Abstract The Neogene expansion of C 4 grasslands transformed terrestrial ecosystems with marked influence on mammalian evolution, including hominins. However, the asynchronous C 4 expansion on different continents makes it difficult to identify the environmental drivers, especially for higher latitudes. Here we show that rainfall seasonality governed extratropical Plio-Pleistocene C 4 distributions in East Asia. Rainfall oxygen isotope ratios and clumped isotope soil temperatures exhibit coupled variations on the Chinese Loess Plateau (CLP) from 7 to 2.5 million years ago, indicating more spring rain during warmer times when the subtropical westerly jet was further poleward, and more concentrated summer rain under cooler climates. We attribute these changes to meridional shifts of a summer rain band on orbital and longer timescales. The most C 4 -rich ecosystems, as identified by organic carbon δ 13 C records, tracked this summer rain band, eventually eclipsing the southern CLP margin during the late Pleistocene cooling. Our model refines the East Asian paleomonsoon concept and explains the equatorward migration of extratropical C 4 ecosystems, highlighting the tight coupling between regional rainfall seasonality and vegetation.

The early Pleistocene represents a critical period for understanding the formation and evolution of the modern East Asian landscape. During this period, the intensification of Northern Hemisphere glaciation and the East Asian summer monsoon system exerted a strong influence on landscape evolution through hydrologic shifts and surface erosion and deposition in East Asia, while tectonic processes, another significant driver, shaped landforms through mountain growth and basin subsidence. Intermontane basins record the interplay among climatic variability, tectonic activity, and sediment supply, providing archives for evaluating their relative contributions. The Shanxi Rift in northern China is a prominent example, where thick late Cenozoic lacustrine successions record long-term tectonic regimes and East Asian summer monsoon variability through changes in sediment supply. Here we present a new lacustrine−deltaic succession and high-resolution magnetic susceptibility data to reconstruct lake-level evolution in the Taiyuan Basin, central Shanxi Rift, northern China. Using magnetostratigraphy combined with 10Be burial dating, we establish a robust age framework from 2.59 Ma to 2.14 Ma and constrain a major lake regression to ca. 2.2 Ma. Our anisotropy of magnetic susceptibility results show no tectonic overprinting, supporting a tectonically quiescent state during the early Pleistocene. In contrast, a regional stepwise cooling and drying trend associated with the weakening of the East Asian summer monsoon is closely coupled with paleolake evolution in the Taiyuan Basin. These results demonstrate that climate forcing outweighed tectonics in controlling lake-level fluctuations in the Taiyuan Basin, highlighting the dominant role of climate change in shaping the modern East Asian landscape during key periods.

The Pliocene warm period is regarded as an analogue of future warming, and quantitative reconstruction of palaeovegetation and palaeoclimate during this period is helpful for predicting vegetation and climate changes in the future. Here, we quantitatively reconstructed the late Pliocene vegetation and climate based on phytolith assemblages from the Upper Zhangcun Formation in the Yushe Basin, Northern China. The results show that the vegetation was dominated by grasses with few trees, which conflicts with the pollen assemblage results. The possible reason for this contradiction is that phytoliths tend to mirror local, shoreline vegetation (grasses with few aquatic plants), while pollen tend to mirror both local and regional vegetation (trees in surrounding mountains and piedmont, grasses on lakeshores and aquatic plants in wetlands) in a small structurally confined lake. The phytolith-based quantitative reconstruction of mean annual precipitation (812-1673 mm) and warm season precipitation (417-1197 mm) provides values that are higher than those at present, revealing an increase in Asian monsoon rainfall during the late Pliocene, which is consistent with the pollen results, although the reconstructed vegetation is different. This study highlights the usefulness of phytoliths in reconstructing Cenozoic vegetation and climate and underlines the importance of landforms in determining phytolith and pollen assemblages in sediments.

In this study, we employ biological, geochemical and mineral, and physical proxies to quantitatively and semi-quantitatively reconstruct regional paleoclimate variations in China over the past-21 thousand years (ka). We have constructed state-of-the-art transfer functions between proxies and climatic variables in East Asia, revealing substantial paleoclimate variability, and demonstrate significant diversity of paleoclimate variations in regions of China over the past-21 ka. Compared with observational data between 1961 and 1990, averaged mean annual temperature (MAT) was-5 degrees C (3 -8 degrees C) lower during the Last Glacial Maximum (LGM,-21 +/- 3 ka), and- 2 degrees C (1 -3 degrees C) higher during Holocene Optimum (HO, +/- 9 ka) in China; while averaged mean annual precipitation (MAP) and averaged summer precipitation varied between 30 and 150%, with enhanced seasonality during the warmer Holocene (8 -5 ka). Our quantitative and semi-quantitative paleoclimate reconstructions reveal both similarities and contrasts with previous studies of regional temperature and precipitation variability. The most remarkable paleoclimate variability is recorded in the transitional zone between the humid monsoon and arid desert regions of central and northern China. We conducted a dynamic downscaling paleoclimate simulation with a regional climate model (RegCM4), using the output from the fully-forced transient simulation of the global climate (TraCE-21 K) as the prescribed boundary conditions, to simulate regional climate changes at high spatial resolution in China over the past-21 ka. The results improve paleoclimate simulations at regional scales, but reveal differences in comparison with TraCE-21 K, thereby highlighting uncertainties in the simulation modeling. Moreover, we compare proxy-based paleoclimate reconstructions and the output of TraCE-21 K to identify inconsistencies in relation to regional paleoclimate variations, and confirm a generally consistent warming trend in MAT from the LGM to the HO followed by a cooling trend during the late Holocene. An overall increase in both annual and summer precipitation is observed from LGM to Holocene. This general paleoclimate pattern is likely to have been driven by northern hemisphere ice volume and atmospheric greenhouse gas concentrations (GHGs) during the last deglaciation, and boreal summer insolation during the Holocene. This study represents the first attempt to use multi sources and large datasets of proxy reconstructions and numerical simulations to evaluate regional paleoclimate variability in China since the LGM. Our research provides a comprehensive overview of climate change over the past 21 ka and underscores the critical importance of conducting high-resolution simulations and quantitative paleoclimate studies. This approach is essential for deciphering patterns of paleoclimate change that are currently poorly defined.

The Weihe Basin, situated in the central part of Shaanxi Province between the Qinling and Weibei Mountains, falls under the influence of the Asian monsoon system. The basin's thick and continuous Cenozoic sedimentary layers offer a valuable repository for investigating environmental changes within a typical monsoon climate. Based on previous chronological research, our study delved into the microcharcoal concentration (MCC) of the samples extracted from Bahe Formation. This analysis aimed to reconstruct the paleo-fire and drought history during the late Miocene, shedding light on the region's evolutionary trajectory. Our findings unveil five distinct peaks in the microcharcoal record, occurring at approximately 9.9-9.7 million years ago (Ma), similar to 9.5 Ma, similar to 8.1 Ma, similar to 7.6 Ma, and 7.4-7.2 Ma. These peaks signify high-frequency fire events, primarily taking place during periods of aridity. The combustion of broadleaved and coniferous trees was the predominant source of fuel for fires during 9.9-9.7 Ma, similar to 9.5 Ma and similar to 8.1 Ma, with elevated temperatures acting as the principal ignition catalyst. In contrast, the subsequent two fire events (similar to 7.6 Ma, and 7.4-7.2 Ma) coincided with drier climatic conditions, featuring xerophytic herbs s as the primary biomass. Drought emerged as the pivotal driving force behind these fire occurrences in this phase. The microcharcoal records of the Bahe Formation reveal a note-worthy pattern: the MCC during the latter two periods surpassed that of the initial three, indicating an escalated frequency of fires during dry intervals. This trend signifies a transition towards a dry and cold climate post similar to 8.0 Ma. The expansion of grasslands and the occurrence of drought events since the late Miocene (similar to 8.0 Ma) can be attributed to the weakening of the Asian Monsoon. In summary, our investigation of microcharcoal concentration in the Bahe Formation provides valuable insights into the late Miocene paleo-fire and drought dynamics. By deciphering the interplay between vegetation, climate, and fire occurrences, our study contributes to a more comprehensive understanding of the environmental evolution within the Weihe Basin under the influence of the Asian monsoon system.

Asia has a unique set of landscapes, notably characterized by the highest plateau in the world, the strongest monsoon circulation, and an immense arid region. When and how this landscape was formed have long been investigated, but explanations remain elusive. In this paper, through a synthesis of both terrestrial and marginal marine sedimentary records and numerical simulation analyses, we propose that tectonic uplift/deformation and global cooling during the Cenozoic have controlled the evolution of Asian topography and climate, respectively, and, the Asian landscape. The Asian landscape has undergone three main stages of evolution, viz: development of low-relief topography and warm-dry climate during the Eocene (~50-34 Ma); emergence of high relief topography in the southwest, along with a diverse range of landforms elsewhere, associated with a warm monsoon-arid climate coupling system during the Oligocene to early Pliocene (34-3.0 Ma); and development of the typical Asian summer and winter monsoon circulation and present landscape since the late Pliocene, accompanied by significant global cooling. Our analyses reveal that the distribution of river catchments, flora, fauna and soils are controlled by tectonic uplift/deformation and palaeoclimate changes. Stepwise evolution of the Asian landscape since ~50 Ma was driven by tectonic deformation and global temperature changes, each of which may play different role(s) in landscape evolution. For instance, the India-Asia collision played a vital role in the formation of the Asian topographic configuration in the middle Eocene, which generated regional atmospheric circulation. On the other hand, global cooling during the late Pliocene played an important role in generating the modern-like Asian landscape including the rapid accumulation of loess deposits, strengthening of the Asian monsoon circulation, and the evolution of modern topography. To summarize, we broadly propose a three-stage history of landscape evolution in Asia during the Cenozoic. The detailed processes of Asian landscape evolution and the specific roles of tectonism and global temperature in controlling Asian landscapes and palaeoclimate evolution need to be further investigated.

The formation and evolution of the landscape of the Chinese Loess Plateau (CLP) is debated because of uncertainties regarding dust provenance. We present a quantitative estimation of dust source contributions to the CLP, based on more than 37,100 detrital zircon U-Pb ages, combined with mineral assemblages and isotope analyses. Our results reveal that the CLP was stepwise formed by ~8 million years (Ma) and is mainly composed of material from the Northeastern Qinghai-Tibetan Plateau, with stepwise shifts in relative contributions of different eolian silt sources occurring at ~2.6 Ma and 1.5 to 1.2 Ma. We infer that these changes were driven by stepwise global cooling, which induced aridification and enhanced silt production in glaciated-cold climate dust source regions, as well as dust ablation in the expanded arid regions. We propose that global cooling, rather than regional tectonic deformation, was the main driver of the formation and evolution of the CLP during late Cenozoic.

East Asian Monsoon variations during the Plio-Pleistocene transition have attracted much scientific interest, but they are still not well understood. We analysed the trace and major element concentrations of the Red Clay and loess-paleosol sequence of the XSC section, on the southern Chinese Loess Plateau (CLP), over the time interval of 4-2 Ma. From the results of geochemical and mineralogical analysis, we conclude that the Na/K ratio can be used to reflect the weathering intensity of plagioclase. Grain-size effects on the Na/K ratio were minimized based on the analysis of multiple size fractions. The Na/K ratios show similar trends between different grain-size fractions during the Pliocene-Pleistocene transition. Additionally, the Na/K ratio for various Holocene eolian sediments is well correlated with the regional mean annual precipitation (MAP). Based on this observation, we relate the Na/ K ratio to East Asian Summer Monsoon (EASM) precipitation and propose that the EASM is the primary control of the post-depositional weathering intensity. The Na/K record of the EASM precipitation, as inferred from the Na/ K record of the XSC section, progressively weakened and increased in amplitude between 4 and 2 Ma, indicating that the climate on the monsoonal margin evolved from warm and moist during the Late Pliocene to dry and cold during the Early Pleistocene. Our results support the hypothesis that global cooling was responsible for driving the decrease in EASM-derived rainfall via the migration of the intertropical convergence zone (ITCZ) and the associated monsoon precipitation belt during the Plio-Pleistocene transition.

The rise of grasses using C4 photosynthesis and dominating grasslands during the latest Cenozoic is one of the most dramatic events in Earth's history. A growing body of geological records adds more details to this process, such as the study of fossil phytoliths. Phytolith data make it possible to track major grass lineages over time, and distinguish which kind of C4 grasses rise to dominate in a particular region. If the environmental niches of this kind of C4 grass are well studied, the corresponding environmental controls and driving mechanisms could be identified. Here, we combine geospatial data and climate data from two public archives to produce a database of-12 million collections spanning-6000 species of grasses with corresponding climate data to explore the quantitative relationship between the major grass lineages (subfamilies) and climate at global and regional scales. Our results show that the 10 C isotherm of mean annual temperature is the transitional boundary of Pooideae and Panicoideae/Chloridoideae distribution in North America and East Asia; the 400 mm isohyet of summer precipitation is the transitional boundary of Panicoideae and Chloridoideae distribution in North America and South Africa. However, the detailed environmental niches of certain grass lineages vary from region to region and are controlled by regional climate, topography and local species. Based on these data, the reanalysis of phytolith data since the Neogene reveals a distinct evolutionary history of grassland ecosystems. The onset of modern like grassland happened in the early Miocene in both North America and East Asia, those original grasslands were most likely dominated by C3 Pooideae with minor Panicoideae (C4) and few Chloridoideae (C4); C4 expansion on both continents was based on substantial heterogeneity in vegetation, with similar aridity in climate as a possible driver, but with different timings and results: the rise of Chloridoideae in North America at 8-5 Ma and the rise of Panicoideae in East Asia at-11 Ma. We suggest that synchronous changes in Asian monsoon precipitation and temperature are responsible for the rise of Panicoidaeae in East Asia, whereas the combination of warm and semiarid climates is responsible for the rise of Chloridoideae in North America. We emphasize the importance of regional environmental control on the evolution and distribution of the major grass lineages and offer a database that could be used to reconstruct palaeoclimate by phytoliths in different regions.

Pliocene climate is regarded as an analogue of future global warming (Burke et al, 2018; IPCC, 2021). How was the Pliocene precipitation in the monsoonal East Asia is not well known, although the Pliocene eolian silt ‘Red Clay’ deposit sequences have been investigated (Gallagher et al., 2021; Wang et al., 2022.). The poor preservation of floral and fauna fossils, and low sedimentation rate of the Red Clay makes it inappropriate to use as proxies that quantitatively reconstructing the Pliocene paleoclimate. In this study, a thick lacustrine deposit sequence at the Taigu-Yushe Basin (TYB) in central China is investigated, in order to semi-quantitatively reconstruct the East Asian monsoon precipitation variations during the Pliocene and early Pleistocene. These lacustrine sediments are rich in fossils. The thick lacustrine deposit sequences are dated by paleomagnetic stratigraphy analysis and correlated with the loess-paleosol time-series. The results show that the TYB lake deposit was accumulated during circa 4.0 -1.5 Ma. The Xiaobai Formation, which indicates a humid climate, was formed during 4.0-2.4 Ma. The pollen assemblage of the lake deposits and fluvial sediments reveals a dry climate after 2.4 Ma. Our proxy analyses show the precipitation during the middle Pliocene was 30% more than the present. This sedimentary record unravels the strengthened East Asian monsoon circulation which transported more vapor to the monsoon marginal during the Pliocene warmth.

Paleosols preserved in the Red Clay depositional sequence of the Chinese Loess Plateau record information about vegetation and regional hydrology responses to global temperature variation throughout the late Miocene and Pliocene. Reconstructing spatial and temporal patterns of environmental change across the Loess Plateau from carbon isotopes of pedogenic carbonate (δ 13 C carb ) is complicated because multiple factors affect δ 13 C carb values and higher resolution records do not exist along the northern margin of the Loess Plateau. To address these needs, we present paired carbon isotope records of pedogenic carbonate and occluded organic matter (δ 13 C org ) from 697 discrete nodules sampled from 119 different depths at the Jiaxian section, North Central China. Between 7.6 and 2.4 Ma, δ 13 C carb values increase by nearly 5‰, while δ 13 C org values increase by 2.5‰. These increases are explained by a progressive decline in moisture availability through time, and there is no definitive evidence from these δ 13 C data for C 4 vegetation at the Jiaxian site until after 3.6 Ma. Comparison of the Jiaxian record to other Loess Plateau sections reveals a consistent spatial gradient with δ 13 C carb values becoming higher and more variable to the N‐NW. Additionally, an independent index of monsoonal precipitation from a southern site corresponds to fluctuations in δ 13 C carb values at Jiaxian, while southern δ 13 C carb records remain more stable. These spatial patterns are explained by a progressive decline in moisture availability across the Loess Plateau through the Late Miocene and Pliocene, with δ 13 C carb values being more sensitive to moisture availability under consistently more arid conditions to the NW.

Late Miocene and Pliocene climate changes provide an analogue for understanding linkages between variations in precipitation, the intensity of the Asian Monsoon (AM) and vegetation in a warm world with high atmospheric CO2. This study presents a reconstruction of vegetation and paleoclimate based on a pollen sequence between similar to 10.8 and 7.2 Ma, in addition to an analysis of pollen assemblages of Pliocene and Pleistocene, from the Weihe Basin, central China. Based on the Coexistence Approach (CA), the reconstruction indicates that the late Miocene and Pliocene climate was warmer and wetter than today, and that the vegetation responded to a strengthened AM prior to the onset of the Northern Hemisphere glaciations (NHG) during the early Pliocene. A significant vegetation shift from forest to grassland occurred at similar to 9.0 Ma, suggesting a climate shift from warm-wet to cool- dry in central East Asia earlier than previously thought. The quantitative reconstruction suggests that mean annual precipitation exceeded similar to 800 mm/year and the warm season (June to September) precipitation exceeded similar to 560 mm during similar to 10.8-7.2 Ma. Based on pollen analysis, the late Pliocene, however, appears to have been relatively cool and dry, followed by a colder and drier Pleistocene, associated with an overall weakening of the AM. The paleoclimate reconstruction reveals that the AM exhibited phased weakening since similar to 10.8 Ma, which is consistent with stepwise global temperature variations. It is clear that vegetation variations were mainly driven by the AM precipitation and global cooling in the semi-humid region of the Weihe Basin since the late Cenozoic. This study provides insights into vegetation dynamics under global warming conditions.

A terrestrial record reveals that East Asian monsoon was forced by high- and low-latitude temperature variability in Pliocene.

The Asian monsoon variations under global temperature changes during the Pliocene are still debated. Here we use a sedimentary record of phytoliths (plant silica) from the Weihe Basin, central China, to explore the history of C 4 grasses and quantitatively reconstruct the Asian monsoon climate since the late Miocene. Our results show that C 4 grasses have been a dominant grassland component since ~11.0 Ma. A subsequent marked decrease in warm- and humid-adapted C 4 grasses and an increase in cool- and dry-adapted C 3 grasses occurred in the Pliocene, ~4.0 Ma; the phytolith-based quantitative reconstruction of mean annual precipitation marked a decrease from 800~1673 mm to 443~900 mm, indicating a reduction in Asian monsoon rainfall in the Pliocene. Our newly obtained records conflict with the hypothesis that the growth of the Tibetan Plateau strengthened the Asian monsoon rainfall. Nevertheless, they emphasize the importance of global temperature as a determinant of Pliocene Asian monsoon variations.

AbstractWe investigated climate niches of grasses at regional scales and quantitatively reconstruct Asian monsoon precipitation at the sand-loess transitional zone in northern China. Our results provide direct evidence that certain grass lineages have been specialized in specific habitats: Pooideae grasses stand out and occupy a much cooler environment than all other subfamilies; Pooideae, Aristidoideae, and Chloridoieae occupy dry environments. Pooideae grasses occupy the coldest and driest environments compared to all other subfamilies, with a mean annual temperature (MAT) and precipitation (MAP) of ~13.6 to ~15.3°C and 224 to ~1674 mm, respectively, at a regional scale. We built a database for grasses and their corresponding climate parameters. Based on this database, past climate parameters at the margin of the Asian summer monsoon since ~70 ka were quantitatively reconstructed by phytolith assemblages. They show that this area was dominated by cold- and dry-adapted grasses since ~70 ka with a MAT and MAP of ~3.3 to ~11.0 °C and ~442 to ~900 mm, respectively, generally consistent with the results of phytolith-based transfer function reconstructions and with the results of previous nearby pollen-based quantitative reconstructions. With the improvement of the species-climate and ecosystem dataset, our database-based method is a promising quantitative reconstruction approach to past climatic change in the monsoon region.

植硅体形态测量学是植硅体研究的重要方向之一,随着学科交叉研究的深入,植硅体形态测量学在植物分类与生态学、环境考古学、全球变化与生态响应等领域得到快速发展.综合已有研究成果表明,长鞍型植硅体形态测量学在日本、中国的竹亚科属一级竹类生态学具有独特的指示作用,而扇型和长鞍型形态测量学在中国西南西双版纳竹亚科木本竹子属一级分类中具有重要的参考价值;稻亚科扇型形态测量学可以有效区分籼稻与粳稻,且扇型鱼鳞状纹饰与颖壳双峰植硅体形态测量学结合可以准确判别亚洲栽培稻与普通野生稻;黍亚科树状表皮长细胞形态测量学被成功运用到区分中国西北黍和粟及其亲缘物种的关系,葫芦科南瓜属刻面球型植硅体形态测量学揭示了野生种、半驯化种和驯化种之间植硅体形态大小及其关系,证实南美洲低地地区早全新世出现的南瓜驯化历史;中国东北不同环境条件下的禾本科羊草、芦苇植硅体形态测量学研究反映了陆生植物对全球变化的生理生态响应,为研究陆地生态系统对全球变化的响应及古环境重建提供了重要参考.

The relative importance of global cooling and Tibetan Plateau uplift in driving the aridification of Asia during the late Cenozoic is debated, largely due to the lack of appropriate proxy indicators. Here we address this problem by investigating changes in the source of Chinese loess and Red Clay, which is directly controlled by changes in the extent and distribution of the arid zone of Asia and the intensity of the East Asian winter monsoon, using zircon U-Pb dating of 27 levels in a near-continuous eolian sedimentary sequence in southern Chinese Loess Plateau. The results show that source regions expanded stepwise at similar to 7.2, similar to 2.6, 1.2-0.9Ma, and at the Last Glacial Maximum. These changes were synchronous with global cooling and ice cover expansion in the Northern Hemisphere, suggesting that the drivers of aridification of the Asian interior were intimately related to global cooling in the late Cenozoic. Plain Language Summary The arid and semiarid regions of Central Asia are one of the most important dust sources on Earth. Dust emitted from these regions is deposited in the Chinese Loess Plateau, the North Pacific Ocean, and even in Greenland, with broad environmental impacts. Although there is evidence that the drying of the Asian interior occurred gradually over several tens of million years, the driving factor remains unclear. Here we investigate the evolution of the sediment sources of the Chinese Loess Plateau and find that the changes in the source regions of wind-blown sediment were synchronous with global cooling since similar to 7.2 Ma. This indicates that the long-term aridification of the Asian interior was most likely driven by global cooling.