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Research of carbon storage assessment of island vegetation based on UAV multispectral remote sensing:A case study of Dazhuzhi Island in Dongtou
XIE Jiaqi, ZHANG Zhao, ZHOU Wen, WANG Jinwang, CHEN Yahui
Journal of Marine Sciences    2023, 41 (4): 84-93.   DOI: 10.3969/j.issn.1001-909X.2023.04.008
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Taking Dazhuzhi Island (Dongtou, Wenzhou) as the research area, UAV equipped with multispectral sensors was used to acquire high-resolution remote sensing images, the optimal spectral band combination was selected to classify the island vegetation, and the vegetation types was divided into arbors, shrubs and herbs by supervised classification. The accuracy of vegetation classification was 99.72%, and the Kappa coefficient was 0.995 4. The spatial distribution of dominant species of arbors and shrubs was obtained by using the deep convolutional neural network (the precision rate was 0.79), and combined with the biomass equations, the spatial distribution of the biomass of dominant species of arbors and shrubs was inversed (arbors’ R2=0.97, shrubs’ R2=0.99). The biomass inversion equations of 3 shrub dominant species (Ficus erecta, Mallotus japonicas, and Eurya emarginata) were constructed by field sampling, and the other dominant species biomass inversion equations were obtained from literature. Based on the biomass and spatial distribution of dominant species, the carbon storage of arbors and shrubbys was 300.36 t and 47.59 t, respectively. Using normalized difference vegetation index (NDVI) to invert the spatial distribution of herb biomass (R2=0.99), combined with the biomass equation of the dominant herb species (Zoysia sinica) constructed from the measured data, the carbon storage of herbs was 21.59 t on Dazhuzhi Island.

Numerical investigation of the super typhoon Mangkhut based on the coupled air-sea model
LÜ Zhao, WU Zhiyuan, JIANG Changbo, ZHANG Haojian, GAO Kai, YAN Ren
Journal of Marine Sciences    2023, 41 (4): 21-31.   DOI: 10.3969/j.issn.1001-909X.2023.04.003
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Based on the mesoscale atmospheric model WRF and the regional ocean model ROMS, a two-way coupled WRF-ROMS air-sea model was constructed to simulate the super typhoon Mangkhut in 2018. The results showed that the simulation results of the coupled air-sea model were better than those of the only atmospheric or ocean model, and the error of the typhoon track obtained from the coupled model was within 60 km, which was in good agreement with the best track. Compared with the observation results, the simulation results of wind speed and sea level pressure in the coupled model were better than others model. Based on the simulation results of the coupled air-sea model, the spatial and temporal distribution of the wind field, pressure field, sea surface flow field, and storm surge under the super typhoon Mangkhut were further analyzed. The results showed that: (1) In terms of spatial distribution, after the typhoon entered the South China Sea, the radius of the seven-level wind circle was larger behind the right side of the typhoon; the cyclonic flow field showed a significant Ekman effect with the typhoon wind field, and the flow direction was 45° from the wind direction. The wind field, pressure field, wind-generated flow field and water gain distribution all had obvious asymmetry, and the typhoon intensity, flow velocity and water gain were greater on the right side of the typhoon path than on the left side. (2) In terms of time distribution, the distribution of the wind field and the pressure field were similar and synchronized with the typhoon center, while the wind-driven flow field and storm surge were three hours behind the typhoon track.

The seasonal blooming characteristics of phytoplankton and POC export flux in the waters around South Georgia Island: Based on BGC-Argo and satellite remote sensing observations
ZHAO Yueran, FAN Gaojing, WU Jiaqi, SUN Weiping, PAN Jianming, HAN Zhengbing
Journal of Marine Sciences    2023, 41 (4): 1-11.   DOI: 10.3969/j.issn.1001-909X.2023.04.001
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The waters surrounding South Georgia Island are one of the highest primary productivity regions in the Southern Ocean with enormous carbon sequestration potential. However, the strength of the biological pump efficiency in this area is still uncertain due to the lack of continuous upper ocean observation data.In this study, the hydrological and biogeochemical parameters obtained from the Biogeochemical Argo (BGC-Argo) floats deployed in the South Georgia Island vicinity during the period of 2017-2020 were utilized to investigate the impacts of physical processes on biogeochemical processes and to estimate the carbon export flux in the Antarctic summer. Results indicated that both upstream (northeast of the Antarctic Peninsula) and downstream (Georgia Basin) regions of South Georgia Island exhibited strong seasonal characteristics in Chl-a, with the latter area having a 4-month sustained period of phytoplankton bloom, suggesting a stable and continuous supply of iron. Using the temporal variability of the seasonal particulate organic carbon (POC) export, the summer POC export fluxes of the upstream and downstream regions were estimated to be 7.12±3.90 mmol·m-2·d-1 and 45.29±5.40 mmol·m-2·d-1, respectively, indicating that the difference might be due to enhanced downward export of organic carbon after the deepening of the mixed layer. The study found that the region maintained a high biological pump efficiency, contrary to the previous conclusion that the Georgia Basin had “high productivity low export efficiency”, which might have been caused by the limited “real-time” representation of the entire seasonal characteristics during ship-based surveys. BGC-Argo provides high spatiotemporal resolution of multi-parameter observation data, and this study demonstrates that it can more accurately quantify and evaluate marine biogeochemical processes and carbon sequestration potential.

Effects of different vegetation types on the source and storage of organic carbon in muddy tidal flats: Taking Maoyan Island as an example
LIU Yuwei, YU Peisong, ZHENG Minhui, ZHAO Zhengjia, ZHANG Cai, HAN Chenhua
Journal of Marine Sciences    2023, 41 (4): 94-101.   DOI: 10.3969/j.issn.1001-909X.2023.04.009
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Coastal wetlands are known for their significant capacity as carbon sinks, with different types of vegetation playing a crucial role in both sourcing and storing organic carbon in sediments. In this study, sediment core samples (1-meter length, sampled at 10 cm intervals) were collected from four different tidal flats on Maoyan Island, including bare mudflat, mature mangrove, young mangrove, and Spartina alterniflora wetland. The particle size, total organic carbon (TOC), total nitrogen (TN) and other parameters of each layer of sediment were measured at 10 cm interval. The source, storage and influencing factors of sediment organic carbon were analyzed and discussed. The results showed that: (1) The average TOC content in sediments from bare mudflat, mature mangrove, young mangrove, and Spartina alterniflora wetland were 0.71%±0.03%, 0.76%±0.16%, 0.69%±0.12%, and 0.83%±0.09%, respectively. Vegetated flats had significantly higher TOC content than that in bare mudflat in the 0-20 cm layer, while Spartina alterniflora wetland had higher TOC content than those in other tidal flat types in the 20-100 cm layer. (2) Among the 1 m of sediment from Maoyan Island tidal flats, the carbon storage in the Spartina alterniflora wetland was the highest, reaching 5.79 kg/m2, followed by the mature mangrove forest (5.61 kg/m2), the young mangrove forest (4.95 kg/m2), and the bare mudflat (4.84 kg/m2) with relatively lower organic carbon storage. The coverage of Spartina alterniflora and mangroves enhanced the carbon storage capacity of tidal flat to a certain extent. (3) The organic carbon in the tidal flat sediments of Spartina alterniflora was mainly from terrigenous sources, accounting for 57.75%; the contribution of native plants accounted for the largest proportion in the mature mangrove sediments, accounting for 32.65%; the organic carbon in the sediments of young mangroves and bare mudflat was dominated by marine sources, accounting for 61.47% and 50.45%, respectively.

Journal of Marine Sciences    2024, 42 (1): 117-118.  
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Numerical simulation study on influences of onshore wind on overtopping characteristics of solitary wave under coastal seawall
ZHANG Liangbin, QU Ke, HUANG Jingxuan, WANG Xu, GUO Lei
Journal of Marine Sciences    2023, 41 (4): 32-45.   DOI: 10.3969-j.issn.1001-909X.2023.04.004
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Seawalls play an important role in protecting coastal towns from extreme waves damage. Based on two-dimensional incompressible two-phase flow numerical model, the influences of onshore wind on overtopping characteristics of solitary wave under coastal seawall were systematically studied in this paper. The reliability of the numerical model was verified by comparing the numerical results with experimental data, and the influencing factors such as onshore wind speed, incident wave height, crest freeboards of the coastal seawall, beach slope and seawall slope on the hydrodynamic process of solitary wave overtopping of coastal seawalls were discussed in detail. The research results show that with the increase of onshore wind speed, incident wave height and the decrease of crest freeboards of the coastal seawall, the maximum overtopping volume, maximum runup height and spatial distributions of the maximum water elevation gradually increase. With the increase of beach slope and seawall slope, the maximum overtopping volume increase and decrease, respectively, while the maximum runup height gradually increase. Onshore wind can affect the hydrodynamic characteristics of solitary wave overtopping of coastal seawall, increase the wave steepness and the wave crest propagation speed and cause the wave breaking earlier. Compared with the windless condition, the maximum wave overtopping volume, maximum runup height, maximum hydrodynamic forces and spatial distributions of the maximum water elevation are increased under onshore wind. The results of this study can provide a reference for the design of coastal engineering.

Study on frequency shift of typhoon-excited near-inertial waves in northwestern South China Sea
FU Dianfu, XIE Botao, HUANG Bigui, JIN Weifang, MOU Yong, LIN Feilong
Journal of Marine Sciences    2023, 41 (4): 12-20.   DOI: 10.3969/j.issn.1001-909X.2023.04.002
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Near-inertial waves (NIWs) play an important role in the response of ocean to typhoon. Their frequency varies with the depth and is the main factor in determining the propagation rate of near-inertial energy to the ocean interior. Based on the observation data from mooring, the factors affecting the blue-shift frequency of NIWs excited by typhoon were investigated in northwestern South China Sea. By analyzing the vorticity effect and Doppler effect caused by background currents, this study suggests that the Doppler effect of background currents was the main factor in the blue-shift frequency of NIWs. As depth increased, inertial wave frequencies increased. Quantitative calculations further demonstrated that within the upper 200 meters, the Doppler effect of the background currents was negative, approaching zero in depth around 200 meters. However, in the depth range of 230 to 400 meters, the Doppler effect became positive. This depth range exhibited the maximum strength of the background currents, with their direction aligned with the propagation direction of inertial waves. Consequently, the positive Doppler shift induced by the background currents was most pronounced. The results of this study are important for improving the understanding of the ocean response to typhoons, especially the propagation of near-inertial waves in areas with complex background current structure (e.g., the western boundary current region).

Method for determining the foot point of continental slope in complex geological background: Take the southern continental margin of Mozambique as an example
ZHUANG Baojiang, TANG Yong, LÜ Xiaohui, YANG Chunguo, WU Zhaocai, LI He
Journal of Marine Sciences    2024, 42 (1): 13-22.   DOI: 10.3969/j.issn.1001-909X.2024.01.002
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A new method for determining the foot point of the continental slope (FOS) was proposed for the delineation of the continental shelf in a complex geological context. This method calculated the location of the foot of slope based on the mean gradient of water depth and optimized it by combining the contrary evidence and the principles of convexity, segmentation and continuity. Using the southern continental margin of Mozambique as the study area, the method was applied to extract the most critical basis—FOS for continental shelf delineation using high-precision multibeam topographic data measured in 2021, and the result was confirmed by comparison with those extracted by the Geocap software which is used by the United Nations Commission on the Limits of the Continental shelf, proving the effectiveness and accuracy of this method.

Vulnerability and driving factors of coastal erosion: A case study of the central coast of Jiangsu
ZHANG Zhi, LIU Xianguang, ZHOU Kai, LIN Weibo, MAO Shifeng, LI Lanman
Journal of Marine Sciences    2023, 41 (4): 70-83.   DOI: 10.3969/j.issn.1001-909X.2023.04.007
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Coastal erosion leads to land loss and seriously threatens people’s life and property safety. It is great significant to identify coastal erosion vulnerability for disaster prevention and mitigation. The evaluation index system was constructed from three aspects: coastal dynamics, coastal morphology and social economy. Using the DSAS model and remote sensing data, the coast was discretized into equally spaced units based on section method, the weight and grade of the evaluation index were determined based on the entropy weight method, the coastal erosion vulnerability in the study area was calculated, and the spatial differentiation and influencing factors of coastal erosion vulnerability were identified by geographic detector. The results showed that the proportions of coastal erosion vulnerability for extremely high vulnerability, high vulnerability, medium vulnerability, low vulnerability and extremely low vulnerability in central coast of Jiangsu were 5.60%, 15.80%, 30.93%, 24.21%, and 23.46%, respectively, that showed a decreasing trend from north to south. The extremely vulnerable areas of coastal erosion were mainly located in the coastal area between the Zhongshan Estuary and the Sheyang Estuary. The spatial differentiation of coastal erosion vulnerability in central Jiangsu was the result of the synergistic effect of multiple factors such as coastal dynamics, coastal morphology, and economic and social activities. Among them, tidal slope, land cover, average tidal range, and coastline change rate were the dominant factors for the spatial differentiation of coastal erosion vulnerability.

Prediction of UIva prolifera drift and transportation based on remote sensing data and numerical models: A case study in the offshore area of Jiangsu Province
LIN Lianjie, DONG Changming, JI Yuxiang, LIM KAM SIAN Kenny Thiam Choy, LI Zhaoxin, JIANG Xingliang, CAO Yuhan, GAO Hui, WANG Shengqiang, CAO Qian
Journal of Marine Sciences    2024, 42 (1): 69-82.   DOI: 10.3969/j.issn.1001-909X.2024.01.007
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UIva prolifera outbreak is one of the most serious marine disasters affecting the global offshore waters, which has attracted the attention of all sectors of society. According to the location of UIva prolifera extracted from satellite data, the Lagrangian drift model was used to track and predict the drift path of UIva prolifera based on the sea-air-wave set model. Compared with satellite observation, this prediction model can better predict the position, distribution and drift transport of UIva prolifera. In addition, this study also discussed the impact of Stokes Drift on the model prediction. The results show that adding Stokes Drift can correct the drift path of UIva prolifera and effectively improve the accuracy of prediction.

Macrobenthos community and living organic carbon pools on muddy tidal flat: Implications from Aiwan Bay of Wenling in summer
TIAN Sujie, TANG Yanbin, YU Peisong, LIU Chenggang, LIU Qinghe, ZHANG Rongliang, SHOU Lu, ZENG Jiangning, LIAO Yibo
Journal of Marine Sciences    2023, 41 (4): 102-112.   DOI: 10.3969/j.issn.1001-909X.2023.04.010
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The intertidal zone is a key area connecting terrestrial ecosystems and marine ecosystems, among which muddy tidal flat is an important and easily overlooked CO2 collection habitat, and the macrobenthos play a central role in the input, transport and preservation of carbon. Macrobenthos community and living organic carbon pools of muddy tidal flat were analyzed in Aiwan Bay, eastern coast of Zhejiang Province in summer. The average abundance of macrobenthos was 105.2 ±37.2 ind/m2, and the average biomass was 46.9 ±6.4 g/m2. The major taxa components within the habitat were crustaceans and mollusks, and the ecosystem health status was excellent. The organic carbon contents of macrobenthos at Aiwan Bay from highest to lowest were other animals including fish and nemertinea (40.95%), polychaetas (22.98%), crustaceans (17.24%), echinoderms (15.90%), mollusks (10.76%), and estimated the macrobenthos carbon pool was 163.90 Mg, of which crustaceans have the largest contribution rate, accounting for 59.80%. The exploration of macrobenthos community structure and living organic carbon pools size in muddy tidal flat can provide scientific suggestion for constructing the blue carbon survey system and supply fundamental data to further quantify the overall carbon pool size in coastal habitats.

Deep-sea rare earth resource potential in the Eastern Pacific Clarion-Clipperton Fracture Zone: Constraint from sediment geochemistry
WU Xinran, DONG Yanhui, LI Zhenggang, WANG Hao, ZHANG Weiyan, LI Huaiming, LI Xiaohu, CHU Fengyou
Journal of Marine Sciences    2023, 41 (4): 46-56.   DOI: 10.3969/j.issn.1001-909X.2023.04.005
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Deep-sea sediments have attracted much more attention in recent years because of their potential resources for rare earth elements plus Yttrium (REY). However, the host minerals and enrichment mechanism of REY in deep-sea sediments, and the spatial distribution characteristics and metallogenic regularity of the REY-rich sediments are still unclear. The Clarion-Clipperton Fracture Zone (CCZ) in the East Pacific is the most important polymetallic nodule metallogenic belt, and its potential of REY resources has not been well evaluated. In this study, the whole-rock geochemistry (728 groups of major elements and 625 groups of trace elements) of sediments from 125 stations in the west CCZ over an area of 27 800 km2 was analyzed. The results show that the sediments in the study area are significantly rich in MnO, P2O5 and REY than those from Australian shales and global subducting sediments. Spatially, ∑REY has a positive correlation with P2O5, CaO, and Ce negative anomalies, indicating that calcium apatite is the main host minerals of REY. The average value of ∑REY in the sediments over the study area is 470±202 μg/g, some samples meet the criteria of REY-rich sediments (∑REY>700 μg/g), indicating that the study area has a certain potential of REY resources. Spatial interpolation analysis shows that REY-rich sediments are mainly distributed in the northern area characterized by hilly terrain, while they are poorer in the southern basin with flat terrain. The difference of geomorphology in the study area affects the regional deposition rate and the hydrodynamic sorting of calcium apatite, leading to the north-south zoning of REY resources distribution in the study area.

Simulation study on oblique in situ acoustic longitudinal wave measurement of seafloor inhomogeneous sedimentary layer
WANG Ying, TAO Chunhui, ZHANG Guoyin, ZHOU Jianping, SHEN Honglei
Journal of Marine Sciences    2023, 41 (4): 57-69.   DOI: 10.3969/j.issn.1001-909X.2023.04.006
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Acoustic characteristics of seafloor sediments are the basic elements of marine sound field calculation and engineering geological evaluation. In situ measurement is an effective means to accurately obtain acoustic characteristic parameters. The structure stratification characteristics and the existence of geological anomalies such as boulders lead to vertical and lateral heterogeneity, and the existing acoustic in situ measurement system is difficult to detect and recognize the nonuniform features, and there is a lack of discrimination reference for the identification of stratigraphic non-uniformity. In this study, an oblique acoustic in situ longitudinal wave measurement method based on the heterogeneity of seafloor deposition was proposed, and a simulation study on the oblique acoustic in situ measurement of sediments within a hundred meters was carried out by using the finite element method. According to the data of regional geological engineering exploration data in the East China Sea, three models of uniform sedimentary layer, stratified sedimentary layer, and a sedimentary layer containing the boulder were constructed, and a simulation of acoustic velocity measurement in the sedimentary layer was carried out based on oblique in situ measurement method. The results show that the oblique in situ measurement method was effective in identifying the inhomogeneity in the large-depth sedimentary layer. By introducing the concept of equivalent offset, the original acoustic velocity calculation formula was improved, effectively improving anomaly identification accuracy. The oblique acoustic in situ measurement method proposed in this study was an effective extension of the existing in situ measurement methods of sedimentary layers, which will help to promote the further application of in situ measurement in marine engineering surveys.

Composed structure of mesoscale eddy in the Northwest Pacific Ocean and its influence on acoustic propagation
ZHANG Xudong, QIU Zhongfeng, MAO Kefeng, WANG Penghao
Journal of Marine Sciences    2024, 42 (1): 58-68.   DOI: 10.3969/j.issn.1001-909X.2024.01.006
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Mesoscale eddies widely exist in the ocean and affect the sound propagation. Using AVISO altimeter and Argo buoy data from 2000 to 2018, the multi-year average three-dimensional structure of mesoscale eddies in the Kuroshio and Oyashio extension regions in the Northwest Pacific Ocean was constructed by synthesis method, and the structural characteristics of temperature anomalies, salt anomalies and sound velocity were analyzed. The sound propagation in eddies is simulated by using Bellhop ray acoustic model. The results show that : (1) Under the background of the cold eddy, the temperature anomaly is negative, the salinity anomaly is negative in the upper layer and positive in the lower layer, and the sound velocity contour rises. Under the background of warm eddy, the temperature anomaly is positive, the salinity anomaly is positive in the upper layer and negative in the lower layer, and the sound velocity contour is sinking. (2) The cold eddies cause the convergence region to shift towards the sound source direction and the width of convergence zone to decrease; the warm eddies cause the convergence zone to move away from the sound source and increase its width. The convergence area in the Kuroshio extension region is wider than that in the Oyashio extension region, and is further away from the sound source. (3) The cold eddies make the convergence zone turning depth shallower, while the warm eddies make the convergence zone turning depth deeper. In the Kuroshio extension region, the inversion depth is shallower with the increase of longitude,but in the Oyashio extension region, the inversion depth is deeper with the increase of longitude.

Acoustic propagation characteristics of horizontally varying double duct waveguides under Arctic ice
KE Lei, WU Shaowei
Journal of Marine Sciences    2024, 42 (1): 47-57.   DOI: 10.3969/j.issn.1001-909X.2024.01.005
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Acoustic propagation in horizontally varying double duct waveguides under ice cover was investigated for the phenomenon of double duct waveguides in some Arctic seas. The ice reflection coefficients on the rough undersurface were derived and determined by the perturbation method, and the acoustic propagation characteristics of the horizontally varying double duct waveguide in the measured sea area were computed and analyzed by combining with the Bellhop ray model, and the influences of the depth of the sound source, the angle of incidence of the sound source and the frequency of the sound source on the acoustic propagation in the horizontally varying double duct waveguide were also investigated. The results show that in the Arctic, acoustic propagation in the deep-sea sound duct is mostly confined to the upper and lower edges of the deep-sea sound duct; the acoustic propagation loss is smaller when the sound source is at the same depth as the horizontally varying deep-sea sound duct axis, and the horizontally varying sound velocity profile has a lower acoustic propagation loss compared to the horizontally unchanged one when the sound source is located outside of the boundary of the deep-sea sound duct; the angle of incidence has a smaller effect on the acoustic propagation in the double duct waveguide; as the frequency of the sound source increases, the acoustic propagation loss in the surface duct increases, but the effect on the deep-sea duct is not obvious, and the horizontally varying sound velocity profile is more favorable for acoustic propagation at the same frequency.

Journal of Marine Sciences    2023, 41 (4): 113-114.  
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Investigation of carotenoid biosynthesis genes in marine Erythrobacteraceae strains
YUE Xiaolan, XU Lin, FU Geyi, XU Xuewei
Journal of Marine Sciences    2024, 42 (1): 91-105.   DOI: 10.3969/j.issn.1001-909X.2024.01.009
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Erythrobacteraceae is widely distributed in marine environments and can synthesize various pigments such as carotenoids. Carotenoids have photoprotective and antioxidant abilities, and they can play a crucial role in the adaptation of Erythrobacteraceae to marine ecosystems. In this study, we obtained the genomes of 107 marine Erythrobacteriaceae strains, analyzed the distribution characteristics of carotenoid biosynthesis genes including crtEBIGYZW in their genomes, constructed phylogenetic trees based on the amino acid sequences of the carotenoid biosynthesis genes, and elucidated the presence and distribution of carotenoid biosynthesis genes in Erythrobacteriaceae from deep-sea and shallow-sea sources. The results suggested that all of marine Erythrobacteriaceae strains contained the crtEIGZ genes, 98.1% of strains contained the crtBY genes, and 43.9% of them contained the crtW gene, which differed among strains but no any specificities found among the deep-sea or shallow-sea sources. Additionally, in the comparison of the phylogenetic topology, it was found that the crtBYZW genes were vertically transferred from their ancestor, while the crtEIG genes were mainly horizontal gene transferred. Our study aids in the understanding of the carotenoid biosynthesis gene evolution in the family Erythrobacteriaceae and also serves as a scientific basis for the study of carotenoid synthesis pathways and genes in other marine bacteria, enables a thorough understanding of marine carotenoid-synthesizing strains.

Responses of a warm mesoscale eddy to bypassed typhoon Megi in the South China Sea
LI Sheng, XUAN Jiliang, HUANG Daji
Journal of Marine Sciences    2024, 42 (2): 1-14.   DOI: 10.3969/j.issn.1001-909X.2024.02.001
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Based on multi-platform observed data, an unexpected response of a warm mesoscale eddy to bypassed typhoon Megi in the South China Sea in 2010 was observed and investigated. During the passage of typhoon Megi, the SLA maximum of the warm eddy increased from 30 to 36 cm, the radius increased from 78 to 116 km, the eddy kinetic energy increased from 166 to 303 m2/s2, and the amplitude increased from 3 to 9 cm. On the right side of the typhoon, the thermocline water at Argo station on the edge of the warm eddy sank by 20 to 40 m. Diagnosis of the wind stress curl alone indicates that the warm eddy should be weaken and the thermocline should be raised, which are inconsistent with the observation results. Diagnosis based on the reanalysis sea surface velocity indicates that during the passage of typhoon Megi, the water diverges below the typhoon path, while the water converges on the right side of the path in the warm eddy region, and the SLA maximum as well as the amplitude of warm eddy are positively correlated with the convergence intensity. Estimation based on the reanalysis sea surface velocity also indicates that the water at Argo station will sink 29 m. Both the warm eddy characteristics and the thermocline depression are consistent with the observation. The case study shows that the response of mesoscale eddy on the edge of typhoon influence to typhoon is constrained not only by wind stress curl but also by the oceanic background conditions, and further attentions are required to explore the corresponding response and mechanism of upper ocean to typhoon.

Classification and genesis of deep-sea REY-rich sediments in the Pacific Ocean
WANG Tianyi, DONG Yanhui, CHU Fengyou, SHI Xuefa, LI Xiaohu, SU Rong, ZHANG Weiyan
Journal of Marine Sciences    2024, 42 (1): 23-35.   DOI: 10.3969/j.issn.1001-909X.2024.01.003
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Deep-sea REY-rich sediments that are rich in lanthanides and yttrium (REY) extensively distributed in regions such as the Western Pacific, Eastern Pacific, Southeastern Pacific, and the Indian Ocean. This study analyzed the mineralogical and geochemical characteristics of deep-sea REY-rich sediments from two sites in the Clarion-Clipperton Fracture Zone (CCFZ) of the Eastern Pacific. Additionally, geochemical data on elements from 92 deep-sea REY-rich sediment sites across the Pacific were collected. Based on geochemical characteristics in conjunction with mineral composition, the Pacific deep-sea REY-rich sediments are categorized into three types: Al-rich, Fe-rich, and Ba-rich. The Al-rich type, prevalent in the Western Pacific region, primarily consists of zeolite clay, with an average whole-rock Al2O3 content reaching up to 14.9%. The Fe-rich type, found near the Eastern Pacific Rise in the Southeastern and Northeastern Pacific, exhibits a high average TFe2O3 content of 18.8%. Some samples within this type show a significant positive Eu anomaly, indicating that hydrothermal activity may contribute to the enrichment of REY and associated carrier minerals. The Ba-rich type, mainly located in the CCFZ of the Eastern Pacific, consists predominantly of (siliceous) clay, with an average Ba content of approximately 8 092×10-6. The elevated Ba levels suggest that the area of sediment formation may have experienced high primary productivity. This environmental condition likely resulted in extensive biogenic apatite deposition, which coupled with strong bottom currents in the CCFZ since the Oligocene, enhanced the accumulation of apatite, thereby promoting the enrichment of rare earth elements.

Acoustic characteristics of rocks from the SWIR hydrothermal fields
JIE Tianyu, ZHOU Jianping, TAO Chunhui, WANG Hanchuang, LI Qianyu, WU Tao, LIU Long
Journal of Marine Sciences    2024, 42 (1): 1-12.   DOI: 10.3969/j.issn.1001-909X.2024.01.001
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The hydrothermal fields of the Southwest Indian Ridge (SWIR) have the potential to develop large scale sulfide deposits, and the SWIR sulfide mineral resource evaluation is currently underway. Measurement and analysis of petrophysical characteristics such as P-wave velocity of sulfides and different host rocks are the basis for processing and interpretation of near-bottom seismic exploration data. Through the systematic measurement of the physical properties of sulfides and host rocks in the SWIR hydrothermal areas, we have analyzed the characteristics of rock P-wave velocity variation and its influencing factors by combining rock physical properties (including density, porosity, P-wave velocity) and minerals. The results show that the P-wave velocity of SWIR rocks is influenced by the rock skeleton minerals, pore space and confining pressure. Due to the overall small porosity of the rocks, the effect on P-wave velocity is not significant, but the increase of the confining pressure gradually closes the rock microfractures and pores, and the P-wave velocity varies non-linearly exponentially. The alteration causes the change of mineral composition, which is the most critical factor affecting the P-wave velocity of the confining rocks. The results of single physical parameter measurements may have multiple solutions, and the joint measurement of multiple physical parameters such as wave velocity, density, magnetic and electrical properties is beneficial for lithological differentiation. The research results help identifying sulfides and host rocks, and provide important support for the seismic exploration of polymetallic sulfides in the Southwest Indian Ocean contract area of China.