The composition of clinopyroxene in pyroclastic rocks at the bottom of the Xisha Islands was determined in detail by electron microprobe analysis. The results show that the clinopyroxenes are mostly rich in calcium and have a zonal structure. Ca, Fe and Ti concentrations increased from the core to the outer layers, reflecting the normal sequence of magmatic crystallization. The chemical characteristics of the pyroxene, including low Si, high Al (SiO₂=41.40%–48.44%, Al₂O₃=5.54%–10.20%) and even higher Al^IV concentrations, coincide with those of basic magma. The main element data of the clinopyroxene show that the concentration of monoclinic Ca is high. The Ca/(Ca+Mg+Fe) ratio is between 46.1% and 51.4%. The large amount of high-calcium clinopyroxene may be attributed to the high concentration of Ca in magma. Combining this with the earthquake and tectonic data of the Xisha sea area, we speculate that the basement of the coral reefs of Chenhang Island is a flat-topped seamount composed of basaltic volcanic clastic rocks. Further, we infer that its formation involved the passing of magma through the lithospheric layer of the fault and its eruption in the seabed of the Xisha Islands. The volcanic clastic material is thus formed by accumulation and consolidation, and the original rock of the volcanic clastic rock is an intraplate alkaline basalt.

Based on the daily reanalysis from 1982 to 2017, this paper focuses on the analysis of the extreme characteristics, historical evolution, spatial pattern and possible impactions of sea surface temperature (SST) in coastal China seas (CCS), and discusses the correlation with global change and regional climate variability. The SST in the CCS overall increased significantly in recent more than 30 years, especially in the spring near the Changjiang River Estuary and offshore areas south of it with the warming rate up to 0.2℃/(10 a). Nevertheless the response of nearshore waters to the global warming hiatus is likely to be more pronounced. The extreme high (low) temperature intensity is mainly enhanced (weakened), especially in spring (summer). The increase of extreme temperature difference in the nearshore area in spring can easily lead to frequent ecological disasters such as biological migration and red tide. The consecutive days of extreme events in the northern sea areas are longer than in the south. The consecutive days of extreme high temperature in the Yellow Sea and East China Sea increased significantly, which may have a potential impact on fishery resources. Mostly due to the global warming hiatus, the consecutive days of extreme low temperature is also increased significantly. The cumulative frequency of extreme high temperature near the Changjiang River Estuary, the Taiwan Strait and the northern part of the South China Sea (SCS) increased significantly. In the future, extreme marine heat waves are likely increase continuously, which will have a greater impact on the coral reefs in the SCS and so on. The cumulative frequency of extreme low temperature is mainly reduced. The extreme low temperature along the Changjiang River Estuary and the southern nearshore sea areas increased obviously in winter and spring, which may have some influence on mangrove. During the warm phase of the Pacific decadal oscillation (PDO), the ENSO warm event is enhanced, which is likely to cause the frequent occurrence of extreme low temperature in the CCS. In addition, as the Arctic oscillation (AO) is in positive phase, the cold air in the polar region is restricted to expand southward, and the frequency of extreme high temperature in the CCS surface tends to increase, which enhances the disaster risk.

Internal solitary waves (ISWs) are widely distributed and have a large scale in the Andaman Sea. The velocity of ISWs is an important dynamic parameter. In this paper, approaches are proposed and demonstrated for calculating the propagation velocity of ISWs by optical remote sensing. The optical remote sensing data of MODIS in the Andaman Sea are collected and two methods are adopted to aquire velocity. One is to track the same ISWs based on two remote sensing satellites. The other is to find two or more packets of ISWs from the same generation in a single image. The overview of velocity distribution in the whole Andaman Sea is obtained by combining two methods. The results show that the propagation velocity of the Andaman Sea internal solitary wave ranges from 0.5 m/s to 2.7 m/s. The direction of the velocity is mainly influenced by the bottom topography, and the velocity decreases with the depth of water. In addition, different seasons correspond to different velocities in the deep water areas.

Based on the ionospheric correction data of Global Ionospheric Map (GIM) and dual-frequency, extracting the Pacific Ocean dataset from the Jason-2 Altimeter’s Geophysical Data Set (GDR) including 38-period in 2015. The dataset is divided into small twelve cell according to the features of ionosphere over seasons and in latitude. The result shows that there is a significant difference between the GIM and the dual-frequency correction value, and the GIM correction value is generally higher than the dual-frequency correction value, indicating that GIM overestimates the ionosphere path delay, also, the difference between the GIM and the dual-frequency is related to the season and latitude. Applying the modified equation to the 2016 Jason-2 annual data, the corrected GIM value is very close to the dual-frequency correction value, and the applicability of the modified equation remains the same over time. In the case where the single-frequency altimeter cannot use the ionospheric dual-frequency correction algorithm, the GIM value of the altimeter of the same height can be corrected by using the correction equations of different quarters and different latitude regions to achieve the accuracy level of the dual-frequency correction value.

Variation of pore pressure between soil particles, which caused by the cyclic loading from waves to seabed, is the main reason for soil liquefaction. By using a self-designed pore pressure monitoring equipment, we monitored pore pressure with a long-period, high-precision way in the easy-liquefied zone in Chengdao sea area of Yellow River Estuary. The monitoring results show that the maximum wave-affected depth is between 0.5 m to 1.5 m and no obvious pore pressure response in the deeper sediment during this period. Pore pressure variation in soil is mainly determined by tide level and wave height. Tide level changes can result in smooth change in pore pressure but can not cause the emergence of excess pore pressure while wave height changes can result in severe oscillation in pore pressure and lead to the appearance of excess pore pressure.

Based on the in-situ data from mooring deployed in the northwest South China Sea, we investigate the dynamical and thermal dynamical response of upper ocean to Typhoon Doksuri. In the aspect of dynamic response, as the Typhoon passing, the currents in upper layer enhanced strikingly, the zonal currents in the mixed layer reaches 1.20 m/s. After the passage of Typhoon Doksuri, the currents in the upper layer are dominated by near-inertial oscillation, which rotate clockwise with a period between 36–40 hours. The kinetic energy of near-inertial wave shows two high energetic cores in vertical, which locates at the mixed layer and the thermocline layer, respectively. The estimated e-folding time-scale of near-inertial energy decay is about 3.7 d, and we believe that the downward propagation of energy is the major reason for the decay. The power spectra analysis of currents reveals that power density at inertial frequency, during the period of Typhoon Doksuri, increases about 29.4 times larger than that before the Typhoon arriving. Nevertheless, power density both at diurnal (K₁) and semidiurnal (M₂) frequency decreases during Typhoon period. Additionally, a blue shift at inertial frequency is identified. We find that the averaged near-internal frequency in upper 400 m is 1.167 f₀ for zonal near-inertial currents and 1.170 f₀ for meridional near-inertial currents (where f₀ is the local inertial frequency). This blue shift is connected with the downward propagation of near-inertial waves and input of positive relative vorticity. In the aspect of thermodynamic response, the temperature rises in the upper layer between 40–250 m depth, due to the stirring induced by strong wind, and the maximum increased temperature amplitude is about 1℃. In addition, the decrease of salinity above 70 m may be related to the precipitation caused by the Typhoon. While the upwelling induced by Ekman pumping may have significant contribution to the increase of salinity at the depth of 70–100 m.

The tide gauge data provide an effective way to evaluate the accuracy of satellite altimeter data. The HY-2A data are filtered based on the data edited criterion and the model of real-time atmospheric pressure provided by NCEP are used to solve the problem caused by the unavailable dry tropospheric correction and inverse barometer correction in the later stage of the HY-2A exact repeat mission (ERM). By matching the HY-2A altimeter data and the tide gauges data in temporal and spatial, the correlation coefficient and standard deviation between the two kinds of altimeter data are calculated in the nine selected tide gauges area. According to the analysis results, the average correlation coefficient is about 0.676 9, the optimum is up to 0.898 7, and the average standard deviation is 0.089 5 m. The results show that the quality of HY-2A satellite altimetry data meet the design target and achieve the expected level. It provides a new reliable data source for the application research of the marine gravity field inversion.

The shipboard ADCP (Acoustic Doppler Current Profilers) backscatter intensity data in the Eighth Arctic Science Expedition are analyzed for the temporal and spatial characteristics of the sound scattering layer (SSL), by combining the solar altitude, the sea ice concentration and the in-situ data of the water environment parameters. The results show that the higher the latitude is, the shorter the time of the SSL is on the sea surface. Even during the period of polar day and all covered by sea ice, the migration amplitude and backscattering intensity of the SSL are weakened, but they are still affected by the change of the solar elevation, and there is a strong temporal correlation between them and solar altitude angle. In the middle section of the Arctic, the migration of the SSL is weak, and there is no obvious SSL observed, the reason may be that the concentration of zooplanktons and fishes are relatively lower and the migration is weak, which is beyond the accuracy range of ADCP used in this paper. ADCP data in the back and forth from the Okhotsk Sea to the southwest of the Bering Sea, show that there are two SSLs, the shallower depth and the greater backscatter intensity, but their vertical migration time is synchronized, and the spacing between them is gradually reduced and combined as the latitude increases, it may be caused by marine organisms with different life habit.