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Nitrate is the main nitrogen form available for phytoplankton life activities in the ocean, and its nitracline depth (Z_N) directly affects the vertical transport of nitrate and the ocean primary productivity, and then further influences the carbon cycle. With the advancement of ocean observation technologies, the profile data of nitrate have been collected in diversified ways, such as ship-based CTD observations and BGC-Argo automatic observations. The vertical sampling resolution of these techniques varies significantly (the vertical sampling resolution of CTD is lower than that of BGC-Argo). In view of different sampling data, it is urgent to conduct systematic and quantitative comparative analysis and study on the computing methods of Z_N. In this study, three different methods: difference method, gradient method and threshold method, are adopted to compute the corresponding Z_N by using the historical ship-based CTD data and BGC-Argo buoy data in the Northwest Pacific Ocean. The results show that in the case of single nitrate profile, based on BGC-Argo data, the difference between observed Z_N and the Z_N calculated by difference method is only 0.2 m, followed by threshold method is 20.0 m and gradient method is 202.8 m at most. Based on CTD data, the difference between observed Z_N and Z_N calculated by difference method is 2.0 m, the threshold method is 49.0 m, and the gradient method is 155.0 m. Compared with the gradient method and threshold method, the difference between the Z_N calculated by the difference method and the observed Z_N is the smallest. According to the results of statistical error analysis, it is found that the Z_N calculated by the three methods based on BGC-Argo data show a good correlation with the observed Z_N. Among them, the error of difference method is the smallest (R²=0.77, RMSE=28.48 m). The R² and RMSE of threshold method are 0.64 and 34.85 m, and the R² and RMSE of gradient method are 0.52 and 53.80 m. For CTD data, due to its low vertical sampling resolution, the Z_N calculated by the three methods is quite different from the observed Z_N. However, compared with the gradient method and threshold method, the error of the difference method is still the smallest (R²=0.81, RMSE =16.13 m). The R² and RMSE of threshold method are 0.47 and 27.65 m, and the R² and RMSE of gradient method are 0.42 and 36.41 m. The applicability of each method is preliminarily explored through comparing and analyzing the characteristics and differences of them so as to provide some scientific reference for the in-depth research on the vertical distribution characteristics and upward transport process of nitrate.

Based on the high frequency data of sea-air interface buoys, the variation pattern and driving factors of sea-air partial pressure of carbon dioxide (pCO₂) were analyzed and the sea-air CO₂ flux in the coastal waters of Qingdao in spring was estimated. During the observation period, the sea area changed from a carbon sink of atmospheric CO₂ to a carbon source, which was mainly caused by the continuous increase of sea surface pCO₂. By analyzing the controlling factors of pCO₂, it was found that temperature was the main driving factor of pCO₂ growth, and biological processes played a certain inhibiting role. The sea surface pCO₂ showed a diurnal variation. The effects of temperature and biological factors on the diurnal variation of pCO₂ were related to solar radiation, but they had opposite effects. In addition, the analysis showed that different sampling frequencies of buoys affected the estimation of sea-air CO₂ flux and shortening the sampling interval could effectively reduce the deviation of CO₂ flux estimation and improve the accuracy of estimation.

The spatiotemporal variation of surface eddy kinetic energy (EKE) in the South Australian Basin was studied using sea level anomaly during 1993-2019. The results show that in spatial scale there are two regions of high EKE: one to the west, and one to the east. On the seasonal scale, surface EKE is the strongest in austral winter with a maximum (57±9 cm²/s²) in July and the weakest in autumn with a minimum (40±5 cm²/s²) in March. On the interannual scale, surface EKE is related to El Niño-Southern Oscillation (ENSO) and Southern Annular Mode (SAM). Partial correlation analysis indicates that surface EKE shows negative correlations with ENSO, lagging the Niño3.4 index by 9 months, and EKE is significantly weakened (strengthened) in the decaying year of El Niño (La Niña). Meanwhile, surface EKE shows positive correlations with SAM, lagging SAM index by 14 months, and EKE is significantly strengthened (weakened) in the next year of the positive (negative) SAM phases.

Tidal current energy is the kinetic energy carried in the horizontal movement of tidal water, which has great development prospects. Accurate simulation and characterization of regional tidal currents can help to efficiently evaluate the spatial and temporal distribution of tidal energy resources, which is the key to the development and utilization of tidal current energy resources. In this paper, a high-resolution numerical model of tidal currents is constructed by applying FVCOM ocean model in Zhoushan sea area where has rich tidal current energy, and the reliability of the model is confirmed by tidal level and current verification. According to the simulation results, six waterways with dense tidal current energy resources in the Zhoushan sea area were identified, among which the average energy density of Xihoumen waterway, Cezi waterway and Taohuagang waterway exceeds 2.0 kW/m², and the maximum energy density exceeds 20 kW/m², and the flow speed over 1.0 m/s of the whole month is more than 80%. During tidal current ebb and flow, the reflow is dominant, while the asymmetry and rotation of tidal current are low. The flow stability coefficient is more than 0.98, so it is more suitable for the development and utilization of tidal current energy than other three waterways. The best location for tidal current energy development in these three waterways was then determined by calculating the significant hours and available hours, and the corresponding exploitable tidal current energy resources were evaluated using the Farm method, which were 27.53 MW, 39.96 MW, and 130.26 MW, respectively.

Based on the one-year measured wave data in the coastal area of Cangnan, Zhejiang Province, the characteristics of wave parameters were statistically analyzed, the correlation between wave parameters was analyzed by using the least square method, the relationship between the average wave duration and wave height was studied, the wave energy was estimated, and the characteristics of typical typhoon waves during typhoon “Lekima” were analyzed.The results show that the study area is mainly composed of light waves with spectral peak period of 5-9 s, the annual average significant wave height of 1.22 m, the normal wave direction is E, the strong wave direction is ENE.There is a significant linear relationship between the characteristic wave heights, which conforms to the typical Rayleigh Distribution.In typhoon free period and cold wave free period with significant wave height below 2.7 m and typhoon period with significant wave height above 4.1 m, the average duration of wave decreases exponential decays with the increase of wave height, and the attenuation rate of typhoon period with significant wave height above 4.1 m is higher than that of typhoon free period and cold wave free period with significant wave height below 2.7 m.During the impact of typhoon “Lekima”, the maximum wave height, spectral peak period, and spectral peak density show a basically synchronous process of first increasing and then decreasing, with a maximum spectral peak density of 55.10 m²/Hz;the typhoon wave spectrum before and after the impact of the typhoon show a bimodal spectrum, while the wave spectrum during the most significant period of typhoon impact show a unimodal spectrum.

The clay mineral assemblage in abyssal sediments can reflect the paleoclimate and paleoenvironment changes of the provenance area. Predecessors have many studies about the characteristics of clay mineral assemblages in the Pacific sediments west of the Mariana Trench, but the less research on the characteristics of clay mineral assemblages in the east of the Mariana Trench limits a deeper understanding of the relationship between the Asian aeolian dust input and the Pacific deep-sea sedimentary environment. In this study, 31 surface samples and 1 core sample collected in the Malkus-Wake Seamount area of the Western Pacific during the 2019 DY54 cruise were analyzed for clay minerals, combined with the data collected in the Western Pacific and nearby areas, we discussed the characteristics of composition, distribution and the provenance of clay minerals. The results showed that illite was the main clay mineral in surface sediments of the study area, with an average value of 69%; the content of chlorite and kaolinite were the second, with an average of 16% and 11% respectively; that of smectite was the least, with an average of 3%. In the core P04, the assemblage of the clay mineral was basically the same as surface samples, but below 250 cm depth, the content of smectite increased significantly, while the content of illite decreased relatively. Provenance analysis showed that Asian aeolian dust was the main source of illite in the study area, and kaolinite and chlorite might also be from Asian aeolian dust, and the East Asian winter monsoon was the main transport force of these clay minerals. The smectite in sediments could be mainly formed by weathering of submarine volcanic materials. The increase of illite content while the decrease of smectite content in the upper layer of core P04 sediment was responded to the increase of Asian aeolian dust input since the Middle Pleistocene.

The selection of extreme value samples and the determination of distribution models are two crucial aspects when calculating the design wave height. When selecting extreme value samples using the peaks over threshold method, the standard storm length method is commonly used to “de-cluster” the exceedances in order to make the samples conform to independence standards. However, the crucial parameter in the standard storm length method needs to be manually selected which increases the uncertainty of samples. In this paper, an automatic standard storm length estimation method is proposed, then the wave height peaks over threshold sample in the western Guangdong sea area is selected based on this method. To accurately fit the sharp peak and heavy tail of the wave height peaks over threshold sample, the combined distribution method is used to construct a new model: Gumbel-Pareto distribution model. Based on this model, the design wave height calculation is carried out in the western Guangdong sea area. The result shows that the goodness of fit for the Gumbel-Pareto distribution model to the wave height peaks over threshold sample is higher than that of Gumbel distribution and Generalized Pareto distribution, which can offer a reasonable reference for the design of large offshore engineering.

To evaluate the environmental changes before and after the operation of the green petrochemical project, polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the adjacent sea area of Yushan Island where the project is located, were investigated and monitored for four consecutive years from 2018 to 2021. The results showed the total PAHs contents ranged from 16.9 to 178.0 μg·kg^-1 with the average content of 75.9±24.0-102.6±41.4 μg·kg^-1, showing an overall downward trend over the past four years, with a lower overall concentration compared to other sea areas in China. The average content of different PAHs components in the investigated surface sediments from high to low were: 4 rings PAHs, 5 rings PAHs, 3 rings PAHs, 6 rings PAHs and 2 rings PAHs. The surface sediments of the surveyed sea area was mainly composed of silt, and the spatial distribution of PAHs was influenced by various factors. The sources of PAHs in the surveyed sea area were relatively stable, with small interannual differences, mainly originating from the long-distance migration of combustion products of substances such as oil, firewood, and coal. According to the sediments quality baseline method evaluation, the ecological risk level of PAHs in the surveyed sea area sediments was relatively low. The green petrochemical project did not cause an increase in PAHs of sediments in adjacent sea areas during the construction and production periods. However, as the project continues to operate, its impact on the surrounding ecological environment still needs to be continuously monitored.

Based on Western Pacific surface seawater as matrix, a series of reactive phosphorus reference materials with the concentration of 0.5-4.0 μmol/L were prepared. By investigating the uniformity and stability of the 4 batches of samples, it was confirmed that the performance met the needs of requirements. For the determination of reactive phosphorus in aqueous sample, segmented continuous flow analysis system with UV detector was used. The experimental conditions were optimized, the limit of detection(LOD) of the method was 0.03 μmol/L, and the relative standard deviation (RSD) of 4 different concentration batches was 0.37%-2.45%. The reliability of the method was verified by testing a CRM. The error was not more than 0.05 μmol/L. The concentration standard value of the series of reference substances was determined by 6 laboratories, and the relative expended uncertainty of characterization was evaluated, which was 2%-10%.

The unique geographical features of the island countries in South Pacific, which are surrounded by sea and small in size, make most of the island countries in this region "ecologically fragile areas". Based on this, multi-source satellite data were used to monitor the marine ecological environment of Nauru, Palau, Tuvalu, and the Marshall Islands. It was also focused on whether there have been significant changes in the ecological environment of various countries before and after the Tonga volcanic eruption, to help to understand the impact of the Tonga volcanic eruption. The results show that: (1) In terms of temporal and spatial distribution of climatic states, the sea surface temperature and transparency of the surrounding waters of the South Pacific island countries maintain a relatively high level, while chlorophyll and net primary productivity decrease rapidly with the increase of offshore distance. (2) Warming, acidification and sea level rising are common problems faced by the sea areas of the four island countries. (3) The eruption of the Tonga Volcano has no significant impact on the coastal TSM mass concentration and SST. (4) The phenomenon of abnormally rising surface temperature and changed suspended matter mass concentration of the island in the first half month of the volcanic eruption has implications for disaster warning and forecasting using remote sensing methods.