New dating indicates intermittent human occupation of the Nwya Devu Paleolithic site on the high-altitude central Tibetan Plateau during the past 45,000 years

The timing and mechanisms of the human occupation of the demanding high-altitude Tibetan Plateau environment are of great interest.Here,we report on our reinvestigations and dating of the Nwya Devu site,located nearly 4600 meters above sea level on the central Tibetan Plateau.A new microblade techno-complex was identified on a lower lake shore at this site,distinct from the previously reported blade tool assemblage.These two lithic assemblages were dated to 45.6±2.6 and10.3±0.5 ka using optically stimulated luminescence and accelerator mass spectrometry^(14)C methods.They represent,respectively,the earliest known Paleolithic and microlithic sites on the interior Tibetan Plateau,indicating multiple occupation episodes of hunter-gatherers during the past 45 ka.Our studies reveal that relatively stable depositional conditions and a paleoenvironment characterized by a comparatively warm climate facilitated these multiple occupations at Nwya Devu.The contemporaneous occurrence of the Upper Paleolithic blade technology on the Tibetan Plateau and most of Eurasia between 50 and 40 ka indicates rapid,large-scale dispersals of humans that profoundly affected human demography on a large scale.Combining new archaeological evidence and previously reported genetic data,we conclude that the Tibetan Plateau provided a relatively stable habitat for Upper Paleolithic hunter-gatherers,which may have contributed to the complex and multiple-origin gene pool of present-day Tibetans.

Late Cenozoic uplift of the Liupan Mountains:Evidence from the Neogene loess deposits

The Liupan Mountains,one of the important mountain ranges in western China,are located on the boundary between the northeastern Tibetan Plateau and the Ordos Block.The uplift history of the Liupan Mountains remains controversial.Loess deposits are good tracers of regional tectonic and geomorphic changes,because loess is sensitive to erosion and the formation and preservation of loess requires relatively flat highlands and relatively stable tectonic environments.We investigated the distribution of Neogene loess deposits on the western piedmont of the Liupan Mountains and examined a near-continuous loess section(Nanping section)on the piedmont alluvial highlands.Correlation of magnetic susceptibility stratigraphy with the QA-ⅠMiocene loess sequence dates this 56-m section covering the interval from~8.1 to 6.2 Ma.The lower boundary age of this section,together with previously reported Zhuanglang red clay(sand-gravel layers with intercalated loess during~9–8 Ma and near-continuous loess during~8–4.8 Ma)and Chaona red clay(~8.1–2.58 Ma),indicates that the Liupan Mountains were uplifted in the late Miocene(~9–8 Ma)and basically formed by~8 Ma,attesting to no intense mountain building since that time.In addition,based on the information from the Zhuanglang core and the QA-Ⅰsection,we infer that sizable parts of the Liupan Mountains were uplifted during the late Oligocene–early Miocene and did not experience intense uplift during~22–9 Ma.

Glacial-interglacial cycles recorded in clay minerals from the eastern Tibetan Plateau over the last 800 ka and their indications

Clay mineral proxies have been widely used to reconstruct changes in provenance and the paleoclimate.However,high-altitude clay mineral indications and long-term and orbital variations have not been fully explored.Herein,we present an800-ka clay-mineral record from a lacustrine sediment core(ZB13-C2)from the Zoige Basin on the eastern Tibetan Plateau(TP).X-ray diffraction and scanning electron microscopy were used to identify the clay mineral assemblages and their micromorphological characteristics of core ZB13-C2.The results revealed that the clay minerals in core ZB13-C2 are mainly illite,with small amounts of chlorite,kaolinite,and smectite(including irregular mixed-layers of illite-smectite(I/S)and chloritesmectite(C/S)).The clay mineral assemblages and proxies exhibit three stages of change,which are mainly controlled by the Zoige watershed range under different climate conditions.The watershed was limited to the southeastern region with altitudes ranging from~3500 to~4200 meters above sea level(m a.s.l.),and glacial-interglacial hydraulic erosion controlled the input of bedrock debris during 800-621 ka BP.It expanded to higher altitudes(~4200 to~4700 m a.s.l.)due to stronger seasonal freezethaw weathering without significant glacial-interglacial variations under a cooling and drying climate during 621-100 ka BP.Finally,it expanded to its highest altitudes of~4700 to~5200 m a.s.l.northwest of the watershed after 100 ka BP,and hydraulic erosion increased obviously under a warm climate of the interstadial MIS 3 on the TP.The watershed underwent two major expansions under different climatic conditions at~621 ka and 100 ka BP,with the wet/dry alternation became strong at~621 ka BP.These results reveal that long-term temperature changes and the wet/dry alternation at high altitudes controlled the watershed range and degree of the physical erosion,and that the indications of clay minerals should be carefully clarified before they are used as climate indicators,especially on the TP.

水循环地质演变研究的重要性

水是维持地球生物多样性和生态系统健康的根本保障,更是地球表层系统机体运作的“血液”.当今全球变暖背景下,与水循环变化密切相关的干旱、森林大火和洪涝等极端灾害天气频发,以及海平面上升、海洋热浪与酸化等全球性生态危机问题日益突出,深刻影响了全球生态系统健康和人类社会的可持续发展.政府间气候变化专门委员会(Intergovernmental Panel on Climate Change,IPCC)第6次评估报告中,特别突出了系统性评估气候变化对全球水循环影响的重要性[1].毋容置疑,水循环是地球系统中的基本过程之一.

水循环的地质演变:研究现状与关键问题

由大陆-海洋-大气之间水的3种相态(固态-液态-气态)相互转换和位移构成的水循环,是地球气候系统的主要过程之一.太阳辐射量在地球表面分布不均匀,是地表水循环的基本驱动力.水循环与碳循环密切关联,是气候系统演变中的两条主线.不同时空尺度的水循环和碳循环受天文、地质和生物因素以及它们之间相互作用的控制,揭示水循环地质演变过程及其与气候变化之间的关系,可为了解当今水文气候变化提供宝贵启示.通过水循环地质演变研究现状回顾,提出如下5个科学问题应在未来予以重点关注:(1)雪球地球时期的水循环;(2)植被起源和演化对水循环的影响;(3)深时热带辐合带(inter-tropical convergence zone, ITCZ)的演变与水循环;(4)暖室期地下水与海平面变化;(5)深时水循环中的氧同位素示踪.同时建议我国未来亟须加强的4个研究方向:(1)深时冰室期向暖室期转变中的水循环;(2)深时水循环与生态系统演变;(3)深时水循环研究方法的发展;(4)深时水循环与长周期地球系统演变的数值模型.

轨道驱动对高低纬水循环的影响特征:海冰和降水

轨道尺度上的水循环及其对轨道三要素、温室气体和冰盖的响应一直是古气候学界研究的热点科学问题之一.海冰和降水作为水循环的两个重要组成部分,其变化更是备受关注.研究海冰和降水在轨道尺度上的变化,特别是对外部驱动的响应机理、内部过程和反馈机制,有望对现代海冰和降水变化的理解及其未来趋势预测提供长尺度的背景参考.最新研究结果表明,在轨道尺度上北半球海冰对太阳辐射的变化更敏感,而南半球海冰对温室气体的变化更敏感.就轨道三要素而言,北半球海冰主要受岁差控制,而南半球海冰主要受斜率控制.岁差、斜率和CO_(2)在全球不同区域降水中的相对重要性随时间和空间不同而发生变化.受赤道最大太阳辐射影响,热带降水中还含有明显的半岁差信号.此外,缓慢的轨道尺度太阳辐射变化可以通过影响北极海冰变化来引起大西洋经向翻转环流(Atlantic meridional overturning circulation, AMOC)百年-千年尺度的突变,从而引起全球温度和降水随之发生改变.在东亚季风区,中国南方夏季降水受冰盖影响显著,冰盖主要通过影响热带辐合带(inter-tropical convergence zone, ITCZ)的季节性摆动来影响降水;而中国北方夏季降水主要受太阳辐射控制,以岁差信号占主导;太阳辐射和冰量对夏季风降水的影响具有较强的区域性和非线性特征.

两极冰盖控制的12 Ma以来南亚夏季风演化

季风是指由于大陆及邻近海洋之间存在温度差异而形成大范围盛行的、风向随季节发生改变的大气环流,是全球气候系统的重要组成部分[1].全球约有70%的人口生活在季风区,季风变化对这些地区人民的生产生活、国民经济和社会发展等方面具有重要影响.我国美丽富饶的“鱼米之乡”即是得益于充沛的季风降水而形成.但异常的季风气候也会导致干旱、洪水和其他极端天气和气候事件的发生,从而造成各种自然灾害及人民财产和生命的损失.因此,对季风变化及其机制开展研究,不仅有助于揭示季风演变与全球气候变化的联系,而且对加强防灾、减灾及实现社会的持续发展具有非常重要的理论和现实意义.

Dynamic modeling of tectonic carbon processes:State of the art and conceptual workflow

Plate tectonics plays a critical role in modulating atmospheric CO_(2)concentration on the geological timescale(≥106year).A growing consensus on tectonic and Earth’s CO_(2)history in the Cenozoic and deeper time provides solid restrictions and standards for testing tectonic carbon processes against global measurements.Despite this,modeling the causal relationship between tectonic events and atmospheric CO_(2)levels remains a challenge.We examine the current state of the global tectonic CO_(2)research and suggest a conceptual workflow for numerical experiments that integrates plate tectonics and deep carbon dynamics.Future tectonic carbon cycle modeling should include at least four modules:(1)simulation of carbon-carrying processes,such as carbon ingassing and outgassing at the scale of minerals;(2)calculation of CO_(2)fluxes in tectonic settings like subduction,mantle plume,and plate rifting;(3)reconstruction of carbon cycling within the plates-scale tectonic scenario,particularly involving the processes of supercontinent convergence and dispersion;and(4)comparison with atmospheric CO_(2)history data and iterations,aiming to find the coincidental link between different tectonic carbon fluxes and climate changes.According to our analysis,the recent advancements in each of the four modules have paved the path for a more general assembly.We envision that the large variety of carbon transportation parameters across more than ten orders of magnitude in both time and space is the primary technical hurdle in simulating tectonic carbon dynamics.We propose a boundary-condition-connected approach for simulating the global carbon cycle to realize carbon exchange between the solid earth and surface spheres.

新特提斯洋俯冲与大气二氧化碳浓度变化的动力学联系

新特提斯洋的脱碳俯冲被认为在新生代气候变化中发挥了重要作用,但仍然缺少定量的研究.本研究使用改进的地震层析成像重建方法构建了过去的俯冲情景,并计算了印度-欧亚大陆碰撞区域的俯冲板块通量.新生代时期的俯冲板片通量和古气候参数的变化之间存在显著的同步性,表明这些过程之间存在因果关系.新生代早期,新特提洋内俯冲的关闭导致更多富含碳的沉积物沿着欧亚大陆边缘俯冲,为大陆弧火山的岩浆作用提供了更多的碳源,进一步引发了全球变暖.在全球气候达到早始新世峰值后,印度-欧亚大陆碰撞导致的新特提斯俯冲的突然终止造成了距今50~40 Ma期间大气中二氧化碳浓度的快速下降.距今40 Ma后,大气中的二氧化碳浓度逐渐降低,这可能是由于青藏高原的生长导致大陆风化作用增强所致.本文结果有助于更好地理解新特提斯洋演化的动态含义,并可能为未来的碳循环模型提供新的约束条件.

Evidence of advancing spring xylem phenology in Chinese forests under global warming

Phenological responses of vegetation to the ongoing warming trend impact current and future primary productivity.However,few studies focus on wood phenology because its observed data are much scarcer,which hinders the estimation and prediction of forest carbon budgets over large regions.Here,we use a physiological process-based tree-ring growth model(Vaganov-Shashkin model)to investigate the spatial and temporal variations of spring xylem phenology(start of the growing season of xylem,SOS_(x))in tree-ring sites of China during 1962-2016 CE.The model is calibrated on measured tree-ring width chronologies(70 tree-ring chronologies)and successfully validated with field observations of xylogenesis.We found that spring xylem phenology significantly advances during 1962-2016 CE period under global warming,with the rate of advance quickly increasing after the 1990s to an average of 0.25 days per year.The preseason daily mean temperature is the main climatic driver for spring xylem phenology as indicated by its significant correlations with SOS_(x)at most sites(71%).Warmer preseason allows heat requirements for tree growth to be reached more quickly,with increase of 1℃in temperature of preseason anticipates SOS_(x)by 6 to 7 days,which will benefit the radial growth of trees in the relatively cold-humid environments.In addition,the significant positive correlation between the simulated spring xylem phenology and remote sensing derived phenology highlights the primary and secondary growth may be governed by the same variable(temperature)and change in the same direction with global warming.This study provides the long-term perspective on the spring xylem phenology variations covering most of China.

Quantitative attribution of Northern Hemisphere temperatures over the past 2000 years

Quantitative assessment of natural internal variability and externally forced responses of Northern Hemisphere(NH)temperatures is necessary for understanding and attributing climate change signals during past warm and cold periods.However,it remains a challenge to distinguish the robust internally generated variability from the observed variability.Here,largeensemble(70 member)simulations,Energy Balance Model simulation,temperature ensemble reconstruction,and three dominant external forcings(volcanic,solar,and greenhouse gas)were combined to estimate the internal variability of NH summer(June–August)temperatures over the past 2000 years(1–2000 CE).Results indicate that the Medieval Climate Anomaly was predominantly attributed to centennial-scale internal oscillation,accounting for an estimated 104%of the warming anomaly.In contrast,the Current Warm Period is influenced mainly by external forcing,contributing up to 90%of the warming anomaly.Internal temperature variability offsets cooling by volcanic eruptions during the Late Antique Little Ice Age.These findings have important implications for the attribution of past climate variability and improvement of future climate projections.

宜居地球的过去、现在与未来——地球科学发展战略概要

人类对地球和生命起源的好奇心与探索精神促使近代科学的启蒙,从古希腊到文艺复兴,再到工业革命,始终如此.回顾20世纪地球科学发展史,板块构造理论揭示了行星地球的动力学特征,引发了20世纪的地学革命,极大地改变了人类对地球演化历史的认知[1,2].面对第四次工业革命的前夜,地球科学前沿问题究竟是什么?近年来天文学与深空探测将"宜居性:适宜生命存在的空间"作为首要研究目标.

Quaternary integrative stratigraphy and timescale of China

Quaternary strata in China mainly comprise continental deposits in a variety of depositional settings. The continental Quaternary in temperate northern China consists mainly of eolian and fluvio-lacustrine deposits; that in subtropical southern China, mainly of vermiculated red soils, cave/fissure deposits, and fluvio-lacustrine deposits; and that in the alpine Tibetan Plateau, mainly of fluvio-lacustrine and piedmont deposits. The marine Quaternary in China consists of detrital deposits and biogenic reef deposits. The integration of biostratigraphy, magnetostratigraphy, climatostratigraphy and an astronomically calibrated chronology has led to the establishment of high-precision climatochronostratigraphic timescales for the detrital marine Quaternary in the South China Sea and the loess-paleosol sequence in the Chinese Loess Plateau. Extremely high-precision230 Th dating has provided a high-precision absolute age model for cave stalagmites over the past 640000 years as well as highresolution oxygen isotope records representing orbital-to suborbital-scale climate changes. By combining magnetic stratigraphy and biostratigraphy, robust chronostratigraphic frameworks for non-eolian continental Quaternary deposits on the scale of Quaternary geomagnetic polarities have been established. The continental Pleistocene Series consists, from oldest to youngest,of the Nihewanian Stage of the Lower Pleistocene, the Zhoukoudianian Stage of the Middle Pleistocene, and the Salawusuan Stage of the Upper Pleistocene. Stages of the continental Holocene Series have not yet been established. This review summarizes recent developments in the Quaternary chronostratigraphy of representative Quaternary strata and associated faunas, and then proposes an integrative chronostratigraphic framework and a stratigraphic correlation scheme for Quaternary continental strata in China. In the near-future, it is hoped to establish not only a Chinese continental Quaternary climatochronostratigraphic chart on the scale of glacial-interglacial cycles but also a Quaternary integrative chronostratigraphic chart including both continental and marine strata in China.

The use of fire at Zhoukoudian:evidence from magnetic susceptibility and color measurements

In order to provide direct evidence for the use of fire by humans at Locality 1,Zhoukoudian,we examine the burnt and unburnt sediments of newly excavated area in Layer 4 by detailed measurements of magnetic susceptibility,color,and diffuse reflectance spectrum.Results show that the magnetic susceptibility and redness of the burnt sediments are remarkably higher than those of other areas on the same level:up to*22 times for magnetic susceptibility and*3 times for redness of those of the adjacent unburnt sediments.Fine-grained(superparamagnetic/stable single-domain)magnetite and hematite grains make dominant contributions to the distinctly high values of magnetic susceptibility and redness in the burnt sediments.Diffuse reflectance spectroscopy results show that the burnt sediments contain more hematite than those of other areas and localities 2 and 3.High-temperature magnetic susceptibility measurements demonstrate that the burnt sediments have been heated above 700°C.Those changes in low-frequency magnetic susceptibility and redness are impossibly resulted from natural fires,thus most likely signaling the human activities of controlled use of fire.However,further work is needed to confirm whether or not these heat-affected sediments were produced in situ.

A tropical paleosol at high elevation in the Yulong Mountains and its implication on the uplift of the Tibetan Plateau

A paleosol dated for about 500-700 kaBP and developed on a glacial deposit at -3 000 in a.s.l. in the Yulong Mountains is studied using soil chemical, morphological and mineralogical methods. The analytical results indicate that this soil was formed under tropical and humid conditions and can be classified as red soil, which cannot be formed in the present alpine environment at the studied site. This implies that the southeast margin of the Tibetan Plateau has experienced intense uplift since the formation of the paleosol. According to the necessary conditions for the formation of the modern red soil in China, we estimate that the

Sedimentary and geochemical evidence of Eocene climate change in the Xining Basin, northeastern Tibetan Plateau

The northeastern Tibetan Plateau began to grow during the Eocene and it is important to understand the climatic history of Asia during this period of so-called ‘doubthouse' conditions. However, despite major advances in the last few decades,the evolutionary history and possible mechanisms of Eocene climate change in the northeastern Tibetan Plateau remain unclear.The Xining Basin in the northeastern Tibetan Plateau contains a continuous sequence of Early to Late Eocene non-marine sediments which provides the opportunity to resolve long-term climate changes during this period. In this study, we report the results of analyses of lithofacies, sediment color and geochemistry of bulk samples collected from the Xijigou section of the Xining Basin. An abrupt lithofacies change between the Early(~52–40 Ma) and Late Eocene(~40–34 Ma) indicates a change in the depositional environment from a shallow lake to a playa lake in response to a significant climatic shift. During ~52–40 Ma,higher values of sediment redness(a*), redness/lightness(a*/L*) and higher modified Chemical Index of Weathering(CIW′)indicate a relatively warm and humid climate, while from ~40–34 Ma the lower values of a*, a*/L*and lower CIW′ imply subhumid to semi-arid climatic conditions. The paleoclimatic records indicate a long-term(~52–34 Ma) trend of decreasing chemical weathering, consistent with global climate change. An abrupt sharp excursion of the proxy records during ~42–40 Ma suggests a relatively brief warm interval, corresponding to the Middle Eocene Climatic Optimum(MECO). We suggest that global cooling substantially reduced humidity in inner Asia, resulting in sub-humid to semi-arid climatic conditions after 40 Ma in the Xining Basin, which may have been responsible for the long-term trend of decreasing chemical weathering during the Eocene.

Perspectives on the role of terrestrial ecosystems in the ‘carbon neutrality' strategy

The Chinese government has made a strategic decision to reach ‘carbon neutrality' before 2060. China's terrestrial ecosystem carbon sink is currently offsetting 7–15% of national anthropogenic emissions and has received widespread attention regarding its role in the ‘carbon neutrality' strategy. We provide perspectives on this question by inferring from the fundamental principles of terrestrial ecosystem carbon cycles. We first elucidate the basic ecological theory that, over the long-term succession of ecosystem without regenerative disturbances, the carbon sink of a given ecosystem will inevitably approach zero as the ecosystem reaches its equilibrium state or climax. In this sense, we argue that the currently observed global terrestrial carbon sink largely emerges from the processes of carbon uptake and release of ecosystem responding to environmental changes and, as such, the carbon sink is never an intrinsic ecosystem function. We further elaborate on the long-term effects of atmospheric CO_(2) changes and afforestation on China's terrestrial carbon sink: the enhancement of the terrestrial carbon sink by the CO_(2) fertilization effect will diminish as the growth of the atmospheric CO_(2) slows down, or completely stops, depending on international efforts to combat climate change, and carbon sinks induced by ecological engineering, such as afforestation, will also decline as forest ecosystems become mature and reach their late-successional stage. We conclude that terrestrial ecosystems have nonetheless an important role to play to gain time for industrial emission reduction during the implementation of the ‘carbon neutrality' strategy. In addition, science-based ecological engineering measures including afforestation and forest management could be used to elongate the time of ecosystem carbon sink service. We propose that the terrestrial carbon sink pathway should be optimized, by addressing the questions of ‘when' and ‘where' to plan afforestation projects, in order to effectively strengthen the terrestrial ecosystem carbon sink and maximize its contribution to the realization of the ‘carbon neutrality' strategy.

Clay mineralogy of an Eocene fluvial-lacustrine sequence in Xining Basin, Northwest China, and its paleoclimatic implications

The Eocene was marked by significant cooling during which the global climate was transformed from greenhouse to icehouse conditions. Notable coeval events were the India-Asia collision and the retreat of the Paratethys Sea in Asia. The Eocene section of the long and continuous sedimentary succession of the Xining Basin in Northwest China is characterized by red mudstones with intercalated gypsum and muddy-gypsiferous layers. In this study, we conducted a semi-quantitative analysis of the mineralogy of bulk samples and the clay fraction using X-ray diffraction, with the aim of characterizing the Eocene climatic evolution of the northeastern margin of the Tibetan Plateau and inland Asia. We used a new pretreatment method to address the problem of extracting sufficient clay particles from the gypsum and gypsiferous layers. The bulk mineralogy is dominated by quartz, feldspar, calcite, gypsum and dolomite; and the clay mineralogy is dominated by illite, chlorite, and smectite(including irregular mixed-layer illite-smectite(I/S)). The variations of the clay mineral assemblages indicate the occurrence of alternations between warm humid conditions and hot dry conditions, with relatively high humidity during ～52–50,～41.5–39 and ～35–34 Ma. Comparison of the results with the timing of Tibetan Plateau uplift, transgressions and regressions of the Paratethys Sea, and the marine oxygen isotope record suggest that the Eocene climatic evolution of the study region was driven fundamentally by global climate change.

Reconstructing early Eocene(～55 Ma) paleogeographic boundary conditions for use in paleoclimate modelling

The early Eocene is a period with very high atmospheric CO2 levels, which receives many interests from climate modelling aspects. To simulate the early Eocene paleoclimate, a realistic reconstruction for land-sea distribution, paleotopography and paleobathymetry is the fundamental step. Here, we present global paleogeographic reconstructions for the early Eocene(~55 Ma), based on integrated paleogeographic data set, the plate-tectonic reconstruction software(GPlates) and geographic information system software(ArcGIS). Comparing with previous paleogeographic reconstructions, we improve the reconstructions by incorporating many recent geologic data and data set, including:(1) Better representations of the Tethys Sea,some marginal or inland seas in the East and Southeast Asia, Atlantic and Arctic region, and the Drake Passage and Tasmanian Gateway;(2) integrated paleoelevation data of global high plateaus and mountains, especially the paleotopography of East Asia,and adopting the latest paleotopographic reconstruction data of the Antarctica;and(3) using the latest data set of oceanic crust paleo-age and oceanic sediment thickness to reconstruct the paleobathymetry.