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Geochemical characteristics and provenance of metals in surface sediments of hydrate area, northern South China Sea has not been reported yet, therefore this paper aimed to reveal metals' distribution, assess the pollution of potentially hazradous metals (Cu, Pb, Zn, Cd, Cr, As, Hg), and inferred provenance of metals using principal component analysis. Twenty-five surface sediments were collected by box sampler from 2014 to 2015 in the national special project on gas hydrate. The concentration of MnO and Hg varied greatly. Most of metals were higher in the north of study area. The sediment was mainly polluted by Hg either pollution status or ecological risk, while it's also moderately polluted by Cr and moderately ecological polluted by Cd. The metals were mainly related to terrigenous detrital, biological source, some volcanic activities, and also little atmospheric deposition. Our findings would further improve the understanding of metals and their related biogeochemical process. • The sediment was moderate weathering intensity in this area. • The sediment was mainly polluted by Hg, and moderately polluted by Cr. • The sediment was considerable ecologic risk by Hg and moderated risk by Cd. • Terrigenous detrital, biological and volcanic activities were main sources of metals. [ABSTRACT FROM AUTHOR]

Cross-front transport is a vital process in the offshore transport of terrestrial materials. The factors influencing cross-front transport are multifaceted and exhibit regional variability. As important factors regulating material transport patterns in the shelf seas of eastern China, the East Asian Winter Monsoon (EAWM) and Kuroshio current (including its branches) vary on multiple time scales, yet their role in controlling offshore transport is not fully understood. In this paper, cross-front offshore transport in the North Yellow Sea is chosen to investigate the aforementioned issue using numerical simulation. By excluding other potential processes for offshore transport, frontal instability is identified as the primary mechanism for offshore transport, which is triggered by winter storms (bursts of the EAWM); hence, the intensity of offshore transport is highly associated with the strength of winter storms on synoptic scales. However, on the inter-annual scale, the intensity of offshore transport is more likely regulated by the strength of the Kuroshio current, and a warming Kuroshio facilitates offshore transport. Although the role of each factor in controlling the intensity of offshore transport is delineated, the interactive effects of the EAWM and Kuroshio current on offshore transport are quite intricate, and how to quantitatively estimate their roles on multiple time scales remains a challenge using modelling. The results obtained from this study can be applied to analyse cross-front transport throughout the eastern China seas and bear significant implications for future studies on pollutant diffusion, nutrient distribution, and sediment transport in the coastal area. • Cross-front transport around the Shandong Peninsula was revealed using a numerical model. • EAWM and Kuroshio affect the strength of cross-front transport on different time scales. • With global warming, the temperature of Kuroshio might gradually become the primary control of cross-front transport. [ABSTRACT FROM AUTHOR]

This paper investigates sediment settling process during summer seasons based on in-situ observation and sediment analysis at the east tip of the Shandong Peninsula, which is a pathway for sediments from the Bohai Sea and the North Yellow Sea to enter the South Yellow Sea in China. Bottom-tethered sediment traps, together with platforms equipped with current profilers/meters and temperature/salinity and turbidity sensors, were deployed for approximately 10 days in August 2017 over an elongated deposit off the coast of the Shandong Peninsula. A computed tomography (CT) scan and grain size and 210Pb analyses of trap sediment were carried out to determine the settling process of suspensions at the study site. Twenty-three couplets were found in the CT images of the trap, the time series of which was established using intervalometer disks. Quantitative characterization of rhythmites using a hounsfield unit indicates that the period of couplets is approximately quarter-diurnal, and the settling process could be divided into three stages during Aug. 21st – 27th. Current, wave, wind, and SSC data illustrate that the diversion of the bottom current leads to the formation of couplets, and the thickness of the couplet is controlled by the vertical current velocity and wind direction. Northerly winds enhance the difference in settlement between flood and ebb tides, whereas southerly winds smoothen the difference. The gale event inhibited the settlement of the suspended matter, and the source of the suspensions was converted from local to remote after the event, as evidenced by 210Pb data. No evident erosion can be detected in the sediment traps. The results are of significance to better understand the sedimentary dynamics near the Shandong clinoform and inspire the practical efficiency of bottom-tethered sediment traps in the settling process in coastal areas. • Quarter-diurnal couplet were found by CT scan of sediment in the Anderson-type sediment trap. • Flood and ebb tides lead to the formation of couplets, and the thickness of the which is controlled by vertical velocity and wind direction. • Gale events could inhibit the settling of suspensions at the clinoform off the Shandong Peninsula. [ABSTRACT FROM AUTHOR]

This special issue deals with transport and deposition processes of shelf sediments along the coast of China and comprises eleven papers. These articles can be broadly categorized into three themes: (1) Sediment dynamic process; (2) Characteristic of modern sediment deposit; and (3) Evolution of the Holocene sedimentary system. Various approaches, including but not limited to, in-situ hydrodynamics measurement, sediment core analyses, and numerical modeling, were utilized in these studies that resulted in new insights in all three themes. Here we summarize the major findings that aim to, in a wider context, improve our knowledge of the shelf sediment processes. The contributions in this special issue will be of interest to a broad readership of marine and earth system scientists. [ABSTRACT FROM AUTHOR]

Although many studies have investigated archaeal distribution in various environments, studies regarding the archaeal community structure in intertidal mudflat sediments in coastal areas are not enough. In addition, the response of archaea to bivalves bioturbation has not been reported before, nevertheless, bioturbation effects on microbes are key to many aspects of ecosystem function. In this paper, clone library construction, Restriction Fragment Length Polymorphism (RFLP) and Denaturing Gradient Gel Electrophoresis DGGE (DGGE) were used to study the archaeal community structure in two typical intertidal mudflats in Southeast coast of China: the one mainly used for aquaculture in a semi-enclosed Bay (Sansha Bay), and the other one mainly used for recreation in a developed city (Xiamen). In addition, the potential influence of sampling time and the in situ bioremediation by artificially introducing bivalve ark shell ( Tegillarca granosa ) to mudflat sediments on archaeal communities were also investigated. A total of 283 clones were randomly selected from four clone libraries and were divided into 42 RFLP patterns. All the cloned sequences fell into three phyla: the Thaumarchaeota (group MGI), Crenarchaeota (group MCG) and Euryarchaeota (groups MBG-D, MBG-E, VAL III and DHVE 6), in which Thaumarchaeota MGI was dominant, occupying 75.6% of total clones. Crenarchaeota MCG and Euryarchaeota accounted for 15.2% and 9.2% respectively. The archaeal diversity in Xiamen intertidal sediment was lower than that of Sansha Bay. Introducing ark shell seemed to increase archaeal diversity and the proportion of MCG and decrease the proportion of MGI in the clone library. DGGE profiles showed that most of the archaea populations were metabolically active, and the fingerprint clustering results were basically consistent with the results from clone libraries. [ABSTRACT FROM AUTHOR]

Numerous estuaries worldwide have been modified in the past decades by human interventions. The shoreline and bathymetry in the Pearl River Estuary (PRE) have changed greatly over the past 40 years due to the influence of land reclamation and waterway dredging, which have resulted in the corresponding adjustment of its hydrodynamics. Utilizing the ROMS numerical model, this paper studies the hydrodynamic responses to changes in shoreline and bathymetry in the PRE from 1971 to 2012. The results show that, on one hand, during neap tide, the change in the shoreline makes the residual current in the West Channel (WC) increase by 0.10 (0.05) m/s at maximum in the surface (near bottom) layer. Therefore, the exchange flow increases by 9.5% and the longitudinal circulation strengthens. The surface isohalines move southward up to 18 km, but the bottom isohalines move northward ∼2 km in the WC and East Channel (EC), which is different from the previous conclusion that the seaward extension of coastlines inhibits saltwater intrusion. The decrease in salinity in the upper layer reduces the upper seaward salt transport, resulting in a larger net landward salt transport from 25.21 × 103 kg/s to 35.44 × 103 kg/s. During spring tide, the changes are relatively weaker, but the direction of salt transport changes to seaward and the net seaward transport also increases. Moreover, the change in shoreline reduces the water area and volume in the PRE by 21.3% and 15.6% respectively, which causes a reduction of 11.3% (17.1%) in tidal prism during spring (neap) tide. The wave celerity is enhanced (>23%) and the amplification of semidiurnal tide is strengthened (>20%) in the WC and West Shoal (WS). The reduction in tidal prism together with the strengthened reflection of tidal waves with a larger phase lag between elevation and velocity of M 2 tidal component cause a significant decrease of 19.0% in tidal energy flux entering the PRE. However, the tidal range increases by ∼0.30 m (mainly due to the increase in M 2 tidal amplitude) in the EC , which is induced by lower tidal energy dissipation there. On the other hand, during neap tide, the change in bathymetry greatly enhances the bottom landward residual current whose peak value increases by 80% in the WC , thereby increasing approximately 14 km of the intrusion distance of saline water, enhancing the exchange flow by 27.5% and strengthening the longitudinal circulation. The net landward salt transport increases to 38.39 × 103 kg/s. The results during spring tide are similar to those during neap tide but with smaller changes, and the net seaward salt transport decreases. Moreover, the wave celerity is slightly reduced (<8%) and the amplification of semidiurnal tide is also decreased (<10%) in the WC and WS. Meanwhile, the change in bathymetry only decreases the water volume by 4.7%, leading to a relatively smaller effect on the tidal prism, and it strengthens (weakens) the reflection of tidal waves in the West Shoal and Middle Shoal (WC and EC), resulting in a slight reduction in tidal energy flux entering the bay. In the WC , the tidal range is basically unchanged since the increased tidal energy flux is offset by the increased dissipation. The quantitative results obtained in this study may provide some references for the development and protection of the PRE and other estuaries that are subject to strong human interventions. • Seaward extension of coastlines increases tidal range, wave celerity and saltwater intrusion. • Change in bathymetry increases ∼14 km of the intrusion distance of saltwater. • Change in bathymetry enhances exchange flow by 27.5%, reduces tidal energy flux by 2.4%. [ABSTRACT FROM AUTHOR]

Accurate inversion of sound velocity in a Holocene stratum and a Quaternary stratum was achieved based on rich high-resolution sub-bottom profiles and boreholes in the Jinzhou Bay, Bohai Sea of China. The average value of the sound velocity is 1540.2 m/s in the Holocene stratum and 1764.7 m/s in the Quaternary stratum. The fitting analysis shows that there is an obvious positive linear correlation between the sound velocity and the burial depth of the stratum, with a gradient of 4.5 s−1. The method involving the solution of over-determined equations was innovatively put forward to explore the sound velocity characteristics of different types of sediments. The eigenvalues of the sound velocities of seven types of sediments and weathered rock in the study area are solved: the sound velocities of mud, muddy sand, muddy silty clay, muddy clay, silty clay, clay, silty sand, and strongly weathered rock are 1513.7 m/s, 1484.3 m/s, 1532.0 m/s, 1511.3 m/s, 1693.9 m/s, 1602.7 m/s, 1599.4 m/s, and 2137.7 m/s, respectively. And statistical analysis shows that the sound velocity of the sediment in the study area has obvious quadratic correlations with the void ratio and compressibility. • Based on sub-bottom profiles and boreholes datasets, this paper develops a method of acoustic inversion of seabed sediment. • Innovatively establishing over-determined equations to solve sound velocities of different types of sediments. • Findings can provide important reference values to the geophysical survey and the development of seabed geoacoustics. [ABSTRACT FROM AUTHOR]