Current Issue

Based on multi-platform observed data, an unexpected response of a warm mesoscale eddy to bypassed typhoon Megi in the South China Sea in 2010 was observed and investigated. During the passage of typhoon Megi, the SLA maximum of the warm eddy increased from 30 to 36 cm, the radius increased from 78 to 116 km, the eddy kinetic energy increased from 166 to 303 m²/s², and the amplitude increased from 3 to 9 cm. On the right side of the typhoon, the thermocline water at Argo station on the edge of the warm eddy sank by 20 to 40 m. Diagnosis of the wind stress curl alone indicates that the warm eddy should be weaken and the thermocline should be raised, which are inconsistent with the observation results. Diagnosis based on the reanalysis sea surface velocity indicates that during the passage of typhoon Megi, the water diverges below the typhoon path, while the water converges on the right side of the path in the warm eddy region, and the SLA maximum as well as the amplitude of warm eddy are positively correlated with the convergence intensity. Estimation based on the reanalysis sea surface velocity also indicates that the water at Argo station will sink 29 m. Both the warm eddy characteristics and the thermocline depression are consistent with the observation. The case study shows that the response of mesoscale eddy on the edge of typhoon influence to typhoon is constrained not only by wind stress curl but also by the oceanic background conditions, and further attentions are required to explore the corresponding response and mechanism of upper ocean to typhoon.

Combined with the Holland wind fields and the ERA5 wind fields, the mixed wind fields was set up by introducing a weight coefficient varying with the radius of wind speed, and a typhoon wave model in Zhejiang sea area was established using MIKE21 SW. Then, the Holland, the ERA5 and the mixed wind fields were used as the input wind fields to simulate the wind speed and the significant wave height during No.1918 typhoon Mitag, respectively. The verification shows that the simulated results obtained using the Holland wind fields and the ERA5 wind fields cannot agree accurately with the observed data, while the mixed wind fields proposed in this study can improve the simulation accuracy. In order to study whether the above conclusion is universal in Zhejiang sea area, five typical typhoons that have the most serious impact on Zhejiang sea area in the recent 5 years were selected for typhoon wave numerical simulations and the error statistical analysis. The results indicate the wind speed around the typhoon center is relatively good using the Holland wind fields and the average relative errors of the maximum wind speed are 8.62%-10.19%, but the average relative errors of the wind speed below 10 m/s is relatively bigger, reaching 29.76%-44.29%. However, the wind speed around the typhoon center using the ERA5 wind fields is smaller than the observed data, and the average relative errors of the maximum wind speed are 17.64%-25.77%, but the average relative errors of wind speed below 10 m/s are smaller than that using the Holland wind fields, which are 19.64%-32.00%. During the five typhoon processes, the average values of the average relative errors of the significant wave height driven by Holland, the ERA5 and the mixed wind fields are 29.92%, 25.62% and 22.82%, respectively. Correspondingly, the average root mean square errors are 0.46 m, 0.42 m and 0.39 m and the consistency indexes are 0.94, 0.95 and 0.96. The above results shows that the mixed wind fields proposed in this study is universal in Zhejiang sea area and can improve the simulation accuracy of typhoon waves.

Sea surface temperature (SST) is a key climate variable in oceanographic and meteorological research, widely applied in studies of ocean-atmosphere interactions, ocean mixing, boundary layer processes, and ocean state forecasting. The hourly SST data provided by the European geostationary meteorological satellite Meteosat-8/SEVIRI (M8) is an important data source for these studies. However, the spatiotemporal variations in the errors of SST data from M8 are not yet clear. To assess the reliability and applicability of SST data from M8, this study uses in-situ SST data from the iQuam quality monitoring platform which includes data from ships, drifting buoys, and Argo floats, to validate the hourly SST data from M8 in the Indian Ocean region. The results show that the average bias between M8 and the three types of in-situ data ranges from -0.06 to -0.10 ℃, the root mean square error ranges from 0.48 to 1.03 ℃, and the coefficient of determination ranges from 0.96 to 0.99. Among these, drifting buoys have the most matchups with M8 and the widest coverage, making them an ideal validation data source. Analysis of the spatiotemporal distribution of SST data biases from M8 reveals a -0.6 ℃ bias at night in the northwestern Arabian Sea and northwestern Bay of Bengal, with larger negative biases during the day in these areas, and a bias exceeding -1.0 ℃ during the day in parts of the 40°S-60°S region. SST data from M8 tends to show maximum positive biases in summer and minimum negative biases during the spring-to-summer transition period.

The ocean heat content is one of the most critical and stable indicators of the global climate change research. It’s systematic and accurate evaluation depends on the ocean internal observation of long time series and global coverage. Based on a global multi-parameter reanalysis data set (gradient dependent correlation scale method Argo, GDCSM-Argo) as well as the trend analysis, spatiotemporal series analysis and delayed regression analysis, the spatiotemporal evolution of global ocean heat content was investigated, and the relationship between ocean heat content change and the abnormal climate during 2004-2021 were discussed. The results showed that the global ocean heat content of 0-2 000 m had increased with different levels since 2004, with a increment of more than 2×10⁸ J/m². After 2013, the deep sea (700-2 000 m) had shown a continuous warming trend. The warming of all depths ranging from 0 to 2000 m was intensified after 2017. The temperature anomaly of 700 m made a prominent contribution to the overall change of the ocean heat content. The tropical eastern Pacific Ocean accumulated heat before El Niño, lost heat and distributed heat to the north and south during/after El Niño in order to offset the accumulated heat from earlier stages. The warming range extended to the north and south of the equator. The positive peak of heat content anomaly in the tropical Pacific Ocean preceded the ENSO (El Niño-Southern Oscillation) index by about 0-1 month. All of the results indicate that GDCSM-Argo will be able to provide more detailed of the ocean heat content evolution.

The one-dimensional theoretical model of internal solitary waves has been widely used in their prediction. However, on one hand, these theoretical models usually rely heavily on temperature and salinity data when calculating wave functions, which requires the use of moorings equipped with temperature and salinity observation instruments, resulting in high observation costs. On the other hand, they tend to have large prediction errors in complex current environments, such as lower accuracy in calculating the nonlinear phase speed and wave function of internal solitary waves. In this study, a Velocity-Gaussian Function Model was proposed, which reversed the amplitude and wave function of internal solitary waves based on the measured current velocity of the upper layer of the South China Sea from a single mooring. Furthermore, key parameters such as wave-induced current and nonlinear phase speed of internal solitary waves were calculated using a one-dimensional theoretical model. By comparing the measured data from the moorings with the results calculated by the Velocity-Gaussian Function Model, it was found that the model can simulate the wave-induced current throughout the entire water depth by inputting only the measured current velocity from the upper 150 meters of the ocean. Additionally, the error in the nonlinear phase speed can be controlled within 10% compared to the measured value. The application of the Velocity-Gaussian Function Model enables accurate prediction of internal solitary waves in the complex South China Sea, without the need for moorings equipped with temperature and salinity observation instruments, thus significantly reducing the cost of internal solitary wave observation.

The influence of sampling period of precision point positioning (PPP) of Global Navigation Satellite System (GNSS) on tide accuracy was studied by using GNSS receiver to collect observation data on marine mobile platform. Different data sets were extracted at periods of 30 s, 60 s, 90 s and 120 s, and dynamic processing was carried out with Trip software to obtain the coordinates of each measuring period. The tide level measurement results of two receivers at four sampling periods were compared respectively, and the standard deviation was used as the evaluation index of accuracy. The results show that the shorter the sampling period, the higher the precision of PPP tide test. When the sampling period is shortened to 60 s, the change is no longer obvious. The sampling period gradually decreases from 120 s to 90 s, 60 s and 30 s, and the accuracy increases by 63.0%, 60.4% and 10.0%, respectively. In addition, the difference of PPP accuracy between BDS/GPS/GLONASS three-system combination GNSS and GPS/GLONASS dual-system combination GNSS is compared. At the sampling periods of 30 s, 60 s, 90 s and 120 s, the PPP tide test accuracy of the three-system combination is 88.9%, 90.4%, 78.7% and 44.7% higher than that of the dual-system combination, respectively.

Based on Global Navigation Satellite System (GNSS) dynamic precision point positioning technology (PPP), the influence factors of precipitable water vapor (PWV) detection over the ocean were studied. The sampling interval, satellite masking angle, PPP solution method (fixed solution or floating point solution), and the influence of Beidou satellite system combination on ocean PWV retrieval were mainly analyzed. In the marine observation environment, the results show that the accuracy of PWV inversion is the highest when the sampling interval is 30 s. When the number of available satellites is small, the accuracy of PWV inversion is better when the satellite masking angle is set to 5°-10°, and the accuracy decreases gradually with the increase of the satellite masking angle. Whether the PPP solution is fixed or not, it has little effect on the accuracy of PWV inversion. On the basis of GPS/GLONASS system combination, adding Beidou observation value will improve the redundancy of observation and improve the accuracy of PWV inversion.

The towed marine three-component magnetic gradiometer can obtain the geomagnetic three-component and magnetic gradient data at the same time. Compared with the traditional towed geomagnetic total field magnetometer, the towed marine three-component magnetic gradiometer has the advantages of reducing the ship magnetic interference and resisting the influence of geomagnetic daily variation, but it also has some shortcomings such as sensitivity error, zero offset error, orthogonality error and position error. In the actual voyage, a section data measured by the towed marine three-component magnetic gradiometer was calibrated to the total geomagnetic field data measured by the G880 magnetometer, which proved its high stability and reliability. Based on the three component magnetic gradient data, the tensor invariants and the trend of magnetic boundary were obtained, and combined with the Euler deconvolution calculation, the magnetic source body on the measurement line was effectively identified and interpreted. The results show that the towed three-component marine gradiometer can effectively obtain the information of geomagnetic field, component and gradient, which can provide a more effective technical means for marine geomagnetic field measurement.

By interpolation of high and low tide data and application of NS_TIDE model, the tidal characteristics of the tidal reach of Xijiang River (Makou-Dahengqin) were analyzed. Compared with cubic spline interpolation and linear interpolation, it is found that Hermite interpolation is the best method to simulate the hourly tide level. The verification results of tide level show that the overall error of NS_TIDE model is low, and the outliers mainly come from the influence of typhoon and flood. The mean water level and the amplitude of tidal component in the tidal reach of Xijiang River are different in wet and dry season. The influence of runoff in the upper reaches is greater than that of the tides, and the opposite is true in the lower reaches. With the increase of runoff and tidal difference, the mean water level of the upper reaches increases, and the influence on the amplitude and the phase of tidal component is different in different section, which is related to the spatial location and the frequency of the tidal component.

Abyssal peridotite is widely distributed in tectonic environments such as mid-ocean ridges, subduction zones, and continental margins, and typically undergoes subsequent alterations, among which serpentinization is the most significant type. Serpentinization refers to the chemical process wherein ferromagnesium-rich minerals in peridotite, such as olivine and pyroxene, are replaced by a series of secondary minerals like serpentine, magnetite, and brucite. The conditions of serpentinization are closely linked with hydrothermal circulation and the migration of mineral-forming substances, bearing significant implications for indicating hydrothermal mineralization. Traditional methods of petrology and geochemistry exhibit polysemic interpretations and uncertainties when reflecting serpentinization conditions, with different minerals or chemical indicators possibly suggesting different outcomes. Oxygen isotopes are ubiquitous in nature and the oxygen isotope tracing method, due to its wide applicability, ease of comparison, and support for in-situ micro-zone analysis, can clearly reflect the reaction conditions and processes of the mineral or rock-fluid system. This study primarily provides an overview of the principles of oxygen isotope thermometry, the process of abyssal peridotite serpentinization, application cases of oxygen isotope thermometry in the serpentinization of abyssal peridotite, factors influencing the oxygen isotope compositions of serpentinites, as well as the advantages and limitations of oxygen isotope thermometry. It aims to offer a reference for a more profound understanding of the serpentinization process of abyssal peridotite.

Due to its advantages of strong adaptability and high safety,the jacket platform has been widely used in offshore oil and gas development. As more and more jacket platforms will reach or exceed the design life, the platform decommissioning has become one of the important problems in the field of offshore oil and gas development. This paper systematically introduces domestic and international regulations on jacket platform decommissioning, focuses on the decommissioning constraints, application fields, similarities and differences between different international conventions, and summarizes the key points of regulations and requirements on jacket platform decommissioning among China, the United Kingdom, Norway and the United States, and analyzes four typical decommissioning projects worldwide. In view of this, the different decommissioning schemes, and scope of application of jacket platform are summarized and analyzed, as well as the operational difficulties and implementation details of the three key process technologies of dismantling, cutting and transportation during decommissioning. The review can provide a theoretical basis for optimizing the decommissioning plan and key technical methods of the offshore jacket platforms, and has important engineering significance for marine environmental protection, navigation and fishery production.