North Yellow Sea Research Articles

Prevalence and distribution of dissolved paralytic shellfish toxins in seawater in the Yellow Sea and the Bohai Sea, China

Paralytic shellfish toxins (PSTs) could be secreted by PSTs-producing microalgae or released by ruptured cells in seawater. In this study, the distribution of dissolved PSTs in the Yellow Sea and the Bohai Sea, China, was investigated by two cruises in April and July 2023. Seawater samples were collected from the surface, middle and bottom layers, and the profiles of PSTs were analyzed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), and the spatial distribution characteristics of dissolved PSTs and their correlation with environmental factors were explored. Results showed that C1/2, GTX1/4, GTX2/3 and dcGTX2/3, were detected in seawater samples in both spring and summer, with the detection rates 100 % and 97.6 %, respectively. The total PST (ΣPSTs) concentrations ranged in 12 ∼ 590 pmol L−1, 9.3 ∼ 546 pmol L−1, 12 ∼ 2,452 pmol L−1, and not detected (nd) ∼ 188 pmol L−1 in seawater samples collected from the surface, middle and bottom layers in spring, and the surface layer in summer, respectively. Concentrations of PSTs markedly varied in the vertical water column in different sea regions. Generally, concentrations of ΣPSTs in the bottom seawater were higher than those in the surface and middle layers in the Bohai Sea and the North Yellow Sea, but no significant difference in the different water layers in the South Yellow Sea. In addition, concentrations of ΣPSTs in surface waters were much lower in summer than those in spring. In both spring and summer, dissolved PSTs in surface seawater were mainly distributed in the South Yellow Sea. These results indicate that PSTs were prevalent in the Yellow Sea and the Bohai Sea, of which the potential hazard to marine organisms should be highly concerned.

Formation and preservation mechanisms of magnetofossils in the surface sediments of muddy areas in the yellow and Bohai Seas, China

Magnetofossils in the continental shelf sediments of the Yellow and Bohai Seas have long been overlooked. Based on the magnetic results of 88 surface sediments (0–10 cm depth), first-order reversal curve (FORC) diagrams, isothermal remanent magnetization (IRM) acquisition curves from 6 representative samples, and transmission electron microscopy (TEM) observations of 2 samples, the formation and preservation mechanisms of magnetofossils in this region are elucidated. The FORC diagrams consistently show a clear central ridge feature, which indicates the presence of intact magnetofossils in all representative samples. The morphologies observed by TEM are primarily equant and elongated, with minimal or no bullet-shaped (magnetite) magnetofossils. Analysis further reveals a widespread distribution of magnetofossils in the mud areas of the Bohai Sea, North Yellow Sea, and South Yellow Sea, with proportions (contribution to SIRM; SIRM is defined as the remanent magnetization that remains constant as the external magnetic field increases) of <32.5 %, 40.9 % ∼ 44.6 %, and 59.9 % ∼ 66.5 %, respectively. Despite the presence of non-biogenic single domain magnetite, the proportion of magnetofossils can be estimated by the χARM/SIRM value, as they are positively correlated. The surface sedimentary environment of these mud areas is primarily suboxic and characterized by abundant dissolved iron, which facilitate the formation of magnetofossils by magnetotactic bacteria (MTB). It is unlikely that the surface sedimentary environment becomes sulphidic, thereby enabling the preservation of magnetofossils after their formation. The redox state of the study area, crucial for magnetofossil formation, is mainly controlled by the total organic carbon (TOC) content. From north to south, the higher proportion of magnetofossils is coupled with higher TOC content, possibly due to the intensified reducing degree of the suboxic environment, promoting MTB proliferation and thus forming more magnetofossils. The mechanisms governing the formation and preservation of magnetofossils proposed in this study may also be applicable to geological records.

Zooplankton community variations in response to summer hypoxia in Sishili Bay, North Yellow Sea, China

Zooplankton community variations in response to summer hypoxia in Sishili Bay, North Yellow Sea, China

Different pacemakers of marine organic carbon burial in the North Yellow Sea from the early to late Holocene

Marginal seas play a crucial role in the global carbon cycle, contributing approximately 20% of the net CO2 uptake by the world's oceans. The North Yellow Sea (NYS), a semi-enclosed marginal sea in the western Pacific Ocean, serves as a significant carbon sink influenced by factors such as sea level changes, monsoon dynamics, ocean currents, and El Niño-Southern Oscillation (ENSO) activity. This study examines a 538 cm-long sediment core W03 from the NYS (10.3 kyr BP to present). We analyzed Organic Carbon (OC) proxies, including total organic carbon (TOC), the stable carbon isotope (δ13C) of TOC, total nitrogen (TN) and marine-produced lipid biomarkers. Our findings demonstrate a strong correlation between OC burial and sea-level fluctuations during the early Holocene, driven by the exposure of the continental shelf. During the mid-Holocene, the intrusion of the Yellow Sea Warm Current increased salinity and temperature conditions and nutrient levels of sea water, thereby enhancing marine OC burial. Over the last 3.3 kyr BP, ENSO variability and intensified East Asian Winter Monsoon (EAWM) strengthened the coastal currents, contributing to better OC preservation. Additionally, human activities on the surrounding mainland increased terrestrial input, altering the OC burial. The heightened activity of the Kuroshio Current also introduced more saline and warm water masses into the NYS, impacting phytoplankton productivity and community structure, as indicated by increased C37 alkenones. This study highlights the complex interplay of geological factors in OC burial processes within the NYS, providing valuable insights into OC dynamics in marginal seas under the impact of global change.

1500-Year Sedimentary Records of the East Asian Summer Monsoon and Yellow Sea Warm Current from the Muddy Area of the North Yellow Sea, China

Advances in reconstructing the East Asian monsoon have provided important insights into the natural climate variability in Asia during the pre-instrumental period. However, there are still unresolved paleoclimate issues that necessitate the use of geological proxy data to further our understanding of past climate changes. This study focused on core B13, located in the muddy area of the North Yellow Sea (NYS), to investigate the evolutionary history over the past 1500 years and reconstruct the records of the East Asian summer monsoon (EASM) and Yellow Sea warm current (YSWC). The mean grain size of sediment ranged from 4.2 Φ to 5.6 Φ, with the sorting coefficient ranging from 1.9 to 2.2, indicating poor sorting. The C–M pattern showed a limited range of values, with the M values being between 33 and 83 μm and the C values being between 165 and 287 μm, suggesting uniform-suspension transport. The L* index ranged from 40.41 to 44.12, while the a* and b* indexes ranged from 0.55 to 1.78 and 2.86 to 5.94, respectively. A stable and relatively strong sedimentary environment is indicated through a comprehensive analysis of the C–M plot, triangular plot, the relationship between the mean grain size and sorting, and the changes in grain-size and color parameters. The sedimentary evolution in the muddy area of the NYS over the past 1500 years can be categorized into three distinct stages. In this study, proxies for the EASM and YSWC were extracted using the VPCA method from the sediment grain size and diffuse spectral reflectance (DSR) data, respectively. The reliability of these proxies has been confirmed through comparison with other validated proxies. The results indicated that the strength of the EASM and YSWC also exhibited three stages, corresponding to the Dark Ages Cold Period (DACP), Medieval Warm Period (MWP), and Little Ice Age (LIA), respectively. On a centennial scale, the correlation between the EASM and YSWC was predominantly negative. This research validates the reliability of the VPCA method for paleoclimate reconstruction, contributes important climate records in a special muddy area, and provides a new perspective on how to eliminate temporal errors in verifying the correlation between the two climate systems.

Accumulation of trace metal elements in ophiuroids with different feeding types in the North Yellow Sea

Ophiuroids, as an important group of echinoderms, are widely distributed in marine benthic habitats. Previous studies have identified two primary feeding types of ophiuroids in the Yellow Sea, including carnivorous (Ophiura sarsii vadicola and Stegophiura sladeni) and suspension feeders (Ophiopholis mirabilis). Despite their ecological role in the benthic food webs, little is known about their accumulation of trace metal elements (TMEs). In this study, the content of TMEs (Pb, As, Cd, Hg, Cr, Cu, Zn), methylmercury (MeHg) and δ15N value of three ophiuroids species from the North Yellow Sea were determined. Our results showed that the contents of some TMEs (As, Cd, Cr, Cu and Zn) and MeHg were significantly different in three species of ophiuroid (p < 0.05). There were significant correlations between the accumulations of trace metal elements (Pb, Cd and Zn) and the δ15N value of the ophiuroids (p < 0.05). Additionally, As and Zn exhibited opposite correlations in ophiuroid with two feeding types, which may be related to their host species and different feeding habits. This study provided fundamental data for understanding the distribution of trace metal elements in echinoderms.

Spatial distribution of lipophilic shellfish toxins in seawater and sediment in the Bohai Sea and the Yellow Sea, China

Lipophilic shellfish toxins (LSTs) are widely distributed in marine environments worldwide, potentially threatening marine ecosystem health and aquaculture safety. In this study, two large-scale cruises were conducted in the Bohai Sea and the Yellow Sea, China, in spring and summer 2023 to clarify the composition, concentration, and spatial distribution of LSTs in the water columns and sediments. Results showed that okadaic acid (OA), dinophysistoxin-1 (DTX1) and/or pectenotoxin-2 (PTX2) were detected in 249 seawater samples collected in spring and summer. The concentrations of ∑LSTs in seawater were ranging of ND (not detected) –13.86, 1.60–17.03, 2.73–17.39, and 1.26–30.21 pmol L−1 in the spring surface, intermediate, bottom water columns and summer surface water layers, respectively. The detection rates of LSTs in spring and summer seawater samples were 97% and 100%, respectively. The high concentrations of ∑LSTs were mainly distributed in the north Yellow Sea and the northeast Bohai Sea in spring, and in the northeast Yellow Sea, the waters around Laizhou Bay and Rongcheng Bay in summer. Similarly, only OA, DTX1 and PTX2 were detected in the surface sediments. Overall, the concentration of ∑LSTs in the surface sediments of the northern Yellow Sea was higher than that in other regions. In sediment cores, PTX2 was mainly detected in the upper sediment samples, whereas OA and DTX1 were detected in deeper sediments, and LSTs can persist in the sediments for a long time. Overall, OA, DTX1 and PTX2 were widely distributed in the water column and surface sediments in the Bohai Sea and the Yellow Sea, China. The results of this study contribute to the understanding of spatial distribution of LSTs in seawater and sediment environmental media and provide basic information for health risk assessment of phycotoxins.

Anthropocene 129I Record in the Yellow Sea Sediments and Its Indication for River-Delivered Radioactive Pollution to Marginal Seas.

As the number of coastal nuclear facilities rapidly increases and the wastewater from the Fukushima Nuclear Plant has been discharged into the Pacific Ocean, the nuclear environmental safety of China's marginal seas is gaining increased attention along with the heightened potential risk of nuclear accidents. However, insufficient work limits our understanding of the impact of human nuclear activities on the Yellow Sea (YS) and the assessment of their environmental process. This study first reports the 129I and 127I records of posthuman nuclear activities in the two YS sediments. Source identification of anthropogenic 129I reveals that, in addition to the gaseous 129I release and re-emission of oceanic 129I discharged from the European Nuclear Fuel Reprocessing Plants (NFRPs), the Chinese nuclear weapons testing fallout along with the global fallout is an additional 129I input for the continental shelf of the YS. The 129I/127I atomic ratios in the North YS (NYS) sediment are significantly higher than those in the other adjacent coastal areas, attributed to the significant riverine input of particulate 129I by the Yellow River. Furthermore, we found a remarkable 129I latitudinal disparity in the sediments than those in the seawaters in the various China seas, revealing that sediments in China's marginal seas already received a huge anthropogenic 129I from terrigenous sources via rivers and thus became a significant sink of anthropogenic 129I. This study broadens an insight into the potential impacts of terrigenous anthropogenic pollution on the Chinese coastal marine radioactive ecosystem.

Impact of summer hypoxia on macrobenthic communities in a semi-enclosed bay: A long-term observation in the North Yellow sea of China

The O2 content of the global ocean has been declining progressively over the past decades, mainly because of human activities and global warming. Despite this situation, the responses of macrobenthos under hypoxic conditions remain poorly understood. In this study, we conducted a long-term observation (2015–2022) to investigate the intricate impact of summer hypoxia on macrobenthic communities in a semi-enclosed bay of the North Yellow Sea. Comparative analyses revealed higher macrobenthos abundance (1956.8 ± 1507.5 ind./m2 vs. 871.8 ± 636.9 ind./m2) and biomass (8.2 ± 4.1 g/m2 vs. 5.6 ± 3.2 g/m2) at hypoxic sites compared to normoxic sites during hypoxic years. Notably, polychaete species demonstrated remarkable adaptability, dominating hypoxic sites, and shaping community structure. The decline in biodiversity underscored the vulnerability and diminished resilience of macrobenthic communities to hypoxic stressors. Stable isotope analysis provided valuable insights into food web structures. The average trophic level of macrobenthos measured 2.84 ± 0.70 at hypoxic sites, contrasting with the higher value of 3.14 ± 0.74 observed at normoxic sites, indicating the absence of predators at high trophic levels under hypoxic conditions. Moreover, trophic interactions were significantly altered, resulting in a simplified and more vulnerable macrobenthic trophic structure. The findings underscored the importance of comprehensive research to understand the complex responses of macrobenthic communities to hypoxia, thereby informing future conservation efforts in impacted ecosystems.

Lacustrine environment evolution in the Mesozoic North Yellow Sea Basin, eastern China: Insight from the transition of Jurassic grey mudstones to Cretaceous red successions

During the Cretaceous, terrestrial red beds appear on a global scale. Previous reports have suggested that these red beds were intricately linked to hot paleoclimates and unique paleogeographic configurations. This study focuses on petrological, mineralogical, and geochemical analyses conducted on samples that capture the transition from grey to red mudstone successions dating from the Middle Jurassic to Early Cretaceous within the North Yellow Sea Basin, with a focus to investigate the evolution of lacustrine environments and paleoclimates during their deposition. The findings revealed four episodes of hydrothermal activity occurring during the deposition of the Jurassic grey to Cretaceous red mudstone successions. Some mudstone samples have identified positive Eu anomalies, but the hydrothermal signal may not be as strong due to the open lake environment. Hf vs La/Th and ∑REE vs La/Yb graphs indicate that most grey mudstones originated primarily from upper crustal felsic sources, while certain red mudstones contain mantle material, and the provenance of both has changed significantly. Noteworthy indicators like Sr/Ba, B/Ga, U/Th, Ni/Co, V/Cr and V/(V + Ni) values denote that the sedimentary environments of both grey and red mudstones were oxidized, deviating from conventional viewpoints. However, this deviation may stem from hydrothermal contamination impacting trace elements such as Ni, Co, and Sr. Assessment using indicators like Rb/Sr and Sr/Cu reflects a transition from a warm and wet Jurassic climate to a hot Early Cretaceous climate. Variations in lake levels, prompted by climate fluctuations, led to increased oxygenation on the lake bottoms, resulting in the deposition of red mudstones. These findings suggest a close correlation between the red mudstones and the hot climate, driven by the tectonic evolution of Eastern China. The transformation from grey to red mudstones during the Middle Jurassic to Early Cretaceous periods signifies a response to paleoclimatic and paleoenvironmental changes in East Asia.

High-resolution water temperature and salinity evolutions and associated drivers of the North Yellow Sea during the Late-Holocene

The mud deposit areas on continental shelf have developed in a relatively steady sedimentary condition with high sedimentation rates, thus rendering them ideal regions for exploring high-resolution paleo-sedimentary environment records. Since the sedimentary environment of the continental shelf is subject to the compound influence of multiple factors, the reconstruction of water salinity and temperature and comprehensive analysis of their response to global climate change remains challenging. Therefore, the present study characterized water salinity and temperature of the North Yellow Sea (NYS) using proxies, such as ratios of halogen elements of sediments and stable isotopic compositions of benthic foraminifera, and found the halogen elements of Cl in sediments was good proxy for water salinity. The evolutions of water salinity and temperature of the NYS for the past 3000 years were reconstructed, while the evolution stages and drivers of the sedimentary environment were explored. From approximately 3000 cal yr BP, the sea bottom salinity and temperature of the NYS were found to follow the same evolution trends predominantly consisting of the three stages: relatively low seawater salinity and temperature during 3000−2000 cal yr BP; relatively high seawater salinity and temperature during 2000−460 cal yr BP; and rapid changes of seawater salinity and temperature since 460 cal yr BP. The changes in seawater salinity and temperature of the NYS were largely driven by the East Asian winter monsoon (EAWM) as well as the influence of the Kuroshio Current. As the EAWM fluctuated, changes occurred in the flux of low temperature, low salinity coastal current water into the Yellow Sea, with concomitant changes in bottom temperature and salinity. Strengthening of the Kuroshio Current promoted the development of the Yellow Sea Warm Current, while the influx of warm, salty water into the Yellow Sea influenced the respective sea region. The abrupt global climate changes such as the “Little Ice Age” and the Medieval Warm Period first affected the East Asian monsoon, followed by the respective sea region.

Characterization and application of submarine seismic ambient noise in the Bohai Sea and Yellow Sea

Submarine seismic ambient noise imaging combines current marine and on-land seismic detection technologies. Based on data from several broadband shallow-sea type ocean bottom seismometers (SOBSs) deployed in the Bohai Sea and north Yellow Sea, this paper analyzes the submarine seismic ambient noise characteristics. It explores the theory, technology, method and application of the submarine seismic ambient noise imaging using the single-point horizontal and vertical spectral ratio method (HVSR). The observations yield the following results: 1) Submarine seismic ambient noise has consistent and constant energy, making it an appropriate passive seismic source for submarine high-frequency surface wave investigation. 2) Using the HVSR approach, a single three-component OBS could differentiate between the basement and sediments. Array seismic observation could be utilized to extract the frequency dispersion curve and invert it to obtain the velocity structure for more accurate stratification. 3) The SOBS we use is suitable for submarine surface wave exploration. 4) Tomography results with greater resolution and deeper penetration could be obtained by combining active and passive sources in a simultaneous inversion of the HVSR and frequency dispersion curve. Seamless land-to-ocean seismic research can be accomplished with submarine seismic ambient noise imaging technologies.

Factors influencing the intensity of cross-front transport: An example from the offshore transport around the Shandong Peninsula, China

Cross-front transport is a vital process in the offshore transport of terrestrial materials. The factors influencing cross-front transport are multifaceted and exhibit regional variability. As important factors regulating material transport patterns in the shelf seas of eastern China, the East Asian Winter Monsoon (EAWM) and Kuroshio current (including its branches) vary on multiple time scales, yet their role in controlling offshore transport is not fully understood. In this paper, cross-front offshore transport in the North Yellow Sea is chosen to investigate the aforementioned issue using numerical simulation. By excluding other potential processes for offshore transport, frontal instability is identified as the primary mechanism for offshore transport, which is triggered by winter storms (bursts of the EAWM); hence, the intensity of offshore transport is highly associated with the strength of winter storms on synoptic scales. However, on the inter-annual scale, the intensity of offshore transport is more likely regulated by the strength of the Kuroshio current, and a warming Kuroshio facilitates offshore transport. Although the role of each factor in controlling the intensity of offshore transport is delineated, the interactive effects of the EAWM and Kuroshio current on offshore transport are quite intricate, and how to quantitatively estimate their roles on multiple time scales remains a challenge using modelling. The results obtained from this study can be applied to analyse cross-front transport throughout the eastern China seas and bear significant implications for future studies on pollutant diffusion, nutrient distribution, and sediment transport in the coastal area.

Field Determination and Spatial Distribution of Se (IV) in Coastal Seawater of China

A portable electrochemical system based on rGO/AuNPs/Nafion was constructed for selenium (IV) field determination in coastal seawater of the North Yellow Sea, East China Sea and South China Sea. This system demonstrated a low determination limit (0.03 μg/L), a wide linear range of concentration (0.1–30 μg/L), exceptional reproducibility and repeatability, and excellent selectivity. Each individual, entire test could be accomplished within 8 min. In Yantai Sishili Bay, the Se (IV) concentrations ranged from 0.16–3.59 μg/L (average 1.43 μg/L). In Shengshan Island, the Se (IV) concentrations ranged from 0.20–5.18 μg/L (average 2.06 μg/L). In Zhelin Bay, the Se (IV) concentrations ranged from 0.87–4.87 μg/L (average 3.13 μg/L). The average concentrations of Se (IV) in surface seawater showcased an increasing trend from the north to the south of China, suggesting Zhelin Bay &gt; Shengshan Island &gt; Sishili Bay. The system develops a new, competitive method for water quality assessment, and contributes to the accurate study of the biogeochemical cycles of selenium.

Water stratification alters phytoplankton assemblages in scallop farming waters of the North Yellow Sea in China

As evaluation indicators of the primary productivity, the phytoplankton biomass and community structure are of great significance to the fishery industry, which can be driven by ocean currents, nutrients and water stratification. In the present study, the characteristics of phytoplankton assemblages in different water layers of a typical Yesso scallop farming area in Zhangzi Island, the North Yellow Sea were investigated from March 2021 to January 2022. According to the vertical distribution of temperature, water stratification was observed from June to August (stratification period), and disappeared in March, October and the following January with vertical homogeneity (mixing period). 18S rRNA gene sequencing results revealed that Pyrrophyta was the most dominant phylum during the sampling period, with high gene proportions in the stratification (63.36%) and mixing periods (77.35%). The gene proportion of Bacillariophyta in the stratification period was 5.44%, which was significantly lower than that in the mixing period of 8.93% (p < 0.05). Moreover, Pseudo-nitzschia, a toxin-producing taxon affiliated with Bacillariophyta, exhibited a significantly higher proportion in the stratification period than in the mixing period. During the stratification period, a number of toxin-producing taxa such as Pseudo-nitzschia and Karlodinium were enriched in the bottom layer, which was 1.29-fold and 1.37-fold of that in the surface layer, respectively. Redundancy analysis showed that phosphate and water temperature were major environmental factors driving the vertical distribution of phytoplankton assemblages. The phosphate (0.11 μM) and silicate (2.09 μM) concentrations in the surface layer approached the minimum threshold for phytoplankton growth, and the stoichiometric limitation of phosphate was detected in the surface and middle layers. Collectively, these results indicated that the decreased proportion ratio of Bacillariophyta to Pyrrophyta and unfavorable community composition of Bacillariophyta for scallops were observed during summer, which might result from the phosphate limitation driven by water stratification. The results will further our understanding of the dynamics of phytoplankton communities under the background of intensifying ocean stratification and provide ecological guidance for mollusc mariculture.

High-precision retrieval of offshore sea surface temperature: A machine learning framework based on MODIS and in-situ measurements

High-precision sea surface temperature (SST) data is essential for monitoring and management of offshore environment. SST retrievals from thermal infrared remote sensing have the advantages in time frequency and space coverage over measurements from ships and buoys. However, traditional SST retrieval models are not fully applicable for offshore waters where seawater conditions change a lot, due to simple functional forms and empirical fitting of model parameters. Machine learning (ML) is introduced because it doesn’t need to define specific model rules or unknown parameters, which is more intelligent to deal with complex retrieval problems in a data-driven way. But the applicability of ML has not been investigated in the North Yellow Sea of China, and the selection of driving features for model construction has not been fully discussed. Here, we designed a high-precision SST retrieval framework based on random forest (RF) with optimal feature combination using MODIS data and in-situ SST measurements during 2013–2020 in the northern part of the North Yellow Sea. The performances of different feature combinations were assessed based on model testing accuracies and the RF output feature importance. Compared with previous ML-based SST retrieval studies, we added two time-related features (i.e., day of the year and month) and one feature as initial temperature (i.e., SST retrieval from split-window algorithm), which reduced the testing error by around 15 % and 11 %, respectively. The retrieval results were validated with in-situ measurements, showing that the RF model achieved better accuracies (R2 = 0.987, SD = 0.842 °C, MAE = 0.675 °C, RMSE = 0.841 °C) than the improved split-window algorithm (named as ISW) and deep neural network. Compared with ISW, the spatial distribution of RF retrieval map exhibited similar variation across four seasons, mainly differed in the coastal areas or at the formation of temperature fronts. Note that the constructed RF model was still reliable when applied to the independent samples in 2021. This study contributes to improve the accuracy of offshore SST retrieval under different seawater conditions and provides references for SST monitoring.

Evolution of Suspended Particles in the Autumnal North Yellow Sea: Grain-Size Distributions Measured by Laser In Situ Scattering and Transmissometry

Evolution of Suspended Particles in the Autumnal North Yellow Sea: Grain-Size Distributions Measured by Laser In Situ Scattering and Transmissometry

Correlation between polycyclic aromatic hydrocarbons and total organic carbon in surface sediments of the Bohai Sea and the North Yellow Sea.

The correlation between polycyclic aromatic hydrocarbons (PAHs) and organic carbon is an important indicator of the marine environment. In this paper, twenty-six surface sediment samples were collected from the Bohai Sea and the North Yellow Sea as the study area, and the contents of sixteen PAHs ranged from 71.34 ng·g-1 to 240.78 ng·g-1 with an average of 143.26 ng·g-1 by gas chromatography. The source analysis indicated the source of PAHs in the surface sediments of the study area was more complex, and the percentage of combustion sources was higher than that of petroleum sources, which might cause less negative ecological risks. The average content of total organic carbon (TOC) was 5.25%, as determined by automatic potentiometric titration, and the content of TOC was higher in the Bohai Sea than in the North Yellow Sea. TOC was significantly correlated with HWM-PAHs but was not correlated with LWM-PAHs, which proved organic matter was more effective in controlling high-molecular-weight PAHs than low-molecular-weight PAHs in the surface sediments of the Bohai Sea and the North Yellow Sea.

The contribution of intraspecific variation to future climate responses of brown algae

AbstractIntraspecific variation, which may arise through the interplay between environmental heterogeneity and adaptive variation, has consequences for the resilience of species to climate change. Here, we revealed the levels of intraspecific genomic variation and its causes in a widespread brown alga (Sargassum horneri). Our datasets included both benthic and floating samples from 20 populations sampled along a latitudinal gradient in the Chinese marginal seas. We prepared two datasets: 1) 4628 filtered single nucleotide polymorphisms (SNPs) for all samples, and 2) 20,735 filtered SNPs for only benthic samples. We conducted genotype‐environment association analyses and outlier tests to identify adaptive loci for each dataset. Both neutral and adaptive SNPs revealed a deep genetic split between benthic populations in the North Yellow Sea (NYS) and East China Sea. Redundancy analysis demonstrated that temperature is a major factor driving adaptive divergence of benthic populations. Predictions of the lineage‐level species distribution model revealed severe habitat loss of S. horneri in the NYS and eastern coasts of Korea under RCP8.5 in the 2100 s; however, the low‐latitude boundary remained stable. Based on these results, we speculate that low‐latitude populations may have high resilience to global warming. The dispersal routes of floating samples were determined by coastal currents; however, restricted gene flow between regions was detected. Thus, we speculate that opportunities for the recovery of depleted populations through natural gene flow may be limited. This study highlights the importance of applying conservation strategies (e.g., assisted gene flow) to protect coastal species from local extinction in the future.

Molecular insights into nitrogen constraint for niche partitioning and physiological adaptation of coastal Synechococcus assemblages

Coastal nitrogen input has substantially increased due to human activity. However, much remains unknown about the nitrogen-driven patterns and the underlying genetic basis of coastal picoplankton. To investigate the response and mechanisms of picoplankton induced by nitrogen variation, we conducted in-situ investigations using high-throughput sequencing in the Bohai Sea and performed laboratory nitrogen simulation experiments accompanied by physiological, genomic, and transcriptomic analyses, with Synechococcus as a representative. The results of in-situ investigation revealed that Synechococcus clades I, III, WPC1, and VI of subcluster 5.1 (S5.1) are prevalent in strait areas characterized by robust water exchange with the North Yellow Sea, while clades II, VIII, and IX of S5.1, as well as subcluster 5.2 (S5.2) and subcluster 5.3 (S5.3) are more abundant in central and bay areas experiencing elevated nitrate and nitrite loads. The laboratory experiments further confirmed that inorganic nitrogen is a crucial determinant of diversity and niche partitioning of Synechococcus lineages. Besides, the raising inorganic nitrogen concentration within the current in-situ range (0.1–10 μmol L−1) enhances photosynthesis and carbon fixation of Synechococcus, however further escalation of inorganic nitrogen (100 μmol L−1) may hinder these processes instead. The phenomenon could be associated with the differential expression of genes in metabolic pathways regulating nitrogen metabolism, photosynthetic system II, and photosynthesis-antenna proteins in response to nitrogen concentration and type variation. These findings expand our understanding of the impact of macronutrient variation resulting from human activities on marine picoplankton and biogeochemical cycles.