Yellow Sea Research Articles

Importance of dissolved organic nutrients on nutrient stoichiometry in the Yellow Sea and the East China Sea

We investigated seasonal variations in the dissolved nutrients and organic matter (DOM) in the Yellow Sea and the East China Sea shelf waters from 2017 to 2021. Dissolved organic nitrogen and phosphorus (DON and DOP) concentrations were the highest in the upper layer (<30 m) during the time of spring and autumn bloom and were the lowest in summer. In spring, DON and DOP contributed up to approximately 90% and 80% of the total dissolved nitrogen (TDN) and phosphorus (TDP), respectively. The C:N:P stoichiometry of the DOM pool in spring and autumn indicates that freshly in-situ produced DOM is N-rich compared to the DOM observed in summer and winter, resulting in a dissolved inorganic nitrogen (DIN)-limited environment in the upper layer of seawater during spring and autumn. Conversely, in summer, the highest C:N ratios (∼27) of the DOM pool revealed the DOM remained after the degradation and formation of the refractory pool by marine bacteria. In winter, all nutrients were vertically uniform due to active vertical mixing. This study highlights notable seasonal variations in the cycling of DON and DOP, leading to changes in their bioavailability and subsequent ecosystem responses in the shelf sea.

Spatio-temporal distribution and source analysis of nutrients and antibiotics in the waters of a mariculture area in Haizhou Bay, Yellow Sea

Due to the continuous expansion of China's urban areas, there has been a growing trend of discharging marine aquaculture tail water directly into the sea. This phenomenon has had a significant impact on the marine ecological environment.To determine the status of pollutant discharge from marine aquaculture tailwater and facilitate its treatment.This paper analyses the spatiotemporal distribution characteristics of nutrients and antibiotics in the pond culture mode of Penaeus monodon. The influent, tail water, and adjacent seawater of the aquaculture concentration area in the port industrial zone of Guanyun County, Lianyungang City were monitored. The study aims to explore potential correlations between the variables.The data indicates that nitrogen and phosphorus are the primary pollutants in the Lianyungang aquaculture sea area. In 2022, the average total nitrogen content was 104.475 mg/L, and the average total phosphorus content was 3.83 mg/L.Sulfanilamide and norethindrone antibiotics were found in the culture tailings. The residual content of sulfonamide antibiotics ranged from 0.6 to 33.4 ng/L, while the residual content of norethindrone antibiotics ranged from 0.15 to 1.0 ng/L.This paper analyses the monitoring data statistically to provide basic support for the protection of the marine ecological environment in Haizhou Bay. Additionally, to enhance the environmental management of China's coastal waters, it is necessary to formulate an environmental management policy for coastal waters and provide a scientific basis for the implementation of the total amount of pollutants discharged into the sea.

Community organization and network complexity and stability: contrasting strategies of prokaryotic versus eukaryotic microbiomes in the Bohai Sea and Yellow Sea.

Unraveling the effects of spatial gradients on microbiome assembly and association is a challenging topic that remains understudied in the coastal ecosystem. Here, we aimed to investigate the effects of spatial variation on the network complexity and stability of plankton microbiomes in the Bohai Sea and Yellow Sea. These seas serve as spawning and nursery grounds for economically important fisheries valued at billions of dollars annually. Environmental heterogeneity structures microbial communities into distinct spatial patterns, leading to complex direct/indirect relationships and broader ecological niches of bacterioplankton compared to microeukaryotic communities. Interestingly, salinity gradients positively influenced the richness of rare subgroups of bacterioplankton, while the rare microeukaryotic subgroups showed an opposite trend. Abundant subgroups of prokaryotic/eukaryotic microbiomes exhibited greater environmental niche breadth and lower phylogenetic distance compared to the rare subgroups. Stochastic processes contributed greatly to microbiome dynamics, and deterministic processes governed the bacterioplankton organization with a lower phylogenetic turnover rate. Compared to microeukaryotes, bacterioplankton exhibit higher network modularity, complexity, and robustness and lower fragmentation, and vulnerability. These observations offer vital insights into the anti-interference ability and resistance of plankton microbiomes in response to environmental gradients in terms of organization and survival strategy as well as their adaptability to environmental disturbances.IMPORTANCEAn in-depth understanding of community organization and stability of coastal microbiomes is crucial to determining the sustainability of marine ecosystems, such as the Bohai Sea and Yellow Sea. Distinct responses between prokaryotic and eukaryotic microbiomes to spatial heterogeneity were observed in terms of geographical distribution, phylogenetic distance, niche breadth, and community assembly process. Environmental variations are significantly correlated with the dynamics of rare eukaryotic plankton subcommunities compared to prokaryotic plankton subcommunities. Deterministic processes shaped prokaryotic plankton community organization with a lower phylogenic turnover rate. Rare subgroups had noticeably higher phylogenetic distance and lower niche breadth than the corresponding abundant subgroups. Prokaryotic microbiomes had higher molecular network complexity and stability compared to microeukaryotes. Results presented here show how environmental gradients alter both the geographical characteristics of the microbial organization in coastal seas and also their co-occurrence network complexity and stability and thus have critical implications for nutrient and energy cycling.

Sea-air CO2 Flux in the South Yellow Sea Based on Seasonal Underway Observations

Sea-air CO2 Flux in the South Yellow Sea Based on Seasonal Underway Observations

Assessment of high-resolution regional ocean reanalysis K-ORA22 for the Northwest Pacific

The Korea Institute of Ocean Science and Technology developed the Korea Operational Oceanographic System-Ocean Predictability Experiment for Marine Environment (KOOS-OPEM), a high-resolution (1/24°, 51 vertical levels) ocean prediction model for the Northwest Pacific Ocean that incorporates ensemble optimal interpolation. In this study, we present KOOS-OPEM ReAnalysis version 2022 (K-ORA22), which covers the period from 2011 to 2022. We conducted a comparative analysis between K-ORA22 and other high-resolution (1/10°–1/12°) global reanalyses, including the Hybrid Coordinate Ocean Model, Global Ocean Reanalysis and Simulation (GLORYS), and Bluelink ReAnalysis (BRAN), to demonstrate the reproducibility and reliability of regional characteristics. Statistical comparisons revealed that while K-ORA22 exhibited some warm biases, its sea surface temperature (SST) anomaly correlation after removing the seasonal cycle was approximately 0.87, comparable to other reanalyses. Additionally, K-ORA22 effectively reproduced coastal upwelling, which is characterized by a sharp decrease in SST, as observed by marine meteorological buoys in the Southwest of the East/Japan Sea. K-ORA22 exhibits a warm bias of approximately 0.50 °C around 200 m, slightly higher than those of GLORYS and BRAN, while maintaining a low salinity bias in the subsurface. Notably, K-ORA22 outperformed the other reanalyses in accurately reproducing the unique characteristics of North Pacific and East Sea intermediate waters, characterized by a salinity minimum layer. In addition, K-ORA22 stands out in its ability to accurately reproduce the Yellow Sea Cold Water Mass with a low-temperature root-mean-square error (RMSE) of 0.76 °C in the Yellow Sea (YS) region. However, it exhibited the highest RMSE for salinity in the YS region and Korea/Tsushima Strait, indicating a potential overestimation of river discharge from Korea and China. While the sea surface height (SSH) anomaly correlation of K-ORA22 did not surpass 0.80 in the entire region because of limitations in the background error covariance used, its ability to reproduce the Kuroshio path was comparable to those of other reanalysis datasets. In conclusion, K-ORA22 excels in reproducing the unique characteristics of Korean marginal seas. Still, it exhibits weaknesses, such as the overestimation of river discharge and a somewhat limited ability to simulate SSH variability, compared with other global reanalyses. We plan to enhance K-ORA22 by updating background error covariance, addressing biases related to river discharge and assimilating the best available in situ observations and satellite data.

Silicon balance in an integrated multi-tropical aquaculture ecosystem, Sanggou Bay, China

Farmed aquaculture species play an important role in regulating nutrient cycles in farming systems. Compared with nitrogen and phosphorus, the role of farmed species in the silicon (Si) cycle remains poorly understood. To help reduce this uncertainty, we clarified the sources and sinks of silicate and quantified the Si pools in an aquaculture system in Sanggou Bay (SGB). The results showed that dissolved inorganic nutrient levels were significantly lower during the dry season than during the wet. Dissolved silicate (DSi) is a potential limiting factor for phytoplankton growth during spring, and phosphorus limitation occurs during summer. The budget results indicated that large amounts of nitrogen, phosphate (DIP), and DSi were buried in the sediment or transformed into other forms during both the wet and dry seasons. The nitrogen and DIP cycles were strongly influenced by bivalve excretion and farmed species harvesting; however, these processes had little impact on the Si cycle. Si availability depends on both external inputs and internal recycling. DSi was primarily supplied from the Yellow Sea, with a minor contribution from the river due to river discharge during spring. However, during summer, riverine inflow (accounting for 83% of the total influx) was the major DSi source followed by benthic flux (12%). Biogenic silica (BSi) burial efficiency in the sediment was estimated to be 78% during spring and 23% during summer. The BSi preservation efficiency in bivalves during spring was high (53%), leading to a higher Si retention than in river discharge. Bivalves biodeposition plays an important role in the Si burial process. We suggest that this high retention is essentially controlled by the biodeposition mechanism, which is directly controlled by the exotic suspension feeders. Bivalves have the potential to alter Si retention in the bay by producing large amounts of biodeposits and accelerating the silica cycle, which may lead to more carbon dioxide being absorbed by diatoms.

Combined Effects of Fishing and Environment on the Growth of Larimichthys polyactis in Coastal Regions of China

In fisheries’ stock assessments, the concept of “growth plasticity”—the ability of organisms to modulate their growth rates in response to environmental conditions—has gained attention in recent years. Historically, the impacts of fishing activities and environmental fluctuations were considered separately, while their combined effects have recently come into focus. This study collected 834 adult small yellow croakers (Larimichthys polyactis) from the northern Yellow Sea, the central Yellow Sea, the southern Yellow Sea, and the northern East Sea by trawling during 2020–2021. Using otolith increments as a proxy for annual somatic growth, the study reconstructed otolith chronologies during 2015–2020 for these four stocks. The results of the mixed-effects modeling suggested that temperature during spawning and previous overwintering seasons had comparable importance for the annual growth of small yellow croakers, with higher temperature promoting growth. The growth of small yellow croakers was also found to be correlated with ENSO events, with a lag of 1 to 2 years. A further investigation into combined effects revealed that higher fishing pressure might inhibit the small yellow croaker’s response to favorable environmental conditions. Furthermore, considering the potential differences in growth plasticity among stocks, an analysis was conducted on the spatial variations in growth response to these factors. The analysis revealed that, compared to the stocks in the Yellow Sea, the stock from the East China Sea could exhibit higher growth, superior adaptability to temperature, and a distinctive response to fishing pressure. In conclusion, the present study, while primarily focusing on temperature, preliminarily analyzed the combined effects of fishing and environment and underscored the differences in growth plasticity between stocks in the Yellow Sea and the East China Sea. Despite the limited factors analyzed in this study, it suggests a direction for future studies, highlighting the necessity to include more environmental factors, and even population factors (e.g., the biomass of preys), for a more comprehensive understanding of the combined effects. Based on the observed differences between the two potential subpopulations, this study also provides new insights for the management of the small yellow croaker based on metapopulation dynamics.

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.

Whether the summer fishing moratorium can improve the status of fisheries resources in the yellow sea and Bohai Sea

The China government has introduced many strategies in fisheries management of the Yellow Sea and the Bohai Sea, the most stringent of which is the summer fishing moratorium. Whether the summer fishing moratorium can restore fishery resources has always been a concern. In this study, we selected eight representative commercial fish species the Yellow Sea and Bohai Sea, including Pampus argenteus, Trichiurus lepturus, Scomberomorus niphonius, Ilisha elongata, Thamnaconus modestus, Scomber japonicus, Engraulis japonicus and Larimichthys polyactis, and used the JABBA method to study their historical exploited dynamics and current stock status. We evaluated the effectiveness of the summer fishing moratorium based on the increments of biomass and catch after its implementation and adjustments. P. argenteus and S. niphonius stocks were in the healthy status in 2022, the other six fisheries stocks were overexploited. The summer fishing moratorium had a strong conservation effect, especially after the first implementation in 1995, with the biomass of six fish species increased and the catch of seven species increased, and the total average biomass and catch increments were 21.22 % and 89.72 %. This positive effect was also reflected after the first adjustment in 2003. Although the moratorium duration was continuously extended after the second and third adjustment, the conservation effect was offset by the flooding of fishing efforts immediately after the moratorium. For the six overexploited stocks, we suggest that the allowable catch of E. japonicus, T. lepturus, L. polyactis, S. japonicus, I. elongata and T. modestus is at most 527.91 kt, 147.51 kt, 93.43 kt, 81.51 kt, 1.25 kt and 4.95 kt in the Yellow Sea and Bohai Sea, respectively.

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.

Seasonal dynamics of amino acids in the Southern Yellow Sea: Feedback on the mechanism of green tides caused by Ulva prolifera

The biogeochemical processes of amino acids in the Southern Yellow Sea (SYS) have become more dynamic under the influence of the world's largest-scale green tide. The potential relationship between amino acids and green tides has not been effectively assessed, despite its critical importance for exploring dissolved organic matter (DOM) cycling processes in marginal seas. In this study, three cruises were conducted to analyze the concentrations and compositions of total hydrolyzed amino acids (THAAs) in the SYS during the spring, summer, and autumn of 2019. The bioavailability potential of DOM was evaluated using the degradation index (DI) and THAA nitrogen normalized yield (THAA (%DON)) (DON as dissolved organic nitrogen). The variation dynamics of amino acid indicators during different stages of green tide were further explored. The results showed that the THAA concentrations and DOM bioavailability in the SYS were considerably influenced by biological processes. The THAA concentrations (0.96 ± 0.34 μmol L−1) exhibited the lowest mean values in the summer, while the DI values (0.106 ± 0.461) and mean THAA (%DON) values (18.20 ± 6.58 %) were the highest during this season. The distribution of amino acid indicators in the summer (the late-tide stage) was regulated by the green tide mechanism, and kept pace with the green tide floating region. In comparison with the waters in south of 35° N, the THAA concentrations and DI values experienced significant seasonal variations (p < 0.05) in north of 35° N, with the highest DI values (1.217) observed in the green tide aggregation area. This indicates the transformation of nutrient sources for Ulva prolifera in the late-tide stage and its impact on DOM bioavailability. Thus, as a potential feedback indicator of green tides, the study of amino acids is meaningful for understanding the occurrence of green tides and the source-sink pattern of organic nitrogen.

Notes on the natural history and identity of the pelagic sea snake Hydrophis platurus (Serpentes: Elapidae) from Golfo Dulce, Puntarenas, Costa Rica

Introduction: The pelagic sea snake Hydrophis platurus has the broadest distributional range of all the snakes and is the only sea snake of tropical waters off the west coast of the Americas. Within the variation in the color pattern of this species, completely yellow specimens were considered very rare or occasional. However, a yellow pattern dominates a population established in the interior of the Golfo Dulce in the Southern Pacific of Costa Rica. Objective: We studied the abundance, activity patterns, morphometry, and feeding behavior of the yellow H. platurus within the Golfo Dulce. Methods: Between February 2009 and July 2018, we conducted surveys for sea snakes from a boat within the perimeter of the Golfo Dulce. Results: Adults from the gulf population are smaller than the bicolor oceanic population, with females having larger bodies. Sea snakes within the gulf float and move with surface currents without being linked to drift lines and debris. These snakes are mainly found in clean, calm waters with little turbulence. They feed on a wide diversity of small fish, which they capture using passive stalking predatory behaviors floating on the surface. Prey are quickly captured and swallowed alive. This species has an almost total absence of predation, a pattern that extends to this yellow population. Conclusions: The characteristics of the gulf and the direction and strength of the surface currents at its entrance might restrict the transit of this yellow population to the outside and the entry of the bicolored snakes of the oceanic population. We do not consider making taxonomic changes in this Golfo Dulce population prudent. This yellow population is relatively common within the basin. However, the high tourist traffic and other activities are risk factors for its conservation. Protection policies must be created to preserve and protect this small population of yellow sea snakes unique within this species' distribution range.

Morphological discrimination of fouling Ulva and Blidingia species on Pyropia rafts in Rudong, China: an in-field protocol for early monitoring of algae forming the Yellow Sea green tide

Abstract Fouling seaweeds on nori cultivation rafts in Subei radial sand ridges (Jiangsu, China) are believed to be the source of the Yellow Sea green tide (YSGT). Although major species are consistent across years, their biomass and proportions undergo significant annual changes, which was speculated to be related to the size of YSGT. Therefore, early detection and biomass assessment of the bloom-forming algae are crucial, increasing the need to develop a morphological identification method suitable for large sample sizes in the field. In this study, fouling seaweeds were collected from this area in spring 2017. Five major species, Ulva aragoënsis, Ulva compressa, Ulva linza, Ulva prolifera, and Blidingia sp. were molecularly identified, and confirmed as the predominant fouling seaweeds on nori rafts over the past decade. In this unique ecological niche, the morphological features of species changed significantly yet stably. Based on morphological observations, an identification key for these five species was established. Furthermore, a simplified version containing only two indices was developed for practical field use, with an average accuracy of 81 % (δ 2 = 0.003) in empirical accuracy assessments. This method can be used to monitor the community structure and succession of fouling seaweeds at the geographical source of YSGT.

Decade-long historical shifts in legacy and emerging per- and polyfluoroalkyl substances (PFAS) in surface sediments of China's marginal seas: Ongoing production and ecological risks

Since the addition of perfluorooctane sulfonate (PFOS) to the Stockholm Convention in 2009, it became imperative to reassess the distribution and ecological risk of per- and polyfluoroalkyl substances (PFAS) in coastal sediments over the past decade as sediment records the history of pollutants from human activities. To achieve this, sediments were collected in 2009 and 2021 from China's coastal regions. Despite the consistent geographical pattern where the highest concentrations of ∑PFAS were found in the Yellow Sea, temporal changes have emerged. During the studied period, ∑PFAS levels experienced an increase in the East China Sea while concurrently witnessing a decrease in the South China Sea. Of significance, emerging PFAS compounds displayed not only rising concentrations but also a broader array, pointing towards their intensified production and utilization within China. Alarmingly, PFOS levels in sediments taken from the East China Sea maintained a consistently high ecological risk status over the last ten years. Significant correlations were found between long-chain PFAS and organic carbon content. Comparisons between datasets from 2009 to 2021 uncovered a shifting ecological risk landscape, with heightened concerns for PFOA in the East China Sea, while PFOS-associated risks appeared to diminish in the South China Sea—potentially reflecting the transition to alternative PFAS chemicals. The research reinforces the importance of continuous monitoring and emphasizes the urgent necessity for deeper exploration into the environmental implications and hazards posed by emerging PFAS.

Pollen evidence of enhanced Yellow River provenance into the South Yellow Sea after the Middle Pleistocene Transition

Quaternary sediment of the South Yellow Sea (SYS) is usually assumed to record climatic changes, tectonic activities and major river evolutions. However, as an important terrigenous indicator, a long sequence of pollen proxy in the SYS lacks for studies of river provenance and climate changes. In this study, we focused on a 150-m pollen record in the SYS that covered most of the Quaternary period over the past 1.8 Ma. The most significant changes of pollen assemblage were caused by river provenance, that high pollen percentages of broadleaved trees such as Castanea/Castanopsis reflect a dominant provenance of the Yangtze River since ca. 1.8 Ma, with a decline trend during the Mid-Pleistocene transition (MPT) mainly between 1.1 and 0.8 Ma. The sharp increase in coniferous pollen, particularly Picea, originated from the Yellow River drainage areas, suggesting a major alteration in terrigenous pollen source from the Yangtze River to the Yellow River at ∼0.8 Ma, which agrees well with the timing of the final integration of the modern Yellow River. The high pollen quantities of Artemisia and Ephedra also shows the enhanced Yellow River provenance where most landscape was covered by semi-arid open vegetation (e.g. steppe). The alternate appearances of marine foraminifera and dinoflagellate cysts, and freshwater wetland plants (Cyperaceae, Poaceae) through the interglacial intervals from MIS 19/21 demonstrate different estuary sedimentary environments and diverse salinity, associated with the sea-level fluctuations. The pollen concentration suggests an increase in terrigenous materials towards the interglacial MIS 11 and the preliminary delta formation of the Yellow River. We propose that the terrigenous input from the Yellow River accelerated after the MPT, and combined effects of tectonic movement drove the evolution of the river delta plains in eastern China. Our data also reveal some secondary periodic changes in evergreen broadleaved forest during the past 1.8 Ma and cold-tolerant coniferous forest since particularly the MPT, which are generally linked with the 400-ka long eccentricity cycle and the variability of monsoon climate.

The evolution and relationship of the Yellow Sea warm current and the Yellow Sea Cold Water Mass since the Mid-Holocene and possible ENSO influences

The Yellow Sea Warm Current (YSWC) and Yellow Sea Cold Water Mass (YSCWM) are crucial components of Yellow Sea oceanic dynamics. Investigating their historical relationships since the mid-Holocene, as demonstrated by modern observations, is highly important. We reconstructed their evolution using 37 surface sediment samples and core Z1 from the Yellow Sea. Basic end-member analysis of core sediment grain sizes revealed that end-member two had a dominant peak at 12 μm, indicating the evolution of the YSWC. The analysis of the structure of benthic foraminiferal communities in surface sediments indicated that the combination of Ammonia ketienziensis, Hanzawaia nipponica, and Astrononion italicum serves as a reliable indicator of the evolution of the YSCWM. By integrating sedimentological and micro-palaeontological evidence with published organic geochemical findings, we elucidated high-resolution evolutionary records of the YSWC and YSCWM since the mid-Holocene. Our findings indicate that the YSWC underwent rapid intensification with significant fluctuations during ∼6.0–3.9 ka. It then decreased to modern levels between ∼3.9 ka and ∼1.9 ka, remaining relatively stable during ∼1.9–0.0 ka, with enhancements noted at ∼1.4 ka and ∼0.3 ka. The YSCWM evolved synchronously with the YSWC after ∼6.0 ka, weakened and then strengthened during ∼6.0–1.9 ka, and maintained relative stability during ∼1.9–0.0 ka, with decreases observed at ∼1.4 ka and ∼0.3 ka. The YSWC and YSCWM exhibited opposite changes, similar to modern oceanographic patterns, except for synchronous variations during ∼4.0–3.9 ka, when the YSCWM was formally established. The decoupling of the YSCWM and the YSWC during ∼4.0–3.9 ka and the significant enhancements of the YSCWM at ∼2.5 ka and ∼2.0 ka when the YSWC slightly weakened are associated with the substantial influence of the ENSO climate phenomena on the coastal regions of East Asia from ∼4.0 ka to ∼1.9 ka. We propose that the YSCWM is more sensitive to ENSO, potentially making it more suitable for reconstructing the palaeoceanography and palaeoclimatology of the Yellow Sea.

The causal link between nitrogen structure and physiological processes of Ulva prolifera as the causative species of green tides

Harmful algal blooms (HABs) increase with eutrophication depending on the nutrient structure (availability and ratios), but an unequivocal causal link between these factors is rarely established. Here, we provide support for the causal link between the nitrogen structure and physiological processes of Ulva prolifera as the causative species of Yellow Sea green tides (YSGTs) using in situ and laboratory experiments. The results showed that the components of nitrogen nutrients in seawater exhibited significant spatiotemporal variation. The concentration of NO3−-N showed a notable decreasing trend from south to north. Sufficient dissolved inorganic nitrogen (DIN) induced increases in thalli nitrate reductase (NR) and glutamine synthetase (GS) activities. This could accelerate thalli uptake of nitrogen nutrients. The glutamate dehydrogenase (GDH) activity was significantly upregulated with the increasing proportion of dissolved organic nitrogen (DON) in seawater. The change in nitrogen structure regulated the activity of NR during the long-distance floating migration of the YSGTs. And the activity of NR could modulate the nitric oxide (NO) content in the thalli. NO was used as a signal molecule to enhance the antioxidant defense system of thalli. The efficient antioxidant system in the thalli could reduce oxidative stress and effectively maintain high photosynthetic activity. The findings deepen our understanding of the relationship between nitrogen structures and key biological processes in macroalgae. This study also suggest that NO can enhance key biological processes in U. prolifera under varying nitrogen structures.

Long-Chain Alkenones in the South Yellow Sea Sediments and Their Indicative Significance for Haptophytes Species

Long-Chain Alkenones in the South Yellow Sea Sediments and Their Indicative Significance for Haptophytes Species

Changing circulations challenge the sustainability of cold water mass and associated ecosystem under climate change

Bottom cold water mass provides abundant nutrients and cool water in summer, playing a pivotal role in the productivity of marine ecosystem and sustainable aquaculture development. Located in the most densely populated region, the Yellow Sea cold water mass (YSCWM) is a unique one influencing hundreds of millions of people living in the rim of the Yellow Sea. As anthropogenic carbon emissions continue, how the YSCWM will be altered by climate change becomes a pressing issue, but remains elusive. Using an unprecedented set of climate models with high resolution and biogeochemical components, we find that the volume of the YSCWM will shrink by 48% to 2040–2050, along with the bottom temperature warming of 0.4 ± 0.1 °C dec−1 and the dissolved oxygen concentration declining of 0.09 ± 0.04 mg (L dec)−1. The significant destruction of the YSCWM is driven by the strengthened Yellow Sea Warm Current (YSWC). The reduced land-sea thermal contrast is the cause of the circulation change, by weakening the East Asian winter monsoon. Due to the resultant profound habitat reduction for marine life, predicting the change of the YSCWM will have far-reaching influences on the future policy-making for sustainable development of offshore aquaculture.

Sound speed prediction of seafloor sediments in the South Yellow Sea based on BP-AdaBoost model

Based on the sound speed and physical property measurements of seafloor sediments obtained in the central part of the South Yellow Sea, a multi-parameter prediction model for the sound speed of seafloor sediments based on seven parameters, including density, porosity, water content, liquid limit, plasticity index, compression coefficient, and median grain size, was developed by using the BP-AdaBoost fusion algorithm. The results show that the model, configured with 7 input layer neurons, 10 hidden layer neurons, 1 output node, a learning rate of 0.1, and 300 training iterations, achieved a correlation coefficient of 0.962. The mean absolute error (MAE) of the predicted sound speed was 10.19 m/s, and the mean relative error (MAPE) was 0.66%. These results are better than those of single-parameter and dual-parameter prediction equations and other machine learning models. The BP-AdaBoost model prediction method of sound speed of seafloor sediments established in this paper is better than the single-parameter and dual-parameter prediction equations and other prediction models, and it can provide a new way for the prediction of sound speed of seafloor sediments in the study area.