Science China Earth Sciences

The 2014–2016 El Niño events consist of a stalled El Niño event in the winter of 2014/2015 and a following extreme El Niño event in the end of 2015. Neither event was successfully predicted in operational prediction models. Because of the unusual evolutions of these events that rarely happened in the historical observations, few experience was ready for understanding and predicting the two El Niño events when they occurred. Also due to their specialties, considerable attention were attracted with aims to reveal the hidden mechanisms. This article reviews the recent progresses and knowledge that were obtained in these studies. Emerging from these studies, it was argued that the key factor that was responsible for the stalled El Niño in 2014 was the unexpected summertime Easterly Wind Surges (EWSs) or the lack of summertime Westerly Wind Bursts (WWBs). Most operational prediction models failed to reproduce such stochastic winds and thus made unrealistic forecasts. The two El Niño events awakened the research community again to incorporate the state-of-the-art climate models to simulate the stochastic winds and investigate their roles in the development of El Niño.

A three-dimensional model was established to investigate water exchange in coastal waters, and applied to Qinzhou Bay (QZB) in the South China Sea. Given the strong tidal current in QZB, a half-life time was calculated for water exchange by filtering the tidal signal from the concentrations of a conservative substance. In a control run driven by the tide, without external inputs and an open boundary concentration of zero, it was estimated that the average half-life time in QZB was 54.8 d. Numerical experiments showed that wind accounted for an 11.9% reduction in the half-life time to 48.3 d. When rivers were included in the model, the half-life time decreased by 74.6% to 13.9 d. Sensitivity experiments showed that the half-life time for water exchange was greatly affected by the concentration of the conservative substance which was used at the open boundary. In response to 10, 20, 30, and 40% increases in the boundary concentration, the half-life time increased to 91.5, 168.3, 186.2, and 229.1 d, respectively. Results also suggested that for coastal bays with large intertidal areas such as QZB, consideration of the wet and dry processes produced more accurate simulations of the hydrodynamics and the half-life times. Simulations, which did not incorporate wet and dry processes, were more than likely to have overestimated or underestimated the half-life times for water exchange.

Rocks of the Qinghai-Tibetan Plateau (QTP) host abundant Triassic fossils. So far, the well established marine fossil sequences based on ammonoids, conodonts, bivalves, brachiopods, radiolarians, and terrestrial spora-pollen sequence have become standard for biostratigraphic correlation of the QTP. For much of Triassic time, the QTP occupied a marine setting as suggested by the dominance of marine deposits. The main sedimentary types represented in the Triassic successions include littoral to shallow marine clastic rocks, shallow marine carbonate platform carbonates, bathyal to abyssal slope carbonates intercalated with clastic and siliceous deposits, coal-bearing clastic strata contained within paralic facies deposits, and littoral and terrestrial volcaniclastic rocks. These deposits are organized into four stages in ascending order: (1) Early Triassic deposits that record marine transgression, including extensive shallow marine carbonate platform strata. (2) Middle Triassic Ladinian to Late Triassic Carnian deposits, including thin-bedded limestone, fine clastics, and siliceous rocks, that accumulated at greater depths than underlying Early Triassic strata and reflect the peak of the transgression. Magmatic activity appears to have occurred in some areas during this stage. (3) Late Triassic Norian deposits that record the onset of marine regression as suggested by the widespread occurrence of platform carbonates. It is noteworthy that stage 3 deposits of the Qin-Qi-Kun area in the northernmost region of the QPT is dominated by terrestrial strata and displays evidence of local erosion. (4) Late Triassic Rhaetian littoral and shallow marine clastic and coal-bearing deposits that preserve the record of continued marine regression continued. The Indus-Yarlungzangbo Suture Zone (IYSZ) appears to have been the rifting axis during Triassic time as suggested by sedimentary facies trends that reflect deepening to south and north. Thus, the Himalaya Block to the south of the IYSZ was part of the passive margin of Gondwana whereas the north side of the IYSZ, including the Gangdis (or Lhasa) and South Qiangtang blocks, belonged to the passive margin of Eurasia. The similarity of rocks of the Bangongco-Nujiang Suture Zone (BNSZ) to the north of the IYSZ with those of the Gangdis Block to the south and the South Qiangtang Block to the north does not support the contention that the BNSZ was a rift axis during Triassic time. Results of palaeobiological research also suggest that the IYSZ rather than BNSZ was a biogeographic boundary during the Triassic. Early and Middle Triassic break-up of Pangea was accompanied on the QTP by rifting along the IYSZ. The expression of crustal shortening induced by the Indosinian Orogeny on the QTP is largely a change of sedimentary facies induced by Late Triassic uplift. Deposits of the Gangdis to South Qiangtang regions of the QTP record a transition from shallow marine carbonate platform deposits to littoral and paralic coal-bearing strata. Moreover, the stratigraphic succession of the Qin-Qi-Kun area preserves a transition from littoral clastic deposits to terrestrial facies and local erosion.

The urban agglomeration in the middle reaches of the Yangtze River (UAMRYR) is a key area to promote the central region rise and the green development of the Yangtze River Economic Belt. In this paper, an evaluation index system was comprehensively constructed for the green development level of the UAMRYR from five aspects: resource utilization, green environment, green economy, green life, and support mechanisms. Entropy weight-TOPSIS method and multivariate statistical method, including spatial autocorrelation analysis and geographic detectors, were used to analyze the regional differences and influencing factors of the green development level of the UAMRYR from 2008 to 2018. The results showed that: (1) the overall green development level of the UAMRYR showed a fluctuating upward trend from 2008 to 2018, among which the provincial capital cities such as Wuhan, Changsha, and Nanchang, as well as the cities covered by the Poyang Lake urban agglomeration had relatively higher green development levels. (2) The green development level of the 31 cities in the UAMRYR showed insignificant spatial heterogeneity within the study period. Compared with other areas, the green development levels varied greatly among the regions of the Wuhan metropolitan area, which was a typical high-low aggregation type. (3) Green economy, green life, and support mechanisms were the highly influential aspects of the green development of the UAMRYR, and the main influencing factors were the total value added of secondary and tertiary industries, urbanization rate, and fixed asset investment. The explanatory power of the interaction of influencing factors on the green development of the UAMRYR was greater than that of a single factor. This study is intended to provide a reference for the green transformation development and the coordinated development of the “resources-environment-economy” in the UAMRYR.

Recently found materials indicate that the steppe mammoth, Mammuthus trogontherii, survived in northern China into the late Pleistocene. East Asia is the key area of mammoth evolution after the initial radiation of early forms out of Africa and into Eurasia at the beginning of the late Pliocene (c. 3.5-3.0 Ma). M. rumanus, M. meridionalis, M. trogontherii, and M. primigenius probably formed a continuous and transitional evolutionary lineage within the pan-Eurasian mammoth radiation in East Asia. Each speciation event of the Eurasian mammoths was followed by a rapid and large-scale dispersal event: out of East Asia. Allopatric speciation is the main speciation pattern of Mammuthus. The climatic vacillation was severe and frequent in East Asia from the early part of early Pleistocene (c. 2.6 Ma) onward, which probably brought about successive speciation in East Asia and the subsequent dispersal of the mammoths.

The predominant types of high-grade iron deposits in China include skarn, sedimentary metamorphic (banded iron-formation, BIF-type), continental/submarine volcanic-hosted and magmatic Fe-Ti-V oxide deposits. Based on a comprehensive review of current studies on these deposits, this paper suggests that the oxygen concentration in atmosphere played an important role for the formation of BIFs, whereas the tectonic setting and deep magmatic differentiation processes are more important for the other types. Notably, both high temperature and high pressure experiments and melt inclusion studies indicate that during the differentiation, high temperature magmas could develop iron-rich magma via liquid immiscibility but not pure oxide melt (“iron ore magma”). Fe-P melt could be generated directly by liquid immiscibility under hydrous and oxidized condition. The formation of high-grade iron deposits is mostly associated with the processes related to multiple stages of superimposition, e.g., desiliconization and iron enrichment, removal of impurity, and remobilization and re-precipitation of iron. According to the temporal evolution, the high-grade iron deposit could be divided into multi-episode superimposition type (temporally discontinuous mineralization) and multi-stage superimposition type (temporally continuous mineralization). The former is represented by the sedimentary metamorphic iron deposit, and the latter includes those related to magmatic-hydrothermal fluids (e.g., skarn, volcanic-hosted and magmatic types).

Climate and climate change have always been a research focus of atmospheric sciences. This paper summaries research efforts, achievements and international contributions of the Chinese scientific community on climate and climate change over the past 70 years. The review is based on papers published officially in national or international scientific journals, and is organized to cover six aspects: (1) general climate studies; (2) impact of the Qinghai-Tibetan Plateau; (3) impact of the East Asian monsoon; (4) influences of teleconnection oscillation and westerlies; (5) climate dynamics and development of climate models; and (6) climate change. It is, however, to be noted that the present review can not be considered as an exhaustive one, since there is a huge body of literature in the field.

European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-Interim) reanalysis data and satellite data, and trajectory model were applied to analyze the dynamical, thermo-dynamical, and chemical structure in the upper troposphere and lower stratosphere (UTLS) of an intense cut-off low (COL) event occurring over East Asia during June 19–23, 2010, and to characterize the process and transport pathway of deep stratospheric intrusion. The Atmospheric Infrared Sounder (AIRS) ozone data and the Global Positioning System Ozone (GPSO3) sonde data showed that the air mass originating from the polar formed a region with relatively high values of potential vorticity (PV) and ozone in the center of COL, and a secondary ozone peak appeared in the upper troposphere during mature stage of the COL. Forward trajectory simulation suggested that during the first stage of COL, deep stratospheric intrusion associated with strong northerly wind jet on the west side of the upper-level trough transported ozone-rich air from the polar lower stratosphere into the middle and lower troposphere in the mid-latitude, and increased the ozone concentration there. During the mature stage of the COL, stratospheric air was transported counterclockwise into the troposphere. Backward trajectory model was used to find the source regions of air mass within the COL during its mature stage. Model results show that air masses with high ozone concentration in the center of the COL have two source regions: one is the subpolar vortex which lies in northern part of Center Siberia, where ozone-rich air plays a major role in increasing the ozone concentrations, and the other is the strong shear region which is near by the cyclonic side of the extratropical jet axis (west of 90°E, near 50°N). The air masses with low ozone concentration around the COL also have two source regions: one is the anticyclonic side of the extratropical jet axis, where the air mass with the relatively low ozone concentration at the bottom of the COL is mainly controlled by horizontal movement, and the other is the warm area of the south side of COL, where the air mass on the east and west side of the COL is mainly dominated by upward motion.

We calculated and analyzed variation of the non-dipole (ND) magnetic field at the millennium scale over the Chinese mainland during 2000 BC-1900 AD using the newest global geomagnetic model, CALS3K.4 (3K.4). The newest-generation IGRF (IGRF11) was used to verify the results. Taking component Z for example, we calculated and analyzed the distribution and annual change rates of the ND field during 1900–1990 AD every 5 yr, using two models. To thoroughly analyze the contributions of field sources, quadrupole and octupole fields, and others within the ND field at the surface and core-mantle boundary (CMB) were investigated. Results show that there were three main variation phases of the field during the period 2000 BC-1900 AD. The mean amplitude roughly reflected the ND field because of the distribution and variation of that field, corresponding somewhat to the mean amplitude change. A magnetic anomaly of the ND field over East Asia (EA) first emerged in 1682 AD, and its extreme intensity had increased a total of 15276.95 nT by 1900 AD. Its location moved continuously southeastward after 1690 AD. The asymmetry between location and intensity of extreme points over EA, particularly during 1740–1760 AD, indicates irregularity of fluid motion inside the outer core. Mean annual changes of Z are generally divided into four phases, which first oscillated between 2000 and 800 BC, then increased, decreased and increased in the periods 800 BC-300 AD, 300–900 AD and 900–1900 AD, respectively. The intensity of mean annual change increased a total of 22.87 nT/yr. Anomaly extreme locations based on 3K.4 and IGRF11 over EA centered around 44°N and 103°E for degree (n) greater than 5, and intensities continuously increased with n. During 2000 BC-1990 AD, ND energy of Z at the surface and CMB had decreased in total by 18.29% and 23.23%, respectively. The field source of 26–210 pole fields are more or less affected by the lithospheric field. Energies of higher degree at the surface attenuate by almost 99% compared with CMB, but mean attenuation speeds of the low-degree ND field are faster than high-degree, which implies that the low-degree ND field has a deeper source.