Nutrient enrichment, followed by economic development, has already had a significant impact on the costal ecosystem of China. Field investigations on seaweed beds adjacent to Lingshui River in Dalian were conducted in present studies to elucidate the response of the seaweed communities to the sewage effluents along a natural nutrient gradient. Further, the studies were conducted in the laboratory on the uptake and growth kinetics of NO₃ ^–, NH₄ ⁺ and PO₄ ^3– of the clone of Enteromorpha linza, r-strategic green alga dominating in the nutrient-rich estuaries, and Ceramium tenerrimum, k-strategic red alga distributing in the oligotrophic areas. Comparative analyses were carried out on the absorption and utilization of nutrient, and reproduction strategies of the two species to explain the responses of seaweed communities to different nutrient environments. The results show that with the decrease of environmental nutrients, species number of seaweed increases, and the coverage of dominant species decreases. According to the response of seaweed communities to nitrogen nutrient, it is considered that the threshold of category I of inorganic nitrogen in the current seawater quality standard should be revised from the current 14.29 μmol/L to 6.69 μmol/L. In a nutrient-rich area, increasing nutrient concentration promotes the competitiveness and fertility of shoots of r-strategic seaweeds, which makes them occupy a large number of space niches and form dominant populations, resulting in decreasing of the diversity of seaweed communities. However, in the oligotrophic environment, r-strategic algae is limited in the fertility of shoots, occupying only small amount of space niche, while those k-strategic algae with high efficiency in nutrient utilization shows greater competitiveness and could quickly break through early environmental sieves and grow into adults, which contributes to the rich diversity of seaweed communities.

Selective chemical extraction method was utilized to fractionally extract platinum group elements (PGE) in cobalt-rich crusts from Caiwei Seamount in the Pacific, and PGE contents were determined by inductively coupled plasma mass spectrometry (ICP-MS). Occurrence phase analysis results in cobalt-rich crusts show that the PGE enrichments in different phases conform to the following order: iron oxide phase, residual phase, manganese oxide phase, carbonate phase, adsorbed phase. PGE in the new non-phosphate layers and the old phosphate layers are mainly enriched in the iron oxide phase, with the enrichment ratio from 59.26% to 82.19%, and the phosphate in residual phase has certain enrichment ability for PGE, with the enrichment ratio from 17.23% to 35.37%. Meanwhile, occurrence phase analysis results in different geological bodies show that the PGE enrichment in cobalt-rich crusts and seamount nodules is mainly affected by iron oxide phase and residual phase. In addition, the enrichment mechanism of PGE in cobalt-rich crusts is presumed to the iron oxide/iron hydroxides colloid particles adsorption, and the soluble $ {\rm PtCl}_4^{2-}$ in seawater is adsorbed into the iron oxide phase, so PGE are enriched in cobalt-rich crusts.

Previously, it was a broad consensus that transparent exopolymer particles (TEP) resulted in carbon flux output to the seabed due to its unique aggregation effect. Recently, some studies have shown that TEP could be retained in the water column and even ascend to the surface layer, which profoundly contributed to the elevated TEP concentrations and decreasing of air-sea carbon fluxes in the Surface Micro-layer (SML). The sinking or ascending of these TEP originated aggregates was finally depended on its density. TEP and further aggregated with other micro-particles became the surface-active substances in the SML, produce a thin layer film at the ocean-atmosphere interface, will heavily affect the exchange fluxes of sea-air CO₂ and further the global climate changes.

Phytoplankton, as the base of the oceanic food chain, plays a fundamental role in marine ecosystems. Since the Bohai Sea, the largest inner sea in China, is an important spawning ground and nursery field as well as a feeding ground for marine creatures, it is critical to understand variations of phytoplankton in the area. Chlorophyll a (Chl a) concentration is an important proxy for phytoplankton biomass. Chl a derived from both the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) from 1997 to 2010 and the MODerate resolution Imaging Spectroradiometer (MODIS) sensor on satellite Aqua from 2002 to 2018 were combined into one time series to investigate the spatial and temporal variability of Chl a concentrations in the Bohai Sea using Google Earth Engine. Annual Chl a concentrations increased significantly by 14.1% in the study area over the past two decades. Chl a concentrations in every season and in all months except November have stagnated or increased. Chl a concentrations increased mainly in the middle part of the sea. Sea surface temperature (SST), wind speed and precipitation were also analyzed. Increases in precipitation over the land around the Bohai Sea and wind speed in summer, as well as decrease in SST in autumn, all contributed to the rises of Chl a concentrations. Nutrients from land may play an important role in phytoplankton growth.

Simple Ocean Data Assimilation reanalysis and other data were used to explore seasonal variation characteristics of freshwater transport between the Arabian Sea (AS) and the Equatorial Western Indian Ocean (EWIO), and the Gulf of Oman (GOO). Freshwater budget in the AS is characterized by a basic balance and its seasonal variation is also present. Our results indicate that the amount of input freshwater from the EWIO and river discharge is roughly equal to the amount of freshwater output to GOO and lost caused by the evaporation overwhelming the precipitation (P–E). The lost freshwater via air-sea exchange (i.e. P–E) is compensated by freshwater flux from the EWIO and the Bay of Bengal (BOB), which plays a key role in maintaining the basic balance of salinity over the AS. Net freshwater flux in the AS is negative (i.e. lost freshwater) from January to June together with December, and positive (i.e. receive freshwater) during July and November with a maximum positive value in September. The seasonal variation characteristics of net freshwater flux in the AS shows a single remarkable peak. Along the 9°N section, freshwater exchange between the EWIO and the AS primarily occurs from the surface to 200 m depth, with a multi-year averaged net flux into the AS of about 0.1×10⁶ m³/s. From October to next March, the BOB low-salinity water extends into the AS at above 60 m depth through the southwest of the Indian peninsula. In summer and autumn, the transport associated with the Great Whirl located at the east of Somali Peninsula, is characterized by low (high) salinity water in the west (east) of the whirl transported northward (southward) into the AS (equatorial Indian Ocean). This transport during these two seasons is largest in a year with its influence can extend downward to about 300 m depth, which forms in June, then peaks in August and September, and finally decays rapidly in November. Water exchange between the AS and the GOO is relatively weak, and has a sandwich-like three-layer structure in vertical direction: high salinity water intrudes from GOO into the AS in the upper 10 m layer and in the bottom layer between 175 m and 400 m depth; whereas in the middle layer (i.e. 15 m to 170 m depth) low salinity water is transported from the AS to the GOO. On multi-year average, a net freshwater transport of about 0.39×10⁴ m³/s is further estimated into the GOO from the AS across the section along the GOO mouth.

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 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.

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.

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.

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.