Dissolved PAHs in the Beibu Gulf and adjacent waters of the South China Sea: Physical and biochemical processes-driven distributional variations.

Polycyclic aromatic hydrocarbons (PAHs) in semi-enclosed gulfs are influenced by physical and biochemical processes, which haven't been well understood. This study aims to investigate the spatial distribution and vertical profiles of dissolved PAHs in the Beibu Gulf (BG) and adjacent waters of the South China Sea, along with hydrological, meteorological, and biochemical variables. Particularly relevant are the effects of atmospheric pressure, salinity, ammonium, chlorophyll-a, as well as riverine inputs (RI), sea currents, and upwelling. In surface seawater, the total concentrations of eight dissolved PAHs (∑8PAHs) were 7.76 ± 2.16 ng/L, with a distribution pattern of western Guangdong waters (WGWs) > BG > Qiongzhou Strait (QS). ∑8PAHs in the northern BG (9.10 ± 2.00 ng/L) was significantly higher than that in the southern BG (6.65 ± 1.54 ng/L) (p < 0.01), suggesting that local anthropogenic activities and unique environmental characteristics significantly influenced PAHs distribution. In water column, PAHs in BG displayed enrichment in surface and bottom but decreased in medium water, while those in WGWs and QS decreased with increasing depth. Source apportionment concluded that PAHs in QS and WGWs were primarily from petroleum sources, and PAHs in BG were mainly from coal combustion. RI, combined with circulation, coastal current, and intrusion of SCS water influenced the surface PAHs distribution in BG, with eddy impacts observed. Specifically, regarding the surface PAHs distribution, differences in atmospheric pressure may influence the air-sea exchange of PAHs, especially positively affecting 4-ring PAHs. Salinity factors further corroborated the contribution of RI to 3-ring PAHs, followed by the regulation of PAHs through biological pumps (ammonia and chlorophyll-a). Moreover, upwelling-induced biodegradation and resuspension affected the vertical distribution of PAHs. While most PAHs posed a negligible risk, coking-generated fluorene posed a moderate risk to ecosystems due to changes in the energy structure, warranting further investigation into its toxicological impacts.

Ocean Stratification Impacts on Dissolved Polycyclic Aromatic Hydrocarbons (PAHs): From Global Observation to Deep Learning.

Ocean stratification plays a crucial role in many biogeochemical processes of dissolved matter, but our understanding of its impact on widespread organic pollutants, such as polycyclic aromatic hydrocarbons (PAHs), remains limited. By analyzing dissolved PAHs collected from global oceans and marginal seas, we found different patterns in vertical distributions of PAHs in relation to ocean primary productivity and stratification index. Notably, a significant positive logarithmic relationship (R2 = 0.50, p < 0.05) was observed between the stratification index and the PAH stock. To further investigate the impact of ocean stratification on PAHs, we developed a deep learning neural network model. This model incorporated input variables determining the state of the seawater or the stock of PAHs. The modeled PAH stocks displayed substantial agreement with the observed values (R2 ≥ 0.92), suggesting that intensified stratification could prompt the accumulation of PAHs in the water column. Given the amplified effect of global warming, it is imperative to give more attention to increased ocean stratification and its impact on the environmental fate of organic pollutants.

Enhanced Sinks of Polycyclic Aromatic Hydrocarbons Due to Kuroshio Intrusion: Implications on Biogeochemical Processes in the Ocean-Dominated Marginal Seas.

The biogeochemical processes of polycyclic aromatic hydrocarbons (PAHs) in the South China Sea (SCS) are influenced by the exchanges of water masses, energies, and materials between this marginal sea and the Pacific Ocean. To investigate the impact of oceanic water intrusion on semivolatile compounds, we collected seawater samples in the Western Pacific, northern, and central SCS in 2017 and analyzed for dissolved PAHs. PAH concentrations in the water columns of the Pacific Ocean and SCS were 1.7-11 and 1.1-7.3 ng L-1, respectively, showing spatial distinctions in terms of the composition and source characteristics. A common depletion for three-ring PAHs was found in the northern SCS by comparing the modeling results of conservative mixing by Kuroshio intrusion. Kuroshio water increased the levels of temperature, dissolved oxygen, and nutrients when intruding into the northern SCS and was likely to enhance the bioavailability of PAHs and stimulate their biodegradation process. In the water column, the most effective layer under the Kuroshio intrusion impact is different for three- and four-ring PAHs, where the three-ring PAHs' depletion was most significant at the surface; however, for four-ring PAHs, that was at the deep chlorophyll maximum layer. This study highlighted the effect of ocean currents on PAHs for their water-column processes both from physical and biogeochemical perspectives.

Enhanced Biomass and Astaxanthin Production of Haematococcus pluvialis by a Cell Transformation Strategy with Optimized Initial Biomass Density.

: Astaxanthin from H. pluvialis is an antioxidant and presents a promising application in medicine for human health. The two-stage strategy has been widely adopted to produce astaxanthin by the Haematococcus industry and research community. However, cell death and low astaxanthin productivity have seriously affected the stability of astaxanthin production. This study aims to test the effect of cell transformation strategies on the production of astaxanthin from H. pluvialis and determine the optimal initial biomass density (IBD) in the red stage. The experimental design is divided into two parts, one is the vegetative growth experiment and the other is the stress experiment. The results indicated that: (1) the cell transformation strategy of H. pluvialis can effectively reduce cell death occurred in the red stage and significantly increase the biomass and astaxanthin production. (2) Compared with the control group, the cell mortality rate of the red stage in the treatment group was reduced by up to 81.6%, and the biomass and astaxanthin production was increased by 1.63 times and 2.1 times, respectively. (3) The optimal IBD was determined to be 0.5, and the highest astaxanthin content can reach 38.02 ± 2.40 mg·g-1. Thus, this work sought to give useful information that will lead to an improved understanding of the cost-effective method of cultivation of H. pluvialis for natural astaxanthin. This will be profitable for algal and medicine industry players.

Differences between Motile and Nonmotile Cells of Haematococcus pluvialis in the Production of Astaxanthin at Different Light Intensities.

Haematococcus pluvialis, as the best natural resource of astaxanthin, is widely used in nutraceuticals, aquaculture, and cosmetic industries. The purpose of this work was to compare the differences in astaxanthin accumulation between motile and nonmotile cells of H. pluvialis and to determine the relationship between the two cells and astaxanthin production. The experiment design was achieved by two different types of H. pluvialis cell and three different light intensities for an eight day induction period. The astaxanthin concentrations in nonmotile cell cultures were significantly increased compared to motile cell cultures. The increase of astaxanthin was closely associated with the enlargement of cell size, and the nonmotile cells were more conducive to the formation of large astaxanthin-rich cysts than motile cells. The cyst enlargement and astaxanthin accumulation of H. pluvialis were both affected by light intensity, and a general trend was that the higher the light intensity, the larger the cysts formed, and the larger the quantity of astaxanthin accumulated. In addition, the relatively low cell mortality rate in the nonmotile cell cultures indicated that the nonmotile cells have a stronger tolerance to photooxidative stress. We suggest that applying nonmotile cells as the major cell type of H. pluvialis to the induction period may help to enhance the content of astaxanthin and the stability of astaxanthin production.

Roles of temperature and ventilation in oxygen consumption: A chemical kinetics view from the van't Hoff-based formulation.

In this study, we successfully estimated the apparent activation energy of a microbially driven oxygen-consuming reaction (microbial-driven) based on tracer data. The concept of the apparent chemical reaction rate constant was employed to estimate various thermodynamic parameters associated with the oxygen consumption rate in conjunction with Arrhenius/Eyring equations. Normal Ea values of 80-90 kJ mol-1 were found in the upper layers of the South China Sea and Sulu Sea, while higher Ea values (300-1000 kJ mol-1) were observed in the rapidly ventilated Mediterranean Sea, the Sea of Japan, and the Bering Sea with lower temperatures. We classified the characteristics of typical sea basins into four categories. The temperature-dependent oxygen consumption rate relationship in each marine region was systematically calculated to derive the respective thermodynamic characteristic values. This allowed us to parameterize the rate-temperature relationship into thermodynamic quantities, enabling more effective integration of distinct basin characteristics within different sea areas into the marine biochemical model. Parameterization facilitates relatively accurate prediction of changes such as temperature, oxygen consumption rate.

Quantitative assessment of the response of seawater environmental quality to marine protection policies under regional economic development --A case study of Xiamen Bay, China.

Xiamen is the epitome of having steady economic growth and non-negligible environmental stress over decades. Several restoration programs have been applied to address the conflicts between heavy environmental pressures and human activities, but the response of current coastal protection policies to the marine environment remains to be assessed. Therefore, to assess the effectiveness and efficiency of marine conservation policies under regional economic growth in Xiamen, quantitative techniques including elasticity analysis and dummy variable regression models were applied. Here we show the potential relationship between seawater quality (pH, COD, DIN and DRP) and economic growth including Gross Domestic Product (GDP) and Gross Ocean Product (GOP), to evaluate the ongoing related policies by using over 10 years of data (2007-2018). According to our estimates, a GDP growth rate of 8.5% represents a stable economic climate that is favorable for the overall rehabilitation of the local coastal environment. The results of the quantitative research indicate a strong relationship between economic development and seawater quality, with marine protection regulations serving as the direct cause. As GDP growth and pH are significantly positively correlated (coef. = 0.8139, p = 0.012), ocean acidification has decreased over the last decade. With an inversely proportional correlation with GDP (coef. = 0.8456, p = 0.002) and GOP (coef. = 0.8046, p = 0.005), the trend in COD concentrations effectively meets the targets of current pollution control legislation. By using a dummy variable regression model, we found that legislation is the most effective way in seawater recovery in the GOP section, and positive externalities of marine protection frameworks are also estimated. Meanwhile, it is predicted that the negative effects from the non-GOP section will gradually affect the coastal environmental quality gradually. An overall framework for controlling marine pollutant discharges, giving equal attention to maritime and non-maritime anthropogenic activities should be promoted and updated.

Microplastics in the Taiwan Strait and adjacent sea: Spatial variations and lateral transport.

This study investigates the distribution, structural properties, and potential impacts of oceanic processes on microplastics (MPs) in the Taiwan Strait (TWS) and surrounding seas. With an average of 174 particles/m3, the MP abundance in surface seawater ranged from 84 to 389 particles/m3. MP abundance ranged from 16 to 382 particles/kg in sediments, with a median of 121 particles/kg. Fragment and fiber were the two most frequently detected shapes. These MPs were found to be composed primarily of carbon and oxygen elements at 70-90% levels using energy-dispersive X-ray spectroscopy. Additionally, several examples had trace levels of metallic components. Black was the color that MPs saw the most often out of all the hues. The two main types of polymers are polyester and rayon, and their production is influenced by home sewage discharge and synthetic fiber production. The main routes of MP transport were land source input, riverine input, and oceanic currents. This study showed that salinity affects the distribution of MPs, with high-salinity seawater serving to saturate their presence. On the other hand, upwelling raises MP concentrations by bringing nutrients from the deep to the surface. Furthermore, it has been discovered that the dilution of the Pearl River plume increases the MP prevalence in the region. The South China Sea Warm Current had the highest lateral MPs transport flux (2.1 × 1014 particles/y), which was followed by the Taiwan Strait Current area (1.0 × 1014 particles/y) and the Guangdong coastal areas (8.6 × 1013 particles/y). In sediments, the MP prevalence was inversely correlated with particle size. Flocculation processes probably made it easier for MPs to travel down the water column and deposit themselves on the aquatic substrate. Although the relationship between MPs, total organic carbon, and total organic nitrogen was not correlated, a favorable trend showed that MPs may discreetly contribute to carbon storage in coastal sediment.

Heavy metals and Pb isotopes in sediment cores from the Bering and Chukchi seas: Implications for environmental changes and human activities over the past century.

The Bering Sea and the Chukchi Sea are important regions for marine ecosystems and climate change. However, the historical deposition and sources of metals in these regions are poorly understood. In this study, we utilized Pb isotopes and multi-element concentrations (Ni, Cu, Fe, Mn, Zn, Cd, Pb) coupled with Pb-210 dating to investigate the historical deposition and source identification of metals in sediment cores collected from the Bering Sea and the Chukchi Sea. Our findings reveal that the transport of organic matter was mainly transported by marine and terrestrial sources in the Bering and Chukchi Sea, respectively. Historical variations of metals were similar in both seas, showing an increasing trend of metals (excluding Mn) from the 1960s to the 1990s, followed by a gradual decrease after the 1990s, which can be attributed to the development of industrial and gasoline emission. The results of the geo-accumulation index indicated that sediment in both seas was relatively unpolluted with metals. Additionally, Pb isotopic ratios suggested that natural weathering was the primary source of Pb in the area, but the use and phase-out of gasoline were also well-reconstructed. This study provides valuable information for assessing environmental changes and human activities over the past century in the Arctic and subarctic Ocean.

Can water dating trace the transport history of HCHs in the ocean?

Long-range atmospheric and oceanic transport play a crucial role in the accumulation of persistent organic pollutants (POPs), including hexachlorocyclohexanes (HCHs), in the Arctic Ocean. Herein, transient tracers, specifically chlorofluorocarbon-12 and sulfur hexafluoride, were used to determine the ventilation time of HCHs. Results revealed that dissolved HCHs can penetrate to a depth of ~500 m in the western Arctic Ocean, corresponding to water masses with a mean age of 45 ± 14 years. The average long-range transport time for α-HCH from initial atmospheric release to entering the western Arctic Ocean was estimated to be >30 ± 5 years, indicating continued moderate to high ecological risks from HCHs in the Arctic. This study demonstrates that transient tracers serve as effective water dating tools to elucidate the transport history of stable POPs in the ocean, contributing to a better understanding of their environmental characteristics and fate.

Gaseous polycyclic aromatic hydrocarbons over the South China Sea: Implications for atmospheric transport under monsoon influences.

The seasonal monsoon variations have significant impact on the atmospheric transport of semi-volatile organic pollutants over the South China Sea (SCS). We analyzed polycyclic aromatic hydrocarbons (PAHs) over the basin and island areas (Yongxing Island and Yongshu Island) in 2017. Gaseous PAHs (0.17-1.4 ng m-3) showed spatio-temporal distinctions in their composition and sources among the basin and island areas. Mixed combustion sources of PAHs were identified over the SCS, including a petroleum source near the island areas. The transport routes of PAHs were inferred by the air mass back trajectories and potential source contribution factor analysis, identifying strong biomass burning signals from the Indochina Peninsula and other Southeast Asian countries. Emissions from approximately 90 % of the combustion sources were transported to basin areas by monsoons, whereas the island areas were dominated by local emissions. This study emphasizes the main potential terrestrial source of PAHs over the SCS under monsoon influences.

Policy impact on microplastic reduction in China: Observation and prediction using statistical model in an intensive mariculture bay.

Plastic pollution in the environment has spurred debate among scientists, policymakers, and the general public over how industrialization and consumerism are wreaking havoc on our ecosystem, but some policies might assist to ameliorate the problem in the near future. In this study, the decision tree classifier and Bayesian Structural Time Series (BSTS) model was used to anticipate the possible sources of microplastics and their near future state in 26 surface sediment and a sediment core, respectively in Sansha Bay, which has been criticized for its intensive mariculture applications. An inventory of microplastics in the sediment core was estimated, and it was discovered that during the previous six decades, an average of 181.95 tons of microplastics were deposited, with an average deposition (by a layer of sediment) of 179.44 tons/cm. According to the DT classifier, mariculture was the primary source of microplastics, whereas urban and industrial areas were the primary sources of POPs. The Bayesian Structural Time Series (BSTS) model revealed a microplastic downward slope, indicating that regional and national strategies implemented might successfully reduce microplastic pollution regionally.

Upwelling impact and lateral transport of dissolved PAHs in the Taiwan Strait and adjacent South China Sea.

The spatial distribution and depth profile of dissolved polycyclic aromatic hydrocarbons (PAHs) were investigated in the western Taiwan Strait (TWS) and northeastern South China Sea (SCS) during the southwest monsoon for a comprehensive study of spatial distribution, potential sources, upwelling, and lateral PAHs transport flux to assess the impacts of oceanic processes. The concentrations of ∑14PAHs were 33 ± 14 ng L-1 and 23 ± 11 ng L-1 in western TWS and northeastern SCS, respectively. A minor difference in potential sources in different areas was shown in principle component analysis results, which illustrated mixed sources (petrogenic and pyrogenic) in western TWS and petrogenic sources in northeastern SCS. An "enrichment in surface or deep but depletion in medium water" distribution pattern of PAHs depth profile during summertime was observed in Taiwan Bank, which was potentially influenced by the upwelling. The greatest lateral ∑14PAHs transport flux was found along the Taiwan Strait Current area (43.51 g s-1), followed by those along South China Sea Warm Current and Guangdong Coastal Current areas. Though the oceanic response to PAHs varied relatively slowly, the ocean current was a less-dominant pathway for PAHs exchange between the SCS and the East China Sea (ECS).

Oyster (Crassostrea gigas) polysaccharide ameliorates obesity in association with modulation of lipid metabolism and gut microbiota in high-fat diet fed mice.

Oyster is nutritious shellfish, wildly consumed throughout the world. Its polysaccharide (OPS) has various bioactivity. In the present study, the anti-obesity effect of OPS was evaluated in obese mice induced by a high-fat diet (HFD). The results showed that OPS significantly alleviated weight gain, dyslipidemia, and metabolic endotoxemia of obese mice, and accelerated the production of short-chain fatty acids. OPS also regulated lipid metabolism of adipose and liver by activating the expression of p-AMPKα to further down-regulate the expression of SREBP-1c, PPARγ, and p-ACC-1. 16S rRNA results indicated that OPS corrected HFD-induced gut microbiota dysbiosis by enriching beneficial bacteria (Bifidobacterium, Lactobacillus, Dobosiella, and Faecalibaculum) and decreasing harmful bacteria (Erysipelatoclostridium, Helicobacter, and Mucispirillum). In summary, these results revealed that OPS could serve as a potential prebiotic to improve obesity.

Evidence for the growing importance of Eurasian local source to PAHs in the Arctic central basin.

Polycyclic aromatic hydrocarbons (PAHs) are traditionally considered to enter the Arctic Ocean through long-range transport. Arctic warming, especially sea ice retreat, will certainly increase the contribution from local source (such as river input and ice melting). However, this hypothesis remains poorly constrained for lack of quantitative evidence. Here PAHs in surface seawater (67°N-89°N, 152°E-177°E) and sea ice (82°N-89°N) were collected in the western Arctic in 2010. Dissolved concentrations of 15 PAHs (Σ15PAHs) in surface layer ice (26.2 to 49.8 ng/L) were one order of magnitude higher than the underlying seawater. The content of dissolved Σ15PAHs was significantly higher in the marginal ice zone than those in the Chukchi Sea shelf, and the dissolved Σ15PAHs concentration differed by nearly an order of magnitude in two closely adjacent sections in the basin area, which both showed high fraction of river water and sea ice meltwater. This pattern could be explained by the different local inputs from Eurasia and North America. This scenario was further visualized by ice back trajectories capturing significantly higher PAH signals from the Eurasian margin than those from North America and stable oxygen isotopic data finding a positive correlation of PAH levels with the fractions of river runoff and ice-melting water coming from the Eurasia. The PAHs budget of the Arctic Ocean was also dominated by local sources (river and ice melting) as inputs (76 %) and volatilization as outputs (47 %). This study reveals the importance of Eurasian local inputs in supplying PAHs to the central Arctic Ocean. Those processes, which have not been well recognized for PAHs previously, are expected to increase and will undermine global efforts to reduce exposure by remobilizing PAHs stored in permafrost and ice.

Spatial and temporal trends of anthropogenic carbon storage in typical marginal seas along the Asia continent in the northern hemisphere.

Global climate change is an indisputable fact, and anthropogenic disturbances are the likely driving mechanisms; moreover, marginal seas tend to respond faster than the global ocean. In this study, the transit time distribution method was used to estimate the anthropogenic carbon (Cant) in the typical marginal seas along the west side of North Pacific Ocean and the Arctic Ocean. From the South China Sea (SCS) to the Arctic Ocean (AO), the range of Cant storage gradually increased with latitude. The maximum and minimum rates of ~0.6 mol C·m-2·yr-1, and ~0.2 mol C·m-2·yr-1 were seen in the AO and SCS, respectively. In the short term, warming and decline of ice cover may promote the transfer of excess CO2 from the atmosphere to the water interior; but on a longer time scale, a positive feedback (i.e., reduced CO2 absorption) may occur due to warming. Accordingly, the AO will likely no longer be a CO2 sink in the future when the sea ice disappears completely.

Occurrence and sources of microplastics and polycyclic aromatic hydrocarbons in surface sediments of Svalbard, Arctic.

Due to the distinct environment condition and geographic location, Svalbard has been recognized as a potential pollution reservoir in the Arctic. In this study, 8 surface sediment samples were collected from two fjords in Svalbard (Kongsfjorden and Rijpfjorden) in 2017, and they were searched for microplastics and polycyclic aromatic hydrocarbons (PAHs). PAHs were also investigated in 10 soil samples of Ny-Ålesund for local anthropogenic source analysis. The level of microplastics and other anthropogenic particles ranged from not detected (ND) to 4.936 particles/kg dry weight (DW). Fiber was the only shape of the microplastics found and three polymers (polyester, rayon and cellulose) were detected, which suggested that fisheries-related debris and textile materials were possible sources of microplastics and anthropogenic particles. For PAHs, the level of ∑26PAH was 9.2 ng/g to 67.1 ng/g (DW), and were dominated by lnP and BghiP, indicating petroleum combustion source. Further analysis revealed that traffic emissions from cars and diesel combustion from a local power plant were major sources of PAHs in soils of Ny-Alesund, while traffic emissions from ships were the dominate source of PAHs in sediments of Kongsfjorden and Rijpfjorden. A higher level of PAHs was observed in Ny-Alesund, confirming an anthropogenic input, while transport via ocean currents might contribute to the higher abundance of microplastics in Rijpfjorden. Further research and even long-term observation of pollutants are needed to fully understand the pollution status in polar regions.

Dissolved PAHs impacted by air-sea interactions: Net volatilization and strong surface current transport in the Eastern Indian Ocean.

In the Indian Ocean, the marine fate of polycyclic aromatic hydrocarbons (PAHs) is impacted by the unique air-sea interactions with great monsoon characters. By collecting water-column samples during the monsoon transition period, we found PAHs (∑8PAH: 1.1-27 ng L-1) showed significantly different distributions from the Bay of Bengal, Equatorial Indian Ocean, Eastern Indian Ocean, and the South China Sea (p < 0.001). Their vertical profiles showed natural logarithm relationships with depth in the Bay of Bengal and Equatorial Indian Ocean. PAHs were mainly from wood/coal combustion and vehicle emission. The estimation of PAHs' air-seawater exchange flux revealed net volatilizations from seawater except in the Eastern Indian Ocean. The Wyrtki Jet, a surface current driven by the westerly wind, was observed in the equatorial area. This swift current could transport PAHs eastward efficiently with a mass flux of 636 ± 188 g s-1. The subsurface current, Equatorial Undercurrent, played a less crucial role in PAHs' lateral transport with a flux of 115 ± 31.3 g s-1. This study preliminarily revealed the role of air-sea interactions on PAHs' transport and fate in the open ocean. The coupled air-sea interactions with biogeochemical processes should be considered in future work.

Microplastics in the surface waters of the South China sea and the western Pacific Ocean: Different size classes reflecting various sources and transport.

Microplastic transport in the marginal seas is a key process influencing their ultimate fate in the open oceans. In the present study, we collected seawater samples from the western Pacific Ocean (WP) and the South China Sea (SCS) to investigate the distribution, transport, and possible sources for microplastics. Generally, the range of microplastic levels were 187-1816, 146-1563, and 34.2-622 particles/m3 (averaged in 797 ± 512, 744 ± 330, and 201 ± 134 particles/m3) for the northern SCS, the western SCS, and the WP, respectively. Based on the size distribution, the highest value (390 ± 288 particles/m3) was found for 100-200 µm, followed by 200-500 µm (131 ± 155 particles/m3), and 500-1000 µm (29.7 ± 39.2 particles/m3), with the lowest for 1-5 mm (13.6 ± 14.2 particles/m3). Granule, yellow, and size <1000 µm were their most prevalent characteristics. The main polymer types of microplastics were polyester, rayon, and nylon. A negative correlation between microplastic proportion and particle size was observed in the SCS and the WP. Furthermore, the main sources of microplastics in the northern SCS probably came from the Pearl River. Surface currents and the vertical mixing processes might be two different mechanisms that affect microplastic transport from the WP and the SCS. Future comparison to measured particle size distributions data allows us to explain size-selective microplastic transport in the marine environment, and probably provide guidance on microplastic longevity.

Microplastics in the western Pacific and South China Sea: Spatial variations reveal the impact of Kuroshio intrusion.

Surface currents play an essential role in the worldwide distribution of microplastics in the coastal seas and open oceans. As a branch of the western boundary currents (WBCs), Kuroshio changes seawater properties and pollutant levels of the South China Sea (SCS) during its intrusion process. To study the impact of Kuroshio intrusion on microplastics, we conducted field observations on surface water from the western Pacific (WP) and SCS. Microplastic abundances in the surface water of WP (0.02-0.10 particles m-3) were generally lower than those in the SCS (0.05-0.26 particles m-3). Fragments and granules dominated their apparent characteristics, and showed spatial classifications in different areas. The abundance of fragment, granule and foam showed a similar unimodal trend, as they peaked when the Kuroshio fraction was 0.1, implying the effect of Kuroshio intrusion was a combination of the dilution and biogeochemical influence. The polymer types of microplastics, dominated by polypropylene (PP), polyethylene (PE), polyester (PES), polymethacrylate (PMA) and phenoxy resin (PR), showed complicated compositions in the northern SCS, and Kuroshio intrusion was not the dominant influencing factor. Further study is needed to discover the comprehensive effect of Kuroshio intrusion on the fate of microplastics and is expected for the whole WBC system.