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Using the data of high resolution satellite sea surface temperature (SST) from January 1, 1990 to December 31, 2020, the spatial characteristics of marine heatwaves (MHWs) in the South China Sea were identified with a deep-first-search algorithm, and the characteristics of marine heatwaves at different spatial scales were further investigated. The results indicated that the small-scale marine heatwave events in the South China Sea (Type I MHWs, area<1.8×10⁴ km²) occurred the most frequently, accounting for 94.20% of the total marine heatwave occurrences. Large-scale marine heatwaves with areas exceeding 1.2×10⁵ km² (Type III MHWs) occurred only 74 times during the 31-year period, with the largest event recorded in 2015. Further analysis revealed significant differences in the spatial distribution of intensity, duration, and frequency of marine heatwaves for different spatial scales. Compared to Type I MHWs, Type II MHWs (1.8×10⁴~1.2×10⁵ km²) exhibited a noticeable increase in the average coverage area with an intensity exceeding 1.5 ℃. Statistical analysis showed that the intensity, duration, and cumulative intensity of South China Sea MHWs increased with the spatial scale of the MHWs. The intensity of Type III MHWs was 1.4 times that of Type I MHWs and 1.2 times that of Type II MHWs. In addition, the response of South China Sea MHWs areas to the El Ni?o-Southern Oscillation (ENSO) was also investigated. The results showed a significant increase in the areas of Type I to III MHWs during El Ni?o periods, with a lag of 6 to 7 months. The duration of Type III MHWs during El Ni?o was longer by 2 days compared to La Ni?a periods. This study explored the fundamental characteristics of South China Sea MHWs areas and further analyzed the commonalities and differences of MHWs at different spatial scales, providing new insights into the characteristics and mechanisms of the formation and dissipation of South China Sea MHWs.

Using eddy-resolving numerical simulation data and historical hydrological observation data, this study investigates the sources, seasonal and interannual variability of two subsurface undercurrents under the Indonesian Throughflow—the Ombai Undercurrent located in the Ombai Strait and the Timor Undercurrent located in the Timor Channel. The results indicate that these two undercurrents exist at depths of approximately 200-800 m, which are a quasi-permanent undercurrent system. The formation of the Ombai Undercurrent is mainly related to the eastward extension of the South Java Undercurrent, while the water source of the Timor Undercurrent is more complex, mostly a mixture of the South Java Undercurrent and the Leeuwin Undercurrent. Both subsurface undercurrents exhibit significant seasonal and interannual variations, with a significant semiannual period at the seasonal scale, typically peaking during the Indian Ocean monsoon transition period (April, May, and October). Combining historical wind, satellite altimeters, and temperature and salinity observation data, it is found that the meridional pressure gradient in the subsurface layer related to local wind and their upwelling is the dominant factor leading to their seasonal changes. At the interannual scale, there is a period of 2-4 years for subsurface undercurrents, which is significantly correlated with the Indian Ocean dipole.

Based on a survey in Hangzhou Bay in March 2022, the distribution and sea-air exchange flux of N₂O in Hangzhou Bay and its adjacent waters in spring were investigated, and the influencing factors were analyzed. The dissolved N₂O concentration and saturation of surface water were 12.5-21.3 nmol·L^-1 and 115%-183%, respectively. The average N₂O concentration in the upper, middle and lower waters were 17.2±2.9, 14.1±0.8 and 13.2±0.7 nmol·L^-1, respectively, and the average saturation were 151%±17%, 125%±6% and 123%±6%, respectively. Dissolved N₂O in all sampling sites were in a supersaturated state. The spatial distribution of N₂O concentration and saturation in the surface water exhibited significant variations, with high values concentrated in the upstream area and gradually decreasing from west to east, while these showed a decreasing trend from north to south in middle and lower areas. The distribution of N₂O in the Hangzhou Bay and its adjacent waters was influenced by multiple factors such as temperature, estuarine mixing, river input and in situ bioproduction. The sea-air N₂O exchange flux ranged from 11.4 to 71.2 μmol·m^-2·d^-1, with an average of 29.5±16.0 μmol·m^-2·d^-1. Comparing with other domestic estuaries and bays, this is relatively high in Hangzhou Bay, indicating a significant potential for N₂O release. Combining the sea-air exchange flux and sea area, this study preliminarily estimated that the N₂O emission in Hangzhou Bay and its adjacent waters in spring was 3.5×10⁵ mol·d^-1, indicating its important role in atmospheric N₂O emissions.

The occurrence of a “triple-dip” La Ni?a event is historically rare, yet it has exerted profound impacts on global weather and climate systems. To enhance the understanding of the causes of multiple La Ni?a events and improve the prediction capabilities for weather and climate, a comparative analysis of the ocean-atmosphere processes in the tropical Pacific during the 2020-2023 “triple-dip” La Ni?a period was conducted based on multiple sets of observational and reanalysis data, employing composite analysis and other methods. Results showed that: The peak of the 2020 La Ni?a event occurred in winter and lasted the longest among this “triple-dip” La Ni?a events; the peak of the 2021 La Ni?a event also occurred in winter, with the cold anomaly centered near the eastern Pacific, classified as an “Eastern Pacific” type; the peak of the 2022 La Ni?a event occurred in autumn, relatively weaker in intensity and the shortest in duration, with the cold anomaly centered in the central Pacific, classified as a “Central Pacific” type. Further research revealed a coupling relationship between zonal wind and sea surface temperature (SST) variations. However, during this “triple-dip” La Ni?a period, the intensity and location of the eastward wind anomalies showed little variation across different La Ni?a events. In contrast, subsurface SST changes align with changes in SST anomaly centers, it may be a crucial factor influencing the intensity and type differences among this “triple-dip” La Ni?a events. Although eastward-propagating Kelvin waves had a certain impact on the ocean system, but their propagation speeds and intensities exhibited minimal variations during this “triple-dip” La Ni?a events. Additionally, the study found that variations in the growth rate of warm water volume contributed to the differences in La Ni?a intensities, while the meridional convergence and divergence of warm water led to the seasonal phase-locking phenomenon of La Ni?a events.

To reveal the spatial and temporal distribution patterns of internal wave-induced mixing in global ocean and investigate its influencing factors, this study employs an internal wave fine-scale parameterization method to statistically analyze Argo temperature and salinity data at 250-500 m depth from 2006 to 2021. The analysis characterizes the spatial and temporal features of internal wave mixing and identifies the impact of wind-induced near-inertial energy flux on mixing across global oceans under varying seasonal conditions. In space, there is strong wind-induced near-inertial energy flux in the four seasons of the North Atlantic and Southern Ocean in the whole year, resulting in significant internal wave mixing. However, in the western Pacific and the north of 40°N in the North Pacific, the spatial distribution of internal wave-induced mixing are inconsistent with the wind-induced near-inertial energy flux. Instead, it follows the spatial distribution of eddy kinetic energy since internal wave-driven mixing can be also regulated by eddies. In terms of time, the strongest internal wave-induced mixing of global occurs from December to February, followed by September to November and March to May, and June to August. This is consistent with the seasonal variation of global wind-induced near-inertial energy flux. In the northern hemisphere, the wind-induced near-inertial energy flux and mixing are the strongest in winter, while the weakest in summer. In the southern hemisphere, the variation of wind-induced near-inertial energy flux and mixing over four seasons is inconsistent. However, the seasonal cycles of mixing and wind-induced near-inertial energy flux in the northern and southern hemispheres are roughly consistent, especially in the North Atlantic, where the wind-induced near-inertial energy flux and mixing match well.

This study was conducted to explore the contribution of silicon dissolution from beach sediments to the dissolved silicon budget in the coastal waters. From March to September in 2017, six field surveying cruises were conducted in the Muping offshore area (Yantai, China), the southern North Yellow Sea. By investigating monthly distributions and the averaged values of dissolved inorganic nutrients, monthly accumulation of dissolved silicate anomaly (ΔSi, as defined with the difference between dissolved inorganic nitrogen and silicate concentrations)of 1.5 μmol·L^-1 was observed in this offshore area with weak circulation from May to August. Further combining laboratory incubation experiments, theoretical calculation and field data analyses, It was found that the permeable particles in beaches could be dissolved, leaching active silicate to seawater, and increasing the offshore silicate concentration by 0.7~2.0 μmol·L^-1 every month, roughly consistent with the monthly accumulation rate of field ΔSi. Extrapolating the beach silicate-leaching flux to the length of the coastline rounding the Yellow Sea, the previously reported imbalance in silicate budget in this coastal sea could roughly be bridged. This study indicated again that the dissolving of permeable particles might contribute significantly to coastal silicate budget.

Accurate monitoring and assessment of the temperature rise intensity and spatio-temporal distribution of thermal discharge from power plants are of great significance for ensuring safe operations of the power plants and protecting the ecological environment of surrounding marine areas. Based on thermal infrared remote sensing observation technology, information such as the spatial distribution, temperature rise intensity, and temporal variation of thermal discharge from coastal power plants can be obtained, making it an important means for monitoring thermal discharge from these plants. The current research status and progress in monitoring thermal discharge from coastal power plants using thermal infrared remote sensing technology are systematically reviewed, including remote sensing data sources, water temperature retrieval, thermal discharge background temperature information extraction, spatio-temporal statistics of thermal discharge, and analysis of influencing factors. Furthermore, the paper proposes future directions for remote sensing research on thermal discharge from coastal power plants.

Antarctic krill (Euphausia superba) is a key species sustaining the biodiversity of the Southern Ocean and is a protected and restricted fishing target. In the context of significant impacts of climate change on the ecological environment of the Southern Ocean, it is urgent to understand the spatio-temporal distribution, change trends, and habitat suitability of Antarctic krill. In this study, based on Antarctic krill presence records and time series satellite and reanalysis data, a Maxent model for habitat suitability in the Cosmonauts Sea and the D’Urville Sea were constructed using timing parameters of phytoplankton phenology and sea-ice dynamics, along with related environmental parameters. It was found that timing parameters were more suitable for assessing habitat suitability for Antarctic krill compared to conventional environmental parameters. Using the Maxent model, the data over 20 years on the occurrence time and frequency of Antarctic krill in these two study areas were retrieved, and the mechanisms through the interannual trends of multiple environmental parameters were analyzed. Environmental parameters at the time of krill occurrence showed that the overall chlorophyll a mass concentration in the Cosmonauts Sea was lower than that in the D’Urville Sea, with a shorter ice-free period, lower temperatures, and later krill presence dates primarily composed of larval and young individuals along the coast. From 1997 to 2019, the presence time of krill in the coastal Cosmonauts Sea gradually advanced, and the number of presence days increased, mainly due to earlier onset of algal blooms, while increased chlorophyll a mass concentration provided more abundant overwintering food for krill larvae. In the D’Urville Sea, influenced by warming water, shortened ice-free period, and reduced chlorophyll a mass concentration, mature krill may migrate to a more suitable environment, leading to a decline in annual presence frequency. Based on the constructed habitat suitability model, this study showed the long-term distribution of Antarctic krill occurrence in the Cosmonauts Sea and the D’Urville Sea for the first time, which can help to understand the impact of climate change on the ecological environment in the Southern Ocean, and the planning of conservation areas and fishery management in the Southern Ocean.

Coastal estuaries are influenced by terrestrial inputs and usually act as sources of atmospheric carbon dioxide (CO₂), whereas mangrove ecosystems generally serve as sinks of atmospheric CO₂. Therefore, accurately measuring the CO₂ emissions at mangrove estuaries is of great significance for constructing regional and global carbon budgets. Dongzhai Harbor locates in the northeastern of Hainan Island, and connects to the Qiongzhou Strait outward, surrounding by 5 major small rivers. Mangroves are mainly distributed in the west and south of Dongzhai Harbor. This study conducted four field surveys in Dongzhaigang, the surrounding major rivers and the adjacent sea areas in December 2022 (dry season), December 2023 (dry season), May 2022 (wet season) and August 2023 (wet season) respectively. The results show that the surface water partial pressure of CO₂ (pCO₂) presents a decreasing trend from rivers to inner and outer harbor. Temperature, river-sea mixing, and biological respiration jointly affect the spatial distributions of pCO₂ in the dry and wet seasons. The CO₂ flux in wet season (8.8±8.2 mmol·m^-2·d^-1) is greater than that in dry season (3.4±3.6 mmol·m^-2·d^-1), and the annual CO₂ flux (6.1±6.3 mmol·m^-2·d^-1) is lower than that in other tropical mangrove estuaries around the world. This study estimates that the estuarine CO₂ emission could offset about 10.4%~21.9% of the carbon sequestration by plants in Dongzhai Harbor.

Submarine earthquake is one of the most major factors causing deep-water international submarine cables damage. Understanding the process of submarine cables damage and the mechanism of submarine cables damage caused by turbidity currents after earthquake are of great significance to the security maintenance of international submarine communications. Combined with the lastest research result of global seabed topography and using professional international submarine cables engineering software Makaiplan, the process of plenty of submarine cables damage after Grand Banks Earthquake and Hengchun Earthquake were studied, then the relationship between the pattern of submarine cable damage and the developing process of turbidity currents after earthquake was found, and the mechanism of submarine cables damage caused by turbidity currents after earthquake was summarized. Study result shows that submarine cables break points are located intentively in submarine canyons and trenches. The movement speed of turbidity currents in submarine canyon and submarine trench, which caused submarine cable damage, can reach several ten kilometers to several hundred kilometres per hour. Terrestrial rivers and continental shelf undersea river channels provide materials transportation for the development of turbidity currents. Submarine canyons and trenchs are the pathes of turbidity currents movement then damage plenty of submarine cables. The turbidity currents that developed from upper continental slope in passive continental margin after earthquake can damage submarine cables laid on continental slope, continental rise and abyssal plain. This kind of turbidity currents achieves maximum speed on continental slope, then self-accelerate on abyssal plain. Multiple turbidity currents can develop at different positions of continental slope at the same time in active continental margin, then strike submarine cables which laid on canyons and trenches for multiple times. This kind of turbidity currents achieves maximum speed and self-accelerates in submarine trenches. There are several earthquake-resistance measures: submarine cable routes trying to avoid crossing submarine canyons and trenches which connected to terrestrial rivers or continental shelf channels; using shallow water type submarine cable which has outer armor protection when crossing inevitably; laying submarine cables suspended slightly on the bottom of canyons or trenches with Uraduct protection on them; changing the cross-section shape of submarine cable.

Island group is a typical form of existence for offshore islands in China. Investigating the evolution of landscape patterns in an island group and among individual islands can provide theoretical foundations and technical support for island resource management. Based on the high-resolution remote sensing images of six inhabited islands (Dongtou Island, Banping Island, Dasanpan Island, Huagang Island, Niyu Island and Zhuangyuanao Island) in Dongtou District in 2008, 2014, 2018 and 2022, the landscape pattern indices of island groups and individual islands were calculated. The results indicate the following: (1) During the study period, the proportions of forest land, water areas, and cultivated land in the landscape of island group have been continuously declining, while the proportions of building land, industrial and mining land, and road areas have been steadily increasing. (2) The landscape pattern changes on Dongtou Island, Dasanpan Island, Niyu Island, and Zhuangyuanao Island are significant, with the former two primarily characterized by an increase in building land and the latter two by an increase in industrial and mining land; the landscape patterns of Banping Island and Huagang Island are relatively stable. (3) Development activities among the islands are interrelated, with the landscape evolving in an orderly manner. The transformations of forest land into mining areas on Niyu Island and Dasanpan Island have supported the reclamation and subsequent development of water areas on Dongtou Island and Zhuangyuanao Island; as the larger islands develop, the development of surrounding smaller islands has also begun.

In December 2023, the project “Construction of Regional Deep-Argo Observation Network” sponsored by Laoshan Laboratory deployed a domestically-produced HM4000 profiling float with the maximum profiling depth of 4 000 m (the World Meteorological Organization number is 2902895) in the Philippine Sea, which was equipped with an RBRargo³ deep 6k Temperature-Conductivity-Depth (CTD) sensor produced by RBR, Canada. It was found that the salinity observation data reported by the float exhibited a systematic deviation compared to the shipboard CTD and climatological salinity. In order to correct the salinity data of the float, the conductivity slope of the RBR CTD was calculated by using bottle salinity measured by the Autosal 8400B salinometer and salinity measurements from the shipboard CTD cast. Salinity profiles of the float were then calibrated, and the calibrated salinity was found to be basically consistent with the nearby float and the climatological data. With the implementation of the “Construction of Regional Deep-Argo Observation Network” project, an increasing number of domestically-produced deep Argo floats will be deployed. Compared to the Core Argo floats that measure temperature and salinity profiles in the upper 2 000 m of the ocean, Deep-Argo requires higher accuracy to resolve smaller variations in deep waters. Currently, technical problems are still found in deep CTD sensors, and improper handling and operation during storage, transportation, and usage of some floats and sensors are inevitable, resulting in large errors in the observations, especially the salinity data. Therefore, this study proposes a method of calibrating Deep-Argo floats’ observation data using in-situ shipboard CTD cast, which can provide essential technical support for quality control of the Deep-Argo floats.

Based on the satellite altimeter data from January 1993 to December 2021, the least squares method and the ensemble empirical mode decomposition (EEMD) were used to analyze the long-term changes of the sea level in Zhoushan and the adjacent East China Sea and its influencing factors. The study found that the sea level in the study area was generally on an upward trend, and the upward trend was more obvious in the coastal waters on the east side of the Zhoushan Islands. The average linear rate was 0.36±0.10 cm/a, and the upward trend had been somewhat mitigated since 2018. The sea level in the study area showed obvious seasonal differences. Its linear rate was the largest in autumn (0.37±0.12 cm/a), followed by in winter, and slightly smaller in spring and summer (approximately 0.34±0.10 cm/a). The nonlinear change trend over the past 30 years showed that the upward rates in summer and autumn had almost remained unchanged, the upward rate in winter had shown a slowdown trend, and the upward trend in spring had been accelerating. There was a trend of increasing annual amplitude of the sea level in the study area. The long-term changes of the sea level were closely related to the seawater thermal expansion effect caused by temperature and the water increase-decrease effect caused by changes in wind stress.

The anaerobic oxidation of methane (AOM) is a pivotal component of elemental cycling within cold seep sediments. This process is usually performed by anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB), which usually exist as symbionts. However, pure cultures of ANME have not yet been obtained, and their slow metabolism hinders further exploration and research into their metabolic characteristics and collaborative mechanisms. In this study, we utilized hybridization chain reaction-fluorescence in situ hybridization (HCR-FISH) technology and high-throughput 16S rRNA gene sequencing to investigate the composition and state of ANME communities at different depths of the sediments in the black microbial mat area of the South China Sea Formosa cold seep. The results showed that ANME-1 and ANME-2 were the dominant groups in the sampled Formosa cold seep sediments. Specifically, ANME-2 was found to form consortia with SRB, while no such associations were detected for ANME-1. This observation suggested that ANME-2 and SRB primarily engage in symbiotic AOM processes, highlighting potential differences in physiological roles and methane metabolism pathways between ANME-1 and ANME-2. Furthermore, in sediment samples of all layers, the diameters of ANME-2/SRB consortia were predominantly concentrated between 3-10 μm. Correlation analysis indicated a significant link between the distribution of consortium diameters and environmental factors such as sulfate concentration in the sediment, underscoring the impact of environmental factors on the growth of ANME/SRB consortia. Additionally, using HCR-FISH, we further discovered the presence of multiple consortium clusters in the Formosa cold seep sediment, characterized by orderly connected and uniform-sized consortium, implying possible connections or cooperative relationships among consortia. This study revealed the presence and distribution patterns of ANME groups and sizes of symbiotic microbial consortia in sediment samples from different depths of the Formosa cold seep, laying the foundation for further understanding methane metabolism mechanisms and ecological functions of different ANME groups in situ cold seep sediments.

A simple tropical cyclone tracker based on wind stress characteristics was designed in this study, using the best track dataset from the United States Joint Typhoon Warning Center, wind speed data and sea level pressure field data from the European Centre for Medium-Range Weather Forecasts. The tracker was used to detect tropical cyclones in the Northwest Pacific from 1985 to 2014, and its performance metrics were evaluated. The results showed that the tracker was able to accurately reproduce the spatiotemporal structure of tropical cyclones in the Northwest Pacific. The peak period of activity was concentrated from August to October, and the latitudinal positions varied with the seasons, consistent with the observations. Additionally, the tracker used the minimum sea level pressure as a criterion for determining cyclone intensity, and the number of cyclones identified at different intensities closely matched the observations. The tracker performed well in terms of probability of detection and false alarm rate for tropical cyclones, comparable to previously used trackers. Regarding the tropical cyclones detected by the tracker, the research findings showed that approximately 90% of the center positions were within a deviation of 1 degree from the observed positions, and the lifetime deviation was within 2 days, indicating a good representation of the complete movement and evolution of tropical cyclones.

The topographic and geomorphologic features of mid-ocean ridges are directly controlled by tectonic movements and magmatic activities, and study of them can help us to understand the tectonic evolution history and magmatic processes of mid-ocean ridges, and is also of great significance to the exploration of deep-sea mineral resources. In this paper, the shipboard multibeam sonar data collected during the China Ocean 24 Cruise were utilize to study the topographic and geomorphologic features of the Carlsberg Ridge in the Northwest Indian Ocean by applying the quantitative analysis method with the 61°24'E-61°48'E segment as the research target, the magma intrusion ratio and the fault correlation index were calculated, and the magma-tectonic significance of the study area was discussed. The study area can be divided into four secondary mid-ocean ridge segments (A, B, C, and D). The active intervals of magma-tectonic periods for segments A, B, C, and D are 0.15, 0.50, 0.70 and 0.21 Ma, respectively. The mid-ocean ridge segments A and B are asymmetric dilatation sections with poor magma and mainly tectonic action, belonging to the period of tectonic activity; the mid-ocean ridge segment C is a symmetric dilatation section with sufficient magma and mainly magmatic action, belonging to the period of axial volcanic ridge construction; the mid-ocean ridge segment D is a symmetric dilatation section with poor magma and mainly tectonic action, belonging to the period of tectonic activity. Faults area with high kernel density on the two flanks of the mid-ocean ridge section has a possibility of forming an area of hydrothermal activity, which is a target area of further exploration.

This study was based on the actual gravity, magnetic and multichannel seismic data obtained during the international cooperative survey in 2021. Through joint inversion of gravity and seismic along the CMD01 profile traversing the southwestern margin of Madagascar, combined with interpretation and analysis of seismic profiles, the crustal structure, tectonic units, and evolution of the southwestern margin of Madagascar were studied. A crustal density model of the southwestern margin of Madagascar was established, revealing thinned continental crust and the presence of magmatic underplating in certain segments. Structural units such as thinned continental crust, continental-ocean transition zone and oceanic crust domain can be delineated from land to sea, among which, due to the influence of Davie Fracture Zone strike-slip tectonics on the margin, the continental-ocean transition zone exhibited typical characteristics of a transform margin. By combining plate reconstruction and crustal density model, the developmental evolution of the southwestern margin of Madagascar was reconstructed. The research results have important theoretical significance and practical application value for deepening the understanding of the breakup and separation of the Gondwana, the developmental evolution of the East African passive margin, and maritime delineation.

Deep-sea sediments and polymetallic nodules are rich habitats for microorganisms. Exploring their community structure and functionality is crucial for understanding microbial genetic resources and their role in mineral formation. Current research on the bacterial diversity and structure within the nodules and surrounding sediments is limited, especially regarding microbial contributions to nodule formation. Using full-length 16S rRNA sequencing, we analyzed the bacterial composition of various nodule types and surrounding sediments in the Pacific Ocean. Scanning electron microscopy and energy dispersive spectroscopy revealed bacterial-like microsphere structures and metal element distribution on their surfaces. The bacterial community composition varied among different nodules and sediments, with Proteobacteria and Bacteroidetes dominating. Functional groups like Shewanella and Colwellia, known for metal oxidation-reduction and biofilm formation, may contribute to nodule formation. These microsphere structures promoted metal aggregation, potentially serving as mineral precipitation sites. This study enhanced our understanding of microbial functions and mineral interactions, crucial for insights into deep-sea biogeochemical cycles and microbial mineralization.