scenarios may deviate from the average, thereby introducing variations in the observed phenomena.

The closure of the Paleo-Asian Ocean was a significant geological event in northern Pangea during the Carboniferous-Permian. It had a significant effect on climate, biota, and environmental conditions of the Late Paleozoic Ice Age, and resulted in the development of vast energy resources. This paper reports on the first discovery of marine red algal fossils in the Junggar Basin and its linkage to hydrocarbon generation. Red algae occur mainly in the Fengcheng Formation (ca. 300 Ma) and provide direct fossil evidence for closure of the Paleo-Asian Ocean. The red algal fossils contain well-preserved reproductive organs, such as cystocarps and carpospores. High concentrations of C₂₇ steranes (C₂₇ regular steranes/sum of C₂₇–C₂₉ regular steranes×100=14.30%–21.30%) and the marine biomarker 24-n-propylcholesterane (C₃₀ diasterane [βα20S]/sum of C₂₇–C₃₀ diasteranes [βα20S]×100=1.15%–1.85%) were detected in the red-algae-bearing hydrocarbon source rocks. Thermal experiments that simulate hydrocarbon generation show that the oil generation potential of the red-algae-bearing source rocks is 363.71 mg g⁻¹ total organic C. This result, combined with oil-source rock correlations, indicates these rocks contributed to the formation of oil and gas resources, particularly in the marginal areas of the depression. The lake basin inherited the water and biological conditions of the Paleo-Asian Ocean during a marine regression, which was an important factor in the development of these high-quality hydrocarbon source rocks in an alkaline saline lake. The results advance our understanding of the evolution of the Paleo-Asian Ocean, interactions between the ocean and a lake during the deposition of terrestrial hydrocarbon source rocks, and whether red algae can effectively generate hydrocarbons.

Tropical cloud clusters (TCCs) can potentially develop into tropical cyclones (TCs), leading to significant casualties and economic losses. Accurate prediction of tropical cyclogenesis (TCG) is crucial for early warnings. Most traditional deep learning methods applied to TCG prediction rely on predictors from a single time point, neglect the ocean-atmosphere interactions, and exhibit low model interpretability. This study proposes the Tropical Cyclogenesis Prediction-Net (TCGP-Net) based on the Swin Transformer, which leverages convolutional operations and attention mechanisms to encode spatiotemporal features and capture the temporal evolution of predictors. This model incorporates the coupled ocean-atmosphere interactions, including multiple variables such as sea surface temperature. Additionally, causal inference and integrated gradients are employed to validate the effectiveness of the predictors and provide an interpretability analysis of the model’s decision-making process. The model is trained using GridSat satellite data and ERA5 reanalysis datasets. Experimental results demonstrate that TCGP-Net achieves high accuracy and stability, with a detection rate of 97.9% and a false alarm rate of 2.2% for predicting TCG 24 hours in advance, significantly outperforming existing models. This indicates that TCGP-Net is a reliable tool for tropical cyclogenesis prediction.

Based on the significant weather report, CG lightning, composite radar reflectivity, and ERA5 reanalysis data, we first studied the spatiotemporal distribution characteristics of four types (only severe convective wind (SCW); SCW and hail; SCW and short-duration heavy rainfall (SDHR); and SCW, hail, and SDHR) of convective weather events related to SCW during the warm season (May to September) from 2011 to 2018 in North China. Second, severe convective cases producing SCW were selected to statistically analyze the initiation, decay, lifetime, and organizational characteristics of convective systems. Finally, using ERA5 reanalysis data and conventional surface observation data, preconvective soundings were constructed to explore the differences in environmental conditions for initiating convective systems between SCW and non-SCW. The results indicate that mixed-type of SCW and SDHR events occur more frequently over plains, while other types of convective weather occur more frequently over mountains. The frequency peak of SCW occurs in June, while mixed convective weather peaks in July. The initiation time of convective systems is concentrated between 1000 and 1300 BST, with apeak at 1200 BST. Over mountains, the daily peaks of ordinary and significant SCW generally occur at 1700–1800 BST and 1600–1700 BST, respectively, while over plains, the peak of ordinary SCW typically lags behind that of mountains by 1–2 hours. Additionally, SCW systems are mainly initiated over mountains, with most lifetimes lasting 7–13 hours. Nonlinear convective systems produce the most SCW events, followed by trailing-stratiform convective systems. The convective available potential energy (CAPE), downdraft convective available potential energy, and the temperature difference between 850 and 500 hPa can all distinguish between SCW systems and non-SCW systems occurring over plains. Compared to non-SCW convective systems, SCW convective systems over mountains are more likely to occur in environments with less precipitable water, while SCW convective systems over plains are more likely to occur in environments with higher CAPE and stronger deep-layer wind shear.

Fluids in subduction zones can have major effects on subduction dynamics. However, geophysical constraints on the scale and impact of fluid flow during continental subduction are still limited. Here we analyze the V_P/V_S ratios in the Western Alpine region, hosting one of the best-preserved fossil continental subduction zones worldwide, to investigate the impact of fluid flow during continental subduction. We found a belt of high V_P/V_S ratios >1.9 on the upper-plate side of the subduction zone, consistent with a partially serpentinized upper-plate mantle, and a belt of unusually low V_P/V_S ratios <1.7 on the lower-plate side, at depths shallower than 30 km. We propose that these low V_P/V_S ratios result from a widespread network of silica-rich veins, indicating past fluid flow along the continental subduction interface. Our results suggest that past fluid flow may have reduced the effective stress along the subduction interface thus favoring continental subduction.

Magnetic holes at the ion-to-electron kinetic scale (KSMHs) are one of the extremely small intermittent structures generated in turbulent magnetized plasmas. In recent years, the explorations of KSMHs have made substantial strides, driven by the ultra-high-precision observational data gathered from the Magnetospheric Multiscale (MMS) mission. This review paper summarizes the up-to-date characteristics of the KSMHs observed in Earth’s turbulent magnetosheath, as well as their potential impacts on space plasma. This review starts by introducing the fundamental properties of the KSMHs, including observational features, particle behaviors, scales, geometries, and distributions in terrestrial space. Researchers have discovered that KSMHs display a quasi-circular electron vortex-like structure attributed to electron diamagnetic drift. These electrons exhibit noticeable non-gyrotropy and undergo acceleration. The occurrence rate of KSMH in the Earth’s magnetosheath is significantly greater than in the solar wind and magnetotail, suggesting the turbulent magnetosheath is a primary source region. Additionally, KSMHs have also been generated in turbulence simulations and successfully reproduced by the kinetic equilibrium models. Furthermore, KSMHs have demonstrated their ability to accelerate electrons by a novel non-adiabatic electron acceleration mechanism, serve as an additional avenue for energy dissipation during magnetic reconnection, and generate diverse wave phenomena, including whistler waves, electrostatic solitary waves, and electron cyclotron waves in space plasma. These results highlight the magnetic hole’s impact such as wave-particle interaction, energy cascade/dissipation, and particle acceleration/heating in space plasma. We end this paper by summarizing these discoveries, discussing the generation mechanism, similar structures, and observations in the Earth’s magnetotail and solar wind, and presenting a future extension perspective in this active field.

Extensive research efforts have revealed that the Martian dust storms can perturb the upper atmospheric condition and as a consequence, enhance plasma density and photoelectron flux in the ionosphere. However, previous observational studies of the Martian dust storm impacts have been restricted to regions below 400 km, which limits our understanding of the Martian dust storm effects in the upper ionosphere and magnetosphere. Here, based on the suprathermal electron measurements made by the Solar Wind Electron Analyzer onboard the Mars Atmosphere and Volatile Evolution, we identify with an automatic procedure the occurrences of all photoelectron boundary (PEB) crossings at solar zenith angle below 120° (with a dust-free median altitude of about 600 km). Using the dayside PEB as a proxy of the upper ionospheric and magnetospheric condition, we analyze the variations of the PEB altitude during the 2018 global dust storm (GDS) of Mars Year 34 (MY34) and compare them with the period in MY33 when there was no global dust storm. We conclude that the column dust optical depth (CDOD) emerges as one of the main driving factors for PEB altitude variations during the GDS. Our analysis implies that the GDS can affect the Martian upper atmosphere and ionosphere over considerable distances and extended time scales.