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Paleoclimatic records reveal spatially asynchronous changes of East Asian summer monsoon (EASM) precipitation during the Holocene, but the underlying mechanisms are not fully understood. This study explores the role of the zonal shift of the Asian westerly jet (AWJ) core on the spatial‐temporal variability of EASM precipitation based on Holocene climate simulations using the KCM and CESM forced by orbital variations. We analyzed the composite differences of summer precipitation and associated atmospheric circulations between the early (middle) and middle (late) Holocene. Simulations suggest a dipole pattern of summer precipitation with increasing (decreasing) precipitation in central (southern) China from the early to late Holocene, which was shaped by the eastward shift of the AWJ core. The eastward shift of the AWJ core and the accompanied eastward movement of the upper‐level convergence over the AWJ's right exit region weakened the low‐level downward motions over central China. Meanwhile, the low‐level upward motions over southern China were weakened by the concurrent eastward (westward) migration of the South Asian High (western Pacific subtropical High) during the Holocene. Consequently, summer precipitation increased (decreased) in central (southern) China from the early to late Holocene. The eastward shift of the AWJ core was primarily driven by amplified meridional insolation gradient at middle latitudes via strengthening upper‐level westerly intensity during the Holocene. In addition, land cover difference between East Asia and central Asia caused a greater enhancement of westerlies intensity in East Asia, further modulating the eastward movement of the AWJ core during the Holocene. Key Points: Our simulations reveal a dipole pattern of summer precipitation between central and southern China during the HoloceneThe dipole precipitation pattern was strongly modulated by zonal shift of the Asian westerly jet coreInsolation variation and land cover caused the eastward shift of the Asian westerly jet core during the Holocene [ABSTRACT FROM AUTHOR]

Numerous paleoclimate records on reconstructed monsoon precipitation isotopes (δDp and δ18Op) have been published to infer past hydroclimate changes in Asian monsoon region. However, there are still debates on whether or not these reconstructed δDp or δ18Op can represent changes of monsoon precipitation. In this study, we report a ~ 5000 year record of leafwax hydrogen isotope (δDwax) from a 6.67-m-long sediment core collected in Beilianchi (BLC) Lake in the southwestern Chinese Loess Plateau. Based on analyses of the instrumental precipitation isotopes, precipitation amounts, and moisture sources, we find that δDp in the southwestern Chinese Loess Plateau shows distinct negative correlation with amounts of summer (from April to September) monsoon precipitation at inter-annual scales. This is further supported by the observed negative relation between precipitation amounts and regional lake-sediments and speleothems inferred δDp (or δ18Op) values at decadal scales over the past 60 years. Therefore, our reconstructed ~ 35-year resolution monsoon precipitation, inferred from δDwax, reveals a long-term decrease since the mid-Holocene. Superimposed on this trend, there are several multi-centennial to millennial-scale fluctuations for increased monsoon precipitation at 4500–4000 years BP, 2900–2400 years BP and 1200–700 years BP and decreased precipitation at 3900–3000 years BP, 2200–1300 years BP, and 500–0 years BP. Reanalyses of instrumental data and Kiel Climate Model on regional atmosphere circulations show that moisture of this region is mainly derived from the western Pacific Ocean through the East Asian summer monsoon circulation at inter-annual to inter-decadal, and millennial timescales. We conclude that monsoon rainfall in the southwestern Chinese Loess Plateau is likely connected with changes in sea surface temperatures and migrations of the ITCZ in the western Pacific Ocean. [ABSTRACT FROM AUTHOR]

Projecting how the East Asian summer monsoon (EASM) rainfall will change with global warming is essential for human sustainability. Reconstructing Holocene climate can provide critical insight into its forcing and future variability. However, quantitative reconstructions of Holocene summer precipitation are lacking for tropical and subtropical China, which is the core region of the EASM influence. Here we present high-resolution annual and summer rainfall reconstructions covering the whole Holocene based on the pollen record at Xinjie site from the lower Yangtze region. Summer rainfall was less seasonal and ~ 30% higher than modern values at ~ 10-6 cal kyr BP and gradually declined thereafter, which broadly followed the Northern Hemisphere summer insolation. Over the last two millennia, however, the summer rainfall has deviated from the downward trend of summer insolation. We argue that greenhouse gas forcing might have offset summer insolation forcing and contributed to the late Holocene rainfall anomaly, which is supported by the TraCE-21 ka transient simulation. Besides, tropical sea-surface temperatures could modulate summer rainfall by affecting evaporation of seawater. The rainfall pattern concurs with stalagmite and other proxy records from southern China but differs from mid-Holocene rainfall maximum recorded in arid/semiarid northern China. Summer rainfall in northern China was strongly suppressed by high-northern-latitude ice volume forcing during the early Holocene in spite of high summer insolation. In addition, the El Niño/Southern Oscillation might be responsible for droughts of northern China and floods of southern China during the late Holocene. Furthermore, quantitative rainfall reconstructions indicate that the Paleoclimate Modeling Intercomparison Project (PMIP) simulations underestimate the magnitude of Holocene precipitation changes. Our results highlight the spatial and temporal variability of the Holocene EASM precipitation and potential forcing mechanisms, which are very helpful for calibration of paleoclimate models and prediction of future precipitation changes in East Asia in the scenario of global warming. [ABSTRACT FROM AUTHOR]

Abstract The East Asian summer monsoon (EASM) is a complex system that brings precipitation to East Asia showing considerable spatiotemporal variations. This study explored the zonal differences of summer precipitation in Northeast Asia at orbital timescales during the Holocene by comparing proxy records with simulation results. At orbital timescales, there was generally an east–west antiphasing of summer precipitation in Northeast Asia during the Holocene. Model–proxy comparison revealed that the driest interval occurred during the late Holocene in western Northeast Asia and during the early to middle Holocene in eastern Northeast Asia. Changes of summer precipitation in western Northeast Asia were mainly influenced by precession-driven EASM circulation. On the one hand, a weaker EASM circulation during the late Holocene weakened water vapor transport from the North Pacific Ocean to Northeast Asia, and on the other hand it was associated with anomalous downward motions in western Northeast Asia. Both factors were in favor of a reduction of summer precipitation in western Northeast Asia during the late Holocene. In contrast, anomalous downward motions prevailed in eastern Northeast Asia during the early to middle Holocene, which were probably related to stronger western Pacific subtropical high and weaker westerlies. The effect of the anomalous downward motions overwhelmed the enhanced water vapor transport, leading to a dry climate in this area from the early to middle Holocene. This study suggests that special care should be taken when discussing the meridional shift of the Holocene climatic optimum in the EASM region due to the zonal precipitation contrast. Highlights • We compare proxy moisture records in Northeast Asia with the results from a transient simulation. • An east–west antiphasing of summer precipitation in Northeast Asia during the Holocene is found. • The East Asian summer monsoon circulation and mid-latitude westerlies caused the zonal precipitation contrast. [ABSTRACT FROM AUTHOR]

The precipitation changes on the northeastern Tibetan Plateau during the Holocene remain unclear due to discrepancies among different proxy records. We compared proxy records with the results from a transient simulation performed using the Kiel Climate Model forced by orbital variations, to analyse summer precipitation changes in this area during the Holocene (9.5-0 ka BP). The model results suggested increasing amounts of summer precipitation from 9.5 to ~6.2 ka BP and a persistent decline thereafter, which matched well with pollen records but was inconsistent with ostracod δ18O records. The Holocene climatic optimum lagged the Northern Hemisphere summer insolation maximum by ~3.5 ka, caused by the interplay between the East Asian summer monsoon (EASM) circulation and the mid-latitude westerlies. The ostracod δ18O values reflected the strength of the EASM circulation. A strong EASM circulation increased the transport of water vapour towards the northeastern Tibetan Plateau from the northwestern Pacific. Weakened mid-latitude westerlies increased the incursion of cold air masses into the northeastern Tibetan Plateau. During the early Holocene, relatively strong mid-latitude westerlies, resulting from an enhanced Arctic Oscillation, reduced summer precipitation on the northeastern Tibetan Plateau, in spite of a strong insolation-driven EASM circulation. The weakening EASM circulation and the strengthening westerlies together induced the decreasing trend of summer precipitation from the middle to late Holocene. In addition, summer precipitation variations were further modulated by sea-surface temperatures in the northwestern Pacific, through weakening the strength of the EASM. [ABSTRACT FROM AUTHOR]

Quantitative proxy-based and high-resolution palaeoclimatic datasets are scarce for the lower reaches of the Yangtze River (LYR) basin. This region is in a transitional vegetation zone which is climatologically sensitive; and as a birthplace for prehistorical civilization in China, it is important to understand how palaeoclimatic dynamics played a role in affecting cultural development in the region. We present a pollen-based and regionally-averaged Holocene climatic twin-dataset for mean total annual precipitation (PANN) and mean annual temperature (TANN) covering the last 10,000 years for the LYR region. This is based on the technique of weighted averaging-partial least squares regression to establish robust calibration models for obtaining reliable climatic inferences. The pollen-based reconstructions generally show an early Holocene climatic optimum with both abundant monsoonal rainfall and warm thermal conditions, and a declining pattern of both PANN and TANN values in the middle to late Holocene. The main driving forces behind the Holocene climatic changes in the LYR area are likely summer solar insolation associated with tropical or subtropical macro-scale climatic circulations such as the Intertropical Convergence Zone (ITCZ), Western Pacific Subtropical High (WPSH), and El Niño/Southern Oscillation (ENSO). Regional multi-proxy comparisons indicate that the Holocene variations in precipitation and temperature for the LYR region display an in-phase relationship with other related proxy records from southern monsoonal China and the Indian monsoon-influenced regions, but are inconsistent with the Holocene moisture or temperature records from northern monsoonal China and the westerly-dominated region in northwestern China. Overall, our comprehensive palaeoclimatic dataset and models may be significant tools for understanding the Holocene Asian monsoonal evolution and for anticipating its future dynamics in eastern Asia. [ABSTRACT FROM AUTHOR]

The moisture history in arid central Asia (ACA) differs from that in the Asian monsoon region during the Holocene. Much less is known about causes of Holocene moisture changes in ACA than Asian monsoon precipitation changes, hampering our understanding of their spatiotemporal differences. In this study, orbital-scale evolution of winter rainfall in northwestern China (a part of the core zone in ACA) during the Holocene and possible driving mechanisms are investigated using results from a long-term transient simulation performed by an atmosphere–ocean–sea-ice coupled general circulation model, the Kiel Climate Model, forced by orbital variations. Our results reveal a persistent wetting trend in northwestern China in winter throughout the Holocene, which is in response to winter insolation at mid-northern latitudes. Winter insolation can influence the rainfall via three ways. First, increasing latitudinal gradient of the incoming solar insolation at mid-latitudes strengthens the westerly intensity. Second, the evaporation is enhanced because of insolation-induced winter temperature rising, resulting in an increase in the air humidity. Intensified westerly winds and the increased water vapour together are conductive to enhance moisture transport towards northwestern China and thus increase winter precipitation in this area. Third, the increasing trend of winter insolation weakens the East Asian winter monsoon, which is favourable for the formation of rainfall via crippling the Siberian High that is beneficial for atmospheric lifting motion. [ABSTRACT FROM AUTHOR]

To better understand the long-term changes of the East Asian summer monsoon precipitation (Pjja), quantitative reconstructions and model simulations are needed. Here, we develop continental-scale pollen-based transfer functions for Pjja with weighted averaging–partial least squares (WA-PLS) regression and a Bayesian multinomial regression method. We apply these transfer functions to a set of fossil pollen data from monsoonal China for quantitatively reconstructing the Pjja changes over the last 9500 years. We compare the reconstructions with Pjja simulations from a coupled atmosphere–ocean–sea ice general circulation model (the Kiel Climate Model, KCM). The results of cross-validation tests for the transfer functions show that both the WA-PLS model (r2 = 0.83, root mean square error of prediction (RMSEP) = 112.11 mm) and the Bayesian model (r2 = 0.86, RMSEP = 107.67 mm) exhibit good predictive performance. We stack all Pjja reconstructions from northern China to a summary curve. The stacked record reveals that Pjja increased since 9500 cal. yr BP, attained its highest level during the Holocene summer monsoon maximum (HSMM) at ~7000–4000 cal. yr BP and declined to present. The KCM output and the reconstructions differ in the early-Holocene (~9500–7000 cal. yr BP) where the model suggests higher Pjja than the reconstructions. Moreover, during the HSMM, the amplitude of the Pjja changes (~20–60 mm above present) in simulations is lower than the reconstructed changes (~70–110 mm above present). The rising (declining) Pjja patterns in reconstructions before (after) the HSMM are more pronounced and fluctuating than in simulations. Other palaeohydrological data such as lake-level reconstructions indicate substantial monsoon precipitation changes throughout the Holocene. Our results therefore show that the KCM underestimates the overall amplitude of the Holocene monsoon precipitation changes. [ABSTRACT FROM AUTHOR]

The term 'westerlies-dominated climatic regime' describes the pattern of precipitation/moisture variations between westerlies-dominated arid Central Asia (ACA) and mid-latitude monsoon-dominated Asia on decadal to multi-millennial time scales. However, no attempts have been made to define its core region and the possible physical mechanisms responsible during the period of instrumental observations. The present study investigates the spatiotemporal variations of summer and winter precipitation on interannual to decadal time scales over mid-latitudes of the Eurasian continent using Empirical Orthogonal Function (EOF) analysis. Our results suggest the existence of an opposing pattern of summer precipitation variations between ACA and mid-latitude monsoon-dominated Asia and Mediterranean on decadal time scales. Based on these results, the core region influenced by the westerlies is outlined, including arid central Asia and Xinjiang in China (36°-54°N, 50°-90°E). By using monthly NCEP-NCAR reanalysis, the relationship between the 'westerlies-dominated climatic regime' and atmospheric circulation were also analyzed. The combination of the zonal climatic teleconnection pattern and anomalous Indian summer monsoon precipitation (ISMP) causes the precipitation characteristics of the 'westerlies-dominated climatic regime' precipitation pattern. In addition, the Atlantic Multidecadal Oscillation (AMO) may also have an important effect on the 'westerlies-dominated climatic regime'. [ABSTRACT FROM AUTHOR]

Sensitive changes in precipitation influence the stability of semiarid ecosystem, rain‐fed agriculture, and densely populated society in northern monsoonal China (NC). However, shortage of regional‐scale quantitative syntheses imposes restrictions on investigating long‐term relationships among precipitation dynamics, possible climatic forces, and prehistoric demographic fluctuations. Herein, we contribute a regionally compiled anomaly record for Holocene annual mean precipitation (PANN) relative to its modern‐day values in NC. The Holocene PANN variations in NC may be essentially determined by changing thermal gradients of continental land‐ocean and west‐east equatorial Pacific, profoundly affecting strength and location of West Pacific Subtropical High that may principally modulate intensity of East Asian summer monsoon and resultant rainfall in NC. Importantly, variation partitioning analysis quantitatively demonstrates that the overall changes of precipitation (43.3%) may play a more important role than temperature (3.2%) and their shared effects (0.8%) in independently accounting for long‐term variation of regional‐scale Holocene population fluctuations in NC. Plain Language Summary: Quantitative inferences of regional‐scale precipitation fluctuations on time spans longer than instrumental climatic records are requested to better predict long‐term changes of East Asian summer monsoon that influences the lives of nearly one fourth of the total population in our world. Evaluating the possible role of large‐scale climatic changes on affecting human population sizes of the distant past is a pressing concern and remains contentious. In this study, for the first time, we provide a regionally synthesized record of Holocene precipitation anomalies relative to present‐day values for the monsoon‐influenced northern China. This composite record has been demonstrated to be reliable as a representative for reflecting broad‐scale precipitation variations across northern China. In addition, we first quantify the relative contribution from both precipitation and temperature on influencing the Holocene demographic changes in northern China. Our results suggest that precipitation may be more important compared with temperature when independently explaining the total variation in long‐term prehistoric population patterns. Key Points: First, we provide a regionally synthesized quantitative record for Holocene precipitation anomalies over northern China (NC)Precipitation dynamics in NC may be essentially related to changing thermal gradients of land‐ocean and west‐east equatorial PacificPrecipitation possibly plays a more important role than temperature in independently affecting long‐term prehistoric demographic variations in NC [ABSTRACT FROM AUTHOR]

Monsoon precipitation over China exhibits large spatial differences. It has been found that a significantly enhanced East Asian summer monsoon (EASM) is characterized by increased rainfall in northern China and by reduced rainfall in southern China, and this relationship occurs on different time scales during the Holocene. This study presents results from a diverse range of proxy paleoclimatic records from northern China where precipitation variability is traditionally considered as an EASM proxy. Our aim is to evaluate the evolution of the EASM during the Holocene and to compare it with all of the published stalagmite δ 18 O records from the Asian monsoon region in order to explore the potential mechanism(s) controlling the Chinese stalagmite δ 18 O. We found that the intensity of the EASM during the Holocene recorded by the traditional EASM proxy of moisture (or precipitation) records from northern China is significantly different from the Chinese stalagmite δ 18 O records. The EASM maximum occurred during the mid-Holocene, challenging the prevailing view of an early Holocene EASM maximum mainly inferred from stalagmite δ 18 O records in eastern China. In addition, all of the well-dated Holocene stalagmite δ 18 O records, covering a broad geographical region, exhibit a remarkably similar trend of variation and are statistically well-correlated on different time scales, thus indicating a common signal. However, in contrast with the clear consistency in the δ 18 O values in all of the cave records, both instrumental and paleoclimatic records exhibit significant spatial variations in rainfall on decadal-to-centennial time scales over eastern China. In addition, both paleoclimatic records and modeling results suggest that Holocene East Asian summer monsoon precipitation reached a maximum at different periods in different regions of China. Thus the stalagmite δ 18 O records from the EASM region should not be regarded as a reliable indicator of the strength of the East Asian summer monsoon. Furthermore, modern observations indicate that the moisture for precipitation in the East Asian monsoon region is mainly derived from the Indian Ocean. The moisture transport route from the Indian Ocean to the East Asian monsoon region during the Holocene is almost identical to that of modern precipitation. Therefore the strong correlation of δ 18 O records in the EASM and Indian summer monsoon (ISM) regions, and the similarity of the pattern of latitudinal changes in δ 18 O values in stalagmites and in modern meteoric precipitation along the water vapor transport route, further suggests that the stalagmite δ 18 O records from the EASM region are essentially a signal of the isotopic composition of precipitation, which is determined mainly by changes in the δ 18 O of atmospheric vapor in the upstream source region over the Indian Ocean and Indian Monsoon region via the upstream depletion mechanism. Finally, the main trends of the stalagmite δ 18 O records are strongly correlated with the known evolution of the ISM, and therefore these records reflect the history of the ISM rather than that of the EASM. Our findings support the conclusion that EASM variability is mainly controlled by Northern Hemisphere summer insolation and was strongly modulated by ice volume during the last deglaciation and early Holocene, which delayed the response of the EASM maximum to peak insolation forcing. [ABSTRACT FROM AUTHOR]

Our understanding on the spatial-temporal patterns of climatic variability over the last few millennia in the East Asian monsoon-dominated northern China (NC), and its role at a macro-scale in affecting the prosperity and depression of Chinese dynasties is limited. Quantitative high-resolution, regionally-synthesized palaeoclimatic reconstructions as well as simulations, and numerical analyses of their relationships with various fine-scale, numerical agro-ecological, social-economic, and geo-political historical records during the period of China's history, are presented here for NC. We utilize pollen data together with climate modeling to reconstruct and simulate decadal- to centennial-scale variations in precipitation or temperature for NC during the last 2200 years (-200–2000 AD). We find an overall cyclic-pattern (wet/warm or dry/cold) in the precipitation and temperature anomalies on centennial- to millennial-scale that can be likely considered as a representative for the entire NC by comparison with other related climatic records. We suggest that solar activity may play a key role in driving the climatic fluctuations in NC during the last 22 centuries, with its quasi ∼100, 50, 23, or 22-year periodicity clearly identified in our climatic reconstructions. We employ variation partitioning and redundancy analysis to quantify the independent effects of climatic factors on accounting for the total variation of 17 fine-grained numerical Chinese historical records. We quantitatively illustrate that precipitation (67.4%) may have been more important than temperature (32.5%) in causing the overall agro-ecological and macro-geopolitical shifts in imperial China with NC as the central ruling region and an agricultural heartland over the last 2200 years. [ABSTRACT FROM AUTHOR]

Abstract: Paleoclimate proxy records of precipitation/effective moisture show spatial–temporal inhomogeneous over Asian monsoon and monsoon marginal regions during the Holocene. To investigate the spatial differences and diverging temporal evolution over monsoonal Asia and monsoon marginal regions, we conduct a series of numerical experiments with an atmosphere–ocean–sea ice coupled climate model, the Kiel Climate Model (KCM), for the period of Holocene from 9.5 ka BP to present (0 ka BP). The simulations include two time-slice equilibrium experiments for early Holocene (9.5 ka BP) and present-day (0 ka BP), respectively and one transient simulation (HT) using a scheme for model acceleration regarding to the Earth's orbitally driven insolation forcing for the whole period of Holocene (from 9.5 to 0 ka BP). The simulated summer precipitation in the equilibrium experiments shows a tripole pattern over monsoonal Asia as depicted by the first modes of empirical orthogonal function (EOF1) of H0K and H9K. The transient simulation HT exhibits a wave train pattern in the summer precipitation across the Asian monsoon region associated with a gradually decreased trend in the strength of Asian summer monsoon, as a result of the response of Asian summer monsoon system to the Holocene orbitally-forced insolation change. Both the synthesis of multi-proxy records and model experiments confirm the regional dissimilarity of the Holocene optimum precipitation/effective moisture over the East Asian summer monsoon region, monsoon marginal region, and the westerly-dominated areas, suggesting the complex response of the regional climate systems to Holocene insolation change in association with the internal feedbacks within climate system, such as the air-sea interactions associated with the El Nino/Southern Oscillation (ENSO) and shift of the Intertropical Convergence Zone (ITCZ) in the evolution of Asian summer monsoon during the Holocene. [Copyright &y& Elsevier]