Phytoplankton blooms are complex environmental phenomena driven by multiple factors. Understanding their relationships with meteorological factors and climate oscillations is essential for advancing data-driven and hybrid statistical-dynamical models. However, these relationships have rarely been investigated across different temporal scales. This study employs wavelet transform coherence and multiple wavelet coherence to examine the multiscale and multivariate relationships between phytoplankton blooms, meteorological factors, and climate oscillations in eight large marine ecosystems of the western North Pacific. The results reveal that all phytoplankton blooms in the studied ecosystems exhibit significant annual oscillations, while seasonal climate patterns demonstrate either unimodal or bimodal distributions. A comparison of the wavelet transform coherence and multiple wavelet coherence results indicates that meteorological factors primarily drive short-period variations in phytoplankton blooms, whereas climate oscillations exert more influence on long-term changes. The explanation of phytoplankton blooms increases as the driver factors increase, but there are also some decreasing due to the collinearity between different factors. The sea-air temperature difference emerges as the most significant driving factor, with its mechanisms varying across marine ecosystems: one type influences mixed-layer depth, while the other arises from interspecific differences in temperature sensitivity. Furthermore, the results underscore the importance of integrating non-dominant large-scale circulation indices with predominant meteorological factors for a more comprehensive understanding.

By establishing a distribution and environmental factor database of 21 typical harmful dinoflagellates in global waters, the MaxEnt model was used to predict shifts in the habitat of harmful dinoflagellates in Chinese waters under global climate change. The results revealed that offshore distance was the most important predictive factor and that surface seawater temperature (SST), primary productivity, and nitrate concentration were the key ecological factors influencing the distribution of harmful dinoflagellates. Under the low greenhouse gas emission scenario defined by the Intergovernmental Panel on Climate Change (IPCC), by approximately 2050, 17 of the 21 harmful dinoflagellate species in high-suitability areas (HSA) will migrate northward, six species will migrate eastward, and six species will expand their HSA. By 2100, approximately 18 of the 21 harmful dinoflagellate species in HSA will have migrated northward, seven species will have migrated eastward, and four species will have expanded their HSA. Notably, the HSA content of highly toxic Alexandrium minutum is expected to increase by 13.4% and 9.4% by 2050 and 2100, respectively. Under the high greenhouse gas emissions, there will be 17 species migrating northward, 6 species migrating eastward, and 4 species increasing in their size in HSA by 2050; moreover, there will be 16 species migrating northward, 2 migrating eastward, and 4 species according to their size of HSA by 2100. Specifically, the HSA of A. minutum is predicted to increase by 7.0% and 25.9% by 2050 and 2100, respectively. Notably, A. ostenfeldii, which is currently seldom present in the China seas, is predicted to exhibit an HSA in most coastal areas of the Yellow Sea, the Bohai Sea, the Hangzhou Bay, the Zhejiang Coast, and the Beibu Gulf of the South China Sea. Conversely, the HSA of Noctiluca scintillans, a typical red-tide species, will be reduced by 7%–90%. The northward migration of Karenia mikimotoi exceeded 100 km and 300 km under low and high greenhouse gas emission scenarios, respectively. These changes underscore the significant impact of climate change on the distribution and habitat suitability of harmful dinoflagellates, thus indicating a potential shift in their ecological dynamics and consequent effects on marine ecosystems.

As our understanding of ecology deepens and modeling techniques advance, species distribution models have grown increasingly sophisticated, enhancing both their fitting and predictive capabilities. However, the dependability of predictive accuracy remains a critical issue, as the precision of these predictions largely hinges on the quality of the base data. We developed models using both field survey and remote sensing data from 2016 to 2020 to evaluate the impact of different data sources on the accuracy of predictions for Scomber japonicus distributions. Our research findings indicate that the variability of water temperature and salinity data from field suvery is significantly greater than that from remote sensing data. Within the same season, we found that the relationship between the abundance of S. japonicus and environmental factors varied significantly depending on the data source. Models using field survey data were able to more accurately reflect the complex relationships between resource distribution and environmental factors. Additionally, in terms of model predictive performance, models based on field survey data demonstrated greater accuracy in predicting the abundance of S. japonicus compared to those based on remote sensing data, allowing for more accurate mastery of their spatial distribution characteristics. This study highlights the significant impact of data sources on the accuracy of species distribution models and offers valuable insights for fisheries resources management.

The proposed study focuses on the reported oil spill detection and assessments of oil impacts on marine ecosystems. Five selected oil spills, including those in East China Sea, Balikpapan Bay, Red Sea, Mauritius coast, and Colombo coast were detected using the Sentinel-1 satellite dataset. Sentinel-2/Landsat 8, and Sentinel-5 Precursor (S-5P) satellite datasets were utilized to observe the impacts of oil spills on vegetation cover and air quality respectively. Synthetic aperture radar-based oil spill detection techniques are effective in monitoring oil pollution. Impacts of oil spills on vegetation are monitored via different vegetation indices. The East China Sea spill moved around 190 km from the source point. The area of vegetation cover impacted by the Balikpapan Bay oil spill was 118 km². Near real-time data of different toxic gases from S-5P were analyzed for Sri Lanka and the Red Sea using the Google Earth Engine. It is concluded that wind speed was between the range of 3 m/s to 9 m/s that is favorable for the oil spill detection, and it is also observed that wind direction had impacts on oil spill movement as well. Vegetation Indices provide highly reliable results for the four events but the Red Sea oil spill findings were not satisfactory due to low vegetation cover in this area.

Based on in-situ observations in the East China Sea (ECS) during October 2021, we investigated a cross-shelf penetrating front (PF) in the inner shelf and explored its potential biogeochemical-ecological effects from a multidisciplinary perspective. The results show that a pronounced tongue-shaped PF was present at the southeast of the Hangzhou Bay, with salinity of 29−32 and a seaward horizontal penetration scale of ~200 km. It mainly occurred in the upper layers, and a spatial separation existed between this PF and the bottom salinity front in the northern coastal region off Zhejiang. In contrast, the salinity fronts at surface and bottom were well matched in the southern coastal area. Compared to the surface-to-bottom consistent coastal front in the southern region off Zhejiang, a stronger thermocline and halocline were sustained in the northern PF-dominated region, and suitable conditions could be achieved for phytoplankton growth and accumulation. The in-situ observed high-chlorophyll a (Chl a) zone in a seaward tongue shape was further an important indicator or signal for PF occurrence, and it was responsible for the decoupling of nutrient distributions and PF. The southern coastal front off Zhejiang might largely restrict the seaward transport of nutrients, and the dynamic environment under weak stratification in this region was disadvantageous for the growth of phytoplankton; thus the Chl a content was maintained at a relatively low level near the southern coastal region. Our results demonstrate that the PF combined with the coastal front may play an important role in shaping/regulating hydrodynamics, nutrient distributions and the Chl a regime over the inner ECS shelf.

Estuaries are often a significant source of atmospheric CO₂. However, studies of carbonate systems have predominantly focused on large estuaries, while smaller estuaries have scarcely been documented. In this study, we collected surface and bottom seawater carbonate samples in the subtropical Jiulong River Estuary across different tidal levels from 2019 to 2021. The results showed that estuarine mixing of freshwater from the river with seawater was the dominant factor influencing the estuarine carbonate system. Moreover, estuarine mixing is concomitantly impacted by the net metabolism of biological production and decomposition, groundwater input, release of CO₂ from the estuary, and precipitation or dissolution of calcium carbonate. The estuarine partial pressure of CO₂ (pCO₂) varied from 530 μatm to 7715 μatm, which represents a strong source of atmospheric CO₂. The mean annual air-sea CO₂ flux estimated from three different parameterized equations was approximately (25.63 ± 10.25) mol/(m²·a). Furthermore, the annual emission to the atmosphere was approximately (0.031 ± 0.012) Tg C, which accounts for a mere 0.0077%−0.015% of global estuarine emissions. Dissolved inorganic carbon (DIC), total alkalinity (TA) and the pCO₂ exhibited high variability throughout the tidal cycle across all cruises. Specifically, the disparities observed between DIC and TA during low and high tides at identical stations during all cruises ranged from approximately 15% to 30%. The variance in the pCO₂ was even more pronounced, ranging from approximately 30% to 40%. Thus, tidal discrepancies may need to be taken into consideration to estimate the CO₂ flux from estuarine systems more accurately.

Trace metals emitted from human activities may have penetrated into the deep seas, and the underlying control mechanisms remain poorly understood. Sinking particles collected by moored time-series sediment traps from the northern South China Sea (NSCS) basin showed significant enrichment of anthropogenic aerosol Pb relative to lithogenic Fe. Total mass flux was primarily driven by seasonal primary production, and significant positive correlations were found between Pb/Fe flux and major biogenic components, indicating the crucial role of the biological pump in Pb/Fe scavenging in the water column. Notably, Pb exhibited 30−50 times higher affinity to biogenic components than Fe. A comparison was made between the enrichment factors of Fe and Pb in aerosols, euphotic particles, and sinking particles, which revealed that Pb exhibited significantly higher particle reactivity than Fe. This higher particle reactivity may encompass processes such as adsorption/desorption, bioaccumulation and decomposition release. The differential scavenging behavior of Pb suggested that the majority of Pb was rapidly scavenged in the euphotic zone and was preferentially released for accumulation in the twilight zone. This accumulation may further outflow through the Luzon Strait and result in the high dissolved Pb concentration observed in the subsurface water columns in both the NSCS and western Pacific Ocean. The rest of anthropogenic Pb in sinking particles tended to penetrate into deeper water layers and continue to be released below the twilight zone. These findings provide new insights into the biogeochemical cycling of trace metals originating from anthropogenic aerosols in marginal seas and serve as an example of the fate of other anthropogenic atmospheric pollutants.

Ridges are common features found on continental shelves and understanding their formation processes is crucial for sedimentology, stratigraphy, and geological engineering. This study investigates the development of ridges on the broad shelf of the East China Sea using a core (DH03) and associated seismic profile. Lithology analysis of the core revealed a 50 m thick shallow sandy sequence which consisted mainly of silty fine sands with intercalations of mud beds composed of sand-mud couplets. Benthic foraminifera examination indicated the offshore species were dominant. The seismic profile indicated that the ridges were separated from the older delta layers due to a boundary formed by river erosion during the last glacial maximum. Radiocarbon dating of the sandy sequence revealed an irregular chronological sequence, with most age ranges falling within the past 3 ka. Based on the chronological data from DH03 and other cores, we propose that the ridges, which were formed during the early Holocene transgression, have been active on a shelf scale in the recent 3–2 ka. Synthetic analysis of the shelf-scale ridge formation processes indicates that the sea-level fluctuations during the mid-late Holocene sea-level highstand triggered the ridge activities. A center for ridge activity developed in the southern shelf, facilitated by thicker ridge deposits in the paleo-Changjiang River Estuary and stronger currents (tidal currents and possibly internal waves) induced by the remaining funnel-shaped estuary topography. Based on these findings, we propose a conceptual model for ridge development, which includes a ridge formation stage during the early Holocene transgression and a ridge activation stage during the mid-late Holocene sea-level highstand.

The deltas serve as the primary interactive zone where terrestrial and marine environments converge, playing a pivotal role in the coastal deposition. In the Holocene, climate changes and sea level fluctuation are the principal driving factors in the evolution of deltas. However, human activities such as the construction of dams and reservoirs in the Anthropocene have significantly altered sediment transport in rivers, leading to depositional pattern variation during deltaic evolution. In this study, we have conducted a comparative analysis of the morphological variations (1986–2021) in the barrier system of the Hanjiang River Delta (HRD) using satellite remote sensing (SRS) method. Additionally, we have examined the lithological changes and facies alterations observed in eight boreholes on the present barrier spit. Our findings indicate that the intensification of anthropogenic activities led to a significant reduction in the sediment flux of the Hanjiang River (HR), resulting in depocenter landward migration at the estuary. SRS analysis reveals their periodical morphological characteristics and spatial variations of estuarine sandbars (1986–1992), barrier islands-lagoons (1993–2009), and barrier spits (2010–2021) during 1986 to 2021. The stratigraphy of boreholes demonstrates a south-to-north facies transition from lagoon to lagoon-barrier spit and barrier spit in vertical lithology. Therefore, the depositional evolution of the HRD barrier system is categorized into three phases: estuarine sandbar-barrier island phase (1986–1998); barrier island-lagoon phase (1999–2009); and barrier spit phase (2010–2021). During the estuarine sandbar-barrier island phase, fluvial processes played a predominate role in the deposition. Consequently, with a significant decrease in river sediment load, the dominant factors driving depositional processes shifted towards wave action and alongshore current. Based on the conceptual model in the Holocene, we propose a modified depositional model of wave-dominated deltas during Anthropocene that encompasses three evolutionary phases: estuarine sandbars and delta front platforms, barrier island-lagoon formation and landward migration of barrier spits. This pattern highlights that human-induced reduction in river sediment flux has led to a seaward deltaic progradation driven by barrier landward migration.

The establishment of effective proxies for the differentiation of sedimentary facies in the tide-dominated river mouth is fundamental to the delineation of stratigraphy and the study of paleoenvironments. Geochemical signatures of the acetic acid (HAc) extractive phases of alkaline earth metals, such as Sr, Ba, and Ca, are closely related to sedimentary environments and thus provide a novel method for discriminating the sedimentary facies of river mouth. In this study, 50 surface water and surface sediment samples were obtained from different geomorphological units of the Jiulong River mouth, i.e., river channel, distributary channel, delta front, delta front slope, prodelta, and shallow marine area, and the salinity of the water, the grain size, and the Sr, Ba, and Ca contents and Sr/Ba molar ratio (Sr/Ba) in HAc leachates of the sediments were determined. Contents of alkaline earth metals in HAc leachates of surface sediments from the Changjiang (Yangtze) River coast were also collated. The goals of this study were to reveal the spatial distribution of alkaline earth metals in the Jiulong River mouth, define their depositional mechanisms, and search for effective geochemical proxies for identification of the various sedimentary facies in the fluvial to marine transition zone. The results revealed several land-to-sea gradients. The Ba content decreased rapidly from the distributary channel to the sea, and the Sr and Ca contents and Sr/Ba increased gradually with the increase in salinity. Salinity, marine biomass, and sedimentary dynamic processes, were speculated to be the main reasons for the differences in their spatial distributions. There were significant differences in Ba, Sr, Ca, and Sr/Ba between the river channel and the distributary channel, in Ca and Ba between the distributary channel and the delta front (slope), and in Sr, Ca, and Sr/Ba between the delta front (slope) and the prodelta–shallow marine region. The Sr–Ba scatterplot showed that the sediments of the river channel and alluvial plain were located as a high Ba and low Sr element-defined end-member, whereas samples of the prodelta and shallow marine formed a high Sr and low Ba end-member. These can be used as characteristic end-members indicating terrestrial facies and marine facies, respectively. The sediments of the delta plain, tidal river, distributary channel, delta front, and delta front slope are located between these two end-member regions of the scatterplot, and this region of the diagram can be used to identify land–sea transitional sedimentary facies.