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Xianxian geothermal exploitation area is one of the areas with the best occurrence conditions of geothermal resource in North China, rich in medium and low temperature geothermal resource, and is a typical carbonate geothermal field. However, its hydrogeochemical evolution process is not clear, and no complete conceptual model of geothermal genesis has been established to guide the exploration, development and utilization of geothermal resource in the area. It restricts the sustainable development of regional geothermal resource and the realization of carbon emission reduction targets. In this study, geothermal fluids in the area were collected for testing and analysis in terms of hydrochemical characteristics and stable isotopes. Based on systematic geochemical research, the formation mechanism of geothermal fluids was analyzed, and a conceptual model of geothermal genetic in the study area was established. The main understanding is as follows: the hydrochemical type of geothermal water in the study area is Cl-Na type, and the water-rock interaction is not balanced. The formation of geothermal water in the area is affected by the infiltration of atmospheric precipitation, and it is terrestrial leached water. The flow path of geothermal water is long, the water circulation is slow, and the metamorphism is deep. Dolomite, calcite and gypsum dissolution are the main sources of Mg2+, Ca2+, , and in geothermal water, besides, other minerals containing calcium and magnesium are also part of their sources. The source of geothermal water recharge is atmospheric precipitation, and the recharge elevation of geothermal water is about 619–1069 m. The age of the geothermal water is between 16 000 and 18 000 years. The sulfur in geothermal water mainly comes from the leaching of sedimentary layer. [ABSTRACT FROM AUTHOR]

The North China Plain, which is the central part of the lithospheric thinning in the North China Craton, is rich in clean geothermal energy. However, a current lack of understanding about the thermal accumulation mechanisms of the deep geothermal resources in this area is hindering the exploration, exploitation, and utilization of these resources and the achievement of the carbon reduction targets. Based on deep drilling and the tests of thermal property parameters at different depths, this study calculated the terrestrial heat flow and the heat flux at different depths of the lithosphere in the North China Plain and revealed the lithosphere thermal structure characteristics and the thermal accumulation mechanisms in the plain, obtaining the following results. The North China Plain has widely varying terrestrial heat flow of 33.5–92.1 mW/m2 (average: 62.1 ± 17.04 mW/m2). The average mantle heat flow and crustal heat flow in the plain are 42.05 ± 13.90 mW/m2 and 20 mW/m2, respectively, which account for approximately 67% and 33% of the total surface heat flow in the plain, respectively. This plain has a greatly varying Moho depth of 30–40 km and a Moho temperature of 420–920 °C mostly. The thermal lithosphere in the North China Plain has a thickness of 80–100 km and a thermal structure of the cold crust and hot mantle type. It has thinned on a large scale due to the extensional process, and the mantle-derived materials have migrated upward along the weak structural plane (e.g., deep faults) after pressure release and remelting. The resultant high mantle heat flow serves as a stable heat source for the formation of layered medium-low temperature geothermal fields. [ABSTRACT FROM AUTHOR]

The precise exploration of the characteristics of geothermal fields in sedimentary basins, such as the temperature and burial depth of their deep geothermal reservoirs, is of great significance for improving the probability of penetration and reducing exploration risks and development costs. This study proposed a joint exploration method combining magnetotelluric (MT) sounding and geothermometers. Using this method, this study estimated the geothermal reservoirs' temperature and the circulation depth of geothermal water in the Xianxian geothermal field, a typical geothermal field in a large sedimentary basin in northern China, and prepared the temperature and depth maps of the geothermal reservoirs. The main results are as follows. First, the bedrock's geothermal reservoirs with karst fissures in the Xianxian geothermal field have great potential for development. Among them, geothermal reservoirs in the Jixianian Wumishan formation have a top depth of 1100–1500 m and a thickness of 700–1700 m, and the geothermal reservoirs in the Jixianian Gaoyuzhuang formation have a top depth of 3700–4000 m and a maximum drilled thickness of 400 m. The geothermal reservoirs of the Xianxian geothermal field mainly have medium and low temperatures of 138–160 °C and the circulation depth of the geothermal water is 5873 m. [ABSTRACT FROM AUTHOR]

• A doublet system was selected to carry out reinjection tracer test with sodium naphthalenesulfonate as the tracer. • 1D and 3D models were established to simulate and optimize the multiple exploitation-reinjection schemes. • A dominant fissure channel with a length of 513.7 m was shown between the exploitation well and reinjection well. The imbalance between large-scale exploitation and reinjection year by year has led to the decline of the water level of the geothermal reservoirs in the North of China. The reinjection tracer test was carry out based on the doublet system in the Xianxian geothermal field in China with sodium naphthalene sulfonate as the tracer in this paper. The 1D and 3D models were modeled on the software COMSOL in this study to simulate the predictive analysis of multiple exploitation-reinjection schemes and optimize the design. The monitoring data of the tracer concentration in the water samples collected at the wellhead of the exploitation well showed that the tracer was firstly detected on 30th days after the tracer test started. Afterwards, the tracer concentration reached a peak on the 100th day and then gradually decreased until ∼ 140th day, with a tracer recovery rate of 0.0225%. And one dominant fissure channel between the exploitation well and reinjection well with a length of ∼ 513.7 m was shown in the test. The thermal breakthrough time of the exploitation well was defined as the time when the temperature decreases by 2 °C after 100 years of geothermal exploitation. Based on this, the optimal exploitation solution of the geothermal resources was proposed as the spacing between the exploitation well and reinjection well should be set as ∼ 375 m and the exploitation and reinjection volume is 75 m3/h. [ABSTRACT FROM AUTHOR]

ABSTRACT Millennial-scale monsoon variability has been investigated intensively using loess-based proxies; however, the amplitude and rhythms of millennial-scale signals have seldom been disentangled from the background glacial-interglacial changes. Here we present the results of high-resolution scanning X-ray fluorescence analysis of a 75-m-thick loess sequence from the north-western Chinese Loess Plateau to address glacial-interglacial to millennial monsoon variability over the last two climatic cycles. Variations of the Si/K, Fe/K and Ca/K ratios are separated spectrally into low- and high-frequency components corresponding to glacial-interglacial and millennial-scale monsoon variability, respectively. The results indicate that the three elemental ratios exhibit similar glacial-interglacial variability but with varying spectral densities at the 100-, 41- and 23-kyr periodicities. Millennial-scale variability is quite similar between the three elemental ratios, and comparable to those inferred from records of Chinese speleothem δ18O, Greenland palaeotemperature and North Atlantic cooling events. Comparison of various proxies indicates the broad similar magnitudes of abrupt climate changes, at least during the last two glacial-interglacial cycles, whereas the timing and amplitude of abrupt climatic events are not well correlated. We suggest that refinement of loess chronology and intensive data-model integration in the future are critical to decipher the characteristics and dynamics of rapid monsoon changes. [ABSTRACT FROM AUTHOR]

Pyrethroids are increasingly receiving attention as aqueous micropollutants, but their presence has been reported only in a few small coastal areas. In this study, we investigated the distribution, sources, and risks of nine pyrethroids in large marine zones. The 40 seawater samples were collected from the South Yellow Sea (SYS) and East China Sea (ECS) in China, during the spring of 2020, using a high-volume, solid-phase extraction method. The total pyrethroid concentrations ranged from 0.72 to 1.82 ng L−1 in the SYS and from 0.02 to 11.0 ng L−1 in the ECS. We used cluster analysis to classify pollutant sources into five categories, and discussed the influence of sources on the transport and distribution of pyrethroids in each group. Ecological risk assessment indicated that pyrethroids pose a high risk to crustaceans and a negligible risk to others. These results are important for understanding the behavior of pyrethroids in marine environments. [Display omitted] • Efficient Hi-throat/Hi-volume SPE was used to concentrate pyrethroids from seawater. • Occurrence of nine pyrethroids was investigated at South Yellow and East China Seas. • Distribution and sources are influenced by both human activities and ocean currents. • Ecological risk assessment indicated that pyrethroids pose a high risk to crustaceans. [ABSTRACT FROM AUTHOR]

High demands for but strict regulatory measures on Organophosphorus Flame Retardants (OPFRs) have resulted in mainland China transitioning from the region that imports OPRFs to one that exports these substances. Simultaneously, large quantities of terrigenous OPFRs have been exported to adjacent seas by the major river systems, particularly the Yangtze River. This study examined the presence of ten OPFRs in China's adjacent seas. High levels of OPFRs were observed in seas south of mainland China, with Tris (2-chloroethyl) phosphate (TCEP) and Tris (1,3-dichloro-2-propyl) phosphate (TDCPP) dominant. The terrigenous OPFRs were redistributed by the ocean surface currents, with OPFRs tending to accumulate in regions with lower current speed. The producers of OPFRs are mainly distributed along the Haihe, Yellow, and Yangtze river systems. The application of OPFRs to electric vehicle charging stations, charging connectors, and 5G infrastructure in the Chinese mainland will likely drive rapid growth in OPFR related industry in the future. The diffusion trend map of OPFR indicated that the Bohai Sea and the central northern Yellow Sea are at high risk of ecological damage in the spring. The offshore region of the north of the South China Sea tended to aggregate more OPFRs in summer. Regions of the OPFR aggregation effect were at a higher risk of ecological damage. [Display omitted] • The sea to the south of the Chinese mainland tends to aggregate OPFRs. • Ocean surface currents redistribute terrigenous OPFRs. • China has transitioned to an OPFR export region. [ABSTRACT FROM AUTHOR]

Surface sediment samples collected off the Huanghe (Yellow) River mouth during the period 2007-2009 were analyzed for major and trace element concentrations. Concentrations of 16 elements were measured using X-ray fluorescence spectrometry. Results demonstrate that sediment grain size is the dominant factor controlling the spatial variations of elemental concentrations. Correlation and cluster analyses allowed classification of the study area into four geochemical regions: Regions I and III are characterized by high concentrations of AlO, FeO, MgO, NaO, KO, Cr, Cu, Mn, Ni, Pb, V, and Zn, and contain fine-grained sediments with mean grain size ( M)<22 μm; and; Regions II and IV contain mostly coarse-grained sediments, and are characterized by high concentrations of SiO, NaO, and Zr. The sediment entering the sea from the Huanghe River and its tributaries is enriched in Ca. Thus, the Ca/Al ratio was used as an indicator of the proportion of sediments in the study area that originated from the Huanghe River. Ca/Al ratios decrease from Regions I and II (located in the nearshore zone of the Huanghe River delta) to Regions III and IV (distributed in the offshore zone of the northern Huanghe River delta, southern and southeastern Laizhou Bay area). [ABSTRACT FROM AUTHOR]

In this study, we reported the occurrence of eight organophosphorus pesticides (OPPs) in the East China Sea. Forty samples were collected and analysed with a high volume solid phase extraction method (Hi-throat/Hi-volume SPE) in the early summer of 2020. All the target OPPs were detected in the surface water at one or more stations in the East China Sea, and the concentrations of ΣOPPs were in the range 0.0775–3.09 ng/L (mean: 0.862 ± 0.624 ng/L). Terbufos sulfone and fenthion were the main pollutants in this area, probably resulting from pesticide use in China and other countries. The off-shore input from coastal regions was suggested to be a major source of OPP pollution in the East China Sea, and the movement of ocean currents played an important role in their transportation because around 0.86 t OPPs passed through the Tsushima Strait from the East China Sea each month. An ecological risk assessment showed that these OPPs presented a high risk to species in the East China Sea, whereas they posed no health risk to humans under both the median and high exposure scenario. [Display omitted] • Hi-throat/Hi-volume SPE was suitable for collecting and analyzing OPPs in seawater. • The total concentration of eight OPPs was 0.0775–3.09 ng/L in the East China Sea. • Around 0.86 t OPPs entered the Japan Sea from the East China Sea per month. • There was a high ecological risk of OPPs to organisms in the East China Sea. Hi-throat/Hi-volume SPE is effective in the collection and analysis of OPPs in seawater, and there is emerging risk of OPP exposure to organisms in the East China Sea. [ABSTRACT FROM AUTHOR]

Sedimentation rates and sediment budgets are important agents to understand the source-to-sink dynamics in marginal seas. As a classical representative of mega-river dominated marginal seas globally, the South China Sea (SCS) receives huge amounts of fluvial input from mega rivers covering different climate zones. Despite its well-documented prevalence, quantifying the spatial distribution of sedimentation rate and sediment budget over the entire SCS remains a challenge due to limited data availability. In this study, we employed a comprehensive approach to quantify the modern sedimentation rates and sediment budget in the SCS. This approach combined 210Pb measurements from 409 cores, AMS14C data from 112 cores, and 33 sediment trap observations. Our results show that higher sedimentation rates >0.3 cm/a mainly occur in deltas, shelf mud areas, and upper continental slope that connects the submarine canyon. In the subaqueous Mekong Delta, for example, the sedimentation rates can exceed 10 cm/a. In contrast, there is no substantial modern sedimentation in sandy and gravelly areas of the shelf due to strong erosion by a combination of waves, tides and ocean currents. We further compare these results with the eastern China seas including the Bohai Sea, Yellow Sea and East China Sea. A similar spatial distribution of sedimentation rates can be observed in the continental shelf of the eastern China seas. The Holocene sedimentation rates in the deep-water regions of the SCS are generally <100 cm/ka. The basin floor experiences the slowest accumulation, with rates below 3 cm/ka. In contrast, sedimentation rates on the eastern island slopes range from 3 to 8 cm/ka, while the northern, western, and southern continental slopes accumulate sediment most rapidly, exceeding 25 cm/ka. Approximately 1191.1 × 106 t of fine-grained sediment is deposited annually in the continental mud areas of the SCS, with a comparable amount of 1185.4 × 106 t/a deposited on the continental shelf of the eastern China seas. The continental slope accumulates sediment at a significantly higher rate (∼161.0–239.4 × 106 t/a) compared to the deep-water basin (∼16.5–20.1 × 106 t/a) in the SCS. Most of the modern sediments (>98%) are deposited on the continental shelf and slope. In the SCS, fluvial inputs dominates modern sediment sources, contributing over 80% of the total. Coastal/seabed erosion and biogenic deposition account for approximately ∼18%, with eolian dust contributing less than <2%. The findings presented here are critical for elucidating the sources, transport pathways, and deposition patterns of modern sediments in marginal seas. • Distribution of modern sedimentation rates in the South China Sea was illustrated at the basin scale. • The sediment budget and mass balance from a source–to–sink perspective was constructed. • Comparison of sedimentation rates and sediment budgets of the South China Sea and east China seas was conducted. [ABSTRACT FROM AUTHOR]

Sediment accumulation in continental margins during the Quaternary Period was substantially influenced by both sea-level fluctuations and climate changes. However, the response of sediment accumulation to these changes on an orbital timescale, remains poorly understood, for two main reasons: the scarcity of sedimentary records with a high-resolution chronology, and the difficulty in distinguishing the role of sea-level from regional climate signals. Here we present the results of sediment color reflectance (c*), grain size and total organic carbon (TOC) content of core BH08 (212.4 m in length, spanning the last ~1 Myr) recovered from the Bohai Sea, China. The chronology of core BH08 on the orbital timescale is constrained by both magnetostratigraphy and astronomical tuning. Sedimentary facies analysis suggests that the sedimentary sequence is dominated by the alternation of a deltaic system and floodplain deposition. Principal components analysis of the grain-size data reveals two principal components (PCs), including PC1, reflecting the 31–500 μm fraction, and PC2, reflecting the 18–66 μm fraction. Comparison of sample scores on PC1, PC2 and c* with the alternation of sedimentary environments reveals that PC1 and c* reflect cycles of deltaic and floodplain deposition at ~100-kyr and ~40-kyr periodicities, while PC2 exhibits a ~20-kyr periodicity, in addition to the ~100-kyr and ~40-kyr cycles. We infer that PC1 and c* are mainly sea-level dependent, whereas PC2 is controlled by the combination of changes in monsoon climate and sea level. We suggest that Milankovitch-scale monsoon climate fluctuations controlled the sediments supply to the Bohai Sea during the last ~1 Myr, while the redistribution of sediments by marine processes (e.g., tidal currents) has partially obscured the monsoonal signal in the grain-size proxy (e.g., PC1) which instead is sensitive to sea-level change. Our results provide an example of the influence of climate and sea-level on sediment accumulation in a shallow continental margin setting influenced by monsoonal climate in an icehouse world. • A 1-Myr record of orbitally-forced continental margin deposits is presented. • Principal components analysis of grain size reveals sea-level and climate signals. • Sedimentation in the Bohai Sea is influenced by sea level and monsoonal climate. • Monsoon signal could be obscured by marine process (e.g., tidal currents). [ABSTRACT FROM AUTHOR]

Sediment accumulation and budget in the continental margins provides abundant information of source-sink processes from the land to the sea, including weathering, human activities and sedimentary environment. Here we show the distribution of mud areas, modern sedimentation rates and sediment budget in the Bohai Sea, Yellow Sea and East China Sea. Using grain size data of > 18,000 surface sediment samples and 210 Pb data from 413 sites, we identify five areas with sediments mainly composed of fine-grained fractions (mean grain size > 6 φ) and find a relatively high sedimentation rates of > 1.5 mm/yr in the mud areas. Near the Yellow and Yangtze River deltas sedimentation reaches > 95.0 mm/yr. Approximately 1185.4 × 10 6 tons of fine-grained sediment accumulate annually in the mud areas of the east China seas. Atmospheric deposition contributes < 2% (18.37 × 10 6 tons/yr), while the riverine sediment inputs account for > 75% (917 × 10 6 tons/yr). The remainder comes from all other sources including coastal erosion and resuspension of bottom sediments. In addition, ~ 45% of the fluvial sediment supply deposits on the subaerial delta, ~ 40–50% is trapped on the subaqueous delta and shelf, and the remainder < 5% escapes the shelf edge. The results will be a strong foundation for understanding of the transport, deposit and preservation of sediment and other relevant material (e.g. carbon and nutrient etc.) of terrestrial materials in the sea. [ABSTRACT FROM AUTHOR]

Abstract: Chinese loess is a unique continental archive of Quaternary climate change, and its elemental components or ratios can provide significant insights into variations in the East Asian palaeomonsoon at tectonic to millennial timescales. However, high-resolution elemental analyses of loess deposits have seldom been reported. To investigate geochemical variations of loess sediments at millennial and centennial timescales, and their potential for recording abrupt climate change, powder and U-channel (long plastic single-boxes used to sub-sample the center of split core sections) samples were collected from the Gulang loess section on the northwestern Chinese Loess Plateau for conventional and scanning X-ray fluorescence (XRF) analyses. Results suggest that although ten elements (Al, Si, K, Ca, Ti, Fe, Zn, Rb, Sr and Zr,) can be detected robustly using scanning XRF method, only five elements (Si, Ca, Fe, Sr and Zr) can be employed confidently to infer the chemical weathering and grain size sorting effects. Comparison of scanning XRF-derived elemental data with magnetic susceptibility, grain size and speleothem records indicates that high-resolution elemental records have great potential for evaluating rapid fluctuations of the East Asia monsoon. [Copyright &y& Elsevier]

Abstract: Two gravity cores collected off the modern Huanghe (Yellow River) delta in the southern Bohai Sea were analyzed for grain size, the total organic carbon (TOC)/total nitrogen (TN) ratio, color diffraction, magnetic susceptibility, 14C dating and 137Cs and 210Pb isotope contents to clarify changes in the sedimentary environment during the Holocene. In particular, the effect of natural and artificial river-course shifts of the Huanghe on the Bohai Sea sediment was investigated. A peat layer, scouring surface and sharp changes in the grain size, TOC/TN ratio, sediment color (L ⁎, a ⁎) and magnetic susceptibility were identified and are likely to be due to the early-Holocene sea-level rise resulting in environmental changes from coastal to shelf environments in the Bohai Sea. After the sea level reached its maximum at 6–7kaBP, the lateral shifts in the river course of the Huanghe formed 10 superlobes, and superlobe 7 (11–1048 AD) and superlobe 10 (1855–present) of the Huanghe delta affected the core sites. The northern site of BH-239 has been more affected by the Huanghe since the middle Holocene. Notably, in the superlobe 10 period, the reshaping of the northern Huanghe delta due to an artificial river-course shift from northward to eastward in 1976 (e.g., a∼10km shoreline retreat due to coastal erosion) was recorded in the core sediments, particularly in terms of the TOC/TN ratio, sediment color (L ⁎ and a ⁎) and magnetic susceptibility, owing to the huge sediment supply from coastal erosion of the former river mouth area. [Copyright &y& Elsevier]

Abstract: Hydrological and sedimentological investigations were carried out off the Yellow River (Huanghe) mouth and the nearby Bohai Sea during August–September 2007 to examine the distribution and transport of suspended sediments. Our data witnessed that suspended sediments from the Yellow River mouth primarily extend southerly and southeasterly during the flood season. High suspended sediment concentration (SSC) occurs as turbid plume on both sides of the river mouth, where it can reach >20mgl−1 in the surface water and >40mgl−1 in the bottom water. Accordingly, salinity varies from 25 to 29psu, mean grain size (Dmz) is >200μm, and volume concentration (VC) is >100μll−1. High SSC was concentrated in the river mouth area as two muddy patches, i.e. the North Mud and South Mud, consisting mostly of fine-grained silt and clayey silt sediments. Our results have verified the larger extent of the South Mud than that of the North one, implicating south- and southeastward sediment dispersal paths that prevail near the river mouth area. The existing anti-clockwise and clockwise flows in the river mouth area were synthesized as the major hydrodynamics responsible for forming the two muddy patches. Tidal and residual currents are considered as the key hydrodynamic factors controlling the sediment distribution and transport in the region. [Copyright &y& Elsevier]

[Display omitted] • The Qianlishan granite complex last for 38.8–57.4 Ma. • The duration of the QGC has positive correlation with the volumetric heat production. • Mineralization events well accord with the protracted hydrothermal lifespan. The Dongpo ore field, containing a series of W-Sn-Mo-Bi-Pb-Zn granite-related deposits, is a typical reduced intrusion-related system centered with the causative zoned Qianlishan granite complex (QGC). The QGC comprises porphyritic granite, equigranular granite and granite porphyry. According to zircon U-Pb age data, the emplacement timing of the QGC was constrained to 155–151.7 Ma. Here, we conducted a set of geochronological analyses with different closure temperatures (including monazite, apatite U-Pb, biotite and muscovite Ar-Ar and zircon fission track dating) on the QGC, revealing that the QGC experienced a protracted magmatic-hydrothermal timespan of 38.8–53.8 my. The protracted lifespan is probably due to radiogenic heat supplied by highly enriched high-heat-producing elements. The mineralizing blossom time (149–154.2 Ma) in the Dongpo ore field is in accordance with the prolonged lifespan (5.7 my: from 149.3 Ma to 155 Ma) of the magmatic-hydrothermal process caused by the QGC over the temperature range of 300–800 °C. This result implies that successive inputs of magma with high heat-producing elements (U, Th, K) play a fundamental role in the metal enrichment process of intrusion-related deposits and the formation of large economic ore fields. [ABSTRACT FROM AUTHOR]

Millennial scale variations of terrigenous provenance in marine realm are closely related to regional environment and climate changes. Therefore, a wealth of information of past environment and climate can be constrained via fingerprinting sediment provenance. The Sea of Japan is a unique marginal sea in the North Pacific due to its high sill and distinct thermohaline circulation. The modern hydrography in the Sea of Japan is mainly affected by the East Asian Monsoon and Tsushima Warm Current, one branch of the Kuroshio Current. The Sea of Japan communicates with neighboring seas through four shallow and narrow straits, indicating great effects of global eustatic sea level change on its environment over glacial-interglacial cycles. Here we examine the terrigenous provenance in fine-grained fraction (<63 μm) of core KCES1, located near one end of the Tsushima Strait of the Sea of Japan over the last 48 ka, using radiogenic isotopes of strontium (Sr) and neodymium (Nd). Our data suggest that the terrigenous provenance in core KCES1 was mainly derived from the Yangtze River after 7 ka and a mixture of Yangtze and Yellow Rivers during the last glacial and deglacial periods. Notably, pronounced negative excursions of εNd values at HS1 were attributed to minor additions of unradiogenic Nd contribution from China-Korea cratonic hinterland. A binary mixing model further reveals that >85% terrigenous material is derived from the Yangtze and Yellow Rivers over the last 48 ka. Moreover, abrupt variations in sediment provenance occurred at ~18 ka and ~ 7 ka, which coincide with variations in oceanic surface circulation and deep ventilation recorded in the Sea of Japan. We suggest that paleo-Tsushima Warm Current invaded into the Sea of Japan with reopening of the Tsushima Strait at HS1 and the Tsushima Warm Current substantially entered the Sea of Japan after 7 ka due to intensified Kuroshio Current and rising eustatic sea level. The inflow of Tsushima Warm Current gives rise to a range of changes in surface hydrography, deep ventilation, ecological communities and productivity and sediment texture. The combination of fluxes of paleo-rivers and the intensity of Kuroshio Current, which are closely tied to the eustatic sea level and the East Asian Monsoon, plays a key role in controlling the variations in sediment provenance in the Ulleung Basin. Our study provides unique insight into the tight coupling between changes in sediment provenance and oceanic environment over the last 48 ka in the Sea of Japan. • Radiogenic Sr and Nd isotopes reveal the main provenance of terrigenous materials in the Ulleung Basin over the last 48 ka • Abrupt shift in terrigenous provenance at ~18 ka and ~ 7 ka indicates intrusions of Tsushima Current into the Sea of Japan • Main mechanisms controlling variations in terrigenous provenance in the Ulleung Basin are revealed [ABSTRACT FROM AUTHOR]

This study investigates Holocene sedimentary evolution and hypoxia development using borehole cores CJK06 and CJK09, in combination with other published core data. Based on lithology and microfossil (benthic foraminifera) characteristics, seven types of sedimentary facies were identified from the base upward: river, tidal flat, tide-influenced river, transgressive lag, estuary, inner-shelf, and prodelta. Isochronous correlation among the cores was established relying on accelerator mass spectrometry 14C dates. Facies succession indicates that a weak progradation occurred in coastal environments (12–10 ka BP) due to the Younger Dryas-induced deceleration of sea-level rise; rapid deposition locally occurred in the southern marginal area of tide-dominated estuary environments (10–8 ka BP), likely due to the junction of the Yangtze and Qiantangjiang River currents; and marine current-induced fluid mudflows prevailed in the shallow marine environments (8–1 ka BP), with the cooling climates of 5–1 ka BP. Furthermore, prodelta and shallow marine environments co-occurred with an uneven progradation of the delta within the last 1 ka, while deposition occurred just inside the more southern, delta-influenced area. The occurrence of euryhaline benthic foraminifera suggests that an enhanced freshwater discharge of the mid-Holocene (8–5 ka BP) was followed by a sharp decline in the late Holocene (5–1 ka BP) with climate change. The occurrence of cold-water benthic foraminifera indicates a severe cold-water condition during the mid-Holocene due to the intrusion of upwelling currents triggered by the propelling force of warm currents and summer monsoon winds. In addition, the occurrence of low-oxygen foraminiferal assemblages reveals that hypoxia has developed since 10 ka BP in stages consistent with the sedimentary evolution: localized hypoxia formation coincident with the southern depocenter during the early Holocene (10–8 ka BP); severe hypoxia with enhanced freshwater discharge and upwelling current intrusion during the mid-Holocene; and weakened hypoxia of the late Holocene, mainly due to the sharp decline in freshwater discharge. Within 1 ka BP, freshwater discharge from the approaching river mouth and increased nutrient inputs from enhanced human activities on land have contributed to the prevalence of hypoxia, especially in the southern deltaic area. Overall, it was revealed that the freshwater discharge modulated with climate variations and delta progradation plays a primary role in controlling the sedimentary evolution and hypoxia development during the mid-late Holocene. • Gravity flows (fluid mudflow) prevailed during the late Holocene (5–1 ka BP). • Holocene freshwater discharge was enhanced (8–5 ka BP) and then sharply declined. • Severe upwelling current intrusion occurred during the mid-Holocene (8–5 ka BP). • Hypoxia boomed during the mid-Holocene (8–5 ka BP). [ABSTRACT FROM AUTHOR]

Sediment accumulation and budget in the continental margins provides abundant information of source-sink processes from the land to the sea, including weathering, human activities and sedimentary environment. Here we show the distribution of mud areas, modern sedimentation rates and sediment budget in the Bohai Sea, Yellow Sea and East China Sea. Using grain size data of more than 18 000 surface sediment samples and 210Pb data from 413 sites, we identify five areas with sediments mainly composed of fine-grained fractions (mean grain size more than 6 φ) and find a relatively high sedimentation rates of >1.5 mm/yr in the mud areas. Near the Yellow and Yangtze River deltas sedimentation reaches >95 mm/yr. Approximately 1185×106 tons of fine-grained sediment accumulate annually in the mud areas of the east China seas. Atmospheric deposition contributes <2% (18.37 ×106 tons/yr), while the riverine sediment inputs account for >75% (917×106 tons/yr). The remainder comes from all other sources including coastal erosion and resuspension of bottom sediments. In addition, ~45% of the fluvial sediment supply deposits on the subaerial delta, ~40–50% is trapped on the subaqueous delta and shelf, and the remainder less than 5% escapes the shelf edge. The results will be a strong foundation for understanding of the transport, deposit and preservation of sediment and other relevant material（e.g. carbon and nutrient etc.）of terrestrial materials in the sea. [ABSTRACT FROM AUTHOR]

Conazole fungicides (CFs), the common-used pesticide in agriculture distributed widely in the environment. This research analyzed the occurrence, potential sources, and risks of eight CFs in the East China Sea surface seawater in the early summer of 2020. The total CF concentration ranged from 0.30 to 6.20 ng/L, with an average value of 1.64 ± 1.24 ng/L. Fenbuconazole, hexaconazole, and triadimenol were the major CFs that comprised >96 % of the total concentration. The Yangtze River was identified as the significant source of CFs from the coastal regions to the off-shore inputs. Ocean current was the first-order factor controlling the content and distribution of CFs in the East China Sea. Although risk assessment revealed CFs posed a low or no substantial risk to ecology and human health, long-term monitoring was also encouraged. This study provided a theoretical foundation for assessing CFs' pollution levels and potential risks in the East China Sea., Competing Interests: Declaration of competing interest The authors declare that they have no conflicts of interest regarding this work., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

We studied 19 targets currently using organochlorine pesticides (CUOCPs) from 98 samples in the Western Pacific Ocean and the East China Sea collected in 2019, 2020, and 2021. The samples were analyzed using a novel High-throat/High-volume Solid-Phase Extraction method. Eighteen individual CUOCPs were above the method detection limits. The levels of ∑ 19 CUOCPs ranged from 0.13 to 17.80 ng/L, with an average of 3.13 ± 14.67 ng/L. Dicofol was the main pollutant in the Western Pacific Ocean, while Pyridaben dominated the East China Sea. In the summer, land-source input was the primary source in the Western Pacific Ocean and the East China Sea. Historical residues were the main source in the East China Sea in spring. In the summer, the ecological risk assessment results indicated a relatively low risk to the Western Pacific Ocean and the East China Sea., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Twenty-eight samples of surface seawater were collected from the West Pacific Ocean during 2019 using a high-volume solid-phase extraction with high-throughput organic analysis (Hi-throat/Hi-volume SPE) method, and concentrations of 10 organophosphate ester flame retardants and plasticizers (OPEs) were determined. The total OPE concentration in the samples was 3.02-48.4 ng L -1 (mean 25.0 ± 10.5 ng L -1 ), with tris(2-chloroethyl) phosphate (TCEP) being the largest contributor. Cluster analysis results showed off-shore input from the coast of East and Southeast Asia was an important source of these chemicals. Tri-p-tolyl phosphate (TpTP) should also be considered for long-term monitoring, because of its high detection frequency. Results of a risk assessment indicated low ecological risk to species in the West Pacific Ocean for TPhP and ΣOPEs. Hazard quotients (HQs) were all <1, indicating that the health risk to humans from these chemicals was at acceptable levels., (Copyright © 2021 Elsevier Ltd. All rights reserved.)