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Recent research has suggested that East Asia has experienced a prevailing monsoon climate since the Eocene. However, there is little knowledge about the development of the East Asian monsoon system before the Miocene, particularly in southern China, due to a lack of well‐dated continuous sediment records. Here, we present new magnetic proxy records from International Ocean Discovery Program Site U1501 in the northern South China Sea. We conducted rock magnetic experiments, made scanning electron microscopy observations and performed diffuse reflectance spectrum analysis on the late Eocene‐early Oligocene core sediments. The magnetic signal of the sediments is dominated by detrital magnetite and titanomagnetite formed during the silicate weathering and erosion processes, which were used to infer the evolution of summer monsoon precipitation in southern China. Our results along with geochemical and clay mineral data from Site U1501 strongly indicate that the East Asian summer monsoon generally weakened across the Eocene‐Oligocene transition. This change was linked to coeval global cooling rather than tectonic processes. Prior to the Eocene‐Oligocene transition, the summer monsoon intensified, likely due to the latest Eocene warming event caused by the enhancement of the Atlantic Meridional Overturning Circulation, which may have preconditioned the Earth system for the greenhouse‐to‐icehouse transition. Plain Language Summary: To date, there is little knowledge regarding the long‐term evolution of monsoon climate in South China before the Miocene due to a lack of well‐dated continuous sediment records. The recent International Ocean Discovery Program Expedition 368 retrieved continuous late Eocene‐early Oligocene sediments at Site U1501 within the northern South China Sea, thus providing an opportunity to fill this gap. In this study, we investigate the evolution of the East Asian summer monsoon in South China during the late Eocene‐early Oligocene through a comprehensive analysis of the magnetic properties of the sediments. The results strongly indicate that the summer monsoon generally weakened across the Eocene‐Oligocene transition, which was linked to coeval global cooling. A short‐term strengthening of the summer monsoon prior to the Eocene‐Oligocene transition was also recorded. This change is attributed to the warming caused by the latest Eocene strengthening of the Atlantic Meridional Overturning Circulation, which may have preconditioned the Earth system state before causing a transition into an icehouse Earth. Key Points: The environmental magnetic record in the northern South China Sea indicates monsoon evolution during the late Eocene to early OligoceneThe East Asian summer monsoon weakened across the Eocene‐Oligocene transitionGlobal cooling drove the long‐term weakening of East Asian summer monsoon [ABSTRACT FROM AUTHOR]

Quaternary East Asian winter monsoon (EAWM) evolution has long been attributed to high‐latitude Northern Hemisphere climate change. However, it cannot explain the distinct relationships of the EAWM in the northern and southern East Asian marginal sea in paleoclimatic records. Here we present an EAWM record of the northern East China Sea over the past 300 ka and a transient climate simulation with the Kiel Climate Model through the Holocene. Both proxy record and simulation suggest anticorrelated long‐term EAWM evolution between the northern East China Sea and the South China Sea. We suggest that this spatial discrepancy of EAWM can be interpreted as El Niño–Southern Oscillation (ENSO)‐like controlling, which generates cyclonic/anticyclonic wind anomalies in the northern/southern East Asian marginal sea. This research explains much of the controversy in nonorbital scale variability of Quaternary EAWM records in the East Asian marginal sea and supports a potent role of tropical forcing in East Asian winter climate change. Plain Language Summary: The modern East Asian winter monsoon (EAWM) is influenced by the combined effects of both the high‐latitude Northern Hemisphere (e.g., Siberian High) and the low‐latitude Western Pacific (e.g., El Niño–Southern Oscillation) and plays a major role in regulating atmospheric energy of East Asia and even the Northern Hemisphere. Its anomalies may cause extremely cold/warm winter weather or climate events, which result in profound societal and economic influences on the densely populated region of East Asia. Especially, some studies found the EAWM displays spatial discrepancies in northern and southern East Asia and can result in a colder/warmer north corresponding to a warmer/colder south. Our study shows anticorrelations of EAWM evolution between the northern East Asian marginal sea and the South China Sea since the late Quaternary. We suggest that such spatial discrepancies of EAWM evolution were controlled by El Niño–Southern Oscillation‐like processes in the tropical Pacific. During El Niño‐like conditions, the anomalous northwesterlies in the northern East Asian marginal sea led to a strengthened EAWM in this region. In contrast, anomalous southwesterlies in the South China Sea favored the occurrence of a weakened EAWM. The opposite situation occurred under La Niña‐like conditions. Key Points: Clay minerals in northern Okinawa Trough were derived from Yellow River and KyushuReversed EAWM evolution in the northern and southern East Asian marginal sea was revealedENSO‐like processes cause spatial discrepancy of Quaternary EAWM evolution [ABSTRACT FROM AUTHOR]

Abstract: Changes in paleoenvironments over the last 17,500yr have been documented by a high-resolution clay mineralogy and grain–size records of Core KNG5 from the northern slope of the South China Sea. Our results indicate that clay minerals are mainly from the Pearl River from 17,500 to12,500calyr BP, and the South China Sea modern current system began to form since 12,500calyr BP, as a result, Taiwan turns to be the major contributor of clay minerals after 12,500calyr BP. Two grain-size populations with high variability through time were identified in the 13–28μm and 1–2.2μm grain-size intervals. The 1–2.2μm grain-size population are mainly controlled by provenance supply and current transport. The 13–28μm grain-size fraction could be controlled mainly by the sea-level change. The 1–2.2μm grain-size population record demonstrates that East Asian Summer Monsoon intensity generally follows changes in insolation and that the response is similar for a large area of China and other northern low-latitude records, implying the globality of the monsoon evolution since Holocene. The anomalous environmental conditions in the northern South China Sea may imply intensified ENSO activity during the late Holocene. [Copyright &y& Elsevier]

The emergence and expansion of terrestrial C 4 vegetation represent the most striking evolutionary adaptation of ecosystems to climate change during the Cenozoic. However, the long-term history of terrestrial C 4 ecosystem expansion in East Asia remains poorly documented, and its links to tectonic and/or climate changes remain unclear due to the complexity of its forcing factors. Here, we reconstruct the long-term evolution of terrestrial C 3 –C 4 plants biomass in South China since the late Eocene using continuous records of the stable carbon isotopic compositions (δ13C) of black carbon extracted from sediments at International Ocean Discovery Program (IODP) Site U1501 in the northern South China Sea (SCS). This study reveals remarkable stepwise expansions of C 4 plants in South China at ∼20 Ma and 15 Ma with a gradual expansion trend at 7–4 Ma. We demonstrate that stepwise drying (long-term weakening of the East Asian summer monsoon and simultaneous strengthening of the East Asian winter monsoon), as well as the enhanced seasonality of precipitation, is responsible for the ecological evolution in South China since the early Miocene. Our black carbon records, combined with previous studies, indicate a coupled evolution of East Asian drying, vegetation shifts and global cooling. We suggest that the major Asian topography framework was established before the middle Miocene, and global cooling overwhelmed tectonic controls of the long-term evolution of the East Asian monsoon thereafter. This study highlights that both Tibetan uplift and global cooling have played a significant role in the long-term evolution of regional climate and vegetation. • Stepwise expansion of C 4 plant in South China occurred at 20 Ma, 15 Ma and 7–4 Ma. • Stepwise drying and enhanced seasonality of precipitation induced C 4 plant expansion in South China. • Both Tibetan uplift and global cooling played a significant role in evolution of East Asian monsoon. [ABSTRACT FROM AUTHOR]

Clay mineralogical analysis and scanning electron microscope (SEM) analysis were performed on deep-sea sediments cored on the Benham Rise (core MD06-3050) in order to reconstruct long-term evolution of East Asian Summer Monsoon (EASM) rainfall in the period since 2.36 Ma. Clay mineralogical variations are due to changes in the ratios of smectite, which derive from weathering of volcanic rocks in Luzon Island during intervals of intensive monsoon rainfall, and illite- and chlorite-rich dusts, which are transported from East Asia by winds associated with the East Asian Winter Monsoon (EAWM). Since Luzon is the main source of smectite to the Benham Rise, long-term consistent variations in the smectite/(illite + chlorite) ratio in core MD06-3050 as well as ODP site 1146 in the Northern South China Sea suggest that minor contributions of eolian dust played a role in the variability of this mineralogical ratio and indicate strengthening EASM precipitation in SE Asia during time intervals from 2360 to 1900 kyr, 1200 to 600 kyr, and after 200 kyr. The EASM rainfall record displays a 30 kyr periodicity suggesting the influence of El Niño–Southern Oscillation (ENSO). These intervals of rainfall intensification on Luzon Island are coeval with a reduction in precipitation over central China and an increase in zonal SST gradient in the equatorial Pacific Ocean, implying a reinforcement of La Niña-like conditions. In contrast, periods of reduced rainfall on Luzon Island are associated with higher precipitation in central China and a weakening zonal SST gradient in the equatorial Pacific Ocean, thereby suggesting the development of dominant El Niño-like conditions. Our study, therefore, highlights for the first time a long-term temporal and spatial co-evolution of monsoonal precipitation in East Asia and of the tropical Pacific ENSO system over the past 2.36 Ma. [ABSTRACT FROM AUTHOR]

Abstract: Clay mineral assemblage of the core MD06-3047 in the western Philippine Sea has been used to trace sediment provenance and transport process and thus to constrain the East Asian monsoon evolution as well as its forcing mechanism over the past 700kyr. Clay minerals mainly consist of smectite (61%) and illite (23%), with minor chlorite (10%) and kaolinite (6%). Provenance analyses suggest that the smectite originates predominantly from the alteration of nearby Luzon volcanic rocks. Illite is primarily derived from the Asian continent with eolian origin. Illite contents show strong glacial/interglacial cyclicity as constrained by oxygen isotope stratigraphy. Variations of illite contents are ultimately controlled by the East Asian monsoon evolution, characterized by higher illite values during glacials with relatively stronger East Asian winter monsoon but weaker East Asian summer monsoon. During interglacials, enhanced East Asian summer monsoon and rainfall could produce more smectite with poor crystallinity from Luzon to the study core. Spectral analyses of illite content and smectite crystallinity display a strong periodicity at 100kyr for the East Asian winter monsoon and 100kyr, 30kyr, and 23kyr periodicities for the East Asian summer monsoon, respectively, suggesting the unique forcing processes of the East Asian winter monsoon from high-latitudes (i.e., ice volume) and the East Asian summer monsoon from both high-latitudes and low-latitudes (i.e., tropical Pacific). [Copyright &y& Elsevier]

The Quaternary East Asian summer rainfall evolution reconstructed with the Chinese speleothem δ18O records shows the consistency throughout the region of East Asia, and has long been considered equivalent to the monsoon intensity. Its variation and teleconnection with global climate were usually interpreted by the meridional shift of the intertropical convergence zone (ITCZ). However, many other proxy records, climate simulations and meteorological observations suggest the inconsistent rainfall patterns in the different regions of East Asia on multi-timescales. Such spatial heterogeneity in Quaternary East Asian summer rainfall indicates that the hydroclimate in this region is not fully paced by the migration of the ITCZ. Here, we report a sediment record of rainfall evolution during the last 400 ka in the northern East China Sea, and this record, in combination with a transient climate model simulation, indicates an out-of-phase relationship between rainfall over middle-southeastern East Asia and northern and southwestern East Asia on the precession band, with high boreal summer insolation corresponding to the increased rainfall intensity in the northern and southwestern East Asia, however, decreased rainfall intensity in the middle East Asia. We attribute this regional heterogeneity in East Asian rainfall to the reorganization of the Hadley circulation, including shifts in the ascending branch (ITCZ) and descending branch (subtropical westerly jet), in response to changes in the hemispheric meridional temperature gradient. Our results highlight the crucial role of the Hadley circulation in the East Asian hydroclimate and have important implications for future climate projections. • East Asian rainfall evolution was reconstructed from the sediment flux from the southern Japanese islands. • Heterogeneous phase of rainfall change in East Asia different regions on precession band has been found. • The spatial heterogeneity in East Asian rainfall was paced by the Hadley circulation reorganization. [ABSTRACT FROM AUTHOR]