As a key component of the mid-latitude arid belt in Eurasia, arid West Asia is characterized by perennial aridity, low precipitation, intense evaporation, and fragile ecosystems, making it highly sensitive to coupled precipitation-temperature variations. Clarifying the climatic evolution patterns in West Asia is therefore crucial for predicting future climate trends and ensuring regional economic development and social stability. However, long-term trend analyses of precipitation in West Asia remain challenging due to the sparsity of paleoclimate records, which are often contradictory. This study synthesizes hydroclimatic records from the past three decades to summarize Holocene moisture patterns in West Asia and discuss their potential drivers. Existing pollen records suggest a long-term increase in effective moisture during the Holocene. In contrast, speleothem and lacustrine carbonate δ¹⁸O records demonstrate a progressive aridification trend during the Holocene. After reviewing existing hydroclimatic records in West Asia, we infer that the δ¹⁸O variations in secondary carbonates in West Asia are dominated by seawater δ¹⁸O dynamics in eastern Mediterranean, rather than directly recording local precipitation amount. Based on multi-proxy hydroclimatic records and reliability assessments of paleoclimate indicators in West Asia, this study infers that the millennial-scale climatic patterns in the arid regions of West Asia during the Holocene were closely linked to the intensity and latitudinal shifts of the westerlies, which were primarily modulated by summer insolation. During the early Holocene, increased summer insolation led to higher surface temperatures, driving a northward shift of the westerly circulation. It reduced moisture transport by the westerlies to West Asia, resulting in drier conditions. However, increased precipitation in the East African monsoon region enhanced freshwater discharge from the Nile and other rivers into the Mediterranean Sea, resulting in a negative δ¹⁸O excursion in Mediterranean seawater. Consequently, this modified moisture source signature led to depleted δ¹⁸O values in precipitation records across West Asia. The late Holocene exhibited opposite characteristics.

The deep water of the Eastern Indian Ocean is a crucial component of the global deep-sea system, playing a significant role in the global carbon cycle and the distribution of heat and nutrients. It is divided by the Ninety East Ridge into the Central Indian Basin (CIB) and the West Australian Basin (WAB). These two basins exhibit distinct differences in their water mass characteristics and circulation patterns. To further understand the deep-sea circulation and water mass features in the Eastern Indian Ocean, this paper reviews existing research findings and summarizes the following aspects: 1) the unique topography of the deep Eastern Indian Ocean; 2) the sources and pathways of deep-sea water masses; 3) the deep meridional overturning circulation; and 4) the differences and connections between the deep-sea water masses in the CIB and the WAB. Finally, this paper highlights key scientific issues that need to be addressed in future research on the deep sea of the Eastern Indian Ocean, providing a reference for related studies.

The Indian Ocean, the third largest ocean in the world, is surrounded by tropical seas such as the Red Sea, Arabian Sea, Gulf of Aden, Persian Gulf, and Mozambique Channel. It covers a vast area with a highly complex environment and abundant resources. In recent years, the exploration and study of its marine resources have attracted significant global attention. Over the past decade, Chinese institutions such as the Ministry of Natural Resources (originally the State Oceanic Administration) and the Chinese Academy of Sciences have organized annual large-scale scientific expeditions to investigate the region’s geology, biology, and mineral resources, actively supporting the Belt and Road Initiative. With advancements in multiple research fields, China has achieved notable results in exploring microbial resources in the Indian Ocean. Based on available statistical data, this review systematically summarizes the discovery and distribution of novel microbial species in Indian Ocean habitats, discusses the identification of bioactive natural products and their potential application, and evaluates future prospects for the conservation and exploitation of these microbial resources. The review aims to enhance China’s scientific understanding of Indian Ocean microbial resources and further consolidate and strengthen China’s leading position in this field.

As an active convergent margin, the Sunda Arc is renowned for its intense seismic activity, tsunamis, and volcanic eruptions, and yet relatively less attention has been paid to its eastern segment. This study describes the along-strike variations of the subducting oceanic crust, trench, and accretionary wedge from eastern Java to Sumbawa Island. It investigates the control of subducting plate topography on the deformation of the overriding plate and reveals the influence of subduction on shallow geological hazards. The results show significant segmentation of the subduction structure in the study area, with the western and eastern parts controlled by the subduction of the Roo Rise and the Argo Abyssal Plain, respectively. The seafloor topography and structures of the subducting plate lead to distinct variations of trench and forearc deformation: the subduction of the Roo Rise results in prominent erosion and the development of a narrow and steeply inclined accretionary wedge, while that of the abyssal plain results in a broad and gently sloping accretionary wedge. Both seamount/rise subduction and normal faulting generated by plate bending may trigger geological hazards. These findings provide a theoretical basis for understanding accretion processes of subduction zones, as well as earthquake and tsunami hazards.

The Indian Ocean is one of the most tsunami-prone regions globally, with numerous historical events causing significant loss of life and economic damage. Establishing effective early warning systems is critical for enhancing regional disaster prevention and mitigation capabilities. This study reviews historical tsunami events in the Indian Ocean and their impacts, and conducts an in-depth analysis of three representative cases to examine the relationship between tsunami generation and tectonic settings. We specifically discuss the three primary tsunami generation mechanisms—earthquakes, submarine landslides, and volcanic activity—and analyze their characteristics and potential interactions. Furthermore, we explore the potential use of T-waves in tsunami early warning in the Indian Ocean and evaluate the feasibility of this approach, offering new insights into more efficient early warning strategies for the Indian Ocean in the future.

Enhanced observation and research on the vertical settling gradient variation of siliceous radiolarian remains, an important component of marine settling particles, is conducive to understanding the deep-sea silicon cycle process and the indicative significance of radiolarians in paleoceanographic environmental reconstruction. This study selected two deep-sea regions in the tropical southeastern Indian Ocean. Utilizing a Maxi multinet plankton sampler, continuous stratified sampling of the 0-3000 m water column was conducted across nine layers. Based on the Rose Bengal staining method combined with traditional morphological analysis, this research systematically reveals, for the first time, the settling patterns of siliceous radiolarian remains at different water depths in this region. Vertically, the layer with the highest abundance of radiolarian remains occurs either within or directly below the layer with the highest abundance of living radiolarians. The entire settling process consistently displays a three-layer differentiation pattern for radiolarian remains: the shallow layer serves as the accumulation zone, the middle layer constitutes the stable settling zone, and the deep layer functions as the dissolution zone. Spumellarian dominant species exhibit high stability and strong resistance to dissolution during vertical settling, whereas nassellarian content decreases with increasing water depth, particularly in deeper layers. Regionally, variations in radiolarian remains abundance are related not only to their productivity but also local hydrodynamic environments. For instance, at the southern station, the density, species number, and diversity of remains within the 100-2000 m depth interval are significantly higher than those at the equatorial station, closely corresponding to higher living radiolarian productivity. However, within the 2000-3000 m deep water layer, radiolarian density at the southern station is lower than at the equatorial station, which is potentially related to the lateral transport by deep-water dynamics. The quantitative data on radiolarian remains collected in this study will provide crucial observational evidence and scientific support for estimating radiolarian silicon export flux and its biological pump effect in the tropical eastern Indian Ocean.

This study addresses the scientific question of the spatial differentiation mechanisms of calcium carbonate (CaCO₃) in surface sediments across the 90°E Ridge in the northeastern Indian Ocean, employing a multi-scale analytical approach to elucidate controlling factors and biogeochemical processes. Through bulk and size-fractionated ( > 150 μm, 63-150 μm, 38-63 μm, 25-38 μm, < 25 μm) CaCO₃ contribution analyses of surface sediments from 10 stations, combined with quantitative statistical analysis of scanning electron microscopy (SEM) microfeatures, the following findings were obtained: (1) The CaCO₃ content exhibits significant spatial variability (36.95%-74.76%, mean 56.05%), forming a tripartite gradient pattern of 30%-45%, 45%-60%, and 60%-75%. (2) In regions with water depths above 3000 m, the dominant CaCO₃ component is planktonic foraminiferal shells (> 150 μm, contributing > 65%), while stations near or above the lysocline are dominated by the < 25 μm fine-grained fraction (contribution > 58%). (3) Quantitative microfeature analysis reveals, for the first time, a co-deposition pattern of calcareous dinoflagellate fossils (relative abundance up to 73.68%) with coccoliths and foraminiferal fragments in the 25-38 μm fraction. Further investigations demonstrate that CaCO₃ distribution is governed by a ternary regulatory mechanism involving water depth-dependent dissolution effects, terrigenous clastic input, and siliceous biological dilution. This study innovatively establishes an integrated methodology of “grain-size separation-microscopic statistics-environmental interpretation”, which not only refines theoretical models of CaCO₃ distribution in seamount geomorphic units but also expands the understanding of deep-sea inorganic carbon reservoirs by identifying calcareous dinoflagellate fossils as a novel carbon source. The findings provide a critical case study for comparative research on CaCO₃ preservation mechanisms in global ridge systems and offer vital scientific insights for parameterizing marine carbon cycle models through improved algorithms for size-specific CaCO₃ flux calculations.

The northeastern Indian Ocean Ridge area along the 90°E meridian exhibits complex and unique topographic features. To gain deeper insights into the benthic ecological characteristics, regional biological productivity, and terrigenous input influences across different parts of the ridge, a comprehensive identification and statistical analysis of benthic foraminifera (> 150 μm) was conducted on 13 surface sediment samples from this region. The study revealed that benthic foraminifera in the 150-250 μm size fraction dominated the area, with relative abundances of 60% to 84%, while the fraction larger than 250 μm exhibited lower relative abundances of 16% to 40%. The dominant benthic foraminiferal species were primarily epifaunal and shallow infaunal types. Among the three major benthic foraminiferal shell types, hyaline shells predominated, followed by agglutinated shells, with porcellaneous shells being the least abundant. Although no significant differences in dominant species were observed among stations, distinct regional variations emerged in shell-type proportions and epifaunal or infaunal distributions: the abundance of benthic foraminifera is relatively high on both sides of the northern ridge and relatively low on the ridge itself; the relative content of agglutinated benthic foraminifera is significantly higher in the northeastern side of the study area compared to other areas, and increases with water depth in the central part of the Indian Ocean Ridge. The particles selected for the construction of the shell walls of agglutinated benthic foraminifera are mainly composed of detrital minerals in the northeast, while multi-species planktic foraminifera have been used to build their tests in the central part of the Indian Ocean Ridge. Analysis suggests that benthic foraminifera in the northeast Indian Ocean Ridge area are mainly influenced by the transport of terrestrial materials, surface productivity distribution, and dissolution caused by changes in water depth. In addition, we note for the first time that the content of surface species is much higher than that of epifaunal species in the components larger than 250 μm. We believe this is the result of the adaptive evolution of benthic foraminifera to high-oxygen ecological environments.

The Indian Ocean Dipole (IOD) is an intrinsic climate mode in the Indian Ocean, typically occurring during the boreal fall, influencing weather and climate in surrounding regions and even China. The IOD is affected by both the El Niño-Southern Oscillation (ENSO) and internal variability within the Indian Ocean. However, the quantitative contributions of two types of ENSO, namely the eastern Pacific (EP) and the central Pacific (CP), and internal variability to the IOD remain unclear. Here, a binary combined linear regression method is used to separate and estimate the contributions of these three factors. The results show that internal variability is the primary source of IOD sea surface temperature (SST) changes, accounting for more than 60% of the variance. The contribution of ENSO is about one-third, predominantly driven by the CP ENSO, whereas the EP type tends to exert a stronger influence on the IOD during extreme events. Their influencing mechanisms are different: ENSO affects the Indian Ocean wind field primarily via the Walker circulation, with the efficiency depending on the location of the warming cores (EP vs. CP). In comparison, internal variability tends to induce SST anomalies through oceanic processes within the Indian Ocean, facilitating IOD development. Due to the longer lifetime of El Niño events, a co-occurring positive IOD has a higher chance of transforming into an Indian Ocean basin-wide warming event in the following spring, for which ENSO contributes more than 70% of the transition. Although internal variability does not show a significant statistical relationship with this transition, a strong positive IOD still has the potential to induce subsequent basin-wide warming. These findings improve our understanding of climate modes and inter-basin interactions.

Previous studies on the interannual climate variability in Sri Lanka have primarily focused on precipitation characteristics, while the understanding of the interannual variability of air temperature and its climatic drivers remains limited. This study analyzes the interannual variability of surface air temperature over Sri Lanka and its influencing factors based on high-resolution climate reanalysis data and interannual climate indices of the tropical Indian-Pacific Ocean. The results indicate that the air temperature across Sri Lanka exhibits relatively consistent interannual fluctuations, with larger amplitude variations north of the central highlands and smaller changes in coastal areas. Partial correlation analysis reveals that the interannual variability of air temperature in Sri Lanka is significantly regulated by the El Niño-Southern Oscillation (ENSO), while the influence of the local Indian Ocean Dipole (IOD) is not significant. Further partial regression analysis shows that during El Niño events, the Indian Ocean basin warms as a whole, continuously heating the surrounding atmosphere and affecting air temperature. Meanwhile, enhanced shortwave radiation in the tropical southeastern Indian Ocean and the Bay of Bengal leads to significant land warming, further heating the near-surface air through sensible heat exchange. In contrast, during positive IOD events, the air temperature pattern shows cold anomalies in the eastern Indian Ocean and the Bay of Bengal, and warm anomalies in the western Indian Ocean and the Arabian Sea. As Sri Lanka is located at the transitional zone between these warm and cold anomalies induced by IOD, the net temperature response is relatively weak. These findings enhance the understanding of interannual climate variability in Sri Lanka and its surrounding regions and provide a scientific reference for addressing climate risks such as extreme heat events.

Previous studies have suggested that the mean position of the intertropical convergence zone (ITCZ) rain belt shifted southward due to the cooling of the Northern Hemisphere during the Heinrich Stadial 1 (HS1) early period (approximately 18.3-16.3 cal ka BP). However, recent studies indicate that wet conditions prevailed in the low-latitude region (3°N-9°N) of the Northern Hemisphere during the early HS1 period, while adjacent regions to the north and south were arid. It can be seen that the response and displacement amplitude of the ITCZ to the cooling event in the North Atlantic during early HS1 remain controversial. Marine charcoal records from the Bay of Bengal may preserve critical information about climate-driven palaeo-fire events from the surrounding land. In this study, we observe that the total concentration of charcoal and the percentage of woody charcoal in core YDY09 (located at 9°54′N) decreased to their lowest levels in early HS1, while the percentage of herbaceous charcoal increased. This suggests a sharp reduction in the strength of fire events, consistent with decreased rainfall inferred from the δ¹⁸O records of foraminifera and stalagmites and other proxies. The decline in fire strength may be related to reduced vegetation cover under drier climate and cooler climatic conditions, which aligns with evidence of aridity from low pollen values of evergreen broad-leaved forests in core YDY10 (located at 10°N) and core E87-32B (located at 15ºN) from the Bay of Bengal. During the same period, the charcoal and pollen contents in two cores on Sumatra Island (located at 6°N and 6°S, respectively) also showed humid and arid conditions, indicating that the charcoal and pollen source areas were inside and outside the ITCZ rain belt at that time. Reconstructed results of Indian Summer Monsoon precipitation based on micro-charcoal, pollen, foraminifera, and other indicators are consistent. For the first time, combined charcoal and pollen records reveal the evidence of drought outside the range of 10°N to 6°S in the early stage of HS1, while moist evidence from the 6°N core on Sumatra Island indirectly supports the inference that the ITCZ centered around 6° N during this period.

The climate and surface currents of the northeastern Indian Ocean are controlled by the Indian Monsoon. Its marine primary productivity is the foundation of the ecosystem and connects the atmosphere and ocean carbon cycles. In this study, we carried out a quantitative analysis of coccolith from the marine sediments in Core I105A on the 90°E Ridge in the northeastern Indian Ocean. By examining variations in coccolith absolute abundance and the relative percentages of dominant coccolithophore species, we reconstructed marine primary productivity changes in the northeastern Indian Ocean since the Last Glacial Period. The results show that marine primary productivity in this area experienced three stages since last 54 ka: (1) relatively high during the last glaciation; (2) significantly decreased during the deglaciation; and (3) maintained at low levels during the Holocene. This pattern is generally consistent with the variations of other paleoproductivity proxies in the Bay of Bengal. Comparison with paleoenvironmental records from the Indian Ocean indicates that marine primary productivity decreased when freshwater input to the northeastern Indian Ocean increased due to intensified Indian Summer Monsoon. These findings imply that the evolution of marine primary productivity in the northeastern Indian Ocean since the last glaciation has most probably been driven by seawater stratification associated with Indian Summer Monsoon precipitation, a process regulated by the Earth orbital precession cycle as well.

This paper examines the intraseasonal variability of equatorial deep currents (below 1200 m) in the Indian Ocean, utilizing time series data spanning from 2015 to 2021. These data were obtained from TIOON (tropical Indian Ocean observation net) moorings positioned at 80°E, 85°E, and 93°E on the equator, supplemented by continuous current velocity data from BRAN2022, wind velocity data from JRA-55, and temperature-salinity data from WOA23. Observations reveal that the standard deviation (STD) of zonal current velocities at these locations ranges from 2.5 to 3.1 cm·s⁻¹, while the STD of meridional current velocities ranges from 2.6 to 3.1 cm·s⁻¹. Notably, intraseasonal variability accounts for 88%-91% and 74%-84% of the total current variability for the zonal and meridional currents, respectively, underscoring its significance. Wavelet analysis indicates that the primary period of intraseasonal deep zonal currents is 10-100 days, with a longer period (50-90 days) observed at 80°E and a shorter period (< 50 days) at 93°E. This suggests a blue-shift phenomenon, where the variability in deep currents shifts to higher frequencies toward the east. Additionally, intraseasonal meridional currents exhibit a significant peak at the 60-day period. Equatorial wind stress anomalies are a crucial forcing factor driving intraseasonal variability in deep currents through both direct and reflected wave processes. In the central basin (80°E and 85°E), intraseasonal variability is primarily driven by zonal wind stress anomalies and modulated by a reflected wave process. Energy is transferred to the deep layers via Rossby waves formed by Kelvin waves reflected at the eastern boundary, primarily involving low-order baroclinic modes. Conversely, in the eastern basin (93°E), intraseasonal variability is driven by both zonal and meridional wind stress anomalies and modulated by a direct wave process. Energy is transferred to the deep layers via Yanai waves generated directly west of the current, involving multi-order baroclinic modes. Based on linear wave theory, this study illustrates the energy propagation rays of equatorial beams, emphasizing the critical role of topography in deep circulation dynamics. The flat topography of the central basin facilitates downward and westward energy propagation through reflected wave processes, while the ridge near 90°E may impede downward and eastward energy propagation through direct wave processes. Barotropic conversion (T₄) analysis reveals strong nonlinear dynamics near the 90°E ridge, with significant energy transfer from intraseasonal variability to the mean flow. In contrast, over flat topography, the energy transfer is reversed—from the mean flow to intraseasonal variability—though notably weak. This study enhances our understanding of deep current dynamics and provides observational evidence to improve deep ocean circulation simulations.

Ocean salinity serves as a key indicator of the global water cycle and exerts important controls on oceanic circulation, sea level, and stratification, thereby playing a critical role in marine thermodynamic and dynamic processes. In recent years, salinity variability in the tropical Indian Ocean, particularly its dynamic mechanisms and climatic effects, has attracted growing scientific interest. Using 31 years of satellite observations, in-situ data sets, and model reanalysis data, this study investigates the decadal variability and formation mechanisms of the low salinity tongue in the South Indian Ocean between the equator and 20°S. The results indicate that both the volume and mean salinity of the low-salinity tongue exhibit a quasi-12-year oscillation, which is primarily associated with the Interdecadal Pacific Oscillation (IPO). Further analysis reveals that on decadal timescales, variability in the volume of the upper 50 m low-salinity tongue is mainly driven by local precipitation. Through anomalous atmospheric circulation, sea surface temperature anomalies in the tropical Pacific lead to multi-year precipitation anomalies in the southeastern Indian Ocean, which subsequently alter the westward extension of the surface low-salinity tongue and ultimately govern its volume variability in the upper 50 m. However, in the subsurface layer (50 to 200 m), variability in the volume and average salinity of the low salinity tongue is dominated by freshwater transport associated with the Indonesian throughflow (ITF). During negative IPO phases, wind anomalies over the tropical Pacific trigger oceanic wave adjustments, which enhance the ITF salinity transport. This process subsequently leads to an expansion of the low salinity tongue and a decrease in its average salinity in the southeastern Indian Ocean. Based on the three-dimensional variability of the low salinity tongue, this study reveals the relationships between the volume and average salinity of the tongue at different depths and local freshwater forcing, as well as salinity transport by the ITF, thereby contributing to an improved understanding of how regional water mass changes respond to long-term climate variability.

In marine areas, the study of the gravity field is of great significance for understanding marine dynamic processes, submarine geological structures, and global climate change. High-precision marine gravity exploration technology has become the current development trend in marine gravity field investigation. The R/V “Shiyan 6” of the South China Sea Institute of Oceanography, Chinese Academy of Sciences, is equipped with a DGS AT1M-11 marine gravimeter, which is characterized by high precision, high reliability, and the ability to conduct global dynamic measurements. Before the gravimeter was put into use, the accuracy was evaluated, including static tests and internal conformity accuracy tests, all of which met the requirements of the Marine Survey Measurement Specification. The measured data collected in the northeastern Indian Ocean in 2022 was compared with the gravity field data from the Gravity Recovery and Climate Experiment (GRACE), which showed a basically consistent trend. Additionally, the results of the pre- and post-cruise benchmark tests of the voyage and the gravity intersection point difference are −0.73 mGal and 1.15 mGal respectively, indicating that the data of this instrument is highly accurate and can be used for high-precision marine gravity measurements. The gravitational field of the 90°E Ridge north of 10°S is not proportional to the water depth, suggesting differences in equilibrium compensation for crustal thickness and that the ridge consists of non-homogeneous material. Gravity modeling of the free-air gravity anomalies obtained from the measured data indicates the presence of a thickened crust beneath the 90°E Ridge, associated with compensation for topographic relief loads.

Seabed sediment type maps play a crucial role in marine environmental analysis, marine engineering construction, and the exploration of marine mineral resources. This paper proposes a novel mapping method for seabed sediment type assignment based on the Folk classification. Using spatial interpolation analysis of surface sediment data from the southwestern waters of Hainan Island, a Folk classification system was developed. After data classification, a grid was overlaid to integrate with the Folk classification system. Subsequently, grid erosion was performed to generate the seabed sediment type map. In a comparative analysis of interpolation methods, including Sibson, IDW (inverse distance weighting), Kriging, and Spline, the Sibson method was used as the foundation for mapping in this study. This method features a simple operational process, high mapping efficiency, and is unaffected by subjective factors, resulting in relatively accurate mapping and strong practicability. It can be applied to the mapping of seabed sediment types at different scales or with different sampling station spacings, demonstrating broad potential for practical application.

Marine cable insulation oil sensors are primarily applied for detecting extremely low concentrations of insulating oil in seawater. Compared to conventional water-oil sensors, the detection of insulating oil imposes stricter requirements on sensor calibration processes and the preparation of standard solutions. This paper introduces a novel calibration scheme that features a non-contact inverted calibration structure designed to reduce contamination risks, thereby enhancing operational convenience and calibration accuracy. Additionally, ultrasonic emulsification technology is employed to prepare standard solutions that more closely resemble the natural water-oil emulsion state formed during seawater oil spill accidents. A systematic investigation into calibration-influencing factors reveals that environmental light interference is negligible, whereas controlling the liquid level height is critical to minimize signal interference at the gas-liquid interface. A subsequent comparative analysis with industry-standard methods demonstrates that the relative deviation of the calibration results under this scheme ranges from 6% to 10%, exhibiting excellent accuracy within the target concentration range. This method provides highly reliable technical support for marine ecological environment monitoring.

As secondary producers, zooplankton play an important role in marine food webs and biogeochemical cycles. Due to their small body size, rapid metabolism, and passive drifting lifestyle, zooplankton can respond sensitively to marine environmental changes, making them effective indicators of oceanic variability. Based on a review of scientific investigations of zooplankton in the South China Sea, this paper summarized current knowledge on species composition in the South China Sea, and compared and analyzed the distribution of zooplankton communities in typical ecological habitats (such as the Pearl River Estuary, Daya Bay, coral reefs, and the deep sea) as well as in the northern and southern waters of the South China Sea. It also discussed the effects of monsoons, monsoon-driven ocean currents, water masses and habitat heterogeneity on zooplankton community structure. In light of current hotspots and challenges under the background of climate change and anthropogenic stress, this article pointed out the shortcomings in zooplankton research in the South China Sea and proposed future research directions in biodiversity, ecological functions, and biological oceanography. The aim is to provide a scientific basis for biodiversity conservation, biogeochemical cycle studies, sustainable utilization of marine resources, and scientific support for predicting the adaptability of marine ecosystems to climate change in the South China Sea.

To address the limitations of penetration analysis methods for jack-up platforms in multi-layer soils, this paper systematically reviews the ISO (international organization for standardization) methods and latest proposed approaches in two-layer and multi-layer soils (three or more layers). Additionally, field-measured data collected from eastern Guangdong are evaluated through back analysis. The study reveals that the ISO methods neglect issues such as soil layer interface variations, soil plugging effects, and clay strain rate and strain softening. While new methods based on soil failure mechanisms improve prediction accuracy, they are only applicable to specific soil conditions and lack general applicability in practical engineering. Through back analysis, this paper further clarifies the applicability of different methods under complex geological conditions and proposes that future research should focus on developing universal calculation methods that account for realistic soil failure mechanism, soil layer interface variations, and soil plug effects, so as to enhance the reliability of penetration risk assessment for spudcan in multi-layered soil profiles.

Cnoidal waves can effectively characterize wave motion in shallow water regions, holding significant practical value for the precise description of nearshore hydrodynamic processes. To investigate the propagation and evolution patterns of cnoidal waves over typical reef-lagoon systems, this study conducted physical model experiments in a wave flume, with particular focus on the effects of incident wave height, reef flat submergence, and wave period on wave nonlinear characteristics, energy dissipation, and hydrodynamic parameters. The results demonstrate that reef topography substantially enhances wave nonlinearity, with conspicuous waveform steepening in the fore-reef slope zone and sawtooth-shaped wave profiles accompanied by phase lags over the reef flat. Increased incident wave height induces stronger nonlinear effects, promoting higher harmonic growth and significantly enhancing wave setup and run-up, while reducing reflection coefficients due to enhanced transmission. However, greater reef flat submergence weakens nonlinear wave effects and causes a monotonic decrease in reflection coefficients. Under deeper water conditions, vertical momentum flux intensifies, and run-up exhibits nonlinear growth. The influence of wave period manifests complex patterns: the maximum wave energy concentration and the most pronounced higher harmonics occur at T = 2.25s. Short-period waves (T < 2.25s) experience intensified shoaling deformation that aggravates waveform distortion, whereas long-period waves (T > 2.25s) exhibit characteristic attenuation through energy dissipation. This research provides critical experimental evidence for coral reef ecosystem conservation and coastal engineering design.

Studying changes in estuarine saltwater intrusion patterns can deepen the understanding of its mechanism and help better ensure the safe use of freshwater resources. Based on measured topographic and salinity data, this paper analyzes changes in river regime and saltwater intrusion patterns in the Changjiang Estuary. A numerical model is used to reveal the causes of these pattern changes. From 2007 to 2021, major reclamation projects in the estuary led to channel narrowing and significant local topographic changes. Due to severe siltation on the south side of the lower North Branch and the emergence of a new sand body at its upper end, the channel volume decreased by 33.33% and 13.26% (with the negative sign denoting northward transport from the south), respectively. Salinity observations in the dry seasons of 2007 and 2025 indicate a significant weakening of saltwater intrusion and of the North Branch saltwater backflow into the South Branch. In the North Channel, saltwater intrusion weakened under prevailing climatic winds but intensified under strong northerly winds. Overall, the saltwater intrusion pattern in the Changjiang Estuary has changed. Numerical simulations, considering multi-year monthly mean river discharge and wind, show that from 2007 to 2021, saltwater intrusion weakened significantly in the North Branch, weakened in the upper and most middle reaches of the North Channel, but intensified significantly in the South Channel, North Passage, and South Passage. The saltwater backflow from the North Branch into the South Branch was greatly reduced, resulting in weakened saltwater intrusion in the South Branch, which is conducive to water intakes at source areas. In the North Branch, the tidal prism decreased by 2.88×10⁸ m³ and 1.98×10⁸ m³ during spring and neap tides in February, respectively. The net water flux into the South Branch decreased by 423 m³·s^-1 and 369 m³·s^-1, and the net salt flux into the South Branch decreased by 10.06 kg·s^-1 and 1.10 kg·s^-1. The variation of net unit-width salt flux in the upper North Branch also indicates a major reduction in salt transport to the South Branch. Significant North Branch backflow observed in 2007 had nearly disappeared by 2021. In the North Channel, during February spring and neap tides, the tidal prism decreased by 1.92×10⁸ m³ and 1.86×10⁸ m³, while the net water flux increased by 857 m³·s^-1 and 1379 m³·s^-1. The water diversion ratio increased by 12.79% and 7.79%, and the net seaward salt flux decreased by 2.28 kg·s^-1 and 5.42 kg·s^-1. These changes explain the weakening of saltwater intrusion in the upper and most middle reaches of the North Channel. The obvious increase in the North Channel’s water diversion ratio (corresponding to a decrease in the South Channel’s ratio) also accounts for the intensification of saltwater intrusion in the South Channel, North Passage, and South Passage. A localized salinity rise in a small part of the North Channel during spring tide is caused by a significant increase in the net salt flux from the North Passage into the North Channel. This paper reveals the hydrodynamic causes of the changing saltwater intrusion pattern in the Changjiang Estuary through changes in net water flux, net salt flux, tidal prism, and water diversion ratio.

Locally generated typhoons in the South China Sea (SCS), referred to as “local typhoons”, are characterized by strong abruptness, complex trajectories, and high forecasting difficulty, posing significant challenges to regional disaster prevention and mitigation. Systematic statistical research is urgently needed to enhance understanding of their genesis and evolution patterns. For comparison, typhoons originating in the Northwest Pacific outside the SCS and entering the region are termed “non-local typhoons”. Current research on local typhoons remains fragmented, with insufficient systematic analysis of long-term data and inadequate comparison with non-local typhoons, limiting the in-depth understanding of their climatic characteristics. Based on the China Meteorological Administration (CMA) Northwest Pacific typhoon best-track dataset (1949—2024), this study systematically analyzes the frequency, intensity, trajectories, and genesis distribution of local typhoons in the SCS, with comparisons to non-local typhoons, to reveal their spatiotemporal variation patterns. Key findings include: 1) The annual average number of local typhoons is 5.86, showing a unimodal seasonal distribution with peak occurrence from June to October (accounting for 78.9% of the total), especially in September (21.7%), and exhibiting a significant decreasing trend (-0.05·a^-1); 2) Local typhoons have an annual average minimum central pressure ranging from 965.0 to 999.5 hPa, also showing a significant decreasing trend, predominantly follow westward or northwestward trajectories, and mostly originate in the central and northern SCS; 3) Compared with non-local typhoons, local typhoons are generally weaker (only 13.7% reach typhoon intensity or above, versus 61.7% for non-local typhoons), but intensify more rapidly, with higher landfall proportions, greater abruptness, and stronger locality. This study provides critical data support for understanding the formation mechanisms and climatic patterns of local typhoons, while offering a reference for improving regional disaster early warning capabilities and risk management strategies.

Hurricane Paulette (2020) underwent two critical track shifts over the North Atlantic: first, a turn from northwestward movement toward North America to northeastward movement, followed by extratropical transition; second, a shift from a northeastward track to a southward track, subsequently regenerating into a tropical storm. To investigate the influence of multi-level steering flows and surrounding circulation systems on these two turning processes, numerical simulations of Paulette were conducted using the Weather Research and Forecasting (WRF) model. The results show that: 1) The regeneration of Paulette was closely associated with its anomalous southward turning, during which it moved into a region of warm sea surface temperature, acquiring favorable conditions for redevelopment. 2) During the movement of Paulette, the steering flow exhibited significant vertical variation and evolution. The northwestward movement was primarily governed by low- to mid-level steering flows, while upper-level steering flows became more dominant during the northeastward turn and northeastward movement. During the southward-turning stage, low-level steering flows shifted from westerlies to northerlies, gradually extending upward to the upper levels and forming a deep northerly flow, ultimately leading to an abnormal southward turning of the hurricane's track. 3) In its early developmental stage, Paulette was located to the southern periphery of the subtropical high and moved northwestward under its blocking influence. As the hurricane intensified, the subtropical high weakened and broke, allowing Paulette to move northward into a mid-latitude westerly trough and turn northeastward under the influence of southwesterly flow ahead of the trough. However, as the high-pressure ridge to the south of Paulette continued to strengthen with a significant increase in meridional extent, the hurricane ultimately turned southward ahead of the ridge.

As a key indicator of global climate change, ocean heat content (OHC) accurately reflects the net energy budget of the Earth system, and its spatiotemporal variations significantly influence the genesis and intensification of typhoons. Based on the long-term, multi-parameter GDCSM_Argo global ocean reanalysis dataset, this study preliminarily investigates the regulatory and responsive roles of upper- and middle-layer OHC in typhoon activity using lagged regression and correlation analysis. The results demonstrate that near-surface OHC directly modulates typhoon occurrence frequency, while middle and deep OHC sustains typhoon energy through vertical mixing, with all layers exhibiting a lagged response of 1 to 6 months to typhoon activity. The typhoon-induced “cold wake” effect significantly reduces ocean stratification stability along storm tracks, particularly in the typhoon intensification zone (10°—25°N, 120°—145°E), where areas of low Richardson number values below the mixed layer highly coincide with the position of the typhoon’s maximum wind speed. The OHC-typhoon relationship exhibits notable sensitivity to anomalous climate conditions. During El Niño events, typhoons move eastward and affect areas with deeper thermocline layers, making it easier for wind stirring to penetrate the subsurface and transport heat downwards, temporarily weakening stratification. During La Niña events, the number of typhoons increases relatively and their paths shift westward, with typhoons predominantly active in the high-heat-content western Pacific. These findings provide theoretical foundations for further research on ocean-atmosphere interaction mechanisms governing extreme weather events and validate the GDCSM_Argo reanalysis data as a robust resource for systematic air-sea interaction studies.

The sea surface current system in the tropical western Pacific is not only of great significance to local air-sea interactions but also extends its influence to the global level. However, at present, the understanding of its evolution during hydrological, ecological, climatic and environmental changes, as well as its response mechanism under the influence of the El Niño-Southern Oscillation (ENSO) cycle, is still unclear. To explore this issue in depth, this paper focuses on the changes in the ecological-hydrological-climatic environment of the tropical western Pacific from 2003 to 2023 and analyzes its response to ENSO events. The study finds that there are three high-value regions of sea surface chlorophyll a concentration in the tropical western Pacific: the coastal zone (with an average value of 0.152 μg·L^-1), the Halmahera warm eddy zone (with an average value of 0.130 μg·L^-1), and the source region of the North Equatorial Countercurrent (with an average value of 0.109 μg·L^-1). As important carriers of nutrients, the New Guinea Coastal Current and the Mindanao Current transport nutrient-rich coastal seawater and jointly converge into the eastward-flowing North Equatorial Countercurrent, contributing to the formation of these three high-value regions. At the same time, the cyclonic upwelling at the center of the Mindanao cold eddy lifts the nutrient-rich deep seawater to the surface, making the chlorophyll a concentration in this region (with an average value of 0.059 μg·L^-1) slightly higher than that in the general open ocean (with an average value of 0.048 μg·L^-1). The concentration of sea surface chlorophyll a exhibits significant variations in different stages of ENSO events. During El Niño events, the velocity of the New Guinea Coastal Current increases, which indirectly leads to an overall rise in the concentration of sea surface chlorophyll a; during La Niña events, the velocity of the New Guinea Coastal Current decreases, which indirectly causes an overall decline in the concentration of sea surface chlorophyll a. Based on these findings, this paper proposes two brief response mechanisms linking ecological-hydrological-climatic processes in the tropical western Pacific to the El Niño and La Niña events. (1) During El Niño events, the North Equatorial Countercurrent, the New Guinea Coastal Current, and the upwelling in the Mindanao cold dome all enhance significantly. By accelerating the coastal current and strengthening the upwelling, they create a “nutrient pump” effect, which promotes the upwelling of deep nutrients and ultimately leads to a significant increase in chlorophyll a concentrations in most regions. (2) During La Niña events, the North Equatorial Countercurrent, the New Guinea Coastal Current and the upwelling in the Mindanao cold dome all weaken significantly. By slowing down the flow velocity and inhibiting the upwelling, they diminish the “nutrient pump” effect and ultimately reduce the chlorophyll a concentration in most regions. These results not only highlight the broad prospects of utilizing the ENSO cycle in the research of local and global hydrological and climate changes, as well as the carbon cycle, but also provide important theoretical support for a comprehensive understanding of the Earth system and carry profound scientific significance.

To explore the spatiotemporal changes, trends, and environmental impact factors of dissolved organic carbon (DOC) in Sanya Bay, water physicochemical parameters collected from 2008 to 2023 in Sanya Bay were used as the input data for analysis based on stepwise regression analysis (SR) and random forest algorithm (RF). The results showed that the DOC concentration increased significantly from 2008 to 2018 due to coastal development in Sanya. A subsequent decline in DOC concentration might have resulted from the combined effects of reduced land-based inputs during the COVID-19 pandemic and the government’s efforts to strengthen the management of the marine environment. High-value zones of DOC were observed on the coastal areas of Sanya Bay. The mean value of DOC concentration was (2.00 ± 1.34) mg·L^-1, which maintained at a lower level compared to other semi-enclosed bays. Both SR and RF results indicated that DOC concentrations generally exhibited an initial increase followed by a decrease with rising temperature, total alkalinity, and silicate concentration, and showed significant negative correlations with total phosphorus, dissolved oxygen, and phosphate. These findings demonstrate that temperature, total alkalinity, total phosphorus, silicate, dissolved oxygen, and phosphate are the main factors affecting DOC in Sanya Bay.

Mangrove forests, located at the interface of marine and terrestrial ecosystems in tropical and subtropical regions, harbor highly productive environments that support diverse microbial communities. These communities play a pivotal role in sustaining mangrove ecological functions and driving biogeochemical cycles. This study investigated the Ximen Island mangrove ecosystem in Zhejiang Province, employing high-throughput sequencing to systematically analyze the bacterial communities in surface sediments. We explored seasonal variations in bacterial diversity and assessed their correlations with environmental parameters. Results revealed that the sediment bacterial community in Ximen Island mangroves was dominated by Proteobacteria (39.11%), Desulfobacterota (10.02%), and Bacteroidota (9.17%). Among these, Proteobacteria and Desulfobacterota exhibited significant enrichment in spring, while Bacteroidota enriched in summer. Bacterial diversity indices exhibited significant seasonal dynamics: The richness index peaked in winter (2136 ± 235), while the Shannon index in spring (6.05 ± 0.15) was significantly lower than in autumn and winter (P < 0.05). Principal component analysis (PCA) and linear discriminant analysis effect size analyses (LEfSe) results demonstrated seasonal specificity in bacterial community composition across spring, autumn, and winter.

Halophila ovalis is a dioecious seagrass species capable of both sexual reproduction and clonal propagation. This study investigated the seasonal growth and reproductive characteristics of H. ovalis population through quarterly monitoring in Zhulin, Guangxi, with particular focus on reproductive differences between female and male individuals at the center and edges of seagrass patches. Results showed that the density, coverage, and biomass of H. ovalis peaked in spring, reaching 47% (±9%), (2967.36 ± 661.96) ind·m^-2, and (37.68 ± 8.85) gDW·m^-2, respectively. Annual averages were 38% (±14%) for coverage, (1851.02 ± 1036.81) ind·m^-2 for shoot density, and (27.60 ± 13.97) gDW·m^-2 for biomass. Sexual reproduction occurred in spring, with distinct female and male flowers. Both seagrass density and biomass were significantly higher at patch centers than at edges - a pattern also mirrored in macrobenthic biomass. Male individuals exhibited significantly shorter internode lengths than females, though no significant differences were observed between center and edge positions within either sex. These findings provide fundamental insights into the reproductive ecology of H. ovalis, offering scientific support for the conservation and restoration of seagrass beds.

Seismic reflectivity inversion based on basis pursuit denoising produces sparse solutions through the application of l₁ norm regularization. However, due to the presence of the regularization term, there is always a deviation between the solution obtained by basis pursuit denoising and the true solution. To reduce this deviation, this paper introduces the “adding back the residual (ABR)” strategy in the seismic reflectivity inversion, thereby improving the accuracy of the solution. The ABR strategy uses a moderate trade-off factor to iteratively perform the Fast Iterative Soft Thresholding Algorithm (FISTA) to solve the objective function of basis pursuit denoising, and the residuals obtained each time are continuously added back to the original input. Compared with a single solution using FISTA, the solution obtained by FISTA combined with the ABR strategy is closer to the true solution. In this paper, this method is applied to the Wenchang Formation reservoir in the Zhuyi Depression of the Pearl River Mouth Basin in the South China Sea, and calcareous sandstone and beach-dam sandstone are effectively distinguished through high-precision impedance inversion results.

As an important economic microalga, the efficient extraction and comprehensive utilization of bioactive compounds from Spirulina are crucial for enhancing its value. This study investigated the effects of different extraction sequences on the extraction efficiency, characteristics and economic benefits of phycobiliproteins, lipids, and polysaccharides from Spirulina. Six sequential extraction protocols were designed by integrating low-temperature extraction (phycobiliprotein), 95% ethanol extraction (lipid) and hot water extraction (polysaccharide), including 1) phycobiliprotein-lipid-polysaccharide (PLS); 2) phycobiliprotein-polysaccharide-lipid (PSL); 3) polysaccharide-phycobiliprotein-lipid (SPL); 4) polysaccharide-lipid-phycobiliprotein (SLP); 5) lipid-phycobiliprotein-polysaccharide (LPS); and 6) lipid-polysaccharide-phycobiliprotein (LSP). The extraction efficiency and characteristics of bioactive compounds were evaluated using UV-Vis absorption spectra, three-dimensional fluorescence spectra, infrared spectra, fatty acid composition, and monosaccharide composition. The results showed that phycobiliproteins should be extracted preferentially (yield: 68.29% in PLS, 66.77% in PSL), while heating or ethanol pretreatment induced its denaturation (yield < 8%). The results of absorption spectra and fluorescence spectra show that the phycobiliprotein quality was better in the PLS and PSL groups. Lipid extraction efficiency varied significantly with extraction sequence (94.07% in LSP vs 66.76% in PSL), while the fatty acid composition remained stable. Polysaccharide extraction efficiency declined markedly after protein or lipid extraction (71.80% in SPL, 39.90% in LSP and 19.57% in PSL). Infrared spectroscopy showed that the polysaccharides in each group had stable structures and there was no significant difference in monosaccharide compositions. Residual biomass analysis revealed the highest protein content in LPS-treated microalgal residue (71.4% DW). Sequential extraction enabled the recovery of phycobiliproteins, lipids and polysaccharides, but the extraction order critically influenced both yields and quality. The PLS sequence achieved the maximum economic value (162 RMB·kg^-1), tripling the value of raw Spirulina powder (40 RMB·kg^-1). This study provides theoretical and technical foundations for the full-component valorization of Spirulina biomass.

As a key tourist area in Shenzhen, Dapeng Bay faces an annual accumulation of hundreds of tons of beach and marine debris. This study focuses on the Dapeng Bay region, establishing a marine numerical model based on the finite volume community ocean model (FVCOM). Simulated flow and wind field data were integrated into the Lagrangian particle-tracking model OpenDrift to investigate the migration patterns of marine debris in Dapeng Bay, combined with observational data from drift buoys. The results indicate that the prevailing winds in Dapeng Bay are easterly, northeasterly, and southeasterly. Under these wind conditions, more than 70% of the nearshore floating debris in the northern and eastern parts of Dapeng Bay accumulates in Yantian Port and the four Hong Kong islands (Crooked Island, Wong Nai Chau, Ngo Mei Chau and Double Island). Therefore, daily marine debris cleanup efforts in Dapeng Bay should prioritize the above areas. Through comparative experiments across different months and tidal conditions, this study reveals that wind direction primarily governs the overall movement trajectories of marine debris, wind speed influences drift duration and distance, and tidal variations affect stranding zones and the quantity of debris reaching different regions. The movement and distribution patterns of marine debris in Dapeng Bay uncovered in this study can provide valuable references for debris cleanup operations.

Exotic mangrove species have been widely introduced in mangrove restoration projects across China due to their adaptability and high afforestation efficiency. However, their potential ecological invasion risks remain controversial, and systematic evaluations of their effects on ecosystem health and service functions are still lacking. This study investigated three representative mangrove ecosystems located in eastern Guangdong (Gaoshawei), western Guangdong (Shuidong), and the Pearl River Delta region (Yanzhou), based on field surveys conducted in 2024. A comprehensive evaluation of ecosystem health and ecosystem service values was conducted, incorporating key variables such as the proportion of exotic mangrove species, water quality, and biodiversity. Results showed that all three mangrove ecosystems were in sub-healthy condition, with per-unit-area ecosystem service values of 31.9×10⁴CNY·hm^-2 in Yanzhou, 27.5×10⁴CNY·hm^-2 in Shuidong, and 27.1×10⁴CNY·hm^-2 in Gaoshawei. The proportion of exotic species showed a significant negative correlation with both health index and ecosystem service value. A linear mixed-effects model revealed that for every 1% increase in exotic species proportion, the health index declined by 0.936, and the service value decreased by 1.456×10⁴CNY·hm^-2. These findings highlight the multidimensional impact of exotic mangrove introductions on ecosystem structure and function. This study proposes restoration strategies that emphasize native species, water quality improvement, and enhancement of ecological functions, providing scientific guidance for exotic mangrove management and functional restoration.

Seagrass bed ecosystems have important ecological service functions, and analyzing their threat degree and influencing factors is helpful for proposing targeted conservation strategies for these ecosystems. Focusing on the seagrass bed ecosystem of Hainan Island, this study integrates survey data, historical records, and literature. The IUCN (International Union for Conservation of Nature) Red List of Ecosystems assessment method was adopted to evaluate the threat status of these ecosystems, determine their degree of endangerment and explore the impacts of both human activities and natural factors. Corresponding conservation countermeasures are proposed. The results show that the seagrass bed ecosystems in Wenchang and Sanya are facing a Critically Endangered (CR) situation, while those in Lingshui are Endangered (EN). Ecosystems in Qionghai are assessed as Vulnerable (VU), while those in Chengmai and Danzhou are classified as Near Threatened (NT) and Least Concern (LC), respectively. The seagrass bed ecosystem across Hainan Island is under multiple pressures, with coastal reclamation and fishing activities being the dominant factors of degradation, followed by environmental pressures imposed by sewage discharge and aquaculture. Additionally, climate change factors, such as tropical cyclones, also exert a certain degree of influence. In view of this, this study proposes strengthening the regulation of fishing activities, advancing research on seagrass asexual reproduction, and establishing long-term monitoring of seagrass health and ecological connectivity to promote the sustainable development of the seagrass bed ecosystem in Hainan Island.