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The investigation of two profiles (DYS1 and DYS5) from the Daiyun Mountains in southeastern China sheds new light on the history of regional climate changes and the variability of the intensity of the East Asian Summer Monsoon (EASM) over the past 10350 years based on the degree of peat humification, loss on ignition (LOI), magnetic susceptibility (MS) and geochemical (Rb, Zr and Zr/Rb) data. The records indicate that three main climatic regimes have occurred over the past 10350 years: 1. relatively warm and wet conditions from ~10350 to 8800 cal BP; 2. a warmer and wetter climate from 8800 to 3000 cal BP that was interrupted by four cold episodes at 7500, 6400, 5400, and 4400 cal BP; and 3. a dry and cool climate after ~3000 cal BP. These climatic changes were probably associated with a weak EASM, which was related to the latitudinal movement of the Intertropical Convergence Zone (ITCZ). Other important influences include solar radiation, etc. [ABSTRACT FROM AUTHOR]

The reconstruction of past climates and vegetation can provide valuable information for understanding the mechanisms of the variability of the East Asian summer monsoon in eastern China. In this study, organic geochemical evidence from the compositions of sedimentary leaf-wax stable isotopes and n -alkane parameters investigates the changes in vegetation and climate over the last 1200 years in the Xiyaohu peatland, Jiangxi Province, southeast China. Combined with temperature records, three climatic periods are presented: (a) a warm and humid period with an increase in C4 plants from 900 to 1450 AD, which coincides with the Medieval Warm Period (MWP); (b) a cool and dry period with the expansion of C3 plants from 1450 to 1800 AD, coinciding with the Little Ice Age (LIA); and (c) the Present Warm Period (PWP) from 1800 AD until the present, with warm and wet conditions. The sub-stages within the MWP and LIA intervals are also presented. The earlier MWP stage (900–1125 AD) was drier than the latter one (1125–1450 AD), and the earlier LIA stage (1450–1650 AD) was drier than the late LIA (1650–1800 AD). Increased solar irradiance and enhanced El Niño activities are related to the warm and humid climate during the MWP and PWP, whereas reduced solar irradiance and La Niña activities correspond to the cool and dry climate during the LIA. The present results provide insights into paleoclimatic changes in eastern monsoonal China and provide an understanding of centennial-scale climatic fluctuations and their driving factors. [ABSTRACT FROM AUTHOR]

We identified four climatic stages between 6.2 and 1.3 cal kyr before present (BP) based on pollen and charcoal concentrations by high‐resolution Accelerated mass spectrometer (AMS) 14C‐dated sediment profile from Taiwan's Toushe Basin. From 6.2 to 4.6 cal kyr BP, the region was warm‐wet with infrequent wildfires and dominant subtropical evergreen broad‐leaved forests. The climate was cooler‐drier from 4.6 to 3.0 cal kyr BP, with a decline in forest and increased fire frequency. From 3.0 to 2.1 cal kyr BP, climate further cooled and dried, with the development of alpine meadows and higher fire frequency. The region became warmer and wetter from 2.1 to 1.3 cal kyr BP, accompanied by forest recovery. Climatic changes were linked to changes in East Asia Summer Monsoon intensity, which is mainly controlled by solar radiation. Wildfires were likely controlled by precipitation variability that is influenced by East Asia Summer Monsoon and El Niño–Southern Oscillation. Toushe Basin experienced drought conditions and frequent wildfires during the El Niño years. Plain Language Summary: The purpose of our study is to reveal the relationship between paleoclimate, vegetation, and wildfire. The study area is located in the Toushe Basin, central Taiwan. Through palynological and charcoal analysis, the vegetation, climate, and wildfire history of the past 6,000 to 1,000 years in the study area were reconstructed. The study found that after 4,600 years, the East Asian summer monsoon continued to weaken until approximately 2,000 years ago, during which time the climate was dry and cool, and wildfires were frequent. In addition, it is found that the climate in this region is mainly controlled by the changes in solar radiation. The cycle of climate change coincides with that of solar activity. In El Niño years, the Toushe Basin was dry and frequent wildfires occurred. Key Points: Four climatic stages identified between 6.2 and 1.3 cal kyr BP based on pollen and charcoal concentrationsClimatic changes were linked to changes in East Asia Summer Monsoon intensity, which is mainly controlled by solar radiationThe Toushe Basin experienced drought conditions and frequent paleowildfires during the El Niño years [ABSTRACT FROM AUTHOR]

Climate evolution and hydrological conditions have been crucial factors for cultural development on the east coast of China. The Hangjiahu Plain, given its unique geographic and bioclimatic location, and plentiful Neolithic sites, is an ideal area in which to examine the relationship between environmental change and cultural development along the Lower Yangtze River. We report high-resolution pollen, algae, spore, charcoal, total organic carbon and grain size data from core BHQ2, collected from the Beihu Wetland on the Hangjiahu Plain. The record spans the period from 6300 to 400 cal yr BP. We infer that the climate shifted from warm and wet during the middle Holocene to dry in the late Holocene. Warm and stable hydrological conditions in the Beihu Wetland area during the intervals 6300–6000 and 5300–4250 cal yr BP were optimal for the development of the Majiabang and Liangzhu Cultures. Turbulent, brackish-water conditions in the Beihu Wetland area from 6000 to 5300 cal yr BP, however, led people of the Songze Culture to abandon the area. Collapse of the Neolithic culture and abandonment of the site at Liangzhu City could have been linked to climate drying in the interval 4250–3500 cal yr BP. Dry climate and the turbulent, saltwater environment that prevailed from 3800 to 3600 cal yr BP made conditions difficult for the Maqiao Culture. After 3600 cal yr BP, brackish water gradually receded and local rice agriculture expanded. Persistent warfare during the Warring States Period and the Qin-Han Dynasties may have been a response to colder climate from 2300 to 2000 cal yr BP. The decrease in monsoon precipitation in the Hangjiahu Plain region was influenced by summer solar radiation during the middle to late Holocene. [ABSTRACT FROM AUTHOR]

Our knowledge about the Holocene evolution of the East Asian summer monsoon (EASM) and its relation to human activities remains incomplete. A detailed palynological investigation of two sediment sections from the Daiyun Mountain Nature Reserve (ca. 25°38′–25°44′N, 118°05′–118°21′E, Fujian Province) suggests EASM-controlled subtropical climate conditions that were wetter and warmer than present over the early and middle Holocene. After 5700 cal. yr BP, steadily increasing non-arboreal pollen and fern spore percentages imply an attenuation of the EASM. The general climate trend is interrupted by several century-scale changes in composition and concentration of arboreal pollen taxa around 8200, 7200, 6300, and 4400 cal. yr BP, coinciding with weaker precipitation (and lower temperature) as suggested by the EASM oxygen isotope record. Our results further support the hypothesis that the natural vegetation cover of southern China was not markedly affected by human activities until 3000 cal. yr BP. The pollen records suggest a quick decrease in the forest cover ca. 3000–2450 cal. yr BP followed by a generally open (agricultural) landscape and spread of secondary pine forests. This pattern is in line with a major population growth promoted by the southward expansion of rice-based agriculture across the region that postdates the widely accepted ‘Holocene climate optimum’ by several millennia. This highlights the multidimensional significance of this term, which is commonly used in palaeoenvironmental and archaeological studies and should be consequently applied with respect to the specific issue under consideration. [ABSTRACT FROM AUTHOR]

The Taihu Lake basin is one of the most sensitive areas to climate change in the East Asian summer monsoon (EASM) influenced region. There are significant differences regarding the interpretation of climate history for this area during the Holocene due to a lack of high-resolution paleoclimate records. To better understand this scientific issue, here we provide a new record of Holocene climate change from the western part of Taihu Lake region, East China. A 4-m-depth profile from Gaochun has provided a 13,200-year record of climate change. Holocene climate change was reconstructed for the western part of Taihu Lake area based on various proxy records including pollen, charcoal, degree of humification (DOH), and loss on ignition (LOI) from the Gaochun site. The results indicate that climate during the late Pleistocene (13,200–10,700 cal yr B.P.) and early Holocene (10,700–8000 cal yr B.P.) was warm and humid, alternated with several cold and dry intervals. The late Pleistocene and early Holocene was a transitional period from cold-dry to warm-wet climates. The middle Holocene (8000–4400 cal yr B.P.) was still warm and humid, with a relatively stable climate. The period between 8000 and 5300 cal yr B.P. was the Holocene climate optimum (HCO). During the late Holocene (4400–0 cal yr B.P.), the climate was cool but still humid. In addition, climate change at the western part of Taihu Lake during the late Pleistocene and Holocene was unstable, containing several short-term climate events such as Younger Dryas (YD), 8.2 ka, and 4.2 ka events. These abruptly occurred climate events were indicated by various paleoclimatic proxy indicators, and can be compared with related records from other regions. Our findings suggest that the EASM strength was strongest during the middle Holocene between 8000 and 5300 cal yr B.P. which can be depicted as the period of HCO. [ABSTRACT FROM AUTHOR]

Numerous environmental archaeology studies have been undertaken in the middle and lower reaches of the Yangtze River, but limited research has been carried out in the upper reaches of the Yangtze River (UYR). During the period of the Baodun Culture (approximately 4500–3700 cal. yr BP), the inhabitants of the Chengdu Plain (CDP) in the UYR of southwestern China were confronted with a dynamic climate. Archaeological sites, including 9 walled sites located in a relatively small region, were built during the migration process. This paper attempts to demonstrate the linkage between the evolutionary history of the Baodun Culture and paleoclimate change. Subsistence strategies during the Baodun period, such as farming, tool use and food resources were investigated. Furthermore, the spatiotemporal distribution of the archaeological sites, the construction method of the sites' walls, and the growth of weeds were examined and assessed based on archaeological excavations and the literature. The ancient water network at the Baodun site was investigated based on auger surveys and borehole data. By comparing multiple paleoclimatic proxies from regions mainly controlled by the Indian Monsoon, we found that: (1) the drying and cooling climate conditions were responsible for the increases of proportions of millet and supplementary food resources and for the transformation of tool assemblages during the late Baodun period; (2) the increasing numbers of flood events were caused by the weakening of the monsoon and the dramatic climate during the Baodun period, and the interconnected river networks at low elevations in the CDP exacerbated the impact of flooding, which may have partially caused the frequent human migration and the construction method of the site walls; (3) the Baodun people that originally lived in the southwestern and western CDP were forced to gradually migrate to higher elevations in the northern and central territories because of the rapid climate change; and (4) the topography and river-grade also influenced human migration and settlement selection. Climate deterioration hindered the sustainable development of the Baodun Culture and eventually caused it to decline. Common subsistence strategies in human history, such as site location, migration, flood-control methods, agricultural changes, and food diversification, played important roles in the Baodun people's adaptation to climate change. [ABSTRACT FROM AUTHOR]

Reconstructing the vegetation history of southwest China since the Last Glacial Maximum is crucial for understanding the evolution of the Indian summer monsoon. In this study, we present a high-resolution palynological investigation from a 5 m core from the Ganchi peatland (southwest margin of the Sichuan Basin, southwest China) in order to reconstruct regional vegetation and climate over the last 25 kyrs. The succession, from bottom to top, comprises lake, wetland, and peat deposits, and wetland/aquatic pollen types are found to be a sensitive indicator of palaeoenvironmental change. Deciduous broad leaf forests dominated by Betula were present between 25-18 cal kyrs BP, suggesting a cold and dry climate during the Last Glacial Maximum. After 18 cal kyrs BP, temperature and summer insolation increased gradually, marking the Lateglacial transition. Thermophilous and hygrophilous species expanded between 11-8 cal kyrs BP, indicating a progressively warmer and wetter climate. From 8-4 cal kyrs BP, evergreen forests developed, while Tsuga reached its maxim abundance, implying a warm and humid climate coincided with the mid-Holocene climatic optimum. Results indicate that residual ice sheets may have impeded the northward shift of the Intertropical Convergence Zone, resulting in peak Holocene warmth lagging behind peak summer insolation forcing. Vegetation change was primarily controlled by climate, with no obvious evidence of anthropogenic disturbance until the last 1 cal kyrs BP. Our study shows that vegetation and climate in the southwest margin of the Sichuan Basin were controlled by summer insolation and ice sheet dynamics, and also influenced by sea surface temperature in the Indian Ocean. • High-resolution pollen records revealed vegetation and climate history since 25 cal kyrs BP • Variations in proxies were highly correlated with depositional processes • Paleovegetation records suggest that the Holocene climate optimum occurred during 8-4 cal kyrs BP • The most conspicuous landscape transformation caused by human impact in the Sichuan Province began at ∼1 cal kyrs BP [ABSTRACT FROM AUTHOR]

Nearly 200000 animal skeletons are unearthed in the Unit T0202 from Zhongba Site of Zhongxian County. According to the analysis of 129165 specimens, these skeletons may be classified into 5 kinds, namely, Mammalia, Osteichthys, Ayes, Amphibian and Reptilia, which belong to 13 orders, 28 families and 42 genera. In this paper, based on archeological dating and AMS14C data, through statistically analyzing the unearthed skeletons and studying the change of the smallest individual numbers, these research results detected the following: 1) In almost all the time of 2370-200 BC, in Zhongba region, some animals distributed widely, such as Muntiacus sp, Elaphodus cephalophus and Muntiacus sp. inhabiting in glade and grassland, Scrofa sp. and Canis famiiaris raised by the ancient people, rodentia rabbit and Rattus rattus, which suggested that a fairly good ecological environment of forest and grassland was preserved at that period and the predecessors began to raise domestic animals from 1750 to 1000 BC, which has lasted until today. 2) Rhinoceros only lived during 2000-1750 BC, 1000-700 BC and 700-500 BC, which indicates that the ecological environment of grassland and wetland might be better in these phases. 3) Macaca sp. and Ursus arctos appeared only after 1750-1000 BC, which may show that the forest condition is better for animals to live during 1750-200 BC. 4) The smallest individual numbers of Bublus sp., bos sp. and otters emerged during about 2370-1750 BC, which perhaps infers that water area during the early period was wider than that of the late period. 5) Since skeletons of rhinoceros are discovered in strata of Zhongba Site during 2000-1750 BC and 1000-500 BC, according to the climate and ecology environment which rhinoceros live in now, the average annual temperature and precipitation during 2000-1750 BC and 1000-500 BC are supposed to be probably higher than that of today. Although Zhu Kezhen considered that the first low temperature period in the past 5000 years of China was between 1100 BC and 850 BC, massive pollen of Morus, Ulmus, Fagus, Quercus, Castanea, etc. were found in Dajiuhu peat at that time, which should indicate that the climate was still moderate for living things to live at least in Dajiuhu basin and Zhongba Site. 6) Because skeletons of Gervus albirostris were unearthed during 310-200 BC at Zhongba Site, based on the climate and the ecological environment those animals live in now, the average annual temperature and the average annual precipitation in Zhongba area between 310 BC and 200 BC should be lower than those of today, which is confirmed by the TOC research of Zhongba Site strata. [ABSTRACT FROM AUTHOR]

The identified results of 121 surface sediment spore-pollen samples in Shennongjia and meteorological data base of 30 years (January, 1971-December, 2000) of 7 meteorological stations around Dajiuhu, Shennongjia are used in this study. Selecting 55 species of common spore-pollen with the method of space fitting and stepwise regression we construct the pollen climate factor transfer function of annual mean temperature: T= 7.649 - 2.33097XAbles-0.10873XBetula-0.17352XCompositae-0.131 76XCruciterae + 0.13356XEuphorbiaceae-0.83069XCampanuiaceae + 1.96494XPyrrosia + 0.38411 XPteris + 2.77741 XSelaginetta + 0.04439XMonoIites. We had reconstructed annual mean temperature series by use of the sporo-pollen samples concentration percentage in peat section with 297 cm thickness in Dajiuhu since 15.753 kaBP. The temperature series reflect well the character of climatic change since the late glacial, which indicates extreme cold climate event of the Oldest Dryas, the Older Dryas, the Younger Dryas and the 8.2 kaBP, the same to the climate fluctuations of Boiling Warm Period and Allerod Warm Period, and the character of temperature change fluctuating frequently at the transition age from the late glacial to the Holocene. The reconstructed temperature also indicate Holocene Optimum, late Holocene warm-dry climate, and the character of climatic change in Dajiuhu in the last 1 ka. The conclusion is that the sporo-pollen samples have important climatic significance to surface sediment and the section of Dajiuhu, Shennongjia and important reference value to studying climatic change during the last glaciation by the temperature transfer function and reconstructed temperature series. [ABSTRACT FROM AUTHOR]

Constructing a mathematic transfer function of pollen and climatic factors is one of the most important approaches in the quantitative reconstruction of paleoclimate elements. In the function building, the key point is the response sensitivity to the climate change for different pollen families and categories. As an example in this paper, the pollen samples from the surface and stratum in Dajiuhu basin, Shennongjia are used to estimate the sensitivity of pollen factor-temperature in the transfer function by the EOF analysis, multiple regression and stepwise regression techniques. Thereafter, the selection methods of pollen factors are discussed and compared with other results from different researchers. The results show that in the pollen samples, the quantity of woody plants is larger than others, but the woody plants have relatively lower sensitivity and slow responses to the climate evolution and abrupt climate change. While the pollens from lower grade plants (herb and fern) have a relatively high sensitivity to the temperature change and fast response to the abrupt climate changes. Therefore, the pollen of herb and fern may significantly record the extreme events in the climate change. Also in different regions, the pollen samples have different sensitivity and optimum combination in the transfer functions. Final conclusion is that the stepwise regression is one of the best methods for transfer function building since it can obtain the maximum multiple correlation coefficients and optimum combination of sensitive pollen factors. [ABSTRACT FROM AUTHOR]

• Four phased sea-level rise were observed during ~7.9–~7.1 cal ka BP. • The abrupt cooling event from 7460 to 7230 cal a BP may have been a global event. • Broadleaved tree was high suggesting a strong monsoon during ~8.2–~7.0 cal ka BP. To understand vegetation dynamics and their response to climate changes and sea-level rise (SLR) on the northern coast of the Bohai Sea during a marine transgression period (8.2–7.0 cal ka BP), we obtained two sedimentary cores (HG01 and HG02) with high-resolution accelerator mass spectrometry carbon-14 (14C) data from the coastal plain of Bohai Bay in northeastern China. A general warming and wetting trend from 8190 to 7920 cal a BP was indicated by the greater abundance of deciduous broadleaved forest, which showed that the Asian summer monsoon was stronger over this period. The abundance of deciduous broadleaved trees was relatively high, which revealed that the climate was relatively warm and wet and that the Asian summer monsoon was strong, during the periods of 7920–7690 cal a BP and 7230–7020 cal a BP. Broadleaved tree abundance decreased over the intervening period—from 7610 to 7230 cal a BP—suggesting a declining monsoon, and relatively cool, dry climate. The abrupt cooling event from 7460 to 7230 cal a BP may have been a global event, closely related to the decrease in solar activity and rapid SLR before 7460 cal a BP. The results also showed that the large number of halophytes mainly Chenopodiaceae, sharply increased at times, mirroring four SLR fluctuation periods: 7940–7860 cal BP, 7760–7700 cal BP, 7560–7460 cal BP, and 7230–7130 cal BP. SLR in Bohai Bay occurred during warm and wet climate periods, and the phased SLR observed during ~7.9–~7.1 cal ka BP may have been the local manifestation of a global event. [ABSTRACT FROM AUTHOR]

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 °C (3–8 °C) lower during the Last Glacial Maximum (LGM, ∼21 ± 3 ka), and ∼ 2 °C (1–3 °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 first synthesis of regional paleoclimate variations in China over the past ∼21 ka. • State-of-the-art transfer functions between proxies and climate varibales in East Asia. • Averaged MAT in China was ∼5 °C lower during LGM, and 1–3 °C higher during HO. • Averaged MAP varied between 30 and 150%, with a greater seasonality during 8–5 ka. [ABSTRACT FROM AUTHOR]

The Holocene Temperature Conundrum refers to the mismatch between proxy-based temperature records and those based on climate model simulations. A possible reason for this mismatch is a putative proxy-based bias in reconstructed summer temperatures, and therefore, regional reconstructions of seasonal temperature are crucial for resolving the conundrum. In this paper, we reconstruct vegetation and climate changes over the last ∼10,000 years BP based on a high-resolution pollen record from Gushantun peatland, Changbai Mountains, Northeast China. Multiple quantitative reconstruction approaches were used and weighted averaging partial least squares regression (WAPLS) was found to be the most appropriate method for reconstructing Holocene temperature and precipitation. The reconstructed climate record shows that the Holocene Climate Optimum occurred between 8 ka and 6 ka and exhibited a cold month mean temperature that was 3 °C warmer than modern temperatures. Climate gradually cooled during late Holocene with a minimum cold month temperature of −19.6 °C. Four prominent cold events occurred around 8.7 ka BP, 7.8 ka BP, 5.7 ka BP, and 2.5 ka BP with an amplitude variation up to 3 °C. The synthesized seasonal temperature time series and a comparison with other proxies show that the decreasing trend in mean annual temperature is not a seasonal bias caused by summer temperature change. This study provides evidence of a Holocene seasonal temperature change at a regional scale and insights for further understanding of the Holocene Temperature Conundrum. • Reconstructed seasonal temperature changes based on a new high-resolution fossil pollen record in the Changbai Mountains • Synthesized climatic series in Northeast China to investigate the characteristics of regional temperature changes and their driving factors • Reconstructed winter temperature as evidence to address the alleged seasonal bias for the Holocene temperature conundrum [ABSTRACT FROM AUTHOR]

The East Asian summer monsoon (EASM) system plays a crucial role in regulating climatic and hydrological variability in East Asia. The hydrological effects of the EASM in eastern China during the Little Ice Age (LIA) remains controversial, however. Here, we established a relatively high-resolution palaeohydrological record over the last 700 years in East China via analyzing n -alkanes from a peat core. Mid- and long-chain (C 21 –C 25 and C 27 –C 31) n -alkanes account for more than 95% of the total odd‑carbon-numbered n -alkanes, with short-chain n -alkanes (C 17 –C 19) accounting for only 2.3% on average, suggesting that organic matter in the peat core originated primarily from vascular plants. Organic geochemical indices, including P aq (an indicator of contributions from aquatic plants), the average chain length (ACL) of long-chain n -alkanes, and C 31 /C 27 and C 23 /C 29 n -alkane ratios, suggest a transition from dry conditions during the middle LIA to wet conditions in the late LIA. Comparing P aq records from the study profile with previous records from the EASM region, we found that the northern and southern parts of eastern China showed contrasting changes in humidity during the LIA. Specifically, the southern part shifted from mid-LIA dry conditions to late-LIA wet conditions, whereas the northern part shifted from mid-LIA wet conditions to late-LIA dry conditions. This spatial heterogeneity in hydroclimate could be attributed to La Niña-like conditions and intense summer monsoons during the middle LIA and El Niño-like conditions and weak summer monsoons during the late LIA. Our study demonstrates the importance of understanding spatial heterogeneity of hydroclimatic changes to probe the mechanisms whereby EASM modulates regional climatic changes during the LIA. • We analyzed alkane proxies from a peatland in SE China to rebuild palaeohydrology. • Organic debris originate from a mixture of terrestrial and aquatic plants. • Alkanes reveal shifts from moderate wet to dry to wet conditions during the LIA. • Northern and southern parts of the EASM region show humidity contrast in the LIA. • This spatial heterogeneity in palaeohydrology may be linked to EASM and ENSO. [ABSTRACT FROM AUTHOR]

The quantitative reconstruction of Holocene paleoclimate is pivotal for unraveling the evolution of East Asian Monsoon (EAM). Some recent studies have highlighted the escalating human activities in the late Holocene, which could potentially pose significant challenges to the precise quantitative reconstruction of paleoclimate. In this study, we undertake a quantitative reconstruction of Holocene climate and human influence index (HII) based on pollen data from the Shiwangutian (SWGT) in Southern China. This is achieved by developing and applying a pollen-based calibration model utilizing Locally Weighted Average-Partial Least Squares Regression (LWWA-PLS) and the Modern Analogue Technique (MAT). Our findings reveal that evergreen forests experienced expansion between 11.6 and 9.0 cal ka BP, coinciding with elevated Mean Annual Precipitation (Map) and Mean Annual Temperature (Mat) levels. These patterns signify a progressively warm and wet climate during this period. Subsequently, evergreen forests achieved their maximum abundance between 9.0 and 4.0 cal ka BP, aligning with a notable increase in vegetation richness, indicating a warmer and wetter climate during the mid-Holocene. Notably, during the interval of 6.0–4.0 cal ka BP, the Map, Mat, and Precipitation of Warmest Month (Mpwa) reached the Holocene optimum, approximately 14% higher than modern. Consequently, we deduce that in the early and middle Holocene, when the monsoon was particularly strong, synchronous changes in precipitation fostered the regional expansion of evergreen broad-leaved forests. Furthermore, the record demonstrates a substantial reduction in forest cover and a noteworthy increase in the HII value since 4.0 cal ka BP, likely attributable to anthropogenic impacts. Our analysis suggests that the influence of anthropogenic activities surpassed that of natural climate factors in shaping regional vegetation cover. These findings offer insights into potential drivers of climate change. As a preliminary conclusion, we propose that the summer insolation, ice sheets, and meltwater fluxes were the primary controlling factors for climate variations during the early to mid-Holocene in Southern China. • Map, Mat, and Mpwa reached a Holocene peak between 6.0 and 4.0 cal ka BP. • An increased HII values since 4.0 cal ka BP, indicating anthropogenic influence. • Summer insolation, ice sheets, and meltwater fluxes were the primary drivers of climate change. [ABSTRACT FROM AUTHOR]

• The construction of water conservancy facilities is related to ancient floods. • Frequent flooding may be related to the climate background of about 4000a BP. • The floods are synchronized with those in the Yangtze and Yellow River basins. The earliest water conservancy facilities in the Chengdu Plain were found at the Hongqiaocun Site of about 4.0 ka before present, nearly 2,000 years earlier than the world-famous Dujiangyan Irrigation Project. In order to understand the background of the construction of the water conservancy project, we sampled and analyzed the ancient river profile TS20W13 near the water conservancy facilities. Sedimentology demonstrated that the 4th to 6th layers of the TS20W13 profile were the strongest stage of hydrodynamic force in the river. The Zr/Rb and Ba/Nb values indicated that the 4th to 7th layers might have been those layers of a time of frequent flooding in this ancient river. The results of zircon psephicity analysis also showed that the psephicity of the zircon at the 4th to 6th layers were the best, indicating that along this stage of the river, the average transporting force was the strongest. According to the OSL dating results and the above analysis, at around 4.0 ka BP, the Hongqiaocun Site was in the midst of a flood-prone period, which was synchronous with the ancient flood records of the Yangtze River and Yellow River Basin. The increase in flooding during this period might be related to the aggravation of climatic fluctuation by about 4.0 ka BP. In the context of the above environmental background, the ancient people at the Hongqiaocun Site built water conservancy facilities to withstand floods. [ABSTRACT FROM AUTHOR]

Quantitative reconstruction of past climate plays an important role in understanding global and regional climate changes and validating climate models. Although some important progress has been made in quantitative paleoclimate reconstructions based on terrestrial records in the Indian summer monsoon region, high-resolution quantitative studies spanning the last ∼20 ka are still relatively sparse with differing results. This study presents high-resolution quantitative variations in mean temperature of the coldest month (MTCM, the first controlling factor of the regional vegetation), mean annual temperature (MAT, the second controlling factor), and mean annual precipitation (MAP) from Lake Tengchongqinghai in southwestern China, based on an updated modern pollen dataset and the fossil pollen record spanning the last 18.5 ka. The results show that temperature and precipitation increased gradually from 18.5 ka, and peaked from 7.2 to 4.5 ka when MAT was on average 1.0 °C higher than the modern observational value (14.5 °C), corresponding to the mid-Holocene thermal maximum (HTM), and then decreased gradually. The total reconstructed ranges are between −2.2 and 9.2 °C for MTCM, 7.7 and 17.2 °C for MAT, and 840 and 1300 mm for MAP. On top of this overall climate trend, seven abrupt cold and dry events were detected during the periods of 16.2–14.8 ka, 12.8–11.5 ka, ∼11.1 ka, 9.1–8.4 ka, ∼7.7 ka, 4.3–3.7 ka, and 0.68–0.009 ka (1270–1950 CE). The results of this quantitative reconstruction were validated by both statistical and ecological evaluations. We conclude that the trend of climatic change since 18.5 ka in this study area was primarily driven by June, July, August, and September solar insolation and changes in radiative forcing and greenhouse gas concentrations. The abrupt changes may be caused by changes in the Atlantic meridional overturning circulation, solar activity, the position of the Intertropical Convergence Zone, and volcanic activity. • We present high-resolution pollen-based quantitative variations in MTCM, MAT and MAP from southwestern China. • The period 7.2–4.5 ka was the warmest and wettest period since 18.5 ka. • Seven abrupt cold and dry events were detected over the past 18.5 ka. • This study provides quantitative data support for ecological responses and climate mechanisms. [ABSTRACT FROM AUTHOR]

Vegetation–climate relationships are often different at varying spatial scales, which is seldom taken into account in reconstructing past climate changes from fossil pollen spectra represent more local vegetation composition but using regional or extra-regional modern pollen–climate calibration set. In this paper, we employ 2620 surface pollen spectra and six pollen sequences from continental East Asia to reconstruct Holocene climate with modern analogue technique. A novel data set of vegetation sensitivity index (VSI) is introduced to examine vegetation–climate relationships in 0.5° search windows around the fossil sites (local) and in the tailored calibration sets (regional). Then, we compare them to the explanatory abilities of (reconstructed) climate variables on explaining the pollen variance in calibration sets and in the fossil pollen data sets using constrained ordination, cross-validation and significance test. By this procedure that we called local–regional–fossil comparison, we can better determine which variable reconstruction is valid and useful. In our cases, moisture variable reconstructions in temperate forest-steppe ecotone at the East Asian summer monsoon margin are reliable. Consistent Holocene moisture variations with a strong monsoon influence during 8.6–4.0 cal ka BP which can help us to better interpret human adaptations along the Great Wall. However, quantitative climate reconstructions at some sites are less reliable due to highly heterogeneous vegetation sensitivities surrounding the site, particularly for areas with complicated topographical contexts. We stress that vegetation sensitivities at local and regional scales both need to be investigated before conducting quantitative climate reconstruction. [ABSTRACT FROM AUTHOR]

Terrestrial palaeo-temperature data are of great value in improving our understanding of past climate and they provide a basis for evaluating climate simulations. Such data are, however, poorly constrained for long time-scales. In addition to the scarcity of high-quality continuous time-series, finding proxies with a clear response to past temperature changes and developing appropriate reconstruction methods are major challenges. We present a new and robust method – Locally-weighted Weighted-average partial least squares (LW-WAPLS) to reconstruct quantitative temperature changes based on a high-resolution 1.74-Ma pollen record from the Zoige Basin on the eastern Tibetan Plateau, where the vegetation today is mainly controlled by temperature. The reconstructed mean annual (MAT) and warmest month (MTWM) temperatures reveal a general cooling trend with two major shifts at ~1.54 and 0.62 Ma BP, and regular glacial-interglacial variability ranging from ~ − 4 to 2 °C and from 8 to 16 °C, respectively. They indicate ~4–5 °C (MAT) and ~ 5–6 °C (MTWM) magnitudes of glacial-interglacial temperatures. Both statistical and ecological evaluations validate the reliability of the reconstructions. The reconstructions provide important insights into the spatial aspects of long-term terrestrial temperature change. LW-WAPLS shows advantages over both the traditional modern analogue technique and non-linear transfer-function methodologies such as WAPLS for reconstructing the broad-scale climate changes for the Zoige Basin, by combining the strength of both methods. The LW-WAPLS approach potentially provides a robust tool to develop pollen-based climate reconstructions over long time-scales. • LW-WAPLS approach is a powerful tool for the quantitative reconstructions of climate on glacial-interglacial scales. • Temperature reconstructions of the eastern Tibetan Plateau reveal the stepwise cooling trend with two major shifts at 1.54 and 0.62 Ma BP and with ~4-5oC (MAT) and 5-6oC (MTWM) magnitude. • Our long-term temperature reconstruction fills a data gap in mid-latitude terrestrial regions • The results provide valuable data for model simulations to elucidate the climate mechanisms [ABSTRACT FROM AUTHOR]