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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]

Thermocline conditions in the tropical western Pacific are closely linked to regional- and basin-scale hydrological variation and may have played a critical role in global climate evolution on various timescales. However, long-term changes in thermocline hydrology in the subtropical northwestern Pacific and their connection to the tropical Pacific remain unclear. Based on planktonic foraminiferal Mg/Ca and δ18O, we reconstructed the temperature and salinity of thermocline water since the last deglaciation, using core OKI02 from the Okinawa Trough (OKT) in the subtropical northwestern Pacific. The results indicated a discrepancy in evolution of both temperature and δ18O between the thermocline and surface water over the past 19 ka. Unlike for surface water, changes in thermocline hydrology correlated with changing conditions in the tropical western Pacific, indicating a close relationship between these regions since the last deglaciation. Thermocline temperature and salinity gradients between the OKT and the tropical western Pacific increased from ∼16.5 to 10 ka BP, reached their maximum values at approximately 10 ka BP, and then decreased from the Early Holocene to present. Variations in temperature and salinity gradients correlated with changes in the El Niño–Southern Oscillation (ENSO) over the past 19 ka, which were coupled with equatorial summer insolation variations. We suggest that the ENSO-like process, forced by equatorial summer insolation, regulated thermocline dynamics in the subtropical northwestern Pacific Ocean since the last deglaciation, by influencing the strength of the Kuroshio Current. • TWT changes were different from those of SST in OKT for the past 19 ka • Thermocline conditions in OKT linked to hydrological climate variations in the tropical western Pacific through the KC • ENSO state could have controlled the thermohaline variations in the OKT • Reduced TWT and salinity gradients between the tropical western Pacific and OKT since the Early Holocene [ABSTRACT FROM AUTHOR]

The Pearl River drains the South China Block and delivers large amounts of sediments to the northern South China Sea, and its development can be closely linked to the regional paleoenvironmental changes. However, the evolutionary history of the Pearl River has been poorly understood, mainly because of the lack of continuous and high-resolution sedimentary records over a long geological time. In this study, we present multiple new analytical results, including clay mineral assemblages and Sr-Nd isotopic compositions of the <2 μm siliciclastic sediments, from the latest deep sea drilling core in the northern South China Sea from International Ocean Discovery Program (IODP) Site U1501. We aim to reconstruct the evolutionary history of the Pearl River by tracing changes in clay mineral assemblages and Sr-Nd isotopic compositions. Provenance analysis indicates that the sediment source experienced a significant change between 32 and 30 Ma. Specifically, sediments prior to 32 Ma were derived from the southeastern Cathaysia coast, whereas sediments post to 30 Ma were mainly supplied by a proto-Pearl River. This provenance transition indicates that the modern-scale Pearl River has fully developed at least ∼30 Ma and began to contribute sediments to the northern South China Sea. We additionally compared the timings of major climatic and tectonic events in this region, and suggest that the topographic uplift of the SE Tibetan Plateau most likely drove the large-scale westward expansion of rivers drainage from the coast located in the Cathaysia Block to the interior of Yangtze Block. As a result of this fluvial drainage evolution followed by the development of Pearl River, geochemical and clay mineralogical characteristics of the deposits in the northern South China Sea correspondingly changed. • The first continuous record of South China erosion from the South China Sea since ∼35 Ma. • The provenance records reveal the formation of the modern-scale Pearl River at ∼30 Ma. • The uplift of Southeastern Tibetan Plateau promotes the formation of the Pearl River. [ABSTRACT FROM AUTHOR]

Changing weathering intensity, sediment transport, and provenance variations over the past 22.0 ka BP have been investigated by high-resolution clay mineralogy, grain-size and stable oxygen isotopes of planktonic foraminifera records along core CG2 recovered from the continental slope of the Sunda Shelf (southern South China Sea). Our results indicated that the reworking of older sediments outcropping on the Sunda Shelf exerted a great influence on the sediment supply during the last glacial and most of the last deglacial, modulated by sea level and monsoon rainfall changes. During the last 9.0 ka BP, relative increased kaolinite and heavier δ 18 O seawater values might reflect the higher influence of the tropical Indonesian Islands sources due to the reopen of southern straits, implying the formation of modern oceanic circulation and depositional patterns. High sediment fluxes in core CG2 during Heinrich stadial 1 might be a synthetic result of the intensified monsoon rainfall originated from the southward shift of the Intertropical Convergence Zone and the proximal location of the study core before the flooding of the Sunda Shelf. Fluctuations in smectite/(illite + chlorite) ratios correlated well with monsoon intensity, and periods of strong monsoon rainfall (lighter δ 18 O seawater values) were associated with an intensification of erosion of pre-existing, more weathered materials on the Sunda Shelf. Finally, we concluded that sediment composition and mineralogy in the southern South China Sea slope were controlled by varying degrees of reworking on the Sunda Shelf, as well as climatically modulated sediment supply from the Mekong River and southern tropical islands over the last 22.0 ka BP. [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]

Asian dust deposition in the northwestern Pacific is generally linked to high-latitude paleoclimate evolution during the Quaternary. However, whether low-latitude tropical Pacific processes, such as El Niño-Southern Oscillation (ENSO), influence Asian dust input into the northwestern Pacific remains uncertain. Here, we present clear periodic variations in potassium content (K (wt%)) and gamma-ray attenuation (GRA) bulk density, which are closely linked to the variations in Asian dust, in a sediment core recovered at Site U1438 in the Amami Sankaku Basin (ASB), northwestern Philippine Sea. Based on the shipboard age-depth model, we tuned the GRA to the mass accumulation rate curve on the Chinese Loess Plateau and the 8-kyr-lagged obliquity curve, and established the astronomical timescale. The K (wt%) content and GRA were higher during glacials and lower during interglacials, as driven by the variability in the Northern Hemisphere ice sheet (NHIS) during the Quaternary. In addition, strong long eccentricity 405-kyr cycles were observed in the dust records (K (wt%) content and GRA) during the early Pleistocene. The 405-kyr filter results showed that increased (decreased) Asian dust corresponded to the La Niña-like (El Niño-like) state, suggesting that Asian dust input into the northwestern Pacific was modulated by ENSO on 405-kyr cycles in the early Pleistocene. Our study illustrated the possible link between long eccentricity 405-kyr cycles in the Asian interior and low-latitude forcing, including potential modulation by ENSO. • K (wt%) and GRA from Site U1438 are related to input of Asian dust. • Dust signals were used to reconstruct the orbital chronological model. • Dust signals have clear 405-kyr cycles during the early Pleistocene. • Long eccentricity forcing Asian dust input into the northwestern Pacific. [ABSTRACT FROM AUTHOR]

To synthetically realize the character of major-element compositions as well as its significance for provenance and paleoenvironment recorded in core sediments of the West Philippine Sea over the last 700 ka, grain size and major elements of 221 bulk sediments, together with major-element compositions in the detrital phase of 16 typical samples, in core MD06-3047 collected from the Benham Rise were analyzed. Both discrimination plot and R-mode factor analysis indicate that vertical changes of major elements are mainly controlled by the sedimentation of nearby volcanic matter and the eolian dust input, whereas influences from marine biologic deposition and hydrothermal activity are minor. In particular, AlO and KO are representative of an eolian dust factor. The variation in the eolian dust factor score is characterized by the obviously glacial-interglacial periodicity and can be well compared with the paleotemperature record of the Antarctic ice core and the evolution of the East Asian winter monsoon (EAWM) recorded in the Chinese loess sequence, and then offers a new proxy for the evolution history of eolian dust input into the study area that is controlled by the EAWM intensity and aridity in the continental source regions of atmospheric dust. [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]

This study examines how geochemical signals regarding the source and transformation in suspended particles are transported in the marine portion of the sediment dispersal system. In the source-to-sink sedimentary continuum of a world major river, the Changjiang (Yangtze) River, is used to demonstrate the close coupling between the marine physical processes and the geochemical signals carried by suspended particles. A sediment trap mooring configured with a non-sequential sediment trap, a downward-looking ADCP, CTD, LISST-100× were deployed for 29 days in the winter of 2014 off the coast of Zhejiang Province, China in water depth of 22.5 m. The mooring rendered two types of data. Physical processes included temporal changes of water depth, currents at 11 depths, temperature at two depths, and salinity at one depth. There was 15-cm accumulation of captured particles in the trap, which rendered the total mass flux of 233.3 g/cm2/day. The trap material was analyzed for grain-size composition, total 210Pb, minerals including mica/illite, kaolinite, chlorite, k-feldspar, plagioclase, quartz, and dolomite. Organic material (TOC, TN) and carbon isotope δ13C were also measured. The range of terrestrial fraction (F t) of the trap material was between 45–60%. EOF analysis was used to examine the covariability in both data sets. For the physical data set, 37 variables were used in the analysis. For the sediment trap material, 15 variables were used. The EOF results of the physical processes indicate the tidal flow was the most important physical forcing for the transport of suspended particles and water masses that carried marine- and terrestrial-sourced particles. Wave and current combined resuspension entrained reworked sediment off the seabed, which was then transported landward or seaward. The most important covariability of the particle properties in the sediment trap was caused by hydrodynamic sorting that separated the clay from silt and sand sizes. Geochemical signals of the particles were carried by clay and the particle mass (dry weight) was associated with silt and sand. The temporal characteristics of the sorting show the spring-neap tidal cycle. The next major distinction was the contrast between terrestrial- and marine-sourced materials. The EOF analysis further distinguish contributions from the distal Changjiang River and proximal small rivers at the tertiary level of the covariability. The coverabilities in both data sets show close correspondence. Our findings give firm evidence to show marine processes dominated the transport of land-derived fluvial sediment and the incorporation of marine-sourced particles into the dispersal system. There is complexity in both physical processes and geochemical signals of suspended particles. However, our study points out the close coupling between the two. • Tidal flow was the most important physical process to transport sediment and water masses to the site. • Waves and tides together entrained reworked sediment into the CJR sediment dispersal system. • Hydrodynamic sorting by spring-neap tides separated clay from silt and sand in the trap material. • Geochemical signals were carried by clay and mass flux was contributed by silt and sand. • Suspended particles of terrestrial and marine origins were transported to the site from different sources. [ABSTRACT FROM AUTHOR]

Modern source-to-sink processes in the southern South China Sea (SCS) remain poorly understood. In this study, clay minerals and magnetic properties are used to identify the sources and transport pathways of surface sediments in the southern SCS. The distributions of four clay mineral species in the deep southern SCS are mainly controlled by sediment sources, while clay minerals on the outer Sunda Shelf mostly reflect reworking/recycling of older weathered sediments. Clay mineral analyses indicate that the Mekong River is the predominant contributor of clay minerals to the southern SCS, with minor contributions from Luzon and/or Palawan and northern Borneo. The contribution from the Luzon and/or Palawan arc to the southern SCS is semi-quantitatively evaluated as 20% and is mainly smectite. Most sediments in the southern SCS are magnetically dominated by mixtures of magnetite, hematite and goethite in variable proportions. Concentration-dependent magnetic parameters decrease gradually seaward and then sharply towards the outer deep sea. The grain size of magnetite particles also shows a significant fining trend with distance from the southwestern sources. In addition, the magnetic minerals change from hematite- and goethite-dominated to magnetite-dominated type as going further offshore. These magnetic characteristics suggest that the magnetic minerals in the southern SCS are mainly sourced from the southwest through summer monsoon-driven surface currents. Finally, combining the provenance signature indicated by clay minerals and the transport information revealed by magnetic properties, this study highlights that the Mekong River plays a major role in modern source-to-sink processes in the southern SCS. In brief, our study sets a good example for tracing sediment provenance and transport in other marginal seas worldwide. • Clay minerals and magnetic properties are used to identify the sources and transport pathways. • The Mekong River plays a predominant role in the source-to-sink processes of the SW SCS. • Magnetic minerals are sourced from the southwest through summer monsoon-driven surface currents. • Coupled analyses of clays and magnetic minerals can yield valuable and complementary information. [ABSTRACT FROM AUTHOR]

Reconstructing the Cenozoic sedimentary history of the Bay of Bengal (BoB) is significant for understanding the evolutionary history of South Asian river systems and the links between river development, tectonic deformation and global climate change. Here, we present the first long-term clay mineral record combined with Sr-Nd isotopic compositions from a 200-m-long sediment core from Ocean Drilling Program (ODP) Site 758 in the southern BoB to establish past variations in sediment sources and river evolution that have occurred since the late Eocene. Provenance analysis suggests that the contribution of the Himalayan source materials from the Irrawaddy and Brahmaputra Rivers to the study site became more important and stable since 22 Ma and 8 Ma, respectively. This new evidence indicates that the Brahmaputra and Irrawaddy Rivers were possibly initiated in the early Miocene (~22 Ma). Considering the timing of major tectonic and climatic evolution in South Asia, we conclude that the two phases of tectonic uplift of the Himalayan orogen that occurred in the early and late Miocene were the primary controls on river development in South Asia and provenance changes in the southern BoB. Global cooling and Indian drying after the late Miocene could also have strengthened Himalayan erosion and contributed more illite and chlorite to the South Asian margin. • First long-term clay-sized sediment record of Himalayan erosion from the Bay of Bengal since the last 37 Ma. • South Asian river system (Brahmaputra and Irrawaddy Rivers) might have initiated and established at the early and late Miocene, respectively. • Himalayan uplift exerts primary controls on river evolution in South Asia since the early Miocene. [ABSTRACT FROM AUTHOR]

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]

A high-resolution fire history in the Yangtze River Basin over the past 7.0 ka BP is reconstructed based on the proxy of black carbon of sediment core ECMZ on the continental shelf of the East China Sea in order to reveal the interactions among fire, climate, vegetation and human activity on a regional scale. A comparison of fire activity with climatic and vegetation proxies suggests that changes in fire activity prior to 3.0 ka BP on both millennial- and centennial-timescales were closely related to variations in temperature and precipitation, with more fire during warm and humid periods, suggesting climatic control on regional fire activities. In contrast, the significant decoupling between fire and climate on multi-timescales since ∼3.0 ka BP implies increasing anthropogenic impact on regional fire activity. There is also a distinct response of fire activity to human disturbance at different time scales. Long-term reduction in regional fire activity since ∼3.0 ka BP was caused by a general decrease in forest cover with increasing human activity while short-term (centennial-timescale) enhancement in biomass burning usually coincides with periods characterized by increasing human activity associated with population migration or technological advances. • We reconstruct a regional fire history in the Yangtze River Basin since 7 ka. • Human impact changed the link of fire and climate in Yangtze Basin since 3 ka. • Human activity can suppress (promote) fire on millennial (centennial) timescale. [ABSTRACT FROM AUTHOR]