East Asian Monsoon Evolution Research Articles

Reconstruction of the topographic evolution of the Nanling Range in South China and its implications for the East Asian Monsoon evolution

The East Asian monsoon is the largest periodic airflow on Earth and significantly affects the climate of East Asia. However, considerable controversy exists about the onset timing of the East Asian monsoon. As one of the southern barriers blocking the northward movement of the warm and humid airflow, the Nanling Range has likely recorded key topographic information related to the East Asian monsoon onset and development. We used apatite and zircon (UTh)/He data obtained from the Shaoguan–Guidong horizontal cross-section to reconstruct the two-dimensional (2-D) paleotopography of the Nanling Range on a long-term scale. Four vertical profiles in Shulouqiu, Erjian, Sanfenshi, and Leiwangdian were used to constrain the exhumation history of the Nanling Range. The result revealed the following: 1) The drainage divide began to move from south to north at 80 Ma. At 80 Ma, the south segment of the cross-section reached a peak elevation of ∼3.6 km. The asymmetric topography experienced a rapid elevation (and relief) decrease from 80 Ma to 40–30 Ma. The four vertical profiles also experienced increased cooling and high exhumation rates from 100 Ma to 40–30 Ma. 2) The south segment experienced more rapid exhumation than the north segment from 80 Ma to 40–30 Ma. The rapid exhumation of the south segment during the Late Cretaceous–Paleocene is probably related to the activity of the Nanxiong Fault, and the rapid exhumation of the south segment during the Eocene probably results from the onset of the East Asian Monsoon.

Fagus diversification in China in relation to East Asian monsoon evolution

When and how the extraordinary species diversity in subtropical East Asia formed is intensely debated, and the available evidence is often inconsistent. In this study, we evaluate the effects of pre- and post- Quaternary events on the evolutionary and biogeographic history of Chinese beech (Fagus species that now occur in China) to gain new insights into the historical establishment and future fate of the East Asian subtropical forest (EASF). A series of approaches and datasets were used to reconstruct biogeographic and evolutionary history of the Chinese beech. They include phylogeography based on the polymorphisms of the complete chloroplast genomes, species distribution models, and a large palaeobiogeographic dataset including 59 pre-Quaternary fossil records, 296 Quaternary fossil records and 3515 modern pollen records. Our multidisciplinary approach suggests that (i) Chinese beech has dispersed to subtropical East Asia and diversified in the early Miocene when the Asian monsoon (AM) intensified; (ii) the last post-glacial warming resulted in limited poleward displacement but significant contraction at southern and lower elevations; (iii) the poleward dispersal of Chinese beech was limited by drought in the early growing season in temperate China, controlled by the East Asian summer monsoon. Our results support the hypothesis that the establishment of the EASF is closely related to the evolution of the AM. More importantly, we suggest that with continued climate warming (e.g., during the last post-glacial period or under current climate change), the monsoon probably hindered rather than promoted the persistence of deciduous beech species, resulting in a decline in species richness.

Geochemical evidence of provenance diversity in Holocene sandy land of Qinghai Lake Basin in the north‐eastern margin of Qinghai–Tibet Plateau and its implications for climate change

ABSTRACTThe Qinghai Lake Basin, located in the north‐eastern Tibetan Plateau, is crucial for understanding the East Asian monsoon evolution and its interaction with westerlies. Palaeoclimatic studies in this region since the Holocene have primarily focused on interpreting proxy significance from sediments, resulting in being highly controversial. However, exploring palaeoclimate evolution through sediment provenance and proxy integration remains rare. This study analysed the elemental geochemical properties of two fluvial–lacustrine–aeolian profiles in Hudong Sandy Land, east of the Qinghai Lake Basin, and compared these with published modern basin sediments and extensively investigated Late Quaternary aeolian deposits. It was found that Hudong Sandy Land sediments exhibit similar geochemical compositions to other modern basin sediments, primarily consisting of SiO2, Al2O3 and CaO. Contrary to previous understanding, lacustrine sediments in the Hudong Sandy Land are closer to the upper continental crust average than aeolian deposits. Geochemical ratios and parameters suggested that Hudong Sandy Land sediments primarily derived from mixed source rocks of felsic igneous, quartzose sedimentary and intermediate igneous provenances. A comparison with published elemental geochemical data from the basin reveals distinct sediment sources during different periods in the Hudong Sandy Land. From 9.6 to 4.0 ka bp, Hudong Sandy Land hosted numerous lake environments, with sediments displaying a dominant role in sedimentary recycling and reworking, implying a continuously stronger East Asian summer monsoon. During 8.2 to 5.1 ka bp, the Hudong Sandy Land was a fluvial depositional sink for sediments from the Dabanshan Mountains. Bedrock clastic material generated by intense erosion and monsoonal runoff transport contributed to Hudong Sandy Land sedimentation, indicating the East Asian summer monsoon's peak since 9.6 ka bp. After 4.0 ka bp, thick aeolian sands accumulated in the Hudong Sandy Land, primarily derived from Lake Qinghai sediments due to declining water levels, indicating that westerlies and East Asian winter monsoon dominated the basin, with a weaker East Asia summer monsoon. This study facilitates a deeper understanding of the interaction between the East Asia summer monsoon and East Asia winter monsoon/westerlies.

Irreversible intensification of the East Asian winter monsoon and aridity in Asian interior linked to the uplifted Tibetan Plateau: Evidence from magnetoclimatology of the Xining loess since 1.3 Ma

The impact of the uplifted Tibetan Plateau on the East Asian monsoon (EAM) evolution is not an uncontroversial topic. Disentangling complex paleoclimatic signals derived from solar insolation, global ice volume, and the rise of Tibetan Plateau in the EAM domain is challenging because of the paucity of continuous Quaternary sedimentary records shed from the Tibetan Plateau. The 260-m-thick Xining loess deposits in the northeastern Tibetan Plateau (NETP) with ultra-high average accumulation rate of ∼23 cm/ka during 0.2–1.3 Ma provide an excellent opportunity to delineate the long-term influence of the uplifted Tibetan Plateau on paleoclimatic variations in the western margin of the EAM. High-resolution grain size and mineral magnetic analyses for this unique record reveal a much more significant long-term increasing trend of the East Asian winter monsoon strength and aridification compared with those of typical loess records on the Chinese Loess Plateau, confirming that the uplifted Tibetan Plateau may play an important part in enhancing the EAM circulation and aridity of Asian interior under global cooling. It is further proposed that the negative correlation between physical erosion and chemical weathering in the NETP does not contradict the prevailing uplift-weathering hypothesis, but probably suggests a strong climate-silicate-weathering feedback in this tectonically active region. This result provides robust evidence that the existence of the NETP and adjacent topography exerts a profound impact on the irreversible intensification of Asian interior aridity.

Chemical Weathering of the Mekong River Basin With Implication for East Asian Monsoon Evolution During the Late Quaternary: Marine Sediment Records in the Southern South China Sea

Clay mineralogy, major-element geochemistry, and Sr-Nd isotopic compositions from Core MD05-2896 collected in the southern South China Sea have been utilized to investigate the discrimination of sediment provenance and to reconstruct a history of chemical weathering in the Mekong River basin over the last 45 ka. The results display that the clay mineral assemblage of the core is characterized by abundant smectite (27%–56%) and illite (18%–32%), with moderate kaolinite (13%–23%) and chlorite (11%–18%), and the 87Sr/86Sr ratio and εNd value narrowly vary in the ranges of 0.7232–0.7272 and from –10.9 to –9.6, respectively. According to clay mineralogy and Sr-Nd isotopic compositions, the Mekong River is the main terrigenous sedimentary source to the southern South China Sea, with no detectable change over the time span of the study, despite having strong sea-level fluctuations. Clay mineralogy and elemental geochemistry analyses reveal that higher smectite/(illite + chlorite), smectite/kaolinite, TiO2/K2O, and SiO2/K2O ratios during Marine Isotope Stage (MIS) 3 and 1 suggest enhanced chemical weathering, whereas lower values of these ratios during MIS 2 indicate weakened chemical weathering. These proxies reveal a close relationship with the available climate records of the East Asian monsoon evolution, implying that the chemical weathering in the Mekong River basin has been strongly controlled by the East Asian monsoon rainfall.

Tectonic and Orbital Imprints in the Redox History of Japan Sea Since the Pliocene

AbstractOxygen content in the deep ocean plays a vital role in biogeochemical processes and has significant impacts on the global carbon cycle. The Japan Sea is a semiclosed basin with only shallow water connection to the Western North Pacific, and its redox history has been sensitively affected by tectonic and climatic changes in the past. Studies of paleo‐redox changes in the Japan Sea focused on the tectonic and orbital scales since the Pliocene remain scarce to date. Here, we present two high‐resolution paleo‐redox records during the last 4 Ma at IODP Sites U1425 and U1430 drilled in the Japan Sea. Our authigenic U (uranium) and U/Al records suggest remarkable changes of Japan Sea redox history from relatively oxic to periodic oxic‐anoxic conditions at ∼1.7 Ma. This was mainly caused by the restricted input of North Pacific oxygen‐rich water due to the uplift of northeastern Japan during late Pliocene and early Pleistocene, and opening of the Tsushima Strait and the periodic intrusion of Tsushima Warm Current following sea level change during glacial‐interglacial cycles since ∼1.7 Ma. Orbital changes of Japan Sea redox history suggest the existence of a long eccentricity cycle of 400 ka associated with East Asian summer monsoon rainfall evolution throughout the last 4 Ma. Changes of the amplitude of sea level and inflow of Tsushima Warm Current combined with the East Asian monsoon evolution produced eccentricity and obliquity cycles in Japan Sea redox environment after ∼1.7 Ma, as well as a transition from relatively oxic to anoxic conditions during glacials before and after Middle Pleistocene Transition.

Geochemical characteristics of Holocene loess-paleosol sequences in central Chinese Loess Plateau and their implications for East Asian monsoon evolution

The geochemical composition and magnetic susceptibility (MS) of three sections (Weinan, Jingchuan and Jingbian) in the central Chinese Loess Plateau, located along a north-south climate gradient, were analyzed at high resolution in order to reconstruct changes in weathering intensity and hence Asian monsoon evolution during the Holocene. The results show distinct differences in element composition between the loess and paleosol layer, as well as spatial differences which reflect changes in mean annual temperature and annual precipitation along the climatic gradient. The measured major element compositions, combined with the results of previous research, indicate that the provenance of the Holocene loess-paleosol sequences in the central Chinese Loess Plateau was constant over time and space. The degree of chemical weathering in the study area is relatively weak and at an intermediate weathering stage. Based on a magnetic susceptibility age model, the East Asian summer monsoon changes recorded by the loess-paleosol sequences show a distinct two-stage pattern of evolution, with a gradual increase during 13.1–8.5 ka and a gradual decrease thereafter. Comparison of the results with climate records from elsewhere indicates that the East Asian monsoon evolution was mainly controlled by changes in Northern Hemisphere summer insolation and ice sheets.

Response of Terrigenous Sediment Input to Sea Level Change and East Asian Monsoon Evolution Since 30kyr in the Southwestern Taiwan Basin

Response of Terrigenous Sediment Input to Sea Level Change and East Asian Monsoon Evolution Since 30kyr in the Southwestern Taiwan Basin

East Asian monsoon and sea-level controls on clay mineral variations in the southern South China Sea since the Last Glacial Maximum

Clay minerals preserved in marine sediments carry important information about sediment transport processes from sources to sinks. To reveal the dynamic transport processes of clay minerals and related controlling factors in the southern South China Sea, spatiotemporal variations of clay mineral assemblages from previous studies (Cores MD05-2893, CG2, SO18287-3, MD01-2393, SO18383-3, and MD97-2150) are integrated to assess their controlling factors over the past 30 ka. Based on the smectite/(illite + chlorite) ratio in six cores, we found that the clay mineral variations on the continental slope off Sunda Shelf (Cores MD05-2893, CG2, and SO18287-3) have been controlled by the sea-level changes during the last glacial sea-level lowstand and by the East Asian monsoon during the Holocene sea-level highstand periods. Meanwhile, the clay mineral variations on the continental slope off the Mekong River (Cores MD01-2393, SO18383-3, and MD97-2150) have been driven by the chemical weathering in the Mekong River basin that associates with the East Asian summer monsoon evolution. Accordingly, we conclude that the glacial-interglacial variation of clay minerals in an integrated picture of the southern South China Sea region since the Last Glacial Maximum has been mainly controlled by sea-level change and East Asian monsoon evolution. However, these controlling factors play independent roles in different parts of the southern South China Sea, which appears more heterogeneous than generally expected.

Asian monsoon evolution linked to Pacific temperature gradients since the Late Miocene

Considerable uncertainty remains over the nature and causes(s) of East Asian monsoon evolution since the Late Miocene, a significantly warmer period characterized by substantially weaker meridional and zonal Pacific sea surface temperature (SST) gradients than today and therefore regarded as a potential analog for current and future global warming. However, the extent to which these temperature gradients impacted rainfall patterns across East Asia, and particularly the northern extent of the monsoon domain, remains controversial. Here we present the first hydrological record extending back eight million years (Ma) for North China Plain derived from organic biomarkers preserved in a terrestrial sediment sequence. Our record shows a significant increase in monsoon rainfall during the Early Pliocene (∼4.2-4.5 Ma), coincident with strengthening of Pacific meridional and zonal SST gradients, and the eastern equatorial Pacific cold tongue. This marked intensification of the monsoon rainfall in northern China is also observed in paleoclimate archives from southern Asia, but anti-phased with those from central-eastern China (including southern China), indicating a ‘tripole-like’ rainfall pattern over East Asia. Through a set of climate model experiments, we show that this redistribution of monsoon rainfall across East Asia during the Early Pliocene (5.33-3.6 Ma) was likely due to an equatorward contraction of the western Pacific warm pool, reduced summer convection in the western subtropical Pacific, and the strengthening of the Hadley and Walker circulations. Our study thus highlights the strong influence of Pacific Ocean temperature gradients on East Asian hydroclimate.

Terrigenous sediment variations in the western South China Sea and their implications to East Asian monsoon evolution during the last glacial-interglacial cycle

Major-element geochemistry from two Cores MD05-2899 and MD05-2901 off central Vietnam in the lower continental slope of the western South China Sea is investigated to reconstruct a history of terrigenous sediment variations and East Asian monsoon evolution during the last glacial-interglacial cycle. The results suggest that the Pearl River can play a more important role in contributing terrigenous sediments to the western South China Sea than the Red River in the north, while the Mekong River can transport more terrigenous sediments to the region than the Sunda shelf and the Indonesian islands in the south. The Pearl River provides terrigenous sediments with higher Al2O3, but lower K2O, MgO, and Fe2O3 (Total Fe) than the Mekong River. K2O/Al2O3, MgO/Al2O3, and Fe2O3/Al2O3 ratios are then used as proxies to trace terrigenous sediment variations in the western South China Sea. Higher K2O/Al2O3, MgO/Al2O3, and Fe2O3/Al2O3 ratios indicate strengthened terrigenous sediments input from the southern source and lower the ratios suggest increased terrigenous sediments received from the northern source. These ratios show a glacial-interglacial cycle over the past 130 ka, implying a close relationship with the East Asian monsoon evolution. Northward surface currents forced by strengthened summer monsoon during interglacial periods bring relatively higher amounts of terrigenous sediments from the southern source to the western South China Sea, while relatively higher amounts of terrigenous sediments from the northern source are transported to the western South China Sea by southward surface currents in strengthened winter monsoon during glacial periods. Our study indicates that the terrigenous sediment variations in the western South China Sea are significantly controlled by surface currents under the strong influence of the East Asian monsoon evolution during the last glacial-interglacial cycle.

Chronostratigraphic framework and paleoenvironmental interpretation of the Holocene loess-paleosol sequence in the Luoyang Basin, Central China

Abstract The loess-paleosol sequences in the Loess Plateau are major paleoclimatic archives which document the evolution of East Asian Monsoon (EAM) during the Quaternary glacial-interglacial cycles. A complete Holocene loess-paleosol sequence was identified by detailed field investigations in the Luoyang Basin, which is located at the southeastern margin of the Loess Plateau, Central China. Laboratory analysis including magnetic susceptibility, hygroscopic water, grain-size distribution, geochemical elements characteristics, AMS 14C dating, Bacon age-depth modelling and stratigraphic correlations have been carried out. Our results show that the stratigraphic sequence, from top to bottom, is topsoil (TS), recent loess (L0), mid-Holocene paleosol (S0), early Holocene transitional loess (Lt) and Malan loess (L1). The intensity of weathering and pedogenesis varies significantly in different layers and presents such a tendency of S0 > L0 > Lt > L1. This indicates four distinct stages in the EAM evolution: 1) an extreme dry-cold climate with strengthened East Asian winter monsoon (EAWM) during the last glacial period, 2) an episode of gradual transition to the warm-humid climate with intensive East Asian summer monsoon (EASM) in the early Holocene (11,500–8500 yr BP), 3) a warm-humid climate affected by intense EASM in the mid-Holocene (8500–3100 yr BP), and lastly 4) an episode of gradually shifting to dry-cool climate with weakened EASM (3100–0 yr BP). These results provide basic data for exploring the Holocene weathering and pedogenesis and paleoenvironmental evolution in Central China.

East Asian monsoon evolution since the late Miocene from the South China Sea

The South China Sea (SCS) has become a global focus for paleoclimatic and paleoceanographic studies due to its location, which makes it highly sensitive to the East Asian monsoon and to Pacific Ocean changes. We present here a refined magnetostratigraphy for the last 6.5 Ma for Hole U1431D, which was recovered during IODP Expedition 349 in the central SCS. Magnetic analyses demonstrate that magnetite is the dominant magnetic carrier except for within a greigite-bearing layer at 130.5-132.0 meters below sea floor. The greigite layer coincides with the timing of intensification of northern hemisphere glaciation and records an oceanographic response to this event. Environmental magnetic results indicate that the East Asian summer and winter monsoon were stable from 6.5 to 5 Ma. The summer monsoon intensified at 5 Ma, and then weakened gradually since 3.8 Ma. In contrast, the winter monsoon weakened at 5 Ma, and has then been enhanced since 3.8 Ma and more stable from 0.6 Ma. Spectral analysis indicates that the East Asian summer monsoon was driven directly by low-latitude insolation changes before ∼3.2 Ma, and that it has been affected by both low-latitude insolation and high-latitude ice volume changes since ∼3.2 Ma.

Past East Asian monsoon evolution controlled by paleogeography, not CO2.

The East Asian monsoon plays an integral role in human society, yet its geological history and controlling processes are poorly understood. Using a general circulation model and geological data, we explore the drivers controlling the evolution of the monsoon system over the past 150 million years. In contrast to previous work, we find that the monsoon is controlled primarily by changes in paleogeography, with little influence from atmospheric CO2. We associate increased precipitation since the Late Cretaceous with the gradual uplift of the Himalayan-Tibetan region, transitioning from an ITCZ-dominated monsoon to a sea breeze-dominated monsoon. The rising region acted as a mechanical barrier to cold and dry continental air advecting into the region, leading to increasing influence of moist air from the Indian Ocean/South China Sea. We show that, apart from a dry period in the middle Cretaceous, a monsoon system has existed in East Asia since at least the Early Cretaceous.

New paleomagnetic constraints for Platybelodon and Hipparion faunas in the Linxia Basin and their ecological environmental implications

Abstract The Linxia Basin in northwestern China lies topographically at the northeastern margin of the Tibetan Plateau and climatically at the western margin of the East Asian monsoon region, and bears abundant mammalian fossils with environmental significance on central Asian aridification and east Asian monsoon evolution. However, these mammals have not been precisely dated, hindering our ability to address the ecologic environment changes associated with the evolution of the Asian monsoon and multiple uplifts of the Tibetan Plateau. We present a detailed paleomagnetic study of a sedimentary sequence from the Laogou section in the Linxia Basin containing many mammalian fossils with ages ranging between middle and late Miocene. The 203 m thick section revealed 11 normal and 10 reversed zones that correlate well with chrons 3An to 5An of the Geomagnetic Polarity Time Scale, constraining its age to ~12.56–6.0 Ma, and suggesting that the middle Miocene Platybelodon fauna existed at about 11.5 Ma and the late Miocene Hipparion fauna occurred at about 6.4 Ma. These ages, combined with other magnetostratigraphic results from the whole basin, show that these two major mammal faunas lived during 12.5–11.1 Ma and 11.5–6.3 Ma in the Linxia Basin. The presence of well-developed floodplain paleosols, the color change of the fluviolacustrine sediments and the transition of large bodied mammals suggest that strong climatic and environmental changes happened in the Linxia Basin during late – middle Miocene, in the form of a transition from the warm and humid forest to the warm and subarid steppe at about 11.1 Ma.

Terrigenous sediment input responding to sea level change and East Asian monsoon evolution since the last deglaciation in the southern South China Sea

Abstract Siliciclastic grain size, clay mineralogy, and major element geochemistry of Core MD05–2893 from the lower continental slope off the Sunda Shelf in the southern South China Sea were investigated to assess the response of terrigenous sediment input to sea-level and climatic changes since the last deglaciation. The chronology is based on foraminiferal AMS 14C dates and oxygen isotope records combined with carbonate stratigraphy. In this study, we reconstruct variations in terrigenous sediment input using clay/silt, TiO2/CaO, SiO2/Al2O3, Al2O3/K2O, and smectite/(illite + chlorite) proxies. Clay/silt, TiO2/CaO, and SiO2/Al2O3 ratios are clearly correlated to sea-level change, showing high values during the early phase of deglacial sea-level rise (17.2–14.5 cal ka BP, Stage I) and rapidly decreasing values during the meltwater pulse 1A and further sea-level rise (14.5–11.1 cal ka BP, Stage II). Meanwhile, variations in Al2O3/K2O and smectite/(illite + chlorite) correspond well to monsoon rainfall variability during the late phase of deglacial sea-level rise and Holocene sea-level highstand (11.1–1.5 cal ka BP, Stage III). Based on these records, we recognize three stages of evolution of terrigenous sediment input to the southern South China Sea continental slope. Dominance of terrigenous sediment input occurred during Stage I, when most part of the Sunda Shelf was still exposed and drained by several rivers. The stepwise elevated sea level by meltwater pulse 1A and subsequent rising sea-level after 14.5 cal ka BP could have led to a drop in terrigenous sediment input to this area due to regression of the paleo-Sunda river systems (Stage II). Thereafter during last phase of sea-level rise and sea-level highstand with the evolution of the modern coast, sediments have a clear fingerprint of chemical weathering induced by a strengthening of the East Asian summer monsoon (Stage III). Our findings highlight that the variability of terrigenous sediment input to the lower continental slope in the southern South China Sea was first in the late Pleistocene mainly driven by sea-level change and later in the Holocene by a strengthened East Asian summer monsoon.

Responses of the East Asian Summer Monsoon in the Low‐Latitude South China Sea to High‐Latitude Millennial‐Scale Climatic Changes During the Last Glaciation: Evidence From a High‐Resolution Clay Mineralogical Record

AbstractHigh‐resolution clay mineral assemblage combined with Nd and Sr isotopic compositions of Core MD12‐3434 located in the northern South China Sea was investigated to reveal terrigenous sediment response to the East Asian monsoon evolution during the last glaciation. Clay mineralogical variations indicate clear millennial‐scale oscillations that are mainly due to rapid changes in the proportion of smectite to illite and chlorite. Smectite is derived predominantly from rapid chemical weathering of volcanic rocks in Luzon under strong summer monsoon, while illite and chlorite are mainly sourced from Taiwan through reinforced physical erosion. Thus, the smectite/(illite + chlorite) ratio is adopted to reconstruct the East Asian summer monsoon evolution during the last glaciation. Rapid increases in the smectite/(illite + chlorite) ratio imply strengthened summer monsoon occurred during Dansgaard‐Oeschger and Bølling‐Allerød interstadials. In contrast, rapid decreases in the ratio indicate relatively weakened summer monsoon happened during Heinrich and Younger Dryas stadials. These millennial‐scale climatic signals documented by clay mineralogical compositions of deep‐sea sediments in the South China Sea can be better preserved in calm deeper‐water sedimentary environments. Our study highlights the prompt responses of the East Asian monsoon system to millennial‐scale climatic changes occurred in high‐latitude Northern Hemisphere through contemporaneous chemical weathering of volcanic rocks and/or sediment supply variations under strong physical erosion in the low‐latitude South China Sea, implying an atmospheric teleconnection from the North Atlantic to the Asian monsoon region.

High-resolution clay mineral assemblages in the inner shelf mud wedge of the East China Sea during the Holocene: Implications for the East Asian Monsoon evolution

The inner shelf mud wedge of the East China Sea (ECS) is a high-sedimentation-rate fine-grained sediment unit that has preserved a continuous environmental evolution history since the last deglaciation. We present a high-resolution clay mineralogical study from Core MD06-3040 to semi-quantitatively evaluate terrigenous sediment contributions from various potential provenances throughout the Holocene. The results showed that the clay mineral assemblage is composed of dominant illite (34–49%), moderate smectite (16–41%) and chlorite (15–28%), and minor kaolinite (5–12%). Provenance analysis suggested that most fine-grained terrigenous sediments originated from the Yangtze River, with minor sediments derived from Taiwan island and negligible sediments from nearby Zhejiang and Fujian provinces. Time series variation in the contribution of the Yangtze source fluctuated in the range of 38–80%, whereas that of Taiwan island had a converse variation pattern from ~10% to ~55%, and the contribution of Fujian was relatively stable in the range of 7–11% throughout the Holocene. The fluctuations of clay mineral assemblages and variations of clay mineral contributions from different provenances of Core MD06-3040 were controlled by the variability of precipitation in the Yangtze drainage associated with periodic fluctuations in the East Asian monsoonal circulation.

Rock magnetic record of late Neogene red clay sediments from the Chinese Loess Plateau and its implications for East Asian monsoon evolution

The Quaternary loess–paleosol and underlying Neogene red clay sequences on the Chinese Loess Plateau (CLP) contain a remarkable continental record of past East Asian monsoon changes and aridification of the Asian interior. While monsoon variability during the Quaternary is reasonably well understood, the evolution and dynamics of the monsoon during the Neogene are still debated. The rock magnetism of aeolian sediments is a well-established tool for reconstructing the palaeoclimatic history of Asia. Here, we present a rock magnetic record from Late Neogene red clay sediments of the Chaona section in the central CLP. The results indicate that the main magnetic minerals in the red clay are magnetite, maghemite, hematite and goethite, similar to the overlying Quaternary loess-palaeosol sequences. The high-resolution rock magnetic record, combined with the results of other proxies, demonstrate a stepwise intensification of the summer monsoon and a progressive enhancement of the winter monsoon in East Asia during the Late Neogene. Based on the results, the climatic evolution of East Asia can be divided into three intervals: Interval III, from 8.1 to 6.8Ma, is characterized by a cool, dry climate with a relatively weak East Asian Summer Monsoon (EASM) and East Asian Winter Monsoon (EAWM); Interval II, from 6.8 to 4.3Ma, is characterized by cool/warm cycles; and Interval I, from 4.3 to 2.8/2.6Ma, was warm and humid, and within which the EASM strengthened rapidly and the EAWM fluctuated considerably, with an increasing trend. We infer that before 4.3Ma the variations of both the EASM and EAWM were closely related to global cooling and that the intensified EASM during the late Pliocene was primarily caused by tectonic events, including the gradual closure of the Panama Seaway and the uplift of the Tibetan Plateau, rather than by global cooling.

The mid-Holocene decline of the East Asian summer monsoon indicated by a lake-to-wetland transition in the Sanjiang Plain, Northeast China

A comprehensive and integrative view of East Asian monsoon evolution during the Holocene is still under debate, and additional high-resolution proxy records from climatically sensitive locations ar...