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To understand the acoustic and physical properties of piston core samples collected from the Sunda continental shelf and analyze their distribution patterns, the samples were analyzed in laboratory, from which three provinces were divided in sound speed, sound speed ratio, porosity, wet bulk density, and maximum shear strength. Province I had lower sound speed and sound speed ratio (<1.04), high porosity, and low wet bulk density. Province II had higher sound speed and sound speed ratio (>1.04), low porosity, and high wet bulk density. Province III had the lowest sound speed and sound speed ratio (0.99), highest porosity (81%), and lowest wet bulk density (1.34 g/cm3). The distribution pattern indicates that sediment movement, sediment source, topography, and hydrodynamic conditions influenced the distribution of acoustic and physical properties. Furthermore, we investigated the relationship of the maximum shear strength to the porosity and wet bulk density, and found that the maximum shear strength was proportional to both the porosity and wet bulk density. This finding has significant implications for ocean engineering applications. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS), situated in southern China, at the junction of the Pacific Plate, the Eurasian Plate, and the Indian Ocean Plate, is a northeast-southwest trending semi-enclosed sea. It spans an area of approximately 3.5 million square kilometers and has an average water depth of about 1 200 m, its deepest point reaching 5 559 m. In 2021, a scientific expedition (called as U1 voyage) in the South China Sea was organized by the Innovation Research Team of Guangdong Special Key Program from March to April, this marks the first comprehensive scientific research voyage to the southern U-boundary corridor. Consisting of a total of 30 papers, this special issue is to share a portion of the research findings from this scientific expedition U1 voyage, covering six aspects: 1) characteristics of the marine ecosystem in the SCS and its response to marine dynamic processes; 2) multi-scale marine dynamic processes, sea-air interactions, and forecasting techniques in the SCS; 3) geomorphology and geological structure; 4) sedimentary processes and resource potential in the SCS; 5) geostrategy, rights and interests maintenance and strategic countermeasures in the SCS; 6) marine scientific instruments. By integrating the scientific research with the study of history, jurisprudence and international strategies, this issue presents new insights into the formation history and scope evolution of the SCS, and it also seeks to establish a new scientific framework based on the marine governance and development of the SCS. [ABSTRACT FROM AUTHOR]

The acoustic properties of seafloor sediment are essential parameters in the exploration of marine resources, ocean scientific research and ocean engineering. Seafloor sediment samples were collected at the southern U-boundary of the South China Sea (SCS), and the acoustic and physical properties were measured in the laboratory. The correlation between physical and sound speed ratio (SSR) was discussed, and SSR-physical property empirical regressions in the Sunda Shelf were established for the first time. Compared with the northern continental shelf of SCS, the Sunda Shelf are mainly silty and sand sediment, and the SSR ranges from 0.994 9 to 1.094 4, which has higher SSR than the northern continental shelf, implies that the Sunda Shelf is a high SSR area. Since the same kind of sediment has different physical properties, the single physical parameter of sediment cannot fully represent the acoustic properties of sediment, therefore, the multiple parameter prediction model should develop in the future to improve the prediction precision. [ABSTRACT FROM AUTHOR]

A new gravity sensor based on electromagnetic damping for the JMGrav marine gravimeter is presented. The new gravity sensor considered the advanced construction methods of the electromagnetic damping system of the gravimeter. The design features of the new system are discussed and the research survey data in the South China Sea are shown. Numerical simulations are applied to model the magnetic and mechanical characteristics of the system using finite element analysis and to evaluate the force distribution and the resulting damping effects. The performance characteristics of the system were tested on a motion simulator in laboratory, and the gravimeter was subjected to vertical accelerations of up to 100 Gal in 1–1 000 s. It was found that the amplitude reduction of vertical accelerations in 3–15 s is 30–45 dB, with a time lag of 2–5 s, while the effect on gravity in period greater than 600 s is less than 0.5 dB, with a time lag of less than 100 s. The accelerations cause discrepancies of approximately only 1 mGal between the static value and the mean dynamic value. The sea tests were conducted in September 2020. Gravity measurements were taken with a JMGrav marine gravimeter onboard the R/V Dongfanghong 3, and the effective survey line exceeded 2 000 km. Completely irregular accelerations with peaks up to 100 Gal yielded a reduction of approximately 40 dB in amplitude. The survey data were evaluated using ocean gravity field models and grid line tests. The results show that the accuracy of the gravity measurements is better than 2 mGal. [ABSTRACT FROM AUTHOR]

To dampen periodic off-levelling motions within an inertial platform while undergoing horizontal accelerations of the same period and to achieve a levelling accuracy of a few tens of arcseconds with that system, an internally damped inertial platform for a marine scalar gravity system was the developed. Methods for attenuating horizontal acceleration and reducing off-levelling error by a satisfactory gyro-levelling loop, which are fundamental to the internally damped inertial platform, were designed and implemented. In addition, phase delays are introduced by the levelling loop. The resulting off-levelling gravity errors were analyzed and modeled. A series of tests on a motion simulator were performed in laboratory for a variety of simulated sea conditions. We found that the motion of the platform is a function of the amplitude and period of the simulated ship motions and ranges between 10 and 40 arcseconds. In addition, the phase lag between platform motion and ship motion is not constant but ranges 180°–270°, depending on the period and amplitude of the motion. Then, the platform, on which a gravimeter was mounted, was installed on the R/V Shiyan 2 to conduct a gravity survey in the South China Sea. Despite rough sea conditions, it was shown that in short periods of 2–30 s, the off-levelling angle was less than 30 arcseconds, and the phase lagged the horizontal acceleration by 230°–260°. From a repeated survey line and intersecting survey points, the estimated errors of gravity measurements were between 1.3 and 1.7 mGal. The marine measurements results were compared with those of satellite altimetry data and show a mean value of 0.5 mGal in a standard deviation of 1.5 mGal. [ABSTRACT FROM AUTHOR]

Bivalve shell fossils, cemented by authigenic carbonates, are widely spread in the Haima cold seep, Qiongdongnan Basin of the South China Sea (SCS). In this study, we examined an element profile of Gigantidas platifrons in the Haima cold seeps at a water depth of 1 381 m. Based on the scanning electron microscope (SEM) analyses, the prismatic layer and nacreous layer were identified, which are characterized by prismatic structure and stratified structure, respectively. In addition, the profile can be subdivided into two parts: altered and unaltered zones. Laser inductively coupled plasma mass spectrometry (LA-ICP-MS) mapping shows that the element concentrations of the altered zones were influenced by the authigenic carbonate rocks, whereas the element concentrations of unaltered zones remain stable. In-situ X-ray diffraction (XRD) analyses show that the mineral constituent of the nacreous layer is mainly composed of aragonite. Along with the growth profile, Mg/Ca ratios of unaltered zones have minor variations, ranging 0.72–0.97 mmol/mol (mean=0.87 mmol/mol), with estimated temperatures of 3.8–4.1 °C, indicating that the temperature of the surrounding seawater remains constant and agree with the measured data of 3.9 °C which was conducted by a conductivity-temperature-depth system (CTD). The minor variations of Ba/Ca ratios (0.01–0.06 mmol/mol; mean=0.04 mmol/mol) indicate a relatively stabilized salinity of the surrounding seawater. S/Ca ratios show large variations of 0.04–4.15 mmol/mol (mean=1.37 mmol/mol). S/Ca ratios have regular variations which generally correspond to the variations of the Mg/Ca ratios, highlighting that the S/Ca ratios of bivalve shells show the potential to reflect the growth rate of the Gigantides. However, further studies should be carried out on the understanding of the links between the S/Ca ratios and seepage intensity of cold-seep fluids. [ABSTRACT FROM AUTHOR]

Purpose: The efficacy of routine antibiotic prophylaxis for prevention of surgical site infection (SSI) after elective inguinal hernia repair with a mesh patch remains uncertain. The authors of a recent Cochrane meta-analysis based on 17 randomized trials were unable to draw a definitive conclusion on this subject. The purpose of this study was to determine the effectiveness of prophylactic antibiotics for prevention of SSI after elective inguinal hernia repair with mesh and the risk factors for SSI. Methods: All low-risk patients who underwent elective inguinal hernia repair with mesh at our institution between 2010 and 2015 were enrolled in this study, with the exception of patients with recurrent hernias or immunosuppressive diseases. All patients received a single intravenous (i.v.) injection of cefuroxime (1.5 g) within 2 h prior to surgery at the discretion of the surgeon. SSI was defined using criteria of the Centers for Disease Control and Prevention. The variables which could influence the rate of SSI were analyzed by multivariate analysis to determine the independent risk factors for SSI. Results: Among the 605 patients who underwent elective inguinal hernia repair with mesh during the study period, 553 were eligible for enrolment in the study. Of these, 331 received a single dose of cefuroxime preoperatively. The overall SSI rate was 5.4 %; 9.4 % of those patients who did not receive preoperative antibiotic prophylaxis developed SSI versus 2.8 % of those who did receive prophylaxis ( P = 0.001). All infections were superficial. Factors independently associated with SSI were advanced age, smoking and preoperative stay. Conclusions: The incidence of SSI among low-risk patients who did and did not receive preoperative antibiotic prophylaxis after elective inguinal hernia repair with mesh differed significantly, particularly among patients of advanced age, smokers and patients with a prolonged preoperative stay in the hospital. [ABSTRACT FROM AUTHOR]

This study examines changes in the local oceanographic and atmospheric conditions over the southern Bay of Bengal and adjacent Indian Ocean waters after the 2004 Indian Ocean tsunami based on satellite remote sensing data and atmospheric reanalysis fields. After the tsunami that occurred on 26 December 2004, the accumulated rainfall had a notably increase (600 mm per month) in January of 2005 over deep waters to the southeast of Sri Lanka. This rainfall increase after the tsunami was accompanied with cooling in the sea surface temperature (SST) (up to −2 °C). Four-day averaged SST anomalies had a noticeable increase (1-4 °C) after the tsunami over the deep waters to the southwest of the epicenter. Series of ocean atmospheric and biological variables changed successively after the change of SST. The chain of causality between the tsunami and the changes in the local atmospheric conditions is suggested. [ABSTRACT FROM AUTHOR]

Sishili Bay is the most important aquiculture and tourism area for the city of Yantai, China; however, red tides occurred frequently and have caused huge economic losses in this bay in recent years. To gain a better understanding of the local ecological environments in the bay, we conducted this research between 2003 and 2008 to analyze variations in nutrients and chlorophyll (chl- a) during high frequency red tide period (May to September). The results show that the chl- a concentration increased from 2.70 in 2003 to 7.26 mg/m in 2008, while the concentration of total inorganic nitrogen (TIN) and silicate (SiO-Si) increased lineally from 5.18 and 1.45 μmol/L in 2003 to 18.57 and 9.52 μmol/L in 2008, respectively, and the annual phosphate (PO-P) varied between 0.15 and 0.46 μmol/L. Special attention was given to a red tide in August 2007 occurred when water temperature was high and nutrient concentrations increased sharply because of a heavy rainfall. Overall, the results show the P limitation in Sishili Bay, and reveal that red tides were caused by eutrophication from terrestrial inputs and local warm weather, particularly during rainy periods. Therefore, to control red tide, greater efforts should be made to reduce sewage discharges into Sishili Bay, particularly during rainfall seasons. [ABSTRACT FROM AUTHOR]

Metagenomics is a powerful tool for mining the genetic repositories from environmental microorganisms. Bacteria associated with marine sponges (phylum Porifera) are rich sources of biologically active natural products. However, to date, few compounds are discovered from the sponge metagenomic libraries, and the main reason might be the difficulties in recovery of high molecular weight (HMW) DNA from sponge symbionts to construct large insert libraries. Here, we describe a method to recover HMW bacterial DNA from diverse sponges with high quality for bacterial artificial chromosome (BAC) library construction. Microorganisms concentrated from sponges by differential centrifugation were embedded in agarose plugs to lyse out the HMW DNA for recovery. DNA fragments over 436 kb size were recovered from three different types of sponges, Halichondria sp., Haliclona sp., and Xestospongia sp. To evaluate the recovered DNA quality, the diversity of bacterial DNA comprised in the HMW DNA derived from sponge Halichondria sp. was analyzed, and this HMW DNA sample was also cloned into a shuttle BAC vector between Escherichia coli and Streptomyces sp. The results showed that more than five types of bacterial DNA, i.e., Proteobacteria, Nitrospirae, Cyanobacteria, Planctomycetes, and unidentified bacteria, had been recovered by this method, and an average 100 kb size insert DNA in a constructed BAC library demonstrated that the recovered HMW DNA is suitable for metagenomic library construction. [ABSTRACT FROM AUTHOR]

Harmful algal blooms (HABs) occur frequently in the South China Sea (SCS), causing enormous economic losses in aquaculture. We analyzed historical HAB records during the period from 1980 to 2003 in SCS. We found that HABs-affected areas have expanded and the frequency of HABs varied during this period. The seasonal and annual variations, as well as causative algal species of HABs are different among the four regions. Areas with frequent HABs include the Pearl River Estuary (China), the Manila Bay (the Philippines), the Masinloc Bay (the Philippines), and the western coast of Sabah (Malaysia). HABs occurred frequently during March–May in the northern region of SCS, May–July in the eastern region, July in the western region, and year-round in the southern region. Among the species that cause HABs, Noctiluca scintillans dominated in the northern region, and Pyrodinium bahamense in the southern and eastern regions. Causative species also varied in different years for the entire SCS. Both P. bahamense and N. scintillans were the dominant species during 1980–2003. Some species not previously recorded formed blooms during 1991–2003, including Phaeocystis globosa, Scrippsiella trochoidea, Heterosigma akashiwo, and Mesodinium rubrum. Variations in HABs are related to various regional conditions, such as a reversed monsoon wind in the entire SCS, river discharges in the northern area, upwelling in Vietnam coastal waters during southwest winds and near Malaysia coastal waters during northeast winds, and eutrophication from coastal aquaculture in the Pearl River estuary, Manila Bay, and Masinloc Bay. [ABSTRACT FROM AUTHOR]