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The 4.2 ka event was a period of global drought and climate cooling linked to the widespread disruption of Neolithic culture. However, the detailed climatic changes during this period are not completely understood. In this paper, we report a high-resolution pollen record for the Dayanghu wetland in the Zhejiang region of southeastern China, which we use to infer mean annual precipitation (MAP) fluctuations during the period spanning 4600–4000 calendar years before present (cal. yr BP). There was a long-term trend of decreasing MAP during this interval, consistent with weakening of the East Asian Summer Monsoon since the mid-Holocene. This trend was punctuated by episodes of relatively high MAP at 4350–4320, ca. 4260, and 4220–4200 cal. yr BP, and extreme droughts at 4200 and 4150 cal. yr BP. We propose that solar activity promoted El Niño events and contributed to dramatic MAP fluctuations in the Dayanghu wetland. La Niña events and negative-phase intervals of the Pacific Decadal Oscillation may have been responsible for the extreme drought at 4200–4150 cal. yr BP. In summary, we propose a close relationship between MAP and solar forcing, with short-term enhanced solar activity increasing the intensity of the East Asian Summer Monsoon and contributing to increasing decadal variability in the inner tropical Pacific, which ultimately leads to increased precipitation variability in southeast China. The results improve our understanding of the detailed climatic features of the 4.2 ka event. • High-resolution pollen record for ca. 4.2 ka for the Zhejiang region, China. • Pollen-based mean annual precipitation was quantitatively reconstructed. • Long-term droughts tended to occur during 4600–4000 cal. yr BP. • La Niña-dominated ENSO contributed to a catastrophic drought at 4200–4150 cal. yr BP. [ABSTRACT FROM AUTHOR]

The abrupt weakening of the East Asian summer monsoon (EASM) during Younger Dryas (YD) has been attributed to freshwater discharge into the North Atlantic ocean and resultant Northern Hemisphere cooling. Recent studies have found that sea ice variability in the Nordic Sea during the YD exerted a great influence upon the northern high-latitude climate. However, the influence of sea ice upon EASM evolution during YD event remains unclear. In this paper, we report two precisely-dated speleothem oxygen isotope records from the EASM-dominated region of central China. Our records archive abrupt changes in EASM variability during the YD event. Initially, there was a significant strengthening of the EASM during the mid-YD following the gradually increased Atlantic meridional overturning circulation (AMOC). Later this trend reversed at ∼12.15 ka due to northern high-latitude sea ice fluctuations and a consequent reduction of AMOC. At the YD termination, abrupt intensification of the EASM was synchronous with the rapid decline of sea-ice and recovery of the AMOC indicating that sea ice variability was a significant influence on high latitude climate and EASM variation during the YD. • A new speleothem δ18O record show significant EASM strengthening during mid-YD. • Mid-YD oscillation in EASM linked with NH sea ice variability. • Abrupt EASM intensification at YD termination synchronous with the rapid decline of sea ice. • Drier interval following the YD termination in central China. [ABSTRACT FROM AUTHOR]

The Salawusu River Valley cuts through the Mu Us Desert in north central China, and lies at the interface of the East Asian Summer and Winter Monsoonal regions. Exposed at numerous locations in the valley side are extensive late Quaternary deposits, consisting of interbedded aeolian sands, fluvio-lacustrine units and palaeosols. Due to the importance of the location in potentially elucidating both summer and winter monsoonal regimes, and the quality of the sedimentary record, the region has a rich history of study, and yet even within the Holocene sequence, many conflicting interpretations have arisen based on studies on different sections. This paper aims to synthesize and explore these differences by exploring the lateral continuity of the Holocene sequences along a ~ 45 km reach of the valley, and presenting new, detailed physical and geochemical analyses of three sections, focusing on the lacustrine Holocene Dagouwan Formation. The absence of the lacustrine unit at several locations confirms that rather than representing a single lake, the Dagouwan Formation instead represents a series of palaeolakes, probably at least partially hydrologically isolated from each other by aeolian sands. All begin with sand-dominated deposits during the early−/mid-Holocene, which is interpreted as the result of abundant sand-supply to the north and west, under the influence of an enhanced East Asian Winter Monsoon, and all switch to silt-dominated, more carbonate-rich deposits during the mid−/late-Holocene, which is attributed to an enhanced East Asian Summer Monsoon bringing loessic silts from the Chinese Loess Plateau to the east and south. The timing of this change, perhaps as late as 5.5 ka, supports the idea of a relatively enhancement late mid-Holocene of the summer monsoonal circulation in the region. However, despite the proximity of the sections and consistent analytical approaches, marked differences between the sections occur in all proxies studied. The timing and rate of the switch from sand- to silt-dominated lacustrine deposition varies between the sites by as much as 2000 years within just a few kilometres of each other, and at some sites the switch was gradual, whereas at others it was very rapid. Similar dramatic variations are also seen with organic carbon content, carbonate content, C:N ratio, and especially the δ13C isotopic ratio. These point to the lake basins behaving very differently, and emphasize that consideration must be given to the local geomorphology and palaeolimnological evolution of individual sections. • Differences in lacustrine Holocene monsoon records in northern China are explored. • The occurrence of the lakes is geomorphologically, not climatologically, controlled. • Different sections of similar units represent different lakes with varied histories. • Consistent changes in sediment suggest mid-Holocene decline of winter monsoon. • Study of individual sections or proxies cannot be used to infer regional climate. [ABSTRACT FROM AUTHOR]

Abstract The Eocene was an interval of climate evolution, when the extreme high temperatures of the earliest Cenozoic gave way to a global cooling trend. Fine-grained lacustrine sediments of Eocene age from northeastern China represent an excellent archive to study long-term environmental and climatic changes at high-resolution. The Huadian Basin is a Cenozoic, fault-bounded basin in Jilin Province, northeastern China. Though small in area, it contains numerous oil shale- and coal-bearing layers, which provide an abundant Middle to Late Eocene palynoflora. Eighty-five palynomorph genera and one hundred palynomorph species were identified in the Huadian Formation, allowing to distinguish 4 palynozones. The nearest living relatives of the recovered palynomorph taxa suggest the presence of subtropical evergreen and deciduous broad-leaved forests during deposition of the Huadian Formation. Using the coexistence approach (CA), we calculated seven paleoclimatic parameters, which indicate a subtropical warm and humid climate with a mean annual temperature above 13.6 °C and a mean annual precipitation of at least 887 mm. However, the climate became cooler and drier during the transition from the lower Oil Shale Member to the upper Carbonaceous Shale Member. Palaeoclimatic data from the various Middle and Late Eocene basins of northeastern China (i.e., the Huadian, Fushun, Yilan, Hunchun and Jishu basins) were compared with data from North American and European basins. Middle Eocene climate in the Northern Hemisphere was generally warm and humid, and the mean annual temperature and precipitation in northeastern China were similar to those in North America, though slightly lower than those of Europe. Similar trends in temperature and precipitation on different continents support the existence of a global Mid-Eocene cooling event. This paper is the first systematic study of Middle to Late Eocene seasonality in the Huadian Basin. Our results show an apparent differentiation in both temperature and precipitation between summer and winter, supporting the view that the East Asian Monsoon was established in northeastern China already during the Middle to Late Eocene. This Middle and Late Eocene monsoon was likely driven by the development of Pacific trade winds and an alternating, seasonal high- and low-pressure system over Siberia. The climatic changes observed in our dataset, especially the precipitation changes, appear to have played an important role in controlling oil shale formation in the Huadian Basin. A warmer and more humid climate, with abundant precipitation and high subsidence rates, formed a deeper Huadian depositional lake. High productivity and stable stratification provided the abundant organic matter and favorable preservation conditions necessary for oil shale accumulation. Highlights • The Middle-Late Eocene palynoflora were firstly systematically studied in Huadian Basin. • We quantitatively estimated the Middle-Late Eocene climate based on CA method. • A globally cooler phase was recognized in the Middle Eocene. • Climate seasonality in the Middle-Late Eocene supports the EAM was already prevalent in NE China. • Changes in climate, especially precipitation, play an important role in oil shale formation. [ABSTRACT FROM AUTHOR]

Abstract: In their recent paper, ; Anti-phase oscillation of Asian monsoons during the Younger Dryas period: Evidence from peat cellulose δ13C of Hani, Northeast China, Palaeogeography, Palaeoclimatology, Palaeoecology 297, 214–222) discuss bulk peat sample cellulose δ13C data from a fen in northeast China as a proxy for East Asian summer monsoon intensity during the Late Glacial period. Based on their own results, cited papers, and an extensive re-interpretation of sedimentological and palynological data from nearby Lake Sihailongwan, construct a hypothesis of contrasting moisture conditions in northern and southern China, with wet conditions in the north during the Younger Dryas period and an anti-phase behaviour of Indian- and East Asian summer monsoon intensity. However, we do not approve of the re-interpretation of our Lake Sihailongwan data by and must strongly reject it. We show here that neither the fen data, nor the Lake Sihailongwan data or any other cited data allow for the sound assumption of an intensified East Asian summer monsoon in northeastern China during the Younger Dryas. The Late Glacial variability of the fen data found by can be easily explained by changes in the plant assemblage down core and thus by the composition of the peat. Furthermore, the use of bulk peat cellulose δ13C data as a precipitation proxy remains unproven for that area. Hence, there is no basis for a model contrasting Indian and East Asian summer monsoons during that period. [Copyright &y& Elsevier]

The Oligocene marked the beginning of the present 'icehouse' epoch and witnessed the development and evolution of the Asian monsoon system (AMS). In this paper, the early Oligocene Ningming flora of Guangxi, southern China, is analysed to investigate the AMS based on climate proxies derived from Climate Leaf Analysis Multivariate Program (CLAMP). CLAMP results suggest that the prevailing climate experienced by the Ningming flora was humid subtropical with hot summers and warm winters. Although the record of precipitation seasonality is muted, it is about half as strong as that seen today in monsoon climates of South China, indicating a very weak monsoonal signal. Despite suggesting weak rainfall seasonality, the position of the Ningming flora in physiognomic space indicates that leaves exhibit monsoon-adapted morphologies, comparable to today's vegetation exposed to the Indonesia–Australia monsoon (I-AM) and the transitional monsoon area (influenced by the East Asia monsoon, South Asia monsoon and I-AM). Leaf architectural signatures reveal that the Ningming flora grew under a humid subtropical climate with subtle monsoon signatures. Although it is difficult to distinguish the different domains of the Asian monsoon under such a subtle monsoon influence, based on leaf signatures from southern Asia, it can be inferred that the Ningming Basin during the early Oligocene was exposed to a climate regime similar to that today influenced by the I-AM. In addition, the moist enthalpy method was applied to quantitatively reconstruct the paleoelevation of the Ningming Basin. This approach suggests a paleoelevation estimate of ~1.24–1.35 ± 0.52 km for the early Oligocene, suggesting that a drop in paleoelevation of the Ningming Basin took place after the early Oligocene (Rupelian). The CLAMP results suggest that the early Oligocene Ningming area was at a mid-altitude and experienced a humid subtropical climate with subtle monsoon signatures. • Leaves from the early Oligocene Ningming Basin were subjected to a CLAMP analysis. • The prevailing paleoclimate was humid subtropical with hot summers and warm winters. • Leaf physiognomic spectra shows an adaptation to monsoon climates. • The paleoclimate is similar to a climate regime today influenced by the I-AM. • The early Oligocene Ningming Basin was likely at a height of ~ 1.24–1.35 km. [ABSTRACT FROM AUTHOR]

Abstract: The Miocene Lincang leaf assemblage is used in this paper as proxy data to reconstruct the palaeoclimate of southwestern Yunnan (SW China) and the evolution of monsoon intensity. Three quantitative methods were chosen for this reconstruction, i.e. Leaf Margin Analysis (LMA), Climate Leaf Analysis Multivariate Program (CLAMP), and the Coexistence Approach (CA). These methods, however, yield inconsistent results, particularly for the precipitation, as also shown in European and other East Asian Cenozoic floras. The wide range of the reconstructed climatic parameters includes the Mean Annual Temperature (MAT) of 18.5–24.7°C and the Mean Annual Precipitation (MAP) of 1213–3711mm. Compared with the modern Lincang climate (MAT, 17.3°C; MAP, 1178.7mm), the Miocene climate is slightly warmer, wetter and has a higher temperature seasonality. A detailed comparison on the palaeoclimatic variables with the coeval Late Miocene Xiaolongtan flora from the eastern part of Yunnan allows us to investigate the development and interactions of both South Asian and East Asian monsoons during the Late Miocene in southwest China, now under strong influence of these monsoon systems. Our results suggest that the monsoon climate has already been established in southwest Yunnan during the Late Miocene. Furthermore, our results support that both Southeast Asian and East Asian monsoons co-occurred in Yunnan during the Late Miocene. [Copyright &y& Elsevier]

The 60-year quasi-periodic variability of the Asian monsoon in the mid-late Holocene has been found to be widespread in instrumental and various terrestrial records. However, whether this period exists in the older interglacial periods remains to be further studied. This paper is based on an 1840-mm-long stalagmite with clear annual laminae (with a growth rate of about 1 mm/yr) from Yongxing Cave, China, that allows for the reconstruction of the Asian monsoon evolution sequence during the period ~123.20–121.21 kyr BP. The stalagmite record closely tracks the 65°N solar insolation changes as a whole, indicating the dominant control of solar insolation on the Asian summer monsoon. After removing the solar insolation signal from the YX108 record, the δ 18O residuals (Δ δ 18O) show 28 multidecadal monsoon cycles. The average amplitude of these fluctuations is larger than 0.8‰, with a duration typically ranging from 50 to 80 yr (about 64 yr on average), which is very similar to the mid-late Holocene Asian monsoon variability. Further, wavelet analysis displays a significant quasi-periodicity of 60 years throughout the studied period, providing further evidence for assessing whether the 60-year quasi-periodic variability of the Asian monsoon found in the Holocene exists in older periods. Our study thus suggests that this quasi-periodic variability not only occurred during the modern period but also existed in the Last Interglacial, and their influence may even be an intrinsic characteristic of the Asian monsoon system during glacial-interglacial cycles. We manifested that the interactions between solar activity and the Atlantic Multidecadal Oscillation may be the main reason for the 60-year quasi-period of the Asian monsoon. • An 1840-mm-long annually laminated stalagmite was discovered from Southern China. • The sample was used to investigate the influences on Asian monsoon periodicity. • U Th absolute dating, laminae relative age, and spectral analysis were used. • Evidence of a 60-year quasi-period was found in the Last Interglacial. • Solar activity and ocean–atmosphere coupling impact the Asian monsoon 60-year cycle. [ABSTRACT FROM AUTHOR]