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  • LIANG Hanqiao CHEN Wenfeng FAN Yikai ZHU Zidong MA Guoxu CHEN Deli TIAN Rongrong
  • doi:10.11978/2022190
  • Accepted: 2022-12-08
  • Abstract (45) | PDF (2934KB) (10)
  • 2022 Vol.41 No.6
  • 2022 Vol.41 No.5
  • 2022 Vol.41 No.4
  • 2022 Vol.41 No.3
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    International collaboration of ocean exploration in the South China Sea enhanced by International Ocean Discovery Program Expeditions 367/368/368x
    SUN Zhen, LIN Jian, WANG Pinxian, JIAN Zhimin, LI ChunFeng
    Journal of Tropical Oceanography    2020, 39 (6): 18-29.   DOI: 10.11978/YG2020002
    Abstract289)   HTML59)    PDF(pc) (23169KB)(90)       Save

    With the support of the Ministry of Science and Technology, China joined the International Ocean Drilling Program (IODP) in 1998. IODP-China has so far led the organization of 4+1 expeditions. Through the complimentary proposal project (CPP), Chinese scientists led the drilling expeditions of 349/367/368/368x to investigate the full history of rifting- breakup-spreading of the South China Sea (SCS) basin. In this paper, we summarize the latest achievements of IODP Expeditions 367/368/368x, which revealed surprising evidence for abundant magma intrusion and underplating at the distal northern margin of the SCS as well as rapid continent-ocean transition. Extensive in-depth exchanges and cooperation with the international scientific community have greatly enhanced the operation of ocean drilling platforms, management of the IODP organization, scientific and technical staff training, and public outreach. These experiences will further enhance international cooperation of China's oceanographic research.

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    Variation of summer marine heatwaves in the Northwest Pacific and associated air-sea interaction
    MIAO Yuqing, XU Haiming, LIU Jiawei
    Journal of Tropical Oceanography    2021, 40 (1): 31-43.   DOI: 10.11978/2020016
    Abstract500)   HTML56)    PDF(pc) (39556KB)(146)       Save

    More frequent and persistent marine heatwaves (MHWs) under global warming have exerted severe ecological and socioeconomic impacts. However, there are still limited studies on the air-sea interaction related to MHWs and how MHWs modulate regional climate. Spatiotemporal distribution of summer MHWs in the Northwest Pacific (NWP) and associated air-sea interaction were systematically studied based on daily Optimum Interpolation Sea Surface Temperature (OI SST) dataset from the National Oceanic and Atmospheric Administration (NOAA) and reanalysis dataset from the National Centers for Environmental Prediction (NCEP) during the period of 1982-2017. Empirical orthogonal function (EOF) analysis of MHWs' frequency shows a linear increasing trend in the first mode except for the Kuroshio extension region, while a north-south “dipole” pattern appears in the second mode, with characteristic of inter-decadal oscillation. Maximum intensity, duration, and cumulative intensity of MHWs all show a linear increasing trend. Maximum intensity and cumulative intensity rise most in the high latitudes, and the duration of MHWs varies significantly in the Kuroshio extension region. Analysis of air-sea interaction illustrates that, when MHWs occur in the mid or low latitudes, latent heat and sensible heat fluxes from the ocean to the overlying atmosphere play a dominant role, which impacts atmospheric circulation in the surrounding area. The atmospheric forcing is more significant when MHWs occur in the high latitudes, including longwave radiation and sensible heat fluxes.

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    Study on the health assessment method of typical coral reef ecosystem in the South China Sea
    WU Yingying, LEI Xinming, HUANG Hui, ZHANG Yuyang, DING Dewen
    Journal of Tropical Oceanography    2021, 40 (4): 84-97.   DOI: 10.11978/2020070
    Abstract278)   HTML39)    PDF(pc) (1234KB)(292)       Save

    In this paper, we discuss the principle of ecosystem complexity, and propose a method for evaluating the health of typical coral reef ecosystems in the South China Sea-"Organization and System Function Evaluation." The evaluation framework of this method includes four modules: the structure and function of coral reef ecosystems, the relationship between coral reef ecosystems and other marine ecosystems, the relationship with human social ecosystems, and the development constraints of coral reef ecosystems. The evaluation index system is divided into six levels, including target level, criterion level, factor level, and element level, totaling 67 indicators. We systematically put forward the process of coral reef ecosystem health evaluation, which improves the standardization and timeliness of coral reef health evaluation. The organizing power and system function evaluation method was used to evaluate the health of the coral reef ecosystem of the Paracel Islands from 2011 to 2018. The results show that the health index has fallen by 2.3%-2.4% annually since 2011. Except for a slight rebound in 2012 and 2015, the health index has shown a downward trend in the rest of the years. The overall evaluation is that the coral reef ecosystem of the Paracel Islands is sub-healthy. This result is consistent with the results of field investigations and questionnaire surveys on residents' lives around the Qilianyu Islands. We find that the development of fisheries in 2006-2008, the flooding of starfish in 2012, and the construction of islands and reefs in 2014-2015 had great impacts on the coral reef ecosystem. The fishery output dropped by 50%-80% in 10 years, which is also consistent with the evaluation results. It verifies the science and feasibility of the evaluation method from another angle.

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    Research status and development trends of natural products from marine microorganisms
    MA Lili, TIAN Xinpeng, LI Guiju, ZHAO Yanqiang, YIN Jianping
    Journal of Tropical Oceanography    2021, 40 (5): 134-146.   DOI: 10.11978/2020104
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    Because of their unique habitat and metabolic pathways, marine microorganisms can produce a variety of bioactive substances with novel structures and functions, which make natural products from these marine microorganisms become a research hotspot of new marine drugs. Combining the methods and perspectives of bibliometrics, we review in this paper the research status of natural products from marine fungi and marine bacteria, the artificial synthesis of natural products of marine microorganisms, the biological activity and druggability evaluation of natural products from marine microorganisms, to clarify the current status and development trend of natural products from marine microorganisms.

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    Analysis of submesoscale characteristics of summer upwelling fronts in the western South China Sea
    Xiaolong HUANG, Zhiyou JING, Ruixi ZHENG, Xu ZHANG
    Journal of Tropical Oceanography    2020, 39 (3): 1-9.   DOI: 10.11978/2019086
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    We investigate submesoscale characteristics of summer upwelling fronts in the western South China Sea (WSCS) and associated ageostrophic processes by using satellite measurements and high-resolution ROMS simulations. Active submesoscale filaments with a typical horizontal scale of O(1-10) km are detected to be characterized by O(1) Rossby number (Ro) from the fine-resolution satellite images and simulation results. The diagnostic analysis shows that down-front wind forcing drives a net cross-front Ekman transport and advects heavy water over light water. This process at submesoscale tends to reduce the stratification and potential vorticity (PV), exacerbates the frontal instabilities, and forms the cross-front secondary circulation. The high-resolution simulation results show that the maximum vertical velocity in the frontal zone can reach 100m?d -1, which significantly enhances vertical material exchange. In this context, active submesoscale processes may contribute to enhanced vertical exchanges of the upper ocean in the summer upwelling front of the western SCS.

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    Anisotropy of submesoscale eddy in Kuroshio Extension based on high resolution ROMS output analysis
    Xiaowen ZHOU, Haijin CAO, Zhiyou JING, Guanghong LIAO
    Journal of Tropical Oceanography    2020, 39 (3): 10-18.   DOI: 10.11978/2019056
    Abstract459)   HTML48)    PDF(pc) (4267KB)(242)       Save

    Submesoscale eddies have smaller Richardson number and larger Rossby number, with horizontal scales between 0.1 and 10 km and time scale of ~0(1 day). They act to extract energy from the mesoscale circulation, drive forward energy cascade to the smaller scale turbulence and meanwhile contribute to the vertical flux of what in the upper ocean. In this study, anisotropy of submesoscale eddies in the Kuroshio Extension in a high-resolution simulation (?x≈500m) by the regional ocean modeling system (ROMS) is evaluated using the nummular variance ellipse method. A correlation between eddy anisotropy and submesoscale features is also analyzed. The results show that the submesoscale eddies, as well as the anisotropy, near the flow stream get intensified compared to those in the flanks. The isotropic ratio is well correlated with the strength of submesoscale processes, suggesting that the submesoscale processes tend to be isotropic. The nummular variance ellipse, known as the feedback of eddies to mean flow, may implies forward cascade of kinetic energy.

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    Research on buoy data security management system based on multi-encryption
    ZHANG Xinwen, LIU Yuqiang, LIU Tongmu, LIN Guanying, HUANG Hua
    Journal of Tropical Oceanography    2020, 39 (5): 117-123.   DOI: 10.11978/2019127
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    In view of data security problem concerning ocean buoy data, such as hacker attack, illegal access, data leakage, etc., a data security management system based on multi-encryption is proposed and implemented. We introduce the system architecture, multi-encryption storage and key management scheme in this paper. In this system, the buoy data is encrypted and stored by using multi-encryption technology, and the confidentiality of data transmission is ensured by encrypted transmission in business application. The analytic results of system security indicate show that this system can ensure data security in the process of storage, transmission and application.

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    Causative species of Phaeocystis blooms in Beibu Gulf
    XU Yixiao, HE Xilin, ZHANG Teng, LAN Wenlu
    Journal of Tropical Oceanography    2020, 39 (6): 122-130.   DOI: 10.11978/2020030
    Abstract333)   HTML16)    PDF(pc) (9405KB)(44)       Save

    In recent years, Phaeocystis has become the main causative species for algal blooms in the Beibu Gulf of China. It has deleterious effects on marine ecosystem and aquaculture, and causes nuclear power plant safety problems in Fangcheng. It is thus urgent to further analyze the causative species of Phaeocystis in the region. In February and March 2017, nine strains of Phaeocystis sp. identified by optical microscope were isolated during algal blooms in Qinzhou Bay and Weizhou Island; their SSU rDNA sequences were then analyzed using Maximum Likelihood (ML) phylogenetic tree. The results showed that all nine strains of Phaeocystis sp. were morphologically consistent with those of Phaeocystis globosa. Their genetic distance varied between 0.0000-0.0073; and in the phylogenetic tree, all clustered in the same branch with those P. globosa from other seawaters. Among them, WZS3-1 strain in the Beibu Gulf had the closest genetic relationship with P. globosa from Gulf of Mexico CCMP627, Surinam CCMP628, Ecuador CCMP1528, South Africa P162, China Sea RCC:K1398 and Santou97, exhibiting a genetic distance of 0.0000. Strains of WZS1, WZS2, WZS4, and WZS5 in the Beibu Gulf had a genetic distance of 0.0000 with Hong Kong SKLMP_T005 and Bohai BOHAI1. The intraspecific genetic distance of P. globosa (0.0000-0.0071) is significantly smaller than the interspecific genetic distance of P. globosa (0.0084-0.0440). As a result, these nine strains from Beibu Gulf all belong to P. globosa. The phylogenetic distance for strains of P. globosa do not reflect their geographical distance. The findings of this study are essential for Phaeocystis culture collection, their further ecophysiological study and understanding of occurrence mechanisms for Phaeocystis blooms in the Beibu Gulf.

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    Thoughts on the key scientific issues of Shiptime Sharing Project/Open Cruise in the South China Sea—From the perspective of multi-scale ocean dynamics
    DU Yan, CHEN Ju, JING Zhiyou, WANG Xiangpeng, CHEN Gengxin, XU Chi, CHU Xiaoqing, CHEN Zhiwu, XU Jie, SHI Zhen, TANG Shilin, HE Yunkai, LIANG Yun, SHI Ping
    Journal of Tropical Oceanography    2020, 39 (6): 1-17.   DOI: 10.11978/YG2020001
    Abstract579)   HTML139)    PDF(pc) (1085KB)(313)       Save

    The South China Sea (SCS) is the largest marginal sea in the western Pacific Ocean, connected with the western Pacific Ocean and the Indian Ocean through a series of straits. Multi-scale dynamic processes of ocean circulation and their environmental effects on marine biology and ecology have been a focus of SCS regional oceanography research. Since the first national marine census at the end of the 1950s, China has kept on increasing its support on marine research, especially on the construction of marine scientific observation platforms on research vessels. Entering the New Millennium, the main marine research institutes and universities in China, which operate research vessels, organized and supported Open Cruise for domestic scientists without charging for the shiptime. As a milestone, the Natural Science Foundation of China (NSFC) set up a Shiptime Sharing Project to support the Open Cruise since 2009, which has further promoted communications and cooperations among the domestic ocean research communities. Many important achievements have been made in the SCS regional oceanography. From the perspective of multi-scale ocean dynamics, we briefly review the history of ocean observations in the SCS and summarize the research progresses of key scientific issues in the SCS in recent years, including the water exchange between the SCS and western Pacific Ocean, the mesoscale and sub-mesoscale processes, the multi-scale interaction and its ecological environmental effects, among others. We also share some thoughts and prospects on observations and scientific investigations in the SCS in the future.

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    Construction and classification of coral reef geomorphic unit system based on high-resolution remote sensing: using 8-band Worldview-2 Image as an example
    Juan DONG, Guangbo REN, Yabin HU, Jinzhao PANG, Yi MA
    Journal of Tropical Oceanography    2020, 39 (4): 116-129.   DOI: 10.11978/2019100
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    Coral reef ecosystem is one of the ecosystems with the highest primary productivity in the world. It plays an important role in maintaining marine biodiversity, preventing waves and consolidating beaches, and it is great resources for mankind. At the same time, the remote sensing geomorphological classification system of coral reefs is the necessary basis for the protection, management and sustainable development of coral reefs. However, there is no corresponding classification system taking coral coverage into account. Based on WorldView-2 high-resolution remote sensing image, we selected the reef of Zhaoshu Dao and Xisha Zhou in the north of Qilianyu Island, Xisha Islands, South China Sea as our study area. In this paper, coral coverage, regional geomorphic composition and hydrodynamic conditions are used to establish a coral reef geomorphic unit classification system suitable for remote sensing monitoring and are related to the survival of coral reefs. The method of object-oriented support vector machine (SVM) and random forest (RF) were used to extract the coral reef geomorphic units, and the accuracy of the extraction results was evaluated. The results showed that both SVM and RF classification methods can extract reef geomorphic units, and the classification accuracy was 87.59% and 79.81%, respectively. Aiming at the problem of misclassification and omission in the process of classification, we modified the classification results according to the causes and distributions of coral reefs. And the accuracy of modified classification was 91.3%, and the kappa coefficient was 0.9041. They showed that the coral reef geomorphic unit classification system constructed in this paper can meet the need of information extraction of coral reefs to some extent.

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    Response of phytoplankton community to atmospheric deposition along Pearl River plume front
    Weiwen ZHOU, Qian LI, Zaiming GE, Zijia LIU, Yiping SHUAI, Mengzhen MA
    Journal of Tropical Oceanography    2020, 39 (4): 50-60.   DOI: 10.11978/2019101
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    The Pearl River plume water can form an active plume front along the coastal northern South China Sea. A higher biomass of phytoplankton could exist along the plume front affected by hydrological factors. Atmospheric deposition from land-source input has a significant impact on the ecosystem of the Pearl River Delta zone. A field survey at the western part of the Pearl River Estuary was conducted in March 2019. Substantial variations of size-fractionation phytoplankton community and picoplankton were determined along a section, which affected by the plume front. Meanwhile, atmospheric deposition amendment experiments of three stations, covering different regions of the plume front, were conducted. Results showed that the size-fractionation phytoplankton community was dominated by microphytoplankton at the shore side of the front, picophytoplankton at the sea side of the front, and evenly distributed at the frontal zone with relatively higher biomass. At the frontal zone, the total phytoplankton community was limited by Nitrogen, while the Synechococcus showed a Phosphorus-limitation. Species among the frontal zone could show different nutrients demands. Atmospheric dry or wet deposition could stimulate the growth of three size-fractionation phytoplankton community. The microphytoplankton showed higher growth rate with atmospheric dry or wet amendments at shore side or sea side of the front, while the growth of three size-fractionation phytoplankton community could be stimulated indistinguishably. The addition of atmospheric deposition significantly stimulated the growth of Picoeukaryotes in the frontal system and of Synechococcus at the shore side of the front. Inhibited effects on Synechococcus and Prochlorococcus were found at the frontal zone and sea side of the front.

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    Sedimentary record from Core S05-2 and its implication of provenance and monsoon evolution in a muddy area of the inner shelf of the Southern East China Sea since 4870 a BP*
    ZHANG Jie, LI Qi
    Journal of Tropical Oceanography    2020, 39 (5): 84-97.   DOI: 10.11978/2019112
    Abstract187)   HTML59)    PDF(pc) (3660KB)(111)       Save

    For better understanding of the sedimentary process and climate evolution in the East Asian continental shelves, we investigated the core sediments collected from the inner shelf of the East China Sea in terms of aspects of Accelerator Mass Spectrometry (AMS) radiocarbon dating, grain-size, clay minerals, and geochemical element concentrations. The studied sediments were deposited in the last 4870 a BP according to radiocarbon dating. The results show that silt is the dominant component of the sediments from the mud area of the East China Sea. The rivers on Taiwan Island contributed to the deposits in the studied area dominantly, whilst materials from the Yellow River and Yangtze River occurred episodically in the last 4870 a BP. The East Asian winter monsoon could be indicated by element ratio, sensitive grain-size and clay mineral content ratio. It suggests that the East Asian winter monsoon was stable, strengthening, weakening, and re-strengthening from 4870 a BP onward.

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    Growth characteristics of four representative fishes and their responses to seagrass resource changes in typical tropical seagrass beds of Hainan Island
    CHEN Qiming, LIU Songlin, ZHANG Chi, CUI Lijun, JIANG Zhijian, WU Yunchao, HUANG Xiaoping
    Journal of Tropical Oceanography    2020, 39 (5): 62-70.   DOI: 10.11978/2020007
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    The functions of seagrass beds to provide food and shelter in response to changes in seagrass coverage are still unclear. Xincun Bay, Li’an Port and Tanmen Port seagrass beds of Hainan Island were chosen as our research areas; and Siganus fuscessens, Siganus guttatus, Pelates quadrilineatus, and Terapon jarbua were selected for our research. The relationships between body length and body mass of these four representative fishes, and their responses to seagrass resource changes were addressed. The results showed that the four species inhabiting the Tanmen seagrass bed had negative allometric growth, and the ones in other seagrass beds had positive allometric or constant growth. The body mass growth rate (allometric growth factor b) and the fatness of these four fishes showed the trend of Li’an Port > Xincun Bay > Tanmen Port, which was consistent with the trend of seagrass coverage, density and biomass of the three seagrass beds. We speculate that the decreasing resources of seagrass increase the predation pressure of fish and reduce their food sources, and might consequently decrease growth rates of these representative fishes. Therefore, the protection of seagrass beds needs to be strengthened to promote the restoration of coastal fishery resources.

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    Temporal and spatial patterns of dust deposition in the North Pacific Ocean and its potential impact on ecosystem in the subarctic ocean
    CHEN Huanhuan, WANG Yuntao, QI Yiquan, CHAI Fei
    Journal of Tropical Oceanography    2021, 40 (1): 21-30.   DOI: 10.11978/2020009
    Abstract379)   HTML61)    PDF(pc) (12007KB)(68)       Save

    As one of the three high nutrient and low chlorophyll (HNLC) regions in the global oceans, the growth of phytoplankton in the subarctic North Pacific Ocean is restricted by the trace element iron, which plays an important role in nitrogen fixation, photosynthesis and metabolism of phytoplankton. For an open ocean, atmospheric deposition (atmospheric pollutants produced by human activities as well as dust) is an important source of iron, which can impact biological activities in the upper layer of the ocean. In this study, we use the daily-averaged atmospheric deposition model outputs from the Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS) for the period between December 1997 and November 2017, to quantify the flux of atmospheric deposition in the North Pacific Ocean and the corresponding spatial and temporal variability. The results show that the annual flux of atmospheric deposition into the North Pacific Ocean is 26.81 Tg·a-1, with clear seasonal variation: high flux of atmospheric deposition flux happens during spring and peaks in May, and low values occur in winter. The spatial distribution of atmospheric deposition shows a prominent increasing from the Northwest Pacific Ocean to Northeast Pacific Ocean. In this study, we analysis the response of Particulate Organic Carbon (POC; Aug. 2010) and chlorophyll (Apr. 2001, Apr. 2008 and Aug. 2010) at station K2 (47°N, 160°E) in the Northwest Pacific Ocean to strong dust events, which are defined as the times when high flux of atmospheric decomposition happens. The results show that the POC flux and chlorophyll increase obviously after each dust event because the iron from atmospheric deposition can regulate the growth of phytoplankton and biological pump Thus, the dust events can stimulate the responses of marine ecosystem by promoting ocean primary production.

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    Retrieval of diffuse attenuation coefficient in high frequency red tide area of the East China Sea based on buoy observation
    ZHANG Yu, WANG Guifen, XU Zhantang, Yang Yuezhong, ZHOU Wen, ZHENG Wendi, ZENG Kai, DENG Lin
    Journal of Tropical Oceanography    2020, 39 (5): 71-83.   DOI: 10.11978/2019084
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    The optical data measured by a buoy, with long time series and high temporal resolution, can be reliably used for obtaining the rapidly changing diffuse attenuation coefficient (Kd). The biomass of phytoplankton and the concentration of suspended sediment vary widely in the high-incidence red tide area of the East China Sea, resulting in complex changes in optical properties. In this article, the spectrum data collected by a marine optical buoy from September 2013 to January 2014 were used to obtain the apparent optical characteristics of the sea area, then an empirical algorithm of Kd(490) was established based on the correlation between Kd(490) and remote sensing reflectance (Rrs(λ)), and compared with seven kinds of existing algorithms. The results indicated that Kd(λ) and Rrs(λ) present significant features of class Ⅱ water body spectrum, Kd(490) varies from 0.01 m-1 to 4.31 m-1, and the turbidity also varies greatly. According to the good correlation of Kd(490) and Rrs band ratio, a dual-band ratio empirical algorithm was established, taking Rrs(650) / Rrs(510) and Rrs(555) / Rrs(510) as independent variables. New algorithm is superior to the other seven algorithms, the root mean square error, absolute percentage difference and coefficient of correlation coefficient are 0.27 m -1, 27.08 % and 0.77, respectively, between the new algorithm inversion Kd(490) and the measured values. The improvement of the accuracy of the algorithm is due to the fact that the Rrs selected by the new algorithm can fully reflect water body information and adapt to the changes of water composition in this sea area. This study provides a better choice for the inversion of the high-incidence red tide area in the East China Sea, and an example for the application of marine optical buoy in water environment monitoring.

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    Effects of human intervention on tidal dynamics in the Modaomen Estuary, Pearl River
    JIANG Chenjuan, ZHOU Jianan, YANG Qingshu
    Journal of Tropical Oceanography    2020, 39 (6): 66-76.   DOI: 10.11978/2019137
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    The Modaomen Estuary is the main outlet of the Xijiang River, where large-scale human intervention occurred since the 1980s, including sand excavation in the river network and estuarine regulation project, which inevitably caused the variation of tidal dynamics in the Modaomen Estuary. In this paper, we investigate the variation of tidal dynamics and its response to human intervention in recent 50 years by using statistical analysis and harmonic analysis on hydrological data, and hydrodynamic numerical simulation. The results reveal that the variation of tidal dynamics indicates a natural evolution trend of a river-dominated estuary, characterized by increase in tidal level and decrease in tidal range prior to the 1980s. However, after the 1980s sand excavation in the river network induced a decrease in tidal level and increase in tidal dynamics, while estuarine regulation project resulted in an increase in tidal level and decrease in tidal dynamics. In the inner estuary, tidal dynamics was more affected by sand excavation, with decrease in tidal level and increase in tidal dynamics. In the central estuary, tidal dynamics was affected by both sand excavation and estuarine regulation project, with increase in tidal level and decrease in tidal dynamics during the regulation project (1983-1993) but increase in tidal dynamics after the regulation project (1993-2003). In the outer estuary, tidal dynamics was co-affected by global sea-level rise and estuarine regulation project, with increase in tidal level and decrease in tidal dynamics.

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    Geomorphological records of turbidity current activity in the northeastern margin of the South China Sea and analysis of triggering mechanism
    LI Shuang, LI Wei, ZHAN Wenhuan
    Journal of Tropical Oceanography    2021, 40 (1): 111-121.   DOI: 10.11978/2020022
    Abstract316)   HTML44)    PDF(pc) (19227KB)(101)       Save

    Cyclic steps caused by supercritical turbidity currents are distributed widely along the West Penghu Canyon in the Taixinan Basin of the northeastern South China Sea. Turbidity currents occur frequently in this area due to high tectonic activities, marine factors such as typhoon and delivery of large sediments from rivers. Using high-resolution bathymetric data, we conduct quantitative analysis on the morphology of 23 net-erosional cyclic steps and 10 net-depositional cyclic steps along the West Penghu Canyon, and compute flow velocity of turbidity currents flowing through these cyclic steps. We find that the flow velocity of turbidity currents has an abrupt change in the transition of net-erosional cyclic steps, while the velocity decreases significantly in the transition from net-erosional to net-depositional cyclic steps. The former is mainly caused by the slope break in the canyon, while the latter is caused by the change from confined to unconfined environment. In addition, the net-depositional cyclic steps are located closer to the southwestern flank of the West Penghu Canyon; and we propose that this phenomenon should be mainly caused by turbidity currents affected by the Coriolis force. Investigating the evolution and controlling factors of cyclic steps in this area can help us better understand the interaction of submarine bedforms and turbidity currents, which plays a significant role in the geomorphological evolution along submarine canyons.

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    Coral reef growth of Weizhou Island and its response to climate change in the past millennium
    Ting ZHANG, Minhang HU, Wenjing ZHANG, Tianran CHEN, Meng LIU
    Journal of Tropical Oceanography    2020, 39 (4): 70-79.   DOI: 10.11978/2019102
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    Whether high-latitude coral habitat could become “refuge” for tropical coral species under global warming is still unclear, and related research on the northern South China Sea is especially rare. Based on two reef cores drilled from Weizhou Island, the development history of coral reefs surrounding Weizhou Island and its response to climate change in the past millennium are explored with the help of U-Th dating technology, sedimentary component analyses and coral species identification. Three rapid accretion stages of Core1 (collected from Shiluokou) deposition roughly correspond to the Roman Warm Period, Medival Warm Period and Present Warm Period, respectively. And two slow accretion stages roughly correspond to the Dark Age Cold Period and Little Ice Age. They suggested that warm climate promotes reef development, while cold climate has adverse impacts on coral reef development. Strong local disturbances may have caused the rapid degradation of Weizhou Island coral reefs in recent decades. Core2 (collected in Southern Bay) has high terrigenous sediment content. U-Th ages in Core2 are concentrated in a relatively narrow time interval of 800AD—950AD and present, probably referred to environment changes, storms and the distribution of modern corals. By comparing the two sites on the same island, we further suggest the concepts of “Complete Refuge” and “Incomplete Refuge”, and reveal that Weizhou Island corals may have both developmental characteristics and trends of low-latitude tropical coral reefs and high-latitude coral communities.

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    New understanding about Chemical Oceanography in the South China Sea since 1980
    SONG Jinming, WANG Qidong
    Journal of Tropical Oceanography    2021, 40 (3): 15-24.   DOI: 10.11978/YG2020010
    Abstract268)   HTML61)    PDF(pc) (550KB)(186)       Save

    As the largest marginal sea in the western Pacific, the South China Sea (SCS) plays an important role in the global ocean and the global oceanographic research. In the past 40 years, chemical oceanographic research in the SCS achieved systematic new discoveries and new understandings; researchers put forward many new theoretical viewpoints, making important contributions to the development of oceanography. A subsurface layer was revealed in the SCS, maximum values of ecological environmental parameters represented by nitrite are present; and the depth ranges of water layers for different parameters are different, forming a thermocline ecosystem that has significantly different characteristics from the other ecosystems. The carbon cycle process in the SCS is very complex, and changes of the biological pump controlled by biological activities, and the regional and seasonal changes of carbon sources and sinks, are all great. The characteristics and intensity of carbon sources and sinks in the SCS are unique in different regions at different times. Annually, the SCS is a weak source of atmospheric carbon dioxide. The characteristics of ecological environment and the cycling process of chemical material in the Pearl River Estuary and deep-sea basins were found not only closely related to but also significantly different from that in shelf marginal seas and coral reefs, as the dissolved oxygen concentration is low in the bottom, and the Pearl River Estuary is basically an ecologically fragile area characterized by hypoxia. Based on the systematic understanding of the rapid material circulation and vertical transfer of chemical substances controlled by biological processes in the Nansha coral reef ecosystem, a new mechanism - “resembling drift-net theory” - was proposed to explain how the coral reef ecosystem could maintain high productivity. Systematic studies on the sedimentary chemistry of the SCS show that there is a close coupling between the sediments and chemical cycling of water bodies. The distribution of chemical substances in coral reefs or in sediment cores of the SCS can be used to retrieve historical environment changes. The paleo productivity of surface seawater in the SCS during the glacial period was 1.6 times higher than that of the interglacial period. A "biological explosion event" occurred in the southern SCS in the late Miocene. The productivity in that period was mainly affected by the monsoon and terrigenous nutrients input, while the influences of northeast monsoon and southwest monsoon differed in different regions. These new discoveries and new understandings in chemical oceanography of the SCS in the past 40 years have laid a strong foundation for further systematic and in-depth understanding of the oceanographic processes in the region. In the future, chemical oceanographic research will definitely provide scientific support for the sustainable utilization of resources and environment in the SCS.

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    Functional study of coupling protein CheV and CZB domain of chemoreceptors in the Epsilon-proteobacteria chemotaxis signaling pathway
    LIU Yugeng, MAO Yingjin, ZHANG Canchuan, GAO Beile
    Journal of Tropical Oceanography    2021, 40 (2): 27-38.   DOI: 10.11978/2020055
    Abstract258)   HTML53)    PDF(pc) (1984KB)(138)       Save

    Epsilon-proteobacteria is widely distributed, from deep-sea hydrothermal vent to surface sea water, from free-living environment to host-associated one. Chemotaxis plays an important role in bacteria survival through sensing and responding to environmental changes. Thus, some bacteria have evolved into many complex and diverse chemotaxis systems. Epsilon-proteobacteria can adapt to different environments; especially, some species can survive in the deep-sea extreme environments including hydrothermal vent and cold seep, whose chemotaxis system may have special characteristics. Bioinformatics analyses by BlastP and MIST database revealed that most Epsilon-proteobacteria species in the deep-sea hydrothermal vent have F3 type chemotaxis system. They all contain a single copy of CheV, which is a double domain fusion protein. Besides, a unique domain, CZB (C-terminal Zinc-Binding) domain, exists in chemoreceptors of deep-sea Epsilon- proteobacteria. A CZB-like domain is also identified in Epsilon-proteobacteria. Using the model strain Campylobacter jejuni 81-176, we confirmed that CheV can interact with all chemoreceptors with MA domain by bacterial two-hybrid experiments. Additionally, we demonstrated that CZB-like domain cannot bind Zn by ICP-Mass, but it can promote the interaction between chemoreceptor Tlp9 and CheV.

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    Progress on the community distribution and ecological functions of nitrite-oxidizing bacteria
    HONG Yiguo, JIAO Lijing, WU Jiapeng, LONG Aimin, WANG Wei
    Journal of Tropical Oceanography    2021, 40 (2): 139-146.   DOI: 10.11978/2020043
    Abstract338)   HTML20)    PDF(pc) (1111KB)(162)       Save

    Microbe-mediated nitrification is an essential part of global nitrogen cycle; and nitrite-oxidizing bacteria (NOB), which catalyze the second step of nitrification, have received more and more attention recently. Up to date, those isolated NOB have been identified as four phyla, belonging to seven genera. Among them, Nitrospira bacteria become a hotspot for research due to the high diversity and wide ecological distribution. In this paper, we reviewed the composition, phylogenetic relationship, nitrite oxidizing and carbon fixation pathways of NOB. We also emphasized the functional importance on global nitrogen and carbon of NOB, and highlighted research prospect for NOB.

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    Study on the correction of SST prediction in South China Sea using remotely sensed SST
    ZHANG Peijun, ZHOU Shuihua, LIANG Changxia
    Journal of Tropical Oceanography    2020, 39 (6): 57-65.   DOI: 10.11978/2019128
    Abstract294)   HTML34)    PDF(pc) (6801KB)(109)       Save

    A new error-correction forecast model for sea surface temperature (SST) is proposed in this paper, where the SST errors are derived from the Group for High Resolution Sea Surface Temperature (GHRSST) data and operational numerical prediction SST product. First of all, the reliability of the GHRSST data was validated with the upper temperature data of Argo floats in the South China Sea. The results showed that the Root Mean Square Error (RMSE) between the two sets of data was about 0.3℃ while the correlation coefficient was 0.98; the GHRSST data could be used for the correction of operational numerical forecast model on SST in the South China Sea. After being corrected, the RMSEs of 24-hr, 48-hr and 72-hr SST forecast results were dropped from 0.8 ℃ to 0.5 ℃ compared with the upper temperature data of Argo floats. Meanwhile, the 24-hr, 48-hr and 72-hr SST forecast errors between the GHRSST data and model results were significantly reduced after the correction in the northern South China Sea (110°E -121°E, 13°N -23°N). During the influence of the cold air or the mesoscale eddy in the South China Sea, the effect of SST forecast correction was also quite significant. Therefore, this method should be considered to apply in the operational numerical forecast system on SST in the South China Sea.

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    Genetic polymorphism of the Brushtooth lizardfish Saurida undosquamis based on mitochondrial D-loop sequences
    Min LI, Xiaolan KONG, Youwei XU, Zuozhi CHEN
    Journal of Tropical Oceanography    2020, 39 (4): 42-49.   DOI: 10.11978/2019115
    Abstract291)   HTML40)    PDF(pc) (637KB)(267)       Save

    The Brushtooth lizardfish (Saurida undosquamis) is one of the economically important demersal fishes. The population genetic structure and genetic diversity of S. undosquamis from the coast of China were examined based on the complete control region (D-loop) sequences. A total of 129 individuals from six geographic populations were sequenced. Seventy-one polymorphic sites were detected, which defined 101 haplotypes. Results show S. undosquamis from the coast of China are characterized by quite high haplotype diversity (0.9873 ± 0.0048) and relative low nucleotide diversity (0.0132 ± 0.0067). Phylogenetic tree for haplotypes based on Neighbour-joining method shows shallow topology and reveals no significant divergent clades. Haplotypes from each geographic population were scattered throughout the NJ tree, showing no significant genetic differentiation between populations. Analyses of molecular variance suggest nearly all the genetic variation (99.87%) is attributed to variability within populations, while little variations (0.13%) are found between populations. Most of the pairwise FST values between different populations are quite low, which implies a high rate of gene flow and genetic homogeneity between populations. The results demonstrate high genetic diversity and little genetic differentiation for S. undosquamis from the coast of China. They belong to the same population (panmixia), and a single-stock management regime could be supported in fishery management.

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    Studies on bacterial diversity in coral reef sediments in Khai Island and Pathiu Island and bacterial crude extract retards aging activity of Caenorhabditis elegans*
    HAN Minmin, LI Mi, LIU Xinming, LIU Yonghong, LONG Chao, ZHONG Zhenguo, YI Xiangxi, GAO Chenghai
    Journal of Tropical Oceanography    2020, 39 (5): 19-29.   DOI: 10.11978/2019126
    Abstract240)   HTML60)    PDF(pc) (1615KB)(115)       Save

    Two coral reef sediment samples were collected from the coral reef growth areas of Khai Island and Pathiu Island After the samples were pretreated, six kinds of separation medium were adopted to obtain the active Marine bacterial strains. Through PCR amplification and 16s rRNA gene sequencing, species diversity was analyzed and phylogenetic trees were constructed. The effect of fermentation extract of Caenorhabditis elegans strain on senescence was investigated. The results showed that 22 strains of bacteria were isolated and identified from four samples, belonging to 11 orders, 13 families and 14 genera. There were two strains of bacteria with 16S rRNA gene sequence similarity less than 98.65 %, which were suspected to be potential new species. The crude extracts of 500 μg·mL -1bacteria from GXIMD014 (Vibrio galatheae) and GXIMD112 (Kocuria kristinae) have the activity of delaying the aging of Caenorhabditis elegans, and can prolong the life of Caenorhabditis elegans to different degrees, improve the oviposition, motility, heat-induced injury, ability to resist oxidative damage, enzyme activity in vivo, and improve the epidermal morphology of Caenorhabditis elegans. Coral reef sediment bacteria of Khai Island and Pathiu Island have high species diversity and rich microbial and bacterial resources, and some bacterial strains have anti-aging biological activity.

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    Risk assessment of extreme typhoon disasters based on information diffusion technology
    Hexiang LIU, Yaojian LU, Meng WANG, Guangtao LI
    Journal of Tropical Oceanography    2020, 39 (3): 31-41.   DOI: 10.11978/2019071
    Abstract225)   HTML17)    PDF(pc) (9409KB)(41)       Save

    Based on 12 cases of extreme landfalling typhoon disasters in South China from 2005 to 2016, extreme landfalling typhoon disaster risk assessment in South China was carried out by considering the vulnerability of disaster bearers and the ability of disaster prevention and mitigation. First, based on the grey relational degree of each index, the risk index, vulnerability index and disaster prevention and mitigation ability index of extreme typhoons in South China are constructed. Then, according to the mathematical expression of disaster risk, based on the system weight determined by analytic hierarchy process, an extreme typhoon disaster risk index in South China is constructed. Next, the original information matrix, fuzzy relation matrix and factor space theory are constructed by using two-dimensional normal diffusion technology. In this paper, the fuzzy approximate reasoning is carried out to obtain the risk estimate value of the direct economic loss index estimated by the risk index approximately. Finally, the super probability evaluation model is used to evaluate direct economic loss rate of each extreme typhoon. The results show that the constructed risk index is in good agreement with the actual situation, and the calculated risk estimate is consistent with the change trend of direct economic loss index, the mean square error is 0.20, and the correlation coefficient is 0.78 The results also show that the direct economic loss rate caused by extreme typhoons is 0.1%, which means it has become the normal risk, the transcendence probability and direct economy loss rate of extreme typhoon disaster in South China shows a good linear relationship.

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