The Indonesian Throughflow (ITF) plays important roles in global ocean circulation and climate systems. Previous studies suggested the ITF interannual variability is driven by both the El Niño-Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) events. The detailed processes of ENSO and/or IOD induced anomalies impacting on the ITF, however, are still not clear. In this study, this issue is investigated through causal relation, statistical, and dynamical analyses based on satellite observation. The results show that the driven mechanisms of ENSO on the ITF include two aspects. Firstly, the ENSO related wind field anomalies driven anomalous cyclonic ocean circulation in the western Pacific, and off equatorial upwelling Rossby waves propagating westward to arrive at the western boundary of the Pacific, both tend to induce negative sea surface height anomalies (SSHA) in the western Pacific, favoring ITF reduction since the develop of the El Niño through the following year. Secondly, the ENSO events modulate equatorial Indian Ocean zonal winds through Walker Circulation, which in turn trigger eastward propagating upwelling Kelvin waves and westward propagating downwelling Rossby waves. The Rossby waves are reflected into downwelling Kelvin waves, which then propagate eastward along the equator and the Sumatra-Java coast in the Indian Ocean. As a result, the wave dynamics tend to generate negative (positive) SSHA in the eastern Indian Ocean, and thus enhance (reduce) the ITF transport with time lag of 0–6 months (9–12 months), respectively. Under the IOD condition, the wave dynamics also tend to enhance the ITF in the positive IOD year, and reduce the ITF in the following year.

Marine heatwaves (MHWs) are extreme ocean events characterized by anomalously warm upper-ocean temperatures, posing significant threats to marine ecosystems. While various factors driving MHWs have been extensively studied, the role of ocean salinity remains poorly understood. This study investigates the influence of salinity on the major 2013–2014 MHW event in the Northeast Pacific using reanalysis data and climate model outputs. Our results show that salinity variabilities are crucial for the development of the MHW event. Notably, a significant negative correlation exists between sea surface temperature anomalies (SSTAs) and sea surface salinity anomalies (SSSAs) during the MHW, with the SSSAs emerging simultaneously with SSTAs in the same area. Negative salinity anomalies (SAs) result in a shallower mixed layer, which suppresses vertical mixing and thus sustains the upper-ocean warming. Moreover, salinity has a greater impact on mixed layer depth anomalies than temperature. Model sensitivity experiments further demonstrate that negative SAs during MHWs amplify positive SSTAs by enhancing upper-ocean stratification, intensifying the MHW. Additionally, our analysis indicates that the SAs are predominantly driven by local freshwater flux anomalies, which are mainly induced by positive precipitation anomalies during the MHW event.

The impacts of the Luzon Strait transport on shallow meridional overturning circulation (SMOC) in the South China Sea (SCS) have been pointed out by previous studies, but the issue whether the Luzon Strait transport dominates the SMOC formation still remains open. The Helmholtz decomposition is applied based on the ocean general circulation model for the earth simulator products to address this issue. Results show that the motion caused by the Luzon Strait transport is characterized as an obvious southward flow between 13°N and 20°N. After this motion being removed, the clockwise winter SMOC and the anticlockwise summer SMOC can still exist significantly. The SMOC existence and its seasonal variation are also reproduced in the numerical simulation with the Luzon Strait closed. Both results of the Helmholtz decomposition and numerical experiment suggest that the SMOC formation and its seasonal variation are not dominated by the Luzon Strait transport. The SCS monsoon is the primary driving factor for the SMOC, which is related to the physical processes within the SCS.

Marine heatwave (MHW) events refer to periods of significantly elevated sea surface temperatures (SST), persisting from days to months, with significant impacts on marine ecosystems, including increased mortality among marine life and coral bleaching. Forecasting MHW events are crucial to mitigate their harmful effects. This study presents a two-step forecasting process: short-term SST prediction followed by MHW event detection based on the forecasted SST. Firstly, we developed the “SST-MHW-DL” model using the ConvLSTM architecture, which incorporates an attention mechanism to enhance both SST forecasting and MHW event detection. The model utilizes SST data from the preceding 60 d to forecast SST and detect MHW events for the subsequent 15 d. Verification results for SST forecasting demonstrate a root mean square error (RMSE) of 0.64℃, a mean absolute percentage error (MAPE) of 2.05%, and a coefficient of determination (R²) of 0.85, indicating the model’s ability to accurately predict future temperatures by leveraging historical sea temperature information. For MHW event detection using forecasted SST, the evaluation metrics of “accuracy”, “precision”, and “recall” achieved values of 0.77, 0.73, and 0.43, respectively, demonstrating the model’s capability to capture the occurrence of MHW events accurately. Furthermore, the attention-enhanced mechanism reveals that recent SST variations within the past 10 days have the most significant impact on forecasting accuracy, while variations in deep-sea regions and along the Taiwan Strait significantly contribute to the model’s efficacy in capturing spatial characteristics. Additionally, the proposed model and temporal mechanism were applied to detect MHWs in the Atlantic Ocean. By inputting 30 d of SST data, the model predicted SST with an RMSE of 1.02℃ and an R² of 0.94. The accuracy, precision, and recall for MHW detection were 0.79, 0.78, and 0.62, respectively, further demonstrating the model’s robustness and usability.

Significant wave period is an important parameter in coastal and offshore engineering design. Traditional spectral wave models do not directly calculate this parameter, which means that it needs to be estimated from the spectral periods using empirical formulas. The wave energy period is one of the wave periods directly output by many wave models and is often used in studies of wave energy. This study investigated the relationship between significant wave period and wave energy period using wave data measured at three stations in the coastal waters of China. The observations recorded at these stations in the South China Sea, the East China Sea, and the Bohai Sea covered a wide range of surface wave conditions. Analysis indicated that the ratio of significant wave period to wave energy period is closely related to the Goda peakedness parameter of the wave spectra. Therefore, we proposed an empirical formula in which significant wave period is a function of wave energy period and the Goda peakedness parameter. Evaluation results showed that the performance of this formula is substantially better than that of fitting formulas that use constant coefficients.

Nonlinear internal waves (NLIWs) exhibit robust dynamic submesoscale motions, connecting large-scale tides to small-scale shear instabilities in the ocean. Previous studies have mainly focused on their generation mechanisms and evolution along their paths. Considering their global distribution resulting from the primary origin in tide-topography interaction, there is an increasing cross-disciplinary interest in understanding how these energetic and ubiquitous NLIWs contribute to sediment redistribution in the ocean. This paper presents fundamental theories on NLIWs and comprehensively reviews triggering mechanisms, different types of instability, and sediment responses by summarizing recent theoretical parameterizations, numerical simulations, laboratory experiments, and in-situ observations. We specifically focus on elucidating various types of instability along with their impact on sediment dynamic processes. Finally, we outline several unresolved issues that require further exploration for a quantitative investigation into NLIW-induced sediment transfer in the ocean.

The exchange of inorganic nutrients at the coastal sediment-water interface (SWI) plays a crucial role in regulating the nutrient budget in overlying water. The related studies mainly focus on the mid-to high-latitude regions, leaving a significant gap in the quantitative assessment of nutrient exchange and environmental controls at the SWI in low-latitude coastal regions. We quantitatively assess the exchange of inorganic nutrients at the SWI in three tropical bays (Dongzhai Harbor, Xiaohai Lagoon, Qinglan Harbor). Sediments act as a source of ammonium, phosphate, and silicate, but for nitrate, sediments can be both a source and sink, although with substantial spatial and temporal variations in their fluxes. Labile organic matter is a critical regulator for the fluxes of inorganic nutrients at the SWI. The sedimentary nutrients input with high N/P molar ratio will alter the nutrient stoichiometry to mitigate the nitrogen limitation in coastal waters. However, the internal sediment release in these tropical bays plays a relative weak role in contributing to the nutrient addition in comparison with the other external nutrient sources including riverine input, submarine groundwater discharge, and atmospheric deposition. According to the global compilation on SWI nutrient fluxes, we propose that water column primary production and external inputs to interpret the variation in exchange and fluxes of nutrients at the SWI in different ecosystems. Such a conceptual understanding of these chain biogeochemical processes involving external nutrient input, primary production, particulate organic matter settling, and the accumulation and release of inorganic nutrients in sediments will be helpful for the scientific-based pollution prevent and control in coastal waters.

To explore the geochemical characteristics and genesis of the elements in ferromanganese nodules from the Northwest Pacific, this study analyses the mineral composition, elemental content, occurrence phase and genetic mechanisms of samples by X-ray diffraction (XRD), inductively coupled plasma-optical emission spectrometry (ICP-OES), inductively coupled plasma-mass spectrometry (ICP-MS) and phase analysis methods. The results show that ferromanganese nodules are mainly hydrogenetic, and Mn/Fe content ratio ranges from 0.95 to 2.05. The major minerals are vernadite (δ-MnO₂) and amorphous ferric oxyhydroxide (FeOOH), and the secondary minerals include todorokite, birnessite, quartz and plagioclase. Ferromanganese nodules contain high contents of Co (0.24%–0.42%), Cu (0.23%–0.73%), Ni (0.33%–0.86%) and rare earth elements (REEs, 1192–1990 µg/g), which have positive Ce and negative Y anomalies but no Eu anomaly. A cluster analysis suggests that the elements in ferromanganese nodules can be divided into three groups: hydrogenetic components, including Fe, Ti, Zr, P, Pb, Co, Ba, Sr, V and REEs; diagenetic components, including Mn, Ni, Mg, Zn and Cu; and detrital components, including Al, Na, K and Ca. According to chemical leaching, ferromanganese nodules can be divided into four phases: Na, Ca, Mg and Sr are mainly enriched in the carbonate phase; Mn, Co, Ni and Ba are mainly enriched in the Mn-oxide phase; Fe, P, Ti, Cu, Pb, V, Zn, Zr and REEs are mainly enriched in the Fe-oxide phase; and Al and K are mainly enriched in the residual phase. A combination of the two different methods reveal selective enrichment of metal elements from seawater by ferromanganese nodules, featuring multisource mineralization. Moreover, through ion exchange and adsorption, approximately 71.2% of REEs are enriched in the Fe-oxide phase, 15.4% in the Mn-oxide phase and 12.4% in the residual phase, while REE contents in the carbonate phase are relatively low. In addition, under the oxic conditions of seawater, the oxidation of soluble Ce³⁺ to insoluble CeO₂ together with Fe-Mn minerals results in Ce enrichment in ferromanganese nodules. This study provides a reference for the metallogenesis of ferromanganese nodules from the Northwest Pacific.

The correct understanding of fish population structure plays a positive role in their fishery management. The dotted gizzard shad, Konosirus punctatus, is widely distributed in the coastal waters of the northwestern Pacific. With the over-exploitation of economically important fishes, its importance is increasingly prominent. To further examine the population genetic structure of K. punctatus across the northwestern Pacific, the amplified fragment length polymorphism (AFLP) and the inter-simple sequence repeats (ISSRs) were employed to perform genetic variation analysis. The results showed that the combination of polyacrylamide gel electrophoresis and silver staining can effectively detect genetic variation for K. punctatus populations. The average proportions of polymorphic loci were 46.26% and 87.13% for AFLP and ISSR markers, respectively, and the genetic diversity parameters showed no obvious differences among populations. Both analysis molecular variance (AMOVA) and pairwise F _st suggested that there was significant genetic differentiation between Chinese and Japanese populations. All samples also clustered into two clades based on the unweighted pair-group method analysis (UPGMA) tree by two markers, which indicated significant genetic differentiation among populations. Consistent with the previous studies, there are two highly differentiated groups at the nuclear gene level and they were suggested to be treated as two separate genetic management units. The results of the present study could provide the genetic management strategy for this important economic species.

Macrobenthic organisms are commonly employed as biomonitors for environmental risk assessment. In this study, we aimed to investigate the spatial and temporal patterns of the macrobenthic community, which is influenced by environmental factors of sediments and bottom water layer. We sampled a total of 12, 11, 10, and 11 stations in the Shengsi Archipelago during June 2010, August 2010, November 2020, and April 2021 respectively. A total of 124 species of macrobenthos were identified, with polychaetes being the dominant group. The abundance, biomass, and diversity indices exhibited no significant temporal differences. Similarly, biodiversity did not exhibit a clear spatial gradient, likely due to the small study area and the absence of significant differences in key factors such as depth. However, the stations with the lowest biodiversity values consistently appeared in the southwest region, possibly due to the impact of human activities. Significant differences in the macrobenthic community were observed between all months except between June and August, and mollusk Endopleura lubrica and polychaete Sigambra hanaokai were important contributors to these differences according to the results of the Similarity Percentages analysis. Suspended particulate matter (SPM) was identified as the primary driving factors of macrobenthic variability. In summary, the community structure underwent temporal changes influenced by complex current patterns, while biodiversity remained relatively stable. This study contributes to our understanding of the key environmental factors affecting macrobenthic communities and biodiversity. It also provides valuable data support for the long-term monitoring of macrobenthos and the environment in the Shengsi Archipelago.

All vertebrates have a definitive thyroid gland, or thyroid for short. As a critical organ for growth, development and metabolism, its origin and evolution have long received attention. On the basis of anatomical position, endodermal origination and histological features, the endostyle of amphioxus has been proposed as a homologue to the thyroid of vertebrates. This homology is further supported by the findings that the amphioxus endostyle abounds in thyroid hormones, possesses several thyroid-specific proteins such as thyroperoxidase, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and thyroglobulin, and expresses the thyroid-related transcription factors involved in the regulation of development of the vertebrate thyroid, including Nkx2.1, FoxE4 and Pax2/5/8. Importantly, our study on functionality, together with others, indicates significant similarities between the amphioxus endostyle and the vertebrate thyroid gland. Moreover, we show that the production of thyroid hormones by the amphioxus endostyle is mediated in a fashion similar to that of the vertebrate thyroid. These provide solid evidences that the amphioxus endostyle is the homologue of the vertebrate thyroid. From a phylogenetic viewpoint, we propose that the hypobranchial ridge, or endostyle-like structure, of hemichordates is the most primitive forerunner of the thyroid, from which the vertebrate thyroid is formed through the transformation of non-follicular endostyle of amphioxus to follicular endocrine organ of vertebrates. We also raise a couple of questions that demand further study.

Microsatellite markers with polymorphic advantages are widely used in the exploration and utilization of marine fishery resources. In this study, 16 polymorphic microsatellite markers were used to evaluate the diversity and population structure of Setipinna tenuifilis, a nearshore fish of economic and ecological value in the western Pacific Ocean and Indian Ocean. The genetic diversity of S. tenuifilis showed a high level [mean N _a (number of alleles) is 23.25, mean H _o (observed heterozygosity) is 0.639, mean R _a (allelic richness) is 11.625, and the polymorphic information content (PIC) is 0.844] similar to other Clupeiformes fish species. The nine wild S. tenuifilis populations showed significant differentiation (F _ST ranging from 0.00384 to 0.19346) and were generally divided into southern and northern populations based on genetic structure, except for the Zhoushan population, which exhibited genetic mixture. Our results provide fundamental but significant genetic insights for the management and conservation of S. tenuifilis fishery resources.

Scientific and precise evaluations of the megafaunal and landform characteristics of seamounts are important guides for their protection and study. A series of manned and unmanned submersibles have provided invaluable observational imaging data for the ecological study of seamounts. However, traditional methods of artificial observation of seamount imaging data cannot accurately and efficiently determine the characteristics of megafauna and landforms. This research harnesses data-driven technology to systematically investigate the distributional traits and morphological features of megafaunal organisms, as well as the topographical characteristics, in the Caiwei Guyot region of the western Pacific’s Magellan Seamounts. To construct the landform and megafauna dataset of the Caiwei Guyot region, we used a data preprocessing technology based on image enhancement to provide high-quality imaging data for data-driven technologies. A megafaunal identification and counting algorithm based on YOLOv5 (You Only Look Once Version 5) was developed to efficiently assess the abundance, variety, and dominant species of megafauna. Simultaneously, a landform three-dimensional (3D) reconstruction algorithm based on PatchmatchNet was developed to reconstruct the 3D form of the terrain accurately. This study pioneers the application of data-driven technology to deep-sea imaging within the Caiwei Guyot region, offering an innovative approach to accurately and efficiently characterize the region’s unique megafauna and landforms.