Science China Earth Sciences最新文献

The Xianshuihe fault is a major tectonic boundary between the Sichuan-Yunnan rhombic and Bayanhar blocks in Southwest China. With an average left-lateral strike-slip movement of 10–15 mm/yr, it is a fast-moving strike-slip continental fault. On September 5, 2022, the M_s6.8 Luding earthquake occurred along the Moxi segment of the Xianshuihe fault, reaching a maximum intensity of IX and resulting in a significant number of casualties and severe property damage. This earthquake broke the long-standing seismic quiescence of the Xianshuihe fault, which lasted for more than 40 years, and was followed by a significant number of aftershocks. An outstanding question is how the behavior of the Xianshuihe fault and major earthquakes changed following this mainshock. In this study, we examined the changes in regional seismicity following the Luding earthquake and identified the potential for future strong earthquakes along the Xianshuihe fault. We used a finite element numerical method to simulate the environment of the seismogenic fault and its adjacent areas. In addition, we used the coseismic slip model of the Luding earthquake with the split-node method to calculate how the stress and strain fields in the surrounding area were affected by the 2022 mainshock. Coulomb stress changes were resolved in the main faults, and the seismicity of adjacent faults was analyzed in conjunction with the observed seismic data. The results indicate that regional tectonic movement primarily occurred to the southeast along the Moxi segment. The stress field is approximately north-south in tension and east-west in compression. Variation in the stress field in the epicentral region of the Luding earthquake exceeded 1 MPa. The maximum displacement of the coseismic deformation field was concentrated between Moxi town and Tuanjie village, and the Coulomb stress of the fault zone in this region experienced the largest decrease. However, the b-value of the Gutenberg-Richter magnitude-frequency relationship at the epicenter and the surrounding area exhibited an abnormal pattern of decrease-decrease-increase, indicating that the regional stress may not be fully released. This earthquake increased the Coulomb stress in other segments of the Xianshuihe, Anninghe, and Daliangshan faults, whereas the Coulomb stress in the Longmenshan and Xiaojinhe fault zones decreased. In addition, it triggered a series of normal-fault, moderate-sized earthquakes in nearby areas. The Dagangshan reservoir, located ∼20 km from the epicenter of the Luding earthquake, received an increase of ∼5.3 MPa in the tensile stress along the NWW-SEE direction. The Xiluodu Reservoir, located approximately 225 km from the epicenter, was less affected by this earthquake, and the seismic activity near the reservoir remained relatively unchanged. In this study, post-earthquake seismicity in the vicinity of the M_s6.8 Luding earthquake was analyzed and predicted by numerical si

The North Pacific sea surface salinity (SSS) decadal variability (NPSDV) and its potential forcing were evaluated from 25 coupled models of the Coupled Model Intercomparison Project phase 6 (CMIP6) considering the prospects for decadal climate predictions. The results indicated that the CMIP6 models generally reproduced the spatial patterns of NPSDV. The large standard deviation of the SSS anomaly over the strong current regions, such as the Kuroshio-Oyashio Extension (KOE), North Pacific Current (NPC), California Current System (CCS), and Alaskan Coastal Current (ACC), is reflected in the two leading modes of NPSDV: a dipole with out-of-phase loadings in the KOE-NPC versus CCS-ACC and a monopole with positive loading over the KOE-NPC. The order of modes is sensitive to individual models that exhibit discrepancies, especially in temporal phases and power spectra. An autoregressive model of order-1 was used to reconstruct the NPSDV with several forcing terms. The generally weaker influence of forcings in an autoregressive model of order-1 is partly related to the overestimated response time of NPSDV relative to forcings. Most NPSDV variances originate from the persistence of SSS anomalies, but the dominant forcing factors are diverse among models. The model diversity for the NPSDV simulation mainly arises from the influence of the tropical El Niño-Southern Oscillation through teleconnection on the North Pacific Oscillation or Aleutian Low with timescale dependence. Conversely, models that can reproduce the NPSDV well are not dependent on those with larger impacts from the North Pacific oceanic processes.

The evolution of solar magnetic fields is significant for understanding and predicting solar activities. And our knowledge of solar magnetic fields largely depends on the photospheric magnetic field. In this paper, based on the spherical harmonic expansion of the photospheric magnetic field observed by Wilcox Solar Observatory, we analyze the time series of spherical harmonic coefficients and predict Sunspot Number as well as synoptic maps for Solar Cycle 25. We find that solar maximum years have complex short-period disturbances, and the time series of coefficient g₇⁰ is nearly in-phase with Sunspot Number, which may be related to solar meridional circulation. Utilizing Long Short-Term Memory networks (LSTM), our prediction suggests that the maximum of Solar Cycle 25 is likely to occur in June 2024 with an error of 8 months, the peak sunspot number may be 166.9±22.6, and the next solar minimum may occur around January 2031. By incorporating Empirical Mode Decomposition, we enhance our forecast of synoptic maps truncated to Order 5, validating their relative reliability. This prediction not only addresses a gap in forecasting the global distribution of the solar magnetic field but also holds potential reference value for forthcoming solar observation plans.

Carbon emission accounting is an important basis for global climate governance. Based on the consumption-based accounting (CBA) method, the characteristics of carbon flow between national, regional, and product processes could be more clearly reflected. Therefore, CBA is more conducive to clarifying the attribution of responsibilities between producers and consumers, with the principles of fairness and justice. By accounting for carbon emissions in typical countries from 1990 to 2019, we found that the CBA emissions are higher than the production-based accounting (PBA) emissions in major developed countries, while the results are reversed for developing countries. In the past 30 years, the CBA emissions in targeted developed countries generally have shown a downward trend, while in developing countries, they have shown an upward trend. CBA emissions in China have shown a continuous growth trend from 1990 to 2019, but the pace has slowed down significantly over the last decade. Meanwhile, the embodied carbon intensity of China’s exports continues to decline, indicating that China is providing more green and low-carbon products to the world. Taking the PV industry as an example, this study further reveals the contribution of specific product industries to the country’s carbon transfer through product carbon footprint analysis. In order to provide a scientific basis for global mitigation and climate governance, it is urgent to innovate a scientific, practical, and standardized CBA technology system.

Oceanic submesoscales can significantly influence phytoplankton production and export owing to their similar timescales of days. Based on two-year Biogeochemical Argo (BGC-Argo) observations, this study investigated the development of submesoscale instabilities, particularly symmetric and mixed-layer baroclinic instabilities, and their impacts on biological production and export in the oligotrophic South China Sea basin. In the northern basin, near-surface winter blooms consistently cooccurred with seasonally deepened mixed layers. However, significantly stronger and weaker winter blooms were observed over two consecutive winters within the BGC-Argo observation period. During the first winter, symmetric-instability-induced upward nutrient entrainment played a crucial role in initiating the strong winter bloom in early December, when the mixed layer was approximately 20–30 m shallower than the nutricline. This bloom occurred approximately 20–30 days earlier than that anticipated owing to the contact between the seasonally deepened mixed layer and mesoscale-cyclone-induced uplifted nutricline. The symmetric instability also facilitated the export of fixed phytoplankton carbon from the surface to deeper layers. Conversely, during the second winter, remarkably intense mixed-layer baroclinic instability associated with an intense mesoscale anticyclone led to more significant shoaling of the mixed layer compared to the nutricline, thus increasing the vertical distance between the two layers. Under this condition, upward nutrient injection, phytoplankton bloom, and carbon export were suppressed. In contrast, the BGC-Argo float in the central basin revealed significantly inhibited seasonality of phytoplankton biomass and submesoscale instabilities compared to those in the northern basin, primarily owing to the significantly shallower winter mixed layer.

The strategy of carbon neutrality is reshaping the global landscape of resource flow and recycling. As the final sink of geological minerals, the proliferated anthropogenic minerals, also called secondary resources, play an increasingly important role in resource supply enrichment. Niobium is a critical metal that lacks full concern for its sustainability. The fundamental principle of niobium circularity is to recycle and maintain the material as close to the manufacturing process as possible. Here we estimate the niobium-containing applications lost at their end-of-life, underscoring the imperative to minimize such disposal. Additionally, we elucidate the extraction processes for scrap and alloy quantities throughout the industry’s lifecycle. Drawing from anticipated waste generated by the majority of niobium applications, a forecast indicates a potential loss of approximately 168 kt by 2090 in the absence of recycling. Contrastingly, with a recycling efficiency of 90% for niobium, the projected loss diminishes to approximately 16 kt. We delve into the significance of niobium’s circular economy and explore various aspects that demand further investigation for a seamless transition from linear to circular practices.

The proto-atmosphere serves as a crucial starting point for the carbon cycle. Estimations based on atmospheric data from Mars and Venus suggest that Earth’s proto-atmosphere contained >110 bar of CO₂ and >2.6 bar of nitrogen. The proto-atmosphere had over 1000 bar of water vapor during the magma ocean stage, assuming the proto-ocean had a volume of two oceans of water. During this stage both water and carbon dioxide were in a supercritical state at the magma-atmosphere interface. Intense serpentinization reactions occurred due to rock-water interaction, producing abundant hydrogen. Consequently, nitrogen is reduced to ammonia, and carbon dioxide to methane, forming carbonate simultaneously. The proto-atmosphere dominated by methane, ammonia, and hydrogen formed a significant amount of amino acids through lightning. This process is essential not only to the origin of life, but also to the early carbon-nitrogen cycle on Earth. By the Hadean eon, a large amount of CO₂ was sequestered as carbonate and organic material. Subsequently, it mainly entered the deep mantle through mantle overturn or subduction. In the mantle transition zone, carbonate undergoes “Redox freezing”, where carbonate is reduced to diamond through oxidation of ferrous iron in the melt. In the lower mantle, Fe²⁺ undergoes disproportionation reactions, forming Fe³⁺ and metallic iron. Among these, Fe³⁺ mainly resides in bridgmanite, thereby increasing the oxygen fugacity of the lower mantle, while metallic iron falls to the Earth’s core. The distribution of carbon in the mantle is crucial for deep carbon cycling. The density curves of diamond and mantle peridotite melt intersect at the bottom of the mantle transition zone (about 660 km). This density crossover leads to the accumulation of diamond during the magma ocean stage. When materials such as subducting slabs enter the lower mantle, compensatory upwelling of lower mantle material occurs. Bridgmanite enters the upper mantle, decomposes, releasing Fe³⁺ ions and oxidizes diamond to carbonate, which under thermal disturbance from kimberlite and igneous carbonatites, moves upward. This carbonate layer may have caused significant topographic fluctuations at the 660 km boundary. Currently, diamond in this layer may still not have been completely oxidized to carbonate or carbon dioxide, serving as a redox buffering layer. This is a key factor in constraining deep carbon cycling. Subduction zones are important pathways for facilitating the cycling. Processes in the Earth’s deep carbon cycle significantly influence the carbon content of surface reservoirs. The fluctuations in atmospheric CO₂ content since the Neogene are closely linked to the uplift of the Tibetan Plateau and the subduction of the western Pacific Plate. Around 60 million years ago, the closure of the Neo-Tethys Ocean led to subduction of the Indian passive margin. The massive sediments

The diverse climates, distribution of snow and glaciers, and geographic locations directly affect the runoff response to climate change in the upper basins of the Third Pole. At present, a comprehensive analysis of runoff variations and their distinct responses to climate change in the westerlies- and monsoon-dominated upper basins is still lacking. This study comprehensively analyzed annual runoff variations in westerlies-dominated basins (the upper basins of the Aksu (UAKS), Syr Darya (USRD), Yarkant (UYK), Hotan (UHT), Amu Darya (UAMD), and Indus (UI)) and monsoon-dominated basins (the upper basins of the Yangtze (UYA), Yellow (UYE), Lancang (ULC), Nujiang (UNJ), and Yarlung Zangbo (UYZ)) of the Third Pole from 1961 to 2015. Using multi-source meteorological data and large-scale circulation factors, this study investigated the divergent responses of runoff in the upper basins to climate change, and explored the large-scale circulation mechanisms underlying runoff variations in these upper basins. The results showed that: (1) The annual runoff in the majority of upper basins (except for the UYE and UYZ) exhibited an increasing trend, and the annual runoff in the UAKS, UYK, and UI showed a significant increasing trend from 1961 to 2015. The annual runoff in the upper basins of the Third Pole changed abruptly from decreasing to increasing between the 1980s and 2000s, with the exception of the UYE. (2) The runoff in the monsoon-dominated upper basins has been controlled primarily by changes in precipitation over the past 55 years. In contrast, the runoff in the westerlies-dominated upper basins exhibited three distinct long-term responses to climate change: temperature-dominated (UYK and UHT), precipitation-dominated (USRD and UAMD), and the combined influence of precipitation and temperature (UAKS and UI). Since the 1960s, the sensitivity of runoff to warm season temperature changes in the most westerlies-dominated upper basins has decreased, while the response of runoff to precipitation changes has intensified. (3) The study revealed the connection between large-scale circulation, climate, and runoff in the upper basins of the Third Pole. The Atlantic Multidecadal Oscillation, the Westerly Index, and the El Niño-Southern Oscillation predominantly impact the precipitation or temperature in the upper basins of the Third Pole, which in turn affect the runoff variations in the upper basins dominated by either the westerlies or the monsoon. This study will be a valuable scientific reference for water resource management and climate change adaptation for both the westerlies- and monsoon-dominated upper basins in the Third Pole.