Current Issue

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.

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.

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.

Based on the L2B sediment data of HY-1C CZI from 2019 to 2020 and the meteorological and hydrological data of the same period, spatial analysis and statistical methods were applied to analyze the spatio-temporal variation characteristics and dynamic factors of suspended sediment mass concentration in the sea area of Liaohe Estuary. The results show that tide is the dominant factor in the diurnal variation of suspended sediment, and the average suspended sediment mass concentration at ebb period is higher than that at flood period. The influence of runoff on suspended sediment mass concentration in the Liaohe Estuary is mainly in the shore area, and generally does not exceed 5 m isobath. When the flow direction of ebb current is opposite to the wind direction, the turbidity zone expands horizontally in the estuary, while when the flow direction of ebb current is the same as the wind direction, the turbidity zone contracts at the top of the estuary. There is a significant correlation between wind speed and suspended sediment mass concentration, and the closer to the offshore, the stronger the effect of wind on suspended sediment. Under the influence of tidal currents, runoff and wind waves, the inner part of the 8 m contour usually develops into the maximum turbidity zone.

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.

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.

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.

Aiming at the problems of difficulty in verifying the accuracy of the interpolation model of single-beam bathymetric data, a method based on high-precision UAV data to verify the accuracy of the interpolation model was proposed by using the intertidal tidal law. At low tide, UAV photogrammetry was used to construct a high-precision digital surface model (DSM) of the intertidal zone, and at high tide, the single-beam bathymetry data was obtained and the three-dimensional coordinates of the intertidal topographic points were calculated by combining the global navigation satellite system (GNSS) technology, and constructed an intertidal digital elevation model (DEM) by using the following 4 interpolation methods: Kriging, inverse distance weight, completely regularized spline and natural neighborhood interpolation method. Based on UAV data, the accuracy analysis of intertidal zone DEM was carried out. The results show that: (1) PPK technology-assisted UAV photogrammetry can construct high-precision intertidal zone DSM. (2) In the intertidal zone, UAV data can be used as an evaluation criterion for the accuracy of single-beam bathymetry data. (3) When the seabed topography is relatively flat, the completely regularized spline method has higher accuracy than the other three methods, and the coarse difference rate is 12.5%.

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.

The influence of sea surface temperature (SST) on the resource change of Sthenoteuthis oualaniensis in Nansha Sea area was studied based on the catch data and remote sensing data of SST in 2018 and 2019. Empirical orthogonal function (EOF) results showed that the seasonal variation of the SST was obvious and the monthly variability showed a bimodal pattern. Peaks mainly appeared in May-June and October. In 2019, El Niño occurred in the Nansha Sea area, and the high temperature frequency of SST increased, and the annual average temperature value increased by 0.3 ℃ compared with 2018. The catch per unit effort (CPUE) of S. oualaniensis was higher in spring (from March to May)but lower in summer (from June to July) in 2018, while it was higher in winter (February) and lower in summer (June) in 2019.The optimal generalized additive model (GAM) consisted of four factors: month, SST, latitude and longitude, and the total deviation of CPUE was interpreted as 55.0%, in which the deviation of month and SST was explained more than other factors. 27.5 ℃-29.5 ℃ was suitable for the distribution of S. oualaniensis and the CPUE would be reduced by higher temperatures. The fishing ground of S. oualaniensis was distributed in 10°N-12°N, 113°E-116°E, and the center of the fishing ground changed with temperature in each month, shifting eastward when warming up, and westward when cooling down.