Science China Earth Sciences最新文献

Prokaryotes play a fundamental role in global ocean biogeochemical cycles. However, how the abundance and metabolic activity of ecologically distinct subgroups (i.e., high nucleic acid (HNA) and low nucleic acid (LNA) cells), and their regulating factors, change in response to changing marine environmental conditions remains poorly understood. Here, we delved into the time-evolving dynamic responses of the HNA and LNA prokaryotic subgroups to declining resource availability and selective grazing by protozoa by conducting a 73-day incubation experiment in a large-volume (117,000 L) macrocosm that facilitates community-level exploration. We found that the metabolic activity of the HNA subgroup was higher than that of the LNA subgroup when the macrocosm was resource replete but that the HNA subgroup declined more rapidly than the LNA subgroup as the resources became increasingly scarce, leading to a steadily increasing contribution of LNA cells to prokaryotic activity. Meanwhile, as resources in the macrocosm became limited, protozoan grazing preference shifted from the HNA to the LNA subgroup and the contributions of the LNA subgroup to the carbon flow within the macrocosm increased. The findings highlight the resilience of LNA cells in resource-limited environments, illuminate the critical role of selective grazing by protozoa in balancing distinct prokaryotic subgroups under changing resource conditions, and demonstrate the complex and adaptive interactions between protozoa and prokaryotes across diverse environmental contexts.

Anthropogenic revegetation is an effective way to control soil erosion and restore degraded ecosystems in China’s northwest drylands (NWD). However, excessive vegetation cover expansion has long been known to increase evapotranspiration, leading to reduced local water availability, which can in turn threaten the health and services of restored ecosystems. Determining the optimal vegetation coverage (OVC) is critical for balancing the trade-off between plant growth and water consumption in water-stressed areas, yet quantitative assessments over the entire NWD are still lacking. In this study, a modified Biome BioGeochemical Cycles (Biome-BGC) model was used to simulate the long-term (1961–2020) dynamics of actual evapotranspiration (ET_a), net primary productivity (NPP), and leaf area index (LAI) for the dominant non-native tree (R. pseudoacacia and P. sylvestris) and shrub (C. korshinkii and H. rhamnoides) species at 246 meteorological sites over NWD. The modified model incorporated the Richards equation to simulate transient unsaturated water flow in a multilayer soil module, and both soil and eco-physiological parameters required by the model were validated using field-observed ET_a data for each species. Spatial distributions of OVC (given by the mean maximum LAI, LAI_max) for the dominant species were determined within three hydrogeomorphic sub-areas (i.e., the loess hilly-gully sub-area, the windy and sandy sub-area, and the desert sub-area). The modified Biome-BGC model performed well in terms of simulating ET_a dynamics for the four plant species. Spatial distributions of mean ET_a, NPP, and LAI_max generally exhibited patterns similar to mean annual precipitation (MAP). In the loess hilly-gully sub-area (MAP: 210 to 710 mm), the OVC respectively ranged from 1.7 to 2.9 and 0.8 to 2.9 for R. pseudoacacia and H. rhamnoides. In the windy and sandy sub-area (MAP: 135 to 500 mm), the OVC ranged from 0.3 to 3.3, 0.5 to 2.6 and 0.6 to 2.1 for P. sylvestris, C. korshinkii and H. rhamnoides, respectively. In the desert sub-area (MAP: 90 to 500 mm), the OVC ranged from 0.4 to 1.7 for H. rhamnoides. Positive differences between observed and simulated plant coverage were found over 51% of the forest- and shrub-covered area, especially in the loess hilly-gully sub-area, suggesting possible widespread overplanting in those areas. This study provides critical revegetation thresholds for dominant tree and shrub species to guide future revegetation activities. Further revegetation in areas with overplanting should be undertaken with caution, and restored ecosystems that exceed the OVC should be managed (e.g., thinning) to maintain a sustainable ecohydrological environment in the drylands.

In the context of global warming, the extreme summer precipitation over the Tibetan Plateau (TP) has changed significantly. In this study, the summer (June–August) extreme precipitation on the TP was classified into three spatial types by applying the K-means clustering method to the Third Pole Region long time-series high-resolution (1/30°) precipitation dataset (TPHiPr, 1979–2020). The characteristics of the circulation anomalies and precursors corresponding to the extreme precipitation on the TP in summer during 1979–2020 were investigated. The results showed that the summer extreme precipitation of the TP can be categorized into northwestern (NW), southeastern (SE), and southern Himalayan (HS) types based on extreme precipitation thresholds. The NW and SE types are mainly influenced by anomalous signals in the mid-to-high latitude regions upstream of them, whereas the HS type is controlled by the localized subtropical anomalous circulation. On the 8th day before the onset of the NW type, an anomalous cyclone was observed in the western Atlantic Ocean (60°W, 50°N), which triggered the west-to-east quasi-latitudinal propagation of Rossby waves. On the onset day of the NW type, the upper troposphere showed positive-negative-positive geopotential height anomalies along the latitudinal 40°N from the Caspian Sea, the western part of Xinjiang, to the northeastern TP. Moisture entered from the Arabian Sea along the southeastern edge of the anomalous cyclone on the southwestern TP and converged in the northwestern TP. Compared to the NW type, the precursors of the SE type appeared at higher latitudes and were more intense. On the 8th day before the onset of the SE type, an anomalous cyclone occurred near Greenland (60°W, 70°N) and excited Rossby waves propagating southeastward. On the onset day of the SE type, the upper troposphere showed negative-positive-negative geopotential height anomalies across Eurasia from the Ural Mountains and the Iranian Plateau to the northern TP in the northwest-southeast direction and entered the southeastern TP from the Bay of Bengal along the southeastern edge of the anomalous cyclone in the southern TP. On the 6th day before the onset of the HS type, the anomalously high pressure in the middle and lower layers of the low-latitude region extended westward, and a significant anticyclonic anomalous circulation occurred on the southern TP on the onset day of the HS type, enabling the delivery of moisture from the Bay of Bengal to the southern foothills of the Himalayas. Additionally, an anomalous cyclone perched in the northeastern TP at a geopotential height of 200 hPa strengthened westerly winds in the southern TP and contributed to the maintenance of the anticyclonic system on the southern TP.

This article examines the abundant marine mollusc, and fish remains at the Jingtoushan shell midden (8,300 to 7,800 cal a BP) in Zhejiang Province, China, to investigate the fishing economy, community development, the palaeoenvironment, and their interactions among the prehistoric populations in the lower Yangtze River Basin and southeastern coastal China. It also attempts to explore the prosperity and decline of coastal settlements in China during the Neolithic Age and the potential reasons for their rise and fall, respectively. Based on the ecological and biological principles of marine animals, standard zooarchaeological methods and radiocarbon dating analysis are used for sampling, identification, measurement, and quantification. Results show that at least 11 mollusc taxa and 14 fish taxa can be identified from the Jingtoushan faunal assemblage. The ancient Jingtoushan residents possibly lived in a settlement close to the coast and engaged in inshore and offshore fishing, hunting, and gathering as their primary subsistence strategies, with low-level rice cultivation as a supplementary means of sustenance. Eventually, the changes in the coastal environment could be one of the reasons why the Jingtoushan residents abandoned their settlement. The research contributes to Chinese Neolithic archaeology with new evidence of the exploitation of marine resources around 8000 a BP in the eastern coastal areas and the relationship between Neolithic community development and environmental changes.

As a famous deep and large fault in eastern China, the Tanlu Fault passes through Anhui, Jiangsu, and Shandong and into northeastern China. It is important to improve the understanding of seismic hazard assessments in areas near faults. We start a scenario earthquake simulation in the M7.5 earthquake potential area of the Xinyi-Sihong segment of the Tanlu Fault. The fault rupture length and width are constrained according to the scaling law of large intraplate earthquakes, the background normal stress is depth dependent, and the initial shear stresses are determined using trial and error by matching the earthquake magnitude. Considering the 120 km rupture length of the M7.5 earthquake, we compare the horizontal uniform stress model and self-similar stress perturbation model. Our findings reveal that the seismic source time function of the horizontal uniform stress model is similar to that of the Haskell model and that of the self-similar stress perturbation model is more similar to that of a real earthquake case. We compare the dynamic rupture simulation and ground motion results under four different stress conditions and find that the shorter the characteristic length of the self-similar function is, the rougher the initial stress. For the M7.5 earthquake with an epicenter in the vicinity of Suqian, the Xinyi-Tancheng segment, which is located in the IX-intensity zone north of the epicenter, vibrates more strongly on the northern side than on the southern side due to the influence of the low-velocity zone and the peak slip rate. The response spectra analysis at stations in the study area is useful for improving the earthquake resistance capability.

Mercury (Hg) enrichments in ancient sediments have been used as a proxy of volcanism, especially large igneous province (LIP) eruptions. However, considering the existence of other potential Hg sources besides volcanoes and the diverse factors (e.g., organic matters, clay minerals, sulfide minerals and Fe oxides) that can affect Hg sequestration, there are considerable uncertainties to simply regard sedimentary Hg anomalies as signatures of volcanic activities. Mercury stable isotopes, a promising tool for tracing the origins and transformations of Hg, have been increasingly used for determining the causes of Hg spikes and understanding the geochemical behavior of Hg in the geologic record. To date, lots of researches have applied Hg concentrations and Hg isotopes to identify LIP volcanisms linking with significant geological events such as mass extinctions, ocean anoxic events and other environmental perturbations that mainly occurred in the Phanerozoic. However, the results in previous studies clearly show that not all Hg enrichments are derived from volcanic inputs, which emphasize the need for more caution in using Hg as a fingerprint of volcanism. With a better understanding of Hg isotopes in the future, there will be important implications for Hg isotopes to reconstruct volcanic activities in the rock records and their impacts on biological evolution.

Microblade assemblages are among the most common prehistoric archaeological materials found on the Tibetan Plateau (TP) and are thought to indicate large scale migration to and settlement of the TP. Few microblade sites, however, have been systematically excavated, especially in the remotest, highest-elevation regions of the TP. The timing of the large-scale arrival, spread, and permanent settlement of people on the TP therefore remains controversial. In this paper, we report on a recently excavated site, Locality 3 of the Nwya Devu Site (ND3), located at 4600 meters above sea level (masl), near the shore of Ngoin Lake, on the interior TP. Our analyses reveal a fairly typical microblade technological orientation and two types of microblade cores: wedge-shaped and semi-conical, which are similar to those found throughout North China. Using Optically Stimulated Luminescence (OSL) dating and AMS ¹⁴C dating, the age of ND3 ranges from 11 to 10 ka. This date range indicates ND3 is the oldest microblade site yet recorded in the remote, high-elevation regions of the TP and thus provides important information about when and how hunter-gatherers using microblades began exploiting the higher altitudes of the TP. Taken together, studies at ND3 and throughout the TP suggest that a microblade adaptation is associated with the first prolonged human occupation of the plateau and that microblades played a significant role in mediating the risks and facilitating the mobility necessary to permanently inhabit the TP.

The spatiotemporal evolution of lunar impact craters is crucial for investigating lunar interior structure, internal and external dynamic processes, and interplanetary impact history. Advances in lunar crater identification are reviewed based on topography and gravity data, and the features and mechanisms of topographic or buried craters are analyzed regarding morphology, gravity anomalies, gravity gradients, and the underlying crust-mantle interface relief. Based on the compiled crater catalog, the early lunar impact flux and thermal evolution are further discussed according to the basin ages and their interior structures. For some ancient impact basins, the crater size-frequency distribution measurements revealed age discrepancies from previous studies, suggesting that the lunar late heavy bombardment event started at ∼3.95 Ga. The degraded bulge structures of the crust-mantle interface beneath mare basins reveal that these basins formed on the lunar crust surface under high-temperature conditions and underwent prolonged relaxation compared to highland basins. Finally, we reveal that the up-to-date identification of lunar buried craters remains inaccurate and incomplete, preventing us from accurately reconstructing lunar and interplanetary impact histories. Therefore, we propose that a gravity model constructed using localized orthogonal basis functions can be useful for identifying lunar craters.

In this research, an arbitrarily oriented electric dipole at subsurface is used to simulate Seismogenic Electromagnetic (SEM) radiation emanating from a seismic zone during its gestation phase. Analytical synthesis of responses at the Lijiang magnetotelluric (MT) station has revealed that SEM radiation could induce identifiable anomalies in the electromagnetic (EM) spectrum, apparent resistivity and phase within specific frequency bands. Background variations were extracted from long-term observation data of Dali and Lijiang MT stations, enabling the identification of SEM anomalies related to the Yunlong and Yangbi earthquakes. Multiple parameters of dipole sources at subsurface were obtained by applying the Differential Ant Colony Optimization (DACO) algorithm to anomalous data of two stations with multi-frequencies and various response functions. The spatial distribution of these predicted dipoles is predominantly clustered in or around the seismogenic area, with their azimuthal orientation aligning towards the seismogenic fault in general. This study has demonstrated the potential of using subsurface electric dipole simulations for SEM radiation analysis, offering a feasible approach for the prediction and understanding of seismogenic zones.

Ice core provides a valuable vertical timeline of past climates and anthropogenic activities. Environmental proxies have been widely used in these studies, but there are few biological indicators available. To address this gap, we investigated the bacterial community from a 74 m ice core of Muztag ata glacier on the Tibetan Plateau to link biological indicators with past climate and anthropogenic activities. By analyzing the portion of the ice core with environmental proxies available (corresponding to 1907 to 1991), we observed an increase in bacterial richness throughout the ice core, which was associated with higher NH⁺₄, an indicator of agricultural development. The bacterial community was jointly determined by human activity, natural input, and air temperature, with a strong human influence after the 1950s. Furthermore, the relative abundance of animal gut-associated bacteria, including Aerococcaceae, Nocardiaceae, Muribaculaceae, and Lachnospiraceae, was associated with livestock number changes in the Central Asian region. Together with other bacterial lineages, they jointly explained 59.8% of the livestock number changes. This study provides quantitative evidence of the associations between bacterial indicators and past climate and human activities, highlighting the potential of using bacterial proxies for ice core studies.