Parece Vela Basin (PVB), the most typical and largest back-arc basin in the western Pacific, is divided into the main PVB and the southern PVB based on its morphological distribution. In this study, the gravity anomalies and seafloor topographic features of the southern PVB are analyzed based on the open source gravity data, the measured swath bathymetry data and the sub-bottom profile data, and the particularity of this region and its genetic mechanism are further discussed. According to the seafloor topographic and geophysical characteristics, the southern PVB is mainly divided into five regions, namely, A, B, C, D, and E, which represent that the NW−SE seafloor fabrics formed during the NE−SW spreading, that the N−S spreading fabrics formed during the stage of E−W spreading of the PVB, that the NEE−SWW fabrics formed by the interaction between N−S trending spreading axis propagated from the north and the southernmost rift system during the rotation of the basin, that the seamounts formed at the same time as the PVB, and that the deeps formed by the interaction of the rift systems, respectively. The southern PVB shows obvious east-west asymmetry, that is, only the part west of the spreading center exists in the basin. We speculate that a part of the eastern half of the southern PVB thrusted over the Yap Arc, and another part was offset by a transform fault and the region now lies west of the West Mariana Ridge affected by the collision of the Caroline Ridge. With the continuous thrusting and migration of the oceanic crust, the gradually exposed spreading center of the southern PVB merged with the Yap Trench to form the present Yap Trench, and finally resulting in the absence of the eastern counterpart of the southern PVB.

The scatterometer onboard China-France Oceanography Satellite (CFOSAT) observes sea surface with abundant viewing geometries, opening up new opportunities for sea ice detection. This paper proposes a Bayesian sea ice detection method for the CFOSAT satellite scatterometer (CSCAT), which only uses the minimal inversion residual derived from the wind inversion procedure, hence it does not need to develop a sea ice geophysical model function (GMF) and to calculate the distance between CSCAT backscatters and sea ice GMF. The results are compared with the sea ice edge data from European Organisation for the Exploitation of Meteorological Satellites, which shows that the normalized standard deviation error of CSCAT daily sea ice extent is about 1% and 7% in the Antarctic and the Arctic, respectively, agreeing well with the prior scatterometers. In summary, the proposed method is advanced in terms of model input parameters, processing speed and detection accuracy, so it is of great significance to the operational ice detection in the satellite ground segment.

In this paper, 185 iron manganeses crustal samples of 14 seamounts in 5 seamount groups of the Pacific seamount group (Central Pacific seamounts, Line seamount Chain) and the Western Pacific seamount group (Magellanic seamounts, Markus−Wake seamounts, marshall seamounts) have been analyzed for tellurium, and their spatial distribution, geochemical characteristics, chemical form and resource potential have been studied. The results show that the variation range of tellurium in cobalt-rich crusts is from 17.8 μg/g to 145.2 μg/g, and the average value is 47.4 μg/g. The content range and regional enrichment degree of tellurium in each seamount are quite different. The enrichment degree in descending order is the Magellanic seamounts, Marshall seamounts, Marcus−Wake seamounts , Central Pacific seamounts and Line seamount Chain, showing a trend of gradually decreasing from west to east, and different seamount groups also show obvious regional distribution characteristics. Tellurium content and water depth profile show the same radial and opposite latitudinal trends, indicating that the enrichment of Te is not only related to the depth of crust in seawater, but also related to the longitude and latitude, seamount topography, and regional metallogenic environment. The leaching results show that tellurium is mainly enriched in iron oxides and residues, and the oxygen-rich environment and biological action of phosphorylation play a decisive role in the enrichment of tellurium. Concerning the minimum industrial grade requirements for terrestrial associated useful elements, the tellurium content in cobalt-rich crusts of seamount samples in the Mid-West Pacific Ocean study areas meets the industrial grade requirements, which has potential development value. According to the estimation of cobalt-rich crust reserves, the tellurium reserves in cobalt-rich crusts in the Mid-West Pacific Ocean are more than 76300 tons, which is an important reserve base for seafloor tellurium resources.ic

The relative contents of clay minerals in 34 surface sediment samples were analyzed by X-ray diffraction. The results showed that the content of clay minerals in the surface sediments was illite (35%), palygorskite (20%), smectite (20%), kaolinite (16%) and chlorite (10%). Q-cluster analysis using SPSS software shows that clay minerals can be divided into two provinces (Province I and Province II). Province I covers most of the northern area, and the source is mainly the dust influx from the deserts of Arabian Peninsula, western India and Somali coast; Province II is located at the southwest of the study area, mainly receiving the weathering matters from the granite bedrock of Seychelles Plateau. A comprehensive analysis of the sources of fine particulate matter in the study area and the regional dynamical environment reveals that the southward transport of the aeolian dust from the Arabian Peninsula, western India and the Somali coastal deserts by the South Asian summer monsoon controls the composition of clay minerals in the Province I. The south equatorial low latitude ocean current system promotes the meridional diffusion of fine particles in the study area. The southern Equatorial Counter Current drives the eastward diffusion of kaolinite and chlorite-rich fine materials from Seychelles Plateau.

Submarine pockmark is a depression landform formed by fluid spilling out of the seabed along the migration path and eroding the seafloor sediments. In this paper, the distribution and development of pockmarks on the south side of Riji Reef in the South China Sea are studied by using high-resolution bathymetric data and sub-bottom profile data. Based on the characteristics of high-resolution geomorphology and the laws of sub-bottom profile, 219 large scale pockmarks in the area were identified and counted, there is weak correlation between seawater depth and pockmark scale: seawater depth has no obvious positive correlation with diameter and depth of pockmark, and has no obvious negative correlation with inner slope of pockmark. It reveals the internal relationship between the special geomorphology and the distribution, shape and change of pockmark: the round and elliptical pockmarks are mostly distributed on the top of the sea knoll, the half-moon type pockmarks are mostly distributed in the middle and lower part of the sea knoll, while the bead-like elongated type pockmarks are mainly distributed in the canyon between the deep sea knolls. It is concluded that the change of the pockmark shape and scale which are from the top of the sea knoll to the canyon directly corresponds to the development process of the pockmark in different stages, and that the pockmarks are essentially influenced by the tectonics and dynamics control of the area.

The surge process, magnitude and timing are of critical importance for accurate storm prediction and warning as well as hazard mitigation. A total of 28 tropical cyclones that most affected the head Bay of Bengal during 1991−2020 are selected and simulated with interactive forces including wind, tide, wave and river discharge. The occurrence frequencies of the maximum surge cluster in the rising tide, amounting to 89.3%, mostly 3 h and 4 h before the peak tide. The larger maximum surges are associated with phase shift of storm tide from astronomical tide. The surge processes can be classified into “(quasi-) solitary wave” and “(quasi-) periodic” oscillations. The solitary-wave-like surge may last only the rising tide or both the rising tide and the falling tide. The non-linear interactions between the storm surge and astronomical tide have the same period of a semi-diurnal tide, and their amplitudes are controlled by tidal range. The surge-tide interaction curves demonstrate two types: one is “peak in rising tide and trough in falling tide”, the other is the opposite. They are 180°out of phase, i.e. 6 h for a semi-diurnal tide. The advancing direction of cyclones relative to tidal current, the tidal phase at a cyclone landfall and the formation & propagation of trapped edge surge waves are the dominant mechanism to determine the timing of maximum surges.

Compared with the fast and intermediate spreading mid-ocean ridges, the hydrothermal fields forming at slow and ultra-slow mid-ocean ridges usually contain abundant metal sulfide resources. Previously statistical results suggested the gold concentrations in massive sulfide deposits decreases with the increase of spreading rate, and the hydrothermal fields, located in ultra-slow mid-ocean ridges, have the highest gold concentrations. Previous studies carried out detailed research on the tectonic environment and sulfide assemblage of the Longqi hydrothermal field, but the occurrence and precipitation mechanism of gold in the Longqi hydrothermal field still need further research. In this paper, the texture and trace element concentration of sulfides in the Longqi hydrothermal field are analyzed in order to investigate the occurrence and precipitation mechanism of gold. The sulfides in the Longqi hydrothermal field are mainly pyrite, along with chalcopyrite (isocubanite) and sphalerite. Minerals such as ferronatrite and native gold have also been observed. According to the mineral texture and morphology, pyrite is divided into two types the first type (Py1) is fine-grained or colloidal, while the other type (Py2) shows subhedral-euhedral with coarse grain. Py1 usually exists in Py2 or is surrounded by Py2 as inclusions, and Py2 coexists with euhedral-subhedral chalcopyrite and sphalerite. Native gold mainly exists in the internal pores of Py1, and minor grains exist between Py2 and other sulfides. Compared with Py2, Py1 contains higher trace element contents of Ni, Zn, Pb, Ba, Mn, V, Mg, U, Au, Ag, Cd, and lower contents of Co, Se, As, Sb. Under the physico-chemical conditions of the Longqi hydrothermal field, Au(HS) is the main existing form of Au. The decrease of HS⁻ concentration and the increase of pH value will promote the precipitation of gold. The mixing of hydrothermal fluids with seawater in the Longqi hydrothermal field results in an increase in pH values and a decrease in temperature, which can lead to pyrite crystallization and consequently decrease of sulfur fugacity of hydrothermal fluid. An increase in pH and decrease of sulfur fugacity both contributed to the precipitation of gold.

The wave energy converter-type floating breakwater is an integrated device of floating breakwater and wave energy converter, with both functions of wave protection and wave energy capture. The integration can effectively reduce the cost of wave energy converter with one single function. Researchers have proposed a variety of structural types of this integrated device. Among them, the asymmetric type has some advantages in hydrodynamic performance compared with the symmetric type under one single direction wave. In this study, two structural types of a square box-triangle baffle and a square box-vertical baffle are chosen to investigate the hydrodynamic characteristics and wave energy capture characteristics by numerical models. Based on the viscous fluid theory, the numerical model takes the Navier-Stokes equation as the control equation, and uses VOF method and immersion boundary method to solve the free surface boundary and fluid-structure interaction. The variation trend of hydrodynamic performances (transmission coefficient, energy dissipation and energy capture ratio) of the integrated device under different conditions of incident wave period, water depth and displacement volume are explored. The results show that, for the near shore waves, the vertical baffle type integrated device is suitable for the smaller period waves of 5−6 s, while the triangular baffle type integrated device is suitable for the bigger period waves of 6−8 s. As the water depth increases, the wave energy capture ratio generally shows a slow growth trend. In the case of the same draft of the main floating body (different displacement volume), the transmission coefficients of the two structures are basically the same. In the case of the same displacement volume (different draft of the main floating body), the vertical baffle structure has better wave-proof effect, and the wave energy capture performance of the triangular baffle structure is better than that of the vertical baffle structure.

Based on the NOAA optimal interpolated sea surface temperature and other data from 1982 to 2021, seasonal variability of marine heatwave in the Bay of Bengal and associated formation mechanism were analyzed in this study. The results show that, bounded by the connection between Sri Lanka Island and the mouth of the Irrawaddy river in Myanmar, the frequency and days marine heatwave show different seasonal variation characteristics in the northwest and southeast of the Bay of Bengal. In the northwestern of the bay, both the frequency and the number of days of marine heatwaves are the largest in summer followed by spring and autumn, and the least in winter. In the southeastern of the bay, the seasonal variation of both is relatively weak. According to the cumulative intensity of marine heatwave, marine heatwaves are divided into four categories from weak to strong: I−IV. The analysis shows that the weak marine heatwave of category I and II mainly occurred in western or northwestern of the bay in summer and autumn; severe marine heatwaves of category 3 and above are mostly found in the Andaman Sea and the southeastern of the bay in spring and off southwestern Myanmar in summer. Further analysis shows that in most active areas of marine heatwaves in spring, summer and autumn, the change of net surface heat flux and the shallow mixed layer depth play a major role in these areas, while the formation and maintenance of marine heatwave in the southern of bay may be related to the remote forcing from the equator.

Focused on the differences and accuracy of passive microwave sea ice concentration products (PM-SIC) released by domestic and foreign institutions, the sea ice concentration retrieved by MODIS and Sentinel-1 is analyzed. The products of University of Bremen (UB-AMSR2/ASI), National Snow and Ice Data Centre (NSIDC-SSMIS/NT, NSIDC-SSMIS/CDR, NSIDC-AMSR2/NT2), European Organization for the Exploitation of Meteorological Satellites (OSI-SAF/BR-BST), National Satellite Ocean Application Service (NSOAS-SMR/NT) and the National Satellite Meteorological Center (NSMC-MWRI/NT2) were conducted. The results show that: (1) The sea ice concentration of NSIDC-SSMIS/NT and NSIDC-SSMIS/CDR has a high consistency (mean deviation of − 0.08%, correlation coefficient of 0.99), and the difference between NSOAS-SMR/NT and NSIDC-AMSR2/NT2 is the largest (mean deviation of −14.41%, correlation coefficient of 0.99); (2) The variation trends of the seven PM-SIC are consistent, and the deviations of NSOAS-SMR/NT and NSMC-MWRI/NT2 show obvious seasonal differences with other PM-SIC; (3) The absolute deviation between NSOAS-SMR/NT, NSMC-MWRI/NT2 and other PM-SIC sectors is large in the Indian Ocean sector, Bellingshausen Sea and Amundsen Sea sector, and the difference is the smallest in the Ross Sea sector. The area with large deviation is mainly distributed in the sea ice margin area and near the land sea, and the difference is small in the high sea ice concentration area; (4) Seven PM-SIC are validated by the MODIS and Sentinel-1 retrieved sea ice concentration, and the consistency between NSMC-MWRI/NT2 and validation data is the highest. sea ice concentration of NSOAS-SMR/NT, UB-AMSR2/ASI and OSI-SAF/BR-BST was low, while the sea ice concentration of NSMC-MWRI/NT2, NSIDC-AMSR2/NT2, NSIDC-SSMIS/CDR and NSIDC-SSMIS/NT is high. The comparison and evaluation of different sea ice intensity products can provide the basis and reference for the development of remote sensing inversion algorithm, the development and application of high-quality sea ice intensity products, and the better monitoring of Antarctic sea ice changes.