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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]

Abstract: We here reconstruct the past change of the East Asian monsoon since 20 Ma using samples from Ocean Drilling Program (ODP) Site 1146 in the northern South China Sea based on a multi-proxy approach including a monomineralic quartz isolation procedure, identification of clay minerals by X-ray Diffraction (XRD) and grain-size analysis of isolated terrigenous materials. Terrigenous supply to ODP Site 1146 was dominated by changes in the strength of multiple sources and transport processes. Grain-size data modeled by an end-member modeling algorithm indicate that eolian dust from the arid Asian inland and fluvial input have contributed on average 20% and 80% of total terrigenous material to ODP Site 1146, respectively. Specifically, about 40–53% of the total (quartz+feldspar) and only 6–11% of the total clay is related to eolian supply at the study site. Detailed analysis of the sedimentary environment, and clay minerals combined with previous studies shows that smectite originates mainly from Luzon, kaolinite from the Pearl River and illite and chlorite from the Pearl River, Taiwan and/or the Yangtze River. The proportion and mass accumulation rate (MAR) of the coarsest end-member EM1 (interpreted as eolian dust), ratios of (illite+chlorite)/smectite, (quartz+feldspar)% and mean grain-size of terrigenous materials at ODP Site 1146 were adopted as proxies for East Asian monsoon evolution. The consistent variation of these independent proxies since 20 Ma shows three profound shifts in the intensity of East Asian winter monsoon relative to summer monsoon, as well as aridity of the Asian continent, occurred at ∼15 Ma, ∼8 Ma and the youngest at about 3 Ma. In comparison, the summer monsoon intensified contemporaneously with the winter monsoon at 3 Ma. The phased uplift of the Himalaya–Tibetan plateau may have played a significant role in strengthening the Asian monsoon at ∼15 Ma, 8 Ma and 3 Ma. [Copyright &y& Elsevier]

Abstract: 128 samples from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea were analyzed for grain size, clay minerals, biogenic opal content and quartz in order to reconstruct changes in East Asian monsoon climate since 8.5 Ma. An abrupt change of terrigenous mass accumulation rate (MAR), clay mineral assemblage, median grain size and biogenic opal MAR about 5.2 Ma suggests that between 8.5–5.2 Ma the source of terrigenous sediment was mainly in the region of surface uplift and basaltic volcanism in southern Vietnam. A simple model of East Asian summer monsoon evolution was based on the clay/feldspar ratio, kaolinite/chlorite ratio and biogenic opal MAR. The summer monsoon has two periods of maximum strength at 8.5–7.6 Ma and 7.1–6.2 Ma. Subsequently, there was a relatively stable period at 6.2–3.5 Ma, continued intensification about 3.5–2.5 Ma, and gradually weakening after 2.5 Ma. Since 1 Ma the monsoon has intensified, with remarkable high-frequency and amplitude variability. Simultaneous increase in sedimentation rates at ODP Sites 1143, 1146 and 1148, as well as in MAR of terrigenous materials, quartz, feldspar and clay minerals at ODP Site 1143 at 3.5–2.5 Ma, may be the erosional response to both global climatic deterioration and the strengthening of the East Asian summer monsoon after about 3–4 Ma. [Copyright &y& Elsevier]

Abstract: AMS14C dating and grain-size analysis for Core PC-6, located in the middle of a mud area on the inner shelf of the East China Sea (ECS), were used to rebuild the Holocene history of the East Asian winter monsoon (EAWM). The 7.5-m core recorded the history of environmental changes during the postglacial transgression. The core’s mud section (the upper 450 cm) has been formed mainly by suspended sediment delivered from the Yangtze River mouth by the ECS Winter Coastal Current (ECSWCC) since 7.6 kyr BP. Using a mathematical method called “grain size vs. standard deviation”, we can divide the Core PC-6’s grain-size distribution into two populations at about 28 μm. The fine population (<28 μm) is considered to be transported by the ECSWCC as suspended loads. Content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation. Thus, variation of mean grain-size from the fine population would reflect the strength of ECSWCC, which is mainly controlled by the East Asian winter monsoon. Abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ECSWCC, which was caused by the strengthened EAWM. Thus, the high resolution mean grain-size variation might serve as a proxy for reconstruction of the EAWM. A good correlation between sunspot change and the mean grain-size of suspended fine population suggests that one of the primary controls on centennial- to decadal-scale changes of the EAWM in the past 8 ka is the variations of sun irradiance, i.e., the EAWM will increase in intensity when the number of sunspots decreases. Spectral analyses of the mean grain-size time series of Core PC-6 show statistically significant periodicities centering on 2463, 1368, 128, 106, 100, 88-91, 76-78, and 70-72 years. The EAWM and the East Asian summer monsoon (EASM) agree with each other well on these cycles, and the East Asian Monsoon (EAM) and the Indian Monsoon also share in concurrent cycles in Holocene, which are in accord with the changes of the sun irradiance. [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]

We present a multi-proxy geochemical analysis of core KNG5 retrieved from the northern South China Sea slope spanning the last 13.0 ka BP to assess the response of weathering and erosion processes in the Southwestern Taiwan River basin to climate change. A provenance analysis indicates that the core sediments were primarily derived from the Southwestern Taiwan River, and can be used to reconstruct the erosion and/or weathering history of this river basin. The chemical index of alteration, the plagioclase index of alteration, Rb/Sr, Al/Ti, principle component 1, and K/Al combined with terrigenous mass accumulation rates and the proportion of clay exhibit sharp excursions from 12.0 to 5.5 ka, peaking at 10.0 ka, which suggests strong chemical weathering and physical erosion during the Early-Mid Holocene, the period of the maximum summer monsoon. Abrupt falling weathering trends during 5.2 and 3.5 ka BP correlate with a weaker monsoon. After 3.5 ka BP, a stable lower weathering trend to the present day was evident, indicating the deposition of less weathered sediments in the slope when the monsoon rainfall was weakening. A good correlation between our proxy records of chemical weathering and variations of the monsoon intensity in South China emphasizes that variation in monsoon intensity is most likely the primary drive of the intensity of weathering and erosion in Southwestern Taiwan River sediments over the last 13.0 ka BP. Finally, we concluded that geochemical parameters can be used as reliable proxies for climate variation on a millennial-centennial time scale in such areas as Taiwan, where weathering-limited regimes exist. [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]

Abstract: The eolian component in Pacific Ocean sediments has been recognized as providing a direct link between the continental loess and marine δ 18O climate records over orbital timescales since 500ka. Here we extend this eolian record over the past one million years. We constructed high-resolution clay mineral stratigraphies based on δ 18O chronology in sediments from the International Marine Past Global Change (IMAGES) Core MD06-3050 from the West Philippine Sea in order to trace the sources of clay minerals and reconstruct proxy records of past changes in the Asian eolian input to the basin since 1.0Ma. The clay mineral assemblage in Core MD06-3050 mainly consists of smectite (~65%) and illite (~25%), with minor kaolinite (~5%) and chlorite (~5%). Provenance analysis suggests that smectite was derived mainly from the weathering of volcanic rocks on Luzon island, whereas illite, chlorite and kaolinite were mainly transported as eolian dust by the East Asian winter monsoon from central Asia. Illite/smectite values in Core MD06-3050 are generally higher and more variable during glacial periods and lower during interglacials, suggesting that higher eolian input to the West Philippine Sea generally co-varied with East Asian winter monsoon intensity and more aridity in continental Asia since 1.0Ma. Spectral analysis further reveals the close link between the extent of high-latitude glaciation, East Asian winter monsoon intensity and eolian input to the West Philippine Sea at eccentricity (100ka), obliquity (41ka) and precession (23ka) bands since 1.0Ma. [Copyright &y& Elsevier]

Abstract: The Late Pliocene is thought to be characterized by the simultaneous intensification of both the East Asian winter monsoon (EAWM) and East Asian summer monsoon (EASM). However, the evolution of the EASM during the Pliocene remains still controversial and only little is known about the dynamics of the EASM during the Pliocene on orbital time scales. Here we use clay mineral assemblages in sediments from Ocean Drilling Program (ODP) Site 1143 in the southern South China Sea (SCS) to obtain proxy records of past changes in the EASM climate during the Pliocene. Provenance analysis suggests that illite, chlorite and kaolinite originated mainly from the Mekong River drainage area. Smectite was derived mainly from the Indonesian islands. The kaolinite/illite ratio and the chemical index of alteration (CIA) of siliciclastic sediments allowed us to reconstruct the history of chemical weathering and physical erosion of the Mekong River drainage area and thus, the evolution of the EASM during the Pliocene. Our clay minerals proxy data suggests a stronger EASM during the Early Pliocene than during the Late Pliocene. We propose that the long-term evolution of the EASM has been driven by global cooling rather than the uplift of the Tibetan Plateau. Spectral analysis of kaolinite/illite ratio displays a set of strong periodicities at 100ka, 30ka, 28ka, 25ka, and 22ka, with no clear obliquity-related signal. Our study suggests that the Pliocene EASM intensity on orbital time scales is not only controlled by the Northern Hemisphere summer insolation, but also strongly influenced by equatorial Pacific ENSO-like ocean–atmosphere dynamics. [Copyright &y& Elsevier]