Cenozoic ultrahigh-temperature metamorphism in pelitic granulites from the Mogok metamorphic belt,Myanmar

Science China Earth Sciences - Ultrahigh-temperature (UHT) metamorphism is critical for understanding the most extreme thermal evolution of continental crust. However, UHT metamorphism...     

A multiple-proxy stalagmite record reveals historical deforestation in central Shandong,northern China

Evaluating anthropogenic impacts on regional vegetation changes during historical time is not only important for a better understanding of the Anthropocene but also valuable in improving the vegetation-climate models. In this study, we analyzed stable isotopes(δ~(18)O, δ~(13)C) and trace elements(Mg/Ca, Sr/Ca) of a stalagmite from Huangchao Cave in central Shandong, northern China.~(230)Th and AMS~(14)C dating results indicate the stalagmite deposited during 174BC and AD1810, with a hiatus between AD638 and 1102. Broad similarities of the δ~(18)O and trace elements in the stalagmite suggest they are reliable precipitation indexes. The δ~(13)C of the stalagmite, a proxy of vegetation change, was generally consistent with local precipitation and temperature variations on a centennial-scale before the 15th century. It typically varied from –9.6‰ to –6.3‰, indicating climate controlled C3 type vegetation during this period. However, a persistent and marked increasing trend in the δ~(13)C record was observed since the 15th century, resulting in δ~(13)C values from –7.7‰ to –1.6‰ in the next four centuries. This unprecedented δ~(13)C change caused by vegetation deterioration cannot be explained by climate change but is fairly consistent with the dramatically increasing population and farmland in Shandong. We suggest that the increasing deforestation and reclamation in central Shandong began to affect vegetation in the mountain region of central Shandong since the 15th century and severely destroyed or even cleared the forest during the 16th–18th century.     

Water balance of Earth / Bilan hydrologique de la Terre

Abstract

The paper presents a compact picture of the occurrence of water on Earth, including the temporal development of water resources of the planet, the current water balance, and the future of water on Earth. In examining numerous standard hydrological references and new developments in quantification of the water resources of planet Earth, several corrections are proposed to the hydrological water balance of Earth. Particular attention is drawn to the areas of open water surfaces on land, which according to current estimates are much larger than reported in standard hydrological references. The paper stresses the need for improvements in our understanding of the hydrological cycle and presents several conclusions on the ways to improve this understanding and future visualizations of the water balance of Earth.     

高精度地球物理学是创新未来的必然发展轨迹

地球物理学在整个地球科学研究与探索中占有重要地位,突破该领域以描述、推断为主体的框架,并逐步向量化或半量化前进确为必然.地球物理学逐步向高精度升华乃深化理解各有关科学问题的时代需求.基于物理学概念,从定义出发促使多学科交叉和不断创新,是地球物理学能否抢占地球科学制高点的核心所在.为此,真正意义上的高精度观测、高分辨率的数据采集和精细结构的刻画构成了高精度地球物理学的基石,是深化理解地球科学中有关壳幔形成、演化问题的深层次的内核.本文通过较系统地分析和研究提出,(1)地球科学研究进程中的定性描述和依据于浅表层过程与现象的推断有待突破;(2)夯实与把握基础科学理论是高精度地球物理学捕获真谛的“钥匙”;(3)高精度地球物理学是深化认识地球本体和逼近彼岸的基石.     

The Earth’s plasmasphere: State of studies (a Review)

The main results of the experimental and theoretical studies of the Earth’s plasmasphere physics obtained until the present are reviewed. The review is aimed at attracting attention of scientists to studying this region of the Earth’s magnetosphere since many problems of the plasmasphere physics, first of all, the problems of plasmapause formation and plasmasphere filling and erosion, which are of importance in understanding the relation of the processes proceeding in the Sun and solar wind to the processes observed in the Earth’s ionosphere and atmosphere, remain unclear.     

地球:我们的变化着的行星--IUGG动态

本文概述了国际大地测量学与地球物理学联合会(IUGG)的历史发展,介绍了IUGG的近况。IUGG作为一个致力于研究地球及把研究所获得的知识应用于造福人类社会的科学组织,近年来在推动地球科学各相关学科的交叉融合、加强国际合作、关心与帮助发展中国家或地区地球科学的发展以及探讨地球科学未来的发展趋向等方面,开展了许多活动,这些活动对于认识人类赖于生存的、不断变化的行星地球、促进人与自然的和谐相处以及人类社会的发展具有重要的意义。     

Response to the comment by M. Lustrino on “High-pressure melting experiments on garnet clinopyroxenite and the alkalic–tholeiitic transition in ocean-island basalts” by Keshav et al. [Earth Planet. Sci. Lett. 223, 365–379 (2004)]

We welcome the comments made by Lustrino [M. Lustrino, Pyroxenites everywhere, Earth Planet. Sci. Lett., this issue.] on the high-pressure experimental melting phase relations of anhydrous garnet pyroxenite reported by Keshav et al. [S. Keshav, G.H. Gudfinnsson, G. Sen, Y. Fei, High-pressure melting experiments on garnet clinopyroxenite and the alkalic-to-tholeiitic transition in ocean-island basalts, Earth Planet. Sci. Lett. 223 (2004) 365–379.]. Such healthy debates, in our view, are needed to promote our understanding on the origin of oceanic-island basalts (OIB).     

Pollen-based Holocene quantitative temperature reconstruction on the eastern Tibetan Plateau using a comprehensive method framework

Quantitative climate reconstruction on long timescales can provide important insights for understanding the climate variability and providing valuable data for simulations. Unfortunately, the credibility of some attempts was hampered by incomplete reconstruction procedures. We here establish a comprehensive framework resting on high-quality Chinese modern pollen database, including modern pollen data screening, calibration set selection, major climate factor analysis, appropriate model selection, strict statistical assessment of results and ecological interpretation. The application of this framework to three high-resolution pollen records from the eastern Tibetan Plateau allows accurate quantitative inferences of Holocene temperature changes, which is the major control of regional vegetation. The results show that the mean warmest month temperature(MTwa)during the early Holocene was ca. 10.4℃ and reached the highest value at 8.5–6 ka BP(ca. 11℃). The early and mid-Holocene(11–5 ka BP) warmth was followed by 1.2℃ temperature decrease, culminating in the coolest temperatures of the Holocene during the Neoglacial cooling. Superimposing on the general cooling trend, MTwareveals a significant 500-yr periodicity with varying intensities through time, showing that warm(cold) intervals are in phase with solar maxima(minima) periods. This spectral similarity indicates a possible connection of multi-century scale climate fluctuations with solar forcing.     

Responses of water use efficiency to phenology in typical subtropical forest ecosystems——A case study in Zhejiang Province

Ecosystem-scale water-use efficiency(WUE) is an important indicator for understanding the intimately coupled relationship between carbon and water cycles in ecosystems. Previous studies have suggested that both abiotic and biotic factors have significant effects on WUE in forest ecosystems. However, responses of WUE to phenology in the context of climate change remain poorly understood. In this study, we analyzed the sensitivity and response patterns of seasonal WUE to phenology in Zhejiang Province where typical subtropical forest ecosystems are located, and discussed potential causes of the changes of the sensitivity and response patterns along different climate gradient during 2000–2014. The results of interannual partial correlation analysis showed widespread negative correlations between WUE and the start of growing season(SOS) in spring. This is because the increase in gross primary product(GPP) is larger than that of evapotranspiration(ET), resulting from an advanced SOS. The positive correlation between WUE and SOS was widely observed in summer mainly because of water stress and plant ecological strategy. The autumn WUE enhanced with the delay in the end of growing season(EOS)mainly because of the increase in GPP meanwhile the decrease or steadiness in ET, resulting from a delayed EOS. In space, the sensitivity of spring WUE to SOS significantly decreased along the radiation gradient, which might be related to strong soil evaporation in high radiation area;the sensitivity of WUE to SOS in summer showed a positive correlation with precipitation and a negative correlation with temperature, respectively, which might be attributed to the compensation of GPP to the delayed SOS and water stress caused by high temperature. The sensitivity of WUE to EOS increased significantly along the radiation and precipitation gradients in autumn, which may be because the increase of radiation and precipitation provides more water and energy for photosynthesis.     

Patterns and trajectories of macrophyte change in East China’s shallow lakes over the past one century

Macrophytes play important roles in maintaining ecosystem health and stability of shallow lakes. Better understanding of their long-term dynamics has important theoretical and practical significance for both lake ecosystem restoration and eutrophication control. However, the knowledge about the historical status and changing patterns of macrophytes in China's shallow lakes is still controversial and lacks systematic research. Here, we reviewed and synthesized the published records of submerged macrophytes from 14 typical shallow lakes in the eastern plain covering the past 100 years. The results suggest that submerged macrophytes have experienced three clear stages of change: rare period(the 1900 s–the 1950 s), growth period(the1950 s–the 1980 s), and recession period(the 1980 s–now). This finding is different from the traditional understanding that submerged macrophytes were abundant in the early 20 th century and have been degrading since then. On this basis, we proposed the possible evolution pattern(less-more-less) of submerged macrophytes in the eastern plain lake region over the past 100 years,which provides new perspectives about the long-term evolution process of macrophytes in shallow lakes. Furthermore, we found that the decline of submerged macrophytes during the regime shift shows a gradual process at the interdecadal scale; this finding contradicts the classical regime shift theory that macrophytes decline sharply during the critical transition. This study has important theoretical value for the restoration of the eastern plain lakes in China from "turbid lake" to "clear lake", especially for establishing the historical reference condition and restoration path of macrophytes.     

Quantitative climatic reconstruction of the Last Glacial Maximum in China

Quantitative paleoclimatic reconstruction is crucial for understanding the operation and evolution of the global climate system.For example,a quantitative paleoclimatic reconstruction for the Last Glacial Maximum(18±2 ka~(14)C,LGM)is fundamental to understanding the evolution of Earth’s climate during the last glacial-interglacial cycle.Previous quantitative palaeoclimate reconstructions in China are generally based on statistical comparison of modern pollen assemblages and modern climate data.These methods are based on the premise that vegetation-climate interactions remain the same through time,and implicitly assume that the interactions are independent of changes in seasonality and atmospheric CO_2concentration.However,these assumptions may not always be valid,which may affect the reconstructions.Here,we present the results of a quantitative study of the LGM climate of China based on an improved inverse vegetation model which incorporates physiological processes combined with a new China Quaternary Pollen Database.The results indicate that during the LGM,mean annual temperature(ANNT),mean temperature of the coldest month(MTCO)and mean temperature of the warmest month in China were lower by～5.6±0.8,～11.0±1.6 and～2.6±0.9°C,respectively,compared to today,and that the changes in ANNT were mainly due to the decrease of MTCO.The ANNT decrease in southern China was～5.5±0.5°C.Mean annual precipitation was lower by～46.3±17.8 mm compared to today and was especially low in northern China(～51.2±21.4 mm)due to the decrease in summer rainfall.Comparison of our results with recent outputs from paleoclimatic modelling reveals that while the latter are broadly consistent with our estimated changes in mean annual climatic parameters,there are substantial differences in the seasonal climatic parameters.Our results highlight the crucial importance of developing seasonal simulation on paleoclimatic models,as well as the need to improve the quality of paleoclimatic reconstructions based on proxy records from geological archives.     

Migration of barchan dunes in the western Quruq Desert,northwestern China

Barchan dunes are common on Earth, Mars and Titan. Previous studies have shown that their formation, migration and evolution are influenced by the wind regime and other factors, but details vary among regions. Understanding barchan morphology and migration will both improve our understanding of dune geomorphology and provide a basis for describing the environmental conditions that affect the formation and development of these dunes on Earth and other planets. Here, we provide detailed measurements of barchan dune migration in China's Quruq Desert, in the lower reaches of the Tarim River. We monitored their migration direction and rate, and their morphological changes during migration, by comparing Google Earth images acquired in 2003 and 2014. The dunes migrated west-southwest, close to the local resultant drift direction. The migration rate averaged 8.9 to 32.1 m year⁻¹, with obvious spatial variation. In addition to the wind regime, the migration rate depended on dune morphology, density and vegetation cover; the rate was negatively related to dune height, density and vegetation cover, but positively linearly related to the length/width ratio (L_U/W) and to the decrease in this ratio from 2003 to 2014. We found correlations among the dune morphometric parameters, but the relationships were weaker than in previous research. Due to the complexity of the factors that affect the processes that underlie sand dune development and migration, the morphological changes during dune migration were also complex. Our measurements suggest that the aeolian environment played a dominant role in dune migration and its spatial variation in the Quruq Desert. These results will support efforts to control dune migration in the western Quruq Desert and improve our understanding of dune morphodynamics. © 2019 John Wiley & Sons, Ltd.     

The partitioning behavior of trace elements in subduction zones: Advances and prospects

Science China Earth Sciences - The partitioning behavior of trace elements is of key importance for understanding the geochemical process and material cycle mechanism in subduction zones. This...     

New views of the Earth's interior

The Earth beneath our feet is a complex place. James Wookey reports on a meeting that took a broad multidisciplinary approach to understanding its composition, structure and dynamics.     

Tectonics of the offshore Red River Fault recorded in the junction of the Yinggehai and Qiongdongnan Basins

Science China Earth Sciences - The Red River Fault, which originated from the southeastern margin of the Tibetan Plateau, has a great significance for obtaining a further understanding of the...     

Shear-wave velocity structures of the shallow crust beneath the Ordos and Sichuan Basins from multi-frequency direct P-wave amplitudes in receiver functions

Science China Earth Sciences - As the two largest cratonic basins in China, the Ordos Basin and the Sichuan Basin are of key importance for understanding the evolutionary history of the Chinese...     

Crustal velocity structure of the Northwest Sub-basin of the South China Sea based on seismic data reprocessing

Science China Earth Sciences - The deep crustal structure of the Northwest Sub-basin (NWSB) of the South China Sea (SCS) is of great importance for understanding the tectonic nature of the...     

Diffusion of helium in FCT zircon

To gain a better quantitative understanding of zircon(U-Th)/He ages and evaluate the applicability of zircon(U-Th)/He dating, the diffusion characteristics, He diffusion kinetics, helium partial retention zone(HePRZ), closure temperature, and(U-Th)/He ages were investigated using high-precision laboratory step heating experiments based on the thermally activated diffusion process. The ln(D/a~2) in Fish Canyon Tuff(FCT) zircons determined from laboratory step heating experiments was negatively correlated with reciprocal temperature, as expected for thermally activated volume diffusion. The zircon activation energies ranged from 144 to 184 kJ mol~(-1) with a mean of 169±12 kJ mol~(-1). The closure temperatures ranged from 144 to 216°C(a cooling rate of 10°C Ma~(-1) and an effective grain radius of 38–60 μm) with an average of 176±18°C. The calculated closure temperature increased with increasing cooling rate, yielding an average zircon He closure temperature of ～136°C at a slow cooling rate of 0.1°C Ma~(-1), whereas the closure value was ～199°C at a cooling rate of 100°C Ma~(-1). The closure temperature increased with the equivalent spherical radius assuming a constant cooling rate. The He ages from FCT zircons were negligibly affected by grain size because of the rapid cooling. He preserved in the zircon was sensitive to temperature and holding time, and the temperature range for zircon HePRZ gradually decreased with increasing holding time. The(U-Th)/He ages from 26 FCT zircons yielded an algorithmic mean of 28.3±0.3 Ma(S.E.) and a geometric mean of 28.4±0.3 Ma(S.E.), consistent with the ages of 28.4±1.9 Ma reported by other laboratories. The FCT zircons were characterized by rapid cooling, young(U-Th)/He ages with good reproducibility, and low alpha doses. Weak correlations between the He ages and effective uranium(eU) concentrations from the FCT zircons indicated radiation damage did not significantly affect He diffusivity.     

Seismicity,Tectonics, and GPS Geodynamics of the Caucasus

Izvestiya, Physics of the Solid Earth - The style of the seismotectonic deformation of the Earth’s crust in the Caucasus and its immediate surroundings corresponds to the thrust setting with...