East Sea Research Articles

Metagenomic insights and biosynthetic potential of Candidatus Entotheonella symbiont associated with Halichondria marine sponges.

Korea, being surrounded by the sea, provides a rich habitat for marine sponges, which have been a prolific source of bioactive natural products. Although a diverse array of structurally novel natural products has been isolated from Korean marine sponges, their biosynthetic origins remain largely unknown. To explore the biosynthetic potential of Korean marine sponges, we conducted metagenomic analyses of sponges inhabiting the East Sea of Korea. This analysis revealed a symbiotic association of Candidatus Entotheonella bacteria with Halichondria sponges. Here, we report a new chemically rich Entotheonella variant, which we named Ca. Entotheonella halido. Remarkably, this symbiont makes up 69% of the microbial community in the sponge Halichondira dokdoensis. Genome-resolved metagenomics enabled us to obtain a high-quality Ca. E. halido genome, which represents the largest (12 Mb) and highest quality among previously reported Entotheonella genomes. We also identified the biosynthetic gene cluster (BGC) of the known sponge-derived Halicylindramides from the Ca. E. halido genome, enabling us to determine their biosynthetic origin. This new symbiotic association expands the host diversity and biosynthetic potential of metabolically talented bacterial genus Ca. Entotheonella symbionts.IMPORTANCEOur study reports the discovery of a new bacterial symbiont Ca. Entotheonella halido associated with the Korean marine sponge Halichondria dokdoensis. Using genome-resolved metagenomics, we recovered a high-quality Ca. E. halido MAG (Metagenome-Assembled Genome), which represents the largest and most complete Ca. Entotheonella MAG reported to date. Pangenome and BGC network analyses revealed a remarkably high BGC diversity within the Ca. Entotheonella pangenome, with almost no overlapping BGCs between different MAGs. The cryptic and genetically unique BGCs present in the Ca. Entotheonella pangenome represents a promising source of new bioactive natural products.

Assimilation of Surface Geostrophic Currents in the East Sea Using the Ensemble Kalman Filter

The conventional ocean data assimilation process typically involves assimilating hydrographic data, such as temperature and salinity measurements, obtained from both satellites and in-situ observations. This study introduces a novel approach to enhance ocean circulation modeling by assimilating surface geostrophic currents derived from satellite altimetry data using the ensemble Kalman filter. To match the time scales for the variability in the observed surface geostrophic currents and the model currents, the current velocities from the model were low-pass filtered. The optimal cut-off period for the low-pass filter was determined to be 31 days in the East Sea. Eight sensitivity experiments were then conducted to examine the effects of observation error and low-pass filtering during the assimilation of surface geostrophic current data. Assimilation experiments with surface geostrophic current data improved surface currents but had minor negative impacts on the temperature and salinity when compared with assimilation experiments without surface geostrophic current data. Notably, the experiment with an observation error of 10 cm/s for the geostrophic current outperformed the other experiments. Surface geostrophic current assimilation improved the sea surface temperature during winter and effectively modified surface current patterns during autumn in the East Sea. Assimilating satellite-derived surface geostrophic currents in the ocean circulation model thus enhanced the accuracy of surface circulation simulation. This improvement in ocean analysis data offers significant benefits for understanding ocean climate change and for developing marine management strategies.

Statistical analysis of the association between El Niño and the biological carbon pump in the East Sea (Japan Sea)

Understanding the impacts of climate change on oceanic carbon cycling is important from a carbon sequestration perspective. A sediment trap study focused on the biological carbon pump system in the Ulleung Basin (UB) in the southwestern part of the East Sea (Japan Sea) was conducted from 2011 to 2017. Particulate organic carbon (POC) flux significantly increased by 37, 56, and 43% from 2014 to 2016 during the El Niño phase. We examined data related to water current variability, such as sea surface height, current velocity, and eddy frequency to understand their roles in particle transport. In addition, a Martin curve was employed to analyze the rate of vertical attenuation of POC flux in the UB. Current variability could be the most important factor influencing the increase in sinking-particle flux during the El Niño phase.

Predicting Changes in Potential Habitats of an Endemic Plant Species under SSP Scenarios: A Case Study of <italic>Eranthis byunsanensis</italic>

Background and objective: Climate change significantly impacts the growth environments of organisms that have adapted to natural environments. Endemic plants, which are native to specific regions, are particularly vulnerable to these changes. The conservation of these plants is a crucial national task. Currently, there is a lack of research on the habitat characteristics and conservation measures of specific species in Korea. This indicates a need for systematic research on field surveys of habitats for valuable species, the establishment of environmental variables, and long-term changes in suitable habitat areas. Therefore, this study aimed to identify the geographical distribution characteristics and select the optimal environmental variables for Eranthis byunsanensis, an endemic plant in the Korean Peninsula.Methods: To achieve this, we utilized an ensemble model in the R package biomod2 to analyze the current potential habitat and understand its distribution characteristics. We then predicted the changes in potential habitats for the mid-future (2041-2070) and the long-term future (2071-2100) based on climate change scenarios (SSP 1-2.6 and SSP 5-8.5). Finally, we conducted a comparative analysis of the differences between the scenarios.Results: Long-term projections indicate that potential habitat area is larger under SSP1-2.6, a scenario with active climate change mitigation policies, than under SSP5-8.5. Under SSP1-2.6, habitat remained relatively stable with expansion observed in coastal Gangwon-do. In contrast, SSP5-8.5, characterized by extreme climate change, led to significant habitat decline in Jeollabuk-do. Inland Jeollabuk-do experienced rapid habitat loss with a northeastward shift, while habitat along the East Sea coast of Gangwon-do expanded.Conclusion: This study's analysis of habitat change can serve as a crucial foundation for the conservation and management of endemic plants. Furthermore, it is expected to contribute to the development of response strategies to climate change and the identification of alternative habitats for endemic plants.

실전(失傳)된 비극과 신화(新話)의 탄생 - 창극 <변강쇠 점 찍고 옹녀>의 서사 분석을 중심으로

This study aims to define <Madame Ong> as a “tragedy,” a story about confronting fate and destiny, through the gender/sexuality theories and “melancholy” of Judith Butler. Despite its comedic narrative structure, it is a “sad” story of the separation of a man and a woman who were in love. Furthermore, it can be interpreted as a story about “fate.” Ong’s fate is “dying out husbands (sangbusal),” and she dreams of “a normal relationship” to resolve it. It is a “myth” that Ong proposes to overcome fate. However, Ong’s dream as a myth is frustrated by the violence of the gods. Based on this, Ong withdraws her myth and wages war against the gods. This is a “tragic” figure who is in conflict with fate. In the end, Ong abandons her conflict with the gods and reconciles with the myth by appropriating “chastity (Sujeol),” or chastity that is not approved by the community, which can be different from the existing “chastity.” In this sense, the myth ceases to be a myth but becomes a “new story.” In <Madame Ong>, Gangsoe obtains “Jangseung Dongti” because he harmed Hamyang Jangseung after recognizing him as another man who often flirts with Ong. Furthermore, Byeon, who demanded “chastity” in the original <Byeongangsoega>, exhibits a more mature love by requesting Ong to get remarried in <Madame Ong>. However, the community disapproves of the love between these two people. They are outsiders, and their “spiritual” love is denied, while the performance emphasizes their “physical” love, and their sexuality becomes “bad.” At this time, the important axis in <Madame Ong> is religiousness or transcendence. The scenes of Songbongsa’s fortune telling and the female doctors performing a variation of the “East Sea ritual (Donghaean Byeolshingut)” are depicted as rituals in shamanism. In the latter case, the female doctors act as mediators between the nearly-dead Byeon and the living Ong. The world of the gods is a space that shares issues of gender and class with the human world. Therefore, the gods and myths represented in <Madame Ong> are indistinguishable. The “humanic” gods are further depicted as “self-destructing vulgarians.” The scene of the “Jangseung meeting (Jangseung hoeui)” demonstrates the discussion of killing Byeon in the most painful way because their divinity has been damaged. Consequently, Byeon, in addition to Jangseung Dongti, becomes a “jangseung” like themselves and shares their suffering. At this point, the dignity of the gods has shattered, as they argue that their situation is worse than that of humans. However, although divinity has been damaged, the power they possess as gods has not disappeared. Accordingly, Ong uses her body to wage a “guerrilla war” and confront the jangseungs. After the battle with the jangseungs, Ong has the opportunity to negotiate, but she is unable to reclaim the steel bars that she desires most. Daebangjangseung advises Ong to “live your life” and leaves another request or order for her. Ong refuses and says that she will also become a jangseung, seemingly choosing to remain chaste in the form of suicide (Jongsa), but ultimately says, “I will not do it (Anhallayo)” again, leaving a double refusal. In response, Ong becomes a woman who does not remain chaste (sujeol) and cannot be trusted, but she defines her life as “chaste” through appropriation. At this time, chastity is considered “obscene” in terms of sexual politics because it is with the objectified Byeon, and it is “worse” than the first real relationship with Byeon. However, Ong affirms such love for herself. Furthermore, she internalizes Byeon’s loss by spitting out and becomes the subject of “melancholy.” This transfers the loss of the past to the present and the future and opens the possibility of new ethics and politics. Ong, who appropriates this with the (unrecognized) language of chastity, becomes the

Hydrate management strategies for CO2 injection into depleted gas reservoirs

Sequestering CO2 in depleted gas reservoirs using carbon capture, utilization, and storage technologies has emerged as a viable strategy for mitigating global carbon emissions. However, CO2 hydrate formation during injection processes is challenging and poses a risk to the operational integrity and efficiency of sequestration projects. This study investigated CO2 hydrate formation dynamics within silica gel environments that closely mimicked the median pore size of natural sandstone reservoirs, particularly targeting depleted gas fields in the East Sea of Korea. Integrating kinetic insights into experimental hydrate formation assessments and molecular dynamics simulations provided a comprehensive understanding of the CO2 hydrate formation mechanisms, as well as the formation dynamics and stability of the CO2 hydrates. For example, the hydrate formation kinetics were significantly reduced in the small pores, suggesting the feasibility of implementing more economical hydrate inhibitor injection strategies during CO2 injection. Moreover, this study evaluated the inhibitory effects of NaCl and methanol on CO2 hydrate stability by accurately measuring the three-phase (H-Lw-V) equilibria and employing silica gels (6 nm pore size). The presence of methanol and amorphous silica significantly impacted hydrate formation, with methanol potentially influencing the local structure around the hydrate phase and silica hindering hydrate growth through dynamic interactions with CO2 molecules. In addition, we elucidated the complex interplay between CO2, water, and methanol (hydrate inhibitor) within the constrained environments of porous media, offering strategic insights for the development of effective CO2 injection and sequestration strategies. Integrating molecular-level observations with real-world geological modeling presents a novel methodology for enhancing the safety, efficiency, and environmental sustainability of carbon capture and storage operations. The findings of this study provide critical insights into hydrate phase behavior, highlighting the importance of precise equilibrium determination under simulated reservoir conditions to effectively anticipate and mitigate hydrate formation challenges.

Estimation of tidal energy potential in the Vietnam East Sea: A comprehensive analysis using semi-empirical tide models

This study assesses the tidal energy potential in the Vietnam East Sea (VES), a region with complex hydrodynamics and significant interactions with the Western Pacific Ocean. A rigorous validation of six prominent semi-empirical global ocean tide models (FES2014, DTU16, EOT20, GOT4.10c, HAMTIDE12, OSU12.V1) was conducted against an extensive network of 34 tide gauge stations in the VES region. The validation identified FES2014 as the superior model, exhibiting the closest agreement with observations due to its advanced data assimilation techniques, high-resolution grids, and robust hydrodynamic representation influenced by the complex VES bathymetry. Leveraging the FES2014 model, the influential role of the semi-diurnal component (M2) in dictating energy distribution is prominently evident. Evaluation results of tidal amplitudes revealed three emerging hotspots: the Batang Lupar estuary (Malaysia), Anpu Gang (China), and Bac Lieu (Vietnam), with tidal amplitudes up to 326.2 cm. The Anpu Gang exhibited the highest theoretical potential tidal energy of 14.90 Wh/m2, making it the most promising site for localized tidal power development. Although moderate compared to globally renowned sites, the identified VES hotspots merit consideration for small-to-medium scale projects tailored to local conditions. While limited to potential energy assessments, this study provides a crucial baseline for the VES region, highlighting opportunities for sustainable tidal energy exploitation.

Marine Characteristic Changes Associated with Typhoon Soulik Observed Using Wave and Underwater Gliders

To assess the impact of Typhoon Soulik on the marine environment, unmanned platforms, specifically wave and underwater gliders, are used for surveys in the East Sea. From August 20 to 30, 2018, the wave glider collected meteorological data, while the underwater glider conducts CTD measurements within the typhoon’s impact zone. The data are compared with marine buoy data from the Korea Meteorological Administration and forecast model outputs using RMSE and correlation coefficients to evaluate the characteristics of each data source. The unmanned platform effectively capture the marine environmental changes during the typhoon passage, and the forecast model results show relatively lower RMSE and correlation with the observed data. The study also determines the time required for conditions to revert to pre-typhoon states. This research demonstrates the potential of unmanned platform data for enhancing marine surveys and forecast model accuracy.

Long-Term Changes in Deep Ocean Currents between Ulleung Island and Dok Island in the East Sea from 1996 to 2023

This study presents a comprehensive analysis of long-term deep ocean currents between Ulleung Island and Dok Island in the East Sea, based on data observed from the East Sea Current Measurement 1 (EC1) mooring station spanning from 1996 to 2023. The deep current at the Ulleung Interplain Gap, a trough situated between Ulleung Island and Dok Island, originates from the Japan Basin, a region where deep water formation occurs within the East Sea. The southward flow and velocity of this deep water are reflective of both regional and global climate dynamics. Understanding these dynamics is crucial for assessing environmental impact, both locally in Korea and globally. Significant trends and anomalies were identified in the zonal and meridional velocities within the 1,800 and 2,500-meter depth range. Data from 2012 to 2014 required corrections due to unit inconsistencies, which, after adjustment, revealed a deceleration of the southward bottom current, with speeds decreasing from 1.49 cm s<sup>-1</sup> in November 1996 to 1.14 cm s<sup>-1</sup> in April 2023. These changes may be linked to global climate variations and bottom water formation in the Japan Basin, influencing regional circulation patterns. The findings highlight the importance of sustained ocean monitoring and enhanced data management to ensure the accuracy and utility of long-term oceanographic datasets.

Fish Diversity of East Sea Streams in Nakdong River Region

Fish surveys were conducted near artificial structures installed in eight streams flowing from the Nakdong River region to the east coast of Korea. As a result of the survey, a total of 20,000 individuals belonging to nine orders, 17 families, and 47 species were found. The dominant species was Zacco koreanus, and the subdominant species was Pungtungia herzi. Among the surveyed fish species, endangered species were Pseudobagrus brevicorpus (rank I) and Cottus hangiongensis (rank II). In addition, migratory fish species were Oncorhynchus keta, Plecoglossus altivelis, and Tribolodon hakonensis. As a result of community analysis, the highest diversity, dominance, richness, and evenness indices were Wangpi, Chuksan, Gokgang, and Janggi Stream respectively. The highest number of species was surveyed in Gokgang Stream (25 species). Alpha diversity, the number of species at each survey point in each stream, was the highest at a survey point in Wangpi Stream (20 species), and beta diversity, species at each stream survey point that does not overlap with nearby survey point, was the highest at survey points in Gokgang Stream (12 species). As a result of the similarity analysis, surveyed streams were divided into four groups: group 1 (Chuksan, Baeknok Stream), group 2 (Uljinnamdae, Wangpi, Yungdeokosip Steam), group 3 (Gokgang Stream), and group 4 (Janggi, Hoeya Stream). This study is expected to serve as basic data for managing the aquatic ecosystem of streams flowing from the Nakdong River region to the east coast.

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.

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.

Metazoan parasite fauna of grey mullet (Mugilidae) from the coastal waters of Vietnam

A total of 201 fishes of the family Mugilidae caught off central Vietnam (Nha Trang Bay) were examined for parasites. Eight species of Mugilidae were identified based on cytb and 16S rRNA sequences. Protozoa were not revealed. The metazoan parasites belong to six higher taxa. Myxozoa Grassé, 1970 is represented by six genera, three of which were first found in grey mullets off Vietnam. The specimens of Monogenea Van Beneden, 1858 belong to two genera: Ligophorus Euzet et Suriano, 1977 and Metamicrocotyla Yamaguti, 1953. Twelve species of the former were recorded for the first time both in the coastal waters of Vietnam and in the East Sea. Trematoda Rudolphi, 1808 is represented by the members of the four families, of which only three species, Haplosplanchnus pachysoma (Eysenhardt, 1892), Pseudohaploporus planilizum Atopkin, Besprozvannykh, Ha, Nguyen, Nguyen & Chalenko, 2019 and Spiritestis arabii Nagaty, 1948, were identified. The latter was first recorded in the East Sea. Acanthocephala Rudolphi, 1808 specimens belong to the species Neoechinorhynchus dimorphospinus Amin & Sey, 1996. Crustacea Brünnich, 1772 are represented by five families, of which only the copepod Lernanthropsis mugilii (Shishido, 1898) and the isopod Nerocila orbignyi (Guérin, 1832) were identified. Hirudinea Savigny, 1822 were not determined to genus and species level. A total of 25 species of parasites were found in the Mugilidae fishes examined in Nha Trang Bay. In general, 96 species of parasites are currently documented in these fishes in the East Sea, 55 of which occur off Vietnam. As a result of this study, carried out off central Vietnam, 16 parasite species were recorded in grey mullet for the first time in Vietnamese coastal waters and 15 for the first time in the East Sea. Thus, extending the geographical range of the studies may result in new records of parasites in these fishes.

Dark Carbon Fixation Measurements in the East Sea (Sea of Japan)

The vertical distribution patterns of daily primary production and dark carbon fixation were investigated at three stations in the East/Japan Sea (hereafter East Sea), a semi-enclosed marginal sea in the northwest Pacific Ocean. Our results displayed consistent vertical patterns of daily primary production at two of the stations, while the third station exhibited a markedly different distribution pattern, highlighting localized variations in production dynamics. In contrast, dark carbon fixations displaying varying vertical patterns among the stations are not specific enough to have much meaning. Water column-integral values showed differences in the contribution of dark carbon fixation to total primary production, ranging from 4.5% to 27.1%. These variations may reflect environmental parameters such as nutrient concentrations. However, our study is limited by the lack of direct data on the microbial community structure and chemoautotrophic activities, which are crucial for a more comprehensive understanding of these patterns. Understanding the environmental drivers of dark carbon fixation is crucial for elucidating carbon cycling dynamics in the East Sea. Notably, dark carbon fixation could contribute up to one-third of primary production in the region as an additional source of newly produced organic matter, highlighting the need for further investigation into this previously overlooked process.

Improved Bathymetry Estimation Using Satellite Altimetry-Derived Gravity Anomalies and Machine Learning in the East Sea

This study aims to improve the accuracy of bathymetry predicted by gravity-geologic method (GGM) using the optimal machine learning model selected from machine learning techniques. In this study, several machine learning techniques were utilized to determine the optimal model from the performance of depth and gravity anomalies. In addition, a tuning density contrast calculated from satellite altimetry-derived free-air gravity anomalies (FAGAs) was applied to estimate enhanced bathymetry. By comparison with shipborne depth, the accuracy of the bathymetry estimated by using satellite altimetry-derived FAGAs and machine learning was evaluated. The findings reveal that the bathymetry predicted by the optimal machine learning using the Gaussian process regression and the GGM with a tuning density contrast can enhance the accuracy of 82.64 m, showing an improvement of 67.40% in the RMSE at shipborne depth measurements. Although the tuning density is larger than 1.67 g/cm3, bathymetry using satellite altimetry-derived FAGAs and machine learning can be effectively improved with higher accuracy.

Geological implications for submarine geohazards, Ulleung Basin, East Sea

Geological implications for submarine geohazards, Ulleung Basin, East Sea

Continent‐Side Uplifted Mantle and Geological Imprints Along a Paleo Rift in the Western East Sea (Sea of Japan)

AbstractWe investigate the continent‐size lithospheric structures of paleo rift around the central Korean Peninsula using ambient noise tomography and earthquake‐based Eikonal tomography based on dense seismic networks. We determine Rayleigh‐wave group velocities at periods of 1–15 s from ambient noise tomography and Rayleigh‐wave phase velocities at periods of 20–80 s from earthquake‐based Eikonal tomography. We determine a 3‐D shear‐wave velocity model in the lithosphere from the Rayleigh wave velocities. The model exhibits high lateral variations ranging from ‒9% to 8%, depending on depth. The shear‐wave velocities at shallow depths (2 km) are relatively high in mountain regions and low in coastal and basin regions. Strong velocity contrasts are observed around major earthquake hypocenters at depths of 3–20 km, which may be due to the presence of seismogenic faults. Shear‐wave velocities at depths of 30–40 km are high along the east coast, suggesting uplifted mantle that is responsible for the opening of the East Sea (Sea of Japan). High velocity structures beneath Moho around the coast may suggest solidified underplated magma caused by the paleo rifting. The root of coast‐parallel high‐mountain range (Taebaek Mountain Range) is bounded by the uplifted mantle, presenting mountain range development in rift flank along paleo‐rift axis. Low shear‐wave velocities along the coast at depths km may imply elevated temperature beneath the solidified underplated magma. The continent‐side paleo rift affects the geological, thermal, and seismological properties around the continental margin at present.

Comparing spatial differences in behavioral pattern transition of Black-tailed gull during post breeding season in the Korean peninsula

Parents adjust their foraging effort according to the chick and their own body condition and dual foraging strategy is one of the foraging tactics parents replenish their own reserves while feeding their chicks. During the post-breeding season, seabirds disperse to recover their own body condition and prepare for the next breeding season. Recently, we discovered Black-tailed gulls (Larus crassirostris) breeding around the Korean Peninsula occasionally foraging long trips during the late fledging, however, our understanding of the behavioral patterns of Black-tailed gulls during the late fledging and post-breeding, as well as its inter-colonial differences, remains considerably limited. Here, we employed 92 GPS trackers to adult Black-tailed gulls (Larus crassirostris) from six breeding colonies around the Korean peninsula (Yellow Sea—three colonies, South Sea—one colony, and East Sea—two colonies). To determine the foraging investment during the fledging, we suggested the flight efficiency in each trip as the ratio of maximum foraging distance (i.e., straight line distance) to total foraging distance (i.e., sum of all consecutive distance for each trip). Overall, the mean flight efficiency of the long foraging trips were lower than 57% (40.76 ± 13.07%) whereas that of the short foraging trips were over 74% (80.87 ± 4.03%). This may suggest that Black-tailed gulls may visited more than one foraging site during the long foraging trip while they flew directly between the foraging site and breeding colony during the short foraging trip to invest more in their juvenile. Moreover, longer maximum foraging distance with higher flight efficiency observed in the East Sea may indicate a balance between the costs (such as energy expended during foraging or food competition near breeding sites) and the benefits (quantity and quality of food obtained). Our findings revealed the flight behavior of Black-tailed gulls during the late fledging and post breeding, across six breeding colonies, which have different competition pressures and proximity to foraging site.

Biomarker reconstructions of temperature and hydroclimate variability in Vietnam during Marine Isotope Stage 3

Limited hydrological data coupled with a reliance on the monsoon rains for agriculture make Southeast (SE) Asia vulnerable to climate change. To develop a better understanding of how SE Asia responds to climatic forcings, we provide a paleoclimate perspective by reconstructing temperature and hydroclimate from a wetland outcrop in the Central Highlands of Vietnam (CHV) during Marine Isotope Stage 3 (MIS 3). Mean annual atmospheric temperatures inferred from brGDGTs (branched glycerol dialkyl glycerol tetraethers) indicate an increase from 23 to 26 °C between ∼54 and 37 cal ka BP, which follows an increase in mean annual insolation at the latitude of the site. δDwax data show a shift from a greater proportion of summer monsoon rain derived from the Bay of Bengal between 54 and 49 cal ka BP toward more autumn rain from the South China Sea (also known as the Vietnam East Sea) for most of the rest of the record. brGDGT-inferred soil pH suggests that the climate was wetter at 54 to 49 cal ka BP, then became drier, then returned to wet conditions approaching 37 cal ka BP. Both orbital forcing and changes in the exposure of the Sunda Shelf likely influenced hydroclimate in the CHV. δ13Cwax indicates that C4 plants dominate the vegetation cover during MIS 3. Comparison between our new record from the CHV with existing water isotope proxy records reveals coherent changes with nearby speleothem data, but regional differences between the history of hydroclimate in SE Asia and in the central Indian Monsoon domain. As a snapshot of glacial climate conditions, our data provide new information on the past drivers of climate in an understudied region.

Ontogenetic, Sexual, and Monthly Niche Segregation of Sepia esculenta in the Northern East China Sea Revealed by Stable Carbon and Nitrogen Isotopes.

Golden cuttlefish play a significant role in the food web of the East and Yellow Seas and are a valuable fishery resource in Chinese coastal waters. Samples of golden cuttlefish were obtained from the northern East China Sea between September 2021 and March 2022, and stable isotope methods were utilized in this study to examine the variations in the forage ecology of golden cuttlefish. Our findings reveal dynamic shifts in carbon and nitrogen stable isotopes (δ13C and δ15N), highlighting intricate foraging strategies tailored to growth and environmental changes. A notable trend emerges: an initial growth-linked rise in δ13C and δ15N enrichment, followed by seasonal fluctuations mirroring seasonal food availability. The ontogenetic niche evolution displays striking habitat shifts and trophic level escalation in small mantle length stages, transitioning to niche overlap and subtle trophic shifts later on. Sex-specific differences emerge, with females occupying higher trophic levels than males in most samples. This comprehensive study underscores the complexity and adaptability of golden cuttlefish feeding ecology, inviting further inquiry into their intricate relationships within the marine ecosystem.