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The cause of seasonal hydrologic changes in tropical East Asia during interstadial/stadial oscillations of the last glaciation remains controversial. Here, we show seven seasonal drought events that occurred during the relatively warm interstadials by phytolith and pollen records. These events are significantly manifested as high percentages of bilobate phytoliths and are consistent with the large zonal sea-surface temperature (SST) gradient from the western to eastern tropical Pacific, suggesting that the reduction in seasonal precipitation could be interpreted by westward shifts of the western Pacific subtropical high triggered by changes of zonal SST gradient over the tropical Pacific and Hadley circulation in the Northern Hemisphere. Our findings highlight that both zonal and meridional ocean-atmosphere circulations, rather than solely the Intertropical Convergence Zone or El Niño-Southern Oscillation, controlled the hydrologic changes in tropical East Asia during the last glaciation.

Eco-environmental changes during interglacials with an astronomical background similar to that of the Holocene are potentially helpful for understanding the future climatic evolution. Marine oxygen isotope stage (MIS) 19 is similar to the Holocene in astronomical background, both being characterized by a low eccentricity of the Earth’s orbit. However, MIS 19 has attracted research attention only recently and therefore less is known about eco-environmental changes during this interval, especially based on terrestrial records. In the Chinese Loess Plateau (CLP), the S7 paleosol can provide valuable terrestrial paleoclimatic and paleoenvironmental record for MIS 19. Here, high-resolution terrestrial snail records from the L8–L7 strata of the Huining, Xifeng and Luochuan sequences in the CLP were analyzed in order to characterize spatio-temporal changes in climate and eco-environment during MIS 20–18. The results show that in all three sections the late part of MIS 20 was dominated by abundant cold-aridiphilous mollusc species, indicating that cold and dry climatic conditions prevailed across the entire CLP, under the strong influence of the winter monsoon. The mollusc fauna of MIS 19 were dominated by warmth-loving and thermo-humidiphilous species that enable the definition of two climatic stages. The early part of MIS 19 (~790–778 ka) was marked by warm and humid conditions, as evidenced by high abundances of warmth-loving and thermo-humidiphilous species. This interval was slightly warmer than today and it lasted for ~12 kyr. The climate of the later part of MIS 19 (~778–761 ka) was more moderate, and increased proportions of cold-aridiphilous and warmth-loving species were recorded. The warmth of this period was similar to that of today, but the climatic fluctuations were stronger. During the early part of MIS 18 (~761–745 ka), the Xifeng and Luochuan sections in the eastern CLP still maintained high abundances of warmth-loving and thermo-humidiphilous species, indicating that the moderate climatic conditions during late MIS 19 continued during early MIS 18, lasting for another ~15 kyr, and that the influence of the summer monsoon remained strong in the eastern CLP during early MIS 18. However, in the western CLP, cold-aridiphilous species in the Huining section became dominant during early MIS 18, reflecting the prevalence of a cold and dry glacial climate, with the strong influence of the winter monsoon. These findings indicate that a steeper climatic gradient and a pronounced regional environmental difference existed between the eastern and western CLP during the early part of MIS 18. Comparison of our mollusc results with the variation of Earth orbital parameters suggested that climate changes in the CLP during MIS 20–18 were likely controlled mainly by insolation changes forced by the configuration of Earth orbital parameters. The unique orbital configuration during the low eccentricity interglacial-to-glacial transition could have strengthened the East Asian summer monsoon which favored the amelioration of the eco-environment in the CLP, especially in the eastern CLP where the summer monsoon exerted a strong influence. Thus we speculate that, under natural climatic conditions, the climate of the CLP may remain in a warm, humid state for another 30 kyr, although climatic instability and the seasonal differences between winter and summer could strengthen.

In this paper, we devote to investigating a new class of submanifolds, named the self-shrinker type submanifolds. We define a functional and prove its critical point is a self-shrinker type submanifold. We also show that a compact self-shrinker type submanifold with the parallel mean curvature vector in the Euclidean Space $$\mathbb {R}^{n+p}$$ is a minimal submanifold in a hypersphere $$\mathbb {S}^{n+p-1}$$ of $$\mathbb {R}^{n+p}$$ .

Climate-related factors (e.g. environmental energy, water availability and climatic seasonality/variability) and habitat heterogeneity have long been considered as the main drivers of species diversity on a broad spatial scale. However, it is controversial whether the above environmental factors can explain observed diversity patterns in varied communities such as invertebrate taxonomic group, especially mollusks. Moreover, there are until now few systematic assessments of the relative roles of different factors in determining the patterns of mollusk species diversity in monsoon-dominated regions. Here, we depict variations in terrestrial mollusk diversity based on a dataset comprising 282 assemblages collected from surface soils along an similar to 800-km climatic gradient from subtropical to warm temperate and mid-temperate regions in northern China. The results show that mollusk species diversity increases significantly from similar to 3-4 species to similar to 17-19 species when annual temperature and precipitation increase up to similar to 12 degrees C and similar to 700 mm, respectively; however, at or above these values the rate of increase is reduced. These indicate that the relationships between mollusk species diversity and climatic factors are nonlinear. Statistical analysis suggests that water availability (relative humidity) and temperature seasonality (January temperature and annual temperature range) dominate the observed pattern of mollusk species diversity. Moreover, habitat factors such as vegetation condition and soil types were also important in determining mollusk species diversity. They may be an indirect reflection of the effects of monsoonal water-energy dynamic on mollusk communities. Our results suggest that more attention should be paid to water availability and temperature seasonality in predicting future biodiversity changes, especially in the environmentally stressed northwestern part of the East Asian monsoon region. (C) 2019 Elsevier B.V. All rights reserved.

In this paper we first discuss weighted mean curvature and volume comparisons on smooth metric measure space $$(M, g, e^{-f}dv)$$ under the integral Bakry–Emery Ricci tensor bounds. In particular, we add an additional condition on the potential function f to ensure the validity of previous conclusions for some cases proved by the second author. Then, we apply the comparison results to get a new diameter estimate and a fundamental group finiteness under the integral Bakry–Emery Ricci tensor bounds, which sharpens Theorem 1.6 in Wu (J Geom Anal 29:828–867, 2019) and can be viewed as the extension of the works of Myers and Aubry.

International audience; Knowledge of the structures and intensities of past glaciations is crucial for understanding Quaternary palaeoclimatic evolution. Terrestrial molluscs are a reliable proxy of past environmental conditions and can provide specific climatic insights into glacials. Here we compare the climatic evolution of the last two glacials, based on mollusc fossils from the L2 and L1 loess units (equivalent to Marine Isotope Stages (MIS) 6 and 4-2, respectively) of the Xifeng and Luochuan sections of the Chinese Loess Plateau (CLP). The results show that both glacials had a tripartite structure but with different intensities, as indicated by variations in the abundance of the dominant cold-aridiphilous (CA) mollusc species, Vallonia tenera and Pupilla aeoli. The first stage, from~191 to 184 ka for MIS 6, and from~71 to 57 ka for MIS 4, was characterized by a cold, arid climate, as indicated by the abundance of V. tenera and P. aeoli, and the limited occurrence of thermo-humidiphilous (TH) species. The second stage, from~184 to 155 ka for MIS 6, and from~57 to 29 ka for MIS 3, was characterized by a relatively mild, humid climate, indicated bya decrease in V. tenera and P. aeoli, and an increase in TH species. The last stage, from~155 to 130 ka for MIS 6, and from~29 to 11.7 ka for MIS 2, experienced the coldest and driest conditions, as indicated by the dominance of V. tenera and P. aeoli in late MIS 6 and by the reduced occurrence of the grassland biomass, necessary for the growth of CA species, in MIS 2. The climate during MIS 2 was much colder and drier than that during late MIS 6. We suggest that the structures of the glacials were controlled mainly by insolation driven by changing astronomical configurations, amongst which obliquity likely played the major role. The different glacial intensities across the CLP may also have been related to variations in Northern Hemisphere ice sheets and the temperature of the tropical oceans.

This study presents new archaeobotanical evidence for agricultural production in the middle Yellow River region during the Yangshao culture period. Phytolith analyses, together with radiocarbon dating of samples from 10 sites in Zhengzhou, showed that common millet and foxtail millet were cultivated with rice in the region around 4000–3000 cal BC. The ratio of crop remains revealed that common millet was dominant in the crop structure. Rice cultivation was no longer confined to large sites situated in the lowlands and began to spread into the hilly lands and small sites. Furthermore, both dryland and wetland systems may have been used for rice cultivation. This pattern of crop production may have been mainly influenced by social background and artificial selection, which overcame the limitation of environmental factors. Such development of Yangshao agriculture facilitated the establishment of an agricultural society during the fourth millennium BC. It also has implications for understanding the reason why the middle Yellow River region (Central Plain) became known as ‘the cradle of Chinese civilization’.

We show a superplastic diffusion bonding method to join metallic glasses (MGs) via high-speed heating at 2000 K/min taking a timescale of the order of microseconds to milliseconds at ambient pressure because the minimum viscosity of supercooled liquid drastically decreases as the heating rate increases. The results show strong metallic bonds are formed but the amorphous structure is still maintained. Finally, we establish a general equation containing the involved parameters for high-speed heating bonding. This method provides a new path to join MGs rapidly and benefits for improving the critical size of MGs.

The Peiligang culture is the earliest Neolithic culture in the middle Yellow River valley and represents the emergence of cereal farming in the region. Present records imply the concurrence of millet farming and mixed millet-rice farming in the Peiligang culture, but their spatial distribution pattern is still unknown, because of the there is a lack of comparative studies on crop remains from different sites. Here, we present the results of analyses of phytoliths and plant macroremains in archaeological sediments from four Peiligang culture sites, as well as an integration of crop records from nine other sites. These sites are classified into two types in terms of their geographical locations: those in alluvial plains and those in hilly lands. The results confirm the coexistence of millet and mixed farming in the Peiligang culture, rather than one or the other. Their spatial pattern involved millet farming in the hilly lands, with mixed farming done in the alluvial plains. Compared to the sites in the hilly lands, the sites in the alluvial plains have enough water sources and vast amounts of flat land, making it possible to cultivate rice and conduct mixed farming. In all Peiligang culture sites, regardless of any agricultural modes, common millet ( Panicum miliaceum ) was predominant among the crop assemblages. In the same climate background, the agricultural mode selection in different sites was mainly influenced by landform and hydrology. This spatial pattern of farming also reflects human adaptive subsistence practices, which respond to different natural circumstances.

Prehistoric human activities were likely influenced by cyclic monsoon climate changes in East Asia. Here we report a decadal-resolution Holocene pollen record from an annually-laminated Maar Lake in Northeast China, a proxy of monsoon climate, together with a compilation of 627 radiocarbon dates from archeological sites in Northeast China which is a proxy of human activity. The results reveal synchronous ~500-year quasi-periodic changes over the last 8000 years. The warm-humid/cold-dry phases of monsoon cycles correspond closely to the intensification/weakening of human activity and the flourishing/decline of prehistoric cultures. Six prosperous phases of prehistoric cultures, with one exception, correspond approximately to warm-humid phases caused by a strengthened monsoon. This ~500-year cyclicity in the monsoon and thus environmental change triggered the development of prehistoric cultures in Northeast China. The cyclicity is apparently linked to the El Niño-Southern Oscillation, against the background of long-term Holocene climatic evolution. These findings reveal a pronounced relationship between prehistoric human activity and cyclical climate change., Long-term climate cycles can potentially influence population dynamics, including those of humans. Here, the authors combine climate and archaeological records from Northeast China over the past 8000 years and demonstrate ~500 year cycles in both the monsoon and human activity.

Although the summer monsoon is the dominant source of precipitation in the East Asian monsoon region (EAMR), there is long-standing uncertainty about the spatial and temporal variability of precipitation on the centennial time scale. In this study we analyzed two well-dated, high-resolution, published paleoclimatic records in order to determine the variability of precipitation in the EAMR during the Holocene. One record is a decadal-resolution pollen record from an annually-laminated Maar lake in Northeast (NE) China, and the other is a U Th dated, multi-decadal-resolution speleothem record from Central China. Advanced time-series analysis of the two records provides unambiguous evidence for asynchronous summer monsoon rainfall variability on centennial to millennial time scales in the EAMR. The pollen and speleothem records indicate long-term and ~ 500-yr quasi-periodic changes in humid/dry climatic shifts against the background of an insolation-forced climatic trend throughout the past 8580 years. Phases of wetter climate (during ~7000–5500 cal yr BP) and drier climate (during ~1400–300 cal yr BP) in NE China are closely related to different climatic phases in Central China. However, the ~500-yr cyclic rainfall changes in Central China lag those in NE China by several decades to almost two centuries. During the ~500-yr periodic changes in the monsoon, a climatic pattern encapsulated as “Northern drought, southern flooding” prevailed during an El Nino-like phase, whereas the opposite pattern “Southern drought, northern flooding” occurred during a La Nina-like phase. The asynchronous pattern of ~500-yr climatic cyclicity between the northern and southern EAMR may have been caused by the El Nino-Southern Oscillation, linked to low-latitude oceanic and atmospheric interactions.

The cascading impacts of climate-driven vegetation change on terrestrial invertebrates via trophic and habitat routes is a matter of outstanding concern. However, the combined responses of plant-animal associations in terrestrial ecosystems have seldom been reported on geological timescales, which raises the important questions of how frequently and to what extent such multi-trophic shifts in taxa have occurred during previous warming scenarios. Here we use a combination of mollusk, palynological, and climatic proxy evidence preserved within loess deposits in the southern Chinese Loess Plateau (CLP) to demonstrate how long-term changes in hydroclimatic dynamics during the past 26 kyr were reflected in the subsequent ecological changes. Specifically, there was a shift from a predominantly cold-tolerant mollusk fauna in a dry-steppe environment under cold-dry conditions during the last glacial, to a predominantly thermal-mesophilous fauna in a meadow-steppe environment under a warm temperate climate in the early-middle Holocene. Warmth-adapted mollusk species such as Opeas striatissimum and Punctum orphana were found to have been associated with several deciduous tree taxa (e.g., Corylus, Quercus, and Pterocarya) in both the Holocene record and in the modern ecosystem (based on surveys of 356 surface-soil plots). This suggests there is a clear ecological interdependency between specific vegetation types and mollusk assemblages. As such, the long-term vegetation-mollusk fossil records highlight the indirect impacts of climate change on terrestrial invertebrate turnover via plant-derived food structure and habitat routes, with major implications for understanding how these ecosystems are likely to respond to future climate changes.

Let x : M n−1 → R n (n ≥ 4) be an umbilical free hyper-surface with non-zero principal curvatures. Then x is associated witha Laguerre metric g, a Laguerre tensor L, a Laguerre form C, and aLaguerre second fundamental form B, which are invariants of x underLaguerre transformation group. We denote the Laguerre scalar curvatureby R and the trace-free Laguerre tensor by L˜ := L− 1n−1 tr(L)g. Inthis paper, we prove a local classification result under the assumption ofparallel Laguerre form and an inequality of the typekL˜k ≤ cR,where c= 1(n−3) √ (n−2)(n−1) is appropriate real constant, depending onthe dimension. 1. IntroductionLet x : M n−1 → R n be an umbilical free hypersurface with non-zero princi-pal curvatures. Let ξ : M → S n−1 be its unit normal. Let {e 1 ,e 2 ,...,e n−1 }be the orthonormal basis for TM with respect to dx · dx, consisting of unitprincipal vectors. Let r i = 1k i , r = r 1 +r 2 +···+r n−1 n−1 be the curvature radius andmean curvature radius of x respectively, where k

Reconstructing and quantifying human impacts is an important step in understanding how, when, and to what extent humans have changed terrestrial ecosystems via agricultural land use during the Holocene. However, the use of soil-faunal indicators and an associated quantitative model of land use intensity to study anthropogenic disturbance is relatively poorly developed. In this study we collected 139 samples of soil-dwelling snails from urban land and human settlements, cultivated land, modified and natural vegetation mosaics, and natural habitats in northern China, in order to characterize the snail assemblages in human-modified habitats. The results show that cultivated land and planted forest are mainly dominated by snails of Cathaica fasiola, Bradybaena ravida, Vallonia tenera, etc., while natural habitats are characterized by an even distribution of members of the families, such as Ariophantidae, Cochlicopidae, Pupillidae, Subulinidae. Canonical correspondence analysis indicates that human activity (quantified by the human influence index, HII) is one of the most important factors shaping the composition of snail fauna in man-modified habitats. There is a significant relationship between modern snail data and HII, and the transfer function established by weighted-averaging partial least squares (WA-PLS) model for HII exhibits a good statistical performance. We then applied the calibration model to a fossil snail record spanning the last 12 kyr from the Chinese Loess Plateau (CLP). The reconstructed HII increases slightly at ∼5 ka and abruptly at ∼2 ka, coinciding with increases in the human population of the CLP, local cultural development, and human-induced changes in vegetation cover. Our quantitative reconstruction indicates that human activities, via agricultural activity, may have permanently altered natural ecosystems and the soil fauna for at least the last two millennia.

International audience; Abstract. Chinese loess sequences are interpreted as a reliable record of the past variation of the East Asian monsoon regime through the alternation of loess and paleosols units, dominated by the winter and summer monsoon, respectively. Different proxies have been used to describe this system, mostly geophysical, geochemical or sedimentological. Terrestrial mollusks are also a reliable proxy of past environmental conditions and are often preserved in large numbers in loess deposits. The analysis of the mollusk remains in the Luochuan sequence, comprising L5 loess to S0 soil, i.e. the last 500 ka, shows that for almost all identified species, the abundance is higher at the base of the interval (L5 to L4) than in the younger deposits. Using the present ecological requirements of the identified mollusk species in the Luochuan sequence allows the definition of two main mollusk groups varying during the last 500 kyr. The cold-aridiphilous individuals indicate the so-called Asian winter monsoon regime and predominantly occur during glacials, when dust is deposited. The thermal-humidiphilous mollusks are prevalent during interglacial or interstadial conditions of the Asian summer monsoon, when soil formation takes place. In the sequence, three events with exceptionally high abundance of the Asian summer monsoon indicators are recorded during the L5, L4 and L2 glacial intervals, i.e., at about 470, 360 and 170 kyr, respectively. The L5 and L4 events appear to be the strongest (high counts). Similar variations have also been identified in the Xifeng sequence, distant enough from Luochuan, but also in Lake Baikal further North, to suggest that this phenomenon is regional rather than local. The indicators of the summer monsoon within the glacial intervals imply a strengthened East-Asian monsoon interpreted as corresponding to marine isotope stages 12, 10 and 6, respectively. The L5 and L2 summer monsoons are coeval with Mediterranean sapropels S12 and S6, which characterize a strong African summer monsoon with relatively low surface water salinity in the Indian Ocean. Changes in the precipitation regime could correspond to a response to a particular astronomical configuration (low obliquity, low precession, summer solstice at perihelion) leading to an increased summer insolation gradient between the tropics and the high latitudes and resulting in enhanced atmospheric water transport from the tropics to the African and Asian continents. However, other climate drivers such as reorganization of marine and atmospheric circulations, tectonic, and the extent of the Northern Hemisphere ice sheet are also discussed.

The terrestrial mollusk fossils found in Chinese loess strata have been studied for over one hundred years. However, the greatest progress in these studies has been made only in the last two decades. In this paper, we review the advancements, advantages and limitations of terrestrial mollusk studies in Chinese loess deposits. Improvements in research methods and approaches have allowed the extraction of more detailed paleoenvironmental and paleoclimatic information from mollusk assemblages. The broadened research scope and content have yielded many new findings and results. The mollusk record has thus become one of the most important proxies in the paleoenvironmental and paleoclimatic reconstruction of loess-paleosol sequences in China. The greatest progress in the studies of terrestrial mollusks in Chinese loess sequences can be summarized as follows: (1) modern mollusk assemblages can be classified into four ecotypes, based on their temperature and humidity requirements, including eurytopic, semi-aridiphilous and sub-humidiphilous, cold-aridiphilous, and thermo-humidiphilous types; (2) Quaternary mollusk assemblages can be modified into the following three ecological types: glacial loess, interglacial paleosol, and interstadial weakly-developed paleosol assemblages; (3) mollusk records successfully reveal long-term climatic and environmental changes reflective of the history of East Asian monsoonal variations since the Late Cenozoic, and the succession of mollusk species also indicate short-term environmental changes such as millennial climate variability during Last Glacial Maximum and unstable climatic fluctuations during glacial and interglacial periods; and (4) more recently, new analytical approaches have offered increased research potential in areas such as paleotemperature reconstruction using the isotopic compositions of modern and fossil mollusk shells, combined with higher accuracy 14 C dating of Quaternary loess deposits, which will greatly improve future loess paleoenvironmental research.

International audience; Recently, the first late Miocene–Pliocene eolian deposits from the western Chinese Loess Plateau have been reported. These deposits would complement the eolian record between Quaternary loess-paleosol sequences and Miocene loess sequences, if their wind-blown origin could be documented. However, although several lines of evidence indicate the eolian origin of this sequence, it is still necessary to address this issue through further efforts. Among these, biological approaches are of particular value. Here we analyze the composition and preservation conditions of mollusk assemblages in the Dongwan section. Our results show that all mollusk fossil individuals are preserved in perfect condition without indicating any reworking. All identifiable mollusk species are terrestrial, and are mostly identical to those identified in the Quaternary loess-paleosol sequences of the Chinese Loess Plateau. Generally, the cold-aridiphilous species are dominant in the loess layers, while thermo-humidiphilous species are mostly encountered in the paleosols. The close similarity of the mollusk record in both the Dongwan late Miocene–Pliocene deposits and the Quaternary loess sequence in the Chinese Loess Plateau supports the supposition that the Dongwan section is a typical loess-paleosol sequence, and is, without any doubt, of wind-blown origin.