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Abstract The implementation of Water-Sediment Regulation Scheme in the summer season has introduced a new hydrological regime to the Yellow River downstream since AD 2002. The contribution and fate of the soil organic carbon from the Yellow River that reaches the deltaic and coastal environments are important to understand the regional and global carbon cycle. Glycerol dialkyl glycerol tetraethers (GDGTs) are biomarkers with potential implications in the reconstruction of soil OC transportation and paleo-environmental information. In this study, we collected suspended particulate matter samples from downstream waters of the Yellow River from September 2012 to October 2013 to assess 1) the sources of GDGTs, 2) the impact of the operations of reservoirs on the distribution and transportation of GDGTs to the Yellow River estuary region, and 3) the potential implications of GDGTs as proxies for paleoenvironment reconstruction. Our results suggested that over this annual cycle, more than 72.7% of the particulate isoprenoid GDGTs and 82.6% of the particulate branched GDGTs to the Yellow River estuary region were attributed to the intensive discharge during the Water-Sediment Regulation period. The overall GDGT-based BIT (index of branched and isoprenoid tetraethers) values for the particulate matters exported to the Yellow River-dominated continental margin through this annual cycle were higher than 0.5, and thus were capable of tracking soil organic carbon input. As the contribution of soil-derived GDGTs from the Yellow River would potentially influence the GDGT-based TEX 86 and CBT-MBT temperature proxies in the estuary-coastal region, a careful examination is required before applying these proxies to temperature reconstruction in deltaic and coastal areas. Highlights • Hydrological dynamics control on soil OC transportation to the Yellow River estuary. • Annual GDGT flux to the Yellow River estuary comes from soil OC. • BIT index is a proxy for tracking soil OC input in the Yellow River estuary. • Soil OC increases sedimentary TEX 86 values in the Yellow River estuary. • MBT-CBT signal at the estuary reflect temperature from upper reaches. [ABSTRACT FROM AUTHOR]

The late Quaternary paleoceanography and paleoenvironment of the South China Sea (SCS) have been well reconstructed over the last decade. In contrast, the provenance of the terrigenous sediments that have accumulated in the northwestern continental shelf mud area remains enigmatic. This study investigated the provenance of these sediments and the paleoenvironmental changes archived in Core X2 via the analysis of geochemical elements, grain size, and accelerator mass spectrometry (AMS) 14 C ages. Based on the upper continental crust (UCC)-normalized REE patterns and REE fractionation parameters, southwestern and western Taiwanese rivers and the Pearl River were identified as the main sources of the fine-grained sediment deposited in the northwestern shelf mud area off Hainan Island. This finding further confirms the long-distance transport (> 1000 km) of fine-grained sediment from Taiwanese rivers to the northern SCS shelf and slope. Obvious changes in the grain size and Chemical Index of Alteration (CIA) record occurred at approximately 4.0 cal kyr BP and were likely caused by increased Hainan Island inputs due to sea level changes. [ABSTRACT FROM AUTHOR]

A total of 141 surface sediments were collected and analyzed for their geochemistry, total organic carbon, and grain size to assess the heavy metal pollution in the Bohai and Yellow Seas. The enrichment factor (EF) and geoaccumulation index ( I geo ) of Cu, Pb, Zn, Cr, Cd, Ni, As, and Hg were calculated to assess anthropogenic contamination, and the results suggest that moderate Pb, Cd, and As contamination occurs in the study area. Sediment quality guidelines were applied to assess the adverse biological effects of these metals. The spatial distribution of the mean Effects Range-Median quotient for the vast majority of the study area is between 0.1 and 0.5, indicating low impact and potential negative biological effects. Multivariate analysis indicates that Cu, Pb, Zn, Cr, and Ni resulted primarily from lithogenic sources, whereas As, Cd, and Hg were mainly attributed to anthropogenic sources. [ABSTRACT FROM AUTHOR]

In this study, the suspended particulate matter (SPM) of the Yellow River (Huanghe) was collected biweekly at the outlet and analyzed for particulate trace element contents. The seasonal variations of the trace elements were primarily controlled by hydrological processes, which determined different sources of the SPM. Moreover, As, Co, Cr, and Ni primarily originated from lithogenic sources, whereas Cd, Cu, Pb and Zn were influenced by anthropogenic activities. The Yellow River has suffered moderate to considerable ecological risk during the late stage of Water and Sediment Regulation (WSR). Using the discharge-weighted contents method, the annual trace element fluxes were estimated, with ca. 30% of the annual fluxes occurring within the short WSR period (6% of one year). More specifically, 75% of the Cd flux was from an anthropogenic source, which likely posed a significant threat to the estuary and the adjacent coastal ecosystems. [ABSTRACT FROM AUTHOR]

Clay mineralogy of 54 fluvial samples collected from 20 major rivers on Hainan Island are investigated in order to determine compositional changes of clay minerals and to assess the weathering processes. The clay mineral assemblages consist dominantly of kaolinite (31–66%), with a lesser abundance of chlorite (22–44%) and illite (4–33%), and a trace amount of smectite (0–15%). Fluvial sediments from the east and northwest of Hainan Island are characterized by a higher kaolinite content and illite chemical index and poorer illite crystallinity than those from southwest Hainan. Only minor smectite (mean of 7%) occurs in the sediments from west Hainan; smectite is total lacking in east Hainan. Compared with the adjacent basins, Hainan Island is characterized by moderate to intensive chemical weathering with strong hydrolysis. Our results suggest that rainfall is the principal factor controlling the intensity of chemical weathering on Hainan Island, with more intense chemical weathering occurring in eastern and northwestern Hainan. Another practical implication of this study is that it provides a “missing” end member (Hainan Island) in the provenance discrimination study focused on the northern South China Sea (SCS). Hainan fine-grained sediments likely play an important role in providing clay minerals to the northern SCS carried by the South China Sea Warm Current (SCSWC) during the summer. [ABSTRACT FROM AUTHOR]

The Kuroshio current transports large amounts of heat and water vapor into the South China Sea (SCS) through the Luzon Strait and plays a key role in modulating the surrounding hydroclimate. However, there is no detailed high-resolution history of the Kuroshio intrusion into the SCS preceding the Holocene. Here, clay mineral assemblages and Sr–Nd isotopic values (87Sr/86Sr and εNd) of core CS11 represent the relative abundance of Taiwan and Luzon fluvial sediment contributions in the SCS deep basin, which can be further used as proxies of relative variation of the Kuroshio intrusion into the SCS over the past 40 kyr. Combined with linear sedimentation rate (LSR) and results of previous studies, we demonstrate that variations of Kuroshio currents between the SCS and the open Pacific display opposing trends within each marine isotope stage, similar to the waxing and waning of its modern configuration. The El Niño–Southern Oscillation (ENSO) has acted as the key factor driving variations of the Kuroshio currents over the past 40 kyr. During late marine isotope stage (MIS) 3, the Kuroshio intrusion into the SCS gradually decreased due to decline in intensity of El Niño-like conditions, while an El Niño-like state favored the Kuroshio intrusion into the SCS during MIS 2, in particular during the Last Glacial Maximum (LGM) when Kuroshio transport in the open Pacific weakened. The Kuroshio intrusion into the SCS was largely sluggish in the early Holocene, when a La Niña-like condition prevailed, and then the Kuroshio intrusion was enhanced during the middle to late Holocene under the influence of increased El Niño frequency. • Kuroshio Intrusion is the key factor controlling sediments reaching deep basin of the NE SCS over the past 40 kyr. • ENSO drove distinct patterns of Kuroshio in the SCS and in open Pacific during each MIS, similar to the modern configuration. • El Niño-like conditions favored increasing Kuroshio intrusion into the SCS but decreasing the transport in the open Pacific. [ABSTRACT FROM AUTHOR]

We present a provenance study of two cores (YSC-1 and YSC-4) from the Central Yellow Sea Mud (CYSM) to investigate the source and transport processes of clay minerals during the Holocene. Clay mineral assemblages of Cores YSC-1 and YSC-4 mainly consist of illite, followed by chlorite and kaolinite, and scarce smectite. Combined with other published data, it is found that the fine sediments in the CYSM are most likely a mixing product of the Changjiang and Korean Peninsula small rivers sediments. In contrast, the influence of Huanghe sediments is rather limited and only appears in the bottom part of Core YSC-1. Decreased contribution of terrigenous supply from the Changjiang to the CYSM since 6.4 ka may be related to the formation of modern ocean circulation pattern. After 6.4 ka, the finer sediments of Taedong and Chongchon Rivers from the northern Korean Peninsula are dominated in the CYSM. The oceanic fronts likely prevent both the suspended sediments of the west (modern and older Huanghe) and east (southern Korean Peninsula small rivers) sides from dispersing into the central Yellow Sea. Our results thus highlight the highly complex nature of sediment source and dispersal pattern in the Yellow Sea during the Holocene. More detailed studies are needed to better understand the sediment source-to-sink history of Yellow Sea. [ABSTRACT FROM AUTHOR]

Highlights: [•] Spatial distributions of Cr, Cu, Ni, Pb and Zn were determined. [•] Surface sediments have potential ecological risk of Cr, Cu and Ni. [•] Geochemical approach confirms anthropogenic influence of heavy metal pollution (Pb). [Copyright &y& Elsevier]

Highlights: [•] Spatial distributions of selected trace metals were investigated. [•] Occasional biological effect may occur due to As, Cr, Cu, Ni, and Pb. [•] As and Pb are highly influenced by anthropogenic activities. [Copyright &y& Elsevier]

Abstract: Sixty-nine samples of surface sediments (0∼5 cm) recovered from the eastern Beibu Bay were analyzed for TOC and heavy metals to examine the element distribution pattern and potential pollutant sources. The sediments in the study area are characterized by variable heavy metal concentrations that are comparable with those of the surrounding regions. Obvious positive correlations were observed amongst the concentrations of Zn, Cr, Pb, Cd, Cu and the clay contents, suggesting that fine clay particles are important carriers of trace metals in the sediments. Hg and As show a considerable/low positive correlation with TOC, indicating that organic matter may play a discernible role in the sediment chemistry. Cd contamination was detected in the north of the study area primarily due to the input of phosphate fertilizers carried by rivers. In comparison, Zn, Cr, Pb, and partly Cu are predominantly sourced from lithogenic components, and Hg and As are mainly from organic matter related to anthropogenic input. [Copyright &y& Elsevier]

Abstract: The natural hydrologic regime of the Changjiang (Yangtze River) in China has been disturbed considerably by intensified human activities over the past five decades. In this study, sediment rating curves were analyzed based on monthly data of water discharge and suspended-sediment concentration at stations in the upper (Yichang station), middle (Hankou station) and lower (Datong station) reaches of the Changjiang in different periods from 1955 to 2007. Temporal and spatial variations of the sediment rating curves were analyzed with respect to the impact of human activities and watershed characteristics. Results indicate that human disturbances have had a substantial impact on sediment rating parameters, with the magnitude of the impact related to the scale of the river sections. As indicated by the sediment rating parameters, the sediment transport regimes between the upper and the mid-lower reaches differ significantly. In particular, the impoundment of the Three Gorges Dam in 2003 changed the sediment transport regimes in the upper and mid-lower reaches of Changjiang into similar regimes characterized by a decrease in the sediment transport capacity of high water discharge. Furthermore, the sediment rating curve at the Datong station in 1955–1968 was applied to estimate the potential sediment load (1969–2007) in the absence of human influences. The mean annual sediment deficit caused by human activities has increased from 80Mt/yr (1969–1985) to 250Mt/yr (2003–2007). This indicates that intensified human activities in the Changjiang basin, especially the construction of the Three Gorges Dam, have altered the natural sediment transport process, and have thus become a dominant force in Changjiang sediment delivery to the sea. [ABSTRACT FROM AUTHOR]

• Sediments on the continental shelf of southeastern Hainan Island are mainly derived from Hainan. • During the period of significant sea level rise, extreme cold events had a considerable impact on this area. • The sedimentary record during the sea-level highstand was mainly controlled by climate change. • An increase in chemical weathering could be attributed to a rise in typhoon intensity or frequency. The South China Sea, which connects the Indian Ocean and the Pacific Ocean, is an important part of the Indo-Pacific Warm Pool. This study examined the provenance and evolution of the sedimentary environment on the southeastern Hainan Island continental shelf in the northwestern South China Sea through AMS 14C dating, grain size analysis, and clay mineral analysis of sediments from Core QZ4. The clay mineral analysis indicated that the terrigenous detritus originated from Hainan Island, while the grain size data identified three endmembers: EM1 and EM2, corresponding to the fine-grained material transported by the oceanic current system, and EM3, corresponding to the coarse-grained material input by rivers from proximal sources. The sedimentary environment in the study area underwent three stages: foreshore (11.2–9.2 ka BP), nearshore (9.2–6.2 ka BP), and shallow shelf (6.2 ka BP to present). From 11.2 to 6.2 ka BP, the sedimentary environment was mainly controlled by sea level changes, although extreme cold events (such as the 9.4 ka BP and the 8.2 ka BP event) had a significant effect on the southeastern continental shelf of Hainan Island. From 6.2 ka BP to the present, the sedimentary record has mainly been influenced by climate change, and an increase in riverine contribution and the enhancement of chemical weathering may have been caused by rising typhoon intensity or frequency and possibly by an increase in human activities. These findings will be valuable for conducting high-resolution research on typhoons by analyzing sediments on the eastern Hainan Island shelf and neighboring areas. [ABSTRACT FROM AUTHOR]

Sediments from the Yellow Sea (YS) are important archives for investigating the stratigraphic evolution in relation to global and regional sea-level changes. Here, the upper 40-m-thick interval of a 100-m-long drill core (NYS17), retrieved from the eastern North Yellow Sea (NYS), were studied to explore the late Quaternary sedimentary history in this region. To obtain reliable chronological framework of the core, we utilized multiple luminescence signals from sediments for dating. Coarse-grained (CG) and fine-grained (FG) quartz optically stimulated luminescence (OSL), and K-feldspar/polymineral post-infrared (IR) IR stimulated luminescence (pIRIR 50/150) signals were analyzed to obtain age estimates for comparison. Primary results show that quartz OSL ages are consistent with the corrected ages of IR 50 and pIRIR 150 signals. Chronostratigraphy of core NYS17 presents two phases of rapid accumulation. One is at the interval of 35.6–29.8 m deep, as age controls of sedimentary stratigraphy are in the period of 135–130 ka, corresponding to Marine Isotope Stage (MIS) 6/5. Another occurs in the upper section (14.5–0.9 m) as luminescence ages are constrained between 11 and 9 ka. However, the overlying deposits after 9 ka seem to be very thin in the core site. This is likely attributed to the abundant terrestrial sediment supply during the early Holocene and following starvation after further rise of the sea level and transgression. In contrast, the MIS 5–2 interval remains far to be exactly defined in the core as no age constraint is available. Regionally, correlations of chronostratigraphy of our core with other collected cores from the YS and East China Sea, show comparable depositional records for both the late Pleistocene and Holocene sedimentary successions. These findings indicate that the spatiotemporal variations of sedimentary processes in the YS shelf were closely linked to global sea-level changes during the glacial-interglacial cycles. • We provide a new 135-ka-long chronological sequence for the upper 40-m-thick interval of a 100-m-long drill core (NYS17) in the eastern NYS. • The reliability of the new chronology was examined by internal cross-check of ages from multiple luminescence signals and external chronostratigraphy in the YS. • Two phases of rapid accumulation in 135–130 ka and 11–9 ka, associated with the inferred MIS5-2 stratigraphy are controlled by the sea-level changes. [ABSTRACT FROM AUTHOR]

The heavy metals in surface sediments of the continental shelf of the South Yellow Sea (SYS) and the East China Sea (ECS) collected in 2016 were analyzed to assess the heavy metal distributions, contamination status, and likely sources. The metal concentrations generally met the China Marine Sediment Quality criteria. However, the enrichment factor and geoaccumulation index values clearly showed elevated Cd and Pb concentrations in the region. Cd and Pb contamination occurred mostly to the southwest of the Changjiang River mouth and to the east of the Shandong Peninsula because of rapid economic and industrial development. The results are likely to be useful for authorities responsible for sustainable coastal zone management. [ABSTRACT FROM AUTHOR]

The sediments from a piston core ECS12A recovered from the middle Okinawa Trough in the East China Sea were measured for total organic carbon (TOC), total nitrogen (TN), and other biogenic elements to provide constraints on the sources and burial rates of depositional organic matter (OM) and on the changes in primary productivity since 19 ka. The last glacial sediments (ca. 17–19 ka) are characterized by low contents of biogenic elements and well-developed turbidite layers, suggesting low primary productivity but a high component of terrigenous sediment. With rising sea level and enhanced monsoons during the deglacial period, the proportion of marine OM gradually increased. The least negative δ 13 C org values and the smallest grain size of sediments deposited ca. 10–14.5 ka indicate high primary productivity and a sedimentary environment dominated by the marine component. The source and burial rates of OM in the Holocene sediments (ca. 5.4–10 ka) were largely controlled by the intensification of the Kuroshio Current, which caused a slight decrease in primary productivity, but strengthened the oceanic circulation in the East China Sea. Overall, the source-to-sink process of OM in the Okinawa Trough is governed by complex interactions between sea level, climate and ocean circulation. [ABSTRACT FROM AUTHOR]

The South Yellow Sea (SYS) is strongly influenced by large amounts of sediment input from surrounding rivers, but the dispersal patterns of these sediments, especially how they accumulate in the central Yellow Sea mud (CYSM) region, have not been well illustrated. Here, we present a detailed temporal variation record of the clay mineral compositions from core YSC-10 of the northern SYS near the western margin of the CYSM, trying to investigate sediment provenance and to discuss transport processes occurring during the Holocene. The clay mineral assemblages of core YSC-10 mainly consist predominantly of illite (68 ± 3%), followed by chlorite (15 ± 2%) and kaolinite (10 ± 2%), with scarce amounts of smectite (6 ± 3%). Combined with published data, our results suggest that the fine sediments of core YSC-10 are most likely a mixing product of the Huanghe (Yellow River), Changjiang (Yangtze River) and Korean Peninsula small river sediments, with notable temporal changes. During 8.4–6.4 ka, the Huanghe sediments from the Bohai Sea flowed directly into the SYS and played major roles in the sedimentation therein. In addition, as the modern ocean circulation pattern was formed ∼6 ka, the ocean front developed along the Shandong Peninsula coastal area of the SYS, which would have prevented the dispersal of the Huanghe sediments to the CYSM. The Changjiang sediments delivered by the diluted water replaced those from the Huanghe as the main source of the CYSM during the period of 6.4–4.2 ka. After 4.2 ka, the coastal shear front weakened and moved seawards due to the weakening and eastward shift of the Yellow Sea Warm Current (YSWC) in winter and the weakening and shrinking of the Yellow Sea Cold Water Mass (YSCWM) in summer. The Huanghe sediments seem to have increased and fluctuated frequently to core YSC-10 since then. Our study thus highlights that the coastal shear front may have played an important role in the source-to-sink processes of the SYS. • Clay mineral assemblages of core YSC-10 which near the western margin of the CYSM since the Holocene. • The source and transport mechanism of clay minerals of core YSC-10 in different time periods since Holocene. • The oceanic front played critical role in the source to sink processes of the SYS. [ABSTRACT FROM AUTHOR]

Three paleotemperature records (foraminiferal Mg/Ca, TEX 86 and U K′ 37 ) were generated for the past 17.3 ka in the southern Okinawa Trough (OT) using a sediment core (OKT-3) taken at a water depth of 1792 m. Temperature estimates based on the inorganic and organic indices for the OKT-3 core top sample approximated modern sea surface temperature (SST) and extended to the mixed layer (<50 m) in warmer seasons. Reconstructed SSTs from OKT-3 gradually increased towards the top of the core with lower values occurring during Heinrich Stadial 1 (HS1) and the Younger Dryas (YD). These values coincided with the glacial–interglacial cycles established by the Globigerinoides ruber δ 18 O curve. Notably, SSTs decreased during the BØlling-AllerØd (B-A) but warming occurred before and after the B-A, from approximately 16 to 14 ka and 12.5 to 10 ka. The SST cooling during the B-A corresponded to the timing of the Antarctic Cold Reversal (ACR), which is thought to be connected with melt water pulse 1a (MWP1a). The cooling was also concurrent with the spread of millennial-scale cold signals to the OT during the HS1 and YD periods, when widespread melt and collapse of Northern Hemisphere ice sheets occurred along with reduced Atlantic Meridional Overturning Circulation (AMOC) and a southward shift of the Intertropical Convergence Zone (ITCZ). The last deglaciation, which began approximately 16–15 ka BP in the OT, might mark the time when the Kuroshio Current (KC) began to strengthen. [ABSTRACT FROM AUTHOR]

Highlights: [•] Glycerol dialkyl glycerol tetraethers (GDGTs) from the southern Yellow Sea, China were investigated. [•] GDGT-0 and crenarchaeol from Archaea varied similarly with total bacterial GDGTs. [•] BIT was not suitable as a proxy for soil organic matter input. [•] The TEX86-derived sea surface temperature and MBT/CBT-derived mean annual temperature were decoupled. [•] Decoupling might be linked to East Asia Winter Monsoon variability. [Copyright &y& Elsevier]

This study focused on radiolarian diversity in the deep-sea sediments of the East Indian Ocean (EIO) to demonstrate their potential as a paleoceanogrpahic proxy. Radiolarians are in general abundant in deep-sea sediment of the EIO. However, around Sri Lanka, their abundances decrease potentially because of terrigenous matter inputs. The significantly high abundance of radiolarians in the northern Ninety-East Ridge (NER) area may indicate high levels of productivity in the overlying waters. Further, redundancy analysis (RDA) demonstrated that, in the EIO, Tetrapyle group and Phorticium group mainly inhabited the water depth between 25 m and 100 m; Acanthodesmia vinculata , Botryostrobus scutum and Dictyocoryne group can potentially be a nutrient indicator; the distribution of Didymocryrtis tetrathalamus tetrathalamus may possibly be related to the dissolved oxygen concentration; the distributions of Cornutella profunda , Cycladophora sp., and Cycladophora cornuta may be mainly influenced by flows of AAIW. Our analysis documented that the distribution of an Equatorial Undercurrent (EUC) assemblage, including A. vinculata , B. scutum , Dictyocryphalus hispidus , D. tetrathalamus tetrathalamus , Tetrapyle group, Phorticium group and Dictyocoryne group, may be controlled by the eastward-flowing EUC with the salinity-high and dissolved oxygen-rich waters. The Antarctic Intermediate Water may also affect the distribution pattern of Intermediate-Deep assemblage, including Cycladophora sp., C. profunda , Clathrocanium diadema and C. cornuta , with a possible northward spread along the NER into the southern Bay of Bengal. • Clarify the biodiversity of radiolarians in the deep-sea sediment of the East Indian Ocean. • Decipher the environmental control of radiolarian distribution pattern. • Indicate some assemblages as tracers of specific water masses. [ABSTRACT FROM AUTHOR]

The exploration of the deep-sea sedimentary microbial communities could reveal the diversity, composition, as well as biogeochemical relationships. The West Philippine Basin, the world's largest marginal basin plate which surrounded by subduction boundaries, has special location and geological significance, while few studies investigated deep-sea sedimentary microbial community especially functional groups and genes involved in N transformation in this area till now. Here, the combination of microbial community composition through 16S rRNA gene sequencing, N transformation functional genes quantification, and geochemical analysis were jointly employed, aiming to explore the vertical distributions of microbial community and N-transforming microorganisms in an intact sediment core (400 cm depth) from the West Philippine Basin (15.32 °N, 133.23 °E, water depth 4941.9 m). The results showed that phyla Proteobacteria and Thaumarchaeota had higher relative abundances in the surface sediments (0–5 cm), while the relative abundance of phylum Firmicutes increased with depth and became dominant in the deeper sediments (350–400 cm). Based on the sequencing and quantification results, the overall abundances of inferred N-cycling taxa and functional genes decreased with depth, and the archaeal ammonia oxidation and denitrification were the dominant N transformation processes in the surface and below the surface (5–400 cm) sediments, respectively. Depth and organic matter were the key environmental variables driving the microbial community structure and N transformation processes in deep-sea sediments. This study could potentially improve the consensus that N-cycling processes in deep-sea sediments are linked and complicated, which could aid to illuminate the understanding of the role of deep-sea microbes in N cycles. [ABSTRACT FROM AUTHOR]