Central Eastern China Research Articles

Quantification of Asian monsoon variability from 68 ka BP through pollen-based climate reconstruction

The glacial-interglacial variability of precipitation and its driving mechanism in monsoonal regions has long been a subject of debate. However, there are few records of quantitative climate reconstruction dating to the last glacial cycle in areas dominated by the Asian summer monsoon. Here, using a pollen-based quantitative climate reconstruction based on three sites in areas exposed to the Asian summer monsoon, we demonstrate that climate has undergone great variability over the past 68 ka. The differences between the last glacial and the Holocene optimum could have been as much as 35%–51% for precipitation, and 5–7 °C for mean annual temperature. Our findings also reveal regional heterogeneity during the abrupt climate events of Heinrich Event 1 and Younger Dryas, that drove drier conditions in southwestern China dominated by the Indian summer monsoon, and a wetter climate in central eastern China. The pattern of variation in reconstructed precipitation, exhibiting strong glacial-interglacial variability, is broadly consistent with the stalagmite δ18O records from Southwest China and South Asia. Our results of reconstruction quantify the sensitivity of the MIS3 precipitation to orbital insolation changes, and highlight the prominent influence of interhemispheric temperature gradients on Asian monsoon variability. Comparison with transient simulations and major climate forcings has shown that the mode of precipitation variability during the transition from the last glacial maximum to the Holocene has been significantly modulated by weak or collapsed Atlantic meridional overturning circulation events in addition to insolation forcing.

Seismic Reduction Mechanism and Engineering Application of Paste Backfilling Mining in Deep Rock Burst Mines

In the process of coal resources development, a large number of strip coal pillars have been left behind in the coal mines in central–eastern China. With the increase in coal mining depth year by year, the rock burst threat of strip coal pillars is becoming more and more prominent due to the influence of buried depth, geological structure, gob and other factors. Backfilling mining is the main means to recover the residual strip coal pillar. In order to investigate the effect of backfilling mining on the prevention and control of rock burst, taking the paste backfilling workface 1# of Gucheng coal mine as the engineering background, a comprehensive research method of theoretical analysis, numerical simulation and field monitoring was used to study the evolution of stress and of the overburden spatial structure of the backfilling workface under the control of the backfilled ratio. The results showed that the backfilling mining controls the movement and deformation of overburden by reducing the activity range of roof strata. The overburden fracture development height decreases with the increase in backfilled ratio, but there is a boundary effect influenced by the roof deflection before backfilling and the defective distance of roof contact. With the increase in backfilled ratio, the concentration coefficient of front abutment pressure, the vertical displacement of the roof and the development height of the plastic zone of overlying strata decreased obviously, which indicates that filling mining can effectively control the stress of surrounding rock and the movement of overlying strata. The field monitoring data showed that the influence range of the front abutment pressure of the paste backfilling workface was about 90 m and the maximum stress of the surrounding rock of the two entries did not exceed 7 MPa. The average daily frequency of microseism was 1.34, and the average daily total energy of microseism was 1.80 + 103 J, which decreased by 69% and 90%, respectively, compared with the caving method working face with similar geological conditions. The data above showed that the backfilling mining can effectively reduce the working face stress level and dynamic load strength to achieve the effect of prevention and control of rock burst.

Geostatistical and geoarchaeological study of Holocene floodplains and site distributions on the Sha‐Ying River Basin, Central China

AbstractGeostatistics has become a powerful method for investigating complex spatial variations of prehistoric settlements in floodplains and other geomorphological settings. A geoarchaeological drilling program that covers most of the Sha‐Ying River Basin provides a rare opportunity with unusually detailed environmental data to contest and develop the geostatistics method, which proves to be essential, in combination with archaeological data, to understand long‐term (9000–2500 B.P.) patterns of human inhabitation and adaption to volatile floodplain environments in eastern Central China. We analysed the variography and multivariate ordination of the borehole data and explored the complexities of landform evolution, with reference to sedimentation processes and soil development in the floodplain of the Sha‐Ying River. The recurrent impact of river floods on regional landforms is manifested by spatial‐autocorrelated properties over distances up to 10 km, sometimes with directional trends. We then developed a model of landform evolution through kriging and compared the model with detailed reconstruction of archaeological settlement patterns. Our results illustrate long‐term socio‐environmental dynamics by which human communities first populated and then adapted in diverse ways to the changing floodplain environments from the early to middle Holocene. This improved method will have far‐reaching implications for future studies on similar geomorphological settings across vast floodplains of Central China and other global regions.

Different mechanisms for the extremely hot central-eastern China in July–August 2022 from a Eurasian large-scale circulation perspective

In July and August of 2022, unprecedented and long-lasting heatwaves attacked central and eastern China (CEC); and the most affected area was in the Yangtze River (YR) basin. The extreme heatwaves and associated drought and wildfire had significant social impacts, but the underlying mechanisms remain unknown. Observational analysis indicates that the heatwaves were regulated by anomalous anticyclone in the mid-upper troposphere over northern CEC. Specifically, the easterly anomalies at the southern flank of the anticyclone caused air isentropic sliding and transported low moist enthalpy (cold and dry) air to the YR basin, contributing to anomalous sinking motions and extreme heatwaves. In comparison, heatwaves were more serious in August than in July due to stronger upper-level anomalous anticyclone and associated easterlies. Importantly, different mechanisms were responsible for the heatwaves in the two months. In July, the relatively weaker anticyclonic anomaly over northern CEC was dominated by the forcing of diabatic heating over northwestern South Asia (NWSA), corresponding with the record-breaking rainfall in and around Pakistan. In August, a powerful anticyclonic condition for the CEC heatwaves originated from an extreme silk road pattern (SRP), superposing the effect of NWSA diabatic heating due to persistent downpour. We notice that another upstream anticyclonic node in the SRP also created heatwaves in Europe. Therefore, the CEC extreme heat was actually associated with other concurrent extremes over the Eurasian continent through large-scale atmospheric teleconnections in 2022.

Does economic stress matter for the rising divorce rate in China? A provincial perspective

Purpose: Marriage is an infinite bond between two partners that can be caused to fail by several factors. Economic stress leads to psychological stress and in some cases, marriage dissolution. The current study investigates the impact of economic stress (measured by the unemployment rate and inflation rate) on divorce rates using Chinese province-level panel data from 2010 to 2019.
 Design/Methodology/Approach: The panel fixed effects (FE) model, panel random effects (RE) model, and fixed effects- Driscoll and Kraay standard errors (DKSE) model were used for empirical analysis.
 Findings: The research findings support the hypothesized economic stress theory of divorce by Reuben Hill. According to the empirical findings, economic stress indicators such as unemployment and inflation have a positive and significant impact on the divorce rate in China and its regions. Furthermore, urbanization, education and mobile phone variables have a positive relationship with divorce rates except for children’s dependency.
 Contribution to literature: Taking into account both parties' perspectives, this study contributes to the existing literature by looking at economic stress in the context of divorce. We are particularly interested in how economic stress affected the marriage relationship's quality. We investigated the relationship between the unemployment rate, inflation rate and divorce rate in China's 31 provinces for the period 2010-2019. The entire sample is then separated into three sub-samples: Eastern China, Central China and Western China.

Regional impact of aging population on carbon dioxide emissions in China: Evidence from panel threshold regression (PTR).

Carbon dioxide emission is a high-profile issue that can affect both the human economy and human existence, but few scholars have studied the relationship between these two. Therefore, this study constructs the panel threshold regression (PTR) based on the National Bureau of Statistics of China's panel data from 2002 to 2019 in 19 regions. One of the advantages of PTR is to leverage segmented functions, allowing for a more detailed analysis of the data. Besides, by introducing the idea of a threshold, PTR can effectively avoid structural changes in the data. The different between this study and other research is that this study divides 19 regions into two parts: Eastern China and Central China. Based on that, this study researches and compares the different influences of the aging population on carbon emissions in these two regions. The results show that although the Environment Kuznets Curve has been confirmed in both Eastern China and Central China, with the development of the economy, the carbon emissions will increase in Eastern China and decrease in Central China, respectively. In addition, the key factors affecting carbon emissions in Eastern China and Central China are trade dependence and urbanization rate separately. Hence, this study suggests that the regional governments in Eastern China may guide and encourage more international trading companies to move to Central China, and at the same time, the regional governments in Central China should issue more policies to attract these companies, such as: reducing land lease fees and building better transportation infrastructure. Apart from that, the governments in Central China should vigorously increase the rate of urbanization to reduce energy consumption and improve energy efficiency.

A perspective from the past in conservation of plant biodiversity in central China

Biodiversity has increasingly come under threat from human activity everywhere on Earth. China, with over 33,000 species of vascular plants, is a megadiverse region, in part because of its diversity in topography and climates. One of its most extensive biomes is broadleaved evergreen/warm mixed forest which dominates eastern Asia and Central China. There is some debate about how glacial/interglacial cycles across the Quaternary had an impact on this biome. There were certainly broad scale changes in distribution of many key species. Here, we examine the four palaeoecological records from Central China that contain both LGM and Mid-Holocene vegetation records and consider the degree of biodiversity in Central China with the aim of developing a broad overview of the history on plants in the region. It is clear that in the mountainous regions of Central China, many taxa survived the LGM in situ, showing that there was enough stable habitat to support key species. Some mountainous areas have high degrees of endemism which suggests that fragmentation of populations across glacial/interglacial cycles may have been an important component in favoring speciation. The consideration of past records and modern species distributions have significance in selecting conservation areas.

Impact of the COVID-19 pandemic on air pollution from jet engines at airports in central eastern China.

Aircraft engine emissions (AEEs) generated during landing and takeoff (LTO) cycles are important air pollutant sources that directly impact the air quality at airports. Although the COVID-19 pandemic triggered an unprecedented collapse in the civil aviation industry, it also relieved some environmental pressure on airports. To quantify the impact of COVID-19 on AEEs, the amounts of three typical air pollutants (i.e., HC, CO, and NOx) from LTO cycles at airports in central eastern China were estimated before and after the pandemic. The study also explored the temporal variation and the spatial autocorrelation of both the emission quantity and the emission intensity, as well as their spatial associations with other socioeconomic factors. The results illustrated that the spatiotemporal distribution pattern of AEEs was significantly influenced by the policies implemented and the severity of COVID-19. The variations of AEEs at airports with similar characteristics and functional positions generally followed similar patterns. The results also showed that the studied air pollutants present positive spatial autocorrelation, and a positive spatial dependence was found between the AEEs and other external socioeconomic factors. Based on the findings, some possible policy directions for building a more sustainable and environment-friendly airport group in the post-pandemic era were proposed. This study provides practical guidance on continuous monitoring of the AEEs from LTO cycles and studying the impact of COVID-19 on the airport environment for other regions or countries.

Tropical cyclone over the western Pacific triggers the record-breaking ‘21/7’ extreme rainfall in Henan, central-eastern China

During 19–21 July 2021, Henan located in central-eastern China experienced torrential rainfall that caused devastating floods and claimed more than 300 casualties. It remains unclear whether and to what extent this extreme precipitation event is contributed by Typhoon In-Fa (TIF). Here we quantify the contribution of TIF to this record-breaking ‘21/7’ rainfall using an air–sea coupled model with ensemble simulations. The modeling results show that the northwestward moisture transport along the confluence front of TIF and the western Pacific subtropical high (WPSH) contribute mostly to the precipitation extremes across Henan. A sensitivity experiment that removes the TIF effect confirms TIF’s role in shaping extreme rainfall. Specifically, without TIF, WPSH shifts the moisture transport northeastward and causes a heavy rainband over the Korean Peninsula, with much less precipitation over Henan. The water vapor budget over Henan suggests that the TIF-induced moisture advection is nine times greater than the local moisture supply and is effectively converted into clouds therein to reinforce precipitation extremes. The contribution of TIF to the ‘21/7’ Henan torrential rainfall on average could be as large as 42% by comparing the differences between simulated results with and without TIF’s effects.

Modeling study on the roles of the deposition and transport of PM2.5 in air quality changes over central-eastern China

The role of PM2.5 (particles with aerodynamic diameters ≤ 2.5 µm) deposition in air quality changes over China remains unclear. By using the three-year (2013, 2015, and 2017) simulation results of the WRF/CUACE v1.0 model from a previous work (Zhang et al., 2021), a non-linear relationship between the deposition of PM2.5 and anthropogenic emissions over central-eastern China in cold seasons as well as in different life stages of haze events was unraveled. PM2.5 deposition is spatially distributed differently from PM2.5 concentrations and anthropogenic emissions over China. The North China Plain (NCP) is typically characterized by higher anthropogenic emissions compared to southern China, such as the middle-low reaches of Yangtze River (MLYR), which includes parts of the Yangtze River Delta and the Midwest. However, PM2.5 deposition in the NCP is significantly lower than that in the MLYR region, suggesting that in addition to meteorology and emissions, lower deposition is another important factor in the increase in haze levels. Regional transport of pollution in central-eastern China acts as a moderator of pollution levels in different regions, for example by bringing pollution from the NCP to the MLYR region in cold seasons. It was found that in typical haze events the deposition flux of PM2.5 during the removal stages is substantially higher than that in accumulation stages, with most of the PM2.5 being transported southward and deposited to the MLYR and Sichuan Basin region, corresponding to a latitude range of about 24°N-31°N.

Evolution Characteristics of the Flows Around the Tibetan Plateau and the Relationship with the Climate in China in Winter

During the winter half-year (previous October–April), the mid-latitude westerlies flows around the Tibetan Plateau (TP) and generate a dynamic low-pressure trough on its south side and a high-pressure ridge on its north side. In this study, we define the vorticity perturbation as the difference between local vorticity and the meridionally-averaged vorticity. Then, the difference of averaged vorticity perturbation at 600 hPa in the two key areas where the trough and ridge are located is used to represent the intensity of the flows around the Tibetan Plateau (FAT). The evolution characteristics of FAT in the winter half-year, as well as in autumn, winter and spring, are analyzed. Moreover, under global warming, in winter the relationship of FAT to the precipitation and temperature in China are discussed. The results show that FAT steadily exists on both sides of TP during the winter half-year. With the north-south migration of the mid-latitude westerlies, the FAT gradually strengthens in autumn, with the strongest intensity and the widest range in winter, and begins to weaken in spring. The intensity of FAT (IFAT) has a decreasing trend and a quasi-4a period variation on the interannual scale in all the time, both of which are closely related to the mid-latitude westerlies upstream of TP. Represented by the winter when IFAT is strongest, the IFAT is significantly correlated to the change of precipitation and temperature in most parts of China under global warming, especially in the convergence area over central-eastern China. There is also a significant correlation between IFAT and the precipitation and temperature anomalies in Northwest China, TP, and Northeast China. This relationship between the FAT anomaly and the climate anomaly in China in winter can be well explained by analyzing the anomalies of large-scale circulation, outgoing longwave radiation and water vapor flux divergence. The FAT anomaly maybe one of the reasons for the climate extreme events in China in winter.

Ice-volume and insolation influences on hydroclimate changes in central eastern China during the antepenultimate glacial period

Ice-volume and insolation influences on hydroclimate changes in central eastern China during the antepenultimate glacial period

Paradoxically lowered oxygen isotopes of hydrothermally altered minerals by an evolved magmatic water

It has been well known that the influxing meteoric water can hydrothermally lower oxygen and hydrogen isotopes of rocks and/or minerals during continental magmatic or metamorphic processes in certain appropriate cases. Its opposite, however, is not implicitly true and needs independent testing. In terms of a novel procedure recently proposed for dealing with thermodynamic re-equilibration of oxygen isotopes between constituent minerals and water from fossil hydrothermal systems, the initial oxygen isotopes of water ({updelta }^{18}{text{O}}_{text{W}}^{text{i}}) are theoretically inverted from the early Cretaceous post-collisional granitoids and Triassic gneissic country rock across the Dabie orogen in central-eastern China. Despite ancient meteoric waters with low {updelta }^{18}{text{O}}_{text{W}}^{text{i}} value down to − 11.01 ± 0.43‰ (one standard deviation, 1SD), oxygen isotopes of hydrothermally altered rock-forming minerals from a granitoid were unexpectedly but concurrently lowered by an evolved magmatic water with mildly high {updelta }^{18}{text{O}}_{text{W}}^{text{i}} value of 2.81 ± 0.05‰ at 375 °C with a water/rock (W/R)c ratio of 1.78 ± 0.20 for the closed system. The lifetime of fossil hydrothermal systems studied herein is kinetically constrained to no more than 1.2 million years (Myr) via surface-reaction oxygen exchange in the late-stage of continental magmatism or metamorphism. Thereby, caution should be paid when lowered oxygen isotopes of hydrothermally altered rocks and/or minerals were intuitively and/or empirically inferred from the external infiltration of the purely meteoric water with a low {updelta }^{18}{text{O}}_{text{W}}^{text{i}} value alone.

Tectonic Evolution of the Southern Dabie Orogenic Belt, China: Insights from Peak P–T Conditions and U–Pb Zircon Dating of the Susong Metamorphic Complex

The Susong metamorphic complex (SSC) in the southern margin of the Dabie orogenic belt (DOB) in central-eastern China is a key metamorphic unit for understanding subduction and exhumation processes in the DOB. However, the formation age and metamorphic grade of the SSC remain uncertain, hampering our understanding of the mechanism of the formation of the DOB. An integrated study of field survey, regional metamorphic petrology, geothermobarometry, and U–Pb dating of zircon was carried out in this study. Our results reveal that the SSC was metamorphosed under epidote amphibolite- to amphibolite-facies conditions with average metamorphic P–T values of 0.98 ± 0.07 GPa and 531 ± 35 °C. The smooth spatial variation in peak P–T conditions and an apparent geothermal gradient of ~17 °C/km indicate that the SSC as a whole fall into Barrovian-type metamorphic environments. Zircon U–Pb dating for garnet–mica schists of sample ZT003, ZT005 and ZT006 yield five (Groups I to V), six (Groups I to VI) and five (Groups I to V) age groups, respectively, concentrating on the Meso-Neoarchean, early-middle Paleoproterozoic, middle Mesoproterozoic, early Neoproterozoic, Palaeozoic and Triassic-lower Jurassic. Therein, a 259–190 Ma (Group V) from zircons with Th/U ratios of <0.1 in sample ZT006 record the timing of both peak and retrograde metamorphism for the SSC. All other ages are detrital zircon ages, and from age provenances in the DOB or the Yangtze Block (YZB), indicating the YZB affinity of the SSC. The two youngest age populations of 427–415 Ma (Group VI) and 475–418 Ma (Group V) from samples ZT005 and ZT006, respectively, suggest that the formation age of the SSC could be Middle Devonian. The similarity of formation age and peak P-T conditions of the SSC to Foziling Group, located in the northernmost DOB, implies that both units formed the sedimentary cover on the passive continental margin of the YZB during the late Palaeozoic, and subducted into the middle-lower crust of 20–40 km depth as a whole, corresponding to the shallow subduction. Compared to the deep subduction defined by high-pressure (HP) and ultrahigh-pressure (UHP) units, larger differences in peak P–T conditions, age and geothermal gradient between two different tectonic environments happen. Accordingly, it is speculated that a transitional subduction from shallow to deep levels occurred at Moho depths during the Early Triassic, and is due to a change in subduction dip angle.

Effect of different vaccine strategies for the control of Japanese encephalitis in mainland China from 1961 to 2020: A quantitative analysis

BackgroundWe aimed to quantify the impact of each vaccine strategy (including the P3-inactivated vaccine strategy [1968–1987], the SA 14-14-2 live-attenuated vaccine strategy [1988–2007], and the Expanded Program on Immunization [EPI, 2008–2020]) on the incidence of Japanese encephalitis (JE) in regions with different economic development levels. MethodsThe JE incidence in mainland China from 1961 to 2020 was summarized by year, then modeled and analyzed using an interrupted time series analysis. ResultsAfter the P3-inactivated vaccine was used, the JE incidence in Eastern China, Central China, Western China and Northeast China in 1968 decreased by 39.80 % (IRR = 0.602, P < 0.001), 7.80 % (IRR = 0.922, P < 0.001), 10.80 % (IRR = 0.892, P < 0.001) and 31.90 % (IRR = 0.681, P < 0.001); the slope/trend of the JE incidence from 1968 to 1987 decreased by 30.80 % (IRR = 0.692, P < 0.001), 29.30 % (IRR = 0.707, P < 0.001), 33.00 % (IRR = 0.670, P < 0.001) and 41.20 % (IRR = 0.588, P < 0.001). After the SA 14-14-2 live-attenuated vaccine was used, the JE incidence in Eastern China and Northeast China in 1988 decreased by 2.60 % (IRR = 0.974, P = 0.009) and 14.70 % (IRR = 0.853, P < 0.001); the slope/trend of the JE incidence in Eastern China and Central China from 1988 to 2007 decreased by 4.60 % (IRR = 0.954, P < 0.001) and 4.70 % (IRR = 0.953, P < 0.001). After the EPI was implemented, the JE incidence in Eastern China, Central China and Western China in 2008 decreased by 10.50 % (IRR = 0.895, P = 0.013), 18.00 % (IRR = 0.820, P < 0.001) and 24.20 % (IRR = 0.758, P < 0.001), the slope/trend of the JE incidence in Eastern China from 2008 to 2020 decreased by 17.80 % (IRR = 0.822, P < 0.001). ConclusionsEach vaccine strategy has different effects on the JE incidence in regions with different economic development. Additionally, some economically underdeveloped regions have gradually become the main areas of the JE outbreak. Therefore, mainland China should provide economic assistance to areas with low economic development and improve JE vaccination plans in the future to control the epidemic of JE.

Late Permian-Triassic ridge subduction beneath the northeastern margin of the North China Craton: Evidence from the Kaiyuan appinitic to high-Mg intermediate intrusions in northern Liaoning, North China

Recognizing terminal ridge subduction is of first-order importance in chronicling the tectonic timeline of any accretionary orogens, but remains elusive in the final suturing zone of the Paleo-Asian Ocean along the Solonker−Xar Moron−Changchun−Yanji swath. Here we report two generations of ultramafic-mafic to intermediate intrusions from northern Liaoning, North China, linking eastern Central Asian Orogenic Belt and northern North China Craton. The ca. 259 Ma appinites show variable enrichment in large-ion lithophile elements (LILEs) but depletion in high-field strength elements (HFSEs), and variably enriched isotopic compositions with εNd(t) of −11.8 to −2.4 and zircon εHf(t) of −15.7 to +5.0. These petro-geochemical traits argue for their derivation from partial melting of subduction-modified lithospheric mantle. By contrast, the high-Mg diorites of 226−223 Ma display decoupling features between LILEs and HFSEs and juvenile isotopic signatures with εNd(t) of −0.3 to +2.6 and zircon εHf(t) of +5.4 to +11.4. These characters are consistent with a magmatic origin from partial fusion of sediment-fertilized asthenospheric mantle. Synthesizing the two mantle-melting events with regional coeval igneous activities leads to the identification of Late Permian (265−250 Ma) and Middle-Late Triassic (241−218 Ma) magmatic flare-ups with a 10−15 m.y. lull along the northern North China Craton. This magmatic tempo tends to record a salient mantle replacement from hydrous metasomatized lithosphere to anhydrous asthenosphere. In combination with ensuing progressive crustal growth, simultaneous metamorphism, and structural activities, these diverse manifestations make a compelling case of ridge subduction and concomitant slab window formation during the eventual closure of the Paleo-Asian Ocean along the Solonker−Xar Moron−Changchun−Yanji swath.

National Nutrition and Health Systematic Survey for 0-18 years old children in China:study protocol for 6-18 years old children

To systematically collect basic data on nutrition and health of children aged 6-18 years in China. A cross-sectional survey was conducted in 7 regions, including Eastern China, Northern China, Central China, Southern China, Southwestern China, Northwestern China, and Northeastern China. A total of 65 000 children aged 6-18 years were selected from 28 urban and rural survey sites in 14 provinces through multistage stratified random cluster sampling. Through a questionnaire survey, physical examination, laboratory examination, dietary survey, children&apos;s information on dietary intake, physical development, bone development, psychological intelligence, physiological development, and physique were collected to evaluate children&apos;s nutrition and health status; nutrition and health knowledge, physical activity and lifestyle of children and their parents were investigated. The project has basically completed the field investigation and data entry, and it has measured the physical development indicators of 64 999 children aged 6-18 years in China.64 463 completed the student questionnaire; 62 448 completed the body composition measurement, and 3359 completed the assessment of intellectual development. This project brings together the nutrition, epidemiology, child care, mental health experts with the centers for disease control and prevention, and maternal and child health care system in our country. Combining with research institutes and children&apos;s hospitals of professional expertise, the project comprehensively collects children&apos;s dietary nutrition, growth and development, and health-related data in our country. It would put forward strategies to improve the children&apos;s nutrition and health in China and provide the basis for data sharing.

Radiocarbon age offset of lake sediments from central eastern China modulated by both hydroclimate and human activity

The radiocarbon (14C) dating of lake sediments is often beset by the problem of the existence of a carbon reservoir and its effect on the dated materials, which in turn influences the reliability of paleoclimatic reconstructions from lake sediments. Changes in the carbon reservoir of lake sediments are usually attributed to changes in old carbon input from the surrounding catchment caused by climatic variations or human activities. However, there is much uncertainty regarding the main driver of changes in the carbon reservoir when both climate changes and human activities coexist. We compared the 14C ages of bulk sediment samples and charcoals with the published age-model for Lake Nvshan, which is based on terrestrial plant macrofossils. The results show that the use of charcoals 14C ages for dating the sediments of Lake Nvshan is unreliable. We then obtained a time series of changes in the carbon age offset (Δt) of the bulk sediments from Lake Nvshan. The results show that prior to a significant increase in human activities, changes in Δt coincided with changes in precipitation and in the pollen concentration/total organic carbon (TOC) contents of the lake sediments; whereas after the onset of increasing human activities, changes in Δt coincided with the size of the human population of surrounding area. Prior to the increase in human activities, a higher Δt likely resulted from decreases in rainfall and phytomass which caused a reduction in contemporaneous carbon inputs. Thereafter, a higher Δt was caused by intensive human land-use and the resulting input of more old carbon. Our findings reveal a shift in the main factors influencing the Δt of bulk sediments, which was caused by the intensification of human activities in the anthropic zone. Our findings contribute to an improved understanding of the factors modulating the Δt in lake sediments.

Influences of El Niño-Southern Oscillation on summertime ozone pollution over central-eastern China during 1950-2014.

Summertime ozone pollution has become increasingly severe over many parts of China in recent years. Due to lack of historical ozone observations, few studies have analyzed the linkage between natural climate variability and ozone levels for a long time series. This study uses the simulation datasets from CMIP6 to explore the effects of El Niño-Southern Oscillation (ENSO) on summertime (June/July/August) surface ozone concentrations in central-eastern China (CEC; 20°N-42°N, 100°E-123°E) during the period of 1950-2014. Our results show that, after excluding the emission-related trend, the detrended summertime daily mean surface ozone concentrations averaged over CEC in El Niño years (30.69ppb) are higher than those in La Niña events (29.34ppb). Compared to the summertime mean ozone of 1950-2014 (30.25ppb), the maximum anomalies in CMIP6 are 2.88ppb (9.52% higher) and - 5.52ppb (18.25% lower) in El Niño and La Niña years, respectively. In addition, the summertime MDA8 ozone of CEC is significantly correlated with the central-eastern equatorial Pacific SST (5°N-5°S, 170°W-120°W) (R = 0.29, P-value = 0.02). Such ozone increases/declines in El Niño/La Niña years are also found in satellite observations of OMI ozone. The results show that the ENSO affects the large-scale circulations over central-eastern China, which regulate the regional atmospheric stability and meteorological conditions (including horizontal wind fields, geopotential height, vertical velocity, surface air temperature, and precipitation) to influence the efficiency of ozone photochemical formation and transport. Our study makes better estimation and attribution of future surface ozone pollution in China.

Impacts of Horizontal Resolution of the Lateral Boundary Conditions and Downscaling Method on the Performance of RegCM4.6 in Simulating the Surface Climate Over Central‐Eastern China

AbstractThis study investigated the impacts of horizontal resolution of lateral boundary condition (LBC) and downscaling method on the performance of RegCM4.6 in simulating the 2 m air temperature and precipitation over central eastern China. Two groups of experiments (direct downscaling experiments using LBC derived from the same reanalysis data but with different horizontal resolutions [0.75°, 1.5°, and 2.5°] and double‐nested downscaling experiment) with the model horizontal resolution of 20 km over central eastern China have been carried out. Results show that the direct downscaling experiments consistently outperform the double‐nested experiment to simulate the 2 m air temperature and precipitation over central eastern China, suggesting that adopting the direct downscaling method is appropriate to simulate the surface climate over central eastern China. Meanwhile, the direct downscaling experiments driven by the LBC derived from the reanalysis data with the horizontal resolution ranging from 0.75° to 2.5° display very comparable performance with a little better performance by adopting the LBC derived from the reanalysis data of much finer resolution. Further mechanism analysis indicates that much larger errors of LBC produced by the double‐nested downscaling method lead to the positive pressure biases and negative biases of water vapor convergence flux over Jianghuai Valley, which contribute to the much larger biases of precipitation and 2 m air temperature in the double‐nested downscaling experiment compared to the direct downscaling experiments. This study emphasizes that the direct downscaling method is superior to the double‐nested downscaling method for the simulations of 2 m air temperature and precipitation over central eastern China.