Science China Earth Sciences最新文献

The reconstruction of global annual mean temperatures made by the PAGES 2k Consortium in 2019 represents one of the most influential sequences of global climate variability over the Common Era. However, it is still not clear how the reconstruction can be influenced by the selection of reconstruction methods and the selection of proxy records with different temporal resolutions over different regions. We adopt a widely used Composite-Plus-Scale method to elucidate the effects of the selection of the proxy records on temperature reconstruction. To ensure the uniformity of data, different types of proxy records spanning the past ∼2000 years from the PAGES 2k proxy network were used to investigate the potential effects of proxy selection in hemispheric and global temperature reconstructions during the past two millennia. The long-term trends, spectral characteristics, and volcanic responses of the annual temperatures were studied based on the reconstructions. Our results reveal a significant cooling trend in the global annual mean temperature using both tree-ring and non-tree-ring records during the 1–1850 CE period, and show that the cooling exhibits a stronger trend in the Southern Hemisphere (SH) than that in the Northern Hemisphere (NH). Yet, the long-term trends vary according to different combinations of proxy records. Different reconstructions based on different types of proxies also exhibit different features in terms of volcanic responses and spectral properties. Tree-ring-based temperature reconstructions show stronger cooling responses to tropical volcanic eruptions, while non-tree-ring-based reconstructions suggest less robust volcanic responses, which may be related to dating uncertainties and low temporal resolution of the proxies. Tree-ring width records tend to preserve a substantial proportion of high-frequency (<200 years) variability, whereas non-tree-ring proxies tend to capture a larger fraction of low-frequency (>200 years) variations. Efforts are needed to reduce uncertainties of the temperature reconstruction over the Common Era associated with the insufficient spatiotemporal coverage of the current proxy network, especially for the first millennium and for the SH and tropics, also to develop statistical methods and to improve the signal strength and constrain uncertainties in existing proxy records.

Zirconium is one of high field strength elements but its isotope behavior during geochemical processes is still uncertain because of the limited database. While Zr isotopes in magmatic rocks are often used to trace the evolution of magmas through fractional crystallization, it is intriguing how highly heterogeneous Zr isotopes were produced by the growth of zircon during crustal anatexis. We address this issue by in-situ zircon Zr isotope analyses of migmatites from two high-temperature metamorphic terranes in the South Lhasa zone and the North Dabie zone, respectively, in China. The results show highly variable δ⁹⁴Zr values from −0.30‰ to +0.81‰ and from −0.58‰ to +0.49‰, respectively. In addition to the relict zircon of magmatic origin, two types of newly-grown zircons were identified in terms of their occurrences, trace elements and δ⁹⁴Zr values. The peritectic zircon, mainly occurring in the in-situ leucosomes, exhibits the highest Nb-Ta-Hf-U contents and variably higher δ⁹⁴Zr values than those of the relict zircon. The anatectic zircon, mainly occurring in the leucocratic veins, shows higher Nb-Ta-Hf-U contents than and similar δ⁹⁴Zr values to those of the relict zircon. Model calculations demonstrate that the variable Zr isotope compositions of newly-grown zircons would result from decoupled release of Zr from zircon and non-zircon phases. The Zr supply of the peritectic zircon is mainly derived from the decomposition of Zr-bearing minerals in the in-situ anatectic melt (the non-zircon effect), whereas the Zr supply of the anatectic zircon is mainly from the dissolution of pre-existing zircons in the evolved melt (the zircon effect). The significant Zr isotope variations in the migmatites well illustrate the generation, migration and accumulation of the anatectic melts during the partial melting. Therefore, Zr isotopes can be used as a powerful means for distinguishing between the peritectic and anatectic zircons during crustal anatexis.

Co-seismic landslide detection is essential for post-disaster rescue and risk assessment after an earthquake event. However, a variety of ground objects, including roads and bare land, have spectral characteristics similar to those of co-seismic landslides, making it difficult to gather information and assess their impact rapidly and accurately. Therefore, an automatic detection method based on a deep learning model, named ENVINet5, with multiple features (ENVINet5_MF) was proposed to solve this problem and improve the detection accuracy of co-seismic landslides. The ENVINet5_MF method is advantageous for co-seismic landslide detection because it features a landslide gain index (LGI) that effectively eliminates the spectral interference of bare land and roads. We conducted two experiments using multi-temporal PlanetScope images acquired in Hokkaido, Japan, and Mainling, China. The accuracy evaluation and rationality analysis show that ENVINet5_MF performed better than comparative methods and that the co-seismic landslide areas detected by ENVINet5_MF were the most consistent with ground reference data. The findings of this study suggest that ENVINet5_MF can provide an efficient and accurate method for coseismic landslide detection to ensure a rapid response to co-seismic landslide disasters.

This study constructed a high-resolution seismic catalog of 1,623 earthquakes that had occurred within 32 days in the Wulong Yinpan Reservoir area by using the deep-learning picking algorithm PhaseNet and the earthquake-location procedure Loc-Flow. A hidden fault extending up to approximately 20 km within the reservoir area was identified through analysis of precise earthquake locations and geological strata. We proposed that the increase in pore pressure caused by the intrusion of reservoir water in the sealed limestone layer results in induced seismicity along the hidden fault. Our finding sheds new insight on the importance of fluid pathways and fluid pressure in reservoir-induced seismicity and can facilitate seismic risk assessment in reservoir regions.

Storm deposits or tempestites are event sequences formed by storms, requiring at least a water temperature of 26.5°C. While inland lakes are unlikely to form storm deposits because of their limited width and water temperature. The Upper Triassic Xujiahe Formation in the Sichuan Basin is a set of coal-bearing, clastic sequences with dominant sedimentary facies varying from braided river delta to lacustrine settings, with storm deposits widely reported. In the Zilanba of Guanyuan area, in situ tree trunks on a palaeosol surface in Member V of the Xujiahe Formation provide new evidence of a storm event. Six fallen-down directions of nine in situ tree trunks were predominant in the NW direction, contrary to the palaeocurrent direction of the underlying strata, suggesting that the southeasterlies prevailed during the end-Triassic in the northern Sichuan Basin. Massive mud clasts were frequently recorded in sandstones of the Xujiahe Formation, as well as in the Xindianzi section. These mud clasts showed a rip-up or a plastic deformation with upside-down V-shapes, were capped on an erosional surface, showed no transport traces and were therefore interpreted as a storm lag deposit. The megamonsoonal climate prevailed during the Late Triassic, although the megamonsoons themselves could not generate a storm deposition in the Xujiahe Formation due to its low maximum surface wind speed. The driving mechanism for generating storm deposits in the Xujiahe Formation is suggested to be tropical cyclones over the Tethys Ocean moving eastward, further landfalling on the western margin of the Sichuan Basin. Statistics of storm events in the circum-Tethys region show a widespread storm surge in low latitudes during the end-Triassic. The storm deposits at the top of the Xujiahe Formation represent a sedimentary response to the end-Triassic hyperthermal event.

The Guangdong-Hong Kong-Macao Greater Bay Area (GBA) is threatened by potential tsunami hazards from the Littoral Fault Zone (LFZ) and the Manila subduction zone (MSZ), and may suffer huge damage because of its dense population, concentrated infrastructure, and low-lying coasts. Previous tsunami studies for the GBA made simple assumptions on the mechanisms of LFZ earthquakes, and used coarse bathymetry data in tsunami simulation, which limited the prediction of detailed tsunami hazard characteristics. In this paper, we develop a parallel dispersive tsunami model PCOMCOT to efficiently simulate dispersive, nonlinear, and breaking tsunami waves. We also construct large-scale and high-resolution bathymetry models for the GBA by correcting and integrating various data sources. Dynamic rupture simulation is performed for the LFZ to obtain a more reliable earthquake source model. We propose several representative earthquake scenarios for the LFZ and MSZ, and use PCOMCOT to calculate the resulting tsunami waves, currents, and inundation in the GBA. Our results indicate that if an M_w7.5 oblique-slip earthquake occurs in the LFZ off the Pearl River Estuary (PRE), the subsequent tsunami will primarily impact Hong Kong, causing maximum positive and negative waves of around 1 m and −2 m, respectively, along with slightly destructive currents (⩾1.5 m/s). An M_w9.0 MSZ megathrust earthquake can lead to widespread inundation with >1 m depth on the outlying islands of Macao and in the urban areas of Hong Kong around the Victoria Harbour. Besides, it will also cause catastrophic tsunami currents along the narrow waterways in Hong Kong and Macao, and the spatial distribution of strong currents (⩾3 m/s) shows a considerable discrepancy from the areas of serious inundation. Thus, more attention should be paid to the potential impacts of tsunami currents on the GBA.

The scale-dependent predictability of the devastating 7·20 extreme rainstorm in Zhengzhou, China in 2021 was investigated via ensemble experiments, which were perturbed on different scales using the stochastic kinetic-energy backscatter (SKEB) scheme in the WRF model, with the innermost domain having a 3-km grid spacing. The daily rainfall (RAIN24h) and the cloudburst during 1600–1700 LST (RAIN1h) were considered. Results demonstrated that with larger perturbation scales, the ensemble spread for the rainfall maximum widens and rainfall forecasts become closer to the observations. In ensembles with mesoscale or convective-scale perturbations, RAIN1h loses predictability at scales smaller than 20 km and RAIN24h is predictable for all scales. Whereas in ensembles with synoptic-scale perturbations, the largest scale of predictability loss extends to 60 km for both RAIN1h and RAIN24h. Moreover, the average positional error in forecasting the heaviest rainfall for RAIN24h (RAIN1h) was 400 km (50–60) km. The southerly low-level jet near Zhengzhou was assumed to be directly responsible for the forecast uncertainty of RAIN1h. The rapid intensification in low-level cyclonic vorticity, mid-level divergence, and upward motion concomitant with the jet dynamically facilitated the cloudburst. Further analysis of the divergent, rotational and vertical kinetic spectra and the corresponding error spectra showed that the error kinetic energy at smaller scales grows faster than that at larger scales and saturates more quickly in all experiments. Larger-scale perturbations not only boost larger-scale error growth but are also conducive to error growth at all scales through a downscale cascade, which indicates that improving the accuracy of larger-scale flow forecast may discernibly contributes to the forecast of cloudburst intensity and position.

Quaternary palynology plays a pivotal role in investigating global climate change and various other research fields, serving as an essential tool for the quantitative analysis of paleoenvironment changes. However, due to the vast diversity of terrestrial ecosystems and intricate interactions between vegetation, climate, and human activities, further advancements are required in the following aspects within this discipline. (1) The accuracy of classification in pollen morphology and fossil pollen identification needs improvement, particularly at the species level. This represents a significant challenge in present Quaternary palynology. Computer-aided intelligent recognition holds promise as a solution for species identification based on more detail pollen morphology. (2) Most pollen-based vegetation and climate reconstructions overlook the significance of bare ground. Neglecting bare ground can lead to substantial inaccuracies when quantitatively reconstructing past vegetation and climate. (3) While pollen records provide reliable information on paleoclimate changes, current quantitative climate reconstruction models heavily rely on modern pollen datasets derived from present-day vegetation disturbed more or less by human activities. This introduces bias and uncertainties into paleoclimate reconstruction. (4) Although pollen can serve as an indicator of human activities, accurately quantifying the intensity of human influence remains challenging. Improving accurate identification of crop pollen, reconstructing reliable land cover/use data, and integrating multidisciplinary data may enhance the identification and quantification of signals related to human activity in pollen records.

Taklamakan Desert (TD) has been characterized by numerous heatwaves and dust storms, leading to negative effects on societies and ecosystems at regional and global scales. However, the association between heatwaves and dust storms is poorly known. In this study, we describe the association between heatwaves and dust events and propose a mechanism for such compound events in the TD. The results show that, from 1993 to 2022, the frequency and intensity of heatwaves in the TD have increased at a rate of 0.21 days year⁻¹ and 0.02°C year⁻¹, respectively. More than 40% of heatwaves existed with dust events, which significantly lagged behind heatwaves. Mechanically, the higher the air temperature, the hotter and drier the soil, leading to more dust emissions in the TD. In high-occurrence heatwave years, a large-scale wave train of “cyclone-anticyclone-cyclone” in the northwest-southeast direction was found, with the anticyclone of which hovered over the TD region. The anomalous anticyclones favored the formation and maintenance of heatwaves, and subsequent anomalous cyclones in the wave train triggered strong dust events followed by heatwaves. With climate warming, the compound events of heatwave and dust storm are becoming bigger hazards threatening the socioeconomic and ecological security in the TD, the profound study of which is critical to understanding regional extreme responses.