Showing papers in "Science China-earth Sciences in 2021"

Mapping the permafrost stability on the Tibetan Plateau for 2005–2015

Abstract: Data scarcity is a major obstacle for high-resolution mapping of permafrost on the Tibetan Plateau (TP). This study produces a new permafrost stability distribution map for the 2010s (2005–2015) derived from the predicted mean annual ground temperature (MAGT) at a depth of zero annual amplitude (10–25 m) by integrating remotely sensed freezing degree-days and thawing degree-days, snow cover days, leaf area index, soil bulk density, high-accuracy soil moisture data, and in situ MAGT measurements from 237 boreholes on the TP by using an ensemble learning method that employs a support vector regression model based on distance-blocked resampled training data with 200 repetitions. Validation of the new permafrost map indicates that it is probably the most accurate of all currently available maps. This map shows that the total area of permafrost on the TP, excluding glaciers and lakes, is approximately 115.02 (105.47–129.59) ´ 104 km2. The areas corresponding to the very stable, stable, semi-stable, transitional, and unstable types are 0.86 ´ 104, 9.62 ´ 104, 38.45 ´ 104, 42.29 ´ 104, and 23.80 ´ 104 km2, respectively. This new map is of fundamental importance for engineering planning and design, ecosystem management, and evaluation of the permafrost change in the future on the TP as a baseline.

Aboveground biomass and its spatial distribution pattern of herbaceous marsh vegetation in China

Abstract: Herbaceous marsh is the most widely distributed type of marsh wetland ecosystem, and has important ecological functions such as water conservation, climate regulation, carbon storage and fixation, and sheltering rare species. The carbon sequestration function of herbaceous marsh plays a key role in slowing climate warming and maintaining regional environmental stability. Vegetation biomass is an important index reflecting the carbon sequestration capacity of wetlands. Investigating the biomass of marsh vegetation can provide a scientific basis for estimating the carbon storage and carbon sequestration capacity of marshes. Based on field survey data of aboveground biomass of herbaceous marsh vegetation and the distribution data set of marsh in China, we analyzed the aboveground biomass and its spatial distribution pattern of herbaceous marsh on a national scale for the first time. The results showed that in China the total area of herbaceous marsh was 9.7×104 km2, the average density of aboveground biomass of herbaceous marsh vegetation was 227.5±23.0 g C m−2 (95% confidence interval, the same below), and the total aboveground biomass was 22.2±2.2 Tg C (1 Tg=1012 g). The aboveground biomass density of herbaceous marsh vegetation is generally low in Northeast China and the Tibetan Plateau, and high in central North China and coastal regions in China. In different marsh distribution regions of China, the average biomass density of herbaceous marsh vegetation from small to large was as follows: temperate humid and semi-humid marsh region (182.3±49.3 g C m−2)

Orbital-scale Asian summer monsoon variations: Paradox and exploration

Abstract: The Asian summer monsoon (ASM) is a vast climate system, whose variability is critical to the livelihoods of billions of people across the Asian continent. During the past half-century, much progress has been made in understanding variations on a wide range of timescales, yet several significant issues remain unresolved. Of note are two long-standing problems concerning orbital-scale variations of the ASM. (1) Chinese loess magnetic susceptibility records show a persistent glacial-interglacial dominated ~100 kyr (thousand years) periodicity, while the cave oxygen-isotope (δ18O) records reveal periodicity in an almost pure precession band (~20 kyr periodicity)—the “Chinese 100 kyr problem”. (2) ASM records from the Arabian Sea and other oceans surrounding the Asian continent show a significant lag of 8–10 kyr to Northern Hemisphere summer insolation (NHSI), whereas the Asian cave δ18O records follow NHSI without a significant lag—a discrepancy termed the “sea-land precession-phase paradox”. How can we reconcile these differences? Recent and more refined model simulations now provide spatial patterns of rainfall and wind across the precession cycle, revealing distinct regional divergences in the ASM domain, which can well explain a large portion of the disparities between the loess, marine, and cave proxy records. Overall, we also find that the loess, marine, and cave records are indeed complementary rather than incompatible, with each record preferentially describing a certain aspect of ASM dynamics. Our study provides new insight into the understanding of different hydroclimatic proxies and largely reconciles the “Chinese 100 kyr problem“ and “sea-land precession-phase paradox”.

Aftershock sequence relocation of the 2021 MS7.4 Maduo Earthquake, Qinghai, China

Abstract: The 2021 Qinghai Maduo MS7.4 earthquake was one of the strongest earthquakes that occurred in the Bayan Har block of the Tibetan Plateau during the past 30 years, which spatially filled in the gap of strong earthquake in the eastern section of the northern block boundary. In this study, the aftershock sequence within 8 days after the mainshock was relocated by double difference algorithm. The results show that the total length of the aftershock zone is approximately 170 km; the mainshock epicenter is located in the center of the aftershock zone, indicating a bilateral rupture. The aftershocks are mainly distributed along NWW direction with an overall strike of 285°. The focal depth profiles indicate that the seismogenic fault is nearly vertical and dips to southwest or northeast in different sections, indicating a complex geometry. There is an aftershock gap located to the southeast of the mainshock epicenter with a scale of approximately 20 km. At the eastern end of the aftershock zone, horsetail-like branch faults show the terminal effect of a large strike-slip fault. There is a NW-trending aftershock zone on the north side of the western section, which may be a branch fault triggered by the mainshock. The location of the aftershock sequence is close to the eastern section of the Kunlun Mountain Pass-Jiangcuo (KMPJ) fault. The sequence overlaps well with surface trace of the KMPJ fault. We speculate that the KMPJ fault is the main seismogenic fault of the MS7.4 Maduo earthquake.

Influences of three oceans on record-breaking rainfall over the Yangtze River Valley in June 2020

Abstract: The rainfall over the Yangtze River Valley (YRV) in June 2020 broke the record since 1979. Here we show that all three oceans of the Pacific, Indian and Atlantic Oceans contribute to the YRV rainfall in June 2020, but the Atlantic plays a dominant role. The sea surface temperature (SST) anomalies in three oceans are associated with the two vorticity anomalies: negative 200-hPa relative vorticity anomalies over North China (NC) and negative 850-hPa relative vorticity anomalies in the South China Sea (SCS). The rainfall anomalies in the YRV are mainly controlled by atmospheric process associated with the NC vorticity. The positive SST anomalies in May over the western North Atlantic induce positive geopotential height anomalies in June over the mid-latitude North Atlantic, which affect the rainfall anomalies in the YRV by changing the NC vorticity via Atlantic-induced atmospheric wave train across Europe. The Indian Ocean and tropical North Atlantic, as capacitors of Pacific El Nino events in the preceding winter, affect the SCS vorticity associated with the anomalous anticyclone over the SCS and also facilitate the YRV rainfall by providing favorable moisture conditions. This study suggests that the May SST over the western North Atlantic is a good predictor of June rainfall anomalies in the YRV and highlights the important impacts of three-ocean SSTs on extreme weather and climate events in China.

30 m global impervious surface area dynamics and urban expansion pattern observed by Landsat satellites: From 1972 to 2019

Abstract: Using more than three million Landsat satellite images, this research developed the first global impervious surface area (GISA) dataset from 1972 to 2019. Based on 120,777 independent and random reference sites from 270 cities all over the world, the omission error, commission error, and F-score of GISA are 5.16%, 0.82%, and 0.954, respectively. Compared to the existing global datasets, the merits of GISA include: (1) It provided the global ISA maps before the year of 1985, and showed the longest time span (1972–2019) and the highest accuracy (in terms of a large number of randomly selected and third-party validation sample sets); (2) it presented a new global ISA mapping method including a semi-automatic global sample collection, a locally adaptive classification strategy, and a spatio-temporal post-processing procedure; and (3) it extracted ISA from the whole global land area (not from an urban mask) and hence reduced the underestimation. Moreover, on the basis of GISA, the long time series global urban expansion pattern (GUEP) has been calculated for the first time, and the pattern of continents and representative countries were analyzed. The two new datasets (GISA and GUEP) produced in this study can contribute to further understanding on the human’s utilization and reformation to nature during the past half century, and can be freely download from http://irsip.whu.edu.cn/resources/dataweb.php .

A new era of flood control strategies from the perspective of managing the 2020 Yangtze River flood

Abstract: Flood control of the Yangtze River is an important part of China’s national water security. In July 2020, due to continuous heavy rainfall, the water levels along the middle-lower reaches of the Yangtze River and major lakes constantly exceeded the warning levels, in which Taihu Lake exceeded its highest safety water level and some stations of Poyang Lake reached their highest water levels in its history. In August 2020, another huge flood occurred in the Minjiang River and the Jialing River in the upper Yangtze River, and some areas of Chongqing Municipality and other cities along the rivers were inundated, resulting in great pressure on flood control and high disaster losses. The 2020 Yangtze River flood has received extensive media coverage and raised concerns on the roles of the Three Gorges Dam and other large reservoirs in flood control. Here we analyze the changes in the pattern of the Yangtze River flood control by comparing the strategies to tackle the three heavy floods occurring in 1954, 1998, and 2020. We propose that the overall strategy of the Yangtze River flood control in the new era should adhere to the principle of “Integration of storage and drainage over the entire Yangtze River Basin, with draining floods downstream as the first priority” by using both engineering and non-engineering measures. On the basis of embankments, the engineering measures should use the Three Gorges Dam and other large reservoirs as the major regulatory means, promote the construction of key flood detention areas, keep the floodways clear, and maintain the ecosystem services of wetlands and shoals. In terms of non-engineering measures, we should strengthen adaptive flood risk management under climate change, standardize the use of lands in flood detention areas, give space to floods, and promote the implementation of flood risk maps and flood insurance policies. The ultimate goal of this new flood control system is to enhance the adaptability to frequent floods and increase the resilience to extreme flood disasters.

Feedbacks between vegetation restoration and local precipitation over the Loess Plateau in China

Abstract: The implementation of large-scale vegetation restoration over the Chinese Loess Plateau has achieved clear improvements in vegetation fraction, as evidenced by large areas of slopes and plains being restored to grassland or forest. However, such large-scale vegetation restoration has altered land-atmosphere exchanges of water and energy, as the land surface characteristics have changed. These variations could affect regional climate, especially local precipitation. Quantitatively evaluating this feedback is an important scientific question in hydrometeorology. This study constructs a coupled land-atmosphere model incorporating vegetation dynamics, and analyzes the spatio-temporal changes of different land use types and land surface parameters over the Loess Plateau. By considering the impacts of vegetation restoration on the water-energy cycle and on land-atmosphere interactions, we quantified the feedback effect of vegetation restoration on local precipitation across the Loess Plateau, and discussed the important underlying processes. To achieve a quantitative evaluation, we designed two simulation experiments, comprising a real scenario with vegetation restoration and a hypothetical scenario without vegetation restoration. These enabled a comparison and analysis of the net impact of vegetation restoration on local precipitation. The results show that vegetation restoration had a positive effect on local precipitation over the Loess Plateau. Observations show that precipitation on the Loess Plateau increased significantly, at a rate of 7.84 mm yr−2, from 2000 to 2015. The simulations show that the contribution of large-scale vegetation restoration to the precipitation increase was about 37.4%, while external atmospheric circulation changes beyond the Loess Plateau contributed the other 62.6%. The average annual precipitation under the vegetation restoration scenario over the Loess Plateau was 12.4% higher than that under the scenario without vegetation restoration. The above research results have important theoretical and practical significance for the ecological protection and optimal development of the Loess Plateau, as well as the sustainable management of vegetation restoration.

Understanding the dynamical-microphysical-electrical processes associated with severe thunderstorms over the Beijing metropolitan region

Abstract: The Dynamical-microphysical-electrical Processes in Severe Thunderstorms and Lightning Hazards (STORM973) project conducted coordinated comprehensive field observations of thunderstorms in the Beijing metropolitan region (BMR) during the warm season from 2014 to 2018. The aim of the project was to understand how dynamical, microphysical and electrical processes interact in severe thunderstorms in the BMR, and how to assimilate lightning data in numerical weather prediction models to improve severe thunderstorm forecasts. The platforms used in the field campaign included the Beijing Lightning Network (BLNET, consisting of 16 stations), 2 X-band dual linear polarimetric Doppler radars, and 4 laser raindrop spectrometers. The collaboration also made use of the China Meteorological Administration’s mesoscale meteorological observation network in the Beijing-Tianjin-Hebei region. Although diverse thunderstorm types were documented, it was found that squall lines and multicell storms were the two major categories of severe thunderstorms with frequent lightning activity and extreme rainfall or unexpected local short-duration heavy rainfall resulting in inundations in the central urban area, influenced by the terrain and environmental conditions. The flash density maximums were found in eastern Changping District, central and eastern Shunyi District, and the central urban area of Beijing, suggesting that the urban heat island effect has a crucial role in the intensification of thunderstorms over Beijing. In addition, the flash rate associated with super thunderstorms can reach hundreds of flashes per minute in the central city regions. The super (5% of the total), strong (35%), and weak (60%) thunderstorms contributed about 37%, 56%, and 7% to the total flashes in the BMR, respectively. Owing to the close connection between lightning activity and the thermodynamic and microphysical characteristics of the thunderstorms, the lightning flash rate can be used as an indicator of severe weather events, such as hail and short-duration heavy rainfall. Lightning data can also be assimilated into numerical weather prediction models to help improve the forecasting of severe convection and precipitation at the cloud-resolved scale, through adjusting or correcting the thermodynamic and microphysical parameters of the model.

The big mantle wedge and decratonic gold deposits

Abstract: The Circum-Pacific subduction zone is a famous gold metallogenic domain in the world, with two important gold metallogenic provinces, the North China Craton and Nevada, which are related to the destruction of the North China Craton and the Wyoming Craton, respectively Their ore-forming fluids were possibly derived from the stagnant slab in the mantle transition zone The oceanic lithospheric mantle usually contains serpentine layers up to thousands of meters thick During plate subduction, serpentine is dehydrated at depths of 300 km The overlying big mantle wedge is hydrated during the breakdown of these hydrous facies in the mantle transition zone The dehydration of the subducted slab in the big mantle wedge releases sulfur-rich fluid, which extracts gold and other chalcophile elements in the surrounding rocks, forming gold-rich fluid Because the cratonic geotherm is lower than the water-saturated solidus line of lherzolite, the fluid cannot trigger partial melting Instead, it induces metasomatism and forms pargasite and other water-bearing minerals when it migrates upward to depths of less than 100 km in the cratonic lithospheric mantle, resulting in a water- and gold-rich weak layer During the destruction of craton, the weak layer is destabilized, releasing gold-bearing fluids that accelerate the destruction The ore-forming fluids migrate along the shallow weak zone and are accumulated at shallow depths, and subsequently escape along deep faults during major tectonic events, leading to explosive gold mineralization The ore-forming fluids are rich in ferrous iron, which releases hydrogen at low pressure through iron hydrolysis Therefore, decratonic gold deposits are often reduced deposits

Geodynamics of decratonization and related magmatism and mineralization in the North China Craton

Abstract: The North China Craton (NCC) experienced strong destruction (i.e., decratonization) during the Mesozoic, which triggered intensive magmatism, tectonism and thermal events and formed large-scale gold and other metal deposits in the eastern part of the craton. However, how the decratonization controls the formation and distribution of large-scale of gold and other metal deposits is not very clear. Based on a large number of published data and new results, this paper systematically summarizes all the data for the rock assemblages, chronology, geochemistry and petrogenesis of Mesozoic magmatic rocks, as well as for the mineralizing ages of gold and other metal deposits and the evolution of the Mesozoic basins in the eastern NCC. The results are used to restore the extensional rates of Mesozoic to Cenozoic basins and the strike-slip distance of the Tanlu Fault, to ascertain the location of the Paleo-Pacific plate subduction zones during the Mesozoic to Cenozoic, and to reconstruct the temporal and spatial distribution of Mesozoic gold and other metal deposits and magmatic rocks in the eastern NCC. It is obtained that the magmatism and mineralization in the eastern NCC westward migrate from east to west during the Early to Middle Jurassic, but they eastward migrate from west to east during the Early Cretaceous. The metallogenesis of these deposits is genetically related to magmatism, and the magmas provided some ore-forming materials and fluids for the generation of metal deposits. The geodynamic mechanism of decratonization and related magmatism and mineralization is proposed, i.e., the westward low-angle subduction of the Paleo-Pacific slab beneath the NCC formed continental magmatic arc with plenty of porphyry Cu-Mo-Au deposits in the Jurassic, similar to the Andean continental arc in South America. The mantle wedge was metasomatized by the fluids/melts derived from the subducting slab, laying a material foundation for hydrothermal mineralization in the Early Cretaceous. While the rollback of the subducting slab with gradually increasing subduction angle and the retreat of the subduction zones during the Early Cretaceous induced strong destruction of the craton and the formation of extensive magmatic rocks and large-scale gold and other metal deposits.

Tectonic evolution and geodynamics of the Neo-Tethys Ocean

Abstract: The Neo-Tethys Ocean was an eastward-gaping triangular oceanic embayment between Laurasia to the north and Gondwana to the south. The Neo-Tethys Ocean was initiated from the Early Permian with mircoblocks rifted from the northern margin of Gondwana. As the microblocks drifted northwards, the Neo-Tethys Ocean was expanded. Most of these microblocks collided with the Eurasia continent in the Late Triassic, leading to the final closure of the Paleo-Tethys Ocean, followed by oceanic subduction of the Neo-Tethys oceanic slab beneath the newly formed southern margin of the Eurasia continent. As the splitting of Gondwana continues, African-Arabian, Indian and Australian continents were separated from Gondwana and moved northwards at different rates. Collision of these blocks with the Eurasia continent occurred at different time during the Cenozoic, resulting in the closure of the Neo-Tethys Ocean and building of the most significant Alps-Zagros-Himalaya orogenic belt on Earth. The tectonic evolution of the Neo-Tethys Ocean shows different characteristics from west to east: Multi-oceanic basins expansion, bidirectional subduction and microblocks collision dominate in the Mediterranean region; northward oceanic subduction and diachronous continental collision along the Zagros suture occur in the Middle East; the Tibet and Southeast Asia are characterized by multi-block riftings from Gondwana and multi-stage collisions with the Eurasia continent. The negative buoyancy of subducting oceanic slabs can be considered as the main engine for northward drifting of Gondwana-derived blocks and subduction of the Neo-Tethys Ocean. Meanwhile, mantle convection and counterclockwise rotation of Gondwana-derived blocks and the Gondwana continent around an Euler pole in West Africa in non-free boundary conditions also controlled the evolution of the Neo-Tethys Ocean.

Ecological risk assessment of Cd and other heavy metals in soil-rice system in the karst areas with high geochemical background of Guangxi, China

Abstract: Karst areas are widely distributed in China, and the soil derived in these areas is enriched with trace elements and has the typical characteristics of high geochemical background. Therefore, soil ecological risk has gradually attracted extensive attention. In this study, 1090 sets of rice grains and paired rhizosphere soils were collected as research objects from the outcropped karst areas of carbonate rocks in Guangxi, and the concentration characteristics and influencing factors of heavy metals, such as Cd and As, in rice grains and the corresponding soils were studied. According to the Chinese Soil Environmental Quality Standard (GB 15618-2018), the proportion of karstic soil samples in Guangxi with heavy metal (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) concentrations that exceed the standard risk screening values was generally greater than that of surface soils in China or non-karstic soils in Guangxi. Notably, Cd and As were the most prominently enriched heavy metals in soils. According to the Chinese Food Safety Standard (GB 2762-2017), Pb in rice grains from the studied area did not exceed the standard; the exceedance rates of Cr, Hg, and inorganic As were only about 1%; and the exceedance rate of Cd was 12.5%. Soil Cd concentration increased gradually whereas the concentration and exceedance rate of Cd in rice grains decreased gradually with the increase of soil pH. Specifically, the exceedance rate of Cd in rice grains was only 4% when soil pH>6.5. The results indicated that the risk screening values of Cd element in the Chinese Soil Environmental Quality Standard are not satisfactorily applicable to the ecological risk assessment of Cd in karstic soils. Therefore, the recommended threshold values for the safe utilization and risk control of Cd in karstic soils was proposed so as to provide a basis for soil environmental quality hierarchization, pollution risk control and land safety zoning of agricultural land in karst areas in China.

Slip rate of the seismogenic fault of the 2021 Maduo earthquake in western China inferred from GPS observations

Abstract: Seismic and field observations indicate that the Mw7.4 Maduo earthquake ruptured the Jiangcuo fault, which is a secondary fault ∼85 km south of the northern boundary of the Bayan Hor block in western China. The kinematic characteristics of the Jiangcuo fault can shed lights on the seismogenic mechanism of this earthquake. Slip rate is one of the key parameters to describe the kinematic features of a fault, which can also provide quantitative evidences for regional seismic hazard assessments. However, due to lack of effective observations, the slip rate of the Jiangcuo fault has not been studied quantitatively. In this study, we consider the interaction between the Jiangcuo fault and the eastern Kunlun fault, and estimate the slip rates of the two faults using the interseismic GPS observations across the seismogenic region. The inferred results show that the slip rates of the Jiangcuo fault and the Tuosuo Lake segment of the Kunlun fault are 1.2±0.8 and 5.4±0.3 mm a−1, respectively. Combining the slip rate with the average slip inferred from the coseismic slip model, the earthquake recurrence interval of the Jiangcuo fault is estimated to be 1800 −700 +3700 years (1100–5500 years). Based on the results derived from previous studies, as well as calculations in this study, we infer that the slip rate of the Kunlun fault may decrease gradually from the Tuosuo Lake segment to the eastern tip. The Jiangcuo fault and its adjacent parallel secondary faults may have absorbed the relative motion of blocks together with the Kunlun fault.

Conditions and processes leading to large-scale gold deposition in the Jiaodong province, eastern China

Abstract: The gold deposits in the Jiaodong Peninsula constitute the largest gold mineralized province in China. The mineralization shows common characteristics in their tectonic setting, ore-forming fluid and metallogenic system. Sulfidation and fluid immiscibility are two important mechanisms controlling gold precipitation, both of which consume sulfur in the ore-forming fluids. The escape of H2S from the main ore-forming fluids and the decrease of total sulfur concentration not only lead to the efficient precipitation of gold, but also result in the crystallization of reducing minerals such as pyrrhotite and oxidizing minerals such as magnetite. Quartz solubility shows strong dependence on temperature, pressure, and CO2 content. The dependence of quartz solubility on pressure is weak at low temperatures, and progressively stronger at higher temperatures. Similarly, the temperature dependence of quartz solubility is relatively low at low pressures, but becomes gradually stronger at high pressures. The results of solubility modeling can constrain the dissolution and reprecipitation behavior of quartz in the ore-forming veins and the formation mechanism of different types of quartz veins. The multi-stage mineralization fluid activity resulted in the complex dissolution structure of quartz in the Jiaodong gold veins. Pyrite in the main metallogenic period in the Jiaodong gold deposits shows complex microstructure characteristics at single crystal scale. The trace elements (mainly the coupling of As- and Au-rich belt) and sulfur isotope composition also display a certain regularity. The As-rich fluids might have formed by the initial pulse of ore-forming fluids through As-rich metasedimentary strata, while the As-Au oscillation zone at the margin of pyrite grains is related to the pressure fluctuation caused by fault activity and the local phase separation of fluids. There is a temporal and spatial evolution of gold fineness in the Jiaodong gold deposits. Water/rock reaction (sulfidation) was the main ore-forming mechanism of early gold mineralization, forming relatively high fineness gold, while significant pressure drop in the shallow part accompanied by fluid phase separation promoted the late gold mineralization, forming low fineness gold. Under cratonic destruction setting, dehydration of the amphibolite and granulite facies metamorphic lower-crust resulted in the formation of Au-CO2-rich ore-forming fluids, which rose along the deep fault and secondary structure, and formed the largescale fault-controlled gold deposits in Jiaodong.

Lithospheric structure and evolution of the North China Craton: An integrated study of geophysical and xenolith data

Abstract: Determination of the physical and chemical structures of the inaccessible continental lithosphere by comprehensive geophysical and geochemical studies can provide valuable information on its formation and evolution. Extensive studies from various disciplines have revealed complex lithospheric modification of the North China Craton (NCC), but less attention has been paid to an integrated study from different fields. Here we provide an integrated constraint on the lithospheric mantle structure of the NCC by comprehensive semiology, gravity and thermal studies with xenolith data involving depth (levels in the lithosphere), property (chemical and physical), and timing (formation and reworking ages). Our results suggest that the NCC has a relatively heterogeneous lithospheric mantle. Its margins and internal weak zones, especially in the eastern NCC, are generally underlain by the fertile, weakly metasomatized mantle with generally young formation ages. In contrast, its core tends to preserve the refractory, strongly metasomatized mantle with ages roughly coupled to the overlying Archean crust. Such a lithospheric structure shows the preferential modification of the lithospheric mantle in the eastern NCC and in the peripheral regions of the western NCC. The interior of the craton, especially most of the western NCC, remains stable and has been weakly modified.

Nature and secular evolution of the lithospheric mantle beneath the North China Craton

Abstract: The Archean mantle lithosphere beneath the North China Craton (NCC) was transformed in the Mesozoic, leading to the craton destruction. Despite the significant breakthroughs in the craton studies, lithospheric transformation mechanisms are yet to be fully understood. Compositional variations of mantle-derived rocks and xenoliths provide insights into the nature of the mantle lithosphere before and after the craton destruction. The Paleozoic lithosphere of the NCC is ∼200 km thick. It has a refractory mantle with an evolved isotopic signature. The Mesozoic mantle lithosphere was relatively fertile and highly heterogeneous. In the Cenozoic, the lithosphere in the eastern NCC is about 60–80 km thick. It has an oceanic-type mantle that is fertile in composition and depleted in the Sr-Nd isotopic signature. The Central Zone lithosphere is >100 km thick and has a double-layer mantle with an old upper layer and a new lower layer. The Western Block has a lithosphere of ∼200 km thick. The lithospheric mantle beneath the southern and northern margins and eastern part of the NCC has been transformed significantly by peridotite-melt reactions due to the multiple subductions of adjacent plates since the Paleozoic. Paleo-Pacific subduction and the associated dynamic processes significantly alter the lithosphere based on the distribution of craton destruction. The involved mechanisms include mechanical intrusion of subduction plates, melt fluid erosion, and local delamination. The lithospheric thinning of ∼120 km is relevant to the continental extension caused by subduction plate rollback and trench retreat.

Crustal deformation and dynamics of Early Cretaceous in the North China Craton

Abstract: The Early Cretaceous represents a peak period of the North China Craton (NCC) destruction. A comprehensive analysis of crustal deformation during this period can reveal processes and dynamics of the destruction. The peak destruction of the NCC was associated with intense extension whose representative deformation products are metamorphic core complexes (MCCs), extensional domes and rifted basins. These MCCs occurred along both northern and southern margins of the NCC, and resulted from synchronous extension and magmatism, showing difference from the typical orogen-type MCCs in many aspects. The MCCs of the Early Cretaceous were replaced by extensional domes under relatively weak extension and uplift. In contrast to a major depression-type basin of the Early Cretaceous in the western NCC, rifted basins of the same age in the eastern NCC appeared as medium- to small-scale ones extensively. In the eastern NCC, the rifted basins north of the Bohai Bay are characterized by a feature similar to an active rift whereas those south of the Bohai present similarity to a passive rift. Various sorts of extensional structures developed during the peak destruction indicate a stable stress state of NE-SE extension over the entire central to eastern NCC, consistent with the plate margin-driven stress field. Spatial distribution of the extensional structures presents an 1800 km wide back-arc extension region in the central to eastern NCC, consistent with the Paleo-Pacific slab rollback model following flat subduction. Temporal-spatial variation of initial extension and volcanic activity during the peak period also supports the rollback model right after the flat oceanic slab. The crustal deformation evolution demonstrates that the peak destruction of the NCC took place after the B-episode compression of the Yanshan Movement of the earliest Early Cretaceous and terminated with onset of the C-episode compression of the earliest Late Cretaceous.

The soil Microbial Carbon Pump as a new concept for terrestrial carbon sequestration

Abstract: Soil is a huge terrestrial carbon pool, which has higher carbon storage than the sum of atmospheric and terrestrial vegetation carbon Small fluctuations in soil carbon pool can affect regional carbon flux and global climate change As soil organic carbon plays key roles in soil carbon storage and sequestration, studying its composition, sources and stability mechanism is a key to deeply understand the functions of terrestrial ecosystem and how it will respond to climate changes The recently-proposed concept of soil Microbial Carbon Pump (MCP) emphasizes the importance of soil microbial anabolism and its contributions to soil carbon formation and stabilization, which can be applied for elucidating the source, formation and sequestration of soil organic carbon This article elaborates MCP-mediated soil carbon sequestration mechanism and its influencing factors, as well as representative scientific questions we may explore with the soil MCP conceptual framework

Geographic modeling and simulation systems for geographic research in the new era: Some thoughts on their development and construction

Abstract: Regionality, comprehensiveness, and complexity are regarded as the basic characteristics of geography. The exploration of their core connotations is an essential way to achieve breakthroughs in geography in the new era. This paper focuses on the important method in geographic research: Geographic modeling and simulation. First, we clarify the research requirements of the said three characteristics of geography and its potential to address geo-problems in the new era. Then, the supporting capabilities of the existing geographic modeling and simulation systems for geographic research are summarized from three perspectives: Model resources, modeling processes, and operational architecture. Finally, we discern avenues for future research of geographic modeling and simulation systems for the study of regional, comprehensive and complex characteristics of geography. Based on these analyses, we propose implementation architecture of geographic modeling and simulation systems and discuss the module composition and functional realization, which could provide theoretical and technical support for geographic modeling and simulation systems to better serve the development of geography in the new era.

Not vegetation itself but mis-revegetation reduces water resources

Abstract: Increasing greening of planet Earth to slow down the rise of atmospheric CO2 concentrations is certainly desirable; however, its consequences on water resources are less affirmative and thus are a matter of wide concern. China, as the largest and most successful country of the world in terms of artificial revegetation, is naturally the focus of the concerns and warnings. Based on previous studies, we analyzed the mechanism for the effects of climate and watershed characteristics on water resources, explained various hydrological results and phenomena, and considered the ways in which water consumption by artificial revegetation projects can be reduced. Moreover, some guidelines are suggested for artificial revegetation at watershed scale with consideration of water resource sustainability. The findings of this study highlight the need for more top-down approaches when studying the mechanism of “forest and water”.

Paleoclimatic indication of X-ray fluorescence core-scanned Rb/Sr ratios: A case study in the Zoige Basin in the eastern Tibetan Plateau

Abstract: The X-ray fluorescence (XRF) core-scanned Rb/Sr ratios of lake sediments have been widely used as a proxy for chemical weathering intensity and past climate change. However, some factors could affect Rb/Sr ratios, causing misinterpretation and limiting its application. In this study, we present a high-resolution XRF core-scanned Rb/Sr record of core ZB13-C1 from the Zoige Basin in the eastern Tibetan Plateau. To validate its application, we correlated this record with the chemical index of alteration (CIA) and other paleoclimatic proxies. Our results showed that (1) the core-scanned Rb/Sr ratios and CIA were reliable proxies of chemical weathering intensity in fine-grained sedimentary sequences; (2) the low values of core-scanned Rb/Sr ratios and CIA were significantly correlated with high total organic carbon content, arboreal pollen content, carbonate content, and C/N ratios, confirming its reliability as a proxy for the Asian summer monsoon intensity; (3) the core-scanned Rb/Sr ratios at core depths of 25–0.3 and 56–17 m were unable to reliably reflect chemical weathering intensity due to both the grain-size effect and the low test accuracy. Our study highlights the need for mutual verification of multiple indicators before accurately applying Rb/Sr as a paleoclimatic proxy in other similar study areas.

Geoscience knowledge graph in the big data era

Abstract: Since the beginning of the 21st century, the geoscience research has been entering a significant transitional period with the establishment of a new knowledge system as the core and with the drive of big data as the means. It is a revolutionary leap in the research of geoscience knowledge discovery from the traditional encyclopedic discipline knowledge system to the computer-understandable and operable knowledge graph. Based on adopting the graph pattern of general knowledge representation, the geoscience knowledge graph expands the unique spatiotemporal features to the Geoscience knowledge, and integrates geoscience knowledge elements, such as map, text, and number, to establish an all-domain geoscience knowledge representation model. A federated, crowd intelligence-based collaborative method of constructing the geoscience knowledge graph is developed here, which realizes the construction of high-quality professional knowledge graph in collaboration with global geo-scientists. We also develop a method for constructing a dynamic knowledge graph of multi-modal geoscience data based on in-depth text analysis, which extracts geoscience knowledge from massive geoscience literature to construct the latest and most complete dynamic geoscience knowledge graph. A comprehensive and systematic geoscience knowledge graph can not only deepen the existing geoscience big data analysis, but also advance the construction of the high-precision geological time scale driven by big data, the compilation of intelligent maps driven by rules and data, and the geoscience knowledge evolution and reasoning analysis, among others. It will further expand the new directions of geoscience research driven by both data and knowledge, break new ground where geoscience, information science, and data science converge, realize the original innovation of the geoscience research and achieve major theoretical breakthroughs in the spatiotemporal big data research.

The oxygen cycle and a habitable Earth

Abstract: As an important contributor to the habitability of our planet, the oxygen cycle is interconnected with the emergence and evolution of complex life and is also the basis to establish Earth system science. Investigating the global oxygen cycle provides valuable information on the evolution of the Earth system, the habitability of our planet in the geologic past, and the future of human life. Numerous investigations have expanded our knowledge of the oxygen cycle in the fields of geology, geochemistry, geobiology, and atmospheric science. However, these studies were conducted separately, which has led to one-sided understandings of this critical scientific issue and an incomplete synthesis of the interactions between the different spheres of the Earth system. This review presents a five-sphere coupled model of the Earth system and clarifies the core position of the oxygen cycle in Earth system science. Based on previous research, this review comprehensively summarizes the evolution of the oxygen cycle in geological time, with a special focus on the Great Oxidation Event (GOE) and the mass extinctions, as well as the possible connections between the oxygen content and biological evolution. The possible links between the oxygen cycle and biodiversity in geologic history have profound implications for exploring the habitability of Earth in history and guiding the future of humanity. Since the Anthropocene, anthropogenic activities have gradually steered the Earth system away from its established trajectory and had a powerful impact on the oxygen cycle. The human-induced disturbance of the global oxygen cycle, if not controlled, could greatly reduce the habitability of our planet.

Seismic reflection evidence of crustal duplexing and lithospheric underthrusting beneath the western Qilian Mountains, northeastern margin of the Tibetan Plateau

Abstract: The geological processes responsible for outward growth of the Tibetan Plateau are debated. The Qilian Mountains on the northeastern margin of the plateau comprise one of the youngest structural components of the plateau whose understanding is key to deciphering the broader geological evolution of the region. Here, based on a reprocessed deep seismic profile which was originally collected during the 1990s across the northeast margin of the western Qilian Mountains and previous geological and geophysical data, we find evidence for decoupled crustal deformation that was partitioned by a decollement, in which lower-crustal deformation featured by local duplexing preceded upper-crustal deformation featured by imbricate thrusts. Furthermore, we propose that the Asian lithospheric mantle is being underthrust beneath the western Qilian Mountains, as inferred from patterns of lower crustal deformation which is marked by the Moho geometry. Integrating these results yields a better understanding of lithospheric deformation of western Qilian Mountains, northeastern margin of the plateau during the Cenozoic.

Organic-rich formation and hydrocarbon enrichment of lacustrine shale strata: A case study of Chang 7 Member

Abstract: Lacustrine shale is an important target for the exploration of unconventional oil and gas in China beyond marine shale gas. However, the formation environment of lacustrine shale differs from that of marine shale, resulting in a different reservoir composition, organic matter, oil and gas content, and hydrocarbon mobility. In this study, the Chang 7 shale of the Yanchang Formation in the Ordos Basin was used to analyze the effect of volcanic activity on the paleoproductivity and preservation conditions during the formation of lacustrine shale. The results show that algae and bacteria were developed before the eruption. After the eruption, the number of bacteria declined, but the increased prosperity of algae reflects that the volcanic activity enhanced ancient productivity. The sulfate generated by volcanic activity promotes bacterial sulfate reduction, and the produced H2S leads to a strong reducing environment in the waterbody, which is conducive to the preservation of organic matter. Organic geochemical analysis shows that the black shale in the shale strata has a high total organic carbon (TOC) content and strong hydrocarbon generation potential, whereas the tuff has a low TOC content and can scarcely generate hydrocarbons, indicating that the tuff deposited by volcanic activity cannot be considered as effective source rock. In terms of storage space, shale is mainly laminar and dispersed, and it includes organic and inorganic pores. The development of organic pores is affected by thermal maturity, whereas inorganic pores mainly occur between detrital particles and crystals. Tuff is mainly supported by heterogeneous matrix and associated with alteration. Its pores include inter- and intragranular mineral pores. The development of tight sandstone pores is affected by compaction, cementation, and dissolution, which mainly consist of intra- and intergranular pores. The Chang 7 lacustrine shale generally contains oil, but different lithologies have different oil drainage efficiencies. Sandstone and shale exhibit the best and worst oil drainage efficiency, respectively. It is mainly affected by the pore size distribution, fluid properties, and rock wettability. Therefore, the development of shale oil should mainly focus on lacustrine shale formations with interbeds. The mutual dissolution of organic matter and hydrocarbons in the shale section leads to the poor mobility and difficult development of hydrocarbons.

Dust storms in northern China during the last 500 years

Abstract: The history and mechanisms of dust storms in northern China remain unclear owing to the paucity of reliable long-term, high-resolution geological records In this study, we reconstructed the dust storm history of the last ~500 years in northern China, based on sedimentary coarse fraction (>63 µm) of a well-dated core from Lake Daihai, Inner Mongolia The high-resolution data reveal three intervals of frequent dust storms: AD 1520–1580, AD 1610–1720, and AD 1870–2000 The dust storm events in the Lake Daihai area were broadly synchronous with those inferred from other historical or geological records and generally occurred during cold intervals Changes in the intensity of Siberian High and the westerlies modulated by temperature variations are the likely major factors controlling dust storm dynamics An interesting feature is that although the intensities of dust storms have been systematically increased during the recent warming period, a clear decreasing trend within this period is evident The recent increase in average dust storm intensity may be ascribed to an increase in particle supply resulting from a rapid increase in human activity, whereas the weakening trend was likely caused by decreases in average wind speed resulting from the recent global warming

Impacts of meteorology and emission variations on the heavy air pollution episode in North China around the 2020 Spring Festival.

Abstract: Based on the Weather Research and Forecasting model and the Models-3 community multi-scale air quality model (WRF-CMAQ), this study analyzes the impacts of meteorological conditions and changes in air pollutant emissions on the heavy air pollution episode occurred over North China around the 2020 Spring Festival (January to Februray 2020). Regional reductions in air pollutant emissions required to eliminate the PM2.5 heavy pollution episode are also quantified. Our results found that meteorological conditions for the Beijing-Tianjin-Hebei and surrounding “2+26” cities are the worst during the heavy pollution episode around the 2020 Spring Festival as compared with two other typical heavy pollution episodes that occurred after 2015. However, because of the substantial reductions in air pollutant emissions in the “2+26” cities in recent years, and the 32% extra reduction in emissions during January to February 2020 compared with the baseline emission levels of the autumn and winter of 2019 to 2020, the maximum PM2.5 level during this heavy pollution episode around the 2020 Spring Festival was much lower than that in the other two typical episodes. Yet, these emission reductions are still not enough to eliminate regional heavy pollution episodes. Compared with the actual emission levels during January to February 2020, a 20% extra reduction in air pollutant emissions in the “2+26” cities (or a 45% extra reduction compared with baseline emission levels of the autumn and winter of 2019 to 2020) could help to generally eliminate regionwide severe pollution episodes, and avoid heavy pollution episodes that last three or more consecutive days in Beijing; a 40% extra reduction in emissions (or a 60% extra reduction compared with baseline emission levels of the autumn and winter of 2019 to 2020) could help to generally eliminate regionwide and continuous heavy pollution episodes. Our analysis finds that during the clean period after the heavy pollution episode around the 2020 Spring Festival, the regionwide heavy pollution episode would only occur with at least a 10-fold increase in air pollutant emissions.

Degassing of deep-sourced CO2 from Xianshuihe-Anninghe fault zones in the eastern Tibetan Plateau

Abstract: A large number of gases are releasing from the medium-high temperature geothermal fields distributed along the large-scale strike-slip fault zones in the southeastern margin of the Tibetan Plateau. In this study, 11 hot spring water and the associated bubbling gas samples were collected along the Xianshuihe-Anninghe fault zones (XSH-ANHFZ) and analyzed for chemical and isotopic compositions. The $${\delta ^{18}}{{\rm{O}}_{{{\rm{H}}_2}{\rm{O}}}}$$ and $$\delta {{\rm{D}}_{{{\rm{H}}_2}{\rm{O}}}}$$ values indicate that hot spring waters are predominantly meteoric origin recharged from different altitudes. Most water samples are significantly enriched in Na+ and HCO3− due to the dissolution of regional evaporites, carbonates and Na-silicates. 3He/4He ratios of the gas samples are 0.025–2.73 times the atmospheric value. The 3He/4He ratios are high in the Kangding region where the dense faults are distributed, and gradually decrease with increasing distance from Kangding towards both sides along the Xianshuihe fault zones (XSHFZ). Hydrothermal fluids have dissolved inorganic carbon (DIC) concentrations from 2 to 42 mmol L−1, δ13CDIC from −6.9‰ to 1.3‰, $${\delta ^{13}}{{\rm{C}}_{{\rm{C}}{{\rm{O}}_2}}}$$ from −7.2‰ to −3.6‰ and Δ14C from −997‰ to −909‰. Combining regional geochemical and geological information, the CO2 sources can be attributed to deep-sourced CO2 from mantle and metamorphism of marine carbonate, and shallow-sourced CO2 from the dissolution of marine carbonate and biogenic CO2. The mass balance model shows that 11±6% of the DIC is sourced from the dissolution of shallow carbonate minerals, 9±8% formed by pyrolysis of sedimentary organic matter, 80±9% derived from deep metamorphic origin and mantle-derived CO2. Among them, the deep-sourced CO2 in Anninghe fault zones (ANHFZ) is merely metamorphic carbon, whereas ca. 12% and ca. 88% of the deep-sourced CO2 in the XSHFZ are derived from the mantle and metamorphic carbon, respectively. The average deep-sourced CO2 flux in the Kangding geothermal field is estimated to be 160 t a−1. If all the hot springs in various fault zones in the southeastern margin of the Tibetan Plateau are taken into account, the regional deep-sourced CO2 flux would reach ca. 105 t a−1. These results show that the deep-sourced CO2 released from non-volcanic areas might account for a considerable proportion of the total amount of global deep-sourced carbon degassing, which should be paid more attention to.