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Owing to the strategic significance of national oil and gas resources, their exploration and production must be prioritized in China. Oil and gas resources are closely related to deep crustal structures, and Moho characteristics influence oil and gas distribution. Therefore, it is important to study the relationship between the variation of the Moho surface depth undulation and hydrocarbon basins for the future prediction of their locations. The Moho depth in the study area can be inverted using the Moho depth control information, the Moho gravity anomaly, and the variable density distribution calculated by the infinite plate. Based on these results, the influences of Moho characteristics on petroleum basins were studied. We found that the Moho surface depth undulation deviation and crustal thickness undulation deviation in the hydrocarbon-rich basins are large, and the horizontal gradient deviation of the Moho surface shows a positive linear relationship with oil and gas resources in the basin. The oil-bearing mechanism of the Moho basin is further discussed herein. The Moho uplift area and the slope zone correspond to the distribution of oil and gas fields. The tensile stress produced by the Moho uplift can form tensile fractures or cause tensile fractures on the surface, further developing into a fault or depression basin that receives deposits. The organic matter can become oil and natural gas under suitable chemical and structural conditions. Under the action of groundwater or other dynamic forces, oil and natural gas are gradually transported to the uplift or the buried hill in the depression zone, and oil and gas fields are formed under the condition of good caprock. The research results can provide new insights into the relationship between deep structures and oil and gas basins as well as assist in the strategic planning of oil and gas exploration activities.
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Both Pinghu and Huagang formations are important hydrocarbon reservoirs of the Xihu Depression in the East China Sea Shelf Basin. Clarifying the source suppliers and restoring source-to-sink transport routes are of great significance to the future petroleum and gas undertakings. Previous researchers were largely confined by either limitation of geological records, highly dependence on a singular method or low-precision dating techniques. Our study integrated heavy mineral assemblages, geochemical analyses and detrital zircon U-Pb dating to reconstruct multiple source-to-sink pathways, and to provide a better understanding on the provenance evolution for the upper Pinghu–lower Huagang depositions of the Xihu Depression. At least three major provenances have been confirmed and systematically investigated for their separate compositional features. The Hupijiao Uplift (or even farther northern area) was dominated by a major Paleoproterozoic population peaked at ca. 1 830 Ma along with minor Mesozoic clusters. The Haijiao Uplift to the west and the Yushan Low Uplift to the southwest, on the other hand, generate opposite U-Pb age spectra with apparently larger peaks of Indosinian and Yanshanian-aged zircons. To be noted, both Indosinian and Paleoproterozoic peaks are almost identical in proportion for the Haijiao Uplift. The overall sedimentary pattern of the late Eocene-the early Oligocene was featured by both spatial and temporal distinction. The Hupijiao Uplift was likely to cast limited impact during the late Eocene, whereas the broad southern Xihu Depression was transported by a large abundance of materials from the nearby Haijiao and Yushan Low Uplifts. The northern source substantially extended its influence to the farther south during the early Oligocene by delivering plentiful sediments of higher-degree metamorphic parent rocks. Combined with the proximal western and southwestern suppliers, the overall Xihu Depression was under control from both distant and local provenances.
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Acanthogobius ommaturus, which belongs to the family Gobiidae, is a euryhaline and demersal fish that is widely distributed in the coastal areas, harbors, and estuaries of China, North Korea and Japan. In this study, the genetic diversity and genetic structure of five geographical populations of A. ommaturus was assessed using the mitochondrial hypervariable region gene and microsatellite markers. The results of the two genetic markers indicated that the A. ommaturus populations had a high level of genetic diversity. The mitochondrial marker detected weak genetic differentiation among populations, and the Neighbor-Joining tree showed that there was no obvious pedigree branches and geographic structure as well. However, population Zhoushan showed significant genetic differentiation with other populations by microsatellite markers. The population of A. ommaturus has not experienced bottleneck effect recently. We speculated that the climate change, juvenile fish dispersal and Pleistocene climate change played an important role in the population differentiation of A. ommaturus.
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Dissolution mechanism and favorable reservoir distribution prediction are the key problems restricting oil and gas exploration in deep-buried layers. In this paper, the Enping and Zhuhai Formation in Baiyun Sag of South China Sea was taken as a target. Based on the thin section, scanning electron microscopy, X-ray diffraction, porosity/permeability measurement, and mercury injection, influencing factors of dissolution were examined, and a dissolution model was established. Further, high-quality reservoirs were predicted temporally and spatially. The results show that dissolved pores constituted the main space of the Paleogene sandstone reservoir. Dissolution primarily occurred in the coarse- and medium-grained sandstones in the subaerial and subaqueous distributary channels, while dissolution was limited in fine-grained sandstones and inequigranular sandstones. The main dissolved minerals were feldspar, tuffaceous matrix, and diagenetic cement. Kaolinization of feldspar and illitization of kaolinite are the main dissolution pathways, but they occur at various depths and temperatures with different geothermal gradients. Dissolution is controlled by four factors, in terms of depositional facies, source rock evolution, overpressure, and fault activities, which co-acted at the period of 23.8–13.8 Ma, and resulted into strong dissolution. Additionally, based on these factors, high-quality reservoirs of the Enping and Zhuhai formations are predicted in the northern slope, southwestern step zone, and Liuhua uplift in the Baiyun Sag.
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The long-term spatiotemporal changes of surface biogenic elements in the Changjiang Estuary and adjacent waters during the summer of 2008~2016 were analyzed in this study. The concentrations of dissolved inorganic nitrogen (DIN), soluble reactive phosphate (\begin{document}${{\rm {PO}}_4^{3-}}$\end{document}) and silicate (\begin{document}${{\rm {SiO}}_3^{2-}}$\end{document}) were generally stable, with a slight decrease of DIN and \begin{document}${{\rm {PO}}_4^{3-}}$\end{document}, and a slight increase of \begin{document}${{\rm {SiO}}_3^{2-}}$\end{document}, which mainly occurred in the estuarine waters. The grey correlation analysis was carried out between biogenic elements and chlorophyll a (Chl-a). Results showed that compared with the absolute values of biogenic elements, the correlations between the ratio of nitrogen to phosphorus (N/P), ratio of silicon to nitrogen (Si/N) and Chl-a were closer, indicating the important influence on phytoplankton by the structure of biogenic elements. The study area was generally in a state of potential P limitation, and could have potential impact on the phytoplankton community, triggering the shift of red tide dominant species from diatoms to dinoflagellates.
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Accurately building the relationship between the oceanographic environment and the distribution of neon flying squid (Ommastrephes bartramii) is very important to understand the potential habitat pattern of O. bartramii. However, when building the prediction model of O. bartramii with traditional oceanographic variables (e.g., chlorophyll-a concentration (Chl-a) and sea surface temperature (SST)) from space-borne observations, part of the important spectrum characteristics of the oceanic surface could be masked by using the satellite data products directly. In this study, the neglected remote sensing information (i.e., spectral remote sensing reflectance (Rrs) and brightness temperature (BT)) is firstly incorporated to build the prediction model of catch per unit effort (CPUE) of O. bartramii from July to December during 2014–2018 in the Northwest Pacific Ocean. Results show that both the conventional oceanographic variables and the neglected remote sensing data are suitable for building the prediction model, whereas the overall root mean square error (RMSE) of the predicted CPUE of O. bartramii with the former is typically less accurate than that with the latter. Hence, the Rrs and BT could be a more suitable data source than the Chl-a and SST to predict the distribution of O. bartramii, highlighting that the potential value of the neglected variables in understading the habitat suitability of O. bartramii.
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Since 2015, green tides have been blooming in offshore waters of Qinhuangdao, with serious impacts on the local ecological environment and tourism. Ulva australis, Bryopsis plumosa, and Ulva prolifera are the dominant species of Qinhuangdao green tides, following a sequential succession pattern. U. prolifera is the dominant species, with the highest biomass and the greatest influence on the local ecological environment. To study the reason of green tide dominant species succession and U. profilera became the dominant species with the largest biomass, we compared and analyzed the growth and nutrient uptake capacity of the three algae. The results showed that temperature significantly affects the growth of the three species. Within the temperature range of the experimental setup, the optimum temperature for the growth of U. australis, B. plumosa and U. profilera is 10, 15, and 20–25 ℃, respectively. Combined with the temperature variation trend during green tide bloom development, we believe that temperature is the key environmental factor for the succession of the dominant species. U. prolifera has a higher growth rate than U. australisand B. plumosa under the same nitrate, ammonium salt, and phosphate levels. Significant differences in the Vmax and Vmax/Ks values indicated that U. prolifera had an apparent competitive advantage over U. australisand B. plumosa regarding nutrient uptake. Therefore, the strong growth and nutrient uptake capacities of U. prolifera might be the main reason for becoming the dominant species with the largest biomass in Qinhuangdao green tides.
Abstract:
Total dissolved nitrogen (TDN) is an important parameter for assessing the nutrient cycling and status of natural waters. The accurate determination of TDN in natural water is essential for assessing its contents and distinguishing different forms of nitrogen in the water, and the TDN in various systems has been largely documented. The concentrations of TDN are usually obtained using high-temperature catalytic (HTC) or persulfate oxidation (PO). However, the accuracy of these methods and their suitability for all types of natural waters are still unclear. To explore both methods in-depth, assorted samples were tested, including eight solutions composed of nitrogen-containing compounds (3 dissolved inorganic nitrogen fractions: \begin{document}${{\rm {NO}}_3^-}$\end{document}, \begin{document}${{\rm {NO}}_2^-}$\end{document} and \begin{document}${{\rm {NH}}_4^+}$\end{document}; 5 organic compounds: EDTA-2Na, VB1, B12, amino acids (AAS), and urea) and 105 natural waters which were collected from an open ocean (Northwest Pacific Ocean, 28), a marginal sea (the Yellow Sea, 34), an estuary (the Yellow River mouth, 31), rivers (Yellow River, 4; Licun River, 4), and precipitations (4 samples). The results showed that heterocycles and molecular dimensions had certain effects on the oxidation efficiency of the PO method but had little effect on HTC. There was no significant difference between the two methods for natural waters, but HTC was more suitable for deep-sea samples with low TDN concentrations (less than 10 μmol/L) and low organic activity. Overall, HTC has a relatively simple measurement process, a high degree of automation, and low error. Therefore, HTC can be recommended to determine the TDN of samples in freshwater and seawater.
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Nitrogen fixation is one of the most important sources of new nitrogen in the ocean and thus profoundly affects the nitrogen and carbon biogeochemical processes. The distribution, controlling factors, and flux of N2 fixation in the global ocean remain uncertain, partly because of the lack of methodological uniformity. The 15N2 tracer assay (the original bubble method→ the 15N2-enriched seawater method→ the modified bubble method) is the mainstream method for field measurements of N2 fixation rates (NFRs), among which the original bubble method is the most frequently used. However, accumulating evidence has suggested an underestimation of NFRs when using this method. To improve the availability of previous data, we compared NFRs measured by three 15N2 tracer assays in the South China Sea. Our results indicate that the relationship between NFRs measured by the original bubble method and the 15N2-enriched seawater method varies obviously with area and season, which may be influenced by incubation time, diazotrophic composition, and environmental factors. In comparison, the relationship between NFRs measured by the original bubble method and the modified bubble methods is more stable, indicating that the N2 fixation rates based on the original bubble methods may be underestimated by approximately 50%. Based on this result, we revised the flux of N2 fixation in the South China Sea to 40 mmol N m–2 yr–1. Our results improve the availability and comparability of literature NFR data in the South China Sea. The comparison of the 15N2 tracer assay for NFRs measurements on a larger scale is urgently necessary over the global ocean for a more robust understanding of the role of N2 fixation in the marine nitrogen cycle.
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The internal energy distribution of waves can be described using ocean-wave spectra. In many ways, obtaining wave spectra on a global scale is critical. Surface waves investigation and monitoring onboard the Chinese-French oceanography satellite is the first space-borne instrument for detecting wave spectra specially, which was launched on October 29, 2018. It can avoid the shortage of synthetic aperture radar detection results while still having some problems, especially with the effects of speckle noise. In this study, a method to suppress the speckle noise is proposed. First, the empirical formula for background speckle noise is established. Second, many Spatio-temporal representative fluctuation spectra are classified and averaged. Third, rational transfer function filtering is used to obtain speckle noise close to the along-track direction. Finally, a signal-to-noise ratio threshold is used to suppress the abnormal speckle noise. This method solves the problems existing in previous denoising methods, such as excessive denoising in the along-track direction and the inability of some abnormal noises to be denoised in the two-dimensional directional wave spectra.
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The international Argo program, a global observational array of nearly 4 000 autonomous profiling floats initiated in the late 1990s, which measures the water temperature and salinity of the upper 2 000 m of the global ocean, has revolutionized oceanography. It has been recognized one of the most successful ocean observation systems in the world. Today, the proposed decade action “OneArgo” for building an integrated global, full-depth, and multidisciplinary ocean observing array for beyond 2020 has been endorsed. In the past two decades since 2002, with more than 500 Argo deployments and 80 operational floats currently, China has become an important partner of the Argo program. Two DACs have been established to process the data reported from all Chinese floats and deliver these data to the GDACs in real time, adhering to the unified quality control procedures proposed by the Argo Data Management Team. Several Argo products have been developed and released, allowing accurate estimations of global ocean warming, sea level change and the hydrological cycle, at interannual to decadal scales. In addition, Deep and BGC-Argo floats have been deployed, and time series observations from these floats have proven to be extremely useful, particularly in the analysis of synoptic-scale to decadal-scale dynamics. The future aim of China Argo is to build and maintain a regional Argo fleet comprising approximately 400 floats in the northwestern Pacific, South China Sea, and Indian Ocean, accounting for 9% of the global fleet, in addition to maintaining 300 Deep Argo floats in the global ocean (25% of the global Deep Argo fleet). A regional BGC-Argo array in the western Pacific also needs to be established and maintained.
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This study involved outcrop, drilling, seismic, gravity, and magnetic data to systematically document the geological records of the subduction process of Proto-South China Sea (PSCS) and establish its evolution model. The results indicate that a series of arc-shaped ophiolite belts and calcalkaline magmatic rocks are developed in northern Borneo, both of which have the characteristics of gradually changing younger from west to east, and are direct signs of subduction and collision of PSCS. At the same time, the subduction of PSCS led to the formation of three accretion zones from the south to the north in Borneo, the Kuching belt, Sibu belt, and Miri belt. The sedimentary formation of northern Borneo is characterized by a three-layer structure, with the oceanic basement at the bottom, overlying the deep-sea flysch deposits of the Rajang–Crocker group, and the molasse sedimentary sequence that is dominated by river-delta and shallow marine facies at the top, recording the whole subduction–collision–orogeny process of PSCS. Further, seismic reflection and tomography also confirmed the subduction and collision of PSCS. Based on the geological records of the subduction and collision of PSCS, combined with the comprehensive analysis of segmented expansion and key tectonic events in the South China Sea, we establish the “gradual” subduction–collision evolution model of PSCS. During the Late Eocene to Middle Miocene, the Zengmu, Nansha, and Liyue–Palawan blocks were separated by West Baram Line and Balabac Fault, which collided with the Borneo block and Kagayan Ridge successively from the west to the east, forming several foreland basin systems, and PSCS subducted and closed from the west to the east. The subduction and extinction of PSCS controlled the oil and gas distribution pattern of southern South China Sea (SSCS) mainly in three aspects. First, the “gradual” closure process of PSCS led to the continuous development of many large deltas in SSCS. Second, the deltas formed during the subduction–collision of PSCS controlled the development of source rocks in the basins of SSCS. Macroscopically, the distribution and scale of deltas controlled the distribution and scale of source rocks, forming two types of source rocks, namely, coal measures and terrestrial marine facies. Microscopically, the difference of terrestrial higher plants carried by the delta controlled the proportion of macerals of source rocks. Third, the difference of source rocks mainly controlled the distribution pattern of oil and gas in SSCS. Meanwhile, the difference in the scale of source rocks mainly controlled the difference in the amount of oil and gas discoveries, resulting in a huge amount of oil and gas discoveries in the basin of SSCS. Meanwhile, the difference of macerals of source rocks mainly controlled the difference of oil and gas generation, forming the oil and gas distribution pattern of “nearshore oil and far-shore gas.”
[Abstract](57) [FullText HTML](20) [PDF 2413KB](2)
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Sea area is an important area of oil and gas exploration in China. It has been found that China’s sea area mainly consists of coal type oil and gas, and the exploration of coal-bearing series source rocks has become an important link of oil and gas exploration there. Through years of comprehensive geological research in China’s sea area, it has been revealed that it has undergone multiple occurrences of tectonic opening and closing movements in varying degrees in the Paleogene, forming 26 Cenozoic sedimentary basins of various types, such as active continental margin, passive continental margin, transitional continental margin and drift rift basins. In the present study, it is observed for the first time that coal type source rocks are mainly developed in 14 continental margin basins in China’s sea area, revealing that a very large C-shaped coal bearing basin group developed there in the Cenozoic. Next, based on the coupling analysis of paleoclimate, paleobotany, paleogeography and paleostructure, it is observed that there are five coal-forming periods in China’s sea area, namely the Paleocene, Eocene, Early Oligocene, Late Oligocene and Miocene-Pliocene, and the coal-forming age is gradually new from north to south. It is also found that the coal seams in the sea area are mainly developed in three coal-forming environments in Cenozoic, namely delta, fan delta and tidal flat-lagoon. The coal seams developed in different environments are characterized by thin thickness, many layers and poor stability. However, the coal-bearing series source rocks in China’s sea area have a wide distribution range, very high thickness and large amount of source rocks, thus forming a solid material basis for the formation of rich coal-type oil and gas.
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Marine sediments represent a major carbon reservoir on Earth. Dissolved organic matter (DOM) in pore waters accumulates products and intermediates of carbon cycling in sediments. The application of excitation-emission matrix spectroscopy (EEMs) in the analysis of subseafloor DOM samples is largely unexplored due to the redox-sensitive matrix of anoxic pore water. Therefore, this study aims to investigate the interference caused by the matrix on EEMs and propose a guideline to prepare pore water samples from anoxic marine sediments. The parameters determined by fluorescence spectra include 3D-index derived from EEMs after parallel factor analysis (PARAFAC), fluorescence index (FI) (contribution of terrigenous DOM), biological index (BIX) and humification index (HIX) derived from 2D emission spectra. First, we investigated the impacts of extensively-presented ions as typical electron acceptors, which are utilized by anaerobic microbes and stratified in marine sediments: Fe(II), Fe(III), Mn(II) and sulfide in anoxic pore water resulted in biases of fluorescent signals. We proposed threshold concentrations of these ions when the interference on EEMs occurred. Effective removal of sulfide from sulfide-rich samples could be achieved by flushing with N2 for 2 min. Second, the tests based on DOM standard were further verified using pristine samples from marine sediments. There was a significant change in the fluorescence spectra of Rhone sedimentary DOM after O2 exposure. This study demonstrated that the change was caused by oxidation of the matrix rather than the intrinsic alteration of DOM. It was confirmed by extracted DOM via both EEMs analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Slight oxidation of sulfur-containing compounds (e.g., sulfhydryl) and polyphenol-like compounds occurred. Finally, a sample preparation sequence is proposed for pore water from anoxic sediments. This method enables measurement with small volumes of the sample (e.g., 50 µL in this study) and ensures reliable data without the interference of the redox-sensitive matrix. This study provides access to the rapid analysis of DOM composition in marine sediments and can potentially open a window into examining the carbon cycling of the marine deep biosphere.
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The South Yellow Sea basin is filled with Mesozoic–Cenozoic continental sediments overlying pre-Palaeozoic and Mesozoic–Palaeozoic marine sediments. Conventional multi-channel seismic data cannot describe the velocity structure of the marine residual basin in detail, leading to the lack of a deeper understanding of the distribution and lithology owing to strong energy shielding on the top interface of marine sediments. In this study, we present seismic tomography data from ocean bottom seismographs that describe the NEE-trending velocity distributions of the basin. The results indicate that strong velocity variations occur at shallow crustal levels. Horizontal velocity bodies show good correlation with surface geological features, and multi-layer features exist in the vertical velocity framework (depth: 0–10 km). The analyses of the velocity model, gravity data, magnetic data, multi-channel seismic profiles, and drilling data showed that high-velocity anomalies (>6.5 km/s) of small (thickness: 1–2 km) and large (thickness: >5 km) scales were caused by igneous complexes in the multi-layer structure, which were active during the Palaeogene. Possible locations of good Mesozoic and Palaeozoic marine strata are limited to the Central Uplift and the western part of the Northern Depression along the wide-angle ocean bottom seismograph array. Following the Indosinian movement, a strong compression existed in the Northern Depression during the extensional phase that caused the formation of folds in the middle of the survey line. This study is useful for reconstructing the regional tectonic evolution and delineating the distribution of the marine residual basin in the South Yellow Sea basin.
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The East China Sea Shelf Basin generated a series of back-arc basins with thick successions of marine- and terrestrial-facies sediments during Cenozoic. It is enriched with abundant oil and gas resources and is of great significance to the petroleum exploration undertakings. Therein, the Lishui Sag formed fan delta, fluvial delta and littoral-to-neritic facies sediments during Paleocene-Eocene, and the research on its sedimentary environment and sediment source was controversial. This study analyzed the paleontological combination characteristics, and conducted a source-to-sink comparative analysis to restore the sedimentary environment and provenance evolution of the Lishui Sag during Paleocene-Eocene based on the integration of detrital zircon U-Pb age spectra patterns with paleontological assemblages. The results indicated that Lishui Sag was dominated by littoral and neritic-facies environment during time corroborated by large abundance of foraminifera, calcareous nannofossils and dinoflagellates. Chronological analysis of detrital zircon U-Pb revealed that there were significant differences in sediment sources between the east and west area of the Lishui Sag. The western area was featured by deeper water depths in the Paleoce-Eocene, and the sediment was characterized by a single Yanshanian peak of zircon U-Pb age spectra, and mainly influenced from Yanshanian magmatic rocks of South China Coast and the surrounding paleo-uplifts. However, its eastern area partly showed Indosinian populations. In particular, the upper Eocene Wenzhou sediments were featured by increasingly plentiful Precambrian zircons in addition to the large Indosinian-Yanshanian peaks, indicating a possible impact from the Yushan Low Uplift to the east. Therefore, it is likely that the eastern Lishui Sag generated large river systems as well as deltas during time. Due to the Yuquan Movement, the Lishui Sag experienced uplifting and exhumation in the late stage of the late Eocene and was not deposited with sediments until Miocene. Featured by transitional-facies depositions of Paleocene-Eocene, the Lishui Sag thus beared significant potential for source rock and oil-gas reservoir accumulation.
[Abstract](144) [FullText HTML](44) [PDF 1233KB](15)
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Internal solitary wave (ISW) is often accompanied by huge energy transport, which will change the pore water pressure in the seabed. Based on the two-dimensional Biot consolidation theory, the excess pore water pressure in seabed was simulated, and the spatiotemporal distribution characteristics of excess pore water pressure was studied. As the parameters of both ISW and seabed can affect the excess pore water pressure, the distribution of pore water pressure showed both dissipation and phase lag. And parametric studies were done on these two phenomena. Due to influenced by the phase lag of excess pore water pressure, the penetration depth under the site of northern South China Sea with total water depth 327 m, induced by typical internal solitary wave increased by 26.19%, 53.27% and 149.86% from T0 to T0.5 in sand silt, clayey silt and fine sand seabed, respectively. That means the effect of ISW on seabed will be underestimated if we only take into accout the penetration depth under ISW trough, especially for fine sand seabed. In addition, the concept of “amplitude-depth ratio” had been introduced to describe the influence of ISW on seabed dynamic response in the actual marine environment. In present study, it is negatively correlated with the excess pore water pressure, and an ISW with smaller amplitude-depth ratio can wide the range of lateral impacts. Our study results help understand the seabed damage induced by the interaction between ISW and seabed.
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The sedimentary system of Kalimantan has undergone significant development since the Oligocene. Previous research have largely ignored the capacity of the Cretaceous-Eocene sediments to produce hydrocarbons, focusing instead primarily on the Oligocene-Miocene coal as the principal source rocks. Shales and coals from the outcrops in the northern margin of Kalimantan were analyzed with palynological and geochemical methods to characterize the palaeoenvironmental and palaeoecological differences between the Cretaceous-Eocene and the Oligocene-Miocene samples. The high proportion of Cheirolepidoaceae, Schizaeoisporites and Ephedripites in the pollen assemblage from the Cretaceous-Eocene outcrops reflects an arid tropical/subtropical climate. The relatively low abundances of gymnosperm-derived biomarkers including isopimarane, β-phyllocladane, β-kaurane, suggest the gymnosperm features in flora. High C27/C29 ααα 20R sterane ratios, (C19–C29) tricyclic terpanes/C30 αβ hopane and extremely low oleanane/C30 αβ hopane, bicadinane T/C30 αβ hopane, and diterpenoid abundance indicate that there was a dominance of algae relative to higher plants in the organic matter. The gymnosperm-derived biomarkers, including isopimarane, β-phyllocladane, β-kaurane, suggest that palaeovegetation during this period was dominated by gymnosperms. The saline and reducing conditions in the bathyal and abysmal sea, evidenced by rather low Pr/Ph and high Gammarerane index, are beneficial for the preservation of hydrogen-rich organic matter. It is presumed that the Cretaceous-Eocene shales had great hydrocarbon generation potential in the southern South China Sea. During the period of Oligocene to Miocene in the Zengmu Basin and the Baram-Sabah Basin, the climate changed to a dominant humid and warm condition, which is corroborated by abundant pollen of Florschuetzia and Magnastriatites hawardi. Low C27/C29 ααα 20R sterane ratios, (C19–C29) tricyclic terpanes/C30 αβ hopane, and high oleanane/C30 αβ hopane, bicadinane T/C30 αβ hopane suggest that the palaeovegetation was dominated by angiosperms including the mangrove plants. The extremely abundant higher plants provide ample terrigenous organic matter for the formation of coal-measures in delta facies. The low gammacerane index and high Pr/Ph indicate the fresh and sub-oxic water in delta-neritic-abysmal faces, which is not beneficial for the accumulation of hydrogen-rich organic matter. Thus, the Oligocene-Miocene marine argillaceous rocks can be potential sources of natural gas.
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Carbonate cements are the most abundant authigenic mineral and impact on physical properties greatly in sandstone reservoir. In this paper, Pinghu Formation of Xihu Sag was taken as a target. Characteristics, distribution and formation of carbonate cements were investigated via optical microscopy, cathodoluminescence (CL), electron probe and in-situ carbon-oxygen isotope. The results showed that carbonate cements varied in types and shapes. Calcite/dolomite mainly present as poikilotopic cements, while ferrocalcite/ferrodolomite/ankerite generally present as pore-filling cements. Carbon isotope (δ13C) values of carbonate cements were ranging from –7.77‰ to –2.67‰, with an average of –4.52‰, while oxygen isotope (δ18O) values were ranging from –18.94‰ to –12.04‰, with an average of –14.86‰. The δ13C/δ18O indicated that the paleo-fluid of carbonate cement was mainly freshwater. Organic carbon mainly came from organic matter within mature source rocks, and inorganic carbon came from dissolution of carbonate debris and early carbonate cements. Distinctive δ13C/δ18O values manifest that carbonate cements with different types formed in different periods, which make different contributions to the reservoir properties. Calcite/dolomite formed during eodiagenesis (70–90℃) and early mesodiagenesis stage (90–120℃), and were favorable to reservoir owing to their compacted resistance and selective dissolution. Ferrocalcite/ferrodolomite/ankerite formed during middle-late mesodiagenetic stage (above 120℃), and were unfavorable to reservoir due to cementing the residual intergranular pores. Hence, in order to evaluate the reservoir characteristics, it is of significantly important to distinguish different types of carbonate cements and explore their origins.
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The Chinese marine dynamic environment satellite HY-2B was launched in October 2018 and carries a Ku-band scatterometer. This paper focuses on the accuracies of HY-2B scatterometer wind data during the period from November 2018 to May 2021. The HY-2B wind data are validated against global moored buoys operated by the U.S. National Data Buoy Center (NDBC) and Tropical Atmosphere Ocean (TAO), numerical model data by the National Centers for Environmental Prediction (NCEP), and the Advanced Scatterometer (ASCAT) data issued by the Remote Sensing System (RSS). The results showed that the wind speeds and directions observed by the HY-2B scatterometer agree well with these buoy wind measurements. The root-mean-squared errors (RMSEs) of the HY-2B wind speed and direction are 0.74 m/s and 11.74°, respectively. For low wind speeds (less than 5 m/s), the standard deviation (STD) of the HY-2B-derived wind direction is higher than 20°, which implies that the HY-2B wind direction for low wind speeds is less accurate than that for moderate to high wind speed ranges. The RMSE of the HY-2B wind speed is slightly larger in high latitude oceans (60°S–90°S and 60°N–90°N) than in low latitude regions. Furthermore, the dependence of the residuals on the cross-track location of wind vector cells and the stability of the HY-2B scatterometer wind products are discussed. The wind stability assessment results indicate that a clear yearly oscillation is observed for the HY-2B wind speed bias which is due to seasonal weather variations. In general, the accuracy of HY-2B winds meets the operational precision requirement and is consistent with other wind data.
[Abstract](59) [FullText HTML](26)
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The hydrocarbon gases in the L1 gas field of the Lishui-Jiaojiang Sag have been commonly interpreted to be an accumulation of pure sapropelic-type thermogenic gas. In this study, chemical components, stable isotopic compositions, and light hydrocarbons were utilized to shed light on the origins of the hydrocarbon fluids in the L1 gas pool. The hydrocarbon fluids in the L1 gas pool are proposed to be a mixture of three unique components: mid-maturity oil from the middle Paleocene coastal marine Lingfeng source rock, oil-associated (late oil window) gas generated from the lower Paleocene lacustrine Yueguifeng source rock, and primary microbial gas from the paralic deposits of the upper Paleocene Mingyuefeng source rock. Here, for the first time, the hydrocarbon gases in the L1 gas pool are diagnosed as mixed oil-associated sapropelic-type gas and microbial gas via four pieces of principal evidence: (1) the abnormal carbon isotopic distributions of all methane homologues from C1 (CH4 or methane) to C5 (C5H12 or pentane) shown in the Chung plot; (2) the diagnostic 13C-depleted C1 compared with the thermogenic sapropelic-type gas model, while δ13C2 (C2H6 or ethane) and δ13C3 (C3H8 or propane) both fit perfectly; (3) the excellent agreement of the calculated carbon isotopic compositions of the pure thermogenic gas with the results of the thermal simulated gas from the type-II1 kerogen-rich Yueguifeng source rock; and (4) the oil-associated gas inferred from various binary genetic diagrams with an abnormally elevated gas oil ratio. Overall, the natural gases of the L1 gas pool were quantified in this study to comprise approximately 13% microbial gas, nearly 48% oil-associated sapropelic-type gas, and 39% of nonhydrocarbon gas. The microbial gas is interpreted to have been codeposited and entrained in the humic-kerogen-rich Mingyuefeng Formation under favorable low-temperature conditions during the late Paleocene-middle Eocene. The microbial gas subsequently leaked into the structurally and stratigraphically complex L1 trap with oil-associated sapropelic-type gas from the Yueguifeng source rock during the late Eocene-Oligocene uplifting event. A small amount of humic-kerogen-generated oil in the L1 gas pool is most likely to be derived from the underlying Lingfeng source rock. The detailed geological and geochemical considerations of source rocks are discussed to explain the accumulation history of hydrocarbon fluids in the L1 gas pool. This paper, therefore, represents an effort to increase the awareness of the pitfalls of various genetic diagrams, and an integrated geochemical and geological approach is required for hydrocarbon-source correlation.
[Abstract](66) [FullText HTML](22) [PDF 43508KB](4)
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Subduction process is a dynamical bridge for the exchanges of heat between the atmosphere and subsurface ocean water, which is regarded as a central proxy for the ocean climate studies. Given its key indicator in climate signals, it is of importance to examine the ability of a model to simulate the global subduction rate before investigating the climate dynamics. In this paper, we evaluated the ability of 21 climate models from Coupled Model Intercomparison Project Phase 6 (CMIP6) in simulating the subduction rate. In general, the simulation ability of the models to the subduction climatology is better than that to the long-term variation trend. Based on the comprehensive analysis of climatology distribution and long-term trend of the subduction rate, GISS-E2-1-G performs better in reproducing the subduction rate climatology and IPSL-CM6A-LR can simulate positive long-term trend for both the global mean subduction rate and the lateral induction term in the Antarctic Circumpolar Current (ACC) region. However, it is still challenging to capture both the distribution characteristics of the subduction climatology and the long-term temporal trend for the 21 CMIP6 models. In addition, the model results demonstrate that, the ACC area is the major region contributing to the long-term trend of the global mean subduction rate. The analysis in this paper indicates that the poor simulation ability of reproducing the long-term trend of global mean subduction rate might be attributed to the ocean dynamics, for example, the zonal velocity at the bottom mixed layer and zonal gradient of mixed layer depth.
[Abstract](64) [FullText HTML](15)
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Here, we report the results of high-resolution nitrate measurements using an optical nitrate profiler (in situ ultraviolet spectrophotometer, ISUS) along transect across a high-turbidity shelf (East China Sea) and a low-turbidity shelf (Chukchi Sea). The ISUS-measured nitrate concentrations closely reproduced the results measured by conventional bottle methods in low-turbidity waters. However, for high-turbidity waters of the East China Sea (salinity<30), a correction factor of 1.19 was required to match the standard bottle measurements. The high-resolution ISUS data revealed subtle spatial variability (e.g., a subsurface nitrate minimum) that may have been missed if based solely on bottle results. Four main structures of the nitracline on the East China Sea are apparent from the ISUS nitrate profile. High-resolution nitrate data are important for studying nitrate budgets and nutrient dynamics on continental shelves.
[Abstract](28) [FullText HTML](7)
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The sedimentary record of climate change in the Arctic region is useful for understanding global warming. Kongsfjorden is located in the subpolar region of the Arctic and is a suitable site for studying climate change. Glacier retreat is occurring in this region due to climate change, leading to an increase in meltwater outflow with a high debris content. In August 2017, we collected a sediment core Z3 from the central fjord near the Yellow River Station. Then, we used the widely used chronology method of 210Pb, 137Cs, and other parameters to reflect the climate change record in the sedimentary environment of Kongsfjorden. The results showed that after the mid-late 1990s, the mass accumulation rate of this core increased from 0.10 g/(cm2·a) to 0.34 g/(cm2·a), while the flux of 210Pbex increased from 125 Bq/(m2·a) to 316 Bq/(m2·a). The higher sedimentary inventory of 210Pbex in Kongsfjorden compared to global fallout might have been caused by sediment focusing, boundary scavenging, and riverine input. Similarities between the inventory of 137Cs and global fallout indicated that terrestrial particulate matter was the main source of 137Cs in fjord sediments. The sedimentation rate increased after 1997, possibly due to the increased influx of glacial meltwater containing debris. In addition, the 137Cs activity, percentage of organic carbon (OC), and OC/total nitrogen concentration ratio showed increasing trends toward the top of the core since 1997, corresponding to a decrease in the mass balance of glaciers in the region. The results of δ13C, δ15N and OC/TN concentration ratio showed both terrestrial and marine sources contributed to the organic matter in core-Z3. The relative contribution of terrestrial organic matter which was calculated by a two-endmember model showed an increased trend since mid-1990s. All these data indicate that global climate change has a significant impact on Arctic glaciers.
[Abstract](21) [FullText HTML](5)
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The estuarine tapertail anchovy (Coilia nasus) is a high-value commercial fish. Estimating the spawning site or hatchery origin and habitat is essential for its conservation. This study aimed to determine the habitat use and life history characteristics of C. nasus from the Changjiang River Estuary. We investigated the environmental signatures of strontium (Sr) and calcium (Ca) in the otoliths of the collected specimens using electron probe microanalysis; additionally, we examined their gonadal maturity stage. Our results indicate that the 31 adult C. nasus specimens used in this study could be classified into two types based on their otolith Sr:Ca concentration ratios and their gonadal maturity stage. The long freshwater early life history type (Type LF) had wider central region in the otolith with low Sr:Ca concentration ratios ranging from 1.24±0.62 to 1.92±0.78 and a bluish pattern of low Sr content level. These fish are of riverine origin and had a relatively long early life history in freshwater and low gonadal maturation when captured. The short freshwater early life history type (Type SF) had a shorter central region in the otolith with low Sr:Ca concentration ratios ranging from 1.35±0.5 to 2.82±0.97 and a correspondingly bluish pattern. These fish also had a relatively short-term early life history in freshwater and high gonadal maturation when captured. The results of the otolith microchemical analysis indicated that Type LF and Type SF originated in spawning/hatching sites far from and close to the estuary, respectively. The mature gonads of Type SF fish indicated that they may breed in areas close to the estuary, whereas the immature gonads of Type LF fish indicated that they may breed in areas far from the estuary. This study is the first to reveal that the Changjiang River Estuary contains stocks of anadromous C. nasus originating in different spawning sites during the same season. The estuarine habitat plays a critical role in the connectivity between freshwater recruitment and the marine resources available to adult spawners of this commercially valued species. From a conservation perspective, this study provides important information for identifying anadromous C. nasus stocks originating in different spawning sites in the Changjiang River Basin.
[Abstract](142) [FullText HTML](63) [PDF 7648KB](14)
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Taking the advantage of sun glitter (SG) observed from high-resolution satellites Gaofen-1 (GF-1) and Gaofen-6 (GF-6), a new method named Shield and Vortex 1-2 (SAV1-2) for extracting spatial texture information from sun glitter was established. Sea surface texture detail information around Diaoyu Dao and its affiliated islands was extracted using SAV1-2. Meanwhile, the dynamic characteristics of the water environment were analyzed by combining the water color, temperature and dynamic data. The results show the following information. (1) Stable westward shield effect and eastward Karman vortex streets, extracted from SG, appear upstream (westward) and downstream (eastward) of the Diaoyu Dao and its affiliated islands respectively. (2) The dominant direction of the Kuroshio Current in the Diaoyu Dao and its affiliated islands area is east, the Diaoyu Dao and its affiliated islands interacting with Kuroshio, inducing western shield and eastern shelter and wake. Furthermore, wave intervals of the shield in front of the island range from hundreds to thousands of metres, and extend wider than the island itself. (3) Combining with high-resolution sea surface temperature (SST) and chlorophyll a (Chl a) concentration, the directional changes of water color elements are mutually supported and proved with the stable shield (wave packet) effect in the west and vortex street effect in the east. The change of SST upstream of the island (western shield area) is not significant, the temperature in the downstream shelter area decreases slightly, and the SST in the downstream wake area shows a general trend of obvious decrease. The wake area is dominated by Karman vortex streets in shape, supplementing by vortices. The concentration of Chl a in the west shield of island is as low as that in downstream shelter area, while it increases significantly in the downstream wake area with shape in eddy or ribbon. (4) The SAV methods of extracting sea surface texture detail using SG can be widely used in different sea areas and water quality. This paper can provide reference for the protection and development of Diaoyu Dao and its affiliated islands and its surrounding waters. It is suggested that some kind of current buffer, such as marine wind farm, should be established in the western waters of Diaoyu Dao and its affiliated islands to protect the islands, and marine pasture should be developed in the downstream of eastern waters of Diaoyu Dao and its affiliated islands.
[Abstract](97) [FullText HTML](24) [PDF 1492KB](3)
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Toxic harmful algal blooms (HABs) can cause deleterious effects in marine organisms, threatening the stability of marine ecosystems. It is well known that different strains, natural populations and growth conditions of the same toxic algal species may lead to different amount of phycotoxin production and the ensuing toxicity. To fully assess the ecological risk of toxic HABs, it is of great importance to investigate the toxic effects of phycotoxins in marine organisms. In this study, the short-term toxicity of 14 common phycotoxins (alone and in combination) in the marine zooplankton Artemia salina was investigated. The 48 h LC50 of the 14 phycotoxins varied from 0.019 3 µg/mL to 2.415 µg/mL. The most potent phycotoxin was azaspiracids-3 (AZA3; with a LC50 of 0.019 3 µg/mL), followed by azaspiracids-2 (AZA2; 0.022 6 µg/mL), pectenotoxin-2 (PTX2; 0.046 0 µg/mL) and dinophysistoxin-1 (DTX1; 0.081 8 µg/mL). For the binary exposure, okadaic acid (OA) induced potential additive effects with DTX1, probably due to their similar structure (polyether fatty acid) and mode of action (attacking the serine/threonine phosphoprotein phosphatases). On the other hand, OA showed potential antagonistic effects with PTX2, which might be accounted for by their activation on the detoxification activity of cytochrome P450 activity. In addition, DTX1 induced potential synergetic effects with saxitoxin (STX), yessotoxin (YTX) or PTX2, suggesting the hazard potency of the mixtures of DTX1 and other phycotoxins (like STX, YTX and PTX2) with regard to the ecological risk. These results provide valuable toxicological data for assessing the impact of phycotoxins on marine planktonic species and highlight the potential ecological risk of toxic HABs in marine ecosystems.
[Abstract](48) [FullText HTML](19)
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Enderby Land in East Antarctica and its adjacent areas, which are closely related to the Indian Plate in their geological evolution, have become one of the key zones for studies on how the Antarctic continent evolves. Based on the isostasy and flexure theories of the lithosphere and using the CRUST1.0 model as the depth constraint, this paper uses the gravity field model EIGEN-6C4 and topographic data to calculate the isostatic gravity anomalies of Enderby Land and its adjacent areas. Then, the crustal thickness of the study area is calculated, and three comprehensive geophysical interpretation profiles that vertically span the study area are plotted. The results show that the flexural isostatic gravity anomalies in Enderby Land and its adjacent areas are closely related to the regional tectonic setting, and the anomalies in different regions differ substantially, ranging from −50×10−5 m/s2 to 85×10−5 m/s2. A zone of high isostatic gravity anomalies (30×10−5–80×10−5 m/s2) is distributed outside the Cooperation Sea and Queen Maud Land, which may be plate remnants generated by early rifting. Except for the Kerguelen Plateau, which was formed by a hotspot and has a crustal thickness of 15 km, the thickness of the oceanic crust in other parts of the study area changes slightly by approximately 4–9 km, with the thinnest part being in Enderby Basin. The thickness of the inland crust along the coastline increases with the elevation, with the maximum thickness reaching 34 km. The isostatic gravity anomalies corresponding to the zone of high magnetic anomalies along the continental margin of Queen Maud Land are negative and small, with an isostatic adjustment trend indicating Moho surface uplift, and those on the edge of central Enderby Land are near zero, approaching the isostatic state, which may be caused by the magmatism at the early stage of rifting.The continental-oceanic boundary (COB) should be close to the contour line of the crustal thickness 10–12 km on the outer edge of the coastline.
[Abstract](56) [FullText HTML](17)
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The HY-2A satellite, which is equipped with a radar altimeter and was launched on August 16, 2011, is the first Chinese marine dynamic environmental monitoring satellite. Extracting ocean tides is one of the important applications of the radar altimeter data. The radar altimeter data of the HY-2A satellite from November 1, 2011 to August 16, 2014 are used herein to extract global ocean tides. The constants representing the tidal constituents are extracted by HY-2A RA data with harmonic analysis based on the least squares method. Considering tide aliasing issues, the analysis of the alias periods and alias synodic periods of different tidal constituents shows that only the tidal constituents M2, N2, and K2 are retrieved precisely by the HY-2A RA data. The derived tidal constants of the tidal constituents M2, N2 and K2 are compared to those of tidal gauge data and the TPXO tide model results. The comparison between the derived results and the tidal gauge data shows that the RMSEs of the tidal amplitude and phase lag are 9.6 cm and 13.34°, 2.4 cm and 10.47°, and 8.1 cm and 14.19° for tidal constituents M2, N2, and K2, respectively. The comparisons of the semidiurnal tides with the TPXO model results show that tidal constituents have good consistency with the TPXO model results. These findings confirm the good performance of HY-2A RA for retrieving semidiurnal tides in the global ocean.
[Abstract](42) [FullText HTML](12)
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Increasing intense human activities have largely changed the coastal landscape and caused many environmental issues. However, whether human-induced activities could change the coastal land use gradient pattern, an important coastal zonal characteristic along the sea–land direction, remains unclear. Manila Bay was selected as the study area in this work. According to the distance of the land use and land cover (LULC) to the coastline, we clustered the typical coastal land use sequence patterns (CLUSPs) along the sea–land direction between 1988 and 2016 in Manila Bay and found the following. (1) Four typical CLUSPs, including the natural CLUSP dominated by forest land and grassland, the agricultural CLUSP dominated by dry farm and paddy field, the urbanised CLUSP dominated by construction land and the fishery CLUSP dominated by fishing farm, were mined in 1988. Three typical CLUSPs (a natural CLUSP, an intermediate CLUSP between the agricultural and urbanised CLUSPs, and a fishery CLUSP) were mined in 2016. (2) Affected by the dominant LULC, these typical CLUSPs showed a regular spatial pattern along the sea–land direction. For example, the typical natural CLUSP showed a landward pattern due to the long distance between the forest land and grassland and the coastline. (3) However, influenced by urban and aquaculture expansion, the land intensification of the CLUSP exhibited an obvious increase and caused the decrease of the CLUSP diversity from 1988 to 2016. The increase in the area of LULC coverage showed no obvious correlation with its distance from the coastline (DFC), but the net increase rate of LULC coverage had a significant negative correlation with the DFC. Therefore, human-induced activities have a large impact on the gradient pattern of coastal land use along the sea–land direction.
[Abstract](177) [FullText HTML](69)
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Preparis Channel is the very important exchange path of energy and materials between the northern Bay of Bengal and Andaman Sea. A set of hydrographic measurements, a microstructure profiler, and a deep mooring were used to determine the characteristics of water masses, turbulent mixing, and flows in the Preparis Channel. The unprecedented short-term mooring data reveal that a deep current in the deep narrow passage (below 400 m) of the Preparis Channel flows toward the Bay of Bengal (BoB) with a mean along-stream velocity of 25.26 cm/s at depth of 540 m; above the deep current, there are a relatively weak current flows toward the Andaman Sea (AS) with a mean along-stream velocity of 15.46 cm/s between 500 m and 520 m, and another weak current flows toward the BoB between 430 m and 500 m. Thus, a sandwiched vertical structure of deep currents (below 400 m) is present in the Preparis Channel. The volume transport below 400 m is 0.06 Sv from the AS to the BoB. In the upper layer (shallower than 300 m), the sea water of the AS is relatively warmer and fresher than that in the BoB, indicating a strong exchange through the channel. Microstructure profiler observations reveal that the turbulent diffusivity in the upper layer of the Preparis Channel reaches O(10−4 m2/s), one order larger than that in the interior of the BoB and over the continental slope of the northern AS. We speculate that energetic high-mode internal tides in the Preparis Channel contribute to elevated turbulent mixing. In addition, a local “hotspot” of turbidity is identified at the deep mooring site, at depth of about 100 m, which corresponds to the location of elevated turbulent mixing in the Preparis Channel.
[Abstract](64) [FullText HTML](22)
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Sediment collapse and subsequent lateral downslope migration play important roles in shaping the habitats and regulating sedimentary organic carbon (SOC) cycling in hadal trenches. In this study, three sediment cores were collected using a human-occupied vehicle across the axis of the southern Yap Trench (SYT). The total organic carbon (TOC) and total nitrogen (TN) contents, δ13C, radiocarbon ages, specific surface areas, and grain size compositions of sediments from three cores were measured. We explored the influence of the lateral downslope transport on the dispersal of the sediments and established a tentative box model for the SOC balance. In the SYT, the surface TOC content decreased with water depth and was decoupled by the funneling effect of the V-shaped hadal trench. However, the sedimentation (0.002 5 cm/a) and SOC accumulation rates (~0.038 g/(m2·a) (in terms of OC)) were approximately 50% higher in the deeper hadal region than in the abyssal region (0.001 6 cm/a and ~0.026 g/(m2·a) (in terms of OC), respectively), indicating the occurrence of lateral downslope transport. The fluctuating variations in the prokaryotic abundances and the SOC accumulation rate suggest the periodic input of surficial sediments from the shallow region. The similar average TOC (0.31%–0.38%), TN (0.06%–0.07%) contents, and SOC compositions (terrestrial OC: (11%–18%), marine phytoplanktonic OC: (45%–53%), and microbial OC: (32%–44%)) of the three sites indicate that the lateral downslope transport has a significant mixing effect on the SOC composition. The output fluxes of the laterally transported SOC (0.44–0.56 g/(m2·a) (in terms of OC)) contributed approximately (47%–73%) of the total SOC input, and this proportion increased with water depth. The results of this study demonstrate the importance of lateral downslope transport in the spatial distribution and development of biomes.
[Abstract](68) [FullText HTML](20)
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[Abstract](228) [FullText HTML](100)
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The dual isotopes (N and O) of nitrate were measured using a denitrifier bacterial method in the western South China Sea (WSCS) during September 2015 to elucidate key information during N transformation in the lower euphotic zone (LEZ)-upper mesopelagic zone (UMZ, down to 500 m in this study) continuum, which is a vital sub-environment for marine N cycle and sequestration of atmospheric CO2 as well. The N isotopic composition (δ15N) of nitrate generally decreased from 500 m toward the base of the euphotic zone (~100 m), reaching a value of ~4.6‰ (vs. air N2) at the base of the LEZ, suggesting the imprint of remineralization (nitrification) of isotopically light N from atmospheric source. The δ15N and δ18O of nitrate only generally conform to a 1:1 line at 50 m and 75 m, suggesting that nitrate assimilation is a dominant process to shape nitrate isotope signature in this light-limited and relatively N-replete in this lower part of the euphotic zone. The fractionation factors of N and O isotopes during nitrate fractionation (15εASSIM, 18εASSIM) using a steady-state model were estimated to be 4.0‰±0.3‰ and 5.4‰±0.3‰, respectively. The occurrence of nitrification at the base of the LEZ and most of the UMZ is corroborated by the decoupling of δ15N and the oxygen isotopic composition (δ18O) of nitrate. Our results will provide insights for better understanding N cycle in the South China Sea from a perspective of present and past.
[Abstract](132) [FullText HTML](38)
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In the late Miocene, giant ancient pockmarks, which are fairly rare globally, developed in the Qiongdongnan Basin. In this paper, to determine the sedimentary characteristics and genetic mechanism of these giant ancient pockmarks in the Yinggehai Formation of the Qiongdongnan Basin, based on high-resolution 3D seismic data and multiattribute fusion technologies, we analyzed the planar distribution and seismic facies of the ancient pockmarks and compared the characteristics of the ancient pockmarks with those of channels, craters, and hydrate pits. Moreover, we also discussed the implications of the fluid escape system and paleo-bottom current activity in the ancient pockmark development area and analyzed the influence of the ancient pockmarks on the paleoclimate in this region. Finally, an evolutionary model was proposed for the giant ancient pockmarks. This model shows that the giant ancient pockmarks in the southern Qiongdongnan Basin were affected by both deep fluid escape and lateral transformation of paleobottom currents. In addition, the giant ancient pockmarks contributed to the atmospheric CO2 concentration in the late Miocene and played a great role in the contemporary evaluation of deepwater petroleum exploration.
[Abstract](80) [FullText HTML](19)
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Mesopelagic fish, the most important daily vertically migrating community in the oceans, are characterized by high lipid content which may obscure the interpretation of stable isotopes analysis. Demersal fish, which are important consumers in the food web dominated by mesopelagic fish, also have a high lipid content. Here we collected 127 fish samples from the South China Sea and evaluated the effect of lipid contents on δ13C of mesopelagic and demersal fish. In lipid-extracted mesopelagic fish, the C/N content ratio (<5.5) shows a clear correlation with Δδ13C (the offset of bulk and lipid-extracted δ13C values), especially in non-migratory and semi-migratory species; these values were less correlation in demersal fish. Based on our results, we suggest that mesopelagic and demersal fish in different regions of the South China Sea should be studied separately using appropriate correction models and less fit for the traditional model. Moreover, the C/N content ratio should be used cautiously for establishing the lipid normalization model, especially for the fish in migratory mesopelagic fish and demersal fish. Our results also reveal that mesopelagic fish across nearby regions could be analyzed together. The new models described here can be applied in future studies of mesopelagic and demersal fish in the South China Sea.
[Abstract](254) [FullText HTML](101)
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Chlorophyll-a (CHL) concentration is an important proxy of the marine ecological environment and phytoplankton production. Long-term trends in CHL of the South China Sea (SCS) reflect the changes in the ecosystem’s productivity and functionality in the regional carbon cycle. In this study, we applied a previously reconstructed 15-a (2005-2019) CHL product, which has a complete coverage at 4 km and daily resolutions, to analyze the long-term trends of CHL in the SCS. Quantile Regression (QR) was used to elaborate on the long-term trends of high, median, and low CHL values, as an extended method of conventional linear regression. The results showed downward trends of SCS CHL (unit: mg/(m3·a)) for the 75th, 50th, and 25th quantile in the past 15 a, which were −0.004 0 mg/(m3·a) (−1.62% per year), −0.002 3 mg/(m3·a) (−1.10% per year), and −0.001 9 mg/(m3·a) (−1.01% per year). The negative trends in winter (November to March) were more prominent than in summer (May to September). In terms of spatial distribution, the downward trend was more significant in regions with higher CHL. These led to a reduced standard deviation of CHL over time and space. We further explored the influence of various dynamic factors on CHL trends for the entire SCS and two typical systems (winter Luzon Strait (LZ) and summer Vietnam Upwelling System (SV)) with single-variate linear regression and multivariate random forest analysis. The multivariate analysis suggested the CHL trend pattern can be best explained by the trends of wind speed and mixed-layer depth. The divergent importance of controlling factors for LZ and SV can explain the different CHL trends for the two systems. This study expanded our understanding of the long-term changes of CHL in the SCS and provided a reference for investigating changes in the marine ecosystem.
[Abstract](66) [FullText HTML](22)
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Mudflats play a vital role in maintaining the dynamic balance between sea and land. To understand the characteristics, sources, and pollution risks of six heavy metals (As, Cd, Cr, Cu, Hg, and Pb) in the coastal mudflats on the Leizhou Peninsula, 257 surface sediment samples were studied using mathematical statistics, correlation analysis, and factor analysis. The results show that the overall concentrations of these heavy metals are low although there are several high abnormal points in the local areas. The strong correlation between these heavy metals indicates that the sources of some of the metals are similar, yet their elemental combinations in different cities (counties) varied. According to the calculated enrichment factor (EF), anthropogenic activity-induced heavy metals were determined in order of decreasing influence: As, Cd, Pb, Cr, Cu, and Hg. The low EF values of Hg indicate that it is not present as a contaminant in the study area, while low values of Cr and Cu from the Lianjiang City suggest that these two metals were also attributed to natural sources. The presence of As, Cd, Cr, Cu, and Pb from the remaining cities (counties) should be influenced by anthropogenic activities. The overall potential ecological risk index indicates that the ecological risks posed by the six analyzed heavy metals to the Leizhou Peninsula mudflats, in order of decreasing risk, are Cd, As, Hg, Pb, Cu, and Cr. It is noteworthy that only Cd in Lianjiang City demonstrated substantial ecological risk. Other examined heavy metals in other cities of the study area showed slight ecological risk.
[Abstract](59) [FullText HTML](13)
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The shallow-water temperature profile is typically parameterized using a few empirical orthogonal function (EOF) coefficients. However, when the experimental area is poorly known or highly variable, the adaptability of the EOFs will be significantly reduced. In this study, a new set of basis functions, generated by combining the internal-wave eigenmodes with the average temperature gradient, is developed for characterizing the temperature perturbations. Temperature profiles recorded by a thermistor chain in the South China Sea in 2015 are processed and analyzed. Compared to the EOFs, the new set of basis functions has higher reconstruction accuracy and adaptability; it is also more stable in ocean regions that have internal waves.
[Abstract](161) [FullText HTML](47) [PDF 2374KB](4)
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The geochemical signatures of fifty-four rock samples and three supplementary drill stem test (DST) oils from the Yacheng-Sanya formations in the central Qiongdongnan Basin (CQB) were analysed. Reconstruction of the early Oligocene-early Miocene (36–16 Ma) palaeovegetation and source analyses of organic matter (OM) were conducted using aliphatic biomarkers in ancient sediments and DST oils. Both the interpreted aquatic and terrigenous OM contributed to the CQB source rocks (SRs) but have varying relative proportions. The four distribution patterns derived from n-alkanes, terpanes, and steranes are representative of four OM composition models of the Yacheng-Sanya SRs, including model A, model B, model C, and model D, which were classified based on the increasing contribution from terrigenous OM relative to aquatic OM. Some terrigenous higher plant-derived biomarkers, including oleanane, des-A-oleanane, C29 ααα 20R sterane, bicadinanes, the C19/(C19 + C23) tricyclic terpane ratio, and other n-alkane-derived ratios suggest that angiosperms had increased proportions in the palaeoflora from early Oligocene to early Miocene, and the bloom of terrigenous higher plants was observed during deposition of upper Lingshui Formation to lower Sanya Formation. These findings are consistent with the incremental total organic carbon and free hydrocarbons + potential hydrocarbons (S1 + S2) in the lower Lingshui-lower Sanya strata with a significant enrichment of OM in the E3l1-N1s2 shales. The maturity- and environment-sensitive aliphatic parameters of the CQB SRs and DST oils suggest that all the samples have predominantly reached their early oil-generation windows but have not exceeded the peak oil windows, except for some immature Sanya Formation shales. In addition, most of the OM in the analysed samples was characterised by mixed OM contributions under anoxic to sub-anoxic conditions. Furthermore, terrestrial-dominant SRs were interpreted to have developed mainly in the Lingshui-Sanya formations and were deposited in sub-oxic to oxic environments, compared to the anoxic to sub-anoxic conditions of the Yacheng Formation.
[Abstract](154) [FullText HTML](44)
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Studies in the northern South China Sea (SCS) basement remain important for understanding the evolution of the Southeast Asian continental margin. Due to a thick cover of sediments and scarce borehole penetration, little is known about the age and tectonic affinity of this basement. In this study, an integrated study of Zircon U-Pb geochronology, Hf isotopes, and whole-rock major and trace elements on seven basement granitoids from seven boreholes of Qiongdongnan Basin has been carried out. New zircon U-Pb results for these granitoids present Middle-Late Permian ((270.0±1.2) Ma; (253±3.4) Ma), Middle to Late Triassic ((246.2±3.4) Ma; (239.3±0.96) Ma; (237.9±0.99) Ma; (228.9±1.0) Ma) and Late Cretaceous ages ((120.6±0.6) Ma). New data from this study, in combination with the previous dataset, indicates that granitoid ages in northern SCS basement vary from 270 Ma to 70.5 Ma, with three age groups of 270–196 Ma, 162–142 Ma, and 137–71 Ma, respectively. Except for the Late Paleozoic-Mesozoic rocks in the basement of the northern SCS, a few old zircon grains with the age of (2708.1±17) Ma to (2166.6±19) Ma provide clues to the existence of the pre-Proterozoic components. The geochemical signatures indicate that the Middle Permian-Early Cretaceous granitoids from the Qiongdongnan Basin are I-type granites formed in a volcanic arc environment, which were probably related to the subduction of the Paleo-Pacific plate.
[Abstract](106) [FullText HTML](28)
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The increase of total organic carbon content of the late Oligocene-early Miocene terrigenously-dominated marine shales in the shallower depth intervals was reported in the Ying-Qiong Basin, South China Sea. The lower Sanya Formation shales (early Miocene) have biomarker characteristics of tropical/subtropical plants, with abundant high molecular weight n-alkanes, angiosperm-derived oleanane, rearranged oleananes I, II, II, tricyclic/tetracyclic terpanes including des-A-oleanane, X, *, Y, Z, Z1 and bicadinanes W, T, T1, R. The biomarker characteristics are suggestive of larger influx of the dominant tropical/subtropical angiosperms in flora under a warming and more humid climate during depositions of the lower Sanya Formation (early Miocene) than the older Lingshui Formation (late Oligocene). The tropical/subtropical angiosperm input was thought as the prime control of terrigenous organic matter enrichment relative to the redox condition, and the coeval sea level changes and seafloor spreading in the South China Sea. Enrichment of the terrigenous organic matter in the early Miocene shales is likely in association with the coeval peak East Asian summer monsoon intensity in the South China Sea.
[Abstract](190) [FullText HTML](35)
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Compared to single-polarization synthetic aperture radar (SAR) data, fully polarimetric SAR data can provide more detailed information of the sea surface, which is important for applications such as shallow sea topography detection. The Gaofen-3 satellite provides abundant polarimetric SAR data for ocean research. In this paper, a shallow sea topography detection method was proposed based on fully polarimetric Gaofen-3 SAR data. This method considers swell patterns and only requires SAR data and little prior knowledge of the water depth to detect shallow sea topography. Wave tracking was performed based on preprocessed fully polarimetric SAR data, and the water depth was then calculated considering the wave parameters and the linear dispersion relationships. In this paper, four study areas were selected for experiments, and the experimental results indicated that the polarimetric scattering parameter α (alpha) had higher detection accuracy than quad-polarization images. The mean relative errors were 14.52%, 10.30%, 12.56%, and 12.90%, respectively, in the four study areas. In addition, this paper also analyzed the detection ability of this model for different topographies, and the experiments revealed that the topography could be well recognized when the topography gradient is small, the topography gradient direction is close to the wave propagation direction, and the isobath line is regular.
[Abstract](89) [FullText HTML](12)
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The Mohn Ridge separates the Greenland Sea and the Lofoten Basin. Previous studies identified the export across the Mohn Ridge (EMR) from the Greenland Basin into the Lofoten Basin using water mass analysis and the tracer diffusion method, but there is still lack of direct current measurements. A surface mooring with four current meters was deployed on the Mohn Ridge from June 5 to June 18 in 2015, when three cyclones passed in the adjacent area. In the absence of cyclones, the flow on the Mohn Ridge was northeastward, parallel to the ridge. When cyclones appeared, the EMR occurred to transport Greenland Sea water into the Lofoten Basin. The probable mechanism is the sea level height variation caused by the perturbation of the low pressure of cyclones, which yields an outward pressure gradient force to drive the outflow. Our results suggest that the outflow is intermittent and only happens during cyclone activities. The annual mean volume flux of EMR was roughly estimated by the limited data, which is about 3.8×106 m3/s, a little bit smaller than the estimation based on volume conservation. The results indicate that the contribution of the cyclonic storms to EMR is a greatly important mechanism that potentially influences the global thermohaline circulation through the Greenland-Scotland Ridge overflow.
[Abstract](113) [FullText HTML](29)
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Seasonal location and intensity changes in the western Pacific subtropical high (WPSH) are important factors dominating the synoptic weather and the distribution and magnitude of precipitation in the rain belt over East Asia. Therefore, this article delves into the forecast of the western Pacific subtropical high index during typhoon activity by adopting a hybrid deep learning model. Firstly, the predictors, which are the inputs of the model, are analysed based on three characteristics: the first is the statistical discipline of the WPSH index anomalies corresponding to the three types of typhoon paths; the second is the correspondence of distributions between sea surface temperature (SST), 850 hPa zonal wind (u), meridional wind (v), and 500 hPa potential height field; and the third is the numerical sensitivity experiment, which reflects the evident impact of variations in the physical field around the typhoon to the WPSH index. Secondly, the model is repeatedly trained through the backward propagation algorithm to predict the WPSH index using 2011-2018 atmospheric variables as the input of the training set. The model predicts the WPSH index after 6 h, 24 h, 48 h, and 72 h. The validation set using independent data in 2019 is utilized to illustrate the performance. Finally, the model is improved by changing the CNN2D module to the DeCNN module to enhance its ability to predict images. Taking the 2019 Typhoon Lekima as an example, it shows the promising performance of this model to predict the 500 hPa potential height field.
[Abstract](410) [FullText HTML](88)
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Three long-term fixed acoustic Doppler current profilers (ADCPs) were first used for investigating the vertical structure of tidal currents in Xuliujing Section of Changjiang River Estuary. Moreover, three different periods (spring, summer and fall) were also considered for investigating seasonal variations. The semi-diurnal tides were the most energetic, with along-channel speed of up to 80 cm/s for M2 constituent, which dominates at all stations with percent energy up to 65%–75% during seasons. The shape of tidal ellipses of the most energetic semi-diurnal constituent M2 showed obvious polarization of the flow paralleling to the riverbank, with the minor semi-axis being generally general less than 20% of the major one. The maximum velocity of mean current is appeared in top layers at all the three stations, and the velocity decreased with the depth. The seasonal variations of direction are also observed, which is probably caused by complex local topography since the erosion and deposition in riverbed. Observed vertical variation of four parameters of M2 ellipses, agreed well with the optimally fit frictional solutions in top and middle layers. However, there was an obvious difference between frictional model and observed data in the lower water column. Discrepancies are probably on account of stratification, which strengthens in summer and fall due to the freshening influence of the Changjiang River Estuary outflow.
[Abstract](402) [FullText HTML](106)
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Protease-producing bacteria play key roles in the degradation of organic nitrogen materials in marine sediments. However, their diversity, production of proteases and other extracellular enzymes, even in situ ecological functions remain largely unknown. In this study, we investigated the diversity of cultivable extracellular protease-producing bacteria in the sediments of the Bohai Bay. A total of 109 bacterial isolates were obtained from the sediments of 7 stations. The abundance of cultivable protease-producing bacteria was about 104 CFU/g of sediment in all the samples. Phylogenetic analysis based on 16S rRNA gene sequences classified all the isolates into 14 genera from phyla Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria, with Pseudoalteromonas (63/109, 57.8%), Bacillus (9/109, 8.2%), Sulfitobacter (8/109, 7.3%) and Salegentibacter (6/109, 5.5%) as the dominant taxa. Enzymatic inhibition tests indicated that all the tested isolates produced serine and/or metalloprotease, with only a small proportion producing cysteine and/or aspartic proteases. Several extracellular enzyme activities, including alginase, lipase, amylase and cellulose, and nitrate reduction were also detected for strains with higher protease activities. According the results, the protease-producing bacteria could also be participate in many biogeochemical processes in marine sediments. Our study broadened understanding and knowledge on the potential ecological functions of protease-producing bacteria in marine sediments.
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2022, 41(12).
[Abstract](34) [PDF 2887KB](6)
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2022, 41(12): 1-2.
[Abstract](27) [FullText HTML](12) [PDF 69KB](2)
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2022, 41(12): 1-6.   doi: 10.1007/s13131-022-2044-y
[Abstract](221) [FullText HTML](52) [PDF 0KB](4)
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Pituitary gland, or pituitary for short, is characteristic of all vertebrates. As a “master gland” controlling a multitude of important functions in the body, its evolutionary origin has been an object of investigations of evolutionary biology for two centuries. Previous morphological, ultrastructural and immunohistochemical studies suggested the homology of the Hatschek’s pit of amphioxus and vertebrate pituitary. Developmental genetics study showed that the development of Hatschek’s pit and vertebrate pituitary is both subject to regulation by the common genes such as Pit1, Lhx3 and BMP3b. Our recent studies demonstrated that the Hatschek’s pit is able to secrete growth hormone (GH)-like hormone and thyroid-stimulating hormone (TSH)-like hormone that both play functions similar to vertebrate GH and TSH. We thus think that the emergence of Hatschek’s pit represents one of important events during endocrine network evolution, which laid a foundation for the subsequent formation of a hypothalamic-pituitary system in vertebrates.
2022, 41(12): 7-17.   doi: 10.1007/s13131-022-2052-y
[Abstract](199) [FullText HTML](46) [PDF 908KB](30)
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The most important marine coastal ecosystem in the Chilean coast are kelp forests. This review is based on ecological studies regarding different aspects of subtidal kelp ecosystems along the Chilean coast. It highlights the most interesting findings in (1) biology of subtidal kelp in Chile, with particular reference to (2) habitats formed by kelp, and considered the successful examples and promising results in the (3) kelp as an industrial resource (Biotechnological approach of kelps and aquaculture). The impact caused by (4) El Niño-Southern Oscillation is discussed as an important climatic event that could help to forecast the future of the kelp ecosystem. In addition, this literature review outlines the knowledge gaps on subtidal kelp along the Southeast Pacific Coast of Chile, so that research can be strengthened in the future.
2022, 41(12): 18-26.   doi: 10.1007/s13131-022-2066-5
[Abstract](142) [FullText HTML](41) [PDF 1769KB](15)
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Based on long-term tide gauge observations in the last 60 years, the temporal and spatial variation characteristics of sea level change along the coast of China are analyzed. The results indicate that the sea level along the coast of China has been rising at an increasing rate, with an estimated acceleration of 0.07 mm/a2. The rise rates were 2.4 mm/a, 3.4 mm/a and 3.9 mm/a during 1960–2020, 1980–2020 and 1993–2020, respectively. In the last 40 years, the coastal sea level has risen fastest in the South China Sea and slowest in the Yellow Sea. Seasonal sea levels all show an upward trend but rise faster in winter and spring and slower in autumn. Sea level change along the coast of China has significant periodic oscillations of quasi-2 a, 4 a, 7 a, 11 a, quasi-19 a and 30–50 a, among which the 2–3 a, 11 a, and 30–50 a signals are most remarkable, and the amplitude is approximately 1–2 cm. The coastal sea level in the most recent decade reached its highest value in the last 60 years. The decadal sea level from 2010 to 2019 was approximately 133 mm higher than the average of 1960–1969. Empirical orthogonal function analysis indicates that China’s coastal sea level has been changing in a north-south anti-phase pattern, with Pingtan and Fujian as the demarcation areas. This difference was especially obvious during 1980–1983, 1995–1997 and 2011–2013. The coastal sea level was the highest in 2016, and this extreme sea level event was analyzed to be related mainly to the anomalous wind field and ENSO.
2022, 41(12): 27-37.   doi: 10.1007/s13131-022-2027-z
[Abstract](229) [FullText HTML](60) [PDF 4575KB](17)
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Bathing beaches are usually the first to suffer disasters when tsunamis occur, owing to their proximity to the sea. Several large seismic fault zones are located off the coast of China. The impact of each tsunami scenario on Chinese bathing beaches is different. In this study, numerical models of the worst tsunami scenarios associated with seismic fault zones were considered to assess the tsunami hazard of bathing beaches in China. Numerical results show that tsunami waves from the Pacific Ocean could affect the East China Sea coast through gaps between the Ryukyu Islands. The Zhejiang and Shanghai coasts would be threatened by a tsunami from Ryukyu Trench, and the coasts of Hainan and Guangdong provinces would be threatened by a tsunami from the Manila Trench. The tsunami hazard associated with the Philippine Trench scenario needs particular attention. Owing to China’s offshore topography, the sequential order of tsunami arrival times to coastal provinces in several tsunami scenarios is almost the same. According to the tsunami hazard analysis results, Yalongwan Beach and eight other bathing beaches are at the highest hazard level. A high-resolution numerical calculation model was established to analyze the tsunami physical characteristics for the high-risk bathing beaches. To explore mitigating effects of a tsunami disaster, this study simulated tsunami propagation with the addition of seawalls. The experimental results show that the tsunami prevention seawalls constructed in an appropriate shallow water location have some effect on reducing tsunami hazard. Seawalls separated by a certain distance work even better. The analysis results can provide a scientific reference for subsequent preventive measures such as facility construction and evacuation.
2022, 41(12): 38-47.   doi: 10.1007/s13131-022-2060-y
[Abstract](209) [FullText HTML](50) [PDF 4150KB](17)
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High-resolution multi-beam/single-beam bathymetric data and seismic profiling data from the latest surveys are used to map and interpret the detailed seafloor geomorphology of the western region of the North Yellow Sea (NYS), China. The mapping area covers 156 410 km2, and incorporates a flat shelf plain, subaqueous accumulation shoals, tidal scouring troughs, and tidal sand ridge groups. Offshore areas with water depths less than 50 m in the western region of the NYS are mainly covered by thick, loose sediments, forming wide spread accumulation geomorphological features; these include the Liaodong Peninsula subaqueous accumulation system containing shoals and rugged scouring troughs, and the large mud wedge of the Shandong Peninsula. In the central part of the NYS, there is a relatively flat residual shelf plain with coarser sediment deposits. This flat shelf plain has a water depth larger than 50 m and a thin layer of sediment, on which there is a large pockmark field caused by seafloor seepage. These geomorphological structures indicate that modern sedimentary processes are the main driving force controlling the sculpture of the current seafloor surface landform. Extensive strong tidal current systems and abundant sediment sources provide the critical external forces and essential conditions for the formation of seafloor geomorphology. The tectonic basement controls the macroscopic morphological shape of the NYS, but is reflected very little in the seafloor geomorphic elements. Our results provide a detailed seafloor geomorphological map of the western region of the NYS, an area that has not previously mapped and also provide a scientific framework for further research into offshore seafloor geomorphology, shelf sedimentary processes, and submarine engineering construction in this region.
2022, 41(12): 48-57.   doi: 10.1007/s13131-022-2048-7
[Abstract](351) [FullText HTML](121) [PDF 1957KB](24)
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The abundance and health of scleractinian coral communities of Hormuz Island were investigated. For this purpose, we employed 20 m line intercept transects—12 in the intertidal zone and 15 subtidally to evaluate coral cover and community composition. The estimated dead coral coverage was 6.21%±0.81%, while live coral coverage was 16.93%±1.81%, considered as very poor. Totally, 12 genera were recorded, of which Porites with 11.9%±1.4% live cover was the dominant, while Goniopora had the least cover (0.07%±0.08%). Based on Mann-Whitney U-test, live coral coverage, dead coral coverage, algal coverage, cover of other benthic organisms and abiotic components showed significant univariate differences between zones (p<0.05). The Spearman correlation test between the abundance of biotic and abiotic components indicated significant negative correlation of live coral and sand with zoantharian and significant positive correlation of algae and other benthic organisms with rubble. The reef health indices used for the corals indicated that, in general, the environmental conditions were not suitable, which could be attributed to both natural and anthropogenic factors, the most important of which was zoantharian’ overgrowth on the scleractinian corals in this region.
2022, 41(12): 58-72.   doi: 10.1007/s13131-022-2047-8
[Abstract](155) [FullText HTML](30) [PDF 789KB](19)
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Qilianyu Islands coral reefs (QICR), located in the northeastern part of the South China Sea, has been affected by human activities and natural disturbance. To characterize the trophic structure, ecosystem properties and keystone species of this region, a food-web model for the QICR is developed using methods involving a mass-balance approach with Ecopath with Ecosim software. Trophic levels range from 1.00 for detritus and primary producers to 3.80 for chondrichthyes. The mean trophic transfer efficiency for the entire ecosystem is 13.15%, with 55% of total energy flow originating from primary producers. A mixed trophic impact analysis indicates that coral strongly impacts most components of this ecosystem. A comparison of our QICR model with that for other coral reef ecosystems suggests that the QICR ecosystem is immature and/or is degraded.
2022, 41(12): 73-79.   doi: 10.1007/s13131-022-2058-5
[Abstract](150) [FullText HTML](36) [PDF 626KB](15)
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The aim of this study was to evaluate the genetic parameters of the growth performance of Takifugu rubripes. Heritabilities and genetic correlations were estimated for body weight (BW), body length (BL), total length (TL), chest measurement (CM) and trunk length (TKL) of T. rubripes from measurements of progeny at 6 months and 12 months. The results showed that the heritability was 0.37 for BW6, 0.19 for BL6, 0.35 for TL6, 0.29 for CM6, 0.26 for TKL6, 0.36 for BW12, 0.26 for BL12, 0.25 for TL12, 0.31 for CM12 and 0.15 for TKL12. The range of genetic correlations estimated at 6 months was 0.025–0.725 and −0.002–0.706 at 12 months. The results indicated that genetic improvement for faster growth rate or increased body weight in cultured T. rubripes was effective. Based on selection theory, the selection strategy for traits with medium heritability is flexible. Considering that these growth traits do not reach the high level of heritability, family selection should be expected. Given positive genetic correlations among BW, BL, TL, CM, and TKL at 6 months, the five traits could be improved simultaneously through selective breeding. As there was high genetic correlation only between BW12, BL12 and TL12, and negative correlations between TKL12 and BL12 as well as between CM12 and TL12, and only BW, BL and TL at 12 months could be improved simultaneously.
2022, 41(12): 80-86.   doi: 10.1007/s13131-022-2057-6
[Abstract](175) [FullText HTML](50) [PDF 882KB](5)
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With the decline in fish resources worldwide, the ecological dominance and economic importance of crustaceans have obviously increased. Among crustacean species, mantis shrimps are increasingly dominant in many coastal waters of the world. In China, Oratosquilla oratoria is the most widely distributed and productive species of mantis shrimp, and its relative resource density is the highest in the Bohai Sea. In this study, we analysed the long-term and monthly population characteristics of O. oratoria in the Bohai Sea, including its relative resource density, body size and spatial distribution. The results showed that the relative resource density of O. oratoria in the Bohai Sea increased from 3.59 kg/h in 1982 to 14.48 kg/h in 2018, and the percentage of this species that serves as a fishery resource increased from 4.22% in 1982 to 35.27% in 2018, based on the mean relative resource density in May and August. The relative resource density of O. oratoria in the fishing moratorium season from May to August was significantly higher than that in the other months of fishing season, and the relative resource density decreased rapidly after the fishing moratorium ended. The relative resource density of O. oratoria was the highest in summer (August), followed by in autumn (October) and spring (May), and it was the lowest in winter (January). The relative resource density of O. oratoria in the western Bohai Sea was higher than that in the eastern Bohai Sea. The mean body weight of O. oratoria in the Bohai Sea decreased from 21.95 g in 1982 to 14.34 g in 2018, based on the mean body weight in May and August. The body size of O. oratoria in the fishing moratorium season was significantly higher than that in the fishing season, and the body size decreased rapidly after the fishing moratorium ended. Overall, in the context of declining resources of most fishery species, the relative resource density of O. oratoria increased due to its hardiness and adaptability, and its body size decreased under intensive fishing over the past 30 years. The fishing moratorium system had a great influence on the population dynamics of O. oratoria in terms of the relative resource density and body size in the Bohai Sea.
2022, 41(12): 87-97.   doi: 10.1007/s13131-022-1984-6
[Abstract](132) [FullText HTML](37) [PDF 869KB](9)
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While prokaryotes play key roles in nutrient cycling and energy flow during Phaeocystis globosa blooms, the information on the spatial and diel temporal distribution of the prokaryotic community during Phaeocystis blooms remains scarce. In January 2019, we used high-throughput sequencing of the 16S rRNA gene to explore the spatial and diel variations of particle-attached (PA) and free-living (FL) prokaryotic communities during the blooming phase of P. globosa in Beibu Gulf, Guangxi, China. The results suggested a significant spatial variation pattern in the horizontal distribution of prokaryotic communities, while there was no significant difference in the vertical direction. Both spatial distance and environmental variables shaped the horizontal distribution of the prokaryotic community structure, while environmental variables, particularly the abundance of P. globosa colony and Chl a, showed more significant influence and were closely related to the structure and variation of the prokaryotic community. Strong vertical mixing of the water column disrupted the vertical structure heterogeneity of the prokaryotic community in winter. There were significant differences in the diel samples of PA prokaryotic communities, but not in the FL prokaryotic communities. Nitrate, ammonium and the abundance of P. globosa colony were the key environmental variables impacting the diel variations of prokaryotic communities over the sampling period. The present study provided valuable information to depict the spatial-temporal variations of the microbial community and its association with environmental parameters during P. globosa bloom in the tropical gulf.
2022, 41(12): 98-104.   doi: 10.1007/s13131-021-1959-z
[Abstract](113) [FullText HTML](20) [PDF 419KB](1)
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Some deep-sea microbes may incorporate inorganic carbon to reduce CO2 emission to upper layer and atmosphere. How the microbial inhabitants can be affected under addition of bicarbonate has not been studied using in situ fixed and lysed samples. In this study, we cultivated 40 L natural bottom water at ~1 000 m depth with a final concentration of 0.1 mmol/L bicarbonate for 40 min and applied multiple in situ nucleic acids collection (MISNAC) apparatus for nucleic acids extraction from the cultivation. Our classification result of the cultivation sample showed a distinct microbial community structure, compared with the samples obtained by Niskin bottle and six working units of MISNAC. Except for notable enrichment of Alteromonas, we detected prevalence of Asprobacter, Ilumatobacter and Saccharimonadales in the cultivation. Deep-sea lineages of Euryarchaeota, SAR406, SAR202 and SAR324 were almost completely absent from the cultivation and Niskin samples. This study revealed the dominant microbes affected by bicarbonate addition and Niskin sampling, which suggested rapid responses of deep-sea microbes to the environmental changes.
2022, 41(12): 105-114.   doi: 10.1007/s13131-022-2033-1
[Abstract](173) [FullText HTML](49) [PDF 1906KB](13)
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Polycyclic aromatic hydrocarbons (PAHs) pollution, particularly in coastal environments, is a global concern. In this study, the biomonitoring and ranking effects of PAHs in the rockfish Sebastiscus marmoratus were determined in the Maowei Sea, China. The results showed that the concentrations of the 16 priority PAHs detected in the surface seawater were moderate compared with those in other coastal areas worldwide, and the possible sources were rapid industrialization and urbanization combined with atmospheric deposition and runoff. Nested analysis of variance (ANOVA) suggested significant differences in the hepatic ethoxyresorufin-O-deethylase (EROD) activities and phenanthrene-derived metabolites in bile between the port area and the oyster farming area. The fish expert system (FES) was applied to evaluate the biological effects of PAHs on fish. The FES data demonstrated that the biological effect levels of Site S1 (level III, medium stress) were higher than those of the other sampling sites (level II, low stress).
2022, 41(12): 115-122.   doi: 10.1007/s13131-022-2041-1
[Abstract](191) [FullText HTML](50) [PDF 3463KB](7)
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The brain plays a critical role in controlling reproduction through the hypothalamus-pituitary-gonadal (HPG) axis in vertebrates. Turbot (Scophthalmus maximus) has become an economically important marine fish in Europe and North China. Previous research investigating turbot reproduction has focused on the role of the HPG axis in regulating egg and sperm production. However, the morphology and histology of the organs in the HPG axis have not been studied. In this study, we investigated the morphology and histology of brains in female and male turbot at different stages of gonadal development. The results showed that the brains of both female and male turbot were composed of seven parts that are typical of advanced teleosts: the telencephalon, diencephalon, cerebellum, hypothalamus, pituitary gland, myelencephalon, and olfactory bulbs. The telencephalon was well-developed and contained five distinct lobes, with the contiguous diencephalon at the caudal portion. The torus longitudinales and rostral torus semicircularis of the mesencephalon flattened along the dorsal surface, and the rostral corpus cerebellum was located in the dorsal portion. The actual total brain volume in mature males was significantly greater (p<0.05) than that of females with gonadal development. Notably, the pituitary volume in male turbot significantly increased (p<0.05) from immature to mature stage, but this difference did not occur in females. The data together illustrate a distinct sex difference in the turbot brain during gonadal development, providing insight into their HPG axes.
2022, 41(12): 123-132.   doi: 10.1007/s13131-022-2037-x
[Abstract](138) [FullText HTML](34) [PDF 758KB](8)
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Although the adverse impacts of ocean acidification (OA) on marine calcifiers have been investigated extensively, the anti-stress capabilities regulated by increased light availability are unclear. Herein, the interactive effects of three light levels (30 μmol photons/(m2·s), 150 μmol photons/(m2·s), and 240 μmol photons/(m2·s) combined with two pCO2 concentrations (400 ppmv and 1400 ppmv) on the physiological acclimation of the calcifying macroalga Halimeda opuntia were investigated using a pCO2-light coupling experiment. The OA negatively influenced algal growth, calcification, photosynthesis, and other physiological performances in H. opuntia. The relative growth rate under elevated pCO2 conditions significantly declined by 13.14%−41.29%, whereas net calcification rates decreased by nearly three-fold under OA conditions. Notably, increased light availability enhanced stress resistance through the accumulation of soluble organic molecules, especially soluble carbohydrate, soluble protein, and free amino acids, and in combination with metabolic enzyme-driven activities, OA stress was alleviated. The carotenoid content under low light conditions increased markedly, and the rapid light curve of the relative electron transport rate was enhanced significantly by increasing light intensities, indicating that this new organization of the photosynthetic machinery in H. opuntia accommodated light variations and elevated pCO2 conditions. Thus, the enhanced metabolic performance of the calcifying macroalga H. opuntia mitigated OA-related stress.
2022, 41(12): 133-141.   doi: 10.1007/s13131-021-1961-5
[Abstract](172) [FullText HTML](43) [PDF 577KB](19)
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Marine macroalgal sulfated fucose-containing polysaccharides, like fucoidan, have drawn significant attention due to their biotechnological potentials, such as anti-cancer, antioxidant, and anti-cholinesterase activities. The fucoidan derived from brown macroalgae Sargassum angustifolium species (FSA) was investigated for its cytotoxic effects and alterations in cell proliferation, and cell cycle-related gene expression in the present study occurred on NB4 cell line. The results showed that FSA would induce p53, p21, pro-apoptotic genes and increase expression of the p15 gene as a cell arrest marker. Also, FSA inhibited the anti-apoptotic effect of the Bcl-2 gene and decreased dnmt-1 gene expression. FSA significantly exhibited potent 2, 2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity (p<0.05) with an IC50 value of 0.157 mg/mL and showed moderate anti-acetylcholinesterase activity with an IC50 value of 1.20 μg/mL. These results indicated the potential of FSA for the development of therapeutic or preventive agents of cancer and Alzheimer’s disease mainly through cytotoxic effect and AChE (acetylcholinesterase) inhibition as well as additional antioxidant capacities.
2022, 41(12): 142-151.   doi: 10.1007/s13131-022-2036-y
[Abstract](255) [FullText HTML](63) [PDF 680KB](23)
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Assessments of phytoplankton diversity in Sabah waters, North Borneo, have primarily relied on morphology-based identification, which has inherent biases and can be time-consuming. Next-Generation Sequencing (NGS) technology has been shown to be capable of overcoming several limitations of morphology-based methods. Samples were collected from the Sepanggar Bay over the course of the year 2018 in different monsoon seasons. Morphology-based identification and NGS sequencing of the V8–V9 region of the 18S LSU rDNA were used to investigate the diversity of the phytoplankton community. Microscopy and NGS showed complementary results with more diatom taxa detected by microscopy whereas NGS detected smaller and rarer taxa. The harmful algal genera in the study site comprised of Skeletonema, Margalefidinium, Pyrodinium, Takayama, and Alexandrium as detected by NGS. This study showed that that an integrative approach of both morphological and molecular techniques could provide more comprehensive information about the phytoplankton community as the approach captured quantitative variability as well as the diversity of phytoplankton species.
2022, 41(12): 152-155.   doi: 10.1007/s13131-021-1957-1
[Abstract](251) [FullText HTML](76) [PDF 1352KB](31)
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We report for the first time the presence of local populations of the starfish Odontaster penicillatus in the regions of Atacama and Antofagasta, Chile. This finding indicates an extension of the distribution limit of 500 km with respect to the last observation made in 2007 in Isla Grande de Atacama. A total of 121 specimens of O. penicillatus were recorded at depths of between 8 m and 24 m. They were associated with rocky substrate and with different species of barnacles, sponges and bryozoans. The presence of O. penicillatus expands the knowledge of the benthic biodiversity of the region, and the development of studies on its ecological importance will be promoted.